Busak+Shamban announces the launch of a new harder NBR material developed to give optimized ozone resistance. Engineered to prevent cracking when O-Rings are stored in an elongated state in a subassembly, this compound with a hardness of 90 Shore A, is available in addition to their already successful 70 and 80 shore A materials.
Fluid connections, including tube fittings in static or mobile hydraulics, are often of a conical design so a connection is maintained under high pressure. To make sure of sealing integrity, these seals have a small cross section compared to their large diameter and manufactured of NBR, which has good elongation properties. They are designed to elongate in the seal groove between 5% and 17%, to secure their position.
Hydraulic tube fittings are usually stored as ready to use subassemblies, with the seals fitted in an elongated state. When stored, the seals will suffer ozone attack and standard NBR shows signs of cracking, especially when stored at high temperatures. To solve this problem, Busak+Shamban set out to develop a range of NBR sealing materials with high ozone resistance.
Illustration shows typical subassembly with O-Ring fitted
The new ozone resistant NBR, with a hardness of 90 Shore A is available in addition to 70 and 80 Shore A compounds. They all have the same benefits as a standard NBR; an operating temperature (depending on media) of -30°C to 100°C (-22°F to 212°F), good mechanical properties, resistance to mineral oil and grease and excellent elongation characteristics. Also, the material shows no ozone cracking when tested to DIN 53509-1. In this test, samples are tested in an ozone concentration of 50 pphm (+/- 5) when elongated by 20% for 120 hours at a temperature of 40°C (104°F) and humidity of 55% (all percentages at a tolerance of +/- 2%).
The new 90 Shore A material is available as standard O-Rings. The 70 and 80 Shore A material can be manufactured as O-Rings and custom molded parts.
Footnote: The effect of ozone on elastomer seals
Ozone is another form of oxygen, where three atoms of oxygen, rather than two, join to form a molecule. Ozone is formed in the air, for example, from discharges produced by electrical equipment. Since it is chemically very reactive, in contact with rubber materials, it causes them to crack, especially when under tension.
Almost half of all O-Rings are used in ‘outer’ seal, piston sealing applications, which means that they are elongated when fitted. Critical elongation is above a 5% expansion of the inner diameter. Beyond this, in a matter of weeks, ozone cracking will occur unless the seals are protected from the ozone effect in storage.