METHOD FOR MAKING A PIPE

Description

[0001] The present invention relates to a method for producing a steel tube by cold forming a bloom in a first cold pilger rolling mill comprising a rolling stand with rotatably mounted rolls, a mandrel held by a mandrel bar, at least one mandrel support holding the mandrel bar, and at least one feed chuck with a feed chuck for receiving the bloom, comprising the following steps: a) Moving a chuck radially towards the front mandrel support in the feed direction of the bloom and passing a first bloom through the front mandrel support, b) feeding the first bloom to the feed chuck and picking up the first bloom by moving the feed chuck radially and clamping the first bloom by closing the feed chuck radially at a reversal point of the feed chuck located at the front of the feed direction of the bloom, c) after the first bloom has completely passed through the front mandrel support, closing the chuck of the front mandrel support radially in such a way that the front mandrel support holds the mandrel bar carrying the rolling mandrel,d) Rolling out the first bloom by the rolls over the mandrel into a cold-worked tube by gradually advancing the first bloom with the aid of the feed clamping slide and oscillating back and forth movement of the rolling stand between a front and a rear reversal point with the rolls, , wherein, prior to step a), in a step a'), the first bloom is provided wound onto a spindle and the first bloom is unwound from the spindle using an unwinding device.

[0002] To manufacture precision metal tubes, especially from steel, an extended hollow cylindrical blank is cold-reduced, usually in a completely cooled state, by applying compressive stresses. In this process, the blank is formed into a tube with a defined reduced outer diameter and a defined wall thickness.

[0003] The most widespread reduction method for pipes is known as cold pilgering, where the blank is called a bloom. During rolling, the bloom is pushed over a calibrated mandrel (i.e., one with the inner diameter of the finished pipe) and is enclosed on the outside by two calibrated rollers (i.e., ones defining the outer diameter of the finished pipe) and rolled out longitudinally over the mandrel.

[0004] During cold milling, the bloom is advanced incrementally towards or over the mandrel, while the rolls rotate horizontally back and forth over the mandrel and thus over the bloom. The horizontal movement of the rolls is determined by a rolling stand to which they are rotatably mounted. In known milling plants, the rolling stand is moved back and forth in a direction parallel to the mandrel by means of a crank mechanism, while the rolls themselves receive a rotary motion from a rack that is fixed relative to the rolling stand and into which gears rigidly connected to the roll axles engage.

[0005] The bloom is advanced over the mandrel using a feed clamping slide, which allows translational movement in a direction parallel to the axis of the rolling mandrel.

[0006] At the start of the rolling process, the bloom is pushed into the chuck of the feed carriage by a loading driver with rollers. At the forward reversal point of the rolling stand in the feed direction of the bloom, also known as the lead-in dead center, the rolls reach an angular position in which the bloom can be picked up in the so-called entry pockets of the rolls and between the rolls. The conically calibrated rolls, arranged one above the other in the rolling stand, roll over the bloom by rolling back and forth on it in the feed direction of the feed carriage. During one rolling stroke of the rolling stand, the pair of rolls moves a distance L from the forward reversal point to the rear reversal point of the rolling stand in the feed direction of the bloom, also known as the exit dead center, and extends the bloom over the mandrel held inside the bloom.

[0007] The rolls and mandrel are calibrated such that the gap between the roll and mandrel decreases continuously from the wall thickness of the bloom to the wall thickness of the finished pipe within the working range of the rolls. Furthermore, the outer diameter defined by the rolls decreases from the outer diameter of the bloom to the outer diameter of the finished pipe, and the inner diameter defined by the mandrel decreases from the inner diameter of the bloom to the inner diameter of the pipe. In the subsequent smoothing range of the rolls, the wall thickness of the pipe being produced is no longer reduced; only the surface of the pipe is smoothed. Upon reaching the exit point, the finished rolled pipe is released from the exit pockets of the rolls.

[0008] The bloom is advanced between the rolls either only at the front reversal point or at both the front and rear reversal points of the rolling stand. Multiple passes over each pipe section, i.e., feed steps that are significantly smaller than the path of the rolling stand between the front and rear reversal points, achieve a uniform wall thickness and roundness of the pipe, a high surface quality, and uniform inner and outer diameters.

[0009] To achieve a uniform shape in the finished tube, the bloom undergoes intermittent rotation around its axis in addition to a stepwise feed. This rotation occurs at both reversal points of the rolling stand, i.e., when the bloom is released from the entry and exit pockets of the rolls.

[0010] Cold pilger rolling mills are known in the art that can process blooms up to approximately 15 m in length. However, if high-quality pipes—i.e., pipes with a uniform wall thickness and a high surface quality on both the inner and outer surfaces—are required with a length exceeding 150 m, such pipes cannot be produced in a cold pilger rolling mill according to the prior art. Producing one-piece pipes longer than 150 m in a cold pilger rolling mill requires the cold forming of blooms whose length significantly exceeds that of blooms that can be rolled with conventional mills.

[0011] DE 43 42 858 A1 describes a cold pilger rolling mill for rolling long blooms with a reciprocating stand, a main drive for the stand, two feed slides each equipped with a chuck, arranged one behind the other in the slide bed in the rolling direction and movable in the rolling direction via feed spindles connectable to the main drive, at least one gearbox for driving the feed spindles, and at least one holding device (mandrel support) for the mandrel attached to a mandrel bar. In the case of two holding devices, at least one of these is adjustable parallel to the rolling direction to compensate for changes in the mandrel's position relative to the roll gap. In an alternative embodiment, DE 43 42 858 A1 shows a method in which the bloom is unwound from a coil and fed to the cold pilger rolling mill. A retaining rope is threaded through the bloom and held in the mandrel support.

[0012] In DE 43 32 136 A1, to achieve uniform and targeted recrystallization with low energy input in the production of seamless tubes made of non-ferrous metals, in particular copper and copper alloys, it is provided that the semi-finished tube is wound into a coil after the first cold forming process and possibly further cold forming steps and subjected to the recrystallization process as a coil.

[0013] Compared to the prior art, it is therefore an object of the present invention to provide a device and a method that make it possible to cold roll blooms with a length of 30 m or more. A further object of the present invention relates to space-saving processing of blooms with a length of 30 m or more, so that long pipes of high quality can be produced in a cold pilger rolling mill, thereby avoiding high costs resulting from the need for large production halls. A further object of the present invention is to roll long blooms as efficiently as possible without reducing the quality of the pipes to be produced.

[0014] At least one of these problems is solved by a method for manufacturing a steel tube according to claim 1.

[0015] Blooms, especially those longer than 30 m, require considerable space when being fed into the system. The unwinding device allows a bloom, previously wound around a first axis on a spindle, to be fed into the first cold pilger mill in a more space-saving manner.

[0016] In one embodiment, the unwinding device includes a straightening unit which, during operation of the device, straightens the wound, i.e., curved, bloom, i.e., bends it straight. An example of such a straightening unit is a straightening machine, in particular a roll or skew roll straightening machine. In this way, during the unwinding of the bloom, it is straightened and simultaneously loaded by the front mandrel support into the bloom bed between the front mandrel support and the feed chuck, or between the front and rear mandrel supports.

[0017] The unwinding device for the bloom according to the invention ensures a more compact design of the overall arrangement of the cold pilger rolling mill, thereby further reducing operating costs.

[0018] In one embodiment of the invention, the distance between the unwinding device and the front end of the front mandrel support is smaller than the distance between the rear end of the front mandrel support and the front end of the feed chuck of the rear feed chuck at the rear reversal point of the rear feed chuck. In another embodiment, the distance between the unwinding device and the front end of the front mandrel support is smaller than the distance between the rear end of the front mandrel support and the front end of the rear mandrel support.

[0019] In one embodiment of the present invention, the front mandrel support is at least 30 m away from the feed chuck, measured with the feed chuck slide at its rear reversal point.

[0020] Such a selected distance between the front mandrel support and the feed chuck enables the processing of blooms with a length of 30 m or more in a first cold pilger rolling mill according to the invention. In one embodiment, the distance between the front mandrel support and the feed chuck is measured between the rear end of the chuck of the front mandrel support (in the feed direction of the bloom) and the front end of the feed chuck of the feed slide (in the feed direction of the bloom), with the feed slide at its rear reversal point.

[0021] The previously defined distance is at least 30 m and makes it possible to arrange a bloom between the front mandrel support and the feed chuck of the feed slide in such a way that both the chuck of the front mandrel support and the feed chuck of the feed slide can be closed without clamping or jamming the bloom. Accordingly, the distance between the front mandrel support and the feed chuck approximately corresponds to the length of the bloom that can be loaded into and rolled in the first cold pilger rolling mill according to the invention.

[0022] When the bloom is introduced into the first cold pilger rolling mill, the front mandrel support is opened by extending the chuck of the mandrel support radially, allowing the bloom to pass between the front mandrel support and the mandrel bar towards the rolling mandrel. After the bloom has left the front mandrel support, the chuck of the front mandrel support is closed to hold the mandrel bar.

[0023] When, in the context of this application, front and rear positions are mentioned, these positions are designated from the perspective of an observer looking along the bloom in the direction of advance of the bloom.

[0024] In one embodiment of the present invention, the distance between the front mandrel support and the feed chuck, measured with the feed chuck slide at its rear reversal point, is at least 40 m and in another embodiment at least 50 m.

[0025] In one embodiment of the present invention, the material of the mandrel bar of the first cold pilger rolling mill has a tensile strength of 1000 N / mm² or more, or of 1500 N / mm² or more.

[0026] In a further embodiment of the present invention, the mandrel rod is a tube which has an outer diameter, an inner diameter and a wall thickness.

[0027] Tensile strength is a property of a material and describes the maximum mechanical tensile stress that the material can withstand before it breaks. Tensile strength is measured based on the maximum achievable tensile force relative to the original cross-section of the sample being measured.

[0028] The mandrel bar supporting the rolling mandrel must withstand high forces during the rolling of the bloom, so the material from which the mandrel bar is made must have a high tensile strength.

[0029] Suitable materials for this purpose include, for example, heat-treatable steels according to DIN EN 100 83, which achieve high tensile and fatigue strength through heat treatment, i.e., hardening and tempering. The carbon content of heat-treatable steels is typically between 0.2 and 0.65%, with varying alloying elements such as chromium, manganese, molybdenum, and nickel added in different proportions depending on the intended use. Examples of alloyed heat-treatable steels with a tensile strength greater than 1000 N / mm² are steel grades 42 CrMo 4, 34 CrNiMo 6, and 30 CrNiMo 8.

[0030] In one embodiment of the present invention, the mandrel bar also has an elongation of 10% or less, and in another embodiment of 5% or less.

[0031] Elongation is a measure of the relative change in length of a sample under stress, for example, due to a force or a temperature change. High ductility of the mandrel bar is also necessary during rolling to prevent breakage due to excessive elongation. Just as with high tensile strength, heat-treated steels are also suitable for ductility. For example, the heat-treated steel 30 CrNiMo 8 exhibits a tensile strength of 1000 N / mm² and an elongation of 10% or less, making it suitable as a material for the mandrel bar according to the invention.

[0032] In a further embodiment of the present invention, the first cold pilgrim rolling mill has two feed clamping slides, each with a feed chuck attached thereto, and a control system, wherein the control system is designed such that it controls the movement of the two feed clamping slides in such a way that the bloom can be clamped alternately by one of the feed chucks in continuous operation of the first cold pilgrim rolling mill and can be advanced stepwise towards the mandrel, wherein the front mandrel support has a distance of at least 30 m from the feed chuck of the feed clamping slide that is rearward in the feed direction of the bloom, measured with the feed clamping slide at its rear reversal point.

[0033] This enables a higher, i.e., continuous, throughput of blooms through the first cold pilger mill. This makes the rolling process more efficient and cost-effective by reducing operating expenses. Furthermore, a feed clamping carriage with a long travel distance is no longer required; instead, the entire required travel distance is divided into two sections, so that each of the two feed clamping carriages only needs to travel one of these sections.

[0034] In a further embodiment of the present invention, the first cold pilgrim rolling mill has a rear mandrel support with a chuck for holding the mandrel bar in the feed direction of the bloom between the front reversal point of the feed clamping slide and the front mandrel support, wherein the rear mandrel support has a distance of at least 30 m from the front mandrel support, such that the mandrel bar can be held in place by at least one chuck of the front mandrel support or the rear mandrel support during operation of the first cold pilgrim rolling mill.

[0035] In one embodiment, the distance between the front and rear mandrel supports is defined as the distance between the rear end of the front mandrel support (in the feed direction of the bloom) and the front end of the rear mandrel support (in the feed direction of the bloom). A bloom with a length of at most this distance can therefore be loaded, i.e., positioned, between the front and rear mandrel supports while the chucks of both the front and rear mandrel supports are closed and hold the mandrel bar, i.e., without clamping the bloom.

[0036] The arrangement of a rear mandrel support between the front reversal point of the feed chuck and the front mandrel support, in addition to the front mandrel support, enables the processing of multiple long blooms, i.e., those 30 m or longer, in continuous operation. Once a bloom has completely passed the rear mandrel support and is being rolled over the mandrel, the rear mandrel support is moved to hold the mandrel bar. The front mandrel support no longer needs to hold the mandrel bar and, unlike the rear mandrel support, can be moved open, allowing another bloom to be fed to the first cold pilger rolling mill.

[0037] In one embodiment, the first cold pilger rolling mill has, in addition to a rear and a front mandrel support, two feed clamping slides, each with a feed clamping chuck.

[0038] The first cold pilger rolling mill according to the invention is therefore suitable for efficient and cost-effective cold pilgering of long blooms with a length of 30 m or more.

[0039] In a further embodiment of the present invention, each feed carriage of the first cold pilger rolling mill is designed to advance a bloom weighing 100 kg / m or more. In another embodiment of the invention, each feed clamping carriage is designed to advance a bloom weighing between 100 kg / m and 150 kg / m. In order to advance blooms with a length of at least 30 m and a weight per length between 100 kg / m and 150 kg / m with a single feed clamping carriage, in one embodiment the feed clamping carriage has a correspondingly powerful linear drive for advancing the bloom onto the mandrel. In addition, the chuck also has a correspondingly powerful rotary drive for rotating the bloom about its longitudinal axis.

[0040] In a further embodiment of the present invention, each feed carriage of the first cold pilger rolling mill is designed such that it can feed a bloom with a weight of 125 kg / m or more.

[0041] In one embodiment of the present invention, a winding device is arranged in the feed direction of the bloom behind the rollers of the rolling mill, wherein the winding device for the tube produced in the rolling mill has a bending device for bending the tube in such a way that it can be wound around a first axis, and a holding frame, wherein the bending device and the first axis are pivotably mounted on the holding frame about a second axis which is substantially perpendicular to the first axis and parallel to a longitudinal axis of a bloom received between the rollers.

[0042] This space-saving design also significantly reduces the manufacturing costs of long pipes, since the winding of long pipes by a winding device eliminates the need for very large and, in particular, very long halls.

[0043] Such a winding device also makes it possible to receive the fully formed tube exiting the first cold pilger mill and bend it so that it can be wound onto a spiral track. This arrangement results in significant time savings in the production of steel tubes dimensioned for winding. The tube exiting the rolling stand can already be wound onto the winder while a bloom is being fed into the pilger mill and formed between the rolls in the same strand. Furthermore, the winding device allows for considerable space savings for the first cold pilger mill itself, since the entire strand does not first have to exit the rolling stand along its full length before being unwound or coiled onto the winder.

[0044] An essential aspect of the winding device is that the bending unit and the first axis are mounted so that they can pivot around a second axis. This allows the winding device to follow the pivoting movement that the tube or bloom performs during rolling, driven by the feed clamping slide, and ensures that the tube is wound without twisting. Without such a pivotable mounting of the bending unit and the first axis, the tube would twist during winding, resulting in a significant loss of quality in the finished tube.

[0045] The second axis, around which the bending device and the first axis are pivotably mounted on the support frame, is parallel to the axis of symmetry of the finished tube exiting the rolling stand. In one embodiment, the second axis coincides with the axis of symmetry of the finished tube exiting the rolling stand.

[0046] In a further embodiment of the invention, the bending device and the first axis are pivotally driven about the second axis by a motor. While the pivoting movement of the bending device can, in principle, also be effected by the pivoting movement of the finished tube exiting the rolling stand, a motor drive largely prevents the tube from experiencing torsional stresses during winding. A detailed description of embodiments of such a winding device can be found in German patent application 10 2009 045 640 A1.

[0047] In a further embodiment of the present invention, the feed chuck of the feed clamping slide is designed to be pivotably driven by a motor and holds the blank pivotably about its longitudinal axis. The first cold pilger rolling mill also has a control system configured to pivot the feed chuck, the bending device, and the first axis of the winding device synchronously at the same angular velocity during operation of the winding device. In such an embodiment, the bending device is mounted on the support frame and is pivotably driven by a motor about its second axis. The "electronic shaft" between the feed clamping slide and the winding device enables virtually twist-free winding of the finished tube.

[0048] This space-saving design also significantly reduces the manufacturing costs of long pipes, since the winding of long pipes by a winding device eliminates the need for very large and, in particular, very long halls.

[0049] The first cold pilgrim rolling mill also has an annealing furnace which is designed in such a way that, in one operation of the first cold pilgrim rolling mill, it heats the bloom to a temperature in a range of 1000°C to 1200°C or in a range of 1050°C to 1150°C.

[0050] The annealing furnace is designed such that a bloom wound on a spindle can be annealed in the furnace. In one embodiment, the annealing furnace is therefore a shaft furnace.

[0051] In a further embodiment, each of the chucks of the individual mandrel supports has openings for inserting clamping jaws such that at least three clamping jaws of a mandrel support grip the mandrel bar. This enables simple, uncomplicated fixing of the mandrel bar by gripping the clamping jaws, so that during operation of the first cold pilger rolling mill, at least one mandrel support holds the mandrel bar, while the clamping jaws of the other mandrel supports can be open to allow the passage of a bloom.

[0052] In one embodiment, the chucks of the respective mandrel supports alternately hold the mandrel bar. This alternating holding of the mandrel bar enables continuous operation in the first cold pilger rolling mill, so that one mandrel support holds the mandrel bar while the other mandrel supports allow the passage of a bloom.

[0053] At least one of the aforementioned problems is solved according to the present invention by a method for producing a steel tube by cold forming a bloom in a first cold pilger rolling mill with a rolling stand with rotatably mounted rolls, a rolling mandrel held by a mandrel bar, at least one mandrel support holding the mandrel bar and at least one feed clamping slide with a feed chuck for receiving the bloom, comprising the following steps: a) Moving a chuck of a front mandrel support in the feed direction of the bloom in a radial direction and passing a first bloom through the front mandrel support between the chuck of the front mandrel support and the mandrel bar, b) after the first bloom has completely passed through the front mandrel support, closing the chuck of the front mandrel support in a radial direction such that the front mandrel support holds the mandrel bar carrying the rolling mandrel,c) Feeding the first bloom to a feed chuck and picking up the first bloom by moving the feed chuck radially and clamping the first bloom by moving the feed chuck radially towards a reversing point of the feed chuck that is forward in the feed direction of the bloom, and d) Rolling the first bloom out by the rolls over the mandrel into a cold-worked tube by gradually advancing the first bloom with the aid of the feed chuck and oscillating the rolling stand back and forth between a forward and a rear reversing point with the rolls, , wherein prior to step a) in a step a') the first bloom is provided wound onto a spindle and the first bloom is unwound from the spindle with an unwinding device, wherein to provide the first bloom a bloom in a second cold pilger rolling mill is formed into the first bloom entering the first cold pilger rolling mill and wound onto the spindle, so that the tube exiting the first cold pilger rolling mill is a double-rolled tube, wherein the first bloom exiting the second cold pilger rolling mill, wound onto the spindle, is heated to a temperature in the range of 1000°C to 1200°C before being passed through the front mandrel abutment.

[0054] Apart from the fact that the chuck of the mandrel support can only be closed once the bloom has completely passed through the chuck, the numbering above does not necessarily define the sequence of steps to be performed. In particular, the bloom is fed to the feed chuck slide as soon as the chuck of the front mandrel support is open.

[0055] In one embodiment, the bloom wound on the spindle passes through bending rolls during unwinding, which straighten the bloom again in the longitudinal direction before the bloom passes through the front mandrel support. The straightening of the bloom from its curved initial shape by the bending rolls takes place during the loading of the bloom into the first cold pilger rolling mill, i.e., during the passage of the bloom through the front mandrel support.

[0056] Such a process, like a winding device, saves a lot of space in the hall where the cold pilger rolling mill is located, and consequently reduces the manufacturing costs for the long tubes produced in the cold pilger rolling mill.

[0057] The inventive method enables the processing of a long bloom, in particular blooms with a length of 30 m or more, in a cold pilger rolling mill and consequently the forming of the bloom into a one-piece cold-worked tube with a length of at least 300 m. The finished tube exhibits a very high quality due to the manufacturing process in a cold pilger rolling mill. This represents a significant advance compared to the prior art, since prior art cold pilger rolling mills can only process blooms up to a length of approximately 15 m and consequently can only produce one-piece tubes up to a certain length.

[0058] Therefore, in one embodiment of the present invention, the first magnifying glass has a length of 30 m or more.

[0059] One embodiment of the method according to the invention relates to a method for producing a pipe with the following additional step after step a) and before step b): a) Driving a chuck onto a mandrel abutment located at the rear of the magnifying glass in the feed direction and between the front reversal point of a feed clamping slide at the front of the magnifying glass in the feed direction and the front mandrel abutment in a radial direction, wherein the rear mandrel abutment has a distance of at least 30 m from the front mandrel abutment, and passing the first magnifying glass through the rear mandrel abutment,wherein the rolling of the first bloom by the rolls over the mandrel into a cold-worked tube in step d) is carried out by stepwise advancing the first bloom alternately with the aid of the front feed slide from a front reversal point to a rear reversal point of the front feed slide and with the aid of a feed slide located at the rear in the feed direction of the bloom from a front reversal point to a rear reversal point of the rear feed slide, and by oscillating back and forth movement of the rolling stand between a front and a rear reversal point with the rolls, , and the procedure additionally includes the following steps: f) After the first bloom has completely passed through the rear mandrel support, close the chuck of the rear mandrel support radially so that the rear mandrel support holds the mandrel bar carrying the rolling mandrel; g) During the rolling of the first bloom, unwind a second bloom wound on a spindle rotatable about an axis perpendicular to the feed direction of the bloom; h) Move the chuck of the front mandrel support and pass the second bloom through the front mandrel support into the area between the front and rear mandrel supports; i) After the second bloom has completely passed through the front mandrel support, close the chuck of the front mandrel support so that the front mandrel support holds the mandrel bar carrying the rolling mandrel; j) Move the chuck of the rear mandrel support; k) Pass the second bloom through the rear mandrel support.I) Feeding the second magnifying glass to the front feed slide and receiving the second magnifying glass in the feed chuck of the front feed slide and clamping the second magnifying glass by moving the feed chuck of the front feed slide in a radial direction, m) Moving the feed chuck of the rear feed slide in a radial direction, n) Incrementally advancing the second magnifying glass alternately with the aid of the front feed slide and the rear feed slide with the second magnifying glass clamped in place,o) After the tube, fully rolled from the first bloom, has completely exited the rolling stand, the second bloom is introduced into the rolling stand and p) the second bloom is rolled out by the rolls over the mandrel into a cold-worked tube by progressively advancing the second bloom alternately with the aid of the rear feed slide and the front feed slide, and by oscillating back and forth movement of the rolling stand with the rolls between a front and a rear reversal point.

[0060] This method enables the cold pilgering of long blooms, i.e., blooms 30 m or more in length, in continuous operation, allowing a first bloom to be rolled while a second bloom is already being fed into the first cold pilger rolling mill. This is made possible, in particular, by the presence of two mandrel supports. One mandrel support must always be closed to hold the mandrel bar during rolling. In the case of two mandrel supports, a front and a rear one, one holds the mandrel bar firmly in position while the other is open to allow the second bloom to be fed through. The operating sequence in the first cold pilger rolling mill is thus accelerated by the presence of at least two mandrel supports.

[0061] While the front and rear feed carriages alternately advance the second bloom towards the mandrel, the first bloom also receives a further advance towards the mandrel. At this stage of the process, the first bloom is advanced indirectly by the alternating linear drive of the front and rear feed carriages, as the first bloom is pushed by the second bloom, which is advanced by both the front and rear feed carriages.

[0062] Another embodiment of the present invention relates to a method for producing a tube in which a winding of an already finished rolled part of the bloom is carried out simultaneously with the rolling of a part of the bloom yet to be rolled into a cold-worked tube, comprising the steps of: bending an already finished rolled part of the bloom in a bending device, spirally winding an already finished rolled part of the bloom around a first axis, and pivoting the bending device, which is mounted on a holding frame, and the first axis about a second axis that is substantially perpendicular to the first axis and parallel to a longitudinal axis of a bloom held between the rollers, such that the pivoting takes place at the same angular velocity as a pivoting of the bloom about its longitudinal axis during the rolling of the bloom.

[0063] In this process, the already rolled portion of a bloom, i.e., the part of the finished tube, is wound around a first axis using a winding device, while simultaneously another portion of the bloom is being rolled out by the rollers rotatably mounted on the rolling stand above the mandrel, and possibly another portion of the bloom is being fed towards the cutterhead. The winding in the winding device is carried out by first bending the finished tube in a bending unit. As a result of the bending, the tube is then wound spirally around a first axis, whereby, in addition to the winding, the bending unit and the first axis are pivoted about a second axis. The second axis runs essentially perpendicular to the first axis and parallel to a longitudinal axis of a bloom held between the rollers.In one embodiment, the second axis coincides with the longitudinal axis of the received bloom. Furthermore, the pivoting of the bending device and the first axis about the second axis occurs at the same angular velocity as the pivoting of the bloom about its longitudinal axis, thus preventing twisting of the tube during winding and the associated significant loss of quality in the finished tube.

[0064] In one embodiment of the method according to the invention, the bloom is heated to a temperature in the range of 1050°C to 1150°C.

[0065] Further advantages, features and possible applications of the present invention will become clear from the following description of embodiments thereof and the accompanying figures. Figure 1 shows a schematic side view of the structure of a cold pilger rolling mill with an unwinding device. Figure 2 shows a schematic side view of the structure of a cold pilger rolling mill with an unwinding device, a front and a rear mandrel support, and two feed clamping slides. Figure 3 shows a schematic side view of the structure of a cold pilger rolling mill with an unwinding device, a front and a rear mandrel support, two feed clamping slides, and a winding device.

[0066] In the figures, identical elements are designated with identical reference symbols.

[0067] In Figure 1The diagram schematically depicts the structure of a cold pilger rolling mill in a side view. The cold pilger rolling mill 7 consists of a rolling stand 1 with an upper roll 2 and a lower roll 3, a calibrated mandrel 4 (the position of the mandrel is indicated by reference numeral 4 in the figure), a mandrel bar 8 supporting the mandrel 4, a feed chuck 5 with a feed chuck 12 for holding a bloom 11, a front mandrel support 15 with a chuck 19, and a discharge chuck 18 with a chuck 22. In the illustrated embodiment, the cold pilger rolling mill has a linear motor 6 as a direct drive for the feed chuck 5.

[0068] Like all embodiments of the Figures 1 to 3The cold pilgering mill 7 has an unwinding device 26 for spreading the bloom 11. The unwinding device 26 ensures that a bloom wound on a spindle 27 around an axis 28 perpendicular to the feed direction of the bloom 11 is unwound. The spindle 27 is rotated by a motor about the first axis 28 in the direction of the arrow shown, so that the bloom wound on the spindle 27 is guided between five bending rolls 32a. Three bending rolls 32a are arranged in an upper row and two bending rolls 32a in a lower row. The bending rolls 32a bend the bloom evenly and in opposite directions such that the bloom is straightened and aligned between the bending rolls 32a before it is passed through the chuck 19 of the front mandrel support 15.The straightening of the bloom 11 from its curved starting position takes place during the loading of the bloom 11 through the front mandrel abutment 15 into the cold pilgrim rolling mill 7.

[0069] The integration of an unwinding device 26 into the cold pilger rolling mill, as shown in the figures, and thus the unwinding into the rolling process, is particularly advantageous for blooms with a length of 30 m or more. By unwinding a coiled bloom 11 from the spindle 27 and simultaneously feeding the bloom 11 to and through the front mandrel support 15, considerable space can be saved in the hall housing the cold pilger rolling mill.

[0070] During the cold pilgrimage on the in Figure 1In the cold pilger rolling mill shown, the bloom 11 undergoes a stepwise feed towards or over the mandrel 4, while the rolls 2, 3 rotate horizontally over the mandrel 4 and thus over the bloom 11. The horizontal movement of the rolls 2, 3 is determined by the rolling stand 1, on which the rolls 2, 3 are rotatably mounted. The rolling stand 1 is moved back and forth by means of a crank drive 23 via a push rod 24 in a direction parallel to the longitudinal axis of the bloom between a reversal point 9, located forward in the feed direction of the bloom 11 (also referred to as the entry dead center ET), and a reversal point 10, located rearward in the feed direction of the bloom 11 (also referred to as the exit dead center AT). The rollers 2, 3 themselves receive their rotational movement by means of a rack (not shown) which is fixed relative to the rolling stand 1, into which gears (not shown) which are fixed to the roller axes engage.The feed of the bloom 11 over the mandrel 4 is effected by the feed clamping slide 5, which enables a translational movement in a direction parallel to the axis of the bloom 11. The feed clamping slide 5 performs a back-and-forth movement between a reversal point 13 located forward in the feed direction of the bloom 11 and a reversal point 14 located rearward in the feed direction of the bloom 11. The travel distance of the feed clamping slide 5 between the two reversal points 13, 14 is, in the embodiment of the Figure 1 24 m.

[0071] As soon as the bloom 11 has left the front mandrel support 15, the chuck 19 of the front mandrel support 15 is closed radially, so that the chuck 19 firmly clamps the mandrel bar 8. The front mandrel support 15 points in Figure 1A distance of 36 m is maintained from the feed chuck 12 of the feed clamping slide 5 when the feed clamping slide 5 is at its rear reversal point 14. This distance is measured between the rear end of the chuck 19 of the front mandrel support 15 (in the feed direction of the magnifying glass) and the front end of the feed chuck 12 of the feed clamping slide when the latter is at its rear reversal point 14. A magnifying glass with a maximum length of 36 m could therefore be positioned between the front mandrel support 15 and the feed chuck 12 of the feed clamping slide 5 at its rear reversal point 14 without the magnifying glass being clamped or restricted by the chuck 19 of the front mandrel support 15 or by the feed chuck 12 of the feed clamping slide 5.

[0072] The 8-inch pin bar Figure 1It consists of the material 30 CrNiMo 8 and has a tensile strength of 1000 N / mm 2< and an elongation of 8 %.

[0073] At the reversal point 9 of the rolling stand 1, which is the leading point in the feed direction of the bloom 11, the bloom 11 enters between the rolls 2, 3 and is received by the entry rollers (not shown) of the rolls 2, 3. The conically calibrated rolls 2, 3, arranged one above the other in the rolling stand 1, roll over the bloom 11 by rolling back and forth on the bloom 11 in the feed direction of the feed tensioning slide 5. During one rolling stroke, the pair of rolls moves a distance L from the reversal point 9 of the rolling stand 1, which is the leading point in the feed direction (entry dead center ET), to the reversal point 10, which is the trailing point in the feed direction of the bloom 11 (exit dead center AT), of the rolling stand 1. This corresponds to in Figure 1The rollers rotate through an angle of 280°. During this process, the roller pair 2, 3 stretches the bloom 11 over the mandrel 4 held inside the bloom 11. The rollers 2, 3 and the mandrel 4 are calibrated such that the gap between the rollers 2, 3 and the mandrel 4 decreases continuously in the working calibration zone of the rollers 2, 3 from the wall thickness of the bloom 11 to the wall thickness of the finished rolled tube 25. Furthermore, the outer diameter defined by the rollers decreases from the outer diameter of the bloom to the outer diameter of the finished tube, and the inner diameter defined by the mandrel decreases from the inner diameter of the bloom to the inner diameter of the tube. Following the working calibration zone of the rollers 2, 3 is the smoothing calibration zone, in which the surface of the tube 25 being produced is smoothed.Upon reaching the rear reversal point 10 of the rolling stand 1, the exit pocket (not shown) of the rollers 2, 3 releases the finished rolled tube.

[0074] To achieve a uniform shape for the finished tube 25, the bloom 11 undergoes intermittent rotation about its longitudinal axis in addition to being fed forward. This rotation of the bloom 11 takes place at both reversal points 9 and 10 of the rolling stand 1. Multiple rolling passes over each tube section ensure a uniform wall thickness and roundness of the tube, as well as uniform inner and outer diameters.

[0075] The finished tube 25 is picked up by a chuck 22 of an exit clamping slide 18 and pulled out of the cold pilger rolling mill 7.

[0076] Figure 2 shows a schematic diagram of another cold pilger rolling mill 7' in a side view. In contrast to Figure 1 indicates the in Figure 2The cold pilger rolling mill 7' shown, however, has two feed clamping slides 5, 5', each with a feed chuck 12, 12' for holding a bloom 11. The two feed clamping slides 5, 5' can each be moved 12 m between their front 13, 13' and rear reversal points 14, 14' and are distinguished from the one in Figure 1 The feed clamping slide 5 shown is therefore characterized by a smaller travel distance.

[0077] The feed carriage 5', located at the front of the bloom 11 in the feed direction, has already advanced the bloom to just before its rear reversal point 14' in the direction of the mandrel 4. The feed carriage 5, located at the rear of the bloom 11 in the feed direction, moves towards the front feed carriage 5' in the opposite direction of the bloom's feed, so that when the front feed carriage 5' reaches its rear reversal point 14', it can transfer the bloom 11 to the rear feed carriage 5 at its front reversal point 13. After the bloom 11 has been picked up by the rear feed carriage 5, it would then, in the next step, advance the bloom 11 step by step towards the mandrel 4, while the front feed carriage 5' would return to its front reversal point 13' to pick up another bloom 11'.In this way, continuous operation of the rolling mill is enabled, which eliminates dead times when a single feed clamping slide 5 returns, as in the . Figure 1 and 2 shown from its rear to its front turning point, avoiding this.

[0078] Unlike the one in Figure 1 The cold pilgrim rolling mill 7 shown indicates the cold pilgrim rolling mill 7'. Figure 2 In addition to the front mandrel support 15, there is also a rear mandrel support 16 in the feed direction of the bloom 11. The rear mandrel support 16 is arranged between the front reversal point 13' of the front feed clamping slide 5' and the front mandrel support 15 and, like the front mandrel support 15, has a chuck 20 for holding the mandrel bar 8. The bloom 11 in Figure 2The front mandrel support 15 has already been disengaged, so that the chuck 19 of the front mandrel support 15 is closed and clamps the mandrel bar 8 firmly. The chuck 20 of the rear mandrel support 16, on the other hand, is open and allows the magnifying glass 11 to pass between the chuck 20 and the mandrel bar 8.

[0079] In Figure 2 The distance between the front mandrel support 15, measured at the rear end of the chuck 19 in the feed direction of the bloom, and the rear mandrel support 16 is 38 m, while the in Figure 2 The magnifying glass 11 shown has a length of 37 m. Therefore, the magnifying glass 11 can be arranged between the front 15 and the rear mandrel abutment 16, and the chucks 19, 20 of both mandrel abutments 15, 16 can be closed without the chucks 19, 20 clamping the magnifying glass 11.

[0080] In Figure 3A 7" cold pilger rolling mill is shown in a schematic side view, which, in comparison to the one in Figure 2 The cold pilger rolling mill 7' shown has, in addition to the two feed clamping slides 5, 5', the front 15 and the rear mandrel support 16, a winding device 30.

[0081] In order to be able to wind the finished tube 25 into a transportable form behind the rolling mill 1, the following is necessary: Figure 3 The cold pilger rolling mill 7" shown also includes a winding device 30. The winding device 30, which is located in Figure 3 The schematic representation consists of a holding frame 33 and a bending device 31. The bending device 31 has three bending rollers 32b, which in the illustrated embodiment are all three driven by motors and engage with the finished tube 25 in a frictional manner.

[0082] The already rolled portion of the bloom, i.e., the portion of the already finished tube 25, is first picked up by a chuck 22 of an outfeed clamping slide 18 and pulled towards the winding device 30. As soon as a portion of the already finished tube 25 enters the bending rollers 32b of the bending unit 31 of the winding device 30, this portion of the finished tube 25 is initially bent by two bending rollers 32b arranged above the finished tube 25 and one bending roller 32b arranged below the finished tube 25. As a result of a motor-driven rotation of the winding device 30 in the direction of the Figure 3 In accordance with the arrow shown, the curved part of the finished tube 35 is wound spirally around a first axis 34.

[0083] The bending device 31, or rather the three bending rollers 32b, are pivotably mounted on the support frame 33 about a second axis 35, which coincides with the longitudinal axis of the finished tube 25 exiting the discharge clamping slide 18. The pivoting movement of the bending rollers 32b about the second axis 35 is effected by a motor drive. This pivoting, which occurs simultaneously with the winding process, is carried out at the same angular velocity as the pivoting movement of the bloom 11 about its longitudinal axis during the unwinding of the bloom 11. Both pivoting movements therefore occur synchronously. This has the advantage that twisting of the finished tube 35 during winding is completely, or at least substantially, avoided, and the finished tube 25 is wound without torsional stresses during rolling.

[0084] Additionally, an annealing furnace 29 is provided in the same factory hall, in which the bloom 11 is annealed before entering the pilgrim rolling mill 7‴ and after a first rolling in a second cold pilgrim rolling mill.

[0085] For the purposes of the original disclosure, it is pointed out that all features as they can be deduced by a person skilled in the art from the present description, the drawings, and the claims, even if they are specifically described only in connection with certain other features, can be combined individually or in any combination with other features or groups of features disclosed herein, unless this has been expressly excluded or technical circumstances render such combinations impossible or pointless. A comprehensive, explicit description of all conceivable combinations of features is omitted here solely for the sake of brevity and readability.While the invention has been illustrated and described in detail in the drawings and the preceding description, this illustration and description are merely exemplary and are not intended to limit the scope of protection as defined by the claims. The invention is not limited to the disclosed embodiments.

[0086] Variations of the disclosed embodiments are obvious to a person skilled in the art from the drawings, the description, and the accompanying claims. In the claims, the word "have" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude multiple features. The mere fact that certain features are claimed in different claims does not preclude their combination. Reference numerals in the claims are not intended to limit the scope of protection. Reference symbol list

[0087] 1 Rolling stand 2, 3 upper, lower roll 4 Mandrel 5 Feed chuck 6 Linear motor 7, 7', 7" Cold pilgrim rolling mill 8 Mandrel bar 9 Front reversal point of the rolling stand 10 Rear reversal point of the rolling stand 11 Bloomer 12 Feed chuck 13 Front reversal point of the feed chuck 14 Rear reversal point of the feed chuck 15 Front mandrel support 16 Rear mandrel support 18 Outfeed chuck for finished tube 19, 20, 22 Chuck 23 Crank drive 24 Push rod 25 Finished tube 26 Unwinding device 27 Spindle 28 First axis (unwinding device) 29 Annealing furnace 30 Winding device 31 Bending device 32a, 32b Bending roller 33 Holding frame 34 First axle (winding device) 35 Second axle (winding device)

Claims

1. Method for producing a tube (25) from steel by cold forming a bloom (11) in a first cold rolling mill (7, 7', 7") having a roller frame (1) with rollers (2, 3) which are rotatably supported thereon, a roller mandrel (4) which is retained by a mandrel rod (8), at least one mandrel thrust block (15, 16) which retains the mandrel rod (8) and at least one feed clamping slide (5) having a feed tool chuck (12) for receiving the bloom (11), having the steps of: a) opening a tool chuck (19) of a front mandrel thrust block (15) in the feed direction of the bloom (11) in the radial direction and passing a first bloom (11) through the front mandrel thrust block (15) between the tool chuck (19) of the front mandrel thrust block (15) and the mandrel rod (8), b) after the first bloom (11) has been passed completely through the front mandrel thrust block (15), closing the tool chuck (19) of the front mandrel thrust block (15) in the radial direction in such a manner that the front mandrel thrust block (15) retains the mandrel rod (8) which carries the roller mandrel (4), c) supplying the first bloom (11) to a feed clamping slide (5) and receiving the first bloom (11) by opening the feed tool chuck (12) in the radial direction and clamping the first bloom (11) by closing the feed tool chuck (12) in the radial direction at a front reversal location (13) of the feed clamping slide (5) in the feed direction of the bloom (11), d) rolling out the first bloom (11) by the rollers (2, 3) over the roller mandrel (4) to form a strain-hardened tube (25) by gradually feeding forward the first bloom (11) using the feed clamping slide (5) and moving the roller frame (1) forwards and backwards in an oscillating manner between a front reversal location (9) and a rear reversal location (10) with the rollers (2, 3), characterized in that before step a) in a step a') providing the first bloom (11) in a state wound on a spindle (27) and unwinding the first bloom (11) from the spindle (27) using an unwinding apparatus (26) is carried out, wherein in order to provide the first bloom (11) a bloom is formed in a second cold rolling mill with respect to the first bloom (11) which is introduced into the first cold rolling mill (7, 7', 7") and wound onto the spindle (27) so that the tube (25) leaving the first cold rolling mill (7, 7', 7") is a twice-rolled tube (25), wherein the first bloom (11) which leaves the second cold rolling mill (7, 7', 7") and which is arranged in a state wound on the spindle (27) before passing through the front mandrel thrust block (15) is heated to a temperature in a range from 1000° C to 1200° C.

2. Method for producing a tube according to claim 1, characterized in that the first bloom (11) has a length of 30 m or more.

3. Method for producing a tube according to claim 1 or 2, characterized by the step which is additionally carried out after step a) and before step b): e) opening a tool chuck (12') of a mandrel thrust block (16) which is arranged at the rear in the feed direction of the bloom (11) and between the front reversal location (13') of a front feed clamping slide (5') in the feed direction of the bloom (11) and the front mandrel thrust block (15) in the radial direction, wherein the rear mandrel thrust block (16) has a spacing of at least 30 m from the front mandrel thrust block (15) and passing the first bloom (11) through the rear mandrel thrust block (16), wherein the rolling out of the first bloom (11) by the rollers (2, 3) over the roller mandrel (4) to form a strain-hardened tube (25) is carried out in step c) by gradually feeding forward the first bloom (11) alternately using the front feed clamping slide (5') from a front reversal location (13') up to a rear reversal location (14') of the front feed clamping slide (5') and using a rear feed clamping slide (5) in the feed direction of the bloom from a front reversal location (14) up to a rear reversal location (13) of the rear feed clamping slide (5) and moving the roller frame (1) forwards and backwards in an oscillating manner between a front reversal location (9) and a rear reversal location (10) with the rollers (2, 3), and wherein the method additionally has the steps of: f) after the first bloom (11) has been passed completely through the rear mandrel thrust block (16), closing the tool chuck (20) of the rear mandrel thrust block (16) in the radial direction in such a manner that the rear mandrel thrust block (16) retains the mandrel rod (8) which carries the roller mandrel (4), g) during the rolling of the first bloom (11) unwinding a second bloom (11') which is arranged in a state wound on a spindle (27') which can be rotated about an axis (28) which is perpendicular to the feed direction of the bloom, h) opening the tool chuck (19) of the front mandrel thrust block (15) and passing the second bloom (11') through the front mandrel thrust block (15) into the range between the front mandrel thrust block (15) and rear mandrel thrust block (16), i) after the second bloom (11') has been passed completely through the front mandrel thrust block (15), closing the tool chuck (19) of the front mandrel thrust block (15) in such a manner that the front mandrel thrust block (15) retains the mandrel rod (8) which carries the roller mandrel (4), j) opening the tool chuck (20) of the rear mandrel thrust block (16), k) passing the second bloom (11') through the rear mandrel thrust block (16), l) supplying the second bloom (11') to the front feed clamping slide (5') and receiving the second bloom (11') in the feed tool chuck (12') of the front feed clamping slide (5') and clamping the second bloom (11') by closing the feed tool chuck (12') in the radial direction of the front feed clamping slide (5'), m) opening the feed tool chuck (12) of the rear feed clamping slide (5) in the radial direction, n) gradually feeding forward the second bloom (11') alternately using the front feed clamping slide (5') and the rear feed clamping slide (5) with the second bloom (11') being clamped in, o) after the tube (25) which is completely rolled from the first bloom (11) has left the roller frame (1) completely, introducing the second bloom (11') into the roller frame (1) and p) rolling out the second bloom (11') by the rollers (2, 3) over the roller mandrel (4) to form a strain-hardened tube (25') by gradually feeding forward the second bloom (11') alternately using the rear feed clamping slide (5) and the front feed clamping slide (5') and moving the roller frame (1) forwards and backwards in an oscillating manner between a front reversal location (9) and a rear reversal location (10) with the rollers (2, 3).

4. Method for producing a tube according to claim 1 or 2, characterized by a winding up of an already completely rolled portion (25) of the bloom during the rolling out of a portion of the bloom (11) which is still to be rolled to form a strain-hardened tube (25) with the steps of: curving an already completely rolled portion (25) of the bloom in a bending apparatus (31), helically winding up an already completely rolled portion (25) of the bloom about a first axis (34), and pivoting the bending apparatus (31) which is received on a retention framework (33) and the first axis (34) about a second axis (35) which is substantially perpendicular to the first axis (34) and parallel with a longitudinal axis of a bloom (11) which is received between the rollers (2, 3) in such a manner that the pivoting is carried out at the same angular velocity as a pivoting of the bloom (11) about the longitudinal axis thereof during the rolling of the bloom (11).

5. Method according to any one of claims 1 to 4, characterized in that the mandrel rod (8) has a tensile strength of 1000 N or more.

6. Method according to any one of the preceding claims, characterized in that the mandrel rod (8) has an expansion of 10 % or less.

7. Method according to any one of the preceding claims, characterized in that the first cold rolling mill (7, 7") has a rear mandrel thrust block (16) with a tool chuck (20) for retaining the mandrel rod (8) in the feed direction of the bloom (11) between the front reversal location (13) of the feed clamping slide (5) and the front mandrel thrust block (15), wherein the rear mandrel thrust block (16) has a spacing of at least 30 m from the front mandrel thrust block (15) in such a manner that the mandrel rod (8) during operation of the first cold rolling mill (7', 7") can be retained by at least one tool chuck (19, 20) of the front mandrel thrust block (15) or the rear mandrel thrust block (16).

8. Method according to any one of the preceding claims, characterized in that each feed slide (5, 5') of the first cold rolling mill (7, 7', 7") is configured in such a manner that it can feed forward a bloom (11) with a weight of 100 kg / m or more.