technical data Synchronous Belts and Belt Sprockets Selection

Selection by power source/Selection example

Items required for selection

The items required for selection are as follows. Please define the conditions for each.

  • - Motor output (kW), output shaft rotation speed r/min, shaft diameter
  • - Type of driven machine, rotation speed r/min, shaft diameter
  • ・Center distance
  • - Daily usage time and startup frequency
  • ・Speed ratio
  • - Whether or not an idler is used
  • - Other conditions (layout constraints)

Determining design power

The design power is calculated using the following formula.

Pd = Pk × (Ko + Ki + Ks) × Ka × Ke※

*Transmitted power is the power to be transmitted, and is usually expressed as the prime mover output. However, if the actual transmitted power (actual load) is known, use that value.

*When using Ultra PX Belt HA specification (oil/water resistant) in an environment where it may be exposed to oil or water, or when using PX Belt water resistant specification in an environment where it may be exposed to water, multiply the operating atmosphere coefficient (Ke) by 1.2.

Determining belt size and pulley tooth count

  • (1) Use the provisional selection table to provisionally select a belt size based on the design power and pinion rotation speed.
  • (2) Please provisionally select the belt width and the number of teeth of the pinion pulley from the standard transmission capacity table in the Product Info. When doing so, please note the following:
    • - Select a pinion tooth number other than the colored part of the standard transmission capacity.
    • - Select a small pulley so that its pitch diameter is greater than the belt width.
    • - Make sure that the usable range of the small pulley shaft hole satisfies the diameter of the shaft being used.
  • (3) Determine the number of teeth on the large pulley based on the number of teeth on the small pulley and the speed ratio. Also, check the shaft bore diameter to be used.

Selection of belt length and center distance

  • (1) Calculate the approximate length of the belt (L') and select the belt with the closest length to this value from the belt length list.

    L'= 2C + 1.57 (Dp + dp) + (Dp - dp)2 4C

    • L': Approximate belt length mm
    • C: Center distance mm
    • Dp: Large pulley pitch circle diameter mm
    • dp: Pitch circle diameter of small pulley mm
  • (2) Calculate the center distance (C) from the selected belt length (L).

    C = B + B2 - 2(Dp - dp)2 4

    B = L - 1.57(Dp + dp)

    • L: Belt length mm

Correction by number of meshing teeth

It is not recommended to use a pulley with less than six meshing teeth, but if you must use one, please make adjustments based on the number of meshing teeth.

After determining the number of teeth in mesh, determine the meshing correction factor using Table 6.

Also, design the meshing angle so that the drive pulley is 120° or more and the driven pulley is 90° or more.

Zm = N × Φ 360°

Φ = 180° - 57°(Dp - dp) C

  • Zm: Number of meshing teeth on pinion
  • N: Number of teeth on pinion pulley
  • Φ: Belt winding angle around the small pulley (degrees)
  • Dp: Large pulley pitch circle diameter mm
  • dp: Pitch circle diameter of small pulley mm

Checking the belt width

Check that the belt width satisfies the design power.

Pd ≦ Pu × Kw × Km × KL

Kw ≧ Pd Pu × Km × KL

sizing example (selection based on power)

Items required for selection

The items required for selection are as follows:

item Content
Motor output, rotation speed, shaft diameter 5.5kW (peak torque 200%), 1450 r/min, 32mm
Type of driven machine, rotation speed, shaft diameter Pump, 920 r/min, 30mm
Center distance 415mm
Daily usage time and startup frequency 12 hours/day, 100 times/day
speed ratio 1:1.58 deceleration
Whether or not an idler is used Located on the back of the loose side
Other terms The small pulley has an outer diameter of 100 mm or less due to the layout.

Determining design power

The design power is determined by finding the correction coefficients that suit the operating conditions from the table.

  • Load correction factor (Ko) ..... 1.5
  • Correction factor when using idler (Ki) ..... 0.1
  • Acceleration correction factor (Ks) ..... 0
  • Start-stop frequency correction factor (Ka) ..... 1.3
  • Design power Pd = Pk × (Ko + Ki + Ks) × Ka = 5.5 × (1.5 + 0.1 + 0) × 1.3 = 11.44
    Therefore, the design power is 11.44kW.

Determining belt size and pulley tooth count

  • (1) Temporarily select the belt size from the temporary selection table. In this case, P8M-RC is tentatively selected based on the design power (11.44 kW) and motor rotation speed (1450 r/min).
  • (2) Select the belt width and number of pulley teeth from the standard transmission capacity table, taking into consideration the speed ratio, shaft diameters of the prime mover and driven machine, and other conditions.
    Here, we select P8M60-RC (belt width 60 mm) with 28 teeth (dp = 71.30 mm) and 44 teeth (Dp = 112.05 mm). Refer to the dimensions of each pulley.

Determining belt length and center distance

  • (1) Calculate the approximate length of the belt (L').

    L' = 2C + 1.57(Dp + dp) + (Dp - dp )2 4C = 2 × 415 + 1.57(112.05 + 71.30) + (112.05 - 71.30)2 4 × 415 = 1118.86mm

    The belt that comes closest to this approximate length is 1120P8M (140 teeth) from the list of types and dimensions.

  • (2) Calculate the center distance (C) at this time.

    B = L - 1.57(Dp + dp) = 1120 - 1.57(112.05 + 71.30) = 832.14

    C = B + B2 - 2(Dp - dp)2 4 = 832.14 + 832.142 - 2(112.05 - 71.30)2 4 = 415.57mm

Correction by number of meshing teeth

Determine the number of belt teeth that mesh with the pinion pulley and determine the meshing correction coefficient.

Φ = 180° - 57°(Dp - dp) C = 180° - 57°(112.05 - 71.30) 415.57 = 174.41°

Zm = N × Φ 360° = 28 × 174.41 360° = 13.6 teeth

Therefore, the meshing correction coefficient is 1.0 according to the table.

Determining the belt width

The belt width that satisfies the design power is finally determined.

Kw ≧ Pd Pu × Km × KL = 11.44 3.15 × 1.0 × 1.0 = 3.64

Therefore, the belt that satisfies the width factor is P8M60 (belt width 60 mm).

Selection results

  • Belt: BG1120P8M60-RC
  • Small pulley: PT28P8M60AF or BF
  • Large pulley: PT44P8M60AF or BF
  • Center distance: 415.57mm

After deciding on the pulley model number, you can select the pulley fastening method.

Please also refer to the calculation formula used for belt selection.