JPH1015723A - Shearing method for coated steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance of the end face of a steel plate to prevent generation of enamel hair by heating a coated steel plate to a temperature higher than the glass transition point and then setting the clearance at the time of shearing to a suitable range to cut the steel plate. SOLUTION: A steel plate 1 is coated with a plating layer 4, a chemical conversion coating layer 3, and surface and back coats 2, 2' in order from the surface and back sides towards the outside. At the time of shearing, the steel plate 1 is heated to a temperature higher than the glass transition point, and the shearing clearance is set from 5% to 15%, both inclusive to shear the steel plate. If the clearance at the time of cutting is 15% or more, deformation (sagging) of the cut end face, which is a main cause for generation of enamel hair, is enlarged so that breaking of the plating layer is apt to occur. The reason the clearance is set to 5% or more is that if less than 5%, a coat will not follow a cutting edge to produce no end face coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of shearing a coated steel sheet which does not generate enamel hair while improving the corrosion resistance of the end face of the coated steel sheet, and uses a coated steel sheet for building materials, automobiles, home appliances and the like. Available in the field.

[0002]

2. Description of the Related Art Manufacturers of building materials, home appliances, and automobiles have conventionally formed parts using cold-rolled steel sheets or plated steel sheets and painted (post-coated) in a post-process. However,
Solvents used for coating have an adverse effect on the human body and the natural environment, and users have increasingly omitted coatings in order to reduce costs by omitting processes. As a result, a coated steel plate that has been painted in advance by a material maker has been formed by the user. The processing steps of these products necessarily include a punching or shearing step using a shear. Since the cut end face of the coated steel sheet is used without being coated, there is a drawback that the corrosion resistance of the end face is lower than that of a product (post-coated) which is coated after processing. Further, enamel hair (stripping of the coating film on the end face) generated on the cut end face becomes a problem.

[0003] In order to improve the corrosion resistance of the cut end face of a coated steel sheet, there have been studies on the material side, such as using a plated steel sheet or a stainless steel sheet as a coating original sheet, devising a pretreatment for coating, and after cutting. Post-treatments such as painting the end face have been studied, but all of them are insufficient and have a problem that the cost is considerably increased.

On the other hand, as a measure for preventing the generation of enamel hair, for example, as disclosed in Japanese Patent Publication No. 60-5351,
By reducing the thickness of the coating film on the expected cutting line in advance, the generation of enamel hair during cutting is suppressed. However,
In this method, the coating must be performed while considering the cutting position of the product, which significantly increases the cost for a material maker to cope with.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a shearing method capable of improving the corrosion resistance of a cut portion of a coated steel sheet and preventing the generation of enamel hair without using a special method as in the prior art. To provide.

[0006]

The gist of the present invention is to provide a method for shearing a coated steel sheet using a plated steel sheet as a coating base sheet.
A method for shearing a coated steel sheet, comprising heating the coated steel sheet to a temperature higher than the glass transition temperature of the coating film during shearing, and setting the shear clearance to 5% or more and 15% or less to perform shearing.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The coated steel sheet in the present invention refers to a steel sheet having an organic coating layer formed on the steel sheet and used after being cut. Hereinafter, the organic coating layer is referred to as a coating film, and includes both a coating material that has been coated with a coating material and dried, and a film layer to which an organic coating film that has previously been formed is applied.

FIG. 1 schematically shows an example of a cross section of a coated steel sheet. (A) is the cross-sectional structure of the steel sheet, and (b) is the condition of the cut end face. In the figure, 1 is a steel plate, 2 is a surface coating, 2 'is a back coating, 3 is a chemical conversion layer, and 4 is a plating layer. Layer 3 and front and back coatings 2, 2 'are applied in that order.

The present inventors have studied the state of the end face after cutting the coated steel sheet. As a result, the state of the cut end face is different depending on the clearance and the temperature at the time of cutting, and depending on the conditions, the coated end face is coated. It has been found that when the film remains and the end face is partially covered, a cut end face excellent in corrosion resistance, free of enamel hair, can be obtained. In other words, by setting the clearance at the time of cutting to an appropriate range, it is possible to reduce the destruction of the plating layer due to deformation (dripping) of the cut end face, which is a cause of enamel hair (coating peeling of the end face), and to reduce the temperature of the coated steel sheet By increasing the height of
Corrosion resistance is improved by covering the cut end face with the coating as shown in FIG. 1 (b) following the cutting blade.

Here, the reason why the clearance at the time of cutting is set to 15% or less is that if it is larger than 15%, deformation (dripping) of the cut end face, which is a cause of enamel hair, becomes large, and the plating layer is likely to be broken. That's why. The reason why the clearance is set to 5% or more is that if the clearance is smaller than 5%, the coating film does not follow the cutting blade, and the end face coating does not occur.

When the temperature of a coating film is high, the elongation of the coating film is generally large, the elastic modulus and tensile strength of the coating film are small, and the coating film is easily deformed. For this reason, if the temperature is high when cutting the coated steel sheet, the coating film follows the cutting blade well and covers the cut surface well. Furthermore, it is particularly advantageous if the coating is overheated to a temperature above its glass transition point. This is because if the temperature exceeds the glass transition point, the flexibility of the coating film is remarkably increased, and the coating coverage of the end face after cutting is greatly improved.

In the present invention, the glass transition point is determined by a thermomechanical analysis method in a penetration mode in which the load is 20 g / 1 mmφ, and the temperature is 10 ° C.
Although the measurement was performed in / min, the measurement may be performed by any method generally used. The heating temperature may be appropriately selected in consideration of the heat resistance of the coating film. The cutting method can be applied to mechanical shearing such as shear cutting and punching with a punch.

[0013] The heating is performed by heating a room or the whole workplace where the machine for cutting the coated steel sheet is provided, heating only the periphery of the machine, heating the cutting tool, heating only the coated steel sheet, or Any method may be used as long as the temperature of the coated steel sheet at the time of cutting becomes higher than the glass transition temperature of the coating film, such as cutting before heating at another place. Means for heating include raising the ambient temperature with an air conditioner, directly blowing hot air, irradiating near-infrared rays, far-infrared rays or other energy rays, and directly heating with high-frequency induction heating. Any method may be used as long as the temperature of the coated steel sheet is equal to or higher than the glass transition point.

Examples of the coated steel sheet which is the original coating sheet include a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, an electro-zinc alloy-plated steel sheet, an aluminum-plated steel sheet, a lead alloy-plated steel sheet, a chrome-plated steel sheet, and a nickel-plated steel sheet. Plated steel plates and the like can be mentioned.

[0015]

EXAMPLES Table 1 shows the structure of the coated steel sheet used in this example.
Table 2 shows the production conditions. In addition, the plating adhesion amount in Table 1 is the total value of the front and back surfaces, and the front and back of the coated steel sheet here means the side on which the front surface becomes the surface of the final product,
The back points to the opposite side. The cutting is performed from the front side to the back side of the coated steel sheet. As the glass transition point of the coating film, a value obtained by using a Shimadzu DT200 type thermal analyzer in a stir-in mode of thermomechanical analysis at a load of 20 g / 1 mmφ and a heating temperature of 10 ° C./min was used. .

First, each coated steel sheet shown in Table 1 was heated under predetermined conditions and then cut. After confirming the occurrence of enamel hair, the coating ratio of the end face was examined. Thereafter, the swollen width of the coating film after 240 hours of salt spray (SST) test and the occurrence rate of red rust on the cut surface were examined, and the results are summarized in Table 3.

As the heating method, there are two methods, that is, before cutting the coated steel sheet, heating the mold and the mold to a predetermined temperature by irradiating infrared rays, and heating to a predetermined temperature using an induction heating device. It was then cut. If not heating,
The temperature of the coated steel sheet is room temperature (10 ° C), and cutting is performed at room temperature (10 ° C).
C). As a cutting method, two cases were carried out: using an electric shear and punching 50 mmφ. The clearance at the time of cutting is also shown in Table 3.

The coating coverage of the end face was determined by observing the cross section with an optical microscope, and the ratio of the coating coating length to the cross-section thickness direction length was expressed as%. Furthermore, the swollen width of the coating film on the end face after 240 hours of salt spray (SST) test was measured (unit: mm),
The occurrence rate of red rust on the cut surface was visually evaluated and expressed in%.

As apparent from the results shown in Table 3,
By heating the coated steel sheet to a temperature higher than the glass transition point of the coating film, it was confirmed that the coating film coverage on the cut surface increased, and both the red rust generation rate and the coating swelling width decreased. Further, it was confirmed that enamel hair was not generated by setting the clearance within the range of the present invention. From these results, the effectiveness of the present invention became clear.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

As described above, according to the present invention, the clearance at the time of shearing can be appropriately adjusted by heating the coated steel sheet to a temperature higher than the glass transition point with the existing equipment without using particularly difficult equipment. By cutting in a suitable range, the end face corrosion resistance of the coated steel sheet can be improved, and the generation of enamel hair can be prevented.

[Brief description of the drawings]

FIG. 1 shows an example of a cross section of a coated steel sheet, in which (a) is a cross-sectional structural view of the steel sheet, and (b) is a schematic view of a cut end face of the steel sheet viewed in a sheet thickness direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Surface coating 2 'Back coating 3 Chemical conversion layer 4 Plating layer

Claims (1)

[Claims] 1. A method for shearing a coated steel sheet using a coated steel sheet as a coating base sheet, wherein the coated steel sheet is heated to a temperature higher than the glass transition point of the coating film during shearing, and the shear clearance is set to 5% or more and 15% or less. A method of shearing a coated steel sheet, wherein the shearing is performed.