US3425253A

US3425253A - Methods and apparatus for reducing the thickness of metal

Info

Publication number: US3425253A
Application number: US530615A
Authority: US
Inventors: Karel Saxl
Original assignee: Imperial Metal Industries Kynoch Ltd
Current assignee: Imperial Metal Industries Kynoch Ltd
Priority date: 1965-03-08
Filing date: 1966-02-28
Publication date: 1969-02-04
Anticipated expiration: 1986-02-04
Also published as: GB1103952A; DE1527651A1

Description

Feb. 4, 1969' K. AX'L 3,425,253

METHODS AND APPARATUS FOR REDUCING THE THICKNESS 0F METAL Filed Feb. 2a 1966 Sheet of 4 FIG. I

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IBTHODS AND APIARATUS FOR REDUCING THE THICKNESS OF METAL Filed Feb. 2a 1965 Sheet 3 1 4 LT-Z37 FIG. 2.

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Feb. 4, 1969 METHODS AND APPARATUS FOR REDUCING THE THICKNESSOF METAL Filed Feb. 28. 1966 Sheet 3 of 4 Feb. 4, 1969 K. SAXL 3,425,253

METHODS AND APPARATUS FOR REDUCING THE THICKNESS OF METAL Filed Feb. 28. 1966 'Sheet 4 0f 4 4|\ J H I FIG.4. FIGS- tfwv\ l/VVE/Vfdfi- FIG.6.I A/AREL 45 19,? 4

United States Patent Office 3,425,253 METHODS AND APPARATUS FOR REDUCING THE THICKNESS F METAL Karel Sax], Sutton Coldfield, England, assignor to Imperial Metal Industries (Kynoch) Limited, London, England, a corporation of Great Britain Filed Feb. 28, 1966, Ser. No. 530,615 Claims priority, application Great Britain, Mar. 8, 1965,

9,7 39/ 65 U.S. Cl. 72-189 8 Claims Int. Cl. B21b 31/20, 21/00, 45/02 ABSTRACT OF THE DISCLOSURE This invention is concerned with methods of and apparatus for reducing the thickness of metal.

In the specification of our U.S. Patent No. 3,143,010 and our British Patent No. 889,662, there is described a method of reducing the thickness of metal which comprises advancing the metal between and beyond a pair of freely-rotatable work-rolls disposed on opposite sides of the metal, and subjecting the metal to the rolling action of the pair of freely-rotatable work-rolls, the rolls moving in synchronism in pendulum-like manner at high speed and etfecting reduction in both directions of their movement.

In the aforementioned specification is also described apparatus for carrying out the above method, the apparatus comprising a frame, a pair of oppositely disposed swingable arms, the free ends of which are adjacent, a freely rotatable work-roll mounted on the free end of each arm, and mechanical driving means operable so as to cause swinging of the arms forwardly and backwardly in synchronism with each other.

In use of the above method and apparatus, the speed of the work-rolls during oscillation is at least five times the advance speed of the metal after reduction which may, for instance, lie between 30 and 150 feet per minute. It is found that using the above method and apparatus, metal may be reduced in thickness by very large amounts, without preheating and in a single pass. For instance, after being reduced by a single pass, metal may have a thickness which is only or less of its original unreduced thickness. However, in practice, while such large reductions are possible, as the rolls move between their limits of oscillation in engagement with the metal and in a direction opposite to that of the direction of advance of the metal, the metal exerts an increasing rolling load upon the rolls.-This increasing load has a component which also increases and imposes an increasing strain upon the rolls and upon their supporting system so that, as the rolls move in said opposite direction, they are forced to depart, in a direction away from one another, from their theoretical arcuate paths of oscillation at constant radius about their axes of oscillation, which paths they would follow if there was no such component of rolling load. On the return movement of the rolls, the metal exerts a decreasing component of rolling load upon the rolls. The rolls are, therefore, subjected to a 3,425,253 Patented Feb. 4, 1969 decreasing strain and approach their theoretical arcuate paths of oscillation.

The component of rolling load which causes the rolls to depart from their theoretical arcuate paths of oscillation in a direction away from one another will hereinafter be referred to as the roll displacement force.

It is sometimes found that the displacement of the rolls from their theoretical paths caused by the roll displacement force, results in the finished rolled metal having rolled surfaces which are more fiat than they would otherwise be if the rolls had followed their theoretical paths. This is because, under suitable circumstances of the speed of advance of a given metal, the ratio of the advanced speed to the speed of roll oscillation, and the distance of limit of oscillatory movement of the rolls (taken in the direction of metal advance) beyond a common plane extending through the pivotal axes of the arms, the roll dis-placement force varies to cause the rolls on this side of the plane to follow paths which tend towards straight-line parallel relationship. The rolled metal has, in consequence, a gauge which varies to a lesser degree than would be expected if the rolls had followed their theoretical arcuate paths.

According to the present invention, a method of reducing the thickness of metal comprises advancing the metal between and beyond a pair of freely-rotatable work-rolls disposed on opposite sides of the metal, subjecting the metal to the rolling action of the pair of work-rolls while oscillating the rolls longitudinally of the metal to effect reduction in the metal in both directions of movement of the rolls, the rolls oscillating in synchronism about pivotal axes for a distance on each side of a common plane in which said axes lie, and oscillation of the rolls being at a high speed compared with the speed of advance of the metal between the rolls, increasing the resistance to displacement of the rolls away from the theoretical arcuate paths of oscillation as the roll displacement force increases during movement of the rolls towards said plane and in the direction opposite to the direction of advance of the metal, and decreasing said resistance as said roll displacement force decreases during movement of the rolls away from said plane and in the direction of advance of the metal.

As used in this specification, the term theoretical arcuate paths of oscillation is intended to refer to the arcuate paths that the rolls would follow, each at constant radius from its respective pivotal axis, if there was no roll displacement force acting upon the rolls.

In one manner of effecting the method defined in the lost perceding paragraph, the resistance to displacement of the rolls is progressively increased and decreased. However, the increase and decrease in the resistance may be in a step-by-step manner.

It is preferable that the resistance to roll displacement increases and decreases in a manner such that the rolls travel in substantially parallel straight-line paths during said movement of the rolls towards said plane so that after reduction, the metal is substantially fiat.

The invention also includes metal which has been reduced in thickness by the method defined in the last three preceding paragraphs.

According to the invention also, apparatus for reducing the thickness of metal comprises a frame, a pair of oscillatable arms, each pivotally mounted about a pivotal axis upon the frame and having free ends which lie in closer relationship than their pivotal axes, a freely-rotatable work-roll mounted on the free end of each arm, driving means for oscillating the arms in synchronism through the common plane in which the pivotal axes lie and for a distance on each side of said plane, and means for increasing and decreasing the resistance to displacement of the rolls away from their theoretical arcuate paths of oscillation, such displacement being caused by variation in roll displacement force, said means being operable to increase said resistance during movement of the rolls towards said plane and in a direction opposite to the predetermined direction of advance of metal to be passed between the rolls, and being operable to decrease said resistance during movement of the rolls away from said plane and in the predetermined direction of advance of the metal.

In one construction, the means for increasing and decreasing the resistance to roll displacement operates progressively to increase and decrease the resistance. In this case, this means may comprise at least one leaf spring which, before the roll displacement force is imposed upon the roll, lies with a part of the spring in engagement with a bearing surface of the apparatus with either the spring or bearing surface being of arcuate shape, and mean are provided by which any roll displacement force imposed upon the roll is imparted to the spring in a position of force application spaced from its part in engagement with the bearing surface, the spring being defiectable towards the bearing surface upon application of and progressive increase in the roll displacement force, progressively to shorten the effective spring length between the position of load application and the part of the spring in engagement with the bearing surface so as progressively to stiffen the spring and increase its resistance to further deflection. The bearing surface may be of concave shape in which case the ends of the spring only, in the unloaded state, engage the surface. Upon application of and increase in load upon the spring caused by application of and progressive increase in the roll displacement force, the spring is deflected progressively towards the bearing surface. During this deflection, the spring engages the bearing surface progressively from the ends towards the mid-position of the spring so that the effective spring length becomes progressively shorter resulting in progressive increase in resistance to further spring deflection. Alternatively, a spring in the form of a disc may be used instead of the leaf spring, the disc engaging the arcuate bearing surface, when a minimum load is applied to the disc, solely around the edges of the disc. An increase in load upon the disc causes the disc to deflect towards the surface, so as progressively to engage the surface from the edge towards the centre of the disc to result in progressively increasing resistance to further deflection.

Alternatively, said means for increasing and decreasing the resistance operates to increase and decrease the resistance in a stepped manner. In this case, for each roll, said means may comprise at least two tubular members located one radially within the other, and abutment members are provided at the ends of the tubular members, a first of the tubular members having its ends in engagement with both abutment members upon application of roll displacement force while the second tubular member has one end spaced from one of the abutment members, the abutment members being movable one towards the other upon progressive increase in roll displacement force so that the first tubular member is compressed axially until the second tubular member lies in engagement with both abutment members, further increase in roll displacement force causing axial compression of both tubular members so that the resistance to displacement of the roll is increased in a stepped manner.

In a specific case where three tubular members are used, when the roll displacement force is increased during roll oscillation to displace the roll from its theoretical arcuate path, the loaded tubular member is compressed until a second tubular member commences to take a part of the load, so that increase in the roll displacement force compresses both of the loaded tubular members and the resistance to further displacement is thereby increased. As the roll displacement force continues to increase, further compression of the loaded members results in the third tubular member taking a part of the load so that resistance to displacement is further increased.

The invention also includes metal which has been reduced in thickness by the apparatus defined in the last four preceding paragraphs.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is a schematic side elevational view of the apparatus forming a first embodiment and ancillary equipment;

FIGURE 2 is a side elevational view of part of the apparatus of FIGURE 1;

FIGURE 3 is a front elevational view partly in section of the apparatus of FIGURE 1;

FIGURE 4 is a vertical section view of part of the apparatus on a larger scale than that shown in FIGURES 1 to 3;

FIGURE 5 is a view similar to FIGURE 4 of a modification of the apparatus shown in FIGURES 1 to 4;

FIGURE 6 is a view similar to FIGURE 4 of part of an apparatus forming a second embodiment.

In a first embodiment as shown in FIGURES 1 to 4, apparatus for reducing the thickness of metal is basically of similar construction to that described in the specification of our US. Patent No. 3,143,010 and our British Patent No. 889,662. This basic construction will now be described in brief detail followed by a more detailed description of the parts of the apparatus which relate to the present invention.

Briefly, therefore, the apparatus comprises a pair of freely-rotatable work-rolls 1 and 2 (see FIGURES 2 and 3) mounted in end bearings 3 upon the free ends of a pair of arms in the form of

compound pendulums

4 and 5. The pendulums are each pivotally mounted upon a pivotal axis by means of

bearings

6 and 7 provided upon the pendulum, the bearings being rotatably received upon a beam 8 vertically slidably mounted within a frame 9. The free end of each pendulum is provided with three pairs of supporting

rollers

10, 11 and 12 for the associated work-roll, the rollers being freely rotatably mounted for rotation between

pendulum arms

13, 14, 15 and 16.

Each compound pendulum is oscillated about its beam 8 by driving means comprising a lever 17 pivotally mounted at

ends

18 and 19, respectively, to the compound pendulum and to a crank 20 of a crankshaft 21.

The apparatus will now be described in greater detail.

Each crankshaft 21 is driven by a common suitable drive motor and gearing (not shown) which oscillate the pendulums in synchronism (FIGURE 1), on each side of their full outline positions 22 in which they lie on the common plane which extends through their pivotal axes, i.e. the axes of the

bearings

6 and 7, the pendul'ums being oscillatable between limiting chain-dotted

positions

23 and 24.

In addition, the apparatus comprises means for increasing and decreasing the resistance to displacement of the rolls away from their theoretical arcuate paths of oscillation, respectively, during movement of the pendulums from their positions 23 towards positions 22 and during return movement to positions 23. As shown in FIGURES 2 and 3 and more particularly in FIGURE 4, in respect of each roll 1 and 2, this means comprises two leaf springs 25 which are spaced-apart adjacent the associated beam 8 in positions diametrically opposite the

bearings

6 and 7. Each leaf spring lies, in a minimum loaded condition of the pendulum, i.e. before application of a roll displacement force to its associated roll 1 or 2, with only its ends in engagement with an arcuate concave bearing surface 26 of an adjustable screw 27, received within a rigid block 28, secured to the frame 9. Any roll displacement force imposed uopn the roll and to the pendulum is transmitted to each spring, to effect spring deflection, by a means in the form of a projection 29 mounted upon each beam 8 and lying in continuous engagement in a position of force application with the spring, mid-way between the ends thereof as shown in FIGURE 4. Taking into account the variation in roll displacement force which occurs during oscillation of the pendulums in the direction opposite to the advance of the metal, the springs are designed so that, during use, their resilience will alter in a manner such that the Work-rolls will move along substantially parallel straight-line and parallel paths along part of their movement from pendulum positions 23 to 22. The variation in roll displacement force is calculable and measurable and is dependent (for the specific apparatus), upon the speed of advance of the metal, the ratio of this advance speed to the speed of oscillation of the work-rolls, and the distance of oscillatory movement from position 23 to position 22.

In use of the apparatus as shown in FIGURE 1, a strip 30 of metal, the thickness of which is to be reduced, is fed between a pair of

feed rollers

31 and 32 and through a heating chamber 33 and the heated metal is then fed between the pair of freely-rotatable work-rolls which acts on opposite sides of the strip. The reduced strip is then passed between a pair of pinch rolls 34 and 35, a pair of guide rolls 36 and 37, and is wound upon a coiling drum 38.

During the advance of the strip of metal, the rolls 1 and 2 are oscillated continuously between the limiting

positions

23 and 24 of the pendulums, the rolls being in constant engagement with the surfaces of the metal. When the pendulums are located in positions 23, the roll displacement force imposed by the metal upon the rolls is at a minimum, so that the springs 25 lie in substantially rectilinear positions as shown in FIGURE 4 with only the ends of the springs in engagement with the surface 26. As the pendulums swing from the position 23 towards their positions 22, the roll displacement force imposed upon the rolls progressively increases and causes movement of the beam 8 away from one another and towards the rigid blocks 28. This movement of the beams is resisted by the springs 25 which are deflected at their centres by the projections 29, towards the arcuate surfaces 26. As the springs deflect in this manner, each spring comes into a greater area of contact with its surface 26 progressively from the outer ends of the spring towards its force application position. As each spring is progressively deflected, therefore, its effective deflectable spring length gets progressively shorter so that the spring progressively stiffens. In consequences, the resistance to deflection of the springs progressively increases as the roll displacement force increases. When the pendulums reach positions 39, shortly before reaching the positions 22, the springs come into their fully deflected positions in which they intimately engage the arcuate surfaces 26. The progressively increasing roll displacement force is then resisted by the stiffness of the blocks 28 and frame 8. The total stiffness of the springs 25 in their fully deflected positions is substantially equal to, but not greater than, the stiffness of the blocks 28 and frame 8 so that the springs are allowed to reach their fully deflected positions and there is no sudden increase in resistance to the roll displacement force upon the rolls when the springs reach their fully deflected positions.

Further, because of the design of the springs as referred to above, deflection of the springs during movement of the rolls from position 23 to position 39 of the pendulums, progressively increases the resilience of the springs. This results in a progressive increase in resistance of the springs to displacement of the rolls 1 and 2 caused by the progressively increasing roll displacement force so that movement of the rolls is eflected in substantially parallel straight-line relationship from the pendulum positions 23 to 39 to reduce the metal between these positions to a substantially uniform gauge.

As the pendulums continue their oscillatory movement in the same direction from positions 39 to positions 24, the resistance to displacement of the rolls cannot further 6 increase, as the springs 25 are now fully deflected, so that the rolls 1 and 2 are progressively displaced away from their theoretical arcuate paths of oscillation about beams 8, and in a direction away from one another, by progressively increasing roll displacement force.

Upon the return movement of the pendulums from positions 24 to 23, the rolling load, and thus its roll displacement force, progressively reduce until, immediately position 39 is passed by the pendulums, the fully deflected springs 25 commence to return towards their undeflected rectilinear position which they re-assume in position 23 of the pendulums. This reverse movement of the springs results in a progressive reduction in stiffness of the springs, and thus in a progressive reduction in resistance to roll displacement as the roll displacement force decreases so that the rolls tend toward movement in parallel straight-line relationship. However, it is found in practice that the roll displacement force during movement of the pendulums in the direction of the advance of the metal does not vary in a manner which is exactly the reverse of the variation of the force during pendulum movement in the opposite direction. As the springs 25 have been designed in consideration of the variation in the force during movement from positions 23 to positions 22, therefore, in consequence, although during movement of the pendulums from positions 39 to 23 the rolls tend towards movement in a straight-line parallel relationship, they do not move in substantially straight-line parallel relationship as they do during movement in the opposite direction.

The speed of oscillatory movement of the pendulums is high compared with the speed of advance of the metal so that a portion of the metal strip, which is in engagement with the rolls when the rolls are in position 39 during movement towards position 24, does not advance as far as the position 23 when the rolls have completed their return movement. This procedure ensures that every part of the metal strip is rolled by the rolls 1 and 2 during their parallel straight-line movement from positions 23 to 39 to result in finished rolled metal strip of substantially uniform thickness and with substantially level rolled surfaces.

In a modification of the first embodiment shown in FIGURE 5, each spring 25 is replaced by a spring 40. Each spring 40 is secured by its mid-position to a flat surface 41 of the adjustable screw 27, and as shown in FIGURE 5, is of arcuate shape in a minimum loaded condition of the rolls 1 and 2. Each spring 40 is continuously in engagement at its ends with two projections 42 provided upon its associated beam 8. The springs 40 are designed so that their resilience will alter in a manner similar to that specified for the springs 25 of the first embodiment.

In use of this modified apparatus, as the roll displacement force increases during swing of the pendulums from positions 23 to 39, resultant movement of the beams 8 causes the projections 42 to deflect the springs towards straight-line positions in which their ends engage the surfaces 41. During deflection of each spring, it progressively moves into more intimate engagement with its surface 41 from its mid-position towards its ends so that the effective deflectable length of the spring progressively decreases. This results in progressive increase in stiffness of the springs and, therefore, progressive resistance to roll displacement to result in substantially parallel straight-line movement of the Work-rolls from pendulum positions 23 to 39. During return movement of the pendulums from positions 39 to positions 23, the spring stiffness progressively decreases in a reverse manner so that the workrolls tend towards a straight-line parallel movement.

In a further modification of the first embodiment, a plurality of leaf springs are operated in series to deflect to increase resistance to roll displacement.

In a second embodiment as shown in FIGURE 6, apparatus for reducing the thickness of metal is of similar construction to that described in the first embodiment, but

is provided with means for increasing and decreasing the resistance to roll displacement which is of different construction from that described in the first embodiment.

In the description of the second embodiment, parts similar in construction or operation to those described above, will bear like reference numerals.

In the present embodiment, for each of the rolls 1 and 2, this means comprises three

titanium tubular members

43, 44 and 45 of different diameters and contained one within another within a bore 28a of block 28. The three tubular members are spaced-apart from one another by stepped

guide surfaces

46 and 47 provided respectively, upon a metal block 48, secured to the associated beam 8, and upon the adjustable screw 27, the block and screw forming abutment members for the tubular members. For a minimum loaded condition of each of the rolls, i.e. before application of roll displacement force to the roll I or 2, the tubular member 43 lies with its annular end surfaces in engagement with the

surfaces

46 and 47, an annular gap 49 is provided between one end of the member 44 and one of the surfaces, and a relatively larger gap 50 is provided between the member 45 and said surface. In this position of the members, a gap 51 is also provided between an annular flange 52 of the block 48 and the block 23, the gap 51 being greater than that of the gap 50.

In use of the apparatus of the second embodiment, as each roll 1 and 2 oscillates from the pendulum positions 23 to 39 during a reducing operation upon metal strip, the progressively increasing roll displacement force is carried initially into the frame solely by the member 43 which provides a resistance of constant degree to displacement of the rolls by virtue of its stiffness. The increasing load gradually compresses the member 43 in its axial direction to reduce the width of

gaps

49, 50 and 51, until the member 44 is engaged by its end surfaces upon the

surfaces

46 and 47. At this point the load is carried by both

members

43 and 44 into the frame so that the resistance to roll displacement is suddenly increased. The load continues to increase to compress the

members

43 and 44 until member 45 commences to be depressed at which instant the resistance to roll displacement is again increase-d. Further increase in load results in compression of all three members until, at the positions 39 of the pendulurns, the flange 52 engages the block 28 so that the increasing load is suddenly resisted by the stiffness of the block and frame which is greater than the combined stitfnesses of the members 43 to 45. It is apparent, therefore, that in use of this apparatus, the resistance to the progressively increasing roll displacement force is increased in step-by-step manner. The stiffnesses of the three members 43 to 45 are so chosen that although the resistance to roll displacement is in step-by-stcp manner, the rolls 1 and 2 follow generally straight-line parallel paths during movement from position 23 to position 39.

The roll displacement during swing of the pendulums from position 39 to position 24 and then back to position 39 is effected in a similar manner to that described in the first embodiment. However, during the return movement from position 39 to position 23 of the pendulums, the resistance to the roll displacement force is decreased in step-by-step manner by re-opening of the gap 51 and then

gaps

50 and 49 so that the rolls tend towards straightline parallel return paths between these positions but do not move exactly along the paths followed for movement from positions 23 to 39 for the reasons given in the first embodiment.

In a modification of the second embodiment, the tubular members are replaced with a plurality of compression springs, one of which takes the minimum load, the load being taken in step-by-step manner by two, three and possibly more springs as the load increases so as to increase the resistance to roll displacement.

In further constructions, the means for increasing and decreasing the resistance to roll displacement comprises hydraulically or pneumatically operated load-carrying devices.

It is found that metal which has been reduced by apparatus as described in either of the above embodiments or modifications thereof has a more uniform thickness and has rolled surfaces which are more level than metal reduced on apparatus as described in the specification of British Patent No. 889,662, for substantially equal ratios of speeds of pendulum oscillation and metal advance, for substantially equal metal advance speeds, and for substantially equal distances of movement from pendulum positions 23 and 22.

It follows from the above description that if the speed of advance of the metal is increased while the speed of pendulum oscillation remains unchanged upon the apparatus described in the embodiments, the rolled metal is of less uniform thickness and its surfaces are less level than metal rolled in the manner specified in the embodiments. In consequence, therefore, with the increased speed of advance of the metal upon the apparatus of the described embodiments, rolled metal may be produced having surface conditions and uniformity of thickness comparable with that produced by apparatus described in the aforementioned specification, and in greater lengths in a specified time than are obtainable with the apparatus of the aforementioned specification.

I claim:

1. A method of reducing the thickness of metal comprising advancing the metal through a thickness reducing apparatus between and beyond a pair of freely-rotatable work-rolls disposed on opposite sides of the metal, subjecting the metal to the rolling action of the pair of work-rolls while oscillating the rolls longitudinally of the metal to effect reduction in the metal in both directions of movement of the rolls, the rolls oscillating in synchronism about pivotal axes for a distance on each side of a common plane in which said axes lie, and oscillation of the rolls being at high speed compared with the speed of advance of the metal between the rolls, increasing the resistance to displacement of the rolls away from their theoretical arcuate paths of oscillation in a step-bystep manner by increasing the stiffness of the apparatus as the roll displacement force increases during movement of the rolls towards said plane and in the direction opposite to the direction of advance of the metal, and decreasing said resistance in a step-by-step manner by decreasing the stiffness of the apparatus as said roll displacement force decreases during movement of the rolls away from said plane and in the direction of advance of the metal.

2. A method according to claim 1 wherein the resistance to roll displacement increases in a manner such that the rolls travel in substantially parallel straight-line paths during said movement of the rolls towards said plane so that, after reduction, the metal is substantially flat.

3. Apparatus for reducing the thickness of metal comprising a frame, a pair of oscillatable arms, each pivotally mounted, for oscillation, about a pivotal axis upon the frame and having free ends which lie in closer relationship than their pivotal axes, the pivotal axes lying in a common plane, a freely rotatable work-roll mounted on the free end of each arm, driving means operably connected to the arms for oscillating the arms in synchronism through said common plane and for a distance on each side of said plane, and stiffness increasing and decreasing means to increase and decrease the stiffness of the apparatus and thereby to increase and decrease resistance to displacement of the rolls away from their theoretical paths of oscillation, such displacement being caused by variation in roll displacement force, said means being operable by the arms during their oscillation to increase said stiffness during movement of the rolls towards said plane and in a direction opposite to the predetermined direction of advance of metal to be passed between the rolls, and being operable to decrease said stiffness during movement of the rolls away from said plane and in the predetermined direction of advance of the metal.

4. Apparatus according to claim 3 wherein the stiffness increasing and decreasing means is operable progressively to increase and decrease said stiffness of the apparatus, respectively, during said movement of the rolls towards said plane and during said movement of the rolls away from said plane.

5. Apparatus according to claim 4 wherein, in the case of each roll, the stiffness increasing and decreasing means comprises at least one leaf spring, and a part of the apparatus comprises a bearing surface for said spring, the spring lying with a part thereof in engagement with the bearing surface before the roll displacement force is imposed upon the roll and having a force application position spaced from said part thereof and also from but opposing the bearing surface, the spring being resiliently deflectable to move said position towards said surface under the application of and progressive increase in force to said position, to shorten the effective spring length between the position of force application and the part of the spring in engagement with the bearing surface, progressively to effect an increase in stiffness the spring and progressively increase its resistance to further deflection.

6. Apparatus according to claim 3 wherein the stiffness increasing and decreasing means is operable to increase and decrease the stiffness of the apparatus in stepped manner, respectively, during said movement of the rolls away from said plane.

7. Apparatus according to claim 6 wherein, in the case of each roll, the roll displacement resistance means comprises at least two tubular members located one radially within the other, and abutment members provided at the ends of the tubular members, a first of the tubular members having ends which lie in engagement with both abutment members upon application of roll displacement force while a second of the tubular members has one end spaced from one of the abutment members being movable one towards the other upon progressive increase in roll displacement force axially to compress the first tubular member and to move the second tubular member to bring its end into engagement with said one abutment member, the abutment members then being movable more towards one another, by further progressive increase in said force, axially to compress both tubular members and increase the stiffness of the apparatus and the resistance to roll displacement in stepped manner.

8. Apparatus according to claim 7 including a third tubular member, all of the tubular members being contained one radially within another, the third tubular member being spaced from said one abutment member by a distance which is greater than that of the second tubular member upon application of the roll displacement force, the third tubular member also having an end spaced from said one abutment member during said further progressive increase in force to compress the first and second tubular members, and the end of the third tubular member being engageable with said one abutment member and all of the tubular members being compressible simultaneously upon a still further progressive increase in force to further increase the stiffness of the apparatus and the resistance to roll displacement in stepped manner.

References Cited UNITED STATES PATENTS 1,549,527 8/1925 Fielding 72-189 1,810,886 6/1931 Neubuth 72-41 3,143,010 8/1964 Soxl 72240 3,103,139 9/1963 Soxl 72-190 FOREIGN PATENTS 227,219 1925 Great Britain.

CHARLES W. LANHAM, Primary Examiner.

A. RUDERMAN, Assistant Examiner.

US. Cl. X.R.