Having discussed the properties and uses of the most common elastomer types, the question then becomes: How can these properties be succinctly specified when an existing compound is being selected or when a new compound must be formulated?

In order to provide guidance in the selection of vulcanized rubber materials, and to provide a method for specifying these materials by the use of a simple line call-out specification, the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE) established ASTM D 2000 / SAE J200. Though these standards are virtually identical, J200 finds its widest use within the automotive industry. D 2000 is the more common tool among rubber manufacturers. Specifying your elastomer choice via a standardized line call-out is a good idea because it allows the flexibility of using different manufacturers’ compounds while ensuring that the material quality and performance stay consistent.

D 2000 is based on the premise that the properties of all rubber products can be arranged into characteristic material designations. These designations are determined by types, based on resistance to heat aging, and classes, based on resistance to swelling. Here is the line call-out, or specification, for “N470,” a 70 (Shore A) durometer nitrile:

ASTM D 2000-95 M2BG714 B14 EA14 EF11 EF21 EO14 EO34 Z1 Z2

This line call-out contains the following:

A. The document name (ASTM D 2000-95). The two-digit number following the hyphen indicates the revision year (in this case, 1995).

B. The letter “M” may or may not be present. Since it is present in our example, the units of measure in the line call-out (and in any other documentation, such as a test report) are understood to be stated in SI (metric) units. For example, tensile strength is in megapascals (MPa). If the “M” was not present, English units would be in use. For example, tensile strength would be in pounds per square inch (psi).

C. The Grade Number defines specific added test requirements which are desirable in cases where the basic requirements do not always sufficiently ensure an acceptable material. Grade 1 indicates that only the basic requirements are compulsory; no suffix requirements are permitted. All other grades and test requirements are listed in Table 6 of the D 2000 document. In our example, the material is Grade 2.

D. The Type 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 heat aging for 70 hours at a given temperature. The temperatures at which these materials shall be tested for determining type are listed in Table 18. In our example, the material is Type B, which corresponds to a 100° C test temperature.

E. The Class is based on the material’s resistance to swelling in Industry Reference Material (IRM) 903 Oil (now used in lieu of ASTM Oil # 3, which was discontinued due to requirements by the Occupational Safety and Health Administration). Testing involves immersion for 70 hours at the temperature previously determined from Table 18 (100° C), after which swell is calculated. Limits of swelling for each class are shown in Table 19. In our example, the material is Class G, indicating a maximum swell of 40%. Be aware that ASTM Oil # 3 and IRM 903 Oil are similar but not identical, so complete equivalency among results is not possible. For information on converting ASTM oil swell values to IRM values, please refer to ASTM Emergency Standard ES 27-94. Table 20 below lists the D 2000 material designations (type and class) and the elastomers most often used for each.

F. The next three digits (in this case, “714”) specify the hardness and tensile strength. The first digit indicates Shore A durometer. For example, 7 for 70 ±5. The next two numbers indicate the minimum tensile strength, i.e. 14 for 14 MPa. Remember, this will be in SI units if the letter “M” is in the call-out, and English units if not. To convert to psi, simply multiply the MPa number by 145. In this case, 14 MPa would convert to 2,030 psi

MPa X 145 = psi
psi / 145 = MPa

G. Suffix letters and suffix numbers follow the hardness and tensile strength specifications to provide for additional testing requirements. The meaning of each suffix letter is shown in Table 21. For example, the “B” of “B14” specifies a compression set test. Suffix letters are typically followed by two suffix numbers. The first number always indicates the test method, and the second indicates the test temperature. The suffix numbers are covered by Tables 4 and 5 of the D 2000 document. For example, the “1” specifies a 22-hour compression set test as detailed in D 395 (Method B) for solid test specimens, and the “4” specifies testing at 100° C. Keep in mind that in some cases, the second suffix number may be two digits, which means you might see something like “F110.” F110 would indicate a 3-minute low temperature resistance test as detailed in ASTM D 2137 (Method A) and conducted at a temperature of -65° C.

That’s all there is to understanding the D 2000 / J200 call-out system. It is one of the most versatile specifications in the rubber industry. In addition to helping you specify compounds, familiarity with the system will also help you make sense of material test reports. Let’s take a closer look at a sample report next.