JPH0420972B2 - - Google Patents

Abstract

Process for preparing battery lead containing 100-900 ppm Ca (or < 2% Sr) comprises adding less than 100 ppm Mg, which prevents excessive oxidation of Ca.

Description

[Detailed description of the invention]

The present invention relates to a method for producing a lead alloy containing 100 to 900 ppm of calcium. The lead alloy of the present invention is mainly used as a material for plates and grids of lead-acid batteries. Furthermore, the lead alloy of the present invention is used as cable lead and as an anode material in zinc electrolysis. Calcium-containing lead alloys are typically 99.9% pure.
It is manufactured by melting the above lead and adding the required alloying elements to this lead melt. This alloying process gives lead the mechanical properties required for products such as electrode plates and grids, and also improves the castability of lead. Conventionally, a lead-antimony alloy has been used. However, this alloy has the disadvantage that the self-discharge of the negative electrode active material becomes large.
It was proposed to replace antimony with calcium. Furthermore, the lead melt may contain small amounts of tin. Molten lead with added alloying elements is produced as a semi-finished product or directly cast into the desired final product. The semi-finished product is, for example, an ingot, which the battery manufacturer remelts and further processes into plates and grids. The semi-finished product may also be a strip produced by continuous casting and/or rolling, which is likewise processed by the battery manufacturer. When remelting semi-finished products or discarded products, when casting melts with addition of alloying elements or obtained by remelting semi-finished products or discarded products, the melt is exposed to air for a considerable period of time. Contact. This causes the calcium in the melt to undergo oxidation,
It was found that the content of calcium in the melt gradually decreases, as it migrates as an oxide to the slag layer above the melt. Since it is desirable that the calcium content in the lead alloy be constant, the above-mentioned decrease in content is extremely problematic. Calcium is commonly added to lead to impart desired mechanical properties. All or part of the calcium may be replaced by strontium, which has a different effect on the mechanical properties of lead. The desired calcium content is 800 ppm, the maximum amount that can be dissolved in liquid lead at the eutectic temperature (326°C). However, since calcium is burned off in liquid lead, it is necessary to add more calcium than the desired amount when alloying, but it is difficult to predict the degree of burning off, so the addition of calcium is difficult. There is a problem that the amount cannot be set properly.
Furthermore, if calcium is present in the final product in an amount greater than the maximum amount that can be dissolved in liquid lead at the eutectic temperature (326° C.), a problem arises in that the corrosion resistance of the product is significantly reduced. To solve these problems, the present invention proposes adding magnesium to the lead melt in such an amount that less than 100 ppm of magnesium is present in the solid lead alloy produced. Surprisingly, it has been found that the inclusion of very small amounts of magnesium in calcium-containing lead melts almost completely prevents the combustion depletion of calcium. The amount of magnesium that is burned and consumed in place of calcium is small. This is because a stoichiometric amount of magnesium is not necessary to prevent calcium from being burnt out over a certain period of time; rather, a fairly small amount of magnesium is sufficient. Small amounts of magnesium are not burnt out as quickly as calcium or strontium would be burnt out in the absence of magnesium in the melt.
This is because the extremely thin oxide film formed on the melt by magnesium acts as a protective film that prevents the melt from coming into contact with oxygen. In the present invention, it is sufficient to add the ultimately required amount of calcium into the lead alloy by adding magnesium. According to the invention, therefore, 100 to 900 ppm, preferably about 700 ppm of calcium is added to the lead melt. The amount of magnesium added is sufficient to completely or nearly completely prevent combustion depletion of calcium while the lead melt is in liquid form, typically between 1 and 80 ppm.
of magnesium is sufficient. In the present invention, both calcium and magnesium can be added in elemental form as a compound or as an alloy. All percentages given herein are weight percentages. Depending on the density of the additive (which may float on top of the lead melt), the melting point of the additive (higher melting point additives are more of a problem), or the rate at which the additive dissolves into the melt, etc. Therefore, it may be difficult to add additives to the melt. This problem can be solved by adding magnesium, for example as a pre-alloy with lead (high density), with aluminum (low melting point) or with calcium, or as an intermetallic compound. When adding a magnesium-aluminum alloy, it is preferable to choose an alloy containing 30-70% magnesium.
This is because these alloys have melting points that approximate the temperature of lead melts. The addition of a magnesium-calcium alloy instead of a magnesium-aluminum alloy further improves the corrosion resistance of a magnesium-containing lead alloy compared to a lead alloy containing an equal amount of aluminum. Magnesium dissolves more easily in liquid lead than aluminum. The invention is particularly suitable for lead alloys containing tin (usually less than 1%). This is because tin accelerates the burning and consumption of calcium in the melt, making the addition of magnesium even more effective. The invention also relates to lead alloys produced by the method of the invention and to accumulator plates or grids produced from the lead alloys obtained according to the invention. The invention will be explained in more detail with reference to the following examples. Example 1 Melt No. 1 was obtained by adding 700 ppm of calcium to 10 kg of molten lead containing 0.39% tin at 450°C.
was created. Melt No. 2 was prepared by adding 710 ppm calcium and 580 ppm magnesium to 10 kg of molten lead containing 0.39% tin at 450°C. Melt No. 3 was prepared by adding 680 ppm of calcium, 40 ppm of aluminum (as a Mg-Al alloy), and 230 ppm of magnesium to 10 kg of molten lead containing 0.39% tin at 450°C. Melt No. 4 was prepared by adding 700 ppm calcium and 40 ppm magnesium to 10 kg of molten lead containing 0.39% tin at 450°C. Samples were taken over time from each melt produced as described above, and changes in calcium content in the melt were examined. The results are shown in Table 1. Calcium content was measured with an accuracy of approximately 50 ppm.

Table: As is clear from Table 1, the calcium content of the magnesium-free melt decreased rapidly. Example 2 Four types of melts were prepared by adding the following additives to 10 kg of molten lead containing 0.39% tin (analysis of melt during casting): Al was added as a Mg-Al alloy. . Melt No. 5: Calcium 400ppm Melt No. 6: Calcium 690ppm, Magnesium
560ppm Melt No. 7: Calcium 710ppm, Magnesium
220ppm, aluminum 40ppm Melt No. 8: Calcium 690ppm, magnesium
The four 20 ppm melts were cast and analyzed for calcium content, then remelted one or more times, and the remelted lead alloys were cast again and analyzed in the same way. The results are shown in Table 2.

Table 2 As is clear from Table 2, even after repeated melting, the calcium content does not decrease significantly if magnesium is present in the lead. Example 3 Six lead/calcium/magnesium alloys containing 0.35% tin were prepared and tested for corrosion resistance. The results are shown in Table 3.

【table】

[Table] As is clear from Table 3, when the magnesium content is more than 100 ppm, and when the calcium content is more than 900 ppm, the corrosion resistance deteriorates.

Claims (1)

[Scope of Claims] 1. A solid lead alloy produced in a method for producing a lead alloy containing 100 to 900 ppm calcium, which comprises adding calcium in elemental form, as a compound and/or as an alloy to a lead melt. A method for producing a lead alloy, characterized in that magnesium is also added in such an amount that less than 100 ppm of magnesium is present in the lead alloy. 2. Process according to claim 1, characterized in that about 700 ppm of calcium is added to the lead melt. 3. The method according to claim 1, characterized in that 1 to 80 ppm of magnesium is added. 4. The method according to claim 1, characterized in that magnesium is added in the form of a compound or an alloy. 5. The method according to claim 4, characterized in that a magnesium-aluminum alloy is added. 6. The method according to claim 4, characterized in that a magnesium-calcium alloy is added. 7. Process according to any one of claims 1 to 6, characterized in that the lead melt contains less than 1% tin.