Choosing suitable materials for seals or other rubber-metal elements, the following criteria should be taken into consideration:
- chemical resistance
- temperature resistance
- mechanical resistance in the range of:
- break resistance
- elongation at break
- tear resistance
- permanent deformation
- abrasion resistance
Such research can be made in our own laboratory, see laboratory.
Basic elastomers used in the process of production in ”Gumet”.
1. NBR – Acrylonitrile-Butadiene-Rubber (Perbunan, Hycar, Chemigum, Bron, Butakon, Europrene N, Butacril, Krynac, Nipol, Nitriflex, SKN, Perbunan N, Tylac, Elaprim, Paracril).
NBR is characterised by good swelling resistance in mineral oils, greases and fuels, high elasticity, cold flexibility, gas permeability and compression set. Most sealing elements for hydraulics and pneumatics are manufactured from materials based on NBR.
2. HNBR – Hydrogenated Acrylonitrile-Butadiene-Rubber (Therban, Tornac, Zetpol).
HNBR is characterised by high mechanical strength and improved abrasion resistance. Media resistance is a little greater than NBR.
3. CR – Chlorobutadiene-Rubber (Neoprene, Baypren, Butaclor, Denka, Chloroprene).
CR is characterised by resistance to chemicals, to ageing, to weathering effects and to ozone attack, and also by their flame resistance. Average resistance to mineral oils and greases.
4. ACM – Acrylate-Rubber (Cyanacryl, Europrene AR, Noxitite PA, Nipol AR, Elaprim AR).
ACM is more heat resistant than NBR or CR. Their main use is for the manufacture of Simmerring radial shaft seals, O-Rings and mouldings at higher temperatures and in oils containing additives (active oils). Resistance to ageing and to ozone is very good.
5. EAM (AEM) – Ethylene-Acrylate Rubber (Vamac).
EAM is more heat resistant than ACM and it has properties between those of ACM and FPM.
Good resistance to swelling in paraffin-based mineral oils with additives, water and refrigerants.
Good resistance to weathering and ozone attack.
High swell in ATF and transmision oils, mineral oils rich in aromatics,
brake fluid, concentrated acids, and esters of phthalic acid.
6. VMQ (MVQ) – Silicone Rubber (Silastic, Silicone, Wacker-Silikonkautschuk).
VMQ is characterised by high thermal resistance, good cold flexibility, good dielectric properties, very good resistance to oxygen and ozone attack and, above all, physical properties show only very slight dependency on temperature. The permeability to gases at room temperature is higher than that for other elastomers, and this is especially noticeable with thin-walled diaphragms. Where oxygen is excluded, the material is degraded at higher temperatures by depolymerisation.
7. FKM (FPM) – Fluoro-Rubber (Viton, Fluorel, Tencoflon, Dai El, Noxitite).
Materials based on FKM are especially important due to their resistance to high temperatures and their chemical stability. Their permeability to gases is low. FKM elastomers display minimal weight loss in high vacuum. Materials based on this elastomer have excellent resistance to hot water and to steam.
8. FVMQ (MFQ) – Fluorosilicone-Rubber Fluoromethyl Polysiloxane.
Elastomers based on this synthetic rubber are substantially more resistant to swelling in fuels, mineral oils and synthetic oils than elastomers based on silicone rubber.
9. NR – Natural Rubber.
NR is characterised by high mechanical strength and elasticity as well as by good low temperature behaviour. It is therefore preferably used for the production of torsional vibration dampers, engine mountings, machine supports, rubber-metal suspension elements, diaphragms, moulded parts, etc.
10. EPDM – Ethylene-Propylene-Diene-Rubber (Dutral, Keltan, Vistalon, Nordel, Epscyn, Buna AP, Royalene, Polysar EPDM).
Moulded parts and sealing elements in EPDM are preferably used in washing machines, dish washers and in water fittings. Seals in EPDM are also used in hydraulic systems using fire retardant hydraulic fluids of Groups HFC and HFD, and in hydraulic braking systems.
EPDM elastomers have very good resistance to ozone, ageing and weathering and are, therefore, best suited for extruded profile sections and sealing strips which are exposed to weathering.