Heat resistance standards and test methods
Heat resistance – classifications
High-temperature materials and working environments cause an acceleration of the ageing process that results in a hardening and cracking of the rubber covers. Heat also has a very destructive effect on the belt carcass because it damages the adhesion between the covers on the top and bottom of the carcass and also between the inner plies contained within the carcass. If the core temperature of the carcass becomes too high then the belt will quite literally start to fall apart. This is commonly referred to as ‘de-lamination’. The temperature limits that a belt can withstand are viewed in two ways – the maximum continuous temperature of the conveyed material and the maximum temporary peak temperature. The two main classifications of heat resistance recognised in the conveyor belt market are T150, which relates to a maximum continuous temperature of 150°C and T200, which is for more extreme heat conditions up to 200°C.
ISO 4195 Heat resistance test methods
ISO 4195 ‘accelerated ageing’ laboratory tests are used to accurately measure heat resistance and consequently the anticipated working life of the belt. Rubber samples are placed in high-temperature ovens for a period of 7 days. The reduction in mechanical properties is then measured. The three classes of resistance against accelerated aging within ISO 4195 test methods are: Class 1 (100°C), Class 2 (125°C) and Class 3 (150°C). At Dunlop we also carry out routine testing at 175°C in order to ensure that our belts can handle even more extreme temperatures.