4

I have a 6" x 6" x 1/4" piece of carbon filled teflon that is slightly curved (I think it must have come off an roll of enormous diameter) that I need to flatten. The carbon fill is carbon black, not carbon fiber, in order to make the material static dissipative.

Is there any good procedure to flatten it like with an iron?

Alternatively, thickness is not too important so in theory I could try stoning it to flatten. I will have to at some point to remove scratches on the surface but I imagine it will glaze the stone like nothing else and I don't want to need to stone too much of it since this material produces nasty dust.

With a chord of 6", there is a distance of about 2mm to the circumference so it would turn the 6mm plate into a 2-3mm plate if I were to stone it down to flatten it, which is fine if it were not for all the work involved and dust that would be produced.

UPDATE: Stoning does nothing. Just messes up the stone. But wet sanding with Scotch-Brite 7447 (Maroon) cleans up scratches and imperfections real nicely. A circular motion produces a very nice matte finish. Finer grades would probably produce a finer finish. Doesn't flatten it though.

UPDATE: Glass transition temperature is 120C so I think I'll try to heat it up beyond that. This is going to be used to make really thick 2" diameter washers. So I think I will cut out oversized square pieces, mount them on a big bolt with 2" steel washers separating them, maybe with a spring to continuously apply force and then put the whole thing in an oven at 150C or so...if I can get the oven to get that low.

Glorfindel
  • 272
  • 1
  • 4
  • 10
DKNguyen
  • 4,625
  • 1
  • 9
  • 22
  • PTFE has a strong tendency to creep - I don't know how the carbon filler affects things but I would start by jigging it to be bent in the opposite direction for a few days? – Jonathan R Swift Sep 19 '21 at 09:21
  • Adding to Jonathan comment, maybe also put it an oven to speed up the creep process? – NMech Sep 19 '21 at 09:40
  • reworking teflon may require 300+ deg C for an oven given its high melting point. if it were fiberglass filled, would be a no-brainer. With carbon sticking out at edges (in an air-filled oven) might want to start with an oversized sheet, jig and oven flatten followed by cutting out what you need. – Abel Sep 19 '21 at 10:13
  • @Abel Can you elaborate about the carbon? I am not sure what you mean. This is filled with carbon black, not fiber. It's carbon filled to make it static dissipative, not for strength. – DKNguyen Sep 19 '21 at 16:05
  • @Abel I looked up and the glass transition temperature is about 120C. I think that's all I need to get it to form a bit, right? – DKNguyen Sep 19 '21 at 16:09
  • sorry; I thought it was like the fiberglass and teflon mats I sometimes use. try it at 120C and see if it works? If not, try higher temperatures. The bit about carbon was indeed a structural concern for carbon fiber under those conditions so you should be fine. – Abel Sep 19 '21 at 17:21
  • As a bearing surface: I would bet the part will flatten some (if not all) under load, I would also think even if there were high points they will be fairly lubricious to begin with. Even if high points wore, the increasing surface area would even out the stress to relative equlibrium. You're likely to get some carbon powder detritus during use. If thickness is critical then pre-wear (pre-condition it) under load to an acceptable thickness; or make the system adjustable for changing thickness. Teflon can be relatively soft. – Jim Clark Sep 19 '21 at 22:45
  • @JimClark These aren't being used as a bearing surface. They're being used as washers which will clamp down to grip workpieces for soldering circuits boards which is the reason they are teflon (heat resistance) and carbon filled for static dissipation So they will be under flattening stress, but no actual evening wear is expected during use. It's just a little difficult to actually cut round washers out of it with the right dimensions when they are curved even though the in use the part will be under flattening forces. – DKNguyen Sep 19 '21 at 22:48
  • Teflon washers can be bought from McMaster-Carr. You could add a grounding strap or grounding brushes on the fixture that make contact in predefined areas. – Jim Clark Sep 19 '21 at 22:54
  • @JimClark They didn't have static dissipative teflon washers which is why I had to end up getting a plate from them instead to make my own. I would have gotten the conductive silicone if I had known the teflon plate would be curved. – DKNguyen Sep 19 '21 at 22:55
  • The (light blue) mats that are work-surfaces for electronics technicians are uniform thickness and conductive. They are compliant (springy) and cutting a piece from an old mat may provide all you need. Test an old piece for the expected temperature cycling during use to see if it will work. – Jim Clark Sep 19 '21 at 23:06
  • @JimClark Yeah, if I only I had some mats around that I am willing to take cuts out of. heh – DKNguyen Sep 19 '21 at 23:09

0 Answers0