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  • Delrin Question from a newbie

    I bought a lot of 17 pieces of Delrin off eBay and one of the pieces had a sticker on it that read:
    NYTEF Plastic
    3/4" PLATE
    ANNEALED

    Is this Delrin or something else that was pawned off as Delrin?
    Thanks,
    Ed

  • #2
    Without more info I dont think its possible to say, but if there are other markings on it a look here will help.
    Ive never heard of delrin being 'annealed', or any other plastic for that matter, but there will probably be someone along in a mo who has

    can you describe the plastics properties? delrin is quite hard, sort of slippery, adn quite dense. Machines really nicely, apart from the static charged swarf which trys to stick to eveything.

    Dave

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    • #3
      Nytef is the brand name, and they do make Delrin. See here:
      http://www.nytefplastics.com/html/tech-resources.html

      Roger
      Any products mentioned in my posts have been endorsed by their manufacturer.

      Comment


      • #4
        Originally posted by ETG
        I bought a lot of 17 pieces of Delrin off eBay and one of the pieces had a sticker on it that read:
        NYTEF Plastic
        3/4" PLATE
        ANNEALED

        Is this Delrin or something else that was pawned off as Delrin?
        Thanks,
        Ed
        You probably got ripped off. It's quite common to substitute acetals for Delrin.

        AFAIK, DuPont owns the name Delrin and they're the only ones who make and sell it.

        Delrin has different properties than generic acetal. It machines better and has a richer, "wet" look when cut.

        And yes, plastics get annealed.

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        • #5
          Originally posted by DR
          And yes, plastics get annealed.
          Well I learned something today I presume its for the same reasons as metals, but do plastics work harden?

          Dave

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          • #6
            Originally posted by small.planes
            Well I learned something today I presume its for the same reasons as metals, but do plastics work harden?

            Dave
            They're brittle if not annealed. At least acetals can be.

            I used to machine lots and lots of customer supplied Delrin, but actually many times it was generic acetal instead. The generics aren't always annealed and can be quite brittle. Chunks wil break out when machining in places where annealed material will cut cleanly.

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            • #7
              Originally posted by small.planes
              Well I learned something today I presume its for the same reasons as metals, but do plastics work harden?

              Dave
              There is alot of stress in the plastic from cooling, and since plastic is an insulater, the center of a large part cools much slower than the outside. Annealing will reduce the distortion you will get when you machine away some of the outer skin.

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              • #8
                There are other differences between Delrin and generic acetal. Chemically Delrin is acetal homopolymer while all the rest is acetal copolymer, a slightly different compound. They have similar properties except in a few important areas.

                Delrin is about 10% stronger

                Delrin has a tendency to develop low density porosity in the center of extrusions, acetal less so and some brands of acetal not at all.

                Delrin has a slightly higher melting point than the copolymer

                One of the most important differences is in chemical resistance. Delrin is strongly attacked by acids, acetal copolymers much less so. This is especially important when making parts for the food industry since there are many processing applications that deal with acidic products. It can mean a 10 times difference in part lifetime.

                I have found that very few people in the plastic business are aware that there is a difference. They tend to call all acetals Delrin. It's like calling all pop vending machines a Coke machine. It matters to me though, I can't stand Pepsi.

                Plastics don't work harden.
                Last edited by Evan; 04-04-2008, 08:20 AM.
                Free software for calculating bolt circles and similar: Click Here

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                • #9
                  [email protected] can be burned and gives off a formaldehyde smell that will burn your eyes. Try burning a shaving, acetel will not. Delrin when overheated gives off strong formaldehyde fumes and is carcegenic in prolonged use. In injection molding when a sprue closes the heat causes a gaseous release of formaldehyde gases and in the old days could clear out the shop.
                  William

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                  • #10
                    Actually, plastics do work harden. It is a common process used in production of films and sheets. These are biaxially oriented after extrusion by stretching in length and width. Mylar is one of the more common materials produced in this manner.

                    It is also the same mechanism employed in stretch wraps, and you do it every time you wrap your leftovers.
                    Jim H.

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                    • #11
                      delrin plastics

                      I've got some sheets of white and orange "plastics" that have come from the local skating rink and were used there as buffers around the rink. This stuff cuts well, seems to machine well and resists melting and burning. Its about a 1/4 inch thick. Do any of you guys know the proper name? Evan up at Billys Pond, you might have a handle on this. Thanks in advance, Wayne.

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                      • #12
                        Jim,

                        That effect is not a type of work hardening. It is a result of reorienting the long chain molecules so that they are no longer tangled in a random pattern but are instead oriented in the same direction and stretched so that the chains are under tension. In fact, you can do some interesting experiments with plastic garbage bags using this phenomenon. When plastic is stretched and oriented in this manner it will elastically contract with heat. You can build a simple solar powered motor with garbage bag material that takes advantage of this property.

                        It is a common process used in production of films and sheets. These are biaxially oriented after extrusion by stretching in length and width. Mylar is one of the more common materials produced in this manner.
                        Work hardening is a result of strains that dislocate the crystals at the crystal boundaries. While mylar is a crystalline plastic it does not act in the same manner as crystalline materials such as metals. This is because the crystals are in a matrix with low molecular weight substances that act to give flexibility and lubricity to the material structure.

                        Wayne,

                        I'm pretty sure that plastic is HDPE, High Density PolyEthylene. It's used a lot in wood handling equipment.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Theres a lot of misinformation about acetal flying around in here (not from Evan btw), so heres a few facts to correct some of it.

                          1. Flammability
                          They haven't yet made a flame retardent acetal, so whether you're using Delrin or any other brand name it will burn.

                          2. Annealing
                          Wrong term really, acetal won't become less hard if you 'anneal' it, although it is sometimes heat cycled to stress relieve it. Incorrect (too quick) cooling of acetal during processing will allow amorphous zones to form in the material. Over time, the material will slowly re-crystallise by itself leading to residual stress and distortion in components. The stress relieving process allows it to re-crystallise at a faster rate to avoid distortion and dimensional changes.

                          3. Brittle Material
                          Acetal is pound-for-pound the stiffest unfilled polymer you can get. In thin sections it makes fantastic springs, in thicker sections, this very stiffness and it's highly crystalline nature makes it brittle.
                          Acetal that is cooled at a fast rate forms amorphous zones that impart a greater toughness to the material, and hence resistance to fracture (brittleness). Acetal that is cooled at the correct rate and temperature will be harder, and stiffer, and more brittle, but dimensionally more stable and stress free.

                          4. Delrin vs Other Brands
                          DuPont invented acetal homoploymer and patented it. To get around this, the other chemical companies developed acetal compolymer, and for 99% of the jobs you want it for, brand x will be just as good as Delrin, and often better. See Evans comments above.

                          5. Work Hardening
                          Plastics don't work harden. Plastics can become less tough/more brittle due to many environmental considerations, UV (sunlight) being a major one, and exposure to chemicals is another. In particular, Polycarbonate has pathetic chemical resistance to many common substances, yet can stop a bullet. In addition many polymers are very notch sensitive. A sheet of polycarbonate that can stop a bullet will snap in half if you score it with a nice sharp object.

                          Peter

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                          • #14
                            Originally posted by Evan
                            There are other differences between Delrin and generic acetal. Chemically Delrin is acetal homopolymer while all the rest is acetal copolymer, a slightly different compound. They have similar properties except in a few important areas.

                            ............................
                            Evan,

                            For general non-critical uses you forgot to list the biggest difference. Price......

                            Only authorized Dupont dealers can sell it. If your dealer is not authorized they have to source it from a Dupont dealer, this adds another level of markup.

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                            • #15
                              evan

                              Evan, thanks for that info. This stuff is neat because it bends easy and I have used it for spacers when the opposing surfaces may be rough, so that when bolted together, the material conforms to the surfaces. The arena down here periodically replaces this stuff. It has come to me in 4 by 8 sheets as a freebie! Again, thanks Evan for the info. BTW, do you know Larry and Sue Austin up there? Larry used to have Big Country Diesel way back when. Wayne.

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