GB2191966A

GB2191966A - Seamless tube manufacture

Info

Publication number: GB2191966A
Application number: GB08714770A
Authority: GB
Inventors: Karlhans Staat; Hermann Moltner
Original assignee: Kocks Technik GmbH and Co KG
Current assignee: Kocks Technik GmbH and Co KG
Priority date: 1986-06-25
Filing date: 1987-06-24
Publication date: 1987-12-31
Also published as: IT8721000A0; DE3717698A1; GB2191966B; IT1205176B; DE3717698C2; GB8714770D0; FR2600562A1; CA1307681C

Description

1 GB 2 191 966 A 1

SPECIFICATION

Seamless tube manufacture The invention relates to a method of manufacturing seamless tubes in which a n ingot, which has been heated to roiling temperature, is pierced in a skewrol 1 ing stand to form a hollow ingot, thereafter elongated to form a tubula r bloom and then rol led out into a f inished tube.

The manufacture of seamless tubes almost always involves the abovementioned three stages using three different devices. Piercing is frequently carried out in a skew-rolling stand, as such a stand provides a hollow ingotwith a close wall thickness tolerance and a relatively large length. Stretching is often carried out in a second skew-rolling stand which is in the form an Assel or Diescher rolling stand. The tubular bloom thus produced is rolled outto a fin- ished tube following reheating in a sizing or stretchreducing rolling line positioned downstream.

It is already known (from the Journal "BANDER, BLECHE, ROW' 14 (1973), No. 4, pages 150 and 151) to use the same skew-rolling stand to pierce ingotsto form hollow ingots and to stretch hollow ingots to form tubular blooms. In this known method, a number of hollow ingots is obtained by piercing, the skew-rolling stand is then converted from piercing to stretching, and a number of hollow ingots are formed into tubular blooms by stretching.

As some time is required to pierce several ingots in succession and to convert the skew-rolling stand from piercing to stretching, it is not possible in this known method to carry out piercing and stretching in one heat. The hollow ingots must therefore be rehea- 100 ted before stretching, which is uneconomic and time-consuming and, in addition, requires the provision and operation of a suitable furnace.

Furthermore, during both piercing and stretching, the work material is moved from the ingot guide channel, which is disposed atthe entry end, through the rolling stand to the delivery end where it is ejected to this side. A device is thus required to transport the hollow ingotsfrom the exit end to the entry end of the skew-rolling stand, which leads to corresponding investment costs.

In addition, a mandrel rod is inserted at the entry end into the hollow ingot atthe beginning of the stretching operation until its f ront end face comes into abutment againstthe base of the hole in the hollow ingot. The mandrel rod then acts as if in a type of push bench and pushes the hollow ingot into the region of the rolls of the skew-rolling stand in which the stretching operation takes place. As a result, this known method requires a hollow ingotwhich is not pierced through, but has a base againstwhich the mandrel rod can abut. Consequently, the piercing operation in the skew-rolling stand must be prematurely terminated in orderto retain a base part, or the hollow ingot must be manufactured using a piercing press. Both of these have the disadvantage that a considerable amount of material must be scrapped, as this base part must be separated and scrapped following stretching. Forthe above reasons, the known method was thus elaborate, time-consuming and unecomonic, and could be used at bestfora low level of production, which is why it has not gained wide acceptance in practice.

It is an object of the invention to make the above- mentioned method simpler, technically superior and more economic, and to provide a plantwhich will enable the method according to the invention to be carried outwith relatively low investment costs.

According to the invention, stretching takes place immediately following piercing in the same heat, the work material being stretched in the same skewrolling stand, but in the opposite run-through direction to that of the piercing operation.

The method according to the invention differs from the known method in that the skew-rolling stand operates in the reverse rolling mode for piercing and stretching, and in thatthe two run- throughs follow on from each other in quick succession. In the first run- through, the ingot is pierced, while in the second run-through, in the opposite direction, the same ingot is stretched shortly afterwards in the same skew-rolling mill to form a tubular bloom. This ensures thatthere is only a negligible cooling off between piercing and stretching, and thus no need for reheating. Furthermore, no device is requiredto transport the work material from the delivery end to the entryend around the skew-rolling stand.The guiding ofthe mandrel rod is also simplified, because a mandrel rod and supportare only required at the deiiveryend of theskew-rolling stand. Thestroke of the mandrel rod is onlyshort, because itcloes not haveto be pulled outof the hollow ingot, but rather the hollowingot is rolled offthe mandrel rod during the second run-through. Furthermore, the delivery guideforthe hollow ingotcluring piercing is also a good entry guide for the stretching operation, in which guide a hollow ingotcan easily beturned and is nottwisted bystresswith a high torque.

Afurther advantage isto befound in thefactthat the greateststress on the rolling stand and workmaterial atthe beginning of the piercing and stretching operations is reduced in that normal operating speed is reached by gradual acceleration from a standstill orfrom a low roll speed. The rolls are either ata standstill or running at a low speed without additional control as a result of the reverse rolling operation according to the invention, in which, because of the reverse in the direction of rotation of the rolls, they must in any case be accelerated from a standstill on commencement of piercing and stretching.

During the piercing and stretching operations, the mandrel rod remains inside the hollow ingot or tubular bloom, and prevents air, and particularlythe oxygen in the air, from entering intothe hollow ingot ortubular bloom and oxidising the insidewall. Furthermore, using the method according to the invention, it is possibleto keep the space between the mandrel rod and the inside wall of the hollow ingot ortubular bloom particularly small because it is not necessaryto pass the mandrel rod through again. The smallness of this gap means thatthe amount of air and oxygen which can still penetrate into this space is very small, so thatthere is only negligible oxidisation of the inside wall. As a result, no particles of scale are rolled into the inside wall during stretch- 2 GB 2 191 966 A 2 ing, which means that it remains considerably smoother.

Although, in general, the hollow ingot is stretched following piercing over an internal mandrel rod to form a tubular bloom in order to obtain a thinnerwall and greater elongation of the work material, it is often practical to elongate the hollow ingotfollowing piercing in a hollow pass,that is, without an internal tool. Thewall of thetubular bloom obtained isthus thicker, butthis thickness lieswithin particularly narrowtolerance limits, which clearly improves the quality of the finished tubes.

It is particularly recommended to f inish-roll the tubular bloom after piercing and stretching in a siz- ing or stretch i ng-red ucing rolling line without reheating. Thistoo is made possible bythe method according to the invention, because it allows piercing and stretching to take place in very rapid succession and using only one single internal tool which withdraws heatfrom the work material only once. Consequently, the first rolling heat suffices not onlyfor piercing and stretching, but also for sizing orstretchreducing rolling.

Ontheotherhand, itisalso possible to stretch the tubularbloom even further following piercing and stretching in a reverse- rolling stand in one or more subsequent steps. In this way, work done by thefollowing stretching units is reduced and tubular blooms with particularlythin walls are obtained.

Plug rolling stands or Pilger rolling stands can, for example, be used to carry outthe subsequent stretching operations.

The invention further relates to a plantfor implementing the method according to the invention.

The plant according to the invention comprises a skew-rolling stand which is provided atthe entry end with an ingot guide channel and a pusher, and atthe delivery end with a rolling mandrel on a rotatable, axially displaceable mandrel rod mounted in a sup- port, a sizing orstretch-reducing rolling line being disposed downstream of the skew-rolling stand,the drive andthe position of the rolls, and if appropriate, of guides of the skew-rolling stand, being adapted to be converted as required following each run-through operation eitherto piercing orto stretching and the run-through direction of the work material to be reversed, and a device for removing the elongated tubular bloom being disposed in the region of the ingot guide channel.

Variousforms of skew-rolling stand are possible, 115 primarilyAssel and Diescher rolling stands. In the lattercase,the speed of the Diescher discs during el ongation isfourto twentytimes greaterthan during piercing. ltwas recognised, in such skew-rolling stands,that it is possibleto design the devicesfor adjusting the positions of the rolls and also of the guides, such asjorexample, Diescher discs, in such a waythatthey can be converted in afewseconds from piercing to stretching orfrom stretching to pie rcing. It is primarilythe radial position and/orthe an- 125 gular adjustment of the axes of rotation of the rolls which must be altered in orderto convertthe skew rolling stand to the other re-forming operation. The drive speeds and the direction of rotation of the drive can also, if necessary, be changed within a few sec- onds. Some structural alterations must be made to known skew-rolling stands, but these can be carried out. If the devices for adjusting the rolls are designed in such away that they can also operate against the rolling force, that is, with the work material inserted, the rolls are able to drawthe work material into sizing pass on commencement of the subsequent rolling operation withoutthe use of a pushing device.

In a preferred embodiment of the invention,the acute setting angle of the rolls enclosed bythe longitudinal axis of thework material and the rotational axis of a roll during piercing and stretching has an apexwhich is disposed atthe entry end of the skewrolling stand, which is provided with the ingot guide channel. In this specification, theterms entry and delivery end relate to the piercing process only. Asa result, during piercing thework material passes through a roll pass with the rotational axes of the rolls being divergentwith respectto the run-through direction, while, during stretching, it passesthrough a roll passwith the rotational axes of the rolls being convergent. This reduces any undesirable twisting of the work material during piercing, and promotes its expansion. During piercing, the convergent position of the axes of rotation of the roils limits expansion and thus advantageously prevents the formation of cornered ends to the tubular bloom in the case of thin work material walls. In orderto achievethese advantages, in the reverse rolling operation accord- ing to the invention, the rotational axes of the rolls do not have to be given any other direction of inclination, because they are changed from being divergent to convergent by the reverse in run-through direction of the work material. Once thework material has run through, only the size of the setting angle of the rolls needs to be changed. A setting angle of between one and approximately twenty degress is recommended, larger angles being used for piercing. Furthermore, it is practical to dispose the drive motors forthe rolls to the side of the mandrel rod support.

It is advantageous if a device for removing the elongated tubular bloom is provided in the form of a guide tubewhich is rotatable about its longitudinal centre axis, is coaxial with respectto the work material run-through axis and is disposed beyond the ingot guide channel on the side remote from the skew-rolling stand. Such a guide tube is described in German Offenlegungsschrift No. 35 33119.

It is recommended that, on commencement of elongation, the mandrel rod is guided through the roll pass in a speed-controlled manner and projects into the entry region of the guide tube, where it is retained with the help of the support at least until the tubular bloom enters the guide tube. This means that, by means of controlled operation of the support, the mandrel rod is moved forward on commencement of the stretching operation through the region of the rolls into the guide tube and retained in this position so thatthe leading edge of the stretched tubular bloom can be satisfactorily guided in the region of the ingot guide channel and securelyfed into the entry opening of the guidetube. As soon asthis takes place, the mandrel rod can be graduallywith- drawn in the direction of the delivery end while the 3 GB 2 191 966 A 3 stretching operation isstill in progress, although it can also be done following termination thereof.

In an advantageous embodiment of the invention, a shaft rod, which drives the mandrel rod, is coupled coaxially therewith and mounted in the support, has a larger outer diameterthan the hollow ingots and serves as a pusher deviceforthe hollow ingots atthe beginning of the stretching operation. The hollow ingots are thereby pushed into the region of the rolls 10 during the stretching operation bythe shaft rod withoutthe need for any additional structural measures, thus reducing the strain on this side of the skew-rolling stand, which is already veryfull. Because of the large outer diameter of the shaft rod, there is also no need for a radial support against buckling.

In a further embodiment of the invention, that part of the roll carrying outthe expansion during the piercing operation is responsible during stretching for smoothing the work material. This central part of the roll is reiativelywell protected during the piercing operation, such that it can still be used, even aftera longeroperating periodJorthe stretching operation, in which higher requirements are placed on accuracy and qualityof the surface of thework material. Furthermore,the part of the roll which carries outthe reduction in the piercing process is used in the stretching operation for rounding off thetubular bloom, and vice versa.

Moreover, it is also possible to alterthe runthrough direction of the work material by changing the angle of feed of the rolls. In this way, it is not necessaryto reverse the direction of rotation of the roll drive, which would incur considerable rotative moments as a result of which, braking and restarting the drive in the opposite direction of rotation would become expensive and time-consuming. Changing the angle of feed of the rolls makes it possible to operate a reverse rolling system according to the inven- tion without altering the direction of rotation of the rolls.

It is practical to make the run-through speed of the work material slower during piercing than during stretching. The biggertorque required during pierc- ing leads, given a suitable lower run-through speed, to approximately the same requirement& powerof the drive as during the stretching process, which requires a smallertorque, given a correspondingly higher run- through speed. Ideally, the same installed powercan befully utilised during both piercing and stretching.

Finally, it is advisable to provide a separating device upstream of the sizing or stretch-reducing rolling line for cropping the end sections of the tubular blooms. This is to be recommended because, following piercing and stretching, the end section of the tubular blooms are irregular, and this can lead to trouble during finish-rolling.

The invention is further described, by way of ex- ample, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a plant according to the invention; Figure2 shows a skew roll during piercing; and Figure3 shows a skew roll during stretching. 130 In Figure 1, an ingot, which has been heated to rolling temperature, passes from a furnace (not shown) byway of a rollertable 1 and a transverse conveyor2 into an ingot guide channel 3. A pusher 4 pushes the ingot in the axial direction out of the ingot guide channel 3 between the rolls 5 of a skew-roffing stand 6. A mandrel rod with a rolling mandrel 7a projects from the delivery end into the region of the rolls 5, the mandrel rod 7 being guided and retained in the radial direction by a mandrel rod and hollow ingot guide 8 and in the axial direction by a shaft rod 18 and a support 9. The shaft rod 18 has an outer diameterwhich is largerthan that of the hollow ingots. It also serves as a pushing device forthe hollow ingots on commencement of stretching.

During the piercing operation, the ingot 15 is rolled onto the mandrel rod 7; it is, in practice desirable to add a lubricant and/or deoxidising agentthrough the mandrel rod 7 and, if necessary, through the rolling mandrel 7a, into the inner bore 16 of the hollow ingot 15a (see Figure 2). During the stretching operation, which immediately follows the manufacture of the hollow ingot 15a, which surrounds the mandrel rod 7, the hollow ingot is stretched bythe same rolls 5to form a tubular bloom 15b and is returned to the ingot guide channel 3 in the opposite direction (see Figure 3). The mandrel rod 7, with or without its rolling mandrel 7a, which has a larger diameter and may be removed, is moved in the axial direction towards the ingot guide channel 3 by moving the support 9 forward appropriately in a controlled manner until the rolling mandrel 7a is in the entry region of thefirst section 1 Oa of the guide tube 10. The rolling mandrel 7a remains in the entry region of the quidetubesec- tion 1 Oa at least until the leading edge of thetubular bloom has entered therein. The mandrel rod 7 and rolling mandrel 7a can then slowly be withdrawn with the aid of the support 9 and the shaft rod 18. This can be carried out while the stretching operation is still in progress, but only provided the rolling mandrel 7a remains on the side of the rolls 5 facing the ingot guide channel 3. The mandrel rod 7 and shaft rod 18 can only be withdrawn into the position shown in Figure 1, in which the piercing operation forthe next ingot begins, when the stretching operation has been completed.

The stretched tubular bloom is moved through the guide tube sections 1 Oa, 10b, 10cwith the aid of drive rolls 11 to a sizing or stretch-reducing rolling line 12, in which the tubular bloom is rolled out into afinished tube. Asevering device 13 is provided upstream of the sizing orstretch-reducing rolling line 12 and is used to separate a piecefrom the end sections of thetubular blooms should this be necessary as a resultof deviations in dimension orirregularities in the shape of the end.

The rolls 5 of the skew-rolling stand 6 are driven by motors 14 in a known way byway of long drive shafts. The shafts and the motors 14 can also be dis- posed on the side of the skew-rolling stand 6facing the support 9 so thatthe apices of the setting angles formed by the axes of rotation of the rolls lie atthe entry end, approximately in the region of the ingot guide channel 3. The rolls 5 are then also adjusted in the opposite mannerto that shown in Figure 1 at an 4 GB 2 191 966 A 4 angle to the longitudinal axis of the work material. In orderto alter the run-throug h direction, it is possible to alterthe direction of rotation of the motors 14. On the other hand, it is also possible to alterthe angle of feed of the rolls 5 only. This angle of feed cannot be seen in the drawings. It isthe angle between the plane of the paper and the axis of rotation of the rolls 5. In skew-roiling stands, the axes of rotation of the rolls 5 are not parallel to thefloor orto the plane of the paper in Figure 1, but are inclined by several degress thereto. If this inclination is altered to the opposite direction, this alters the direction of conveying of the rolls 5 and hence the run-through direction of the work material.

Figure 2 shows a roll 5 on an enlarged scale and having a different angle of inclination to that shown in Figure 1, during the piercing operation. The rolling mandrel 7a of the mandrel rod 7 penetrates into the ingot 15 and produces an inner bore 16. It can clearly be seen thatthere is only a narrow annular space be- 85 tween the mandrel rod 7 and the inside wall 17 of the inner bore 16 containing only a small amount of air and hardly any oxygen. The roll 5 has a front part5a which servesto drawthe ingot 15 into the pass. An adjoining part 5b,which is more strongly conical, causes the cross-section of the ingotto be reduced, and this part 5b is followed by a rolling shoulder 5c and a cylindrical part 5d which serve to pierce and expand the work material. The last section 5e of the roll 5 rounds off the resulting hollow ingot 15a.

Figure 3 showsthe same roll 5 during stretching of the hollow ingot 1 5a to form a tubular bloom 15b.

The rolling mandrel 17a has been pushed forward through the sizing pass formed bythe rolls 5, wherebythe cylindrical part 5d of the rolls 5, which is 100 used in the piercing operation for expanding, is used in the stretching operation shown in Figure 3, togetherwith the mandrel rod 7, to smooth and cal ibrate the thickness of the wall of thetubular bloom.

The rolling section 5e which is used for rounding off in the piercing operation, is used in the stretching operation shown in Figure 3 to reduce wall thickness and to drawthe hollow ingot 15a into the pass. The lattertask is performed in the piercing operation by the rolling section 5a, which is relativelywell worn dueto the usual irregularities in the ingot 15, the an gular acceleration to be applied, the rolling work and thevarious speeds. As can clearly be seen in Figure 3,this rolling section 5a is no longer in contactwith thefinished tubular bloom 15b, so thatthere is no risk of irregularities being caused by this rolling sec tion 5a, which might possibly show signs of wear.

The position of the rolls in Figure 3 differs from that in Figure 2 essentially in thatthe setting angle is al mostzero and that there has been a corresponding radial adjustment which substantially determines thethickness of the wall of thetubular bloom 15b.

It should, however, be pointed outthat, in both the piercing and in the stretching operations, other roll positions and shapes can be used.

Claims

1. A method of manufacturing seamless tubes in which an ingot which has been heated to rolling tem- perature is pierced in a skew-rol ling stand to form a hollow ingot, then elongated to form a tubular bloom and rolled out into a finished tube, and in which elongation takes place immediatelyfollowing piercing in the same heat, the work material being elongated in the same skew-rolling stand with the run-through direction being opposite to that of the piercing operation.

2. A method as claimed in claim 1, in which the hollow ingot is elongated following piercing in a hollow pass, that is, without an internal tool.

3. A method as claimed in claim 1 or 2, inwhich, following piercing and elongating, the tubular bloom is f inish-rol led without reheating in a sizing or stretch-reducing rolling line.

4. A method as claimed in claim 1 or2, in which, following piercing and stretching in a reversing mill, thetubular bloom isfurther elongated in one or more subsequent steps.

5. A plant for manufacturing seamless tubes, comprising a skew-rolling stand which is provided at the entry end with an ingot guide channel and a pusher, and atthe delivery end with a rolling mandrel on a rotatable, axially displaceable mandrel rod mounted in a support, a sizing or stretch-reducing rolling line being connected beyond the skew-rolling stand, the latter being so adapted thatthe drive and position of the rolls and, if provided, of the guides of the skew-rolling stand, can be setfollowing each run-through eitherto piercing or stretching of the work material and adjusted to move the work material in the opposite run-through direction, a device for removing the elongated tubular bloom being disposed in the region of the ingot guide channel.

6. A plant as claimed in claim 5, in whichthe acute setting angles of the rolls depend bythe longitudinal axis of the work material and the rotational axis of a respective roll have, during piercing and stretching, an apex which is disposed atthe entry end of the skew-rolling stand which is provided with the ingot guide channel.

7. A plantasclaimed in claim 6, in whichthesetting angle is between one and approximately twenty degrees, largerangles being selected for piercing.

8. A plant as claimed in claim 6 or7, inwhich drive motors for the rolls are disposed on the side of the mandrel rod support.

9. A plantasclaimed in anyof claims 5to8,in which the device for removing the elongated tubular bloom contains a guide tube which is rotatable about its longitudinal centre axis coaxiallywith respectto the run-through axis of thework material and is disposed beyond the ingot guide channel atthe side remotefrom the skew-rolling stand.

10. A plantas claimed in claim 9, in which, in operation, at the beginning of the elongation operation, the mandrel rod is passed through the roll pass in a speed-controlled manner and projects into the entry region of the guide tube where it is retained with the aid of the support at least until the tubular bloom enters the guide tube.

11. A plantas claimed in anyof claims 5to 10, in which a shaft rod, which drives the mandrel rod, is coupled axially therewith and mounted in the sup- port, has a larger outer diameter than the hollow GB 2 191966 A 5 ingotand acts as a pushing deviceforthe hoiiowingotson commencement& elongation.

12. A plantas claimed in anyof claims 5to 11, in which the rolling part of the mandrel, which carries out the expansion during piercing, is used to smooth the work material during elongation.

13. A plantas claimed in any of claims 5to 12, in which the rolling part of the mandrel, which is used to carry out reduction during piercing, is used for rounding off the tubular bloom during elongation, and vice versa.

14. A plantas claimed in any of claims 5to 13, in which the feed angle of the rolls can be altered to alterthe run-through direction of the work material.

15. A plant as claimed in anyof claims 5to 14, in which the run-through speed of the work material is slower during piercing than during elongation.

16. Aplantasclaimed in anyof claims 5to 15, in which a severing device is disposed upstream of the sizing or stretch-reducing rolling line for cropping the end sections of the tubular blooms.

17. Methods of manufacturing seamless tubes substantially as herein described with reference to the accompanying drawings.

18. A plant for manufacturing seamless tubes, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (U K) Ltd, 11187, D8991685. Published by The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies maybe obtained.