Adhesive bonding technology has been used for many years in the railway industry for both traction and rolling stock. Adhesives have been used to produce structural joints that are both light and fatigue resistant. Railway coaches and locomotives have longer service lives than road vehicles and are also used more frequently. The structure is subject to track induced vibration and pressure loads from entering tunnels.
Permabond created a 3 part adhesive system which consisted of resin, initiator and catalyst to accelerate the curing process. This allowed the handling time to be adjusted to suit the manufacturing process. One formulation offered superior performance and this became Permabond F241.
GRP / Steel /Aluminium
Acrylic
Acetone wipe/abrasion and degrease with 1,1,1 trichloroethane
GRP solvent wiped with acetone. The steel abraded then solvent degreased. For aluminium adherends abrasion followed by degreasing was found to be sufficient.
Room temperature cure
The bonding was carried out at a workshop location.
Extensive testing carried out by British Rail showed that the adhesive could be used on oily and poorly prepared surfaces making it ideal for mating to different materials under workshop conditions. However, for optimum results it was found that the GRP should be solvent wiped with acetone and the steel should be abraded then solvent degreased, all methods that can be easily performed in a workshop environment. For aluminium adherends, a chromic acid etch gave the best results but due to operator health hazards this was not used. Instead, abrasion followed by degreasing was found to be sufficient.
All of the HS 125 window surrounds built between 1978 and 1982 were bonded with F241 and in 18 years of service there have been no known failures of the joint which can be attributed to adhesive failure.
Careful attention to pre-treatment and surface preparation procedures is invaluable to optimise long term performance of acrylic adhesive joints.
Dick Hall, British Rail, Scientific services, Railway Technical Centre, London Road, Derby, DE24 8UP.
