JPH0146995B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing an expanded lattice for a lead-acid battery, in which the lattice is obtained by expanding a lead-calcium alloy sheet, and its purpose is to improve and stabilize the life performance. Lead (Pb)-calcium (Ca) alloys, which reduce self-discharge in batteries and reduce loss of electrolyte during use, have recently been increasingly used in electrical conductors such as grids. Since this Pb-Ca alloy has poor lattice casting workability, products have been developed that allow expansion processing of sheets cast by the direct method, and sheets obtained by plastic processing such as extrusion or rolling from cast slabs or billets. . The key point when manufacturing a grid using expanded processing is to obtain a structurally complete product with no cracks or damage near the intersections of the grid bars, and for this purpose it is necessary to use sheets with large elongation. be.
To explain this with reference to Figure 1, when a sheet 1 with a length 2 slit 2 is expanded into a diamond shape with a diagonal line of b and a diamond shape of n, the sheet material between the slits is √1+ ²
It has to be doubled. In actual expanding processing, due to twisting and other phenomena, √1+ ²
It may be slightly smaller than double, but elongation is still important. If a material with small elongation is forcibly expanded, cracks may occur near the points P between the slits, that is, the intersections P of the lattice bars 3, and the material may burst. On the other hand, the disadvantage of the expanded lattice is that when it is used as a positive electrode plate, it stretches to a large extent in the expanding direction, which frequently causes short circuits, softening of the active material, and early dropout. The cause is volumetric expansion due to corrosion products, which are formed on the surface and inside the lattice and have a larger molecular volume than lead. The corrosion layer consists of lead monoxide, lead dioxide, and lead sulfate, whose molecular volumes are 1.3, 1.4, and 2.6 times that of lead, respectively. As these corrosion products form on the surface, tensile stress is applied to the bars of the grid and the bars are gradually stretched due to creep phenomena. If corrosion products form inside the grate,
That is, if there is a minute crack in the crosspiece and corrosion progresses along the crack, or if the intergranular corrosion of the alloy crystal is severe, the elongation of the lattice crosspiece becomes extremely large. At this time, the corrosion products act like a wedge, promoting the progress of corrosion inward and causing the lattice to collapse at an early stage. The elongation of the lattice mentioned above can be reduced if its creep resistance is large, but it is powerless against minute cracks in the crosspieces and corrosion at grain boundaries. Lead alloy sheets used for expanded grids include those that are made by plastically working a cast slab at room temperature, and those that are made into thin sheets directly by casting.
A DM sheet is proposed. The former has stable tensile strength when left at room temperature, but has little elongation, and micro-cracks are likely to occur at the intersections of the crosspieces during expansion processing, while the latter suffers from severe corrosion at grain boundaries, causing lattice elongation in both cases. It has the disadvantage that it is large and suffers from severe corrosion near the intersection of the crosspieces. It is an object of the present invention to eliminate such drawbacks and to obtain a battery equipped with an expanded electrode plate that is less elongated in the expanding direction and less corroded at crosspiece intersections. The gist of the present invention is to form a thick sheet by subjecting a cast lead-calcium alloy to plastic working such as rolling or extrusion at a high temperature of 100°C or higher, and then to form a thick sheet at a low temperature of 50°C or lower. The purpose of this method is to form a lattice by expanding the rolled sheet according to a conventional method. A process flow diagram of the present invention is shown in FIG. Next, the present invention will be explained with reference to examples. A billet of Pb-0.07%Ca-0.5%Sn alloy was produced by casting, and it was heated at room temperature, 100-150℃ and
Extruded at 200-250℃ with an extrusion ratio of about 80% to a thickness of 3
mm sheet. Next, store this at room temperature and 100%
Rolling was performed at ~150°C to obtain a sheet with a thickness of 1.2 mm. This sheet is expanded and n in Figure 1 is 0.65.
A prototype automobile battery with a capacity of 35 ampere hours (Ah) was fabricated using the grid as the positive electrode plate, and a JIS charge/discharge cycle (∞) life test was conducted. Table 1 shows the mechanical properties of the 1.2 mm thick sheet, and Table 2 shows the battery life test results. In addition, the discharge capacity is 100 at the 1∞th
It is expressed as a ratio.

【table】

[Table] From Table 1, sheets A and B, which were rolled after extruding a cast billet at room temperature, have a small elongation.
It can be seen that D and F, which were extruded at high temperature and then rolled at high temperature, have low tensile strength, but C and E, which were extruded at high temperature of 100°C or higher and then rolled at room temperature, have relatively high tensile strength and elongation. Also the second
From the table, only the batteries using sheets C and E maintained sufficient capacity at the 100∞th charge/discharge, and the elongation of the positive electrode lattice was small, indicating a good condition. FIG. 2 shows the corrosion state of the positive electrode grid after 100∞ using sheets A and C. This is a micrograph showing a cross section at the intersection of the crosspieces. Sheet A in Figure 2a shows severe corrosion along the grain boundaries;
In sheet C in Figure b, corrosion progresses uniformly from the surface. As already detailed, lead alloy sheets using expanded lattices are desired to have high elongation.
In the above example, n = 0.65, so calculated 20%
More growth is required. Sheets that have been plastically worked at high temperatures have a large elongation and are suitable in this respect. Furthermore, when used as a positive electrode grid, elongation due to corrosion products must be small. When a sheet that has been plastically processed at high temperatures is rolled at room temperature, its tensile strength increases to a certain level, resulting in superior battery performance. As described above, when a thick sheet that has been plastically worked at a high temperature is rolled at room temperature, a sheet that is suitable for expanding processing and has both good tensile strength and elongation can be obtained. The positive electrode plate using this material has less corrosion at the intersection points of the grid bars and less elongation in the expanding direction, and has a significantly improved life performance, so the present invention has great industrial value.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an expanding process, which is one of the manufacturing processes of an expanded lattice. Figure 2 is
This is a microscopic photograph showing the corrosion state of the intersection points of the positive electrode grid after a JIS cycle life test of 100∞. FIG. 3 is a process flow diagram of the manufacturing method of the present invention. 1... sheet, 2... slit, 3... lattice crosspiece, P... intersection of lattice crosspiece.

Claims (1)

[Claims] 1. A cast product of a lead-calcium alloy is subjected to plastic working such as rolling or extrusion at a high temperature of 100°C or higher to form a thick sheet, which is then processed at a low temperature of 50°C or lower. A method for producing an expanded grid for lead-acid batteries, in which the sheet is rolled into a thin sheet and then expanded to obtain a grid.