Can I do injection molding of a plastic mixed with a powered grit?

[mjf89]

Hi,
I’m trying to create a plastic case which has a carbon powder mixed into the injection media. Is this possible with most injection equipment? I’m interested in the electrochemical properties of the grit therefore it’s integral to the usefulness of the case.
Thank you very much,
Mike

[chrisprocess]

I believe so if you have a good auger (gravimeter feeder probably best) and proper screw. Check out RTP website they do a lot of this stuff.
edit: Depending on your cost and Mfg capabilities, you can purchase this pre-compounded for consistent 'mixing' results. Went this route with an electronically conductive PP in the past

[iautry1973]

Mike,

I don't see why you couldn't. Mixing the material would be the main thing to keep an eye on. We shoot MIM. It is metal powder mixed with wax and plastic. So if we can shoot that I am sure carbon powder would be an issue. Separation of the material during injection is something to keep an eye on. We have to watch shear for that.

[JayDub]

There is a huge range of commercially available carbon filled plastics – people mold them on standard equipment all the time. I am a bit confused by your reference to carbon powder as “powdered grit” though: commercial carbon powder is essentially soot. I’m not sure what you mean by “electrochemical” either, but if you want to experiment with electrical properties, you might consider carbon fiber – aspect ratio of the fibers has a major effect on properties. If you have deep pockets, you could even look at carbon nano-fibers, which have very large aspect ratios and give useful electrical properties (ESD or conductivity) at much lower loading than powder, so they have less effect on the mechanical properties of the resin.

Effect of the carbon on equipment depends on its chemical structure. Commercial carbon powder is structurally graphite and has no effect. Carbon fibers are abrasive, so in mass production you’d want to use an abrasion resistant screw and barrel. If your “powdered grit” is pulverized industrial diamond, you may have a bit more of a challenge. Effects also depend on loading and on base resin – LDPE with 10% (by weight) carbon powder is no problem; 30% carbon fiber loaded polycarbonate will eat OEM screws.

In any case, if you have specific property requirements, and unless your powdered grit is something very special, I would strongly recommend talking to a commercial resin compounder before you try to reinvent the wheel.