Belt pulleys need to work smoothly, or they can end up jamming and failing. While basic pulley operation is very simple, most pulley assemblies have a multitude of parts that can all have something go wrong with them. When you have belt pulleys, you need to treat them as a critical part of your equipment and inspect them often. It doesn't take much to make a belt go off-center; even ones manufactured to work in extreme conditions have their limits. It also helps to know what issues can make the belt pulleys stop working so that you can look for those specifically.
Heat and Pulley Integrity
Excessive heat (and cold, too) will affect the pulley just like it would affect anything else. Rubber and plastic parts can dry out and crack or become brittle if cold is the issue instead of heat. Metal parts can warp if they are too close to the source of the heat and if they aren't made to withstand that much. (Yes, even metal can experience problems; think of all the reports you hear about train tracks warping in areas experiencing major heatwaves.) Also, instead of warping, the metal can heat up and transfer that heat to the belt and other parts, possibly warping or melting them.
Any belt is at risk of fraying. The cause can be age, a problem with the pulleys that places too much friction on the belt or any one of a number of other reasons. The result is always the same: You have to inspect the belt regularly and take action if you see signs of fraying, cracking, gouging and so on. For belts that are simply old, replacing the belt is all you need to do. But do investigate the source of the fraying because if it's due to something like friction, you need to solve whatever's causing that to protect the replacement belt from meeting the same fate.
Lack of Lubrication
Sometimes the problem isn't with the belt or pulley itself but with shafts and other moving parts that rely on lubrication to run smoothly. If lubrication oil has dried up, for example, the shaft may not turn easily and could catch, causing the belt to go off-course. Routine maintenance should include adding more lubricating oil (or whatever the assembly uses) when needed, but if you notice anything off, of course, take a look at the assembly then.
If you need another belt pulley replaced or installed, or even if you install them yourself and just want to buy some extras, always look for the toughest, best-built pulleys possible. Those last longer and will help your company's budget in the end.
Contact a manufacturer for more information about belt pulleys.