JPS62296974A - Welding heat input control method at manufacturing time of seam welded pipe - Google Patents

Abstract

PURPOSE:To improve the quality of a weld zone and the yield of a product by controlling the welding electric power according to the wall thickness of a blank pipe, the feeding speed of the same, etc., based on the relation of the optimum welding heat input amount found in advance and various characteristics. CONSTITUTION:The relation of the wall thickness of a blank pipe 3 and the rolling reduction force by a squeezing roll 1 is inputted in a controller in advance and based on this, the roll gap of the squeezing roll 1 is controlled at a optimum value by a driving means 6 according to the wall thickness of the blank pipe 3. The welding electric power is controlled so as to make the welding state optimum from the relation of the feeding speed of the blank pipe and optimum heat input amount which were found in advance and that of the wall thickness and feeding speed of the blank pipe and the optimum heating width of the weld zone. In this way the quality can be improved.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a welding heat input control method during the manufacture of electric resistance welded pipes.

[Prior art and its problems]

As shown in FIG. 1, a method for welding the seam of a blank tube formed during the manufacture of an ERW tube involves installing a work coil 2 for electromagnetic induction on the upstream side of a pair of squeeze rolls 1. As shown in Fig. 2, there is an induction method in which a high-frequency current is passed through the tube 3 to heat the raw tube 3, and a pair of squeeze rolls l as shown in Fig. 2 are used.
There is a resistance method in which a pair of contact tips 4 for contact energization are provided on the upstream side of the welding tube, and a high-frequency welding current is passed through the raw pipe 3 through the contact tips 4.

During welding of the raw pipes mentioned above, the welding heat input is controlled by adjusting the high frequency current flowing through the work roll 2 or the contact tip 4. Conventionally, this control has been performed using the method described below. Ta.

(1) The operator visually observes the color of the welded part and the surface shape of the cut weld bead, and manually adjusts the high-frequency current based on these results.

(2) Detect the feeding speed of the raw pipe, and according to the predetermined relationship between the feeding speed of the raw pipe and the high-frequency current that produces appropriate welding heat input, generate a high-frequency current that matches the detected feeding speed of the raw pipe. automatically set.

(3) Detect the temperature of the weld zone and automatically adjust the high frequency current so that this temperature becomes the appropriate temperature brought about by appropriate heat input.

However, the welding heat input control methods (1) to (3) described above have the following problems.

Since method (1) performs welding heat input control manually, it has poor ability to follow sudden changes in the feeding speed of the raw pipe or the wall thickness of the raw pipe. This causes an excess or deficiency in the welding heat input, resulting in the occurrence of venetrator or cold welding, which deteriorates the quality of the weld.

According to method (2), even if high-frequency current is supplied to the work coil or contact tip immediately after the start of construction, it takes time for the seam to heat up to the welding temperature, while the raw tube moves. Therefore, the seam will not be welded during this time. As a result, the product yield 9 decreases due to the occurrence of open pipes.

Moreover, if the wall thickness of the raw pipe changes, appropriate welding heat is not applied to the seam, resulting in excess or deficiency in welding heat input, and for the same reason as in (1) above, the welding Quality deteriorates.

Also in method (3), the temperature of the welded part is not immediately heated to the welding temperature immediately after the start of pipe production, so that appropriate welding heat input is not applied to the seam part. For this reason, the yield of products in which open pipes occur immediately after the start of pipe manufacturing is reduced.

A problem common to the methods (1) to (3) above is that even if the welding heat input is set constant during pipe making, the pressure to reduce the material pipe by the squeeze rolls will vary depending on the wall thickness and tensile strength of the material pipe. If it is not set accurately according to the standards, it will not be possible to maintain the width H of the weld heat affected zone of the raw pipe (see Figure 3) at an appropriate width, making it impossible to obtain a high quality weld. I can't.

[Purpose of the invention]

An object of the present invention is to obtain a welded part of good quality, prevent the occurrence of open seams, and improve product yield. An object of the present invention is to provide a welding heat input control method during the manufacture of electric resistance welded pipes.

[Summary of the invention]

In this invention, the relationship between the wall thickness of the raw pipe and the appropriate raw pipe rolling force by the squeeze roll is determined in advance, and based on this relationship, the squeeze roll is applied so that the raw pipe rolling force by the squeeze roll is equal to the proper raw pipe rolling force. The roll gap is controlled according to the measured wall thickness of the raw pipe, the relationship between the feed rate of the raw pipe and the appropriate welding heat input is determined in advance, and based on this relationship, the welding heat input is made equal to the appropriate welding heat input. The welding power is controlled according to the measured feeding speed of the raw pipe, and the raw pipe is preheated before starting pipe production.
Furthermore, the relationship between the wall thickness of the raw pipe, the feeding speed of the raw pipe, and the appropriate heating width of the welded part is determined in advance, and based on this relationship, the heating width of the bath contact part of the raw pipe is determined to have the appropriate heating width. be.

[Structure of the invention]

Next, a method for controlling welding heat input during manufacturing of an electric resistance welded pipe according to the present invention will be explained with reference to the drawings.

First, the relationship between the wall thickness of the raw pipe for ERW pipes and the appropriate pressure for rolling down the raw pipe using a squeeze roll when cold was investigated for each tensile strength of the raw pipe. As a result, it was found that there was a relationship between the two as shown in FIG.

Therefore, in this invention, the relationship between the appropriate pressure reduction force of the raw pipe and the wall thickness of the raw pipe by the squeeze roll shown in FIG. 4 is determined in advance, and based on this relationship, the The proper tube reduction force by the squeeze rolls is continuously determined during pipe making, and the roll gap of the squeeze rolls is automatically controlled so that this proper tube pressure is applied to the tube during pipe production.

As a result, the force for rolling down the raw pipe by the squeeze rolls is always controlled to an appropriate rolling force even if the wall thickness of the raw pipe changes during pipe production. As a result, the width of the weld heat-affected zone Hz is always maintained at an appropriate width, and a high-quality weld can be obtained.

In order to automatically control the roll gap of the squeeze roll, as shown in FIG. 5 and the tip of the arm 7, and a position detector 9 for detecting the horizontal position of the squeeze roll 1 is attached to the driving means 6. The relationship between the wall thickness of the raw pipe 3 and the rolling force applied by the squeeze roll 1 with respect to (not shown)
The wall thickness is continuously measured by , and the driving means 6 is operated based on the measurement result of the wall thickness. As a result, the roll gap of the squeeze roll 1 is automatically controlled to be equal to the appropriate gap.

Next, the feeding speed of the raw tube and the appropriate welding heat input (appropriate welding power)
We investigated the relationship between As a result, the feeding speed of the raw pipe V
and the heat coefficient H of 9 per unit area of the raw pipe are the difference between induction method and resistance method, the diameter of the raw pipe, the wall thickness t of the raw pipe, and the distance 1y (for the induction method, the center of rotation of the squeeze roll l) When the distance between the center of rotation of the squeeze roll l and the contact tip 4 (in the case of the resistance method, the distance between the center of rotation of the squeeze roll l and the contact tip 4) is determined, it is found that there is a relationship as shown in Fig. 6. Ta.

Note that the heat coefficient H is expressed as H=p/ty. Therefore, the appropriate welding power P is P =
It can be determined by H-ty.

Therefore, in the present invention, the above-mentioned relationship is determined in advance, and based on this relationship, an appropriate welding power corresponding to the feeding speed of the blank tube is determined, and this power is supplied to the work coil or the contact tip.

As a result, even if the feeding speed of the raw pipe changes during pipe production, the seam portion of the raw pipe can always be welded with an appropriate welding heat input.

However, even if the welding heat input is controlled as described above, it has been found that the welding heat input is insufficient immediately after the start of pipe production, that is, when the feed rate of the raw pipe is close to zero. For this purpose, in the present invention, welding power is supplied to the work coil or contact tip before the start of pipe production. That is,
As shown in Fig. 7, if welding power is supplied before the start of pipe making, the heating width HW of the welded part (see Fig. 3) will be greater than when the welding power is manually adjusted immediately after the start of pipe making. The time required to reach a steady width is significantly reduced. As a result, it is possible to prevent open pipes from occurring immediately after starting pipe production.

Next, since the heating width H of the welded part of the raw pipe is one of the criteria for determining the quality of the welded part, there is a relationship between the wall thickness of the raw pipe, the feeding speed, and the appropriate heating width of the welded part. I looked into it. As a result, it was found that there is a relationship between the two as shown in FIG.

Therefore, in this invention, the relationship between the wall thickness and feed rate of the raw pipe and the appropriate heating width of the welded part is determined in advance for each raw pipe, and the width of the welded part is measured using a linear array camera, etc. Then, the welding power is controlled so that the width of the welded portion thus measured is equal to the target width. As a result, a high quality welded part can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, the roll gap of the squeeze roll is controlled so that the force for rolling down the blank tube by the squeeze roll is equal to the proper force for rolling down the blank tube, and the welding heat input becomes equal to the proper welding heat input. Control the welding power as follows,
In addition, by heating the raw pipe before starting pipe production and controlling the welding power so that the heating width of the raw pipe weld is equal to the appropriate heating width, a high-quality welded part can be obtained and the pipe production can be started. A very useful effect is produced whenever the occurrence of immediate open pipes can be prevented and the product yield can be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a welding method for raw pipes using an induction method, FIG. 2 is a perspective view showing a welding method for raw pipes using a resistance method, and FIG. 3 is a cross-sectional view of a welded part of a raw pipe. Figure 4 is a graph showing the relationship between the wall thickness of the raw pipe and the appropriate pressure for lowering the raw pipe by the squeeze roll, Figure 5 is a front view showing the adjustment mechanism for the lowering force for the raw pipe by the squeeze roll, and Figure 6 is , a graph showing the relationship between the feeding speed of the raw pipe and the heat coefficient, Figure 7 is a graph showing the relationship between the welding power, the heating width of the welded part, and time, and Figure 8 is a graph showing the relationship between the wall thickness of the raw pipe and the heat coefficient. It is a graph showing the relationship between feed speed and appropriate heating width. In the drawing, 1... squeeze roll, 2... work roll,
3...Made pipe, 4...Contact chip, 5...Vertical bearing, 6...Driving means, 7
...Arm, 8...Load cell, 9.
...Position detector. Questions included Natsuo Shioya, representative of Nippon Kokan Co., Ltd. (and 1 other person) Figure 1, figure 2, figure 4, figure 5, figure 6, figure 7, year 7

Claims (1)

[Claims] The relationship between the wall thickness of the raw pipe and the appropriate raw pipe rolling force by the squeeze roll is determined in advance, and based on this relationship, the roll gap of the squeeze roll is adjusted so that the raw pipe rolling force by the squeeze roll is equal to the proper raw pipe rolling force. The control is performed according to the measured wall thickness of the raw pipe, the relationship between the feed speed of the raw pipe and the appropriate welding heat input is determined in advance, and the welding power is adjusted based on this relationship so that the welding heat input is equal to the appropriate welding heat input. Control is performed according to the measured feed rate of the raw pipe, and the raw pipe is preheated before the start of pipe production, and the relationship between the wall thickness of the raw pipe, the feed speed of the raw pipe, and the appropriate heating width of the welded part is determined in advance. , a welding heat input control method during the manufacture of an electric resistance welded pipe, characterized in that welding power is controlled based on this relationship so that the heating width of the welded part of the raw pipe is equal to the appropriate heating width.