JP4602122B2 - Method for producing resin-coated PC steel stranded wire having high yield point ratio and low relaxation characteristics - Google Patents

Description

The present invention relates to a method for producing a resin-coated PC steel stranded wire in which a resin coating is applied to the outer surface of a stranded wire obtained by twisting a plurality of steel wires.

Conventionally, PC (prestressed concrete) that gives a compressive force to concrete is used to improve the rigidity and bending strength of concrete and to prevent cracks.
As a method of applying a compressive force to the PC (prestressed concrete), there is a method of embedding a PC steel stranded wire composed of a stranded wire imparted with a tension force.
In this way, PC steel stranded wires are often used without being covered because they are embedded in concrete or cement grout. For example, concrete strands near the coast or bridge bridges that are in direct contact with the atmosphere. When the use environment such as a material cable or an external cable is bad, the PC steel stranded wire may corrode.
Therefore, a resin-coated PC steel stranded wire whose corrosion resistance is improved by coating the outer surface of the PC steel stranded wire with, for example, a thermoplastic high-density polyethylene resin or the like is used.

However, in the resin coating process, the PC steel stranded wire is reheated to about 280 to 330 ° C., so the yield point ratio is lowered, and the relaxation value is increased, so that the compressive force acting on the concrete is lowered and the PC There was a problem that the effect decreased.
FIG. 6 is a diagram illustrating mechanical properties with respect to the heating temperature of a conventional PC steel stranded wire.
As shown in FIG. 6, when the heating temperature of the PC steel stranded wire is increased, the yield point ratio is gradually decreased, and when the coating temperature is around 260 to 300 ° C., the relaxation value is increased for 1000 hours.
PC steel stranded wire is generally tensioned at 70% of the standard tensile load specified in JISG3536, and is fixed by both-end fixing tools. After tension and fixing, tensile strength is applied during the service life of the PC structure. As a result, creep has occurred in the PC stranded wire, but since both ends are fixed, the tension is reduced accordingly.
This phenomenon is called relaxation (stress relaxation), and if the relaxation value of the PC steel stranded wire is large, it will lead to weakening of the PC structure over the years, so it is necessary to increase the number of PC steel stranded wire as a strengthening method. there were.

Moreover, as a method of resin-coating a PC steel stranded wire, for example, Japanese Patent No. 2510442, Japanese Patent No. 2759166, and Japanese Patent No. 2136181 propose a rust-proof coated PC strand and a rust-proofing method thereof. .
However, the above prior art relates to a resin coating of a PC steel stranded wire, and the resin-coated PC steel stranded wire having a high yield point ratio and a low relaxation property, which is the subject of the present invention, and a method for producing the same, Since it has not been studied, a resin-coated PC steel stranded wire having a high yield point ratio and low relaxation properties has not been realized.
Japanese Patent No. 2510442 Japanese Patent No. 2759166 Japanese Patent No. 2136181

An object of the present invention is to solve the above-described problems of the prior art and to provide a method for producing a resin-coated PC steel stranded wire having a high yield point ratio and low relaxation characteristics.

The present invention has been made as a result of intensive studies in order to solve the above-mentioned problems. By applying a resin coating with the mechanical properties of the steel wire used for the resin-coated PC steel stranded wire and the residual heat of hot stretching, The present invention provides a method for producing a resin-coated PC steel stranded wire having a yield point ratio and low relaxation properties, the gist of which is as follows.
(1) A method for producing a resin-coated PC steel stranded wire in which the outer surface of a stranded wire obtained by twisting a plurality of steel wires is coated with a resin, and the yield ratio of the stranded wire coated with the resin is 90% or more And the 1000 hour relaxation value is 2.5% or less ,
The steel wire constituting the stranded wire was subjected to patenting and wire drawing to increase the tensile strength of the steel wire to 1970-2100 N / mm ^2, and stranded wire processing was performed to match the steel wires from a plurality of wires. Thereafter, a resin-coated PC steel twist having a high yield point ratio and a low relaxation characteristic, characterized in that a tensile strain exceeding 10 μm is applied and hot stretching is performed, and the stranded wire is coated with the residual heat. Wire manufacturing method.

4 and 5 are diagrams showing the effect of reducing the relaxation value of the resin-coated PC steel stranded wire in the present invention. FIG. 4 shows the relaxation curve before resin coating and FIG. 5 shows the relaxation curve after resin coating.
In FIG. 4, the conventional PC steel stranded wire indicated by a dotted line has a 1000 hour relaxation value before coating of 1.3% and a 1000 hour relaxation value after coating of FIG. 5 of 4.0%. According to the PC steel stranded wire of the present invention indicated by a solid line 4, the 1000 hour relaxation value before coating can be reduced to 0.6%, and the 1000 hour relaxation value after coating in FIG. 5 can be reduced to 1.8%. .
Thus, according to the present invention, the mechanical properties of the steel stranded wire used in the resin-coated PC steel stranded wire can be reduced by devising the patenting, wire drawing and hot stretching conditions, and also by reducing the conventional yield point ratio. In addition, it is possible to provide a method for producing a resin-coated PC steel stranded wire having a high yield point ratio and low relaxation characteristics by stopping the reheating to increase the relaxation value and applying the resin coating with the residual heat of hot stretching, etc. There are significant industrially useful effects.

The best mode for carrying out the present invention will be described below.
The resin-coated PC steel stranded wire having a high yield point ratio and low relaxation characteristics according to the present invention is a resin-coated PC steel stranded wire in which a resin coating is applied to the outer surface of a stranded wire obtained by twisting a plurality of steel wires, The yield ratio point of the stranded wire coated with resin is 90% or more, and the 1000 hour relaxation value is 2.5% or less.
As a result of investigating the relationship between the resin coating, the yield point ratio, and the relaxation value, the present inventors have reheated the steel strand in the temperature range of 280 to 330 ° C., and this reheating is a steel twist. It was found that the yield point ratio of the line was lowered and the relaxation value was further increased, and a certain correlation was found between the yield point ratio and the relaxation value before and after resin coating.
Therefore, the present inventor has raised the tensile strength of the PC steel stranded wire to which the resin coating is applied, and has focused on the fact that the reheating for applying the resin coating can be replaced with the remaining heat of the hot stretching, As a result of resin coating in-line, it was found that the yield point ratio can be maintained at 90% or more and the 1000 hour relaxation value can be 2.5% or less.
Here, the yield point ratio means the ratio of the yield load to the rupture load, and the 1000 hour relaxation value means the relaxation value when the tensile load is applied for 1000 hours at 70% of the standard tensile load defined in JIS G3536. .
In the present invention, the number of stranded wires and the resin coating method are not limited, but in order to ensure strength and corrosion resistance, on the outer surface of the stranded wire obtained by twisting three, seven, or nineteen steel wires, A twisted wire filled with a thermoplastic resin (for example, high-density polyethylene resin) that is resistant to ultraviolet rays and has a uniform film thickness is preferable.

FIG. 1 is a diagram illustrating an embodiment of a method for producing a resin-coated PC steel stranded wire having high yield point ratio and low relaxation characteristics according to the present invention.
PC steel stranded wire is specified by JISG3536 to use JISG3502 piano wire, and in order to ensure high strength with a tensile strength of 1970-2100 N / mm2 by processing such as patenting, wire drawing and stranded wire, JISG3502 SWRS87B or SWRS92B high carbon piano wire is required.
Next, the steel wire is patented (S-2), pickled to remove the scale formed on the surface, and then applied with a lubricant to form a film to facilitate drawing (S-3). .

Next, for example, a 13 mmφ steel wire is processed to about 5 mmφ by wire drawing, and the tensile strength is increased to 1970-2100 N / mm ² (S-4).
By increasing the tensile strength to 1970-2100 N / mm ² , the yield point ratio can be increased by stranded wire processing and hot stretching, and the relaxation value for 1000 hours can be reduced.
Next, for example, three, seven, or nineteen steel wires are stranded (S-5).
What is necessary is just to select suitably the number of the steel wires to process a strand wire by the intensity | strength which a strand wire requires.
Next, hot stretching is performed by applying a high tension of about 15 μm in tensile strain (S-6).

For example, by performing hot stretching at 350 to 380 ° C., residual strain generated in the steel wire by wire drawing and twisting can be removed. At this time, the relaxation value can be reduced for 1000 hours by applying high tension with a tensile strain of 15 μm and hot stretching.
Next, the stranded wire that has been hot-stretched is released from high tension and coated with a resin at a residual heat of 300 to 330 ° C. at 350 to 3380 ° C. (S-6).
In the present invention, the resin coating method is not limited, but for example, a method of filling and coating a thermoplastic resin made of a high-density polyethylene resin is preferable, and conventionally, the 1000-hour relaxation value after resin coating was about 4%. However, it can be reduced to about 2% by applying the present invention.
FIG. 2 shows an in-line resin coating method of the present invention, and FIG. 3 shows a conventional offline resin coating method.
In the conventional off-line resin coating method (FIG. 3), after the hot stretching is performed, the relaxation value is increased by reheating to apply the resin coating after being wound up once. In the resin coating method (FIG. 2), after the hot stretch is applied, it is not wound up, and since the resin coating is applied to the stranded wire with the remaining heat, it is not reheated, so that the relaxation value does not increase and the cost of reheating is unnecessary. And the economic effect is very large.

The results of carrying out the present invention under the following conditions are shown below.
Using the steel type piano wire shown in Table 1, it was processed into a coated stranded wire under the conditions shown in Table 1.
<Cross-section reduction rate>
The cross-sectional reduction rate in Table 1 is obtained by [wire cross-sectional area A ₁ −drawing diameter cross-sectional area A ₂ ] ÷ wire cross-sectional area A ₁ and is generally referred to as the degree of wire drawing.
In the drawing of a piano wire, the tensile strength increases as the workability increases. However, if the workability is too high, brittleness appears due to overdrawing. The tensile strength of a PC steel stranded wire can be controlled by the degree of wire drawing of the strand, which is a limit of 85 to 90% in the drawing of the strand for PC steel stranded wire.
<Results of Examples>
(1) Example 1: Demonstration of claim 1 characteristics according to claim 2 manufacturing method Using piano wire SWRS87B, wire drawing with a cross-section reduction rate of 85% and seven strands whose tensile strength is raised to the claim range Twisted wire processing. The stranded wire was hot-stretched with a tension of 15 μm in tensile strain and then coated with a resin. As a result, as shown in Table 2, a wire was obtained from the resin-coated PC steel having a high yield point ratio and low relaxation characteristics.

It is a figure which illustrates embodiment of the manufacturing method of the resin coating PC steel strand wire which has the high yield point ratio and low relaxation characteristic of this invention. It is explanatory drawing of the hot stretching of this invention, and an in-line coating processing method. It is explanatory drawing of the offline coating processing method of a prior art. It is a figure which shows the relaxation curve before resin coating of the resin coating PC steel strand. It is a figure which shows the relaxation curve after resin coating of the resin coating PC steel strand which is a figure shown. It is a figure which illustrates the mechanical property with respect to the heating temperature of the conventional PC steel strand wire.

Claims (1)

A method for producing a resin-coated PC steel stranded wire in which a resin coating is applied to the outer surface of a stranded wire obtained by twisting a plurality of steel wires, wherein the yield ratio of the stranded wire coated with the resin is 90% or more, and 1000 hour relaxation value is 2.5% or less ,
The steel wire constituting the stranded wire was subjected to patenting and wire drawing to increase the tensile strength of the steel wire to 1970-2100 N / mm ^2, and stranded wire processing was performed to match the steel wires from a plurality of wires. Thereafter, a resin-coated PC steel twist having a high yield point ratio and a low relaxation characteristic, characterized in that a tensile strain exceeding 10 μm is applied and hot stretching is performed, and the stranded wire is coated with the residual heat. Wire manufacturing method.

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