JPS61120671A - Production of painted steel material with good concrete adhesive property - Google Patents

Abstract

PURPOSE:To obtain a painted steel material having not only a corrosion inhibiting property but also a concrete adhesive property, by spraying a powder paint having specific physical values during a period from the melting of the powder paint to the curing thereof. CONSTITUTION:In a process for applying a heat-curable powder paint to a steel material such as rod steel for reinforced concrete embedded in concrete, a powder paint spray apparatus 5 is provided between a powder paint coating apparatus 4 and a cooling apparatus 6. In the powder spray apparatus 5, a coarse particulate paint is sprayed to the steel plate 1 to be melted and fixed by the residual heat of said steel material 1 and unevenness due to coarse particles is formed to the coated surface of the steel material 1. The coarse particulate paint used in this case has physical properties such that a flow index is 5 or less at 20 deg.C and a particle size is 100mum-2mm.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing steel materials whose surfaces are coated with anti-corrosion coating.
In particular, the present invention relates to a method for producing coated steel materials with good adhesion to concrete using a thermosetting powder coating.

[Prior art and problems to be solved by the invention] Recently, with the increase in concrete structures using sea sand and the appearance of marine concrete structures, deterioration of structures due to corrosion of steel has become a serious problem. 0 For example, sea salt particles fly into concrete structures near the coastline, or where the atmosphere experiences repeated wet and dry cycles, the diffusion of salt and oxygen is promoted.
Steel materials are corroding, which promotes cracking and damages structures. As a means of solving this problem, a method of applying an organic coating for anticorrosion to steel bars and sections, including those for reinforced concrete. ), Guidelines for Salt Damage Countermeasures for Road Bridges (Draft) and Commentary (
(Japan Road Association, February 1982), etc. have been proposed.

FIG. 2 is a schematic diagram showing a conventional painting process, in which 1 is a steel material to be coated that moves in the axial direction, and 2 is a blasting device for removing mill scale from the surface.

3 is a heating device, 4 is a powder coating device for coating the surface of steel material with a thermosetting powder coating, and 6 is a cooling device. First, mill scale on the surface of the steel material 1 is removed using a blasting device 2.Next, the steel material 1 to be coated is preheated using a heating device 3, and then a thermosetting powder coating is applied using a powder coating device 4.

The coated powder is cured by the heat of the steel to be coated through the process of melting, gelling, and hardening, and when hardening is completed, it is cooled down to around room temperature by the cooling device 6, and the coating is completed. Powder paint is melted→
Levels during the gelation stage to form a glossy and smooth surface. The paint most commonly used for this hot coating is a thermosetting epoxy powder coating, but thermosetting polyester powder coatings and thermosetting acrylic powder coatings can also be used.

It is possible to apply anti-corrosion coating to various steel materials by such means, but deformed steel bars for reinforced concrete in particular are subject to JIS standards.
As stipulated in 3112, various patterned knots and other irregularities are added to the surface to strengthen the penetration into the concrete and increase the adhesion strength to the concrete. However, when painting such deformed steel bars, it is extremely difficult to achieve a uniform coating thickness. For example, when painting the joints of a deformed steel bar, it is not possible to coat the convex surface of the joint with a uniform thickness, and the surface inevitably becomes rounded, which has the disadvantage of making it harder to penetrate the concrete. .

In addition, because the coating film is smooth, chemically stable, and hydrophobic, its adhesion to concrete is stronger than the oxides on the surface of the deformed steel bar before coating.
(mill scale), the adhesion strength of painted deformed steel bars to concrete is approximately 60 to 80% lower than that of unpainted deformed steel bars. In addition, in repeated bending tests of beams reinforced with painted deformed steel bars, there is a problem in that the concrete becomes lumpy and easily falls off.

[Means for solving problems]

Therefore, the inventors of the present invention have conducted various studies on ways to solve the drawback of the adhesion to concrete of the currently used coated steel materials and to obtain coated steel materials that have both corrosion resistance and adhesion to concrete. By introducing a means of spraying a powder coating with specific physical properties between melting and curing.

It has been discovered that the above problems can be solved all at once.

[Effect]

That is, the present invention uses a thermosetting powder coating to produce a powder coating with a flow index of 5 or less and a particle size of 100 μ to 2 mm between the melting of the powder coating and the completion of hardening. This is a method for producing coated steel materials with good adhesion to concrete, which is characterized by spraying molten steel to form irregularities on the coated surface of the steel material.

The invention will be described in detail below.

First of all, in the present invention, the term steel refers generally to steel bars, shaped steel, and copper strips, particularly steel bars for reinforced concrete that are buried in concrete, deformed steel bars, shaped steel, and copper strips.

Next, the present invention will be explained using FIG. 1. The present invention is carried out in almost the same way as the general thermosetting powder coating process described in FIG. During the completion of curing, that is, a powder spraying device 5 is provided between the powder coating device 4 and the cooling device 6, and the coarse powder coating is sprayed, and the coarse particles are melted and fixed by the residual heat of the steel material. Coarse particles form irregularities on the coated surface of the steel material, improving adhesion to concrete. In this case, the powder coating used in the present invention may be any of thermosetting epoxy powder coatings, thermosetting polyester powder coatings, thermosetting acrylic powder coatings, etc. Preferably, the powder coatings are of the same system and color tone, and in the case of epoxy powder coatings, coarse epoxy powder is preferred, and in the case of polyester powder coatings, coarse polyester powder is preferred. However, even if the coarse powder is different from the coating resin system, there is no restriction on the composition or components of the coarse powder as long as it does not interfere with the melting and fixing power.

The main point of the present invention is to specify the physical property values of such coarse powder. First, the particle size of the coarse powder is an important factor for forming surface irregularities necessary for strengthening adhesion with concrete, but due to the residual heat of the steel,
Since the coarse powder is welded onto the coated surface, the particle size of the coarse powder does not directly form the irregularities on the surface. That is, if the melting time is long and the viscosity at the time of melting is low, the coarse powder becomes flattened, making it difficult to efficiently form the desired surface irregularities. Flow index is an index that simultaneously expresses melting time and viscosity at the time of melting. The test method for flow index is to first take 0.3g of powder paint, form it into a 13mm diameter tablet, place it on a metal plate tilted at 60℃ heated to a predetermined temperature, and measure the distance it has flowed in mm. It is.

The present inventors conducted extensive studies on the flow index and roughness of coarse powder, and found that the industrially suitable flow index is 5 or less at 200°C, and that a particle size of 100 μm to 2 mm is suitable for forming surface irregularities. It has been found that when the flow index exceeds 5, the coarse powder is significantly flattened and the surface roughness of the coating is insufficient, making it difficult to strengthen the adhesion to concrete. In addition, if the roughness of the coarse powder is less than 100μ, the formation of irregularities on the coating surface is insufficient, and if the roughness exceeds 2 mm, the distribution density cannot be ensured, and the external force applied to a single piece of fixed coarse powder becomes For example, during a concrete adhesion test after concrete is poured, the adhered coarse powder may fall off due to the shearing force when the steel material is pulled out, causing damage to the paint film. Furthermore, the scattering density. Tsuia is special 9. Although it is not certain, a roughness of No. 48 with a roughness of about 25 pieces/crd or more is appropriate, and it is better to adhere uniformly to the entire surface for better impact resistance and indentation resistance. Hereinafter, the effects of the present invention will be illustrated more specifically by Examples.

〔Example〕

In accordance with JIS G3112, a deformed steel bar with a nominal diameter of 19 mm and a length of 6 m with bamboo knots, that is, test piece number 1
-6, the surface was conditioned by continuous grid blasting according to the process shown in Fig. 1, and the bar was further heated in a high frequency heating furnace while rotating to a temperature of 240°C. Immediately after heating, apply fast-curing epoxy powder coating with an electrostatic powder coating machine so that the cured film thickness is 250±50μ, and after 10 seconds apply a coating with the same composition as the powder coating and a flow index as shown in Table 1. Two types of coarse powder with different particle sizes were sprayed with an air gun at different spraying densities, and after 1.5 minutes, they were cooled with water. For each test condition, a concrete adhesion stress test piece (19φ
300 mm Q x 3 pieces) bending test piece (1 g
φX500mmgX3 pieces), corrosion resistance test piece (19φX5
00 mm α x 2 pieces) were sampled and performance evaluation was performed. The test conditions and test methods are as follows.

(B) Bending test Test 1 using a reinforcing bar bending machine in accordance with ASTM D775 Bending diameter: 6DD (diameter 6 times the reinforcing bar diameter) Temperature: 20'
C (b) Rebar and specimen used for pull-out test in accordance with ASTM C234: 19φy 15cm Moving material age, curing, concrete strength: material age 288.20±3℃ moist curing, 300kg/c resistance test Method: Loading Speed power sea minute 500k
Apply tensile stress at g/crrl' and measure the amount of burr with a dial gauge at the free end. A sliding amount-adhesive stress curve is drawn, and the average adhesive stress at a sliding amount of 0.04 mm is determined.

(c) Corrosion resistance test concrete specimen: 15 x 15 x 50 cm, fog 2 cm test method: [3% saline solution immersion, 12 hours,
High temperature humidity (50°C x 98% RH) for 12 hours, - drying (1
2°C x 25% RH) 24B fence) Conduct a corrosion test for 1 cycle, 100 cycles (200 days), dismantle the concrete, and observe the state of rust.

On the other hand, in order to compare with the above Nos. 1 to 6, a test piece No. 7 was manufactured using the conventional process shown in FIG. Furthermore, in the process of the present invention shown in FIG. 1, coarse powders outside the numerically limited range of coarse powders, that is, coarse powders with a flow index of 10 and an average particle size of 400μ, and coarse powders with a flow index of 4°5 and an average particle size of 2.5m
Comparative materials were manufactured in which coarse grain powder of m was fixed, and the test numbers were set as 8 and 9, respectively. Note that the test conditions and test method were the same as above.

Furthermore, in order to compare the adhesion to concrete with unpainted rebar, we conducted a similar concrete adhesion test on the rebar with mill scale attached, and when the amount of slip was 0°04 mm, the adhesion stress was 62 kg/d. I got it. The physical property values, scattering density and test results of the coarse powders of the invention examples and comparative examples are also listed in Table 1.

〔Effect of the invention〕

The painted reinforcing bars to which coarse particles of the present invention were fixed had improved adhesion to concrete compared to conventional painted reinforcing bars, and the adhesion to concrete was equal to or higher than that of unpainted reinforcing bars. Furthermore, it is clear that bending workability and corrosion resistance are not affected at all.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the manufacturing method of the present invention, and FIG. 2 is a schematic diagram showing the conventional manufacturing method. 1... Steel/material to be coated 2... Blasting device 3... Heating device 4... Powder coating device 5... Powder blowing device 6... Cooling device

Claims (1)

[Claims] In the process of manufacturing coated steel materials using thermosetting powder coatings, a powder coating with a flow index of 5 or less and a particle size of 100μ to 2mm is sprayed between the time the powder coating melts and the hardening is completed. A method for producing a coated steel material with good adhesion to concrete, which is characterized by melting and fixing the material and forming irregularities on the surface of the steel material.