DK156490B - BLYLE ALLOYING CONTAINING CALCIUM AND MAGNESIUM - 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

DK 156490 B

The present invention relates to a lead alloy containing calcium and magnesium. The main use for calcium-containing lead is in the form of batteribly. It also finds use as a lead and anode material in the zinc electrolysis process.

Calcium-containing lead is usually prepared by melting a lead with a purity of more than 99.9% and then adding the required amount of alloying element to the lead melt. This alloy step serves to impart to the lead the individual mechanical properties of battery plates and grids and any other product and also to improve the stiffness of the lead.

So far, antimony has usually been added to the lead. However, antimony causes self-discharge in batteries, so it has been suggested to replace antimony with calcium, a change that has been successful. Furthermore, some tin is often added to the melt, and it is also possible to add other individual alloying elements. After the addition of the alloying elements, the molten lead is either made into a semi-make or cast directly to the individual finished product. A semi-make may consist of die blocks which are re-melted by the battery manufacturer and further processed into sheets and grids. The semi-finished product may also consist of a strip made by continuous casting and / or rolling, and further processed into sheets or gratings by the battery manufacturer.

Baths when the semi-finished product is re-melted and when discarded final products are re-melted and also for the considerable period of time elapsed during the casting of the original melt after the alloy or of the melt obtained by re-melting of the stub blocks or discarded end products, the molten lead is in contact with air.

It has now been found that the calcium content of the melt is gradually reduced by the oxidation of calcium, which in the form of oxide passes into the slag layer 30 on top of the melt. Since a certain calcium content in the batteribly is individual, the reduction of the content has proved to be very inappropriate.

The individual calcium content is usually the maximum percentage of calcium soluble in liquid lead at the eutectic temperature (326 ° C). Unfortunately, it is not enough to add more

DK 156490 B

2 than the desired amount of calcium at the alloy stage in order to counteract the expected burning of calcium, as the degree of burning is difficult to predict, and the presence in the final products of more calcium than can be dissolved in liquid lead at the maximum 5 eutectic temperature (326eC ) can significantly reduce the corrosion resistance of the products.

The most well-known prior art is disclosed in U.S. Patent No. 2,306,899, which describes lead alloys containing 1-90 ppm calcium and 1-90 ppm magnesium, and British Patent No. 499,549, 10 concerning lead alloys containing 100-1000 ppm calcium and 100 -3000 ppm magnesium, which alloys have good composition stability after re-melting and good corrosion resistance, even when they contain tin as additional alloying element.

To solve these problems, the present invention relates to a lead alloy containing 1-80 ppm magnesium and a small amount of calcium, which alloy is characterized in that it contains 690-900 ppm calcium. Surprisingly, it has been found that even very low percentages of magnesium in an alkaline-containing lead melt lead to almost complete prevention of the burning of this calcium. So far, no clear explanation has been found for this phenomenon.

It is not, or at least not to a large extent, that the magnesium is sacrificed instead of the calcium, since in order to prevent a certain amount of calcium from being burned for a certain period a stoichiometric amount of magnesium is not required, but a substantial ring 25 amount of magnesium is sufficient. This lower amount of magnesium is also not burnt proportionally as quickly as the calcium metal would have been if no magnesium had been present in the melt.

The maximum solubility of calcium in liquid lead at the eutectic temperature (326 ° C) is 800 ppm. Therefore, in accordance with the present invention, less than 900 ppm calcium is added, while it is particularly preferred to add approx. 700 ppm calcium.

To prevent the burning of calcium completely or in the

DK 156490B

3 late completely during the usual periods in which the melt is liquid, it is sufficient to add 1-80 ppm magnesium.

In preparing the alloy of the present invention, both calcium and magnesium can be added in elemental form, in the form of a compound or as an alloy. The percentages given here are all percentages by weight, and when the relevant figure is added in a bound form, they refer to the proportion of this figure.

In some cases, difficulties may be encountered in adding the additives to the melt, e.g. due to the density of the additive 10 (it may float on the lead melt), due to the melting point of the additive (which will cause fewer difficulties at low melting points than at high melting points) or due to the rate at which the additive is read into the melt.

These problems can be solved by the addition of the magnesium in the form of a preliminary alloy or in the form of an intermetallic compound, e.g. with lead (high density) or with calcium.

The present invention is particularly suitable for those lead alloys containing tin (usually less than 1%), since tin accelerates the burning of calcium-containing lead in a melt, so that the addition of magnesium in this case is so much more significant.

The invention is elucidated in more detail below by a number of examples.

1. (By comparison) An amount of 700 ppm (0.07%) of calcium is added at 450 ° C to 10 kg of molten lead containing 0.39% tin and after some time samples are taken from the melt. The results are given in Table 1.

2. An amount of 40 ppm magnesium and 700 ppm calcium is added at 450 ° G to an equal amount of 10 kg of molten lead containing 30 0.39% tin, and some samples are taken from the melt after some time. The results obtained are given in Table I.

DK 156490 B

4 label ï

Melt Initial Calcium Content in ppm by Composition 5 _

No. Approx Mg 30 min. 60 min. 90 min. 120 min. 160 min.

(in ppm) 10 1 700 - 500 - 400 400 710 2 700 40 700 720 710 690

The calcium content is determined with an accuracy of approx. 50 ppm. It is clear from Table I that the calcium content of a melt without magnesium 15 fades quickly and that the addition of magnesium gives a change.

3. Two melts are produced from each 10 kg of lead containing 0.39% tin, to which are added the following additives (analysis of melt as cast):

Melt # 3: for comparison, 400 ppm calcium,

Melt No. 4: 20 ppm magnesium, 690 ppm calcium.

These lead melts are each individually re-melted after being cast and analyzed, and the thus-melted lead amounts are further stiffened and analyzed:

Melt # 3: 230 ppm calcium,

Melt No. 4: 10 ppm magnesium, 630 ppm calcium.

4. A number of lead / calcium / magnesium / tin alloys containing 0.35% tin are prepared and tested to determine their corrosion resistance.

Claims (1)

These tests show that a reduction of the magnesium content promotes corrosion resistance and that an increase in the calcium content reduces the corrosion resistance. Lead alloy comprising 1-80 ppm magnesium and a small amount of calcium, characterized in that the calcium content of the alloy is 690-900 ppm.