JPS5853320A - Controlling method for wall thickness in mandrel mill - Google Patents

Abstract

PURPOSE:To accurately control the wall thickness of a material with a relatively simple method, by controlling the relative speed of the speed of a mandrel and the rolling speed of a pipe-shaped material, and changing the rolling speed, in rolling the material. CONSTITUTION:A mandrel bar 2 is inserted to the inside of a pipe-shaped material 1, which is rolled through plural rolling stands equipped with grooved rolls 3. In this case, the wall thickness of the material 1 is controlled while controlling the relative speed of the speed of a mandrel bar 2 and a rolling speed of the material 1 in rolling. The controlling of the relative speed of the material 1 and the mandrel bar 2, that is in other words, the controlling of rolling load is made possible by the number of revolutions of the roll and a moving speed of the bar 2. Accordingly the change of rolling load is related to the value of a mill rigidity, and then the wall thickness is controlled because the change of the wall thickness depends on the mill rigidity. Further, the speed of the material 1 is calculated from the relation between the peripheral speed of the roll and a forward slip, on the other hand, the speed of the material 2 is easily measured from a driving shaft because the bar 2 moves at a constant speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling wall thickness of a mandrel mill.

As shown in FIG. 1, the conventional rolling method in a mandrel mill involves passing a mandrel bar 2 inside a tubular material 1, and rolling a grooved roll 3 together with the tubular material 1 without any restraint. This method involves rolling using multiple rolling stands, and is called a full-float mandrel mill.

In rolling by this full-float mandrel mill method, as shown in the example of 3-stand continuous rolling in Figure 2, the relative speed between the speed of the tubular material and the speed of the mandrel bar changes, and the Punching has the disadvantage that it sometimes tends to produce defects in wall thickness or shape.

As a method to alleviate these drawbacks, methods of restraining the mandrel bar or actively moving the mandrel bar have been considered.As shown in FIG. There is a method in which the material is flowed in the rolling direction while being restrained, and a method in which the mandrel bar 2 is pulled in the opposite direction to the rolling direction of the material by a mandrel bar drive device 7, as shown in FIG. These methods are superior to the full-float mandrel mill method because they eliminate variations in the relative velocity between the material speed and the mandrel bar speed, eliminating defects in wall thickness and shape. However, due to friction between the material and the mandrel bar, stable operation is difficult to achieve, and a highly accurate method for controlling wall thickness has not been considered.

The present invention provides a mandrel mill that uses a relatively simple method of detecting the rolling speed of the material and the speed of the mandrel bar to control the wall thickness of the material with high accuracy when the mandrel bar is restrained or actively moved. A method for controlling wall thickness is provided.

In a mandrel mill, the rolling load depends on the deformation resistance of the material, the projected contact area, etc., as in normal plate rolling, but the mandrel bar is a unique element of the mandrel mill.
It depends on how the mandrel bar is operated and the speed of movement of the mandrel bar.

FIG. 5 shows an example of changes in rolling load depending on the bar operation method. Keeping the roll rotation speed and roll gap constant,
Mandrel bar operation method: full float method B: Mandrel bar is flown in the rolling direction while restrained by a person
These are the results of three methods, method C, in which a mandrel bar is pulled in the opposite direction to the rolling direction, and differences can be seen depending on the mandrel bar operating method. In other words, this result means that a difference in rolling load occurs due to a difference in the mandrel bar moving speed, and when the results shown in FIG. 5 are arranged based on the mandrel bar moving speed, FIG. 6 is obtained. Here, a positive value represents a moving speed in the rolling direction, and a negative value represents a moving speed in a direction opposite to the rolling direction. The above results are for the case where the roll rotation speed is constant,
Strictly speaking, it is organized by the rolling speed of the material and the moving speed of the mandrel bar, but for convenience it can be organized by the peripheral speed of the roll and the speed of the mandrel bar. Figure 7 shows the ratio of the mandrel bar speed to the peripheral speed of the roll. An example of the relationship between rolling loads is shown. As a result of the above, it is possible to control the rolling load by controlling the relative speed between the material and the mandrel bar, in other words, by the roll rotation speed and the mandrel bar movement speed, and the change in rolling load is related to the mill rigidity. The wall thickness changes depending on the mill stiffness and can be controlled.

The speed of the material can be calculated from the relationship between the peripheral speed of the roll and the advance rate, or there is also a method of directly detecting the speed of the material based on the time it takes to pass between the detectors of two HMDs.

Furthermore, in the method of detecting the mandrel bar speed, since the bar is moving at a constant speed, it can be easily measured from the drive shaft.

In this way, the value of the relative velocity between the measured material and the mandrel bar was confirmed in advance.

If the rolling load fluctuates from the specified rolling load due to the relationship between the rolling load and the relative speed of the material and mandrel bar, the rolling load can be returned to the original load value by changing the roll rotation speed, and the rolling load can be kept constant at all times, preventing fluctuations in wall thickness. It is also clear that the mandrel bar speed may be varied as a method of varying the relative velocity between the material and the mandrel bar.

Figure 8 summarizes the above.

Furthermore, although the present invention allows control to keep the rolling load constant, it is also possible to actively change the rolling load and change the roll gap by changing the relative speed between the material and the mandrel bar. It is also possible to roll a pipe with a minute thickness distribution in the rolling direction.

As described above, according to the present invention, in mandrel rolling, the results can be obtained by a relatively simple method of detecting the rolling speed of the tubular material and the mandrel bar speed. By keeping the rolling load constant by changing the relative speed between the material and the mandrel bar, variations in wall thickness and shape can be prevented, making it possible to obtain products of superior quality than conventional methods.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an outline of the full float method, which is one of the rolling methods of a mandrel mill, and Figure 2 is an example of the case of 3 stands when masonry rolling is performed using the full float method, and the material tip speed is 4. , mandrel bar speed 5, material tip speed 6
Figure 3 is a diagram showing an outline of a method of rolling in the rolling direction while restraining the mandrel bar, which is one of the rolling methods of a mandrel mill. Figure 5 is a diagram showing the relationship between mandrel bar operation method and rolling load, and Figure 6 is a diagram showing the relationship between mandrel bar movement speed and rolling force. FIG. 7 is a diagram showing an example of the relationship between the mandrel bar speed and the roll circumferential speed and the rolling load, and FIG. 8 is a diagram showing the flow of the present invention. 1. Tubular material 2. Mandrel bar
3... Couplet roll 7... Mandrel bar drive device (7317) Agent Patent attorney Noriyuki Chika (and 1 other person) (7) Figure 1 Figure 2 No. 1 = Nobu H4〒Ma Fig. 5 Fig. 6-〇 Mantle Ruba Kukukin Shallow Fig. 7 Fig. 8

Claims (1)

[Claims] In mandrel mill rolling, in which a mandrel bar is passed through the inside of a tubular material and the tubular material is rolled through multiple rolling stands equipped with grooved rolls, the relative speed of the mandrel bar speed during rolling and the rolling speed of the tubular material is determined. A method for controlling the wall thickness of a mandrel mill, characterized by controlling the wall thickness of a tubular material by changing the rolling load.