Jul 26, 2012

Understanding Torque and Its Simplest Explanation

In the past few topic of AC Motor basics we have seen about general motor terms,
different types of motor load and the Calculation of Synchronous speed from Poles. We all frequently use term called Torque in our day to day work life. But do we really know the actual meaning of Torque. We got many request from our readers to explain the torque in simple words. So get a cup of coffee and sit back. Subscribe to Automation-Talk by Email.

What does Torque Signify

In our industrial applications when we have to select the driving motor for any load we are always concerned about the horse power , but believe me the real driving force is TORQUE and not horse power. In the simplest word torque is the twisting/rotational force exerted by drive on the load. Now let us take a simple example. Do you remember that some time you try to open the lid/or open a bottle but after so many tries it does not open. Do you know the reason why it doesn't opened? Because we are unable to supply or apply the adequate torque to open the lid. The solution for this can be a)grit our teeth and try harder, b)use a rubber pad, or cloth, to increase the ability to transmit torque without slippage, or c) use a mechanical device to help multiply our torque producing capability. If still it doesn't opens then give it to some stronger person !!

Well the main motive behind above example was just to make u feel something about torque. We are always confused among HP and Torque. Now let us suppose that after so much try also the lid did not opened and now we will wrap a cord around the lid and supply a force to the end of the cord through a scale. See the below diagram.



Example for Torque Calculation :-

Can we tell the torque required in this case? Yes we can , the torque requirement will be force as depicted on scale multiplied by the radius of the lid. For example if the reading of force on scale is 17 lbs( at the time of breakaway of lid)and radius is 3 inches then the torque requirement would be :-
T = F * R = 17 * 3 = 51 lb.inches


Simplest Explanation of Torque :-

However the above example gives a clear illustration of the torque but let us discuss one more thing which is observed in industrial applications. If we recall the above example then we can derive one more term called “Sticksion”. Sticksion can be defined as the amount of torque required to make a load lose and start the first revolution. Sticksion is nothing but only the second name of the break away torque and frankly speaking for every industrial application the break away torque requirement of any load is greater than the continuous torque requirement for running the machine.


The amount of “sticksion” present in a machine will be dependent on the characteristics of the machine as well as the type of bearings that are used on the moving parts. Below you can see a picture in which the breakaway torque requirement of different machines are shown.



So we have got now a clear view of the torque and its characteristics , in the next few days we will try to see more different types of torques and detailed explanation of torque in a simple way. Till then you can subscribe to get all latest updates via Email.

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