JP2001087803A - Method for monitoring rolling condition of mandrel mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for automating a series of operations including the examination of the presence and absence of the generation of sticking of a bar and means of how to restore it. SOLUTION: Shell temperature on the outlet side of a mandrel mill is measured with thermometers installed on the outlet side of the mandrel mill, the temperature distribution in the longitudinal direction of a shell is determined and, from the relationship between the temperature distribution and operating guidance which is previovsly obtained by the obtained temperature distrtbution, the tension of the mandrel mill and/or a sizer is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring a rolling state of a mandrel mill and a method for rolling a mandrel mill using the same.

[0002]

2. Description of the Related Art FIG. 1 is an explanatory view of a process for manufacturing a seamless steel pipe.
In the piercing step 14, piercing is performed on the heated steel slab 13 by piercing and rolling using the mandrel bar 16 in the piercer 15. The perforated steel slab is then reduced in thickness by a mandrel mill 19 in a pipe making step 18, pipe making is performed, and finally in step 20 a mandrel bar 22 inserted inside by a sizer 21 also serving as an extractor is piped. The outer diameter is rolled to a predetermined size while being pulled out from the body, that is, the shell 23.

The mandrel mill 19 usually has several stands of one stand and two rolls (5 to 8 stands), and the odd stand and the even stand are installed so as to be 90 ° opposite to each other. Mandrel bar
This is performed with the 22 inserted, and the mandrel bar 22 and roll
Due to the gap formed between the steel sheet 24 and the steel sheet 24, the wall thickness is gradually reduced and the steel sheet is continuously rolled.

[0004] On the other hand, a sizer 21 also serving as an extractor
Usually, 5 to 12 stands are installed, and the first half acts to pull out the mandrel bar 22, and the outer diameter is finished to a predetermined size by the finishing stand at the second stage.

[0005] In such a mandrel mill, the step of removing the mandrel bar from the shell (burst ripping) is an important step, and there is a risk that the operation may be stopped due to stripping failure.

Further, for example, when a phenomenon in which the shell comes into close contact with the mandrel bar due to excessive tension between the stands (hereinafter, referred to as “bar tension”) occurs, uneven wall thickness occurs due to a temperature difference in the shell circumferential direction, and product dimensions are reduced. This leads to a decrease in accuracy.

Conventionally, in order to prevent such sticking of the bar and appropriately manage the burst ripping timing, it has been conventionally performed based on experience while visually observing the temperature distribution of the shell visually by an operation operator.

For example, when the shell temperature is lowered, it is determined that heat is excessively removed from the bar, and the tension between the stands of the mandrel mill is changed (by changing the rotation speed of the specific stand and the tension between the stands to the compression side). The operation prevents the shell and the bar from sticking together).

Japanese Unexamined Patent Publication No. 1-284407 discloses a method for checking a change in the current value of a roll drive motor of a sizer, but only for checking whether or not bar sticking has occurred. Is not disclosed.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention not only to check for occurrence of bar sticking, but also to recover bar sticking once it has occurred. To provide such means. It is a further object of the present invention to provide means capable of automating such a series of operations.

[0011]

The inventor of the present invention has conducted various studies on means for solving such problems, and in order to operate the mandrel mill in a stable state, at least two shell temperatures in the circumferential direction are required. It is important to accurately measure the rolling state of the mandrel mill from the shell temperature at that time.

Further, when it is found that the rolling state is unstable due to the temperature deviation, whether the temperature at that time is above or below the reference temperature range depends on whether the temperature is outside or below the reference temperature range. It has been found that there is a difference in means for recovering an unstable rolling state.

That is, the present invention measures the shell temperature on the mandrel outlet side at least at two places in the circumferential direction by using a thermometer installed on the mandrel mill outlet side,
A method for monitoring a rolling state of a mandrel mill, comprising determining a temperature distribution in a longitudinal direction of a shell and estimating a rolling state of a mandrel mill from the obtained temperature distribution.

From another aspect, the present invention measures the shell temperature on the mandrel outlet side at least at two locations in the circumferential direction by a thermometer installed on the outlet side of the mandrel mill, and determines the temperature distribution in the longitudinal direction of the shell. A mandrel mill rolling method characterized by performing tension adjustment of a mandrel mill and / or a sizer from a relationship between a temperature distribution obtained in advance and an operation guidance based on the obtained and obtained temperature distribution.

[0015]

2 (a) to 2 (c) show an outline of an apparatus for carrying out the present invention. FIG. 2 (a) is a schematic sectional view of the apparatus, and FIG. FIG. 2A is a sectional view taken along the line Z-Z in FIG. 2A, and FIG. 2C is a sectional view taken along the line YY in FIG. 2A.

As shown in FIG. 2A, the mandrel bar 22
The shell 23 sent to the mandrel mill 19 is rolled to a predetermined pipe thickness by a mandrel roll 24, and two thermometers 30 and 32 provided on the outlet side perform measurement, and the surface temperature is measured. Is determined.

In the illustrated example, two thermometers for measuring the shell temperature at the outlet side of the mandrel mill are provided, but more thermometers may be provided in some cases. However, under normal conditions, it is sufficient to arrange two thermometers in the circumferential direction as in this example. That is, both thermometers 30 and 32 are installed at a position inclined by 45 ° with respect to the perpendicular to the central axis.
See FIG. 2 (b).

As shown in FIG. 2 (c), the mandrel roll 24 is installed at a position where the two rolls face each other and are inclined at 45 ° (or 135 °) with respect to a vertical line toward the center axis, and a mandrel mill 24 is provided. The direction of the flange of the 19 last stand matches the position of one thermometer 32. The other thermometer 30 is installed so as to coincide with the roll groove bottom position of the final stand of the mandrel mill 19.

The measurement is performed continuously, and the temperature distribution in the longitudinal direction of the shell by each thermometer is recorded.

The thermometer at this time is a radiation thermometer in the illustrated example, but is not particularly limited.

The shell on which the measurement was performed is the sizer 21 of the next process.
, And supplied to the sizer 21, the mandrel bar is pulled out of the shell.

As described above, the thermometer installed on the outlet side of the mandrel mill monitors the sticking of the bar to monitor the rolling state of the mandrel mill. When the sticking of the bar occurs, the bar is used as a recovery measure. Appropriate adjustment of the tension between the stands of the mandrel mill or the tension between the mandrel mill stand and the sizer stand, which is located in the direction of the bottom of the roll groove, is detected.

Hereinafter, a monitoring method according to the present invention and a recovery measure with a bar will be described. In the present invention, first, it is necessary to accurately measure the temperature of the shell surface.

<Signal Processing of Thermometer> FIG. 3 is a graph of thermometer signal processing showing the temperature distribution in the longitudinal direction of the shell surface temperature actually measured at this time. The upper part is the primitive data, and the middle part is the moving average. The subsequent data and the lower row show the pattern determination temperatures in the form of graphs. This is the temperature distribution in the longitudinal direction of the running shell, and one is obtained for each thermometer. In the present invention, if two thermometers are provided, at least two such graphs are obtained.

As described above, since the temperatures measured by the two thermometers each include noise in this embodiment, the noise is removed by taking a moving average by the following method.

[0026]

(Equation 1)

N: number of sampling points L: number of moving averages Tm: moving average temperature T: sampling temperature Data for temperature pattern determination is obtained from the data obtained from the above moving average by the following processing.

In the following example, the processing for temperature determination is 4
Although the process is performed based on the difference between the temperature at the point and the current temperature, the process is the same for an arbitrary number of points. Pattern judgment temperature Tc (i) = Tm (i + 4) −Tm (i) (2) Expression Tc: pattern judgment temperature.

<Pattern Classification> According to the knowledge of the present inventors, when bar sticking occurs, the temperature pattern thus obtained can be formed into several patterns, and such a pattern must be created in advance. Can be. In this example, when bar sticking occurs, the thermometer pattern obtained by the thermometer signal processing can be classified into three patterns as shown in FIGS. 4 (a) to 4 (c).

I) Pattern A: a pattern in which the temperature drops during rolling and then recovers ii) Pattern B: a pattern in which the temperature drops before the end of rolling iii) Pattern C: a pattern in which the temperature drops immediately after the start of rolling The above pattern is determined based on whether or not it is within a certain threshold (Lu: upper limit, LL: lower limit in the figure) from the temperature distribution of the pattern determination temperature (Tc).

When the rolling situation becomes unstable, such a pattern is obtained for each temperature distribution obtained by one thermometer. However, the mandrel mill stand
As mentioned earlier, the odd and even stands are installed at 90 ° to each other with respect to the central axis, so one thermometer can only grasp the rolling instability of the stand in one direction only. In order to grasp the instability of the stand, it cannot be said that one stand alone is sufficient, and preferably at least two stand.

[0032]

[Table 1]

Table 1 shows each pattern of the temperature distribution in the longitudinal direction when the above-mentioned rolling condition becomes unstable. When the bar is stuck, one of these patterns is taken.

<Rolling State Monitoring Method> The rolling state of the mandrel mill can be monitored based on the above-mentioned temperature pattern. The monitoring method is described below.

First, when a shell low temperature is detected by the thermometer 32 corresponding to the flange direction of the last stand, the flange direction of the last stand of the mandrel mill, that is, the roll groove bottom direction of the stand one stage upstream from the last stand and the mandrel. The heat is removed by the close contact of the bar.

On the other hand, when low temperature of the shell is detected by the thermometer 30, the mandrel bar is in close contact with the last stand of the mandrel mill, two steps upstream of the last stand (final stand-two steps), and the bottom of the roll groove on the stand side. The heat has been removed.

Bar sticking can be detected by detecting a low temperature with a thermometer. Based on the result, proper rolling can be continued by adjusting the tension between the stands of the mandrel mill (correcting the rotation speed of each stand). Becomes

The following table shows the relationship between the distribution pattern of the shell surface temperature measured by the thermometer and the operation guidance.
Such a relationship is created in advance from past operation results. In Table 2, the temperature was measured with two thermometers (32, 30) on a mandrel mill consisting of an odd-numbered stand, and the temperature distribution patterns of the two thermometers were combined. Basically, the tension of the stand corresponding to the roll groove bottom position is adjusted.

The relationship between the temperature distribution pattern and the operation guidance in Table 2 is created in advance based on past operation results. However, by constantly updating the data with the latest data, it is possible to cope with deterioration of the apparatus over time. Note that the specific degree of the tension adjustment indicated in Table 2 can be appropriately set according to the degree of deviation of the upper and lower limits of the patterns A, B, and C.

[0040]

[Table 2]

[0041]

EXAMPLE In this example, a mandrel mill with five stands was used to roll a seamless steel pipe having an outer diameter of 227.0 mm and a wall thickness of 8.0 mm. At that time, two radiation thermometers were installed on the outlet side of the mandrel mill. The temperature of the surface of the shell was measured.

FIG. 5 shows an outline of the apparatus used in the embodiment. The apparatus used in the present embodiment includes a temperature sampling unit 40 that samples the temperatures of the thermometers 30 and 32, a pattern determination unit 60 that determines the sampled temperature and classifies the pattern, and displays operation guidance based on the determined pattern. It comprises a guidance display unit 70.

According to the present invention, the temperature is measured by the thermometer 30 located in the roll groove bottom direction of the final stand and the thermometer 32 also located in the roll flange direction, and the obtained data is obtained by the temperature sampling unit 40. When data processing is performed and a large temperature fluctuation is observed, the pattern determination unit 60 determines which pattern is applicable. After performing the pattern determination, the operation guidance is determined using the relationship in Table 2 described above, and displayed on the guidance display 70.
The operator sees this, and issues a rotation speed change instruction to the motor rotation speed control device 80.

As described above, in accordance with the operation guidance, the operator can change the rotation speed by using the motor rotation speed control device.
Input to 80 and change the rotation speed of the motor appropriately to change the tension between the rolls.

At this time, since the next material to be rolled is inserted between the rolls, the operation guidance based on the previous rolling results is reflected on the next material to be rolled. The operator can perform the rolling operation in a stable state of the mandrel mill while repeating the above operation for each rolling.

The data processing of the measured temperature in this example is based on the four-point moving average value by the same method as described above.
Further, a difference value at four points ahead was calculated. The threshold values for the four-point difference value were + 20 ° C. and −20 ° C. Patterning of the four-point difference value was performed according to Table 2. The results are shown graphically in FIG.

Both the first thermometer and the second thermometer measured a large temperature fluctuation before the rotation speed was adjusted. However, as shown in FIG. At the rear end of the tube.

Therefore, the rotation speed of the fourth stand is reduced by 2% in accordance with the operation guidance of Table 2 described above.
On the other hand, when the rotation speed of the fifth stand was reduced by 4%, the measured temperatures of the first and second thermometers were both around 1000 ° C., as shown in FIG. The cold outer diameter was almost constant at 227.0mm without any variation, and there was no variation, and the sticking of the bar was improved.

[0049]

As described in detail above, according to the present invention,
By monitoring the temperature at the exit side of the mandrel mill, stable rolling can be performed, and a remarkable effect can be obtained, such as avoiding rolling trouble, reducing downtime, and preventing dimensional abnormalities such as uneven thickness. The practical significance of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a schematic view of a seamless steel pipe manufacturing process.

FIGS. 2 (a) to 2 (c) are schematic explanatory views of an apparatus for practicing the present invention. FIG. 2 (a) is a schematic sectional view, and FIG. 2 (b).
2A is a sectional view taken along the line ZZ in FIG. 2A, and FIG.
FIG. 5A is a sectional view taken along line YY of FIG.

FIG. 3 is a graph of thermometer signal processing, in which the upper row shows the original data, the middle row after the moving average, and the lower row shows the pattern judgment temperature.

4 (a) to 4 (c) are graphs showing the shell temperature in a pattern.

FIG. 5 is an explanatory diagram showing a configuration of an apparatus used in the example.

FIG. 6 is a graph showing the results of Examples.

[Explanation of symbols]

19: Mandrel mill, 21: Sizer, 24: Mandrel roll, 30, 32: Thermometer, 40: Temperature sampling unit, 60: Pattern judgment unit, 70: Guidance display unit, 80: Motor speed control device

Claims (2)

[Claims] 1. A method of measuring a shell temperature on a mandrel outlet side by a thermometer installed on a mandrel mill outlet side, obtaining a temperature distribution in a longitudinal direction of the shell, and estimating a rolling state of the mandrel mill from the obtained temperature distribution. A method for monitoring a rolling condition of a mandrel mill. 2. A shell temperature on a mandrel outlet side is measured by a thermometer installed on a mandrel mill outlet side, a temperature distribution in a longitudinal direction of the shell is obtained, and a temperature distribution obtained in advance is obtained from the obtained temperature distribution. From the relationship with operation guidance,
A method for rolling a mandrel mill, comprising adjusting the tension of a mandrel mill and / or a sizer.