Author Topic: UHMWPE better than Nylon 66 for wear properties? (Read 38277 times)

bry1975 · « **on:** July 14, 2011, 04:57:48 PM »

Chaps,

Is UHMWPE black better than Nylon 66 black for wear properties?

Bry

David Jupp · « **Reply #1 on:** July 15, 2011, 02:58:52 AM »

Truthful answer is probbably 'it depends on the application'.

UHMWPE is often used in situations where abrasive wear is an issue - coal/mineral handling for example. I believe it's also used in some synthetic ice rink surfaces.

If the temperature increases, I'd intuitively expect that to move the balance towards Nylon.

It would be good if you can find some experience of same or similar application, otherwise do some trials.

BTW - I'm surprised you can get Black UHMWPE, the molecular weight is so high that normal compounding (the process by which colour is mixed in) isn't possible. I've only ever come across 'natural' (translucent white).

bry1975 · « **Reply #2 on:** July 15, 2011, 05:01:49 AM »

Thanks David,

There you go:_ http://www.directplasticsonline.co.uk/UHMWPE_Rod.html

I'm very interested in using plastics that have metal/steel performance so is UHMWPE difficult to cut and drill? For now I've settled for PA 66 with disulphide so should machine well but would like to try the UHMWPE I want a nice plastic that's difficult to mark in normal use.

David Jupp · « **Reply #3 on:** July 15, 2011, 06:25:02 AM »

I used to work in a Polyethylene R&D lab, though our company didn't actually make/sell UHMWPE.

UHMWPE is basically High Denisty Polyethylene but with very, very long polymer chains - so much so that it doens't really flow at all when reaching its melting point - this makes it difficult to process as a melt. Rather than conventional extrusion, it is more normal to sinter the powder to form solids.

It isn't actually very hard, and the softening temperature is low. It is very resistant to the majority of chemicals.

Drilling/cutting etc should be easy as long as speeds are kept down (to avoid softening/melting).

bry1975 · « **Reply #4 on:** July 15, 2011, 07:02:53 AM »

Very interesting David,

HDPE is quite a well used polymer so does UHMWPE resist acetone like HDPE does also I'm guessing UHMWPE isn't designed to be blow moulded?

David Jupp · « **Reply #5 on:** July 15, 2011, 08:11:34 AM »

Correct - chemically they are the same stuff, but the length of the polymer chains is much much longer in UHMWPE, making it difficult to impossible to process in conventional plastics processing equipment.

Blow moulding involves an extrusion step to form the parison, which is then inflated in the mould. Both steps are melt processing, so not suited to UHMWPE.

bry1975 · « **Reply #6 on:** July 15, 2011, 09:55:02 AM »

Arr interesting and the parison acts like an internal balloon? I briefly worked at an injection moulding and blow moulding firm found the operator work to tedious as every 20 seconds I'd have to remove parts.

Kinkajou · « **Reply #7 on:** July 16, 2011, 09:46:59 AM »

UHMWPE has been used to produce implants for some times now. They used to make them with teflon but found it to be better.
Total hip replacements and knee replacements are a good example of the aplication. They are usually used to be the counterpart of an articulation system in which a metal component has to move around a plastic one to increase wear capabilities.

UHMWPE is very resistant to abrasion but can eventually fail due to wear, that is the reason that some hip and knee replacements have to go through a revision every 10 to 15 years of use.

Very biocompatible .
Hip replacement

Knee replacement

Slow feeding and very sharp tools are needed to machine this plastic.

bry1975 · « **Reply #8 on:** July 16, 2011, 02:08:17 PM »

Thanks Kink,

Sounds a useful polymer I'll have to buy some rod sometime.

PekkaNF · « **Reply #9 on:** July 16, 2011, 02:27:16 PM »

Interesting. Is there easy to find reference for mating surface roughness and hardness requirements as a "bearing" IE. rotary or universal bal joint as in auto parts? Also failure modes would be nice to know. I don't have any immediate need, but I used some POM and found it easy to work with. Teflon creeped easily, was hard to use with mechanical fasteners, hard to glue and worked with a very narow window of mating surface finish (for an amateur).

Pekka

Rob.Wilson · « **Reply #10 on:** July 16, 2011, 03:32:22 PM »

Pekka

Found this the other day when i was looking for info on plastics (PEEK) http://www.machinist-materials.com/comparison_table_for_plastics.htm

Rob

bry1975 · « **Reply #11 on:** July 16, 2011, 03:41:35 PM »

Looks a good link Rob,

Shame the materials can't be compared so easily always find it interesting comparing the mechanical properties.

Bry

Rob.Wilson · « **Reply #12 on:** July 16, 2011, 03:57:26 PM »

Hi Bry

Looks like the wear factors are on the table ,,,,,,,,,,,,,,,, What are you making ?

Rob

bry1975 · « **Reply #13 on:** July 16, 2011, 04:49:27 PM »

Hi Rob,

Just some hand tools for wrist watches for meself and others just need to be non marking really and have decent strength, am waiting for some PA 66 black that should be fine for now.

Plastics are interesting materials ever used Kynar?

Rob.Wilson · « **Reply #14 on:** July 16, 2011, 05:17:12 PM »

Hi Bry

Never come across Kynar ,,,,,,,,,,,, I don't use allot of plastics ,odd bushing and insulator here and there,,,,,,,, but i have an up coming project that may need some plastic parts .

The engineer has a hole lot of materials to chose from now a days ,,,,,,,,, list just gets longer

Rob

bry1975 · « **Reply #15 on:** July 16, 2011, 05:27:09 PM »

Yup they say Nylon has enough grades to cover just about everything.

Have you ever looked at Iglidur plastic bearings? also Igus do some handy energy chains.

fatal-exception · « **Reply #16 on:** November 21, 2011, 06:01:34 PM »

Black UHMW is very easy to machine by all normal methods. I've produced a few tanker trucks full of chips from CNC machining this material. Typical feed rates that I use are 200IPM with a 1/4" end mill, 1/8" to 1/4" DOC, 25-30kRPM. 2 Flute polished solid carbide tools are the best IMO.

Yes, this stuff dosen't really melt. I've tried to reform it, but it just becomes brittle when it cools. I'm sure I'm missing something there.

We also use the natural white UHMW for steel on plastic sliding parts in industrial machinery for the grain industry. The 'wipers' and 'slides' last a very long time, and are highly resistant to grain flowing over them.

John Hill · « **Reply #17 on:** January 19, 2012, 12:49:30 AM »

A very interesting topic...

I have some scraps of engineering plastic, small bits of sheet and some thicker blocks, black and white bits. How can I tell what is what among these bits? Does it really matter?

My last project was a power feed for my mill using an aluminium plate worm wheel and a worm cut from stainless steel. I dont think the wheel will lost for long so I am casting around for alternatives. Can I heat and pressure form a new worm wheel?

Thanks

john

dvbydt · « **Reply #18 on:** January 19, 2012, 06:45:53 AM »

John,

Plastics Identification - this might help.

http://ixian.ca/pics8/plastics.gif

Ian

Rob.Wilson · « **Reply #19 on:** January 19, 2012, 12:47:28 PM »

Quote from: dvbydt on January 19, 2012, 06:45:53 AM

John,

Plastics Identification - this might help.

http://ixian.ca/pics8/plastics.gif

Ian

Thanks for sharing that Ian

I too have a box of assorted plastics that i have no idea of what type they are ,,I stand a fighting chance now

Rob

John Hill · « **Reply #20 on:** January 19, 2012, 01:41:34 PM »

Thanks Ian, at least I should be able to put a name to the bits now.

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Author Topic: UHMWPE better than Nylon 66 for wear properties? (Read 38277 times)

Rob.Wilson

Rob.Wilson

Rob.Wilson

Rob.Wilson