Reducing the weight of race and rally cars has long been an integral part of extracting ultimate performance; every gram saved makes a contribution to success. But when the source car is an already stripped-down production model with all nonessentials already removed, there are particular challenges.
To help meet those, Surface Processing Ltd. (SPL) has developed what it claims as a “unique” chemical immersion process that offers motorsport-vehicle-preparation companies quick and effective removal of unnecessary paint, rust, grease, oil, underseal, adhesives, and sound-deadening from a body shell. It can legally take out up to 35 kg (77 lb) of unnecessary mass from a four-door sedan without reducing vehicle strength.
By avoiding release of noxious fumes during post-processing, the process is also claimed by the company to improve the working environment for fabricators.
The increasing use of production-car-based body shells allows motorsport participants to control costs, but those shells carry coatings and materials that are unnecessary for racetrack or rallying use.
“Traditional preparation methods such as media blasting or thermal stripping are used widely by race and rally teams, but they create further problems for the fabricator,” said SPL Managing Director Adrian McMurray. “For example, shot peening relies on the action of a media upon a surface to induce a stress layer, resulting in plastic deformation of the substrate. The panel becomes stress relieved and this often results in rippling, which is undesirable for teams when presentation is crucial.”
SPL’s process of passing the body shell through a series of tanks has been designed to avoid damage or distortion to a body shell, which can leave the surface in a rapidly oxidizing state. The company’s fully immersive process also reaches normally inaccessible areas, leaving them residue free, and avoids trapped media that increases moisture retention and weight.
Compared to thermal or paint stripping, it is said to be faster and protects the user from harmful chemicals such as methylene chloride. It also removes zinc, thus minimizing the risk of getting “metal fume fever,” a condition that produces flu-like symptoms, said McMurray: “Leading WRC and touring car preparation companies such as Prodrive use our safer, cost-effective process before fabrication work.”
Removing paint, adhesive, and rust ensures only clean metal is welded, thus improving strength. It also avoids the release of noxious fumes and reduces the risk of fire hazards; it is possible for paint and some NVH materials to ignite during welding. The process does not involve the type of acid dipping that might affect vehicle strength.
“We achieved a 31-kg reduction with a BMW race sedan project, with no effect on metal thickness,” said McMurray.
The first stage of SPL’s process for mild steel components and shells involves removal of heavy organic coatings such as sealants and NVH material. Stage 2 removes paint, grease, oils, and carbon via immersion in an alkaline hydrocarbon solution. Corrosion, where present, is removed at the third stage, which involves the use of dilute hydrochloric acid with the inhibitors.
Acid-dip processes of three decades ago were sometimes used to reduce metal thickness, saving weight but potentially making the cars unsafe. In the SPL process, the acid dip is only one element of the complete process. The shell is immersed in the dilute solution of inhibited hydrochloric acid, the inhibitors preventing the acid from attacking the mild steel and only allowing it to break down the corrosion.
Developing the inhibitors took considerable research and collaboration with partners in the steel industry to ensure that the process only removed corrosion and not good metal. This is followed by immersion in an alkaline rinse before going immediately to the next stage, an agitated alkaline neutralization and passivation immersion to offer maximum protection, leaving what McMurray describes as a “dry and stable finish.”
Although SPL is established in the classic-car-restoration sector, its process is being used increasingly by OEMs and Tier 1 suppliers to recover parts that were previously scrapped due to unsatisfactory standards of finish. Its involvement with motorsport specialists marks a significant expansion of its application. “We have completed body shells for WRC, Group N/S2000, Touring Car, and GTs such as Porsches,” added McMurray.
Once fabrication work is complete, SPL recommends electrophoretic coating (e-coating). The immersion process is said to deliver “excellent” penetration and uniform coverage of between 22-28 µm (870-1100 µin), offering more than 1000-h salt spray resistance.