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Delrin ~ Acetal confusion

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  • Delrin ~ Acetal confusion

    I have been ordering Acetal Rod from Enco. They say in their catalog.
    Natural - High natural lubricity
    Black- Normal lubricity

    I thought this was Delrin. Is it?

    I used to buy some parts that were suposidly Delrin but it was kind of Gray.

    From Enco's description how do you interpret the lubricity? Is natural slicker?

    I have been ordering Black it machines very nicely. Some of the parts that I make are exposed to Sunlight and I just figured that black would be more UV resistant.

    If this is not Delrin, where and how do you purchase it?
    Byron Boucher
    Burnet, TX

  • #2
    Delrin is a trademarked name for a very specific type of plastic. It's in the acetal family. Delrin is an acetal. Acetals are not Delrin. McMaster-Carr is usually really good about explaining the strengths and weaknesses of their products.

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    • #3
      I forget which way round it is, but one is acetal homopolymer and one is copolymer. No doubt Evan will be along in a min
      Dave
      Just south of Sudspumpwater UK

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      • #4
        Delrin comes in both homo and co flavors you have to decipher the numbers. Delrin 500PNC for example.

        Delrin is a modified acetal, it has different properties than straight up acetal.

        For most machining applications all you need to worry about is the homo- vs co- polymer issue.... unless you are making some very technical parts with special requirements. In that case I would suggest contacting the resin supplier directly (unless it's SABIC they can go %&* themselves) as part of your purchase price is free tech-support.


        As always remember acetel gives off fumes when heated and does burn with a peculiar flame when abused. Just treat it like you would any other thermally sensitive material, perhaps blow compressed air on it as you work.
        This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
        Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
        Plastic Operators Dot Com

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        • #5
          Originally posted by Liger Zero
          Delrin comes in both homo and co flavors you have to decipher the numbers. Delrin 500PNC for example.

          Delrin is a modified acetal, it has different properties than straight up acetal.
          Shame on you Liger, and all that from someone in the Industry too

          Delrin is a Homopolymer ONLY. Dupont made the first Acetal as a Homopolymer and patented it and the process. Hoechst-Celanese and others produced the first Acetal Copolymer a few years later to get around the DuPont patents. Both are Polyoxymethylene (POM)polymers.

          Delrin 500P NC - lets decipher that.
          Delrin- trade name
          500 - refers to the melt-flow index. 500 has an MFI of 5.x gm/10minutes (100 has 1.0gm/10minutes, 900 has 9.0gm/10minutes 1700 has 17gm/10min.)
          P - stands for superior Processing as the additives give it more stability than plain Delrin 500.
          NC - stands for 'No Colour'. BK stands for Black.

          Homopolymers generally have greater mechanical properties than copolymers, whilst copolymers have greater hydrolysis resistance and better dimensional stability. There is no straight-up acetal, all grades are tailored for one reason or another, and tailored again to suit each process (injection, extrusion etc) and tailored again for specific properties to suit end-use applications.

          Either one is a good choice for machining or mechanical applications.

          Peter

          Edit: Boucher - Natural or black in reality will have a lubricity difference that only a Lab can measure. It's pigmented black by the addition of either carbon black or nigrosene (really, that's it's name!) and either one uses a single figure percentage amount dispersed into the resin, so the effect is minimal.
          Last edited by Peter N; 01-29-2010, 06:12 PM.

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          • #6
            There is little to no machining difference between the Homopolymer (Delrin) and the Copolymer (trade name includes Acetron by Quadrant and others).

            Unless the marginal differences are important either will serve for most jobs.

            Important differences, to expand on what Peter wrote, Delrin is about 20 percent stronger but has very poor resistance to acids including acids in foods. Delrin tend toward core porosity and lessened properties in the center of large extruded sections.

            Acetal copolymer has good resistance to acids, is weaker but tends not to have any difference in density even in large sections.

            Both resins have good impact resistance. Delrin has a slightly higher working temperature. Bothe are crystalline thermoplastics meaning that if heated enough they will melt. Both give off trace amounts of formaldehyde when machined. Bothe have essentially the same coefficient of linear expansion with temperature. Both have very low moisture absorbtion. Both are very resistant to oils and solvents and may be run in petroleum oil environments without degradation.

            Both are very machinable although if machined at low speeds will produce nasty long chips strings that can be very tough to break and can even cut if handled carelessly. If machined fast enough, especially when roughing, they will chip break into a shower of fine chips.


            Both are available in a variety of colours which signify nothing. The only exception is that there is black Delrin and acetal that is static conductive and should not be used when insulation is important.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Originally posted by Peter Neill
              Shame on you Liger, and all that from someone in the Industry too
              Interesting because I clearly remember dealing with trials involving name-brand Delrin Homo and Co polymers.

              Now considering some of the shenanigans going on at that shop there may have been some relabeling going on I know we got caught substituting a lower-cost nylon for Zytel at one point... among other spectacular stunts. Amazing part is they are still in business too, I guess dishonesty pays.
              This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
              Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
              Plastic Operators Dot Com

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              • #8
                I have machined a fair amount of both real Delrin and generic acetal and Delrin gives a nicer finish and seems to be more dimensionally stable. Big pieces of generic seem to have more internal stresses that can cause creep and out of spec parts if you are doing a deep pocketing on them. If it is someone else's nickel and the spec does not care which one, use real Delrin and the job will be easier.

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                • #9
                  I have machined a fair amount of both real Delrin and generic acetal and Delrin gives a nicer finish and seems to be more dimensionally stable. Big pieces of generic seem to have more internal stresses that can cause creep and out of spec parts if you are doing a deep pocketing on them. If it is someone else's nickel and the spec does not care which one, use real Delrin and the job will be easier.
                  Plastics can and should be stress relieved (annealed) after rough machining and then fine machined to actual dimension when dimensional tolerances are critical.
                  For Delrin as example: "Delrin® acetal homopolymer, 4 hours to 320°F or 30 minutes per 1/4” thickness, 50°F per hour cooldown, Nitrogen or Air atmosphere"

                  Here is a full table for many plastics:

                  http://www.boedeker.com/anneal.htm
                  Free software for calculating bolt circles and similar: Click Here

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