RU2284876C1 - Exothermic mixture for heating of ingot head part during pouring of steels and alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: exothermic mixture contains 25-60 wt% of aluminum alloy production wastes, 10-40 wt% of heat-insulating material, 8-36 wt% of refractory filler, 4-15 wt% of heat expandable material, up to 3 wt% of cast graphite and up to 3 wt% of fluorite concentrate. Heat expandable material of mixture contains vermiculite or pearlite. Owing to expansion of pearlite or vermiculite, heat-insulating properties of mixture are improved, uniform distribution of mixture over metal surface is provided, apparent density of calcine is decreased and strength thereof is increased. Utilization of said mixture allows wastage due to shrinkage to be reduced by 1.5-2 times.

EFFECT: improved properties of mixture and increased yield.

2 cl, 1 tbl, 1 ex

Description

The invention relates to metallurgy, and in particular to compositions of exothermic mixtures for warming the top of the head of the ingot during casting.

Exothermic mixtures are known, including aluminum, chamotte, charcoal or coke, bauxite and 45% ferrosilicon [1].

The disadvantage of these mixtures is the presence of explosive aluminum and ferrosilicon powders, which are of high cost and require the preparation of equipment in explosion and fireproof design.

Known expanding exothermic mixture for warming the profitable part of the ingot, containing refractory heat insulating material - alumina or bauxite, combustible materials - aluminum, magnesium, silicon powders, oxidizing agent - sodium nitrate, barium and iron oxide, expanding when heated material - vermiculite, perlite and scaly natural graphite treated with concentrated sulfuric acid [2]. This composition provides good insulation of the profitable part of the ingot by increasing the thickness of the insulating layer by 70-90% when it is heated.

However, it has the same drawbacks as the previous composition due to the use of explosive powders of aluminum, magnesium and silicon.

Known exothermic mixture for warming the head of the ingot, containing the following components, wt.%: Waste from the production of aluminum alloys in the form of aluminum-containing slag 25-60, heat-insulating material in the form of coke or fly ash CHP 27-45, refractory filler in the form of fireclay powder 10- 34 [3]. The known mixture is taken as a prototype. This mixture does not contain powders of explosive materials and does not require the use of expensive equipment in explosion-proof performance.

However, it has insufficient heat-insulating ability, as evidenced by a slight decrease in the density of the cinder relative to the bulk density of the mixture, equal to 3.6-14.3%. There is also a violation of the continuity of the resulting crust in the form of cracks and dips. All this ultimately leads to increased heat loss, leading to an increase in the proportion of head trim and marriage associated with shrinkage defects.

The problem to which the invention is directed, is to develop a composition of an exothermic warming mixture that provides a dense structure of the upper part of the ingot with minimal material costs.

The technical result that the invention provides consists in obtaining a dense structure of the upper part of the ingot and reducing metal losses with a head cut and marriage associated with shrinkage defects.

This is achieved by the fact that the exothermic mixture includes aluminum-containing material, heat-insulating material, refractory filler and additionally expanding material when heated, casting graphite and fluorite concentrate, while it contains waste from the production of aluminum alloys and products of secondary processing of aluminum-containing materials as an aluminum-containing material in the following ratio of components: aluminum-containing material 25-60%, heat-insulating material 10-40%, refractory filler 8-36%, expanded 4-15% material that flickers when heated, 0-3% foundry graphite and 0-3% fluorite concentrate. As expanding when heated, the material contains vermiculite or perlite.

An interrelation was established between the content of the material expanding during heating (vermiculite or perlite) in the exothermic mixture, the initial density of the exothermic mixture, the apparent density of the cinder, and the value of the marriage associated with shrinkage defects.

When casting steel, one of the main purposes of the exothermic warming mixture is to preserve the metal in a liquid state in a profitable part to feed the crystallizing body of the ingot. This is achieved due to the uniform heat release during exothermic reactions involving metallic aluminum, providing high heat-insulating properties of the mixture itself and the cinder formed after its combustion.

When loading the exothermic mixture of the proposed composition on the surface of the liquid metal in the profitable part, there is a gradual expansion of materials expanding when heated. The thickness of the insulating layer increases by 35-70%. The expansion of the mixture is accompanied by spontaneous, uniform distribution of the mixture on the surface of the metal, which is also facilitated by the introduction of up to 3% of foundry graphite. The apparent density of the cinder formed after combustion of the mixture decreases from 1.02-1.10 g / cm ³ , typical of the usual composition, to 0.62-0.85 g / cm ³ . At the same time, a crust strong without cracks and dips is formed on the surface.

The amount of aluminum-containing material is determined from the condition of obtaining in the finished mixture 21-28% metal (active) aluminum, providing the required amount of heat 8000-10000 kJ / kg

The limits of the content of heat-insulating material 10-40% are determined by the heat-insulating ability of the mixture, which is estimated by its bulk density and the apparent density of the resulting cinder. The lower limit of 10% is determined by an increase in the bulk density of the mixture of more than 1.20 kg / l. The upper limit of the content of heat-insulating material of more than 40% is determined by the possible carbonization of steel, as well as the destruction of the cinder during its combustion.

The amount of refractory filler is determined from the condition of obtaining a solid cinder with a low apparent density. When the content of the refractory filler is less than 8%, the melting temperature of the cinder decreases, leading to an increase in its density and deterioration of the heat-insulating properties. An increase in the amount of refractory filler of more than 36% is accompanied by the formation of a loose fragile cinder with the subsequent formation of dips.

The amount of expanding material when heated, in particular vermiculite or perlite, is also determined by the heat-insulating properties of the mixture and cinder. When the content of the material expanding during heating is less than 4%, its effect on the decrease in the apparent density of the cinder is negligible and, therefore, does not have a significant effect on reducing the number of shrink defects. The upper limit of 15% is due to a decrease in the refractoriness of the cinder formed, associated with an increase in the amount of magnesium oxide and the transition of the refractory component to the cordierite region with a melting point less than 1450 ° C. This leads to an increase in the density of the cinder and the deterioration of its heat-insulating properties.

The introduction of up to 3% of foundry amorphous graphite provides high flowability and covering ability of the exothermic mixture at the time of its filling with a metal mirror.

The use of up to 3% fluorite concentrate ensures the activation of aluminum metal in the absence of alkali metal fluorides and chlorides in the aluminum-containing material.

The table shows the compositions of the proposed exothermic mixture based on an aluminum-containing material, with an active aluminum content of 40-45%, (compositions 3-5), as well as compositions that go beyond the requested limits for the content of the material expanding when heated (compositions 2, 6, 7) heat-insulating material (compositions 8, 9, 10) and refractory filler (compositions 10, 11), composition 1 - prototype.

A specific example of the manufacture of mixtures.

All materials within the stated limits are used in the delivery state with a free moisture content of not more than 1%.

Aluminum-containing slag was used as an aluminum-containing material in the form of waste from the production of aluminum alloys and secondary products.

As a heat-insulating material used coke or fly ash of CHP plants operating on coke. And as a refractory filler, in particular, chamotte powder. The expanding material when heated is vermiculite or perlite.

The constituent materials of the exothermic mixture were loaded into consumables, and after weighing were fed into the mixer, where they were mixed for 25-30 minutes. The optimal mixing time was determined by sequential sampling at regular intervals of 5 minutes until the stabilization of the composition of the exothermic warming mixture, which was estimated by the carbon content. After that, the finished exothermic warming mixture was unloaded into the container and sent to the steelmaking workshop. Exothermic warming mixtures were tested during siphon casting of structural alloyed steel grades. The exothermic warming mixture was filled up after filling 2/3 of the profitable extension height with metal at the rate of 2.5-3.0 kg / t.

The carbon content in the warming mixture was determined by coulometric method on the AN 7529 coulomatics (XK 235-98 certificate), fluorine by the pyrohydrolysis method (XK 180-95 certificate), chlorine by inductively coupled plasma mass spectrometry on an ELAN-6000 setup, metal (active) aluminum - according to the NDP-MX64-2003 methodology of KHA "Aluminum slag and materials based on it", the remaining elements - X-ray spectral method on a CPM 25 analyzer.

The exothermic warming mixtures shown in the table were used in casting structural alloyed steel grades into ingots by the siphon method. From the above data it follows that when using the proposed compositions of exothermic mixtures (compositions 3-5), the marriage associated with shrinkage defects is significantly reduced and metal losses associated with additional cutting are reduced.

Exceeding the upper limit on the vermiculite content (compositions 6, 7) leads to a decrease in the refractoriness of the cinder formed, associated with an increase in the amount of magnesium oxide and the transition of the refractory component to the cordierite region with a melting point less than 1450 ° C. This leads to an increase in the density of the cinder, a deterioration in its heat-insulating properties and an increase in marriage associated with shrinkage defects. When you go beyond the lower limit for the vermiculite content (composition 2), a noticeable decrease in the apparent density of the cinder is not provided and, therefore, its heat-insulating properties do not increase, which does not lead to a decrease in marriage associated with shrinkage defects. Going beyond the upper limit for coke content (composition 9) leads to the destruction of the cinder after combustion, which leads to increased heat loss and an increase in the number of defects associated with shrinkage defects. Going beyond the lower limits in coke content (compositions 8, 10) leads to an increase in the bulk density of the exothermic mixture to 1.25-1.29 g / cm ³ and increased heat loss at the beginning of the combustion of the mixture, which also leads to an increase in defective defects shrink character. Going beyond the upper limits for the content of chamotte (composition 10) leads to an increase in the bulk density of the exothermic mixture and the apparent density of the cinder. There is a decrease in the strength of the cinder, leading to local damage and the formation of dips. All this ultimately leads to a deterioration in the thermal insulation of the head of the ingot and an increase in marriage associated with shrinkage defects. Going beyond the lower limits for the content of chamotte (composition 11) leads to a decrease in the fire resistance of the cinder (less than 1450 ° C) and is accompanied by an increase in its apparent density. This leads to increased heat loss and an increase in the number of defects associated with shrinkage defects. The prototype (composition 1) has a higher apparent density and thermal conductivity of the cinder, and a higher level of marriage.

Thus, the developed composition of the exothermic warming mixture due to its high heat-insulating abilities reduces the marriage associated with shrinkage defects due to the introduction of 4-15% expanding when heated material - vermiculite, 0-3% foundry graphite and 0-3% fluorite concentrate.

Information sources

1. Trubin G.K. and Oyks G.N. Metallurgy of steel. M., "Metallurgy", 1964, p. 501.

2. US Patent No. 4261750, cl. 106 / 38.28., 1981

3. A.S. USSR, No. 856649, class B 22 D 7/10, 1979, bull. No. 31, 1981 - a prototype.

Table No pp The content of components, wt.% The bulk density of the mixture, g / cm ³ The apparent density of the cinder, g / cm ³ Approximate coefficient of thermal conductivity at 700-800 ° С, W / m · ° C The number of heats with shrinkage defects,% Note Aluminum containing material Thermal insulation material Refractory filler Expandable when heated Foundry graphite, in excess of 100% one 60 twenty twenty 0 0 1.15 1.10 0.58 6.9 High apparent cinder density 2 60 23 fifteen 2 0 1.12 1,02 0.51 6.8 High apparent cinder density 3 60 21 fifteen four one 1.13 0.85 0.34 4.2 - four 60 fifteen fifteen 10 2 1.14 0.73 0.25 3.6 - 5 60 10 fifteen fifteen 3 1.16 0.62 0.20 3.0 - 6 55 10 fifteen twenty 3 1.12 1.25 0.80 8.2 Seal of cinder due to the formation of a fusible slag phase 7 fifty 10 fifteen 25 3 1.09 1.28 0.85 10.7 Seal of cinder due to the formation of a fusible slag phase 8 60 0 25 fifteen 2 1.25 0.75 0.26 7.8 High bulk density 9 45 45 fifteen 5 one 0.88 - - 10.7 Cinder destruction after 35 minutes after coke combustion 10 fifty 5 40 5 one 1.29 1.18 0.71 8.6 High bulk density of the mixture, low cinder strength - dips eleven 60 19 6 fifteen 3 1,08 1.16 0.63 7.5 Seal of cinder due to the formation of a fusible slag phase

Claims (2)

1. An exothermic mixture for warming the head of the ingot during casting of steels and alloys, including aluminum-containing material, heat-insulating material and refractory filler, characterized in that it additionally contains material expanding during heating, casting graphite and fluorite concentrate, and contains waste material as an aluminum-containing material from the production of aluminum alloys and recycled products of aluminum-containing materials in the following ratio of components, wt.%: Aluminum-containing material 25-60 Thermal insulation material 10-40 Refractory filler 8-36 Expandable when heated 4-15 Foundry graphite 0-3 Fluorite concentrate 0-3 2. The exothermic mixture according to claim 1, characterized in that it contains vermiculite or perlite as expanding when heated.