RU2017575C1 - Composition of exothermoinsulating mixture for heating riser - Google Patents

Abstract

FIELD: foundry. SUBSTANCE: mixture includes aluminium powder as reducer in the amount of 10-30 mas % and dust of melting furnaces of nonferrous alloys based on zinc oxide with ignition temperature not in excess of 520 C in the amount of 70-90 mas %. In this case, dust serves as exothermal and heat-insulating mixture component. Dust includes, mas %: ZnO 60-75; CuO 0.2-10.0; Al₂O₃ 4-8; SnO 0.05-10.0; Fe₂O₃ 1-8; SiO₂ 1-3; Mn₃O₄ 0.1-0.8; NiO₂ up to 0.2 and particles sizing 0.00001 to 0.1 mm. EFFECT: excluded contamination of casting head metal with products of exothermal reaction and provides for directed transmission of heat from mixture to casting head. 3 cl, 2 tbl

Description

 The invention relates to foundry and is used to heat the profits of castings and ingots of ferrous and non-ferrous metals and alloys (brass, bronze, ductile iron, aluminum and magnesium alloys).

 Known mixtures for heating profits based on dust of various metallurgical units. However, these are either exothermic or heat insulating mixtures that require the use of other ingredients. Therefore, their use is not so effective, since part of the heat is spent on heating additional ingredients.

 A known composition in which aluminum is used and waste in the form of slag containing zinc oxide, which is both insulating and exothermic. However, the use of slag requires additional costs for its grinding. Moreover, the content of zinc oxide in it does not exceed 20% with a high content of silicon and calcium oxides. Such a mixture will have a low thermal effect.

 Closest to the proposed is a mixture containing aluminum powder and non-ferrous metal oxide (copper). However, this mixture is uneconomical due to the high cost of copper oxide, for the production of which it is necessary to specifically burn copper in a stream of oxygen.

 The aim of the invention is to reduce the cost of the mixture, as well as improving the quality of castings by eliminating the contamination of the metal profit by products of an exothermic reaction and ensuring directed heat transfer from the mixture to profit and casting.

This is achieved using the aluminum powder composed of the mixture together with the dust from the melting furnace nonferrous alloys based on zinc oxide ignition temperature not exceeding 520 ^{° C,} with the following ratio of ingredients, wt.%: Aluminum powder 10-30
Dust from smelters
Zinc oxide-based non-ferrous furnace furnaces 70-90
Dust from zinc oxide-based smelters is generated in the silos of the ventilation system of induction, arc and gas furnaces in the production of non-ferrous alloys containing copper, such as brass. The chemical composition of such dust contains the following ingredients, wt.%: ZnO 60-75; CuO 0.2-10.0; Al ₂ O ₃ 4-8; SnO 0.5-10.0; Fe ₂ O ₃ 1-8; SiO ₂ 1-3; Mn ₃ O ₄ 0.1-0.8; NiO is up to 0.2, and the dust particle size is 0.00001-0.01 mm.

 The dust from zinc oxide smelting furnaces in the mixture has not only high oxidizing properties, but also thermal insulation and therefore does not require the use of other additional ingredients.

 The dimensions of aluminum powder do not exceed 0.3 mm.

 The compositions of the mixture according to the invention are given in table 1.

Mixtures can be used both without fasteners and with fasteners (water glass, sulphite liquor, etc.) in the amount of 9-15% (in excess of 100%). Their density before the exothermic reaction is up to 0.2 g / cm ³ , and after the reaction 0.15 g / cm ³ - 0.30 g / cm ³ depending on the composition. Therefore, such mixtures exhibit high thermal insulating properties both before pouring and after pouring the melt.

 The properties of the mixture are given in table.2.

 Initially, after the molten alloy comes into contact with the mixture, an exothermic reaction occurs mainly with zinc oxide.

The released heat heats the alloy in profit, and the mixture itself is heated to ≈1600-1800 ^о С.

 Due to the low thermal conductivity, the mixture after the reaction becomes heat-insulating, which reduces the weight of the metal for non-ferrous alloys in profit by 5-7 times.

Based on the thermochemical reaction: 3 moles of ZnO = 243 g, for 2 moles of Al = 108 g, the maximum amount of aluminum in the mixture is set for the complete reaction taking into account the presence of other oxides of MnO, Fe ₂ O ₃ , etc., which is equal to thirty% . This mixture will have a maximum Al content of 30%. Excess of aluminum> 30% (composition I): thermal conductivity increases, thermal insulation properties decrease due to aluminum in the unreacted mixture.

 When the aluminum content in the mixture is less than 10% in small profits, an exothermic reaction does not occur.

 The exothermic effect increases with an increase in aluminum content of more than 10%, and the maximum effect is achieved at 30%.

 As can be seen from the data in Table 2, the optimal composition is composition N 2 - a complete exothermic reaction occurs in this composition. Composition N 4 works with maximum thermal effect. In composition No. 5, an exothermic reaction was observed only in the surface layer in contact with the metal without spreading through the thickness of the exothermic lining. The mixture works as heat insulating and the presence of aluminum powder in its composition reduces its effectiveness.

 To increase the efficiency of the reaction with an Al content of 25-30%, up to 25% of the scale can be added to the mixture by reducing the dust of metal oxides. In this case, the heat-insulating properties of the mixture deteriorate.

 An increase in the scale content of more than 25% leads to the melting of the mixture with a complete loss of the insulating properties of the mixture with contamination of the metal with a termite alloy.

The mixtures according to the invention, as noted above, have high heat-insulating properties prior to the exothermic reaction with the melt. This provides a low heat transfer of the molten metal from profit and leads to rapid heating of the contact surface of the exothermal insulation mass. At a temperature of 520 ^{° C} the exothermic reaction starts between the aluminum powder and zinc oxide dust.

 The generated heat heats the metal in profit and raises the temperature of the exothermic mass. With increasing temperature, an exothermic reaction of oxides with a higher thermal effect (FeO, CuO, etc. included in the dust) begins, which enhances the heating of the metal in profit, transferring the maximum heat to profit in the direction. After the end of the exothermic reaction, the overheated mixture, while cooling slowly, transfers heat to the profit metal, and from it to the casting, creating directional crystallization of the metal in the casting-profit system.

 In the process of profit solidification, its shape does not change, keeping the hydrostatic pressure constant, pollution of the profit is eliminated by the reaction products, while maintaining minimal heat transfer through the profit surface due to its economical shape (in the form of a ball).

, где d_n=

- диаметр или толщина прибыли;
V_n - объем прибыли;
S_n - охлаждающая поверхность прибыли;
D=

- приведенный размер питаемого узла отливки;
V_o - объем питаемого узла отливки;
S_o - поверхность охлаждения питаемого узла отливки;
b_фn, b_фо - коэффициент тепловой аккумуляции прибыли, отливки;
b_фо - для песчаной формы 15-20 ккал/м² ˙ ч/20
n - постоянный коэффициент, зависящий от формы прибыли, для плиты 2, цилиндра 4, шара 6;

; H_n - высота прибыли.Profit calculation with exothermal insulation shells from the mixture according to the invention is carried out according to the following relationship:
d _n = n

where d _n =

- diameter or thickness of profit;
V _n - profit margin;
S _n is the cooling surface of the profit;
D =

- the reduced size of the feed unit of the casting;
V _o - the volume of the feed node of the casting;
S _o - the cooling surface of the feed node of the casting;
b _fn , b _fo - coefficient of thermal accumulation of profit, castings;
b _fo - for the sand form 15-20 kcal / m ² ˙ h / 20
n is a constant coefficient, depending on the form of profit, for plate 2, cylinder 4, ball 6;

; H _n - profit margin.

 The mixture according to the invention allows to reduce the cost of production by reducing the cost of the mixture, increase the yield of casting by reducing the size of the profits, improve the quality of castings by increasing their density and eliminate contamination of the alloy recovered from the mixture of metal, reduce the amount of harmful emissions into the atmosphere.

Claims (1)

1. COMPOSITION OF EXTERM INSULATION MIXTURE FOR HEATING PROFITS, ferrous and non-ferrous metals and alloys, including aluminum powder and an oxidizing agent based on non-ferrous metal, characterized in that it contains dust from non-ferrous melting furnaces based on zinc oxide with an ignition temperature, not exceeding 520 ^o With the following ratio of ingredients, wt.%:
Aluminum Powder 10 - 30
Dust from smelting furnaces of non-ferrous alloys based on zinc oxides 70 - 90
2. The composition according to claim 1, characterized in that the dust from the smelting furnaces of non-ferrous alloys based on zinc oxide has the following composition, wt.%:
ZnO 60 - 75
CuO 0.2 - 10.0
Al ₂ O ₃ 4 - 8
SnO 0.5 - 10.0
Fe ₂ O ₃ 1 - 8
SiO ₂ 1 - 3
Mn ₃ O ₄ 0.1 - 0.8
NiO Up to 0.2
3. The composition according to claim 1, characterized in that the dust from the smelting furnaces of non-ferrous alloys based on zinc oxide has a particle size distribution of 0.00001 - 0.01 mm

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