Brake Roller Epoxy Coating - for bonding surface friction gritsto MOT Rollers
Summary - How to re-coat brake rollers for testing vehicle braking (MOT Testing)
1. Grind and solvent clean - surfaces must be immaculate - white cloth test
2. Warm - using a dry source of heat (not bottled gas)
3. Apply resin - Thixotropic Epoxy Resin - 3mm thick
4. Apply grit - Grit Grade 12, 16 or Mixed - 2.5kgs per square metre.
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Brush Thixotropic Epoxy Resin onto the cleaned roller.
Coating Brake Rollers - to refinish Brake Rollers used for the testing of vehicle braking systems
Your brake test rollers must provide a certain level of friction to maintain their accuracy. It is therefore important that the rollers are resurfaced as soon as the friction surface becomes worn.
Thixotropic Epoxy Adhesive has a strong bond, high chemical resistance, is easy to apply, and does not slump or run. It is a no odour, two part epoxy with the consistency of Vaseline or Swarfega.
How much resin do I need to re-coat brake rollers?
Thixotropic Epoxy Adhesive is available in 400cc or 1000cc packs.
Allow up to 2 litres per square metre (max. 2mm of resin thickness) for fine aggregate (16 Grade)
Allow up to 3 litres per square metre (max. 3mm of resin thickness) for coarse aggregate (12 Grade)
Allow up to 3 litres per square metre (max. 3mm of resin thickness) for coarse aggregate (1mm to 3mm Mixed Grade)
Thixotropic Epoxy 2 part - vivid blue and cream colour before mixing
How to re-coat brake rollers for testing vehicle braking (MOT Testing)
1. Electrically isolate and remove rollers or remove fitting plates to allow full access (depending on type).
2. Strip existing grit with an angle grinder, grit blast or needle gun.
3. Strip the roller surface to bare metal.
4. Clean the roller with a solvent cleaner to ensure no oil or grease remains in the metal.
5. Regrind to eliminate any solvent cleaner smear film. Wipe over with a clean White Cloth.
6. Wipe thoroughly again with the White Cloth - if any dark marks appear on the White Cloth repeat steps 4 - 6 until the cloth remains perfectly white - this is the secret of success - any dirt left on the roller, no matter how little, with reduce the resin bond and lead to bald patches, where the resin has fallen off the roller.
6. Lay clean cardboard under the roller to catch aggregate (grit) that falls off during coating, for reuse.
7. Heat the rollers with dry heat - use electrical heaters with fans. Avoid gas heating (particularly Propane), because of the water produced, which can cause condensation on the roller and loss of adhesion. Maintain background heat until the resin is completely hard. This may take up to 2 days during cold weather. Lack of heat may also allow condensation to form on the resin and the aggregate (grit) may then fail to bond properly.
8. Apply Thixotropic Epoxy Adhesive with a smooth plastic spreader or brush, to a depth of at least 75% of the average diameter of the aggregate (grit), typically Grade 12, 2mm - 3mm, or Grade 16, 1mm - 2mm, or Mixed Grade 1mm - 3mm.
9. Apply clean, dust free Aggregate (grit) to the adhesive so that cover is complete, with some excess. Pat the aggregate (grit) into the resin very firmly with a clean wooden or metal object (plastering float, batten, cricket bat), or use a piece of clean hard plastic material. It is not necessary to apply another coat of resin, as long as the first coat is thick enough and the aggregate (grit) is fully bedded in. The grit must only protrude out of the resin by 1/4 of its average diameter - for example, a 3mm grit should only stick above the resin by about 0.75mm. If too much of the grit shows above the resin the bond will fail and the grit will be torn out of the resin layer, leaving bald patches.
10. Leave to cure for at least 24 hours, subject to temperatures being above 15 degrees C at all times. Maintain the heating for the whole period.
11. Clean and grease the end bearings and refit the rollers.
IMPORTANT NOTES FOR RECOATING BRAKE ROLLERS
Try to do this job in the Summer months.
In cold weather you must keep the rollers above 5 degrees C. Below 5 degrees the resin curing will slow and curing will be delayed.
On cold, damp days condensation on the rollers or on the resin can reduce resin and grit adhesion, so screen off the area to prevent draughts and warm up with heaters in the pit overnight.
In Winter adjust the resin temperature by placing the pots of resin in warm water.
For cleaning only use our Epoxy Cleaning Fluid.
To save grit, make a simple trough out of cardboard. Remove the side plates on Brake Rollers, & fit the 'catcher'.
The Rollers MUST NOT BE USED until the coating is really hard. Make a test piece (of metal or wood) when the resin coating is complete. Coat the test piece with resin, without grit, and leave next to the gritted area. Test by first thumb pressure and then with a screwdriver before using the roller. When hard, the coating still continues to gain strength over several days, so build up the work load.
Using the Roller too early, before the resin is properly cured, is a false economy - you will lose your coating and have to repeat the process.
TROUBLESHOOTING THE RECOATING OF BRAKE ROLLERS
Resin comes off the roller - roller not clean enough, roller too cold when coated, condensation on the roller when coated, rollers used too hard too soon, resin not fully cured.
Grit comes off the resin - condensation on the resin when gritted, grit too dusty, wet grit, grit not tamped into the resin when applied, rollers used too hard too soon, resin not fully cured.
Resin remains sticky - not mixed fully (look for blue streaks), too cold (resin stops curing at 5C), too damp, condensation on resin before or after gritting due to low temperature, or through using bottled gas heating.
Thixotropic Epoxy Adhesive for recoating brake rollers
Available in 400cc and 1000cc (1 litre) packs, applied at about 2 to 4 litres per square metre.
Supplied in two coloured parts, vivid blue and cream - makes mixing easy - when the colour is an even light blue/grey the product is properly mixed.
How do I calculate the roller area?
Roller Area = Diameter of Roller in Metres x 3.142 x Width of the roller in Metres
Example: Diameter 300mm = 0.3 metres, Width 1.5 metres
Calculation: 0.3 x 3.142 x 1.5 = 1.41 square metres roller area
Resin volume needed: say at 2 litres per square metre = 2.8 litres = 3 packs of 1 litre.
To buy resin click here for Resins Shop
Grits for Brake Roller refurbishing - blasting and refinishing
Alumac prime quality fused Alumac produced from stringently controlled raw materials form the most durable grit surfaces for Brake Rollers.
Al203 content 94 -99%.
Packed in plastic tubs.
Grade 12, 2mm - 3mm, or Grade 16, 1mm - 2mm, or Mixed Grade 1mm - 3mm.
Grit Required per square metre, average:
Allow 2.5kgs per square metre
Typical Roller Grit Sizes used:
Class 4 Rollers - 12 or 16 Grit
Class 5 Rollers - 12 or 16 Grit
Class 7 Rollers - Mixed Grit 1mm to 3mm - natural aggregates
Grit to excess and collect for reuse. When dry brush off excess grit.
Call us on 01626 872886 for calculation of your Brake Roller cleaning and finishing needs.
Discuss the Grades of Grit available to ensure satisfaction.
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Site written by: David Moore
David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author
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