US3247697A - Strip rolling mill - Google Patents

Description

A ril 26, 1966 s. cozzo 3,247,697

STRIP ROLLING MILL Filed Dec. 6, 1962 2 Sheets-Sheet 1 INVENTOR. G/USE'PPE C0220 BY M ATTORNEY April 26, 1966 ca. cozzo 3,247,697

STRIP ROLLING MILL Filed Dec. 6, 1962 a Sheets-Sheet 2 SCREW 3 CONT/70L RAD/4770A! GAUGE,

C OA/T/FOI AUTOMAT/C 6,4062

CONTROL C/RCUT NVE TOR. GIUSEPPE C0220 /00 BY MZZSM ATTORNEY United States Patent 3,2416% STlRll RQLLENG MELL Giuseppe Cozzo, Yonkers, N.Y., assignor, by means assignments, to HlfiW-IQHGX 0rnpauy, Pittsburgh, Pa, a corporation of Delaware Filed Dec. 6, 1962, Ser. No. 242,684 8 Claims. (Cl. 72-2 ltl) In general, this invention relates to a new and improved strip rolling mill. More particularly, it relates to a strip rolling mill adapted to be utilized with automatic gauge control equipment which eliminates errors induced by the stretch of the mill'housing.

With the increased demands of modern production, the linear speeds at which strip rolling mills operate have reached the point where it is very difficult to make large corrections in maintaining a predetermined value of gauge or strip thickness.

The apparatus presently in use to monitor strip gauge is in the form of radiation, eddy current induction, or simple micrometric devices. These devices cause a corrective signal to be applied to the mill screwdown, tension or speed in such a way as to nullify errors in gauge. However, such devices are increasingly incapable of dealing with the problem of maintaining gauge because of the transport time delay between the measured reading and the application to the control equipment. The time delay between measurement and application has caused instability in the correction system. In addition, the inertia of the rolling mill equipment and the control apparatus add further to this delay. The instability caused by the combination of these effects has resulted in large variations in gauge and, therefore, a high rate of rejection of finished strip.

An analysis of the contributing factors to the variations in the mill gap as they affect the ability of the mill to roll on gauge indicates that the separating force between the rolls is the largest single ivariation as it causes (1) stretch in the mill, (2) compression of the screwdowns and chocks, and (3) the deformation or flattening of the rolls at the contact with the strip.

In a standard rolling mill, the approximate work roll gap is set before the strip enters, the rolls being maintained apart by a hydraulic or mechanical counterbalancing means. After the strip enters, the mill assumes an initial position based on many factors including entering gauge, temperature of the strip, etc. If the initial gauge setting results in an output strip thickness which is off the pre-set amount, the mill screwdowns, speed or tension is varied by the regulating apparatus until equilibrium condition at the desired gauge is reached. In this regulation process, one of the many factors that is varied is the stretc of the mill. The stretch of the mill is the largest single factor in the error correction, however, so that particular attention has been made by designers to reduce this effect. The approach heretofore used has been to build the mill stands of a larger cross section and more squat construction as the stretch is essentially an elastic tensile deformation, i.e., the mill housing stretches in accordance with the separating force between the rolls in accordance with Hookes law. The elastic tensile deformation is inversely proportional to the cross sectional area of the mill stand posts and proportional to the height between the top and bottom cross ties. A mill stand which is of squat construction and has a large cross sectional area has to be manufactured from expensive castings and has a high initial cost without actually eliminating the problem. This type of mill stand construction merely reduces the stretch of the mill.

Previous attempts at eliminating the stretch of the mill as a factor in automatic gauge control have led to commercially available.

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the introduction at each side of the mill of a hydraulic cylinder in the mill window between the lower chock and the bottom cross tie. The opposed upper chock in the same mill window was positioned and sustained in the mill window by the top cross tie, thus applying a constant pressure to the rolls and thereby causing an initial stretch prior to the entry of the strip between the work rolls. This initial stretch was approximately the, amount obtained after introduction of the strip and thereby eliminated to some extent the separating force as a factor in gauge error. However, the separating force can only be approximated through prior analysis and estimation. In the absence of means for continuously varying the applied hydraulic force through corresponding pressure changes, the gauge of the strip leaving the mill will be some fixed fraction of that entering so that correction of errors in gauge in the primary material cannot be effected in this manner. Further, the changes of other variables such as the strip hardness or temperature will cause the outgoing strip to vary in gauge even though the entering strip may have been of constant thickness.

If gauge control is attempted by varying the hydraulic pressure from continuous gauge monitoring devices, the problems of conventional mills except for the absence of stand elongation are still present. The. rapidity of response of the chain of control and corrective equipment in the hydraulic and instrumentation circuitry is slow compared to the strip speed. Further, the interrelatedness of the various factors in gauge error produces a combination of effects due to interaction that mitigates against rapid stabilization on gauge. For example, increases of hydraulic pressure are produced by the introduction of hydraulic fluid into the system. Pressure rises cause the mill stand to stretch and the hydraulic cylinder to extend accordingly. This necessitates that additional fluid be introduced as hydraulic fluids are relatively incompressible and extension of the cylinder would otherwise not permit the required pressure rise. The converse is true if the pressure is to be decreased. System pressure may be constantly monitored by strain gauge types of instruments It can be seen that the spacing of the rolls or the gap is not constant with consequent effect on gauge.

Additionally, with the system described above, it is not possible to have an initial gap between. the work rolls. That is, it is necessary to have what is known as a negative gap in order to achieve the prestressing of the mill stands.

If a positive gap is initially set, and there is no prestressing of the mill stands, the operational time lapse between the gauge measuring and the actual adjustment to on gauge is inevitably large. Consequently, a great deal of strip length passes through the rolls during the time of correction resulting in excessive scrap of strip material particularly if the adjustment procedure has a degree of instability.

A variation in the pass line of the mill stands causes rough entry of the strip between the rolls. This factor did not enter into adjustments for extremely thin strip metals such as foil mills, but became a problem where the operating gap on the work rolls was large.

Therefore, it is the general object of this invention to avoid and overcome the foregoing and other difficulties of the prior art practices by the provision of a new and improved strip rolling mill.

Another 'object of this invention is to provide a new and improved strip rolling mill for use: with automatic gauge control apparatus.

A further object of this invention is to provide a better strip rolling mill which eliminates the stretch of the mill housing as a factor in automatic gauge control.

Another object of this invention is to provide a new and better strip rolling mill having a mechanically adjustable roll gap in combination with a prestressed mill structure.

Still another object of this invention is to provide a better rolling mill in which initial gauge accuracy is only affected by the amount of roll distortion, compression and elongation of chocks and bearings, and compression spacer expansion from zero to full rolling pressure and .not by mill stand stretch.

A still further object of this invention is to provide a prestressed rolling mill structure in which the pass line can be varied prior to rolling in a simple and easy manner.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentatlities shown.

FIGURE 1 is a cross sectional view of a rolling mill in operation built in accordance with the principles of the present invention.

FIGURE 2 is a cross sectional view of the pass line adjustment shown in FIGURE 1 taken along lines 22.

FIGURE 3 is a schematic showing of the rolling mill of FIGURE 1 utilized with automatic gauge control apparatus.

The present invention achieves its objects by providing a mill for the accurate control of strip thickness in which the chocks are positioned by means of a compression spacer under load of sufficient magnitude so that the po sition of the rolls remains relatively fixed irrespective of the force on the rolls tending to separate them. Therefore, the only correction that need be made by the control apparatus is to compensate for a minute extension of the compression spacer due to a decrease in the clamping force thereon, variations in the compression and elongation of the chocks and bearings, and a minute contraction of the radii of the work rolls due to roll flattening. The spacer extends in a manner proportional to its length and inversely proportional to its cross sectional area. The distortion of the roll surface and the extension of the compression spacer are additive effects which must be compensated by the control system. However, there is no stretch in the mill housing so long as the separating force is less than the initial force on the compression spacer. That is, there is a transfer of a portion of the compression force from the compression spacer to the work rolls equal to the separating force. So long as the separating force remains less than the prestressing compressive force, clamping pressure will still be present on the compression spacer.

The compression spacer is adjustable and is placed between the roll chocks in each side frame of the mill housing. The chocks and spacer are hydraulically loaded by an initial pressure to elongate the side frames to the full extent proportional to the pressure before the start of rolling. This initial pressure, as stated previously, should be equal to or greater than the expected separating force during rolling. This maintains the compression spacers under a positive clamping action thereby maintaining the relatively fixed spacing of the rolls during any condition of operation.

For the purpose of adjusting the pass line, and to take care of varying roll diameter, a suitable wedge or screw arrangement may be interposed between the upper chock and the upper cross tie of the mill housing. This wedge or screw arrangement can be adjusted prior to applying the pre-set hydraulic pressure to thus vary the pass line of the mill.

In FIGURE 1, there is shown one embodiment of a rolling mill built in accordance with the principles of the present invention. The rolling mill in FIGURE 1 has been generally designated by the numeral 10.

The mill has a pair of side posts 12 and 14 along one side thereof joined by bottom and top cross ties l6 and 18 respectively to define a mill window 19.

l/Vithin the mill housing and extending between opposing mill windows, there are an upper backup roll 20 and a lower backup roll 22 in rolling engagement with an upper work roll 24- and a lower work roll 26 respectively. The space between the closest points of the surfaces of rolls 24 and 26 is defined as the mill gap. The force tending to separate the rolls 24- and 26 when a strip 28 is being rolled is known as the separating force. The separating force is the force exerted by the strip 28 on the rolls 24 and 26. p

The roll 26 has an axis 36 and is mounted in an upper backup roll chock 32. The lower backup roll 22 has an axis 34 and is mounted for rotative movement in a lower backup roll chock 36. The lower work roll 26 has an axis 36 and is mounted in a lower work roll chock 40 nested in the lower backup roll chock 36. The upper work roll 24 has an axis 42 and is mounted in an upper work roll chock 44.

The chocks 32 are vertically movable by reason of adjustable screws 46 and 48 located in screw boxes in the chocks. The portions 50 and 52 of the screws 46 and 48 between upper backup roll chock 32 and lower backup roll chock 36 form compression spacers which maintain the distance between axes 30 and 34 relatively fixed. Each of the compression spacers 50 and 52 has an extension 54 and 56 respectively which fits within a suitable recess in the lower backup roll chock 36. Immediately below the extensions 54 and 56 are suitable load sensitive transducers 53 and which determine the pressure on the screws at these points. A similar pair of load sensitive transducers (not shown) is placed in the opposite lower backup roll chocks to give an indication of unequal load distribution on the rolls.

The lower chocks 36 rest on the piston of an hydraulic cylinder 58 located within the bottom cross tie 16. The cylinder 58 is adapted to provide an initial pressure on the chocks to elongate the side frames to the full extent proportional to the pressure applied. As stated previously, this pressure is equal .to or greater than the expected maximum separating force between the work rolls. The cylinder 58 maintains a constant or arbitrarily variable pressure by means of a controlled ballast, accumulator, or pump (not shown). The pressure exerted by the hydraulic cylinder 58 insures that the compression spacers 50 and 52 will always be positively clamped between the upper chocks 32 and the lower backup roll chock 36.

The position of the upper roll chocks 32 with respect to the lower chocks 36 is varied by a worm gear drive motor 60. The drive motor 60 engages gears 62 and 64 which turn screws 4-6 and 48, respectively.

The pass line adjustment means consists of two wedges 66 and 68 shown in FIGURE 2. The wedges 66 and 68 are adapted to be placed between the top cross tie 18 and a block 70 riding on a cammed surface 72 of the upper backup roll chock 32. The lower wedge 68 is placed in one position and is not horizontally movable. The upper wedge 66 is horizontally movable by the turning of a suitable shaft 74 having a screw threaded extension 76 thereon. An internally threaded bushing 78 engages with the threaded extension 76 to move the wedge 66 in a horizontal plane thus varying the vertical position of the chock 32. Movement of the chock 32 varies the pass line of the mill. The pass line of the mill can be defined as the plane bisecting a plane extending between the axes 42 and 38 of work rolls 24 and 26 respectively.

The wedge 66 is also guided for its horizontal movement along a suitable shaft 80. The shaft 80 is connected to the lower wedge 68 so that a counterbalance 82 mounted on an extension 81 of the cross tie 18 will prevent dropping of the wedge 66 when there is no pressure on the chock 32.

When the rolling mill 10 is at rest and there is no pressure on the cylinder 58, the pass line is adjusted by turning the shaft 74 to move the wedges into their correct positions. The upper wedge 66 has rollers 84 and 86 on each side thereof which support the wedge for rolling contact along suitable flanges 88 mounted on the cross tie 18. If desired, the block can be removed during this adjustment period by side shifting on suitable rollers 90 and 92.

The rolling mill of the present invention may be utilized with any type of automatic gauge control equipment.

For example, as shown in FIGURE 3, the rolling mill 10 may control the gauge of the metal strip 28 by suitable screwdown and speed control means. In addition, although not shown, tension control may also be utilized by controlling the speed of mills and working in conjunction with adjacent mill 10, or by control of entry and delivery reels associated with the mill.

In the schematic of FIGURE 3, there is shown the rolling mill 10 adapted to be driven by a suitable motor 94 having its speed controlled through a suitable control circuit 96. The movement of screwdown motor 60 is control-led by another control circuit 98. The operation of the motor speed control circuit 95 and the screwdown control circuit 98 is ultimately determined by an automatic gauge control circuit 100 receiving signals from the load sensitive transducers53 and 55, similar transducers on the other side frame of the mill 10, and a suitable radiation thickness gauge 102.

Any one :of the known automatic gauge control circuits might be utilized in the present invention. For example, the automatic strip thickness control apparatus shown in US. Patent 2,972,268 may be utilized to control the thickness of the strip 28.

It is the distinct advantage of the present invent-ion that the error correction necessary to maintain the output thickness of strip 28 constant has been substantially decreased. The only deviations requiring error correction are those caused by nonuniformity of the input metal strip, expansion of the compress- ion spacers 50 and 52, variations in the compression and expansion of the chocks and bearings, and flattening of the rolls. There is no error correction necessary for the stretch of the mill. As this was the largest single source of error in prior systems, a substantial increase in accuracy and stability of the automatic gauge control system has been achieved. The time delay between measurement and full correction has been substantially reduced as the amount of correction necessary has been substantially reduced.

Upon the initial entry of the strip between the rolls, the stretch of the mill posts 12 and 14 will not vary. In prior systems discussed previously, it was necessary for the control apparatus to correct for the very large change in the stretch in the mill during this initial entry. The time necessary to achieve such correction was relatively long and resulted in expensive wasting of incorrectly rolled metal.

In addition to the method of automatic gauge control discussed previously, the rolling mill of the type shown may be used to maintain gauge by varying the hydraulic cylinder pressures to counteract variations in metal thickness being rolled. Such hydraulic pressure variation may be used simultaneously with screwdown positioning, speed control, or tension control.

A rolling mill of the type described may be operated in such a manner that all of the aforementioned considerations relating to screwdown, hydraulic cylinder, compression spacer, etc., if disposed at each side of the strip in separate stands or frames, could be independently controlled to achieve controlled gauge across the width of the strip and counteract any tendency of the strip to run off laterally.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A rolling mill comprising a mill housing, a pair of work rolls between which metal is to be rolled, individual mounting means for mounting each of said rolls in said housing, compression spacers positioned between said mounting means, pressure means for applying pressure to one of said mounting means to place said compression spacers in compression, said pressure being applied to said mill housing to stress the same prior to and during rolling, the pressure applied by said pressure means being equal to or greater than pressure necessary to maintain a positive clamping pressure on said compression spacers during the rolling operation, said mill housing having windows on opposite sides thereof, said mill housing including top cross ties on each side thereof, said top cross ties forming the top surface of said mill housing windows, said mounting means including chocks for rotatably supporting said work rolls in said windows, and pass line adjustment means located between said work roll chocks and said mill housing top cross ties.

2. The rolling mill of claim 1 wherein said pass line adjustment means includes adjustable wedges, said chocks having a cam surface the highest point of which is in line with the axis of said work rolls, said wedges being adapted to transmit forces from said cross tie to the highest point tween said mounting means, pressure means for applying pressure to one of said mounting means to place said compression spacers in compression, said pressure being applied to said mill housing to stress the same prior to and during rolling, the pressure applied by said pressure means being equal to or greater than pressure necessary to maintain a positive clamping pressure on said compression spacers during the rolling operation, pressure transducers mounted adjacent the ends of said spacer screws, said pressure transducers being operative'to determine the pressures at the ends of said spacer screws, and means for controlling the thickness of metal being rolled in accordance with the output signals of said pressure transducers.

4. A rolling mill comprising a mill housing, a pair of work rolls between which metal is to be rolled, individual mounting means mounting said rolls in said housing for movement towards and away from each other, compression spacers having at least a portion thereof positioned between said mounting means, pressure means supported by said mill housing for applying pressure to said mounting means, said compression spacers, and said mill housing for moving said rolls towards each other and prestretching said housing prior to and during rolling, means for measuring the pressure in at least one of the said compression spacers, and means for controlling the spacing of said work rolls and hence the thickness of metal being rolled in response to said pressure measurement.

5. The rolling mill of claim 4 wherein said measuring means includes a pair of pressure sensing transducers beneath said compression spacers and said control means is responsive to the output signals of said pressure transducers.

6. In a rolling mill comprising rolls for shaping a work piece, chocks supporting said rolls in said mill,

means for holding said chocks in said mill, adjustable means for separating said rolls, drive means for driving said rolls, pressure means in said mill applying a compression force to said separating means and said chocks, indicating means associated with said indicating means detecting changes in said separating means, control means actuated by said indicating means for controlling said adjustable separating means, whereby said adjustable separating means acts upon said rolls to effect constant roll separation in the mill, said adjustable separating means being arranged to transfer a portion of said applied force to and from said rolls in response to variations in the work piece entering the roll bite.

7. A rolling mill comprising a mill housing, mill windows in said housing, a pair of work rolls between which metal is to be rolled, individual chocks for mounting each of said rolls in said housing, said chocks being disposed in said mill windows, said chocks being supported in said mill windows for movement towards and away from each other, elongated compression spacer screws extending between said chocks, said spacer screws being threadedly engaged with one of said chocks in each of said mill windows, hydraulic pressure means for applying pressure to one of said chocks in each of said windows to place said screws in compression, said pressure means applying pressure to said mill housing to stress the same prior to and during rolling, the pressure applied to said pressure means being equal to or greater than the pressure necessary to maintain a positive clamping pressure on said compression spacer screws during the rolling operation, and means to rotate said screws to adjust the roll spacing.

8. A method of controlling the gauge of elongated rolled material, including the steps of storing in the structure of a rolling mill a substantially constant force at least equal to the anticipated reducing force required for material reduction while maintaining said rolling mill rolls free of said force, transferring said stored force to the material for reduction through said mill rolls by placing the material in the reduction area intermediate the mill rolls, transferring a portion of said force back to storage when a decreasing variation occurs in the reducing force of the material being worked for substantially maintain ing constant material gauge, transferring additional stored force to the material when an increasing variation occurs in the reducing force of the material being worked for 5 substantially maintaining constant material gauge, sensing said variations, and adjusting said substantially constant force in response to said variations.

References Cited by the Examiner 10 UNITED STATES PATENTS 1,980,570 11/1934 Biggert 80-56.3 2,166,153 7/1939 Huck 8056.2 2,276,816 3/1942 Bagno 8056.3 2,358,929 9/1944 Inslee 80-56.3 15 2,430,410 11/1947 Pauls 80-56.3 2,575,590 11/1951 Goulding 80-56.3 2,934,969 5/1960 Neumann 80-56.3 2,972,268 2/1961 Wallace 80 56.2 3,018,676 1/1962 Polakowski 80 32.1 3,024,679 3/1962 Fox 80--56.3 3,111,047 11/1963 Metzger 80--56.3 3,130,628 4/1964 Blinn 80 56 CHARLES W. LANHAM, Primary Examiner.

C. H. HITTSON, Assistant Examiner.

Claims (1)

1. 8. A METHOD OF CONTROLLING THE GAUGE OF ELONGATED ROLLED MATERIAL, INCLUDING THE STEPS OF STORING IN THE STRUCTURE OF A ROLLING MILL A SUBSTANTIALLY CONSTANT FORCE AT LEAST EQUAL TO THE ANTICIPATED REDUCING FORCE REQUIRED FOR MATERIAL REDUCTION WHILE MAINTAINING SAID ROLLING MILL ROLLS FREE OF SAID FORCE, TRANSFERRING SAID STORED FORCE TO THE MATERIAL FOR REDUCTION THROUGH SAID MILL ROLLS BY PLACING THE MATERIAL IN THE REDUCTION AREA INTERMEDIATE THE MILL ROLLS, TRANSFERRING A PORTION OF SAID FORCE BACK TO STORAGE WHEN A DECREASING VARIATION OCCURS IN THE REDUCING FORCE OF THE MATERIAL BEING WORKED FOR SUBSTANTIALLY MAINTAINING CONSTANT MATERIAL GAUGE, TRANSFERRING ADDITIONAL STORED FORCE TO THE MATERIAL WHEN AN INCREASING VARIATION OCCURS IN THE REDUCING FORCE OF THE MATERIAL BEING WORKED FOR SUBSTANTIALLY MAINTAINING CONSTANT MATERIAL GAUGE, SENSING SAID VARIATIONS, AND ADJUSTING SAID SUBSTANTIALLY CONSTANT FORCE IN RESPONSE TO SAID VARIATIONS.

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