Bearing properties of glass-filled nylon

Incidentally, I should add, this is a reverse-engineering situation. I'm trying to figure out what material a defunct company used. The plastic layer is transparent with a yellowish tint.

Chris

How long is a piece of string? A few more details about the application would help, dimensions / load / pressure / sliding speed / how many cycles or how far do you need it to slide? Do you want the cheapest solution, or is it an expensive bit of kit that you don't mind spending money on?

Transparent doesn't sound like glass filled nylon, more like acrylic, polycarbonate, perhaps epoxy?

Glass filled nylon is cheap, readily available, easy to machine. There are also nylons which contain some oil to make them more self-lubricating.

PTFE is pretty good, though not so strong. Fabric reinforced phenolic is strong, but less happy at combination of high load and sliding speed. Polyimide (e.g. Vespel) is the Rolls Royce material for many applications, but not cheap.

Thanks for the thoughts. It's a piston in a miniature air pump. Here's a picture. The plastic layer is over the knurling you can see:

Chris

The only issue I can see with Nylon in that application is Nylon is Hygroscopic - it attracts and absorbs moisture to some degree - so make sure you provide ADEQUATE clearance for expansion. Glas filled should wear very well in that application - just make sure cooling is adequate as well as the clearance.

It is too clear to be filled with anything. It could be nylon, polycarbonate or even low density polyethylene. If you can do destructive testing, strong acids will eat nylon, and ketones (lacquer thinner) will eat polycarbonate. Polyethylene will be more resistant to both, but it is not compatible with mineral oil.

There are some easier tests for basic plastic types and more detail can probably be found on the net. 3 of the basic ones I remember are nylon when burned smells like burning hair, polypropylene and polyethylene smell like a burning candle but one floats in water though I can't remember which one, it'll be the less dense one anyway. There are a number of other simple tests like these to help narrow down the basic stuff.

I've seen the following chart several places, but most clearly at:

The tests are destructive but can be done with slivers of plastic, via techniques as at . (On my system, that page didn't display in browser until after I used wget

If OP (C.D.T.) hadn't been told that the piston cover "was thermally moulded", I'd have thought it could have been made by sliding a short length of vinyl tubing over a knurled brass part.

I have actually been told that this proved to be a problem at times. I'm trying to trace the history of this product, and have been told various things about the plastic: that it was thermally moulded, that it was special nylon with a low coefficient of friction, that it was hygroscopic, and lastly that it was glass-filled nylon. I've been told these things by different people, and am trying to figure out the truth. The glass-filled nylon part I had doubts about.

Thanks for the thoughts.

Chris

Well, 'nylon' means polyamide plastic, glass-filled means it was probably thermally molded to a precise size (that's the benefit of the glass filler, that the size is stable).

I suppose you could burn a sliver to see if it has the ammonia-like smell of polyamide. It's more likely that a low-friction plastic (Delrin aka acetal) would be used, rather than polyamide, for a sliding part.