JP2011063844A - Blowing device for hot-dip galvanized steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blowing device for removing surplus zinc on inner and outer surfaces of a hot-dip galvanized steel pipe. <P>SOLUTION: While the steel pipe which has been taken out from a molten zinc bath passes through the outer-surface blowing device installed in the end of the molten zinc bath, the surplus zinc on the outer surface of the steel pipe is removed with a compressed gas and the like. At the same time, a mandrel bar moves an injection nozzle at the head thereof to the position of the outer-surface blowing device while injecting a compressed gas and the like from the injection nozzle thereof to remove the surplus zinc on the inner surface of the steel pipe, stops before the trailer of the steel pipe reaches the position of the outer-surface blowing device, and continues the inner surface blow. Thereby, the blowing device can complete an outer surface blow and an inner surface blow for the trailer of the steel pipe at the same time, at the position of the outer-surface blowing device. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a blow device for removing excess zinc on the inner and outer surface surfaces of a steel pipe that has been subjected to hot dip galvanizing treatment.

Conventionally, various methods have been proposed for removing excess zinc adhering to the inner and outer surfaces of steel pipes drawn from the molten zinc bath in steel pipes that have been immersed in a hot-dip zinc bath and subjected to hot-dip galvanizing treatment on the inner and outer surfaces. Has been.

For example, in the process of lifting the steel pipe from the molten zinc bath, it is passed through an external blow device to remove excess zinc on the outer surface of the steel pipe, and the steel pipe is lifted while gradually increasing the tilt angle of the lifting to the excess zinc on the inner surface of the steel pipe. Thus, a hot dip galvanizing apparatus has been proposed in which excess zinc on the inner surface of the steel pipe is allowed to flow out naturally (see, for example, Patent Document 1).

In general, in the process of tilting the steel pipe and lifting it from the molten zinc bath, it passes through the outer blow device to remove excess zinc on the outer surface of the steel pipe, and then transports the drawn steel pipe to the inner blow device adjacent to the pulling device. Thus, a method of blowing off excess zinc on the inner surface of the steel pipe with a compressed gas or the like is used.

In the case of the above-mentioned method, after the steel pipe is lifted from the molten zinc bath, an apparatus for conveying it to the inner surface blowing apparatus is required. In this contact area between the conveying device and the steel pipe, local cooling occurs, the temperature of the molten zinc adhering to the inner surface of the steel pipe decreases to the freezing point, the zinc on the inner surface of the steel pipe becomes solidified or becomes highly viscous, and excess zinc is blown even if the inner surface is blown. Since it cannot be dropped and irregularities such as bumps occur on the inner surface of the steel pipe, a heater is built in the conveying device, and a device that makes the temperature near the contact portion with the steel pipe a temperature at which the molten zinc does not solidify is proposed. (For example, refer to Patent Document 2).

Further, as an inner surface blowing method, a method has been proposed in which compressed gas or the like is blown from one end of a steel pipe and surplus zinc is blown off from the other end opening (see, for example, Patent Document 3).

Furthermore, as a means of shortening the time required from the drawing of the steel pipe to the inner surface blower, a blower pipe with an injection nozzle and an air insertion port mounted on the front and rear in the middle of the transfer path of the steel pipe drawn from the molten zinc bath And an apparatus that sprays compressed gas or the like while passing the injection nozzle through the transfer pipe into the ongoing steel pipe and blows off excess zinc on the inner surface of the steel pipe to the outside of the pipe (for example, Patent Document 4). reference.).

JP-A-48-076741 Japanese Utility Model Publication No. 1-089949 JP-A-6-220599 Japanese Utility Model Publication No. 53-067827

However, in the process of lifting the steel pipe from the hot-dip zinc bath, when using a hot-dip galvanizing apparatus that lifts the steel pipe while gradually increasing the angle of inclination to allow the excess zinc on the inner face of the steel pipe to flow out naturally, There is a problem that a large amount of zinc adheres to the lower side in the longitudinal direction of the inner surface of the steel pipe and the plating thickness becomes non-uniform, and there is a problem that the surplus zinc that has flowed out remains at the bottom end of the steel pipe as a sagging defect.

Also, in the process of tilting the steel pipe from the molten zinc bath and passing the steel pipe through the outer surface blow device, and then transporting the drawn steel pipe to the inner surface blow device and using the inner surface blow, the transport device is used. Since the steel pipe is transported from the lifting device to the inner surface blowing device, the time required for the steel pipe drawn from the molten zinc bath to reach the inner surface blowing device becomes longer, and the temperature of the steel pipe when reaching the inner surface blowing device is allowed to cool. The zinc on the inner surface of the steel pipe is solidified or becomes highly viscous, the surplus zinc cannot be blown off, and there is a problem that irregularities such as bumps remain on the inner surface of the steel pipe, and the surplus zinc on the inner surface of the steel pipe Between the blower and the inner surface blower, there was a problem that the steel pipe dropped and solidified from the rear end of the steel pipe and remained as a sagging defect at the lower end of the steel pipe.

Furthermore, when using the conveyance apparatus incorporating a heater, there existed a problem that the temperature in the contact part of a conveyance apparatus and a steel pipe raised too much, and the zinc membrane | film | coat formed in the steel pipe outer surface discolored brown. Further, since the heater is incorporated in the transfer device, the structure becomes very complicated, the device itself is expensive, and at the same time, there is a problem that the operation cost is high because the power is always supplied. For the sagging defects at the lower end of the steel pipe, a method of blowing off with a gas burner or compressed gas is often used, but it is difficult to obtain a sufficient effect, and an off-line check is essential.

In addition, in the case of a method in which compressed gas or the like is blown from one end of the steel pipe and surplus zinc is blown off from the other end opening, when compressed gas or the like blown from one pipe end is blown from the rear end of the steel pipe There was a problem that the molten zinc on the rear end side of the steel pipe was removed and a large amount of molten zinc was taken away, and the inner plating thickness on the rear end side of the steel pipe was reduced.

In the middle of the transfer path of the steel pipe drawn up from the molten zinc bath, the device that sprays compressed gas etc. while passing the injection nozzle into the steel pipe in progress and blows off the excess zinc inside the steel pipe outside the pipe However, if this inner surface blow is performed simultaneously with the outer surface blow, it is necessary to consider it, and if the blower tube comes into contact with the steel tube, the blower tube Is bent by heat transfer from a steel pipe (about 420 ° C.), but this countermeasure is not described in the patent documents of the prior art.

In order to advantageously solve the above-mentioned problem, the blow device for the inner and outer surface of the hot dip galvanized steel pipe of the present invention has an end on the molten zinc bath side on the outer surface blow device of the lifting portion and the magnet roll of the inner surface treatment portion. The mandrel rod connected to the injection pipe at the end and the compressed gas inlet at the other end and connected by the connecting pipe is arranged in the pulling direction so as to penetrate the steel pipe, and the compressed gas inlet moves the mandrel rod The structure is composed of an internal blow device that is connected / detached with the compressed gas supply fitting of the device. The steel pipe drawn out from the molten zinc bath passes through an outer surface blower installed at the end of the molten zinc bath, and while the excess zinc on the outer surface of the steel pipe is removed by compressed gas or the like, the mandrel rod is at the tip of the steel pipe. The jet nozzle is moved to the position of the outer blow device and stopped before the end of the steel pipe reaches the position of the outer blow device, while removing excess zinc on the inner surface of the steel pipe by jetting compressed gas etc. By continuing the inner surface blowing, the outer surface blowing and the inner surface blowing at the end portion of the steel pipe can be completed simultaneously at the position of the outer surface blowing device.

After completing the outer surface blow and the inner surface blow at the position of the outer surface blower at the same time, stop the compressed gas, etc., hold the mandrel rod with the V groove roll and the rectangular block, and supply the compressed gas of the mandrel rod moving device from the compressed gas insertion port It is characterized in that the steel pipe can be delivered to the delivery device by removing the air bracket.

Furthermore, since the moving distance of the mandrel bar is short from the standby position of the injection nozzle to the position of the outer surface blowing device, the support ring or the support roller as a method for preventing the mandrel bar from bending and contacting the steel pipe is a short distance. It is characterized in that even a small-diameter steel pipe (minimum outer diameter 21.7 mm) can be kept out of contact with the mandrel bar.

According to the hot dip galvanizing method of the steel pipe of the present invention, the mandrel rod is penetrated into the steel pipe being lifted, and the compressed gas is injected from the injection nozzle to blow out the excess zinc on the inner surface of the steel pipe to the outside of the steel pipe. The plating thickness on the inner surface can be made uniform.

In addition, since the inner surface is blown in the process of lifting the steel pipe from the molten zinc bath, the time required for the steel pipe drawn from the molten zinc bath to reach the inner surface blowing device is short, and the temperature of the steel pipe is allowed to cool and the molten zinc solidification point is reduced. The inner surface can be blown before being lowered to a level, and no irregularities such as bumps are generated on the inner surface of the steel pipe.

Furthermore, in order to remove surplus zinc on the outer surface of the steel pipe and the inner surface of the steel pipe by compressed gas in the process of lifting the steel pipe from the molten zinc bath, it is not necessary to transport the steel pipe to the inner surface blower using the transport device after the steel pipe is lifted. It is possible to solve the problem that the zinc coating is discolored to brown or the like, which is caused by incorporating a heater in the apparatus, and the problem that the apparatus itself is expensive and expensive to operate.

Also, instead of blowing compressed gas etc. from one end of the steel pipe, the excess zinc on the inner surface of the steel pipe is removed from the steel pipe by injecting compressed gas etc. from the injection nozzle while penetrating the mandrel rod into the steel pipe being lifted. Therefore, the plating thickness on the inner surface of the steel pipe can be made uniform.

Furthermore, when the steel pipe end reaches the outer surface blow position, the injection nozzle of the mandrel rod stops reaching the outer surface blow position, so the surplus zinc blown off by the outer surface blow and the surplus zinc blown out by the inner surface blow are mixed. And since it blows off into a molten zinc bath, it can adhere to the outer surface of a steel pipe rear-end part, and can solve the problem of a sagging defect which makes the finish of the outer surface of a steel pipe rear-end part worse.

Side view of galvanized steel pipe lifting equipment Side view of a hot-dip galvanized steel pipe lifting device showing the condition at the start of internal blow Side view of a hot-dip galvanized steel pipe lifting device showing the moving state of the mandrel bar Side view of a hot-dip galvanized steel pipe lifting device showing the state after completion of blow on the inner and outer surfaces Side view of a hot-dip galvanized steel pipe lifting device showing a state in which the steel pipe 6 is being sent to the delivery section 5 Side view of a hot-dip galvanized steel pipe lifting device showing the state where the steel pipe is held horizontally Side view of joined state of air supply fitting 21A of mandrel rod moving device 21 and compressed gas insertion port 19D of mandrel rod Side view of detachment state of air supply fitting 21A of mandrel rod moving device 21 and compressed gas insertion port 19D of mandrel rod Plan view of conventional equipment

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view of a galvanized steel pipe lifting device. As shown in FIG. 1, a hot dip galvanized steel pipe lifting device 2 includes a lifting portion 3, an inner surface treatment portion 4, and a delivery portion 5.

The lifting unit 3 of the lifting device 2 is installed above the molten zinc bath 1, and a lifting unit frame 7 that is installed inclined with respect to the bath surface of the molten zinc bath 1, and the lifting unit frame. 7, a steel pipe lifting rod 8 attached to 7; a V-groove magnet roll 9 which is rotatably attached to the lower surface of the lifting portion frame 7 at a predetermined interval; and a lower surface of the lifting portion frame 7. It is comprised with the outer surface blow apparatus 10 which is. As shown in FIG. 1, when the longest steel pipe is lifted by the V-groove magnet roll 9, the rear end of the steel pipe is molten zinc when the tip of the steel pipe comes to the outer surface blowing device 10 as shown in FIG. 1. Determined from the conditions above the surface of bath 1.

The inner surface processing unit 4 of the lifting device 2 is an inner surface processing unit in such a manner that the inner surface processing unit frame 11 installed so as to be adjacent to the molten zinc tank and the steel pipe 6 sent from the lifting unit 3 are received from below. A first V-groove magnet roll 12A, an intermediate V-groove magnet roll 12B, a final V-groove magnet roll 12C, and a first V-groove magnet roll 12A that are freely attached to the upper surface of the frame 11 with a predetermined interval. In order to hold the cylindrical surface roll 13 for guiding the tip of the steel pipe above and the mandrel bar 19 up and down, the V-groove roll 14 and the operation air cylinder 15 are arranged downward, the rectangular block 16 and the operation air are arranged upward. It comprises a cylinder 17 and a tube end detector 18 for detecting the front and rear ends of the steel pipe.

Further, a mandrel bar 19 is installed above the V-groove magnet roll 12B in the steel pipe pulling direction. The mandrel rod 19 has an injection nozzle 19A at one end and a compressed gas injection port 19D at the other end, and is supported so as not to contact the steel pipe 6 between the injection nozzle 19A and the compressed gas injection port 19D. The ring 19C is structured to be held at a predetermined interval by the connecting pipe 19B.
The spray nozzle 19A is directed toward the molten zinc bath 1 and is supported by the mandrel bar support roll 20 so as to be positioned in the vicinity of the first V-groove magnet roll 12A and at the center of the steel pipe 6 being drawn up. . The mandrel bar support roll 20 has a structure in which when the steel pipe 6 passes, the mandrel bar is rolled down at the front end of the steel pipe and pushed down to the lower part of the steel pipe, and the rear end of the steel pipe returns to the mandrel bar support position with a weight after passing.
As shown in FIG. 7, the compressed gas insertion port 19D at the other end can be injected with compressed gas or the like by connecting an air supply fitting 21A of the mandrel rod moving device 21, and the mandrel rod can be moved. As shown in FIG. 8, the steel pipe 6 can pass if the air supply fitting 21 </ b> A is cut off and moved downward.

The feeding unit 5 of the lifting device 2 is installed so as to be adjacent to the inner surface processing unit 4, and receives the steel pipe 6 fed from the bottom V-groove magnet roll 12 </ b> C of the inner surface processing unit 4 from below, so that the feeding unit frame is received. After being received by a V-groove roll 25 that is rotatably attached to the upper surface of the body 24 at a predetermined interval, the rear end surface of the steel pipe is guided by a stopper 23 to lower the delivery part frame body 24, and the steel pipe 6 is placed horizontally. The steel pipe 6 held in a state and held horizontally is transferred to a transfer device (not shown) and transferred to a water cooling tank in the next step.

FIG. 1 is also a side view of a hot-dip galvanized steel pipe lifting device showing a state of starting outer surface blowing.
As shown in FIG. 1, the steel pipe 6 immersed in the molten zinc bath 1 is pulled upward from the molten zinc bath 1 by the steel pipe lifting rod 8 of the lifting section 3, and is attracted to the magnet roll 9 and lifted obliquely upward. Then, it passes through the outer surface blower 10 and is sent to the inner surface processing unit 4 while removing excess zinc on the outer surface of the steel pipe with compressed gas or the like. The supply of compressed gas and the like for inner surface blowing and outer surface blowing is started simultaneously when the steel pipe lifting rod 8 reaches the upper limit.

FIG. 2 is a side view of the hot-dip galvanized steel pipe lifting device showing the state of inner surface blow start. In the inner surface processing unit 4, the steel pipe 6 sent from the lifting unit 3 is composed of a magnet roll 12 </ b> A and a cylindrical surface roll 13 installed so as to be in contact with the steel pipe 6 on the upper portion thereof after the outer surface blow. After positioning the center of the steel pipe 6 between the pipes, the pipe end detector 18 is blown through the nozzle 19A of the mandrel rod 19 that is waiting by jetting compressed gas or the like immediately after the magnet roll 12A while performing inner surface blowing. Sent in the direction of.

FIG. 3 is a side view of a hot-dip galvanized steel pipe lifting device showing a moving state of a mandrel rod. When the front end of the steel pipe 6 is detected by the pipe end detector 18, the injection nozzle 19A of the mandrel bar 19 injects compressed gas or the like, while the end of the steel pipe 6 is moved by the air cylinder 21F of the mandrel bar moving device 21. Before reaching the position of the outer surface blowing device 10, it stops after moving to the position of the outer surface blowing device 10, and the inner surface is blown by injecting compressed gas or the like. That is, the outer surface blowing and the inner surface blowing are performed simultaneously at the position of the outer surface blowing device. Further, the support roll 20 where the front end portion of the steel pipe 6 has passed is overturned and pushed down to the lower part of the steel pipe, and the mandrel bar 19 is supported on the inner surface of the steel pipe 6.

FIG. 4 is a side view of a hot-dip galvanized steel pipe lifting device showing a state after completion of blow on the inner and outer surfaces. When the rear end of the steel pipe 6 passes through the pipe end detector 18, the supply of compressed gas for inner surface blowing and outer surface blowing stops, the V-groove roll 14 for mandrel bar pinch is raised, and the rectangular block 16 is lowered. After the mandrel rod 19 is held, as shown in FIG. 8, the steel pipe 6 can pass if the air supply fitting 21A of the mandrel rod moving device 21 is disconnected from the compressed gas inlet 19D of the mandrel rod and moved downward. Is

FIG. 5 is a side view of a hot-dip galvanized steel pipe lifting device showing a state in which the steel pipe 6 is being sent to the delivery section 5. When the rear end of the steel pipe 6 passes the pipe end detector 22, as shown in FIG. 7, the air supply fitting 21A of the mandrel rod moving device 21 is raised to join the air supply fitting 21A to the compressed gas insertion port 19D of the mandrel rod. The mandrel bar pinch rectangular block 16 is raised, the V-groove roll 14 is lowered and the mandrel bar 19 is opened, and then the mandrel bar moving device 21 is used to return the mandrel bar 19 to the position shown in FIG. .

FIG. 6 is a side view of a hot-dip galvanized steel pipe lifting device showing a state in which the steel pipe is held horizontally. The steel pipe 6 is moved by the inertia force until the stopper 23 of the feeding section 5 is overturned by the attracting force of the final V-groove magnet roll 12C of the inner surface processing section 4, and then reversely travels and the stopper 23 is returned by the weight. While the rear end is aligned, the delivery unit frame 12 is lowered and held horizontal until it becomes horizontal. The steel pipe 6 held horizontally is transferred to a transport device (not shown) and transported to the water cooling tank in the next process.

FIG. 7 is a side view of the joined state of the air supply fitting 21A of the mandrel rod moving device 21 and the compressed gas inlet 19D of the mandrel rod. As shown in the figure, after the air supply fitting 21A of the mandrel rod moving device 21 is raised by the air cylinder 21E with guide and the air supply fitting 21A is joined to the compressed gas inlet 19D of the mandrel rod by the parallel air chuck 21D, If the rectangular block 16 for mandrel bar pinch is raised and the V-groove roll 14 is lowered, the mandrel bar can be moved by the air cylinder 21F of the mandrel bar moving device 21.

FIG. 8 is a side view showing a state where the air supply fitting 21A of the mandrel bar moving device 21 and the compressed gas inlet 19D of the mandrel bar are detached. As shown in the figure, the steel pipe 6 can pass if the air supply fitting 21A is cut and moved downward.

An example of a blow dip galvanized steel pipe blower will be described below. The steel pipe 6 immersed in the molten zinc bath 1 is pulled up from the molten zinc bath 1 by the magnet roll 9 of the lifting unit 3 constituting the lifting device 2. The steel pipe 6 to be lifted passes through the outer surface blowing device 10 of the lifting portion 3 and is sent to the intermediate portion 4 constituting the lifting device 2 while removing excess zinc on the outer surface of the steel pipe with compressed gas or the like. Excess zinc on the outer surface of the steel pipe removed by compressed gas or the like is recovered in the molten zinc bath 1 and reused.

The steel pipe 6 sent from the lifting unit 3 is received by the magnet roll 12 </ b> A of the intermediate unit 4 and sent to the sending unit 5 constituting the lifting device 2 via the inner surface processing unit 4. While the steel pipe 6 is being sent from the inner surface processing section 4 to the delivery section 5, the front end of the steel pipe 6 pierces the injection nozzle 19A of the mandrel rod 19 that is waiting by jetting compressed gas or the like immediately after the magnet roll 12A. When the pipe end detector 18 is reached, the mandrel bar drive device 21 moves to the outer surface blower 10 so that the mandrel bar 19 penetrates into the steel pipe, stops, and injects compressed gas, etc. The excess zinc is removed by blowing from the rear end of the steel pipe. Excess zinc on the inner surface of the removed steel pipe is recovered in the molten zinc bath 1 and reused.

As shown in the conventional system of FIG. 9, when the inner and outer surface blowing devices are separately performed, the dust box 30 and the dust collector 31 for collecting excess zinc and zinc oxide generated by the inner surface blowing, However, in the present invention, all of the excess zinc and zinc oxide are recovered in the molten zinc bath 1 and reused, although equipment such as a zinc receiving plate dripping from the rear end of the steel pipe is required in the middle of the steel pipe conveyance path. Therefore, the facilities are not necessary, and the economic profit is great.

The relative speed of the injection nozzle 19A of the steel pipe 6 and the mandrel bar 19 is the same as the pulling speed at the front end and the rear end, and the middle part is increased by about 20%. Whether or not this is a change in the plating thickness is determined to be insignificant and insignificant because the ejection speed of compressed gas or the like from the ejection nozzle is several tens of times faster.

Further, the method of determining the speed at which the injection nozzle 19A of the mandrel bar 19 moves from the standby position to the outer surface blower is such that when the length of the steel pipe 6 is the shortest and the conveyance speed of the magnet roll 9 is the fastest, This is the speed at which the rear end of the steel pipe 6 reaches the outer surface blowing device 10 at the same time, and even if the steel pipe 6 becomes longer, speed adjustment is unnecessary.

When the rear end of the steel pipe 6 passes through the outer surface blowing device 10 in which the outer surface blowing and the inner surface blowing are performed at the same time and reaches the position of the tube end detector 18, the steel pipe 6 is thereafter referred to as the above-described (0030) to (0032). ) Is transferred to the water-cooled tank in the next step, but it is also possible to increase the speed of the intermediate V-groove magnet roll 12B and the final V-groove magnet roll 12C of the inner surface processing unit 4 to shorten the processing time and increase the production volume. It is.

As described above, the required time from the steel pipe lifting to the inner / outer surface blowing device is short, and the inner / outer surface can be blown before the temperature of the steel pipe 6 is lowered to the freezing point of the molten zinc by cooling. As a result, irregularities such as bumps are not generated on the inner surface of the steel pipe, and a uniform plating layer can be formed on the inner and outer surfaces of the steel pipe 6. In addition, there is no need to use a special device such as a heater, and the problem that the zinc film turns discolored to brown etc. and the problem that the device itself is expensive and expensive to operate are eliminated. Can do.

Further, the surplus zinc removed by the inner and outer surface blows is recovered in the molten zinc bath 1 and reused for an economical effect.

1 --- Molten zinc bath 2 --- Lifting device 3 --- Lifting section 4 --- Internal processing section 5 --- Delivery section 6 --- Steel pipe 7 --- Lifting section frame 8 --- Steel pipe Lifting rod 9 --- V-groove magnet roll 10 --- Outside blow device 11 --- Inner surface processing part frame 12A --- First V-groove magnet roll 12B --- Intermediate V-groove magnet roll 12C --- Final V-groove magnet roll 13 --- Cylindrical roll 14 --- V-groove roll 15 --- Air cylinder 16 --- Rectangular block 17 --- Air cylinder 18 --- Pipe end detector 19 --- Mandrel rod 19A --- Injection nozzle 19B --- Connecting pipe 19C --- Support ring 19D --- Compressed gas inlet 20 --- Mandrel support roll 21 --- Mandrel rod moving device 21A --- Air supply bracket 21B-- --Compressed gas supply port 21C --- Guide pin 21D --- Parallel air chuck
21E --- Air cylinder with guide 21F --- Air cylinder 22 --- Pipe end detector 23 --- Stopper 24 --- Feed-out part frame 25 --- V groove roll 26 --- Intermediate transport part 27 --- Transverse device 28 --- Blow ring table 29 --- Inner surface blow device 30 --- Dust box 31 --- Dust collector 32 --- Water cooling tank

Claims (2)

In the blow device for removing surplus zinc on the inner and outer surface surfaces of the steel pipe subjected to the hot dip galvanizing treatment, the steel pipe drawn from the hot dip zinc bath passes through the outer blow device installed at the end of the hot dip zinc bath, While the excess zinc on the outer surface of the steel pipe is removed by compressed gas or the like, the mandrel rod simultaneously ejects compressed gas or the like from the injection nozzle at the tip of the steel pipe to remove excess zinc on the inner surface of the steel pipe, Before reaching the position of the blow device, the injection nozzle is moved to the position of the outer surface blow device and stopped, and the inner surface blow continues, so that the outer surface blow and inner surface blow at the end of the steel pipe are simultaneously performed at the position of the outer surface blow device. A blower for removing excess zinc on the inner and outer surface of a steel pipe, characterized in that it can be completed. In the structure of a mandrel rod used for an internal blow device that removes excess zinc on the inner surface of a hot dip galvanized steel pipe, compression is possible with the injection nozzle at the end of the hot dip zinc bath and the compressed gas supply fitting at the other end An inner surface blower for removing excess zinc on the inner surface of a steel pipe, characterized in that a gas injection port is provided and a support ring or a support roller for preventing the connecting pipe from coming into contact with the steel pipe is provided in the intermediate portion The blow device according to claim 1, wherein the blow device has a structure of a mandrel rod used for the above.

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