Expansion/contraction sounds a bit weird as a cause of electrical potentials. How about it being the liquid plastic acting sort of like a Van de Graaff generator as it passes through the nozzle?
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Replying to @NYarvin
I think what's actually happening there is the heating/cooling warping pulling the plastic up from the bed slightly in bursts. Certainly, popping a thin PETG part free with tweezers is a sure-fire way to bork the display/spontaneously reset the printer.
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Replying to @xiphmont
Hmm. That could be already-charged plastic suddenly moving and generating a change in electric fields, or it could be plastic picking up a charge as it detatched.
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Replying to @NYarvin
I would expect parting to create a charge. I would also expect a sharper-edged metal implement that picks up the charge to be more effective than the plastic at concentrating the charge to the point it gets past the powdercoat.
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Replying to @xiphmont
You don't need conduction through the powdercoat; electric fields going through it are enough. Electrostatic charges are commonly kilovolts; even a slight echo of that will scramble signals.
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Replying to @NYarvin
True. That said, there's usually a discernible discharge, and I've not noticed the same tendency with the smooth PEI sheet (made from continuous PEI as opposed to powdercoat). I'll go test.
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Replying to @xiphmont
Okay, if the surface texture matters that definitely means the charge is generated by the interaction with the surface as it breaks loose, not (as I'd suggested) some bulk thing.
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I'm still a bit confused as to what you mean by "powdercoat", though; to me it means a finish applied as a powder and held on by electrostatic charge until it's baked, usually ending up smooth and glossy.
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That sort of powdercoat is usually applied to metal, since it can take the high heat and can be uniformly charged to attract the powder.
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Replying to @NYarvin
Yeah, the spring steel textured sheets are powdercoated using the process you describe. It crosslinks with heat. It actually tends to make for a pretty poor insulator; lots of voids, nonuniform linking.
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That's about what I'd expect if they decided to make the surface rough by lowering the bake temperature: a coating that's not fully consolidated.
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Replying to @NYarvin
It's more an intentional feature of the coating, optimizing for the rough texture over anything else. It's not intended to be an insulator, and it really isn't. Static discharges go right through.
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If the bake was too low, adhesion and crosslink would suffer. It's surprisingly durable; really I'm kind of astounded at how well it holds up in use. So I don't think the bake temp was off.
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