JPH0286432A - Manufacture of composite steel plate having excellent resistance welding property - Google Patents

Abstract

PURPOSE:To mold a composite steel plate having an excellent resistance welding property by holding resin obtained by dispersing particle conductive powder softer than metallic material of an outer layer and having a specific particle diameter between steel plates, and pressurizing the conductive powder body to make it have a predetermined thickness. CONSTITUTION:Particle conductive powder 4 being softer than an outer metallic material and having a particle diameter of (d) of 1.2t<d<3.0t (t denotes the thickness of a resin layer) is dispersed into resin 3 at 2-30vol.%. The resin 3 is held between steel plates 1, and the conductive powder is pressurized so as to crush the particle conductive powder to a predetermined product resin thickness, thereby molding a composite steel plate. And, a steel plate or the like can be employed having at least a cold stretched steel plate and an electrically galvanizing treated layer 2 for the steel plate 1. As a concrete example of conductive powder being softer than the steel plate, there can be given by copper, nickel, aluminum, lead, zinc, silver and the like, or the metallic particles of an alloy of these metals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to a composite steel plate that can easily be resistance welded.

[Conventional technology 1] In recent years, as energy saving has become more widespread, lighter steel plates are required for use in car bodies and parts in the field of transporting automobiles and other vehicles. It has become.

In order to promote weight reduction, it is essential to reduce the thickness of the components themselves by using high-tensile steel, etc.
When the plate thickness is reduced, a problem arises in that the rigidity decreases.

In order to solve this problem, a composite W4 slope, a so-called light steel sheet, has been proposed in which a three-layer structure is formed by sandwiching an intermediate layer made of a resin having a lower density than the steel sheet between two metal layers.

On the other hand, in the automobile and building materials industries, composite steel plates (distributed steel plates) are made by sandwiching a vibration-absorbing resin between two skin steel plates as an intermediate layer to dampen the vibrations of the steel plates in order to make the steel plates more sophisticated and quiet. has also begun to be used.

In this case, at least one side of the skin steel sheet is made of cold-rolled steel sheet, surface-treated steel Fi (electrogalvanized steel sheet,
(hot-dip galvanized steel sheet, tin plate, etc.), stainless steel sheet, electromagnetic steel sheet, pre-painted steel sheet, etc., and for the other side, in addition to steel sheet, most metals such as aluminum, titanium, etc. can be selected.

These composite steel plates had a problem in that it was difficult to weld them. That is, the resin layer has a high specific resistance value, and even if a voltage is applied to the electrodes of a resistance welding machine, no current is passed between the electrodes. For this reason, the conventional welding process for composite JLIL has been to connect two steel plates with a lead wire to create a bypass circuit, apply voltage to this circuit, melt the resin, and perform welding.

However, this method has the disadvantage that it is impossible to weld objects with thick resin layers, and that the welding steps are increased and complicated.

Therefore, in the past, the intermediate layer of composite steel sheets was made conductive,
As an attempt at resistance welding, a method of filling conductive filler (JP-A-50-79920゜53-128687.5
6-31540.57-146649.57-1635
59.57-163560, 61-40150, 61
-41540.63-74634, Special Publication Showa 60-912
, Japanese Utility Model Application No. 61-128025, etc.), a method of sandwiching a metal net (Japanese Patent Application Publication No. 58-132550), or a method of forming irregular patterns on a metal plate (Japanese Patent Application Publication No. 58-197045.5).
9-103748.59-145142) have been proposed.

In the conventional resistance weldable composite steel sheets mentioned above, the method of sandwiching a metal net complicates the work during the manufacturing of the composite steel sheets and has an impact on press workability, and the method of adding irregular patterns to the metal sheets also The steel plate must be processed before manufacturing, and there are problems such as patterns appearing on the surface of the composite steel plate.

On the other hand, the method of filling with conductive filler is an excellent method in terms of process. The form and relative size of the conductive filler to the resin layer, as well as the blending ratio to the resin, are important, and affect weldability, adhesion, and splitability.

Therefore, various forms such as granular, scaly, and fibrous forms have been proposed. Granular or scaly conductive filler has a small contact area with the upper and lower skin steel plates, so a large filler is required to obtain sufficient weldability, which causes a decrease in bond strength and resistance. . Furthermore, it also increases costs. Further, although the fibrous filler improves the conductivity in the lateral direction, the conductivity in the vertical direction is not diffused and the weldability is not sufficient. Furthermore, the resin film thickness easily varies depending on the compression conditions, and the relative size to the resin layer changes, which is a factor in the variation of weldability.

[Problem to be Solved by the Invention 1] The present invention was devised in view of the above points, and it is possible to resistance weld a composite steel plate in the same way as a conventional steel plate, and improve the resistance weldability with a minimum amount of filler. The present invention provides a method for manufacturing a composite steel plate that stably exhibits the following properties.

[Means for Solving the Problems] The present inventors have conducted intensive research on improving the weldability of a composite steel plate in which a resin layer is provided between two skin steel plates, and have determined the contact area between the conductive filler and the skin steel plate. It was found that the weldability was significantly affected by the weldability. It has been found that in order to increase the contact area between the filler and the skin steel plate, it is better to make the filler flat.

In the present invention, the thickness of the resin layer of the composite steel plate is t, the resin layer is softer than the outer layer metal material, and the average grain size d is 1.2t<d<3. Ot
After dispersing 2 to 30% by volume of conductive powder in resin, when pressing the upper and lower skin steel plates, this resin is sandwiched between the skin steel plates and the conductive powder is pressed down to form granular conductive powder. This is a method for manufacturing a composite steel plate with excellent resistance weldability, which is characterized by crushing the body to a predetermined product thickness.

The present invention will be explained in detail below.

FIG. 1 shows a schematic cross-sectional view of a composite steel plate manufactured by the method of the present invention. The composite steel plate according to the present invention has a conductive synthetic resin 3 as a central layer between two skin steel sheets, which are sandwiched and fixed to each other to enable stable resistance welding. be. In particular, the material of the present invention is made by dispersing conductive powder 4 in a volume ratio of 2 to 30% in the synthetic resin of the central layer in order to impart the conductivity necessary for resistance welding.

The composite steel sheet manufactured by the present invention may use cold-rolled steel sheet, surface-treated steel sheet (electrogalvanized steel sheet, hot-dip galvanized steel sheet, tin plate, etc.), stainless steel sheet, electromagnetic steel sheet, pre-painted steel sheet, etc. on at least one side of the composite steel sheet manufactured by the present invention. On the other hand, most metals such as steel plate, aluminum, and titanium can be selected, and the plate thickness is not limited.

Conductive powder (filler) is blended into the resin to impart conductivity. Metal is preferred as the conductive powder, but
The entire powder does not need to be metal. For example, a plastically deformable resin or the like coated with metal may be used. The shape of the conductive powder may be a cube, a triangular pyramid, or the like, but considering that it will be dispersed in the pJ fat layer, it is best to have as much symmetry as possible, and a spherical shape is preferred.

The size of the conductive powder used is 1.2t<, where d is the average particle size of the conductive powder and L is the thickness of the resin layer.
d<3. It is necessary to be Ot. FIG. 2 shows the effect of the d/l ratio on weldability and adhesiveness based on Examples and Comparative Examples. When the average particle diameter d is 1.2 or less, the amount of crushing of the conductive powder is small, the conductive powder does not become flat, and the contact area between the conductive powder and the skin steel plate becomes small, so it is stable. Resistance welding cannot be achieved, and the grain size d is 3. If it is more than OL, the adhesive strength of the resin will decrease, making it difficult for air to escape between the upper and lower plates during pressure bonding, and when used as a vibration-damping steel plate, vibration-damping properties will also deteriorate, so it is not acceptable.

The conductive powder must be a metal that is softer than the skin steel plate and can be plastically deformed.If it is harder than the skin steel plate, the shape of the conductive powder will be transferred to the skin steel plate during crimping or press processing, or plastic deformation will occur. Material 1: For example, carbon is unsuitable because it shatters when compressed.

Examples of the conductive powder softer than the skin steel plate include metal particles of copper, nickel, aluminum, lead, zinc, silver, etc., and alloys of these metals.

On the other hand, even though it is conductive, tin has a low melting point and may melt during crimping, so it is not suitable. These conductive powders can be used alone or in combination of two or more.

The amount of conductive powder in the resin was limited to 2-30% by volume. FIG. 3 shows the effect of the amount of conductive powder blended on weldability based on Examples and Comparative Examples. If it is less than 2% by volume, sufficient conductivity for welding cannot be obtained. If it exceeds 30% by volume, the adhesive strength of the resin decreases, causing wrinkles and peeling during press processing.

Furthermore, this results in a decrease in vibration damping performance and an increase in cost.

Next, the resin used in the present invention includes polyester, polyurethane, polyethylene, polypropylene, epoxy resin, etc., and can be selected depending on the use of the composite steel sheet. In addition, if a chemical conversion treatment such as chromate treatment or coupling treatment is performed to improve the adhesion between the steel plate and the resin, better effects on the adhesion and corrosion resistance can be expected.

[Example] Examples of the present invention will be described below along with comparative examples.

A method of the present invention in which conductive powders of various particle sizes are mixed with polyester resin, coated on chromate-treated steel plates of 0.5 mm thickness for both upper and lower plates, and hot-pressed to produce a composite steel plate. The experimental conditions and results of Examples are shown in Table 1. The experimental conditions and results of the comparative example are shown in Table 2. The predetermined product thickness refers to the total thickness of the two skin steel plates and the resin thickness.
For a composite steel plate with a resin thickness of 50 μm, it is 1.05 mm.

Weldability evaluation The welding test was performed using a pressure of 200 kgf and a current of 8 kA.

The test was conducted using an 8R spherical electrode tip. A total of 10 composite steel plates were welded, and the weldability was evaluated by showing the percentage of the welds that were successfully welded relative to the total.

T-beer strength (TPS) The T-beer test was conducted according to JIS K 6854. A value of 15 kgf/25 mm or more was considered good.6 The particle size and compounding ratio of the conductive powders of Examples and Comparative Examples were plotted against weldability and T-beer strength, respectively, and are shown in FIGS. 2 and 3. The particle size of the conductive powder is 1.2 of the thickness of the resin.
It can be seen that when the ratio is less than 3 times, the weldability decreases, and when it exceeds 3 times, the adhesive strength decreases. A similar graph appears for the blending ratio of conductive powder, and when it is less than 5%, weldability decreases, and 30
%, the adhesive strength decreased.

Furthermore, in the case of SUS or Mn, in which the conductive powder is harder than the outer layer metal, the shape of the conductive powder is transferred to the outer layer metal, resulting in abnormal appearance. In the case of graphite (C).

Since no plastic deformation was performed, the graphite was crushed by pressurization, resulting in insufficient weldability.

[Advantageous Effects of the Invention 1] The present invention makes it possible to easily manufacture composite steel sheets that have good adhesion and excellent resistance weldability.
This made it possible to use split steel plates.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a composite steel plate manufactured by the method of the present invention, Fig. 2 is a graph showing the influence of the ratio of conductive powder particle size and resin thickness on resistance weldability and adhesive strength, and Fig. 3 is a graph showing the influence of the blending ratio of conductive powder on resistance weldability and adhesive strength. l...Skin m treatment 2...Chromate treatment layer 3-...Resin layer 4...Conductive powder

Claims (1)

[Scope of Claims] 1. In manufacturing a composite steel plate in which a resin layer is provided between two skin steel plates, the material is softer than the outer layer metal material and has a particle size d.
However, 1.2t<d<3.0t, where t: the thickness of the resin layer After dispersing 2 to 30% by volume of granular conductive powder in the resin, the resin is sandwiched between steel plates. A method for producing a composite steel sheet with excellent resistance weldability, which comprises compressing conductive powder in granular form to a predetermined product resin layer thickness by rolling down the conductive powder.