What is ASTM D1056 and what does the letter/numbering system mean?
The American Society for Testing Materials D1056 (ASTM D1056) is the US standard for cellular materials, both Sponge (Open Cell) and Expanded (Closed Cell)
Cellular products are referred to by a three character Grade Number which will often be presented on a print as such:
ASTM D1056 2A1
The characters represent Type, Class and Grade.
Type: The first character and denotes whether or not a material is Open or Closed cell (In the example above the “2” indicates a closed cell rubber)
Note: Crushed cellular foams start out as closed cell, then have their cells ruptured – they are listed as Type 1.
Class: The second character with A through C showing oil resistance, and D denoting extreme temperature resistance. (In the above example “A” indicates no oil resistance needed)
|A||Non-oil resistant (EPDM or SBR*)|
|B||Oil resistant, low swell (Nitrile)|
|C||Oil resistant, medium swell (Neoprene)|
|D||Extreme temperature resistance (Silicone)|
*General examples. Check the individual rating of the material. Blends of the base materials can also meet different classes.
Note: These specs are used two ways: 1) Requirements for a component are listed on the print. 2) Material specifications sheets list the specifications the material does meet.
So if a print lists Class “A” which shows no oil resistance required, Class A, B or C materials can be used- since B and C meet A.
If a specific material specification sheets lists A– that means it cannot be used if a print call out for B and/or C, since A is a non-oil resistant material and Class B and C require a material that is oil resistant.
Grade: The last character and refers to Compression Deflection, or the force in pounds per square inch required to compress the material 25% of its thickness. (In the example above the “1” denotes a compression deflection of 2-5 psi)
|0||Less than 2 psi|
Note: ASTM D1056 uses Compression Deflection as a major metric for cellular rubber, not density, which many people erroneously use. Compressibility is directly related to sealing and gasketing- while density is an indirect metric. It is generally true that denser materials are harder than less dense ones- but not always, and different polymers can be softer or harder at the same density.
So- for the 2A1 example listed above – the requirement is for a closed cell expanded rubber which does not need to be oil resistant, and requires only 2-5 psi to compress the material by 25% of its original thickness.
After the three main characters other specifications can be noted by Suffix Letters and Numbers.
Suffix Letter Definitions
|A||Heat Resistance||L||Water absorption|
|B||Compression set||M||Flammability resistance|
|C||Ozone resistance||N||Impact resistance|
|D||Compression deflection resistance||P||Staining resistance|
|F||Low temperature resistance||T||Tensile and Elongation|
|J||Abrasion resistance||Z||Any special requirements|
Numbers may follow the Suffix Letter to denote specific conditions.
Example: The 2A1 material listed above might have additional requirements listed as follows:
ASTM D1056 2A1 A1 C1 Z: Color Grey
So- the closed cell foam (2), with no specific oil resistance requirement (A), with a Compression Deflection at 25% of 2-5 psi (1), also needs to meet:
A1: ≤ 30% change in compression deflection after aging 22 hours at 212°F
C1: Ozone resistance to Test Method ASTM D1171, ozone chamber exposure, Exposure Method A or B
Z: Color Grey
Hopefully this section is useful to you. Don’t worry if you find it confusing, Atlantic Gasket has worked with ASTM D1056 for decades and is always available to answer any questions.
Why do I see different ASTM D1056 specifications like SCE41 and 2C2?
ASTM D1056 is a 50+ year old spec that has been revised many times (the most current revision was in 2014)
RE/SBE/SCE are 1960's terms. Over the years they were replaced by 2A/2B/2C, respectfully. The older terms are still in heavy use on both old and current prints. Atlantic Gasket refers to its products using several variations of the ASTM D1056 standard for the convenience of customers.
|CALLOUT FOR NON-OIL RESISTANCE MATERIAL|
In the latest revision the “A” rating in 2A1 means that there is no requirement for oil resistance. SBR, EPDM and Neoprene/EPDM/SBR blends will often have an “A” rating.
|CALLOUT FOR OIL RESISTANCE – LOW MASS CHANGE MATERIAL|
In the latest revision the “B” rating in 2B1 means that there is a mass change of ≤ 50-100% (depending on density of the cellular rubber), after being immersed in oil. Nitrile (NBR) is often used for “B” requirements due to its excellent oil resistance.
|CALLOUT FOR OIL RESISTANCE- MEDIUM MASS CHANGE MATERIAL|
In the latest revision the “C” rating in 2C1 means that there is a mass change of ≤ 150-250% (depending on density of the cellular rubber), after being immersed in oil. Pure Neoprene (CR) will usually be rated “C” as will various NBR/PVC and PVC/NBR/CR blends.
If A is little to no oil resistance and B has more resistance than C- why that order? C was added later and ASTM wanted to minimize confusion.
|MIL-STD-670B VERSUS ASTM D1056|
Note that other than using slightly different numbers/names- MIL-STD 670B was basically identical to ASTM D1056 and was discontinued in the 1980’s.
An identical “mirror image” spec to ASTM D1056, discontinued in 2005. Due to its connection to the Society of Automotive Engineers it is often seen on automotive prints and many other designs.
The International Standard Organization’s specification of elastomers. Part 1- Sheeting- is very similar to ASTM D1056. Part 2 covers Moldings and Extrusions. Both versions are often seen on European prints.
Covers PVC closed cell foams. Very similar to ASTM D1056.
Covers polyolefin foams. Often material specification sheets will use the ASTM D3575 test method to define density.
JIS K 6767
Covers testing methods for polyethylene foams. Similar to ASTM D3575 and frequently seen in Japanese applications.