Hard Chroming Molds
Q. I would like to create a mold which overmoulds plastic to a TIN plated
Copper terminal. Previous efforts have yielded flaking of the tin coating on
the mold surface which is unacceptable for an upcoming project. A colleague
of mine mentioned the use of Hard Chroming to the mold surface which comes
into contact with the metallic terminal in order to reduce such ill effects.
Therefore I have two questions:
Do you know if hard chroming has such remedial effects to this situation?
What base material is most suitable for a hard chrome layer to adhere to?
Many thanks and regards.
A. Chrome plating the working side of molds is common. The best type of
chromium for this purpose would be a thin hard "crack free" plating deposit.
Also referred to as "thin dense" hard chrome. The base metal would need to
be polished to a smooth finish as the chromium coating will mirror that of
the base metal.
In addition to providing increased wear resistance, chromium has a low
coefficient of friction, and good "release" properties. The successful
performance and longevity of the coating would depend on how many cycles,
how hot the mold gets and the frequency of inspections, cleaning and
For molds, a coating of chromium should be in the ballpark of 0.0002 to
0.0007 thick and be smooth and adherent. This may require special conforming
anoding and rack set up which can run into some extra cost.
Electroless nickel coating is a suitable alternative to chromium and may be
less costly to apply.
In any case my best advise would be to take the mold to your local chrome
plater and discuss your situation. Generally plating shops have the
necessary experience to make the best recommendations.