JP2020049502A - Traffic safety facility such as signal pole or sign pole with use of double steel pipe and manufacturing method thereof - Google Patents

Abstract

To improve a circumferential gap of a double steel pipe 1, make easy immersion and exudation of molten plating into the circumferential gap, and achieve good assemblability of the double steel pipe.SOLUTION: A traffic safety facility comprises an inside core steel pipe 2 and an outside outer steel pipe 3, an air vent hole 7 for ventilation of air staying in a plating process is formed at a lower part of the core steel pipe 2, and an upper end part of the outside outer steel pipe 3 and the core steel pipe 2 are circumferentially welded and fixed above the air vent hole 7. A circumferential opening 5a is formed between a lower end part of the outer steel pipe 3 and the core steel pipe 2, and an opening holding material is located in order to hold the opening 5a. Thus, immersion and exudation of molten plating into the opening 5a can be easily performed. As the opening holding material, three or more spacers are interposed at intervals in the circumferential opening 5a, several spacers thereof are welded to an inner peripheral surface of the outer steel pipe 3, the core steel pipe 2 is inserted in the outer steel pipe 3, and thereafter, residual spacers 8d are interposed in the opening 5a, thereby improving the work of inserting and assembling the core steel pipe 2 and the outer steel pipe 3.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a double steel pipe used for signal poles, signposts, and the like, and a method for manufacturing the same.

  Conventionally, as a first example of a body-wound double steel pipe 101 used for a signal pole or a signpost, an inner core steel pipe 102 having an outer diameter of 165.2 mm, a thickness of 5 mm, and a length of 9 m, an outer diameter of 177.8 mm, a thickness of 17 mm The outer steel pipe 103 having a length of 4.5 mm and a length of 2.5 m constitutes a body-wound double steel pipe 101, and a 1.2 mm circumferential gap 5 is opened between the outer steel pipe 103 and the core steel pipe 102. The upper and lower parts of the outer steel pipe 103 are hermetically welded 104 to the core steel pipe 102, and air vent holes 107 and 108 are formed in the upper and lower parts of the core steel pipe 102 in the internal space between the core steel pipe and the outer steel pipe. The plating is circulated so as to flow in and out of a circumferential gap 105 between the core steel pipe 102 and the outer steel pipe 103, so that a plating layer is formed on the surface. However, in the above-described circumferential gap (1.2 mm), there is almost no gap 105, and there is a problem that a plating layer is not sufficiently formed.

  As a second example of the body-wound double steel pipe 101, an inner core steel pipe 102 having an outer diameter of 190.7 mm, a thickness of 5.3 mm, and a length of 9 m, an outer diameter of 216.3 mm, a thickness of 4.5 mm, and a length of 2 A 1.5 m outer steel pipe 103 constitutes a body-wound double steel pipe 101, and an upper and lower part of the outer steel pipe 103 is formed with a 8.2 mm circumferential gap 105 between the outer steel pipe 103 and the core steel pipe 102. Sealed and welded to the core steel pipe 102, air vent holes 107 and 108 are formed in the upper and lower portions of the core steel pipe in the internal space between the core steel pipe 102 and the outer steel pipe 103, respectively. A double steel pipe 101 that forms a plating layer on the surface of the circumferential gap 105 while circulating is also known.

  Further, Patent Literature 1 discloses a double steel pipe that is not a signal pillar or a sign pillar but is used as a foundation pile of an upper structure. This double steel pipe includes an outer steel pipe provided on the ground and an inner steel pipe provided inside the outer steel pipe, and the inner space of the inner steel pipe is hollow, and a time-hardening material is provided between the inner steel pipe and the outer steel pipe. In the state filled with, the upper structure is constructed above the outer steel pipe and the inner steel pipe, and the inner steel pipe is provided with a perforated steel plate on the outer surface to maintain a predetermined interval with the inner surface of the outer steel pipe. There is disclosed a double steel pipe provided with a member and capable of reducing stress generated in an outer steel pipe and an inner steel pipe as compared with the surrounding ground.

Japanese Patent No. 6286882

  By the way, in the double steel pipe, if the circumferential gap 5 (1.2 mm) is small and the hole diameter of the air vent hole is small as shown in the first example, degreasing, washing, pickling, washing, and flux treatment are performed. In a plating process that involves hot dip galvanizing bath immersion, an aqueous solution is used from degreasing to flux treatment, and in a plating bath immersion process at a temperature of about 450 ° C. (435 ° C. to 465 ° C.), an aqueous solution or hot dip galvanizing is applied to a core steel pipe. It is difficult to infiltrate / leak into the circumferential gap from the upper and lower air vent holes. In particular, the pickling scale residue in the pickling step is likely to remain, resulting in poor plating on the inner surface of the circumferential gap in the plating step.

  Also, as shown in the second example, even if the circumferential gap (8.2 mm) of the double steel pipe is wide, the air vent hole cannot be made too large due to the strength of the core steel pipe. It becomes difficult for the zinc plating to intrude and leached from the air vent hole into the circumferential gap. In particular, it is almost the same as the first example that the pickling scale residue in the pickling step is likely to remain and the inner surface of the circumferential gap becomes poor in plating. In addition, in the hot-dip galvanizing bath immersion step at a high temperature (around 450 ° C.), the air that has entered the circumferential gap of the double steel pipe hardly escapes from the air vent hole, and the steam explosion easily occurs. For this reason, cracks D may occur in the outer steel pipe, resulting in a defective product. In addition, there is a fear of danger of plating work due to steam explosion.

  By the way, when this type of double steel pipe is buried underground as a signal pole or a sign pole, as shown in FIG. 7, the pillar S (core steel pipe 2) shakes due to wind or vibration, and the load is reduced. Stress was concentrated on the welded portion between the outer steel pipe 103 and the core steel pipe 102, and there was a possibility that the outer steel pipe 103 might be cracked from near the welded portion. In particular, when the outer steel pipe 103 is formed of an electric resistance welded steel pipe, the probability that a crack is most likely to occur in a fragile part near the electric resistance welded part is increased. Therefore, in the signal pole S or the signpost exposed to the weather, rainwater infiltrates into the circumferential gap 105 between the outer steel pipe 103 and the core steel pipe 102, and when the plating process is not good, the steel pipe surface is oxidized and rust is generated. As a result, the strength of the double steel pipe may be reduced.

  In view of the above, the present invention improves the circumferential gap of the double steel pipe, and eliminates the closed space between the outer steel pipe and the core steel pipe to make it easy to release air, so that the plating process can be easily performed. It is an object of the present invention to provide a double steel pipe capable of improving safety and a method for manufacturing the same.

  In order to achieve the above object, the present invention provides a method of manufacturing a double steel pipe comprising an inner core steel pipe and an outer steel pipe, wherein an air vent hole for removing air stagnant in a plating step is provided below the core steel pipe. Formed, the core steel pipe is inserted into the outer steel pipe, and the upper end of the outer steel pipe and the core steel pipe are welded and fixed circumferentially above the air vent hole, and the lower end of the outer steel pipe and the core steel pipe are fixed. A circumferential gap is formed between the steel pipes, a plurality of gap holding members are provided to hold the gap, and then hot-dip plating is introduced into the gap between the core steel pipe and the outer steel pipe to form a circumferential gap. A plating layer is formed on the inner surface of the gap. Thereby, plating of the steel pipe surface in the circumferential gap can be favorably performed.

  Further, as the plurality of gap holding members, three or more spacers are set at intervals in the circumferential direction in a circumferential gap between the core steel pipe and the outer steel pipe, and at least one of these spacers is provided. Except for the spacers, a plurality of spacers are fixed in advance by welding to the inner peripheral surface of the outer steel pipe or the outer peripheral surface of the core steel pipe, and then, after the core steel pipe is inserted into the outer steel pipe, the remaining spacers are attached to the outer circumference of the core steel pipe. The gap holding material is installed in the gap between the lower end of the outer steel pipe and the core steel pipe by welding to the surface or the inner peripheral surface of the outer steel pipe. As a result, it is possible to prevent excess stress from being concentrated on the outer steel pipe, thereby preventing the outer steel pipe from being cracked.

  According to the present invention, in a double steel pipe composed of an inner core steel pipe and an outer steel pipe, as shown in FIGS. 7 to 9, instead of sealing the upper and lower ends of the outer steel pipe, the lower end of the outer steel pipe is not sealed. A circumferential gap is formed between the core steel pipe and the spacer, and a spacer for holding the circumferential gap is provided, so that a hot-dip plating layer can be favorably formed on the inner surface of the circumferential gap. .

  Further, when inserting the core steel pipe into the outer steel pipe, a plurality of gap retaining materials are welded to the outer steel pipe or the core steel pipe, and at least one remaining spacer is retrofitted, so that the core steel pipe is inserted into the outer steel pipe. In this case, the center axes of both steel pipes can be easily aligned, and the work of inserting the core steel pipe can be easily performed.

It is the schematic which shows the example which used the double steel pipe which concerns on this invention for a signal pillar. FIG. 3 is a cross-sectional view showing a state when the double steel pipe of the present invention is immersed in a plating bath, wherein (a) shows a state of infiltration of hot-dip plating, and (b) shows a state of leaching of hot-dip plating. FIGS. 4A and 4B are perspective views showing an assembling process of a double steel pipe according to the present invention, wherein FIG. 4A shows a state in which a spacer is welded to an outer steel pipe, and FIG. Shows the fixed state. It shows the lower side of the double steel pipe, (a) is a bottom view, and (b) is a sectional view. It is a flowchart which shows the manufacturing process of a double steel pipe. It is a flowchart which shows the plating process of FIG. It is the schematic which shows the example which used the conventional double steel pipe for the signal pillar. FIG. 4 is a schematic perspective view showing a part of a conventional double steel pipe. FIG. 4 is a cross-sectional view showing a state when a conventional double steel pipe is immersed in a plating bath, wherein (a) shows a state of infiltration of hot-dip plating, and (b) shows a state of leaching of hot-dip plating.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the configuration of the double steel pipe 1 will be described. The double steel pipe 1 of the present embodiment includes an inner core steel pipe 2 and an outer steel pipe 3 and is used for, for example, a signal pole S having a signal S1 as shown in FIG. The double steel pipe 1 is a lower part of the signal pole S or the like, and the lower one third of the underground part and the exposed part exposed from the ground is covered with the outer steel pipe 3.

  The inner core steel pipe 2 is, for example, a carbon steel pipe for general / building structure having an outer diameter of 190.7 mm, a thickness of 5.3 mm, and a length of 9 m. As the outer outer steel pipe 3, a steel pipe having an outer diameter of 216.3 mm, an inner diameter of 206.9 mm, a thickness of 4.5 mm, and a length of 2.5 m is used. The outer surface of the outer steel pipe 3 is embossed on a satin finish so as to have a sticking prevention function. The installation height of the outer steel pipe 3 can be set to, for example, 0.5 m for the underground buried portion and 2.0 m to the ground exposure length so as to exert the function of preventing sticking, but is not limited thereto. Not something.

  In the body-wound double steel pipe 1 including the core steel pipe 2 and the outer steel pipe 3, the upper end of the outer steel pipe 3 and the core steel pipe 2 are welded circumferentially and fixed. At this time, the upper end of the outer steel pipe 3 is subjected to drawing processing 4 on the side of the core steel pipe 2 so that the inner peripheral edge of the upper end of the outer steel pipe 3 contacts the outer surface of the core steel pipe 2. Thereby, the upper end portion of the outer steel pipe 3 and the core steel pipe 2 can be firmly fixed by welding.

  If the above-mentioned core steel pipe 2 and outer steel pipe 3 are used, a circumferential gap 5 of 8.1 mm in the radial direction is opened between them. The circumferential gap 5 is a gap sufficient for the hot-dip galvanizing to infiltrate and leach out. A sufficient plating layer 6 is formed on the outer surface of the core steel pipe 2 facing the circumferential gap 5 and the inner circumferential surface of the outer steel pipe 3. Will be applied.

  In the lower part of the core steel pipe 2, a plurality of air vent holes 7 are formed at the same height, through which the hot-dip plating can enter and leak between the inside of the core steel pipe 2 and the inside of the outer steel pipe 3 during immersion in the hot-dip plating bath. ing. The air vent hole 7 is formed at a position immediately below a circumferential welded portion W which is a joint portion between the core steel pipe 2 and the outer steel pipe 3. In this example, the hole diameter of the air vent hole 7 is set to about 32 mm in diameter from which air can be vented. As a result, even when immersed in the hot-dip plating bath, the air remaining in the circumferential gap 5 is sufficiently discharged to the core steel pipe 2 side.

  A circumferential gap 5 is formed between the lower end of the outer steel pipe 3 and the core steel pipe 2, and a plurality of spacers 8 a to 8 d are provided as gap holding members 8 for holding the gap 5. In the present example, four spacers 8 a to 8 d are interposed at regular intervals in the circumferential gap 5 between the core steel pipe 2 and the outer steel pipe 3 as the gap holding material 8. At this time, the three adjacent first to third spacers 8a to 8c are fixed to the inner peripheral surface of the outer steel pipe 3 by welding. The remaining one fourth spacer 8d is welded to the outer peripheral surface of the core steel pipe 2 so as to cope with a twist around the central axis of the steel pipe generated between the core steel pipe 2 and the outer steel pipe 3. The thickness of the spacers 8a to 8d is substantially the same as that of the circumferential gap 5, and is set to be about 25 mm in length and about 20 mm in width in the circumferential direction so that the gap 5 between the spaces 8a to 8d is sufficiently molten-plated. Is done.

  Next, a method of manufacturing the double steel pipe 1 will be described with reference to FIGS. First, as shown in FIG. 5, drawing 4 is performed so that the upper end of the outer steel pipe 3 can be welded to the core steel pipe 2. Next, the first to third spacers 8a to 8c are welded to the lower inner peripheral surface of the outer steel pipe 3. Next, an air vent hole 7 is formed in the lower part of the core steel pipe 2. Then, the core steel pipe 2 is inserted into the outer steel pipe 3, and the upper end of the outer steel pipe 3 is circumferentially welded W to the core steel pipe 2. When the core steel pipe 2 is inserted into the outer steel pipe 3, it is desirable that the core steel pipe 2 is inserted so that the central axes of the two coincide. In this example, when the core steel pipe 2 is inserted into the outer steel pipe 3, only three spacers 8a to 8c of the outer steel pipe 3 are welded as the gap holding material 8, and the remaining one spacer 8d is retrofitted. When the core steel pipe 2 is inserted into the outer steel pipe 3, the insertion can be facilitated, and the work of aligning the central axes of the steel pipes 2 and 3 can be easily performed by the fourth spacer 8d that is attached later.

  Next, when the fourth spacer 8d is welded to the core steel pipe 2, the center axes of the core steel pipe 2 and the outer steel pipe 3 coincide with each other, and the lower end portions of the core steel pipe 2 and the outer steel pipe 3 are regulated in the circumferential direction. Since it is not performed, it is possible to cope with torsional deformation around the central axis of both steel pipes 2 and 3.

  After assembling the double steel pipe 1, the core steel pipe 2 and the outer steel pipe 3 are plated. FIG. 6 is a flowchart showing the plating process. First, the product is immersed in a heated alkaline degreasing solution to remove adhering fats and oils. Then, it is immersed in clean water to remove the alkali adhering to the surface of the steel pipe. Then, it is immersed in hydrochloric acid of a predetermined concentration to remove rust and scale.

  After pickling, the product is immersed in clean water to remove the acid adhering to the surface. Thereafter, the substrate is immersed in a heated ammonium chloride solution to clean the surface to be plated and to perform a flux treatment for preventing generation of rust until the plating treatment. After the flux treatment, the product is immersed in a hot-dip galvanizing bath to perform a plating treatment. The plating process is usually immersed in a high-temperature processing solution, and thus may cause distortion in some cases. In order to avoid this, cooling is performed to form a stable plating film.

  In such a double steel pipe 1 composed of the inner core steel pipe 2 and the outer steel pipe 3, the upper and lower ends of the outer steel pipe 3 are not sealed, but the gap between the lower end of the outer steel pipe 3 and the core steel pipe 2. Is formed, and spacers 8a to 8d are provided as gap holding members 8 for holding the gaps, so that the hot-dip plating layer 6 is preferably formed on the surface of the steel pipe inside the circumferential gap 5. Can be formed. Moreover, the molten plating circulates through the circumferential gap 5 and the air vent hole 7 between the inside of the core steel pipe 2 and the inside of the outer steel pipe 3 on the outside. Also excellent in nature.

  The fourth spacer 8d to be welded to the core steel pipe 2 side and the first to third spacers 8a to 8c to be welded to the outer steel pipe 3 side as the gap holding material 8 are welded to the other steel pipes facing each other. Therefore, when the double steel pipe 1 is used for the signal pole S or the signpost, the outer steel pipe 3 is allowed to move even if the pillar shakes due to wind, vibration, or the like. In this case, it is possible to prevent the external steel pipe 3 from being cracked by avoiding concentration of excess stress on the outer steel pipe.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made within the scope of the present invention. For example, in the above embodiment, traffic safety facilities such as signal poles and signposts have been exemplified. However, the present invention is not limited to this, and a double steel pipe in which the surface of the circumferential gap 5 is plated can be used for other purposes. It can also be applied to double steel pipes.

  Further, in the above-described embodiment, an example is shown in which spacers 8a to 8c are welded to three places on the inner peripheral surface of the outer steel pipe 3 as the gap holding material 8, and one spacer 8d is welded to the core steel pipe 2 side. Conversely, the spacers 8a to 8c may be welded and fixed to three places on the outer peripheral surface of the core steel pipe 2, and the remaining one spacer 8d may be welded and fixed to the outer steel pipe 3 side. Furthermore, the spacers 8a to 8d may be welded to one or both of the core steel pipe 2 and the outer steel pipe 3.

  Furthermore, the number of the gap holding members 8 is not limited to four as in the present embodiment, and is not particularly limited as long as it is three or more. That is, in the gap holding material 8, three or more spacers are set at intervals in the circumferential direction, and a plurality of spacers except for at least one of these spacers is previously formed on the inner circumferential surface or core of the outer steel pipe. Any mode may be used as long as it is welded to the outer peripheral surface of the steel pipe. At this time, the number of remaining spacers that are not welded in advance is not limited to one and may be two or more. Further, the spacing between the spacers is not limited to the regular spacing, and the spacing can be set appropriately according to the situation.

DESCRIPTION OF SYMBOLS 1 Double steel pipe 2 Core steel pipe 3 Outer steel pipe 4 Drawing 5 Circumferential gap 6 Plating layer 7 Air vent hole 8 Gap holding material 8a-8d Spacer S Signal column S1 Signal W Welding

The present invention relates to a traffic safety facility such as a signal pole or a signpost using a double steel pipe and a method of manufacturing the same.

  Conventionally, as a first example of a body-wound double steel pipe 101 used for a signal pole or a signpost, an inner core steel pipe 102 having an outer diameter of 165.2 mm, a thickness of 5 mm, and a length of 9 m, an outer diameter of 177.8 mm, a thickness of 17 mm The outer steel pipe 103 having a length of 4.5 mm and a length of 2.5 m constitutes a body-wound double steel pipe 101, and a 1.2 mm circumferential gap 5 is opened between the outer steel pipe 103 and the core steel pipe 102. The upper and lower parts of the outer steel pipe 103 are hermetically welded 104 to the core steel pipe 102, and air vent holes 107 and 108 are formed in the upper and lower parts of the core steel pipe 102 in the internal space between the core steel pipe and the outer steel pipe. The plating is circulated so as to flow in and out of a circumferential gap 105 between the core steel pipe 102 and the outer steel pipe 103, so that a plating layer is formed on the surface. However, in the above-described circumferential gap (1.2 mm), there is almost no gap 105, and there is a problem that a plating layer is not sufficiently formed.

As a second example of the body-wound double steel pipe 101, an inner core steel pipe 102 having an outer diameter of 190.7 mm, a thickness of 5.3 mm, and a length of 9 m, an outer diameter of 216.3 mm, a thickness of 4.5 mm, and a length of 2 A 1.5 m outer steel pipe 103 constitutes a body-wound double steel pipe 101, and an upper and lower part of the outer steel pipe 103 is formed with a 8.2 mm circumferential gap 105 between the outer steel pipe 103 and the core steel pipe 102. Sealed and welded to the core steel pipe 102, air vent holes 107 and 108 are formed in the upper and lower portions of the core steel pipe in the internal space between the core steel pipe 102 and the outer steel pipe 103, respectively. A double steel pipe 101 that forms a plating layer on the surface of the circumferential gap 105 while circulating is also known.

  Further, Patent Literature 1 discloses a double steel pipe that is not a signal pillar or a sign pillar but is used as a foundation pile of an upper structure. This double steel pipe includes an outer steel pipe provided on the ground and an inner steel pipe provided inside the outer steel pipe, and the inner space of the inner steel pipe is hollow, and a time-hardening material is provided between the inner steel pipe and the outer steel pipe. In the state filled with, the upper structure is constructed above the outer steel pipe and the inner steel pipe, and the inner steel pipe is provided with a perforated steel plate on the outer surface to maintain a predetermined interval with the inner surface of the outer steel pipe. There is disclosed a double steel pipe provided with a member and capable of reducing stress generated in an outer steel pipe and an inner steel pipe as compared with the surrounding ground.

Japanese Patent No. 6286882

By the way, in the double steel pipe, if the circumferential gap 5 (1.2 mm) is small and the hole diameter of the air vent hole is small as shown in the first example, degreasing, washing, pickling, washing, and flux treatment are performed. In a plating step through hot dip galvanizing bath immersion, in an aqueous treatment from degreasing to flux treatment, or in a plating bath immersion step at a temperature of about 450 ° C. (435 ° C. to 465 ° C.), an aqueous solution or hot dip galvanizing It is difficult to infiltrate / leak into the circumferential gap from the upper and lower air vent holes. In particular, the pickling scale residue in the pickling step is likely to remain, resulting in poor plating on the inner surface of the circumferential gap in the plating step.

Also, as shown in the second example, even if the circumferential gap (8.2 mm) of the double steel pipe is wide, the air vent hole cannot be made too large due to the strength of the core steel pipe. It becomes difficult for the zinc plating to intrude and leached from the air vent hole into the circumferential gap. In particular, it is almost the same as the first example that the pickling scale residue in the pickling step is likely to remain and the inner surface of the circumferential gap becomes poor in plating. In addition, in the hot-dip galvanizing bath immersion step at a high temperature (around 450 ° C.), the air that has entered the circumferential gap of the double-walled steel pipe is less likely to escape from the air vent hole, and a steam explosion is likely to occur. For this reason, cracks D may occur in the outer steel pipe, resulting in a defective product. In addition, there is a fear of danger of plating work due to steam explosion.

  By the way, when this type of double steel pipe is buried underground as a signal pole or a sign pole, as shown in FIG. 7, the pillar S (core steel pipe 2) shakes due to wind or vibration, and the load is reduced. Stress was concentrated on the welded portion between the outer steel pipe 103 and the core steel pipe 102, and there was a possibility that the outer steel pipe 103 might be cracked from near the welded portion. In particular, when the outer steel pipe 103 is formed of an electric resistance welded steel pipe, the probability that a crack is most likely to occur in a fragile part near the electric resistance welded part is increased. Therefore, in the signal pole S or the signpost exposed to the weather, rainwater infiltrates into the circumferential gap 105 between the outer steel pipe 103 and the core steel pipe 102, and when the plating process is not good, the steel pipe surface is oxidized and rust is generated. As a result, the strength of the double steel pipe may be reduced.

  In view of the above, the present invention improves the circumferential gap of the double steel pipe, and eliminates the closed space between the outer steel pipe and the core steel pipe to make it easy to release air, so that the plating process can be easily performed. It is an object of the present invention to provide a double steel pipe capable of improving safety and a method for manufacturing the same.

In order to achieve the above object, the present invention relates to a method for manufacturing a traffic safety facility such as a signal pole or a signpost using a double steel pipe composed of an inner core steel pipe and an outer steel pipe, wherein a lower part of the core steel pipe is provided. to form a vent for venting air staying in the plating step, the core steel pipe with inner fitting inserted into the outer steel pipe, the upper than said air vent hole and the upper end portion of the outer steel tube and the core steel pipe more in order to weld fixed circumferentially and form a sufficient circumferential opening for molten coating from entering-leaching between the lower end portion and the core steel pipe of the outer steel pipe, to hold the opening established the opening holding material, then immersing the double Tube to the molten bath, the circumferential gap between the core steel through circumferentially of said opening and said air vent hole and the outer steel pipe Infiltration of hot-dip plating and its circumferential gap Inside of the steel pipe surface to form a plated layer. Thereby, the plating of the steel pipe surface in the circumferential gap can be favorably performed.

Also, as the plurality of openings holding material, in a circumferential shape of the opening between the outer steel pipe and the core steel pipe, set at intervals of three or more spacers in the circumferential direction, of the spacers except at least one spacer fixed by welding to the outer peripheral surface of the inner peripheral surface or the core steel tube advance the outer steel pipe a plurality of spacers, then, after the inner fitting inserted the core steel pipe to the outer steel pipe, the remaining by welding of the spacer on the outer peripheral surface or inner peripheral surface of the outer steel tube of the core steel pipe, installing the open holding material in the opening between the lower end portion of the outer steel pipe and the core steel pipe. As a result, it is possible to prevent excess stress from being concentrated on the outer steel pipe, thereby preventing the outer steel pipe from being cracked.

According to the present invention, in a double steel pipe composed of an inner core steel pipe and an outer steel pipe, as shown in FIGS. 7 to 9, the upper and lower ends of the outer steel pipe are not sealed, but the lower end of the outer steel pipe is sealed. A circumferential opening is formed between the core steel pipe and the core steel pipe, and an opening holding material for holding the circumferential opening is installed . The circumferential opening between the core steel pipe and the outer steel pipe is formed through the circumferential opening and the air vent hole. The molten plating is infiltrated into the gap between the steel pipes, and the plating layer can be favorably formed on the surface of the steel pipe inside the circumferential gap .

Further, when inserting the core steel pipe into the outer steel pipe, a plurality of opening holding members are welded to the outer steel pipe or the core steel pipe, and at least one remaining spacer is retrofitted, so that the core steel pipe is inserted into the outer steel pipe. In this case, the center axes of both steel pipes can be easily aligned, and the work of inserting the core steel pipe can be easily performed.

It is the schematic which shows the example which used the double steel pipe which concerns on this invention for a signal pillar. FIG. 3 is a cross-sectional view showing a state when the double steel pipe of the present invention is immersed in a plating bath, wherein (a) shows a state of infiltration of hot-dip plating, and (b) shows a state of leaching of hot-dip plating. FIGS. 4A and 4B are perspective views showing an assembling process of a double steel pipe according to the present invention, wherein FIG. 4A shows a state in which a spacer is welded to an outer steel pipe, and FIG. Shows the fixed state. It shows the lower side of the double steel pipe, (a) is a bottom view, and (b) is a sectional view. It is a flowchart which shows the manufacturing process of a double steel pipe. It is a flowchart which shows the plating process of FIG. It is the schematic which shows the example which used the conventional double steel pipe for the signal pillar. FIG. 4 is a schematic perspective view showing a part of a conventional double steel pipe. FIG. 4 is a cross-sectional view showing a state when a conventional double steel pipe is immersed in a plating bath, wherein (a) shows a state of infiltration of hot-dip plating, and (b) shows a state of leaching of hot-dip plating.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the configuration of the double steel pipe 1 will be described. The double steel pipe 1 of the present embodiment includes an inner core steel pipe 2 and an outer steel pipe 3 and is used for, for example, a signal pole S having a signal S1 as shown in FIG. The double steel pipe 1 is a lower part of the signal pole S or the like, and the lower one third of the underground part and the exposed part exposed from the ground is covered with the outer steel pipe 3.

The inner core steel pipe 2 is, for example, a carbon steel pipe for general / building structure having an outer diameter of 190.7 mm, a thickness of 5.3 mm, and a length of 9 m. As the outer outer steel pipe 3, a steel pipe having an outer diameter of 216.3 mm, an inner diameter of 206.9 mm, a thickness of 4.5 mm, and a length of 2.5 m is used. The outer surface of the outer steel pipe 3 is embossed on a satin finish so as to have a sticking prevention function. The installation height of the outer steel pipe 3 can be set to, for example, 0.5 m for the underground buried portion and 2.0 m for the ground exposure length so as to exert the function of preventing sticking, but is not limited thereto. Not something.

In the body-wound double steel pipe 1 including the core steel pipe 2 and the outer steel pipe 3, the upper end of the outer steel pipe 3 and the core steel pipe 2 are welded circumferentially and fixed. At this time, the upper end of the outer steel pipe 3 is subjected to drawing processing 4 on the core steel pipe 2 side, so that the inner peripheral edge of the upper end of the outer steel pipe 3 is in contact with the outer surface of the core steel pipe 2. Thereby, the upper end portion of the outer steel pipe 3 and the core steel pipe 2 can be firmly fixed by welding.

If the above-mentioned core steel pipe 2 and outer steel pipe 3 are used, a circumferential gap 5 of 8.1 mm in the radial direction is formed between them. The circumferential gap 5 is a gap sufficient for the hot-dip galvanizing to enter and leak out, and is sufficiently formed on the outer surface of the core steel pipe 2 and the inner circumferential surface of the outer steel pipe 3 facing the circumferential gap 5. The plating layer 6 will be applied.

In the lower part of the core steel pipe 2, a plurality of air vent holes 7 are formed at the same height, through which the hot-dip plating can enter and leak between the inside of the core steel pipe 2 and the inside of the outer steel pipe 3 during immersion in the hot-dip plating bath. ing. The air vent hole 7 is formed at a position immediately below a circumferential welded portion W which is a joint portion between the core steel pipe 2 and the outer steel pipe 3. In this example, the hole diameter of the air vent hole 7 is set to about 32 mm in diameter from which air can be vented. As a result, even when immersed in the hot-dip plating bath, the air remaining in the circumferential gap 5 is sufficiently discharged to the core steel pipe 2 side.

Between the lower end portion of the outer steel pipe 3 and the core steel pipe 2, a circumferential opening 5 a is formed which is continuous with the circumferential gap 5 and is sufficient for the hot-dip galvanizing to enter and leak . A plurality of spacers 8a to 8d are provided as an opening holding material 8 for holding the opening 5a . In this example, four spacers 8 a to 8 d are interposed at regular intervals in the circumferential opening 5 between the core steel pipe 2 and the outer steel pipe 3 as the opening holding material 8. At this time, the three adjacent first to third spacers 8a to 8c are fixed to the inner peripheral surface of the outer steel pipe 3 by welding. The remaining one fourth spacer 8d is welded to the outer peripheral surface of the core steel pipe 2 so as to cope with a twist around the central axis of the steel pipe generated between the core steel pipe 2 and the outer steel pipe 3. The thickness of the spacers 8a to 8d is substantially the same as that of the circumferential opening 5a, and the length is about 25 mm and the circumferential width is about 20 mm, so that the molten plating can sufficiently enter the opening 5a between the spacers 8a to 8d. Is set to

Next, a method of manufacturing the double steel pipe 1 will be described with reference to FIGS. First, as shown in FIG. 5, drawing 4 is performed so that the upper end of the outer steel pipe 3 can be welded to the core steel pipe 2. Next, the first to third spacers 8a to 8c are welded to the lower inner peripheral surface of the outer steel pipe 3. Next, an air vent hole 7 is formed in the lower part of the core steel pipe 2. Then, the core steel pipe 2 is inserted into the outer steel pipe 3, and the upper end of the outer steel pipe 3 is circumferentially welded W to the core steel pipe 2. When the core steel pipe 2 is inserted into the outer steel pipe 3, it is desirable that the core steel pipe 2 is inserted so that the central axes of the two coincide. In this example, when the core steel pipe 2 is inserted into the outer steel pipe 3, only the three spacers 8a to 8c of the outer steel pipe 3 are welded as the opening holding material 8, and the remaining one spacer 8d is retrofitted. When inserting the steel pipes 2 and 3 into the core steel pipe 2 and the outer steel pipe 3, the work can be easily performed, and the center axes of the steel pipes 2 and 3 can be easily matched by the fourth spacer 8 d that is attached later.

Next, when the fourth spacer 8d is welded to the core steel pipe 2, the center axes of the core steel pipe 2 and the outer steel pipe 3 coincide with each other, and the lower end portions of the core steel pipe 2 and the outer steel pipe 3 are regulated in the circumferential direction. because they are not, it is possible to cope with torsional Ri deformation of the central axis of the two steel pipes 2 and 3.

  After assembling the double steel pipe 1, the core steel pipe 2 and the outer steel pipe 3 are plated. FIG. 6 is a flowchart showing the plating process. First, the product is immersed in a heated alkaline degreasing solution to remove adhering fats and oils. Then, it is immersed in clean water to remove the alkali adhering to the surface of the steel pipe. Then, it is immersed in hydrochloric acid of a predetermined concentration to remove rust and scale.

After pickling, the product is immersed in clean water to remove the acid adhering to the surface. Thereafter, the substrate is immersed in a heated ammonium chloride solution to clean the surface to be plated and to perform a flux treatment for preventing generation of rust until the plating treatment. After the flux treatment, the product is immersed in a hot-dip galvanizing bath to perform a plating treatment. The plating process is usually immersed in a high-temperature processing solution, and thus may cause distortion in some cases. In order to avoid this, cooling is performed to form a stable plating film.

In such a double steel pipe 1 composed of the inner core steel pipe 2 and the outer steel pipe 3, the upper and lower ends of the outer steel pipe 3 are not sealed, but the gap between the lower end of the outer steel pipe 3 and the core steel pipe 2. Is formed, and spacers 8a to 8d are provided as opening holding members 8 for holding the openings . Therefore, molten plating is intruded and leached from the circumferential openings 5a. The hot-dip layer 6 can be favorably formed on the steel pipe surface between the inner core steel pipe 2 and the outer steel pipe 3 . In addition, since the hot-dip plating circulates through the inside of the core steel pipe 2 and the inside of the outer steel pipe 3 outside through the circumferential opening 5a and the air vent hole 7, there is little danger of steam explosion due to the conventional closed space. Excellent in safety.

Further, as the opening holding material 8 , the fourth spacer 8d welded to the core steel pipe 2 side and the first to third spacers 8a to 8c welded to the outer steel pipe 3 side are welded to the other steel pipes facing each other. Therefore, when the double steel pipe 1 is used as a signal pole S or a sign pole, even if the pillar is shaken by wind or vibration, the outer steel pipe 3 is allowed. In this case, it is possible to prevent the external steel pipe 3 from being cracked by avoiding concentration of excess stress on the outer steel pipe.

The present invention is not limited to the above embodiments, Ru course der You can make many modifications and changes within the scope of the present invention.

For example, in the above-described embodiment, an example is shown in which spacers 8a to 8c are welded to three places on the inner peripheral surface of the outer steel pipe 3 as the opening holding material 8, and the remaining one spacer 8d is welded to the core steel pipe 2 side. Conversely, the spacers 8a to 8c may be welded and fixed to three places on the outer peripheral surface of the core steel pipe 2, and the remaining one spacer 8d may be welded and fixed to the outer steel pipe 3 side. Furthermore, the spacers 8a to 8d may be welded to one or both of the core steel pipe 2 and the outer steel pipe 3.

Further, the number of the opening holding members 8 is not limited to four as in the present embodiment, and is not particularly limited as long as it is three or more. That is, in the opening holding material 8, three or more spacers are set at intervals in the circumferential direction, and a plurality of spacers except for at least one of these spacers is previously formed on the inner circumferential surface or core of the outer steel pipe. Any mode may be used as long as it is welded and fixed to the outer peripheral surface of the steel pipe. At this time, the number of remaining spacers that are not welded in advance is not limited to one, and may be two or more. Further, the spacing between the spacers is not limited to the regular spacing, and the spacing can be set appropriately according to the situation.

Reference Signs List 1 double steel pipe 2 core steel pipe 3 outer steel pipe 4 drawing 5 circumferential gap
5a Circular opening 6 Plating layer 7 Air vent hole 8 Opening holding material 8a to 8d Spacer S Signal pillar S1 Signal W Welding

Claims (5)

  In the method for manufacturing a double steel pipe comprising an inner core steel pipe and an outer steel pipe, an air vent hole for removing air staying in the plating step is formed in a lower part of the core steel pipe, and the core steel pipe is inserted into the outer steel pipe. Then, the upper end of the outer steel pipe and the core steel pipe are circumferentially welded and fixed above the air vent hole, and a circumferential gap is formed between the lower end of the outer steel pipe and the core steel pipe, A plurality of gap holding materials are installed to hold the gap, and then molten plating is introduced into the gap between the core steel pipe and the outer steel pipe to form a plating layer on the inner surface of the circumferential gap. Characteristic method of manufacturing double steel pipe.   As the plurality of gap holding members, three or more spacers are set at circumferential intervals in a circumferential gap between the core steel pipe and the outer steel pipe, and at least one of these spacers is set. A plurality of spacers are fixed in advance by welding to the inner peripheral surface of the outer steel pipe or the outer peripheral surface of the core steel pipe, and then, after the core steel pipe is inserted into the outer steel pipe, the remaining spacers are attached to the outer peripheral face of the core steel pipe or The method for manufacturing a double steel pipe according to claim 1, wherein the gap holding material is installed in a gap between a lower end portion of the outer steel pipe and the core steel pipe by welding to an inner peripheral surface of the outer steel pipe.   In a double steel pipe composed of an inner core steel pipe and an outer steel pipe, an air vent hole is formed at a lower portion of the core steel pipe for removing air stagnant in a plating step, and the outer steel pipe is formed above the air vent hole. The upper end portion and the core steel tube are welded and fixed in a circumferential shape, and a circumferential gap is formed between the lower end portion of the outer steel tube and the core steel tube. Wherein a plated layer is formed on an inner surface of a circumferential gap between the core steel pipe and the outer steel pipe.   As the gap holding material, in a circumferential gap between the core steel pipe and the outer steel pipe, a plurality of spacers are installed at intervals in a circumferential direction, and an outer peripheral surface of the core steel pipe and an inner peripheral surface of the outer steel pipe are provided. The double steel pipe according to claim 3, wherein the double steel pipe is fixed by welding to one or both of them. A traffic safety facility such as a signal pole or a signpost using the double steel pipe according to claim 3.

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