A reliable and successful application requires a good elastomer specification. It’s important that an elastomer is compounded to exactly what the application requires. Obviously, testing in the subject application is also extremely important and can’t be emphasized enough.
There are troves of rubber and plastic specifications that callout details of what the material must be tested to, what the results must be, including minimums and maximums of what the rubber must hold. Sometimes there are tolerances which the testing must hold.
Some specifications callout for how long a test must be administered, under what temperature, humidity, and other environment expectations. These specifications make it easy for the person designing the components that will go into the final application to know what they are getting when they put a specification and a callout on their drawing.
The below graph lists just a few of the different specifications that different types of rubber have including Fluorosilicone, EPDM, fluorocarbon elastomer, silicone, nitrile/Buna-N, natural rubber, cork rubber, and others.
ASTM D2000 is a classification system that classifies different types of rubber, but should not be used alone in designing a rubber for an application. In the Rubber industry there is a well-known entity called a line callout, for example, ASTM D200099 2 BC 515 A14 B14 C12 E034 F17 Z.
- The first step in reading this callout is to understand what ASTM D2000 (1999) is, where it came from, and its purpose. The purpose of ASTM D2000 was originally geared toward the Automotive industry to describe rubber.
- The second step is to identify what measurement system the line callout is using, the metric or the English measurement system. An M at the beginning of the callout indicates that all the data that is presented in metric. If there is no M present, this indicates that all the data is on the English measurement system.
- The third step is to start with the first number, which indicates the grade number of the material. The requirements of the first letter is the ‘type’ or the temperature grade of the material. (There is a chart below that breaks down what each letter signifies)
- The next step is to read the following letter, which is the class that indicates the volume oil swell for this elastomer.
With the type and class put together, one can discern the typical materials that come out of the first part of the callout. (For example, BC normally indicates neoprene) After the type and class, the durometer and tensile strength are specified in their appropriate terms.
The rest of the line callout gives a letter, which is the quality that the line callout is looking for. The next two numbers are the type of test and how long the test is administered for. The subsequent number indicates the temperature of the test. (For example, A14 indicates Heat resistance per ASTM D573, Standard Test Method for Rubber Deterioration in an Air Oven for 70hrs, the 4 indicates the test must be administered at 100 C) Normally, ASTM D2000 callouts only refer to the beginning part of the callout with the specific grade, type, durometer, and tensile. However, the remaining parts are always there in case they are needed. For example, it is common for an ASTM D2000 callout to just read ASTM D2000 3BA 615, or ASTM D2000 M1BC510.
Here are examples of a callout:
Example 1: ASTM D2000 M1BC407
This starts with ASTM D2000. M1 follows, meaning that it is grade 1 material. BC, which is normally neoprene. Keep in mind it is possible that another elastomer could be used to meet that type and grade. 4 indicates the durometer, so in this case it is 40 Shore A. 07 indicates the tensile strength of 07 MPa or 1015 psi. This tensile strength is a minimum tensile strength.
Example 2: ASTM D200099 M3BC614C12F17
In this example, the 99 indicates the revision year. M indicates that the callout will be listed in metric. ‘3’ indicates the grade of the material. BC indicates the type and class of the material to be Neoprene as well. 6 indicates the durometer, in this case translating to 60 Shore A. 14 indicates 14 MPa (Metric) or 2030 psi (English system). C12 indicates the material shall be tested IAW (in accordance with) ASTM 1171 Method A. F17 indicates low temperature test, per ASTM D2137 (Standard Test Methods for Rubber Property Brittleness Point of Flexible Polymers and Coated Fabrics) for 3 minutes at 40C.
There are a few notes with the ASTM D2000 that should be mentioned:
- Except for FC, FE, FK, and GE (unless otherwise specified), the elastomer will be black.
- To go from MPa to psi, it is a fairly simple multiplication of 145. To calculate from psi to MPa you divide by 145.
- The flexibility that the specification offers does not mean any and all materials are available. It is best to consult with manufacturers and then test/confirm through the channels available.
- Grade 1 (only the basic requirements of the elastomer required) is almost always available
- Z at the end of a callout typically indicates a meaning that is not included in the ASTM D2000 classification. It may range from dielectric strength to the surface quality of the material in question. Z should be very specific when required as well.
|BA||Ethylene propylene, high ¬temp SBR, and butyl compounds|
|BG||NBR polymers, urethanes|
|CE||Chlorosulfonated polyethylene (Hypalon)|
|CH||NBR polymers, Epichlorohydrin polymers|
|DA||Ethylene propylene polymers|
|DF||Polyacrylic (buytl¬acrylate type)|
|DH||Polyacrylic polymers, HNBR|
|C||Ozone and Weather Resistance|
|D||Compression¬ Deflection Resistance|
|EA||Fluid Resistance (Aqueous)|
|EF||Fluid Resistance (Fuels)|
|EO||Fluid Resistance (Oils, Lubricants)|
|F||Low Temperature Resistance|
|Z||User Defined Requirements|
NEDC is very familiar with ASTM D2000 line callouts because of its experience with the aerospace and military industries. With ASTM D2000 line callouts, it makes it a lot easier for an application to get exactly what it needs to do the job right.