How Do You Calculate Torque for an Anchor Type Agitator Motor?

AI Thread Summary
To calculate the torque for an anchor type agitator motor, the maximum or startup torque should consider the moment of inertia, angular acceleration, drag force, and frictional forces. The analysis suggests that for scraping crust, acceleration torque can be ignored, focusing instead on the force required to cut through the crust. Since there are no published values for this force, conducting experiments to measure the scraping force is recommended. It is also advised to incorporate a safety factor based on the worst-case scenario. Understanding the operational conditions of the agitator is crucial for accurate torque calculations.
Nickf_Zar
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Calculating the torque required for an agitator/scraper.
Hi All,

I must calculate the torque and for an agitator motor. An anchor type agitator/scraper, removing crust off the edge of a tank.

My instinct is the max or startup torque will be = (Moment of Inertia) x (Angular Acceleration) + (Drag force of the submerged impeller)* Max radius + (Frictional forces on the edge of the tank)* Max Radius

Tmax = ( I * α ) + [ ( Cd * A * ρ * V² * ½ ) + (µ * F) ] * D/2

• The motor has a soft start but is operated at constant RPM.
• The idea is to get a worst-case scenario to design from.
• Please suggest if you think this problem can be solved with a better solution.

I have very little experience with this type of stuff and would greatly the feedback.

My Questions to the community

• Is this analysis correct?
• What would be an acceptable coefficient of drag to use for a plate with cut-outs in it without doing an experiment
• What would be an acceptable coefficient of friction to use, for the solidified sealing compound attached to the walls?

Thank you
 

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Nickf_Zar said:
I must calculate the torque and for an agitator motor. An anchor type agitator/scraper, removing crust off the edge of a tank.
If it's scraping crust, then it's a slow speed machine, and you can ignore the acceleration torque. Scraping crust is not a friction problem, it's a "cutting through the crust" problem. There are no published numbers for the force to do this, so you need to run some experiments. One possible experiment is to pull a hand scraper with a spring scale to directly measure the scraping force. Do your best to measure the worst case force, then add a substantial safety factor.
 
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How the material could solidify if the agitator is constantly working?
Or it is the case that the agitator is only activated after the solidification occurs?
 
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