JPS634312B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a strap welding method for a group of electrode plates for a lead-acid battery, in which the ears of a plurality of electrode plates for a lead-acid battery are welded together using a molded strap. [Prior art] As is well known, the electrode plates of lead-acid batteries have traditionally been
A lattice made of a Pb-Sb alloy is used.
Additionally, maintenance-free batteries are rapidly becoming more common, especially in automotive lead-acid batteries.
Along with this, the material of the grid alloy was also changed as mentioned above.
There is a transition from Pb-Sb alloys to Pb-Ca alloys. By using a Pb-Ca alloy with a high hydrogen overvoltage, gas generation during charging can be suppressed, and electrolyte loss can be significantly reduced compared to batteries using conventional Pb-Sb alloy grids. Because it can be done. As described above, the use of a Pb-Ca alloy lattice has the great advantage of making the battery maintenance-free, but it is not always an advantage. It also has the same drawbacks. These problems include, for example, an oxide film formed on the surface of the Pb--Sb alloy or Pb--Ca alloy lattice, which makes it difficult to weld between the ears and the formed strap. This difficulty becomes more apparent when a Pb--Ca alloy lattice is used, so the case will be specifically explained below using a Pb--Ca alloy as an example. As is well known, automotive lead-acid batteries with a terminal voltage of approximately 12V are normally used, but this battery is composed of six batteries (cells) each having an electromotive force of approximately 2V connected in series. There is. FIG. 1 shows a part of a cross section of an automobile battery. An anode plate 3,
3' is housed with cathode plates 4, 4' stacked alternately. And the anode plates 3, 3' and the cathode plate 4,
4' is isolated by a bag-shaped separator 5 so as not to come into contact with it. Also, the anode plate 3 in the cell 2 and the cathode plate 4' in the cell 2' are connected by straps 9,
They are electrically connected via inter-cell connection conductors 6, 6' and straps 9'. Here, the inter-cell connection conductor 6 and the strap 9 are integrated, and each anode plate 3 is welded to the strap 9 when the strap 9 is formed. Similarly, each cathode plate 4' is welded to a strap 9' which is integral with the intercell connecting conductor 6'. The inter-cell connection conductors 6, 6' are integrally connected through holes 7 provided in the partition wall 1. Although not shown in the figure, each cathode plate 4 in the cell 2 or each anode plate 3' in the cell 2' is also connected to each anode plate and each cathode plate of the adjacent cell in a similar manner. . FIGS. 2a to 2c are partial simplified views of welding parts for explaining in more detail the welding of the ears of each electrode plate and the strap. The ears 8 of a large number (four in this figure) of the anode plates 3 constituting the group and the intercell connection conductor 6 are integrated via the strap 9 at least when the strap 9 is formed. When forming the strap 9 here, it is often done by pouring a molten lead alloy called additional lead into this part, but sometimes the ear part 8 of the electrode plate is made sufficiently long in advance. It may also be formed by melting without adding molten metal from the outside. Furthermore, in a so-called cast-on method, melting is applied to the upper part of the ear part 8 of each electrode plate.
Pb alloy is poured and the inter-cell connection conductor 6 and strap 9 are formed simultaneously, and the ear portion 8 of each electrode plate is formed.
There is also a method of welding with. In any case, the inter-cell connection conductor and each electrode plate are ultimately welded together via the strap, but
Obtaining reliable connections without defects is quite difficult. Of course, this also applies when the electrode plate is made of a Pb-Sb alloy, but especially when the lattice used in the electrode plate is
This tendency is extremely remarkable in the case of Pb-Ca alloys. Therefore, defects appear prominently in Pb−
The reason for this will be described below, taking the case of using a Ca-based alloy as an example. As is well known, Pb--Ca alloys have lower fluidity than Pb--Sb alloys and contain Ca, which is highly active, so that an oxide film is extremely easily formed on the surface of the molten metal in a molten state. It is the presence of this oxide film that makes it difficult to weld electrode plates with a Pb-Ca alloy lattice. For example, when the plates of a Pb-Ca alloy lattice are welded together using a strap using the cast-on method, the upper part of the ear of each plate is placed in a mold at a temperature of approximately 500°C. By casting a certain amount of Pb-Sb alloy, the inter-cell connecting conductor and strap are formed and welded so that the ears of each electrode plate are held inside the strap. At this time, the time required for the cast Pb-Sb alloy to solidify is about 3 to 5 seconds. During this time, the edges of each electrode plate receive heat from the molten Pb--Sb alloy poured around them, causing the surface to melt and become integrated with the formed strap. As mentioned above, Pb--Ca alloys are extremely easily oxidized, and in particular, oxide films are easily formed in the molten state. Therefore, as described above, even when molten metal is poured into the surrounding area and melts the surface of the ear, an oxide film is formed by reacting with oxidation in the air involved. Also, it must be considered that the oxide film on the surface of the ear has been present since before the cast-on. For example, in the case of an expanded lattice, there is an oxide film formed during the ingot stage for producing the raw material Pb-Ca alloy sheet, and an oxide film formed during the rolling process into the sheet. In the case of cast grids, a molten Pb-Ca alloy at about 500°C is cast into a mold, so an oxide film is formed on the surface of the finished grid. There is also an oxide film formed not only in the grid manufacturing stage but also in the electrode plate manufacturing process, for example during drying after pasting. [Problems to be Solved by the Invention] If such an oxide film exists, welding cannot be performed satisfactorily as described below. Needless to say, oxides generally have high melting points and do not melt easily. However, since the specific gravity of lead alloy itself is smaller than that of lead alloy, even if the oxide film does not melt, if the surrounding metal melts, the oxide film with low specific gravity should float to the surface of the molten metal.
If the surface of the ear part melts by receiving heat from the molten lead alloy poured around it during cast-on, the oxide film should be able to move through the molten metal and float to the surface. However, especially Pb-Ca alloys, Pb-Sb
It has very poor fluidity compared to other alloys, and even when melted, it is difficult to fuse with the Pb-Sb alloy poured into the surrounding area during cast-on. This means that the oxide film present on the surface of the ear part moves through the surrounding molten metal and is difficult to float up to the surface of the strap. Furthermore, the solidification time of the lead alloy poured during cast-on is about 3 to 5 seconds, which also makes it difficult for the oxide film to float. If it takes a long time to solidify, it should be possible to levitate a considerable amount, but if it takes such a long time, the temperature of the ear will rise too much and the entire ear will melt. A phenomenon occurs in which the ears melt down at the bottom of the strap. For the reasons mentioned above, the oxide film cannot float,
It remains inside the strap. Figure 3 shows this situation. Figure 3a shows the cross-sectional shape when extremely good welding is achieved, with a beautiful fillet (A section) formed between the strap 9 and the ear 8, and the ear 8 inside the strap 9. The surface of the strap 9 has melted to an appropriate degree, and the boundary between the strap 9 and the ear 8 (dotted line in the figure) is indistinguishable. Figure b is a typical example of a defect produced in a normal process. First of all, the fillet formation seen in FIG. 3a is not observed. This is because the molten metal forming the strap 9 is difficult to wet the surface of the ear part 8 due to the oxide film present on the surface of the ear part 8. Not only is it difficult to form a fillet, but also a large crevasses-like defect as shown by symbol B appears. In addition, the oxide film that existed on the surface of the ear part 8 cannot float up to the surface of the strap 9 and becomes trapped inside the strap 9, so the metal on the upper, lower, left, and right sides are separated by the oxide film in this part. This results in the occurrence of defects such as so-called inclusions or poor fusion. C in the figure shows the occurrence of this type of defect, and this defect exists at a position corresponding to the surface of the ear just before melting occurs. It is clear that if such a defect occurs, the ears will easily fall off the strap. In particular, the large crevasses that develop from the inability to form fillets, as shown in B, act as notches, and if the plate is bent slightly from side to side, a crack will occur at the tip of the crevasse, causing the plate to fall off from the strap. There is.
Furthermore, when such a defect occurs, it reduces the effective cross-sectional area for current to flow, which increases the voltage effect in this area, especially in the case of large current discharge, and causes a reduction in the starting performance of the automobile engine. It is becoming. The explanation above has been given as an example of cast-on welding using a Pb-Sb alloy to a plate using a Pb-Ca alloy lattice. The same is true when the strap is made of a Pb-Ca alloy. Further, even when a Pb--Ca alloy lattice is used, welding defects due to the presence of an oxide film similarly occur, although there are differences in the degree of formation of the oxide film. The present invention solves the above-mentioned problems that occur when welding the ears of lead-acid battery plates to each other when forming a strap, and provides a material that is excellent metallurgically and mechanically and has excellent corrosion resistance. The purpose of this paper is to propose a strap welding method for a group of electrode plates for a lead-acid battery, which makes it possible to obtain a welded part with a uniform weld. [Means for Solving the Problems] In order to solve the above problems, in the present invention, the surface of the ear portion 8 of the electrode plate 3 is irradiated with a beam 11 having a high energy density such as a laser beam. Part 8
A surface treatment is performed to remove a film such as an oxide film existing on the surface of the ear portion 8 by evaporating the surface layer of the ear portion 8, and then a strap forming process is performed. [Operation of the Invention] As is well known, a laser beam is a special type of light having a uniform phase, and by condensing the beam with an appropriate means, it is possible to obtain extremely high energy density. Therefore, when a properly focused beam is irradiated onto an object, the area where the beam hits becomes extremely hot, causing not only melting but also boiling and evaporation of the material.
In addition, the high energy density means that it is possible to minimize the thermal effect and heat only the necessary parts. can be limited. As a result, only the surface layer of the ear portion 8 of the electrode plate 3 to be welded is melted and evaporated, oxides, etc. present in this portion can be removed, and a clean metal surface can be exposed. . By carrying out the strap forming process after performing such treatment, welding can be performed in an extremely good welding state and with sufficient mechanical strength and corrosion resistance of the welded part. [Example] Hereinafter, the present invention will be explained in detail with reference to Examples.
In the present invention, a laser beam having the properties described above is irradiated onto the surface of the ear portion of the electrode plate, and the situation is as shown in FIG. 4, for example. A laser beam 11 emitted from a laser oscillation device 10 is focused by a concave mirror 12 so that the diameter on the surface of the ear portion 8 of the electrode plate 3 is about 0.5 to 1.0 mm. Further, by repeatedly moving the concave mirror 12 in the directions of arrows X and X', the focused beam 11 is repeatedly moved left and right (in the directions of arrows Y and Y') on the surface of the ear portion 8. Further, the polar plate 3
move. FIG. 5 shows the movement of the focused laser beam 11 on the surface of the lug 8 of the electrode plate 3 when such an operation is performed, and the arrow in the Z direction indicates the direction of movement of the electrode plate 3. , 15 indicate the movement of the laser beam 11 on the surface of the ear 8. Now, under these circumstances, by appropriately selecting the energy of the beam 11 when it exits the laser oscillation device 10, the beam diameter at the surface of the ear part 8, and the moving speed of the beam 11 at which it is repeated in the Y and Y' directions, , only the surface layer (for example, 0.05 to 0.1 mm thick) of the portion of the ear portion 8 to be welded is heated to a significantly high temperature to remove the oxides existing on the surface and the Pb of the fabric.
-It becomes possible to evaporate and remove a part of the Ca-based alloy or the Pb-Sb-based alloy. Preferably, such operations are carried out under an inert gas such as Ar or N2. By the above operation, the surface of the ear portion 8 formed by irradiation with the laser beam 11 becomes the original clean surface of metal from which the oxide film has been removed. As described above, by applying the method according to the present invention, it is possible to remove the oxide film etc. present on the surface of the ear, but as described above, the laser beam 11 irradiated on the surface of the ear can be removed from the ear. Since the diameter is narrowed down to about 0.5 to 1 mm to remove only the very surface layer of 8, for example, the clean metal formed by moving the beam 11 once in the Y and Y' directions in FIG. The surface becomes a band whose width is approximately the same as the beam diameter. Therefore, in order to form a clean metal surface over the entire surface of the ear portion 8 to be subjected to welding, it is necessary to keep the moving speed of the electrode plate 3 relatively low. However, it is not preferable to reduce the moving speed of the electrode plate 3 too much because it reduces production efficiency. As a solution to this problem, several heads may be provided for irradiating the laser beam 11, and the surface that has been irradiated once may be irradiated repeatedly. However, it is not necessary to prepare multiple laser oscillation devices 10 for this purpose.
This purpose can be achieved by splitting the beam 11 emitted from the oscillator 10 with suitable mirrors. next,
An experimental example of the present invention will be explained. In the experiment, Pb−
After filling a paste into a grid made by casting a 0.07Ca-0.5Sn alloy, the electrode plate 3 was subjected to primary drying, aging, chemical formation, and secondary drying, and the surface treatment of the ears 8 was performed using the method according to the present invention. The appearance of the welded part (fillet formation status), the occurrence of defects by cross-sectional structure inspection, and the welded part where group welding was performed by cast-on after drying, and the welded part which was welded by cast-on as usual after secondary drying. Mechanical strength was measured by a tensile test to evaluate the effects of the present invention. The surface treatment of the ear portion 8 according to the present invention was carried out as follows. The laser beam 11 is a CO ₂ gas laser oscillator 1 with a maximum output of 2kw.
0, and as shown in FIG.
The light was focused so that Furthermore, concave mirror 12 is 10
The beam 11 was swung repeatedly at a speed of Hz in the X and X' directions in Figure 4 so that the amplitude on the ear surface was 15 mm. At this time, the polar plate 13 is moved by 0.5 in the direction perpendicular to the amplitude direction of the beam 11 (see Fig. 5).
The thickness of the ear surface layer that is removed by being heated by the laser beam 11 is approximately
The output of the oscillator 10 was controlled so that the distance was 0.05 mm. The laser beam 11 was irradiated from both the upper and lower sides of the electrode plate 3 so that the entire surface of the portion of the ear portion 8 to be welded was sufficiently treated. Further, the treatment was performed in an Ar gas atmosphere. The forming of the strap and the welding of the strap and the edge of the electrode plate were performed using the cast-on method, and the material of the cast alloy at this time was Pb-3.0Sb-0.3As.
The temperature of the molten metal during casting is 480°C, and the preheating temperature of the cast-on mold is 180°C. Further, this welding was performed in the atmosphere, and no special treatment such as inert gas coating was performed. The results of investigating the effects of the present invention using the method described above are shown in the table below.

[Table] As is clear from the above table, the electrode plate according to the present invention, in which the surface of the electrode plate was subjected to surface treatment using a laser beam, showed extremely superior results compared to the electrode plate which was not subjected to such treatment. It can be seen that the present invention is effective as a method for obtaining excellent welded parts. Note that the explanation so far has been made with reference to the electrode plate using the Pb-Ca alloy lattice, but the present invention is applied to the edge of the electrode plate using the Pb-Sb alloy lattice. The effect will not be diminished or lost in any way. Furthermore, the beam treatment can also be performed in air. Furthermore, the method according to the invention can also be carried out using an electron beam instead of a laser beam. However, since electron beam irradiation requires irradiation in a vacuum, it is inevitable that workability will be sacrificed to some extent. Needless to say, it is preferable to use a laser beam in practice. [Effects of the Invention] As described above, according to the present invention, by irradiating the surface of the lug of a lead-acid battery plate with a beam having a high energy density, oxidation existing on the surface of the lug is removed. Since the edges of the electrode plates are welded at the same time as the strap is formed after removing coatings that are harmful to welding, such as films, it is possible to perform welding with extremely good welding conditions. This not only greatly improves the yield of welding electrode plates for lead-acid batteries, but also increases the mechanical strength and corrosion resistance of the welded portion, which is of great practical benefit.

[Brief explanation of the drawing]

Figure 1 is a partial sectional view showing an example of the structure of a lead-acid battery, Figures 2 a to c are a plan view, front view, and left side view schematically showing the structure of a welded part, and Figure 3 a is a An explanatory diagram showing a good condition of a welded part, Figure b is an explanatory diagram showing a defective welded part, and Fig. 4 shows a state in which the beam is irradiated to the edge of the electrode plate in an embodiment of the present invention. An explanatory diagram, FIG. 5, is an explanatory diagram showing the trajectory of the beam irradiation mentioned above at the ear portion of the electrode plate. 3, 3'... anode plate, 4, 4'... cathode plate, 6,
6'...Inter-cell connection conductor, 8...Ear portion, 9,9'...
...Strap, 10...Laser oscillation device, 11...
...laser beam.

Claims (1)

[Claims] 1 The ears 8 of the plurality of electrode plates 3 formed of a lattice made of Pb-Ca or Pb-Sb alloy are attached to straps 9.
In a strap welding method for a group of electrode plates for a lead-acid battery, the straps are welded to each other during molding,
By irradiating the surface of the ear portion 8 of the electrode plate 3 with a beam 11 having a high energy density such as a laser beam to evaporate and remove the surface layer of the ear portion 8, the surface layer of the ear portion 8 is removed. 1. A method for welding straps for a group of electrode plates for a lead-acid battery, comprising performing a surface treatment to remove a coating such as an oxide film, and then performing a step of forming the strap.