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Old R&D Folks, Learn me up about Nylon/Delrin history

rcoope

Stainless
Joined
Sep 25, 2010
Location
Vancouver Canada
I had a former engineering co-op student drop by the shop tonight to make parts for her class robot project and it led me to wonder when did we stop using nylon, because it sucks, and start using Delrin? Briefly, we redesigned her part, she machined the nylon she'd been given (to save course money over Delrin), had some major dimensional problems after it came out of the vice where it had flexed, so I gave her a piece of Delrin and she did it right. Then I wasted her time with anecdotes about my experiences with nylon's dimensional changes and water absorption problems and gave her a bunch of rude things to say to the guys up at the physics department (where I came from) so it was worth it for that. Poor girl.

The thing is, when I was an engineering shop rat through much of the 90's in that department, I recall the shop mostly had nylon and acrylic, and then PEEK, Teflon, Vespel and other exotic stuff, but no one really mentioned acetal that I can recall. The special thing in physics though is that much machining is related to vacuum systems and Delrin is not a good vacuum material due to out gassing. So I was wondering if people can recall when it became a common engineering plastic and were we just old-school or just very vacuum-centric?
 
My Harrison lathe made around 1977 has delrin molded gearhead cover. Molded in black painted green to match the iron. On my Father's South Bend lathe the same part was cast in Aluminum around 1945-50. I believe it is aluminum not pot metal.
my parks planer from around 1975 the gear box is cast iron but hte lid is aluminum. It was designed around 1930 same vintage as the south bend. the early models the lid was also cast iron.
I think aluminum became much more common after WW2 since there was a lot of scrap around. before that it might be brass for small stuff like tags and knobs or cast iron for big pieces.
Bill D.
 
I had a former engineering co-op student drop by the shop tonight to make parts for her class robot project and it led me to wonder when did we stop using nylon, because it sucks, and start using Delrin? Briefly, we redesigned her part, she machined the nylon she'd been given (to save course money over Delrin), had some major dimensional problems after it came out of the vice where it had flexed, so I gave her a piece of Delrin and she did it right. Then I wasted her time with anecdotes about my experiences with nylon's dimensional changes and water absorption problems and gave her a bunch of rude things to say to the guys up at the physics department (where I came from) so it was worth it for that. Poor girl.

The thing is, when I was an engineering shop rat through much of the 90's in that department, I recall the shop mostly had nylon and acrylic, and then PEEK, Teflon, Vespel and other exotic stuff, but no one really mentioned acetal that I can recall. The special thing in physics though is that much machining is related to vacuum systems and Delrin is not a good vacuum material due to out gassing. So I was wondering if people can recall when it became a common engineering plastic and were we just old-school or just very vacuum-centric?

Acetal resin co-polymer first hit my eyes as "lifetime" plain-bearing replacements for ball-bearings in one of the major automaker's steering columns. 1950's?

Sure enuf - it had issues. Also squeaked like a mouse while it degraded. DAMHIKT.

E.I. Dupont de Manures & Co. then introduced a MONO-polymer variant, as usual starting the name with a "D", so we got "Delrin". Claims of "crystaline" structures as made it stiffer and more stable? Also "as usual" Dupont flogged the product hard and wide. And still do:

Acetal Resin | DuPont ™ Delrin (R) | DuPont USA

Folks such as W.F. Berg and PIC Design - providers of the bits and pieces mechanical R&D used rather a lot of instead of scarce machining time for bespoke parts were filling catalogs with Delrin goods by the end of the 1960's and into the early 1970's.

And - for the most part - it worked "as claimed", so that was a lovely place to be in time - just as the computer peripherals and office automation industries took-off into high volume need of low-cost, rapidly made gears, pulleys, guides, actuators and such for printers, copiers, scanners, disk and tape drives - and similar goods.

Molded more often than machined, BTW. "We" - in subtractive machining - see only a tiny fraction of the overall consumption of Delrin & cousins.

+1 On Nylon's faults. It sucks. Literally, where water is to be had.

2CW
 
Delrin had been used in light and medium truck steering knuckles from the 1950s or 60's. They would get pounded out of existence but were cheap and easy to replace. In the 80's Rockwell introduced Garlock DX acetal bushings in heavy truck axles replacing steel backed bronze. Steering effort went down 25% and bushing life tripled to 1 million miles+. The DX bushings are steel backed pourous bronze with the acetal impregnated in. Thickness of the naked acetal only about 7 thou to the pourous bronze. Not enough acetal thickness to get pounded out of the joint.

So it seems as if some of the vacuum you were working with did affect your bushing sources.
 
Thanks for the thoughts. Upon reflection I do think a pro-vacuum bias had crept into the shop over the years and possibly also a perception that Delrin was expensive. Which it might have been at one time compared to Nylon but I have to go tell the guys teaching this robot course that if you go on McMaster right now, Nylon and Delrin are essentially the same price!
 
In the mid 70s I worked on a drafting pen to like the Kohinoors and Rotrings. I made a prototype with some nylon internal parts and took it to a commercial artist for a trial. When I got there, it was locked up. The company chemist was not a bit surprised (except possibly at my naivete) and switched us to Celcon. I did a test on a piece of nylon, keeping it submerged in India ink and measuring it every day. It kept swelling a little more each day until I got tired of measuring it. Celvon swelled slightly in the first couple of days, then quit.

Bill
 
Acetal on acetal is a poor friction couple. Just a little pressure and it will have horrible stick/slip characteristics. Nylon/acetal on the other hand is excellent. Very slippery.

Steel/acetal I think is ok but I have less experience with that couple.

Nylon/nylon with grease lubrication is an excellent material for gears but you have to account for moisture swelling as mentioned above.
 








 
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