Procedures for preliminary testing and bonding heaters on the SCT end
cap OTE.
Heater circuit, thermistor and tab definition.
The drawings below give the definitions of the connections, viewed from the
solder side of the foil. Heater circuits H1 and H2 are those furthest from the
connection tabs and H3 and H4 the nearest. The thermistors are defined similarly,
T1 being the furthest and T4 the nearest.
1. Initial measurements.
Measure and record the resistance of each heater and thermistor circuit and also
record the ambient temperature and heater serial number. Inspect carefully for
any signs of damage.
2. Surface preparation.
A. Dissolve 20g of sodium hydroxide in 1 litre of water (warm water can be
used to speed up the process) to form a 0.5M aqueous solution.
B. Cover a bench with polythene sheeting to use as a work surface.
C. Prepare the mating (adhering) surface of the film as follows:
(i)
(ii)
(iii)
(iv)
Wipe the surface of the film with a lint-free wipe moistened with the
sodium hydroxide solution. The surface will become very slightly matt.
Wash off the surface with a lint-free wipe moistened with plain water.
Repeat ten times.
Dry off with a lint-free wipe moistened with ethanol or industrial
methylated spirit (IMS).
Allow to air-dry for two hours.
Caution – sodium hydroxide is caustic. Nitrile gloves, overalls and eye protection
must be worn. Follow all instructions in the MSDS. Used wipes must be disposed
of by double-bagging in polythene bags and consigning to the hazardous waste
disposal route. Used solution can be stored in a (preferably polythene) wellstoppered container. It can be disposed of through the hazardous waste disposal
route or by neutralisation and then drain disposal.
3. Adding the heat-spreader foils.
Clean 4 heat spreader foils with alcohol and attach to one heater immediately
beneath the thermistors (i.e. on the non-solder side of the heater) using Araldite
2011. Smooth into place. Repeat for the other 11 heaters. Leave to cure for at
least 8 hours.
4. Identification of heater bonding areas on the OTE.
A. Place the heaters in their nominal positions on the OTE as shown in drawings
TD-1012-401 (2 sheets) by securing with low-tack tape. Adjust the positions until
all axial gaps are equal to a precision of about ± 1mm. The drawing below shows
the numbering scheme for the locations used previously. The top is the gap
between locations 1 and 12 and is given from the hole spacings shown in
drawing TD-1012-406 (All drawings by RAL).
B. Mark the positions of the heaters (marking at the corners with a fine
permanent ink pen works well).
5. Bonding the heaters to the OTE.
A. Remove the heaters from locations 2, 4, 6, 8, 10, and 12.
B. Remove the heater in location 1. Lightly burnish the copper surface of the
OTE using a fine nylon scourer.
C. Wipe the burnished surface well with a wipe moistened with ethanol, IMS
or propan-2-ol until no metallic residue can be seen on the wipe.
D. Apply and spread a thin coat of Araldite 2011 over the bonding surface
previously marked, avoiding the areas shown in drawings TD-1012-401.
Estimate the amount of adhesive used in g.m -2 and record.
E. Add the heater, carefully smoothing it into place. Wipe away any excess
adhesive from the edges using a wipe moistened with acetone.
F. Secure with low-tack tape.
G. Repeat A to F for heaters 3 to 11 inclusive.
H. Leave to cure for 8 hours at least.
I. Remove the low tack tapes.
J. Prepare the surface at location 2 and proceed to mount heaters 2, 4, 6, 8,
10, and 12 as described in B to I.
6. Measurements after bonding.
Repeat the measurements made in section 1, this time also recording the
location of each heater.