Controlling the movement of the axial stand in the ring mill

Two steps to control the movement of the axial stand in the ring mill

We know what the axial stand is and how it moves(Movement of the axial stand in the ring mill).  As we know, the axial stand moves backward as the ring grows.  And now I’ll explain how the ring rolling machine developers like me control the axial stand’s movement.  You may not be a ring rolling machine develper, but it could be helpful to troubleshoot the problems with axial stand’s movement if you understand how it works and is being controlled.


When the vertex of the axial roll coincides with the center of the ring, there’s no slip between the ring and the roll(main roll or axial roll).   So we control the position of the axial stand to be coincided with the center of the ring.  But when the ring grows and reaches the maximun range of the axial roll, we cannot make the vertex of the axial roll be coincided with the center of the ring.  We need to change the way we control the stand’s movement at this point.

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The axial stand’s movement is divided into two steps by the OD(Outer Diameter) size of the ring and the effective length of the axial roll. 


EL, Effective length of the axial roll

The EL(effective length of an axial roll) means the maximum length of the axial cone’s surface through which the ring can be passed.  That is, the maximum length of the axial cone from the vertex of the axial roll to the point where the ring can pass through the axial roll.

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The two steps of controlling the axial stand’s movement

The axial stand’s movement is divided into two steps as follows:

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Controlling the movement of the axial stand in step 1.

In the first step, the ring mill program controls the position of the axial stand so that the vertex of the axial roll coincides with the center of the ring.

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The OD dimension is the sum of the position encoder values of the AS(Axial Stand) and the TR(Tracer Roll) (Measuring the dimension of the ring). 

OD=AS+TR (eq 1)

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When the vertex of the axial roll matches the center point of the ring, the encoder value of the axial stand is half of the OD

OD=2*AS (eq 2)

We can see that the encoder value of the axial stand is same as that of the TR when the vertex of the axial roll matches the center point of the ring.

AS=TR

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We control the position of the axial stand by the PID control.  We put the TR as the setpoint and AS as the output.

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It’s not easy to control the axial stand’s position because the setpoint TR value changes continuously as the ring grows.

The axial stand moves at the half speed of the ring’s growth rate in step 1.  If the ring grows by 2 mm, the center of the ring moves 1 mm and axial stand also moves 1 mm.

VAS=VOD/2

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Controlling the movement of the axial stand in step 2.

The OD of ring will reach at the limit of the effective length of the axial roll because ring grows faster than axial stand’s moving speed.  We need to change the way to control the axial stand’s movement at this moment because we have a limited length of axial roll(EL, effective length of the axial roll).

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Axial stand moves at the same speed of ring from this moment.  Ring passes through the same point of the axial roll.  TR encoder value is always same as the EL in Step 2.  As ring rollig goes, ring will grow and push the TR to the axial stand direction.  And axial stand will move and TR will go back to the EL position.  This cycle will be repeated in Step 2.

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I’ll take an example of a ring with 1,000 mm OD.

Suppose the ring reaches the effective length of the axial roll with 1,000 mm OD.

This means TR reaches the effective length of the axial roll and TR encoder value is 500 mm.

AS encoder value must be 500 mm.(OD=TR+AS)

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Ring rolling continues and ring grows.  Ring pushes the TR to the axial stand and TR encoder value becomes bigger.

TR becomes 510 mm and ring OD becomes 1,010 mm.

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Axial stand moves away from the main roll to keep the ring pass through within the EL range of the axial roll.

But the OD is same as 1,010 mm because the TR always touch the OD face of the ring.

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