320102b
Agricultural Equipment Technician
Oxy-Fuel Equipment
Electric Welding and Oxy-Fuel Cutting
First Period
Table of Contents
Objective One ............................................................................................................................................... 2 Oxygen ...................................................................................................................................................... 2 Acetylene (C2H2)....................................................................................................................................... 4 Propane ..................................................................................................................................................... 8 Objective Two............................................................................................................................................. 10 The Oxy-Fuel Outfit ............................................................................................................................... 10 Regulators ............................................................................................................................................... 10 Hoses ....................................................................................................................................................... 14 Check Valves .......................................................................................................................................... 15 Torch Handle .......................................................................................................................................... 16 Welding and Heating Tips ...................................................................................................................... 16 Objective Three ........................................................................................................................................... 20 Oxyacetylene Set-Up Prior to Use .......................................................................................................... 20 Balance the Pressures for Welding and Heating ..................................................................................... 21 Flame Types ............................................................................................................................................ 24 Oxy-Fuel Cutting .................................................................................................................................... 29 Factors for a Quality Cut......................................................................................................................... 31 Objective Four ............................................................................................................................................ 33 Goggles ................................................................................................................................................... 33 Objective Five ............................................................................................................................................. 34 Cutting .................................................................................................................................................... 34 Common Cutting Faults .......................................................................................................................... 38 Fusion Welding Steel .............................................................................................................................. 40 Brazing .................................................................................................................................................... 43 Braze Welding ........................................................................................................................................ 46 Objective Six............................................................................................................................................... 48 Effect of Heat on Metal........................................................................................................................... 48 Rules to Remember when Welding ........................................................................................................ 50 Self-Test ...................................................................................................................................................... 51 Self-Test Answers ....................................................................................................................................... 57 NOTES
Oxy-Fuel Equipment
Rationale
Why is it important for you to learn this skill?
Oxy-fuel equipment is used in many phases of agricultural equipment repair. You must
know the safety requirements, heat control, and cutting principles for using oxy-fuel
equipment in order to make these necessary repairs. This module provides the
information required to perform heating and cutting operations safely.
Outcome
When you have completed this module you will be able to:
Demonstrate the use of the torch for welding, heating, brazing and cutting.
Prerequisites
In order for you to fully understand the information presented in this module, you must
first complete the following module:
 320102a Welding Safety
Objectives
1.
2.
3.
4.
5.
6.
Describe the characteristics and safe handling procedures for gases and cylinders.
Describe care and maintenance procedures for the oxy-fuel outfit.
Demonstrate equipment set-up, adjustment and shut down procedures.
Demonstrate use of personal protective equipment and safe operating procedures.
Perform heating, welding and cutting operations using oxy-fuel equipment.
Describe temperature indicators and the effect of heat on metal.
Introduction
This module will cover safe set-up and use of oxyacetylene equipment, including the
techniques required to perform heating, welding and cutting operations on metals.
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Objective One
When you have completed this objective you will be able to:
Describe the characteristics and safe handling procedures for gases and cylinders.
Oxygen
Oxygen (O2) is a colourless, odourless and tasteless gas. It is not flammable itself but
supports combustion of other materials. Atmospheric air is composed of approximately
21% oxygen. Oxygen used for oxy-fuel equipment is 99.5% pure. In this nearly pure
form, oxygen must be considered a potential danger because it greatly speeds up
combustion of known flammable materials. It combines readily and often violently with
many other materials including some that are not generally considered combustible.
Rubber, burning in pure oxygen, burns rapidly with a white flame, practically no smoke
and little odour. Fabric burns rapidly in oxygen with intense heat. If your clothing is
saturated with oxygen, a spark or misdirected flame could easily ignite the fabric causing
severe burns to your body. If oil or grease is exposed to pure oxygen under pressure or
friction, it can spontaneously explode without external ignition. When steel is heated to a
red heat and oxygen is applied, it oxidizes quite rapidly, reducing the reacted metal to
iron oxide or ash. This is the principle behind the cutting torch.
DANGER
Keep oxy-fuel equipment away from oil, grease, cleaning fluids and
gasoline! Never oil regulators or torch parts. Do not use compressed
air to blow out oxy-fuel equipment.
O2 + Oil = Explosion
Oxygen Cylinders
Oxygen for oxy-fuel equipment is stored as a compressed gas in a seamless cylinder.
Oxygen cylinders come in several different sizes. The two most popular sizes being the K
(241 cu ft or 6.82 cu m) and the M (121 cu ft or 3.43 cu m). When an oxygen cylinder is
filled, the gas is compressed to approximately 2200 psi (15 000 kPa) at 21°C. Half size
and smaller cylinders will carry the same pressure as larger cylinders and their
construction is very similar. Although the preferred orientation of the oxygen cylinder is
upright, it can be used in any position. The contents of the cylinder are indicated by a
WHMIS label stating that the cylinder contains oxygen. The colour of the cylinder is not
a reliable indicator of its contents.
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A typical oxygen cylinder with the valve and protective cap installed is shown in
Figure 1.
NOTES
Figure 1 - Oxygen cylinder with protective cap installed.
Valve
The valve on an oxygen cylinder has a right-hand (RH) thread to connect the regulator
(Figure 2).
The oxygen cylinder is protected from extreme pressure, or pressure rise caused by heat
or fire, by a safety device known as a frangible disk, a fusible metal rupture disk. This
disk is mounted between the cylinder valve and a drilled nut on the rear side of the
cylinder valve opening. The melting point of fusible metal is around 115°C. Its purpose is
to melt or burst, as the case may be, and allow for slow controlled escape of gas, thus
avoiding the violent bursting of the cylinder.
Figure 2 - Oxygen cylinder valve.
The oxygen cylinder valve is a double seated valve. One seat seals to prevent the flow of
oxygen from the cylinder when the cylinder valve is closed. The other seat seals when the
cylinder valve is fully open to prevent leakage around the stem of the valve. Since there
can be leakage around the valve stem, it is recommended the oxygen valve be fully open
when using the oxy-fuel equipment.
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A drawing of an oxygen cylinder valve is shown in Figure 3.
\
Figure 3 - Oxygen cylinder valves: closed, partially open and fully open.
Acetylene (C2H2)
Acetylene is a colourless, flammable gas and has a strong pungent odour. Acetylene is an
endothermic compound, which means it absorbed extra heat energy at some stage during
its formation. When acetylene is burned, this endothermic heat is released along with the
heat generated by burning the carbon and hydrogen, which forms the acetylene gas. This
endothermic heat contributes to the high temperature of the oxyacetylene welding flame
(3300°C), making it the most efficient fuel gas for welding purposes.
This gas is very unstable when compressed beyond 15 psi (100 kPa). The critical point
for acetylene is reached at 28 psi (193 kPa) with a minimum temperature of 21°C. At this
critical point, acetylene will ignite spontaneously in the presence of air. This critical point
lowers as the temperature of the gas rises. Because of this, the maximum safe working
pressure is considered to be 15 psi (100 kPa).
DANGER
Do not set acetylene operating pressure in hoses or manifold systems
above 15 psi (100 kPa).
Acetylene gas is highly flammable and, compared with other fuel gases, has the widest
explosive range when mixed with air. As little as 2.5% acetylene in air is an explosive
mixture. Unlike other combustible gases, these explosive mixtures continue right up the
scale as the acetylene content is increased and the air is decreased.
This flammability of all the fuel gases listed in Table 1 is greatly magnified when mixed
with pure oxygen. You should treat all mixtures of acetylene and air or oxygen as being
explosive. Acetylene gas is approximately the same weight as air and tends to collect in
pockets rather than dissipate into the air. If you can smell acetylene, do not take any
chances. Extinguish all open flames and ventilate the room before turning on a light
switch. Test for leaks by brushing soapy water onto suspected joints or areas. Watch for
bubbles. Never test for leaks with an open flame.
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Fuel Type
Range of Flammability (% Gas in Air)
Propane
Butane
Natural Gas
MAPP Gas
Acetylene
NOTES
2.4 - 9.5%
1.9 - 8.4%
5 - 15%
3.4 - 10.8%
2 - 89%
Table 1 - Range of flammability of common fuel gases.
Over time, moist acetylene gas under pressure will react with copper. The endothermic
heat will be released. Pressure will rise, which will possibly lead to an explosion. Never
use copper or red brass fittings or tubing for acetylene pipeline systems or for hose
splices.
NOTE
Use only yellow brass, steel or stainless steel fittings and piping for
acetylene systems. Never use copper or red brass.
Acetylene Cylinders
An acetylene cylinder has a WHMIS label indicating that it contains acetylene. Two
types of acetylene cylinders are shown in Figure 4. Acetylene cylinders are completely
filled with a porous filler mass. This material can be asbestos, balsa wood, corn pith or
many other products. This serves to break up the large cylinder cavity into tiny cells.
Acetylene is most unstable when compressed in a large cavity. The voids within the
porous material of an acetylene cylinder are then filled to approximately 40% capacity
with acetone. Acetone is an alcohol derivative that has the ability to absorb large volumes
of acetylene. When gaseous acetylene is pumped into the cylinder, the acetylene is
absorbed into the acetone. The cylinders are filled by weight. The combination of a
porous filler and acetone allows acetylene to be stored safely in the cylinder at high
pressures (250 psi [approximately 1700 kPa]). Because the acetone is a liquid, it is
essential to use acetylene cylinders in a vertical position to prevent acetone from being
drawn off as the acetylene gas is used. It is thought that the action of lying a cylinder and
standing it up can contribute to the acetylene (C2H2) compound disassociating, relative to
its critical pressure point, resulting in a time delayed pressure increase and subsequent
cylinder rupture.
DANGER
Keep acetylene cylinders upright at all times during transport, storage
and use.
Acetylene cylinders come in several different sizes, the two most popular sizes being:
 WK (300 cu ft or 8.5 cu m) and
 WS (130 cu ft or 3.7 cu m).
Half sized and smaller cylinders will carry the same pressure as a full sized cylinder and
their construction is very similar.
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When acetylene is drawn out of a cylinder, it is possible for acetone to be drawn out of
the cylinder with the acetylene. It takes time for the acetylene to bubble out of the liquid
acetone. The maximum amount of acetylene that can be taken from the acetone is
referred to as the draw limit. To prevent drawing off acetone with the gas, a cylinder must
be emptied no faster than one-seventh of its capacity per hour (or less than 7 hours).
When large tips are used with small size cylinders, the draw limit can be exceeded. Fuel
consumption specifications for heating and cutting tips are available from the
manufacturer. Use a cylinder that has a large enough capacity to supply the largest tip in
your outfit. When the heating and cutting equipment requires larger volumes than can be
supplied from one cylinder, two or more cylinders must be connected together using an
approved manifold system.
Minimum cylinder size (cu ft) = tip consumption (cu ft per hr) x 7
Acetone drawn with the acetylene will produce a flame that is cooler and can be
identified by a pale blue colour with orange flecks. The acetone, being a solvent, will
cause damage to any plastic or rubber parts in the regulator, hoses and torch assembly.
Loss of acetone from the cylinder will also reduce the safety factor of that cylinder.
Fusible metal plugs are installed in the cylinder to allow a controlled release of acetylene
in the event of a fire. The plugs will melt out at 100°C and allow acetylene to discharge.
Common locations for the plugs are:
 on the concave bottom of the cylinder,
 a filled passage on the back side of the cylinder valve,
 on the reinforcing collar or neck ring or
 the shoulders of the cylinder.
Figure 4 - Acetylene cylinders.
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NOTES
Valves
Generally, two styles of valves are used. These are shown in Figure 5. Acetylene cylinder
valves use a left-hand (LH) thread to connect the regulator. The cylinder with the
recessed top uses a special wrench to operate the valve.
NOTE
The wrench should be attached to the valve whenever the cylinder is in
use.
Figure 5 - Acetylene cylinder valves.
The most commonly used acetylene valve is the exposed type as shown in Figure 6.
Figure 6 - Acetylene valve.
Unlike an oxygen cylinder valve, the acetylene valve does not have a double seating
system and thus, is not required to be fully open when acetylene is being used. The
cylinder valve should be opened only about 1 to 11/2 turns to allow enough fuel flow for
the heating or cutting operation. In the event of a fire, this allows the cylinder valve to be
closed quickly.
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Propane
There are other fuel gases available for use in the welding industry (see Table 1).
Propane (C3H8) (liquid petroleum gas (LPG)) is the most common and is readily
available. The other gases function similar to propane. Propane is colourless with an
added odour. The advantages of propane over acetylene is that it is more stable to handle
and store, it is less expensive and is more readily available. Propane can be purchased at
your local gas station and you do not require a rental contract for the cylinders. The
disadvantage is that the oxy-propane flame is not hot enough (2500°C) nor concentrated
enough for welding. It can, however, be effective for heating and cutting applications.
The oxyacetylene equipment, in general, will work with propane. The propane cylinder
will receive a normal acetylene regulator and similar gas pressures are used. It is
necessary to use specific heating and cutting tips designed specifically for propane. The
oxy-propane flame requires slightly different techniques to light and adjust compared to
oxyacetylene. You are advised to handle propane with the same safety procedures and
precautions as are described for acetylene.
Handling Compressed Gas Cylinders
Normally, you purchase a yearly lease agreement (contract) with a gas supply company
for all your welding gases. That contract entitles you to have possession of specified
cylinders. When a cylinder is empty, you return the empty cylinder to the supplier, trade
it for a full cylinder and pay for the gas in the full cylinder. To avoid mixing empty
cylinders with full cylinders, it is helpful to mark a large "MT" (which means empty) with
chalk or soapstone on the empty cylinder when the regulator is removed. Leave the valve
closed on an empty cylinder to prevent contamination of the cylinder.
Cylinders should not be stored or used in close quarters with welding activities or
machines. If the cylinder should become grounded, any contact made with the electrode
or electrode holder could result in an arc being struck against the cylinder. A flame, hot
slag or sparks directed at a cylinder could result in damage to the valve, cylinder or
equipment. A cylinder damaged in any way is very unsafe and could easily explode.
Any cylinder that is faulty, leaks or is damaged, must be taken out of service and isolated
for safety reasons. Place it outside away from buildings, combustible material and any
source of ignition. Tag it as to the type of fault and notify the supplier. Do not attempt
any repairs to cylinders. Cylinders must be fastened in place or supported in a cart when
in use. When supported, the caps can be removed. Figure 7 shows how acetylene,
propane and oxygen cylinders can be secured to a cart.
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NOTES
Figure 7 - Cylinders secured to cart.
For safety reasons, it is very important you adhere to the following guidelines.
 Store cylinders in a cool, dry, well-ventilated location.
 Store oxygen and fuel gas cylinders separately (a minimum of 6 m (20 ft) apart).
 Store, transport and use acetylene cylinders in the vertical position.
 Keep protective caps on the cylinders during transportation and storage.
 Keep cylinders tied in place during transport, storage and use.
 Do not attempt to transfer acetylene from one cylinder to another.
 Do not drop, bump or pound on cylinders of either type.
 Do not use cylinders as rollers, dollies or supports.
 Do not attempt to interchange equipment (such as regulators or hose) from one
type of gas to another type.
 Call the gases by their proper names. Do not refer to acetylene as gas or oxygen
as air.
 Operate cylinder valves according to instructions.
 Keep oxy-fuel equipment away from oil or grease.
 Do not use compressed air to blow out oxy-fuel equipment. The air may contain
oil from the compressor.
 Do not use oxygen for dusting purposes or for blowing off mechanical parts.
 Keep oxy-fuel equipment clear of electric arc welding equipment. An accidental
arc strike against the cylinder could cause a fire or serious explosion.
 Avoid directing a flame, hot slag or sparks at the oxy-fuel equipment.
 Do not attempt any repairs to cylinders.
 Do not attempt to use oxygen or fuel gas directly from the cylinder at cylinder
pressures. Always use a proper pressure regulator.
 Close empty cylinder valves snugly and place protective caps on the cylinders to
protect the valves. This will prevent contamination of the cylinder by moisture,
dust and foreign gases. Cylinder valves left open are always an explosive hazard
since a change in temperature could cause the release of gas from within the
cylinder.
 When lifting cylinders with a crane, use a properly designed cradle.
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Objective Two
When you have completed this objective you will be able to:
Describe care and maintenance procedures for the oxy-fuel outfit.
The Oxy-Fuel Outfit
The combination oxy-fuel outfit consists of the following and are shown in Figure 8.
1. one oxygen and one acetylene regulator,
2. a torch handle complete with torch valves,
3. cutting tips,
4. a cutting attachment,
5. welding tips with individual gas mixers,
6. an accessory package (includes hose, goggles, spark lighter and tip cleaners) and
7. one set of check valves.
Figure 8 - Oxyacetylene outfit.
Regulators
Pressure regulators are used on both the oxygen and fuel cylinders. They are required to
reduce cylinder pressure to an usable working pressure. They are designed to maintain a
constant delivery pressure regardless of pressure changes in the cylinders.
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Two gauges are mounted on the regulator. The high pressure gauge indicates the pressure
in the oxygen or fuel cylinder (pressure into the regulator). The low pressure gauge
indicates the regulated hose or working pressure.
NOTES
Pressure regulators have a non-serviceable filter at the inlet fitting to prevent foreign
particles from entering the regulator.
Types
Although similar in design, the oxygen and fuel regulators are not interchangeable.
An oxygen regulator has right-hand threads on both the inlet and outlet fittings and
generally has green markings. The gauges are calibrated with high reading numbers.
An oxygen regulator is shown in Figure 9.
Figure 9 - Oxygen regulator.
The fuel regulator has left-hand threads on both the inlet and outlet fitting and generally
has red markings. The gauges are calibrated with lower reading numbers. An acetylene
regulator is shown in Figure 10.
Figure 10 - Acetylene regulator.
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Single Stage
Single stage regulators change cylinder pressure to operating pressure in one step. Using
the hand, (adjusting screw), clockwise rotation increases pressure and counter-clockwise
rotation reduces pressure. When the hand control is turned fully counter clockwise until it
freewheels the outlet pressure is reduced to zero. The operating principle of a single stage
regulator is shown in Figure 11. Single stage regulators are the most common and
function well for general cutting and heating applications.
Figure 11 - Single stage regulator.
Two-Stage
Two-stage regulators, as shown in Figure 12, have two diaphragms, two metering needles
and two seats. The first stage reduces the high gas pressure that comes from the cylinder
to some intermediate pressure. The second stage is the low-pressure stage that reduces the
intermediate pressure to a constant volume and pressure needed by the torch. The second
stage can be adjusted to the desired pressure in the same way a single stage regulator is
adjusted. The two-stage regulator provides more consistent delivery flow and pressure
and would be chosen for high quality welding applications.
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NOTES
Figure 12 - Two-stage regulator.
Regulators are available in several different levels of quality. Generally speaking, if you
use industrial quality regulators, observe safe handling practices and operate them
according to manufacturer's recommendations, you will experience few, if any, regulator
malfunctions. They are precision-built instruments. If your regulator malfunctions, you
should send it to an authorized service centre for repairs.
Regulator Malfunctions
Creep is a condition where the low pressure gauge, which indicates working pressure,
slowly rises when the torch valves are shut off. It is possible for the working pressure to
rise as high as cylinder pressure. This high pressure could rupture the diaphragm, the low
pressure gauge or the hose. Creep is caused when the regulator valve does not seat
completely, possibly from dirt or scarring.
Surge is a condition where the regulator does not provide a constant pressure and flow.
This is indicated by the flame not staying where it is set. The flame changes from neutral
to carburizing or oxidizing without you touching the torch valves. The internal
mechanism is not moving freely.
CAUTION
Do not attempt to repair a faulty regulator yourself. Send it to an
authorized service centre for repair. Attempting a regulator repair
without proper training and equipment may lead to equipment being
damaged and/or serious injury.
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Hoses
Hoses are made of neoprene rubber and linen braid. They are flexible, durable, resistant
to gas and oil and able to withstand pressures up to 400 psi (2760 kPa). The hoses may be
individual lines, but most often the oxygen and fuel hoses are bonded together. Table 2 is
a quick resource for identifying oxygen and fuel hoses.
Oxygen Hose


Acetylene Hose
Connections have right-hand thread.
The colour of the hose is green.



Connections have left-hand thread.
An annular groove is cut in the
hexagonal of the fitting.
The colour of the hose is red.
Table 2
Position the hoses to avoid damage from the flame, hot slag, welding sparks, falling steel
and traffic. Hoses should be checked periodically for physical damage or signs of aging.
The hoses in Figure 13 show cracking due to normal use and aging and should be
replaced.
Figure 13 - Cracked hoses.
When making repairs and modifications to the oxy-fuel hoses, use the approved fittings
(shown in Figure 14), available at your gas or welding supply outlet.
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Figure 14 - Oxy-fuel hose fittings.
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NOTES
CAUTION
Never use copper tubing to repair acetylene hoses because acetylene
and copper react together causing explosive conditions.
Check Valves
One-way check valves (flash back arrestors) help minimize mixing of the fuel gas and
oxygen in the hoses or regulators by disallowing the flow of gas backwards up into the
hose. The gas is allowed to flow from the cylinder source through the hose and exit out
the torch assembly. The most common location for the check valve is at the torch as
shown in Figure 15.
Figure 15 - One-way valves installed at torch.
The construction and operation of a check valve are illustrated in Figure 16.
Figure 16 - Check valve construction and operation.
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Torch Handle
The torch handle shown in Figure 17 provides a mounting area for heating or welding
tips and for the cutting attachment. The valves on the torch handle are needle valves that
allow fine, individual adjustment of oxygen and fuel gas flow.
The oxygen and fuel gases flow through separate tubes through the length of the handle.
Typically, torch handles are constructed from brass, thus, they are easily damaged if
dropped or abused.
Figure 17 - Torch assembly.
Welding and Heating Tips
The tip and mixer combination (Figure 18) is installed as a unit onto the torch handle and
held in place by the retaining nut, which should only be hand-tightened. The mixing
chamber attaches into the torch handle. Its function is to mix the combustion gases as
they enter the welding tip. The mixing chamber is calibrated to match a specific tip size.
Do not interchange tip and mixer sizes. The tips are made of copper to dissipate heat
rapidly.
Figure 18 - Heating tip installed on torch handle.
Typical welding tips designed for use with acetylene gas are shown in Figure 19. Tips are
available in numerous sizes. Tip numbering systems are not standardized amongst
manufacturers; however, a larger number on a tip indicates a larger orifice. A larger
orifice is capable of providing more heat. Tips and torch handle combinations are not
interchangeable amongst manufacturers.
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NOTES
Figure 19 - Welding tips showing sizes.
A Rosebud or multi-flame heating tip is shown in Figure 20 and Figure 21. These are also
available in a variety of sizes and are commonly used for heating applications requiring
high heat inputs.
Figure 20 - Multi-flame tip.
Figure 21 - Intense acetylene heating flame.
NOTE
Welding, heating and cutting tips are specifically designed for use with
each fuel gas. You will experience less than satisfactory results, for
example, if you use propane with tips designed for acetylene.
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Checking Seals
Prior to installing a heating tip, welding tip, or cutting attachment, you should check for
and replace damaged O-ring seals. A damaged O-ring can allow gas leakage resulting in
a fire where the tip connects to the torch handle. Figure 22 shows good O-rings and one
broken O-ring.
Figure 22 - Good O-ring seals and bad O-ring seals.
Tip Cleaning
A tip cleaner is shown in Figure 23. Tip cleaners are designed to remove foreign material
from the tip. You should use the largest tip cleaner that will just fit the tip. You can draw
it back and forth in the tip. The tip cleaner is designed to minimize removal of copper
from the tip. Do not use too small or too large a tip cleaner as this will tend to cause more
tip damage. Use the small file with the tip cleaner to polish the end of the tip. It is
optional to maintain a small flow of oxygen through the tip during the cleaning procedure
to remove foreign material from the tip.
Figure 23 - Tip cleaner with file.
NOTE
The copper tips and brass torches are soft and easily damaged. Take
care when handling and cleaning.
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NOTES
Safe Handling of Oxy-Fuel Equipment
The following techniques and procedures will help maximize the performance and safety
factor relative to the operation of your oxy-fuel outfit.
 When shutting the outfit down, bleed the gas pressures down to zero and turn out
the regulator adjusting screws, thus leaving no tension on the spring and
diaphragm.
 When opening the cylinder supply valve, first ensure that the regulator adjusting
screw is in the neutral position, then open the cylinder valve slowly to prevent a
sudden surge of pressure which could do damage to the diaphragm and gauges.
 Do not stand directly in front of the regulator when opening the cylinder valve.
 Send malfunctioning regulators out for repair by trained technicians via your gas
supply dealer. Do not attempt to repair regulators yourself.
 Crack the cylinder valve (open and close briefly) to blow dust out of the valve
before installing the regulator.
 Do not force the threads on any part of the equipment.
 Tighten all connections firmly.
 Check for leaks with soapy water.
 Position the outfit and hoses to avoid damage from hot slag, sparks, flame or
falling metal parts.
 Coil up hoses off the floor away from the shop traffic.
 Close torch valves firmly with your finger tips. Overtightening will cause
damage to the valve seat and will stretch the stem threads.
 Adjust the packing gland nut on the torch valves so the valves are comfortable to
manipulate; yet their setting will not be inadvertently altered by a light touch of a
sleeve or glove.
 Provide a secure storage apparatus for the torch and tips so they are readily
available and to prevent accidental damage.
 Do not use the torch assembly as a hammer.
 Clean the tips gently and sparingly with the correct sized tip cleaner.
 Do not use copper tubing or red brass fittings to repair or modify oxy-fuel hoses.
 Use approved hose fittings.
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Objective Three
When you have completed this objective you will be able to:
Demonstrate equipment set-up, adjustment and shut down procedures.
Oxyacetylene Set-Up Prior to Use
A complete oxyacetylene outfit is shown in Figure 24. This will be useful in
understanding the following information.
Figure 24 - Complete oxyacetylene outfit equipped for heating and welding.
Prior to using oxyacetylene equipment or after any components are changed, the
following set-up procedure should be followed.
1. Secure the cylinders in the vertical position to a wall, stand or cart.
2. Uncap the cylinders. Check all fittings and remove oil, grease or other
contaminants with a clean cloth or shop towel.
3. Crack the cylinder valves (open momentarily and close) to blow out dust or dirt
from the cylinder valve openings.
4. Attach the pressure regulators to the cylinders and tighten the fittings.
5. Attach the hoses to the regulators and then attach the check valves and torch
handle to the hoses. Tighten all fittings.
6. Install desired cutting attachment or heating tip.
7. Ensure that all torch valves are closed.
8. Ensure that the regulator adjusting screws are fully released (turn counterclockwise until they turn freely).
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9. Open the cylinder valves slowly to the desired amount (oxygen fully open and
acetylene to a maximum of 11/2 turns).
10. Turn in the regulator adjusting screws (clockwise) to set the approximate
working pressures for the job at hand.
11. Flush or purge each individual hose to remove all foreign gases that may be
within that hose. This is done by opening each torch valve individually (one at a
time) and allow sufficient time for the gas to flush from the cylinder through the
entire length of the hose (5 seconds for each 3 m of hose length). Close that torch
valve and repeat purging procedure for the other torch valve.
12. Check the entire system for leaks with soap and water. Correct any leaks before
proceeding.
NOTES
Balance the Pressures for Welding and Heating
When performing welding or heating operations, it is recommended that the working
pressures of oxygen and acetylene be equal to each other. This enhances the safety factor
of the system by reducing the possibility of a higher pressured gas forcing its way back
into the line of the other gas. This balancing procedure also establishes the correct
working pressure for any specific tip size. The following procedures are to be performed
subsequent to the above set-up procedures or at the start of a work project.
1. Select and install the desired sized welding or heating tip.
2. Set the working pressure of both oxygen and acetylene to be approximately 3 psi
(20 kPa).
3. Purge each hose individually.
Set Maximum Acetylene Pressure
To set the maximum acetylene pressure, follow these steps.
1. Open the acetylene torch valve 1/4 turn and then ignite the torch with the flint
lighter. (Figure 25).
Figure 25 - Flint lighter.
2. Open the acetylene torch valve fully (about 3 turns).
3. Increase the acetylene pressure with the regulator adjusting screw to a point
where there is a gap of 5 mm to 8 mm between the base of the flame and the
copper tip. This can be referred to as blowoff and is shown in Figure 26. Note:
excessive blowoff may cause the flame to blow out when setting the oxygen
pressure in subsequent steps. A larger tip will require more pressure to establish
the correct blowoff than does a smaller tip. Normal welding tips will require from
3 psi to 6 psi (20 kPa to 40 kPa) and large rosebud heating tips may require up to
10 psi (65 kPa).
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NOTES
DANGER
Do not set acetylene pressure over 15 psi (100 kPa). There should
never be an occasion when you need more than 10 psi (65 kPa).
Figure 26 shows blowoff.
Figure 26 - Blowoff.
Set Matching Oxygen Pressure
To set matching oxygen pressure, follow these steps.
1. Close the acetylene torch valve until the base of the flame returns to the tip.
Then, open the acetylene torch valve sufficiently for the flame to burn smokefree.
2. Open the oxygen torch valve to achieve an approximate neutral flame.
3. Open the individual torch valves alternately (acetylene, then oxygen) small
increments at a time, keeping between a neutral flame and a 4X carburizing
flame, until both torch valves are at full volume (about 3 turns).
4. With both torch valves wide open, adjust the oxygen regulator screw until a
neutral flame is achieved (when the feather has just disappeared into the primary
flame).
NOTE
Your original oxygen working pressure setting may have been too
high. In this case, an oxidizing flame will be formed before you have
the oxygen torch valve opened to full flow. You must reduce the
oxygen pressure at the regulator until you can open the oxygen torch
valve to full flow and have a feather showing on the flame. Then, with
both torch valves fully open, slowly increase oxygen pressure at the
regulator until the feather just disappears. You have now established a
neutral flame.
22
The oxygen regulator is now set at the same pressure as is the acetylene pressure. The
torch is said to be balanced with equal pressures in each hose. This is the maximum
pressure required for that tip. You will seldom use a welding tip with the torch handle
valves wide open as in the balancing procedures.
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With the valves wide open, the subsequent noisy aggressive flame causes excessive
turbulence to the molten puddle. It is best to operate in the mid-range of the available
pressure setting. If you feel you require the torch valves to be wide open to achieve
sufficient heat, you will experience better puddle control by using a bigger tip and
balance the pressures accordingly. Once the gas pressures are balanced for any given
sized tip, you should not need to readjust the pressures at the regulator for the duration of
the job. You must, however, repeat the above-described procedure when changing to a
larger tip size.
NOTES
Extinguish Flame
To extinguish a flame, follow these steps.
1. Close the acetylene torch valve to extinguish the flame quickly without leaving
carbon deposits within the tip.
2. Close the oxygen torch handle valve.
Set Welding Flame
To set a welding flame, follow these steps.
1. Light the torch, acetylene only, and adjust the acetylene torch handle valve until
the black smoke just disappears. This establishes a heat setting that you can
repeat each time you light the torch. If you operate the torch below the black
smoke range, the torch will backfire excessively.
2. Open the oxygen torch handle valve, slowly increasing the flow of oxygen until a
neutral flame is achieved (when the feather has just disappeared into the primary
flame).
3. If you would like more heat, simply open the acetylene torch handle valve to
create a carburizing feather of a length that you determine will produce sufficient
heat.
4. Then, open the oxygen torch handle valve until a neutral flame is achieved.
NOTE
You must be specific when setting a neutral flame. Add oxygen to the
point when the feather just disappears; no more, no less. A neutral
flame is the choice for most of your welding and cutting applications.
Carburizing and oxidizing flames produce detrimental effects.
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NOTES
Shutdown
After a leak check is performed and any time cutting or heating operations are
terminated, follow these steps to shut down the outfit.
1. Extinguish the flame.
2. Close both the cylinder supply valves.
3. Open the torch handle valves, one side at a time, to bleed all gas pressure from
the respective hose and regulator. Close each torch handle valve when the
pressure reads zero. It is not important which side of the system is bled first, but
it is critical while bleeding one side that the opposing side remains closed.
4. Unscrew the regulator adjusting screws until they turn free in the neutral
position.
5. Remove the tip from the torch handle. Place the tip in its storage holder and coil
up the hoses neatly.
6. Check again to ensure that you have closed the cylinder supply valves, closed the
torch handle valves and backed off the regulator adjusting screws.
Flame Types
The four types of flame you will encounter are:
 acetylene flame,
 carbonizing flame,
 neutral flame and
 oxidizing flame.
Acetylene Flame
The flame burning with acetylene (Figure 27) only has the following characteristics.
 The flame is yellow and bushy.
 The flame temperature is 800°C.
 This type of flame is not successfully used for heating applications.
Figure 27 - Acetylene flame.
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NOTES
Carbonizing Flame
When oxygen is added to the acetylene flame and as the oxygen flow approaches the
preset flow of the acetylene, the flame becomes carbonizing (carburizing). The
carbonizing oxyacetylene flame shows as a feather on the end of the cone (Figure 28).
The amount of feather indicates the amount of excess acetylene in the flame. Excess
acetylene produces excess carbon in the flame and hence the title carbonizing flame.
 The whole flame in general takes on a blue colour.
 A white feather encloses and extends beyond the primary flame cone as shown.
Figure 28 - Carbonizing flame.



A longer feather indicates a surplus of acetylene versus oxygen being consumed
within the flame.
The flame temperature is cooler than a neutral flame.
A carbonizing flame adds carbon to the molten puddle and thus has limited use.
There are a wide variety of tip sizes and types and each one has its own length of cone
and feather. Therefore, the comparison of the amount a flame is carbonizing is made in
relation to the length of the neutral cone, regardless of tip size. This method of
comparison is known as the X system of carbonizing flames. Thus with a 2X flame, the
feather and cone are equal in length. With a 3X flame, the feather is twice as long as the
neutral cone and with a 11/8 X flame, the feather is 1/8 the length of the neutral cone
(Figure 29).
Figure 29 - Carbonizing flame.
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NOTES
Neutral Flame
A neutral flame, such as that shown in Figure 30, occurs when the oxygen flow, relative
to the preset acetylene flow, is increased to the point when the feather just disappears into
the primary flame.
 The primary flame is bright, luminous and has a distinct round tipped cone shape
about 1 cm long. The secondary flame (envelope) is bluish in colour with red
flecks and extends 20 cm to 30 cm beyond the primary flame.
Figure 30 - Neutral flame.


The flame temperature is approximately 3300°C.
A neutral flame is the recommended flame for heating and cutting mild steel. The
neutral flame adds nothing nor takes anything away from the steel.
Oxidizing Flame
An oxidizing flame (Figure 31) occurs when the oxygen flow, relative to the preset
acetylene flow, is increased beyond the point when the feather disappears.
 The primary flame cone becomes shorter, sharper and paler blue than a neutral
flame. The secondary flame becomes shorter. This flame type is accompanied by
a harsh sound.
 There is an excess of oxygen versus acetylene being consumed within the flame.
Figure 31 - Oxidizing flame.



26
The flame temperature is hotter than a neutral flame.
Carbon will be oxidized and removed from steel.
Avoid using an oxidizing flame.
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NOTES
Backfires
A backfire occurs when the flame backs up into the tip and mixer. See Figure 32. This
results in a small explosion within that area where the gases are normally mixed. You
hear a loud snap or pop and the flame goes out. The flame re-establishes itself almost
instantly from the hot steel. Other than the loud pop, this is generally not a serious
malfunction. When a backfire occurs, correct the cause and continue heating.
Figure 32 - Backfires occur in the torch where shown.
Backfires are caused by the following conditions.
 Too slow gas flow may occur when lighting the torch if you do not open the
acetylene torch valve enough. (Adjust the gas flow to above the black smoke
range.)
 Obstruction of gas flow, such as when holding the torch tip too close to the work,
can cause backfire.
 Loose or faulty seat connections between the tip and mixer will cause backfire.
 A dirty tip, such as metal particles collecting on the tip end, tends to retard gas
flow and cause backfires.
 A worn out tip will have an enlarged orifice allowing the gases to flow slower
and thus backfire easier. Worn tips should be replaced as required. Use
recommended tip maintenance procedures to maximize the life of your tips.
 A hot tip can be caused by working in deep grooves or blind holes. The hot tip
pre-ignites the gases in the tip. The flame burns inside the tip and a rapid series
of backfires occurs.
Continuous Backfire and Burnback
A continuous backfire is a rapid, repeated backfiring (popping) within the tip and mixer.
A burnback is continuous combustion within the tip and mixer, indicated by a screeching
sound as well as black smoke emitted from the tip. The probable cause is a hot tip preigniting the gases. The tip and torch handle become hot immediately. If the condition
continues, the torch could melt down within a few seconds. Both the acetylene and
oxygen torch valves should be closed immediately stopping the flow of gases to
extinguish the combustion. To cool a hot tip, close the torch valves, open the oxygen
valve and quench the torch in water. The oxygen will blow the water out of the tip. Shut
off the oxygen and re-light the torch.
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NOTES
Figure 33 shows continuous backfire, burnback and flashback.
Figure 33 - Continuous backfire, burnback and flashback.
Flashback
Under normal operating conditions, the oxygen and acetylene gases remain separate and
pure in their respective hoses including the torch handle, hose and regulator. It is
possible; however, for the gases to become mixed, such as oxygen in the acetylene hose
and acetylene in the oxygen hose. A flashback is the combustion or explosion that can
occur within the hoses when this gas mixture is ignited. This is a very serious
malfunction that will do major damage to the equipment. If a flashback has occurred and
the ruptured hoses are burning, shut off the cylinder supply valves. Flashback occurs
within oxyacetylene equipment in the areas shown in Figure 33.
Flashbacks can only occur if the gases have become mixed in the separate lines. The
gases can become mixed due to the following situations.
 Grossly unequal pressures. The higher pressure gas backs up into the lower
pressure hose.
 Mildly unequal pressure plus an obstruction. Should tip blockage occur, always
close off both torch valves immediately. Then you can clean the tip.
 Failure to purge each hose individually before lighting the torch. A torch that has
been sitting idle for awhile may have an explosive mixture present in one or both
hoses.
 Faulty manipulation of valves. This may occur by lighting a torch with both torch
valves open or otherwise failing to operate equipment in the recommended
manner.
Use these methods to avoid flashbacks.
 Purge each hose individually and thoroughly before lighting the torch.
 Install one-way check valves.
 Closely adhere to recommended set-up and operating procedures.
 Keep equipment in good repair.
 Balance gas pressures when heating and welding.
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NOTES
Oxy-Fuel Cutting
Steel is heated until it reaches its kindling temperature (red heat). Then, a stream of pure
oxygen is introduced which rapidly oxidizes (burns) the steel in its path. The molten iron
oxide is removed by the stream of oxygen resulting in a kerf or cut gap. Heat from the
burning process helps preheat the steel ahead so the cut is continuous and progressive.
The temperature of the burning steel is lower than the melting point of steel; thus, the
edges of the kerf remain square. Ferrous materials (iron and steel) can be cut with the
oxy-fuel cutting process. Cast iron, stainless steels and non-ferrous metals will not burn
progressively and thus, cannot be cut.
The cutting attachment (Figure 34) fixes to the torch handle in the same manner as a
welding or heating tip. The cutting attachment channels the fuel, as controlled by the
torch handle fuel valve, directly to the preheat holes of the cutting tip. When using the
cutting attachment, keep the oxygen torch handle valve fully open (3 or 4 complete
turns). The cutting attachment directs the oxygen flow through two different paths. When
you open the oxygen preheat valve located on the cutting attachment, oxygen flows to the
preheat holes on the cutting tip and mixes with the fuel to feed the preheat flames.
When you depress the oxygen cutting lever, the oxygen cutting valve opens and allows a
large volume of oxygen to flow through the oxygen outlet at the centre of the tip to form
the cutting stream. Propane is a popular alternative to acetylene as a fuel for cutting
applications. Select the appropriate tip type designed for the gas being used. Various tip
sizes and styles are available for various job applications.
Figure 34 - Cutting attachment.
Figure 35 shows cutting tip outlets.
Figure 35 - Cutting tip outlets.
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NOTES
Set-Up Procedure
Follow the same basic set-up procedures for the oxy-fuel outfit as described earlier in this
objective.
1. Install the cutting attachment onto the torch handle.
2. Select the cutting tip size for the job at hand.
3. Ensure torch valves and cutting attachment valves are closed and regulator
adjusting screws are fully released.
4. Open the cylinder valves slowly to the desired amount (oxygen fully open and
acetylene to a maximum of 11/2 turns).
5. Set approximate regulator pressures for the job at hand relative to metal thickness
and tip size. (See Table 3 for approximate sizes.)
6. Purge both oxygen and fuel gas lines individually before lighting the torch.
Approximate Cutting Torch Gas Pressures
1/4
3/8
1/2
3/4
1
11/2
2
0
1
1
2
2
3
4
18
20
21
23
25
28
30
Oxygen Pressure psi (kPa)
(124 kPa) (138 kPa) (145 kPa) (159 kPa) (172 kPa) (193 kPa) (207 kPa)
5
5
5
5
5
6
6
Acetylene Pressure psi (kPa)
(34 kPa) (34 kPa) (34 kPa) (34 kPa) (34 kPa) (41 kPa) (41 kPa)
*Cutting tip sizes may vary from manufacture to manufacture.
Metal Thickness (Inches)
Cutting Tip Size *
Table 3 - Approximate cutting torch measures.
Lighting the Torch
Follow these procedures when lighting the torch.
1. Open the oxygen torch handle valve fully (3 to 4 complete turns) and leave it
open until you are shutting the torch down.
2. With the preheat oxygen valve closed, open the acetylene torch valve about one
half turn and ignite the flame. Increase acetylene flow to desired proportions, but
do not attempt to take the flame beyond the smoke range or preheat will likely be
excessive.
3. Add oxygen to preheat flames by slowly opening the oxygen preheat valve on the
cutting attachment. Continue to adjust the oxygen preheat valve until the preheat
flames are neutral.
4. Depress the cutting lever and adjust the preheat oxygen valve to achieve a neutral
flame while cutting. Be specific; add oxygen to the point when the feather just
disappears.
Extinguish Flame
To extinguish the flame, follow these steps.
1. Close the acetylene torch valve to extinguish the flame quickly without leaving
carbon deposits within the tip.
2. Close the oxygen preheat valve on the cutting attachment. Leave the oxygen
torch handle valve open until you are shutting down the outfit.
Shut Down Procedures
Follow the same shut down procedures for the oxy-fuel outfit as described earlier in this
objective.
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NOTES
Factors for a Quality Cut
There factors that determine a quality cut are outlined in this section.
Clean Tip
Before beginning the cut, inspect the preheat flame inner cones, as in Figure 36). When
set at a neutral flame, they should be equal in length, size and adjustment. If the primary
flame cones are malformed or of different lengths, this may be caused by an obstruction
to the preheat orifice or there may be a build-up of carbon fluff within the length of the
tip. Shut off the torch and carefully clean the preheat orifices with tip cleaners. The
carbon fluff can be cleaned out by removing the tip, disassembling and blowing out the
orifices with compressed air.
Figure 36 - Unequal length preheat inner flame cones.
CAUTION
The fine tip cleaners are easily wedged and broken off inside the
preheat holes. Avoid cleaning the preheat holes, if possible. Try
scraping the spatter from the end of the tip first. The larger cutting
orifice can be cleaned with less risk.
A straight oxygen stream (Figure 37) is most important for a good quality cut. Depress
the cutting oxygen lever and observe the oxygen jet stream. The jet stream should be
straight through the length of the secondary flame and you should hear an aggressive
raspy sound. If the cutting jet stream is not straight and you hear a hissing sound, shut off
the torch and clean the cutting orifice in the tip. A worn or abused tip may not provide a
straight jet stream with a crisp sound and will need to be replaced for best results.
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NOTES
Figure 37 shows an oxygen jet stream.
Figure 37 - Oxygen jet stream.
Correct Gas Pressures
Approximate gas pressures are indicated in Table 3, but you can establish more precise
pressures using flame characteristics as indicators.
Oxygen pressure is most critical to the cut quality. You can establish the precise oxygen
pressure by listening to the sound emitted from the torch. Using a clean tip with an
appropriate cutting flame lit, depress the cutting lever and make adjustments to the
oxygen regulator adjusting screw while observing the sound of the torch. When the
oxygen pressure is too low, the sound will be soft, lazy and non-aggressive. When the
oxygen pressure is too high, the torch will have an aggressive hissing sound. There will
be a range between too low and too high where the torch will have a crisp, raspy sound.
Set the oxygen pressure within that range to suit your needs with respect to the limits of
that tip size. Set toward the lower end for cutting thin metals and through one layer of a
lamination (removing a bearing). Set toward the higher limit when cutting thick objects.
Set in the middle for medium thicknesses. The acetylene gas pressure can be established
in the same manner as described in the balancing procedures using a welding tip. Light
the cutting torch with acetylene only. Open the acetylene torch valve 3 to 4 complete
turns. Adjust the acetylene regulator to a point where there is a gap of approximately 5
mm between the base of the flame and the copper tip. When using propane, a gap of 2 cm
to 3 cm. will provide the correct results.
Heat Build-Up
32
When the heat build-up within the object being cut is just right, the cutting speeds will be
efficient, the kerf marks will be smooth, uniform and straight, the top edge of the plate
will be square, the bottom edge will be relatively slag free and clean up will be minimal.
Heat build-up is determined by the selected tip size and flame setting, by the amount of
preheat and by the rate of travel. A little preheat (200°C to 300°C) will allow the cut to
initiate easily and to progress smoothly and efficiently across the plate. Not enough heat
(small tip, small flame setting) will make it difficult to start the cut and will require slow
rate of travel to keep the cut going. Too much heat (large tip, big flame, slow travel) will
cause the top edge of the plate to melt and large amounts of slag to hang up on the
bottom.
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NOTES
Objective Four
When you have completed this objective you will be able to:
Demonstrate use of personal protective equipment and safe operating procedures.
In this section, we refer back to module 320102a Welding Safety. Be aware of the hazards
associated with oxy-fuel welding and cutting activities. Use the recommended personal
protective clothing and equipment as described.
Goggles
You must wear approved welding and cutting goggles when using oxyacetylene
equipment. These goggles are essential to protect your eyes against light rays, heat rays,
flying sparks and slag. The lenses for welding and cutting goggles are identified by
number and by colour. The most suitable lens for heating and cutting is either a #4 or the
darker #5 in a green shade. If you are nearsighted, you can insert additional corrective
lenses with the darkened lens. Two common types of goggles are shown in Figure 38.
Figure 38 - Goggles.
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NOTES
Objective Five
When you have completed this objective you will be able to:
Perform heating, welding, and cutting operations using oxy-fuel equipment.
Cutting
With the torch lit and adjusted, hold the torch with both hands to position the cutting tip
90° to the plate and the tips of the preheat flames approximately 4 mm above the plate
surface. Do not touch the primary flames to the steel. If the plate is cold or is thicker than
1
/4", pass the flame back and forth a few times adjacent to the line of cut to preheat the
plate to above the boiling point of water. Then, where you want to start the cut, heat the
steel to the red heat. It is always best and fastest to start the cut at the plate edge, at a
projection or at a hole. Move the torch out beside the plate edge so a portion of the flame
is still heating the steel, but the oxygen stream will miss the steel. Depress the cutting
lever fully and slowly move the oxygen stream into the steel allowing time for the cut to
be established through the entire depth of the material. With careful attention to smooth
rate of travel, torch angle, height of the torch above the plate and, following the line of
cut, proceed across the steel plate. The cut or burn should be continuous. Release the
cutting lever to stop the cut (Figure 39).
It may be to your advantage to drill a hole through the plate or build up a projecting weld
metal bead as a starting point. A chisel may also be used to raise a sliver or chip of metal
on which to start the cut. When cutting a round bar, it will be necessary to preheat the
entire shaft diameter close to the red heat before starting the cut.
Figure 39 - Starting the cut.
Travel Speed
Kerf line drag is affected by your torch travel speed. Use the draglines to assist you in
determining whether your travel speed is too slow, too fast or just right for the job at hand
(Figure 40). If your travel speed is too slow, the kerf lines will be ragged because your
hand will wiggle more times in one spot and cause gouges. If your travel speed is too
fast, this often results in slag bubbling up to the surface of the plate because the cutting
jet stream cannot blow through the full thickness of the material. Using a tip that is too
small or insufficient oxygen pressure can lead to the same problems. In Figure 40:
 A has satisfactory drag for general cutting and shape cutting,
 B shows curved draglines created with increased cutting speed and
 C has excessive drag that may result in the cut being incomplete in places and
slag removal being difficult.
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NOTES
Figure 40 - Draglines and travel speed.
Torch Inclination
The use of correct torch inclination (slope in the direction of travel) is important to both
the quality and speed of the cut. In general, the torch should be 90° to the plate when
shape cutting and, when cutting plate, thicker than 3/8". Thinner materials require more
inclination than thicker materials. Torch inclination for several different thicknesses of
material is shown in Figure 41.
Figure 41 - Torch inclination.
NOTE
Always use the recommended tip size for the thickness of the material
you are cutting. For example, in Figure 40, you would likely be using
a larger tip for the 12.7 mm (1/2") material than for the 20 gauge
material. On the other hand, the smallest tips for standard cutting
torches are generally too large for light gauge sheet metals. This is
where torch inclination is of particular importance.
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NOTES
Cut Slag to Scrap or Waste and Save Cleaning Time
Wherever bevel cuts are made, the slag always collects on the piece that the tip is
pointing toward. If the operator cuts a slight bevel, the slag will collect on the scrap
material leaving the wanted piece free of slag (Figure 42). This practice can save you
valuable cleanup time.
Figure 42 - Angling the torch toward the scrap portion.
Hole Piercing
If it is not possible to start a cut from an edge, projection or hole, you can pierce a hole
with the torch. The greatest problem with hole piercing is that molten oxide and slag can
blow back into the tip partially obstructing the cutting oxygen stream and cause a
backfire. To avoid this, use the following procedure.
1. Adjust oxygen pressure to be minimal for that steel thickness.
2. Preheat to the red colour completely through material thickness.
3. Raise the torch 2 cm to 3 cm above the plate as you begin to depress the cutting
lever. This allows the slag to blow clear of the tip.
4. Depress the cutting lever slowly to avoid a sudden splash of slag.
5. If space allows and when piercing 1/2" plate and thicker, travel forward as you
depress the lever to allow the slag to blow out behind the tip.
6. Once the material is pierced completely through, lower the torch to normal flame
position and continue with the cut holding the cutting lever fully depressed.
The steps in piercing are shown in Figure 43.
Figure 43 - Hole piercing.
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NOTES
Cutting Nuts, Bolts and Rivets
When cutting nuts, bolts and rivets, you must cut with caution so you avoid cutting or
gouging the surrounding material. Set oxygen pressure at minimum. Preheat the complete
nut, bolt or rivet head to the red heat quickly by pointing the flame directly at it while
minimizing heat input to the surrounding plate. Quickly position the torch so the cutting
stream will be parallel with the plate surface and the preheat flames are 1 cm back.
Depress the cutting lever slowly. Observe the results making flame position corrections
as you cut. Cut quickly to minimize heat build-up in the plate. This process is shown in
Figure 44.
Figure 44 - Cutting nuts, bolts and rivets.
Cutting a Bearing from a Shaft
When cutting a bearing from a shaft, as shown in Figure 45, it is imperative that you do
not scar or gouge the shaft. Make every effort to preheat and cut the bearing ring quickly
before the shaft warms up to the kindling temperature. If you do gouge the shaft, the
resulting stress concentration will be less severe if the gouge is lengthwise relative to the
shaft, rather than crosswise. The outer bearing race can be cut in the same manner, but
with considerably less risk to the shaft. The following is the procedures for cutting the
inner race.
1. Set the oxygen pressure at a minimum.
2. Concentrate the preheat directly onto the bearing ring using a fairly large flame
so the bearing heats quickly before the heat transfers into the shaft.
3. When some red heat begins to show on the ring, quickly lay the torch angle over
so the oxygen stream is parallel with the shaft.
4. Start the cut at the outer circumference of the ring. Depress the lever slowly and
draw the torch away from the ring to minimize flame heat into the shaft.
5. Allow time for the burn to progress across the full width of the ring before you
move the cut down toward the shaft.
6. Stop immediately when the cut reaches the lamination between the ring and the
shaft.
Figure 45 - Cutting inner bearing race from a shaft.
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NOTES
Common Cutting Faults
You need to be able to recognize acceptable quality cuts and be capable of problem
solving when the cut is of poor quality. An examination of the kerf lines can tell you
much about what variable needs correcting. Figure 46 illustrates cross-sections of several
oxy-fuel cuts. You can see what the cross-section of a good cut should look like and you
can also see some examples of poor cuts and their likely causes.
Figure 46 - Common cutting faults. (Courtesy ESAB Welding &Cutting Products)
Cutting Methods
The three common methods of controlling the torch when performing a cut are:
 across cut,
 push cut and
 pull cut methods.
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Across Cut
With this method, (see Figure 47 for illustration), the torch body is held at approximately
90° to the cut line. This angle is not strict and can be changed to suit your own comfort
zone. A right-handed person will usually use their right hand to control the oxygen
cutting lever. The forearm and wrist of your other hand is supported on the work table or
the material being cut. This support hand holds the torch in your finger tips along the
barrel. With finger movement, wrist action and arm rolling, you can smoothly guide and
manipulate the torch through a wide range of movement along the cut line without having
to slide your hand. That front support hand can also act as a pivot point when cutting an
arc.
Figure 47 - Across cut method.
Push or Pull Methods
The push and pull methods are sometimes referred to as drag methods. With these two
methods, hold the torch in line with the cut and either push it away from you or pull it
toward you. With both of these methods, the pivot hand becomes a balance point. Rest
the torch on the balance hand and push or pull across it. In some instances, the balance
hand is pushed or pulled along with the torch in order to achieve longer cuts without
having to stop and restart the cut.
Figure 48 - Bevel cutting using the pull method.
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Fusion Welding Steel
It is possible to weld almost any metal with excellent results using the oxyacetylene
process. You have the heat source in one hand and the filler material in the other hand
and you are in control of when and how much of each is added. You would choose the
oxyacetylene process to repair or modify relatively small or thin steel parts. Welding on
large, thick bodies of steel is slow, inefficient and hot. You should choose an arc welding
process for these situations.
Fusion Welding Procedure
The welding procedure listed below is illustrated in Figure 49.
1. Select acetylene gas as the fuel for flame welding applications.
2. Install a welding tip sized to match the job at hand.
3. Balance the pressures for the tip you are using.
4. Use a neutral flame.
5. Select the filler rod to match the parent material to be welded.
6. Hold the torch in your dominant hand and the filler rod in the other hand.
7. Position the flame so the primary flame is about 4 mm away from the plate. Do
not touch the primary flame to the plate or the molten puddle.
8. Angle the flame so it splits the included angle of the joint to be welded (45° for a
90° joint).
9. Incline the flame so it is pointing about 15° forward in the direction of travel.
10. Hold the torch in this position and wait for a molten puddle to develop the size
and depth that you require (8 mm approximately on 11-gauge plate).
11. Move the torch across the plate adjusting the speed to maintain a constant puddle
size and fluidness.
12. Add filler material by periodically dipping the filler rod into the puddle and allow
time for the puddle to melt the desired rod length. Bring the rod in from the front
of the puddle.
13. Vary the frequency of adding the rod and the time holding the rod in the puddle
to control the amount of fill forming the weld bead.
Figure 49 - Fusion welding.
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Variables of Molten Puddle Control
The following factors are important to the control of the molten puddle and ultimately to
the size, shape and quality of the weld bead:
 amount of heat, tip size and size of flame;
 torch angle;
 torch inclination;
 torch-to-work distance;
 speed of travel;
 addition of filler rod and
 torch manipulation.
Amount of Heat
Manufacturers of oxyacetylene welding equipment provide different size welding tips so
you can take advantage of different heat volumes. You also have the option of setting the
flame larger or smaller within each given tip size. Your own experience can be your best
guide to selecting the right size tip and torch setting. If the puddle is sluggish and you
have to wait a long time for metal flow, you need to increase heat input. On the other
hand, if the puddle is very fluid and difficult to control, you need to reduce heat input.
This may only require an adjustment of the torch valves or may require you to change to
another tip size. The following are some points to consider for tip size and torch heat
setting.
Consideration must be given to the thickness, body mass and type of material to be
welded. Large, thick masses require large faster heat input. Thin light gauge plate
requires small heat inputs. Some materials conduct heat more readily than others, thus
require faster input of heat.
The type of weld to be made (for example a fusion weld, braze weld or brazing
application) affects required heat setting, flame type and tip size selection.
The position of the weld may well influence tip size and torch heat setting. For example,
many welders use less heat in the vertical and overhead positions than they would in the
flat position.
Angle
This term relates to the angle that is formed between the flame and the workpiece across
the direction of travel. The angle of the flame is generally one half the angle formed by
the pieces making the joint. This rule may be altered by local conditions such as joint
configuration, gravitational pull, position of work or when welding pieces of different
thickness. Use the angle of your flame to direct the weld puddle where you want it. The
puddle tends to flow in the direction the flame is pointed.
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Inclination
The two terms forehand and backhand refer to the inclination of the flame in relation to
the workpiece when welding. With forehand, you point the flame in the direction of
travel. With backhand, the flame is pointed back at the puddle. When oxyacetylene
welding, the forehand method is used far more extensively than backhand. Changing the
inclination affects the size and shape of the weld profile and the depth of penetration.
With the flame inclined perpendicular with the plate, most of the available heat is
directed into the plate. The puddle will tend to be hotter, larger, more fluid and deeper.
The weld bead will be wider, flatter and with deeper penetration. As the flame inclination
increases, a greater amount of heat is lost into the air. The puddle will tend to be narrower
and cooler, producing a weld bead that is narrow with a higher build-up.
Torch-To-Work Distance
How close you hold the torch to the work has a direct bearing on puddle flow and
penetration. When you shorten this gap, you concentrate the heat, which increases the
depth of penetration while, at the same time, narrows puddle flow. Touching the primary
flame to the puddle creates adverse puddle turbulence that is difficult to control. When
you increase this gap, the heat spreads out, the puddle flow is wider and penetration is
reduced.
Travel Speed
Your travel speed (rate or progression across the weld joint) influences heat build-up and
rate of fill. Travelling slow will cause the puddle to become hotter and more fluid.
Travelling slow gives you the chance to put in more fill in any one spot. You will get the
opposite effect by travelling faster.
Addition of Filler Rod
Add filler by laying the rod directly into the puddle. As you add filler rod to the puddle,
you should see the puddle build up. Then, when you remove the filler rod, you should see
the puddle flow ahead and flatten. Staying in the puddle longer and going back in sooner
will provide more fill. When the rod is in the puddle, it will tend to cool the puddle.
Select the rod size proportional to the puddle size. The filler rod needs to be large enough
to chill the puddle, yet small enough to melt quickly when added. Filler rods come in
sizes of 1/16", 3/32", 1/8" and 3/16" diameters. Welding on 11 gauge plate would require a
3
/32" filler rod.
Torch Manipulation
A stepping and a weaving action may be used in some welding operations to help control
weld puddle temperature. Joint configuration and welding position often dictates whether
a torch manipulation is necessary. A stepping and weave action is often accompanied
with a momentary pause. The pause time is used to help control weld puddle fluidity,
wetting at the toes of the weld and finished bead appearance.
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NOTE
The above listed welding variables are what you use to control the weld
puddle, regardless of the welding process you use or the type of
material you weld. They cannot be treated as individual entities as they
all work together. Welders improve weld quality as they master control
of these variables simultaneously. Your welding instructor will assist
you in learning puddle control via demonstrations, prescribed exercises
and personal coaching.
Brazing
The term brazing refers to several processes using a variety of heating devices, types of
fluxes, base metals and alloy filler materials. Brazing enables the joining of dissimilar
metals by bonding rather than fusion. The filler material melts, but the base metal does
not melt. The filler metal is a non-ferrous alloy (for example, copper, brass or silver) and
has a melting point above 425°C, but below the melting point of the base metal.
The bond between the filler metal and the base metal is obtained by the penetration of a
low viscosity brazing alloy into the grain boundaries of the base metal. This means a
certain amount of mutual diffusion takes place to produce a band of intermediate alloy
composition. This is sometimes referred to as surface alloying.
Brazing is selected rather than fusion welding in the following situations:
 joining dissimilar metals (for example, copper tube to a steel fitting);
 joining light gauge metals, especially galvanized steel;
 where less heat is an advantage, (eliminate burn through, less distortion, minimal
effect on mechanical properties) and
 where sweating between two surfaces is essential (for example, sealed joint for
fuel line fittings).
Disadvantages of Brazing
The disadvantages of brazing are listed below.
 Braze welded joints will fail when subject to intense heats such as exhaust
manifolds.
 Braze welded joints are a poor choice where colour match is essential.
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Factors Necessary for a Good Quality Bond
The factors necessary for a good quality bond are listed below.
1. The base metal must be clean and free of any scale, rust, grease, oil, dirt and
oxides that may interfere with the filler material coming in contact with the base
metal. This can be accomplished by grinding, filing, sanding or sandblasting. Do
the cleaning just prior to brazing.
2. Apply a flux (Figure 50) to cover the cleaned surface to be bonded. Flux is the
term given to a group of chemicals that function as deoxidizers and prevent the
formation of oxides during the brazing operation. The flux may be applied prior
to the heating process (as with the silver brazing) or simultaneously with the
filler material (as with braze welding).
Figure 50 - Some of the fluxes used for oxy-fuel welding and brazing.
3. The base metal must be heated to the correct temperature; not too hot and not too
cold. When the base metal is at the correct temperature, the flux will be a clear
liquid. When silver brazing, the steel will have a faint red tinge of colour. When
using a brass filler, the steel will be a dull red colour. When the filler material is
added, it will melt and flow freely onto the surface of the base metal. When the
base metal is too cool, the filler material remains in a ball and will not flow.
Overheating will cause the flux to burn off, the surface of the base metal to
oxidize and the filler metal to be scorched.
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Silver Brazing
Silver brazing (low temperature brazing, silver solder) uses silver and copper alloys as
filler material.
Common alloys are:
 Easy Flo #45 - melts at 620°C and is used for ferrous applications and
 Sil-fos - melts at 800°C and is used for copper based metals.
The molten filler metal distributes freely between closely fitted surfaces by capillary
action. Most ferrous metals can be brazed with this process. It is essential the joint
surfaces are well cleaned. Handy flux is manually spread throughout the joint surfaces
prior to the heating process.
The strength of the bond between the filler alloy and the base metal is greater than the
yield strength of the base metal. For optimal joint strength, it is critical to have no more
than .003" to .004" clearance between the parts.
Procedure
Follow this procedure when brazing.
1. Design the joint or a support jig to maintain alignment during the heating
process.
2. Clean all joint surfaces to be bonded.
3. Apply flux paste to all surfaces to be bonded.
4. Assemble the unit. Ensure alignment and support. Parts can move or sag when
the brazing alloy becomes liquid.
5. Heat the parts slowly and uniformly to allow time for the heat to penetrate
through the parts and so they all reach the bonding temp at the same time. Keep
the torch moving around and use the secondary flame as the heat source.
6. Observe the temperature indicators carefully. The flux will be clear liquid, the
steel will have a faint red colour and the filler alloy will melt and flow freely.
Avoid getting things too hot.
7. Add the filler alloy by laying it into the joint against the hot steel. Let the heat of
the steel melt the alloy rather than direct heat from the flame. It is sometimes
beneficial to place a shim of filler alloy within the joint prior to heating.
8. Let the joint cool slowly in air. Do not attempt to move until the alloy solidifies.
Uses for Silver Brazing
Some uses for silver brazing are as follows.
 Install fittings on pressurized fuel lines, refrigeration units and hot water heating
systems.
 Manufacture of carbide tipped tools.
 Repair fractured cast iron and high carbon steel. Such brittle breaks will usually
fit back together in perfect alignment. The joint is bonded by sweating the silver
alloy between the two parts.
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Figure 51 - Lap joint for brazing copper tubing.
Braze Welding
This process uses brass as the filler metal. The molten brass exhibits little or no capillary
action. The welder places the brass filler material by manipulating a molten puddle. The
parent plate does not melt. The weld is started at one end of the joint and progresses
across the joint similar to fusion welding. Braze welding is used in fillet and groove type
joints. A good bond can be obtained with most ferrous metals. It is essential to have clean
surfaces and use flux. The flux for braze welding is designed to function at the higher
melting point of brass (900°C). It is most convenient to use a flux coated filler rod.
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Procedure
Follow this procedure when braze welding.
1. Grind clean the surfaces that will come in contact with the brass filler. On cast
iron repair jobs, make the vee joint 90° wide to provide maximum surface area
for bonding. To help alignment of cast iron parts, leave portions of the original
break surfaces un-ground so the parts will align themselves.
2. You will probably require one size smaller tip for braze welding compared to
fusion welding on steel plate of the same proportions.
3. If the parent material is cast iron, preheat the whole unit slowly and uniformly to
avoid cracking problems relative to unequal expansion. On thin sections of steel,
you will have to consciously avoid applying any extra heat to the surrounding
plate.
4. Heat the plate at the starting point to a faint red colour. Hold the filler rod in
close to the flame so it also gets hot.
5. Lay the filler rod on the plate and with the primary flame in close, heat the plate
surface and the filler rod a little bit more to melt the filler and have the plate
warm enough to accept the brass.
6. Like fusion welding, you will manipulate the flame and add filler material
observing the brass flow and bond with the plate and fill the joint to the desired
level.
7. Allow the joint to cool in air when completed.
Uses for Braze Welding
Use for braze welding include the following.
 Repair welding of small cast iron items. Brazing is not practical on large
transmissions and engine blocks.
 Joining a copper component to a steel component.
 Joining light gauge sheet metal and galvanized sheet metal. The joint can be
made without destroying the zinc coating.
DANGER
Zinc and cadmium are metals found in common brazing alloys. Zinc
and cadmium fumes are toxic. Use extreme caution. Do not overheat
these alloys. Make sure you have adequate ventilation.
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Objective Six
When you have completed this objective you will be able to:
Describe temperature indicators and the effect of heat on metal.
Effect of Heat on Metal
The mechanical properties of metals are greatly influenced by heating and cooling
processes. The maximum temperature reached and cooling rates are important. Metal
machinery parts have been engineered and manufactured and, at times, heat-treated to
possess specific properties relative to their function. You must understand that any time
you heat or weld on steel, there is a possibility that the mechanical properties will be
altered. Also, while heating or welding on one part, the heat transfer either through the
metal or from the flame can affect other nearby components.
The following are descriptions of important heat indicators and the results that you must
be aware of.
48
Condition
Result
sub-freezing
temperatures
Steel is very brittle when subjected to temperatures below
the freezing point of water. It cannot handle shock and
impact. High impact stress points such as axles, drawbars
and frames will suffer catastrophic failures under
seemingly small loads during the cold winter. Take it slow
and easy when operating machinery under cold conditions.
Gently preheat steel up to room temperature or higher
before doing any bending or pounding.
room temperature
Most metals are designed and engineered to function at
normal summer temperatures.
boiling point of water
Steel becomes less brittle, more malleable, tougher and
able to withstand greater external forces. It tends to bend
rather than fracture. From boiling point and hotter, you
can be burnt from contact.
two to three hundred
degrees Celsius
The metal is now hot enough to melt or burn rubber seals
and O-rings, burn insulation from electrical wires and
damage electronic components. Petroleum products could
spontaneously ignite.
temper colours
The yellow, brown, purple and blue temper colours
indicate steel temperatures ranging from 250°C to 350°C.
These are oxides forming on the steel surface. These are
specific indicators used by heat treaters when tempering a
chisel or centrepunch following a hardening heat
treatment. Steel is now hot enough to lose some of its
original hardness.
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Condition
Result
black heat
There is a range beyond the temper colours up to 900°C
when the steel takes on a shiny bluish/black surface
colour. At the top end (700°C through 900°C), the atomic
structure of steel undergoes a complete transformation.
The mechanical properties and grain structure are
dramatically altered. There are no visual indicators
relative to exact temperatures within this range. You may
be required to preheat parts to specific temperatures within
this range for stress relieving purposes or to expand them
prior to installing. Temperature indicator crayons are used
to determine precise temperatures as needed. Medium to
high carbon steels will crack very easily within this range
either due to unequal expansion or external force. Heat
and cool slowly and uniformly and avoid bending and
shaping steel through this range. It is easy to burn yourself
on steel in this temperature range because it looks the
same as room temperature steel and you may touch it
before realizing that it is hot.
dull red
The steel body is red in colour with dark shadows (900°C
to 1000°C). The atomic transformation is complete. Steel
is heated to this temperature and quenched in water to
harden it. Or if cooled very slowly over several hours
from this dull red heat, the steel will end up soft and
ductile when back at room temperature. Upon cooling
from the dull red heat, the grain size will be very fine.
This is the approximate temperature for braze welding.
Combustible materials will ignite on contact.
cherry red
The steel body is glowing red (1200°C to 1300°C). The
steel is now very malleable and tough and it takes little
force to deform the steel. Heat to this temperature to shape
and bend steel. This is too hot for brazing. The flux will
burn off, the steel surface will oxidize and the zinc will
oxidize from the brass. You will not get a good bond.
Cooling from the cherry red heat will create medium size
grains.
white red
The steel body gives off a bright luminous white glow
(1400°C). The melting point is approaching.
melting point
The steel is molten (1480°C). The steel is glowing white
while the puddle surface is shiny and reflective. Steel must
melt for fusion welding. Cooling from the molten state
will create very coarse grains within the steel.
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Rules to Remember when Welding
The heating and cooling process has a great influence on mechanical properties of metals.
You are not expected to have full knowledge and understanding. However, you will have
occasion to weld, cut and heat steel as you practice your trade. Be aware and practice the
following rules to maximize your success.
 Heat only as hot as necessary to get the job done. Higher temperatures cause
more dynamic changes.
 Preheat cold and thick sections before arc welding to prevent cracks relative to
the welds. Having the steel warm slows the cooling rate of the weld metal.
 Preheat high carbon steels, tool steels and cast iron slowly and uniformly to
prevent cracks due to unequal expansion and contraction.
 Cool welds and surrounding metal slowly in air. Some high carbon steels and
cast iron will be best buried in insulation to further slow the cooling rate.
 Do not quench from a red heat unless you desire high hardness as a property.
 The welding of broken objects, which have been hardened and tempered, is not
generally satisfactory unless you are prepared to match the filler material to the
analysis of the steel and, after welding, reharden and temper the entire object to
the specifications which existed before welding. For example, springs,
automotive axles or spindles should not be welded. Do not jeopardize the lives of
others by welding such objects!
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Self-Test
1. Goggles are worn when using oxyacetylene equipment to protect the eyes from:
a) light.
b) heat.
c) sparks and slag.
d) all of the above.
2. To check for leaks in oxyacetylene equipment, you should use:
a) a match.
b) a lighter.
c) soap and water.
d) any of the above.
3. When using oxygen from a cylinder, you should open the valve:
a) fully.
b) no more than 2 turns.
c) no more than 1 turn.
d) no more than 1/2 turn.
4. Acetylene should only be drawn from an acetylene cylinder when the cylinder is:
a) located with the words UP ONLY pointing up.
b) upright.
c) on its side.
d) upside down.
5. As cylinder pressure decreases, the outlet pressure from a pressure regulator:
a) goes down.
b) remains constant.
c) goes up.
d) goes up at first and then down.
6. The colour of an oxygen hose used with oxyacetylene equipment is:
a) yellow.
b) orange.
c) red.
d) green.
7. The colour of an acetylene hose used with oxyacetylene equipment is:
a) red.
b) green.
c) orange.
d) purple.
8. All fittings used for oxygen in oxyacetylene equipment:
a) are identified with an annular groove.
b) are left-hand thread.
c) are right-hand thread.
d) are metric.
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9. Check valves used with oxyacetylene equipment are installed in:
a) the oxygen hose.
b) the acetylene hose.
c) both a) and b).
d) neither a) or b).
10. When you are finished using oxyacetylene equipment, the oxygen and acetylene
should be shut off at the:
a) cylinders and the regulators should be left alone.
b) torch valves and the regulators should be left alone.
c) cylinders and torch valves and the regulators should be left alone.
d) cylinders, the pressures bled off and the regulators should be backed out to
the free position.
11. The most suitable flame to use when heating with oxyacetylene equipment is:
a) an acetylene flame.
b) a carbonizing flame.
c) an oxidizing flame.
d) a neutral flame.
12. When should you purge the oxyacetylene equipment?
a) After you have balanced the pressures.
b) Prior to lighting the torch.
c) Prior to opening the cylinder supply valves.
d) After you have installed the welding tip.
13. If a backfire occurs when using an oxyacetylene heating tip, it may be caused by:
a) oxygen pressure higher than acetylene pressure.
b) acetylene pressure higher than oxygen pressure.
c) the flame being set too high.
d) the flame being set too low.
14. The arrow in Figure 52 is pointing at the:
a) acetylene torch handle valve and it should be fully opened when cutting.
b) oxygen torch handle valve and it should be fully opened when cutting.
c) oxygen preheat valve and it should be adjusted to obtain a neutral flame.
d) oxygen cutting valve and it should be opened no more than two turns.
Figure 52
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15. When an oxyacetylene torch is used for cutting, the torch is:
a) always held at 90 degrees to the material.
b) inclined more for thin material.
c) inclined more for thick material.
d) held at a 45 degree angle to start the cut and straightened to 90 degrees as the
cut progresses.
NOTES
16. Explain why oxygen is dangerous.
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
17. Oil or grease in contact with pure oxygen can _______________________________
____________________________________________________________________.
18. The maximum safe working pressure of acetylene is ________ kPa (_________ psi).
19. What should be done before the cylinder valve protective caps are removed?
a) Cylinders should be pressure-tested.
b) Cylinders should be secured.
c) Cylinder valves should be cracked.
d) Equipment should be lubricated and ready for installation.
20. List the hose fittings that have a left-hand thread?
____________________________________________________________________
21. What is the difference between a backfire and a flashback?
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
22. Why do you purge each line individually on an oxy-fuel outfit before lighting the
torch?
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
23. Why should the acetylene torch valve always be set to work above the smoke range?
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
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24. List the steps for balancing gas pressures when using welding tips.
a) ______________________________________________________________
b) ______________________________________________________________
c) ______________________________________________________________
d) ______________________________________________________________
e) ______________________________________________________________
f) ______________________________________________________________
25. List the three (3) oxyacetylene flame types.
a) ______________________________________________________________
b) ______________________________________________________________
c) ______________________________________________________________
26. Describe the oxy-fuel cutting process.
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
27. Which ferrous-based metals cannot be cut satisfactorily with an oxy-fuel cutting
torch?
____________________________________________________________________
28. List the two (2) fuel gases that are commonly used for oxy-fuel cutting.
a) _________________________________
b) _________________________________
29. The space created when a piece of metal is cut is called the:
a) groove.
b) bead.
c) kerf.
d) crater.
30. When operating a combination cutting torch, the oxygen valve on the torch handle
must be:
a) closed tightly.
b) partially open.
c) fully open.
d) used to adjust to a neutral flame.
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31. The larger the orifices of a cutting tip, the:
a) less gas you burn.
b) greater the heat loss.
c) faster you cut.
d) thicker the plate that you can cut.
32. Which metals can be readily cut using the oxy-fuel cutting process?
a) cast irons
b) mild steels
c) stainless steels
d) nickel alloys
33. List three (3) methods used for starting a cut on round stock.
a) ______________________________________________________________
b) ______________________________________________________________
c) ______________________________________________________________
34. When preheating for flame cutting, the metal should be heated until it reaches:
a) the liquid state.
b) the bright yellow colour.
c) the dull red colour.
d) the transition temperature.
35. When the cut is rough and slag accumulates on the bottom edge, the likely cause is:
a) using propane fuel gas.
b) using oxygen that is only 99.5% pure.
c) using a dirty tip.
d) using a cutting attachment type torch.
36. When piercing holes in a plate, you should:
a) press the cutting lever sharply to start the cut.
b) allow the preheat cones to touch the material surface.
c) raise the oxygen pressure by 25%.
d) raise the tip as the cutting lever is depressed.
37. What is likely to happen if the cutting travel speed is too fast?
a) Productivity increases and your employer is very impressed.
b) Slag bubbles to the surface and the cutting action eventually stops.
c) The tip overheats and begins to backfire.
d) A clean, slag-free cut is produced.
38. What is the likely problem if the kerf edges are melting back together behind the cut?
a) The tip is too large for the material thickness.
b) Impurities are in the fuel gas.
c) The steel has too high a carbon content.
d) You are running low on fuel gas.
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39. A good quality cut can be determined by:
a) inspecting the kerf lines.
b) asking the foreman.
c) the amount of welding experience the operator has.
d) the amount of oxygen and acetylene consumed.
40. Kerf draglines on a properly performed shape cut should be:
a) irregular in profile.
b) curved to match the shape.
c) perpendicular to the plate surface.
d) horizontally inclined.
41. Briefly explain the difference between fusion welding, braze welding and brazing.
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Self-Test Answers
1. d) all of the above.
2. c) soap and water.
3. a) fully.
4. b) upright.
5. b) remains constant.
6. d) green.
7. a) red.
8. c) are right-hand thread.
9. c) both a) and b).
10. d) cylinders, the pressures bled off and the regulators should be backed out to the
free position.
11. d) a neutral flame.
12. b) Prior to lighting the torch.
13. d) the flame set too low.
14. b) oxygen torch handle valve and it should be fully opened when cutting.
15. b) inclined more for thin material.
16. Oxygen readily supports combustion and may react violently with some materials.
17. Oil or grease in contact with pure oxygen can react violently and cause an explosion.
18. The maximum safe working pressure is 103.5 kPa (15 psi).
19. b) Cylinders should be secured.
20. Fuel gas fittings have a left-hand thread.
21. A backfire occurs in the mixer and tip and a flashback occurs beyond the mixer into
the torch handle and hose and regulator.
22. To prevent flashbacks, purge the lines of any air or explosive mixture that may be
present in the lines.
23. This ensures that adequate gas flow is maintained and reduces the possibilities of
backfires and burnbacks.
24. a) Roughly set both regulator pressures to 3 to 4 psi and purge each line
individually.
b) Open acetylene torch valve one half turn and light. Now open valve fully.
c) Now adjust the acetylene regulator so that the flame blows away from the tip, but
not too harshly. This adjustment must be made with the acetylene torch valve
fully open. Use the regulator to adjust the flame.
d) Reduce the acetylene flow with the torch valve until you are just above the
smoke range and the flame is burning at the tip. Then, using the oxygen torch
valve, slowly add oxygen until a cone is produced. Then, alternately increase
acetylene and oxygen using the torch valves until they are at full flow.
e) With both torch valves fully open, adjust the flame with the oxygen regulator
until a neutral flame is established.
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f) Reduce flame size to mid-range proportions using the torch valves; this must not
be down in the smoke range.
25. a) oxidizing
b) carbonizing
c) neutral
26. Oxy-fuel cutting is a controlled process of rapid oxidation in which steel is heated to
its kindling temperature and a high-pressure jet of pure oxygen is directed to the
heated area. Metal exposed to the oxygen oxidizes and is blown away by the oxygen
jet stream.
27. Cast irons and stainless steels.
28. a) acetylene
b) propane
29. c) kerf.
30. c) fully open.
31. d) thicker the plate that you can cut.
32. b) mild steels
33. a) Use a chisel to nick the surface.
b) Drill into the surface.
c) Apply a bead of arc weld.
34. c) the dull red colour.
35. c) using a dirty tip.
36. d) raise the tip as the cutting lever is depressed.
37. b) Slag bubbles to the surface and the cutting action eventually stops.
38. a) The tip is too large for material thickness.
39. a) inspecting the kerf lines.
40. c) perpendicular to the plate surface.
41. a) Fusion welding requires the melting together of the base metal with or without
the use of a filler metal of like composition.
b) Braze welding depends on a tinning action, is used to fill wide joint areas and
occurs above 850°C (1600°F).
c) Brazing is accomplished on closely fitted joints by capillary attraction at
temperatures between 450°C and 850°C (840°F and 1600°F).
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© 2011, Her Majesty the Queen in right of the Province of Alberta
Alberta Apprenticeship
Excellence Through
Training and Experience
Module Number 320102b
Version 1.3
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