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What is the difference between NR, SBR, NBR, EPDM, and neoprene rubber?

Natural Rubber (NR): derived from Hevea brasiliensis latex; excellent tensile strength (30+ MPa) and resilience; wide hardness range; good for dynamic applications; poor resistance to oils, oxidation, and ozone; service temperature -50 to +80 degrees C; widely used in tyres, conveyor belts, and vibration isolators. SBR (Styrene-Butadiene Rubber): synthetic substitute for NR; similar properties at lower cost; better abrasion resistance than NR; poor oil, ozone, and UV resistance; service temperature -50 to +100 degrees C; most common general-purpose compound; widely used for cheap gaskets, flooring, conveyor belts, shoe soles. NBR (Nitrile Butadiene Rubber): best oil and fuel resistance of common rubbers; tensile strength 10-20 MPa; temperature range -30 to +100 degrees C (up to +120 degrees C for heat-resistant grades); poor ozone and UV resistance; used for oil seals, oil-resistant gaskets, fuel hoses, hydraulic system components. EPDM (Ethylene Propylene Diene Monomer): excellent ozone, UV, heat, and steam resistance; poor oil resistance; service temperature -50 to +150 degrees C; used for outdoor seals, HVAC gaskets, water and steam service, roofing membranes. CR (Chloroprene/Neoprene): good balance of oil resistance, weather resistance, and flame retardance; moderate resistance to most chemicals; temperature -40 to +120 degrees C; used for marine, automotive weatherstripping, moderate oil exposure applications.

What is Shore A hardness and how do I select the right hardness for my application?

Shore A hardness is a measure of the resistance of a rubber to indentation by a standardised conical probe under a specified force; measured on a Shore A durometer scale of 0 (softest, no resistance) to 100 (hardest, glass-like); most industrial rubber sheets fall in the range 20-90 Shore A. Application selection guide: 20-35 Shore A – very soft foam/sponge rubber; thermal and acoustic insulation; light cushioning; very-low-compression-force gaskets for fragile equipment. 35-50 Shore A – soft rubber; light gasketing; vibration damping pads; gaskets where bolt load is limited (glass-flanged joints, inspection hatches); rubber lining for gentle impact protection. 50-65 Shore A – medium rubber; general industrial gasketing; anti-vibration mounts; most pump and valve gaskets; flooring for comfortable standing; most common hardness range for industrial rubber sheets. 65-75 Shore A – medium-hard rubber; high-pressure gasketing; pump liner; wear-resistant applications; industrial conveyor covers; anti-static flooring. 75-85 Shore A – hard rubber; high bolt-load gaskets; wear plates; roll coverings; heavy-duty applications where dimensional stability under load is important. IS 638 specifies minimum and maximum hardness values for each compound type and grade – specifying the IS 638 type automatically sets the hardness band.

What is IS 638 and how does it help in rubber sheet procurement?

IS 638 (Specification for Sheet, Slab and Moulded Rubber) is the Bureau of Indian Standards specification for industrial rubber sheets and slabs. IS 638 classifies rubber sheets into types based on compound and performance: Type 1 – General purpose (NR/SBR); Type 2 – General purpose, heat resistant; Type 3 – Oil resistant (NBR); Type 4 – Oil and heat resistant (NBR/CR high temperature); Type 5 – Ozone resistant (EPDM/CR). For each type and hardness grade, IS 638 specifies: minimum tensile strength (MPa); minimum elongation at break (%); maximum compression set (%); hardness range (Shore A or IRHD); ageing resistance (tensile and elongation retention after heat ageing). Specifying the IS 638 type and hardness grade in procurement ensures: compound is appropriate for the application (oil-resistant, ozone-resistant, etc.); minimum physical properties are met; the supplier's product can be verified against the standard. How to use IS 638 in procurement: specify 'rubber sheet to IS 638 Type 3 [for oil resistant], Grade 60 Shore A, 3mm thickness' – this gives the supplier an unambiguous specification and gives you a verifiable quality standard to test against.

What is EPDM rubber and what are its main applications?

EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber with outstanding resistance to ozone, UV radiation, weathering, heat, and water – properties that make it ideal for outdoor and temperature-demanding applications. Key properties: ozone resistance – EPDM does not crack or degrade under ozone exposure, unlike NR, SBR, and NBR (which crack rapidly in ozone); UV resistance – stable under prolonged sunlight exposure; heat resistance – service up to 150 degrees C continuous; excellent for hot water and low-pressure steam up to 150 degrees C; cold flexibility down to -50 degrees C; steam resistance – better than most rubbers for steam service below 150 degrees C. Typical EPDM rubber sheet applications: building and construction – expansion joint seals, window gaskets, roofing membranes, HVAC duct sealing; automotive – weatherstripping, body seals, door seals, sunroof gaskets; water and wastewater treatment – pipe joint gaskets, manhole seals, pump gaskets for water service; electrical – cable insulation, weather-resistant enclosure gaskets. NOT suitable for: petroleum oils and fuels (swells significantly in hydrocarbon contact); engine oil service; fuel system applications; petroleum-based solvent contact. EPDM vs. CR (neoprene): EPDM has better ozone, water, and heat resistance; CR has better oil resistance and flame retardancy; for applications combining weather resistance with moderate oil exposure, CR is often preferred over EPDM.

When should I specify silicone rubber sheet vs. EPDM or neoprene?

Specify silicone rubber sheet when: Temperature range exceeds EPDM or neoprene limits – silicone operates from -60 to +230 degrees C continuously (-60 to +260 degrees C intermittent); for oven door gaskets, high-temperature process equipment sealing, engine bay sealing above 150 degrees C. Food and pharmaceutical contact – FDA 21 CFR approved grades; no taste or odour migration; stable at sterilisation temperatures (autoclave 121 degrees C); accepted by FSSAI for food contact equipment. Electrical insulation – silicone has excellent dielectric properties; for high-voltage cable insulation sheathing and electrical enclosure seals at elevated temperature. Low compression set requirement – silicone maintains its sealing force over long periods at elevated temperature better than EPDM or NR; for static seals that are not frequently replaced. Medical and cleanroom applications – inert, no extractables at low concentrations, sterilisable. Disadvantages that make EPDM or neoprene preferable: silicone has poor tear strength and abrasion resistance – not suitable for dynamic seals or applications with mechanical wear; silicone is 5-10x more expensive than EPDM or CR; silicone is attacked by concentrated acids, petroleum fuels, and ketones (use FKM/Viton for these media). Use EPDM instead of silicone for: outdoor weather sealing below 150 degrees C (EPDM is much cheaper); water and steam service below 150 degrees C; HVAC sealing; general industrial gasketing not requiring food contact.