Controlling the roation speed of main roll

I explained that the rotation speed of the main roll is constant in the ring rolling machine(Rotation speed control of axial roll).

But it isn’t constant in the CALTEK ring mill.

I’ll tell you why the rotation speed of the main motor is not constant in our ring mill.


Increasing the rotation speed of the roll during rolling can reduce the rolling force because the coefficient of friction between the roll and the workpiece becomes smaller.  That’s why I always ask the ring mill operators to make the rotation speed of the main roll as fast as possible.  However, if the size of the ring is small, the ringmill operator should not rotate the main motor in the maximum speed.

I’ll explain the reason with this ring mill belows:

* Main motor rpm : 0 ~1,200

* Main roll gear box reducer ratio : 1/40

* Axial roll cone angle : 40

* Axial roll gear box reducer ratio : 1/10

* Axial motor rpm : 0~1,400

* TR range : 200~600

Tis is a graph of the rotational speed of the axial motor according to the TR value when the main motor rotational speed is 1,200 rpm.  You can see how to calculate the axial motor rpm in this post Axial motor rpm control.

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If the TR value is less than 310, the rotation speed of the axial motor should be 1,400 or more.

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However, the maximum rotational speed of the axial motor of this ring mill is 1,400 rpm.  If the ring size is small and the TR is less than 310, the axial motor will not rotate at the commanded rotation speed.  In this case, the linear velocity of the axial roll does not match the linear velocity of the main roll, which can cause problems with the quality of the ring.  Also, there is a slip between the main roll and the ring or between the axial roll and the ring, which increases the wear of the rolls.

So what should a ring mill operator do for a ring with TR less than 310?  In this case, the ring mill user must reduce main motor rpm. 

When TR is 300 and main motor rpm is 1,200, the command ratation speed for the axial motor exceeds the maximum rotation speed of the axial motor.

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However, if we reduce the speed of the main motor to 1,100 rpm, the command speed of the axial motor will be less than 1,400.

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Most ring mill operators are unaware of this.  A typical ring-mill facility allows the user to adjust the rpm of the main motor.  But most ring-mill operators rotate the main motor's rpm at a constant speed and do not care about it.  I often get a call from the engineer of a company that uses a large ring mill, such as Φ7,000 ring mill, to report that the ring is defective when producing a small ring.  When I get these calls and go to the on-site technical support, I find that most of the problems have occurred because the ringmill operators have not adjusted the rpm of the main motor while producing a small ring.


So I developed a function that automatically adjusts the rpm of the main motor according to the size of the ring.

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Depending on the size of the ring, the ring mill operating program automatically adjusts the rpm of the main motor so that the command rpm of the axial motor does not exceed the maximum specification rpm of the axial motor.  The ring mill operator can concentrate more on the ring production because the operator does not have to adjust the rotation speed of the main motor, whether the ring is small or large.

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Only CALTEK ring mill has this feature.  I have patents on this feature.


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