Material gloat

[Evan]

I had to go to a neighbouring city to pick up my wife from the airport because of a chain of events that landed her in the wrong town.

Since I was there I took the opportunity to stop in at one of her suppliers of plastic products to see what they had in the crop bin. It turned out to be a good move. Very well organized place, there is no doubt what is what, all the crops are clearly separated and labeled.

Well, what a fine day for plastic shopping. I picked up a large box of virgin PTFE scraps, strips and blocks, large blocks of UHMW Poly, about 4 feet of 1.125" black Delrin and the piece de resistance, a 16" x 3" x .5" slab of Rulon LR. All for $50. Including the Rulon.

For those that don't know, Rulon LR and AR are a type of ceramic filled PTFE (Teflon) that has exceptionally good properties for use as unlubricated sliding bearings of all types and in all conditions up to 500 degrees.

It is also exceptionally expensive. For the 1/2 inch thick material I got it sells for $1,100.00 per square foot. The piece I have would normally sell for about $400, never mind the other plastics I scored.

The nice thing about having a good size chunk of an exotic material is that it makes possible designs that I could not have considered otherwise.

[aostling]

We have learned from your earlier posts that Rulon is great stuff. Any idea why is it so shockingly expensive?

[Evan]

I have no idea why it is so expensive. It may have something to do with the fact that PTFE doesn't act like a thermoplastic although technically it is. It can't be melted and injection molded, it must be pressed from powder. As a result it is also anisotropic in strength having about twice the compressive strength in the axis it was pressed compared to the other axes. The fact that it is processed as a powder probably makes it difficult to ensure that different density filler powders are well mixed during molding.

Having said all that I can't see it costing so much to make as to justify the price. I think it is much more likely that the price is proportionately related to the pocket depth of the average user of the product. Rulon isn't something that Joe Ordinary has on his shopping list.

[ptjw7uk]

PTFE is a funny plastic. Some years ago I was examining plastics in an SEM and producing freeze fractures to examine the inside surface and someone said try PTFE but that stuff just doesnt freeze well not at liquid nitrogen temperatures anyway stuff just moved away from the blade.
Only downside is if it gets very hot and melts when it becomes very nasty on skin!!

Petr

[lathehand]

I though I remembered running some injection molding jobs in teflon, so I had to google about molding it.

"PTFE is not injection moldable, but there are several grades within the fluoropolymer family such as PFA and FEP that have similar characteristics and can be injection molded. Components currently machined from PTFE tube, PTFE rod, or PTFE strip might be candidates for cost reduction with fluoropolymer molding techniques. Net shape or near net shape parts can be injection molded in a number of fluoropolymer resins, eliminating or significantly reducing machining operations, providing huge cost savings."

We must have called it teflon on the shop floor, but it wasn't PTFE

[wierdscience]

Good haul Evan,the Delrin alone covers the $50,not to mention the Rulon,were you wearing baggy pants?

[Evan]

Delrin and acetal here are about half the price they are in the US. I'm not sure what accounts for the difference.

[quasi]

Nice score Evan. If anyone needs small pieces of UHMW , Lee Valley sells an assortment of drops for a reasonable price.

http://www.leevalley.com/wood/page.a...10&cat=1,43455

[Evan]

Yep, the big blocks of UHMW will nicely replace big blocks of aluminum in a lot of applications. The main thing you have to watch with plastics is the coefficient of linear expansion with temperature if the item is going to be exposed to varying environments.

[Michael Moore]

Some plastics will also absorb water and change size from that too.

cheers,
Michael