US3049950A

US3049950A - Manufacture of metal sheet or strip

Info

Publication number: US3049950A
Application number: US761231A
Authority: US
Inventors: Pearson William Kenne Jamieson
Original assignee: British Aluminum Co Ltd
Current assignee: British Aluminum Co Ltd
Priority date: 1957-09-17
Filing date: 1958-09-15
Publication date: 1962-08-21
Anticipated expiration: 1979-08-21

Description

Aug. 21, 1962 w. K. J. PEARSON MANUFACTURE OF METAL SHEET OR STRIP 3 Sheets-Sheet 1 Filed Sept. 15, 1958 FIGI Vol/age Reference Tacho Genera/5r Aug- 21, 19 w. K. J. PEARSON MANUFACTURE OF METAL SHEET OR STRIP 3 Sheets-Sheet 2 Filed Sept. 15, 1958 Aug. 21, 1962 w. K. J. PEARSON 3,049,950

MANUFACTURE OF METAL SHEET OR STRIP Filed Sept. 15, 1958 3 Sheets-Sheet 3 FIGS {3 36 57 E- I 9 13 United States Patent 3,049,950 MANUFACTURE OF METAL SHEET OR STRH William Kenneth .Iamieson Pearson, Denham, England, assignor to The British Aluminium Company Limited, London, England, a company of Great Britain Filed Sept. 15, 1958, Ser. No. 761,231 Claims. (Cl. 56)

The term flatness" refers to the surface of the sheet.

or strip produced and the term, shape refers to the cross-sectional shape of the sheet or strip. Sheet or strip may be considered to be of good shape when it does not possess a double curvature. Usually the cross-sectional shape is uniform throughout the length of the sheet or strip but the sheet or strip may taper along its length whilst still being of good shape. I g

In the manufacture of metal sheet or strip by pass ing the material through a pair of co-operating rolls in a rolling mill it is usual to provide at least one of the rolls with a cambered surface, initially by appropriately grinding the roll and additionally by superposing a thermal camber thereon, in order to compensate for deflections of the rolls due to the separating force exerted by the rolled material. Thus each cambered roll has a surface which. is curvilinear in a plane containing the roll-axis, is circular in a plane transverse to the rollaxis, is symmetrical about a transverse plane passing through the centre of length of the r'ollaxis and has its greatest diameter in the last-mentioned plane when at its working temperature. During the rolling operation the thermal camber of the cambered roll surface is controlled by controlling the temperature gradient existing in the roll in a direction parallel to its axis. In the operation of the rolling mill the flatness or shape of the sheet or strip entering the bite of the co-operating rolls is retained or improved as required according to the shape of the surfaces of the rolls at the bite and this shape depends upon the initial shape of the surfaces of the co-operating rolls and the reactionary forces exerted on these surfaces at the bite by the material to deform these surfaces. These reactionary forces in turn depend upon the screw-down force applied to urge the rolls towards each other, the friction influenced by lubrication of the roll surface and the tension (if any) applied 3,49,950 Patented Aug. 21, 1962 highly skilled operators to assess the flatness or shape and take the correct remedial action.

Variation in the roll camber can be corrected by suitably controlling the temperature gradient across the roll or it can be compensated for by modifying the screwdown force and/or the tension (if any) in the sheet;or strip.

It is an object of the present invention to providean improved method and apparatus for controlling theflatness or shape of metal sheet or strip produced in a rolling mill.

to the sheet or strip. The roll surface friction is usually substantially constant during the rolling operation and is difficult to vary during such operation. The remaining factors, namely the roll shape, the screw-down force and the sheet or strip tension (if any) are capable of being varied during a rolling operation and are hereinafter referred to as the controlling factors.

During the rolling operation the camber of the rolls tends to change due to fluctuations in the temperature gradients across the rolls and it has hitherto been diflicult to control or compensate for this effect owing to the lack of a precise and continuous method of and means for measuring it. This variation in the camber of the rolls has resulted in undesirable variations in the flatness or shape of the sheet or strip produced. This defeet is particularly undesirable in strip material which is too long to be corrected by subsequent flattening operations. Hitherto it has been customary to assess the flatness or shape of the sheet or strip by visual inspection and the use of tension on the sheet or strip and high rolling speeds has made it increasingly diflicult even for According to one feature of the present invention a method of controlling the flatness or shape of metal sheet or strip produced by passing the material through the bite of a pair of co-operating rolls in a rolling mill comprises measuring the difference between the radii of at least one of the rolls at at least two axiallyspaced locations, and modifying at least one of the controlling factors in ac: cordance withthe magnitude of the departure of said difference from a predetermined value in the sense to correct or compensate for such departure.

Preferably the difference between the roll radii is measured by measuring the' linear velocity of the surface of the roll at said locations and this is conveniently done by applying aroller in non-slip frictional engagement with the roll at each "such location and measuring the angular velocity imparted to each such roller, the rollers advantageously having. their axes contained in a common plane containing the roll axis, and one roller being disposed substantially centrally of the length of the roll.

Accordingfto. another feature of the invention apparatus for carrying into effect the method according to either of the two immediately preceding paragraphs comprises means for measuring the difference between the radii of at least one of the rolls at at least two axially spaced locations and means responsive to such difference to provide an output signal having a magnitude which is a function of the departure of said difference from a predetermined value.

Preferably the measuring means comprises a roller applied in non-slip frictional engagement with the roll at each such location.

Advantageously means is provided responsive to said output signal automatically to modify at least one of the controlling factors in the sense referred to.

In order that the invention may be more clearly understood an example thereof will now be described with reference to the accompanying drawings in which:

FIG. 1 is an elevational view of a roll for use in a rolling mill and having a camber which is exaggerated for the purpose of clarity;

FIG. 2 is a somewhat diagrammatic elevational view of a strip rolling mill;

FIG. 3 is a section taken on the line IIIIII of FIG. 2; 1

FIG. 4 is a block circuit diagram, and

FIG. 5 is a circuit diagram showing in greater detail a circuit similar to FIG. 4.

The roll 1 illustrated in FIG. 1 is shown with an exaggerated camber and it will be seen that it is substantially barrel-shaped, ire. the roll 1 has a surface which is curvilinear in a plane containing the roll-axis, is circular in a plane transverse to the roll-axis, is symmetrical about a transverse plane passing through the centre of length of the roll-axis and has its greater diameter in the lastmentioned plane when at its working temperature. In practice the camber is very slight and is usually formed by grinding the roll which may be ground initially to convex shape or it may be ground initially flat or concave to allow for thermal expansion during the rolling operation. Two-such cambered rolls 1 are provided in shaft 2 of the lower roll 1 is carried in fixed bearings (not shown) and. the shaft 2 of the upper roll 1 ismovable towards the lower roll by means of screwdown members 4 whereby the force urging/the rolls 1 together is controlled. 1 I

This example is concerned with the manufacture of metal strip and the primary material indicated at 5 (FIG. 3) is fed to the bite of the rolls and emerges'therefrom "as the final strip 6. As will be appreciated the primary material 5 may have been pre-rolled to a. predetermined thickness. The strip 6 is taken up on a positively driven roller 7 carried on a shaft 8 whereby tension is imparted to the strip 6. Two measuring rollers 9 are arranged to bear on the upper roll 1 in non-slip frictional contact so as to be driven thereby, the axes of these rollers 9 being contained in a common plane containing the axis of the upper roll 1. The rollers 9 are preferably of equal diameters as shown, although they need not necessarily be so and one is disposed substantially centrally of the width of the upper roll 1 and the other is disposed between the centrally disposed roller 9 and one end of the roll. j

I The angular velocity imparted to each roller 9 by: the

upper roll 1 is proportional to the'linear' velocity of that part of the surface driving it andhence is proportional-to the radius of the roll at that location. It will be seen therefore that'the dilierence hr the angular velocities imparted to'the rollers 9 is a measure of the difference between the radii of the'roll 1 to which they are applied at the locations at which they are applied, and any departure of this difference from a predetermined value may be utilized to modify at. least one of the controlling factors, ie the roll camber, the strip tension or the screw-down force exerted on the rolls 1 ,by the screwdown member or members 4.. V

In this example the camber of the, upper roll 1 is controlled by means of an oilpipe 10 feeding pipes 10a, ltib and Ida extending parallel to the axis of the roll 1 by way of

branch pipes

10d, 10c and 10 respectively. The

pipes

10a, 10b and 100 are provided with a'number of spraying apertures 11 along their length through which oil is sprayed on to the surface of the r0111 on that part thereof advancing towards thebite of the rolls. The pipe 1% is disposed between the pipes 10a and 19c so that the oil therefrom controls the temperature of the mid-part of the surface of the roll 1 parallel to its axis and the oil from the

pipes

10a and 100 controls the temperature of the surface of the roll 1=along its marginal edges. A manually adjustable valve 11a controls the oil flow to the pipe 10 and an automatically controlled valve 111; controls the flow of oil to the pipe 10b thereby controlling the flow of oil from the latter relative to the oil fiow from the

pipes

10a and 100. After the surface of the upper roll 1 has passed the bite, any oil remaining thereon together with dirt and metal slivers is wiped therefrom by a wiper 110. Thus by suitably controlling the valve 11b the oil flow from thespraying apertures 11 of the pipe 102': may be cont-rolled and hence the temperature gradient and the roll camber and strip shape may be controlled. This control may be exercised. by an operator observing the d-ilference in the angular velocities imparted to the rollers 9 or automatically in accordance with such dilference.

The block schematic circuit diagram of FIG. 4 shows an apparatus for automatically utilizing the diiference in the angular velocities imparted to the rollers 9.

One of the rollers 9 drives a synchro transmitter 12 through a gear 13 and the other roller 9 drives a synchro differential transmitter 14 through a gear 15, the electrical output from the synchro differential transmitter 14 being a three phase electrical signal with electrical rotation at the difference speed which is fed to a synchro control transformer 16. The latter is a comparison I camber 0f the rolls.

element in a servo loop which causes the rotor of the transformer 16 to track the electrical rotation and the mechanism of the servo loop operates as a torque amplifier which produces an output of sufficient magnitude to be utilized to exercise the desired control. The servo loo-p comprises a demodulator 17, a DC. amplifier 18 and a servo-motor 19 the output from which drives the highspeed end of a gear 20 the low-speed end of which drives the control transformer-16 to provide a mechanical monitoring feed-back. Stabilizing feed-back is provided by a tachogenerator 21 mechanically coupled to the servo-motor 19. This tachogenerator 21 provides an output which is an integral function of the output from the differential transmitter 14 and hence provides a voltage analogue of the difierence between the angular velocities imparted to the rollers 9, and this output is amplified by amplifier 22 and utilized to provide a visual indication .at 23 of the difference between the angular velocities for manual control purposes.

To correct for the influence of changing mill speeds, a second tachogenerator 24 is coupled to the mill-motor, mill rolls 1 or the strip 6 (indicated generally by the reference .25) to provide a voltage analogue of the rolling speed. This voltage analogue is subtracted from a fixed reference voltage provided at 26 in an amplifier 27 to produce an output from the latter which is inversely proportional to the rolling speed and which is utilized to energise the field of the tachogenerator 21. In this way the output of the tachogenerator 21 and the indication at 23 is a linear function of the quotient of the difierence between the angular velocities imparted to the rollers 9 and the rolling speed and hence is a measure. of the An interlocking stabilizing feedback signalmay be provided by feeding the amplified output of the tachogenerator 21 through a stabilizing network 29 to the amplifier 18.

The output from the tachogenerator 21 is compared in the amplifier 22 with a predetermined reference value supplied as a voltage from 22A, which latter bears the legend Setting Camber or Shape in FIG. 4. This predetermined value supplied by 22A corresponds. to the desired camber of the rolls 1and the resultant output from the amplifier 22 is fed to a final controlling element 28 which controls at least one of the controlling factors, which in this example is the camberof the rolls 1 by controlling the valve 11b and hence the oil supply through the spraying apertures 11 of the pipe 10b, in the sense to reduce the difference between the angular Velocities imparted to the rollers 9.

It 'will be appreciated that the output signal may be used to control the drive of a motor to the spindle 8 to control the strip tension or to control a screw-down motor connected to the members 4 to control the screwdown force.

It will be appreciated'that the rollers 9 need not necessarily be of the same diameter in which case the difference between the angular velocities imparted to them will have to be compared with a reference value to obtain a signal useful for control purposes.

It will be further appreciated that if sufiiciently accurate speed measuring elements are available they may be used in place of the

synchros

12 and 14 to give a difference voltage which. could be fed directly to the amplifier 22, a computing element being provided to divide this signal by a voltage analogue of the mill speed and the

units

16, 17, 18, 19, 20, 21, 26 and 27 being no longer required.

FIG. 5 illustrates an electric circuit similar to that of FIG. 4 but in greater detail. In this example one roller 9 drives through gear 13 the rotatable winding 30 of a synchro transmitter 31 the fixed winding 32 of which is electrically connected to the rotatable winding 33 of a synchro differential transmitter 34. The rotatable winding 30 is connected across terminals 35 to a source of AC. supply. The other roller 9 drives through gear 15 the rotatable winding 36 of a synchro differential transmitter 37 the fixed winding 38 of which is electrically connected to the fixed winding 39 of the transmitter 34. The fixed windings 4t) and 41 of

synchro control transformers

42 and 43 respectively are connected in parallel across the rotatable winding 36. The respective rotatable windings 44 and 4-5 of the

transformers

42 and 43 have their outputs respectively supplied across the fixed pairs of

terminals

46 and 47 of a double-pole switch 48 the movable pair of contacts of which may be switched to take the output from either one of the

rotatable windings

44 and 45 and apply it across a pre-set sensitivity resistor 49 to feed a phase-sensitive rectifier 50. The

rotatable windings

44 and 45 are respectively geared through ratios of :1 and 100:1 to a shaft 51 geared through a ratio of 100:1 to a split-field motor 52 the armature 53 of which is connected across terminals 54 to a DC. supply. The field winding 55 of the motor 52 is connected to the output of a DC. amplifier 56 the input of which is connected to the output of the phase-sensitive rectifier 50. The motor 52 also drives a tachogencrator 57 having an output applied across a feed-back resistor 58 connected to the input side of the phase-sensitive rectifier St). The motor 52 also drives a square-law D.C. tachogenerator 59 through gearing 60, the tachogenerator 59 having a separately excited field and being capable of being used for multiplication. One winding 61 of the tachogenerator is connected in series with a linear wire-wound potentiometer resistor 62 of about 4K across terminals 63 connected to a D.C.

' supply of about 25 volts, the movable tapping 64 being connected to the one end of the resistor 62 connected directly to one of the terminals 63. The position of the tapping 64 therefore controls the magnitude of the field produced by the winding 61 and the output of the tachogenerator 59 produced in armature winding 65 is a function of the product of this field and the speed of rotation of the tachogenerator 59 driven by the gearing 60.

A roller 66 bearing upon the metal strip is driven at a speed which is a function of the speed of advance of the strip and drives through gearing 67 having a ratio of about 3:1 a permanent magnet tachogenerator 68 so as to produce an output of about 80 volts from the latter at a strip speed of 800 feet per minute. This output is applied across a 100K linear wire-wound potentiometer 69.- The potentiometer 69 has a limit stop 70 at 10K from the high voltage end and the tapping 71 is con nected to a source 72 of a reference voltage which is applied across the tapping 71 and the high voltage end of the potentiometer 69 and the input of an amplifier 73 the output of which is supplied to a motor74 which drives both

tappings

64 and 71 which are mechanically linked. The output of the winding 65 of the tachogenerator 59 is applied through a resistor 75 to the input of an amplifier 76 the output of which is fed both to an indicator 77 and an actuator 78 for the valve 11b. The output of the amplifier 76 is connected to the input of the latter through a feedback resistor 79 and is also connected to a biased relay 8% connected through an amplifier 81 to a motor 82 connected to the rotatable winding 33 of the synchro differential transmitter 34. The motor 82 also drives a tachogenerator 83 the output of which is fed back to the input of the amplifier 81 to provide a stabilizing loop. A reference voltage is supplied to the input of the amplifier 76 from a source 84 connected thereto through resistor 85.

The operation of this circuit will now be described. For the purpose of this description the fixed winding 32 of the synchro transmitter 31 may be considered to be connected directly across the fixed winding 38 of the synchro differential transmitter 37. It will be apparent that in this case the rotating fields produced in the fixed

windings

40 and 41 of the

transformers

42 and 43 is a function of difference in the velocity of rotation of the 6. rollers 9 and the rotation of the

windings

44 and 45 thereof will be a similar function. The movable contact of the switch 48 is connected across the

terminals

46 or 47 to select the output either from the rotatable windings 44 or the winding 45 respectively driven by the motor 52 through permanently meshed gearing of 1000z1 and 10,0801. The motor 52, phase-sensitive detector 5%) and amplifier 56 provided with stabilising feedback from tachogenerator '52 track either trans-former 42 or. 43 according to the speed ratio selected and hence enable the apparatus to be made effective over a wide range of speed difference of the rollers 9. The motor 52 drives the tachogenerator 57 and hence the square-law tachogener-ator 59 at a speed which is a linear function of the velocity difference of the rollers 9. The permanent magnet generator 68 provides an output which is an integrated function of the speed of advance of the strip measured by the roller 66 and this is inverted by the self-balancing

potentiometer system

62, 69 and applied across the winding 61 of the square-law tachogenerator 59. The latter integrates the velocity difference signal from the rollers 9 and provides an output which is the product of this integral and the reciprocal of the integral of the velocity of the strip. This product is the desired signal and is compared in the amplifier 76 with the reference voltage from the source 84 to produce the desired indication in the indicator 77 and the appropriate operation of the valve 1112 due to the actuator 78. In practice thereference voltage of the source 84 will usually be zero when the rollers 9 are of equal r'adii but it may be set up initially to a predetermined value where the rollers 9 are not of equal radii or adjusted from time to time to compensate for changes in the radii of therollers 9 due to wear and can also be used to compensate for drift in the amplifier 56 although this could be better dealt with by providing a separate zero check. The source 84 may also be set up initially to a predetermined value when a given deviation from flatness is desired.

The synchro difierential transmitter 34 and the connections thereto, the motor 82, tachogenerator 83, amplifier 81 and relay 8% are provided to ensure a rapid electrical line-up of the rotating fields of the

transmitters

31 and 37. Thus should

transmitters

31 and 37 get out of phase when the apparatus is started up, the amplifier 76 will saturate and operate the relay 8t and cause the motor 82 to drive the rotatable winding 33 to bring the rotating fields into synchronism in a matter of seconds. When synchronism is nearly achieved the relay 80 opens and the motor 32. ceases to function.

It will be understood that where a number of pairs of rolls 1 are provided in series in a tandem rolling mill the signal derived from a pair of rollers 9 bearing on a roll 1 of a pair of such rolls may be utilised to modify at least one of the controlling factors relating to a preceding or succeeding pair of rolls 1 in the series so as to ensure that the stripfinally emerging from the mill shall have the 1 desired flatness or shape.

It will be further understood that more than two rollers 9 may be provided across the roll 1 and switch means may be provided successively to compare the angular velocities imparted to pairs of such rollers or a pair of rollers may be traversed axially along roll 1 in order to seek camber irregularities.

When sheet is being rolled it is usually not placed under tension and in such a case the signal derived from the angular velocities imparted to the rollers 9 is utilized to modify the screw-down force applied to the rolls 1 and/ or the camber of the roll or rolls 1.

It will be understood that the invention is applicable to controlling the shape of profiled sheet or strip material.

What I claim is:

l. A method of controlling the flatness or shape of metal strip produced by passing the strip through the bite of a pair of cooperating rolls in a rolling mill, which includes the following steps: measuring the difference becontrolling factor that is contributing to any departure in the difference between said radii from said predetermined difference value in accordance with the magnitude of such departure from the predetermined difference value in order to correct and compensate for such departure and restore the difference between said radii to a difference corresponding to said predetermined difference value.

2. A method according to claim 1, which includes the step of measuring the difference between said roll radii by measuring the linear velocity of the surface of the roll at each of said axially spaced locations thereon.

3. A method according to claim 1, which includes the step of measuring the linear velocity of the surface of the roll at said two axially spaced locations, respectively, by measuring the angular velocity of a roller in non-slip frictional engagement with the roll at each such location.

4. A method according to claim 1, which includes the steps of deriving an electrical signal from rollers in nonslip frictional engagement with one of said rolls at said axially spaced locations thereon, respectively, which electrical signal is a function of the rolling speed; and then producing from said electrical signal a control signal which is a function of the product of the difference of the angular velocities imparted to the rollers and the reciprocal of said rolling speed electrical signal;

5. A method of controlling the flatness or shape of metal strip produced by passing the strip through the bite.

of a p'air of cooperating rolls in a rolling mill, which includes the steps of: measuring the difference between the radii of at least one of said rolls at at least two axially spaced locations along the roll; establishing a predetermined difference value between said radii; measuring any difference between said radii of said roll at such spaced locations against said predetermined difference value; and

then modifying the shape of one of said rolls in accordance with the magnitude of the departure of any difference between said radii from said predetermined difference value to correct and compensate for such departure and restore the difference between said radii to a difference corresponding to said predetermined difference value.

6. In a rolling mill, in combination, a pair of cooperating rolls for passing through the bite thereof a metal strip; means for measuring the difference between the radii of at least one of said rolls at at least two axially spaced locations along said roll; means for establishing a predetermined difference value between said radii; means for measuring any difference between said radii against said predetermined difference value; and means responsive to difierences in said radii providing an output signal having a magnitude which is a function of the extent of any such departure from said predetermined difference value.

7. In a rolling mill, in combination, a. pair of cooperating rolls for passing a metal strip through the bite thereof; means for measuring the difference between the radii of at least one of said rolls at at least two axially spaced locations therealong; means for establishing a predetermined difference value between said radii; means for measuring the difference between said radii against said predeterjmined difference value; means responsive to differences in said radii to provide an output signal which is a function of the magnitude of the departure of any such difference from said predetermined difference value; and means responsive to said signal to automatically modify a controlling factor contributing to a departure from said predetermined difference value to correct and compensate for such departure and restore the difference between said radii to one corresponding to saidpredetermined difference value. a

8. In a rolling mill, in combination, a pair of cooperating rolls for passing through the bite thereof a metal strip;- means for modifying the shape of at least one of said pair of cooperating rolls; measuring means for measuring the difference between the radii of at least one of said rolls at at leasttwo axially spaced locations therealong; means for establishing a predetermined difference value between said radii; difference measuring means formeasuring the difference between said radii against said predetermined difference value; means responsive to differences in said radii providing an output signal which is a function of the magnitude of the departure of any such difference from said predetermined difference value; and means responsive to said signal to automatically effect operation of said means for modifying the shape of one of said rolls to correct and compensate for such departure and automatically restore the difference between said radii to one corresponding to said predetermined difference value; I

9. In a rolling mill, in combination, a pair of cooperating rolls for passing through the bite thereof a meta-l strip; means for applying a screw-down force to said rolls urging said rolls radially toward each other to engage the strip between the bite of said rolls; measuring means for measuring the difference between the radii of at least one of said rolls at at least two axially spaced locations therealong; means establishing a predetermined difference value between said radii;.difference measuring means for measuring the difference between said radii against said predetermined difference value; means responsive to differences in said radii to provide an output signal which is a function of the magnitude of the departure of any such difference from said predetermined difference value; and means responsive to said signal to automatically effect operation of said means for applying a screw-down force .to said rolls to correct and compensate for such departure and restore the difference between said radii to one corresponding to said predetermined difierence value.

10. In a rolling mill, in combination, a pair of cooperating rolls for passing through the bite thereof a metal strip; means for applying tension to the metal strip in the direction of its advancement from the bite of said rolls; measuring means for measuring the difference between the radii of at least one of said rolls at at least two axially spaced locations therealong; means for establishing a predetermined difference value between said radii; difference measuring means for measuring the difference between said radii against said predetermined difference value; means responsive to differences in said radii to provide an output signal which is a function of the magnitude of the departure of any such difference from said predetermined difference value; and means responsive to said signal to automatically effect operation of said means for applying tension to said strip to modify the tension applied thereby to correct and compensate for such departure and restore the difference between said radii to one corresponding to said predetermined difference value.

References (lit-ed in the file of this patent UNITED STATES PATENTS 2,292,535 MacChesney Aug. 11, 1942 2,811,059 Appleby Oct. 20, 1957 2,851,911 Hessenberg Sept. 16, 1958