DE3537281A1 - Method for producing casting powder for casting steel - Google Patents

Abstract

The invention relates to a method for producing a homogeneous, quickly meltable casting powder for casting steel in continuous-casting plants. A casting aid is to be produced with a small number of process steps and with reduction of the expenditure of energy in comparison with conventional methods, in such a way that some of the reactions which occur during the melting of the powder are even transferred to their manufactured phase. According to the invention, the mixture components affected are comminuted together in an aqueous phase and mixed. The suspension which is produced in this way is subsequently dried and granulated in a fluidised bed.

Description

a) Title of the invention

Process for the production of casting powder for casting steel b) Field of application of the invention The invention relates to a method for production a homogeneous, quickly meltable casting powder for casting steel in Continuous casting plants.

c) Characteristics of the known technical solutions for potting A large number of casting powders for steel are known to perform the following tasks have: - protection of the steel surface from secondary oxidation - absorption of non-metallic Inclusions - ensuring even heat transfer - lubrication between Strand shell and mold wall It is known that oxic, carbonatic and silicate raw materials mechanically mixed after they have been crushed, sintered or premelted.

Dry raw materials are used to produce mechanically mixed powders necessary. In the case of the mechanically dry mixed powders, particle sizes become aimed at less than 0.063 mm in order to achieve satisfactory homogeneity, i.e. H. an even To achieve distribution of the raw materials in the mixture, however, a considerable amount Dust pollution, poor pouring behavior and thus inadequate dosing capacity when using these powders.

In the production of sintered or premelted casting powders becomes the number of process steps in manufacturing versus mechanical mixing elevated.

The premixed powders are melted and quenched, then dried and crushed. Compared to the mechanically mixed powders, a higher homogeneity achieved, which is caused by chemical reactions.

Separation phenomena are compared to mechanically mixed powders locked out.

From DE-OS 2917 763 it can be seen that for the production of premelted Powders require a lot of equipment and costs because of the large Number or

the energy intensity of the individual process stages is required.

According to the composition of the casting powder (GP) it is necessary to that when the mixture is used, its silicate network value is broken down.

In mechanically mixed powders, forms at the beginning of melting an alkali melt in which alkaline earth ions are dissolved. This ion melt takes effect the silicate network and breaks it down.

The melting time of GP mixtures and thus the effectiveness of a Slag film on the bath level of the mold is determined by these reactions. In the case of the sintered or premelted powders, this process becomes an increase anticipates homogeneity and leads to alkali and alkaline earth silicates, which in their structure are for the most part amorphous.

Since the flux is completely converted during the premelting process, there may be delays in melting the powder on the bath surface, especially since the silicates formed during the premelting process are relatively thermally stable.

Some manufacturers mix one after premelting for this reason small proportion of flux to the powder (US-PS 3926 424 and 4092 159).

d) Object of the invention The object of the invention is to develop a Process with which economically advantageous with a small number of process steps and while reducing energy consumption, a casting powder with improved melting behavior can be produced on the bath level of the mold.

e) Statement of the essence of the invention The invention is the task based on creating a process for the production of a homogeneous casting powder, in which some of the reactions that take place when the powder is melted already occur is relocated to the manufacturing process without affecting the effect of the flux is canceled in the mixture, so as to ensure good melting behavior of the feedstock to reach.

According to the invention the object is achieved in that the crushing and all mixture components are mixed together in an aqueous phase. By wet grinding the solids together in suitable units with a high Efficiency is the reactivity of the smallest parts of the components increased considerably. The following changes are produced on the solid, the reaction possibilities open up: - additional disorder in the crystal lattice, Expansions - formation of new surfaces, which are particularly disturbed surfaces are reactive - additional lattice disturbances by increasing the ratio from surface to volume, cracking, dislocations - additional ones close to the surface radical Because of these tribochemicals occurring during wet grinding Effects, the presence of water, as well as any temperature increases that occur between the known casting powder raw materials with conversion of part of the flux Silicate formation reactions, d. That is, products are created in which the breakdown of the silicate network has already started. With the help of the remaining flux content these reactions on the bath level of the mold are completed quickly. Opposite to conventionally mixed as well as premelted powders of comparable composition An effective layer of slag is thus formed much faster.

Mixtures prepared in this way also show greater homogeneity than previously mechanically mixed powders.

The suspension produced from the wet grinding is subsequently in a Fluidized bed dried and granulated. The resulting casting powder has as Granules have a predominantly spherical shape, which gives them a good pouring behavior, a exact dosing and better distribution on the metal bath level is achieved will. Due to the intensive drying of the casting aid in the fluidized bed it is free of moisture despite the previous wet grinding.

The spherical shape, the delimited grain size range and the special surface of fluidized bed granules allow the granules or the mixture with active components, for example carbon carriers.

f) Exemplary embodiment The mold powder according to the invention can be used as follows are produced: The raw materials selected for the recipe are used in a Wet drum mill ground up to grain sizes of 0.063 mm.

During the grinding process, silicate formation reactions set in. the Ground raw material mixture is used as a suspension with a moisture content of 50% in processed in a fluidized bed granulation plant with classifying discharge. As a result the treatment in the fluidized bed granulation plant produces granules that are preferably in a grain range between 0.1 mm to 3 mm, for example 0.1 mm to 0.5 mm or 0.5 mm to 3 mm. By setting the process variables quantities and The target grain belt is adjusted to the fluidizing medium and the amount of classifying air.

The casting powder according to the invention was produced with the following grain sizes: Mesh size mm Sieve residue% 0.500 4.35 0.500 - 0.315 17.08 0.315 - 0.250 20.11 0.250-0.200 24.15 0.200-0.125 26.20 0.125-0.100 5.47 0.100 2.58 The invention Cast powder has the following chemical analysis: SiO2 35 - 30% Al203 2 - 3% CaO 3 MgO ) 26 - 27% Na, O) K20) 0 w 203 P each F 1 - 2% Gv 16 - 19% (casting losses) H20 0.8% C 3 - 6%

Claims (1)

Invention claim 1. A method for producing casting powder for Casting of steel, in which the components are crushed, mixed, moistened, be granulated and dried, characterized in that the crushing and Mixing of all mixture components takes place together in an aqueous phase and the resulting suspension is then dried in a fluidized bed and granulated will.