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 are the steps to design a v-belt system for types of machinery.
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Steps To Design V-Belt Mechanism
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 the system. This moving energy would come from an electric motor or 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 the driving motor or shaft, you need to multiply it with a unitless number called ‘service factor’ to obtain ‘design power’. The service factor is determined 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;
With this service factor, you need to multiply the rated power of the driving mechanism to obtain ‘design power’.
Step 3: Standard V-belt selection;
You need to select a standard v-belt from catalogs provided by v-belt producers. These catalogs are generally prepared according to changing design power and rpm of the input(smaller) sheave.
We introduce an example catalog that you can select your v-belt. There are dozens of catalogs are available from v-belt producers.
Select the standard V-belt according to the design power and speed of the 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 be known. If your belt speed is known;
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 the second output sheave.
Step 5: Select standard sheave sizes from catalogs;
You can find the standard driving sheave size from sheave catalogs, which is close to the found diameter. Deviations around 1-2% are no 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;
The 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 information of small sheave pitch diameter and rpm of the small sheave.
We gave an example of power rates for 3V belts below;
As you can see above, you need to specify your pitch diameter at the x-axis of the graph and find the related rpm interval. You can find the power rate on the y-axis.
Step 7: Specify a proper center distance(C) between sheaves;
In general, the proper range for C is given as;
According to the 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 catalogs 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 calculatoravailable in the given link easily.
For example, you found the length requirement of 5V v-belt must be 101,5 in. The nearest value for this is 100 as you see above table.
Step 9: Re-calculate center distance of sheaves with this standard 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 specified range.
Click on the given link to open the center distance(C) calculator available in Mechanicalland.
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 the v-belt system. You can calculate the wrap angles of sheaves by using its calculator available in Mechanicalland.
Step 11: Determine the correction factors;
Different kinds of correction factors can be obtained to multiply them with the rated power of the selected standard v-belt.
For example, you can specify a correction factor with the information of the angle of wrap above.
Also, you can determine the belt length correction factor-like the above example. Use the standard belt length(L) that you specified.
Step 12: Find the corrected power rate and number of 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 the corrected power rate of the selected standard v-belt.
Divide the design power with the corrected power rate of the v-belt. For example, if you found 2.71, you must use 3 of the selected standard v-belt in the system.
Important Points To Remember In The Design Of V-Belt System
- In the installation phase of the v-belt system, an initial tension must be provided that is recommended by the v-belt manufacturer.
- The temperature of the environment that the v-belt system is used must be between the recommended temperatures.
- Wrap angle of small sheave must be bigger than 120 degrees because the problems may occur(slipping) in-service time below 120 degrees.
- In the installment of the v-belt system, center distances must be decreased to attach the v-belts easily.
- If the belt speed is less than 1000ft/min, you need to use other kinds of constructions such as gear systems, chain systems, etc.
- The alignment of sheaves is an important thing for the proper working of the v-belt system. Sheaves must be in the same direction and parallel.
This is the general information about the v-belt system design according to the environmental parameters.
In your calculations take special care of your units. The use of proper sets of units is very important.
Do not forget to leave your comments and questions about the v-belt design below. Your precious feedbacks are very important for us.
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Source Of Graphs And Tables: Robert L. Mott – Machine Elements For Mechanical Design