GB2181377A - Manufacture of tubes - Google Patents

Abstract

In the manufacture of seamless tubes, a billet is heated to rolling temperature, is pierced in a skew rolling stand 7, is stretched into a tubular bloom in a transverse rolling line 14 and rolled out into a finished tube in a finish-rolling line 15. The stretching of the hollow billet into a tubular bloom is carried out in several stages, these stages being carried out simultaneously on the same hollow billet using a transverse rolling method. To do this, the transverse rolling mill 14 does not require a reheating furnace upstream of the finish-rolling process and, with the aid of a rolling-block-type arrangement of a plurality of exchangeable transverse rolling stands, permits particularly large stretching or cross-sectional reduction as entry of the tubular bloom into the finish-rolling line 15 which is disposed at a short distance directly therebeyond. <IMAGE>

Description

SPECIFICATION Manufacture of tubes The present invention relates to the manufacture of seamless tubes from hollow billets.

Different methods, which vary considerably from one another, are used to manufacture seamless tubes, depending on the starting material available, the desired finished dimensions, the quantities to be manufactured per unit of time, the quality required, and similar criteria. However, these methods all have three main stages in common, namely piercing, and hence production of a hollow billet, stretching the hollow billet into a tubular bloom, and finish-rolling the tubular bloom into a finished tube, which then only has to be divided into the required lengths. Apart from the pierce-pressing method,the skew-rolling method is used particularly often to manufacture hollow billets. The tubular bloom is almost always finish-rolled into a finished tube by the stretch-reducing rolling method or the sizing rolling method, that is to say, by continuous methods.As a result, the main difference between the individual methods of manufacturing seamless tubes is to be found in the second method stage, that is, the stage in which the hollow billet is stretched into tubular bloom. Hence the different methods are named after their second stage.

In the plug-rolling method, after the hollow billet has been pierced, it is usually stretched in a second skew-rolling mill, as only a limited cross-sectional reduction is possible in the following plug-rolling mill. Following skew-rolling and plug-rolling, the wall thickness tolerance is reduced in two smoothing rolling mills connected in tandem such that the tubular bloom can be finish-rolled. In this method, the stretching process following piercing requires a skew-rolling mill, a plug-rolling mill and two smoothing rolling mills; this requires high investment costs and a large amount of space.

Due to the relatively small cross-sectional reduction and, above all, as a result of the high thermal stress on the plug, the finished lengths attainable using the plug-rolling method are relatively short, which leads to a large number of unusable end pieces, and hence to a high proportion of scrap.

In the push bench method, piercing, which is frequently carried out by means of a piercing press, is followed by the stretching of the hollow billet, usually in a skew-rolling mill.

Then the actual push bench is used, followed by a detaching mill and an extracting device for removing from the tubular bloom the mandrel rod used during the pushing process. In this method, too, a total of four relatively expensive units is required, and the very long push bench takes up a large amount of space.

The proportion of scrap is also relatively high because, after pushing, the closed end of the tubular bloom must be cut off and scrapped.

Due to the limited mandrel rod lengths, the lengths of the tubular blooms are generally less than 20 metres, so that it is only possible to produce finished tube lengths of a maximum of approximately 20 metres.

In the continuous tube rolling method, the billet is pierced in a skew-rolling mill and is stretched on a mandrel rod, which is inserted in the hollow billet, in rolling stands which are disposed one after the other and which have sizing openings having a substantially closed periphery. The closed form of the pass openings and the large contact area between the work material and the relatively cold mandrel rod cause the work material to lose a considerable amount of heat and the mandrel rod to be heated up. In order to limit both these phenomena by mean of reduced contact time, rolling is carried out at a high run-through speed. This requires high drive power. The resulting large motors make it difficult to adapt the speed exactly to the optimum speed, which leads to losses in efficiency.

This method further requires additional devices beyond the continuous tube rolling line for removing the mandrel rods from the tubular blooms. Furthermore, a continuous rolling line having six to eight rolling stands, which must be very heavy because of the high rolling pressures, a powerful drive and an additional drawing mill as well as a mandrel rod return system, is a particularly expensive system and is uneconomic for small and medium production quantities.

In the Diescher method, in which the hollow billet is stretched in a skew-rolling mill having rotating guide discs, the maximum obtainable cross-sectional reduction is relatively small and the thickness of the wall of the starting material is relatively small, so that it may be necessary to add a second skew-rolling mill upstream of the Diescher rolling mill. As a result of the small stretching, it is only possible to obtain a tubular bloom of relatively short length, with the disadvantages already described above for plug-rolling. Moreover, the mandrel rod must be accclerated by the rolls via the work material at commencement of rolling. For this reason, the mandrel rod must not exceed certain dimensions, which also limits the lengths of the tubular blooms.Above all, however, the surface of the work material is subjected to extreme stress by the rotating guide discs in the Diescher rolling method, which causes damage to many work materials. Furthermore, the guide discs require increased power, and hence increased operating costs, which costs are further increased by the wear on the guide discs.

The planetary skew-rolling method attempts to obtain as large as possible a cross-sectional reduction in one pass only. This leads to high rolling pressures, heavy types of construction and large rotating masses. In order to keep the centrifugal forces containable, the rotational speed, and hence the delivery speed, must remain low. Particularly in the case of tubular blooms of small diameters, the result is a low throughput of work material.

Furthermore, the considerable reforming gives rise to problems in the manufacture of tubular blooms with thin walls. Moreover, problems of gripping occur when the hollow billet is introduced into the pass opening. Furthermore, it is difficult to obtain a particular outer diameter of the tubular bloom. Finally, difficulties are caused by the large cross-sectional reduction at one point only, because the temperature of the work material increases greatly, which can cause great damage to the material.

With the exception of the planetary skewrolling method, the other methods require intermediate heating following stretching and before finish-rolling, for example in a stretch-reducing rolling mill, and hence an additional heating furnace, which results in considerable investment and operating costs. Furthermore, the other methods do not allow direct entry into the following finish-rolling line. All the known methods of manufacture produce tubular blooms which have unsatisfactory wall thickness tolerances as measured at various points on the periphery of the tubular bloom.

These irregularities interfere with finish-rolling and can still be found on the finished tube.

The invention relates to a method of manufacturing a seamless tube, in which a hollow billet, which has been heated to rolling temperature and which is pierced through in the longitudinal direction, is stretched, without being rotated and with a mandrel rod inside it, into a tubular bloom, and said tubular bloom is subsequently rolled out into a finished tube without intermediate heating. A similar method is known from German Patent Specification (Offenlegungsschrift) No. 26 57 823, in which the hollow billet is stretched into a tubular bloom by means of a planetary skew-rolling mill. In this method, there is no need for a furnace for intermediate heating, and the tubular bloom can enter the finish-rolling line directly, However, this planetary skew-rolling method has the above-mentioned disadvantages.

It is an object of the invention to provide a method, a rolling mill plant and a rolling line for manufacturing seamless tubes, during which the second main stage of the method, that is the stretching of the hollow billet into a tubular bloom, can be improved, both with regard to the quality of the tubular bloom as well as to economy.

The present invention resides in a process for manufacturing seamless tubes in which a hollow billet, which has been heated up to rolling temperature and which is pierced through in the longitudinal direction, is stretched, without being rotated and with a mandrel rod inside it, into a tubular bloom and said tubular bloom is subsequently rolled out to a finished tube without intermediate heating, and in which stretching of the hollow billet is achieved only by means of a transverse rolling method which is divided into a plurality of steps which, in the steady operating state, are carried out simultaneously on the same hollow billet.

In the method according to the invention, cross-sectional reduction is not carried out in one step and at one point of the work material, as in all the other known skew-rolling methods, but in several steps of relatively small reductions. The special feature of this subdivision consists in the fact that the individual steps are carried out simultaneously on the same hollow billet but as different points thereon. This can only be carried out in the steady state, that is, when the leading end of the work material is already finished, and the trailing end of the work material has not yet been formed. Furthermore, the subdivision of the stretching process into several small stages and the simultaneous implementation of the stages on the same hollow billet can also be carried out in a transverse-rolling method.

Hence, the method according to the invention comprises a combination of three features, which together achieve the above-mentioned object.

Dividing the stretching process into several smaller steps produces a small cross-sectional reduction per pass opening, and hence a stage-by-stage forming process which protects the work material. Furthermore, several successive steps can together produce a large cross-sectional reduction, so that billets having a heavy weight can be used, thus enabling the production of extremely long tubes. As a result of the danger of the mandrel rod buckling, and because of the thermal stress on the plug, it is not possible, in the case of piercerolling in a skew-rolling mill, to produce a hollow billet longer than approximately 12 metres. Heavier billets can therefore only be obtained by reason of greater thickness of the hollow billet wall. In order to do this, it is required that, on stretching the hollow billet into a tubular bloom, a correspondingly larger cross-sectional reduction can be achieved, which, for a variety of reasons, is not possible using the known methods, even when a plu- rality of rolling mills are disposed one after the other. The upper limit for cross-sectional reductions, and hence stretching of the work material into tubular blooms, is approximately 20 metres for the push bench method, and approximately 42 metres for the continuous method. In contrast, the method according to the invention can be used to obtain a much larger overall reduction, and hence overall stretching, of the work material, which can be as much as twelve times greater or more, so that tubular blooms of 120 metres and longer can be obtained.Such a tubular bloom can be used in the known finish-rolling methods to produce tubes of 1,200 metres and longer.

Because of the division of the cross-sectional reduction into a plurality of stages, and the large overall reduction obtained thereby during stretching, it is not necessary to attempt to obtain particularly thin walls during piercing in the skew-rolling mill, and hence the difficulties associated therewith are avoided. Because the large cross-sectional reduction during stretching is obtained simultaneously on the same hollow billet, that is, in only one rolling line, processing time remains short and heat losses low. In most of the known methods, crosssectional reduction does not take place simultaneously, but in a plurality of different rolling mills in succession, whereby a large amount of heat is lost through transport, changing the mandrel rod, and the like.As stretching is carried out in the method according to the invention by a transverserolling method, this enables a considerable improvement to be obtained in wall thickness tolerances, in particular about the periphery of the tubular bloom, which cannot be achieved by longitudinal rolling.

It is expedient to carry out the transverserolling method in both possible directions of rotation, preferably alternating from stage-tostage. The torsional strain exerted on the work material is thus largely eliminated, thus reducing stresses during forming. Furthermore, this leads to crosswise overrolling of individual sections of the work material, which renders narrow tolerances possible.

Advantageously, the hollow billet is stretched at the entry end in larger steps than at the delivery end. This produces closer rolling tolerances and avoids the difficulties which occur in the case of large cross-sectional reductions on thin tubular bloom walls. As a result of the cross-sectional reduction, which becomes increasingly smaller towards the delivery end, the transverse-rolling method gradually becomes a smoothing-rolling method with an almost negligible cross-sectional reduction. In doing so, the overall drive power is distributed in a largely uniform manner to all stands, and the torques are also kept approximately constant.

A further object of the invention is the provision of a rolling mill plant for implementing the process according to the invention.

A rolling mill plant according to the invention comprises a piercing skew-rolling mill, a finish-rolling line and a transverse rolling line which is disposed directly after the piercing skew-rolling line and directly in front of the finish-rolling line and which is of block-like construction.

Therefore all that is required beyond the skewrolling stand for piercing is a single device for stretching, and not a plurality of rolling mills and devices, as in most of the known systems. Auxiliary devices, such as mandrel rod return devices, detaching mills and the like, are also no longer necessary.

Furthmore, a furnace for intermediate heating following stretching is also no longer needed.

Moreover, a tubular bloom produced in this way can directly enter the finish-rolling line, which comprising a sizing mill or stretch-rolling mill and which is disposed at only a short distance beyond the transverse rolling line.

Unimpeded or unrestricted delivery of the work material following stretching is not necessary. These advantages have already been achieved in a system equipped with a planetary skew-rolling mill, but this system also has the disadavantages mentioned at the beginning, in particular problems in manufacturing tubular blooms with thin walls. The system according to the invention, and in particular its transverse rolling line, is able to achieve a large cross-sectional reduction during Stretching with narrow tolerances, so that very heavy billets can be rolled out in one heat into very long tubes having thin walls. It is recommended to equip all three units of the plant with three-roll passes, although other alternatives are possible.

A particularly important component of the present invention is the transverse rolling line in which the work material is stretched. Thus, the invention includes a transverse rolling line comprising a rolling-block-type arrangment of a plurality of exchangeable transverse rolling stands, which each have at least one motordriven support cage which is rotatable about the pass line and in which a plurality of skew rolls are rotatably mounted at an angle to the pass line to form a pass opening, and a mandrel rod which is held in the axial direction at the entry end and projects from there into the pass openings of he stands of the skew-rolling line.

The rolling-block-type arrangement of a plurality of transverse rolling stands allows a hollow billet to be stretched in steps, but simultaneously, in the method according to the invention. As a result of the division of the overall cross-sectional reduction into several stages, the cross-sectional reductions in the individual transverse rolling stands remain small, so that low rolling pressures suffice.

The advantegeous consequences of this are small rolls, light rolling Stands, low drive powers and a particularly high degree of forming efficiency. The rotating masses are low, so that the centrifugal forces occurring can easily be controlled. Despite the large number of rolling stands, considerably less space is required compared with the known types, as the transverse rolling stands have only small dimensions and can be disposed very closely one after the other. Furthermore, the rollingblock-type arrangement of a plurality of exchangeable transverse stands allows the thickness of the walls of the tubular blooms to be altered in a simple manner by using more or fewer transverse rolling stands.The large number of transverse rolling stands results in a gradation in the thickness of the walls of the tubular bloom, which in most cases is usually completely adequate to obviate the need for stepless radial adjustment of the rolls. The closely stepped division required for the finished tubes can be achieved with the finish-rolling line which is connected in succession. If the thickness of the tubular bloom wall is altered by using a mandrel rod having a different outer diameter, this can be carried out very simply in the invention, because only one mandrel rod is used, and hence only one mandrel rod has to be changed. Furthermore, the rolling-block-type arrangement of exchangeable transverse rolling stands allows the rolls to be changed and the entire transverse rolling line to be set up in a workshop set up for this purpose, while other transverse rolling stands are in use.The system thus provides for a particulary long uninterrupted rolling time, which leads to a considerable improvement in performance due to a high degree of utilisation of the plant. The economic efficiency of the plant is furthermore assured by the high output, because the possibility of using heavy billets leads to long tubular blooms and large tubular lengths, with the result that only a few unuseable end sections are obtained and the proportion of scrap is low. Furthermore, apart from low operating costs, investment costs are also lower, in particular as a result of the fact that a reheating furnace is no longer required, than in other known plants, which have numerous large or heavy units as well as auxiliary devices.

It is expedient to have the mandrel rod displaceable in the axial direction and rotatable about its longitudinal axis. By displacing the mandrel rod, the longitudinal sections which are worn in the region of the skew rolls can be replaced in a quick and economical manner by other longitudinal sections of the mandrel rod which have not yet become worn. The amount of broadening of the work material can be influenced by means of the rotatable mounting of the mandrel rod, by virtue of either a motor drive or braking.

It is recommended to counter-rotate the support cages of adjacent transverse rolling stands. On the other hand, it is also possible to rotate all the support cages of all the transverse rolling stands in the same direction.

Furthermore, it is also possible to provide each transverse rolling stand with two support cages disposed one after the other in the directon of rolling, and counter-rotated. In all these embodiments, the work material can be formed with less stress, and it is possible, in particular, to have repeated over-rolling of each point of the work material, thus reliably preventing the formation of unwanted swellings and achieving extremely close wall thickness tolerances. Forward feed, roll width and the distance between rolls can be matched to one another such that a particular point on the work material can be repeatedly over-rolled by different points on the roll working surfaces, and not always, for example, by the edge sections.

In a preferred embodiment of the invention, if the skew rolls are not motor-driven, at least one drive stand is disposed upstream of and between adjacent transverse rolling stands, such drive stands having a plurality of, and preferably three, drive rolls driven in the direction of rolling and having drive roll axes which are transverse to the axis of rolling or pass line, the arrangement and design of the drive rolls being such that an annular gap remains between the work material and the mandrel rod. The lack of a motor drive for the skew rolls simplifies the construction of the transverse rolling stands considerably. Due to the motor-driven support cage, the skew rolls still roll along and about the surface of the inserted work material, which ensures that the material is worked or reshaped.The drive stands are however necessary in this embodiment of the invention in order to ensure that the work material is fed despite the lack of a roll drive. An alternating sequence of transverse rolling stands and drive stands is to be recommended, although other sequences are possible. One or two drive stands upstream of the first transverse rolling stand ensures reliable entry of the hollow billet into the transverse rolling line. A last drive stand at the delivery end is generally only required if direct entry into a finish-rolling line disposed shortly beyond the transverse rolling line is not possible.Furthermore, it is sometimes advantageous to use two drive stands one after the other, because the drive rolls can only be pressed against the work material in the radial direction in a limited manner, and as a result can generate only a limited feed force, so that a plurality of drive stands connected one after the other can be usefui. In the case of several, for example two, drive stands, a series of different pass openings can be used. A first oval pass opening prevents the work material from being squeezed into the gaps between the rolls, and a second round pass opening gives the work material in the second drive stand its round cross-sectional shape back, whereby it is also prevented from penetrating into the roll gaps. As a result of limited radial pressing force, a free gap remains between the inner surface of the work material and the outer surface of the mandrel rod, which gap prevents friction between the mandrel rod and work material. Friction only occurs in the region of the skew rolls, beyond which, however, the work material is separated from the mandrel rod in the radial direction, as in the known skew-rolling mills. In this respect, the transverse rolling line according to the invention also differs from the known continuous rolling line, in which the work material is pressed very firmly against the surface of the mandrel rod, which is one of the causes of the high rolling pressures and the high power requirements.In operation of the transverse rolling line according to the invention, however, the rolling pressures and drive power are kept low, which allows the use of small and light transverse rolling stands, which may be disposed in a rollingblock-type arrangement. Furthermore, the gap between the work material and the mandrel rod, which is usually internally cooled, acts in an insulating manner, so that heat loss from he work material is kept low. At the same time, heating of the mandrel rod also remains relatively low, so that it can be used repeatedly and there is no need for a complex mandrel rod return arrangement with a large number of expensive mandrel rods.

In another embodiment of the invention, the skew rolls can be driven by way of their bearing shafts. No drive stands are required in this case, which results in a particularly short transverse rolling line. In this embodiment, the skew rolls can be driven by gear wheels which are rigidly disposed on the bearing shafts of the skew rolls and, driven by their rotating support cage, roll along a gear rim in the housing of the transverse rolling stand.

In a further embodiment of the invention, the feed angle of the skew rolls is adjustable.

This is necessary if, for example, the outer diameter of the tubular bloom is to be changed or if the stand location is to be changed. Feeding can thus be optimally adjusted at each stand location separately. The skew rolls can also be radially adjustable with respect to the pass line. The is can be implemented in a particularly simple manner by the use of shims of corresponding thickness. As a result of this, the size of the pass openings can be adapted to tubular blooms of different outer diameters. Furthermore, it is possible to design the skew rolls to be axially adjustable relative to their axis of rotation. This has the advantage that, in the case of worn and refinished working surfaces of the skew rolls, the pass opening can be reset to its original size.

It is advantageous to provide the last transverse rolling stand at the delivery end with smoothing rolls instead of skew rolls.

The skew rolls of the transverse rolling stands are barrel-shaped rolls, familiar from the known skew-rolling stands, but with considerably smaller dimensions. The above-mentioned smoothing rolls, however, have a substantially cylindrical, or even hyperbolic, form, such as the type used in the rolling straightening machines. Like the barrel-shaped skew rolls, they are disposed at an angle so as to cause the work material to be fed. Their feed angle is also adjustable, and it is recommended to dispose them, and the skew rolls, in such a way as to be radially and exactly adjustable with respect to the pass line. This type of transverse rolling stand equipped with smoothing rolls essentially serves only to im prove the wall thickness tolerances, which are already close, for which the transverse rolling method is particularly suitable.

It is expedient for the transverse rolling stands to be provided on both sides of their outer surface with a drive shaft and drive jour nals or drive coupling. Each transverse rolling stand can then be inserted into any reception pocket in the transverse rolling line and can be operated in either direction of rotation of the support cage. It is then only necessary to turn around the transverse rolling stands, which are suspended from a crane, about their vertical centre axis if they are to be driven in a different direction of rotation of the support cage.

It is recommended to drive the transverse rolling stands and/or drive stands by way of a group drive. The transverse rolling stands and drive stands can have separate group drives too. Such group drives are known from stretch-reducing rolling lines operated as fin ish-rolling lines, and have proved to be ex tremely successful. The external structural shape of the transverse rolling line according to the invention, that is, above all, the rolling stand receptacles and the drive, correspond to a large extent to the rolling stand receptacles and the drive of the known stretch-reducing rolling lines. It is therefore also recommended to dispose the transverse rolling stands an d/or drive stands on exchange carriages, such as those described, for example, in German Patent Specification No. 15 27 659.

The invention is further described, by way of example, with reference to the accompany ing drawings, in which: Fig. 1 is a plan view of a rolling mill plant according to the invention; Fig. 2 is a plan view of a transverse rolling line according to the invention; Fig. 3 shows a forming section of the transverse rolling line in partial longitudinal section; Figs. 4 and 5 are respectively a sectional plan view and a front view of a transverse rolling stand without roll drive; Fig. 6 is a sectional view of a transverse rolling stand without roll drive and having two support cages; Fig. 7 is a section of a transverse rolling staid with roll drive; Fig. 8 is a plan view of a transverse rolling line without drive stands; Fig. 9 shows a further embodiment of a transverse rolling stand without roll drive; and Fig. 10 is a front view of a transverse roll ing line with a stand exchange carriage.

Fig. 1 shows a rotary-hearth furnace, which is charged with billets (not shown) weighing, for example, 1000kg and approximately 5 metres long, by means of a charging device 2. Having been heated to rolling temperature, these billets leave the rotary-hearth furnace 1 by way of a roller table 3, pass through a descaling device 4 and pass by way of a transverse conveyor 5 into an insertion channel 6 of a skew-rolling stand 7, where each billet is made into a hollow billet by piercing, in accordance with the known skew-rolling method. After the mandrel rod has been removed, the resulting hollow billet is passed by way of a further transverse conveyor 8 to a feed table 10.An initially stationary pair of drive rolls 11 is moved in the radial direcion against the billet and holds it while a mandrel rod 12, which may be internally cooled, is inserted into the billet by means of a second pair of drive rolls 13. The mandrel rod 12 is inserted until its leading end projects into the last pass at the delivery end of a transverse rolling line 14. Using the first-mentioned pair of drive rolls 11, which are now started running, the hollow billet is pushed into the transverse rolling line 14, the mandrel rod 12 being held at the entry end. It is also possible to insert the mandrel rod 12 and the hollow billet thereon into the transverse rolling line simultaneously.There the hollow billet, which may, for example, be approximately 9 metres long, is rolled out into a tubular bloom, which may, for example, be approximately 108 metres long, whereby the tubular bloom is rolled off the mandrel rod 12, which is still held at the entry end. While rolling in the transverse rolling line 14 is still going on, the leading end section of the resulting tubular bloom passes into a finish-rolling line 15 which is disposed directly therebeyond and at a short distance therefrom, which finish-rolling line can, for example, be in the form of a stretch-reducing rolling line. Using a cutting device 16, the finished tube, which may have an uncut length of over 1,000 metres depending on the finished diameter, can be divided into the required lengths before being passed by way of a roller table 17 to a cooling bed 18.

Fig. 2 shows the transverse rolling line 14 on a larger scale. The transverse rolling line 14 comprises a block-type arrangement of roll stands which are disposed as closely as possible one after the other in a straight line along the pass line or rolling axis. The roll stands are driven by a group drive 19, which is similar to the one used in the known stretch-reducing rolling line 15, and are of two different types. The first ones are transverse rolling stands 20 having skew rolls 21 which are rotatably mounted in a support cage or basket 22 which rotates about the rolling axis or pass line 23, and is driven by a bevel gear drive 24. Instead of skew rolls 21, the last transverse rolling stand 20 at the delivery end has smoothing rolls 25 having a slightly hyperbolic form.

A drive stand 26 is disposed upstream of each transverse rolling stand 20 and beyond the last transverse rolling stand 20, which driven stand 26 has drive rolls 27 which are also driven by the group drive 19. Although Fig. 2 only shows two skew rolls 21 and two drive rolls 27, in order to show their shape and the pass opening more clearly, each pass comprises a total of three rolls distributed about the periphery, the same applying to the finish-rolling line 15, which also comprises a block-type arrangement It can be seen from Fig. 3 that the skew rolls 21 operate in a similar way to that known from the known skew-rolling methods. The cross section of the work material 28 moving from left to right in Fig. 3, in particular with regard to its wall thickness, is reduced by the skew rolls 21, following which the work material 28 is separated from the mandrel rod 12.In the region of the drive rolls 27 disposed upstream and downstream of the skew rolls 21, the work material 28 is compressed in the radial direction, to a point at which a gap 29 remains between the work material 28 and the mandrel rod 12. Direct contact between the work material 28 and mandrel rod 12 exists in the form of a line, that is only in the region of the reduction part of the skew rolls 21, which facilitates feeding of the work material, reduces wear on the mandrel rod and keeps its heating or heat loss from the work material 28 low.

Figs. 4 and 5 show how the support cage 22 is mounted in a housing 30 of the transverse rolling stand 20 and the way in which the skew rolls 21 are mounted in the support cage 22. The bevel gear drive 24 for the support cage 22 can also clearly be seen.

A drive shaft 31 transmits the drive torque from the group drive 19 by way of a coupling 32. The dash-dotted lines on the opposite side of the outer surface of the housing 30 indicate a second drive shaft 31 with a coupling half 32 in order to show that the transverse rolling stand 20 can be turned around about its perpendicular centre axis, so that the skew rolls 21 can be positioned at the right-hand side of the transverse rolling stand 20 in Fig. 4 and can then be counterrotated. Furthermore, Fig. 5 shows that the skew rolls 21 are doubly inclined to the roller axis 23.

Fig. 6 essentially corresponds to Fig. 4, but shows that it is possible to dispose two support cages 22 and two sets of skew rolls 21 in a housing 30, the two support cages 22 being counter-rotated.

Fig. 7 also essentially corresponds to Fig. 4, but shows a way in which the skew rolls 21 may be driven. The skew rolls 21 are rigidly secured on their bearing shafts 33 whose ends remote from the skew rolls 21 are also rigidly connected to a gear wheel 34. These gear wheels 34 mesh with a stationary gear rim 35 fixedly connected to the housing 30, so that, when the support cage 22 is rotated, each gear wheel 34 rolls along the gear rim 35 and hence the skew rolls 21 are driven by way of the bearing shafts 33.

Fig. 8 shows a transverse rolling line 14 which is equipped only with transverse rolling stands 20 of the type shown in Fig. 7. As a result of the drive of the skew rolls 21 and of the smoothing rolls 25, drive stands 26, as shown in the embodiment of Fig. 2 are not required.

Fig. 9 shows two drive stands 26 and a transverse rolling stand 20 with the drive disposed at the side, which allows of small bevel gear diameters and low peripheral speeds.

The skew rolls 21 are no longer overhung, but are journalled at both ends, and furthermore, the feed angle of the skew rolls 21 can be finely adjusted by means of a plurality of interengaged toothed annular discs 36. To do so, the bearing body 37 of the skew rolls 21 is turned in the direction of the arrow. The skew rolls 21 can be adjusted radially with respect to the work material 28 by corresponding shims (not shown) or by using toothed annular disc 36 of different thickness.

Fig. 10 shows how the transverse rolling stands 20 are held during operation, which also applied to the drive stands 26 not shown in Fig. 10. The transverse rolling stands 20 are carried by a change-over carriage 38 which can be moved to the left in Fig. 10 as indicated by dot-dashed lines. During operation, each stand is held by clamping device 39 in the radial and axial directions. In this respect, the transverse rolling line according to the invention corresponds to the conventional type known in stretch-reducing rolling lines 15. As in the latter case, the transmission of the group drive 19 is accommodated in a housing 40 of the transverse rolling line 14, where it is driven by motors 41 by way of shafts 42. Apart from the group drive 19, it is also possible to drive the transverse rollings stands 20 and the drive stands 26 individually. In order to protect both the skew rolls 21 and the drive rolls 27, it may be advisable to dispose guides between the transverse rolling stands 20 or drive stands 26, which guides are able to guide the mandrel rod 12 in the radial direction when its leading end section is inserted, without the hollow billet, into the pass openings at the beginning of the rolling process. During operation, these guides are not required, nor are they required if the leading end of the mandrel rod is inserted together with the hollow billet thereon into the pass openings of stands 20 and 26.

Claims (27)

1. A process for manufacturing seamless tubes in which a hollow billet, which has been heated up to rolling temperature and which is pierced through in the longitudinal direction, is stretched, without being rotated and with a mandrel rod inside it, into a tubular bloom and said tubular bloom is subsequently rolled out to a finished tube without intermediate heating, and in which stretching of the hollow billet is achieved only by means of a transverse rolling method which is divided into a plurality of steps which, in the steady operating state, are carried out simultaneously on the same hollow billet.

2. A process as claimed in claim 1, in which the transverse rolling is carried out in both possible directions of rotation.

3. A process as claimed in claim 2, in which the directions of rotation alternate from step to step.

4. A process as claimed in claim 1, 2 or 3, in which the hollow billet is stretched at the entry end in larger steps than at the delivery end.

5. A process as claimed in any of claims 1 to 4, in which the transverse rolling is carried out by means of skew rolls which are motordriven.

6. A process as claimed in any of claims 1 to 4, in which each step of the transverse rolling method is carried out by means of at least one respective set of skew rolls which are freely rotatable about their axes and the hollow billet being stretched into a tubular bloom is engaged by driving rolls disposed between the sets of skew rolls.

7. A rolling mill plant comprising a piercing skew-rolling mill, a finish-rolling line and a transverse rolling line which is disposcd directly after the piercing skew-rolling line and directly in front of the finish-rolling line and which is of block-like construction.

8. A transverse rolling line comprising a rollingblock-type arrangment of a plurality of exchangeable transverse rolling stands, which each have at least one motor-driven support cage which is rotatable about the Pass line and in which a plurality of skew rolls are rotatably mounted at an angle to the pass line to form a Pass opening, and a mandrel rod which is provided with means at the entry end of the rolling line for holding the mandrel rod back in the axial direction such that the mandrel rod projects from the entry end into the pass openings of the stands of the skew-rolling line.

9. A transverse rolling line as claimed in claim 8, in which the mandrel rod is displaceable in the axial direction.

10. A transverse rolling line as claimed in claim 8 or 9, in which the mandrel rod is rotatable about its longitudinal axis.

11. A transverse rolling line as claimed in claim 8, 9 or 10, in which the support cages of adjacent transverse rolling stands are counter-rotated.

12. A transverse rolling line as claimed in claim 8, 9 or 10, in which all the support cages of all the transverse rolling stands rotate in the same direction.

13. A transverse rolling line as claimed in claim 8, 9 or 10, in which the transverse rolling stands each have two support cages disposed one after the other in the direction of rolling and which are counter-rotated.

14. A transverse rolling line as claimed in any of claims 8 to 13, in which the skew rolls do not have a motor drive, at least one driving stand is disposed upstream of and between adjacent transverse rolling stands, said driving stands having a plurality of drive rolls which driven in the direction of rolling and whose axes extend transversely to the pass line, the arrangement and formation of the drive rolls being such that an annular gap is left between the work material and the mandrel rod.

15. A transverse rolling line as claimed in any of claims 8 to 13, in which the skew rolls are driven by way of their bearing shafts.

16. A transverse rolling line as claimed in claim 15, in which gear wheels are rigidly disposed on the bearing shafts of the skew rolls and, driven by their rotating bearing cage, roll along a gear rim in a housing of the transverse rolling stand, whereby the skew rolls are driven by virtue of the rotation of the support cage.

17. A transverse rolling line as claimed in any of claims 8 to 16, in which the feed angle of the skew rolls is adjustable.

18. A transverse rolling line as claimed in any of claims 8 to 17, in which the skew rolls are adjustable radially with respect to the pass line.

19. A transverse rolling line as claimed in any of claims 8 to 18, in which the skew rolls are axially adjustable relative to their axes of rotation.

20. A transverse rolling line as claimed in any of claims 8 to 19, in which the last transverse rolling stand at the delivery end is provided with smoothing rolls instead of skew rolls.

21. A transverse rolling line as claimed in any of claims 8 to 20, in which the transverse rolling stands are provided at both sides of their outer surface with a drive shaft having a drive trunnion or a drive coupling.

22. A transverse rolling line as claimed in any of claims 8 to 21, in which the transverse rolling stands and/or drive stands are driven by way of a group drive.

23. A transverse rolling line as claimed in any of claims 8 to 22, in which the transverse rolling stands and/or drive stands are disposed on carriages for changeover of the stands.

24. A rolling mill plant as claimed in claim 7, in which the transverse rolling line is as claimed in any of claims 8 to 23.

25. A process for manufacturing a seamless tube substantially as herein described with reference to the accompanying drawings.

26. A rolling mill plant constructed and adapted to operate substantially as herein described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

27. A transverse rolling line constructed substantially as herein described with reference to and as illustrated in Figs. 2 to 10 of the accompanying drawings.