Flat Belt Basics: Subtle Adjustments Contribute to Efficient Belt Operation
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Leather belts should be run with the hair (smooth) side toward the pulley and must be kept clean and flexible. The old belt dressing contained a good deal of resin, along with cod-liver and neat’s-foot oil (I looked up the ingredients in modern spray-on belt dressings and it’s a bunch of obscure chemicals that I don’t recognize). Rubber belts shouldn’t need any dressing as they shouldn’t slip if tight enough. In fact, sticky belt dressings have a tendency to pull off the outer layer of rubber and hasten the deterioration of a rubber belt. All belts should be kept clean and free of oil and grease. Leather belts should not be allowed to get wet.
Right side up
When a belt is running under load, there is a tight side and a slack side to the belt preventing transmission of 100 percent of the power. The tight side stretches under the tension, while the slack side contracts, resulting in belt creep, which is normal and is not the same as belt slip, the result of improper tensioning of the belt.
Belts should be run only tight enough to prevent slippage. A long belt doesn’t need to be as tight as a short belt because of its weight. If a belt is run too tight, however, it puts undue strain on the belt, pulleys, shafts and bearings. On the other hand, a loose belt has a tendency to flap and is easily thrown off if a sudden load is encountered. In the old days of steam threshing engines, the threat of fire from exhaust sparks was serious. Belts were long (as much as 150 feet) in order to keep the engine as far from the separator as possible. With gas or oil tractors, the possibility of exhaust sparks is much less and a 50-foot belt is plenty long enough; I’ve run a thresher with a 25-foot belt, and short belts are commonly used on hammer mills and silo fillers.
If possible, the lower side of a belt should be the driving side. The direction in which the machine must be run and the direction of the driving pulley must be taken into consideration. If necessary, the direction may be reversed by putting one twist in the belt, which also helps keep a long belt from flapping in a cross wind. However an uncrossed belt is more efficient as both heat and friction are generated at the point where the two sides of a crossed belt rub together.