MECH 3440-Notes 4 - Gear Reducers

Card Set Information

Author:
mackoy
ID:
138400
Filename:
MECH 3440-Notes 4 - Gear Reducers
Updated:
2012-02-28 12:54:18
Tags:
Gear Reducers
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Description:
Gear Reducers
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  1. Gear Reducers
    - A packaged mechanical power transmission unit with output shaft speed lower than input shaft speed with power being transmitted by means of one or more geared stages
  2. Advantages of Gear Reducers
    • • positive drive
    • • compact
    • • resistant to hostile environment
    • • wide range of ratios possible (clock, ship)
    • • available in very small to very large sizes
  3. disadvantages of Gear Reducers
    • - can not avoid the harmonic vibration
    • - some difficulties for the installation of the gear drives
    • - Belt alignment issues
    • - oil leak
    • - water intrusion
  4. Basic Construction of Gear Reducer
    • - input shaft
    • - output shaft
    • - housing
    • - bearing
    • - oil seal
    • - overhung load
  5. Overhung Loads OHL
    • - Overhung loads act on the shaft extensions when belt pulleys, chain sprockets or gears/ pinions are mounted on them to transmit power.
    • - Misalignment between two coupled shafts can also give rise to overhung loads
    • - Overhung loads on shafts result in bending moments and additional radial loads on the supporting bearings
  6. Reducing the effects of overhung loads
    • 1. Using pulley, sprocket, pinion etc. of the largest possible diameter
    • 2. locate them as close to the reducer as possible.
    • 3. When belt transmission is used, the belt tensions should be maintained just sufficient to ensure operation without slippage.
    • 4. Direct coupling the load with the appropriate coupling type
    • 5. Use outboard bearings to support the shaft and offset the OHL
  7. Classifying Gear Reducers
    • 1. By Gear Type
    • – spur gears
    • – helical / herringbone
    • – worm
    • – combinations of these

    • 2. By Configuration
    • – parallel shaft
    • – right angle
    • – vertical shaft

    • 3. By Mounting
    • – base mounted
    • – shaft mounted (needs a torqe arm)
  8. Mechanical Rating vs Thermal Rating
    • Mechanical Rating
    • - gives horsepower capability at unit service factor based on strength or durability for a statistical life expectancy

    • Thermal Rating
    • - gives a horsepower capability for continuous running with 100 F temp rise
    • - thermal rating may be increased by built-in fan

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