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  Materials (O-Rings)
   
 
  pic_banbury, open mixers compoundsElastomers that are intended for, but not limited to, use in automotive applications, are designated by ASTM D2000 on the basis of type (heat resistance) and class (oil resistance).

Resistance to special fluids or environments (fuels, water, ozone, etc.) are also classified in a similar manner. ASTM D1418 lists different polymers by an abbreviated coding system (NBR, EPDM, ECO, SBR, FKM, etc.). By utilizing this classification system, guidance is provided to the engineer in the selection of practical, commercially available rubber materials, and to also provide a method for specifying these materials by use of a simple "line call-out" designation.

   
 
  Standard compounds have been formulated to meet a number of laboratory and industry standards for a wide range of applications.

Basic characteristics of standard compounds are given in table 1.

Table 1: Standard compounds - basic characteristics

Code Polymer ASTM D2000
Line Call-out
Basic characteristics
K6 NBR 70 2BG 714 B14 EA14 EF11 EF21 EO14 EO34 Excellent mechanicalstrength and resistance to wear, mineral oils, heat.
Poor resistance to fuels and out-door weathening.
C6 EPDM 70 3DA 710 A26 B36 C32 EA14 F19 G21 Good resistance to water, steam, brake fluids, alkalies and diluted acids.
Outstanding weather resistance.
M6 HNBR 70 3DH 710 B16 C20 FO36 F17 Very good mechanical characteristics.
Wear, ozone and high temperature ageing resistance.
Recommended for fuels and oils contact.
Low gas permeability.
Good for high and low temperature.
F6 MVQ 70 2GE 706 A19 B37 Very good heat and chemical resistance.
Recommended for food contact. Poor mechanical characteristics.
G6 FKM 75 2HK 810 A1-10 B38 EF31
Z1 Durezza 75 5
High temperature resistance. Very good chemical resistance. Poor low temperature flexibility.
   
 
  Physical characteristics of our standard compounds are listed to provide assistance in selecting the proper compound.
A number of proprietary compounds with unique characteristics and hardnesses are available along with additional information from our Technical Sales and Services Department.
   
 
  Selection of elastomers is normally the final result of a compromise between fluid resistance and last, but not least, the cost of the product.
Chemical resistance of different elastomers are listed in
standard compounds - chemical resistance.
   
 
  Tear resistance of elastomer (ASTM D624-B) is very important for those applications where rubber parts are subject to strain and stresses, particularly when surface cuts could cause tears and severely damage the effectiveness of the seal.Wear resistance (ASTM D394) is very important for the correct evaluation of any O-Ring in a dynamic sealing application.Critical factors to be considered are: polymer type, hardness, surface finish, lubrication, relative speed and environment.
   
 
  Elastomers have a large use in electric and electronic fields due to their dielectric characteristics and versatility.
Typically, the attention of the project engineer is focused on the electric insulation obtainable with rubber. On request, rubber can also be supplied as an electric conductor or anti static, by means of special additives to the compound.
The most common standards regarding electric characteristics are ASTM D257 and ASTM D991 (volume and surface resistivity), ASTM D149 (dielectric rigidity) and IEC Standards (International Electric Commission).
   
 
  The factories Compounding Division has the ability to meet the special compounding requirements for a vast number of industries, offering materials previously tested at a variety of temperature and media environments. The factory can also custom formulate compounds with specific characteristics, thus giving an invaluable service to our customers. The techincal data and characteristics of some of those special compounds are listed in a separate brochure.
   
 
  A number of government and independent regulatory agencies maintain standards dealing with elastomers and the environments in which seals are expected to perform. Listed are the agencies deeply involved in O-Ring approvals:
  • WRC (Water Byelaw Scheme) of Great Britain dealing with elastomer gasketing in contact with drinking water;
  • DVGW of Germany dealing with elastomer gasketing in contact with drinking water;
  • UL of USA, which establishes standards and tests materials and products to determine their hazards to life and property;
  • NSF International of USA provides standards in public health safety.

These Organizations operate laboratories for examination and testing to certify compounds and finished parts such as O-Rings.

The factory has a number of compounds certified by these Authorities.

   
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