In most of hot/cold rolling process manuals, torque for each roll is calculated as the product of the rolling force (acting in the center of the contact length) by half the contact length. AFAIK, torque is the product of a force by the distance separating that force from the rotation axis, so naturally shouldn’t this distance be the radius roll instead? What am I missing? (It makes me even more confused when contact zone accounts for the width as well (3D))
In: Engineering
Not an industrial engineer but I touched on this before I specialised in my degree so I’ll have a go at explaining. The process of rolling a sheet of metal thinner includes a change in velocity. Since the volume of the metal is conserved, the thicker sheet comes in slower than the thinner sheet goes out. The speed of the roller is somewhere in the middle, so the roller is too fast for the thick sheet and too slow for the fast sheet. This creates a lot of friction in the contact length.
Now, how can this effect be seen to effect torque? The neutral plane (the point at which the rolling force acts, and also the point where the roller speed matches the material speed) is moved upstream of the roller axle. The torque is given by rolling force multiplied by distance to the neutral plane, the neutral plane position depending on the length of the contact patch. Longer contact patch, neutral plane is further ahead of the axle.
For sheet metal, the torque calculated will be torque per unit width, so you have to multiply by the width of the material to get pure torque.
I hope this helps but please let me know if there’s anything that still isn’t clear. I also welcome corrections / further explanations from those with actual credentials in the field.
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