MECH 3440-Notes 2 - Belt Drives (2 of 2)

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MECH 3440-Notes 2 - Belt Drives (2 of 2)
2012-01-31 12:57:50
Mechanical Equipment BCIT

Belt Drives
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  1. Contributors to Stress in a Belt?
  2. Slip and Creep in Belts?
    = Operating V belts drives are subject to two ‘slipping’ phenomena

  3. Creep
    • = A V-belt under proper tension creeps ahead about .5% due to its elasticity and changes in cross section and length as the belt moves from the tight side of the drive to the looser side and back.
    • = The heat created by creep is of a magnitude which can be dissipated by the sheaves
    • = therefore, V belt drives cannot be used for synchronous or timing applications
  4. Slip
    • Excessive slip is caused by poorly designed or maintained drives where:
    • 1. driving pulley is too small
    • 2. load is too great
    • 3. belt is running too loose
    • 4. belt is not being properly cleaned (glazing)and maintained
  5. Slip can be controlled by?
    • using smaller sheave ratios (angle of contact)
    • ensuring the sheaves are aligned correctly
    • ensuring adequate take-up is available (motorbrackets, idlers) to allow correct belt tension.
    • ensuring the sheaves aren’t worn to the point of bottom V belt contact
  6. Belt Tensioning Techniques
    • slotted motor mounts
    • use of an idler sheave

    Note the belt guard: protective yet ventilated
  7. Idler Sheaves 2 Main Purpose?
    • 1. increase arc of contact
    • 2. act as a belt tensioner for belt drives without a moveable unit.

  8. Measuring Belt Tension?
  9. Run-in period?
    Note: A new belt should have a 12 to 24 hour run-in period. It should then be retensioned to the manufacturer’sspecifications.
  10. The two most common causes of misalignment?
  11. V-Belt Types, Sizes and Codes
    There is an industry standard for belt section sizes and angles so that belts from different suppliers can be used on the same sheaves.

  12. V Belt Types
  13. Cog type
  14. PowerBand® Belt
  15. Serpentine Belt
  16. Synchronous Belt Drive BENEFITS...
  17. Attaching a Sheave to a Shaft
  18. Common Problems of Belts?
    • cracking – heat and/or age related
    • glazing - worn belt grooves
  19. Maintaining Healthy Belt Drives
  20. Belt & Sheave Groove Gauges
  21. V-Belt Bill of Material as solutions to probems...