Racking

Name:
Racking
Detailed information:
Experimental cold-stretching of unvulcanized rubber, whose behavior under stress is unique among natural materials. A thin, narrow strip stretched at, for example, 500–600% at 0C will retain that extension indefinitely after release of stress as long as the low temperature persists. In this state it loses its elasticity and has virtually 100% permanent set. It also displays a crystalline X-ray pattern similar to that of a fiber, in contrast to the amorphous structure of the unstretched state. On exposure to room temperature it slowly retracts to its original length; higher temperature increases its rate of recovery. Tests made on racked rubber have showm that crude rubber can be exposed to any degree of low temperature for any length of time without impairment of its properties.