American Society of Testing and Materials (ASTM) provide a standardized method of calling-out the required physical properties of a rubber product, based primarily on its Type (Heat Resistance) and Class (Oil Resistance).
Specifications for physical properties of elastomeric seals can be very general or extremely specific in nature. Probably the most common general classification system is ASTM D 2000 Standard Classification System for Rubber Products in Automotive Applications. The purpose of this classification system is to aid in the selection of practical rubber products for specific environments. It also provides a line call-out designation for the specification of materials.
Rubber materials are designated by type (heat resistance) and class (oil resistance). The heat resistance of an elastomer is based on changes in tensile strength of not more than ± 30%, elongation of not more than 50%, and hardness of not more than ±15 points after 70 hours of aging at the specified temperature. The oil resistance is based on the volume swell of an elastomer after a 70-hour immersion in ASTM Oil No. 3.
| ASTM D2000 Specification (See Suffix Requirements below) | ||
| Type (Heat Resistance) Indicates high temperature resistance as follows:
A = 70°C / 158°F B = 100°C / 212°F C = 125°C / 257°F D = 150°C / 302°F E = 175°C / 347°F F = 200°C / 392°F G = 225°C / 437°F H = 250°C / 482°F Ref: ASTM D573
Hardness Shore A Durometer x 10; e.g. 7 in the example indicates 70 Shore A hardness.Ref: ASTM D224
Tensile Strength Stated in PSI (pounds per square inch) or MPa (megapascals), depending on whether English or Metric Units are indicated. PSI can be converted to MPa by dividing by 145, or, conversely, MPa values can be multiplied by 145 to abtain PSI. Tensile strength in the sample is 14 MPa or 2,031 PSI. Ref: ASTM D412
Class (Oil Resistance) Indicates oil resistance class by maximum volume swell as follows: A – No Requirement B – 140% C – 120% D – 100% E – 80% F – 60% G – 40% H – 30% J – 20% K – 10% Ref: ASTM D471 |
Typical Type / Class – Elastomer Chemical Group Associations The standard does not directly specify rubber compounds or chemical groups )e.g. Neoprene, Buna-n, etc.). Rather, it sets forth Type and Class (Temperature and Oil Resistance) criterion (“BG” in sample) that, in turn, narrow the field of options based on application requirements. However, for reference only, D2000 lists the following typical associations and elastomer groups:
AA – Butyl (polybutadiene), SBR, Natural,Polyisoprene, Reclaimed rubber AK – Polysulfides BA – Butyl, EPDM (Ethylene Propylene) BC – Neoprene (Chloroprene) BE – Neoprene (Chloroprene) BF – Buna-N (Nitrile, NBR) BG – Buna-N (Nitrile, NBR), Urethanes BK – Buna-N (Nitrile, NBR) CA – EPDM (Ethylene Propylene) CE – Hypalon (Chlorosulfonated Polyethylene) CH – Buna-N (Nitrile, NBR), ECH(Epichlorohydrin) DA – Ethylene PropyleneDF – Polyacrylate DH – Polyacrylate, HNBR EE – Vamac (Ethylene Acrylic, AEM) EH – Polyacrylate (ACM) EK – FZ FC – Silicone (high strength) FE – Silicone FK – Fluorosilicone GE – Silicone HK – Viton (Fluoroelastomers) KK – Perfluoroelastomers |
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| Suffix Requirements (Alpha) Indicates tests and related criteria for various elements like specific aging, fluid compatibility tests. Each element is cited by an alpha code (below) indicating a particular property followed by a numeric code (right) that specifies test criteria (e.g. time, temperature, fluid).
A = Heat Resistance; ref: ASTM D573 B = Compression Set; ref: ASTM D395 C = Ozone or weather Resistance;ref: ASTM D1171 EA = Fluid Resistance (Aqueous);ref: ASTM D471 EF = Fluid Resistance (Fuels); ref: ASTM D471 EO = Fluid Resistance (Oils and Lubricants);ref: ASTM D471 F = Low Temperature Resistance;ref: ASTM D2173 G = Tear Resistance J = Abrasion Resistance M = Flammability Resistance P = Staining Resistance Z = Special Requirements |
Suffix Requirements (Numeric) Testing parameters and related details are further specified by the numeric component of Suffix codes, including test temperatures as follows:Suffix Letters A, B, C, EA/F/O, G, K, L
1 = 23°C / 70°F 2 = 38°C / 100°F 3 = 70°C / 158°F 4 = 100°C / 212°F 5 = 125°C / 257°F 6 = 150°C / 302°F 7 = 175°C / 347°F 8 = 200°C / 392°F 9 = 225°C / 437°F 10 = 250°C / 482°F 11 = 275°C / 527°F
Suffix Letter F 1 = 23°C / 70°F 2 = 0°C / 32°F 3 = -10°C / 14°F 4 = -18°C / 0°F 5 = -25°C / -13°F 6 = -35°C / -40°F 7 = -40°C / -40°F 8 = -50°C / -58°F 9 = -55°C / -67°F 10 = -65°C / -85°F 11 = -75°C / -103°F 12 = -80°C / -112°F |