JPS60228129A - Film thickness controlling method of coated steel pipe - Google Patents

Abstract

PURPOSE:To eliminate film thickness variations and/or air engulfment to interfaces by controlling rotation speeds at the time of a malfunctioning of detection through providing cycle signals and storing them as to the weld bead location signals and through the use of these cycle signals to perform the above control. CONSTITUTION:The cycle signals as to the weld bead 4 location that are detected in series by a sensor 5 are stored in a bead cycle storage 6. Even in the event when the sensing of the sensor 5 completes its function unsatisfactorily, a bead location signal is set to put out to a rotation speed controlling device 7, forming coating of a fixed thickness of film on the outer surface of a steel pipe 1.

Description

Detailed Description of the Invention (Industrial Field of Application) The technical content disclosed in this specification applies to coated steel pipes such as UOE steel pipes and spiral steel pipes that have synthetic resin sheets attached to their outer surfaces, Regarding a method of keeping the film thickness constant, this is a proposal for a film thickness control method that can achieve the necessary film thickness adjustment even in the face of sensor detection failure.

(Prior Art) For the purpose of corrosion prevention, the outer surface of a steel pipe is coated with a polyethylene sheet, and a known example is the so-called T-die method. This technique is a method in which a required sheet is wound spirally around a rotating steel pipe so that a portion of the sheet overlaps the steel pipe.

When this known technology is applied to welded steel pipes, for example, if there is a weld bead build-up on the surface of the steel pipe, the thickness of the polyethylene coating in this area becomes thinner, and there is a risk of air being drawn in near the bead build-up. In order to overcome these problems, Japanese Patent Laid-Open No. 57-133027 proposed a technology in which the weld bead position is detected using a sensor and the skew rotation speed of the steel pipe is controlled using the detection signal to maintain a constant film thickness. .

(Problems to be Solved by the Invention) The above-mentioned prior art still has the following problems.

(b) When the bead sensor does not operate due to, for example, deformation of the steel pipe (poor roundness and locally formed concave portions), the sheet film thickness control mechanism may not work and the film may not be thick. arise.

(b) The sensor does not respond at the end of the tube in the direction of travel, effectively resulting in a state equivalent to detection failure, and the same film thickness control as in (a) above ends in failure.

(c) When joining coated steel pipes together, there is an inconvenience in that the position of the weld bead shifts, making it impossible to control the film thickness at both ends of the pipes.

The purpose of the present invention is to propose a technique for overcoming the above-mentioned problems (a) to (c) of the prior art, and a method for controlling the film thickness of coated steel pipes to achieve this purpose is a series of detection methods. The present invention is characterized in that a cycle signal for the heat position is created and stored from the weld bead position signal, and the cycle signal is used to perform the rotational speed control described above in the event of detection failure.

(Structure of the Invention) One embodiment of the present invention is shown in FIGS. 1 and 2. Welded steel pipe 1 is fed in the axial direction while being rotated while being supported by skew rollers 2 and 2'. A polyethylene extruder (not shown) is installed near the steel pipe 1, and a polyethylene sheet 3 extruded into a strip from the tip of the T-die of the extruder is pressed onto the outer surface of the steel pipe 1 in a spiral shape using rollers. Wrap it around.

The rear of the steel pipe 1 in the rotational self-feeding direction, that is, the polyethylene di-
The sensor 5 of the weld bead 4 is provided in contact with the outer circumferential surface of the steel pipe at a position where the weld bead 4 is not yet wound (=J),
The output end of this sensor 5 is connected to a bead cycle storage device 6, and the storage device 6 is configured to output an output to a skew rotational speed control device 7 that controls the rotational speed of the skew rollers 2, 2'.

The storage device 6 stores cycle (time) signals regarding the position of the welding piece 64 detected by the sensor 5 in series. Even if the detection by the sensor 5 fails, the bead position signal is reliably output to the rotational speed control device 7, and a coating with a constant thickness is formed on the outer surface of the steel pipe 1, eliminating the influence of the bead. so that That is, by utilizing such a cycle signal of the weld bead position, the rotation of the skew rollers 2, 2' is slowed down so that the sheet 3 wrapped around the weld bead becomes thicker.

For example, as shown in Figure 3, when the steel pipe is partially dented and the sensor does not operate at S5゜$6, based on the previous cycle signals from + to 13, , 85.86 and output the actuation signal.

By doing this, it is possible to control the film thickness even if there is a detection failure.

In (a) and (b) of FIG. 4, the beat sensor 5 is connected to the steel pipe 1.
This shows an example of application of the present invention when the tube is removed from the tail end of the tube. In this case, when the sensor 5 comes off the pipe end, it can be detected by the function that determines the presence or absence of a pipe, such as an electromagnetic proximity switch built into the sensor 5, so the cycle before the sensor 5 comes off can be detected. A signal is periodically issued to delay the rotation of the skew rollers 2, 2' by a certain time T until the winding is completed at t2.

In addition, the examples shown in FIGS. 5(a) and 5(b) are examples in which 1°1' of steel pipes are joined and coated continuously.
When the sensor 5 starts to detect the welding beat 4' of the next steel pipe 1', it is activated only for a predetermined period of time in response to the output signal, and eventually both positions S3. Sa, S4.
Sb is adjusted so that a signal that delays the rotation of the skew rollers 2, 2' is output so that a thick film can be achieved.

(Effects of the Invention) As explained above, according to the present invention, it is possible to reliably eliminate the effect of thinning of the film thickness due to the convex portions of the coated steel pipe and the entrainment of air at the interface, and also to eliminate the bead formation caused by the concave portions on the surface of the steel pipe. By overcoming the effects of sensor malfunction, constant film thickness type control becomes possible, and as a result, excellent corrosion-resistant welded steel pipes can be obtained.

[Brief explanation of drawings]

1 and 2 are a side view and a front view showing how a steel pipe is coated with a sheet according to the present invention, and FIG. 3 is a time chart showing how a bead position is detected when a sensor malfunctions. , (a), (b) in Figure 4
) is a perspective view showing what the sheet covering looks like when the sensor comes off the pipe end. Fig. 5 is a time chart showing how the binding position is detected. Figure 5 shows the sheet covering when joining steel pipes. FIG. 2 is a perspective view showing the process and a time chart showing how the bead position is detected. 1... Steel pipe 2, 2'... Skew roller 3...
・Covering sheet 4...Welding bead 5...Sensor
6...Storage device 7...Rotation speed control tiaa device. Figure 1 Figure 2 Figure 3 Figure 1 Figure 4 (b) Figure 5 A (a) (b)

Claims (1)

[Claims] 1. When a coating sheet is fed out and spirally wound on the surface of a skew-rotating welded steel pipe, the film thickness of the weld bead corresponding portion detected by a sensor at a pre-wrapping stage position is In a method of keeping the skew rotational speed of a steel pipe constant by controlling it, a cycle signal for the weld bead position is created and stored from the weld bead position signal detected in series, and the cycle signal is used to perform the above-mentioned operation in the event of a detection failure. A method for controlling the film thickness of a coated steel pipe, characterized by controlling the rotational speed;
.