US3546913A

US3546913A - Method and means for obtaining high modulus rolling mills

Info

Publication number: US3546913A
Application number: US682056A
Authority: US
Inventors: William L Stover; John J Sutyak
Original assignee: Mesta Machine Co
Current assignee: MESTA ENGINEERING COMPANY APARTNERSHIP OF PA
Priority date: 1967-11-13
Filing date: 1967-11-13
Publication date: 1970-12-15
Anticipated expiration: 1987-12-15
Also published as: GB1204750A; DE1807617A1; FR1587193A

Description

Dec. 15, 1970 w, STOVER ET AL 3,546,913-

METHOD AND MEANS FOR OBTAINING HIGH MODULUS ROLLING MILLS Filed Nov. 15. 1967 4 Sheets-Sheet l P/z yT r b WP OQ/ f k1? l I 25 14 l6 I Inventors PA /Or? 497 William L. Stover 8| John J. Sutyck Dec. 15, 1970 w. L. STOVER ETAL 3,546,913

METHOD AND MEANS FOR OBTAINING HIGH MODULU Filed Nov. 13. 1967 S ROLLING MILLS 4 Sheets-Sheet 2 W; Z. inventors William L. Sfover G By John J. Su'yck Dec. 15, 1970 W. L. STOVER ETA]- METHOD AND MEANS FOR OBTAINING HIGH MODULUS' ROLLING MILLS Filed Nov. 13. 1967 4 Sheets-Sheet 8 Inventors William L., Stover 8 John J. Sutyok Dec. 15, 1910 w, L, STOVER ET AL 3,546,913

METHOD AND MEANS FOR OBTAINING HIGH MODULUS ROLLING MILLS Filed Nov. 15, 1967 4 Sheets-Sheet &

V w 6 Q N 26 LI Z6 Inventors William L. Sfover 8 John J. Sutyuk 5 5 97 fifelzwf Ava 02M504 United States Patent US. Cl. 72241 17 Claims ABSTRACT OF THE DISCLOSURE A fully stressed stand for a rolling mill and the like is disclosed. The mill stand is of the four-high variety and includes pressure means coupled for example to the backup roll structures for applying a predetermined prestressing force to the housing and rolls. Means are bearingly inserted between the work rolls and more particularly between the bearing chocks thereof to cause at least a portion of the reactive equivalent of the prestressing force to assume a substantially serpentine path through the work rolls and the backup rolls, their bearing chocks, and associated components. As a result, substantially all of the components of the mill stand (rather than merely the housing therefor) are prestressed and predeformed prior to application of rolling force. Deviations in backup roll bending and in work roll gap width are eliminated. The invention, therefore, eliminates the necessity of employin'g roll gap control equipment and considerably reduces the inventory of rolls with differing crowning compensations.

The present invention relates to strip or plate, hot or cold rolling mills and the like and more particularly to a prestressed, high modulus mill stand for such mills.

When rolling strip or plate material, at least two serious problems are encountered, which have not been satisfactorily solved by the prior art. These problems are associated with control of thickness or gauge and control of flatness or planarity of the strip or plate. Both of these problems represent facets of dimensional control but heretofore have been treated as entirely separate or independent problems and have been approached with completely unrelated and heretofore unsatisfactory solutions.

The disadvantages of improper gauge controls are obvious. In some instances acceptable gauge tolerances are approaching 10.0002 inch. In addition to the obvious disadvantage of non-planarity in the rolled material, nonplanarity (in thin strip) causes center or edge buckling depending upon whether the strip posses negative or positive crown.

In order to atttain an even thickness of the plate or strip, the roll gap or the separation between the work rolls of the mill stand must remain at precisely the rel quired size. During operation of the mill, however, the variable separating forces acting upon the work rolls from the deformation of the rolled material is transmitted through the backup rolls to the frame of the mill stand and causes stretching of the frame and deflection and flattening of both the work rolls and the backup rolls. In addition, the elastic deformation of the mill stand also includes a bowing deformation of the work rolls and the backup rolls. Stretch and other deformations in the mill stand vary the thickness of the rolled material, while bowing deformations of the rolls affect both the planarity and average thickness of the rolled material. Thus, the problems associated with dimensional control of the strip or plate constitute esssentially the single problem represented by the summation of these mill stand deformations. The major facets of this problem comprise variable mill housing stretch and the flattening aspects of roll deforma- "ice tion on the one hand and the variable bowing of the work and backup rolls on the other hand.

As we shall presently show, the treatment by the prior art of these facets of dimensional control as separate and independent problems has resulted in 'generally unsatisfactorily solutions.

Dimensional control of the rolled material has been complicated recently, owing to the present solutional approach of the art, by the advent of extremely high speed rolling mills. Hot rolling mills having exit speeds of 4000 feet per minute or over and cold rolling mills having speeds in excess of 6000 feet per minute are in use or are contemplated at the present time.

With increasing demands of modern production the relative speeds at which rolling mills are operated have reached the point where it is extremely difiicult to maintain the thickness of the strip or the plate on gauge. A variety of monitoring devices, such as radiation, eddy current, induction, or micrometric apparatus are presently in use for check purposes, but cannot develope a sufficiently rapid corrective signal for gauge control in. high speed mills.

In high speed mills, it is impossible for gauge control apparatus to take corrective action after the strip thickness has strayed beyond the required manufacturing tolerances. Hence, in the high speed mills it has become necessary to utilize automatic gauge control systems using load cells (at the screwdowns) to supply a signal to computerized equipment capable of establishing trends from the differential outputs of the load cells in gauge deviation such that corrective equipment can be actuated before the gauge deviates beyond allowable limits. The rolled material transport time and the inherent hysteresis of the load cells results in unavoidable hunting in the correction system. The inertia of the rolling mill equipment and of the control apparatus add further to the inaccuracies of gauge control. The relative sluggishness of even the best automatic gauge control systems has resulted in frequent conditions of excessive gauge deviations and therefore a high rate of rejects in the finished strip. Moreover, such computerized equipment repersents a considerable capital investment and is space consuming and difficult to maintain.

Of the factors contributing to variations in the mill gap, the rolling material deformation or rolling force (R is the most predominant contributor to gauge variations. the inherent accuracy of a rolling mill stand depends upon the mill modulus which is determined by the force required to establish a specific amount of total mill stand deformation. Thus, the mill modulus is cognizant of the summation of deformation factors including stretch in the mill stand housing, the individual deformations of the screwdowns and bearings chocks, flattening of the work and backup rolls and the maximum bowing displacements of the work and backup rolls. The mill modulus can be expressed in terms of tons per lineal inch or in pounds per lineal mil of total mill stand deformation. The mill modulus can also be stated as pounds of force required to produce a deviation of one mil or a fraction of a mil in gauge at the center line of the mill stand, and is representative of both gauge and maximum planarity deviations.

The solutions to the problem of dimensional control of the plate or strip lies in the establishment of a mill modulus that is sufficiently high to obviate the necessity of using external corrective apparatus. That is to say, the provision of a sufficiently high mill modulus will maintain a predetermined work roll gap and the strip gauge determined thereby without subsequent adjustment, as long as the roll force is maintained within the limits discussed below.

The tendency of the backup rolls to bow under the rolling forces occasioned in conventional strip rolling equipment must be compensated by either crowning or bending the work rolls and backup rolls or both to the extent that the associated bowing thereof results in a straight or other desired surface contour, in contact within the strip or plate. The most common practice uses crowning compensations alone for this facet of dimensional control, which necessitates a large inventory of a number of pairs of work and/ or backup rolls each having a degree of crowning commensurate with a given width of strip and a given average rolling force to be employed for that strip. By the same token, it is necessary to exchange the work and/or backup rolls for each change in nominal rolling force, as determined by changes in nominal strip gauge or in strip width. Changing the work rolls for these purposes entails considerable downtime, loss of production and a large inventory in crowns.

Other practices, combine roll bending in conjunction with crowning compensation. For example Fox 3,024,679 provides means for variably bending the work rolls, which reduces the inventory of crowned rolls to some extent, but does not eliminate the necessity of gauge control or of changing crowns for substantial changes in rolling schedules. Moreover, the work roll balance cylinders must be deenergized and strip or other rolled material must be threaded through the mill before the Fox arrangement can be activated. As a result, a quantity of strip may be lost.

In another known arrangement, as typified by the Stone Pat. Nos. 3,171,305 and 3,250,105, the backup rolls are bent by applying forces to projecting or canti lever sections of the backup roll journals. The bending forces, however, are in the same direction as the reactive rolling forces with the result that the loads upon the backup roll bearings are multiplied. The bending means which are coupled to each cantilevered journal section, delay roll changes by their required removel, and must be readjusted for each change in roll crown or size.

As I shall demonstrate below, the degree of deflection of bowing of the backup rolls is a significant factor in computing the overall mill modulus. With an adequately high mill modulus, not heretofore obtainable, the bowing of the backup rolls becomes esentially invariable. As a result a single pair of work or backup rolls, that is to say a single crowning compensation, can be employed for all rolled material handled by the mill independently of dimensional variation (both thickness and width) of the rolled material, as long as the maximum rolling force remains within the designed capacity of the mill stand and the prestressing force as described below, remains unchanged. Thus, only a single crowning compensation is necessary for a given prestressing force regardless of the number of rolling schedules used with such prestressing force. As a result, the inventory of variably crowned rolls needed by the mill operator can be considerably reduced.

Previous attempts to solve the problem of dimensional control by increasing the mill modulus for the most part fall into two categories. Probably first in point of time are brute force attempts to increase the mill modulus by ruggedizing the mill stand, that is by increasing the cross sections of the mill housing and of the backup rolls to minimize stretch in the former and bowing in the latter. Secondly are attempts to increase the mill modulus by prestressing certain components of the mill stand, pri marily the mill housing. Insofar as I am aware, previous attempts at prestressing the mill stand are con-fined entirely to the mill housing itself or additionally to the mill housing screwdowns and backup roll bearing chocks. Such attempts are typified by the following references: British Pat. 955,164; US. patents to Hunter 3,148,565; Tracey 3,286,501; Howard 3,217,525; Brown 3,327,508; Cozzo 3,247,697 and the Hunter Engineering Company Bulletin HE11 (c. 1964).

I shall presently show that these prior attempts increase the overall mill modulus by only insignificant amounts if at all, in contrast to the apparatus of my invention which unexpectedly multiplies the mill modulus by a considerable factor. The shortcomings of prior proposals, either in the form of bulkier mill stands or in the form of prestressed mill housings are attested to by their inclusions of various means for controlling the gauge and flatness of the strip or plate during operation of the rolling mill. Another aspect of their failure to consider all of the many factors affecting the mill modulus is their inability to employ a single crowning compensation irrespective of variations in rolling force or in strip width when a single prestressing force (F is used. While the use of prestressed mill housings produces some improvement in gauge control, it fails almost entirely to solve the basic problem which in a high speed strip mill must be the complete elimination of the requirement of gauge and planarity corrections. Of greater significance is the failure of prestressed mill housings or partially prestressed mill stands, as proposed heretofore, to exhibit any eifect whatsoever upon that aspect of dimensional control involved in maintaining planarity of the rolled material.

I overcome these difiiculties of the prior art by providing a fully stressed mill stand. My novel mill stand i stressed in such a manner as to obtain a mill modulus many time that of previously proposed mill stands. As noted above, prior attempts along this line, as typified by the aforementioned references, remove merely the stretch in the mill stand housing but not the deformations (bowing and flattening) a variable factors of the roll gap width. For the most part the aforementioned references relate to means for controlling the gauge of the rolled material. As I shall show later, the necessity for such controlling means is abundant attestation of an inadequate low mill modulus.

Theextremely high mill modulus provided by my invention results from the application of prestressing forces to substantially all of the components of the mill stand. Thus, the adequately high mill modulus provided by my novel mill stand results from the summation of prestressing forces applied to the mill stand housing, the screwdowns, both the backup bearing chocks and the work roll bearing chocks, and the work rolls and backup rolls to cause both preflattening and prebowing thereof. The summation of the forces applied to the backup and work rolls equal the total prestressing force of the mill stand. The preflattening and prebowing of the work and backup rolls thus established becomes invariable irrespective of subsequently applied rolling forces, as long as the latter forces are maintained at a value below the imposed prestressing force.

Invariable roll flattening and bowing deformations are impossible to achieve with the partially prestressed mill stands of the prior art. In any partial or fully stressed mill housing, the following equations are representative of the various, opposing forces developed:

As explained below more fully, in the prior art approach to prestressed mill stands, the backup and Work rolls are subjected only to R or the rolling force, which obviously is a variable. Therefore, the work and backup rolls have been subjected, during the rolling operation to variable degrees of flattening and bowing, thereby giving rise to the two facets of the dimensional control problem as noted above. In my arrangement, however, the entire prestressing force is applied to both the backup rolls and the work rolls in such manner that both bowing and flattening of the backup and work rolls become invariable, as long as R QP Stated more succinctly, the forces developed between the work and backup rolls during the rolling operation is as follows.

In the prior art:

(a) operation 2r =P W =R (variable) (b) not operating but partially prestressed P W .'.2r =0 (not prestressed) In this invention:

(21) operating ZP R $W =P (constant) (b) not operating but fully prestressed ZP =W =P (constant) In the prior art, the work roll-backup roll interfaces see only the rolling force (R or Zr and are completely unloaded until rolled material is inserted between the work rolls. As the rolling force (R is variable the prior art rolls are subjected to variable flattening and bending deformations throughout the rolling operation. The fully stressed mill of our invention provides a constant load at the roll interfaces irrespective of the instantaneous value of R or lack thereof, since:

and ZP;=PF=WF when R =O.

In the method aspect of our invention, we accomplish these desirable results by providing a method for the dimensional control of elongated rolled material reduced in a rolling mill, said method including the steps of storing in said mill substantially constant force at least equal to the maximum rolling force required for the reduction of said material, transferring at least a portion of the stored force to the material for reduction between work rolls and backup roll forming part of said rolling mill, diverting a reactive equivalent of said stored force in a path through said work rolls and said backup rolls, whereby substantially all of the mill components are prestressed and predeformed to eliminate subsequent deformation during the rolling operation and to maintain dimensional stability of said material irrespective of variations in rolling force within the limits imposed by aid stored force.

We also desirably provide a similar method wherein said reactive equivalent is diverted in a substantially serpentine path through said rolls.

We also desirably provide a similar method including the steps of restricting the maximum value of said rolling force to a value less than that of said stored constant force, and equating said reactive force to the difference between said stored force and said rolling force.

In the apparatus aspect of our invention we accomplish the aforedescribed desirable results by providing a rolling mill stand comprising a mill housing, a pair of work rolls between which elongated rolled material is to be rolled, a pair of backup rolls respectively engaging said work rolls, individual mounting means for mounting each of said rolls in said housing, pressure means coupled to said backup roll mounting means for applying a predetermined prestressing force to said housing, and additional means bearingly inserted between said work roll mounting means for causing at least a portion of the reactive equivalent of said prestressing force to assume a path through said work rolls and said backup rolls and the mounting means therefor.

We also desirably provide similar apparatus wherein said additional means are inserted between said work roll mounting means for causing said reactive portion to assume a substantially serpentine path through said work rolls and said backup rolls and the mounting means therefor.

We also desirably provide a similar apparatus wherein mounting means for each of said work rolls include a pair of bearing chocks coupled respectively to the ends thereof, and said additional means includes a pair of elongated wedge members inserted respectively between juxtaposed pairs of work roll chocks for selectively establishing the work roll gap and the thickness of said material existing from said stand.

We also desirably provide a similar apparatus wherein each of said wedge members is provided with stop means thereon engageable with said work roll chocks for determining a roll-changing position of said work roll chocks.

During the foregoing discussion, various objects, features and advantages of the invention have been set forth. These and other objects, features and advantages of the invention together with structural details thereof will be elaborated upon during the forthcoming description of certain presently preferred embodiments of the invention and presently preferred methods of practicing the same.

In the accompanying drawings we have shown certain presently preferred embodiments of the invention and have illustrated certain presently preferred methods of practicing the same, wherein:

FIG. 1 is a schematic structural view and force diagram of a partially stressed mill stand in accordance with the prior art for purposes of comparison;

FIG. 2 is a similar diagram of a fully stressed mill stand arranged in accordance with my invention;

FIG. 2A is a partial cross sectional view of the apparatus as shown in FIG. 2 taken generally along reference line IIA-IIA thereof;

FIG. 3 is a partially sectioned side elevational view of an improved mill stand arranged according to our invention and showing an exemplary form of prestressing means utilized therein;

FIG. 4 is a partial vertically sectioned view of the apparatus as shown in FIG. 3;

FIGS. 5 and 6 are partial, enlarged sectioned views illustrating operating and roll changing positions of the prestressing means; and

FIG. 7 is a top plan view of the apparatus as shown in FIG. 3.

Referring now to FIGS. 1 and 2 of the drawings a marked contrast is immediately evident between the typical prestressed mill housing (partially stressed mill stand 11) of the prior art (FIG. 1) and the fully stressed, high modulus mill stand 33 of our invention (FIG. 2).

With particular reference to FIG. 1, in accordance wit previous practice, a reactive separating force is applied to legs 9 of bearing chocks 10 of the backup rolls 12 by some means such as a column, wedge or screw, denoted generally by the reference characters 14, are used, and by known means are employed to vary the prestressing force in an attempt to control gauge and compensate for the inherent inaccuracy of these stands. The bearing chocks 16 for the work rolls 18 are confined between the legs of the backup bearing chocks 10 in the conventional manner.

Note in FIG. 1 that the lower work roll bearing chock 16 and the lower backup roll bearing chock 10 are inclined generally in the same direction when the mill stand is loaded as by the insertion of strip or plate material 20 between the work rolls 18. Note also that the upper work roll chock 16 and backup roll chock 10 are also inclined in the same direction but generally opposite to the lower backup roll bearing chocks. The various inclinations of the bearing chocks are shown here in exaggerated form for purposes of illustration. In the arrangement of FIG. 1 the inclination of the chocks and, of course the work roll gap S and roll bowing deformation vary depending upon the instantaneous value of LRF, as described herein.

In the prior art illustration of FIG. 1, the mill stand housing 22 is prestressed by means of a pair of cylinders 24 each of which exerts a force (P /2) upon the mill stand housing 22, which force is opposed by the screwdowns 26 at the upper end of the housing 22. In the absence of strip or plate 20 the entire prestressing force is transmitted through the backup roll chocks 10 and the prestressing wedge 14 or similar columnar support. The wedges 14 or an equivalent maintains a nominal roll gap width S During the rolling operation the deformational forces (2r =R applied to the strip 20 are reactively transmitted through work rolls 18 as denoted by the reactional force arrows 23 to the backup rolls 12, 12. From FIG. 1 it is evident that the wedge forces (ZW /Z) are exerted in parallel with the total rolling force (R between the center lines 30 of the backup rolls. Thus, the rolling force partially unloads the wedge force during the rolling operation, in accord with Equation 1 above. However, such unloading occurs at the engagements of the upper and lower bearing backup chocks 10 with the wedgse 14 or other bearing devices inserted between the legs thereof.

As a result an undesirably variable force, denoted by the aforementioned arrows 28 and by arrows 32 is applied to both the work rolls 18 and the backup rolls 12 throughout the rolling operation. The backup rolls 12 and the work rolls 18, then, are subjected to varying degrees of flattening and bending deformation which have a deleterious influence upon the nominal or preselected roll gap with S Thus, the prestressing in the prior art mill stand 11 is only partial and is confined almost entirely to the housing 22. Only a minor proportion of the deformational instability of the prior art mill stand is removed.

When using the conventional, partially prestressed mill stand 11 of FIG. 1, additional means are essential for stabilizing the nominal roll gap opening S In. partially stressed and other conventional mill stands this can be accomplished by adjusting the screwdowns 26. In most of the known partially stressed mill stands the nominal roll gap S is controlled by changing, during operation, the prestressing force (P or by changing S by means of movable wedges, fillers, screws and their actuating means. For example, in Tracey 3,286,501, the work roll gap is adjusted by motor driven screw jacks interposed between the upper and lower backup roll chocks. In the British Pat. 955,164, and in Brown 3,327,508 the work roll gap is adjusted by varying the prestressing force on the mill housing by means of the hydraulic cylinders 24. In the Hunter mill stand the roll gap is varied by employment of an adjustable wedge. These latter described methods are equally unsatisfactory methods of roll gap control for the reasons mentioned previously. They also involve more sophisticated equipment and higher maintenance costs.

Referring now more particularly to FIG. 2, the radically different force diagram associated with the fully stressed, high modulus mill stand 33 of the present invention is readily apparent. To facilitate comparison, a structurally similar mill stand is shown, with similar reference characters with primed accents denoting similar components of FIG. 1. In FIG. 2, however, a suitable wedge, columnar support, piston and cylinder arrangement, or other suitable separating means denoted generally by the wedges 34, are interposed directly between the work roll bearing chocks 16. The total prestressing force (P thus is applied, as in FIG. 1 to the upper and lower ends of the housing 22 of the mill stand 33.

As a result under no load conditions (in the absence of the plate or strip 20' when W =P all of the reactive prestressing forces must assume a serpentine path sub stantially completely through the mill stand as denoted by force arrows P 2, W 2, the unit backup roll prestressing forces denoted by arrows P; and the unit work roll prestressing forces denoted by arrows W In FIG. 2, note that each of the work roll chocks 16 are inclined in an opposite direction to its associated backup roll Conventional bearing housing (not shown) are provided in the mill stand to permit the aforedescribed inclinations, which, as noted previously, are exaggerated for purposes of illustration. The opposite inclinations of adjacent work and backup roll chocks are indicative of the fully stressed condition of the mill through the mill stand 33 and particularly of the serpentine path assumed by the various reactive components of the prestressing force stored therein. In this example, each work roll 18 and its associated backup roll 12 are bowed in different directions, for the same reason. The bowing desirably is compensated by a negative work roll crown 35 and a positive backup roll crown 37 to provide a fiat strip or plate 20. As is known, the rolled material, if desired, can be provided with a positive or negative crown for guiding purposes as an appropriate selection of roll crowns.

The described prestressing of the backup rolls and work rolls 12, 18' causes the work rolls and the backup rolls to bend to a predetermined extent, which is compensated by crowning the work rolls 18 and backup rolls 12' so that a perfectly rectangular roll gap S' is obtained. However, in contrast to the arrangement of FIG. 1 the gap S retains perfect rectangularity and constant width as long as the summation of rolling forces denoted by force arrows d in the strip material 20' or force arrows r in the work rolls 18 do not exceed the prestressing force P Accordingly, both the thickness of the strip 20 and its planarity are precisely maintained by the work roll 18 regardless of variations in the total rolling force, as long as R P With the prestressing arrangement of our invention every component of the mill stand is prestressed for maximum predeformation with the exception of the relatively small work roll portions 36a adjacent their surfaces 36 (FIG. 2A) which are in actual engagement with the plate or strip 20'. These work roll portions protrude beyond the work roll journals 38 and therefore are not prestressed. For purposes of work roll gap control, however, the very small variations in deformation of the Work roll portions 36a adjacent their arcuate surfaces 36 are negligible in an improved mill stand. This follows from the fact that our prestressing arrangement pre-ovates the Work rolls (exaggerated for clarity in FIG. 2A) in addition to prefiattening the work-backup roll engagements 40. As evident from the following Table I, the flattening at the roll surfaces 40 and the oveating of the rolls account for over percent of the total roll deformation. From FIGS. 2 and 2A, then, it will be apparent that only that area of the mill 33 denoted by I (FIG. 2) is not subject to pre stressing force. This area which includes only the work roll portions 36a results in a maximum total deformation of only 0.0042 inch for the entire mill stand of our invention at a design rolling force of 3,500,000 pounds in contrast to 0.0885 inch at 3,000,000 pounds (Table I) for a standard mill and 0.0663 inch at 3,000,000 pounds for a conventional prestressed mill (FIG. 1).

During the rolling operation, development of unit rolling forces r partially and variably unloads the Wedge forces EW 2). This follows from the variable character of the rolling forces caused for example by variable material, temperatures, and hardness, etc.

However, the prestressing force interposed upon the mill housing 22', the screwdowns 26 (used in our novel mill to enable roll changes not for roll ga control), the prestressing cylinders 24', upper and lower backup roll chocks 10, upper and lower work roll chocks 16, and the backup and work rolls 12', 18 are not intended to be varied during operation of the rolling mill as long as zr P As a result, the only portions of the entire mill stand 33 which are subject to variable deformation are the work roll surfaces 36 and portions 36a adjacent thereto. Any positive change in rolling force (R during operation of the stand 33 is accompanied by an instantaneous and equivalent unloading of the compression means or wedges 34. Any negative change in R is similarly accompanied by equivalent reloading of the Wedges 34.-Thus, the bowing deformation of the backup and work rolls 12', 18' cannot vary at all and the gap S' can vary only a negligible amount as reflected in the insignificant variations caused by flattening deformation of work roll surfaces 36.

There are at least two most important advantages stemming from the use of the fully stressed mill stand 33 as thus far described. In the first place only a single crowning compensation is required as long as R does not exceed P Similarly, it is no longer necessary to provide conventional gauge measuring and control equipment. Variations in rolling force occasioned by changes in hardness, composition, or temperature of the rolled material 20' and the attended variations in R merely load In contrast, the Fully Stressed Mill of my invention eliminates all mill deflections (item Nos. 7-11) with the exception of the very minor amount of roll deformation associated with the work roll portions 36a (FIG. 2A). The much larger values for roll deformation (item No. 9) for the A and B Standard Mills and the Partially Stressed Mill results from failure to apply prestressing forces to the rolls to pre-ovate the rolls and to flatten the engagements 40 (FIGS. 2 and 2A) between the work rolls and the associated backup rolls, which account for virtually all of the roll flattening as pointed out above in connection with FIG. 2A. As shown in Table I in the fully stressed mill of our invention, prestressing and predeformation of every component of the mill stand is effected with the exception of the very minor deformation and unload the compression means or wedges 34 (W 2) of the work roll portions 36a adjacent the rolled material to the extent of such variations. As a result, both the Extremely high mill modulus is thus obtained by work roll gap 8' and backup roll bowing are no longer my fully stressed mill which is many times that of the subject to the vargaries of R Thus, the use of roll gap partially stressed mills of the prior art. corrective devices are eliminated along with the necessity 20 The significance of the vast improvement in mill moduof an inventory of work rolls with differing crowning comlus effected by our apparatus is clearly demonstrated by pensations. items 14-16 of Table I. Item No. 15 of the table shows The contrast between our novel, high modulus mill that in a prior art mill stand having the highest available stand of FIG. 2, the known low modulus, partially mill modulus (Partially Stressed Mill), a change in the stressed mill stand of FIG. 1, a standard heavily connominal rolling load (R of only 1.50% is suflicient to structed mill stand (B Standardnot shown) and a produce a one mil variation in the strip or plate at the standard mill stand (A standardalso not shown) are center line thereof. The gauge variation is intolerable in shown in greater detail by the following table: many applications. On the other hand, in our novel mill TABLE I.MILL MODULUS SUMMARY Partially Fully A Stand- B Stand- Stressed Stressed No. Item ard Mill ard Mill" Mill Mil 1 Mill slze, inch:

(a) Diameter, work rolls 30 3O 30 (b) Diameter, backup rolls.- 55 55 (0) Length of rolls 84 34 84 84 2.. Back up roll bearings 3 Housing post area, in. 1, 000 1, 200 600 600 4 Back up roll choekleg area, 600 5 Nominal rolling load, lbs"--- 3. 0x10 3. 0X10" 3.0X10 3. 5x10 6 Maximum prestress load, lbs 4. 0x10 4.0)(10 7 Mill deflections, inch:

Screw 0054 Nut .0053 Breaker block- 0045 Bearing journals .0079 Housing top-- 0029 Housing bottom 0039 Housing post 0051 Total, inch 0350 8 Roll deflection C.L. mill 55 wide 0245 strip, inch. 9 Rprlll 1flattening, 55" wide strip,

0 I Roll engagement 0161 0159 0161 Strip engagement 0129 0129 0129 0042 Total 0290 0288 0290 0042 10 Wedge and chock deflection, inch 0049 11 Totalrolling deflection, inch .0885 .0757 .0663 .0042 12 Millmodulus tons/in 16, 960 19,820 22,600 417,000 13 ill modulus lbs/.0002 in 6,780 7, 930 9,050 166,800 14 Percent rolling load for .0002 in. 0.23 0.26 0.30 4. 77

deviation. 15. Percent rolling load for 1 mil 1. 15 1. 30 1. 50 23. 85

deviation 16 Stifiness improvement, percent 17 33 2456 l 34 in. and 40 3111. X 26% in 2 39% in. and 51% in. X 26% ln. 3 Not; pertinent.

From the table it will be seen that the B Standard Mill is provided with a heavier housing (items No. 3) and a larger backup roll diameter (item No. l(b)) to reduce the stretch in the mill stand housing and the bending deflection of the backup rolls. The B Standard Mill produces slightly less total rolling reflection (item No. 11) than that of an A Standard Mill. A similarly small improvement is evinced by the Partially Prcstresscd Mill which eliminates the relatively small mill deflections of the mill housing and components associated therewith including the wedge 14 to FIG. 1 (item No. 7). Thus, the partially stressed mill increases the mill modulus (item Nos. 12 and 13) by substantially twice the amount contributed by the ruggedized or B Standard Mill.

stand, a 23.85% deviation in a higher nominal rolling load (Item No. 5) is required to produce the same one mil deviation. As it is well established that rolling loads normally vary only 5 to 10%, it is evident that our apparatus can maintain a tolerance in the order :0.2 mil to 10.4 mil without the use of external corrective equipment for maintaining nominal gauge. With closer control of hardness, composition, and temperature of the roller material 20' even closer tolerances can be maintained.

Item No. 16 shows that a typical Fully Stressed Mill according to our invention (FIG. 2) has a mill modulus of 2456% greater than that of a conventional mill (A Standar while the Partially Stressed Mill (FIG. 1) offers an improvement in mill modulus of only 33%.

With reference now to FIGS. 3 and 4 of the drawings an exemplary construction of a novel mill stand incorporating the prestressing arrangement shown in FIG. 2, is illustrated. In FIGS. 3 and 4 similar reference characters denote similar components of FIG. 2. The construction of the mill stand 33 of FIGS. 3 and 4 is essentially similar to conventional mill construction with the exception of the wedge members 34 and components associated therewith and the use of a lighter housing (Table I) having for this purpose

deep indentations

41, 43, 45. The latter two changes are necessitated by passage of the prestressing force (P through the work roll chocks 16', their bearings 44 and the work rolls themselves (FIG. 2). In this example the Work roll bearings 44 are shown as comprising six circumferential rows of roller bearings 46 instead of the usual four rows. Other equivalent bearing means, of course, can be substituted.

The center lines of the wedges 34 conform to the mill pass line 48 inasmuch as the lateral position of the wedges 34, as subsequently explained, determine the initial height of the work roll gap S (FIG. 2). The gap S' can be varied by moving the Wedges transversely of the rolls by means of jack screws 50 driven by motor and gear arrangements denoted generally by the reference character 52 (FIG. 7). The jack screw 50 is provided with a shouldered nut 54, which is slidably movable in an expanded cavity portion of piston 56. The piston 56 is mounted for reciprocatory movement in cylinder 58 and is secured at its other end to piston rod 60, the distal end of which is connected to the wedge 34. The sliding engagement of the jack screw nut 54 within the piston 56 is delimited inwardly by an inner annular shoulder 62 of the piston 56.

With this arrangement, the central wedge portion 64 can be moved transversely of the rolls while in adjusting engagement with the work roll chocks 16' by rotating the jack screw 50 in either rotational direction. This adjustment is made only for the purpose of establising the initial roll gap S' which if correctly set, need not thereafter be changed (for a given rolling schedule). At the same time the shoulder 62 of the piston 56 is maintained in engagement with the jack screw nut 54 by an opposing force supplied by cylinder 66 having distal end 68 of its piston rod 70 connected to the opposite end of the associated wedge 34.

The adjusting movement of each wedge 34 and thus the variation in the work roll gap S' is limited by stop member 72 (FIG. 5) which is normally movable between stop surfaces 74 and camming surfaces 76 of the work roll chocks 16'. A similar stop 78 is secured to the other end of the wedge 34 for roll changing purposes as described below in connection with FIG. 6. The adjusting movements as defined by the solid and chain outline positions of the

stops

72, 78 of each wedge 34 determines the roll gap width and gauge of the material exiting from a given mill stand. The wedge 34 need not be moved during the rolling operation to compensate for deviations in gauge, as such deviations are prevented by the use of a fully stressed mill stand as explained above.

During roll changing the hydraulic cylinders 66 (FIG. 7) are actuated to quickly move the wedges 34 to their roll changing positions as shown in FIG. 6. The wedge stops 72, 78 are then positioned in contact with

complementary surfaces

82 and 84 respectively of the work roll chocks 16' to separate the work roll chocks 16' while the work rolls 18 are being withdrawn therefrom and new rolls substituted. When the hydraulic cylinders 66 are thus actuated, the pistons 56 are slidably withdrawn from engagement with the jack screw nuts 54 to permit quick movement of the wedges 34 to the left as viewed in FIG. 3.

The aforementioned camming surfaces 76 and additional camming surfaces 86 together with the frusto-conical contours of the wedge stops 72, 78 permit the wedges 34 to cam the work roll chocks 16' to their separated roll 12 changing positions (FIG. 6) without the use of an inordinately long wedge member. Obviously a wedge having a differing overall thickness in its intermediate section 64 can be substituted to provide a different range of predetermined roll gaps 50.

Referring again to FIG. 7 the motor and gear assemblies 52 for each wedge 34 are tied together through a connecting shaft 88 to ensure moving the wedges 34 in step to separate each adjacent pair of work roll chocks 16 by precisely the same amount.

In operation, the desired work roll gap S' (FIG. 2) is established by movement of the wedges 34, as described above, with the central tapering portions 64 of the Wedges in engagement with the associated work roll chocks 16' (FIGS. 3 and 5). With the work roll gap S thus established, a strip 20' or other material to be rolled is then threaded between the work rolls 18 and the rolling operation is commenced. Vernier adjustment in the roll gap S' can be made if desired by adjusting the valving arrangement 31 associated with the cylinders 24'. The rolling force R unloads the work roll bearing chocks 16' to the extent of the value of r Xw so that the rolling load is removed from the work roll bearings and is transferred instead directly through the work rolls 18' (Er It will be apparent, then, that my novel mill stand functions more efliciently in this respect as R approaches P In view of the foregoing, it will be apparent that novel and efiicient forms of rolling mill stands have been disclosed herein. While I have shown and described certain presently preferred embodiments of the invention and have illustrated presently preferred methods of practicing the same, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

We claim:

1. A method for the dimensional control of elongated rolled material reduced in a rolling mill, said method including the steps of mounting work rolls and back-up rolls within said mill and in respective engagement with me another, storing in said mill substantially constant orce at least equal to the maximum rolling force required for the reduction of said material, directing at least a portion of said force to maintain a predetermined opening between work rolls of said mill, transferring at least a portion of the stored force to the material for reduction between said work rolls, diverting a reactive equivalent of said stored force in a path entirely through said work rolls and said back-up rolls, positioning said work roll mounting independently of said back-up roll mounting, and maintaining said rolling force within a predetermined range extending below said constant force, whereby substantially all of the components of said mill are prestressed and predeformed to eliminate subsequent deformation during the rolling operation and to maintain dimensional stability of said material irrespective of variations in rolling force within said range and within the limits imposed by said constant force.

2. The method according to claim 1 including the step of imposing reactive forces between the adjacent ends respectively of said work rolls to define at least partially said serpentine path.

3. The method according to claim 1 wherein said rolls are each provided with a pair of roll bearing chocks, including the additional step of diverting said reactive force in a serpentine path including said bearing chocks.

4. The method according to claim 1 wherein at least said work rolls are each provided with a pair of roll bearing chocks, including the step of imposing reactive forces between each adjacent pair of said work roll chocks.

5. The method according to claim 1 icluding the steps of restricting the maximum value of said rolling force to a value less than that of said stored constant force, and

equating said reactive force to the diiferences between said stored force and said rolling force.

6. The method according to claim 1 wherein said reactive equivalent is diverted in a substantially serpentine path through said rolls.

7. A rolling mill stand comprising a mill housing, a pair of work rolls between which elongated rolled materialis to be rolled, a pair of back-up rolls respectively engaging said work rolls along contact areas coextending substantially with the length of roll faces thereof, individual mounting means for mounting each of said rolls in said housing, means for positioning said back-up roll mounting means independently of said work roll mounting means, prestressing pressure means coupled to said backup roll mounting means for applying a predetermined prestressing force to said housing only directly through said contact areas, and additional prestressing means bearingly inserted between said work roll mounting means for urging said work rolls apart and for causing a reactive equivalent of said prestressing force to assume a path through said work rolls and said backup rolls including the roll faces thereof.

8. The combination according to claim 7 wherein said additional means are inserted between said Work roll mounting means for causing said reactive portion to assume a substantially serpentine path through said Work rolls and said backup rolls and the mounting means therefor.

9. The combination according to claim 7 wherein mounting means for each of said work rolls include a pair of bearing chocks coupled respectively to the ends thereof, and said additional means includes a pair of elongated wedge members inserted respectively between juxtaposed pairs of said work roll chocks for selectively establishing the work roll gap and the thickness of said material exiting from said stand.

10. The combination according to claim 7 wherein each work roll and the adjacent one of said backup rolls are bowed in opposite directions by said prestressing force.

11. The combination according to claim 9 wherein each of said wedge members is provided with stop means thereon engageable with said work roll chocks for determining a roll-changing position of said work roll chocks.

12. The combination according to claim 10 wherein each of said work rolls is provided with a negative crown, and each of said backup rolls is provided with a positive crown.

13. The combination according to claim 11 wherein said stop means and said bearing chocks are provided with camming surfaces to aid in positioning said stop means bet-ween said bearing chocks.

14. The combination according to claim 11 wherein drive means are provided for said wedge members for moving said wedge members relatively slowly for selection of a predetermined work roll gap and for moving said wedge members relatively rapidly to interpose their stop means between said bearing chocks.

15 The combination according to claim 13 wherein said bearing chocks are provided with additional stop surfaces disposed adjacent the path of movement of said stop means for determining the limits of roll gap adjusting movement of said wedge members.

16. The combination according to claim 14 wherein said drive means include opposing drive mechanisms coupled to each of said wedge members, said mechanisms being capable of moving the associated wedge members relatively rapidly in a single one of said transverse directions and independently of the other associated drive mechanism for rapid insertion of said stop means between said bearing chocks.

17. The combination according to claim 16 wherein means are provided for interconnecting said other drive mechanism to ensure prceise simultaneous movement of said Wedge members to permit selection of work roll gap which is invariable along the length of the work rolls.

References Cited UNITED STATES PATENTS 1,980,570 11/1934 Biggert 80-56.3 2,430,410 11/1947 Pauls 8056.3 3,611,150 9/1952 Goulding 8056.3 3,242,711 3/ 1966 Fox 72243 3,422,655 1/ 1969 Stone et a1. 72237 FOREIGN PATENTS 647,039 12/ 1950 Great Britain.

760,698 6/1967 Canada.

RICHARD J. HERBST, Primary Examiner B. J. MUSTAIKIS, Assistant Examiner US. Cl. X.R. 72237, 244

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,546 ,913 December 15 William L. Stover et al It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 53, "atttain" should read attain Column 3, line 44, "esentially" should read essentially Column 4 line 27 "time" should read times Column 6 li ll, "existing" should read exiting Column 7, line 19, wedgse" should read wedges Column 8, line 46, "oveating should read ovating ";'line 49, I should read L Column 9, line 19, "vargaries" should read vagaries same column 9 Table I "Fully Stressed Mil" should read Ful Stressed Mill Column 10, line 69, "roller" should read rolled Column 12, line 73, "icluding" should read includ Column 14, line 26, "prceise" should read precise li 35 "3,611 ,150" should read 2 ,611 ,150

Signed and sealed this 4th day of May 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLE Attesting Officer Commissioner of Pa