Q: Material, finish to mold (and release from) melted plastic?

Greetings all,

I know little about thermoplastic processing, and I'm curious about what materials, finishes (and mold release compounds?) are used to let the molded part come out of the mold, without such a fight that the parts or mold are damaged. Are the molds "simply" highly polished metal? or do they have some special coating that thermoplastics don't stick to very well. Similarly, if one wanted to roll/squeeze one prismatic solid into another size/shape cross section (think of wire drawing), what material/finish could be used to make a die or rollers that the plastic wouldn't stick tightly to?

I'll do some googling, but I thought I'd query the group in parallel.

FYI, I'm interested in exploring how to recycle scrap plastic into either usable structural shapes (e.g. bars and plate stock.) and/or as an alternate path to creating filament. Somebody (Forrest?) demonstrated that melting scrap in a shallow pan resulted in a solid layer with few voids. That sems to get around the (major problem of) transforming scrap (or granules) into a bigger, void-free solid. This is a slower process than one-step injection molding, but in a bootstraping, distributed reprap economy, speed isn't as important as reducing the barriers to entry.

So perhaps filament could be made in a series of steps:

ground scrap => solid plate => sticks or spiral coil => roll/draw sticks into filament.

Edited 1 time(s). Last edit at 07/30/2009 02:12PM by Larry_Pfeffer.

---

Larry Pfeffer,

My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]

You might want to try with ptfe-spray for coating.
You'll find it at the hardware store

Afaik industrial metal molds aren't "greased" at all.


When I was young we took old yoghurt cans (made of PE) and put them in the oven (with baking paper at medium temp.) for a little while to make coasters.

We even made "ghosts" that way by placing some figurines under the cans.

So I guess (without trying) you can fuse more cans to one bigger plate,
but how would that lead to new filament?


'sid

sid Wrote:
-------------------------------------------------------

>
> So I guess (without trying) you can fuse more cans
> to one bigger plate,
> but how would that lead to new filament?

Sid,

If one could make a void-free plate (imagine it's a disk, for now, ~3 mm thick), then one could slit that, in a spiral fashion, into a long spiral of void-free plastic. The cross section of this long, spiral "string" could be adjusted so its cross-sectional area is the same as the desired filament. Then the square-CS string could be rolled through a set of heated rollers to change the cross section from rectangular to round (and could straighten out the spiral as it did so.)

Yes, it's a bit of a long shot, but it might work.

---

Larry Pfeffer,

My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]