Tandem rolling mill

[citation needed] The mill stand spring curve is obtained by pressing the work rolls together with increasing force.

or conversely, the screw-down position where M is called the mill modulus and is the slope of the spring curve in the area of the datum point ( Sd, Fd).

This was necessary with the control computers of the 1960s, such as the GE/PAC 4020 installed at the then Australian Iron & Steel (now BlueScope) Port Kembla plate mill, which used an assembler language that did not like negative numbers.

[clarification needed] The exact equation used to calculate the required screw-down setting for a required force is:[5] where: k is the value to best suit the measured values and Sa is an adapter which corrects for the thermal expansion of the mill housing and rolls as they warm up during rolling.

The term "setup" is used for the calculation of the actuator settings required by each mill stand to roll the product.

These settings include the initial screw-down position, the main drive speed, and the entry and exit tension references where applicable.

This setup calculation is normally performed either in a lower-level computer or a PLC that controls a rolling mill stand(s).

A graphical representation of a mill model can be obtained by plotting the mill stand spring curve and the compression curve for the strip against the same distance axes; then the intersection point gives the solution of expected rolling force F, and final Strip Thickness h, and also the required initial screw-down position So.

Note that the compression curve has a greater or lesser elastic region depending on the entry and exit tension stresses of that next stand.

This tension effect is represented in graphs 2 and 3 by drawing the steel compression curve with the elastic region reduced accordingly.

In sketch 4, observe that the force is offset from the work roll centers because the strip is thicker at the entry than at the exit; this is one component of the torque that the main drives must supply.

To compensate for this, most screw-down control loops include a feed-forward parameter derived from either; an equation of rolling speed, or a value extracted from a lookup table using linear interpolation.

Alternatively; after annealing, the steel strip can be reduced a second time (by up to 30%) to make it both thinner and work hardened.

For "closed-gap" threading of a tandem mill, it is important that the head-end of the strip remains flat so that it enters the next stand easily.

Two examples are shown for BlueScope Steel's No.2 temper mill with the exit stand configured for strip shape (flatness).

With hot rolled slabs and plates, the thickness varies mainly due to the changes in the temperature along the length.

Using ΔF = Q ⋅ Δh gives This factor is used to guarantee that the control of the exit thickness by the screws is independent of the metal being rolled.

The process sensitivities are highly product dependent, so to obtain reasonable values they are calculated off-line in the setup computer, and then incorporated in the real-time control systems.

[19] The maximum tension difference ΔT across a single bridle roll is determined by the wrap angle α (in radians) of the strip around that roll, and the roll-to-strip sliding friction μ, i.e.[18] The power required to drive such a bridle is (T2 – T1) ⋅ (R + h/2) ⋅ ω, i.e. (T2 – T1) ⋅ v The electrical power required by the drive motor = volts ⋅ amps.

The voltage can be regulated according to the strip speed, leaving the current to be proportional to the required tension change.

To perform this test, a sample of strip is taken at least 3 wraps in from the end of the finished coil; this is called a "run-out".

Fine control of the strip's shape is achieved by adding a multi-zone header spraying water (either warm or cool) onto the work rolls at the exit of the last stand of a tandem mill.

[24] If a coil of thin strip is wound with low tension, then it may not have the strength to support itself and may collapse, especially if roughly handled,[26] see figure 1(a).

An early solution was to place a steel sleeve onto the tension reel mandrel before the coil started.

It receives inputs into these dynamic controls directly from the hard-wired desk and gets the targets for the exit thickness, the tensions and the screw-down positions from the setup computer.

The scheduler assembles the coils or plates to be processed within each campaign using his/her Human Computer Interface, HCI terminal.

Elongation, e is defined as the per-unit increase in length due to a decrease in area with respect to the entry, regardless of shape.

If the width is unaffected (as is the case when rolling thin strip <2mm, see sketch 12), then the mass flow concept, gives

An elongation of typically 1.3% is performed to eliminate the discontinuity (seen at the yield point in graph 6) in the stress verses strain reaction of thin steel strip[9] before it is tinned ready for making cans intended for containing preserved foods.

There are many other definitions of the word elongation; such as in astronomy, plasma physics, genetics, and in a more general sense, such as referring to the lengthening of an elastic band.