JPH0637718B2 - Zinc electrolytic stripping method for steel pipes for non-sprinkling snow melting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a steel pipe for snow-free water-sprinkling for melting snowfall on a road surface such as a road. The present invention relates to a zinc electrolytic stripping method for a steel pipe for non-water-spraying snow melting, which comprises electrolytically stripping a zinc coating only on the outer circumference of the end of the steel pipe and joining the ends by TIG welding.

[Conventional technology]

Conventionally, synthetic resin pipes and steel pipes have been mainly used as heat radiation pipes for snow-less sprinkling. However, among these radiating pipes, synthetic resin pipes are inferior in thermal conductivity and load resistance, so that steel pipes excellent in thermal conductivity and load resistance are often used as the radiating pipes. Thus, when a steel pipe is used as the heat dissipation pipe, it has excellent thermal conductivity and also has excellent load resistance, so it can be embedded in a relatively shallow portion of the snowy road surface. Snow that falls on the road surface can be melted simply by running cold water such as groundwater. However, a large number of steel pipes must be connected to form the heat dissipation pipe portion on the road surface using the steel pipes.

In recent years, as a method for joining such non-water-spraying snow-melting steel pipes, the end faces of the non-water-spraying snow-melting steel pipes are brought into contact with each other, and a high-energy welding beam focused on the abutting portion is irradiated to melt the melted portion. Welding method in which a cooling gas is blown onto is used. According to this welding method, a convex portion is not formed in the welded portion, the welded joint portion can have extremely high strength, and a product sufficiently resistant to bending can be obtained. However, in order to complete the welding of the welded part by this welding method and to manufacture a steel pipe for snow-less water-free snow removal with high strength, the surface of the steel pipe was covered in order to cause effective welding with a tungsten electrode as a pretreatment operation. It is necessary to completely remove the zinc coating that is present.

As the zinc removal method, a method of mechanically grinding and removing the pipe end surface of the steel pipe, a method of chemically removing the pipe end surface of the steel pipe with hydrochloric acid, an electrolytic method with NaH ₂ PO ₄ 2H ₂ O,
One of the electrolytic methods using a mixed solution of ZnCl ₂ and NH ₄ Cl has been performed.

[Problems to be Solved by the Invention]

However, these zinc removal methods have the following drawbacks.

That is, the mechanical grinding removal method has a drawback that uniform grinding is difficult and the zinc coating is not completely removed, so that the welded portion cannot be completely melted.

Further, when the zinc is completely removed by this mechanical grinding removal method, the steel pipe of the base material is also ground, and the weld connection in such a state has a drawback that the strength of the steel pipe joint is lowered.

Also, with the chemical removal method using hydrochloric acid, the zinc coating can be completely removed, but peripheral equipment may be corroded by hydrogen chloride gas generated when the zinc coating is chemically removed by hydrochloric acid. However, it has a drawback that even the steel pipe of the base material is eluted to embrittle the material. In addition, in this chemical removal method using hydrochloric acid, after removing the hydrochloric acid film,
It has a drawback that the treatment becomes complicated, such as the need for neutralization treatment and rust prevention treatment. Further, in this method of chemically removing the zinc coating with hydrochloric acid, there is a risk that an operator may inhale the generated hydrogen chloride gas in the treatment process.

Further, in the electrolysis method using NaH ₂ PO ₄ .2H ₂ O, the zinc removal rate is extremely slow unless the electrolytic cell is heated to about 40 ° C., and the cost becomes high.

Furthermore, in the electrolysis method using a mixed solution of ZnCl ₂ and NH ₄ Cl, PH
Is slightly acidic near 5.0, the end surface of the steel pipe after zinc removal is gradually subjected to air oxidation, and thus rust prevention treatment was necessary to prevent this. When a mixed electrolyte solution of ZnCl ₂ and NH ₄ Cl is used, zinc crystals are deposited on the cathode plate and gradually grow, and the electrolytic efficiency is deteriorated by contacting the steel tube of the anode provided in the middle part. In order to prevent this, it was always necessary to remove the crystals generated on the cathode plate. Furthermore, if this mixed electrolyte solution of ZnCl ₂ and NH ₄ Cl is used for a long period of time, the electrolytic solution deteriorates, and the electrolytic capacity cannot be restored to the original state by only supplementing a part of the electrolytic solution. Was occurring in large numbers. This Zn on it
A large amount of heavy metal zinc is contained in the mixed electrolyte solution of Cl ₂ and NH ₄ Cl, and zinc dissolved from the end surface of the steel pipe is also added to this, increasing the concentration of zinc and increasing environmental protection. The waste liquid treatment had many drawbacks such as difficult problems occurring.

The present invention has been made in view of the above circumstances, without easily damaging the steel pipe base material by electrolytically peeling the zinc coating on the outer peripheral surface of the pipe end portion of the non-sprinkling snow melting steel pipe, and It is an object of the present invention to provide a zinc electrolytic stripping method for a steel pipe for snow-free water sprinkling, which can improve bending workability of the steel pipe without causing embrittlement of the steel pipe joint base material even when used for water sprinkling snow-melting. Has an aim.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention arranges a cathode metal plate during electrolyte welding, and uses the tube end of a U-shaped steel pipe as an anode and the tube end of the anode steel pipe in the electrolyte solution. In the method of immersing upright and supplying a direct current to electrolytically strip the zinc coating covering the surface of the steel pipe end portion, a 10% to 13% ammonium nitrate solution is used as the electrolyte solution, and a DC voltage of 30 is used. The present invention is characterized in that after the electrolytic peeling is performed only on the outer surfaces of both ends with a bolt and a current value of 10 amps at the maximum, the ends of the steel pipe are brought into contact with each other and joined by TIG welding.

[Action]

Next, the operation of the present invention will be described. The end of a steel pipe connected to a direct current with a voltage of 30 V and a maximum current of 10 amperes is applied to an end of 1 to 2 cm with 10 to 13% of ammonium nitrate and a pH of 7.5 to 8.5. When it is immersed upright in the electrolyte solution for about 7 minutes, the zinc coating on the outer surface of the steel pipe end that has a large ionization tendency is eluted as ions in the electrolyte solution and the zinc coating is electrolytically peeled off, and the zinc coating on the inner surface of the steel pipe end is removed. It remains as it is. The zinc thus eluted is deposited in the electrolyte solution by depositing zinc zinc on the surface of the metal plate of the cathode in an amount equivalent to the zinc ions eluted. And ammonium nitrate 10% ~
The pH immediately after adjusting the 13% electrolyte solution is around 4.5, which is weakly acidic, but soon after it is used as an electrolyte solution, it stabilizes to a weak alkaline of pH 8.0, and when the electrolyte deteriorates, new ammonium nitrate is used. If the solution is additionally replenished, the electrolytic ability of the electrolytic solution is immediately recovered and is stable at around pH 8.0. Each end of the thus-obtained water-free snow-melting steel pipe is brought into contact with each other and joined by TIG welding to manufacture a water-free snow-melting steel pipe.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In the figure, the bath 1 is filled with an ammonium nitrate (NH ₄ NO ₃ ) electrolyte solution 7, and the electrolyte solution 7 has a concentration of ammonium nitrate of 10% to 13% and a pH of 4.
It is around 5, but soon after starting to use, it stabilizes to a weak alkaline of pH 8.0 and stabilizes, and it is most suitable for zinc peeling only on the outer surface of the end of the steel pipe. .5-8.
The weak alkalinity of 5 can be maintained, and this electrolyte solution has a sufficient electrolytic stripping effect of the zinc coating at a normal temperature (5 ° C to 25 ° C), and it is not particularly necessary to heat it.

A discharge port 11 is provided at the bottom of the bathtub 1,
A pipe line 9 is connected to this outlet. A filtering device 5 is connected to the conduit 9 via a chemical pump 4. This filtering device 5 is for keeping the electrolyte solution 7 obtained by filtering zinc deposited in the electrolyte solution 7 always clear. A pipe line 10 is connected to the filtering device 5, and the pipe line 10 is connected to the bathtub 1. In this way, a reflux path is configured in which the electrolytic solution 7 is discharged from the bathtub 1 via the pipe 9 by the chemical pump 4, filtered by the filter device 5, and supplied again to the bath 1 via the pipe 10. .

An insulating base 6 is provided in the bath 1 at a position lower than the surface of the electrolytic solution 7 by a predetermined position. A U-shaped steel pipe 3 for snow-free snow-spraying formed on the insulating base 6 is erected vertically and a plurality of pipe ends are immersed in the electrolytic solution 7. The steel pipe 3 is a galvanized steel pipe having a chemical composition defined by JIS G-3452, and the anode of the DC power supply 2 is connected to the steel pipe 3. Further, cathode plates 8 are provided on both side surfaces of the insulating base 6 in the bath 1, and the cathode of the DC power supply 2 is connected to the cathode plates 8.

With this structure, when the end of the steel pipe 3 connected to the DC power supply 2 is immersed in the electrolytic solution 7, only the outer surface of only 1 to 2 cm of the outer surface of the end of the steel pipe 3 is present. The zinc coating having a large ionization tendency is eluted as ions in the electrolytic solution 7 and the zinc coating is electrolytically peeled off, and the zinc on the inner surface remains without being removed. The zinc thus eluted is equivalent to the zinc ions eluted on the surface of the cathode plate 8 in the amount of metallic zinc, which floats and precipitates. Therefore, in order to make the concentration of the electrolyte solution 7 in the bath 1 uniform, the chemical pump 4 is operated, and zinc suspended in the electrolyte solution 7 is filtered by the filter device 5 to keep the electrolyte solution 7 clear at all times. Further, even if the electrolyte solution deteriorates with use, the electrolytic ability is restored with a small amount of replenishment.

The steel pipes thus obtained are brought into contact with each other at their pipe ends to perform TIG welding to manufacture a steel pipe for non-sprinkling snow melting.

It is clear as a result of a qualitative test that zinc is completely removed from the outer surface of the pipe end of the steel pipe treated according to this example, and that portion is difficult to oxidize, and the steel pipe outer surface 1 to Only the 2 cm galvanized end is melted and bonded well, and the generation of toxic gas can be prevented. Further, the zinc coating on the inner surface of the pipe end is not electrolytically peeled off, and when TIG welding is performed, the pipe ends that are in contact with each other are rapidly removed from the outside by 10
When heated to 00 to 3000 ° C and melt-bonded, the zinc coating remaining on the inner surface is once vaporized and fills the inside of the pipe, and the vaporized zinc vapor is combined with iron by the rapid cooling of the welded portion by the cooling gas and new An alloy is formed, and this alloy forms a new coating on the inner surface of the pipe end joint where they are welded to each other to protect the inner surface. It was also clear that no convex portion was formed on the inner surface of the steel pipe and the welded portion had a strength higher than that of the base metal.

Therefore, the radiating pipe according to the present embodiment is not damaged even by a heavy vehicle passing on the road, and is not fragile even by long-term groundwater flow.

〔The invention's effect〕

As described above, according to the present invention, electrolytic stripping of zinc is performed by immersing it upright in an electrolyte solution of ammonium nitrate having a high solubility and a property of dissolving a metal oxide for a short time. It can be limited to only ~ 2 cm, and can easily and stably have a pH of 7.5 to 8.5 (especially 8.
An electrolyte solution (stable around 0) is obtained, and even if the electrolyte solution deteriorates with use, the electrolytic ability is restored by simply replenishing a small amount of a new ammonium nitrate solution. For this reason, unlike the case of exchanging the total amount of the electrolyte solution, only a small amount of waste liquid needs to be treated.In this electrolyte solution, it is not necessary to heat the electrolyte solution when electrolytically stripping the zinc coating, and the steel pipe of the base material is not damaged. In addition, the zinc coating can be electrolytically stripped safely at low cost in a short time.

Further, after the electrolytic removal of the zinc coating, the steel pipe base material is less likely to be oxidized by welding, and the end faces of the non-water-spraying snow-melting steel pipes are brought into contact with each other, and an inert gas for shielding is flowed through the contact portions. Since the joining is performed by TIG welding performed in an active atmosphere, only the end portion where the above-mentioned zinc plating is electrolytically peeled is heated and melted, and good quality joining can be performed.

Further, particularly in the zinc electrolytic peeling method of the steel pipe for non-water-spraying snow melting of the present invention, only the zinc on the outer surface of the pipe end is electrolytically peeled, and the zinc on the inner surface remains, so when performing TIG welding, the zinc left on the inner surface is Once heated, it vaporizes, but the zinc vapor melts into the iron to form a new alloy film and protects the inner surface. In addition, the generation of toxic gas can be prevented, the welded joint has extremely high strength, and there are no protrusions on the inner circumference of the welded part, so there is no unevenness in the welding, so there is no resistance to the fluid such as groundwater flowing inside. The present invention has the effect of obtaining a steel pipe for snow-free snow-spraying that can sufficiently withstand flow and bending.

As described above, according to the present invention, since the heat-dissipation pipe of the zinc electrolytic stripping method for the non-sprinkling snow-melting steel pipe has strength higher than that of the base metal, it is not damaged by heavy vehicles passing on the road, and groundwater is not damaged. It has the effect of not causing embrittlement even by long-term water flow.

[Brief description of drawings]

 FIG. 1 is a perspective view showing an embodiment of the present invention. 1 ... Bathtub, 2 ... DC power supply, 3 ... Steel tube, 4 ... Chemical pump, 5 ... Filtration device, 6 ... Insulating base, 7 ... Electrolyte, 8 ... Cathode plate, 9, 10 ... … Pipeline, 11 …… Discharge port.

Claims (1)

[Claims] 1. A cathode metal plate is placed during electrolyte welding, and U
Using the pipe end of the steel pipe formed in a V shape as an anode, the pipe end of the anode steel pipe is immersed vertically in the electrolyte solution, and a direct current is supplied to electrolytically peel off the zinc coating covering the surface of the steel pipe end. In the method, the electrolyte solution contains 10% to 13%.
After performing the electrolytic peeling of only the outer surfaces of both ends of the steel pipe at a DC voltage of 30 V and a maximum current value of 10 amperes using the ammonium nitrate solution, the TIG welding is performed. A method for electrolytically stripping zinc-free steel pipes for water-free snow melting.