Minibot can we use Delrin or acetal?

[Tristan Lall]

Originally Posted by EricH

I know inspectors who can tell Delrin from Lexan very easily; I'd guess that acetal would also be fairly easy (I don't really have any experience with it).

It's basically a matter of seeing how it reacts to a fingernail. Polycarbonate (Lexan, for example) scratches lightly, and feels hard without any waxiness, so consequently has somewhat high friction; it's also quite flexible. Polyethylene will take a bit of an indentation, and feels waxy (the density is proportional to the molecular weight, so you can tell something about the grade too). Polyoxymethylene (which is the same as polyacetal, and which is sold under the trade name Delrin) is slick, but quite hard and stiff. Polytetrafluoroethylene (Teflon) is very slick, but also soft and flexible.

You can sometimes tell a bit about the composition by the colour, but this can be dyed and therefore misleading. Virgin PC is usually clear, while the others are usually whitish (PE and PTFE) or off-white (POM).

Fibre-filled plastics complicate this somewhat, but you can usually observe the surface and tell if there are fibres inside (usually made of glass). That makes it stiffer and harder, on average.

Of course there are other less-common plastics too (polystyrene, acrylonitrile butadiene styrene, etc.), or blends (like in injection moulded items) that are hard to identify. But most of those aren't common in robots because they're weak, unavailable or otherwise objectionable.