US3101016A

US3101016A - Rolling mills

Info

Publication number: US3101016A
Application number: US10977A
Authority: US
Inventors: Gill Hedley
Original assignee: British Iron and Steel Research Association BISRA
Current assignee: British Iron and Steel Research Association BISRA
Priority date: 1959-02-26
Filing date: 1960-02-25
Publication date: 1963-08-20
Anticipated expiration: 1980-08-20
Also published as: BE588024A; GB885784A; FR1249149A; AT225655B; DE1402641A1; LU38301A1; CH363954A

Description

Aug. 20, 1963 H. GILL ROLLING MILLS Filed Feb. '25. 1960 Y. E N Wm 2 o T 5 M Elv Me U M m H United States Patent 3,1tll,016 ROLLING MILLs :Hedley Gill, Shetfield, England, assignor to The British This invention relates to rolling mills and is particularly concerned with the control of a multi-stand rolling mill. While the invention has chief application to the cold roll- 3,101,016 Patented Aug. 20, l 953 and hence a change in speed of the strip leaving the first stand and entering the second stand. This in turn alters the reduction efiected at the second and subsequent stands of the mill, so that the strip leaving the millas a whole may not have the desired thickness. It is therefore necessary, either to adjust one or more of the other stands of the mill or to supply automatic gauge control on at least the last stand of the mill, as Well as the-first stand. Duplication of the automatic control system is expensive.

To ensure that adjustment of screwdown on the first stand of the mill does not affect the rolling performance ing of strip, it may be applied to the rolling of hot strip, 7

provided that there is substantial interstand tension.

In the cold rolling of steel strips in a multi-stand mill, the incoming strip is liable to vary in thickness along its length and it is desirable to provide .means for adjusting at least one of the stands to vary the reduction. This adjustment is usually effected by adjustment of'the screws on the first stand. However, the adjustment on the first stand alters the rolling conditions on subsequent stands and hence the reductions produced by the succeeding stands. An object of this invention is to provide a means for preventing the adjustment of the roll setting on any stand, but more particularly the first stand, from affecting the operation of subsequent stands. v

Inaccordance with the present invention, a multistand rolling mill has on one of the stands preceding the last stand in the train a control system for controlling to a desired value the speed of the strip leaving the stand, irrespective of adjustments to the roll setting of that stand. The roll setting of the selected stand can then be adjusted, during rolling, for example in order to compensate for variations in thickness of the incoming strip, without affecting the operation of succeeding stands.

Preferably, the stand provided with automatic strip speed control has a gauge control system for automatically maintaining substantially constant the thickness of the strip leaving the stand.

The invention will be more readily understood by way of example from the following description of control systems for a multi-stand tandem mill, reference being made to the accompanying drawings, in which FIGURE 1 diagrammatically illustrates the mill,

FIGURE 2 schematically shows the control system for one of the stands, preferably the first stand in the train, and

FIGURE 3 illustrates a tensiometer for the strip.

Referring to FIGURE 1, the mill consists of a number of stands, of which only the first two and the last stand is illustrated. Each stand is represented by a pair of

work rolls

12, 13; 12a, 13a; 12b, 131), a

drive motor

14, 14a, 1 21] and a screwdown motor and control gear therefor 15, 15a, 15b. The screwdown motor 15, when operated, adjusts the roll setting, i.e. the nominal separation of the rolls. It will be appreciated that, Where desired, each of the rolls i2, 13 may be driven by a separate motor In.

The various stands are set up so that each reduces the strip appropriately to produce a desired overall reduction in the mill. For this purpose, the interstand tensions are carefully selected, since the reduction effected at any one stand depends, not only on the roll setting of that stand, but also on the tensions in the strip at each side of the stand. In order to produce strip of reasonably constant gaugc, at least one of the stands must be controlled during rolling either by hand or automatically. This adjustment is usually etfected by controlling the roll setting on the first stand, for example to eradicate changes in thickn ss in the strip entering the mill. However, change in the screwdown on the first mill results in an alteration in the reduction of the strip in that stand of subsequent stands, the motor 14 of that stand, or motors 14 where each of the rolls 12, 13' is driven independently, is automatically controlled so that the speed of the strip leaving the first stand is maintained substantially constant. As a result, the interstand tensions remain constant, irrespective of adjustments efiected at the first stand, and the reductions effected at succeeding stands remain unaltered.

FIGURE 2 illustrates one way in which the speed of the strip leaving the rolls 1-2, 13 may be maintained constant. A tacho-generator 16 is driven by a roller 17 in contact with and driven by the strip 18 at the exit side of the

rolls

12, 13. Roller 17 may be the roller of a tensiometer, as illustrated in FIGURE 3. The DC. signal from the generator 16, which is proportional to the strip speed, is applied in opposition to the voltage from potentiometer 26 to the input of a high-gain amplifier 21. Potentiometer 26 is adjustable by hand to a value representing the desired strip speed, so that the input signal to amplifier 21 is dependent on the divergence of the strip speed from the desired value. Amplifier .21 feeds the field winding 22 of a generator 23, the armature of which is connected to the armature of the motor 14 driving the

rolls

12, 13. If the speed of the strip 18 changes, due for example to alteration of the screwdown of the

rolls

12, 13, the armature voltage of motor 1 is altered to change the speed of

rolls

12, 13 until the strip speed is returned substantially to the value set by the potentiometer 20. 1

During rolling, the screwdown of

rolls

12, 13 is automatically adjusted to maintain substantially constant the thickness of the strip leaving the stand. This adjustment may be effected by hand'but is preferably eitected by an automatic control system such as that described in US. Patent 2,726,54l to R. B. Sims, and illustrated for convenience in FIGURE 2. Sims describes a circuit for generating an electric signal representing the departure of the strip thickness (71) from the desired strip thickness (h) and this error signal is shown in FIGURE 2 as applied to the motor and control circuit 15 to cause the screwdown to be adjusted to maintain the error substantially zero. While reference should be made to Sims for a more detailed description of the circuit, that circuit will now be briefly described for convenience.

A slider 24 on a resistor R1 is coupled to the screws of the

rolls

12, 13 so that the voltage developed between the slider 24 and a second slider 25 on resistor R1 is proportional to the roll setting (S of the

rolls

12, 13, resistor R1 being energised by a battery B1. A Wheatstone bridge network 25 is constituted by four resistance strain gauges supported on a block between the checks for the roll 12 and the screw. The bridge 26 is energised by a battery B3 and the voltage from the bridge is proportional to the separating force (F) generated in the stand. A second resistor R2, energised by battery B2, has a contact 27 which can be adjusted by hand in accordance with the desired thickness of the strip (11'). The contacts 24, 25, 27 and the bridge 26 are connected in series so that the voltage developed across lines 28, 29 is equal to F/M+S -h', where M is the spring factor of the stand,

or to the departure of the strip thickness from the desired vvalue, vh. This signal is applied to an amplifier 30, the

output of which controls the control circuits for the screwdown motor 15.

The speed of the strip 18 leaving the

rolls

12, 13 is, of course, related to the tension in the strip 18 between the

rolls

12, 13 and the rolls 12a, 13a. If the speed is kept constant then the tension will be held within narrow limits, and vice versa. In the modification of FIGURE 3 the tacho-generator 16 of FIGURE 2 is replaced by a conventional strip tensiometer, represented by a jockey pulley 34 biased upwardly against the strip 18 by a spring 35and coupled .to the sliding contact 36 of a potentiometer 37. The voltage on sliding contact as is then dependent on the interstand tension and is applied in opposition to the voltage from potentiometer 20 (FIGURE 2) to control the armature voltage of motor 14, as before, in order to maintain the tension substantially constant.

In another modification, the signal from amplifier 21, when that amplifier is controlled by strip speed or tension, is employed to control the speed-torque characteristic of motor 14. The armature voltage is kept constant but the inclination of the speed-torque line V is varied to adjust the speed of the motor for constant torque.

It has already been explained that the change in the roll setting of the

rolls

12, 13 causes an alteration of the strip speed, due to the changed reduction etfccted by the

rolls

12, 13. Simultaneously, the change in roll setting causes a change in strip speed in the opposite direction, due to the speed-torque characteristic of the motor 14 and the alteration in the torque required of the motor as a result ofthe changed reduction. In a further modification, these facts are used to maintain the strip speed constant, without a closed-loop control system such as that illustrated by the tacho-generator 16, amplifier 21 and generator 23. Thismay be done by appropriately varying in known manner the inclination of the speed-torque characteristic of the motor 14 so that the change in strip speed resulting from the required change in torque is equal and opposite to the change in strip speed resulting from the change in reduction.

' In the systems illustrated in FIGURE 2 and FIGURE 3, means (not shown) are supplied for protecting the control system against failure of the detectors 1 6, 34. In the event of failure of the detector the speed of motor 14 is automatically prevented from rising beyond a safe value.

between and in contact therewith, driving means connected to each pair of said rolls for driving each of said rolls in opposite directions from one another, a gauge control system controlling the roll sett ing of at least one stand preceding a last stand of said plurality of stands to maintain the thickness of a strip of material leaving said one stand at substantially a constant value, a speed 5 control system connected to said driving means for controlling the speed of the rolls of said one stand and responsive to the speed of the strip of material leaving said one stand for maintaining a constant speed of the material leaving said one stand.

2. A rolling mill as set forth in claim 1 wherein said driving means is responsive to electrical signals and said speed control system generates an electrical signal depending on the speed of the strip of material leaving said one stand to energize said driving means to control the speed of the strip of material leaving said one stand.

5 References Cited in the file of this patent V UNITED STATES PATENTS OTHER REFERENCES Bringing Hot Strip Mills Under Automatic Control,

ControlEngineering, September 1960 (pages 146149). (Copy in 80-56E.) I

Continuous Gaging Automation, March 1956 '(pages 52-57). 7 (Copies in 8056E.) I

Claims

1. A MULTI-STAND ROLLING MILL COMPRISING A PLURALITY OF STANDS, EACH STAND HAVING A PAIR OF OPPOSING ROLLS ARRANGED TO RECEIVE A STRIP OF MATERIAL AT THE NIP THEREBETWEEN AND IN CONTACT THEREWITH, DRIVING MEANS CONNECTED TO EACH PAIR OF SAID ROLLS FOR DRIVING EACH OF SAID ROLLS IN OPPOSITE DIRECTIONS FROM ONE ANOTHER, A GAUGE CONTROL SYSTEM CONTROLLING THE ROLL SETTING OF AT LEAST ONE STAND PRECEDING A LAST STAND OF SAID PLURALITY OF STANDS TO MAINTAIN THE THICKNESS OF A STRIP OF MATERIAL LEAVING SAID ONE STAND AT SUBSTANTIALLY A CONSTANT VALUE, A SPEED CONTROL SYSTEM CONNECTED TO SAID DRIVING MEANS FOR CONTROLLING THE SPEED OF THE ROLLS OF SAID ONE STAND AND RESPONSIVE TO THE SPEED OF THE STRIP OF MATERIAL LEAVING SAID ONE STAND FOR MAINTAINING A CONSTANT SPEED OF THE MATERIAL LEAVING SAID ONE STAND.