JP2004066265A - Method for manufacturing metal plated steel tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for manufacturing a hot dip metal plated steel tube having a uniform and excellent plating layer over the whole surface at high productivity. <P>SOLUTION: This manufacturing method of the hot dip metal plated steel tube is provided with a process where a plated steel sheet which is made by applying metal plating on both front and back faces of the steel sheet is formed into a tubular shape, a process where the plated steel tube is made by continuously welding joining parts of the end faces in the longitudinal direction of the plated steel sheet formed into the tubular shape, a process where a weld bead part formed on the outside surface of the plated steel tube is cut, and a process where the hot dip plating is continuously performed on the outer surface of the plated steel tube with the same metal as that of the metal plating. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a metal-plated steel pipe in which the inner and outer surfaces of the steel pipe are metal-plated.
[0002]
[Prior art]
Conventionally, as a method of manufacturing this type of metal-plated steel pipe, a step of continuously forming a double-sided plated steel sheet formed by hot-dip metal plating on both front and back surfaces of a steel sheet into a tubular shape, and a longitudinal direction of the plated steel sheet formed into the tubular shape. A step of continuously welding the end face joints into a plated steel pipe, a step of cutting a weld bead formed on the outer surface of the plated steel pipe, and a part of the plating layer is cut with the cutting of the weld bead. Spraying the same metal or alloy metal (for example, zinc-aluminum alloy, etc.) as the metal plating on the portion that has become the non-plating area, and concealing the non-plating area from the external atmosphere by the sprayed metal layer. There is something.
[0003]
[Problems to be solved by the invention]
However, in the case of a metal-plated steel pipe obtained by the above-described manufacturing method, there are the following problems. That is, since the bonding force of the sprayed metal layer at the steel pipe interface is weaker than that of the hot-dip coating layer, when the bending processing or the like is performed, the sprayed metal layer may peel or crack, which may cause a problem in the corrosion resistance of the steel pipe. There is. In addition, since the sprayed metal layer is porous, the surface of the steel pipe cannot be completely concealed from the external atmosphere, which may cause a problem in corrosion resistance. In metal spraying, it is difficult to control the fine thickness of the sprayed metal layer, and it is difficult to form a uniform sprayed metal layer.
On the other hand, the applicant of the present invention pre-treats one side of the steel sheet on the side corresponding to the inner surface of the steel pipe, then performs single-side plating by pouring molten metal, and continuously cold-forms the steel sheet into a tube. And a step of subjecting the joint formed on the steel pipe to a tubular body by seam welding to form a tubular body, immersing the outer surface of the tubular body in a molten metal plating bath through a pretreatment step, and performing a molten metal plating. A method for producing a hot-dip metal-plated steel pipe has already been proposed (see Japanese Patent Application Laid-Open No. 05-148607).
However, in the case of this manufacturing method, as described above, plating is first performed on one side of the steel sheet. However, it is necessary to prevent molten metal from wrapping around the other side, so that the plating operation on the steel sheet is difficult. In addition, it is necessary to perform pretreatment twice before plating on the steel sheet and before plating on the surface of the tubular body, and there is a problem that the working process is complicated.
[0004]
The present invention has been proposed in view of the above problems, and has as its object to provide a method for manufacturing a hot-dip metal-plated steel pipe having a uniform and good plating layer over the entire surface with high productivity.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a metal-plated steel pipe of the present invention includes a step of continuously forming a plated steel sheet formed by metal plating on both front and back surfaces of a steel sheet into a tubular form, A step of continuously welding the longitudinal end face joints of the steel sheet to a plated steel pipe, a step of cutting a weld bead formed on an outer surface of the plated steel pipe, and an outer surface of the plated steel pipe, Continuous hot-dip plating with the same metal.
[0006]
The metal used for the hot metal plating is preferably zinc, but may be another metal such as an alloy containing zinc or other metal in zinc, tin, or the like.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0008]
The method for manufacturing a plated steel pipe according to the present embodiment includes a manufacturing line illustrated in FIG.
This production line includes an uncoiler 2 that continuously supplies a long plated steel sheet 1 that has been previously hot-dip galvanized on both sides of a steel sheet, and a forming that continuously forms the plated steel sheet 1 supplied from the uncoiler 2 into a tubular shape. Apparatus 3, a welding apparatus 5 for continuously welding the longitudinal end face joints of the plated steel sheet 1 formed into a tube to form a tubular body 4, and a welding bead formed on the outer surface of the tubular body 4 continuously. A cutting device 6 for continuously cutting, a flux coating device 7 for continuously applying a flux liquid for cleaning the surface to be plated and preventing oxidation to the outer surface of the tubular body 4, and a tubular body for drying the outer surface of the tubular body 4 A hot-dip galvanizing steel pipe 4; a hot-dip galvanizing apparatus 9 for continuously hot-dip galvanizing the outer surface of the tubular body 4 to form a hot-dip galvanized steel pipe 40; The includes a sizing device 14 for shaping the size of the standard, and a cutting device 11 for cutting the molten zinc plated steel tube 40 to a predetermined length.
[0009]
Next, a manufacturing method of the present invention using the above-described manufacturing line will be described.
[0010]
First, a plated steel sheet 1 wound in a coil shape with zinc plating on both sides is continuously supplied from the uncoiler 2 toward the line downstream.
[0011]
The supplied plated steel sheet 1 is drawn into the forming device 3 to be cold-formed into a tubular shape, and subsequently, the welding device 5 continuously welds the longitudinal end face joints of the plated steel sheet 1 to form a continuous one. The tubular bodies 4 are sequentially formed.
[0012]
Next, the tubular body 4 is sent to a cutting device 6 equipped with a blade having a shape along the outer surface of the tubular body 4. Then, the weld bead portion formed on the outer surface of the tubular body 4 is shaved off by the blade of the cutting device 6, and the outer surface of the tubular body 4 is formed smoothly.
[0013]
Thereafter, the tubular body 4 is sent to a flux coating device 7, where a flux liquid for cleaning the surface to be plated and preventing oxidation is applied to the outer surface of the tubular body 4.
[0014]
The tubular body 4 is sent to a preheating device and preheated, and its outer surface is dried.
[0015]
Thereafter, the tubular body 4 is sent to a hot-dip galvanizing apparatus 9. The tubular body 4 is dipped in a hot-dip galvanizing apparatus 9 in an upper plating tank filled with pumped-up molten zinc, and hot-dip galvanized on the entire outer surface. The tubular body 4 immersed in the upper plating tank has a new hot-dip galvanized layer having a sound alloy layer shown in FIG. 2 after the zinc plating formed on the outer surface is once melted into the upper plating tank. When n is formed, a hot-dip galvanized steel pipe 40 is obtained. Then, after the excess molten zinc is removed in a wiping device (not shown), it is cooled.
[0016]
After cooling, the hot-dip galvanized steel pipe 40 is cold-rolled in the sizing device 14 in order to make the outer shape a standard size.
[0017]
Then, the hot-dip galvanized steel pipe 40 is cut into a predetermined length by the cutting device 11 to be a steel pipe product 12.
[0018]
According to the method for manufacturing a hot-dip galvanized steel pipe having the above-described configuration, as shown in FIG. 2, the outer surface of the tubular body 4 having the hot-dip galvanized layer m formed on the inner and outer surfaces is hot-dip galvanized again, and A new hot-dip galvanized layer n having a sound alloy layer on the outer surface of the body 4 is formed. Therefore, the hot-dip galvanized steel pipe 40 in which the hot-dip galvanized layer having excellent corrosion resistance and high rust prevention effect is uniformly formed over the entire circumference of the tubular body 4 can be continuously obtained.
[0019]
When the tubular body 4 is hot-dip galvanized again in the hot-dip galvanizing apparatus 9, the hot-dip galvanized layer m formed on the outer surface of the tubular body 4 once melts into the upper plating tank, and thereafter, a sound A new hot-dip galvanized layer n having an alloy layer is formed. Therefore, the zinc used for the hot-dip galvanized layer m can be reused without waste, which is very economical.
[0020]
Since the outer surface of the tubular body 4 is covered with a hot-dip galvanized layer m except for a weld bead portion in advance, when the hot-dip galvanizing is performed on the surface of the tubular body 4, the tubular body 4 is shot-blasted or pickled. It is not necessary to perform pre-processing such as. Therefore, there is no need for noise due to shot blast, replenishment of the pickling solution, and waste liquid treatment costs, thereby reducing manufacturing costs and simplifying the manufacturing process.
[0021]
In addition, since the coated steel sheet 1 is hot-dip galvanized on both the front and back surfaces of the steel sheet, it can be manufactured only by continuously immersing the pre-treated steel sheet in a hot-dip galvanizing tank. Therefore, as in the case of the plated steel sheet of the production method of Japanese Patent Application Laid-Open No. 05-148607, it is possible to prevent the plating from wrapping around the other side of the steel sheet at the time of manufacturing, or to prevent the steel sheet from being bent and the plating from becoming uneven. This eliminates the need for advanced techniques for prevention, and simplifies the work of plating steel sheets.
[0022]
Note that the present invention is not limited to the above embodiment. For example, in the present embodiment, the coated steel sheet 1 previously hot-dip galvanized on both sides of the steel sheet was used as a raw material, but a non-plated steel sheet was used as a raw material, and the steel sheet was placed upstream of the production line of the present embodiment. A pre-treatment step and a step of galvanizing both sides of the steel sheet may be provided, and the steel sheet may be plated in-line.
[0023]
Further, the upper surface of the hot-dip galvanized layer n may be covered with a protective film made of a synthetic resin or the like. By doing so, the rust-preventing effect of the galvanized steel pipe 40 can be further improved. Moreover, after cutting the hot-dip galvanized steel pipe 40 to form the steel pipe product 12, the inner surface of the steel pipe product 12 may be coated with rustproof aluminum or the like. By doing so, the rust prevention effect on the inner surface of the steel pipe product 12 can be further improved.
[0024]
Further, in the present embodiment, molten zinc is applied as plating applied to the steel plate and the steel pipe, but another metal may be applied as necessary.
[0025]
【Example】
Hereinafter, an example of manufacturing the hot-dip galvanized steel pipe of the present invention will be described.
(Example 1)
A plated steel sheet 1 having a zinc layer of about 8 μm formed on both sides of a long hot-rolled steel sheet having a thickness of 1.2 mm and a width of 80 mm with a micro-alloy layer of about 1 μm formed on both surfaces thereof was uncoiled on an uncoiler 2 of the production line shown in FIG. Then, the feed speed of the tubular body 4 and the reduction of the plating by the wiping device were adjusted so that a galvanized layer having a thickness of about 15 μm was formed on the surface, thereby producing a galvanized steel pipe 40. When the thickness of the plated layer of the obtained hot-dip galvanized steel pipe 40 at the bead cut portion and other portions and the thickness of the alloy layer were examined using a metallurgical microscope, it was found that any of the bead cut portion and other portions was obtained. Also, a sound alloy layer of about 1.5 μm and a zinc layer of about 15 μm were formed.
[0026]
【The invention's effect】
As described above, the method for manufacturing a hot-dip galvanized steel pipe of the present invention is performed by hot-dip galvanizing on the outer surface of a steel pipe formed from a galvanized steel sheet that has been hot-dip galvanized on both front and back surfaces. The galvanized layer can be completely hot-dip galvanized as in the other parts, including the part in which the galvanized layer is cut off to become an unplated area.
Therefore, a uniform and good hot-dip galvanized layer can be formed on the entire outer surface of the steel pipe, and as a result, a hot-dip galvanized steel pipe having excellent corrosion resistance and high rust prevention effect can be obtained. In other words, the method of manufacturing a hot-dip galvanized steel pipe according to the present invention solves the problems of the prior art, that is, the problem that only unhealthy plating could be performed because the welding bead portion had to rely on metal spraying. In addition, the plating condition on the outer surface of the steel pipe can be dramatically improved.
[Brief description of the drawings]
FIG. 1 is a schematic view of a production line according to an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view of a hot-dip galvanized steel pipe manufactured by the manufacturing method of the present embodiment.
[Explanation of symbols]
1 Plated steel sheet 3 Forming device (process of forming plated steel sheet into a tube)
4 tubular body 40 hot-dip galvanized steel pipe (hot-dip galvanized steel pipe)
5 Welding equipment (process of welding the longitudinal end joints of plated steel sheets to form plated steel pipes)
6 Cutting device (process of cutting the weld bead formed on the outer surface of the steel pipe)
9 Hot-dip galvanizing equipment (process to continuously hot-dip galvanize the outer surface of steel pipe)

Claims (1)

A step of continuously forming a plated steel sheet formed by metal plating on both the front and back surfaces of the steel sheet into a tubular form, and a step of continuously welding the longitudinal end face joints of the plated steel sheet formed into the tubular form to a plated steel pipe; A step of cutting a weld bead portion formed on an outer surface of the plated steel pipe, and a step of continuously hot-dip plating the outer surface of the plated steel pipe with the same metal as the metal plating. Manufacturing method of metal-plated steel pipe.

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