US3460365A

US3460365A - Rolling mills

Info

Publication number: US3460365A
Application number: US617306A
Authority: US
Inventors: David Robert Howard
Original assignee: Davy Loewy Ltd
Current assignee: Davy Loewy Ltd
Priority date: 1966-02-21
Filing date: 1967-02-20
Publication date: 1969-08-12
Anticipated expiration: 1986-08-12
Also published as: GB1177923A; DE1602046A1; DE1602046B2; DE1602046C3; FR1516309A

Description

Aug. 12, 1969 D. R. HOWARD 3,450,365

ROLLNG MILLS Filed Feb. 20, 1967 2 Sheets-Sheet l mvsmollz` D- R Hav/AR ATTORNEYS Aug. i2, i969 D. R. HOWARD ROLLING MILLS 2 SheetS-Sheet 2 Filed Feb. 20, 1967 H YDRAUL/C RATUR COND! TIO/V INTERLOCKS FG. Jl

u SM A.

am m0 mm E MM P INVENTOR D. R. SlowAnb BY m@ www Bum# um ATTRNEYs s ILS. Cl. 72-21 3 Claims ABS'E'RACT 0F THE DISCLOSURE An automatic control system for a rolling mill comprising means for storing a representation of the eccentricity of a roll of the mill, and means for automatically controlling the roll setting in dependence upon that representation to diminish the effect of said eccentricity on the rolled material.

This invention is concerned with rolling mills, particularly those for the rolling of steel and other metals in elongate form.

All rolls for rolling mills are eccentric to a degree, i.e. however carefully a roll is ground, the roll barrel is eccentric with respect to the roll necks by which the roll is rotatably supported in use. Additionally, all roll bodies depart so some degree from right circular cylinders. If this departure takes the form of a difference in diameters measured through the geometric centre of the roll body the effect is described as ovality.

Eccentric movement of a troll causes the metal to be rolled with a thickness which varies cyclically over its length. The degree to which the eccentricity of the rolls of a rolling mill is reflected in cyclic gauge variations in the rolled material is dependent on the stiffness of the mill itself and on the stiffness of the material being rolled in that mill. A soft mill which deforms under the rolling load arising from a hard r stiff rolled metal will produce only small gauge variations due to eccentricity. A stiff mill, such as a prestressed mill, on the other hand, when rolling a soft material causes the eccentricity of the rolls and their bearings to be reproduced faithfully in the rolled material. l

In one aspect of the present invention, an automatic control system for a rolling mill comprises means for storing a representation of the eccentricity and/ or ovality of a roll or rolls of the mill and means for automatically controlling the roll setting by that representation to diminish the effect of eccentricity and/or ovality on the rolled material. Preferably the representation is fed out as a control signal during each cycle of the mill to control the controlling means during that cycle. By a cycle of the mill is meant a revolution of the work rolls in the case of a two-high mill and a revolution of the back-up rolls in the case of a four-high mill.

In the case of a mill having screws, and/or equivalent hydraulic means for adjusting the roll setting, the representation is applied to those screws or hydraulic means. In the case of a mill, prestressed by hydraulic rams, the pressure of the hydraulic rams may be so adjusted.

The invention will be more readily understood by way of example from the following description of cyclically operating control systems for rolling mills reference being made to the accompanying drawing, in which:

FIGURE l schematicaly illustrates a rolling mill and its eccentricity control mechanism,

FIGURE 2 is a similar drawing illustrating a preferred eccentricity and ovality control mechanism,

FIGURE 3 shows a modification of FIGURE 2.

States Patent O Patented Aug. 12, 1969 In FIGURE 1, the rolling mill is shown as having a pair of work rolls 12 engaging the strip 13 and a pair of back-up rolls 14. The roll necks 15 of the back-up rolls 14 are journalled in bearing chocks 16 which are slidably arranged in the housings (not shown). The roll setting, i.e. the roll gap prior to entry of the strip 13, is set by screws 17 which, in this instance, mate with nuts 18 splined within recesses in parts 2f? of the housings, so that they can slide vertically, but cannot turn relative to the housing parts 20. The screws are as usual rotated by screwdown motors (not shown) and bear against the chocks 16 of the upper back-up roll 14.

interposed between the nuts 18 and the roofs of the recesses in which the nuts lie are sealed hydraulic capsules 21 of the type known as Statimeters These capsules have a limited ability to expand and contract under variations of the volume of liquid supplied to them.

Each roll neck 15 of each back-up roll 14 has attached to it an eccentric cam 22. Each cam 22 is engaged by a piston 23 working within a cylinder 24 which is connected by line 25 to the capsule 1 on the same side of the mill. As the upper back-up roll 14 rotates, the piston 23 reciprocates cyclically, and causes liquid to be supplied to, and withdrawn from, the capsule 21 in cyclic fashion. This in turn results in chock 16 of the corresponding roll neck being reciprocated.

The eccentricity of each cam 22 with respect to the roll neck to which it is attached is selected so as to produce a change in the capsule of the same amplitude as, but in anti-phase with, the eccentricity and ovality of the respective back-up roll 14 at that side of the mill. In this way the effect of the roll eccentricity and ovality on the strip is largely nullied.

Although FIGURE l shows the cams 22 on the necks 15 at the same side of the mill controlling the capsule 21 on the same side, instead the cams on the necks of the lower back-up rolls may be arranged to control further capsules located between the chocks 16 of the lower backup rolls and the housings. The eccentric mounting of the cam in each case is such as to compensate for the eccentricity of the back-up roll of the connected roll neck.

Where the mill is of the type in which there are adjustable spacers between the chocks Which are formed together by a prestressing ram or rams, the pressure of `that ram or rams may be adjusted cyclically to counter the eccentricity of the rolls by the use of cams as described, or otherwise.

FIGURE 2 shows an alternative and preferred method of controlling the capsules 21 of FIGURE l to counteract roll eccentricity and ovality. In this case the piston 23 of the cylinder 24 controlling the left-hand capsule 21 is reciprocated by a solenoid, the linear rotor 26 of which is connected to the piston 23. The winding of the stator 27 is fed by a series of sine wave generators 28A-ZKF of adjustable amplitude. Generator 2SA and 28B are driven by upper back-up roll 14 through

clutches

30A, 30B. Generator 28A is designed to generate a signal at the same frequency as upper roll 14 and in antiphase with the eccentricity of upper roll 14; generator 28B on the other hand generates a signal at double the frequency of upper roll 14 `and in antiphase with the ovality of that roll 14. The phasing between the upper roll 14 and the rotary parts of generators 28A, 28B is selected by use of the respective clutch 30, and the amplitudes of the sine Waves are chosen, so that the capsule 21 operates in antiphase with the eccentricity `and ovality Variation 0f the upper roll 14- to nullify the effect of that eccentricity and ovality.

Each of the work rolls 12- of the mill is connected through a clutch 30C, 30D to an independent

sine wave generator

28C, 28D feeding the same solenoid stator 27 and the amplitude and phase of each generator is chosen to compensate for the ovality of each roll 12. The generators 28E, ZSF with their clutches 30E, SF perform the same function for the lower back-up roll 14 as do the generators 28A, 28B and clutches 39A, ISQB for the upper roll 14. A similar set of generators Z8 and clutches 30 are provided for the right-hand necks of the rolls l2, 14, the generators controlling the right-hand capsule 21 so that differences in bearing eccentricities and ovalities on the two sides of the mill may be accommodated and simultaneously compensated. Where the eccentricity or ovality of a roll is the same at both sides, as is likely to be the case for the work rolls 12, only one generator 3i) need be provided for that roll, the output being applied in parallel to the two solenoid stators 27.

The phasing and amplitudes of the roll eccentricities and ovalities differ from roll to roll and the generators 28 and clutches 30 need to be readjusted each time a roll is changed. Adjustment to remove the effects of eccentricity and ovality is easiest performed with no work in the roll bite, the mill being screwed down below face and the rolls being driven. The accumulated effects of the various eccentricities and ovalities may then be detected by the signals from two load cells 31 interposed between the screws 17 and the upper back-up roll chocks 16 and the generators and clutches are adjusted until the load cell signals contain minimum cyclic variations. When that has been effected further adjustment of the phasing and amplitudes of the generators 23 should be unnecessary until the next roll change.

Instead of manual adjustment of the phase and amplitudes of the signals from the wave generators of FiG- URE 2, circuits may be provided to provide automatic adjustment to reduce the effects of eccentricity and ovality on the rolled strip. One such circuit is illustrated in FIGURE 3, which diagrammatically shows one side of the mill stand, components similar to those of FGURE 2 being given the same reference numerals.

In FIGURE 3, a wave generator 28 is coupled to each of the four rolls in the stack. These wave generators produce simultaneously, but through different windings, sine waves and cosine waves at the same frequency as the angular rotation of the roll to which they are connected (or at some fixed multiple of that frequency). The operation of the system will be described by reference to the signals produced at the wave generator 28 of the lower back-up roll 14, the sine and cosine signals appearing on

lines

32, 33 respectively.

The signal produced by the total apparent eccentricity of the roll stack in the absence of material in the bite is registered by the presence of the load cell 31. The signal from this cell after passing through a low frequency filter F1 is fed to two phase

sensitive detectors

34, 35 which have as their respective reference signals the sine wave and cosine wave outputs on

lines

32, 33. The output of each phase

sensitive detector

34, 35 passes through a low pass filter 36, the signal from each such filter being a unidirectional quantity the average value of which is proportional to the amplitude of the sine or cosine component of the low frequency signal from the load cell 31. rIhe signal from each filter 36 is applied to a separate differential amplifier 37, fed from a power supply 38 and each amplifier 37 drives a servo motor 40, a tach-generator 41, the output potentiometer of which is fed back to the input of amplifier 37, and an output potentiometer 42. One end of the potentiometer 42 associated with phase sensitive detector 34 is fed with the sine signal on line 32 and the other end with the same signal, reversed in signal by a sign changing circuit 43; the potentiometer 42 associated with phase sensitive amplifier 35 is similarly supplied with the cosine signal on line 33. The outputs of the two potentiometers 43 are summed in the summing amplifier 44 and applied to a motor t5 driving an hydraulic generator 46, the hydraulic output of which is applied to the capsule 21.

The combination of the differential amplifier 37, servomotor 46' and tachogenerator si acts as an integrator with a relatively long time constant compared with the periodic time of the eccentricity pattern. Thus the presence of a standing output from one of the

detectors

34 or 35 tends to drive its output potentiometer 4t2 into one or other of its extreme positions. However, when lthe outputs from the potentiometers 5,2 are added and the vector sum of their individual values are used to drive the motor 45 and hydraulic generator 45 to produce a pressure variation in the capsule 2l below the mill screw 17 in the correct sense to reduce the cyclic output of the load cell 31 associated with eccentricity in the lower back-up roll 14 to zero, then the system will tend to reach a position of equilibrium. In this condition the circuit shown in FIGURE 3 will be providing a signal after the summing ampliher 44 which is correctly phased in relation to the eccentricity of the lower back-up roll and the power to the amplifiers 37 can be removed so storing the correct phase relationship in the potentiometers.

A similar circuit may be connected to the outputs of each of the other generators 28 coupled to the other rolls of the stand to compensate similarly for the cornponents of the total eccentricity pattern contributed by the eccentricity of the upper back-up roll 14 and the ovalities of each of the work rolls 12, each circuit being supplied from the load Vcell 31 through a separate filter F2, F3 etc. which is tuned to exclude all frequencies other than those approximating to the frequency of the eccentricity or ovality of the roll in question. To deal with the ovalities of the back-up rolls 14, each of those rolls may drive a further generator 23, the frequency of the output of which is twice the frequency of revoiution of those rolls, and which feeds a further circuit similar to that illustrated. The outputs of all the circuits are applied to the summing amplifier 44 to control in common the capsule 21. The load cell 31 at the other side of the stand may control similar circuits associated with the rolls and controlling the capsule 21 on that side.

In some cases it may be found that adequate eccentricity compensation may be achieved by providing a compensating circuit as described for each of the backup rolls only, the effects on the strip of the ovalitics of the rolls being sufficiently insignificant.

It will be recognised that the closure of the control loop need not necessarily pass through the mill structure but may exclude it by using the circuits described to cancel the eccentricity signal as seen by a recorder 46 connected to the load cell 31. It will also be recognised that it may be necessary to modify the phase relationship of the output signal in relation to the actual phase relationship of the eccentricity of the rolls so that changes in the rotational speed of the rolls do not cause eccentricity patterns to reappear because of phase lags in the response of the hydraulic compensating means. Finally it will be appreciated that differences between the diameters of the two back-up rolls will greatly assist the systems to reach stability.

While the eccentricity correction has been shown and described as being effected by means of the capsules 21, it may alternatively be effected by other means. For example, in the case of FIGURE 2, the signals from the generators 2t; and, in the case of FIGURE 3, the output of the summing amplifier 44 may control the screws 1.7 through the screwdown motors, or wedges interposed between the housings and the back-up chocks, or hydraulic cylinders acting either between the housing and the back-up chocks or between the back-up chocks.

I claim:

1. In a rolling mill having a pair of work rolls, signalresponsive means for adjusting the gap between the work rolls and an individual back-up roll associated with each work roll, an automatic control circuit comprising means for producing a continuous electrical signal representative of the rolling load on the mill,

generator means driven by at east one of the back-up rolls and arranged to provide rst and second continuous alternating electrical signals both of which have a frequency proportional to the angular rotation of the roll, said signals being displaced in phase from one another by 90, and circuit means arranged to receive said signal representative of the rolling load and said first and second signals, to identify the components of the signal representative of the rolling load which are in phase with the first and second signals respectively and are caused by the eccentricity of the roll, and to produce an output signal proportional to the amplitude of said components, which output signal is applied to said adjusting means,

thereby causing adjustment of the roll gap in a direction to oppose the elect on the rolling load of the eccentricity of the roll associated with said generator means. 2. In a rolling mill having a pair of work rolls, signalresponsive means for adjusting the gap between the work rolls and an individual back-up roll associated with each work roll, an automatic control circuit comprising means for producing a continuous electrical signal representative of the rolling load on the mill,

separate generator means, one driven by each of the back-up rolls, each generator means being arranged to provide sine and cosine signals having a frequency proportional to the angular rotation of the roll with which they are associated, and

separate circuit means, each arranged to receive said signal representative of the rolling load and said sine and cosine signals from the generator means associated with one ofthe rolls, to identify the components of the signal representative of the rolling load which are in phase with the sine and cosine signals received by the circuit means and which are caused by the eccentricity and ovality of the roll with which the circuit means is associated, and to produce an output signal proportional to the amplitude of said components,

said output signals from all said circuit means being together applied to said adjusting means, thereby causing adjustment of the roll gap in a direction to oppose the effect on the load of the eccentricity and ovality of said rolls.

3. An automatic control circuit as claimed in claim 2 in which each of said circuit means includes phase sensitive detectors which employ said sine and cosine signals respectively as reference signals, said detectors being arranged to transmit only those components of the continuous electrical signal representative of the rolling load which are in phase with their reference signal.

References Cited UNITED STATES PATENTS 3,049,950 8/1962 Pearson 72-8 3,194,035 7/1965 Smith 72--8 3,331,229 7/ 1967 Neumann et al 72--8 MILTON S. MEHR, Primary Examiner