CS239571B1 - Casting Powder for Continuous Casting Crystallizers - Google Patents

Abstract

The invention solves the improvement of the desired properties of the casting powder, especially the lubricating properties of the powder, the increase of the surface and subsurface quality of the plates or billets while using a wider and more accessible basic raw material. The casting powder for the above purpose according to the invention contains, by weight, 4 to 20% of sodium and/or potassium carbonate and 60 to 90% of a slag-forming mixture formed on the basis of blast furnace slag, coal fly ash and manganese-silicate welding flux, individually or in their mutual combination. The essence of the invention lies in the fact that it contains 4 to 20% of fluorspar, sodium fluoride and cryolite individually or in their mutual combination, while the slag-forming mixture contains basic slag-forming oxides, namely calcium oxide, silicon dioxide and aluminum oxide in a molar ratio of 1: 0.8 to 2.2: 0.01 to 0.5 parts.

Description

The invention relates to casting powder for continuous steel casting crystallizers and solves the problem of improving all desired parameters, in particular the lubricating properties of the powder, increasing the surface and subsurface quality of games or preforms, using a wider and available raw material base.

Powders are added to the crystallizers of the continuous casting machine at the liquid steel level to form a lubricating film between the solidified steel layer and the crystallizer walls, to ensure a steady and uniform heat transfer between the solidified steel layer and the crystallizer. liquid steel against oxidation by air oxygen and ensure its thermal insulation.

Most of the known casting powders are mixtures based on wax-forming substances and lowering the viscosity and melting point of the powder and on powder flow rate controllers. Portland or blast furnace cement, fireclay, limestone, lime, silica sand, basalt, glass, nepheline and others are used as wax-forming components. Components such as fluorspar, cryol, sodium fluoride, sodium carbonate, potassium carbonate and borax are added to reduce viscosity and melting point. As the melting rate regulator, ground coke, carbon black, powder graphite and others are used. Depending on the type and amount of ingredients used, the chemical composition of the powders is very diverse. Most of them have a basicity, expressed as a ratio of calcium oxide and silica, close to 1. Among the most important physical properties of the casting powders are temperature and melting interval, melting rate, viscosity, granulometric composition, surface tension. The slag formed from the casting powder penetrates between the liquid steel layer and the crystallizer wall, acting as a lubricant reducing the frictional forces and erosion of the crystallizer walls. In this case, if the heat transfer is too low, then the solidified steel layer formed is very thin and the steel jet may break; on the other hand, too high a rate of heat removal can cause surface cracks in the slab;

The results of the frictional force measurements of the currently used casting powders with said basicity show that a sharp increase in the frictional force occurs at temperatures of 1000 to 1300 ° C. Below this transition temperature, which for most of the slags corresponds to the start of crystallization, the slags can no longer act as a lubricant. Such behavior is caused by crystalline precipitation during cooling of the bulk melt and results in a deterioration or loss of lubricity and thus an increased possibility of surface defects.

A further disadvantage of most of these powders is that hydroscopic ingredients such as ground lime and Portland or blast furnace cement, which can cause lumps of powders, are used for their preparation. In addition, when ground limestone is used, gaseous components are released in the crystallizer, which may adversely affect the surface quality of the product.

These drawbacks are overcome and the problem is solved by a casting powder according to the invention comprising 4 to 20% by weight of sodium and / or potassium carbonate and 60 to 90% of a slag-forming mixture based on blast furnace slag, coal fly ash and manganese silicon welding fluxes individually or in combination with each other. Manganese-silicon welding flux contains 35 to 45 wt. % silica, 35 to 40 wt. manganese dioxide and as further components titanium dioxide, calcium oxide, alumina and calcium fluoride. SUMMARY OF THE INVENTION The present invention consists of 4 to 20% fluorspar, sodium fluoride and cryolite individually or in combination with each other, wherein the slag-forming mixture comprises basic slag-forming oxides, namely calcium, silica and aluminum in a molar ratio of 1: 0.8 to 2.2: 0.01 to 0.5 parts. The resulting casting powder mixture must contain less than 1% by weight. moisture content and a fraction above 0.1 mm below 10% by weight.

The advantages of the casting powder of the invention are mainly that it has a lesser tendency to crystallize during melt cooling, thereby maintaining the presence of liquid slag on the largest possible steel surface in the crystallizer, up to the lowest surface temperatures at the exit of the crystallizer. At the same time, optimum lubrication effects, optimum heat transfer and thus good surface and subsurface quality of the gates or pre-calcols are ensured, while significantly reducing manufacturing difficulties. The powder according to the invention does not contain hygroscopic ingredients which increase the susceptibility of the powder to clumping and in addition to carbonates. it does not contain other components that would release gaseous products and cause powder changes in the crystallizer. It is also an advantage that the powder can be prepared predominantly from waste products such as blast furnace slag and coal fly ash, thereby expanding the raw material base and eliminating the need for energy intensive products such as cement or lime. There is no need to add melting rate retarders, such as carbon black, ground coke, graphite and the like, since the elemental carbon is contained in the fly ash. Most of the casting powder components of the invention, such as fly ash, floated fluorspar and carbonates, are in powder form, eliminating the need for energy to grind them.

DETAILED DESCRIPTION OF THE INVENTION: Example 1

The casting powder is prepared by mixing 10 wt. % sodium carbonate, 10 wt. Subsidized fluorspar, 36 wt. fly ash of coal and 44 wt. ground blast furnace slag. The molar ratio of calcium oxide to silica and alumina in the slag-forming mixture consisting of coal fly ash and blast furnace slag is equal to 1:

: 1.66: 0.30 parts. The weight composition of the casting powder is: silica 32.3%, calcium oxide 18.9%, aluminum oxide 9.1%, magnesium oxide 4.6%, sodium oxide 5.9%, calcium fluoride 6.7%, eleinentary carbon 6.5% and components up to 100%. The melting start is at 1100 ° C, the melting interval is 50 ° C.

Example 2

The powder is prepared by mixing 10 wt. % sodium carbonate, 12 wt. Finished fluorspar, 23 wt. fly ash of coal and 55 wt. blast furnace debris. The molar ratio of calcium oxide to silica and alumina in the slag-forming mixture consisting of coal fly ash and blast furnace slag is equal to 1: 1.45: 0.23 parts. The weight composition of the casting powder is: silica 31.0% calcium oxide 19.9%, aluminum oxide 8.5%, magnesium oxide 7.5%, sodium oxide 6.0%, calcium fluoride 10.1% , elemental carbon 3,5 ° / o, other components up to 100 θ / o. The melting start is at 1090 ° C, the melting interval is 50 ° C.

Example 3

The casting powder is prepared by mixing 10% w / w. % sodium carbonate, 12 wt. Finished fluorspar, 18 wt. ash from coal, 10% wt. a ground manganese-silicon welding flux containing 35 to 45 wt. % silica, 35 to 40 wt. manganese dioxide and, as other constituents, titanium dioxide, calcium oxide, alumina, calcium fluoride and 50%. wt. ground blast furnace slag. The molar ratio of calcium oxide to silica and alumina in the slag mixture consisting of blast furnace slag from coal fly ash and manganese silicon welding flux is equal to 1: 1.52: 0.18 parts. Mass. casting powder composition is: silica 32.9%, calcium oxide 20.3%, aluminum oxide 6.5%, magnesium oxide 4.5%, inanganate oxide 3.6%, sodium oxide 5.8% , calcium fluoride 10.5%, elemental carbon 3.8 percent, other components up to 100%. The melting start is at 1125 ° C, the melting interval is 50 ° C. .

The invention can be used for production in different steel grades in steelmaking plants where it is used at the same time, in particular in continuous casting of gates or billets.

Claims (3)

SUBJECT Casting powder for continuous steel casting crystallizers containing by weight 4 to 20% of sodium and / or potassium carbonate and 60 to 90% of a slag-forming mixture consisting of blast furnace slag, coal fly ash and manganese-silicon welding flux individually or in combination with each other , characterized in that they contain 4 to 20% of fluorspar, sodium fluoride and cryolite individually or in combination with each other, wherein the slag-forming mixture comprises basic three-forming oxides, namely calcium, silica and aluminum in a molar ratio of 1: 0.8 to 2.2: 0.01 to 0.5 parts.