JPS6363282B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preventing thickening of the tube tip and rear end of the product when manufacturing small diameter circular tubes using a reduction rolling method. The detailed description of the present invention will be given below based on a stretch reducer rolling mill. For example, when rolling a seamless steel pipe, a stretch reducer is installed as the final step after a plug mill, mandrel mill, or semi-floating mandrel mill, and then through a reheating furnace. The rolling equipment consists of several to 20 highly rigid rolling stands each consisting of 2 to 4 rolls.
It has a structure in which several units are arranged in series, and the outer diameter of the raw tube is rolled down by rolls, and the wall thickness is rolled to a predetermined dimension by tension between stands to produce finished products. 1st
The figure shows the principle of the stretch reducer. That is, the angle between the rotational axes and the plane perpendicular to the rolling direction is 180°, 120°, or 90°.
This is a rolling method in which the outer diameter of the tube 1 is reduced by four rolls 2, 2', and the wall thickness is reduced by applying tension T to the tube between rolling mills. When rolling a tube using such a stretch reducer, there are the following problems. In other words, this is a phenomenon in which the wall thickness near the end of the tube becomes thicker than the center. The reason why such a phenomenon occurs can be explained as follows. In a stretch reducer, the wall thickness is adjusted by the tension between the stands, but in actual rolling, tension is not generated until the tip and rear end of the raw tube are placed on the next stand. . In other words, this tension is different between the state in which the tube is rolled by all the stands and the state in which the end of the tube passes through the stand, and the phenomenon of thickening appears as a difference in the deformation of the tube. This increased thickness near the end of the tube does not meet the dimensional specifications and is therefore discarded, which poses a major problem in terms of product yield. The present invention was made in order to solve the problem of thickening the tube end and to improve the yield. That is, an object of the present invention is to maintain the tension during rolling so that the tube is always rolled at all stands, thereby preventing the phenomenon of thickening. The gist of the present invention is that in a pipe rolling method, when a metal tube is subjected to reduction rolling in a tube reduction rolling mill row in which a plurality of rolling stands are arranged in series, the metal tube is rolled in the longitudinal direction at the front stage of the rolling mill row. is to connect to. The present invention will be explained in detail below. When performing reduction rolling with tension applied to the tube, fluctuations in the tension value applied to the tube, i.e., the fact that the tip and rear ends of the tube are not bitten by the rolling rolls of two or more rolling mills at the same time. In order to prevent the tube from becoming unsuitable (too thick) due to being rolled under no tension, it is necessary to lengthen the tube when feeding it to the stretch reducer. It is necessary to sequentially join them in the horizontal direction to eliminate unsteady parts related to tension application. Welding, pressure welding, forge welding, wire explosion welding, etc. can be considered as methods for joining pipes to continuously roll them, but in a stretch reducer, tension is applied to the pipes, so the joints are The strength must be sufficient to withstand the tension applied during the rolling process. Furthermore, in order to carry out rolling continuously, it is necessary to prevent the joining time of the tubes from becoming a factor that changes the rolling speed. In order to solve the above-mentioned problems, the inventors completed the present invention as a result of conducting research on joining the caudal end of a tube. First, when connecting pipes longitudinally by welding or pressure welding, the wall thickness at the end of the pipe is made thicker than that at the center of the length in advance to increase the cross-sectional area. Therefore, it is characterized by increasing the axial expansion tension at the joint to prevent breakage at the joint. Second, after joining the pipes in the length direction, the joint is cooled down to a temperature of 50 to 200°C below the original pipe temperature.
The tensile strength of the joint is increased by decreasing the tensile strength of the joint. Here, when lowering the temperature of the joint than the base pipe temperature, the temperature difference is 50~
The reason why the temperature was limited to 200°C is that below 50°C, there is almost no effect on increasing the tensile strength. On the other hand, 200
If the temperature difference exceeds .degree. C., the deformation resistance of the joint becomes too high, causing problems in terms of roll life. Therefore, when lowering the temperature of the joint, the temperature should be kept within a range of 50 to 200°C lower than the temperature of the raw pipe. To lower the temperature of the joint, water or an inert gas is injected into the joint to cool it, and the joint is cooled by contact with the tool. Third, after joining the tubes, the outer diameter of that part is
For example, by using a press that displaces the tool in the radial direction of the pipe, the pipe is reduced to the hole diameter of the first stand or less, increasing the wall thickness of the pipe, and lowering the temperature of the joint to a level 50 to 200°C lower than the original pipe temperature. urge Fourthly, after the tail end of the leading pipe and the head end of the trailing pipe are fitted together, they are joined by pressing in the pipe diameter direction using a press or the like. This invention can be implemented by using the first to third technical matters described above alone or in appropriate combinations. A more detailed explanation will be given below based on preferred embodiments. FIG. 3 shows one of the apparatuses for carrying out the invention. In FIG. 3, 6 is a tube being rolled by a stretch reducer, and 7 is a blank tube to be rolled next. 8 is a joining device, such as a welding machine or a crimping device shown in FIG. The joining device 8 is movable in synchronization with the axial movement speed of the tubes 6 and 7, and has a supply means and a nozzle for injecting water and inert gas to the joining portion. 9
is a stretch reducer, and for example, the angle between its rotation axes in a plane perpendicular to the rolling direction is
It consists of more than 20 rolling mills with three rolling rolls of 120°. A reheating furnace 10 reheats the tube whose temperature has dropped during the rolling process. To explain the operation of the apparatus configured as described above, the tube reheated in the reheating furnace 10 is supplied to the stretch reducer 9, and tension is applied between the rolling mills in the stretch reducer. Processed to reduce wall thickness and outer diameter. The rear end of the leading pipe 6 and the tip of the trailing pipe are connected to a joining device 8
The joints are brought into axial contact and joined, and then water and inert gas are injected into the joints, and the joints are cooled to a temperature 50 to 200°C lower than that of the stationary part.
The joining and cooling of the tubes is performed while the joining device 8 moves in synchronization with the moving speed of the tubes. In this way, the joint, which has been given sufficient strength, is fed into the stretch reducer 9. After the tubes are joined, the outside diameter of the part can be reduced and the wall thickness increased using the apparatus shown in FIG. In FIG. 4, reference numeral 11 indicates a pipe that is a joined portion, and reference numeral 12 indicates a press. The press 12 is configured to move forward and backward in the radial direction of the tube, and when displaced in the direction of the arrow shown in FIG. 4, the outer diameter of that portion of the tube is reduced. This press 12 is arranged after the above-mentioned joining device 8, and is configured to be movable in synchronization with the movement of the tubes like the joining device 8. Still another method is to, after joining the pipes, roll or press the joined portion to a diameter smaller than the first stand caliber to prevent breakage. This has the effect of firstly lowering the material temperature through contact between the tool and the material and increasing the strength of the joint against tension, and secondly, when the joint passes through the first stand. , rolling deformation by rolls is not performed, and in normal rolling, the rolling force by the rolls is deformed by the forward tension, and the outer diameter and wall thickness are reduced.
Although the cross-sectional area is reduced, since only tension is applied to this part, the reduction in cross-sectional area is minimal.As a result, only this part has a larger cross-sectional area than other parts, and the breaking strength is lower under the same tension. is increased, and subsequent breakage can be prevented until the final stand. Next, a description will be given of means for increasing the wall thickness of the end portions of the tubes to be joined prior to joining the pipes.
Figure 2 shows the device. In FIG. 2, reference numeral 3 indicates tube end portions 4 and 5, which are tools. The tool 4 has a cylindrical shape, which may be divided in the circumferential direction. By displacing the tool 5 axially towards the tool 4, the wall thickness of the tube end 3 is increased. FIG. 5 shows a process in which the tail end of the leading tube and the head end of the trailing tube are fitted together and then joined by pressing the fitting portion in the tube diameter direction using a press or the like. In FIG. 5, 6 is a leading pipe and 7 is a trailing pipe. Reference numeral 13 denotes a press which crimps the fitting portions of the leading pipe and trailing pipe in the diametrical direction. The outer diameter of the tail end of the leading pipe 6 is reduced by, for example, a press shown in FIG. The inner diameter of the head end of the trailing tube 7 is reduced to a size that allows it to fit into the outer diameter of the tail end of the leading tube 6 using a press as shown in FIG. The tail end of the trailing leading pipe 6 and the head end of the trailing pipe 7 are fitted together and further pressed together from above and below by a press 13 in the embodiment shown in FIG. Next, embodiments of the present invention will be described. This embodiment relates to the case shown in FIG. 5, in which steel pipes are connected longitudinally by the above-mentioned joining means. Table 1 shows the specifications of the steel pipe at that time.

[Table] The steel pipe was heated to 950°C in a reheating furnace, and then pressed using the press shown in Figure 4 so that the tail end of the leading pipe and the head end of the trailing pipe could be fitted together, and by the rolls of the stretching reducer. The outer diameter was reduced so as not to be subjected to stretching action. After the tail end of the leading tube and the head end of the trailing tube were fitted together, the joint was crimped using a press as shown in FIG. The steel pipes were thus endlessly rolled and joined one after the other. FIG. 6 and FIG. 7 show the wall thickness of the tube end according to the tube size level, with respect to the results of the prior art and the above-described embodiment in which the present invention was implemented. As is clear from Fig. 6 and Fig. 7, when comparing the amount of truncation when the allowable range of wall thickness increase at the pipe end is set to 12.5%, according to the present invention, it is significantly reduced compared to that in the conventional technology. are doing. Yield loss was halved for both tube sizes 25A and 40A. Since the present invention is constructed and operated as described above, it is possible to significantly reduce the yield loss caused by the wall thickness of the tube.

[Brief explanation of drawings]

Figure 1 is a longitudinal sectional view for explaining the principle of the stretch reducer, Figure 2 is a diagram showing an example of how to thicken the tube end, and Figure 3 is a diagram showing an example of how to thicken the tube end. Fig. 4 is a diagram showing an example of a press when squeezing the joint, Fig. 5 is a progress diagram of the processing situation when the pipe end is processed in advance, and both ends are inserted and then crimped and joined. 6 and 7 are diagrams showing a comparison of wall thickness distribution according to the conventional method and the present invention. 1...Main pipe, 2,2'...Roll, 3...Pipe end, 4,
4', 5...Tool, 6...Main pipe being rolled, 7...Following stock pipe, 8...Welding machine with a cooling device, 9...Rolling stand, 10...Reheating furnace, 11...Joint part of the stock pipe, 1
2,13...Press.

Claims (1)

[Scope of Claims] 1. When a metal tube is subjected to reduction rolling by a tube reduction rolling mill row in which a plurality of rolling stands are arranged in series, the wall thickness of the longitudinal end of the metal tube is thickened in advance. A tube rolling method characterized in that the metal tubes are then connected in the length direction by welding or pressure welding to perform reduction rolling. 2. When reducing and rolling a metal tube using a pipe reduction rolling mill line with multiple rolling stands arranged in series, the wall thickness of the lengthwise end of the metal tube is increased in advance, and then welding or pressure welding is performed. A tube rolling method characterized in that the metal tubes are connected in the length direction by a method, and the temperature of the connected portion is lowered by 50 to 200 degrees Celsius than that of other portions, and then reduction rolling is performed. Law. 3. When reducing and rolling metal tubes using a tube reducing mill row with multiple rolling stands arranged in series, the walls of the longitudinal ends of the metal tubes are made thicker in advance and then welded or pressure welded. to connect the metal tubes in the length direction, and perform a drawing process to make the outer diameter of the connection part smaller than the caliber diameter in the first stand of the reduction rolling mill row, and then perform reduction rolling. A pipe rolling method characterized by the following. 4. When reducing and rolling a metal tube using a line of tube reducing mills in which a plurality of rolling stands are arranged in series, the outer diameter of the longitudinal end of the metal tube is set to be smaller than that of the longitudinal center. The rear end of the small leading metal tube and the tip of the trailing metal tube are machined so that they fit together, and the rear end of the leading metal tube and the trailing metal tube are crimped in the diameter direction of the fitted rear tube to lengthen the metal tube. A tube rolling method characterized in that the tubes are connected in the horizontal direction and the reduction rolling is performed. 5. When reducing and rolling a metal tube using a tube reduction rolling mill row with a plurality of rolling stands arranged in series, the outer diameter of the longitudinal end of the metal tube should be made smaller than that of the longitudinal center. The rear end of the small leading metal tube and the tip of the trailing metal tube are machined so that they fit together, and the rear end of the leading metal tube and the trailing metal tube are crimped in the diameter direction of the fitted rear tube to lengthen the metal tube. 1. A method of rolling tubes, characterized in that the tubes are connected in the transverse direction, and the temperature of the connecting portion is lowered by 50 to 200° C. than that of other portions, and then reduction rolling is performed. 6. When reducing and rolling a metal tube using a tube reduction rolling mill row with a plurality of rolling stands arranged in series, the outer diameter of the lengthwise end of the metal tube should be made smaller than that of the lengthwise center. The rear end of the small leading metal tube and the tip of the trailing metal tube are machined so that they fit together, and the rear end of the leading metal tube and the trailing metal tube are crimped in the diameter direction of the fitted rear tube to lengthen the metal tube. In addition to connecting in the horizontal direction,
A tube rolling method characterized in that after performing a drawing process to make the outer diameter of the connection part smaller than the caliber diameter in a first stand of a row of reduction rolling mills, reduction rolling is performed.