Commercial grade rubber provides insulation and sealing for a broad range of applications. Compounds such as silicone, commercial grade EPDM, and neoprene are also less expensive than specialty rubber materials that meet approvals, standards, or regulatory requirements from organizations such as Underwriters Laboratories (UL), ASTM International, and the U.S. Food and Drug Administration (FDA).
For engineers, selecting the right rubber means understanding when a commercial grade rubber is acceptable and when a specialty material is a requirement. Engineers need to ensure that the products they design meet application requirements, but over-specifying an elastomer can attract unwanted expenses. In addition to paying more per unit of material, engineers may also have to buy greater minimum order quantities (MOQs).
In this article from Elasto Proxy, the differences between specialty rubber and commercial grade rubber in terms of a few real-world examples are considered. Some best practices that can strengthen seal designs are also explained.
Asking for ASTM Rubber
Sometimes, engineers ask for an elastomer that “meets ASTM D2000” or “ASTM rubber”. There are numerous disputes here. First, a single ASTM test standard for rubber materials is not available. In fact, there are many different and specific testing standards. It depends on whether an elastomer that meets the thermal conductivity requirements of ASTM F433-02(2014)e1 is needed. Maybe the need is for a gasket material that meets the minimum liquid leakage requirements of ASTM F 37-06(2013) instead. If there is no requirement for a specialty rubber that meets an ASTM test standard, could you use a commercial grade compound that is less expensive?
ASTM D 2000 is a published specification that presents suppliers and buyers with a standard way to explain vulcanized elastomers. The requirement for “ASTM D 2000 rubber” instead of “ASTM rubber” may seem more specific, but it’s not. ASTM D 2000 uses a combination of letters and numbers to “call out” material properties and covers thousands of elastomers. Using a food-related analogy, just asking for “ASTM D 2000” rubber is similar to ordering a sandwich without specifying the bread, condiments, or fillers. Unless a person is incredibly lucky, the sandwich he or she receives probably would not be the one that was ordered.
Asking for UL 50 Gaskets
UL 50 is the standard that is applied to enclosures for electrical equipment that will be used and installed in non-hazardous locations in accordance with national electrical codes in the United States, Canada, and Mexico. However, this standard applies to the entire enclosure and not to individual components such as gaskets, seals, and insulation. As a matter of fact, UL 50 describes that the requirements for an individual product take precedence if the individual product has requirements that are at variance with UL 50.
Furthermore, in certain places, engineers ask for “UL 50 gaskets” when a UL 50 approved material is not needed. There are numerous drawbacks here. First, a well-designed enclosure may be able to match up to UL 50’s requirements without the use of more expensive UL-approved gasket materials. Second, there is a separate UL standard (UL 50E) for the environmental construction of qualifying environmental enclosures. This might lead to the challenge that engineers may need to account for two separate but related standards during the design process. Instead, UL 94 may apply to the gasket design if the electrical enclosure is for an appliance.
Commercial Grade Rubber, Specialty Rubber, and Best Practices
Requesting for a “rubber gasket” but including “ASTM rubber” or “UL 50 gasket” on the schematic is also problematic. Ultimately, the part drawing is the contract for gasket fabrication. This is where Elasto Proxy helps engineers not just with material selection, but also with seal design. If a CAD application such as SolidWorks® is being used, then DWG files of standard profiles that can be dropped into the design can be sent. The PDF versions of the standard profiles can also be sent.
If the question asked is a choice between commercial grade rubber and specialty rubber and if there are questions about seal design, then engineers should not wait until the end of their next project to ask for assistance. Otherwise, they may be forced to use specialty rubber because a commercial grade compound cannot support a design constraint.
This information has been sourced, reviewed and adapted from materials provided by Elasto Proxy, Inc.
For more information on this source, please visit Elasto Proxy, Inc.