US3431762A - Constant gap rolling mill - Google Patents

Description

J- W. O'BRIEN CONSTANT GAP ROLLING MILL March 11, 1969 Filed June 22, 1966 l of 4 Sheet INVENTOR. 15 5144411 m 03 /5 jL Q- 7111; 4770/?5) March 11, 1969 J. w. O'BRIEN 3,431,762

cousmm GAP ROLLING MILL Filed June 22, 1966 I I Sheet 2 of 4 INVEA ITOR. Jk'M/Af/ M4 Oak/51V ATTORNEY.

March 11, 1969 J. w. O'BRIEN CONSTANT GAP ROLLING MILL Sheet Filed June 22, 1966 INVENTOR. JEREM/AH 14 0292/5 ATTORNEY.

March 11, 1969 J. w. O'BRIEN CONSTANT GAP ROLLING MILL Sheet Filed June 22, 1966 mmmmnmvmwwwwwvwmmmmmflm 1 INVENTOR. JEREMMI/ 14/. 0299/5 ATTOR/VEV;

United States Patent 3,431,762 CONSTANT GAP ROLLING MILL Jeremiah Wagner OBrien, Pittsburgh, Pa., assignor to United Engineering and Foundry Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 22, 1966, Ser. No. 559,474 Claims priority, application Great Britain, July 5, 1965,

28,443/ 65 US. Cl. 72-19 Claims Int. Cl. B211) 37/08, 31/20, 31/16 ABSTRACT OF THE DISCLOSURE The present invention relates to a rolling mill and, more particularly, to a mill adapted to produce a rolled workpiece, such as a strip, sheet or plate, having a substantially constant longitudinal gauge.

While the present invention may be employed in connection with all types of multihigh rolling mills, for the purpose of description and explanation only the application thereof to a 4-High Strip Mill has been selected.

In recent years much attention has been given to developing mills for rolling strip, particularly 4-High Mills, capable of producing strip within very close longitudinal tolerances. Prior to the present invention the mills were controlled by an automatic gauge control system. While this system has taken a number of different forms, the form presently most employed operates on the principle of adjusting the screws of the mill. In this way the gap of the working rolls was corrected for changes in the elongation of the mill parts caused by changes in load which may result from variations in hardness or thickness of the incoming strip. This change in elongation or elastic spring of the mill is a function of the modulus of the mill. An algebraic expression of this system may be written as T=S +P/M wherein T equals delivery thickness, S equals the initial gauge setting of the mill, P equals the rolling load and M equals the modulus of the mill.

While this method of correcting for variation in length wise thickness of the material has had much success, experience has brought to light several serious limitations and disadvantages. One of these disadvantages can be observed in reflecting on the aforesaid formula, wherein it will be noted that in order to obtain a constant T, it is assumed that the mill modulus (M is constant. Based on this assumption, as the value P changes the value S will be changed to compensate for the change in the value P to maintain T constant. However, it is well known that the mill modulus is only approximately constant and varies to a significant extent under rolling conditions over most of the entire range and even to a much greater extent under low load conditions. Not only is this automatic gauge control system subject to the variations in the modulus of the mill; but of equal importance it has been proved to be subject to other variations, such as dynamic influences due to a change in the mill speed.

Faced with these limitations in the automatic guage control system, various attempts have been made to improve the results thereof. Three known methods are all addressed to increasing the stiffness of the mill and, consequently, increasing the modulus thereof. This, of course, is beneficial since it relieves some of the burden of obtaining uniform thickness from the automatic gauge control system. These attempts may be briefly identified as follows:

(1) Increasing the rigidity of the mill by increasing the size of the parts of the mill, thus to narrow the limits of variations due to elastic change;

(2) Prestressing the housings, screws, nuts and backup chocks through the legs thereof or an equivalent means, at a pressure greater than the expected rolling loads, thus to remove the influence of these elements, except for the legs of the backup chocks, from the modulus; and

(3) Applying a prestress pressure on some of the mill parts, such as the housings, backup roll chocks, screws and nuts and at the same time maintaining a substantially constant relationship between the prestress pressure and the rolling loads, i.e. maintaining the distance between the axes of the backup rolls constant. In this method a varying prestress pressure of a fixed relationship is maintained between the prestress pressure and rolling load, which, in eifect, removes the influence of the aforesaid enumerated parts from the mill modulus and, consequently, results in a stiffer mill.

Even with the employment of the most beneficial of the modifications, it must be pointed out that none of them eliminates the spring due to backup roll neck deflection or the compression of the mill rolls, both of which significantly contribute to the total mill spring.

With reference to the deflection of the backup roll necks, it will be appreciated that any measuring of the rolling loads which would be involved, particularly as to the last-noted method, will not reflect the vertical displacement of the rolls which controls the gap, which vertical displacement is caused by the bending of the necks of the backup rolls and the effect that this has on the chocks of the backup rolls. This bending, of course, will vary as the rolling loads vary. It will be noted that, as used here, backup roll deflection is not meant to refer to roll body deflection which also will vary with the applied load.

It is important to note that while the aforesaid modification on theory appear capable of improving the uniformity of the longitudinal thickness of the strip, in practice they have been used with some form of an automatic gauge control arrangement in order to give the most effective results.

It is the object of the present invention to provide an improved rolling mill wherein the modulus of the work roll assemblies are totally independent or isolated from the modulus of the mill proper, backup roll chocks, screws, backup roll assemblies, etc. so that in compensating for the elastic changes under the rolling loads, the work roll assemblies are the only elements that need to be considered.

It is another object of the present invention to provide a rolling mill, having a pair of work rolls and a pair of backup rolls, means for adjusting one of the backup rolls to establish and maintain a given pressure condition between the work rolls and a separate and independent means for adjusting the gap between the work rolls of the mill.

It is a further object of the present invention to provide an auxiliary work roll screwdown arrangement in addition to a primary screwdown arrangement provided for one of the backup rolls of a 4-High Mill, the backup roll screwdown including a rapid, responsive means for quickly eifecting operation thereof.

It is another feature of the present invention to provide, in conjunction with a 4-High rolling mill having a first screwdown mechanism fo one of the backup roll assemblies and a second screwdown mechanism for the work roll assemblies, a control system for automatically controlling and coordinating the'operation of the two screwdown systems to establish and maintain a given pressure condition between the work roll assemblies.

It is the object of the present invention to provide in a rolling mill :1 pair of work rolls and a pair of backup rolls for said work rolls, means for measuring the rolling loads between the work rolls, means independent of the backup rolls for setting the gap between the work rolls, means for establishing a predetermined pressure between the work rolls as measured by the measuring means, and maintaining said pressure at a value always in excess of the rolling loads by an amount equal to said predetermined pressure, thereby to maintain said gap setting irrespective of the varying rolling loads, said last-mentioned means operative through one of said backup rolls for moving the backup roll and its associated work rolls towards and away from the other work roll.

The aforesaid objects and advantages will be better understood when the accompanying specification is read in light of the accompanying drawings of which:

FIGURE 1 is an elevational view, partly in section, of a 4-High rolling mill incorporating the features of the present invention;

FIGURE 2 is a partial sectional view of the lower work roll illustrated in FIGURE 1;

FIGURE 3 is a partial sectional view of the upper work roll illustrated in FIGURE 1;

FIGURE 4 is a plan view of the screwdown of the mill illustrated in FIGURE 1;

FIGURE 5 is a schematic control system for the mill illustrated in FIGURE 1; and

FIGURE 6 is an elevational view, partly in section, of a second embodiment of the present invention.

With reference to the drawings and, in referring first to FIGURE 1, there is illustrated one of the two identical housing posts 11 of a 4-High rolling mill for rolling strip material. In view of this identity, unless otherwise necessary, only the elements associated with one post will be described. This mill, of course, will have many of the customary components so that in certain instances specific details of certain components will not be given. As shown, the housing post 11 is provided with a window 12 into which there is received a lower work roll 13 which cooperates with an upper work roll 14, the lower work roll being backed up in a customary manner by a lower backup roll 15 and the upper work roll 14 by an upper backup roll 16. FIGURE 1 further shows that the work roll 14 has a chock 17; the work roll 13, a chock 18; the backup roll 15, a chock 19; and the backup roll 16, a chock 21. The work rolls 13 and 14 are urged apart from each other in the usual manner by work roll balance piston cylinder assemblies 22. The upper backup roll 16 is urged towards the top of the mill in a customary manner by a balance piston cylinder assembly, not specifically shown in the drawings.

The chock 19 of the lower backup roll 15 rests on a support 24 which is seated on the inside bottom surface of the housing post 11. The upper backup chock 21, at its upper portion, is provided with a recess 25 which receives a thrust bearing 26, the upper portion of which is engaged by the lower end of a screw 27. The screw, in the customary manner, is received in a nut 28 which is contained in the housing post 11, the upper end of the screw projecting towards the top of the housing post to which portion there is secured a worm wheel 29, also shown in FIGURE 4. FIGURE 4 illustrates the top of the mill, in which connection both housing posts are illustrated, and reveals that the worm wheels 29 of each post are driven by worms 32 arranged on the opposite sides of the mill. The worms project towards the front of the mill to which there are secured gear wheels 33 that are driven by worms, not specifically shown, the worms being connected to large screwdown motors 24, the motors themselves being connected together by a coupling 36. The aforesaid elements falling between the main mill screws and the motors 34 constitute the main screwdown assembly of the mill.

Again referring to FIGURE 1, and in addition to FIGURES 2 and 3, it will be noted that in the chock 17 of the upper work roll 14 is provided a nut 41 which receives a vertically arranged screw 42, the screw at its upper end carrying a spur gear 43 which meshes with a pinion 44 which, in turn, meshes with an outer spur gear 45. The lower end of the screw 42 projects beneath the lower surface of the chock 17 of the upper work roll 14 and engages a load cell 46 received in an opening 47 of the chock 18 of the lower work roll 14. The load cell can take the form of several well-known types capable of emitting a current that varies as the applied pressure varies. Directly beneath the load cell 46 there is provided a spring 48 which at its top engages the lower surface of the load cell 46 and at its bottom a filler block 49 also received in the opening 47.

It will be appreciated that the gearing, load cell and spring arrangement are provided for the right-hand side of the work roll chocks 17 and 18 as well and that, as previously noted, a similar arrangement is provided for the work roll chocks of the other housing. Referring still to the left-hand side of the mill in FIGURE 1, the spur gear 45 is adapted to be driven by a shaft 51 having a splined end that is received in the spur gear 45. The shaft 51 passes through the upper backup chock 21 of the upper backup roll 16 by virtue of an opening 52,

which opening is enlarged at the top to receive a spring 53 which tends to urge the shaft 51 in an upward direc tion. The shaft 51 by a coupling 54 is connected to a second similar shaft 55 which extends through the housing post 11 to the top of the mill. At the top of the mill, above the upper surface of the main screwdown motors 34, there is secured to the shaft 55 a worm wheel 56 which is driven by worm 57 to which there is connected a motor 58, the motor and worm Wheel being supported above the mill by a common platform 59. As FIGURE 4 shows, a single motor is provided for each of the two pairs of the individual worm, wheel and shaft arrangements for each housing post. These four arrangements constitute the work roll screwdown assembly.

It will be appreciated that as the trailing end of the strip passes from the rolls, it will be a tendency of the work rolls to forcibly contact each other, thereby creating a danger of breaking of some of the parts of the work roll assemblies. On mills rolling very thin material, it is possible to proportion the parts involved so as to have sufiicient strength to withstand the load caused by the work rolls coming together, and thus to be able to withstand or absorb the shock of the mill springback without overstressing the parts involved. However, on mills rolling thicker material, it is a feature of the present invention to insert the spring 48 between the load cell 46 and the filler block 49 to prevent damage to the work roll parts as the trailing end of the strip leaves the mill. This will permit the work rolls to come together and absorb the shock of the reaction of the mill.

Before discussing the operation of the mill, it may be well at this point to develop the theory behind the present invention to the extent necessary to appreciate the manner in which it operates to accomplish the results herein indicated. As previously noted, one formula for expressing the relative relationships between the factors that are involved in controlling longitudinal strip thickness in the present-day automatic gauge control system is as follows:

In this formula, the elements of which have been heretofore defined in Col. 1, it is assumed that the mill modulus is constant and, as previously noted, the degree of success realized is dependent upon the degree of constancy of the modulus of the mill. Realizing this, the novelty of the present invention can be appreciated when the aforesaid formula is compared with the formula representing the factors involved in practicing the present invention. The latter formula can be written as wherein T equals the strip thickness, S equals the initial work roll screwdown setting, p equals the load on the work roll assemblies, and M equals the modulus of only the work roll necks, a portion of the work roll body, the work roll chocks, the work roll screwdown parts and load cells and the springs. The use of the spring, in addition to being a protection against .springback effect, also allows the selection of a modulus so as to enable the most desired control system to be employed. Since it is intended by the present invention to keep 12 at a constant value, the formula may be written in simplified form as An examination of the immediate-above formula points out one of the most important and novel features of the present invention, namely, that the modulus of the mill proper, the backup roll chocks, neck reflection, roll flattening does not influence the modulus of the work roll parts M they are independent of each other. This is due to the fact that the work roll parts involved in M do not contribute deflections to the main mill modulus except for some very minor secondary effects. It is also important to note that the decrease of the modulus M caused by the employment of the springs inserted below the load cells, will not have any effect on the mill modulus M In general terms the successful operation of the herein-disclosed mills result in, first, rotating the screws 42 the desired amount to establish the initial gap of the work rolls 13 and 14 by the work roll screwdown system; then, applying a nominal pressure on the load cells 46 by the screwdown for the backup roll 16 which establishes the ultimate gap of the work rolls and thereafter maintaining this nominal pressure irrespective of change in the rolling load, by operating the screwdown for the backup roll which will, in turn, maintain the gap of the work rolls constant. Thus, in this arrangement the modulus of the components of the mill, other than those of the work roll assembly and its screwdown, in no way will influence the controlling of the gap which, of course, will control the uniformity of the strip being produced. The effect is that of a near infinitely rigid mill, which enables in a real sense, the gap between the work rolls to be maintained constant. Since any change in the gap can be accurately corrected, the strip produced will have a substantially uniform longitudinal thickness.

Attention is now directed to FIGURE 5, illustrating a control system for correlating the operation of the two screwdown systems, namely, the screwdown associated with the upper backup roll 16 and the screwdown associated with the upper work roll 14. The major components of the mill illustrated in FIGURE 1 have been carried forward, though not identified in all instances as such, to FIGURE 5, in which connection it will be noted that the load cells 46 produce a signal over a line L having a value p. The signal from the line L is fed to an amplifier 61 which feeds a signal to a line L As to the line L it will be noted that .the ampifier 61 converts the sig nal p into a signal representing a value p/M which is transferred to an amplifier 62. The amplifier 62 also receives a signal representative of the factor p /M which is produced by an amplifier 63 which receives an electrical signal from a potentiometer 64 representative of the value p The potentiometer 64, as FIGURE 5 indicates, is set manually, for example, from the main pulpit of the mill.

The signals p/M and pi/M are thus transferred to theamplifier 62 where they are subtracted to produce a signal representing AP/M which is fed over a line L to a servovalve 65. The servovalve is connected by an hydraulic line L to a piston cylinder assembly 66, which, in turn, moves the worms 32 to turn the gear wheels 33 to impart a rotation of the main mill screws 27 and, thus, move the upper work roll 14 vertically. While the piston cylinder assembly 66 is not actually shown in FIGURES l and 4, it is to be understood that to each worm shaft 32 there is secured the rod end of piston cylinder assemblies similar to assembly 66 and that the shafts are permitted to move relative to the gear wheels 33 which are held from moving in a direction axially of the worm shafts 32.

Returning to the ampifier 63, it will be noted that a line L runs from it having a signal representative of the factor p/M to an amplifier 67 that adds the signal p/M with one of two other values. The first of these values is an electrical signal representing T which is produced by a potentiometer 68 which sends a signal to a two-way switch 69. The potentiometer 68, as indicated in FIGURE 5, is set manually, for example, from the pulpit of the mill. The second and alternate signal received by the amplifier 67 comes from a potentiometer 71 which produces an electrical signal representative of a value T which also is fed to the switch 69. The purpose of the signal T is to compensate for the rapid separation of the work rolls as the leading end of the strip enters the bite which will be more fully explained hereinafter.

As indicated in FIGURE 5, the amplifier 67 either receives a signal from the potentiometer 68 or 71 depending upon the position of the switch 69. The amplifier 67 adds the values received from the potentiometers 68 and 71 and from the line L and produces in a line L either a value T -i-P/M or T +P/M Either of these signals is transferred to an amplifier 72 which receives a feedback signal over a line L representative of the actual gap setting of the work roll assembly. The feedback signal is generated by a potentiometer 70 associated with one of the worm wheel sets 56-57, which operates the motors 58 of the work roll screwdown, thereby raising or lower ing the screws to effect a change in the pressure reading of the cells 46 which will cause a corrective adjustment of the gap through the backup roll screwdown, It will be appreciated that when an X-ray system is being employed which will allow complete automatic control, the switch system 69 will not be employed. Also, when the switch system 69 is employed, once the T signal has effected a gap change, it will be understood that no further change will be made by the auxiliary control network.

A brief explanation of the operation of the mill illustrated in FIGURE 5 will now be given and for completeness, let it be assumed that allowance is to be made for the rapid separation of the rolls by the leading end of the strip. Assuming that there is no strip in the mill, the screwdown for the work rolls 13 and 14 is operated so as to position the upper work roll 14 relative to the lower roll 13 to obtain the desired gap, wherein the rolls may or may not be in contact with each other. This adjustment of the upper work roll 14 will be made possible by a previous movement of the upper backup roll 16. In this case while the screws 42 will push against the cells 46, the pressure generated will be nominal, it being appreciated that the initial pressure imposed upon these cells is furnished by the setting of the backup rolls. The backup roll screwdown is then caused to impose a pressure on the load cells 46 in which the mill screw 27 will be operated until the load reading corresponds to a predetermined nominal reading, say of the order of 50,000 pounds on each load cell. Previous to this the potentiometers 64, 68 and 71 will have been set to give the proper reading of the values P T and T The switch 69 will be positioned to pick up the signal T which will be set so as to anticipate the fact that the leading end of the strip, therefore, will require a slight decrease in the roll gap in order to obtain a reasonably constant gauge strip for the leading end of the strip. As the leading end enters the bite of the work rolls and separates the rolls, the load cells 46 will indicate a drop in pressure and, thus, the signal p over line L, will be received by the amplifier 61 which will be integrated to produce a value p/M which is sent over lines L to the amplifier 62. Here, it will be integrated with the value p /M to produce a value Ap/M which may be plus or minus or zero and if a signal is produced, it is sent to the servomotor 65 to operate the cylinder 66 to cause the backup roll screwdown to bring the upper work roll towards the lower work roll to increase and reestablish the predetermined nominal pressure of 50,000 pounds in each load cell. Once the leading end of the strip enters the mill, the switch 69 will be operated to produce a signal T in place of the signal T whereby the signal P/M will be added with the T signal by the amplifier 67. This should result in a slight openin of the roll gap as effected by the operation of the backup roll screwdown.

Should the strip during operation of the mill be thinner than what previously entered into the mill, the load cells 46 will indicate an increase in the pressure reading, which as previously explained, will cause the screwdown for the packup roll 16 to move the upper work roll away from the lower Work roll, thereby reestablishing the predetermined pressure reading. Fluctuation in the signal 12 on line L as received by the amplifier 61 to produce a value p/M will be compared in the amplifier 62 with the signal p /M to produce a signal Ap/M The signal will be carried over line L, to the servovalve 65,

thereby initiating operation of the piston cylinder assembly 66 to operate the main or backup roll screwdown and screws 27 in a manner to raise the backup roll whereby the initial pressure setting is maintained and compensation is made for the entrance into the mill of a thinner strip. To take care of any inaccuracies in the initial gap setting, the primary control of maintaining the pressure constant can be monitored by a secondary control system. This could take the form of a thickness control system, not shown.

With reference to FIGURE 6, which, as previously indicated, represents a second embodiment of the present invention, it is believed unnecessary to point out specifically those elements which correspond to elements shown in FIGURE 1. The embodiment of FIGURE 6 differs from that of FIGURE 1 in that instead of the mechanical screwdown for the backup roll, FIGURE 6 employs a hydraulic screwdown at the bottom of the mill which controls the movement of the lower backup roll. In FIGURE 6 for purposes of discussion, the backup rolls have been identified by reference characters 74 and 75, the upper backup roll 74 engaging the upper work roll 76 and the lower backup roll 75 engaging the lower work roll 77. The lower backup roll 75 is provided with a chock 78, the lower surface of which is engaged by the plunger 79 of the piston cylinder assembly 81, the cylinder 81 being carried by the housing 82. The operation and results of the embodiment shown in FIGURE 6 are similar to what has been described with respect to the mill illustrated in FIGURE 1. I

The embodiment of FIGURE 6, however, has certain features which in certain mill applications may be very desirable. One feature has reference to the quickness of action of the hydraulic arrangement, it being quick enough to eliminate a great percentage of the gauge variation due to the rapid separation of the work roll by the entrance of the front end of the strip. The hydraulic arrangement is inherently capable of sensing the increased rolling pressure and applying a pressure commensurate thereto to obtain a constant gauge by restoring the set value of the load cells.

Another feature has reference to the fact that in the arrangement of FIGURE 1, the Work rolls are loaded by the screwdown and, therefore, its operation depends on position as it requires movement of the screw in order to cancel out variations in mill stretch. In the arrangement of FIGURE 6, this influence is entirely eliminated. Since the hydraulic loading of the work roll parts and the loading of the cells are dependent only on the hydraulic pressure and since this pressure is independeht of position, the mill spring is automatically canceled. Also the load on the cells is dependent on hydraulic pressure which lends itself to very fine control as compared to the mechanical system which is dependent on the control of screw position in order to keep the load on the cells constant.

Another feature of the FIGURE 6 embodiment has reference to reducing or eliminating the danger of breaking the work roll parts due to their reaction when the trailing end of the strip has passed through the bite. A hydraulic arrangement, in view of its inherent quick reaction, is fast enough to at least partially reduce the springback effect of the mill on the work roll parts; however, as explained above, a spring inserted in the work roll system will protect the Work roll parts against damage.

In accordance with the patent statutes, I have explained the principle and operation of my invention and have illustrated and described what I consider to represent the best embodiments thereof. However, I desire to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a rolling mill comprising a housing:

a window in said housing,

a pair of work rolls having bearing chock assemblies for rotatably supporting the opposed ends of the work roll in said window,

a pair of backup rolls for each work roll having hearing chock assemblies for rotatably supporting their opposite ends in said window,

means arranged between the bearing chock assemblies of the work rolls for detecting a change in the rolling load developed between the work rolls during rolling,

means discrete from said backup roll bearing chock assemblies engageable with the bearing chock assemblies of one of said work rolls for adjusting the gap between the work rolls,

means arranged between said housing and one of the bearing chock assemblies of one of said backup rolls to efiect a change in the gap between the work rolls by exerting a pressure to urge the bearing chock assemblies of said work rolls together in a manner that at least a portion of the pressure will be detected by said detecting means, and

means for varying said pressure with reference to a detected change in the rolling load so that the pressure will always exceed the rolling load by a predetermined amount.

2. In a rolling mill according to claim 1, including a pressure exerting means for imposing a pressure that will always exceed the rolling load by a given amount, and

a control system for operating said pressure exerting means to maintain substantially constant said relationship between the imposed pressure and the rolling load as the rolling load changes.

3. In a rolling mill according to claim 1, comprising a screwdown mechanism for setting the gap between the work rolls, a portion of which is included in the bearing chock assemblies of the work rolls:

said screwdown mechanism including a yieldable means arranged to reduce the elastic stiffness of the work roll bearing chock assemblies, the construction being such that the pressure sensitive member is subject also to the elastic change of said portion of the screwdown mechanism and the yieldable means.

4. In a rolling mill having a pair of work rolls that form a roll gap, at least one of which is supported by a backup roll:

bearing chock assemblies for rotatably supporting the ends of said rolls in said mill,

a roll gap adjusting means comprising a pair of screws,

said pair of screws rotatably mounted in the bearing chock assemblies of one of said work rolls, the outer ends of said screws arranged to engage the bearing chock assemblies of the other work roll in order to 9 establish the initial roll gap between the work rolls,- separate means carried by said mill engaging the bearing chock assembly of said backup roll for adjusting one of said backup rolls to alter the initial roll gap, and

driving means carried by said mill for adjusting said roll gap adjusting means.

5. In a rolling mill according to claim 4, wherein said separate means includes a quick-responsive power means operatively associated with said pair of screws.

6. In a rolling mill according to claim 4, wherein said roll gap adjusting means includes a pressure sensitive means arranged to detect a change in the rolling load developed between the Work rolls:

a control system for receiving a signal from the pressure sensitive means, and

said control system associated with said separate means for effectively adjusting said backup roll to maintain a given pressure condition between said work rolls.

7. In a rolling mill according to claim 4, including pressure sensitive means arranged in the bearing chock assemblies of the other work roll engageable by said screws and adapted to detect a change in the rolling load developed between the work rolls, and

a control system for receiving a signal from the pressure sensitive means,

said control system associated with said separate means for eflectively adjusting said backup roll to maintain a given pressure condition between said Work rolls.

8. In a rolling mill according to claim 7, including a yieldable element for each pressure sensitive means mounted in the bearing chock assemblies in the other work roll and engageable by the pressure sensitive means on the sides opposite said screws.

9. In a rolling mill according to claim 4, wherein:

a pair of said screws rotatably mounted in each of the bearing chock assemblies of the uppermost Work roll,

a pair of pressure sensitive means mounted in each of the bearing chock assemblies of the lowermost work roll and engageable by said screws,

a pair of gear trains mounted in each of the bearing chock assemblies of the uppermost work roll adapted to cause rotation of the screw with which it is associated,

a drive shaft for each gear train passing through the bearing chock assemblies of the backup roll, and power means for simultaneously drivin said drive shafts. 10. In a rolling mill having a pair of work rolls, said work rolls being rotatably mounted in bearing chock assemblies:

a backup roll for each work roll, said backup rolls being rotatably mounted in bearing chock assemblies,

pressure sensitive means arranged between and engageable with the bearing chock assemblies of the work rolls adapted to detect a change in the rolling load developed between the work rolls,

the construction and relationship of the mill parts being such with reference to the location and operation of said pressure sensitive means that with reference to the elastic change of the mill parts under the rolling load of the mill, the pressure sensitive means is only subject to the elastic change of the Work rolls and their bearing chock assemblies.

References Cited UNITED STATES PATENTS 2,095,448 10/ 1937 McBane 72245 2,903,926 9/ 1959 Reich] 72-8 3,247,697 4/ 1966 Cozzo 72240 3,315,507 4/1967 Marten 72--16 FOREIGN PATENTS 644,874 9/1962 Italy.

714,301 7/1965 Canada.

955,164 4/1964 Great Britain.

CHARLES W. LANHAM, Primary Examiner.

A. RUDERMAN, Assistant Examiner.

US. Cl. X.R. 72240, 243, 248

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