An alternativer tinning process for engine pistons

In the past, in order to achieve running-in characteristics, pistons have been tin-plated using either stannous fluoborate in an acid enviroment or solutions of sodium stannate in an alkaline environment.

As an alternative to both of these methods, Vopelius Chemie AG has developedits own product, TIN-COAT^®. Not only is the TIN-COAT^® process easy and safe to use but, using the chemical dip method, tincoatings with exellent adhesion and a thicjness of up to 1,5 µm can be obtained on alumium pistons. Compared with conventional alkaline tinning baths the TIN-COAT^® process is more economical and this is reflected in a cost-reduction of up to 0,03 € per piston.

TIN-COAT^® is used at a dilution of approximately 1 part in 20 which gives a tin content of about 15 g per litre in the resulting solution. By using a brightener (e.g. approx. 0,7 % TIN-BRIGHT)and also a leveling-agent(e.g. approx. 0,4 TIN-EGALIZE) the tincoating can be given a really bright finish. The preparatory treatment, which plays an important part in getermining the adhesive quality of the tin-coating, can be carried out for example in an alkaline gegreasing bath (e.g. CLEAN 120) in conjunction with ultrasonics, or by using a sulphuric acid/hydrofluoric acid pickling bath.

As far as waste disposal is concerned, TIN-COAT^® also presents distinct advantages as compared with the conventional acid, tinning bath based on stannous fluoborate, on account of its greatly improved environmental acceptability. Using convential neutralizing agents (e.g. soda lye), more than 99 % of the TIN-COAT^® constituents can be eliminated during the contous neutralization process of the swill and disposed of by normal filtering. As a result, the amounts of flourine and metal in the waste water meet the strict requirements of the WHG (Water Pollution Controll) in Germany and Europe.

Existing production units based on the stannous flouborate method can be converted to the new process without interrupting the normal routine.