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  1. berti

    Rubber hardness calculation

    Hi, that is no rocket science. Most silicone bases are additive concerning hardness, chemists call it mixing cross --> 5 parts of 40 Shore and 25 parts of 70 Shore. (5x40 + 25*70)/30 = 65 Ground quartz has quite low influence on hardness (appr. +2 pts. per 10 parts...
  2. berti

    EPDM Compound

    Hi klemend and all, I am not sure if the problem you describe is maybe a more general problem. Any elastomer takes its elasticity (that is: it returns to old shape after deformation) from internal network of crosslinks. Unfortunately nearly nothing in this world is perfect and so is any...
  3. berti

    Accelerating blooming in EPDM material

    Hi kathlesami, ???, sorry for question marks. What are you looking for ? "Blooming" means imho an unwanted :-(layer of decomposition products on the surface of a part, in case of EPDM e.g. of dithiocarbamate accelerators. Pse clear the point. Regards Berti
  4. berti

    Air entrapments in closed cell foam rubber

    Hi bobfoam, unfortunately you do not mention size of "hole" in relation to foam cell size. If it is not too big I would suspect some coarse pieces or undispersed aggregates of the blowing agentin the compound. Bigger holes should have "mechanical" reason. HTH Berti
  5. berti

    Effect of hardness on chemical compatibility of HNBR

    Hi all, hardness change (of 10 pts) is the variable which I would expect to have very few (if any) influence on chemical and thermal resistance. But take care that the new compound is made from same polymer and by same crosslinking system as your old one, because the type (ACN content and...
  6. berti

    removing discoloration from pvb

    Hi there, from chemical point of view there is a small chance, if discoloration comes from Fe3+. Try a reducing chemical like Sodium dithionite. It is sold (at least here in Germany)as "Entfärber" - discolorator - for stained textiles, used like a simple detergent. But by my experience from...
  7. berti

    Buna-n NBR o-ring cracks industrial atmosphere

    Hi all, description of the failure sounds like ozone indeed. Some mechanical stress increases sensitivity. NBR itself is sensitive because of double bond in main chain, good choice of recipe ( black, ozone protecting chemicals like 6PPD and suitable wax transporting the 6PPD to the surface) can...
  8. berti

    soft or "silky" silicone

    Hi all, some proposals: One of my customers solves the problem by surface fluorination, that means he sends his diaphragms and O-rings to a service company which uses diluted fluorine gas to treat surfaces. Your local SOLVAY representative should know one. If you are in Europe I can give you...
  9. berti

    How can I determine the vulcanization system?

    Hi all, it is possible to determine sulfur or the accelerators analytically (take care: in some rare cases sulfur is also used as a coagent in peroxide cure). But if you have only one ring and maybe need the results for legal purposes (claim), it is a job for a professional lab. Regards Berti
  10. berti

    selection-material

    Hi all, sorry for answering so late. Fluoro rubber (FKM) has a week point in cold flex. Minus 40 °C is very difficult even with incredibly expensive special types. Looking at the requested oil and diesel resistance I would recommend fluorosilicone. Have a look at Dow-Corning page for...
  11. berti

    FFKM o-ring selection for -25 deg C / -15 deg F continuous service

    Hi bssem and all, if you are searching for the combination of good (including amines and other bases) chemical resistance and excellent cold resistance (like FVMQ) have a look at SIFEL (R) of Shin-Etsu (or their daughter SHINCOR in US). This is a quite new polymer concept with slightly...
  12. berti

    additives for NBR?

    Hi all, thanks for the friendly words[blush] Unfortunately most of the literature I would mention is in German ( as I am German), but I am sure there are similar textbooks in English available. Application papers of the NBR producers (e.g. Bayer/Lanxess) are probably available from the net...
  13. berti

    additives for NBR?

    Hi all, let me try some remarks. ... some O-rings, which appear to have suffered from extrusion and cracking damage. Did they tell you more about conditions of failure ? - hot air - any chemicals /solvents (which?) - cold - ozone /intense sunlight (maybe before use, as e.g. waste water tubes...
  14. berti

    What is Duromer ?

    Hi maddog153, imho there is another meaning of duromer. It is used also for heavily crosslinked polymers, usually handled as liquids with a hardener/crosslinker. Think phenolic resins (Bakelite), epoxi resins, hard rubber (ebonite). It was the main polymer material early last century before...
  15. berti

    What is C.I.R.? A type of rubber?

    Hi andy22, only a guess. If you think it it natural rubber actually then C I R could -could !!- mean cis isoprene rubber which is the synthetic twin of NR. HTH Berti
  16. berti

    What is the best Rubber for Watchbands?

    Hi all again, FVMQ is maybe even better then VMQ but it has a very bad property: it is 10 times more expensive. EPDM is probably not bad, one weak point is skin fat resistance, second is: transparent and bright-colored materials are difficult to make. On the other hand it is much cheaper even...
  17. berti

    What is the best Rubber for Watchbands?

    Hi all silicone (VMQ) could be a good choice, maybe with addition cure. It is- provided correct processing including postcure- very skin-indifferent and is available in all bright colors. I remember that WACKER as one of the big producers of the polymer had a wrist-watch as a giveaway. HTH Berti
  18. berti

    Use of Viton (FKM/FPM) with hot water or steam service

    Hi lambda and all, most is said, let me make two more remarks: - "Usual" (cheaper) FKM (Viton is brand name of one of the 4 big producers) is cured by bisphenols and has calcium hydroxide and magnesium oxide as acid acceptors. This type of polymer is affected (typically softening)by hot water...
  19. berti

    Viton

    Hi djuanej and all, do you really mean "hot water" and 150 F = 65 °c ?? I think this temperature is no problem for any rubber, I remember that I put a "hot water bottle" from Natural rubber to the cold feet of my children to warm them.;-) If it comes to 150°C and pressurized water or steam it...
  20. berti

    Viton seals: What are the differences in colour?

    Hi all, "VITON(C)" and "70 Shore A" is not enough information to characterize a sealing material. Viton or more general Fluorocarbon rubber (FKM or FPM)includes different materials. They can have different fluorine content (between 66 and 71 % fluorine) and hence very different swelling...

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