JPH11229106A - Hot dip galvanizing method for steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot dip galvanizing method for a steel tube capable of correctly controlling the amt. of hot dip galvanizing for a steel tube. SOLUTION: A steel tube expelled from a continuous steel tube producing line is preheated to 320 to 600 deg.C, is continuously dipped to through into a hot dip galvanizing bath heated at 430 to 480 deg.C for 0.5 to 8.0 sec and is applied with plating. Next, while the interval between the outer face of the steel tube and an injection nozzle is held to 3 to 16 mm, a gas under 0.3 to 5.0 Kg/cm<2> gas injection pressure is injected from the gas injection nozzle to the outer face of the steel tube, and the coating weight of the plating is controlled to 20 to 400 g/m<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot dip galvanizing method for steel pipes.

[0002]

2. Description of the Related Art As a hot-dip metal plating method for steel pipes, a steel pipe is immersed in a hot-dip metal plating bath to perform metal plating.
Next, cooling and cutting to a predetermined length are disclosed in
-148607.

[0003]

As described above, in hot-dip metal plating of steel pipes, hot-dip galvanized steel pipes capable of accurately controlling the amount of plating applied and capable of plating while maintaining high productivity by high-speed piping. It is an object to provide a plating method.

[0004]

SUMMARY OF THE INVENTION The method of the present invention is characterized in that a steel pipe discharged from a continuous steel pipe production line is preheated to 320 to 600.degree. The plating is performed by immersion and passing continuously for 5 to 8.0 seconds, and then the gas injection pressure from the gas injection nozzle is 0.3 to 5.0 kg / g while maintaining the gap between the outer surface of the steel pipe and the gas injection nozzle at 3 to 16 mm. A hot-dip galvanizing method for steel pipes, wherein a gas of ² cm ² is injected to the outer surface of the steel pipe to control the amount of coating to 20 to 400 g / m ² . And after preheating the steel pipe dispensed from the continuous steel pipe production line and continuously immersing and passing it into a hot-dip galvanizing bath to apply plating to the outer surface of the steel pipe, and then injecting gas onto the outer surface of the steel pipe to control the amount of plating applied, After being cooled and cut to a predetermined length, after extracting the hot-dip galvanized metal in the hot-dip galvanizing bath, the steel pipe is passed through without being plated, and cut to a predetermined length to obtain a hot-dip galvanized steel pipe. And hot-dip galvanizing of steel pipes.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, as described above, a steel pipe discharged from a continuous steel pipe production line is continuously immersed and passed into a hot-dip galvanizing bath without cutting, thereby performing hot-dip galvanizing on the outer surface of the steel pipe. . As described above, prior to hot-dip galvanizing, the steel pipe was
Preheating (such as electric induction heating), but if the preheating temperature is less than 320 ° C, it takes a long time for the surface temperature of the steel pipe in the galvanizing bath to reach the temperature required for forming a galvanized layer. Is required, and the piping speed is reduced, which is not preferable. On the other hand, when the temperature exceeds 600 ° C., the limit as the facility capacity is exceeded, which is disadvantageous.

In this way, the steel pipe is preheated and immersed and passed through a hot-dip galvanizing bath. The hot-dip galvanizing bath temperature is considered in consideration of fluidity and the like since the melting point of zinc is about 420 ° C. A lower limit of 430 ° C. is sufficient. On the other hand, if the upper limit exceeds 480 ° C., the fluidity of zinc increases, making it difficult to stably control the thickness to be thick, and the range of application of the hot-dip galvanized steel pipe as a product is undesirably narrow.

[0007] If the immersion passage time of the steel pipe in such a hot-dip galvanizing bath is less than 0.5 seconds, the diffusion of zinc into the steel is not sufficient, and it becomes difficult to form a plated layer. An immersion passage time of up to 8 seconds is sufficient to obtain a plating weight of up to 400 g / m ² . Therefore, the immersion passage time of the steel pipe in the hot-dip galvanizing bath was 0.1 mm.
5 to 8.0 seconds. Such adjustment of the immersion passage time of the steel pipe is performed by adjusting the length of the hot-dip galvanizing bath and the pipe passing speed.

After hot-dip galvanizing as described above,
Gas is injected from the gas injection nozzle on the outlet side of the hot-dip galvanizing bath to control the amount of zinc deposition to a predetermined amount.The gas injection nozzle is a ring-shaped nozzle because it injects gas all around the steel pipe. When the gap between the nozzle and the steel pipe is less than 3.0 mm, the steel pipe may come into contact with the nozzle due to vibration. Further, if the gap exceeds 16 mm, zinc wrinkles are generated on the surface of the steel pipe, and the appearance is unfavorably deteriorated. Further, by changing the gap between the upper side and the lower side of the steel pipe, it is also possible to control the amount of plating uniformly over the entire surface of the steel pipe.

Next, when the gas injection pressure from the gas injection nozzle is less than 0.3 kg / cm ² , zinc wrinkles are generated on the surface of the steel pipe, and the appearance is undesirably deteriorated. Also, 5.0
Even if it exceeds Kg / cm ^{2, the} effect of removing zinc hardly changes, and hence the amount of adhesion hardly changes, and the gas injection pressure is set to 0.3 to 5.0 Kg / cm ² . Note that a slit width of 0.2 to 1.0 mm is sufficient for the gas injection nozzle. Thus, as described above, depending on the preheating temperature of the steel pipe, the temperature of the hot-dip galvanizing bath, the immersion time of the steel pipe in the bath, the gap between the gas injection nozzle and the steel pipe, and the thin deposition of zinc coating of 20 to 400 g / m ² depending on the gas injection pressure. The plating can be performed stably from the amount to the thick adhesion amount, at a high flow rate of 20 to 120 m / min, while maintaining high productivity.

As described above, the steel pipe to be subjected to hot-dip galvanizing can be applied to various sizes depending on the application. Such an externally plated steel pipe is effectively applied to, for example, a new undercarriage part for automobiles, a steel pipe with a vinyl chloride lining on the inside of the steel pipe, or a steel pipe with a polyethylene powder lining on the inside of the steel pipe, in addition to the conventional electric conduit. Can be very meaningful.

Next, an example of the method of the present invention will be described with reference to the drawings. In FIG. 1, after preheating a steel pipe 1 discharged from a continuous steel pipe production line (not shown) by a preheating device 2, the steel pipe 1 is continuously immersed and passed through a hot-dip galvanizing bath 4 of a hot-dip galvanizing bath 3, and Hot-dip galvanized. A hot-dip galvanizing bath generator 5 equipped with a hot-dip galvanizing bath corresponding to the consumption of the hot-dip galvanizing bath 4 in the hot-dip galvanizing bath 3 heats and melts a zinc lump, and the molten zinc is supplied from a supply pipe 7 through a pump 6. Supply to hot-dip galvanizing bath 3. In the figure, reference numeral 8 denotes a sealing material.

Thus, the plated steel pipe 1a is discharged from the hot-dip galvanizing bath 3 by the gas injection nozzle 9 to form the plated steel pipe 1a.
A gas is sprayed onto the outer surface of a to control the amount to be adhered, and then cooled by passing through cooling water 11 in a water tank 10 and then cut to a predetermined length by a cutting machine 12 to produce a hot-dip galvanized steel pipe product. And

When manufacturing a steel pipe not subjected to hot-dip galvanizing, a valve 13 at the bottom of the hot-dip galvanizing bath 3 is used.
Is opened and the hot-dip galvanizing bath 4 is extracted into the hot-dip galvanizing bath generator 5, and then the discharged steel pipe 1 from the continuous steel pipe production line is passed through the preheating device 2 without preheating, and then the hot-dip galvanizing bath 3 and the gas The cutting machine 1 passes through the gas injection nozzle 9 whose injection has been stopped and the water tank 10 from which the cooling water 11 has been extracted.
It is cut into a predetermined length in 2 to obtain a steel pipe product.

Next, an example of controlling the amount of hot-dip galvanized coating in the method of the present invention will be described.

[0015]

[Table 1]

[0016]

[Table 2] (continuation of Table 1)

Note 1: The test was carried out in an in-line plating facility in which a plating device was connected to the production line of the ERW steel pipe. Note 2: The steel pipe material is ordinary steel (hot rolled steel sheet). Note 3: For hot-dip galvanizing, zinc, a commonly used steel tube plating component, was used. Note 4: Attachment amount control was performed by injecting room-temperature air from the gas injection nozzle having a slit formed all around the inside of the ring-shaped nozzle all around the outer surface of the steel pipe after galvanizing. Note 5: The gap is the gap between the steel pipe and the gas injection nozzle, the upper one is the gap between the upper part of the steel pipe and the gas injection nozzle, the lower one is the gap between the lower part of the steel pipe and the gas injection nozzle, and the uniform is the gap between the upper and lower parts of the steel pipe and the gas injection nozzle. Same spacing. Note 6: The cooling temperature of the coated steel pipe is the temperature at which the coated steel pipe after the coating weight control was immersed and passed through the cooling water at room temperature.

[0018]

According to the method of the present invention, the amount of hot-dip galvanized steel pipe can be accurately controlled, and the use of the hot-dip galvanized steel pipe can be expanded. In the production line, hot dip galvanized steel pipes and steel pipes can be separately manufactured.
Industrially significant effects can be achieved, such as an improvement in the operation rate of the continuous steel pipe production line.

[Brief description of the drawings]

FIG. 1 is a side flow diagram showing an example of the method of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshihisa Ichikawa 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture Nippon Steel Pipe Co., Ltd. Nagoya Office Co., Ltd. (72) Inventor Takehiko Sakagami 5-3, Tokai-cho, Tokai-city, Aichi Prefecture Nagoya Office

Claims (2)

[Claims] Claims 1. Steel dispensed from a continuous steel pipe production line
Preheat the tube to 320-600 ° C and 430-480 ° C
Continuous immersion for 0.5-8.0 seconds in hot-dip galvanizing bath
And apply plating.
Gas injection nozzle while maintaining the gap between the spills at 3-16 mm
From 0.3 to 5.0 kg / cm ^TwoSteel gas
Spray onto the outer surface of the tube to reduce the coating weight from 20 to 400 g / m^Two
Hot dip galvanizing method for steel pipes
Law. 2. A steel pipe discharged from a continuous steel pipe production line is preheated and continuously immersed and passed through a hot-dip galvanizing bath to perform plating on the outer surface of the steel pipe. After controlling, while cooling and cutting to a predetermined length, after extracting the hot-dip galvanized metal in the hot-dip galvanizing bath, the steel pipe is passed through without applying plating and cut to a predetermined length, A hot-dip galvanizing method for a steel pipe, wherein a hot-dip galvanized steel pipe and a steel pipe are separately manufactured.