JPH0575474B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention improves the material yield in a method of coating metal strips on a coating line in which metal strips are successively resistance welded and coated continuously with a roll coater. The present invention relates to a coating method that can be applied.

(Prior Art) Conventionally, coating of metal strips such as steel strips has generally been carried out on a continuous coating line using a roll coating method.
The painting process in this painting line usually involves welding the rear end of the leading metal band and the tip of the trailing metal band with a resistance welder, then pre-processing with a pre-treatment device, painting with a roll coater, and then This is done in a drying process using a baking dryer.

When painting metal strips on this painting line, the metal strips are coated with two coats: an undercoat and a topcoat.
Since the coat-2-bake method is common, two roll coaters and two bake-drying devices are installed, and they are arranged alternately.First, the roll coater applies the undercoat, then bake-dries one end, and then the next. A top coat is applied using a roll coater and then baked to dry.

In addition, roll coaters use a rubber applicator roll that applies the paint to the metal strip, and it moves back and forth against the metal strip during painting so that it can start and stop painting, change the color, stop the line, etc. The structure is such that it can be done. However, the movement of the applicator roll relative to this metal band is
It is becoming more gradual. this is,
If it happens suddenly, the paint pan containing the paint will move along with the applicator roll, so the paint will flow out of the paint pan.
This is because the applicator roll is made of rubber, and if it suddenly comes into contact with the metal band, the drive source motor may be overloaded or the roll may partially wear out, making it unusable.

By the way, metal strip welding on this painting line is
Metal strips are welded with a resistance welder butt against each other or slightly overlapped. However, when welding with the former, a step or a bead-like protrusion occurs at the overlapped part of the metal strips, and when welding with the latter, welding occurs. Even if
A bead-like protrusion forms at the weld and can damage the applicator roll when coated with a roll coater. For this reason, when the weld area approaches during painting, the applicator roll is moved backward, and after passing the weld area, it is moved forward again for painting.

The applicator roll must be moved forward and backward when applying the undercoat, topcoat, and backside coating, but when applying the undercoat and backside coating, it should be done based on the welding area standards, and when applying the topcoat, it should be applied to the base coat of the preceding metal strip. This is done based on the area where painting has finished and the area where the undercoating of the trailing metal band has started. When applying the topcoat, use the end and start points of the undercoat as a reference. If you use the weld as a reference, you will end up painting areas where there is no undercoat, and after painting, you will have to worry about the presence of the undercoat. Since it is not known whether the product is present or not, defective products with just the top coat may be mixed in.

(Problem to be Solved by the Invention) Therefore, there are unpainted parts or parts coated with only an undercoat before and after the weld, but these parts are considerably longer than before because the applicator roll does not advance and retreat quickly. (around 10m).

However, since this part cannot be used as a product, it is scrapped. However, when scrapped, there was a problem in that the yield of the material decreased. In particular, as coating speeds have increased in recent years, the applicator roll has to be moved forward and backward quickly to ensure safety, which has led to an increase in the number of areas to be scrapped, leading to a significant decline in material yield. For this reason,
It was necessary to take measures to improve the material yield.

(Means for Solving the Problems) When painting a metal strip, the present invention performs welding by butt welding or overlap welding in a slightly overlapping state, affixing adhesive tape to the entire welded part, and applying adhesive tape to the welded part. Welded areas with tape were also continuously coated with a roll coater to improve the material yield.

The tape to be applied to the welded part is heated in a baking furnace, so the entire piece melts at around 250℃ (atmospheric temperature of around 350℃), which is the temperature at which the metal strip is heated in the furnace (plate temperature). Use items that will not cause damage. For example, a metal tape or foil made of aluminum or stainless steel, a resin tape made of polyimide resin, or a cloth tape may be used. As for the thickness, it is preferable to use one having a thickness of 30 to 200μ.

If you want to paint both sides of the metal strip, apply tape to both sides.

The attached drawing shows method 1 of applying tape to welded parts.
As an example, Figure 1 shows a state in which a leading metal band and a trailing metal band are welded by resistance welding.
FIG. 2 shows the state after welding is completed, FIG. 3 shows the state in which tape is pasted to the welded part, and FIG. 4 shows the state after tape pasting is completed. In the figure, 1 is a leading metal band, 2 is a trailing metal band, 3 and 3a are electrodes, 4 is a weld bead, and 5 is a tape.

(Function) As mentioned above, if you apply tape to the welding area,
Metal plate steps and bead-like protrusions at welded areas are covered,
It becomes smooth and uneven. Therefore, when painting with an applicator roll, the roll will not be damaged.
Welded areas can be painted continuously. In addition, even if the tape softens or partially melts in the baking oven, it is cooled by the cooling device installed on the exit side of the baking oven, so even if it comes into contact with the deflector roll or support roll after baking, the tape or adhesive will will not stick to the surface.

After painting, there are no unpainted parts or parts coated with an undercoat before and after the weld, so it is only necessary to cut and remove the weld. Note that even if the welded part is painted, the welded part approaching the cutting machine can be identified by the tape.

(Example) Example 1 A continuous coating line using a roll coater method
0.27mm, plate width 914mm leading steel strip rear end and plate thickness 0.35mm,
Butt weld the tip of the trailing hot-dip galvanized steel strip with a width of 914 mm using a resistance welder, and attach 200μ thick aluminum foil with adhesive to both sides of the weld.
The hot-dip galvanized steel strip was painted through the steps of phosphating, undercoating, baking and drying, topcoating and backcoating, and baking and drying. For the undercoat, epoxy paint was applied using the natural rotation method to a dry film thickness of 5 μm.For the top coat and back coating, polyester paint was applied using the reverse rotation method to achieve a dry film thickness of 15 μm. Paint it like this,
The former was baked at a board temperature of 200°C, and the latter was baked at a board temperature of 230°C. When applying undercoat, topcoat and backside coating,
Even when the welding area came, the applicator roll was coated continuously without being separated from the steel strip, but the applicator roll was not damaged. Further, when the aluminum foil was observed at the cutting machine on the exit side of the line, no deformation was observed.

Example 2 In the same manner as in Example 1, hot-dip galvanized steel strips having a thickness of 1.0 mm and a width of 1219 mm and a steel strip having a thickness of 1.2 mm and a width of 1219 mm were continuously coated. A 30μ thick stainless steel foil was used as the tape to be attached to the welded area, and an alkaline pretreatment was applied to the tape. In addition, the undercoat paint is
Apply polyester paint to a dry film thickness of 5μ,
Baked at 215℃ (board temperature), and the top coat was a fluorine-based paint with a dry film thickness of 13μ and baked at 250℃. As a result, the applicator roll was not damaged and the stainless steel foil remained attached.

(Effects of the Invention) As described above, the present invention enables continuous coating of the welded part of the metal strip without damaging the applicator roll of the roll coater, so that the front and back of the welded part can be painted to the desired coating specifications. . Therefore, only the taped part of the welded part is scrapped, and the material yield can be significantly improved compared to the conventional painting method. In addition, since the tape covers the deposited metal scum generated at the welded part due to welding, the welded metal scum adheres to the rolls in the painting line and causes scratches, abrasions, and other damage to the painting metal strip and coating. can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a state in which a leading metal band and a trailing metal band are welded by resistance welding, and FIG.
FIG. 3 is a perspective view of a state in which a tape is attached to a welded portion, and FIG. 4 is a perspective view of a state after completion of welding. 1... Leading metal band, 2... Trailing metal band, 3,3
a... Electrode, 4... Welding bead portion, 5... Tape.

Claims (1)

[Claims] 1. When painting a metal band in a continuous painting line where the rear end of the leading metal band and the tip of the trailing metal band are welded using a resistance welding machine, pretreatment is performed using a pretreatment device, and coating is performed using a roll coater. Continuous coating characterized in that the welding is performed by butt welding or overlap welding in a slightly overlapping state, adhesive tape is applied to the entire welded part, and the welded part to which the tape is applied is also continuously coated with a roll coater. How to paint metal strips on a line.