Tuesday, January 24, 2012

Belt Drives and Ozone Exposure

Ozone is a naturally occuring gas that is found in the air that we breathe. It consists uniquely of three oxygen molucules bonded together rather than the two of normal oxygen. Ozone is produced during lightening storms and is responsible for the fresh smell of the air afterwards. Electrical arcs from arc-welding or from around the brushes of electrical motors or ultraviolet light all produce ozone gas. It can often be detected by it's very unique chlorine bleach like smell in more concentrated form. Ozone is a powerful oxidant, so is sometimes used in air and water purification systems. To much, though, can have detrimental effects on plants, lung tissues, and organic materials like latex, plastics, and rubber.

The potential for excessive ozone concentrations is low for most environments in which belt drive systems are found. There are industrial environments, though, with higher concentrations of ozone gas making belt performance and durability a concern.

While all belts are designed for resistance to ozone, excessive concentrations can still affect rubber belts in much the same way as high environmental temperatures. Ozone slowly errodes the chemical composition resulting in rubber hardening and cracking. The amount of degradation is a function of the ozone concentration and the time of exposure. To prevent excessive detrimental effects on rubber power transmission belts, the following concentration levels should not be exceeded: (pphm = parts per hundred million)

Non-Conductive Belt Constructions: 100 pphm
Conductive Belt Constructions: 75 pphm
Non Marking Constructions: 20 pphm
Low Temperature Constructions: 20 pphm

The polyurethane material used in Poly Chain GT Carbon belts is considerably more resistant to ozone degradation than conventional rubber materials. Poly Chain GT Carbon drives are an excellent choice for drive applications located in environments with ozone concentrations.

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