JP2690575B2 - Continuous drawing method for metal tubes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a seamless metal tube, which includes a mandrel disposed inside the metal tube and a die for reducing the outer diameter of the tube.
In particular, in a method for the continuous drawing of copper tubes, the wall thickness is reduced by the cooperation of a mandrel and a die and the drawing force acts on the drawn tube behind the die and at least in that case. It relates to the above method, wherein the two tubes are connected to each other by welding at their undeformed ends before drawing.

PRIOR ART Such a method is known from German Patent Specification No. 3,739,730.

In the production of seamless metal tubes, one usually starts with a casting bloom and then processes by pressing or hot rolling into a crude tube. In the next processing step, these crude tubes are reduced in wall thickness as well as outside diameter in a cold Pilger tube making machine (Pilger mill). The Pilgered tube is then drawn to its final size by several draws with a die and a mandrel placed inside the metal tube. In preparation for each draw, a mandrel and draw oil are loaded into the metal tube. The tube tip is then sharpened so that it can be introduced into the drawing die of the drawing machine. In several draws, these preparatory operations are carried out several times, the parts of the tube still being sharpened having to be removed from the draws. In order to avoid these drawbacks, it has already been attempted to bond the individual pipes to one another before drawing, for example by butt-welding the ends of the pipes to one another. However, it has been found that the joints of the individual tubes do not have the necessary strength to transfer the drawing forces during the drawing process.
In order to reduce the load on the joint during withdrawal, the known method is to perform an empty drawing over the length of the joint, i.e. without withdrawing the wall thickness of the pipe during this time. Take care. This has the consequence that the wall thickness is large over a relatively long range compared to the rest of the tube. Furthermore, in the case of successive successive withdrawals, it is difficult to reduce the wall thickness in the region of this joint and to perform emptying again, so that the joint must be reliably recognized.

For this purpose, in addition to the provision of suitable tools, a great deal of control engineering costs are required. At the end of the manufacturing process, the joints must be removed from the finished part and treated as scrap.

(Problem to be solved) The problem to be solved by the present invention is to provide a continuous metal pipe in which all the completed parts can be drawn out with the same reduction in wall thickness without incurring a great amount of control technology costs. It is to provide a withdrawal method.

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned problems are solved by first making the joints of the pipes to be in almost the same strength state as the pipe material which directly abuts them by appropriate means and then to the joints. This is solved by the fact that the tube section containing the is withdrawn with a uniform reduction in wall thickness.

The essential advantages of the method according to the invention are that of a drawing device without the need for great control engineering costs and without waste of raw material with a relatively large wall thickness. It is possible to significantly improve the efficiency.

According to a particularly advantageous embodiment of the invention, the metal tube is soft-annealed in the region of the joint. Since the required drawing force depends, among other things, on the strength state of the material to be deformed, it is recognized that softened and annealed materials require lower drawing forces than hardened and drawn materials. depart. A specific heat treatment in the region of the joint of the metal tube keeps the predetermined region in the strength state of the joint, for example the tensile strength of the unstrengthened weld seam. In the case of the subsequent first drawing, the joint is only subjected to a significantly weakened deformation force for the soft-annealed material. Surprisingly, the joint between the tubes has the required strength and is not torn in the case of normal cross-section reduction of about 30-40% in the case of drawing with a moving mandrel. found. In order to reduce the withdrawal force to be transmitted, it is possible to withdraw, preferably with a reduced withdrawal speed in the region of the joint. However, this safety measure is generally only necessary during the first withdrawal after joining the tubes together.

Alternatively, almost the same strength states of the joint and the directly drawn hardened drawn area can also be achieved, preferably by local cold deformation of the joint.

(Example) An example of the present invention will be described.

Example 1: a copper tube with a diameter of 58 mm and a wall thickness of 2.4 mm is first dimensioned; diameter 35 m
It is pulled out to m x wall thickness 1.4mm. Two tubes of equal size are butt-welded at their ends under a shield gas atmosphere (90% nitrogen and 10% hydrogen) by an orbital welder so that the weld seam has a slight ridge on the tube surface. The joint is then subjected to local deformation in the range of approximately 1 mm. For this purpose, for example, the pipes that were joined in the first drawing are dimensioned with only a very slight reduction in cross-section in the region of the joint;
It is pulled out to 34mm x 1.4mm wall thickness (empty pulling without wall thickness reduction). It increased from 22N / mm ² in tensile strength of 26N / mm ² by the local cold deformation regions bordering the welded bonding site. Further drawing can be carried out up to a diameter of 15 mm and a wall thickness of 0.5 mm.

Example 2; Locally restricted heat treatments can also be carried out in order to obtain a strength condition which is equal to the material of the individual tubes and the respective butt-welded joints. A copper tube of the dimensions described in Example 1 is used as the material.

The ends of the two tubes to be joined are each approximately 0.25 to 1 mm
Heated to 650 ° C under an inert gas atmosphere over a region of length. The joints are then butt-welded by means of an orbital welding machine, the gas atmosphere mentioned in Example 1 being maintained. Alternatively, the tube ends are first butt welded and then the corresponding areas are heat treated. The butt-welded tubing is continuously drawn by a drawing machine, which is arranged in sequence, in 6 draws to the final dimensions; diameter 15 mm x wall thickness; 0.5 mm.

Continuation of the front page (72) Inventor Georg Wisshiyumeier Federal Republic of Germany, Osnaburiyuk, Karl-Arnold-Strasse, 68 (56) Reference JP-A-1-202310 (JP, A) JP-A-1-154817 ( JP, A) JP 54-118372 (JP, A) JP 50-22756 (JP, A) JP 25-1268 (JP, B1)

Claims (1)

(57) [Claims] 1. A method for continuous drawing of a seamless metal tube, in particular a copper tube, by means of a mandrel arranged inside the metal tube and a die for reducing the outer diameter of the tube.
The wall thickness is then reduced by the cooperation of the mandrel and the die and the drawing force acts on the drawn pipes behind the dies and at least two pipes are welded at their undeformed end before drawing. In the above method, the joints between the two pipes are first brought into a state of strength almost equal to that of the pipe material which directly abuts them by means of local cold deformation or local heat treatment, and the pipes are joined together. The method as described above, characterized in that the withdrawal is carried out to a uniform wall thickness, the withdrawal rate in the region of the connection being reduced at least during the first withdrawal.