[Jewelry making - Article 00023] - Re: [Orchid] Using Delrin?

[Arthur Behrends]

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    FYI I thought everyone might be interested in this. 

    Art 

          Delrin (typically Delrin 150, or Delrin 100 Series) is a brand
          name for Dupont's acetal resins. Delrin is an engineered
          plastic that is made from the polymerization of formaldehyde.
          It provides the advantages of plastic along with properties
          that are similar to metal. It is available in black, white,
          and natural (tan). It is used for small parts such as pump
          components, valve components, gears, bushings, rollers, and
          electrical insulators. 

          The crystalline structure and chemical composition of Delrin
          provide the following characteristics: 

          * Good dimensional stability and resistance to creep. 
          * Good chemical resistance. 
          * Good electrical insulating properties. 
          * High tensile strength, stiffness, impact resistance, and
          fatigue endurance. 
          * Good end-use temperature range. 
          * Low friction coefficient 

    Property limits include: 

          * Moisture absorption. 
          * Limitations in repeated uses in steam or hot water. 
          * Limitations in exposure to strong acids and bases. 

          The most common processing technique used for Delrin is
          injection molding. This method is used mainly in the
          automotive, consumer goods, and appliance industries. Stock
          shapes such as bars, rounds, tubes, and plate are typically
          extruded. Mechanical properties include: 

          * 10,000 psi Tensile Strength. 
          * 18,000 psi Compressive Strength (at Yield). 
          * 450,000 psi Tensile Modulus 
          * R120 Rockwell Hardness. 
          * 0.20 Sliding Coefficient of Friction (at 40 psi, 50 fpm) 
          * 0.5% Deformation at 120 deg F, 2000 psi Load, for 24 Hours. 
          * 5.8 x 10 in/hr-deg F Thermal Expansion. 
          * 200 deg F Long Term Maximum Service Temperature. 
          * 300 deg F Short Term Maximum Service Temperature. 
          * 347 deg F Melting Point. 
          * 1.42 Grams/CC Specific Gravity. 
          * 0.90% Water Absorption (in 24 Hours, Fully Immersed) 
          * 0.25% Water Absorption (in 24 Hours, at 50% Relative
          Humidity). 

          Delrin is machined using similar techniques for brass. Sharp
          twist drills with a 118 degree point angle, and 10 to 15
          degree lip clearance angle will provide a good finish with a
          slightly undersized hole. Reaming will improve the hole
          finish, but will also produce a slightly undersized hole.
          Delrin can be tapped, provided the thread size is large
          enough. Strong fine threads can be formed by heating a mating
          screw to 330 deg F, and screwing it into the proper sized
          hole. 

          Delrin can be turned using any standard metal-working lathe.
          Tools should be sharp and ground as for soft brass (a back
          rake to allow for free removal of material and a large
          clearance to eliminate drag). Milling requires sharp tools and
          proceeds as for brass. Filing is performed using deep,
          single-cut, coarse, curved teeth (commonly known as a Vixen
          file) as is used on aluminum and other soft materials. Delrin
          can be wet sanded on belt or disc equipment. After sanding,
          the surface can be brought to a high polish using standard
          buffing equipment. 

          Small parts such as washers, grommets, and non-precision gears
          (1/16 inch thick and less) can be produced by punching or
          stamping. Conventional dies are used in either hand or power
          operated presses. Cracking can be minimized by preheating the
          material or soaking it in water until approximately 2%
          moisture has been absorbed (typically 3 to 5 days of soaking). 

          Delrin can be glued with limited success. The bond will
          typically be weaker than the base material. In selecting a
          Delrin adhesive, consider both the end-use environment and the
          stresses that the adhesive must endure. Adhesive joints
          encounter 5 types of stress (compressive, tensile, sheer, peel
          and cleavage). In general, all adhesives have poor resistance
          to peel and cleavage, so joints should be designed to avoid
          these stresses. Also, avoid the use of butt joints. 

          Because of the "greasy" nature of Delrin, the surface
          treatment is typically the most important consideration for a
          glued joint. Common surface treatments include roughening
          and/or applying a primer (a solvent, or an acid). The primer
          etches the material surface giving the glue something to hold
          on to. Typical strength values for a bonded joint are 7000 psi
          with etching/primer, and 500 psi without etching/primer.
          Applicable adhesives are: 

          * Cyanoacrylate & Primer - 770, from Loctite (800-562-8483) 
          * Cyanoacrylate - Permabond 268, from Permabond (800-653-6523) 
          * Epoxy - Lord C3135 A&B, from Lord Corp (814-868-3611) 
          * Epoxy - FE7004 A&B, from H.B.Fuller (800-328-9673) 
          * Epoxy - Fiber Resin C14, from Fiber Resin Corp
          (800-346-9876) 
          * Epoxy - EA934NA & EA9394, from Dexter Corp (510-458-8000) 
          * Rubber - EC1711, from 3M (800-364-3577) 

          Pricing for Delrin stock shapes is somewhat expensive. As of
          March 2000 typical pricing is as follows: 

          * 1/4" Round Rod - $0.54/ft 
          * 1/2" Round Rod - $1.50/ft 
          * 1" Round Rod - $5.34/ft 
          * 3" Round Rod - $58/ft 
          * 1/4" Thick Sheet - $25/ft 
          * 1/2" Thick Sheet - $57/ft 
          * 1" Thick Sheet - $106/ft 
          * 3" Thick Sheet - $375/ft 

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