JPS6012138B2 - Method for controlling the elongation length of a pipe in a continuous elongation rolling mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for measuring the length ( The present invention relates to a control method for making the length (stretching length) match a target value.

Seamless steel pipes are made by drilling the billet material with a piercer.
This raw tube is subjected to the above-mentioned elongation rolling machine to reduce the wall thickness and outer diameter, and is then squeezed to a target outer diameter using a stretch reducer to produce a finished product. Even if the mill setting conditions (gap between rolls, peripheral speed ratio of rolls, etc.) of each process are kept constant, the length of the finished product varies greatly, and as a result, short tubes that are short of the specified length are now being produced, and the yield is decreasing. This is the cause of the decline. This variation in finished product length is due to the variation that occurred before entering the stretch reducer being carried over as is.

Therefore, the present invention aims to eliminate the variation in the elongation length before the stretch reducer is inserted, that is, in the elongation rolling mill, in order to eliminate the variation in the length of the finished product.

A mandrel mill used as a stretching rolling mill has a large number of stands (usually 6 to 8 stands) arranged in tandem, each having pairs of rolls with oval or circular holes. A hollow Qin tube with a lubricated core metal (also called a mandrel bar) inside the tube is passed sequentially through the multi-stand roll-hole mold, and the cross-sectional area and outer diameter of the tube are gradually reduced. It is something that reduces

After use, the core metal is cooled in a cooling tank, reapplied with lubricant, and then subjected to rolling. Usually, ten or more core metals are used in circulation. There are two types of mandrel mills: the so-called full-floating mandrel mill, in which no force other than the rolling force acts on the core metal during rolling, and the semi-floating mandrel mill, in which the end of the core metal is held by a thrust block and restrained during rolling. , the term "mandrel mill" here includes both of these. Now, as a result of various experiments and research conducted by the present inventors regarding the variation in elongation length in such a mandrel mill, we have found that )
Unavoidable variations in the number of rolls used in the same rolling mill1
It has been found that the variation in the outer diameter of the core metal of a set has a dominant influence on the above-mentioned variation, and therefore, it is possible to grasp the occurrence of variation by grasping the changes in these two conditions.

That is, for a plain tube motorcycle, if other rolling conditions are constant, the greater the Qin tube unit weight, the greater the elongation length.

However, in this case, "extended length/raw tube vehicle" (in other words,
The average cross-sectional loss after stretching and rolling remains approximately constant. In addition, even if the nominal dimensions of the core metal are the same, there is an unavoidable size of the outer diameter due to manufacturing errors and differences in the degree of wear caused by use. thickness) becomes smaller.On the contrary, when the outer diameter is small, the opposite is true.
From these facts, it can be said that the variation in the average cross-sectional defect of the tube after elongation and rolling occurs almost exclusively due to the difference in the outer diameter of the core bar under the same mill setting conditions. On the other hand, there is a relationship between this average cross-sectional area and the elongated length (1), as shown by A = weight, W: Sosugane monocycle p: specific gravity, and the elongated length (1) To make it constant, the average cross-sectional area wind can be changed depending on the Sosuga motorcycle (W).

As a method of changing the average cross-sectional density, there is a method of adjusting the circumferential speed of the rolls of each stand of the elongation rolling mill to change the stress in the cross-section direction acting on the tube during rolling. In other words, Figure 1 shows the roll circumferential speed of each stand in a mandrel mill as a circumferential speed ratio with respect to the first stand. Naturally, the cross-sectional area of the tube decreases as you reach the rear stands. However, since the pipe velocity increases accordingly,
The roll circumferential speed ratio is usually set to gradually increase depending on conditions such as the gap between the rolls. Curve A and the end indicate roll circumferential speed ratios with different speed gradients. If other conditions are constant, rolling with curve A will result in a smaller average cross-sectional profile than rolling with curved mouth. That is, the average cross-sectional roughness is changed by adjusting the roll peripheral speed ratio (x) as a so-called function as shown in the figure. Therefore, for each of the above-mentioned core metals, the above-mentioned roll peripheral speed ratio (X) during rolling is determined in advance.
If the relationship between and the average cross-sectional area after rolling is determined experimentally, then during actual rolling, the average cross-sectional area can be adjusted by adjusting the roll peripheral speed ratio (x) based on the above relationship for the core used. It is possible to set debt to a desired value.

If it is possible to arbitrarily select the average cross-sectional area wind in this way, then the actual measurement value of the raw tube wheel brought in during actual rolling (
Predictively calculate the average cross-sectional area (A,) when the target elongation length (1,) is set by filling in the above formula {1) from W,), and calculate the average cross-sectional area (A,) in actual rolling by using this value (A, ,), thereby making it possible to set the elongation length to the target value (1,).In other words, the present invention allows the elongation length to match the target value (1,). Based on the relationship between the roll circumferential speed ratio (×) during rolling and the average cross-sectional area of the pipe after rolling, which was determined experimentally in advance, the average cross-sectional area of the pipe during rolling is calculated as follows: The feature is that the circumferential speed ratio (×) of the rolls is adjusted so that the cross-sectional area (A,) is obtained when the rolled raw tube is rolled to the target elongation length (1.).

Specifically, experimental rolling is performed for each core metal in advance under the same rolling conditions as in actual rolling in an elongation rolling mill, and the roll circumferential speed ratio (x) as a function of all stands is calculated, for example, from the final stand roll. Peripheral speed ratio (Xn
) and define the relationship between this and the average cross-sectional area.

In normal use, this relationship can be expressed as a linear relationship as shown in Figure 2, and even if the core metals are different, the slope A/xn will be approximately the same (as shown in Figure 2). (as shown by the dashed line). During actual rolling, the weight of the rolled tube is actually measured, and from this measured value (W,), the average cross-sectional area when the Qin tube is rolled to the target elongation length (1,) using the formula {1). (
A,) is calculated.

Next, based on the above relationship regarding the core metal used in the rolling, the roll circumferential speed ratio (
Find Xn,). Actual rolling is at this circumferential speed ratio (×n.)
The roll circumferential speed ratio (X) (
function) to control the number of rotations of each stand roll. In addition, the external variation of the core metal used in practical use is usually in the range of +0.1% to -0.5% of the nominal dimension, and even if the variation in the unit weight of the raw pipe is taken into account, it is difficult to adjust the roll circumferential speed ratio. Since the range can be kept within 10%, defects in the rolled tube can be avoided.

Next, an example of control based on the method of the present invention will be explained.
Stretch rolling was performed in an 8-stand mandrel mill under the following conditions.

'1} Nominal dimensions of the raw pipe (弽) Outer diameter 190 x Wall thickness 16 x Length 8500 (2i Nominal dimensions of the pipe after rolling (Rib) Outer diameter 158 x Wall thickness 6 x Length 26000 {3} Mandrel bar At this time, according to the present invention, the roll circumferential speed ratio (X) was controlled based on the following experimental formula derived from the results of experimental rolling conducted in advance (rolling A).

t=65.90-0.3927d-1.9355Xn However, t: Average cross-sectional area of the pipe after rolling Wall thickness d corresponding to the wind:
Mandrel bar outer diameter x n: Roll circumferential speed ratio of final stand This experimental formula is based on 15 (× n
) and the average cross-sectional area ■ as the outer diameter of the mandrel bar (d)
The actual measured values are combined into one formula.

For comparison, rolling was performed under the same conditions as above while keeping the roll circumferential speed ratio constant (rolling B).

Table 1 shows the results of an investigation into the variation in elongation length of the tubes obtained by rolling (1) and bending. As is clear from the above table of Table 1, by controlling according to the present invention, the variation in elongation length during stretching and rolling is almost eliminated, and the elongation length (appointed product length) in the stretch reducer is then reduced.
It becomes possible to substantially match the target value, and the manufacturing yield of seamless steel pipes can be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the stand number and roll circumferential speed ratio in a mandrel mill, and Fig. 2 is an example of the relationship between the roll circumferential speed ratio (Xn) used in the present invention and the average cross-sectional area of the pipe after rolling. shows. 1 screen screen and 2 screen screens

Claims (1)

[Claims] 1. A rolling method in which a large number of stands equipped with pairs of grooved rolls are arranged in tandem, and the raw pipe is sequentially passed between the pairs of rolls of the multiple stands while the inner surface of the pipe is regulated by a metal core to gradually reduce the outer diameter and wall thickness of the pipe. In a continuous drawing machine that performs processing, the relationship between the roll circumferential speed ratio during rolling and the average cross-sectional area of the tube after rolling is experimentally determined for each of the many core metals that are used in circulation. During actual rolling, based on this relationship, the roll circumferential speed ratio is adjusted so that the cross-sectional area of the pipe after rolling is the same as the cross-sectional area when the raw pipe is rolled to the target length. A method for controlling the elongation length of a pipe in a continuous elongation rolling mill, characterized by adjusting the elongation length of a pipe in a continuous elongation rolling mill.