UHMWPE vs. HDPE: diff terms or diff product?

Are these the same thing? If not, how are they different? I've checked a few online sources. Looking for black, 1.75" thick, sheets. Price might compell natural, however, same spec.

Thanks!
smt

2 different products, HDPE finishes nicer and easier and holds shape and tolerances much better. I prefer it over UHMW. Not that uhmw is hard to work with. this site halfway down shows the differences. http://www.boedeker.com/mtable.htm

HD = high density - long chains of ethylene monomers
UHMW = ultra high molecular weight - REALLY long chains of ethylene monomers, and better wear properties

UHMW is quite different, the chips will stretch a lot and not want to break... really interesting type of plastic. Mills easy, not so fun on the lathe though.

Thanks for the advice & links. I am familiar with UHMWPE, use it and machine it for various uses. Did not know about HDPE. Does sound like it might have nicer machining qualities from the specs in the links and posted advice. Now to figure out which one is cheaper, and whether either is cheap enough!

I'm making handles for my straight edges, and ran a bunch in wood. Potential issue is will wood hold up over time. Plastic would be nicer & more predictable to work. No "weak grain" issues with plastic. Problem is it looks like the plastic would end up costing ~$20/pr *or more* materials cost alone.

Thanks!
smt

Stephen,

I've got a ton or two (literally) of Green and Orange UHMW that is 1"- 1 1/8" thick.
It is odd shapes and sizes. I could sell some pretty cheap, at least compared to the $650.00/ sheet new price. I'm trying to figure out what to do with it. Belt scrapers, maybe.

Charlie

Mr. Thomas,
HDPE is the cheapest machinable plastic you can buy. One inch HDPE is 250 bucks for a 48"x96" sheet. The price is pretty much by the cubic inch so you can extrapolate any size up to six inches thick. So far this year I have bought thirty sheets of one inch HDPE. Today I sent three sheets to that big scrap pile in the sky. The stuff is so cheap that wood would be more expensive.

UHMW, or UHMUPE, is just a more dense material, as compared to HDPE. If you are using an endmill or saw to cut UHMW; the chips will be manageable. Single point tools will produce stringy chips that are a real bear. Chipbreakers are totally useless in any configuration. All you can do is program in interrupted cuts by the stop and start method.

I would call Sabic Polymershapes or Curbell Plastics. Personally I use Sabic and I have no intrest in them. My local rep is why I buy there. Sabic was General Electric Polymershapes, last year, and before that they were Cadillac Plastic. I could trace the names back to the sixties, but you get my drift.

Stick with HDPE for handles and other such items. UHMW is about twenty percent higher in price and you will not notice any improvement in your low stress applications.

I need 1.75" thickness. Would only want about 1/2 sheet. So based on Mr. Biler's number that would be workable, about $250 for a 1/2 sheet, 1.75 thick, for 36 prs, or a mere $6 - $7/pr. a little better than a third the numbers I was seeing online vendor prices for UHMW. Will check your sources this week. Seems I bought bullet proof Lexan from Cadillac back in the infamous "Y2K" for a client's home fort... might still have the job envelope on file.

Born 2L8, appreciate the offer, and the colors would actually be interesting. But not much room to play on the thickness.
Thanks!
smt

CharlieBiler said:

Mr. Thomas,
HDPE is the cheapest machinable plastic you can buy. One inch HDPE is 250 bucks for a 48"x96" sheet. The price is pretty much by the cubic inch so you can extrapolate any size up to six inches thick. So far this year I have bought thirty sheets of one inch HDPE. Today I sent three sheets to that big scrap pile in the sky. The stuff is so cheap that wood would be more expensive.

Click to expand...

Charlie, was that a bit of rhetorical exaggeration?

1" x 48" x 96" of wood would be a total of 32 board feet. $250 / 32 bf = $7.81 / bf. Sure, some types of wood are that expensive, and more ... but there are plenty of good hardwoods cheaper than that.

(Or did I miss something, and make a really obvious goof in my calculations ... ? Wouldn't be the first time!)

opinion

Hello,

I'm new to the forum. I've been considering these two products for use as a skid plate on an ATV. I'd like to tap into your knowledge of the materials. I'm thinking that UHMW (black, probably reprocessed) is the product of choice. A few bucks more may be a better investment. I'll be using regular wood shop tools which I think I can get away with. 3/8" thickness so I can try and countersink mounting hardware.

Also any good on-line retail suppliers? There is a Curbell in town but they sell large sheets (3/8x48x120 - $251) I'll never go through it all unless I start building skid plates for friends or something . . .

thanks, Sal

I recently designed a product at work around recycled HDPE. It's a ballasted ground mount for photovoltaic modules for use on a remediated landfill where penetrating the surface of the site isn't permissible. Structurally it's not as robust as UHMW, and in it's natural color it loses alot of it's strength with prolonged UV exposure. I specified that the recycled HDPE (mostly old milk bottles and the like) have 3% carbon black added to mitigate UV aging.

I've machined some of the scrap and it's not bad to work with. Keep speeds down and feeds up.

UHMW is mainly good for scuffing and friction. Motorcycle racer kneepucks are UHMW, as well a guides on conveyers and machines, material handling, that sort of thing. I've gotten by using it as "poor man's Teflon" a few times when a client has been horrified at what their part will cost in PTFE vs UHMW.

In any event, it's versatile stuff, tough and in the case of UHMW slippery as the dickens.

BTW for a bash plate or skid I'd use UHMW if steel plate wasn't an option.

There are different grades of UHMW, it makes quite a difference to performance and price. And colours seem to vary between manufacturers, for example Sal mentioned black as reprocessed, but it can be either reprocessed or virgin.

We used to get our UHMW from Roche, Germany. Here are the specs I have from a few years back:

-White/green was virgin, 4.5 million density.

Some manufacturers use green as the colour of their reprocessed grade.

-Black was either reprocessed (2.5 -4.5 million density) or '5000' Grade, 7 million density.

-Blue was the premium 'filled' quality, 10.5 million density.

Abrasion resistance and price increased with the density. The high grade was UV resistant (and not food grade, by the way).

As for HDPE, I haven't used it, but my catalogues list it alongside HMWPE and don't seem to differentiate between the two in their description. They describe both as high molecular weight PE and give the density as 500,000. It costs quite a bit less than UHMW, has a much lower coefficient of expansion, more like nylon 6 (one of the curses of UHMW is its radical expansion rate), doesn't rate for abrasion resistance (the great quality of UHMW). Impact strength good - but not as good as UHMW.
It is the industry standard for cutting boards.