JPS5927704A - Method for controlling wall thickness of shell in mandrel mill for seamless pipe - Google Patents

Abstract

PURPOSE:To roll a seamless pipe so as to have the specified thickness in the longitudinal direction thereof by determining the outside diameter distribution of a mandrel bar from the temp. distribution thereof in the longitudinal direction measured right after the end of rolling the seamless steel pipe and controlling the caliber heights of rolling rolls of the stands with the measured values. CONSTITUTION:The outside diameter of a mandrel bar 3 measured in the longitudinal direction thereof right after the passage of the trailing end thereof through a final stand 1 (#n) upon ending of rolling of a seamless steel pipe (shell) 2 is inputted to a calculator 6. The calculator 6 calculates the spaces between the caliber surfaces of a pair of rolling rolls 1a, 1b and the surface of the 2nd and succeeding bars 3 in each stand in accordance with said measured value. More specifically, said calculator calculates the caliber height between the rolls 1a and 1b in the respective positions in the longitudinal direction of the 2nd and succeeding bars 3 for each of the stands so that the caliber height is kept constant in the longitudinal direction of the 2nd and succeeding bars 3. The calculator 6 controls a controller 6 in accordance with the calculated values, and the controller 6 adjusts an adjuster 4 in accordance with the signal from the calculator 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thickness control layer of a shell in a seamless pipe mandrel mill capable of rolling a seamless pipe so that the wall thickness is constant in the length direction of the seamless pipe.

Conventionally, in the operating method of a seamless pipe mandrel mill, no method has been established for effectively rolling a shell (seamless pipe) so that the wall thickness is constant in the length direction.

The inventors of the present invention conducted research to solve the above-mentioned problems, and as a result, they obtained the following knowledge.

(1) One of the biggest reasons why the wall thickness changes in the length direction of a shell rolled by a mandrel mill is that the outer diameter of the mandrel bar changes non-uniformly during rolling. This can be mentioned. This change in outer diameter is caused by the mandrel bar moving in a relative direction during rolling.
This is caused by non-uniform thermal expansion of the mandrel bar along its length due to heat transfer at the contact surface between the They are the same (mandrel bars used in multiple sizes are of the same standard).

(2) Conventionally, shells were rolled at a constant force and lever height for each stand in a mandrel mill, and as a result, as mentioned in (1), there was an odor during rolling, and the outside diameter of the mandrel bar was reduced. If the caliber changes unevenly along its length, the gap between the caliber surface of the rolling roll and the surface of the mandrel bar will change at each stand.
changes in the length direction of the shell, which leads to changes in the wall thickness of the shell in the length direction.

(3) FIG. 1 shows an example of the measurement results of the temperature distribution in the length direction of the mandrel bar immediately after the shell was IEE-rolled by the mandrel mill. As shown in Figure 1, the temperature distribution in the length direction of the mandrel bar immediately after rolling is
From the tip (on the downstream side in the direction of travel) to the rear end, it simply increases, and then becomes a flat life curve (the outer diameter distribution of the mandrel bar is also similar to this). Therefore, the relationship between the positions of the shell 2 and mandrel bar 3 in a mandrel mill consisting of eight stands (indicated by #1 to #8) and the estimated temperature distribution in the length direction of the mandrel bar 3. As shown in FIG. 2, which shows an example, the temperature distribution in the length direction of the mandrel bar 3 during rolling can be estimated (the outer diameter of the mandrel bar can also be estimated in the length direction).

(4) Therefore, immediately after rolling the shell, measure the temperature distribution in the length direction of the mandrel bar and determine the outer diameter distribution of the mandrel bar from the measurement results, or use an appropriate measuring method to roll the shell. Directly determine the outer diameter distribution of the mandrel bar immediately after finishing, and based on the outer diameter distribution of the mandrel bar obtained in this way, the caliber height of the rolling roll in each stand is made to correspond to the passing position of the mandrel bar from the next time onward. By changing this, the gap between the caliber surface of the rolling roll and the surface of the next and subsequent mandrel bars can be made constant in the length direction of the next and subsequent mandrel bars in each stand, and as a result,
The new shell attached to the next mandrel bar can be rolled so that the wall thickness is constant in the length direction (the shell after passing through the mandrel mill is rolled to a predetermined outer diameter and (shaped into a perfect circle).

This invention was made based on the above knowledge, and the outer diameter of the mandrel bar is measured along its length immediately after the shell has been rolled by a mandrel mill consisting of a plurality of stands. Based on the measured value of the outer diameter along the length direction, the caliber height of the rolling roll in each of at least two final stands of the plurality of stands is made to correspond to the passing position of the mandrel bar from the next time onwards. Modified, in each of at least the last two stands of the first plurality of stands, a gap between the caliber surface of the rolling roll and the surface of the next and subsequent mandrel bars.
The feature is that the Kerschelno wall thickness control method is applied to the seamless mandrel mill, which keeps the wall thickness constant in the length direction.

The present invention will be explained below by way of examples with reference to the drawings.

FIG. 3 is a schematic configuration diagram of a wall thickness control device for implementing the method according to the present invention. In the figure, ■ is a stand that constitutes a seamless mandrel mill, la,
Ib is the rolling roll (with caliber). In the figure, stand 1 of #] and stand l of #n are shown. 2 is a shell (seamless pipe), and shell 2 is
It passes between a pair of rolling rolls la and Jb of each stand 1.

3 is a mandrel bar placed inside the shell 2.

Thus, as the shell 2 passes through each stand 1,
Each stand is rolled to a predetermined thickness by a pair of rolling rolls la and lb and a mandrel bar 3.

4 is the height K between the pair of rolling rolls 1 a + 1 b in each stand 1, as shown in a partial schematic relationship diagram of J pairs of rolling rolls Ia and Jb (7) in FIG. This is a caliber height adjuster connected to the rolling roll 1a for changing the height of the roll.

Each caliber height adjuster 4 is controlled by a caliber height controller 5. 6 is a computing unit. The outer diameter of the mandrel bar 3 immediately after the shell 2 has been rolled and its rear end has passed through the final stand 1 (#n) is determined by an appropriate measuring means (
(not shown) along its length;
This measured value is input to the calculator 6.

The calculator 6 calculates the size of each stand 1 based on the measured value of the outer diameter along the length of the mandrel bar 3 thus input.
, a pair of rolling rolls la.

Ib (7) In order to keep the gap between the caliber surface and the surface of the mandrel bar from the next time constant in the length direction of the mandrel bar from the next time onward, for each stand, The caliber height between the pair of rolling rolls la and Ib at the position is calculated.

Based on the calculated value thus obtained, the calculator 6 controls the caliber height controller 5, and the caliber height controller 5
Each caliber height adjuster 4 is controlled by a signal from the calculator 6. As a result, when rolling a new shell, each caliber height adjuster 4 adjusts the caliber height K between the pair of rolls la and lb on each stand in accordance with the calculated value.

Since the outer diameter of the mandrel bar 3 corresponds to its temperature, the temperature in the length direction of the mandrel bar 3 is measured immediately after passing through the final stand 1 (#4n), and based on this temperature measurement, the mandrel bar is The outer diameter along the length direction of −3 can be determined.

A mandrel mill with eight stands was prepared, with the caliber height of each stand set.

A plurality of mandrel bars having the same standard of 140.5 mm 9' were prepared. Multiple shells from the same lot were prepared.

Then, the first grain shell was rolled while keeping the caliber height unchanged on each stand. Immediately after the rolling was completed, the temperature in the longitudinal direction of the mandrel bar was measured. Based on this temperature measurement, the outer diameter (distribution) of the mandrel bar was determined along its length. An example thereof is shown in FIG.

When rolling the second shell, the caliber height was changed for each stand, corresponding to each position in the length direction of the mandrel bar, based on the thus obtained data on the outer diameter distribution of the mandrel bar. The thickness distribution in the length direction of the second shell obtained as a result is shown by a in FIG. For comparison, the wall thickness distribution in the longitudinal direction of the first-grain shell, which was rolled with the caliber height unchanged on each stand, is already shown in FIG.

It is clear from FIG. 5 that the invention provides a shell whose wall thickness is constant in the longitudinal direction.

As explained below, in this invention, the shell (
Seamless pipes) can be rolled so that the wall thickness is constant in the length direction.

[Brief explanation of the drawing]

Figure 1 shows an example of the measurement results of the temperature distribution in the length direction of the mandrel bar immediately after the shell has been rolled, and Figure 2 shows the positions of the shell and mandrel bar and the temperature distribution of the mandrel bar.
FIG. 3 is a schematic configuration diagram of a wall thickness control device for carrying out the method according to the present invention, and FIG. 4 is a diagram showing an example of the relationship between the FIG. 5 is a diagram showing an example of the outer diameter distribution of the mandrel bar, and FIG. 6 is a diagram showing the wall thickness distribution in the longitudinal direction of the shell. Applicant Nippon Kokan Co., Ltd.

Claims (1)

[Claims] (1) Measure the outer diameter of the mandrel bar along its length immediately after rolling the shell with a mandrel mill consisting of multiple stands, and measure the outer diameter of the mandrel bar along its length. Based on the value, the caliber height of the rolling roll in each of the last two stands among the plurality of stands is changed in accordance with the passing position of the mandrel bar from the next time onwards, A seamless pipe characterized in that in each of at least two final stands, the gap between the caliber surface of the rolling roll and the surface of the next and subsequent mandrel bars is made constant in the length direction of the next and subsequent mandrel bars. The shell thickness control force i in a mandrel mill is large.