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
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
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:
D 2000-95 M2BG714 B14 EA14 EF11 EF21 EO14 EO34
line call-out contains the following:
document name (ASTM D 2000-95). The two-digit number
following the hyphen indicates the revision year
(in this case, 1995).
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).
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.
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.
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.
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
X 145 = psi
psi / 145 = MPa
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
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.
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.