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Plating compatibility

Dear Readers,

I am a design engineer working with the Mitsubishi World Rally team. I wish to find out if any of you have had problems in the past or know any reason why it would be a bad idea to use a Zinc plated nut with a cadmium plated bolt. We use a torque setting of 100Nm (73.5 lbs-ft) and seem to be getting bad pick up which destroys both the nut and bolt, but not all the time.

This bolt is used to secure the rear cross member to the car. The head of the bolt is floating and so is in perfect tension (all shear loads are taken by dowels coaxial with the bolts.

Regards,

Paul Smyth
Design Engineer - Rugby, Midlands, United Kigdom
2004

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Sorry but I don't understand the phrase 'getting bad pick up'. There are three issues here though. First is that zinc is not fully compatible with cadmium galvanically, so you probably shouldn't be mixing them; second, that zinc does not exhibit freedom from stick-slip like cadmium does, so switching the bolt to zinc is not a good idea; and third that cadmium is a strictly regulated material that you should try to be getting away from, not increasing the use of.

I would suggest you obtain some tin-zinc plated bolts and nuts and evaluate how reliably they torque.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

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Dear Mr Paul Smith,

Torquing strengths can be increased by choosing Zinc-Iron plating with proper dry film lubricants on both the bolt and the nut. Do not use different finishes on mating parts as this will accelerate corrosion.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2004