1. Oil stain: After long-term use, certain oil stain will accumulate on the surface of the machine, which will contaminate the belt and lead to the blackening of the belt.

2. Wear: The belt is easy to wear under the action of long-term friction and stretching, especially when it is used in high temperature and high pressure environment, it is more prone to wear and aging.

3. Friction: The shortcake machine will generate a certain amount of friction heat during operation. If the friction heat is too large, the belt will age and harden, and the surface will turn black.