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  1. polym3

    Rubber Info

    There is a definite trade-off between coeffient of friction and abrasion, and cut and tear resistance. To raise the abrasion resistance properties (as well as cut and tear resistance) you need to add a reinforcing agent, i.e. carbon black or amorphous silica for colored compounds. This naturally...
  2. polym3

    Windshield Wiper Blade

    Many blades are still molded, mostly in China, but even some here in the USA. Chinese mixers do not have access to the high quality/low grit raw materials that we do, and this makes extrusion of this type of product impossible. This is a lousy market to be in...tell your investors to look at...
  3. polym3

    Rubber selection guide

    CHEMICAL RESISTANCE GUIDE FOR ELASTOMERS II Written and researched by Kenneth M. Pruett Published by Compass Publications PO Box 2276 La Mesa, CA 91943 (619) 589-9636 My copy is copyrighted in 194 so I'm guessing they probably have an updated book. It is a 400 page book of tables of...
  4. polym3

    Low Creep Elasomer

    Hi Ed: I guess we differentiate creep, and set in the "rubber" business, because creep is a time dependant increase in deformation under constant load, (not typical of crosslinked elastomers, but is seen in unvulcanized elastomers). Typically under a constant load, crosslinked...
  5. polym3

    Low Creep Elasomer

    Creep is usually associated with thermoplastics; whereas "set" or "permanent set" is usually associated with crosslinked elastomers. At ambient temperatures natural rubber has good low set properties, especially when cured with an EV system. No elastomer is free of permanent set, however. Set...
  6. polym3

    Accurate calculation of profile rubber extrusion

    The amount of shrikage is really dependant on the compound formulation. Highly filled rubber tends to shrink less than unfilled or low filler containing compounds. I believe the rule of thumb in estimating shrikage is in the area of about 3% - but I would suggest you have someone else confirm...
  7. polym3

    white oring coating?

    Sulfur is not very soluble in nitrile (NBR) compounds so regular Rubber-Makers sulfur does not disperse very easily. It is generally recommended that one use a "superfine" (smaller particle size) sulfur. This is usually treated with magnesium carbonate to further assist dispersion. For an NBR...
  8. polym3

    Banbury Fill Factors

    I would appreciate some info concerning the effects of usng too high of a fill-factor in mixing and dispersion. The literature suggests average fill-factors (by volume) at about 0.75 - we seem to be running a lot higher than that; up to 0.9 How does this affect dispersion of blacks, heat...
  9. polym3

    material to make eraser

    Try this: SMR L 100 White factice 100 Maglite D 30 Lithopone 100 Barytes 80 Whiting 150 Titanium dioxide 10 Light process oil 30 Zinc oxide 10 Stearic acid 2 Sulfur 6-8 MBTS 1-1.5 DPG 1-2
  10. polym3

    Internal Mixer Clean out

    We use SIR 10 and a bit of talc.
  11. polym3

    Curing of Buna-N

    The only rough test for identifying cured rubber is the "burn" test. THe following are the "subjective" ways some people describe the smell, etc: NITRILE: 1) Burns with sooty flame leaving untolerable smell. 2) Burns with a characteristic smell which leaves a nasty taste in the mouth. Somewhat...
  12. polym3

    Curing of Buna-N

    Sometimes modulus is a better spec than hardness. It is a better way of describing stiffness so you don't end up with hard, but flexible product. Ask the vendor to make the product with a low sulfur (EV - efficient vulcanization) cure system. This will give you the best compression set...
  13. polym3

    Curing of Buna-N

    Why not just have your supplier make the washers to the hardness you desire? If you are baking these in an oven, the smoke is probably as a result of the oxidation of the product. The best way to cure these would be in an enclosed mold. The cure cycle needs to be completed in the mold, i.e. in...
  14. polym3

    Nitrile Isolator Creep

    Probably the only reference I have seen to a study over any period of time is in a book edited by Alan Gent: Engineering with Rubber. He describes a test done by the British Dept of Transportation of bridge bearings after 20 years. These tests on both NR and CR showed virtually no change in any...

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