JP2540187B2 - Method of preventing backflow of accumulated water inside ERW pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for preventing backflow of inner surface retained water in a welding process in a process for manufacturing electric resistance welded pipes.

[Prior Art] In recent years, after sequentially forming metal strips such as steel strips, both edges of the metal strips are guided, and the city and district are electrically resistance-heated and welded by an electric current method to form an electric resistance welded pipe. Manufacturing methods have been widely practiced. In such a manufacturing process, an induction coil, usually abbreviated as a work coil, which is attached around an open seam tube, is caused to flow an electric current to generate an induction current in a metal strip formed by forming or an open coil upstream of a welding point. A current flowing through the metal strip from a pair of electrodes arranged in pressure contact with the metal strip near the edge of the seam tube, which is usually called a contact tip, to cause a current to flow through the metal strip. Due to the skin effect and the proximity effect, the edge portion of the metal strip is heated and melted, and sequentially pressure-welded by a pressure-bonding forming roll, which is abbreviated as a squeeze roll, to continuously produce an electric resistance welded pipe.

On the other hand, in the production of the electric resistance welded pipe, generally, seizure of the metal strip on the forming roll, cooling water, lubricating oil, etc. are continuously supplied to the roll for the purpose of avoiding scratches, etc. It is observed that cold water such as impeder also stays on the inner surface of the pipe like the above-described roll cooling water and remains on the inner surface of the metal pipe near the welding point. Such accumulated water is, as described in JP-B-59-49110,
Due to the heat remaining in the seam during welding, and the heat of seam heat treatment performed after welding, the accumulated water boils and evaporates, causing a pressure increase on the inner surface of the electric resistance welded pipe, and together with the inner surface accumulated water at the welding point. It may spurt out and cause impurities to get caught in the welding point, or cause welding failure (cold welding).
In the production of electric resistance welded pipes, there has been an urgent need to prevent the jetting phenomenon of the accumulated water (this is abbreviated as the reverse phenomenon of the accumulated water to the welding point).

[Problems to be Solved by the Invention] As a countermeasure, for example, as described in Japanese Patent Publication No. 59-49110, air having a pressure higher than that of an open seam portion,
Although there is a method of injecting water etc., the problem is that foreign matter is caught in the welding point, so in this method it is necessary to inject high pressure air directly to the welding point, conversely from the cooling effect, Generally, cold welding is likely to occur, which has an adverse effect on welding quality. This backflow phenomenon occurs when the cooling water that accumulates on the inner surface rises above a certain water level level, and it is necessary to reduce this accumulated water to a water level level at which the backflow phenomenon does not occur, by any means. This is the essence of and was necessary for high-level stabilization of the welding quality.

[Means for Solving the Problems] The present invention has been made in view of the above problems,
The point is that the water level inside the electric resistance welded pipe is detected by a pressure sensor, and when the detected water level becomes higher than the reference water level, the accumulated water is sucked in from a negative pressure nozzle It is a method for preventing backflow of an electric resistance welded pipe, which is characterized by removing the backflow.

That is, in the present invention, the cooling water that has been the root cause of the above-mentioned backflow phenomenon, which is retained on the inner surface of the electric resistance welded pipe, is suctioned and removed from the negative pressure nozzle according to the water level to prevent backflow. It is in.

[Operation] First, the general manufacturing process of the electric resistance welded pipe will be described, and subsequently, the operation of the present invention will be described with reference to FIG. Note that, here, an example in which the water level is detected by static pressure is described, but the method of the pressure sensor is not specified as long as the water level and the backflow can be detected.

From the inlet side of the ERW pipe making equipment, the metal strips (not shown in the figure) that have been charged are sequentially passed through forming rolls (not shown in the diagram),
After forming an open seam-shaped semi-formed electric resistance welded pipe having a V-shaped opening in the upper part, both edges of the metal band are heated and melted,
Subsequently, it is crimped by the squeeze roll 5 to form the electric resistance welded pipe 6, and then, by the external cutting tool 11 and the internal cutting tool 9, the outer bead 12 and the inner bead 10 generated at the welding point.
After being removed, the product is cut into pieces of a predetermined length.

In the above manufacturing process, the negative pressure nozzle 15 of the present invention,
After being used at the time of forming and welding, it is placed in the accumulated water 14 retained inside the electric resistance welded pipe 6 from the open seam portion of the semi-molded electric resistance welded pipe 1, passes through the duct 17 and the vacuum device 18, and The accumulated water 14 accumulated on the inner surface of the sewing tube is continuously sucked out of the electric resistance welded tube. Further, the pressure sensor 4 is a tool rest for fixing the above-mentioned internal cutting tool 9 and the like, and is generally installed at a position just below the welding point on a device abbreviated as the internal cutting mandrel 2. The type of the pressure sensor 4 is not particularly limited as long as it can detect the above-mentioned backflow phenomenon, and the detection capability is sufficient even with a simple circle such as a Pitot tube or a manometer.

On the other hand, as a backflow monitoring system, the pressure signal from the pressure sensor 4 is received by the converter 8 and the CPU 13, and the vacuum device 18 or the paint marking device 16 is activated depending on the static pressure. FIG. 2 is a diagram schematically showing the water level on the inner surface of the electric resistance welded pipe, that is, the static pressure change until the accumulated water on the inner surface increases its water level and reaches the backflow phenomenon. As the operation progresses (passage of time), the accumulated water 14 on the inner surface of the electric resistance welded pipe increases its water level to increase the static pressure, and eventually exceeds the reference water level, causing a backflow risk area (Fig. It becomes middle a). At this time, a signal for starting the vacuum device 18 is sent from the CPU 13, and the accumulated water 14 on the inner surface of the electric resistance welded pipe is sucked and removed from the negative pressure nozzle 15 to prevent the occurrence of backflow (b in the figure). However, in the event of an unexpected accident, such as when the inner bead 10 is clogged with the inner surface of the electric resistance welded pipe due to some force majeure, the water level of the accumulated water 14 on the inner surface of the electric resistance welded pipe further rises, causing a sudden rise. Backflow occurs as the static pressure increases. At this time, a trajectory signal may be sent from the CPU 13 to the paint marking device 16 in accordance with the strength of the backflow, that is, the magnitude of the static pressure to mark the electric resistance welded pipe as a poor quality portion. In this way, by marking the defective portion, the defective portion can be reliably rejected, and management can be performed so as not to cause a product trouble. In addition, as a criterion for determining the quality defect, it is preferable to perform the reject as shown in FIG. 3 from the defect fracture surface ratio of the welding point and the magnitude of static pressure, which have been generally used as a conventional index. .

Although the operation has been described above, most of the backflow phenomenon that is the background of the present invention is due to the residual heat of the welding or the heat treatment after welding at the welding point located on the upper surface of the electric resistance welded pipe. This is because the water boils and evaporates, causing a pressure increase on the inner surface of the electric resistance welded tube. Therefore, the backflow phenomenon does not occur unless the accumulated water on the inner surface exceeds a certain water level. Therefore, the water level of the accumulated water on the inner surface is monitored,
There is a feature of the present invention in taking appropriate measures depending on the situation, and it is possible to prevent the backflow phenomenon that was the cause of the welding failure in advance, and in the event that the backflow phenomenon occurs, the magnitude of The quality of the welding is superb, and the quality is judged to be bad, and if the quality deteriorates, it is reliably rejected.

The standard water level of the accumulated water on the inner surface involved in the start / stop control of the negative pressure nozzle of the present invention is the size of the electric resistance welded pipe and the operating conditions (pipe forming speed, welding point heat treatment temperature, etc.).
It is about 1/2 to 2/3 of the inner diameter of the electric resistance welded pipe.

[Example] In a medium-diameter ERW pipe mill with an outer diameter of 114.3mm-406.1mm, a backflow phenomenon is likely to occur.
In the production of small-diameter ERW steel pipe up to 77.8 mm, the pressure sensor of the present invention and the inner surface water suction negative pressure nozzle were installed and operated under the conditions shown in Table 1 in the embodiment shown in FIG. Compared with the past, the backflow phenomenon was drastically reduced, the final welding quality was improved, and the reliability was further improved.

[Effects of the Invention] The method of the present invention is a method capable of easily and effectively preventing the reverse flow of the inner surface retained water in the welding process in the electric resistance welded pipe manufacturing process, and shows remarkable effects.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method for preventing backflow of an electric resistance welded pipe according to the present invention. FIG. 2 is a view for explaining a backflow phenomenon at the time of welding in FIG. It is the figure which showed an example about the (sensed static pressure) and welding quality. 1 …… Semi-molded electric resistance welded pipe, 2 …… Internal cutting mandrel 3 …… impeder, 4 …… Static pressure sensor 5 …… Squeeze roll, 6 …… Electric resistance welded pipe 7 …… Roller, 8 …… Exchanger 9… … Internal cutting tool, 10 …… Internal bead 11 …… External cutting tool, 12 …… External bead 13 …… CPU, 14 …… (Inner surface) accumulated water 15 …… Negative pressure nozzle 16 …… Paint marking device 17 …… Duct, 18 ... vacuum device

Claims (1)

(57) [Claims] 1. A pressure sensor detects the level of accumulated water in an electric resistance welded pipe, and when the detected water level becomes higher than a reference water level,
A method for preventing backflow of accumulated water inside an electric resistance welded pipe, which comprises sucking and removing accumulated water from a negative pressure nozzle that is immersed in the accumulated water.