The effect of cyclic thermal stresses in the life of PET shrink´s heating body

An automatic device carries out the size-reducing shrinking of polyethylene (PET) bottles using a heating technology featuring the ¿shape memory¿ polyethylene. In the device a lever pushes the bottle in the furnace at a temperature of 800-1300^°C then it presses and shrinks it. We have a dual aim when examining the furnace. On one hand, our aim is to determine the relationship between weariness (the number of operation, time of operation) and electric resistance. Its practical function is to justify customer complaints via resistance measuring. Another purpose of our measurements is to offer such a controlling procedure that provides the longest life time under given circumstances in case of a given furnace.