August 2019

SBR Rubber Sheet – When (and when not) to Use

It’s hardly surprising the SBR Rubber Sheet (red rubber) is one of the most widely used gasket materials. Firm and smooth, it conforms readily to mating surfaces. Good tensile strength and abrasion resistance ensure durability, providing it’s not used in the wrong places. Here’s what you should know about using red rubber gasket material.

SBR Rubber Sheet:  A Proven Elastomer

Red rubber is produced by blending Styrene Butadiene Rubber (SBR) with natural rubber. SBR was one of the first synthetic rubber materials, produced by polymerizing styrene and butadiene in a roughly 3:1 ratio. Invented early in 20th Century, production increased rapidly during WWII as supply chain challenges limited availability of natural rubber. SBR’s strengths include resistance to cracking, abrasion resistance and low cost. Unlike natural rubber, it hardens with age.

When natural rubber is added to SBR the result is a red-colored elastomer with the best characteristics of each. Several grades are available with varying properties. Hardness is in the range 75 – 80D on the Shore A scale. (For more information, refer to “Understanding Gasket Material Hardness”.) The main limitations of red rubber are a temperature range limited to -20 to 160°F and swelling when exposed to hydrocarbons.

Applications to Avoid with SBR Rubber Sheet

Red rubber is not suitable for use with oils and fuels like gasoline and diesel. It also offers poor resistance to chemicals, solvents and hydraulic oils. In addition, it is degraded by ozone, so electrical, (especially high voltage,) applications are best avoided.

Good Applications for SBR Rubber Sheet

Red rubber gaskets perform well when sealing against air and water, both hot and cold. Saturated steam is also usually sealed effectively by red rubber.

SBR Rubber Sheet:  Often the Right Choice

Many sealing and gasketing applications don’t need high-temperature capability or high levels of chemical resistance. When that’s the case red rubber is often a better choice than newer and more exotic materials. Produced in a range of sheet thicknesses, it lends itself to die as well as water jet cutting and can be a very cost-effective choice. For more information call or email the specialists at Hennig Gasket.

Polyurethane Foam Gasket Not a Seal

Polyurethane, sometimes referred to just as ‘urethane’ is one of the most widely used materials for seals and gaskets. It’s inexpensive and has characteristics that make it very useful. Just be careful not to use urethane gasketing foam when you need a polyurethane seal!  A polyurethane foam gasket is different from a polyurethan seal.

Polyurethane properties

Polyurethane is formed by reacting isocyanate with polyol. Isocyanate is a simple compound of nitrogen oxygen and carbon while polyols are formed from oxygen, hydrogen and carbon. Put them together and you get materials that make excellent seals and gaskets.

Polyurethane seals work well from around -65°F up to 210°F. Below this minimum they become brittle while at higher temperatures they melt. Polyurethane is tough with good impact resistance and load bearing capacity. It’s also resistant to attack by petroleum and hydraulic oils.

Polyurethane is produced in a range of hardnesses, although the bulk of the material used for seals is around 95 Shore A. It’s tough, stronger than natural rubber, and abrasion resistant.

Polyurethane becomes a lot softer when foamed. This entails adding a foaming agent to the isocyanate/polyol reaction to create a gas. As the liquid solidifies this leaves bubbles dispersed throughout the material, which gives it a springy resilience.

Applications for polyurethane foam

Cushioning is probably the biggest application. Polyurethane foam is used in furniture, shoes and anywhere else that compliance and recovery are sought after. Gasketing is another common use. Here it’s compressibility cushions against impacts and takes up manufacturing tolerances.

One time not to use polyurethane foam is when sealing is needed. Most polyurethane foams have an open cell structure, so fluids can pass through.

Polyurethane seal applications

With it’s excellent abrasion resistance, polyurethane is often used in situations where there’s relative movement. Seals around rods in hydraulic cylinders is one example, where the oil resistance also helps ensure long life. Pipe seals are another common application, as are wipers and shaft seals.

Buy the right polyurethane!

Polyurethane, or just plain urethane, is a good choice for many seal and gasket applications. Just remember that in it’s foamed state it may not provide much of a seal!