Delrin,POM,acetal

[trajectory]

Hi, just wondered what grades have been used successfully for which applications. There's a tremendous variety with diverse properties, filled, unfilled, tensile strengths, elongation etc, so I was interested........Rod

[clarky]

Hi, just wondered what grades have been used successfully for which applications. There's a tremendous variety with diverse properties, filled, unfilled, tensile strengths, elongation etc, so I was interested........Rod

True Du Pont Delrin takes soms beating...its stronger than regular Acetal copolymer Pom...only by approx 10 percent but also more rigid even though the 2 materials are virtually identical.
Nylon materails are stronger still but machine badly.....its all about finish and parallel with guides.
You can only get very high of both with Acetal ..
Im currently looking at PEEK....it might be even better.

[TonyL]

I seem to recall that on the directplasticsonline website they go into the various properties / applications / characteristics of many of these wonderful engineering plastics.

[trajectory]

The problem with material selection I have is knowing what the range of properties needed for a particular applicationwould be. How much temperature resistsance do you need for instance if making a piston head? What would be the normal operating temperature... 0 to 35deg C perhaps, but at compression the temperature will rise, & if it diesels then what happens to the material, will its edges soften & fail or alternatively will they cook & crumble after a few cycles. Then there's chemical resistance to the lubrication & a host of other things. So if I was to look at the properties ona selector guide I'd probably pick the toughest, most heat resistant, most chemical resistant one with the highest modulus...ie completely over the top & consequently pick the wrong one based on the false asuption that I was doing the right thing erring on the side of caution, but missing out on the benefits a more flexible shock resistant, beter wearing material might give. The selector guides might mention ellectric motor gears, hydraulic pump valves etc but translating that into relevant applications aint straightforward. So any known applications/ material grades would be interesting. Haven't looked at peek in any detail but there is a (for the unknowing) a bewildering array of engineering plastics available.

[lensman57]

True Du Pont Delrin takes soms beating...its stronger than regular Acetal copolymer Pom...only by approx 10 percent but also more rigid even though the 2 materials are virtually identical.
Nylon materails are stronger still but machine badly.....its all about finish and parallel with guides.
You can only get very high of both with Acetal ..
Im currently looking at PEEK....it might be even better.

You must have too much money.

A.G

[Doxbox]

PEEK-(Poly Ether Ether Ketone) is what Venom Arms used to make their piston heads I believe. Never was anything wrong with those if memory serves me right. Aint cheap though.

[clarky]

You must have too much money.

A.G

lol...im not bad off but it would only be for my own single rifle or pistol ....and not for club member tunes.
Just special for me.
TBH its all about how a material machines. A material can have wonderful properties of everything but if it wants to rag or finish poorly, then all those properties are meaningless.
Its why Acetal/ Delrin takes some beating...
Recently i discovered a number of members complaining of Stainless galling.
You would imagine so much tougher than Delrin but galls for fun.
Hardened silver steel makes great guides and does not gall but Delrin wears well, removes all vibration and is quieter.
It releases all the spring energy and can be made a tighter fit.
Peek interests me though.

[bucketboy]

peek is very hard and also quite brittle, I don't know how it will stand up to repeated impacts on a piston.

bb

[tinbum]

peek is very hard and also quite brittle, I don't know how it will stand up to repeated impacts on a piston.

bb

I do.

[rancidtom]

We have seen PEEK used as supposedly "silent" hammer tips in PCP's. All the ones I've seen have been in good condition (not cracked or distorted) but they are no quieter than a standard steel hammer tip in my opinion. I have a feeling that many people buy them or make them to try and then convince themselves they are quieter than the steel original. As yet I've not been persuaded to make or buy one.
PEEK has many other uses that I would gladly use it for given its properties it is superior to other plastics in some circumstances.

[clarky]

peek is very hard and also quite brittle, I don't know how it will stand up to repeated impacts on a piston.

bb

It actually isnt....but i wasnt planning using it as a piston seal, that job is done very nicely by Urethane parachute seals and such.
I meant the guide ....for that it is beyond words good.
The stuff is damn near perfect .. super slippy, resistant to chemicals and stable at broad temperature range...
None flexing....strong and nice to machine...good stuff

[trajectory]

If I were to contemplate replacing a pump head on a Crosman 1377 (the original seal is worn anyway) with a pump head made of Delrin would the 100 grade be a good starting point? Machined up for a single or perhaps double o ring to B.S. 111. Bucket of water standing by just in case I get shot down in flames.

[lensman57]

lol...im not bad off but it would only be for my own single rifle or pistol ....and not for club member tunes.
Just special for me.
TBH its all about how a material machines. A material can have wonderful properties of everything but if it wants to rag or finish poorly, then all those properties are meaningless.
Its why Acetal/ Delrin takes some beating...
Recently i discovered a number of members complaining of Stainless galling.
You would imagine so much tougher than Delrin but galls for fun.
Hardened silver steel makes great guides and does not gall but Delrin wears well, removes all vibration and is quieter.
It releases all the spring energy and can be made a tighter fit.
Peek interests me though.

I was lucky enough to get a piece of Peek as off cut a few years ago. It machines just fine.

A.G