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  • Identifying plastic type

    I have an approx 2 foot square 3/4" thick sheet of plastic salvaged from a high voltage test rig. The insulator stack was about 2 foot tall through the middle.

    The plastic seems very slippery to the touch. I was going to slice a sliver off the edge and compare it to a bit of HDPE off a milk carton for melting temperature.

    On slicing a sliver off the edge with a Stanley knife the chip fractured into little bits as it was cut and made a sort of crunching noise as I cut. I have never met a plastic like this before.

    Any ideas?

  • #2
    Teflon or PEEK.

    ​​​​​​https://www.gtweed.com/materials/peek-vs-pek-vs-ptfe/
    Beaver County Alberta Canada

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    • #3
      May or may not be helpful for what you have there, but I have seen this info (and the chart linked there) used on a few occasions:

      https://modernplastics.com/technical...tify-plastics/

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      • #4
        Thank you both for the info.

        Regards, Earl

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        • #5
          HDPE, and it's old. That's my guess. Probably has been exposed to various solvents over time- maybe not directly, but through cleaning, etc. Cutting boards do that. Bleach would probably cause the brittleness that makes it crumble like that when trying to peel a shaving.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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          • #6
            My guess is phenolic. Never seen HDPE crack. If it's PEEK that's worth a fortune, McMaster has 12x12x3/4 for $700! Doubt it. Burn test would tell a lot, whether it melts or burns. If it doesn't melt and smells like pee it's phenolic.
            Last edited by gellfex; 01-24-2021, 04:56 PM.
            Location: Jersey City NJ USA

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            • #7
              Helpful PDF downloadable here:

              https://modernplastics.com/technical...tify-plastics/
              "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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              • #8
                Just Google plastics and elastomers identification charts.
                Location: Saskatoon, Saskatchewan, Canada

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                • #9
                  Teflon (PTFE) is quite likely as it is slippery, tends to fracture when cut and is often used in HV applications as an insulator. Also it is quite dense compared to most other plastics. It does not melt like PE, but expands and turns translucent and somewhat pliable upon strong heating. After cooling it becomes opaque white again. Oh yeah, virgin PTFE is most always white as any colorants or pigments would ruin the chemical inertness of the material.

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                  • #10
                    How flexable is the sheet? Will the shavings from it burn? Commodity plastics are very seldom crumbly but, a "high voltage test rig" sounds expensive so there is a chance that they used some exotic materials the rest of us don't use. The other possiblity is that the high voltage degraded the plastic and it's crumbling. I'd start with a burn test.

                    $ If it's HDPE or UHMW-PE then it will not crumble unless it's very degraded
                    $ It could be a glass filled plastic. I have some glass filled nylon rod that is very crunchy when cut.
                    $$ I've never seen PTFE crumble it's alway's been very soft flexable chips.
                    $$$ I've never worked with PEEK but it is common in extreme environments. There are several high end engineering plastics like this that I've never worked with because they can be over $500 for a 12"x12" sheet.
                    $$$$ If it's not flexable and the chips don't burn then there is a slight chance that it's machineable ceramic like Macor. Macor is used in high temp and high voltage applications.
                    https://en.wikipedia.org/wiki/Macor
                    https://www.corning.com/media/worldw...ebead091cb.pdf


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                    • #11
                      A good start might be telling what color it is. And generally if it is quite hard (like glass or ceramic) or if it is "hard" in a way more similar to plastic cutting boards.

                      Fracturing when being cut seems pretty hard, but there could be reasons why an edge is that way. A high voltage test rig may have had things happen to it that would affect the plastic properties.

                      I agree that no PTFE I have dealt with would fracture that way. As to how it behaves after exposure to potential corona discharges over time, possible UV exposure, etc, I cannot tell you.
                      2801 3147 6749 8779 4900 4900 4900

                      Keep eye on ball.
                      Hashim Khan


                      It's just a box of rain, I don't know who put it there.

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                      • #12
                        True story - from a few decades ago. I was working for a Detroit area Tier 1 supplier on a SAAB program. As the vehicle entered pilot build thru to launch I was also the resident engineer (in Trollhattan (there should be umlauts over the first "a"), Sweden). One day as I was discussing an alternative plastic for one of our parts, my SAAB counterpart begins to laugh and says I have to tell you this story. He was on an engineering trip to some potential supplier on the Continent with several other SAAB personnel, including a materials engineer. The group took a taxi from the airport to the meeting site. The taxicab was a model unfamiliar to all of them and they were looking at the rear grab handle in the headliner above the door - wondering what plastic material it was used to mold it. Without giving it any thought, the materials engineer pulls out a pocket knife and a lighter from his pocket, shaves off a sliver and lights it. The taxi drive saw this in his rear view mirror, did not say a word but glared at them for the rest of the trip. My SAAB counterpart said they left the taxi driver very large tip.
                        Metro Detroit

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                        • #13
                          LOL.....

                          It IS a decent way to at least categorize plastic types...... If you know the smells and what the burn result looks like.
                          2801 3147 6749 8779 4900 4900 4900

                          Keep eye on ball.
                          Hashim Khan


                          It's just a box of rain, I don't know who put it there.

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                          • #14
                            Originally posted by darryl View Post
                            HDPE, and it's old. That's my guess. Probably has been exposed to various solvents over time- maybe not directly, but through cleaning, etc. Cutting boards do that. Bleach would probably cause the brittleness that makes it crumble like that when trying to peel a shaving.
                            Ultra-violet can do that to it too. A friend of mine cut a lot of HDPE strips from empty milk bottles to tie up his garden plants. After a couple of years (I can't tell you how many) they became brittle and broke, much to his annoyance.

                            George B.

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