Belt Drives and Chain Drives

Belt Drives and Chain Drives - Belt Drives and Chain Drives...

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1 Belt Drives and Chain Drives Material comes for Mott, 2002 and Kurtz, 1999 Power Train A power train transmits power from an engine or motor to the load. Some of the most common power trains include: Flexible members • V-belt Synchronous belt • Roller-chain Power Train Rigid members • Gearing Drive shafts Other Components Shafts Bearings Springs Seals Universal joints Clutches Brakes Flywheels
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2 Belt Drive Belts Flat: use pulley Grooved: use sheaves Idler Does not transmit power Used to take up slack or change direction of rotation Key Belt Drive Design Characteristics 1. Environment 2. Load cycles 3. Service life 4. Belt characteristics 5. Sheave diameter and Center distance 6. Power requirements Belt Drives Rotary power is created by electric motor, combustion engines, wind mills, and etc. Motors generally operate too fast and deliver too low a torque to be appropriate for the final drive application. The torque is increased in proportion to the amount that rotational speed is reduced. The high speed of the motor makes belt drives good for the first stage of reduction.
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3 Belt Drives con’t** A smaller drive pulley (sheave) is attached to the motor shaft, while a larger diameter pulley is attached to a parallel shaft that operates at a correspondingly lower speed. If very large ratios of speed reduction are required in the drive, gear reducers are desirable because they can typically accomplish large reductions in a rather small package. Belt Drives con’t Gear reducers are only available at discrete reduction ratios, so the output may be adjusted before meeting the requirements of the machine. At the low-speed, high-torque condition, chain drives are desirable. The high torque causes high tensile forces to be developed in the chain. The links of the chain are engaged in toothed wheels (sprockets) to provide positive mechanical drive, needed at the low-speed, high-torque conditions.
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4 Basic Belt Drive Geometry Mott, 2003, Machine Elements in Mechanical Design Types of Belt Drives A belt is a flexible power transmission element that fits securely on a set of pulleys or sheaves. When the belt is used for speed reduction, the smaller sheave is mounted on the high- speed shaft, like the shaft of an electric motor. The larger sheave is then put on the driven machine. Types of Belt Drives con’t Many types of belts are available: The flat belt, the simplest type, is often made from leather or rubber-coated fabric. The sheave surface is also flat and smooth, limiting the driving force by the pure fiction between the belt and the sheave. Some designers prefer flat belts for delicate machinery because the belt slips if the torque rises to a high enough level to damage the machine.
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5 Types of Belt Drives con’t Synchronous belts, or timing belts, ride on sprockets that have mating grooves that the teeth on the belt seat. This is a positive drive, limited only by the tensile strength of the belt and the shear strength of the teeth.
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