JPH059903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art and Problems] The present invention relates to a method of manufacturing a plate grid for a lead-acid battery. Conventionally, lead-antimony alloys have been mainly used for the electrode grids of lead-acid batteries, but recently, lead-calcium alloys have been used for maintenance-free storage batteries. Since the lead-calcium alloy has a higher hydrogen overvoltage than the lead-antimony alloy, it has the advantage of less electrolysis of water in the electrolyte during charging and less self-discharge during storage. However, on the other hand, the castability is inferior to that of lead-antimony alloys, so the lead-calcium alloy material cast into a flat plate is cold-rolled, for example at a slab temperature of less than 50°C, and then expanded and punched. Electrode grids are manufactured by the following methods.

Lead alloys have age hardening properties, and when heat treated, solute metals are precipitated from a supersaturated solid solution, or intermetallic compounds are formed between the solute metals and lead or other additive metals. This precipitation of solute metals and the formation of intermetallic compounds mainly occur at metal grain boundaries, and this is the cause of corrosion of lead alloy materials. In this way, solute metal precipitates at grain boundaries,
Alternatively, when intermetallic compounds are formed, that part becomes more susceptible to corrosion than other parts, and when corroded, oxides with low density are produced and grain boundaries are expanded.
Once the new alloy surface is exposed, corrosion begins again. However, when a lead-calcium alloy is rolled, grain boundaries are dispersed and intergranular corrosion is alleviated, but because the grain boundaries are dispersed, overall corrosion (general corrosion) becomes severe.

[Purpose of the invention]

The electrode grid of a lead-acid battery, especially the positive electrode grid, needs to suppress intergranular corrosion and general corrosion. This is because intergranular corrosion causes elongation and cutting of the lattice, and general corrosion reduces the current collection effect and active material retention. In view of this point, it is an object of the present invention to provide a method for manufacturing a lattice that suppresses both types of corrosion, that is, a lattice with excellent corrosion resistance.

[Structure of the invention]

The present invention casts a flat plate of lead-calcium alloy,
In the step of rolling this flat plate and then expanding or punching it to produce an electrode plate grid, the rolling of the flat plate lowers the surface temperature of the flat plate to 50°C.
℃ to 200℃, and under these temperatures, the following formula t ₁ = 2-2T ² / 50.000 ... (1) t ₂ = 10-2T ² / 10.000 ... (2) [However, t ₁ , t ₂ is the time (minutes) from the time the flat plate is cast to the end of rolling, and T is the surface temperature of the flat plate (°C)] The rolling is completed within the range of the minimum time t ₁ and maximum time t ₂ shown in This is a method for manufacturing an electrode grid for a lead-acid battery.

The corrosion resistance of lead-calcium alloys changes depending on the structure of the metal grain boundaries, and in general, the fewer grain boundaries there are in a cast product, the finer the grain size, and the narrower the grain boundary width, the better the corrosion resistance. improves. Since this alloy has age hardening properties, the structure of these grain boundaries is greatly influenced by the temperature and time of heat treatment after casting and processing conditions.

As mentioned above, intergranular corrosion can be suppressed by rolling, but rolling increases general corrosion. General corrosion can be suppressed by heat treatment. As a method of suppressing this general corrosion, the present invention proposes the above equations (1) and (2) while maintaining a temperature of 50°C to 200°C without cooling the cast slab to ambient temperature. Rolling is performed within the range of the minimum time t ₁ and maximum time t ₂ shown in (see Fig. 1). In other words, thermal energy is used effectively by rolling the cast slab without cooling it, and sufficient mechanical strength is achieved by rolling the slab while maintaining uniform internal and surface temperatures. This results in a lattice that is strong and has excellent corrosion resistance.

Example As an example of a lead-calcium alloy, an alloy consisting of 0.08% Ca (all weight% hereinafter), 0.5% Sn, and the balance lead was melted by heating to 450°C, and then molded into a thick mold using a continuous mold heated to approximately 150°C. A flat plate (slab) with a diameter of 8 mm is cast, and each of these is heated or cooled to 200℃,
175℃, 150℃, 125℃, 100℃, 75℃, 50℃, 30℃
The sheet was rolled with rollers while the sheet was held at 1 mm until the final sheet had a thickness of 1 mm. 1mm from this 8mm
The rolling time was adjusted by the rotational speed of the rollers and ranged from 0.25 minutes to 200 minutes. This time corresponds to the time for heat treatment of the slab. For reference, the following information is available: a cast product, a product rolled at a slab temperature of less than 50°C (conventional example), and a cast product rolled at a slab temperature of 100°C.
A product heat-treated for 15 hours and a cold-rolled product were produced.

In order to evaluate the corrosivity of each of these samples, these materials were cut into pieces of 3 mm wide and 30 mm long, and a pure lead plate was used as the counter electrode, and sulfuric acid with a specific gravity of 1.28 was used as the ^electrolyte . Anodic oxidation was carried out by continuously passing a constant current for 20 days, and after removing the generated oxide, it was weighed, and the weight loss was defined as the oxidation loss.

The results are shown in Figures 2-6. Figure 2 shows an overall observation of the relationship between rolling time (heat treatment time) and oxidation weight loss (corrosion resistance), and Figure 3 shows each sample in the area where the oxidation weight loss sharply decreases in Figure 2. FIG. 3 is a diagram showing specific data on rolling time and oxidation weight loss. In the figure, 1 is as-cast, 2 is cold-rolled,
3 is a heat-treated cast product, and 4 is a cold rolled product; these have no relation to the rolling time on the horizontal axis. 5 has a rolling temperature of 200℃, 6 has a rolling temperature of 175℃, and 7 has a rolling temperature of 200℃.
50°C, 8 is data for each sample at 30°C. Note that the sample between 175°C and 50°C is located between 6 and 7, but is omitted from FIG. FIG. 4 is a diagram showing the relationship between rolling time and slab temperature in the region of FIG. 3 where the oxidation weight loss sharply decreases, and the following equation can be approximately obtained from the curve in FIG. 4.

t ₁ =2−2T ² /50000 (1) Since the minimum value of oxidation weight loss at 30° C.8 is high, it is excluded from the curve in FIG. 4 and equation (1). the above
Equation (1) defines the minimum rolling time that minimizes oxidation weight loss.

FIG. 5 is a diagram showing specific data of the region in FIG. 2 where the oxidation weight loss increases rapidly. 6th
The figure shows the relationship between the rolling time and slab temperature in the region of FIG. 5 where the oxidation weight loss rapidly increases, and the following equation can be approximately obtained from the curve of FIG. 6.

t ₂ =10−2T ² /10000 (2) From the above equation (2), the maximum rolling time that minimizes the oxidation weight loss is defined.

Example The example is for confirming the effect of the electrode plate grid manufactured using the lead alloy material of the example.The lead alloy contains the same lead alloy Pb-Ca (0.08%) as the example.
- Using Sn (0.5%), plate-shaped castings A, B, and C were cast and rolled in the same manner as in the example. The combination of rolling temperature and rolling time is 150℃ for A.
B was 4 minutes at 100°C, and C was 6 minutes at 50°C. Each of these samples A, B, and C was expanded to produce a lattice. The dimensions of the grid are 28 mm wide, 80 mm long, and 2 mm thick. Also, for reference,
A lattice having the same shape and dimensions as those of A, B, and C was cast as D, and sample E was obtained by rolling the cast material at a slab temperature of less than 50° C. to expand it.

Each lattice of Samples A to E was filled with an active material, dried and chemically formed, and two positive electrode plates each were compressed through three conventional negative electrode plates and a glass fiber mat separator to form an electrode plate group. , produced a storage battery using sulfuric acid with a specific gravity of 1.28 as the electrolyte. Note that the discharge capacity is 3Ah at a 10-hour rate discharge. Each of these storage batteries was charged at 0.1℃ for 336 hours, discharged at 0.3C, and cycled to 1.75V per cell, which was 1/1/2 of the initial capacity.
The number of cycles until it reached 2 was determined and this was taken as the life span. The results are shown in FIG. From the same figure, it can be seen that the lifespan of products A, B, and C of the present invention is significantly improved compared to conventional products D and E.

〔Effect of the invention〕

As shown in the examples and data, the electrode grid produced by the manufacturing method of the present invention has significantly improved corrosion resistance compared to the electrode grid produced by the conventional method, and as a result, has an excellent effect of extending the life of the storage battery. has. Furthermore, the grating made by the manufacturing method of the present invention is comparable in mechanical strength to conventional gratings, and together with its improved lifespan, its industrial value is extremely large.

[Brief explanation of the drawing]

Figure 1: A diagram showing the relationship between the minimum time _t1 , the maximum time _t2 , and the surface temperature T of the flat plate, Figure 2: A diagram showing the relationship between the total rolling time and oxidation weight loss in the manufacturing method of the present invention, Figure 3: Diagram showing specific data of the region where oxidation weight loss sharply decreases in Figure 2, Figure 4
Figure: A diagram showing the relationship between rolling time and slab temperature in Figure 3, Figure 5: A diagram showing specific data of the region where oxidation weight loss rapidly increases in Figure 2,
FIG. 6: A diagram showing the relationship between rolling time and slab temperature in FIG. 5. FIG. 7: A diagram showing experimental data of Examples. In the figure, 1, 2, 3, and 4 are data for lead alloy materials produced by the conventional method, and 5, 6, 7, and 8 are data for lead alloy materials produced by the manufacturing method of the present invention.

Claims (1)

[Claims] 1. In the process of manufacturing an electrode grid by casting a flat plate of a lead-calcium alloy, rolling the flat plate, and then performing an expanding process or a punching process, the rolling of the flat plate involves the steps of: Temperature from 50℃
Hold it at an arbitrary temperature of 200℃, and under these arbitrary temperatures, use the following formula: t ₁ = 2−2T ² /50000 ……(1) t ₂ =10−2T ² /10000 ……(2) [ However, t ₁ and t ₂ are the time (minutes) from the casting of the flat plate to the end of rolling _, respectively, and T is the surface temperature of _the flat plate (°C)]. ) A method for manufacturing an electrode grid for a lead-acid battery, characterized in that rolling is completed in a time within the range of .