RU2190669C2 - Method for producing burden from iron based powders - Google Patents

Abstract

FIELD: powder metallurgy. SUBSTANCE: method involves introducing binder into powder; mixing components and forming briquettes. Binder is waste sulfuric acid solution with concentration of 0.5-5%. Method allows briquetted burden to be obtained from waste powdered cast iron and steel shots. EFFECT: increased efficiency and improved mechanical properties and chemical composition useful for manufacture of cast iron shots. 2 tbl, 2 ex

Description

 The invention relates to the field of powder metallurgy, to methods for the chemical treatment of powders of iron-based alloys, in particular, to obtain a briquetted mixture from dusty waste of pig-iron and steel shot generated by the shot blasting of an oxidized metal surface. The mixture is then used as raw material in the steel industry.

 In the process of shot blasting the metal surface, up to 70% of the dust-like fraction of iron-based alloys is formed, particle sizes, as a rule, are in the range of 0.005-1.0 mm. In this form, the waste cannot be used for re-smelting, because during re-melting the particles burn out and the metal passes into liquid slag. Wastes from the spent fraction are collected in workshops or transported to the H.B. and P.O.

 A known method of forming briquettes of alloys on an iron basis without applying cold pressure by the method of slip casting. Slip composition: iron-based alloy powder, liquid (water or alcohol) and surface-active substances (sodium and ammonium alginates) (Powder metallurgy. Handbook. Academy of Sciences of the Ukrainian SSR. Institute of Materials Science, 1985, pp. 162-163) .

 The disadvantage of this method is the large porosity and low strength of the briquettes, since the connection between the powder particles is carried out only due to capillary efforts at the powder-liquid interface.

 A known method of producing a mixture of powder materials, including mixing the components of the mixture in the apparatus with mixing and crushing organs, introducing a liquid binder (5% solution of polyvinyl alcohol), granulating and drying granules by supplying compressed air or blowing a fan to a moisture content of not more than 6% . The whole process is carried out in one apparatus (USSR copyright certificate 1688979, B 22 F 1/100, 11/07/91, BI 41).

 The disadvantage of this method is the complexity of the equipment and process, low strength of the granules.

A known method of forming briquettes of dusty chromium-containing waste in the production of ferroalloys. Magnesium oxide is used as a binder (hardener). The mixture hardens as a result of the hydration reaction and the formation at the grain boundaries of the powder of strong crystals of magnesium hydrochromates (MqO • Cr ₂ O ₃ • 6H ₂ O), (ISSN 0038-920X. Steel, 3, 2000, pp. 36-39 )

 The disadvantage of this method is that in the binder for forming briquettes from dusty fractions of spent cast iron and steel fractions there is a magnesium component, which is unacceptable in the charge used for melting gray cast iron.

 A known method of manufacturing a mixture of powders in which a 0.5-1.0% solution of sodium carboxymethyl cellulose in a 5% solution of boric acid is used as a binder (ed. St. SU 205982, class B 22 F 1/00, publ. 12/01/1967).

 The disadvantage of this method is the inadmissibility of the content in the chemical composition of cast iron boron compounds.

 Closest to the claimed invention in technical essence is the method of forming sponge iron briquettes described in the application DE 2919272, C 22 V 1/243, publ. 11/27/1980, containing the introduction of a binder into powder, mixing the components, the formation of briquettes, the use of 10-30% spent sulfuric acid as a binder - a prototype.

 The disadvantage of the prototype is the high concentration of sulfuric acid, resulting in intense dissolution of iron with the formation of salts, which ultimately reduces the amount of smelted metal, with an acid concentration of 10-30% metal loss reaches 40% or more (according to the results of experimental work). In addition, the presence of sulfur in the chemical composition of cast iron is strictly regulated and its excess leads to marriage.

 The problem to which this invention is directed, is the disposal of waste steel and cast iron with minimal losses and obtaining from them a briquetted mixture with high mechanical properties and chemical composition suitable for the manufacture of cast-iron shot.

 The problem is solved in that in the proposed method for producing a mixture of powders of iron-based alloys, including introducing a binder into a powder, mixing the components and forming briquettes, a spent aqueous solution of sulfuric acid with a concentration of 0.5-5.0% is used as a binder.

 When the components are mixed, a chemical reaction of the interaction of iron and acid occurs with the formation of ferrous salt salts on the grain surface, which bind the individual particles, which leads to the curing of the dust fraction of the spent fraction.

Величина концентрации кислоты 0,5-5,0%, используемой в качестве связующего, обусловлена следующими ограничениями:
- концентрация ниже указанной не приводит к образованию на поверхности достаточной толщины слоя зерен кристаллов соли двухвалентного железа, необходимого для связывания отдельных частиц ферросплавов, брикеты получаются недостаточно прочными;
- при концентрации кислоты выше указанной величины происходит интенсивное растворение железа с образованием солей, что в конечном счете уменьшает количество выплавляемого металла, а также увеличивает содержание серы в сплаве, что ухудшает его качество.

The concentration of acid 0.5-5.0%, used as a binder, due to the following restrictions:
- the concentration below the specified does not lead to the formation on the surface of a sufficient thickness of the layer of grains of crystals of salts of ferrous iron, necessary for bonding individual particles of ferroalloys, the briquettes are not strong enough;
- at an acid concentration above the specified value, intense dissolution of iron occurs with the formation of salts, which ultimately reduces the amount of metal smelted, and also increases the sulfur content in the alloy, which affects its quality.

Example 1. Powder spent pig-iron and steel shot with a particle size of 1.0-0.005 mm and chemical composition, which is listed in table. 1, was mixed in a solution with a capacity of 500 l at a rotation speed of 30-60 rpm with the addition of spent sulfuric acid with a concentration of 3.5% for 10 minutes Then the mixture was reloaded into stationary open forms and compacted with a tamper. Curing of the briquettes took place within 12 hours at 50 ^o C. These briquettes were used in the smelting of gray cast iron in an induction furnace in a proportion of up to 30% of the total mass of the charge, followed by the manufacture of cast-iron shot. The chemical composition of smelted cast iron is given in table. 2.

Example 2. When all the above conditions are met, the curing of cast iron at 25 ^o With occurred within 48 hours

 The results of industrial tests showed the possibility of obtaining a mixture of dusty waste fractions and waste acids with a concentration of 0.5-5.0%.

 The proposed method allows to obtain a briquetted charge from cheap waste steel and cast iron fractions with high strength properties, because powder particles are bonded to each other using the energy of chemical interaction. The chemical composition of the iron smelted with the addition of this mixture satisfies the requirements for the manufacture of a marketable product from it - cast-iron split shots. The process is low temperature, with minimal energy consumption, the cost of waste disposal is reduced and the environment is improved.

Claims (1)

 A method of producing a mixture of powders of iron-based alloys, comprising introducing a binder into a powder, mixing the components and forming briquettes, characterized in that the spent solution of sulfuric acid with a concentration of 0.5-5.0% is used as a binder.

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