GB2172231A

GB2172231A - Process and apparatus for reducing the cross-section of elongate material, such as hot continuously cast material

Info

Publication number: GB2172231A
Application number: GB08604503A
Authority: GB
Inventors: Karl Wiedemer; Peter Frohling
Original assignee: Frohling Walzwerksmaschin GmbH
Current assignee: Frohling Walzwerksmaschin GmbH
Priority date: 1985-03-13
Filing date: 1986-02-24
Publication date: 1986-09-17
Also published as: GB8604503D0; JPS61212409A; DE3508924A1; CN86101620A; FR2578760A1

Abstract

In the described process for reducing the cross-section of hot continuously cast materials by intermittent rolling, gradual rolling forces act in the individual rolling phases on the rolling material which is moved forwardly in a stepwise manner and progressively rolled. A rolling mill for carrying out the process has rolls 4a and 4b with grooves for progressive reduction in cross-section, which are disposed in a movable carriage (2, Fig. 6) driven as by a crank (3a). The rolls are rotated by gears (6a) or sprockets engaging stationary racks or chains. That makes it possible to achieve a reduction in cross-section of up to about 90 to 95% in one rolling mill pass. The rolls may define two passes (15, 16, Fig. 2) between which the material (5) is moved by axial movement of roll 4a. <IMAGE>

Description

SPECIFICATION Process and apparatus for reducing the cross-section of elongate material such as hot continuously cast material This invention relates to a process and an apparatus for reducing the cross-section of elongate material, such as bar material or hot continuously cast alongate matarial.

In daaling with continuously cast matarial, in particular bar steel, by hot rolling, the aim is to reduce the cross-section of the continuous casting, immediately after the casting operation, and as far as possible in one rolling pass, to the final cross-section which is desired for normal structural steel. That would not only minimise the processing time of the cast component, but in addition, by virtue of making full use of the heat of the freshly cast bar matarial or elongate member, it would result in considerable saving of energy.

However, these aims cannot be achieved with the pilgrim rolling mills which operate intermittently and which were hitherto conventionally used for processing continuously cast material. More specifically, if the relative decrease in cross-section (reduction) in the material, per roll run (pass) is increased beyond a given amount, then there is not only the danger of a roll breakage, but the rolled material also suffers from transverse cracks which make it useles.If on the other hand the reduction in the bar or elongate member, in each pass, is kept at a lower level in order to protect the rolling mill and the rolled material, then a plurality of roll runs (pases) are necesary in order to achieve the desired decrease in cross-section, while before each pas the cast material which has cooled down in the meantime must be freshly heated up, that is to say, in order to achieve the desired reduction in cross-section of the material, in addition to the heat which originates from the casting operation, it is necessary to supply further considerable amounts of heat energy.

The problem of the present invention is therefore that of providing a proces for reducing the cross-section of hot continuously cast material by intermittent rolling, as well as a rolling mill for carrying out such a process, which make it possible to reduce the crosssection of the cast member, to the desired final cross-section, in one roll run (pas), from the casting heat and without damaging the working rolls and the rolled material.

According to the present invention in one aspect there is provided a proces for reducing the cross-section of elongate material such as hot-continuously cast material by intermittent rolling of the material which is moved forwardly in a stepwise manner, in individual successive rolling phases, in which (a) in the individual rolling phases, the rolling material which is respectively moved forwardly in a stepwise fashion is progressively rolled down; and (b) deformation forces are applied to the rolling material throughout the entire rolling operation.

According to the present invention in another aspect there is provided an intermittently operable rolling mill for carrying out the process according to the invention, comprising two grooved working rolls which respectively have a rolling groove portion and an idle groove portion and which rotate synchronously and the longitudinal axes or axes of rotation of which are disposed in a common plane through which the rolling material passes substantially perpendicularly between the rolls, in which (a) the roll grooves are shaped for effecting the progressive reduction in cross-section of the rolling material during a rolling phase; (b) the rolls are mounted in a driven carriage which is reciprocable in the roll stand; and (c) rolling elements are disposed laterally of the rolls on the roll spindles and which, upon movement of the roll carriage, roll form-lockingly on co-operating elements which are fixedly connected to the roll stand; and (d) the rolling radius of the rolling elements substantially corresponds to the body radius of the rolls.

The invention makes it possible to achieve, in a single roll run (pass), a relative reduction in cross-section which, at up to about 90 to 95%, is much higher than the reduction in cross-section which could be achieved hitherto, of about 25%, without the rolled material being damaged or without the fear of a roll breakage.

The invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 is a front view and a sectional view of two co-operating rolls of a conventional pilgrim rolling mill for reducing an elongate member of circular cross-section, Figure 2 diagrammatically shows the mode of operation of a conventional pilgrim rolling mill in four successive phases; Figures 3a and 3b illustrate the principle of the invention; Figures 4a to 4e demonstrate the mode of operation according to the invention; Figure 5 is a view in cross-section of a preferred embodiment of a pair of rolls according to the invention for producing a progressive reduction in cross-section; Figures 6 and 7 are diagrammatic side views of an embodiment of a rolling mill for carrying out the process according to the invention;; Figure 8 is a front view and a sectional view of, a preferred embodiment of two working rolls for the rolling mill shown in Figures 6 and 7 for reducing the cross-section of a rectangular cast member; Figures 9a and 9b show the transformation operation with the rolls shown in Figure 8; and Figure 10 diagrammatically shows a front view of a rolling mill as shown in Figures 6 and 7 with the working rolls as shown in Figures 8 and 9.

Figure 1 shows a front view and a sectional view of the two grooved rolls 4a and 4b of a conventional pilgrim rolling mill with their rolling grooves WK and idle grooves LK in the working position, with the peripheral edges U of the sides ST of the rolls being in contact with each other. Reference R denotes the body radius of the rolls 4a and 4b. In this case the surface of the rolls is of a configuration which is suited to reducing elongate cast members of circular cross-section, but the roll surface may also be designed for the reduction of elongate cast members of different cross-section, for example square.

Figure 2 shows the mode of operation of the conventional pilgrim rolling mill in four successive phases, more specifically (a) at the beginning of a rolling operation, (b) during the rolling operation, (c) at the end of the rolling operation, and (d) in the idle phase. The general direction of movement of the rolled material through the rolling mill is in this case from left to right (see the arrow above Figures (a) to (b) showing the phases of the operation).

(a) At the beginning of the rolling operation, when the rolls 4a and 4b which are driven in the direction indicated by the arrow are disposed with their idle grooves LK in opposite relationship, the rolling material 5 is advanced from the left into the roll gap. Upon further rotary movement of the rolls 4a and 4b the portions indicated at A engage the rolling material at the location identified by 11 (Figure 2a).

(b) Now, upon steady further rotation of the rolls 4a and 4b, the rolling phase begins (Figure 2b). The rolling grooves WK of the rolls, which are now in opposite relationship, are in this case in force-locking relationship with the rolling material, by virtue of friction, and drive it back in the opposite direction to its general direction of forward feed (pilgrim step). During that phase of the movement, the reduction in cross-section is achieved, which to the right of the rolling zone is the material B which at this time has not yet been rolled down.

(c) The roils have continued to rotate with the roll groove to such an extent that the cross-section I is to the left of the narrowest roll gap. The distance ll-ll shown in Figure 2a has now been increased in Figure 2c to the distance 11-1 shown therein. As can be seen from this Figure, the rolls 4a and 4b have once again rolled over a portion of material which has already been rolled (distance l-m).

(d) Upon further rotary movement the rolls 4a and 4b make the transition into the idle groove LK (Figure 2d) and thus release the rolling nnateriai for further displacement towards the right. The cross-section II has now been advanced to the iocation 1'. As can be seen from Figure 2d, the distance ll-l is that which is rolled out in each working period.

The working operation can now be periodically repeated.

A disadvantage of the pilgrim step process and rolling mill lies in the restricted reduction in cross-section for each roll run or pass, being at a maximum 25 to 30%. Greater degrees of reduction result in roll breakages or transv erse cracks in the rolled material.

It was found that the portion A (Figure 2a) of the rolls is responsibie for that, that portion being at the transition from the idle groove LK to the roll groove WK and, on engaging into the rolling material at the beginning of the rolling phase, resulting in severe local deformation of the rolling material at the point of engagement, with concomitant overloading of the rolls. Therefore one of the features of the present invention is the provision of a roll which in the roll position at the beginning of the rolling phase has a continuous transitional zone between the idle groove LK and the roll groove WK and wherein moreover the roll groove WK is grooved or calibrated for the progresive reduction in cross-section of the rolling material during a rolling phase.

However, when operating with such rolls, which involved considerable improvements, it was found that the cause of crack formation in the rolling material could not be attributed to the roll shape alone. It was also surprisingly found that a further significant factor in regard to the formation of transverse cracking in the rolling material is that force which by friction and force-locking engagement of the driven rolls with the rolling material, during the rolling phase, displaces the material longitudinally, that is to say, during the rolling phase, apart from the desired deformation forces (which in fact are pure compresion forces), there are additionally also undesired thrust or shear forces acting on the materiai. This realisation forms the basis for a further important feature of the process according to the invention, whereby, during the operation of progressively rolling the rolling material which is moved forwardly in a stepwise manner, substantialiy exclusively deformation forces are caused to act on the rolling material. In that way the unforeseen reduction in cross-section of the rolling material of up to about 90 to 95% is achieved in a single roll run (pas) without damaging the material and the rolls.

In a preferred embodiment of the proces of the invention, at the beginning of the rolling operation in the first rolling phase, the foremost end of the rolling material is rolled only over a length which corresponds to the length of the forward feed steps used. In that way the leading portion of the material is also subjected to the rolling proces and does not need to be thrown away.

Figures 3a and 3b illustrate the basic principle of the process according to the invention and the manner in which it is carried out. In contrast to the pilgrim step method, during the rolling phase the rolling material 5 is not driven back in the opposite direc'tion to its general direction of forward feed movement, but it is stationary. For that purpose in this case the rolls 4a and 4b with a roll groove for the progressive reduction in cross-section roll forwardiy in the direction of the general forward feed of rolling material, by the distance s (see Figure 3b). In accordance with the invention therefore the conventional driv e of the rolls 4a, 4b is discontinued and thus there are no undesirable thrust or shearing forces occurring between the rolls and the roliing material.So that the rolls 4a, 4b in the rolling mill according to the invention can roll in a non-driven manner on the rolling material 5, they are mounted in a reciprocable carriage.

The technical constructions of the rolling mill according to the invention will be referred to again hereinafter. First of all the mode of operation according to the invention will be described with reference to Figures 4a to 4e.

The two rolls may reciprocate (in the carriage which is not illustrated) from the lefthand dead point LT (Figure 4a) to the righthand dead point RT (Figure 4e), with the rolls rotating about the roll centres M in a rotary movement which is adapted to the horizontally directed movement of the carriage.

Mode of operation: In the last rolling operation (see Figure 4e), the contour identified by K, has been produced. The rolls now move from RT towards the left, as far as the lefthand dead point LT, in which case they come with their idle groove into the position shown in Figure 4a. The material 5 is now advanced towards the right by a small forward feed distance (s in preceding Figure 3b) so that the cross-section Il shown in Figure 4a moves into position 11'. The same applies in regard to the crosssection i and 1'. The contour K1 which is taken over from Figure 4e-it is shown in broken lines in Figure 4a-changes into the contour K2 which is congruent with K1, when the above-indicated displacement occurs.In the rolling operation which now begins, the rolls move towards the right, while rotating at the same time; the "spiral groove" SK, that is to say, the roll groove WK in that region which is grooved or calibrated for a progressive reduction in cross-section of the rolling material, first engages the material 5 at the cross-section II. See in connection therewith Figure 4b. Figure 4c shows how the material 5 is rolled from the contour K2 to the contour K1 again, the rolling material which is respectively to the right of the rolls being stretched towards the right.

As can be seen from the sequence shown in Figures 4a to 4e, the cross-section Illa in Figure 4d has moved into the position indicated at Ilid. In that position, the region of the spiral groove SK has run out. Nonetheles a part of the material which in Figure 4a was to the right of the cross-section Illa is still to the right of the rolls, because of the stretching of the material. Accordingly it is not yet of the definitive minimum thickness. Between crosssection Iliad in Figure 4d and cross-section Ille in Figure 4e, that contour which still belongs to the contour K, is rolled down to a definitive constant thickness by a "constant groove" KK (that is to say a region of the roll groove WK which adjoins the spiral groove SK and in which there is no longer any reduction in cross-section).That rolling operation in which the material is brought to the constant final thickness is terminated at cross-section Ille. It is (on the basis of experience) desirable if then the rolls, in the constant groove KK, continue to rotate by the distance Ille to the right-hand dead point RT and thus the element Ille-IVe which was produced in the precious rolling period is in part again covered over by the constant qroove KK.

The form of the spiral groove may be so determined by integral calculation that the relative reduction in cross-section remains almost constant at any point in the region 11' to I. In that regard, the technically possible and technically usual reduction values of 25 to 30% can be achieved. The cross-section which occurs at II' is rolled over a number of times (about 5 to 10 times) with the above-described rolling process, before it reaches position 1', so that total reductions of far above 90%, for example 98%, can be achieved between III' and 1', without any danger in regard to the rolling material or the rolling mill.

Figure 5 shows in detail the construction of the pair of rolls in Figure 4, in cross-section, in the configuration shown in Figure 4a.

The two rolls have a constant axis-to-axis spacing z. They rotate in opposite directions.

In rotating they cover the same angular distances; they rotate synchronously.

1. The idle groove LK.

It is of constant radius. It releases the rolling material which is pushed in between the rolls.

2. The spiral groove SK.

The spiral groove has a minimum radius run at the angle to = O. From that position the roll radius increases in a spiral configuration until it reaches its maximum value r at ,fe = v)RSK The parameter / SK is the angle which characterises the spiral groove region. In that region the radius r is a function of the angle 30.

3. The constant groove KK.

In the region of the constant groove, the roll radius is again constant (rconst) If the rolling material is engaged in the region of the spiral groove, it will be seen that the roll gap h which is defined by the roll spacing and by the spiral groove radius, becomes progresively smaller with an increasing angle WiP. The following applies in regard to the roll gap: h=z-2 r(S).

The form of the spiral is defined by the mathematical function: r=rO8j The mathematical parameters are desirably such that the reduction in cross-section of the material remains approximately constant. It is also possible however to envisage other parameters, thus for example parameters which ensure a constant rolling force.

As already mentioned hereinbefore, the rolls 4a, 4b are mounted in a reciprocable carriage, in the movement of which the rolls roll on the rolling material 5 without being driven. Figures 6 and 7 show diagrammatic side views of an embodiment of a rolling mill according to the invention. It will be seen that the carriage 2 having the rolls 4a, 4b is arranged in the rolling mill 1 and is reciprocated by a crank drive 3a, 3b by way of a lever assembly 3c-3i.

Instead of a crank drive however it is also possible to use other forms of drive of which the man skilled in the art is aware. A hydromechanical drive has been found to be particularly advantageous.

In order now to eliminate the undesirable thrust or shear forces and other troublesome secondary forces, in the rolling operation, the rolling mill according to the invention has special rolling elements which are disposed laterally of the rolls 4a, 4b on the roll spindles and which, upon movement of the roll carriage 2, roll form-lockingly or positively on co-operating elements which are fixedly connected to the roll stand 1. Figure 3a shows, as viewed from the front, the two working rolls 4a, 4b, with material 5 passing therethrough, the roll spindle 9 of the roll 4a carrying- a rolling element 6a and the roll spindle 10 of the roll 4b carrying a rolling element 6b. The rolling elements 6a, 6b roll on corresponding co-operating elements 7a, 7b which are fixedly connected to the roll stand.In Figure 3a the rolling elements 6a, 6b are gears and the cooperating elements 7a, 7b are toothed racks (which are shown in section). The arrangement of the toothed rack 7a, which is asociated with the gear 6a for the upper roll 4a, in the roll stand, can be seen from Figure 7.

Instead of gears with toothed racks, it is also possible however to use other arrangements as rolling elements 6 with cooperating elements 7, for example chain wheels with corresponding wheel chains. The rolling radius of the gears 6a, 6b or other rolling elements substantially corresponds to the radius R (see Figure 3) of the rolls 4a, 4b. That provides that, in their working movement which is towards the right in Figure 3b, the rolls roll almost in a slip-free manner on the rolling material which is held fast by a feed device.

However in order to achieve uniform rollingout of the cast elongate member, it is not sufficient now to use rolls in which the roll groove WK is made up of a spiral groove SK and a constant groove KK (Figure 5).

The rolling operation does not in fact just cause an increase in the length of the material, it also causes deformation of the material in the widthwise direction. Therefore, after the rolling operation, an elongate member for example of square cross-section has been flattened down. It is therefore necessary, after each rolling phase, when in accordance with the invention the roll carriage 2 has returned with a free movement into the lefthand dead point position and the rolls 4a, 4b have there reached the idle groove, for the material 5 to be turned through 90 in order in that way to put the cross-section back into the on-edge position. The material can then be increased in length again in the next rolling step, with the cross-section which is now standing in an on-edge position again being converted into a flat form.

Although such "turning" of the material through 90" is readily possible when rolling "non-continuously moving" bar material, however that turning movement would result in a twisting of the rolling material through 90 in the region between the continuous casting mould and the rolling mill (turning apparatus), in each forward feed step movement. That would not only be detrimental but even highly problematic, in regard to the continuously moving continuously cast material. Now, those additional difficulties are overcome by the particular, preferred embodiment, as shown- in Figure 8, of the working rolls of the rolling mill according to the invention, which provides that, instead of a turning movement, it is only necessary to provide for a simple transverse displacement of the rolled material.

In this case the working rolls 4a and 4b are of such a configuration that in conjunction with each other they form a left-hand groove 16 and a right-hand groove 15. In Figure 8 the material to be rolled or the elongate portion of material 5 is in the left-hand groove 16. After the material 5 has been flattened down during the rolling operation, at the end of that rolling period the material 5 which now rests in its flat condition in the groove 16 is displaced into the groove 15 in such a way that it is disposed in an on-edge upright position therein. In order to be able to do that, the rolls 4a and 4b are axially displaceable relative to each other.After the material 5 has been flattened down again during the next rolling period in the groove 15, the material 5, at the end of that period, is moved back into the groove 16 in the same way, whereupon the next following rolling period can begin, and so forth.

Figure 9a shows the cross-section of the roll groove at the moment of the "gripping" action. Shown therein is the rectangular crosssection of the elongate member 5, with height h1 and width b,. In the course of the further rolling movement, the groove closes down from h1 to h2 (see Figure 9b), with the width b, increasing to b2. The positions m0 and m respectively shown in Figure 9a, as a result of the roll movement, perform a radially directed closing movement at a speed v,,,o and Vrad respectively. That initiates a twist movement of the material which is fed to the rolls, about the centre point M. That means however that the material which has already been rolled and which is material that at the time is coming to the rolls, would become increasingly twisted.

The cross-sectional axes a-a and b-b respectively of the material being fed to the rolls would then no longer be at an angle of 45" relative to the roll axes, as must absolutely be required. In order to suppres that twist effect, the two rolls, during the closing movement, perform an axially directed relative movement which is identified by v,0 0 and v00 respectively.

The resulting speeds are such that they point in the direction of the cross-sectional axis a-a (45 inclination) to the centre point M of the cross-section. That therefore eliminates twisting of the material that is being fed to the arrangement.

The axial relative movement is so coupled to the radial closing movement (spiral form of the groove) that: 1. the points m and m" respectively move in the direction aa towards the centre point M, and 2. at the end of the closing movement (roll gap) the material cross-section As2 = h2 . b2 is achieved.

After the rolls, in the following return stroke movement, have been moved back into the idle groove configuration, the material can be displaced relative to the rolls into the righthand groove. At the same peripheral location, the right-hand groove, in the next transformation stroke movement, is again offered a material cross-section of the same size as previously in the left-hand groove.

When changing over the material from the left-hand into the right-hand groove, the width b2 which is produced on the left becomes the height h, in the right-hand groove. In the operation of rolling over the material which now follows in the right-hand groove, the axial roll movement must point in the opposite direction to the previous one.

The roll form is determined by the spacing h2,2 from the centre point M, as measured at 45,u. The centre point M is disposed at the centre between the two roll axes.

Figure 10 shows a front view of the rolling mill of Figures 6 and 7, with the working rolls shown in Figures 8 and 9. The roll carriage 2 in which the spindles 9 and 10 of the top roll 4a and the bottom roll 4b respectively are mounted will be seen in the roll stand 1. Disposed on the left-hand end of the spindle 9, as a rolling element, is a gear 6a which rolls on the toothed rack 7a. Similarly disposed at the right-hand end of the spindle 10 is a gear 6b which rolls on the toothed rack 7b.

The right-hand end of the roll spindle 9 carries an extension portion 11 which is fixedly connected to a pressure piston 12. The piston 12 is displaceable in a cylinder 13 by virtue of being acted upon by a pressure medium which can be introduced on both sides of the piston by means of connections 14. A movement of the piston 12 causes the top roll 4a to be displaced axially in the direction of the arrow, relative to the bottom roll 4b which is axially non-displaceable. The two rolls together form a left-hand groove 16 and a right-hand groove 15, with the material 5 being shown in the left-hand groove 16.

The rolling process and rolling mill according to the invention make it possible for the first time for the elongate member which has just been cast to be reduced to the desired final cross-section in one rolling mill pass, while making full use of the casting heat. That was made possibie primarily by virtue of the fact that, in comparison with the conventional pilgrim stepping process, the relative reduction in cross-section of the cast member, of at most about 25%, could be increased to 90% and more.The inevitable return movement of the rolling material during the rolling phase, which causes difficulties in the pilgrim stepping process, no longer occurs with the process according to the invention, and in addition it is now possible, in accordance with a particular embodiment of the invention, to avoid turning the material through 90" after each working phase.In addition, as a result of the high reduction in cross-section which can be achieved according to the invention, and the fact that there is now no longer any return movement of the material, the cast member can be rolled during the rolling phase endlessly, that is to say, continuously with the casting operation, whereas the previous piigrim stepping method only made it possible to roll individual elongate cast portions. Another ma- jor advantage is that the rolled material only needs to be moved at the feed side in small forward feed steps of a few millimetres in each working period from the continuous casting mould towards the rolling mill, instead of the previous reciprocating movement involved in the pilgrim stepping process. It is only in that way that it is possible for the continuously cast material to be reduced in a single pass through the rolling mili by from 90 to 98%, making use directly of the casting heat, in which respect, during the transformation operation, reductions of more than 20 to 30% are not required locally at any point and at any time. If the material were to be handled in accordance with the conventional pilgrim stepping process, then the material (bar material) would have to be sent in its entire length through the rolling mill about 5 to 10 times.

However such a process could not be carried out without reheating the material on each occasion.

Claims

1. A process for reducing the cross-section of elongate material such as hot continuously cast material by intermittent rolling of the material which is moved forwardly in a stepwise manner, in individual successive rolling phases, in which (a) in the individual rolling phases, the rolling material which is respectively moved forwardly in a stepwise fashion is progressively rolled down; and (b) deformation forces are applied to the rolling material throughout the entire rolling operation.

2. A process as claimed in claim 1, in which at the beginning of the rolling operation in the first rolling phase the foremost end of the rolling material is roiled down only over a length which corresponds to the length of the forward feed steps and does not exceed same.

3. An intermittently operable rolling mill for carrying out the process claimed in claim 1 or claim 2, comprising two grooved working rolls which respectively have a rolling groove portion and an idle groove portion and which rotate synchronously and the longitudinal axes or axes of rotation of which are disposed in a common plane through which the rolling material passes substantially perpendicularly between the rolls, in which: (a) the roll grooves are shaped for effecting the progressive reduction in cross-section of the rolling material during a rolling phase; (b) the rolls are mounted in a driven carriage which is reciprocable in the roll stand; and (c) rolling elements are disposed laterally of the rolls on the roll spindles and which, upon movement of the roll carriage, roil form-lockingly on co-operating elements which are fixedly connected to the roll stand; and (d) the rolling radius of the rolling elements substantially corresponds to the body radius of the rolls.

4. A rolling mill as claimed in claim 3, in which a crank drive with associated power transmission elements or a hydro-mechanical drive is provided for reciprocating the roll carriage.

5. A rolling mill as ciaimed in claim 3 or claim 4, in which the rolling elements are gears and the co-operating elements are gear racks engaged by the teeth of the gears.

6. A rolling mill as claimed in claim 3 or claim 4, in which the rolling elements are chain wheels whose teeth engage with chains which serve as the co-operating elements.

7. A rolling mill as claimed in any one of claims 3 to 6, in which the rolls are axially displaceable relative to each other and together form a right-hand groove and a lefthand groove for alternate transverse displacement of the rolling material from one groove into the other groove between the individual rolling periods.

8. A rolling mill as claimed in claim 7, in which a piston which is movable in a cylinder is provided for effecting axial displacement of the rolls relative to each other, said piston acting on one of the roll spindles by way of an intermediate portion.

9. A process for reducing the cross-section of elongate material substantially as hereinbefore described with reference to Figures 3a to 10 of the accompanying drawings.

10. An intermittently operable rolling mill substantially as hereinbefore described with reference to and as illustrated in Figures 3a to 10 of the accompanying drawings.