Grinding Wheel Materials 210
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Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Class Outline
Class Outline
Objectives
Material Variety
Abrasive Grain Characteristics
Abrasive Grain Classifications
Aluminum Oxide
Zirconia Alumina
Silicon Carbide
Ceramic Aluminum Oxide
Diamond
Cubic Boron Nitride
Bond Characteristics
Wheel Grade
Bond Material Types
Vitrified Bonds
Organic Bonds
Superabrasive Bonds
Standard Wheel Markings
Superabrasive Wheel Markings
Summary
Lesson: 1/19
Objectives
l Understand the factors that affect grinding material selection.
l List the most important characteristics of abrasive grains.
l Cite different ways abrasive grains may be classified.
l Describe the defining characteristics of aluminum oxide.
l Describe the defining characteristics of zirconia alumina.
l Describe the defining characteristics of silicon carbide.
l Describe the defining characteristics of ceramic aluminum oxide.
l Describe the defining characteristics of diamond.
l Describe the defining characteristics of cubic boron nitride.
l Describe the characteristics of bonds.
l Explain what determines wheel grade.
l Name the four types of wheel bonds.
l Describe the defining characteristics of vitrified bonds.
l Describe the defining characteristics of organic bonds.
l Describe the defining characteristics of superabrasive bonds.
l List the categories on the standard abrasive wheel marking chart.
l List the categories on the superabrasive wheel marking chart.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 2/19
Figure 1. Superabrasive wheels generally have
a metal core with the abrasive bonded to the
wheel perimeter. (Courtesy of The Holland Co.)
Lesson: 1/19
Objectives
l Understand the factors that affect grinding material selection.
l List the most important characteristics of abrasive grains.
l Cite different ways abrasive grains may be classified.
l Describe the defining characteristics of aluminum oxide.
l Describe the defining characteristics of zirconia alumina.
l Describe the defining characteristics of silicon carbide.
l Describe the defining characteristics of ceramic aluminum oxide.
l Describe the defining characteristics of diamond.
l Describe the defining characteristics of cubic boron nitride.
l Describe the characteristics of bonds.
l Explain what determines wheel grade.
l Name the four types of wheel bonds.
l Describe the defining characteristics of vitrified bonds.
l Describe the defining characteristics of organic bonds.
l Describe the defining characteristics of superabrasive bonds.
l List the categories on the standard abrasive wheel marking chart.
l List the categories on the superabrasive wheel marking chart.
Figure 1. Superabrasive wheels generally have
a metal core with the abrasive bonded to the
wheel perimeter. (Courtesy of The Holland Co.)
Lesson: 2/19
Material Variety
Bonded abrasive grinding wheels are made from a number of materials. Different mixtures of
abrasive grains and bonding substances are combined through various means to create wheels with
specific characteristics. The wide variety of wheel types is needed because of the number of factors
that affect a given grinding operation. Job specifications, grinding variables, and workpiece makeup,
among others, all influence what types of wheel materials a particular job requires.
A general rule of thumb is that harder wheels are used to grind softer materials and softer wheels
are used to grind harder materials. However, the actual wheel choice is more complicated. For
example, even slight changes in grain size and bonding material, or work speed and feed, may burn the workpiece and glaze the wheel, as shown in Figure 1. Given the same set of circumstances, one
wheel material might react by getting too hot, while another wheel material might cut faster.
Knowing the characteristics of different wheel materials allows you to predict how wheels behave.
This class will teach you about grinding material types and characteristics, wheel composition, and
wheel material behavior.
Figure 1. Incorrect feeds or speeds for certain
wheel materials may cause glazing.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 3/19
Lesson: 2/19
Material Variety
Bonded abrasive grinding wheels are made from a number of materials. Different mixtures of
abrasive grains and bonding substances are combined through various means to create wheels with
specific characteristics. The wide variety of wheel types is needed because of the number of factors
that affect a given grinding operation. Job specifications, grinding variables, and workpiece makeup,
among others, all influence what types of wheel materials a particular job requires.
A general rule of thumb is that harder wheels are used to grind softer materials and softer wheels
are used to grind harder materials. However, the actual wheel choice is more complicated. For
example, even slight changes in grain size and bonding material, or work speed and feed, may burn the workpiece and glaze the wheel, as shown in Figure 1. Given the same set of circumstances, one
wheel material might react by getting too hot, while another wheel material might cut faster.
Knowing the characteristics of different wheel materials allows you to predict how wheels behave.
This class will teach you about grinding material types and characteristics, wheel composition, and
wheel material behavior.
Figure 1. Incorrect feeds or speeds for certain
wheel materials may cause glazing.
Lesson: 3/19
Abrasive Grain Characteristics
Abrasive grains are chosen based on a number of characteristics that indicate how they will interact
with the workpiece. During grinding, an abrasive grain should remain as sharp as possible as long
as possible, finally fracturing when it becomes dull. Figure 1 illustrates this process.
One of the most important characteristics of an abrasive is its hardness, which is the ability to
resist penetration. But even a hard abrasive can become dull. Both its ability to resist wear and its
friability are important. In addition, the size of an abrasive grain is key because size helps
determine what type of finish will be produced. Larger grains tend to remove more material and
leave rougher finishes than smaller grains.
Finally, the actual composition of the abrasive is important. Different abrasive materials can react
chemically with different workpiece materials, especially when subjected to the heat and pressure of
grinding.
Figure 1. In the best combination of abrasive
grain and bond material, the grains fracture as
they become dull.
Lesson: 4/19
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Abrasive Grain Classifications
Abrasive grains may be classified as either natural abrasives or manufactured abrasives. Natural
abrasives are still used for applications such as lapping. Figure 1 shows lapping pads, which are
Lesson: 3/19
Abrasive Grain Characteristics
Abrasive grains are chosen based on a number of characteristics that indicate how they will interact
with the workpiece. During grinding, an abrasive grain should remain as sharp as possible as long
as possible, finally fracturing when it becomes dull. Figure 1 illustrates this process.
One of the most important characteristics of an abrasive is its hardness, which is the ability to
resist penetration. But even a hard abrasive can become dull. Both its ability to resist wear and its
friability are important. In addition, the size of an abrasive grain is key because size helps
determine what type of finish will be produced. Larger grains tend to remove more material and
leave rougher finishes than smaller grains.
Finally, the actual composition of the abrasive is important. Different abrasive materials can react
chemically with different workpiece materials, especially when subjected to the heat and pressure of
grinding.
Figure 1. In the best combination of abrasive
grain and bond material, the grains fracture as
they become dull.
Lesson: 4/19
Abrasive Grain Classifications
Abrasive grains may be classified as either natural abrasives or manufactured abrasives. Natural
abrasives are still used for applications such as lapping. Figure 1 shows lapping pads, which are
sometimes impregnated with natural abrasive grains. However, almost all bonded abrasive wheels
are made with manufactured abrasives. While natural abrasives can be effective, there is no way to
guarantee their purity. Consequently, it is difficult to control or predict the performance of natural
abrasives.
Abrasives are also classified as conventional abrasives or superabrasives. Conventional
abrasives are common, relatively inexpensive materials of varying degrees of hardness that are
used to grind a wide variety of materials. Aluminum oxide, zirconia alumina, silicon carbide,
and ceramic aluminum oxide are part of this group.
Superabrasives like diamond and cubic boron nitride (CBN) are less common and much more
expensive. They also have unusual properties, such as a great degree of hardness. They are
therefore sometimes reserved for specialty grinding operations.
Figure 1. Natural abrasives are still used to
impregnate lapping pads.
Lesson: 5/19
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2015 Tooling U, LLC. All Rights Reserved.
Aluminum
Of all the conventional abrasives, the most common is aluminum oxide. Aluminum oxide is an
abundant, naturally occurring compound. However, like other natural abrasives, its impurities and
Lesson: 4/19
Abrasive Grain Classifications
Abrasive grains may be classified as either natural abrasives or manufactured abrasives. Natural
abrasives are still used for applications such as lapping. Figure 1 shows lapping pads, which are
sometimes impregnated with natural abrasive grains. However, almost all bonded abrasive wheels
are made with manufactured abrasives. While natural abrasives can be effective, there is no way to
guarantee their purity. Consequently, it is difficult to control or predict the performance of natural
abrasives.
Abrasives are also classified as conventional abrasives or superabrasives. Conventional
abrasives are common, relatively inexpensive materials of varying degrees of hardness that are
used to grind a wide variety of materials. Aluminum oxide, zirconia alumina, silicon carbide,
and ceramic aluminum oxide are part of this group.
Superabrasives like diamond and cubic boron nitride (CBN) are less common and much more
expensive. They also have unusual properties, such as a great degree of hardness. They are
therefore sometimes reserved for specialty grinding operations.
Figure 1. Natural abrasives are still used to
impregnate lapping pads.
Lesson: 5/19
Aluminum Oxide
Of all the conventional abrasives, the most common is aluminum oxide. Aluminum oxide is an
abundant, naturally occurring compound. However, like other natural abrasives, its impurities and
inconsistencies make it generally impractical for use in bonded wheels. However, a widely used
artificial form of aluminum oxide is produced in an arc furnace from bauxite, iron, and coke. The
mass of material produced is then washed, crushed, and graded to size. Finally, this material is
bonded into a wheel, such as those shown in Figure 1. The degree of purity determines what sort
of characteristics the material possesses.
Aluminum oxide is often the choice for grinding carbon steel, high-speed steel, wrought iron,
and other materials. Aluminum oxide is also versatile because it can grind workpieces at light to
heavy material removal rates and leave a superior surface finish. This material is one of the least
expensive abrasives and is considered the workhorse of the abrasives industry.
Figure 1. These wheels contain aluminum
oxide, one of the most widely used abrasive
materials.
Lesson: 6/19
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Zirconia Alumina
Zirconia alumina is a type of abrasive made from different percentages of aluminum oxide and
Lesson: 5/19
Aluminum Oxide
Of all the conventional abrasives, the most common is aluminum oxide. Aluminum oxide is an
abundant, naturally occurring compound. However, like other natural abrasives, its impurities and
inconsistencies make it generally impractical for use in bonded wheels. However, a widely used
artificial form of aluminum oxide is produced in an arc furnace from bauxite, iron, and coke. The
mass of material produced is then washed, crushed, and graded to size. Finally, this material is
bonded into a wheel, such as those shown in Figure 1. The degree of purity determines what sort
of characteristics the material possesses.
Aluminum oxide is often the choice for grinding carbon steel, high-speed steel, wrought iron,
and other materials. Aluminum oxide is also versatile because it can grind workpieces at light to
heavy material removal rates and leave a superior surface finish. This material is one of the least
expensive abrasives and is considered the workhorse of the abrasives industry.
Figure 1. These wheels contain aluminum
oxide, one of the most widely used abrasive
materials.
Lesson: 6/19
Zirconia Alumina
Zirconia alumina is a type of abrasive made from different percentages of aluminum oxide and
zirconium oxide, depending on the characteristics desired. The result is a tough abrasive that is
valued for its ability to maintain sharpness through frequent refracturing.
Compared with aluminum oxide, zirconia alumina is faster grinding and longer lasting, but it is also
more expensive. However, zirconia alumina is generally a cost-effective choice because of its overall
long lifespan. It is useful for grinding a wide range of metals, such as cast iron, steel, and steel
alloys, and it performs well in stressful cutoff operations. Figure 1 shows a zirconia alumina wheel
specially designed for this purpose.
Most zirconia alumina wheels consist of large grain sizes. Consequently, zirconia alumina performs
best when used under heavy pressure and high material removal rates. However, the larger grain
sizes often prevent zirconia alumina wheels from generating smooth surface finishes.
Figure 1. Zirconia alumina is often used to
make cutoff wheels.
Lesson: 7/19
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© 2015 Tooling U, LLC. All Rights Reserved.
Silicon
Carbide
Another type of conventional grain material is silicon carbide. Silicon carbide abrasives are made
by firing a mixture of pure white quartz, petroleum coke, and small amounts of sawdust and salt in
Lesson: 6/19
Zirconia Alumina
Zirconia alumina is a type of abrasive made from different percentages of aluminum oxide and
zirconium oxide, depending on the characteristics desired. The result is a tough abrasive that is
valued for its ability to maintain sharpness through frequent refracturing.
Compared with aluminum oxide, zirconia alumina is faster grinding and longer lasting, but it is also
more expensive. However, zirconia alumina is generally a cost-effective choice because of its overall
long lifespan. It is useful for grinding a wide range of metals, such as cast iron, steel, and steel
alloys, and it performs well in stressful cutoff operations. Figure 1 shows a zirconia alumina wheel
specially designed for this purpose.
Most zirconia alumina wheels consist of large grain sizes. Consequently, zirconia alumina performs
best when used under heavy pressure and high material removal rates. However, the larger grain
sizes often prevent zirconia alumina wheels from generating smooth surface finishes.
Figure 1. Zirconia alumina is often used to
make cutoff wheels.
Lesson: 7/19
Silicon Carbide
Another type of conventional grain material is silicon carbide. Silicon carbide abrasives are made
by firing a mixture of pure white quartz, petroleum coke, and small amounts of sawdust and salt in
an electric furnace. As with aluminum oxide, the mass of material is then crushed and graded.
Silicon carbide makes sharp, fast-cutting wheels that are suited for grinding both very hard
materials, like carbide, and nonferrous or very soft materials like plastics and aluminum. They are
harder, brittler, and faster cutting than aluminum oxide wheels, but they are not as long lasting.
Silicon carbide wheels come in two types: green and black. Green wheels have a higher percentage
of pure silicon carbide than black wheels and are often used for grinding and cutting ceramics. As purity decreases, the color turns from light green to dark green to black. Darker wheels are
generally used for metalworking operations. Also, silicon carbide may appear in other forms, such
as the finishing wheel with special fibers in Figure 1.
Figure 1. This wheel, used in finishing
operations, is made of nylon fibers coated with
silicon carbide.
Lesson: 8/19
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Ceramic Aluminum Oxide
Lesson: 7/19
Silicon Carbide
Another type of conventional grain material is silicon carbide. Silicon carbide abrasives are made
by firing a mixture of pure white quartz, petroleum coke, and small amounts of sawdust and salt in
an electric furnace. As with aluminum oxide, the mass of material is then crushed and graded.
Silicon carbide makes sharp, fast-cutting wheels that are suited for grinding both very hard
materials, like carbide, and nonferrous or very soft materials like plastics and aluminum. They are
harder, brittler, and faster cutting than aluminum oxide wheels, but they are not as long lasting.
Silicon carbide wheels come in two types: green and black. Green wheels have a higher percentage
of pure silicon carbide than black wheels and are often used for grinding and cutting ceramics. As purity decreases, the color turns from light green to dark green to black. Darker wheels are
generally used for metalworking operations. Also, silicon carbide may appear in other forms, such
as the finishing wheel with special fibers in Figure 1.
Figure 1. This wheel, used in finishing
operations, is made of nylon fibers coated with
silicon carbide.
Lesson: 8/19
Ceramic Aluminum Oxide
Ceramic aluminum oxide is a relatively new type of abrasive. It is made from a special chemical
process in which a substance made from alumina is formed into a gel, dried, and then crushed into
particles. These particles then undergo sintering to form abrasive grains.
Each grain has a crystalline structure made up of billions of smaller particles. This gives each grain
the unusual ability to fracture at the sub-micron level. A micron is a measurement equal to one
twenty-fifth of a thousandth of an inch (0.00004 inch). During grinding, the abrasive grains are
losing infinitesimally small particles and constantly revealing tiny new cutting points.
In addition to its sharpness, ceramic aluminum oxide is an exceptionally hard and strong abrasive
that is approximately three times tougher than aluminum oxide. It offers cool cutting and longevity
and is appropriate for precision grinding and other demanding applications. The grains are often
blended with other abrasives to make composite wheels with characteristics geared toward specific
applications.
Lesson: 9/19
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Diamond
Diamonds are the hardest materials available and therefore make excellent abrasives. Figure 1
shows a grinding wheel consisting of diamond. Both natural diamonds and manufactured
Lesson: 8/19
Ceramic Aluminum Oxide
Ceramic aluminum oxide is a relatively new type of abrasive. It is made from a special chemical
process in which a substance made from alumina is formed into a gel, dried, and then crushed into
particles. These particles then undergo sintering to form abrasive grains.
Each grain has a crystalline structure made up of billions of smaller particles. This gives each grain
the unusual ability to fracture at the sub-micron level. A micron is a measurement equal to one
twenty-fifth of a thousandth of an inch (0.00004 inch). During grinding, the abrasive grains are
losing infinitesimally small particles and constantly revealing tiny new cutting points.
In addition to its sharpness, ceramic aluminum oxide is an exceptionally hard and strong abrasive
that is approximately three times tougher than aluminum oxide. It offers cool cutting and longevity
and is appropriate for precision grinding and other demanding applications. The grains are often
blended with other abrasives to make composite wheels with characteristics geared toward specific
applications.
Lesson: 9/19
Diamond
Diamonds are the hardest materials available and therefore make excellent abrasives. Figure 1
shows a grinding wheel consisting of diamond. Both natural diamonds and manufactured
diamonds are used in grinding wheels. Industrial-grade natural diamonds, which are a very
expensive form of crystalline carbon, are mined like other gemstones. Manufactured diamonds are
more common and less expensive than natural diamonds. Traditionally, they have been created
from graphite in a process that uses very high temperatures and pressures.
Scientists have recently developed a technique called chemical vapor deposition, or CVD, to
manufacture diamonds. This method uses heat and radio waves or microwaves to break down
carbon-rich gas into pieces that reassemble themselves into diamond. CVD diamonds are used
both as an abrasive and as a coating on cutting tool inserts and other objects.
Diamonds are best suited for grinding very hard materials like carbide. In fact, diamond is so hard
that it should not be used with softer materials where the diamond grains might become embedded
in the material. Diamond also should not be used to grind ferrous metals because it chemically
reacts to iron at high temperatures and becomes dull.
Lesson: 10/19
Cubic Boron Nitride
Copyright
© 2015
ToolingorU,CBN,
LLC. is
Allsynthesized
Rights Reserved.
Cubic
boron
nitride,
from the differently shaped molecules of hexagonal
boron nitride. It is created in a high-temperature, high-hardness process similar to that of
manufactured diamonds. CBN is the second-hardest known material, with only about half of the
Figure 1. This diamond wheel has an aluminum
core and a resin bond. (Courtesy of The
Holland Co.)
Lesson: 9/19
Diamond
Diamonds are the hardest materials available and therefore make excellent abrasives. Figure 1
shows a grinding wheel consisting of diamond. Both natural diamonds and manufactured
diamonds are used in grinding wheels. Industrial-grade natural diamonds, which are a very
expensive form of crystalline carbon, are mined like other gemstones. Manufactured diamonds are
more common and less expensive than natural diamonds. Traditionally, they have been created
from graphite in a process that uses very high temperatures and pressures.
Scientists have recently developed a technique called chemical vapor deposition, or CVD, to
manufacture diamonds. This method uses heat and radio waves or microwaves to break down
carbon-rich gas into pieces that reassemble themselves into diamond. CVD diamonds are used
both as an abrasive and as a coating on cutting tool inserts and other objects.
Diamonds are best suited for grinding very hard materials like carbide. In fact, diamond is so hard
that it should not be used with softer materials where the diamond grains might become embedded
in the material. Diamond also should not be used to grind ferrous metals because it chemically
reacts to iron at high temperatures and becomes dull.
Figure 1. This diamond wheel has an aluminum
core and a resin bond. (Courtesy of The
Holland Co.)
Lesson: 10/19
Cubic Boron Nitride
Cubic boron nitride, or CBN, is synthesized from the differently shaped molecules of hexagonal
boron nitride. It is created in a high-temperature, high-hardness process similar to that of
manufactured diamonds. CBN is the second-hardest known material, with only about half of the
hardness of diamond. Still, CBN is substantially harder than conventional abrasives like aluminum
oxide.
CBN has many advantages. It is a very hard and sharp abrasive and retains its hardness over a
wide temperature range—up to 2500°F (1370°C). Unlike diamond, CBN is also resistant to chemical
influences, which makes it suitable for use with ferrous metals. CBN is used for grinding tool steels, stainless steels, and cast irons. Figure 1 shows a wheel that is coated with a thin layer of CBN.
Figure 1. Cubic boron nitride is bonded to this
wheel through an electroplating process.
(Courtesy of The Holland Co.)
Lesson: 11/19
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Bond Characteristics
The material that holds the abrasive grains together in a wheel, the “glue” so to speak, is known as
Lesson: 10/19
Cubic Boron Nitride
Cubic boron nitride, or CBN, is synthesized from the differently shaped molecules of hexagonal
boron nitride. It is created in a high-temperature, high-hardness process similar to that of
manufactured diamonds. CBN is the second-hardest known material, with only about half of the
hardness of diamond. Still, CBN is substantially harder than conventional abrasives like aluminum
oxide.
CBN has many advantages. It is a very hard and sharp abrasive and retains its hardness over a
wide temperature range—up to 2500°F (1370°C). Unlike diamond, CBN is also resistant to chemical
influences, which makes it suitable for use with ferrous metals. CBN is used for grinding tool steels, stainless steels, and cast irons. Figure 1 shows a wheel that is coated with a thin layer of CBN.
Figure 1. Cubic boron nitride is bonded to this
wheel through an electroplating process.
(Courtesy of The Holland Co.)
Lesson: 11/19
Bond Characteristics
The material that holds the abrasive grains together in a wheel, the “glue” so to speak, is known as
the bond. Although the bond does not do the cutting, its structure and composition are vital to
the wheel’s performance.
The relationship between bond and grain material is crucial. An effective bond must hold the grains
while they are sharp to allow cutting. Then the bond should release the grains as they dull. Figure 1
illustrates how grains are released. The bond determines the forces needed to dislodge dull grains,
so it influences cutting variables like feed and speed. Overall, the bond determines the strength and
hardness of the wheel and dictates maximum operating speeds.
Figure 1. As the bond wears away, it dislodges
dull grains.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 12/19
Lesson: 11/19
Bond Characteristics
The material that holds the abrasive grains together in a wheel, the “glue” so to speak, is known as
the bond. Although the bond does not do the cutting, its structure and composition are vital to
the wheel’s performance.
The relationship between bond and grain material is crucial. An effective bond must hold the grains
while they are sharp to allow cutting. Then the bond should release the grains as they dull. Figure 1
illustrates how grains are released. The bond determines the forces needed to dislodge dull grains,
so it influences cutting variables like feed and speed. Overall, the bond determines the strength and
hardness of the wheel and dictates maximum operating speeds.
Figure 1. As the bond wears away, it dislodges
dull grains.
Lesson: 12/19
Wheel Grade
The strength of a bond, known as the grade, is controlled by two factors: the actual strength of
the bonding material and the amount of material that holds the grains together. Wheels are graded
as soft, medium, and hard, using letters of the alphabet. Letters A through H are soft; I through P
are medium, and Q through Z are hard.
All abrasive wheels are a combination of grain, bond, and space. Figure 1 illustrates this
combination. Bonding material surrounds the grains and connects them to one another with posts
of material, leaving voids among the grains. Larger voids mean thinner and weaker posts, while
smaller voids mean thicker and stronger posts.
Although there are many variables involved, in general, harder grade wheels last longer and are
more appropriate for high-horsepower machines and narrow areas of contact. Softer grade wheels
are used when the job requires large areas of contact and faster stock removal.
Figure 1. Harder bonds have thicker posts
connecting the grains together.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 12/19
Wheel Grade
The strength of a bond, known as the grade, is controlled by two factors: the actual strength of
the bonding material and the amount of material that holds the grains together. Wheels are graded
as soft, medium, and hard, using letters of the alphabet. Letters A through H are soft; I through P
are medium, and Q through Z are hard.
All abrasive wheels are a combination of grain, bond, and space. Figure 1 illustrates this
combination. Bonding material surrounds the grains and connects them to one another with posts
of material, leaving voids among the grains. Larger voids mean thinner and weaker posts, while
smaller voids mean thicker and stronger posts.
Although there are many variables involved, in general, harder grade wheels last longer and are
more appropriate for high-horsepower machines and narrow areas of contact. Softer grade wheels
are used when the job requires large areas of contact and faster stock removal.
Figure 1. Harder bonds have thicker posts
connecting the grains together.
Lesson: 13/19
Bond Material Types
Many materials are used to bond abrasive grains together. They are chosen for their compatibility
with various kinds of grains and the way they behave under different circumstances, such as
variable wheel speeds, high or low precision requirements, and different workpiece material types.
Even though there are many different types of bonds, the most common types fall into four
distinct groups:
l
l
l
l
Vitrified bonds
Organic bonds
Metal bonds
Electroplated bonds
Most wheels that contain conventional abrasives are made with vitrified and organic bonds. The
wheel in Figure 1 is just one example of a vitrified bonded wheel. Superabrasive wheels also use
vitrified and organic bonds, but they may also have metal or electroplated bonds.
Figure 1. This wheel has a vitrified bond.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 14/19
Lesson: 13/19
Bond Material Types
Many materials are used to bond abrasive grains together. They are chosen for their compatibility
with various kinds of grains and the way they behave under different circumstances, such as
variable wheel speeds, high or low precision requirements, and different workpiece material types.
Even though there are many different types of bonds, the most common types fall into four
distinct groups:
l
l
l
l
Vitrified bonds
Organic bonds
Metal bonds
Electroplated bonds
Most wheels that contain conventional abrasives are made with vitrified and organic bonds. The
wheel in Figure 1 is just one example of a vitrified bonded wheel. Superabrasive wheels also use
vitrified and organic bonds, but they may also have metal or electroplated bonds.
Figure 1. This wheel has a vitrified bond.
Lesson: 14/19
Vitrified Bonds
Most grinding wheels are made with vitrified bonds, which are clays and glasslike materials that
are mixed with abrasives when wet to coat each grain. The mixture is pressed into a wheel shape
and fired in a kiln at very high temperatures, resulting in a hard, strong bond. Figure 1 shows a
wheel resulting from this process.
Vitrified wheels are rigid, porous, and resistant to acid, oil, water, and temperature variation.
Because of their porosity, vitrified wheels allow grinding fluid to be applied effectively to the arc of
the cut, and they have plenty of void area for collecting chips. Vitrified wheels also provide high
rates of stock removal and offer precision results. On the other hand, they also tend to be brittle
and subject to breakage.
Figure 1. A vitrified bond results in a hard,
strong wheel.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 15/19
Lesson: 14/19
Vitrified Bonds
Most grinding wheels are made with vitrified bonds, which are clays and glasslike materials that
are mixed with abrasives when wet to coat each grain. The mixture is pressed into a wheel shape
and fired in a kiln at very high temperatures, resulting in a hard, strong bond. Figure 1 shows a
wheel resulting from this process.
Vitrified wheels are rigid, porous, and resistant to acid, oil, water, and temperature variation.
Because of their porosity, vitrified wheels allow grinding fluid to be applied effectively to the arc of
the cut, and they have plenty of void area for collecting chips. Vitrified wheels also provide high
rates of stock removal and offer precision results. On the other hand, they also tend to be brittle
and subject to breakage.
Figure 1. A vitrified bond results in a hard,
strong wheel.
Lesson: 15/19
Organic Bonds
Although the term “organic” implies something “natural,” organic chemistry actually governs carbon
compounds, regardless of their origin. Thus, organic bonds are simply those that contain carbon,
and they may be natural or synthetic. The most common characteristic of organic bonds is that
they tend to soften under the heat of grinding. The most frequently used types are resinoid
bonds, rubber bonds, and shellac bonds.
Of these three, resinoid bonds are the most common. They are made from synthetic resin and are
sometimes referred to as plastic wheels, although that is not what they are made of. Resinoid
wheels can be used at very high speeds and are often found in cutoff operations.
Rubber wheels, such as the wheel in Figure 1, are tough and strong. They are frequently used
when the specifications call for very fine surface finishes, including more sensitive cutoff operations.
They offer a smooth grinding action and can be run at high speeds.
Shellac is actually a resin secreted on the bark of trees by an insect that has ingested tree sap.
Shellac-bonded wheels tend to produce polished surface finishes. They are often used on parts
such as rolls.
Figure 1. Rubber, like that used to make this
polishing wheel, is an organic material.
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Lesson: 16/19
Lesson: 15/19
Organic Bonds
Although the term “organic” implies something “natural,” organic chemistry actually governs carbon
compounds, regardless of their origin. Thus, organic bonds are simply those that contain carbon,
and they may be natural or synthetic. The most common characteristic of organic bonds is that
they tend to soften under the heat of grinding. The most frequently used types are resinoid
bonds, rubber bonds, and shellac bonds.
Of these three, resinoid bonds are the most common. They are made from synthetic resin and are
sometimes referred to as plastic wheels, although that is not what they are made of. Resinoid
wheels can be used at very high speeds and are often found in cutoff operations.
Rubber wheels, such as the wheel in Figure 1, are tough and strong. They are frequently used
when the specifications call for very fine surface finishes, including more sensitive cutoff operations.
They offer a smooth grinding action and can be run at high speeds.
Shellac is actually a resin secreted on the bark of trees by an insect that has ingested tree sap.
Shellac-bonded wheels tend to produce polished surface finishes. They are often used on parts
such as rolls.
Figure 1. Rubber, like that used to make this
polishing wheel, is an organic material.
Lesson: 16/19
Superabrasive Bonds
Because superabrasives are so expensive, diamond and CBN wheels are usually made in two parts.
The wheel has an interior, core material with the abrasive material bonded to the edge. Figure 1
shows the superabrasive bonded to this core. There are generally four types of bonds used in
superabrasive wheels: resinoid bonds, vitrified bonds, metal bonds, and electroplated bonds.
Resinoid and vitrified superabrasive bonds work similarly to those used with regular abrasives. The
abrasive is mixed with the bonding material and adhered to a small area of the wheel’s perimeter.
Metal bonds are the strongest type of superabrasive bond. Metal-bonded diamond wheels are
generally produced through a sintering process. They are often used on materials like glass and
concrete. Metal-bonded CBN wheels are used on steels and superalloys.
Electroplated wheels generally have a single layer of abrasive grains bonded to the edge surface.
Electroplating involves immersing a metal wheel in an electrically charged chemical bath that contains
metal particles. Electroplated wheels are often used to create forms and complex shapes.
Lesson: 17/19
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Standard Wheel Markings
Figure 1. Superabrasives are often bonded to
metal using electroplating processes.
(Courtesy of The Holland Co.)
Lesson: 16/19
Superabrasive Bonds
Because superabrasives are so expensive, diamond and CBN wheels are usually made in two parts.
The wheel has an interior, core material with the abrasive material bonded to the edge. Figure 1
shows the superabrasive bonded to this core. There are generally four types of bonds used in
superabrasive wheels: resinoid bonds, vitrified bonds, metal bonds, and electroplated bonds.
Resinoid and vitrified superabrasive bonds work similarly to those used with regular abrasives. The
abrasive is mixed with the bonding material and adhered to a small area of the wheel’s perimeter.
Metal bonds are the strongest type of superabrasive bond. Metal-bonded diamond wheels are
generally produced through a sintering process. They are often used on materials like glass and
concrete. Metal-bonded CBN wheels are used on steels and superalloys.
Electroplated wheels generally have a single layer of abrasive grains bonded to the edge surface.
Electroplating involves immersing a metal wheel in an electrically charged chemical bath that contains
metal particles. Electroplated wheels are often used to create forms and complex shapes.
Figure 1. Superabrasives are often bonded to
metal using electroplating processes.
(Courtesy of The Holland Co.)
Lesson: 17/19
Standard Wheel Markings
Because of the large number of combinations of grain and bond materials that make up grinding
wheels, each wheel comes marked with its “ingredients.” Using a standard marking system
developed by the American National Standards Institute (ANSI), wheel labels are printed with a
series of letters and numbers to show their contents, as shown in Figure 1.
The standard abrasive wheel chart categorizes abrasive type, grain size, wheel grade, structure,
and bond type. It also has two open categories for manufacturers’ markings. Grain type is a letter
or letter/number combination that stands for the abrasive type, with A, for example, standing for
regular aluminum oxide. Grain sizes are categorized from coarse to very fine by a number from
eight to 600, as shown in Figure 2. Grades are rated from softest to hardest using the letters from
A to Z. Structure indicates the level of porosity using numbers, with lower numbers indicating
dense structure, and high numbers indicating more open structure. Bond types are marked with
specific letters. For example, V is for vitrified, B is for resin, and R is for rubber bonds.
Figure 1. On many standard wheels, the
markings appear on the paper blotter.
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Figure 2. The specific number indicates the
size of the grain.
Lesson: 17/19
Standard Wheel Markings
Because of the large number of combinations of grain and bond materials that make up grinding
wheels, each wheel comes marked with its “ingredients.” Using a standard marking system
developed by the American National Standards Institute (ANSI), wheel labels are printed with a
series of letters and numbers to show their contents, as shown in Figure 1.
The standard abrasive wheel chart categorizes abrasive type, grain size, wheel grade, structure,
and bond type. It also has two open categories for manufacturers’ markings. Grain type is a letter
or letter/number combination that stands for the abrasive type, with A, for example, standing for
regular aluminum oxide. Grain sizes are categorized from coarse to very fine by a number from
eight to 600, as shown in Figure 2. Grades are rated from softest to hardest using the letters from
A to Z. Structure indicates the level of porosity using numbers, with lower numbers indicating
dense structure, and high numbers indicating more open structure. Bond types are marked with
specific letters. For example, V is for vitrified, B is for resin, and R is for rubber bonds.
Figure 1. On many standard wheels, the
markings appear on the paper blotter.
Figure 2. The specific number indicates the
size of the grain.
Lesson: 18/19
Superabrasive Wheel Markings
Superabrasive wheel markings are similar to standard abrasive markings. Figure 1 shows the
markings on a superabrasive wheel. These markings indicate abrasive type, grit/mesh size, grade,
concentration, bond type, and abrasive depth.
Abrasive type is indicated by an assigned letter or letter/number combination. For example, ASD is
a diamond abrasive. Grit size is indicated with a number designation to indicate the size of the
grain, while grade is shown with assigned letters to indicate types of bonds. For example, R and N
are resin-bonded wheels. Grain concentration is indicated by number, and a combination of letters
and numbers indicate bond type.
Because superabrasive wheels have grains only at the perimeter of the wheel, abrasive layer is
specific to diamond and CBN wheels. Abrasive layer indicates the depth of the abrasive section on
the wheel in inches, usually from one-sixteenth in. (0.16 cm) to one-quarter in. (0.64 cm).
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Figure 1. On this superabrasive wheel, the
markings appear right on the metal core.
Lesson: 18/19
Superabrasive Wheel Markings
Superabrasive wheel markings are similar to standard abrasive markings. Figure 1 shows the
markings on a superabrasive wheel. These markings indicate abrasive type, grit/mesh size, grade,
concentration, bond type, and abrasive depth.
Abrasive type is indicated by an assigned letter or letter/number combination. For example, ASD is
a diamond abrasive. Grit size is indicated with a number designation to indicate the size of the
grain, while grade is shown with assigned letters to indicate types of bonds. For example, R and N
are resin-bonded wheels. Grain concentration is indicated by number, and a combination of letters
and numbers indicate bond type.
Because superabrasive wheels have grains only at the perimeter of the wheel, abrasive layer is
specific to diamond and CBN wheels. Abrasive layer indicates the depth of the abrasive section on
the wheel in inches, usually from one-sixteenth in. (0.16 cm) to one-quarter in. (0.64 cm).
Figure 1. On this superabrasive wheel, the
markings appear right on the metal core.
(Courtesy of The Holland Co.)
Lesson: 19/19
Summary
Numerous grinding wheel materials are available to address the needs for different applications. The
most important properties of an abrasive material are its hardness and friability. However, certain
abrasive materials may also chemically react with certain workpiece materials during the heat and
stress of grinding.
Abrasive materials are divided into conventional abrasives and superabrasives. Conventional
abrasives include aluminum oxide, zirconia alumina, silicon carbide, and ceramic aluminum oxide.
Aluminum oxide is the most common grinding material used on steel. Zirconia alumina is best
suited for high material removal rates. Silicon carbide is used to grind carbide and nonferrous
metals. Ceramic aluminum oxide is a newer material that is exceptionally hard and strong.
The superabrasives include diamond and cubic boron nitride. Diamond is the hardest material
available and is used to grind the hardest cutting tools and workpiece materials. Cubic boron nitride
is the second hardest grinding material and is used on tool steels, stainless steels, and cast iron.
Figure 1. Aluminum oxide is the most common
abrasive material for conventional wheels.
The bond determines the strength and hardness of the wheel and dictates maximum operating
speeds. Most wheels are made with vitrified bonds, which are rigid, porous, and resistant to
temperature variation. Organic bonds are tough and strong but soften under the heat of grinding.
Metal and electroplated bonds are always used with superabrasives.
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Figure 2. This superabrasive wheel has a thin
layer of electroplated cubic boron nitride
Lesson: 19/19
Summary
Numerous grinding wheel materials are available to address the needs for different applications. The
most important properties of an abrasive material are its hardness and friability. However, certain
abrasive materials may also chemically react with certain workpiece materials during the heat and
stress of grinding.
Abrasive materials are divided into conventional abrasives and superabrasives. Conventional
abrasives include aluminum oxide, zirconia alumina, silicon carbide, and ceramic aluminum oxide.
Aluminum oxide is the most common grinding material used on steel. Zirconia alumina is best
suited for high material removal rates. Silicon carbide is used to grind carbide and nonferrous
metals. Ceramic aluminum oxide is a newer material that is exceptionally hard and strong.
The superabrasives include diamond and cubic boron nitride. Diamond is the hardest material
available and is used to grind the hardest cutting tools and workpiece materials. Cubic boron nitride
is the second hardest grinding material and is used on tool steels, stainless steels, and cast iron.
Figure 1. Aluminum oxide is the most common
abrasive material for conventional wheels.
The bond determines the strength and hardness of the wheel and dictates maximum operating
speeds. Most wheels are made with vitrified bonds, which are rigid, porous, and resistant to
temperature variation. Organic bonds are tough and strong but soften under the heat of grinding.
Metal and electroplated bonds are always used with superabrasives.
Figure 2. This superabrasive wheel has a thin
layer of electroplated cubic boron nitride
grains. (Courtesy of The Holland Co.)
Class Vocabulary
Term
Definition
Alumina
Aluminum Oxide
American National Standards Institute
Arc Furnace
Bauxite
The natural form of aluminum oxide.
An abrasive made by fusing bauxite, iron, and coke that is widely used to grind ferrous
materials. The natural form is called corundum.
A private, non-profit organization that administers and coordinates voluntary standards and
systems.
A heating unit that uses electric arcs between carbon electrodes to melt steel and manufacture
abrasives. Also called an electric arc furnace.
A form of aluminum oxide that contains several impurities.
Bond
The "glue" or adhesive material that holds abrasive grains together in a grinding wheel. Bonds
may be vitrified, organic, metal, or electroplated.
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Carbide
A compound developed by the combination of carbon with usually tungsten, titanium, or
tantalum that is used in metal cutting tools for its hardness and wear resistance.
Class Vocabulary
Term
Definition
Alumina
Aluminum Oxide
American National Standards Institute
Arc Furnace
Bauxite
Bond
Carbide
Carbon Steel
Cast Iron
The natural form of aluminum oxide.
An abrasive made by fusing bauxite, iron, and coke that is widely used to grind ferrous
materials. The natural form is called corundum.
A private, non-profit organization that administers and coordinates voluntary standards and
systems.
A heating unit that uses electric arcs between carbon electrodes to melt steel and manufacture
abrasives. Also called an electric arc furnace.
A form of aluminum oxide that contains several impurities.
The "glue" or adhesive material that holds abrasive grains together in a grinding wheel. Bonds
may be vitrified, organic, metal, or electroplated.
A compound developed by the combination of carbon with usually tungsten, titanium, or
tantalum that is used in metal cutting tools for its hardness and wear resistance.
The basic type of steel, which contains less than 3% of elements other than iron and carbon.
A metal consisting of iron, over 2.11% carbon, and 1 to 3% silicon. Cast irons will normally
contain trace amounts of other elements.
Ceramic Aluminum Oxide
An exceptionally hard, strong, sharp abrasive made from a process in which alumina gel is dried
and crushed. Ceramic aluminum oxide has the ability to refracture at the sub-micron level.
Chemical Vapor Deposition
A method of manufacturing diamonds that uses heat and radio waves or microwaves to break a
carbon-rich gas into pieces that reassemble themselves into diamond.
Coke
Conventional Abrasive
Cubic Boron Nitride
Diamond
Electroplated Bond
Ferrous Metal
Friability
Grade
Graphite
Hardness
Hexagonal Boron Nitride
High-Speed Steel
The carbon-containing residue remaining from coal distillation.
One of several inexpensive abrasives of varying hardnesses commonly used in industry for
material removal.
The second-hardest substance after diamond. Cubic boron nitride (CBN) is manufactured in a
high-heat, high-pressure sintering process.
The hardest known substance. Made from carbon, diamond is both a naturally occurring and
manufactured abrasive.
A superabrasive bond accomplished by immersing a metal wheel in an electrically charged
chemical bath that contains metal particles.
A metal containing iron.
The ability of abrasive grains to fracture and self-sharpen under stress.
The strength of the bond in an abrasive wheel.
A soft, black form of carbon. Graphite is used to manufacture diamonds.
The ability of a material to resist penetration and scratching.
A boron-nitrogen compound that has a six-sided crystal structure.
A tool steel used to machine metals at high cutting speeds. High-speed steel stays hard at high
temperatures and resists abrasion.
Iron The fourth most abundant earth element. Iron is alloyed with carbon to make steel.
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Kiln
An oven or furnace used for heating or drying.
temperatures and resists abrasion.
Iron
Kiln
Lapping
The fourth most abundant earth element. Iron is alloyed with carbon to make steel.
An oven or furnace used for heating or drying.
A precision abrasion process used to bring a surface to a desired state of finish or dimensional
tolerance by removing an extremely small amount of material.
Manufactured Abrasive
A material of extreme hardness created through chemical and/or physical processes that is used
to shape other materials by a grinding or abrading action.
Manufactured Diamond
The manufactured form of a carbon mineral that is the hardest substance known to man. It is
manufactured through a high-heat, high-pressure process.
Metal Bond
Micron
A bonding material used most often with superabrasive grinding wheels.
A measurement equal to one twenty-fifth of a thousandth of an inch (0.00004 inch).
Natural Abrasive
A hard material found in the earth that is used to shape other materials by grinding or abrading.
Sand and quartz are both natural abrasives.
Natural Diamond
The mined form of a carbon mineral that is the hardest substance known to man.
Nonferrous
Organic Bond
Porosity
Porous
Post
Resinoid Bond
Roll
A material that does not contain iron. Aluminum, copper, and zinc are nonferrous metals.
An abrasive bonding material that contains carbon. Organic bonds tend to soften with heating.
The relative number of openings or voids in a material.
Having many openings or voids.
A structural beam that connects abrasive grains in a bonded abrasive grinding wheel.
An organic bond made of synthetic resin.
Long, cylindrical metal parts used in mills that make paper, sheet metal, and other similar
products.
Rubber Bond
An organic bond made of natural or synthetic rubber.
Shellac Bond
An organic bond made of shellac, a material secreted on the bark of trees by an insect that has
ingested tree sap.
Silicon Carbide
Sintering
Steel
Sub-Micron
Superabrasive
Superalloy
Vitrified Bond
A hard, brittle abrasive made by firing a mixture of quartz, petroleum coke, and small amounts
of sawdust and salt in an electric furnace. Silicon carbide is known for its green color.
The pressing and heating of powdered materials close to their melting point to create a solid
shape. Sintering creates materials with very uniform contents.
A metal consisting of iron and carbon, usually with small amounts of manganese, phosphorus,
sulfur, and silicon as well.
A measurement less than one twenty-fifth of a thousandth of an inch (0.00004 inch).
One of a group of relatively expensive but effective materials possessing superior hardness and
abrasion resistance. Superabrasives include cubic boron nitride and diamond.
A metal alloy consisting of three or more elements that is very expensive and designed to exhibit
high strength at elevated temperatures.
A clay-like abrasive bond that is generally hard and brittle.
Void
The space or pore between abrasive grains and posts on a bonded abrasive grinding wheel.
Wrought Iron
A tough, malleable, and relatively soft form of iron containing less than 0.3 percent carbon.
Zirconia Alumina
A type of tough, large-grain abrasive made from aluminum oxide and zirconium oxide. Often
used in cutoff operations.
Zirconium Oxide
A toxic, heavy, white powder used to manufacture zirconia alumina.
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Copyright © 2015 Tooling U, LLC. All Rights Reserved.