Letter 048

Materials for bushings of plating barrels

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I HAVE RECENTLY EXPERIENCED TROUBLE WITH A PLASTIC SLEEVE FOR A CENTER HUB IN A BARREL. THIS SUPPLY OF SLEEVES WERE A WHITE PLASTIC TYPE MATERIAL THAT WAS SLIGHTLY DIFFERENT IN APPEARANCE THAN THE NORMAL SUPPLY. THESE HUBS TURNED CHALKY AND FELL APART AFTER 2 WEEKS. I RECALL A DISCUSSION ON THE BBS CENTERING ON MATERIALS INCOMPATIBLE WITH HYDROCHLORIC ACID. CAN ANYONE DIRECT ME TO THAT DISCUSSION OR REFRESH MY MEMORY ON WHAT WAS COVERED. THANKS,   

Jeffrey Grube

Jeff: You want to use polypropylene or Teflon for most applications and stay away from nylon that tends to embrittle. Good luck from PlaterB

"PlaterB" Berl Stein NiCoForm, Inc. Rochester, NY

It sounds like either the new parts are nylon as Berl suggests or, possibly (especially if you are talking that thin sleeve material between the barrel and the hanger arm), that they used to be straight Teflon (resistant to everything) and they are now glass-filled Teflon (which won't hold up to hydrofluoric acid).  

Ted Mooney, P.E.  finishing.com Brick, NJ

Hello Jeff, the "sleeve" you are describing was available in a material that was nylon based. This worked well for many years. The introduction of acid based solutions replacing cyanides caused a problem with this product as the acid base would attack the nylon and make it a gummy looking appearance with severe wear. This product was changed to a polyethylene based material with excellent lifespan. Your note does not state the details, but if the material is white it could be a number of starting products. If it is a "brittle" material, it may well be nylon. Teflon and polyethylene are more "bendable" of a material. Ted, news to me, glass filled Teflon??, well, you'd think it would wear better but the problem [on our end] was never the Teflon wearing out, it was the Teflon sticking to the hanger hub and wearing the barrel. is the glass Teflon a better choice???, again,its news here       Ron Landrette ----- Nylon will dissolve quickly in HCl. As you describe, nylon will first turn a chalky white.       Ken Rosenblum

Hi, Ron. One supplier I was with tried various materials for the bearing surface of the idler gear. In other words, the idler rotated on a stationary shaft, and the polypro the idler gear was made of wore too quickly, hogged out, etc. So we wanted a replaceable bushing and tried many materials. For that particular application Teflon was too soft, it would "flow" out under the heavy load. We had about equal life from glass-filled Teflon and from UHMW polyethylene.  

Ted Mooney, P.E. 
finishing.com
Brick, NJ

Hi Ted, well,that makes a little more sense here,I thought you knew someone trying it as a barrel end bushing. My best experience for gear bushings is u.h.m.w. it seems to be the most tolerant, although delrin works good as well if kept from the solution. c.y.a........ron    

Ron Landrette

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