JPS6283141A - Light-weight steel plate, end section thereof can be spot-welded - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to the structure of a lightweight steel plate among composite laminated steel plates whose main purpose is to reduce the weight, and particularly relates to a lightweight steel plate whose edges can be spot welded. .

Prior art and its problems〉 Laminated steel plates in which thermoplastic resin is sandwiched between steel plates are
It can be broadly divided into two types. One is.

This is a composite type vibration-damping steel plate in which the proportion of the steel plate is larger than that of the resin, and has an excellent vibration-damping effect. The other type is a lightweight material called lightweight steel plate, which uses an extremely thin steel plate for the surface layer to ensure strength, and the middle layer is thick and lightweight resin.

These uniform steel plates and lightweight steel plates are expected to be widely used in automobile materials, construction materials, etc. by taking advantage of their respective advantages.

By the way, when using laminated steel sheets as automobile materials,
Since it is essential that spot welding is possible, the intermediate resin layer must be electrically conductive.

In this regard, the applicant of the present application discloses a damping steel plate in which 10 to 50 wt% of conductive particles having a particle size of 1/2 or more of the resin layer thickness is mixed in the resin layer in JP-A-57-146649. In JP-A-58-160141, a resin layer J! This discloses a lightweight steel sheet in which a predetermined amount (limited wt % and vol % with respect to the resin) of graphite having a particle size of 1/2 to 1 times that of J is mixed therein.

In the ILJ shaken steel sheet of the invention disclosed in JP-A No. 5'l-146649, the resin layer is thin and the particle size of the conductive particles may be small, so it is relatively easy to maintain conductivity in the resin layer. It's easy.

However, the resin layer is thick in a lightweight steel plate such as the one disclosed in JP-A-58-160141.

That is, in light steel plates, the resin layer thickness is preferably several times or more than the steel plate thickness, particularly about three times the optimum value, from the viewpoint of ensuring bending rigidity and achieving weight reduction.

Therefore, in order to impart conductivity to the resin layer, it is necessary to mix carbon graphite with a large particle size (particle size approximately equal to the resin thickness) or to mix a large amount of carbon graphite.

However, when large-grain carbon graphite is mixed into the resin layer, although it is electrically conductive, the electric resistance is maximized during 5-spot welding, resulting in a large amount of heat, which may melt the steel plate itself and create holes.

Furthermore, if laminated carbon graphite is mixed into the entire resin layer, the properties of the resin will change, making it difficult or impossible to mold the resin into a film.

<Objective of the Invention> The object of the present invention is to eliminate the drawbacks of the prior art described above, to easily perform spot welding near the edges while ensuring high bending rigidity, and to enable spot welding of the edges. Our objective is to provide light H1 steel plates.

<Structure of the Invention> In order to achieve such an object, the inventor of the present application, as a result of intensive research, thinned only the resin layer near the end of the lightweight steel plate to be spot welded, and added a layer of relatively small particle size to this. (200μm
By mixing an appropriate amount of carbon graphite (see below), high conductivity is achieved in the resin layer near the edges, and the resin layer near the center of the lightweight steel plate (other than near the edges) is
It was discovered that the thickness required to obtain sufficient bending rigidity can be ensured, and the present invention was achieved.

That is, the present invention provides a laminated lightweight steel plate in which a thermoplastic resin is sandwiched between two steel plates. The resin thickness of the carbon graphite is thinner than the resin thickness of the central part, and the average particle size of the carbon graphite is X (μm
), the resin thickness at the end portion is Y (μm), the resin thickness at the center portion as described above is Z (μm), and the thickness of the steel plate is t (μm), the following formula % formula % is satisfied. The present invention provides a lightweight steel plate whose edges can be spot welded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a lightweight steel plate whose edges can be spot welded according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a partial sectional view of a lightweight steel plate whose end portions can be spot welded according to the present invention.

The lightweight steel plate 1 has a structure in which a resin layer 3 is sandwiched between two steel plates 2.

The steel plate 2.2 may be of any type, such as a cold-rolled steel plate, various plated steel plates, or chemically treated steel plates.

In addition, as the constituent material of the resin layer 3, thermoplastic resins such as polyolefins such as polypropylene and polyamides such as nylon are preferable from the viewpoint of moldability and heat resistance, but stiff copolymers and modified products are preferred. It may also be a composition containing other additives, or it may be a resin other than those mentioned above.

As shown in FIG. 1, in the lightweight steel plate 1 of the present invention, the thickness of the resin layer 3 is different between the end portions 4 and the center portion 5. That is, the resin thickness Z of the end portion 4 is thinner than the resin thickness Z of the central portion 5. The resin Y does not necessarily have to be constant over the entire edge portion 4, and may gradually increase from the edge of the lightweight steel plate 1 toward the center portion 5, for example. In this case, the resin thickness Y may be considered to be an average value over the entire area of the end portion 4.

Further, at least the resin layer 3 near the end portion 4 contains carbon graphite 6 of 50w% or less. With such a configuration, conductivity can be imparted to the resin layer near the end portion 4.

Note that carbon graphite 6 can be mixed uniformly into the entire resin layer as shown in FIG. 1 for ease of resin production, but in order to improve the film formability of the entire resin layer 3, Rather than mixing it into the entire layer,
It is preferable to mix a predetermined amount only in the resin layer 3 of the end portion 4 that requires conductivity.

Here, the end portion 4 of the lightweight steel plate 1 refers to any part where spot welding may be performed, such as the tip, end, both ends, etc. of the lightweight steel plate, and the center portion 5 of the lightweight steel plate work refers to the end portion 4 of the lightweight steel plate 1. Refers to other parts.

The reason why the amount of carbon graphite 6 mixed is set to 50wL% or less is that if it is mixed into the entire resin layer 3, the amount of carbon graphite 6 mixed is 50w.
This is because if it exceeds j%, the film formability of the resin will deteriorate.

In the lightweight steel plate 1 of the present invention, the thickness of the steel plate 2 is t(μ
l11), the average particle size of carbon graphite 6 is X(μ
m), it satisfies the following formulas [1] to (3).

O < This is because a large current concentrates on the graphite grains, generating high heat, which may melt the steel plate 2.2 and create holes.

In formula [2], if Y exceeds 1.5X, 50w
This is because if the amount of carbon graphite mixed is less than t%, conductivity cannot be obtained in the resin layer 3.

In formula [3], if Z is less than 1.0, it will not be possible to achieve sufficient weight reduction, and if zh<tot, sufficient rigidity will not be ensured and the material cost will increase. It is.

<Action of the Invention> Hereinafter, the action of the lightweight steel plate whose end portions can be spot welded according to the present invention will be explained.

FIG. 2 is a partial sectional view when spot welding is performed on the lightweight steel plate 1 of the present invention.

As shown in FIG. 2, the end 4 of the lightweight steel plate 1 and the end of another ordinary steel plate 7 (the lightweight steel plate of the present invention may also be used) are joined, and an electrode 9.9 of a spot welder is attached. .

When a voltage is applied between the electrodes 9 and 9, a current easily flows through the carbon graphite 6 in the resin layer 3 at the end portion 4.
A nugget 8 is formed at the joint between the lightweight steel plate 1 and the steel plate 7,
These are welded. Since the resin layer 3 at the end portion 4 has sufficient conductivity, the amount of heat generated is small even when a voltage is applied between the electrodes 9 and 9.

As a result, the steel plate 2 does not melt and create holes, and the number of continuous spot welding points increases.

On the other hand, in the central portion 5 of the lightweight steel plate 1, the resin layer 3 is thick and the bending rigidity is sufficiently large.

In the lightweight steel sheet 1 of the present invention, even if the resin layer 3 at the end portion 4 is reduced, the thickness of the steel sheet 2.2 and the resin layer 3 is the same over the entire area, and the resin layer 3 at the end portion 4 is made thinner. Compared to conventional lightweight steel plates that do not have this structure, the bending rigidity decreases by only about 2 to 3%, and has no practical effect.

<Example> Spot weldability and bending rigidity were measured for lightweight steel plates having the respective configurations shown in Table 1. The resin sandwiched between the steel plates was polypropylene.

The bending rigidity test is based on ASTM D790-71, and the calculation is based on JIS 7203-1973 (R, T).
I went there.

Spot weldability: CF type electrode, 3.2m
Using a Cu-Cr electrode of /IIlφ, continuous dots were performed under the conditions of 4 cycles of energization, a current of 4 to 8, and a pressure tube of 100 Kgf, and a comprehensive evaluation was made by the number of dots.

The results are shown in Table 1.

As is clear from the results shown in Table 1 above, the lightweight steel plate of the present invention has excellent spot weldability and shows almost no decrease in bending rigidity.

<Effects of the Invention> According to the lightweight steel plate of the present invention whose edges can be spot welded, the thickness of the resin layer at the edges is made thin, carbon graphite is mixed in the resin layer in an amount of 50 t% or less, and the carbon graphite is By setting the particle size and end resin pressure within the specified ranges, it is possible to impart excellent spot weldability to the ends of a lightweight steel plate. That is, when spot welding is performed, the amount of heat generated is small, the steel plate does not melt and holes are formed, and the life of the electrode of the spot welder is extended, resulting in an increase in the number of consecutive welds.

Further, by setting the resin thickness at the center of the lightweight steel plate within the above-mentioned certain range, weight reduction and sufficient bending rigidity can be ensured.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a lightweight steel plate whose end portions can be spot welded according to the present invention. FIG. 2 is a partial sectional view when spot welding is performed on a lightweight steel plate whose end portions can be spot welded according to the present invention. Explanation of symbols 1...Lightweight steel plate, 2... Steel plate, 3...Resin layer,
4... end part, 5- center part,

Claims (1)

[Claims] (1) In a laminated lightweight steel plate formed by sandwiching a thermoplastic resin between two steel plates, 50 wt% or less of carbon graphite is mixed in the resin at least at the ends of the lightweight steel plate, and the resin at the ends of the lightweight steel plate is The thickness is thinner than the resin thickness in the central part, and the average particle size of the carbon graphite is X (μm
), the resin thickness at the end portion is Y (μm), the resin thickness at the center portion is Z (μm), and the thickness of the steel plate is t (μm), the following formula 0<X≦200μm 0<Y A lightweight steel plate whose edges can be spot welded, which satisfies the following: ≦1.5X 1.0t≦Z≦10t.