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How to Determine Belt Needs
Click here for power ratings for PowerTwist Plus, NuTLink and SuperTLink belting
Service Factors (Table 1)
Arc of Contact Correction Factor (K) for V-Belt Drives (Table 2)
Belt Length Correction Factors (LC) (Table 3)
This page offers some information on how to determine the belt type for a particular drive. Before you can proceed, you need to know the following four things:
1. The type of application or driven machine. 2. The type of prime mover, its HP rating and RPM. 3. The speed of the driven machine or speed ratio. 4. The approximate center distance between shafts. |
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Step 1. Find the Design Horsepower
- From Table 1 we select 1.2 SF, i.e. NEMA A motor, Fan up to 7.5 kW
- DkW = 5.5 kW x 1.2 SF = 6.6 DkW
Step 2. Review the Drive
- Calculate the speed ratio. This is large diameter divided by small diameter.
170mm ÷ 140mm = 1.21:1
- Calculate Belt kW Rating
- Refer to the NuTLink power rating table for “B/17” cross section belt. Using the faster shaft RPM of 1450, read across to column headed 140mm and find 4.62. This is the basic kW rating. Read across on the same line under the Add-on Kilowatt rating section, in column headed 1.21 to 1.27, read .12. Adding .12 to 4.62 gives 4.74 rated kW per belt.
- Determine the Arc of Contact Correction Factor
- Calculate (D - d) ÷ C and find factor KØ from Table 2.
Where: D = 170mm, d = 140mm and C = 560mm
(170mm - 140mm) ÷ 560 = 0.06
Factor KØ is 1.00.
- Determine Belt Length and Length Correction Factor (LC) 1. Using the formula below calculate the belt length and from Table 3 find the Length Correction Factor (LC).
Where: D = 170mm, d = 140mm and C = 560mm
Belt Length = 1608mm
From Table 3, under “B/17” cross section and between a 1540mm and 1730mm
belt factor LC is .93.
![Belt Length = 2C + 1.57 (D+d) + [(D-d)2/4C]](../assets/belt_calc.gif){kind=small}
- Calculate Corrected kW per Belt
1. Corrected kW per Belt = Rated kW per belt x Factor KØ x Factor LC
Corrected kW per Belt = 4.62 x 1.00 x .93 = 4.30
Step 3. Find the Number of Belts Required
- Divide the Design Kilowatt power by the Corrected Kilowatt power per belt to find the number of belts required. The answer will usually contain a fraction; therefore always round up to the next whole number of belts. DkW ÷ CkW = 6.6 ÷ 4.30 = 1.53.
Two NuTLink V-Belts are okay for the application.
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