JPS61293580A - Method for continuously coating steel material - Google Patents

Abstract

PURPOSE:To make the coated film uniform and to facilitate the control of painting by forming a continuous body with plural steel materials through a joint having magnetic force. CONSTITUTION:In the process for producing a painted steel material with use of a thermosetting powder paint, a pillar-shaped joint C having magnetic force and provided with a recessed part having a cross section almost identical to that of a steel material is fixed to one or both ends of the steel material to be painted and plural steel materials are combined to form a continuous body which is coated. Consequently, the coated film is made uniform, the control of painting is facilitated and the coating efficiency is improved. Although the part of the steel material which has not been fixed to the joint is not coated, the part can be easily coated after the steel material passes through a line by using a repairing paint or a repairing means by the thermal spray of a plastic, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the continuous coating of steel materials, and particularly to a continuous coating method for coating the surface of steel materials with a thermosetting powder coating for anticorrosion.

[Prior art and problems to be solved by the invention] Recently,
With the increase in the number of concrete structures using sea sand and the appearance of marine concrete structures, deterioration of steel materials has become a serious problem. For example, sea salt particles may fly into concrete structures near the coastline, or in areas where the atmosphere repeatedly wets and dries, the diffusion of salt and oxygen is promoted, corroding steel materials, promoting cracks in concrete, and damaging structures. A phenomenon of damage is occurring. As a means to solve this problem, a method of applying anti-corrosion organic coating to steel materials such as steel bars and sections for reinforced concrete is proposed (Draft) Corrosion Prevention Guidelines for Marine Concrete Structures (Japan Concrete Institute, 1982). (1981) Guidelines for Salt Damage Countermeasures for Road Bridges (Draft) and Commentary (Japan Road Association, February 1981), and ASTM Standard A 775 (1981).
has standards regarding this.

Figure 1 is a schematic diagram showing an example of the coating process in the same technology. In the figure, 1 is the steel material to be painted, 2 is a blasting device for removing scale from the surface, and 3 is a heating device. , 4 is a powder coating device for coating the steel surface with a thermosetting powder coating, and 5 is a cooling device. For painting, first, mill scale on the surface of the steel material 1 is removed using a blasting device 2. Next, the steel material 1 is preheated by the heating device 3, and then the steel material 1 is preheated by the powder coating device 4.
Apply thermosetting paint. Then, it is cooled down to near room temperature by the cooling device 5, and the tamales are completed. Generally, anti-corrosion coatings are applied to various steel materials using such coating methods, but deformed steel bars for reinforced concrete in particular are coated with knots in various patterns to increase the adhesion strength to concrete, as specified in JIS 3112. The surface has irregularities such as When painting deformed steel bars with such protrusions, there is a problem in the relationship between coating film thickness and concrete adhesion strength.If the coating thickness is too thick, the adhesion strength to concrete will decrease; If it is too thick, problems such as pinholes will occur.

In this way, when painting deformed steel bars, the coating thickness is an important point. However, when a steel bar with projections like this is transported, the projections hit the conveyance roller, causing vibrations in the steel bar.Furthermore, this vibration propagates to the ends of the steel bar, resulting in large vibrations at the ends and insufficient film thickness. There is a risk that it will become uniform.

In addition, deformed steel bars are made to a standard length (3° 5m to 20m standard length 5.
Since the ground is divided into sections (5 to 12 m), the ground required for electrostatic painting cannot be continuously obtained, which makes it difficult for the charged paint to adhere and the paint film to become thin. As mentioned above, there are various problems in producing a uniform coating film, and these problems have not been solved at present.

[Means for solving problems]

The inventors of the present invention solved these problems and conducted various studies on methods that could continuously coat steel materials. It has been discovered that the above problems can be solved all at once by forming a .

That is, the present invention has been made based on the above-mentioned knowledge, and its gist is that in the process of manufacturing coated steel using a thermosetting powder coating, one end or both ends of the steel to be coated On the other hand, a continuous coating method for steel materials is characterized in that a columnar joint that is magnetic and has a concave portion having approximately the same cross-sectional shape as the steel material is installed, and a plurality of steel materials are painted as a series of continuous bodies. It is in.

[Effect]

The present invention will be explained in detail below.

First, the process itself of the present invention is schematically similar to the conventional means shown in FIG. First, a joint as shown in the conceptual diagram in Fig. 2 is attached to one end of the steel material to be coated, and then the steel material is successively joined to form a series of continuous steel materials. The coating is performed by sequentially passing through a coating device 4 and a cooling device 5. In this case, suitable joints are columnar as shown in the front view in Fig. 2 (A) and side view in Fig. 2 (B). Depending on the type, shapes such as prismatic shapes can be used. Next, in FIG. 2, recesses 6 are provided at both ends of the joint. The shape of this recess should be approximately the same as the cross-sectional shape of the steel material to be coated, and several types of joints having recesses shaped according to the size and shape of the steel material may be prepared as necessary. Furthermore, the joint must be able to move together with the steel material, have adhesion, and be removable so that it can be easily removed at the end of the painting process. For this reason, the joint body is made of KS steel, MK steel (alnico), etc. with a magnetic flux density of 10 to 2°K J/rn' and a Curie temperature of 500.
It is effective to use a material that has a strong magnetic force of about ℃ or higher.

In that case, it is good to construct the entire joint with the same material, but it is also possible to construct the columnar core of the joint with a magnetic material and the side surface 7.
It can also be made of stainless steel, ceramic, plastic, etc. This has the effect of preventing damage to the joint, preventing a decrease in magnetic force, and reducing weight. Furthermore, if the surface of the side surface 7 is coated or painted in advance with a substance that has a mold release effect on paint such as Teflon mold release agent, the joint can be used repeatedly after passing through the process. The coating film can be peeled off in a short time during the process, and the joint can be easily reused during the process.

The size and shape of the recess should be selected appropriately depending on the size and shape of the steel material, but for example, the nominal diameter D shown in JIS 3112 for a joint as shown in
When painting 22 mmφ, the recess 6 should be 2 mm deep or more.
Approximately 5 mm, the thickness of the edge 8 is approximately 1 mm to 3 m-m
It is appropriate to make both ends of the side surface 7 slightly tapered from the center toward the ends, thereby reducing the possibility of the sheet being caught on the conveying roller. In addition, Fig. 2 (A).

The shape of the edge 8 in (B) is not limited to the shape shown in Fig. 2, and may be a discontinuous cut or slit-like shape in the annular part, or a shape in which protrusions are appropriately arranged. The shape of the edge 8 may be any shape as long as the recess 6 has a shape that is approximately the same as the shape of the steel material and the steel material does not shift during transportation.

With this coating method, the steel material, which was conventionally coated for each individual fixed-length object, is made into a continuous body, so the edges of the steel material do not appear until the end of the process, which prevents the steel material from running out due to the rolls in front of the heating device 3. problem will inevitably disappear. Furthermore, since it is a continuous body, constant conditions can be maintained even within the heating device 3, making it easier to manage the temperature uniformity during preliminary preparation. As a result, even in electrostatic powder coating, where preheating has a large effect on coating thickness, the coating thickness becomes uniform and pinholes are naturally reduced. In addition, since the powder coating device 4 is a continuous unit, the object to be coated is always grounded, making it easier to control the coating by voltage and powder discharge amount, resulting in uniform coating and improved coating efficiency. Inherit. The parts attached to the steel joints will be unpainted, but this can be easily compensated for by using repair methods such as repair paint or plastic spraying after passing through the line.

The effects of the present invention will be illustrated in more detail with reference to Examples below.

〔Example〕

Painting was carried out according to the process shown in Figure 1 using a deformed steel bar with a nominal diameter of 22 mm and a length of 5.5 m that had corrugated knots in accordance with JIS G 3112.

The surface was adjusted using the blasting device 2, and then, as a comparison example, the steel materials were conveyed and painted to a fixed length as before, and the remaining half of the steel materials had dimensions of 24 mm x 100 mm as an example of the present invention, and were coated on the surface. Teflon film thickness 5
While sequentially installing joints made of MK steel coated with a 0μ coating, the continuum was fed into the heating device 3, and the continuous body was conveyed and painted. These steel bars are heated by heating device 3 for 24 hours.
After heating to 0'C, a fast-curing epoxy powder coating was immediately coated with a powder coating device 4 with a target cured coating thickness of 180±50μ, and then cooled with a cooling device 5 to near room temperature. These test specimens were evaluated by paying attention to the film thickness distribution and the presence or absence of pinholes. In addition, for the examples of the present invention, the joints are removed and each specimen is described as one test specimen.

Test method (a) Pinhole test (based on ASTM A-775) The number of pinholes is determined using a wet sponge pinhole detector (applied voltage 67.5V).

(b) Film pressure distribution measurement test (based on the method of the Japan Society of Civil Engineers subcommittee) The film thickness of the flat part was measured at 4 points in the circumferential direction and at 500 mm intervals in the axial direction using an electromagnetic film thickness system (1 point type) and averaged. and ask.

Table 1 shows the test results of the invention examples and comparative examples. As is clear from the table, the steel bars painted by the method of the present invention have better results than the steel bars painted by the conventional method, such as a more uniform film thickness distribution and a reduced number of pinholes. was gotten.

〔Effect of the invention〕

As is clear from the above embodiments, according to the present invention, when painting steel materials, it is possible to improve the uniformity of the paint film and to simplify the painting management, which could not be expected in the past, and the industrial effects are as follows: There are some very notable ones.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a process of applying an anticorrosive organic coating to steel materials, and FIGS. 2(A) and 2(B) are conceptual diagrams showing one embodiment of a joint used in the present invention. 1... Steel material to be coated 2... Blasting device 3... Heating device 4... Powder coating device 5... Cooling device 6... Recess 7... Joint side surface 8... Edge of recess

Claims (1)

[Claims] In the process of manufacturing coated steel using thermosetting powder coating, a columnar joint that has a magnetic force on one or both ends of the steel to be coated and has a recess with a shape that is approximately the same as the cross-sectional shape of the steel. A continuous coating method for steel materials, characterized in that a plurality of steel materials are coated as a series of continuous bodies.