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Complete Guide To Design V-Belt Drive Systems With Calculators

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As you know that V-belt mechanisms are used for power transmissions between different shafts or between power generators and shafts. With a proper design and equipment selection for v-belt systems, power transmission can be done with torque conversion. Here the steps to design a v-belt system for machineries.

Steps To Design V-Belt Mechanism

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V-belts are common construction elements on internal combustion engines.

Step 1: Define the rated power for driving electric motor or shaft;

In v-belt systems, there is always a prime mover that gives the motion to system. This moving energy would come from an electric motor, or from a moving shaft. So, you need to define or know the rated power of this moving energy.

Step 2: Determine the ‘design power’ from rated power information;

If you have the power information of driving motor or shaft, you need to multiply it with a unitless number called as ‘service factor’ to obtain ‘design power’. The service factor is detemined according to some parameters;

  • Driven machinery type with designed V-belt mechanism,
  • Driving motor or mechanism type such AC or DC electric motors,
  • Hours that the designed V-belt system will be used.

Here you can see an example of V-belt service factor determination table according to parameters stated above;

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Table of service factor selection for V-belts(SRC: Machine Elements In Mechanical Design).

With this service factor, you need to multiply the rated power of driving mechanism to obtain ‘design power’.

Step 3: Standard V-belt selection;

You need to select a standard v-belt from catalogs that provided by v-belt producers. These catalogs are generally prepared according to changing design power and rpm of input(smaller) sheave.

We introduce an example catalog that you can select your v-belt. There are dozens of catalogs are avaliable from v-belt producers.

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Example of standard V-Belt selection table(SRC: Machine Elements In Mechanical Design).

Select the standard V-belt according to the design power and speed of faster shaft.

Step 4: Determine the diameters of sheaves according to input and output speeds;

According to these input and output sheave speeds in terms of rpm, you need to determine sheave diameter. So, belt speed must known. If you belt speed is known;

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You can determine the input sheave diameter from the formula above. Input Speed per Output Speed gives the belt ratio. By using this ratio, you can find D2 which is the diameter of second output sheave.

Step 5: Select standard sheave sizes from catalogues;

You can find the standard driving sheave size from sheave catalogues, which is close to the found diameter. Deviations around 1-2% is not problem.

Make the same thing for driven sheave, and compare the output powers. Deviations of 1-2% are not important.

Step 6: Determine the power rate of the selected v-belt;

Power rate of a belt means that the power that a belt can carry. This is obtained by using special graphs that you can find the power rate with the informations of small sheave pitch diameter and rpm of small sheave.

We gave an example of power rates for 3V belts below;

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Rated power table example((SRC: Machine Elements In Mechanical Design).

As you can see above, you need to specify your pitch diameter at the x axis of graph, and find the related rpm interval. You can find the power rate at y axis.

Step 7: Specify a proper center distance(C) between sheaves;

In general, the proper range for C is given as;

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According to your sheave diameters that you specified before, specify a proper C inside this range.

Step 8: Compute the required belt length and determine standard belt length;

In belt catalogues that you selected your v-belt from them, you can find the standard v-belt lengths.

You can compute your required belt length from the calculator avaliable in given link easilly.

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Example of belt length standards((SRC: Machine Elements In Mechanical Design).

For example, you found the length requirement of 5V v-belt must be 101,5 in. The nearest value for this is the 100 as you see above table.

Step 9: Re-calculate center distance of sheaves with this standart v-belt length;

With the information of belt length(L) that you found above, you can re-calculate the center distance which must be inside the speciefied range.

Click on given link to open center distance(C) calculator avaliable in Mechanical Base.

Step 10: Calculate wrapping angles of v-belt on big and small sheaves;

The wrapping angle information is very important to find the required correction factors to calculate the number of belts required in v-belt system. You can calculate the wrap angles of sheaves by using its calculator avaliable in Mechanical Base.

Step 11: Determine the correction factors;

Different kinds of correction factors can be obtained to multiply them with rated power of selected standard v-belt.

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Wrap angle correction graph example(SRC: Machine Elements In Mechanical Design).

For example, you can specify a correction factor with the information of angle of wrap above.

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Belt length correction factor graph example(SRC: Machine Elements In Mechanical Design).

Also you can determine belt length correction factor like above example. Use the standrd belt length(L) that you specified.

Step 12: Find the corrected power rate and number v-belts required;

We found the power rate. of the v-belt in step 6. Multiply the correction factors that you found in step 11 with the power rate to find corrected power rate of selected standard v-belt.

Divide the design power with corrected power rate of v-belt. For example if you found 2.71, you must use 3 of selected standard v-belt in system.

Important Points To Remember In The Design Of V-Belt System

  • In the installation phase of v-belt system, an initial tension must provided that recommended by v-belt manufacturer.
  • The temperature of environment that the v-belt system is used must between the recommended temperatures.
  • Wrap angle of small sheave must bigger than 120 degrees because of the problems may occur(slipping) in service time below 120 degrees.
  • In the installment of v-belt system, center distances must be decreased to attach the v-belts easily.
  • If the belt speed is less that 1000ft/min, you need to use another kinds of constructions such as gear systems, chain systems etc.
  • Alignment of sheaves is an important thing for proper working of v-belt system. Sheaves must be on same direction and parallel.

These are the general information about the v-belt system design according to the environmental parameters.

In your calculationsi take a special care about your units. Use of proper sets of units is very important. You can use MB-Unit Converter tool to obtain proper sets of units by converting your units inside it.

Do not forget to leave your comments and questions about v-belt design below. Your precious feedbacks are very important for us.

Take a look at the other engineering calculators avaliable in Mechanical Base!

Source Of Graphs And Tables: Robert L. Mott – Machine Elements For Mechanical Design

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