RO117712B1 - Desulphurizing blend based on calcium carbide - Google Patents

Abstract

The invention relates to a desulphurising blend for steel pig which comprises at least 50 % by weight of pulverulent calcium carbide with a particle size of less than 0.2 mm, 1 ...20 % by weight of pulverulent or granular magnesium with a particle size of less than 0.8 mm and 5 to 15 % by weight of pulverulent or granular aluminum with a particle size of less than 0.8 mm and optionally other pulverulent additives such as lime, calcium carbonate, carbon products and/or grain coating agents, the total amount of additives is at the most 30 %. According to the invention, the blend reduces the iron losses during desulphuration.

Description

The invention relates to a desulphurizing mixture based on calcium carbide, intended to be injected with a spatula into the liquid iron obtained in the furnace, prior to its passage into the converter.

Although, the cast iron and the slag are poured separately from the furnace, in the pot there remains a sizeable amount of slag, of the order of 5 kg / t.

On the other hand, the use of a desulfurizing product creates a sulfur-rich slag, which must be separated from the metal sent to the converter. At this stage, slag removal is done mechanically, which results in metal losses through entrainment.

It is known that obtaining a fluid desulphurization slag allows for significant reduction of metal losses caused by removing slag from the pot. To this end, before removing the slag, sodium carbonate is added to the metal pot, which decomposes into sodium oxide, the melting point of which is at 1132 ° C. The slag obtained contains sodium which is harmful to the environment, which justifies the efforts made to find other solutions to reduce metal losses.

On the other hand, the addition to reducing metal desulfurizers, such as aluminum or magnesium, in order to accelerate desulphurisation due to the elimination of dissolved oxygen in cast iron, has long been known, for example, from patent FR 116846 filed by IRSID in 1957. Patent FR 2317361 (Owner: KLOCKNER-WERKE) describes a desulphurant based on calcium carbide powder, calcined cyanamide or lime, to 20 to 0.5 to 3.5% aluminum powder, or of magnesium with the same granulation.

It is also known from patent EP 0398674 (Owner: ELKEM METALS), the calcium carbide assay variant of calcium aluminate, with a low melting point, to obtain a more complete desulfurization of the baths at a constant amount. injection mixture.

The applicant noted that a desulphurizing mixture based on micronized calcium carbide powder, containing both magnesium powder and aluminum powder, the latter in a well-defined concentration range, allows a significant reduction in iron losses. during desulfurization.

The desulfurizing mixture for the refining castings according to the invention solves the problem of reducing desulfurization iron losses. being made up of at least 50% (by weight) calcium carbide in the form of powder with a smaller granulation, 0,2 mm, between 1 and 20% magnesium in the form of powder with a smaller granulation, of 0,8 mm, and , between 5 and 15% aluminum in the form of powder with a smaller granulation of 0.8 mm, possibly with other additives in the form of powder, such as lime, calcium carbonate, carbonate products and / or coating agents in quantity total 35 not more than 30%.

The desulfurizing mixture for the cast iron according to the invention has the advantage that it reduces the iron loss when desulphurizing the castings, at low costs.

The invention is as follows:

The mixture, according to the invention, is based on technical calcium carbide, which generally contains about 80% by weight C ₂ Ca, the remainder being lime crushed, up to a granulation of less than 0.2 mm, with less than 25% of the particles in the granulation range: 0,1 0,2 mm. To this carb may be added lime in addition to that resulting from the manufacture of technical charcoal, calcium carbonate, carbonate products, such as: carbon black, graphite or anthracite, or other products intended to improve the fluidity of the mixture or release gas. to allow a good distribution of the desulphurant in liquid iron. Also, up to -2% of granular coating binder, for example: hydrogenated castor oil, as described in EP 0511121 belonging to the applicant, can be added.

RO 117712 Β1

Magnesium is present in the mixture in the form of powder or granules of pure metal or of magnesium base with a smaller granulation of 0.8 mm. The granules can be coated, like calcium carbide, with an organic product, for example, based on 50 saturated aliphatic acids or their esters, as described in patent EP 0485309 of the applicant.

Next, add the mixture, between 5 and 15% aluminum or aluminum alloy powder or granules, which may also be coated with a product identical to that used for magnesium. 55

The mixture of powders or granules is advantageously carried out in a mixer operating under neutral gas, for example, nitrogen.

The mixture according to the invention has a desulphurisation efficiency at least equal to that of mixtures in which aluminum is replaced in an amount equal to magnesium in which aluminum is replaced in an amount equal to magnesium and therefore does not imply an overconsumption of 60 of this product, which it is quite unexpected since aluminum, unlike magnesium, is not itself a desulfurizer. On the other hand, a more fluid slag is formed, easier to remove, so that its removal leads to lower net iron losses. Also, the distant slag does not contain any environmentally harmful products, such as sodium oxide. 65

Example. The efficiency of desulphurisation and iron losses were compared for two desulphurizing mixtures known as technical calcium carbide, the first containing 20% (by weight) magnesium granules and the second 20% lime aluminate powder with those for a third mixture, according to the invention, containing 10% magnesium granules and 10% aluminum granules.

The tests were performed on pots, of 3001 cast iron. The initial sulfur content was about 250 ppm and the final one was about 55 ppm.

The effectiveness of a desulfurant is defined by the ratio between the number of moles removed from the cast iron and the number of moles of desulfurant injected, that is, in this case, C ₂ Ca and Mg moths, since aluminum is not a desulfurizing product per se.

Iron losses are defined by the ratio of the mass of cast iron contained in the distant slag to the mass of cast iron contained in the desulphurization pot.

The results obtained for these three mixtures mentioned, presented below, represent the average of 20 tests performed under the most similar conditions.

Mixture Effectiveness Iron losses 1 22% 1.1% 2 18% 0.9% 3 2. 3% 0.3%

Comparing mixtures 1 and 3, it is found that their efficiency on desulfurization is very close, but the use of mixture 3 leads to a reduction of iron losses by 3.7 times.

Comparing mixtures 2 and 3, it is unexpectedly found that aluminum leads to obviously more efficient desulphurisation and a reduction of iron losses 90 3 times, although similar results would have been expected, as the aluminate introduces alum into the slag, and the aluminum oxidizes into the cast iron to form alumina that dissolves into the slag.

Claims (2)

claims 1. Calcium carbide desulphurizing mixture for liquid refining castings containing at least 50% by weight of calcium carbide in the form of powder with a smaller granulation of 0,2 mm and alumina powder, characterized in that it consists of at least 50% by weight of calcium carbide in the form of powder with a smaller granulation of 0,2 mm, 100 between 1 and 20% magnesium in the form of powder or granules of less granulation, 0.8 mm, possibly with other additives in the form of powder, such as lime, calcium carbonate, carbonate products and / or coating agents of granules, the total quantity of additives being not more than 30%. A desulfurizing mixture according to claim 1, characterized in that less than 25% of the calcium carbide granules have a granulation of between 0.1 and 105 0.2 mm.