EP0317905B1 - Method of drawing weldless tubes - Google Patents

Description

The invention relates to a method according to the preamble of claim 1.

Modern production for seamless copper pipes usually looks like that from a full block z. B. produces a tube by hot rolling or pressing, this tube is reduced in a cold pilger mill both in the wall thickness and in the outer diameter and finally pulls down the pilgrim tube in several moves by means of dies and using flying mandrels to the final dimension. The pilgered tube is prepared for the first train as it is manufactured by inserting a mandrel and drawing oil into the tube and then sharpening the tube end so that it can be passed through the drawing die. The preparation for the next train is similar, with the tip of the previous train also being cut off. In addition to the large waste, this work is very time consuming.

Many attempts have been made to shorten these so-called hand times. For example, it has been proposed to design the tip of the tube so that it can be used for several drawing stages.

Another suggestion was to prepare the pipe length to be drawn while the previous pipe length was still being drawn. All of the proposals failed due to excessive machine work.

From DE-A1-2122935 a method for cold drawing of pipes is known, in which the ends of the pipes are welded together during the production process so that only a very small weld bit remains inside the pipe. However, it has been shown that the weld seams did not have the strength required to transmit the pulling forces which occur when the tube length is pulled through the die with a flying mandrel.

The invention has for its object to provide a method with which the time-consuming sharpening, threading the drawing tip and grasping the drawing tip behind the die is avoided or largely restricted by a drawing machine.

This object is achieved by what is covered in the characterizing part of claim 1.

The main advantage of the invention is that the pulling forces are reduced in the time in which the connection point must transmit the tensile forces, ie between the die and the point of application of the force. During this time, the wall thickness of the pipe is not reduced, but only a hollow pull is carried out, which requires much lower drawing forces. It follows that only the first tube length, as is known, has to be pointed and threaded into the die. The following pipe lengths are automatically threaded by the pipe length arranged in front of them. The performance of the system can be increased significantly. But it is necessary that the subsequent trains must be matched to the inner diameter of the tube reduced by the hollow train. The connection between the tube lengths can be produced by gluing, soldering or welding. The connection is particularly advantageously produced by butt welding the ends of the tube lengths. Arc or oxyacetylene welding is a suitable welding process. Pressure welding is also possible.

According to a particularly advantageous embodiment of the invention, the end regions of the pipe lengths to be connected or connected are provided with cutouts in the wall. These recesses can be longitudinal slots so that the mandrel is accessible from the outside. It appears to be more advantageous to design the recesses in such a way that at least half the circumference of the tube wall is removed. As a result, the weld seam is accessible from the inside, so that when welding u. U. occurring welding burr can be removed. In this embodiment, the mandrel automatically comes out of the engagement area of the die during the drawing process.

The mandrel can also be moved from outside by mechanical intervention. For this purpose, for example, a hook-like tool engages the mandrel and pulls it back against the direction of travel of the tube. After the mandrel has been displaced, it is expediently held by an electromagnet, which only releases the mandrel when the connection point has passed through the die, and acts on the pulling force, seen in the direction of travel of the tube, behind the connection point. U. u. it is also possible to move the mandrel with an electromagnet. To release the mandrel, it may be useful to briefly move the die in the direction of pull. In combination with an electromagnet, this solution is useful. The die is moved back to its starting point when the mandrel is moved. It is also advantageous if the outside diameter of the tube is reduced in the area of the connection point. This can e.g. B. done by cutting or non-cutting deformation, the inner diameter of the tube remains the same. By reducing the wall thickness, the pulling forces to be transmitted are reduced.

According to a particularly advantageous embodiment of the invention, the inside diameter of the tube is widened in the area in which the wall thickness has not been reduced. This results in the advantage that the mandrel required for the next drawing process can be moved in the tube without difficulty.

According to a further embodiment of the invention it is provided that a force acts on at least part of the tube wall in the radial direction between the die and the mandrel and at least part of the tube wall is deformed such that the mandrel is retained by the deformed tube wall.

When pulling a tube with a flying mandrel, mandrels are used that are designed in a stepped manner. The part with the smaller diameter defines the inner diameter of the drawn tube. The decrease in wall thickness of the tube wall is determined by the formation of the conical transition from the small diameter to the large diameter of the mandrel and the so-called drawing cone of the die. The large outer diameter of the mandrel must be smaller in order to be able to push the mandrel into the tube to be drawn and should be slightly larger than the inner diameter of the drawing die so that the mandrel does not slip through the drawing die at the end of the drawing process.

The mandrel as well as the die are only in the conical part and in the drawn part on the pipe to be drawn. Technically, the die with mandrel can initially be displaced simultaneously against the direction of drawing, a deformation force being necessary in order to then, as further described here, move the die alone in the direction of drawing.

As such, it is possible to move the die and act on the deformation force when it is slowed down Pass the pipe through the system. However, it has proven to be advantageous that the passage of the tube through the die is interrupted during the displacement of the die and at the beginning of the action of the force on the tube wall. After the force acts on the pipe wall, the system is started up again, the force acting on the pipe wall until the connection point has passed through the die. It is essential that the mandrel only comes back into the area of action of the die, ie in cooperation with the die causes both a reduction in diameter and a significant decrease in wall thickness when the pulling force acts on the pipe behind the connection point, seen in the direction of travel of the pipe.

The die is advantageously returned to its starting position after the mandrel has returned to the area of action of the die. The return transport of the mandrel is achieved in that a dent is made in the tube wall, in the direction of travel of the tube before the position of the mandrel.

The holding back of the mandrel takes place with particular advantage in that, after the die has been displaced, the tube is pulled so far by means of a split die-like tool arranged in front of the die in the direction of flow that the outside diameter of the tube is smaller than the larger outside diameter of the mandrel. Hollow-drawn means with this procedure that there is no decrease in wall thickness.

The retention of the mandrel can also be advantageously achieved in that at least three beads arranged at 120 ° to one another are formed in the tube after the die has been displaced, and in that the mandrel is retained by the inner surface of the beads becomes.

Since in the subsequent moves the hollow drawing of the area already drawn in the previous move requires a higher expenditure of force, it is expedient to soft anneal the hollow drawn area before the drawing, i.e. to undo the work hardening.

Suitable for carrying out the method is a device which consists of a die, a flying mandrel located in the tube and a withdrawal device engaging the tube behind the die, in which the die can be displaced in the direction of the tube longitudinal axis. In the case of such a device, a shaping tool deforming the tube wall, e.g. a split ring is provided.

It is also possible to provide a so-called Turkish head in front of the die. A Turkish head is a deformation tool that consists of at least two caliber rollers that act on the pipe wall.

It is particularly advantageous if the molding tool is a split die-like tool, the small inside diameter of which is larger than the inside diameter of the drawing die. Such die-like tools are available in every pipe mill and can be easily changed for the intended purpose by separating a die in half. Since high accuracy is not important for these die-like tools, it may be possible to use used dies for this purpose.

If the type of connection between the pipe ends permits this, for example a soldered or welded connection, can be used The die-like tool, which has the sole task of holding back the mandrel until the connection point is behind the actual drawing die, is subjected to a slight reduction in wall thickness. In this case, controlled hollow drawing takes place, as is usual in practice, since the dimensions of the mandrel and die can be matched to one another in such a way that an exactly defined drawing gap is present. This has the advantage that the clear width of the drawn tube is not reduced by the hollow train to the extent that the transport of the mandrel is hindered in the subsequent trains.

The invention is explained in more detail with reference to the exemplary embodiments shown schematically in FIGS. 1 to 21.

A seamless copper tube 1 in the form of a collar is drawn through a die block 3 through a die 3 and is thereby reduced both in the outside diameter and in the wall thickness. The pulling forces required for this are applied by a slide pulling machine 4, the clamping jaws 5 of which engage the drawn tube 6. Such a procedure has long been common in copper pipe production.

According to the teaching of the invention, several pipe lengths are connected to one another before or during the drawing process. For this purpose, a collar 7a with a copper tube length of the same cross-sectional dimension is mounted above the collar 7 and the beginning and end of the collar 7 and 7a are connected to one another. Figure 2 shows the arrangement of die 3 and mandrel 8. The forces occurring in this drawing process are so high that a connection point, the z. B. was produced by soldering or welding, but would tear off in the die 3 at the latest immediately behind the die 3. The mandrel is shaped so that it "floats" in the die 3 when it is pulled, that is to say those which occur as a result of the friction Forces are equal to the restraining forces. According to the invention, the mandrel 8 is displaced counter to the drawing direction at the latest when the connection point 9 reaches the area of the die 3 and thus no longer acts together with the die on the tube wall (see FIG. 3). As a result, the tube 1 is only subjected to a hollow train without a reduction in wall thickness. The displacement of the mandrel 8 can be carried out in various ways, e.g. B. by a finger pulling back the mandrel 8 through a slot in the tube wall, or by magnetic action or also by allowing the die 3 to run with the tube 6. In the embodiment according to FIG. 3, there are recesses 10 at the beginning and end of the tube lengths and 11 introduced, which automatically release the mandrel 8 from the die area. The mandrel 8 is, for example, transported back into the area of the die by a dent (not shown) in the tube wall when the clamping jaw 5 of the slide trigger 4 engages the tube 6 in the direction of passage behind the connection point 9. The invention has been described on the basis of copper tubes in the form of a coil, but can equally be used for straight tube lengths. The machine applying the pulling force can also be chosen as desired, e.g. B. a drawing drum or a so-called. Drawing disc with a V-shaped endless groove on its peripheral surface. Figures 4 to 12 show embodiments of the connection of the pipe lengths. All connections have in common that a passage of the mandrel 8 from one tube length into the subsequent tube length is possible without hindrance and that the strength of the connection is at least so great that the forces arising from the hollow train can be transmitted.

FIG. 4 shows a butt connection of the tubes 1 to one another, which can be produced by gluing, soldering or pressure welding, but also by arc welding. The recesses 10 and 11 allow one Removal of the welding burr that may occur and access to relocate the mandrel 8. If the cutouts 10 and 11 extend beyond half the pipe cross section, the mandrel 8 automatically detaches from the die 3.

In FIG. 5, the connecting seam 9 is produced by spot welding the overlapping ends.

Figure 6 again shows a butt connection 9 z. B. by gluing, soldering or welding. In this connection, the mandrel is z. B. withdrawn and held a tube 1 surrounding annular electromagnet. To support the retraction, the die 3 can run briefly with the tube 1. After the mandrel 8 is held by the magnet, it is moved back into its starting position.

FIG. 7 shows a connection in which the tapered end inserted into the pipe end is fixed by spot welding. FIG. 8 shows the connection according to FIG. 6 with a longitudinal slot 12 into which a holding finger penetrates and the mandrel 8 can withdraw. A magnet is also required here, which holds the mandrel 8 after withdrawal from the die 3 until the connection point 9 has reached behind the point of application of the pulling force. In the connection according to FIG. 9, the outer diameter of the tubes 1 is reduced. A copper sleeve 15 is pushed over these diameter reductions 13 and 14 and is spot-welded, soldered or glued to the surface of the tubes 1. This embodiment reduces the pulling forces resulting from the reduction in wall thickness.

In the connection according to FIG. 10, the inside diameter of the tube lengths in the connection area is increased. The seam 9 is expediently butt-welded.

FIG. 11 shows a connection 9 in which the end of one tube length is reduced in the outside diameter, whereas the end of the other tube length is enlarged in the inside diameter. The ends are inserted into one another and advantageously soldered.

In the exemplary embodiment according to FIG. 12, both ends of the tube lengths are reduced in outer diameter and soldered to a metal sleeve 16.

FIGS. 13 to 16 are intended to illustrate the procedural sequence, while FIGS. 17 to 21 represent particularly advantageous configurations of the device.

During the normal drawing process, the copper tube 1 is reduced both in diameter and in the wall thickness by the interaction of the drawing die 3 and the mandrel 8. The drawing gap between the inside diameter of the drawing die 3 and the outside diameter of the part 8a defines the wall thickness of the copper tube. Since the outer diameter of the part 8b of the mandrel 8 is larger than the inner diameter of the drawing die 3, the mandrel 8 is prevented by the Hike die opening. The mandrel 8 is drawn into the drawing cone 3a by the frictional forces on the surface of the part 8a. The conical transition from part 8a to part 8b of the mandrel is preferably somewhat flatter than the drawing cone 3a, so that there is a continuous decrease in the wall thickness. With a correct selection of pipe cross section and reduction in wall thickness, the cross section of the drawn pipe 6 is sufficient to transmit the forces occurring in the drawing gap. In order to achieve economical production, you usually move near the maximum wall thickness reduction when pulling pipes. A welding point is usually not sufficient to transmit these high pulling forces.

If a welded or soldered connection 9 between two pipes 1 to be drawn comes near the drawing die 3, the drawing process is interrupted, the drawing die 3 is displaced a small distance in the drawing direction, so that the mandrel 8 comes out of its area of influence. The mandrel 8 remains clamped in the tube area deformed by the drawing cone 3a. In order to loosen and hold back the mandrel 8, a die-like tool 17 arranged in front of the drawing die 3 is used, which in a manner not shown consists of two halves divided in the radial direction and is moved together in front of the mandrel 8 instead of the drawing die 3. When restarting, the mandrel 8 loosens inside the tube and is held back by the tool 17. During this phase, only the inner diameter of the tool 17 acts on the pipe wall, ie there is a reduction in diameter without a reduction in wall thickness (see FIG. 15). When the connecting seam is behind the drawing die 3, the tool 17 is moved apart and the mandrel 8 is released again. By means of a dent 18, which was molded into the tube wall, the mandrel 8 is transported back into the drawing gap, so that a reduction in wall thickness can be carried out. The The tool 17 and the drawing die 3 can then be moved back during the drawing process.

However, there is also the possibility of retracting the tool 17 and the drawing die 3 from the position shown in FIG. 14 against the direction of drawing when the system is stationary. For this, however, it is necessary to hold the drawn tube 6.

A displacement of the die 3 and mandrel 8 against the direction of drawing during the drawing process and displacement of the die 3 after stopping in the direction of drawing is also possible. In the exemplary embodiment according to FIGS. 17 and 18, a mold roller 19 takes the place of the tool 17, which forms a slight bead 20 in the tube wall, which loosens and retains the mandrel 8. Advantageously, at least three such rollers 19 are arranged evenly distributed over the circumference of the tube, of which only one is shown. The rollers 19 can be adjusted in the direction of the central axis of the tube 6. After passing the connecting seam 9 through the drawing die 3, they are retracted like the tool 17 and release the mandrel 8.

FIGS. 19 and 20 show a so-called Turkish head instead of the tool 17, which consists of a plurality of adjustable profile rollers 21, of which only one is shown. These profile rollers 21 are set up like the tool 17 after moving the drawing die, so that the caliber formed by them is able to loosen and hold back the mandrel 8.

FIG. 21 shows a particularly advantageous exemplary embodiment based on the teaching of the invention. The split die 17 shown there is almost identical to the drawing die 3. Only the inner diameter is somewhat larger than the inner diameter of the drawing die 3. In the drawing gap between the die 17 and the part 8a of the mandrel 8 there is no appreciable decrease in wall thickness, so the tube 6 is hollow with little effort. Since the drawing die 3 is fed a thick-walled tube, the hollow drawn tube is reduced in diameter by the drawing die 3. In order to reduce this reduction in diameter, the inside diameter of the die 17 can be designed such that a slight reduction in wall thickness occurs in the drawing gap between part 8a and the die 17. However, this must not be so strong that the tube breaks off in the area of the connecting seam.

The reduction in the inner diameter decrease ensures that in the subsequent passes the mandrel 8 in its part 8b never becomes larger than the inside diameter of the tube in the region of the hollow train. In order to reduce the effort required for hollow drawing, it is advantageous to soft-anneal the hollow drawn tube area before the next pull.

The invention is to be further clarified using a train sequence.

Pilgrim tubes of approx. 80 m length, approx. 300 kg weight, an outside diameter of 58 mm and a wall thickness of 2.5 mm are welded together by arc welding under protective gas.

The train sequence could look like this with three sled pullers: Diameter 8b Diameter 8a 1st train 48 mm x 2.08 mm 48.2 mm 43.84 mm 2nd pull 38.5mm x 1.75mm 38.7 mm 35.00 mm 3rd train 31 mm x 1.48 mm 31.2 mm 28.04 mm

The hollow drawn areas are separated from the drawn pipe length. The pipes 31 x 1.48 from the last drawing stage are welded together again and wound up to 5 to 10t weights per bundle. Then a continuous move can take place.

Example:

Diameter 8b Diameter 8a 1st train 24 mm x 1.26 mm 24.2 mm 21.48 mm 2nd train 19 mm x 1.09 mm 19.2 mm 16.82 mm 3rd train 15 mm x 0.95 mm 15.2 mm 13.1 mm

In the exemplary embodiments, it was shown that the tensile force, after the mandrel 8 was returned to the effective area of the die 3, acts on the pipe 1 behind the weld seam 9.

This is particularly not necessary if e.g. after several moves, the wall thickness of the drawn tube 1 has decreased so much that no high tensile forces are required for the "normal" drawing process. The greater wall thickness in the area of the weld seam 9 should be sufficient for the transmission of these lower tensile forces, in particular because the cast structure of the weld seam 9 is converted into a kneading structure by the multiple hollow trains, in particular when the weld seam area is annealed. This means that the pulling force can also act on the pipe 1 before the weld 9 in the subsequent trains.

Claims (16)

1. A process for drawing seamless metal pipes (1), in particular copper pipes, comprising a floating mandrel (8) which is arranged inside the metal pipe and a die (3) which reduces the outer diameter of the pipe, wherein the wall thickness is reduced by the cooperation of mandrel (8) and die (3) and a drawing force acts upon the drawn pipe behind the die, characterised in that two or more pipe lengths are permanently connected to one another at their undeformed ends prior to the drawing, that during the passage of the connection point (9) of the pipe lengths through the die (3) the mandrel (8) is displaced out of the range of action of the die (3), where the metal pipe (1) is drawn along a specified length without reduction in wall thickness, and that following the passage of the connection point (9) through the die (3), the mandrel (8) enters the range of the die (8) and that then the drawing force acts upon the drawn pipe preferably behind the connection point (9).
2. A process as claimed in Claim 1, characterised in that the pipe lengths are connected by gluing, soldering or welding.
3. A process as claimed in Claim 2, characterised in that the connection is effected by butt welding of the ends of the pipe lengths.
4. A process as claimed in Claim 1 or one of the following claims, characterised in that the end zones of the pipe lengths which are to be connected or have been connected are provided with wall openings.
5. A process as claimed in Claim 4 or one of the following claims, characterised in that the mandrel is displaced by external mechanical intervention through the openings.
6. A process as claimed in Claim 1 or one of the following claims, characterised in that the mandrel is displaced and maintained in the displaced state by an electromagnet.
7. A process as claimed in Claim 1 or one of the following claims, characterised in that the mandrel is displaced and maintained in the displaced state by moving the die in the drawing direction.
8. A process as claimed in Claim 1 or one of the following claims, characterised in that the outer diameter of the pipe lengths is reduced in the region of the connection point.
9. A process as claimed in Claim 1 or one of the following claims, characterised in that the inner diameter of the pipe is widened in the zone in which no reduction in wall thickness has taken place.
10. A process as claimed in Claim 7, characterised in that between the die and the mandrel a force acts upon at least a part of the pipe walls in the radial direction and deforms at least a part of the pipe walls in such manner that the mandrel is retained by the deformed pipe walls.
11. A process as claimed in Claim 10, characterised in that the passage of the pipe through the die is interrupted during the movement of the die and at the beginning of the action of the force upon the pipe walls.
12. A process as claimed in Claim 10 or 11, characterised in that the die is moved back into its starting position when the mandrel has re-entered the range of action of the die.
13. A process as claimed in Claim 10, characterised in that during the passage of the pipe the die is moved in opposition to the drawing direction, that the passage of the pipe is interrupted, that when the passage has been interrupted the die is moved in the drawing direction and that before the movement of the die recommences the force acts upon the pipe walls.
14. A process as claimed in Claim 10 or one of the following claims, characterised in that after the movement of the die, the pipe is hollow-drawn by means of a divided die arranged in advance of the die considered in the direction of passage, in such manner that the outer diameter of the pipe is smaller than the larger outer diameter of the mandrel.
15. A process as claimed in Claim 10 or one of the following claims, characterised in that following the movement of the die, at least three beads, mutually offset by 120x, are formed in the pipe and that the mandrel is retained by the inner surface of the beads.
16. A process as claimed in Claim 10 or one of the following claims, characterised in that in the following passes, the hollow-drawn zone is soft-annealed prior to the drawing.

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