US3661005A - Method for producing seamless tubes with small diameters - Google Patents

Abstract

Method for producing seamless tubes of small diameter. The starting tube is subjected to at least one initial cold drawing over an interior tool, decreasing the diameter and the wall thickness of the tube so that the interior tube surface is brought into complete contact with the interior tool. The tube is then subjected to stretch reducing and to final cold drawing over an interior tool.

Description

United States Patent Petersen et al.

[451 May 9, 1972 [54] METHOD FOR PRODUCING SEAMLESS TUBES WITH SMALL DIAMETERS [72] Inventors: Ulrich Petersen, Dusseldorf; Ernst Von Chiari, Solingen; Wilhelm Brutsch, Remscheid, all of Germany Mannesmann Aktiengesellschaft, Dusseldorf, Germany [73] Assignee:

[22] Filed: Oct. 29, 1969 211 Appl. No.: 872,373

US. Cl ..72/206, 72/283, 72/370 ..B21b 23/00 Field of Search ..72/206, 274, 278, 283, 367,

Primary Examiner-Lowell A. Larson Attorney'Nolte & Nolte [57] ABSTRACT Method for producing seamless tubes of small diameter. The starting tube is subjected to at least one initial cold drawing over an interior tool, decreasing the diameter and the wall thickness of the tube so that the interior tube surface is brought into complete contact with the interior tool. The tube is then subjected to stretch reducing and to final cold drawing over an interior tool.

3 Claims, No Drawings METHOD FOR PRODUCING SEAMLESS TUBES WITH SMALL DIAMETERS The present invention relates to a method for producing seamless tubes with small diameters. The object resides in manufacturing tubes economically with improved interior surfaces.

In producing seamless tubes with small diameters it has been the general practice to start with tubes with a diameter of about 90 to 150 mm and to use stretch reducing. When it is desired to obtain even smaller tube diameters than can be achieved by stretch reducing or if there is desired the quality of cold drawn tubes then the tubes are subsequently subjected to several cold drawings. Such method is the more economical the greater the diameter of the starting tube is, and the fewer cold drawing steps are performed.

This is in contrast to technological experience, according to which the interior surface as a result of radial shiftings of the crystallites in respect to each other becomes rougher by stretch reducing and the number of subsequent cold drawing steps must be increased. It can also result that the roughness formed cannot be remedied satisfactorily by cold drawing.

The present invention is a further development of the described methods for producing seamless tubes with small diameter by stretch reducing and subsequent cold drawing and is characterized in that the starting tube before stretch reducing is subjected to at least one cold drawing with interior tool. By such preceding cold drawing the diameter and the wall thickness are to be decreased in such a degree that the interior tube surface is brought into complete contact with the interior tool.

The decrease of diameter, required for this purpose, amounts to only a few millimeters and can be easily obtained by shaping technology. In this connection, drawing with floating plug is preferred, because the same can be easily performed and allows the processing of considerable tube lengths. At least for smaller diameters of the starting tubes there can be used the plug rod technique.

lt is essential that the tool smoothes and compacts the interior tube surface over the complete tube length. The crystallites directly adjacent to the interior tube surface thereby are left easily shiftable radially in respect to each other and the interior tube surface remains smoother upon stretch reducing. In addition to this quality improvement of the tubes the drawing work is decreased in that the initial cold drawing of the tube replaces several drawings which must otherwise follow the stretch reducing.

According to the present invention it is further proposed that the initially cold drawn tube is heated so as to effect the stretch reducing without forming of scale on the smoothed interior tube surface. Generally it is sufficient to provide rapid tube heating as is achieved e.g. by electric heating with inductive or conductive current transfer. It is possible to use a protective gas with which the tubes are filled during the heating up.

It is preferred to restrict the diameter decrease effected by stretch reducing, both as to its total value and per rolling mill. This applies particularly to tubes heavier than those with normal wall thickness. According to such proposal a tube with e.g. 100 mm exterior diameter after initial cold drawing is to be reduced to no less than about 25 mm, on all applied rolling mills of an ordinary stretch reducing plant.

The production of a cold drawn precision tube with a diameter of 22 mm and a wall thickness of 2 mm is accordingly performed e.g. as follows:

The starting tube has an exterior diameter of 108 mm and a wall thickness of 4.0 mm; it is easier to obtain such dimensions by preceding work than to use a tube of the same diameter and a normal wall thickness.

In the initial cold drawing the tube is drawn over a plug with a diameter of mm to an exterior diameter of 102 mm and a wall thickness of 3.5 mm.

When introduced into stretch reducing plant the tube is heated by means of an induction coil to about 950 C, is reduced in e.g. 20 rolling mills to a diameter of 25 mm and a wall thickness of 2.5 mm, and is then discharged.

After the cooling and the usual pre-treatment the tubes are then processed by a single cold drawing over a plug with a diameter of 18 mm to the desired final dimensions.

What we claim is:

1. Method for producing seamless tubes of small diameter comprising the steps of initially subjecting a tube of larger diameter to at least one cold drawing over an interior to decrease said larger diameter so that the interior tube surface is brought into complete contact with the interior tool;

then stretch reducing the cold drawn tube; and

cold drawing the stretch reduced tube to establish the small diameter.

2. Method according to claim 1 wherein the stretch reducing includes heating the tube so as to avoid formation of scale.

3. Method according to claim 1 wherein the stretch reducing is effected with relatively small decreases of the tube diameter, for example decreasing a tube of mm exterior diameter to no less than about 25 mm. in the stretch reducing operation.

Patent No. Dated May 97 Inventor(s) Ulrich Petersen, 8.1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Page 1, column 2, line 35 (line 3 of claim 1), interior to" should read "interior tool to" Signed and "sealed this 8th day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHEJR,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents DRM PO-1 OSO (10-69)

Claims (3)

1. Method for producing seamless tubes of small diameter comprising the steps of initially subjecting a tube of larger diameter to at least one cold drawing over an interior to decrease said larger diameter so that the interior tube surface is brought into complete contact with the interior tool; then stretch reducing the cold drawn tube; and cold drawing the stretch reduced tube to establish the small diameter.

2. Method according to claim 1 wherein the stretch reducing includes heating the tube so as to avoid formation of scale.

3. Method according to claim 1 wherein the stretch reducing is effected with relatively small decreases of the tube diameter, for example decreasing a tube of 100 mm exterior diameter to no less than about 25 mm. in the stretch reducing operation.