44096

ANTIMONY PLATING FOR BELLEVILLE WASHER [California] 

February 21, 2007

I have a Belleville washer made of 4130/40 steel. Upon preliminary material analysis there was about 15% Antimony in the chemical composition. Are there any standard plating/finishes for belleville washers that contain Antimony.

Daniel Hasibuan
MWA - Temecula, CA, USA

Is the coating perhaps a babbitt alloy? From ASTM B23 & ASTM B102, some 15% antimony compositions: (1, 5 or 10)Sn-15Sb-balance Pb & 65Sn-15Sb-18Pb-2Cu. Useful for lubricity & corrosion protection.

The Babbitting chapter in ASM Handbook Vol. 5 Surface Engineering describes the most common application methods: casting and (briefly) thermal spraying. In both, the surface is tinned prior to babbitting. Maybe not suitable for small, lightweight objects. Barrel burnishing sprayed items will give a plated appearance. Hot dip coating of fluxed pieces is apparently done but is perhaps proprietary.

These alloys can be electroplated, but maintaining the solution composition seems laborious and there don't seem to be any general plating specification. The few commercially-available babbitt electroplating solutions (Babbitt Navy Grade 2 & Babbitt SAE 11) are for brush plating, as when refurbishing large, babbitt bearings in ships, described by Rubinstein in Electrochemical Metallizing and MIL-STD-2197 BRUSH ELECTROPLATING ON MARINE MACHINERY.

Mechanical plating seems like the best method to babbitt small items, but isn't mentioned as such in the ASM Handbook or ASTM Standards. No hydrogen embrittlement, so better than electroplating for hardened spring steels.

Antimony can also be evaporated or sputter deposited in vacuum.

Ken Vlach - Goleta, California