US3470722A - Rolling of rod stock - Google Patents

Description

Oct. 7, 1969 D. B. wooDcocK ETAI- ROLLING op Ron STOCKr Filed Dec. 9, 1966 5 Sheets-Sheet l /IS 22 1 17a a '99 9a IMVEMTOQS;

DDNRLD Efwdn meemaak EDN/mj) LJILLIQMS I Oct. 7, 1969 D. B. wOODcOcK ETAL 3,470,722

ROLLING 0F ROD STOCK Filed Dec. 9, 1966 5 Sheets-Sheet A (STAND) p2 t P5 LOAD P (sTIFFNEss I CONTROL uNITsV-Srq SH 2 P I ROLLWAY DIMENSION I" A(5TAND BISTIFFNESS I CONTROL UNIT) LODAD c (COMBINED) Y ab l a7 P7 l I i ROLLWAY DIMENSION V l @I mi www odi. 7, 1969 D, 5, WOQDCOCK ETAL 3,470,722

ROLLING 0F ROD STOCK 5 Sheets-Sheet 3 Filed Dec. 9, 1966 Oct. 7, 1969 ROLLING OF ROD STOCK 5 Sheets-Sheet 4 Filed D60. 9, 1966 m Mm if Nm om m @N l M \\X\ E@ 1.. O1l4/Ill.. L mw \\v\\\ \\\\..r l, \onv ww mv m Uv om m N iN N Nv wn Ow @n vm om n n Nm mm/ m Om, N O N UN A JM J 0 N E n N m y ,k s 2 om o@ 5 woompd( United States Patent O U.S. Cl. 72-245 15 Claims ABSTRACT OF THE DISCLOSURE A piston-andcylinder device with a chamber containing a hydraulic uid or a rubber block is interposed between the head screws and the upper bearing assemblies, or between the upper and lower bearing assemblies, of the stands of a rolling mill to decrease or increase the effective stiffness of the stands and thereby to control the dimensional tolerances of the rolled product.

This invention relates to the rolling of rod stock in rolling mills (hereinafter referred to as being of the kind specified) comprising a plurality of stands disposed at positions spaced apart successively along a feed path for the rod stock, each stand comprising a body and a pair of co-operative rolls rotatably mounted on the body for rotation about spaced parallel axes and defining therebetween an aperture on the feed path for the passage of the stock to be rolled.

The term rod stock as used herein is to be deemed to mean elongated stock of any cross-sectional shape. The invention has, however, been developed primarily in relation to the rolling of rod stock of circular shape in crosssection and has certain advantages, as hereinafter more particularly pointed out, in relation to rolling mills of the kind specified wherein the rolls are formed to produce rod stock of this cross-sectional shape.

One of the general problems which is encountered in rolling rod stock accurately to specified cross-sectional dimensions is that a variety of causes give rise to factors producing a random, or systemmatic, variation in the load applied by the rolls to the rod stock undergoing rolling `in a direction inwardly of the aperture, and such variation results in corresponding variation in at least one dimension of the aperture, leading ultimately to the 1inished product (i.e. the rolled rod stock) departing from the specified cross-sectional dimensions to which such stock is required to be rolled.

In stands of conventional construction employed in rolling mills of the kind specified, the rolls are supported at their ends in bearing assemblies which, for one of the rolls at least, are mounted for translatory movement in the body of the stand in a direction towards and away from the other roll so as to allow the dimension of the aperture in a direction at right angles to the axes of the rolls to be varied as required (this dimension being generally known as, and hereinafter referred to as, the rollway dimension).

Because wear takes place on the surface of the rolls during operation of the rolling mill, it is not practicable to insert rigid dimensionally invariable spacer blocks between corresponding bearing assemblies of the two rolls yof each stand. Such spacer blocks would be subjected to compressive loading by `a head screw means operating between the body of the stand and the movable bearing assemblies to apply the appropriate force to the rolls. It would be impossible to remove and insert such spacer 3,470,722 Patented Oct. 7, 1969 blocks during operation of the rolling mill, and under the conditions of operation it would be 'impossible reliably to select the particular dimension of a fresh spacer block to be substituted in order to maintain the rollway dimension of the aperture at the required value, even if removal and insertion of such blocks could be contrived.

Consequently the rollway dimension is determined Wholly by a balance of forces, namely the force exerted by the head screw means tending to decrease the rollway dimension of the aperture, and an opposing reactive force exerted by the stock for the time being situated in the aperture.

The reactive force can vary due, for example, to changes in the composition of the stock and changes in its cross-sectional dimensions parallel to the rollway dimension which may occur lin a random or systematic manner.

The problem of maintaining a constant rollway dimension is even more serious in multi-strand mills where a plurality of strands of rod stock (usually two) are fed side-by-side along the feed path simultaneously between axially spaced portions of the rolls. In this case there is usually a short gap between the trailing end of one piece of rod stock (formed from a given billet) and the leading end of the succeeding piece of rod stock (formed from a succeeding billet) but this gap in one strand of the rod stock does not necessarily coincide longitudinally with the corresponding gap in the other strand of rod stock (assuming the mill to be one designed for two-strand rolling). Consequently the reactive forces exerted by the rod stock (which tends to separate the rolls) is very substantially diminished when a gap is present in one strand and the whole of the reactive force is exerted by the other strand. As a result of this the rollway dimension decreases. There is consequently a decrease in the rollway dimension of the other (ungapped) strand and although there is some increase in the dimension of this strand in a direction parallel to the axis of the rolls (this dimension being known generally as, and hereinafter termed the guideway dimension) such increase is less than would maintain the cross-section or area of the strand at the value which it would normally have on exit from the rolls. In other words the decrease in rollway dimension produces additional elongation of the strand as well as some increase in guideway dimension.

In rolling rod stock to circular cross-section it is usual for the stands excepting the last two or three in the series to effect reduction in the cross-sectional area of the stock by rolling it to oval cross-section. rl`his may be done only in alternate stands of the series, lthe intervening stands serving to roll the stock back to circular crossasection or approximately to this shape. Alternatively, however, each stand in the series (other than the last two or three) may roll the stock to oval cross-section in which case the rollway dimension is always that of the minor axis of the oval section and devices are then provided in between successive stands to twist the emerging oval section of the stock angularly about its own axis through before it enters the next stand. The decrease from the proper value of the rollway ldimension from the causes previously mentioned can produce necking, that is to say local decrease of the cross-section area of the stock at each stand Where such rollway dimension is so decreased.

The last stand or possibly the last two or three stands have roll apertures which are shaped in conformity with the desired cross-sectional shape of the finished product and the necking of the stock which has taken place in passage through preceding stands can lead in the last stage to the production of stock which is necked, that is to say below its proper cross-sectional area or which fails to conform to the specified rollway and guideway dimensions 0r deviates from the desired specification in both these respects.

The object of the present invention is to avoid or reduce these disadvantages.

According to the present invention we provide, for a rolling mill of the kind specified, a stiffness controlling unit comprising a jack having a block-like body and a movable thrust element in combination defining a chamber containing, or adapted to contain, la selected volume of a solid state medium conformable to the shape of the chamber when under pressure and having the compressibility characteristics of a liquid, the jack being adapted for mounting on or in the body of an associated one of the stands in a position such that its thrust element partakes of the stress set up in the body of the stand in response to the establishment of applied load urging rolls towards each other to decrease the rollway dimension, the selected volume of the medium determining the stiffness of the unit and hence that of the stand in which it is adapted to be mounted.

The stiffness characteristics of the jack include two components; a first component which is invariable for any particular jack and is determined by the wall thickness of the portion of the body which defines the chamber, the wall thickness of the thrust element, the materials of which these components are made, and the kind of medium in the chamber; and a second component which is variable and dependent on the volume of the medium in the chamber.

Such jack may be made conveniently of dimensions enabling it to be mounted or inserted between a bearing assembly of one of the rolls, which assembly is itself movable relatively to the body of the associated stand to vary the rollway dimension, and an abutment so that compressive loading is exerted between the thrust faces of the jack as such bearing assembly is moved in a direction to decrease the rollway dimension. Thus, for example, the jack may be inserted between corresponding bearing assemblies of the two rolls of the stand at adjacent ends of the rolls, so that it opposes movement of the rolls towards each other and applies a reactive force supplementing that of the stock when disposed in the aperture between the rolls.

As thus applied the jack increases the effective stiffness of the stand. The term stiffness as used herein means the change in applied load required to produce unit change in rollway dimension, such load being measured in the case of the jack in the absence of any stock in the aperture between the rolls.

The stiffness of the jack may be made equal, or approximately equal, to the stiffness presented by the stand itself.

It has previously been proposed to control the rollway dimension by means of hydraulic jacks inserted between the bearing assemblies of the rolls in stands of a rolling mill, but according to these proposals the jacks are merely used to adjust the separation of the bearing assemblies in response to measured variations in the rollway dimension or parameters related thereto, and such adjustment is achieved by extending or contracting the jacks to the appropriate extent, Thus according to these proposals the rollway dimension is continuously monitored and the separation of opposed thrust faces presented by the jack con- :erned is continuously adjusted to compensate for any observed variations.

The present invention makes use of an entirely different zoncept. The stiffness of stands in rolling mills is adiusted to a pre-set value dependent on the function of the stand concerned by means of jacks, which are self contained units. The stiffness of such a jack is adjusted by the selection of an appropriate volume of the medium in the chamber, and once adjusted the stiffness of the jack remains unchanged so long as the function of the stand in which it is inserted remains unchanged.

It is contemplated that jacks as hereinbefore described may be employed in some or all of the stands of a rolling mill other than the last or the last group of stands, for the purpose of increasing the effective stiffness of the stands and thereby minimising any decrease which may occur in the rollway dimension of the stand concerned in consequence of a reduction in counterthrust exerted by the stock tending to decrease the separation of the rolls.

In the case of the last stand, or possibly the last two or three stands, where the apertures defined by the rolls thereof are shaped in conformity with the desired crosssectional shape of the nished product required to be produced, the jack may be mounted or inserted in or on the body of the stand concerned in a position such that the load applied to the movable roll is applied effectively through the intermediary of the jack. In this case the stiffness of the jack would be selected to be less than the stiffness of the stand without the jack. This feature of the invention provides an improved compromise in departures from dimensional tolerance as between the rollway dimension and the guideway dimension of the stock emergent from any such stand so equipped.

The invention also resides in a method of rolling rod stock by passing said stock through a rolling mill of the kind specified characterised in that at least one of the stands, of which the rolls define an aperture having dimensions other than those of the desired cross-sectional shape of the finished product required to be produced, has its stiffness increased to a predetermined extent by means of such a stiffness control unit.

At least one of the stands, of which the rolls define an aperture shaped in conformity with the desired crosssectional shape of the finished product required to be produced, may have its stiffness decreased to a predetermined extent by means of such a stiffness control unit.

The invention will now be described, by way of example, with reference to the accompanying drawings wherein:

FIGURE 1 is a diagrammatic view in side elevation of a rolling mill of the kind specified which in accordance with the invention is equipped with stiffness controlling units;

FIGURE 2 is a diagrammatic view in front elevation of first stand of the rolling mill illustrating the position in which the stiffness controlling units are mounted therein, the other early stands being similar;

FIGURE 3 is a view similar to FIGURE 2 showing the last stand of the rolling mill and illustrating the position in which the stiffness control units are applied thereto, the other later stands being similar;

FIGURE 4 is a graph illustrating the operation of the arrangement shown in FIGURE 2;

FIGURE 5 is a graph illustrating the operation of the arrangement shown in FIGURE 3;

FIGURE 6` is a plan view of one of the stiffness con-v trol units shown partly in cross-section in the line VI-VI of FIGURES 7 and 8;

FIGURE 7 is a view of the same unit in cross-section on the line VlI-VII of FIGURE 6;

FIGURE 8 is a view of the same unit in cross-section of the line VIII-VIII of FIGURE 6;

FIGURE 9 shows a further type of stiffness control unit in medial cross-section; and

FIGURE l0 is a graph illustrating typical stiffness characteristics of a stiffness control unit.

Referring firstly to FIGURE l, the rolling mill is of the multi-strand type incorporating a plurality of stands of which the first two, 10 and 11, and the last two, 12 and 13, only are shown. The stock to be rolled may be metal stock such, for example, as steel.

Each stand may be of any conventional construction which is not illustrated in detail, but only diagrammatically. Each stand is of similar construction and the various parts of stands 10, 11, 12 and 13 respectively are designated by the same numbers with sufhxes a, b, c and d. The first stand 10 includes a body in the form of a frame including upstanding side members 14a connected at their upper ends by a head member 15a and at their lower ends to a base 16a. The side members 14a each incorporate a vertical guideway 17a in the form of a slot in which are mounted lower and upper bearing assemblies 1811l and 19a respectively. Lower and upper rolls 20a and 21a are supported at each of their ends by bearing assemblies 18a and 19a respectively, the former abutting the lower end of the guide slot 17a and the latter being movable longitudinally of the guide slot 17a to vary the rollway dimension r of apertures 9a defined by grooves 8a in the rolls 20a and 21a. Downward thrust is applied to the upper roll 21a by means of adjustable head screws 22a which, as seen diagrammatically in FIGURE 1, exert a downward thrust directly on the upper bearing assemblies 1911 and 19h of the early stands 10 and 11, and indirectly on the upper bearing assemblies 19e and 19d of the last stands 12 and 13. These head screws 22a-d operate in threaded bores in the side members of the respective frames. Such downward thrust is normally opposed only by upward counterthrust of stock in the apertures 9a between the rolls, `apart from weight balancing means which may be employed for the upper roll.

As seen in FIGURE 2, stiffness control units 23a are inserted between the bearing assemblies 18a and 19a so as to exert counterthrust assisting that exerted by the stock in the apertures 9a between the rolls. As seen from FIGURE l a similar arrangement is adopted for the second stand 11.

As seen in FIGURE 3, stiffness control units 23d -are inserted between the head screws 22d and the upper bearing assemblies 19d so that the thrust exerted by the head screws is applied to the upper roller 21d etectively through the stiffness control units 23d. As seen from FIGURE 1 a similar arrangement is adopted for the penultimate stand 12.

It will be understood that it is not essential that the stiffness control units should be applied between the upper and lower bearing assemblies for stands equipped similarly to that shown in FIGURE 2; they could be applied between the upper bearing assembly and some other lxed abutment on the side member of the stand concerned. Similarly it is not essential that the stilness control units 23 in stands equipped similarly to that shown in FIGURE 3 should be inserted between the lower ends of the head screws and the upper bearing assemblies; they could be inserted at 4any convenient position where they will reduce the effective stiffness of the stand concerned. For example, if the head screws were to operate in separate nuts mounted for vertical oating movement between abutments in the side members of the frame, the stiffness control units could be mounted between such nuts and the abutment against which the nut presses when the screw is tightened to exert the load. Alternatively, they could be placed between each bearing supporting the bottom roll and the underlying part of the frame.

Referring specifically to FIGURES 6 to 8 which illustrate one form of stiness control unit in accordance with the invention, the stiffness control units 23a-d each comprise a hydraulic jack having a body comprising a block 24 formed with a cylindrical chamber 25. The chamber 25 contains a thrust element in the form of a piston 26, preferably having an upwardly presented, partspherical, concave seating as shown at 27 in which a thrust block 28 having a corresponding convex seating at its underside is mounted. The upper side of the thrust block 28 serves as a thrust face 28f.

The space 29 between the piston 26 and the bottom of the chamber 25 contains a liquid.

The stiffness of the jack is determined by the .materials of which the body and thrust element are made, as well as to some extent by a sealing O ring contained in a groove in the piston 26, the dimensions of these parts and the quantity of liquid in the chamber 29, which, of course, determines the position of the piston 26.

The amount of liquid in the space 29 can be varied by means of an inlet device which is shown in longitudinal section in FIGURE 7 and an outlet device which is shown in longitudinal section in FIGURE 8.

Referring now to FIGURE 7, the inlet device comprises a non-return inlet valve disposed in a cavity 51 formed as a widened portion of a bore 56 extending into the block 24 from its underside, The outer end of the cavity 51 opens out into a counterbored portion and receives a plug 52, a sealing `washer 54 being trapped between the plug S2 and the shoulder 55 aiorded at the inner end of the counterbored portion. The valve includes a ball element 49 which is pressed by a spring 50 into contact `with a co-operating seating 48 afforded by the shoulder at the junction of an inner most part of the bore 56 and the inner end of the cavity 51.

Admission of liquid to the chamber 51 of the inlet valve is by way of a. duct l47 which extends between the inner part of the bore 56 and an inlet socket 45 which is threaded internally at 46 to receive a complementary, externally threaded, male connector. Such connector may, for example, be provided on the end of a flexible pipe from a source of hydraulic fluid under pressure, such as a manually-operated `or power-operated pump.

An inclined bore 53 extends from the inner end of the inlet socket 45 to the lower part of the chamber 26 and intersects the cavity 51. The outlet end of this bore 53 is closed by a screw 57 and sealing washer 58. Thus, when liquid is admitted to the socket 45 at a pressure suiicient to displace the ball element 49 from its seating 48, against the force of the spring 50 and any liquid already in the chamber 26, the liquid can enter the space 29 by Away of the duct 47, the bore 56, the cavity 51 and the inclined bore 53.

Referring now to FIGURE 8, the outlet device includes an outlet valve including a ball element 32 which is -pressed on to a co-operating seating 33 by a rigid element in the form of a thrust rod 34. The seating 33 is formed by a shoulder at the junction of a bore 31 and a widened portion thereof formed in a valve body 59. The valve body 59 is screwed into a recess 61 at the inner end of an outlet chamber 37, the inner end of which is sealed by a washer y60 disposed between a head portion of the valve body 59 and a shoulder around the recess 61. The thrust rod 34 is :screw threaded and extends through an internally threaded bore in a bush 36 which is itself screwed into the forward end of the outlet chamber 37, such bush having an external nut 38 compressing a seal element 39 disposed in a rebate 40 and serving to seal the outer end of the chamber 37. The thrust rod 34 has, at its outer end, an operating member 3S Iwhich may be cylindrical and is equipped with a sealing element in the form of an O ring 41 mounted in a groove 42 and engaging the inner face of a counterbore 43 in the bush 36. A duct 30 extends between the inner end of the recess `61 and the lower part of the chamber 26. Normally the thrust rod 34 is screwed tightly into the bush 36 so that the ball element 32 is pressed firmly into its seating 33 and liquid is not permitted to flow from the space 29. However, when the thrust rod is slackened the pressure of the liquid in the space 29 lifts the ball element from its seating and so liquid can flow from the space 29 through the duct 30, and bore 31 into the outlet chamber 37. A transverse duct 44 extends between the outlet chamber 37 and the inlet socket 45 to allow liquid to be displaced from the outlet chamber 37 into the inlet socket.

In the earlier stands the stiffness of the jacks utilised is selected with reference solely to the rollway dimension presented by the rolls. The thrust face Zf of the thrust element 28 transmits the load to the upper bearing assembly `concerned whilst the thrust face 24f provided by the body 24 of the jack transmits the load to the upper face of the lower bearing assembly concerned. In such cases the stiffness of the jack `comprising the relevant stiffness control units 23a and b may be approximately the same as the stiffness of the stand and this produces approximately 100% improvement in variation of the rollway dimension as a result of any change in the component of counterthrust exerted by the stock (neglecting roll bending and deflection occurring internally of the bearings).

This is illustrated in FIGURE 4 in which the total load P exerted by the head screws 22a is plotted as ordinate against rollway dimension r for the stand and the stiffness control units 23a separately.

Curve A represents the relationship between load P and dimension r for the stand alone (assuming the stiffness control units to be absent) and curve B represents the same relationship with respect to the stiffness control units (assuming no dimensional changes in the stand).

Assuming that on the curve A the point a1 represents operating conditions at any given instant, the component of counterthrust supplied by the stiffness control units has a Value p1 and the component `of c-ounterthrust supplied from the stock is then pz-pl where p2 is the total thrust applied by the head screws.

Assuming that the rolling mill is a two-strand mill, and that a gap occurs between the leading and trailing ends of successive pieces of stock forming one strand, the component of counterthrust supplied by the stock may then decrease to move the working point to a new position a2 in which the component of c-ounterthrust supplied by the stiffness control units 23a is now p3, where p3 is greater than p1, and the thrust supplied by the head screws is p4 which is less than p2.

In the absence of the stiffness control units the working point would have become displaced to a position a3 such that the thrust p5 applied by the head screws would be equal to p4-(p3-p1), assuming that the slopes of the curves A and B in the vworking region are equal and of opposite sign (as would be the case when the stiffness control units afford collectively the same stiffness as the frame).

The proportional reduction in change of rollway dimension is fwhere /'2=2r1. It will be evident that a higher percentage in the reduction of r can be obtained by increasing the stiffness of the units 23 (that is to say the negative slope of curve B) as desired.

The stock passing into the last stand 13 will normally have an oval cross-section arranged `with its major dimension vertical, ie. parallel to the rollway dimension of the stand 13, this being achieved by the provision of a known twisting device (not shown) between the stands. Similar devices will -be provided between each of the other pairs of adjacent stands.

If the stiffness control units 23d provided in the stand 13 were placed in the same positions as those shown in FIGURE 2, to increase the effective stiffness of this stand, the rollway dimension of the stock emergent from the stand 13 would acquire improved accuracy as to any departure from the specified dimension but the guideway dimension of the stock may exhibit an increased departure from the specified dimension merely in consequence of the improvement brought about in the accuracy in the rollway dimension.

Accordingly, improved overall results, taking into consideration the accuracy of the stock in both the rollway and guideway dimensions, are achieved by designedly decreasing the effective stiffness of the last stand 13 and possibly of the penultimate stand 12 also, as shown.

For this purpose stiffness control units 23d in the last stand 13 are inserted in the position already described and shown in FIGURE 3. Here the thrust face of the thrust element transmits the load to the head screw con- 8 v cerned; whilst the thrust face afforded by the body of the jack transmits the load to the upper face of the upper bearing assembly concerned. As also mentioned previously the units could be arranged between the lower bearing blocks 18d and the part of the body of the stand 13 on which such blocks are supported. A similar result is achieved in either case.

The characteristic representing operation is shown graphically in FIGURE 5 in which the load p exerted by the head screws 2.3 is plotted as ordinate against change of dimensions of the stand and stiffness control units.

The curve A represents, as in FIGURE 4, the characteristics of the stand as suchjwhilst curve B represents the characteristics of the stiffness control units. In this case the effective stiffness is the combined stiffness represented by curve C having a lower value than either the stiffness of the stand or the stiffness control unit.

The operating charactistics of the stand, with regard to variation of rollway dimensions, are shown in respect of a reduction of load from a voltage p6 to p7. This produces a shift of the 4working point from a6 to a7 and results in a change of rollway dimension of r3. The corresponding change with respect to the curve C is from a4 to a5, the change of rollway dimension in this case being am which is greater than ra. The increase in 5r produces a corresponding decrease in the change of guideway dimensions, thus achieving an improvement in the accuracy of the means cross-sectional dimensions of the finished product.

When the jack is used to increase the effective stiffness of the stand and change in the quantity of liquid in the chamber is effected, for the purpose of changing the effective dimensions of the jack between the thrust faces, some variation in the stiffness of the jack itself will occur. This latter variation may be confined to a limited range by providing a mechanical adjustment means on, or in association with, the jack. Such means may comprise an assembly of shims or packing pieces between one of the thrust faces and the part of the mill stand against which this face would otherwise lean. When the jack is used to decrease the stiffness desired variation in the latter is effected by changing the quantity of liquid in the chamber. Dimensional variations between the thrust faces consequent on this are not important since they can be accommodated by the head screw means of the mill stand.

It is important to note that once the jack is installed it will not normally require further adjustment unless or until the function of the stand itself is changed. The quantity of liquid in the chamber is adjusted in accordance with the requirements of the stand in which it is installed, and is not varied by external means to accommodate or compensate transistory changes in the rollway dimension. Thus the unit is self contained and preset to provide the requisite increase or decrease in the stiffness of the stand, although it can readily be re-set when necessary to provide different characteristics.

An alternative form of stiffness control unit is illustrated in FIGURE 9. This form of unit has been developed particularly for use in the last stand 13, or one of the last stands, where it is desired to decrease the stiffness of such stand. However, it could be employed in the earlier stands.

The alternative unit as shown in FIGURE 9 is of generally simpler construction than that shown in FIGURES 6 to 8, and employs a solid state medium instead of a liquid to obtain the desired stiffness characteristics. This unit comprises a cylindrical block-like body 74 having a cylindrical chamber 75 therein. This chamber 75 opens out into the upper end of the body 74 and has a slightly flared mouth as indicated at 80. At the lower end of the body 74- is formed with a radial bore 81 extending inwardly from its cylindrical side face and intersecting an inclined bore 82 which leads from the lower end of the chamber 75.

A block 83 of rubber, or other similar material which has compressibility characteristics similar to a liquid when totally enclosed, is arranged within the chamber 75.

The block 83 is shaped approximately into conformity with the chamber 75, i.e. is generally cylindrical, but need not -be made as an exact or close t therein since it will readily conform to the shape or" the chamber when it is compressed.

The height or thickness of the block 83 is selected according to the required stilfness of the unit as a whole.

The block 83 is compressed in the chamber 75 by a thrust element comprising a piston 76, the block occupying the entire space bounded by the walls of the chamber and the piston in combination. The piston 76 is generally cylindrical and has a plain lower end face 77 which contacts the upper face of the solid rubber block 83. The upper end of the piston 76 is formed to provide a head 78 having a part-spherical thrust face 78j, the head 78 being of approximately the same diameter as that of the body 74.

The axial length of the piston 76 received within the chamber 75 is such, in comparison with the axial length of the chamber 75 and the height of the rubber block 83, that the latter is compressed fully into conformity with the shape of tlhe cylinder by downward movement lof the piston under applied load before the Iunderside of the head 78 can abut the mpper end of the body 74.

Any air trapped between the underside of the rubber block 83 and the bottom of the chamber 7S is expelled through the passageway afforded by the bores 81 and 82 as the block is compressed. Similarly any air between the lower end of the piston 76 and the upper side of the rubber block can escape between the piston and the cylinder wall of the chamber 75. Although the piston is a close sliding t within the chamber 75 there is suiiicient clearance to allow air to escape in this way.

However, the piston is formed with a chamfered edge 84 around its lower end face 77 so that when the rubber block 83 is compressed the medium is formed into the annular space afforded around the face 77 so as to seal the chamber completely.

The stiffness of such a unit may be varied with comparatively narrow limits by replacing the rubber block 83 by a block of different thickness. In general however the stiffness of such a unit would not be altered once the unit was assembled, and a range of such units would normally be available, each unit having a speciied stiffness.

FIGURE illustrates the stiffness characteristics of a typical jack. The depth of liquid, or the thickness of the rubber block, in the chamber is plotted as ordinate (the units being inches) and the reciprocal of the stiifness of the unit, or displacement of the thrust element, is plotted as abscissa in units of thousands of an inch per ton of applied load.

From this it will be seen that the compressibility of the unit increases with increase in the amount of the medium (solid or liquid) in the chamber, i.e. the stiffness is inversely related to the volume of the medium. Thus, by selecting the amount of liquid or the size of the rubber block in the chamber a unit of predetermined stiffness can be obtained.

What we claim is:

1. Stiifness control means for a rolling mill stand ncluding a pair of co-operating rolls, such means comprising a hydraulic jack having:

(a) a block-like body,

(b) a movable thrust element,

(c) a chamber defined by said body and said thrust element in combination,

(d) means for mounting said body in said stand in a position such that said thrust element partakes of stress set up in said stand in response to establishment of applied load urging said rolls towards each other, and

(e) said chamber containing a selected volume of a solid state medium which is conformable to the shape of said chamber when underI pressure and having the compressibility characteristics of a liquid, and the selected volume of said medium determining the stiffness of the stiffness control means and hence that of said stand in which it is to be mounted.

2. The structure according to claim 1 wherein said block-like body includes means for permitting the escape of air from said chamber.

3. The structure according to claim 1 wherein said medium comprises a solid block of rubber.

4. A multiple strand rolling mill stand for simultaneously rolling at least two strands of rod-stock and comprising:

(a) a stand body,

(b) a pair of co-operative rolls at least one of which is movable towards and away from the other and each of which is formed with at least two axially lspaced peripheral grooves which in combination with the respective grooves of the other roll dene respective apertures,

(c) a pair of respective bearing assembles at each end of said pair of rolls,

(d) means for applying a load to said movable roll to urge the latter towards the other rolls, and

(e) means for controlling the stiffness of the stand comprising a pair of independent yieldable units each having a stiffness of tihe same order as that of the stand mounted in said stand body in association with said respective pairs of bearing assemblies in a fposition such as to partake of stress set u-p in said stand in response to establishment of applied load urging said rolls towards each other.

5. The structure according to claim 4 wherein said apertures have dimensions other than those of the desired cross-sectional shape of the rolled rod stock required to be produced, and said stiffness control units are disposed between respective abutments fixed to said stand body and each of said bearing assemblies of said movable roll on the side of the latter remote from that at which said load is applied whereby the effective stiifness of the stand is increased.

6. The structure according to claim 4 wherein said apertures have dimensions conforming with the desired cross-sectional shape of the rolled rod stock required to be produced, and said stiffness control units are disposed between each of said bearing assemblies of said movable roll and said means for applying said load to the latter whereby the effective stiifness of the stand is decreased.

7. The structure according to claim 4 wherein said stiffness control units each comprise,

(a) a block-like body,

(b) a movable thrust element, and

(c) a totally enclosed chamber dened by said body and said thrust element in combination and containing a preselected volume of a medium which is conformable to the shape of said chamber when under pressure and has the compressibility characteristics of a liquid, said selected volume of said medium determining the stiffness of the stiifness control means and hence that of said stand.

8. The structure according to claim 7 wherein said medium contained in said chamber of said stiifness control unit comprises a liquid, and said stiffness control means further comprises,

(a) means for admission of a variable, selected, quantity of said liquid into said chamber so as to enable adjustment of the effective stiffness of said stiffness control unit, and

(b) releasable means for preventing release of said liquid from said chamber so that said quantity of said liquid therein can be xed at any selected value.

9. The structure according to claim 7 wherein said medium in said chamber of said stiiness control means comprises a solid state medium.

10. The structure according to claim 9 wherein said block-like body of said stiffness control means includes means for permitting the escape of air from said chamber whilst the latter is electively totally enclosed against escape of said solid state medium therefrom.

11. The structure laccording to claim 9 wherein said medium comprises a block of rubber.

12. In a rolling mill for rolling rod stock and comprising a plurality of rolling mill stands arranged in a line to be traversed successively by said rod stock wherein each stand comprises,

(a) a stand body,

(b) a pair of co-operative rolls at least one of which is movable towards the other and each of which is formed with a peripheral groove which in combination dene an aperture,

(c) a pair of respective bearing assemblies at each end of each of said pair of rolls, and

(d) means for applying a load to said movable roll to urge the latter towards the other roll,

and wherein,

(e) in all of said stands except the last stand in the line said aperture has dimensions other than those of the desired cross-sectional shape of the rolled rod stock required to be produced, and in said last stand in said line said aperture has dimensions conforming with the desired cross-sectional shape of the rolled rod stock required to be produced,

the improvement comprising,

(f) means for decreasing the stiiTness of said last stand comprising a pair of yieldable units each having a stiffness of the same order as that of the stand mounted between said bearing assemblies of said movable roll and said means for applying load thereto, and

(g) means for increasing the stilness of at least one of said stands wherein said aperture has dimensions other than those of the desired cross-sectional shape of the rolled rod stock required to be produced, comprising a pair of yieldable units each having a stiffness of the same order as that of the stand mounted between respective abutments xed relative to said stand body and said bearing assemblies of said movable roll on the side of the latter remote from that .at which said load is applied thereto.

13. In a multiple strand rolling mill for simultaneously rolling at least two strands of rod stock and comprising a plurality of rolling mill stands arranged in a line to be traversed successively by said rod stock wherein each stand comprises,

(a) a stand body,

(b) a pair of co-operative rolls at least one of which is movable towards the other and each of which is formed with at least two axially spaced peripheral grooves which in combination with the respective grooves of the other roll dene respective apertures,

(c) a pair of respective bearing assemblies at each end of each of said pair of rolls, and

(d) means for ,applying a load to said movable roll to urge the latter towards the other roll,

and wherein,

(e) in all of said stands except the last stand in the 12 v line said apertures have dimensions other than those of the desired cross-sectional shape of the rolled rod stock required to be produced, and in said last stand in said line said apertures have dimensions conforming with the desired cross-sectional shape of the rolled rod stock required 'to be produced,

the improvement comprising,

(f) means for decreasing the stiffness of said last stand comprising a pair of independent yieldable units each having a stiffness of the same order as that of the stand mounted between said bearing assemblies of said movable roll and said means for applying load thereto, and y (g) means for increasing the stiifness of at least one of said stands wherein said apertures have dimensions other than those of the desired cross-sectional shape of the rolled rod stock required to be produced, comprising a pair of independent yieldable units each having a stillness of the same order as that of the stand mounted between respective labutments xed relative to said stand body and said bearing assemblies of said movable roll on the side of the latter remote from that at which said load is applied thereto.

14. A method of rolling rod stock by subjecting said stock to a plurality of successive rolling operations and a nal rolling operation between respective pairs of rolls journalled in respective mill stands for rotation about respective pairs of parallel axes of rotation to form rolled rod stock having a preselected rollway dimension in a direction at right-angles to said axes of rotation and also a preselected guideway dimension in a direction parallel to said axes of rotation, each of said pairs of rolls deining in combination a respective aperture through which said stock is passed to alter its cross-section, wherein the improvement comprises controlling the rollway dimension of said stock during said nal rolling operation less closely than during said successive rolling operations preceding said inal rolling operation by decreasing the effective stiffness of said mill stand in which said final operation is carried out.

15. A method of rolling rod stock according to claim 14 wherein the rollway dimension of said stock is controlled during at least one of said successive rolling operations preceding said iinal rolling operation by increasing the effective stiffness of said mill stand in which said operation is carried out.

References Cited UNITED STATES PATENTS 2,796,253 6/ 1957 Schulze et a1. 267--1 3,059,914 10/1962 Williamson 267-1 3,197,986 8/1965 Freedman et al. 72--16 3,272,491 9/ 1966 Knittel 267-1 3,290,034 12/1966 Williamson 267-1 3,314,263 4/1967 Hill 72-237 3,339,393 9/1967 Rice 72-246 3,024,679 3/1962 Fox 72-245 CHARLES W. LANHAM, Primary Examiner B. I. MUSTAIKIS, Assistant Examiner U.S. C1. X.R.

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