You can't have any binding and rubbing on pulleys, belt guards, or on anything that would cause the belt to get hot and smoke and wear out rapidly. All pulleys must be in line and even one a little bit out of line will cause the edge of the belt to fray and wear rapidly. Like the other mechanc said, a blade pulley dragging or binding or frozen up will cause a belt to smoke and break! Get the tension off the belt and manually rotate the blades (with Switch Off for safety) and see if there is any rough turning or binding. Could be a blade spindle bearing seizing up and until that is repaired it will continue to eat belts. By the time the belt starts smoking, it's usually too late to save it.