thickness through a process of electrophoresis. Finally, the ’shell is cured at 180degC (356degF), providing a highly corrosion resistant finish, offering in excess of 1000hrs salt spray protection.
As well as saving weight, bodyshells are washed with a preservative that protects the metal and can be welded through with impunity
before being immersed in a dilute solution of inhibited hydrochloric acid. The purpose of this is to remove any corrosion that may be present, with the inhibitor preventing the steel structure itself being attacked. From there, the ’shell is placed in an alkaline rinse prior to being dipped in an agitated alkaline solution, carefully formulated to ensure complete neutralisation of the metal. Lastly, it is subject to a high pressure manual wash with a preservative solution to protect the bare metal finish. At this point, the ’shell can
be taken away for welding or fabrication work, or can be
subjected to a second process to coat and protect the bare metalwork, which culminates in the application of an electro- phoretic coating. Firstly, the vehicle ’shell is subject to an eight-stage cleaning and phosphate treatment, consisting of decontamination through a number of alkaline silicate rinses before being dipped in a bath of phosphoric acid containing zinc, manganese and nickel. The body then moves to a PPG paint tank where it is immersed and an electrical current of 320v at 1000A is passed through it. This results in a uniform paint covering of 28µ
WELD INTEGRITY And if you are thinking that welding a ’shell that has been chemically coated is not a good idea, Adrian McMurray, managing director of Surface Processing has an explanation: ‘In a modern car plant they have all sorts of ways to prevent problems – they heat the area up first and then flush it with nitrogen so that it is clean and oxide free. [But] where traditionally a fabricator would have to spend a large amount of time cleaning up areas prior to welding, a vehicle that has been through the dipping process can be worked on immediately, with great weld integrity.’ While this offers considerable time (and therefore cost) savings, especially for constructors producing batches of cars, the real benefits can be seen in terms of weight savings. The ’shell of a
modern production saloon, fresh from the production line, is an incredibly complex component. In some places panels can have up to five layers of material, including plastic and foam in-fills. And whereas with media blasting processes, only externally accessible material can be removed, it is in the removal of this hidden material that Surface Processing has found some very impressive weight savings. ‘On a typical road-to-racecar project, it works out at an average of about 31kg saved over the stripped ’shell,’ states McMurray, although apparently significantly greater savings have been seen on some high-end saloon bodyshells. The racing world has taken
notice and a number of top rally constructors and Touring Car teams have already called upon Surface Processing’s facilities to give them an extra edge. At a cost of around £2000 ($3200) for the full process, the cost per kilo saved, combined with the reduced labour requirements, certainly makes it an attractive option.
September 2011 •
www.racecar-engineering.com 49
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