JPS6234682A - Welding method for can stock - Google Patents

Abstract

PURPOSE:To perform the electric resistance welding of various stocks for can starting with a tin free steel by irradiating a laser beam on the surface of the overlapping part of the welding zone in advance prior to the welding. CONSTITUTION:The welding is performed by irradiating a laser beam in advance on the whole part or one part of a steel sheet-steel sheet contact faces, 6, 7 and steel sheet-welding electrode contact faces 5, 8 in case of the electric resistance welding of the can stock like the tin-free steel coating with an extremely thin chrome plating on the steel sheet surface. By this laser irradiation, the chrome oxide layer 1 and metallic chrome layer 2 on the surface of the welding zone are completely removed with evaporation or alloyed with the surface material and yet the produced ultrafine powder is completely removed. The electric resistance welding for various can stocks including the tin free steel which was regarded as impossible in the past can therefore be performed easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for welding can materials, and particularly to a pretreatment method for electric resistance welding of can materials having poor electric resistance weldability.

[Conventional technology]

Traditionally, tinplate for cans (tin coating amount of 2.8 g/lrl" or more) and tin-free steel have been the mainstream materials for cans, but in recent years, the amount of tin deposited has been A variety of new materials have been developed, including thinner plated tinplate that is thinner than standard tinplate, materials plated with metals other than tin such as nickel, and materials plated with 2W1 or a combination of three types of tin and metals other than tin.

Among these, tin-free steel, for example, refers to a steel plate with an extremely thin chrome plating applied to the surface.It has good corrosion resistance and paintability, and is inexpensive. Demand is increasing significantly as a material for cans that can replace can materials (more than /m゛). However, the electrical resistance weldability of tin-free steel is extremely poor, which limits its applications, and in order to further expand its use in the future, it is essential to solve this problem.

That is, can materials are required to have excellent properties such as corrosion resistance, workability, and paintability, as well as excellent electric resistance weldability. The welding methods considered here are the copper wire seam welding method, which has become rapidly popular in recent years due to reductions in can manufacturing costs, and the conventionally used rotating electrode resistance seam welding method.

First, a method for evaluating the electric resistance weldability of can materials will be explained.

The quality of seam welds is evaluated based on joint strength, airtightness, and appearance. In order to satisfy bonding strength and airtightness, it is necessary that electrical resistance heat generation at the bonding interface exceeds a certain limit value. From this, the minimum value of the welding current is determined. Next, as for the appearance properties, it is necessary that Paris be absent. Normally, after welding, the seam weld is coated with repair paint, but the presence of flakes can interfere with paint application, and can also result in exposed areas that are not covered with paint.
Furthermore, if such a can body is used, not only will the contents react with the powder and deteriorate, but there is also a risk that the powder will peel off from the can body and mix into the contents.

Particles are caused by molten metal scattering from the seam weld and adhering to the area near the seam weld. In order for Paris not to exist, it is necessary that electrical resistance heat generation at the bonding interface be below a certain limit value. From this, the maximum value of the welding current is determined. If we define the maximum and minimum values of the welding current, which are determined from the joint strength, airtightness, and appearance properties that evaluate the quality of the seam weld, as the lower limit current value and upper limit current value, respectively, then the appropriate current range for welding is the upper limit current. It is the value obtained by subtracting the lower limit current value from the value (however, if the appropriate current range is negative, it is zero), and the quality of the electrical resistance weldability of the material for the can is determined by
The evaluation will be based on the width of this appropriate current range.

As for the materials for cans, as mentioned above, tinplate for cans (with S adhesion of 2.8 g/rn' or more) and tin-free steel have traditionally been the most popular materials for soldering, but in recent years new materials (
For example, thin plated tinplate and nickel plated steel (plate) have been developed. When these materials are subjected to electric resistance seam welding, the appropriate current range for soldering is wide for can tin and some thin plating tin (tin coating amount 1. Ig/rr 1" or more), and weldability is low. Very good quality.However, some thin tinplates (tin coating amount 1.1g)
7m or less) and tin-free steel have a narrower appropriate current range and inferior weldability when soldering compared to tinplate for cans. In particular, tin-free steel tends to generate flashes during welding, and if the welding current value is reduced to suppress the formation of flashes, the joint strength and airtightness will not be sufficient.

To explain this point in more detail, the surface layer of tin-free steel consists of an extremely thin metallic chromium layer (2) on a steel sheet base (3), and an upper layer of chromium mainly composed of hydrated chromium oxide, as shown in Figure 1. It is composed of an oxide layer (1).

Chromium oxide is an electrical insulator, and the underlying metal chromium M (2) is extremely hard, so the chromium oxide layer (1) is not sufficiently destroyed by the pressure applied by the electrode. It will flow locally and unevenly. Therefore, molten metal is formed at a relatively low current.

However, the high temperature softening region is not sufficiently formed,
The plastic flow has a weak confinement effect on the molten metal due to its shape, so the molten metal easily scatters and forms flakes. Particularly when alternating current is used, cracks are likely to occur in welds near the peak value of the alternating current waveform, while bond strength is reduced in welds near the zero value of the above waveform due to insufficient heat generation. There is a noticeable tendency for shortages.

Furthermore, chromium oxide has extremely poor thermal conductivity, which inhibits heat transfer to the water-cooled welding electrode, causing overheating at the welding electrode-steel plate interface when electric resistance is generated, which tends to cause sparks. also coexisted.

Therefore, in the past, electric resistance seam welding was performed after the steel plate surface coating on the edge of the blank, which is to be the overlapping part, was exposed almost entirely in advance using mechanical means such as a wire brush and an abrasive.

[Problem that the invention seeks to solve]

With the above-mentioned mechanical means, it is difficult to completely remove the coating on the surface of the steel sheet that inhibits weldability, and some of the coating is forced to remain, so that electric resistance weldability cannot necessarily be said to be good. Furthermore, there is a problem in that fine powder when the coating is scraped off is not completely removed from the surface of the steel plate and re-adheres, causing various inconveniences in subsequent steps.

In addition, the exposed iron surface after the surface coating was removed lacked corrosion resistance and had drawbacks such as deteriorating the appearance. For this reason, tin-free steel is not yet used as a material for cans such as food and drink cans.

[Means for solving problems]

The method for welding can materials according to the present invention includes, prior to electrical resistance welding of the can materials, a laser beam is irradiated on the surface of the materials at the overlapping portion that will become the welding portion to evaporate the surface coating.
Thereafter, electric resistance welding is performed by body wire seam welding or rotating electrode resistance seam welding.

[For production]

In the method of the present invention, prior to electric resistance welding of can materials with poor electric resistance weldability, a laser beam is irradiated in advance to the part to be welded, so that the upper layer of the plating layer that inhibits electric resistance weldability is irradiated with a laser beam. The chemical conversion coating mainly composed of metal oxides present in the coating and the plating metal present in the underlying layer are evaporated or removed, or these plating layers and the underlying iron are alloyed. As a result, good electrical conductivity and heat transfer properties can be obtained, and electric resistance weldability can be improved.

Furthermore, the present invention will be explained.

As a typical processing laser, CO laser (wavelength 10.6
.mu.m), YAG laser (wavelength: 1.06 .mu.m), and Q-switch YAG laser (wavelength: 1.06 .mu.m). When these lasers are applied to the surface layer of tin-free steel, which is an example of a can material with poor electrical and resistance weldability, the properties of the irradiated area vary greatly depending on the wavelength, power, and power density of the laser beam.

First, as an influence of the wavelength of the laser beam, there is a problem of laser absorption rate. As mentioned above, in the surface layer of tin-free steel, there is a thin metallic chromium layer on a steel sheet base and a layer of chromium oxide thereon. CO with a wavelength of 10.6 μm
, the laser has an extremely high absorption rate of approximately 100% for chromium oxide, but has a low absorption rate for metallic chromium.
Most of it is reflective. On the other hand, a YAG laser with a short wavelength has a small absorption rate for chromium oxide, but an absorption rate for metal chromium that exceeds that of a CO2 laser. Therefore, when the surface layer of tin-free steel was irradiated with these lasers, the following phenomenon was observed.

In order to modify only the surface layer properties of tin-free steel,
When the CO□ laser was irradiated with low heat input, most of the chromium oxide evaporated, and the metallic chromium layer often remained unmelted. Furthermore, when irradiating with a continuous wave YAG laser, only a small amount of chromium oxide evaporated, and most of the metal chromium and a portion of the steel sheet base were melted and alloyed.

Second, there is the problem of laser power and power density. In terms of power density, Q-switched YAG lasers are the best, with peak power densities reaching 109 to 1012 w/cj. Therefore, when irradiated with this laser, it instantly melted and evaporated. This melting and evaporation depth can be easily controlled by adjusting the laser power, and for example, it was possible to evaporate only the chromium oxide layer or both the chromium oxide layer and metallic chromium. Furthermore, if the power of the CO□ laser is increased, it is possible to melt metal chromium and steel sheet substrates, but in order to form a stable alloy layer, a melting depth of at least 2 μm or more is required.

As described above, the properties of the surface layer of tin-free steel can be changed to various states with good conductivity by irradiating with a laser beam.

〔Example〕

Hereinafter, a case where the present invention is applied to can body manufacturing will be described in accordance with an embodiment of the present invention.

As a result of conducting a can making test using a conventional copper wire seam welding machine by irradiating a laser beam on the part to be welded and using an i-can blank, the electrical resistance was significantly lower than that of tin-free steel as received. Experimental results showed that weldability was improved.

A laser beam was applied under the conditions shown in Table 1 using tin-free steel (metal chromium 150a@/m', chromium oxide gomg/m) with a plate thickness of 0.22mm and a tempering degree of T-4 as an original plate. was irradiated. Four types of laser beam irradiation surfaces,
Test can blanks were produced using three types of laser devices with different power densities.

Table 1 Note) 1) Laser beam irradiation surface (see Figure 2) N1; Double-sided irradiation (all contact surfaces (5) to (8)) N2. Single side irradiation (steel plate-steel plate contact surface (61, (71)) N3. Single side irradiation (steel plate-welding electrode contact surface (5], (8)) N4i alternate irradiation (contact surface (51, (81)) and contact surface (6)
, (any surface of 71) 2) Laser model YAG, YAG laser Q switch; Q switch YAG laser Go, i continuous wave CO2 laser The can making test was set to conditions close to practical welding conditions.

Table 2 shows the welding conditions, and Table 3 shows the welding test results. Note that Table 3 also shows the surface layer properties after laser beam irradiation.

Table 2 Table 3 Note: 1) As-received tin-free steel 2) Cold-rolled steel plate 3) Soldering is tinplate Compared to untreated tin-free steel,
It has become clear that the laser-treated tin-free steel of the present invention has a significantly expanded appropriate current range.

This is achieved by evaporating the metal and chromium oxide that make up the plating layer of tin-free steel using a laser beam, or by forming an iron-chromium alloy to make it conductive. This is thought to be due to a dramatic increase.

It is clear that the degree of weldability improvement effect achieved by laser treatment with laser beams slightly depends on the laser beam irradiated surface and the surface layer properties after laser beam irradiation. Regarding the laser beam irradiation surface, the effect of improving weldability is greater when the welding surface side (6, 7) is irradiated. The reason for this is that in tin-free steel as received, heat generation due to electrical resistance is caused by the steel plate being cooled by the water-cooled welding electrode.
This is because the steel plate-steel plate interface serving as a joint surface is larger than the s8ii interface, and formation of molten metal and eventually generation of paris is likely to occur. In addition, regarding the surface layer properties after laser beam irradiation, when the steel sheet base is exposed, the iron-
The effect was slightly greater than when alloyed with chromium. However, sufficiently good seam welding was possible even with alloyed materials.

In addition, when only the chromium oxide layer on the surface is removed and the metallic chromium layer is exposed, the appropriate current range is slightly smaller than when the base steel plate is exposed, but stable seam welding is still possible. there were.

In addition, even if the laser beam is irradiated on any one of the four steel plate surfaces (5, 6, 7, 8) of the steel plate-steel plate contact surface and the steel plate-welding electrode contact surface, the electrical resistance will not change. Weldability has improved.

〔Effect of the invention〕

As explained above, according to the present invention, by irradiating the surface of the welded part with a laser beam prior to electric resistance welding of can materials, the surface coating of the welded part is completely evaporated or removed, or the base material is is alloyed with, and
Because it completely wipes away the ultrafine powder produced by laser processing, it is now possible to easily perform electric resistance welding of various can materials, including tin-free steel, which was previously considered impossible. . As a result, by applying the method of the present invention, it is expected that the scope of application to beverage and food cans will be greatly expanded.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a plating layer of tin-free steel to which the present invention is applied, and FIG. 2 is an explanatory diagram showing a laser beam irradiation surface of a welded part. (1): Chromium oxide layer, (2): Metallic chromium layer, (
3): Steel plate, (4): Welding electrode, (5), (81:
The steel plate surface at the welding electrode-steel plate contact surface, (61, (71:
Steel plate surface at the steel plate-steel plate contact surface, (9): Can material. Agent Patent Attorney Tadashi Sato III ■ No. 211 □222 Yen' □7 1 + 7a acid aI-m7 ni' 2: Gold scraps black 4 3I-1 Ash - 4: Soi 11 scene 9] Cumulative, 4'

Claims (1)

[Claims] A method for welding can materials, characterized in that, prior to electric resistance welding of can materials, the surface of an overlapping portion to be a welded portion is irradiated with a laser beam to improve the electric resistance weldability of the surface.