JP2003062523A - Method for forming coating film on pc standard steel wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a coating film on a PC standard steel wire which forms a uniform synthetic resin coating film between single wires for comprising the PC standard steel wire and on the outer peripheral parts thereof, and eliminates the generation of the traces of air bubbles caused by entraining air for particle transportation on the surface of the coating film on the PC standard steel wire. SOLUTION: This method for forming the coating film on the PC standard steel wire forms the synthetic resin coating film with uniform thickness in which the traces of air bubbles do not exist between the single wires for comprising the PC standard steel wire and on the outer peripheral parts thereof by applying the first coating to a region in a state that the twist of the PC standard steel wire is temporarily opened and the second coating to a region in a state that the twist is returned to the original condition by using a coating gun having discharge ports for synthetic resin particles at a plurality of parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously forming a synthetic resin coating for corrosion protection on the surface of a prestressed concrete (hereinafter referred to as "PC") steel strand.

[0002]

2. Description of the Related Art As a method of coating a surface of a PC stranded wire with a synthetic resin to prevent the surface from being corroded, a synthetic resin particle for forming a coating is heated in a flowing tank. A method has been proposed in which a wire is continuously fed from PC steel, and synthetic resin powder attached to the PC steel wire is melted to form a film. However, such a method does not form a sufficient synthetic resin film inside the PC steel wire, so that P
There was a problem that corrosion spreads from the gap inside the C-strand wire.

Therefore, a method has been proposed in which a synthetic resin film is formed even inside the PC steel strand. For example, the heated PC steel wire is continuously fed into a spreading machine to further spread it, and in the further expanded state, it is sent into the flow tank of the thermoplastic synthetic resin powder, and the thermoplastic wire is fed inside and outside the PC steel wire. After adhering and melting the synthetic resin powder, return to the original twisted state, further adhering and melting the thermoplastic synthetic resin powder on the outer surface, and then cooling to harden the thermoplastic synthetic resin and to cure it from PC steel. A method of forming a synthetic resin coating layer inside and outside the wire has been proposed (hereinafter,
It is called "fluid immersion method". See Japanese Patent Laid-Open No. 3-1436). In addition, P is heated in the same manner and further expanded.
After the electrostatically charged thermosetting resin powder (epoxy resin powder) is attached to the inside and outside of the C steel stranded wire by Coulomb force and the attached resin powder is melted, the original twisted state is restored, and the outside Apply thermosetting resin powder on the surface,
A method has also been proposed in which the coating resin is melted to form a coating film, and then the coating resin is heat-cured (hereinafter, referred to as "electrostatic coating method".

[0004]

However, in the method of forming a coating by adhering and melting synthetic resin powder in the above-mentioned twisted and untwisted state of the PC steel wire, the above-mentioned PC steel is used. The part where the twist of the wire is expanded,
It rotates while the twist is unfolded, but does not rotate when the twist returns. Therefore, under the present conditions in which these two states are simultaneously subjected to coating treatment under the same conditions, there arises a problem that the coating thickness becomes non-uniform. Occurs, which is not economical because it is necessary to make the film thicker than necessary, and furthermore, when the twist returns to its original state, air for powder supply is entrained and the synthetic resin The present inventors have found that the problem that bubbles generated in the coating leave bubbles on the coating surface occurs.

Therefore, the present invention has been developed to solve the above problems, and a first object thereof is to enclose air bubbles for entraining air in the coating film of PC steel wire for carrying powder. A second object of the present invention is to provide a method for forming a coating film of a PC steel stranded wire which eliminates the occurrence of the occurrence of the above. , PC that eliminates the generation of air bubbles due to the entrainment of air to convey powder inside the stranded wire of PC steel
A method of forming a coating of steel strands.

[0006]

The first object is to provide a PC
Apply the first coating in the area where the twist of the steel stranded wire is temporarily open, and in the area where the twist is returned to 2
This is achieved by applying the second coating, and the second
The object of (1) is achieved by using a coating gun having a resin powder discharge port at one location or at a plurality of locations when applying the first coating and the second coating. At this time, the purpose is achieved at a higher level by electrostatically charging the resin powder and causing the adhesion using the Coulomb force.

That is, the method for forming a coating film of a PC steel strand according to the present invention is a method for forming a coating film of a PC steel strand which comprises forming a resin coating between single wires constituting the strand and on the outer peripheral portion of the strand. It is characterized in that the first coating is applied in the region where the twist of the PC steel wire is temporarily open, and the second coating is applied in the region where the twist is restored. In this way, by applying the coating twice in two areas, the PC
By eliminating the coating in the region where the steel strand is temporarily opened and returned to its original state, it is possible to prevent the generation of air bubbles on the surface of the resin coating film due to the entrainment of air.

Further, in the method for forming a film of a PC steel wire according to the present invention, the above-mentioned coating is carried out by spraying the above-mentioned resin powder together with air onto the twisted wire from a coating gun having one or a plurality of discharge ports. It is characterized by By providing at least one coating gun, the film thickness can be made more uniform than in the case of the conventional fluidized contact method.

Further, the method for forming a film of a PC steel strand according to the present invention is characterized in that the resin powder is electrostatically charged by friction between the powders in a coating gun. In this way, by charging the resin powder, it is possible to improve the coating efficiency on the PC steel wire and to form a uniform and thick film.

Further, the method for forming a film of PC steel strand according to the present invention is characterized in that the resin powder is electrostatically charged by corona discharge in a coating gun. in this way,
By charging the resin powder, it is possible to improve the coating efficiency for the PC steel strand and to form a uniform and thick film.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for forming a coating film of a PC steel strand according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an outline of an embodiment of a method for forming a coating film of a PC steel strand according to the present invention, and FIG. 2 is a sectional view of a coating tank for applying the first coating according to the present invention. 3 is a sectional view of a coating tank to which the second coating of the present invention is applied, and FIG. 4 is a perspective view of a coating gun provided in the coating tank to which the second coating of the present invention is applied.

The method for forming a film of PC steel strand according to the present invention is as follows.
It can be configured by the following steps. <First Step> A step of cleaning a PC steel strand. The washing is a step of washing the PC steel strand with an acid, preferably phosphoric acid, to remove grease and the like from the surface thereof. For example, ultrasonic cleaning can be performed by passing a PC steel wire through an ultrasonic cleaning tank filled with an aqueous solution of phosphoric acid.

<Second Step> A step of heating the strand of PC steel. In the step of heating the resin powder to the PC stranded wire and heating it to a temperature sufficient for melting and fusing, the heating temperature varies depending on the type of the resin used, but is preferably about 200 to 250 ° C.

<Third Step> A step of opening the strand of the PC steel strand. As shown in FIG. 1, a step of passing a PC steel strand 1 through a strand opener 2 or the like to temporarily open the twist so that the individual strands 3 are separated from each other.

<Fourth Process> The first powder coating process. As shown in FIG. 1, in the first coating tank 4 provided in the area where the twist of the PC steel wire 1 is temporarily opened and the individual wires 3 are separated from each other, the first resin The process of powder coating with powder. The powder coating method is not particularly limited, but a spraying method using a coating gun is preferable, and an electrostatic spraying method is more preferable. In the electrostatic spraying method, the resin powder is electrostatically charged inside and / or at the tip of the coating gun by friction between powders or corona discharge. The coating tank 4 for applying the first coating is, for example, as shown in the sectional view of FIG. 2, surrounding the circumference of the temporarily opened PC steel stranded wire 1 and facing the PC steel stranded wire 1. The coating gun 7 has one or a plurality of discharge ports 6 opened.
At least one coating gun 7 is provided in the coating tank 4 according to the number of discharge ports 6. The coating guns 7 may be provided in the coating tank 4 at two or more locations in the length direction of the PC steel wire 1.

The resin powder used for forming the coating film may be any as long as it can be melted by heating to form a coating film, either natural resin powder or synthetic resin powder, or thermoplastic resin powder. A thermosetting resin powder may be used. Specifically, epoxy resin powder, epoxy-
Thermosetting resin powder such as polyester resin powder, polyester resin powder, acrylic resin powder, acrylic-polyester resin powder; polyvinyl chloride resin powder, polyethylene resin powder, polyamide resin powder, fluorine resin powder , And thermoplastic resin powders such as modified polyolefin-based resin powders, but epoxy-based resin powders are preferred.

<Fifth Step> A step of restoring the twist of the PC steel wire. Strands are temporarily opened with strand opener 2 etc., and after the first coating is applied in that state,
The process of returning the twist to the original state by the restoring force of the PC stranded wire to the spiral shape.

<Sixth Step> Second powder coating step. A step of performing powder coating with resin powder for the second time in the second coating tank 5 provided in the area in the state after the twist of the PC steel wire in which the twist is temporarily opened is restored. Even in the second powder coating process, the powder coating method is
It is not particularly limited. The spraying method using a coating gun is preferable, and the electrostatic spraying method is more preferable. In the electrostatic spraying method, the resin powder is electrostatically charged inside and / or at the tip of the coating gun by friction between powders or corona discharge. The coating tank 5 for applying the second coating is, for example, as shown in the sectional view of FIG. 3, around the PC steel stranded wire 1 in the state where the twist is returned to the original state, Three coating guns 7 having one or a plurality of discharge ports 6 opened toward the front are provided at equal intervals along the circumference. The number of the coating guns 7 provided in the coating tank 5 is preferably as large as possible, but of course, one coating gun may be provided. As shown in the perspective view of FIG. 4, the coating gun 7 can have a plurality of discharge ports 6 in the coating tank 5 in the length direction of the PC steel strand 1. The resin powder used for forming the film in the second powder coating step is the same as that used in the first powder coating step.

<Seventh Step> A step of hardening and cooling the resin film. A step of curing and cooling the resin coating formed on the surface of the PC steel wire after the second powder coating. As for the curing treatment, when the resin powder used is a thermosetting resin powder, a heating treatment is applied, and when the resin powder used is a thermoplastic resin powder, a cooling treatment is applied. Of course, when the resin powder used is a thermosetting resin powder, it is cooled after being subjected to heat treatment.

[0020]

EXAMPLES The present invention will now be specifically described with reference to examples of the present invention, but the present invention is not limited to the following examples.

[Example 1] PC of 15.2 mm from 7 pieces
After washing the steel stranded wire with a phosphoric acid aqueous solution, the PC stranded wire is
It is heated to 0 ° C., the twist of the PC steel wire is opened by the strand opener 2, and the twisted wire is passed through the first coating tank 4 shown in FIG. PC steel strands passing through the coating tank at a speed of a minute were subjected to the first triboelectrification coating under the following coating conditions. First coating conditions: Conveying air amount 90 N liters / min Acceleration air amount 70 N liters / min Powder discharge amount 200 g / min Then, the twist of the PC steel wire is restored, and then the twist is restored. 3. Pass the second coating tank 5 shown in FIG. 4 equipped with the coating gun 7 shown in FIG. 3, where the epoxy steel powder is used to make PC steel strands passing through the coating tank at said speed. The second triboelectrification coating was performed under the following coating conditions. Second coating conditions: Amount of conveying air 90 N liter / min Acceleration air amount 70 N liter / min Powder discharge amount 200 g / min After that, heat treatment was further performed at 200 ° C. to cure the epoxy resin film, followed by water cooling treatment. . The epoxy resin-coated PC steel stranded wire (300
The coating film thickness between 0 m) was 520 to 730 μm, and the difference in film thickness between the coating portions was about 210 μm. The number of bubbles on the surface of the epoxy resin coating is 0 / 3000m
Met.

[Example 2] Corona electrification coating was carried out under the following coating conditions for the first coating, and the first coating conditions were as follows: conveying air amount 90 Nl / min static voltage 30 kV powder discharge amount 200 g / min second coating Was performed in the same manner as in Example 1 except that the corona charging coating was performed under the following coating conditions. Second coating conditions: Conveying air amount 90 N liter / min Static voltage 30 kV Powder discharge amount 200 g / min Epoxy resin-coated PC steel wire thus obtained (between 3000 m) has a coating film thickness of 740 to 990 μm
The difference in film thickness between the coated portions was about 250 μm. The number of bubbles on the surface of the epoxy resin coating was 0/3000 m.

For comparison, a similar epoxy resin-coated PC steel wire was obtained according to the invention of Japanese Patent No. 2597795 (Florida invention), and its coating film thickness was 530.
˜1150 μm, the difference in film thickness between coated parts is about 62
It was 0 μm. The number of bubbles on the surface of the epoxy resin coating was 15/3000 m.

[0024]

As described in detail above, according to the present invention, the first coating is applied in the region where the twist of the PC steel wire is temporarily open, and the twist is returned to the original state. By applying the second coating, there is an excellent effect that it is possible to eliminate the generation of bubble traces due to the entrainment of air for the powder transportation on the coating surface of the PC steel strand. Further, according to the present invention, when applying the first coating and the second coating described above, by using a coating gun having one or more resin powder discharge ports, the inside and outside of the PC steel strand can be uniformly coated. The excellent effect that a different resin film can be formed is exhibited. At this time, the resin powder is electrostatically charged and adhered by using the Coulomb force, so that a more uniform resin film can be formed between the single wires constituting the PC steel strand and on the outer periphery of the strand. It has an excellent effect that it can be done.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an embodiment of a method for forming a coating film on a PC steel strand according to the present invention.

FIG. 2 is a cross-sectional view of a coating tank for performing the first coating in the embodiment of the method for forming a coating film of PC steel wire according to the present invention.

FIG. 3 is a cross-sectional view of a coating tank to which a second coating is applied in an embodiment of the method for forming a coating film of a PC steel strand according to the present invention.

FIG. 4 is a perspective view of a coating gun provided in a coating tank for performing a second coating in an embodiment of the method for forming a film of PC steel wire according to the present invention.

[Explanation of symbols]

1 PC steel stranded wire 2 Strand Opener 3 single line 4 1st coating tank 5 Second coating tank 6 outlets 7 Painting gun

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kochi Kiyosu             Sumitomo, 1-1 1-1 Koyokita, Itami City, Hyogo Prefecture             Electric Industry Co., Ltd. Itami Works F term (reference) 3B153 AA02 AA45 AA47 CC13 CC15                       CC16 CC19 CC21 CC22 CC26                       CC52 DD30 DD50 FF02 GG07                 4D075 AA09 AE05 BB81X DA01                       DB02 DC03 EA02 EB33                 4G058 GA01 GB02 GC01 GF03

Claims (4)

[Claims] 1. A method of forming a film of PC stranded wire, wherein a resin film is formed between single wires constituting a stranded wire and on an outer peripheral portion of the stranded wire, wherein twist of the PC steel stranded wire is temporarily opened. A PC characterized by applying a first coating in a certain area and then applying a second coating in an area where the twist has been restored.
Method for forming a coating of steel strands. 2. The coating of PC steel stranded wire according to claim 1, wherein the coating is performed by spraying the resin powder together with air onto the stranded wire from a coating gun having one or a plurality of discharge ports. Method. 3. The PC according to claim 2, wherein the resin powder is electrostatically charged by friction between the powders in a coating gun.
Method for forming a coating of steel strands. 4. The method for forming a film of a PC steel strand according to claim 2, wherein the resin powder is electrostatically charged by corona discharge in a coating gun.