Aug 7, 2018

Understanding Torque and Its Simplest Explanation

In the past few topics 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 term torque in simple words. So get a cup of coffee and sit back. Subscribe to Automation-Talk by Email.

Understanding Torque and Its Simplest Explanation

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 horsepower, but believe me the real driving force is TORQUE and not horsepower. In the simplest word torque is the twisting/rotational force exerted by the drive on the load. Now let us take a simple example.

Do you remember that sometimes 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 open? 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 open then give it to some stronger person!!

Well, the main motive behind the 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 open 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 the force as depicted on scale multiplied by the radius of the lid. For example, if the reading of force on the scale is 17 lbs( at the time of breakaway of lid) and the 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 lets 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 "Stiction". Stiction can be defined as the amount of torque required to make a load lose and start the first revolution. Stiction is nothing but only the second name of the breakaway torque and frankly speaking for every industrial application the breakaway torque requirement of any load is greater than the continuous torque requirement for running the machine.

The amount of "stiction" 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 is 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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