Reducers, worm gears

One of the major advantages of the worm gear is low wear, which is due mostly to a full-fluid lubricant film. In addition, friction can be further reduced using metals having low coefficients of friction. For example, the wheel is typically made of bronze and the worm of highly finished hardened steel. 

The high-speed drive motor is coupled to the low-speed screw with a reducer or gearbox. Typical reduction rations are 15 1 or 20 1. Although helical gears are most common, worm gears are used on older or very small machines. 

Compounded Oils. These are usually petroleum-based oik containing 3 to 5 percent fatty or synthetic fatty oik (usually animal fat or acidless tallow). They are usually used for worm-gear lubrication, where the fatty content helps reduce the friction generated nnder high-sliding conditions. 

Other types of motors that may be encountered in mixer applications are gear motors, pony motors, and brake motors. Gear motors are composed of an electric motor with an attached gear reducer. Spur, helical, or worm gears can be used in single or multiple reductions to achieve a wide range of output speeds. Motor power, output speed, and output torque are all essential design variables. 

Worm-gear reducers are very compact, requiring less space than belts, chains, or trains of open gearing. The right-angle drive often permits compact placement of the driving and driven machines. Since three or more teeth are always in contact. 

Thermal ratings of cylindrical worm gears. Thermal ratings above 100- to 200-rpm worm speed represent the input horsepower and output torque that will provide a stabilized 100°F oil-temperature rise over ambient air temperature when the machine is operated continuously. For example, if the ambient air temperature is 70°F, a reducer carr3dng rated thermal horsepower will operate with an average oil... 

Allowable starting load. Worm-gear reducers have a momentary overload strength rating -i- 300 percent of mechanical-wear rating. Peak starting load of the driven machine should not exceed 300 percent of the mechanical-wear rating. 

Special reducers. Special reducers in various combinations are also available. An example is presented in Fig. P-29, which shows a large vertical-output-shaft imit with a single worm reduction having 38-in gear centers, which is used in pulverized-coal service. 

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