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  1. stancom

    Improving the abrasion & increasing tensile strength of an FKM O-ring

    In my limited experience medium thermal black is the most commonly used black in FKM. Probably not the best for resisting abrasion. HAF comes to mind, as does silica if the compound is non black. But I agree with Tom. Go to a supplier
  2. stancom

    Stretch material

    I agree about NR latex but pitch any specification below 1000%. The trouble with very high EBs is increased batch to batch inconsistency. You're working near the limit. Claims have also been made for some thermoplastic elastomers, notably styrene copolymers, but recovery will be relatively poor...
  3. stancom

    NBR and NR compatibility - any binder?

    I understand polychloroprene has been used as a binder. A NR/NBR blend interlayer may also work. It would be helpful to know the acrylonitrile content of the NBR Stancom
  4. stancom

    Liquid curing for rubber hose extrusion

    I agree with Mr Bennett but don't forget LCM curing as an alternative to a fluidised bed. The Liquid Curing Medium usually consists of a molten entectic mixture of sodium and potassium salts and could have the advantages over a ballotini bed of excluding air and sometimes avoiding need for a...
  5. stancom

    75 Shore NR compound for Vibration control

    Only limited help/advice can be offered in the absence of the complete formulation. I'm always worried about silica reinforcement even with a silane agent, and these can vary considerably. You must ensure that the state of cure is high enough. Increasing the level of vulcanizing system (all...
  6. stancom

    Which rubber-like materials age well?

    I was hoping the questioner would respond to GrahamBennett before adding another view. If the word 'latex' is intended to cover rubber as a whole then I agree about EPDM. However, if we are thinking of products prepared directly from latex, eg by dipping, then an obvious candidate will be...
  7. stancom

    alcium chloride as a coagulant in rubber latex compound dip instead of calcium nitrate

    No personal experience but I know calcium chloride has been used in coagulant dipping. My worry is that it can be corrosive to ferrous metals including stainless steel. That may put some manufacturers off.
  8. stancom

    Resting of rubber bases before acceleration finals (two cycle mixing)

    Stabilization is one of those catch-all terms we're never quite sure of what it means. In this case I don't think of chemical change but primarily of control and sometimes bringing the mix down to room temperature. For test mixes ISO 2393 specifies a minimum of 30 minutes for this purpose and an...
  9. stancom

    sample preparation for Lab test: cooling down hot cured rubber in water is a proper way?

    Just to add to Tom's comment, the equivalent International Standard is ISO 2393. It also allows for the mould to be water cooled before opening. I was involved with the preparation of the standard but our press room seldom bothered to quench in water unless there was a very peaky cure.
  10. stancom

    does the thickness of a rubber sheet affect the tensile strength and the elongation

    I agree with Tom's explanation, and if you're testing using a standard dumbbell the quality of the cross section may be a factor if thickness results in a concave edge. With respect to asankaglove, I would have thought a thicker product would bring the risk of an undercure or a reverted surface...
  11. stancom

    Crystals on vulcanized NBR articles

    Chemical analysis is really the only way to identify the deposit. One always suspects a dithiocarbamate bloom and sometimes you can detect this by rubbing your finger with a copper containing coin or object and then pressing it against the surface. A brown discoloration should develop after the...
  12. stancom

    Rubber Accelerators

    Afraid I've been out of compounding too long to be familiar with more recent accelerators, but don't forget there are two other approaches to this type of problem. Ineffective though this may sound, heating or steaming the product or subjecting it to a blast of air can sometimes help, repeated...
  13. stancom

    physical state of cis-1,4-polyisoprene

    Cis 1,4 polyisoprene (as in natural rubber), free of crystallinity, reamains a solid because its combination of a very high molecular weight (it can be several million) and accompanying chain entanglements. The crystal melting point increases with the temperature at which crystallization occurs...
  14. stancom

    What materials database do you use?

    No database is all-embracing. There are always strengths and weaknesses. So it is important to identify what type of information you need. I have always used CAMPUS (www.campusplastics.com) because my particular interest revolves around properties determined by standard test methods. However, I...
  15. stancom

    Help learn more about crumb rubber molding

    As you mention polyurethane I presume you are dealing with recycled crumb from vulcanized rubber, principally recycled tires. If so, have a look at some of the downloads you'll find on the UK's WRAP website, www2.wrap.org.uk/downloads/ One we used when I was involved with granulated/powdered...
  16. stancom

    Want to learn more about HNBR

    You are asking rather a lot and no single reference is going to be adequate. For HNBR I have always recommended the Zeon webpages for its product Zelpol, ie www.zeonchemicals.com/Zetpol/ For rubber in general have a look at the Harborough Rubber website from the UK , ie www.harboro.co.uk and...
  17. stancom

    Table Tennis Rubbers

    To ensure we’re on the same wavelength, let’s review some rubber chemistry. Natural rubber has the highest rebound resilience and the lowest internal damping. In principle polybutadiene should match or better NR but in practice falls short and has inferior vulcanizate properties. NR is usually...
  18. stancom

    Rubber price

    I was a panel member advising Dr Blow in the mid 60s and good as his book was I'm afraid it, and the 1982 revision with Hepburn, are now well out of date, and there wasn't that much on product manufacture. Perhaps the best book around is Rubber Products Manufacturing Technology, edited by A K...
  19. stancom

    Table Tennis Rubbers

    I don't want to go over old ground but much will depend on the relative thicknesses of the rubber cover and, where it exists, the underlying sponge layer. Increasing the crosslink density will certainly raise the resilience of the rubber, but not that dramatically once optimum cure for other key...
  20. stancom

    Need advice for vulcanizing shore A-70 rubber.

    A typical sulfur level will be between 2 and 3 parts per hundred parts of raw rubber, aided by an accelerator, but that will only give you a vulcanisate hardness of ca 35 t0 40 Shore A. You'll appreciate the need for a loading of filler and the choice will depend on the properties you need. A...

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