Key Concepts of Belt Drives and Mechanics

BELT DRIVES

  • Belts transmit power between shafts using pulleys.
  • Power transmission depends on:
    • Velocity of the belt.
    • Tension on the belt.
    • Arc of contact on smaller pulley.
    • Operating conditions of the belt.

SHAFT AND PULLEY ALIGNMENT

  • Shafts must be aligned for uniform tension.
  • Distance between pulleys affects arc of contact.

BELT SWINGING AND SAGS

  • Long belts may swing causing misalignment.
  • Tight side should be at the bottom for better contact.

TYPES OF BELTS

  • Flat Belt: Suitable for moderate power, max 8m distance.
  • V-belt: Used for close pulleys with moderate power.
  • Circular Belt: Handles large power over distances > 8m.

POWER TRANSMISSION

  • Power transmitted = (T1 - T2) * r * v,
    • Where T1 and T2 = tensions in tight and slack sides.

VELOCITY RATIO

  • Ratio of velocities: V=V<em>2V</em>1V = \frac{V<em>2}{V</em>1}.
  • With thickness, include belt thickness in calculations.

BELT SLIP

  • Slip reduces velocity ratio, expressed as a percentage.
  • Formulas:
    • v<em>1=2πr</em>160(1−S1100)v<em>1 = \frac{2 \pi r</em>1}{60}(1 - \frac{S_1}{100})
    • v<em>2=2πr</em>260(1−S2100)v<em>2 = \frac{2 \pi r</em>2}{60}(1 - \frac{S_2}{100}).

CREEP OF BELT

  • Creep affects speed when belt transitions tight to slack side.
  • Adjusts velocity ratio with varying stress across the belt.

LENGTH OF BELT DRIVE

  • Open belt length = L=2(r<em>1+r</em>2+d)L = 2(r<em>1 + r</em>2 + d),
    • Where d = distance between pulley centers.

TENSIONS IN BELT

  • Centrifugal tension is critical at high speeds (>10 m/s).
  • Calculated: Tc=mv2T_c = mv^2.

INITIAL TENSION

  • Required for grip between the belt and pulleys even at rest.
  • Increase adjusts tension balance across both sides.