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The technically correct term for closed cell sponge rubber is expanded rubber. The cells are like individual balloons, holding gas and not allowing moisture to pass through as long as the cell wall has not burst. The raw compound is mixed on the same type of equipment used to mix solid rubber compounds, but a chemical blowing agent is also added. Under the heat and pressure of a pre-cure or pre-forming process, this additive decomposes and mixes with the rubber compound and generates nitrogen gas. As this reaction is occurring, the mixed batch is placed into an oven and allowed to expand into a bun from 2" to 4" thick.
The bun of closed cell sponge rubber is then aged and split into sheets typically from .062" thick and greater.
Constant deflection of closed cell sponge rubber may cause the gas to permeate through the cell walls. Over compression of the closed cell sponge such as beyond 50 to 70% deflection, may cause the cells to burst. When a closed cell sponge gasket has been over compressed, the gasket may rebound very slowly, or not at all, compromising the integrity of the gasket. Most closed cell sponge gaskets should be deflected 20 to 35% for optimal sealing performance. These properties are discussed in ASTM D1056, ASTM D6576 and Mil-R-6130C.
Although Stockwell Elastomerics, Inc.'s closed cell sponge rubber business frequently involves silicone sponge rubber, there are many situations where non-silicone closed cell sponge rubber is more appropriate. The following is a rundown of the closed cell sponge gasket materials most frequently used by Stockwell Elastomerics, Inc. in service to our customers.
Closed Cell Neoprene Sponge Rubber
Produced from 100% neoprene polymer, most closed cell neoprene sponge products meet UL94HF-1 flame rating. They are generally servicable from -40°F to 158°F continuous and withstand 200°F intermittently. Premium closed cell neoprene sponge products will resist light oil contact, ozone, alkalis and acids, making them a good choice for general enclosure door gaskets.
Closed Cell Blended Sponge Rubber
Produced from a blend of neoprene, EPDM and SBR, these grades are the most frequently supplied for general purpose sponge gaskets. If you would request a commercial closed cell neoprene sponge gasket, this would likely be supplied. These products also normally meet UL94HF-1 and will take -70°F without cracking due to cold embrittlement. The oil resistance will not be as good as on the 100% neoprene sponge products.
Closed Cell EPDM Sponge Rubber
These materials will not meet the UL flame rating without additives and they will not withstand oils or fuels. However, they will stand up to outdoor conditions such as water, ozone and indirect sunlight better than neoprene.
Closed Cell ECH Epichlorohydrin Sponge Rubber
These sponge materials are often specified for under-the-hood automotive gasket applications due to its ability to handle continuous temperatures of 300°F and some light oil and fuel contact. ECH also has very good resistance to weather, ozone, sunlight and oxidation.
Ensolite Vinyl Nitrile / Neoprene
These blends of closed cell sponge are versatile, having a temperature range of -40°F to 180°F, and availability in 50 ft continuous rolls for gasketing. Certain Ensolite products have flame ratings of UL94V0 and UL94HF-1 depending on thickness. They tend to have slightly lower density than most closed cell sponge products, and the water absorption properties are slightly higher than closed cell neoprenes.
As of May 2005, the Rubatex International closed cell sponge production facility is operational and making bun and sheet stock. In the following table, we will list the Rubatex materials available from Stockwell Elastomerics, Inc. and some of the alternatives we suggested prior to the reopening of Rubatex by Sedo.
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Comparative Properties of Closed Cell Sponge Gasket Materials Table
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