IMPROVEMENT OF THE TECHNOLOGY FOR OBTAINING SYNTHETIC CAST IRON USING LOCAL SECONDARY WASTE RAW MATERIALS

ABSTRACT

In this article, the problems of creating and implementing a technology for the production of synthetic cast iron using local secondary waste raw materials were studied. In the research process, the composition and quality of processed scrap metal, industrial waste, and other secondary raw materials were analyzed, and their influence on cast iron solutions was considered. The main problems arising in the production process the variability of the raw material composition, difficulties in controlling harmful impurities, high energy consumption, and compliance with environmental requirements - were analyzed. Improved technological solutions and environmentally safe methods have been recommended to improve the quality of synthetic cast iron and ensure production efficiency.

АННОТАЦИЯ

В данной статье изучены проблемы создания и внедрения технологии производства синтетического чугуна с использованием местного вторичного отходного сырья. В процессе исследований проанализирован состав и качество перерабатываемого металлолома, промышленных отходов и другого вторичного сырья, рассмотрено их влияние на чугунолитейные растворы. Проанализированы основные проблемы, возникающие в процессе производства: изменчивость состава сырья, трудности контроля вредных примесей, высокая энергоемкость, соблюдение экологических требований. Рекомендованы усовершенствованные технологические решения и экологически безопасные методы для повышения качества синтетического чугуна и обеспечения эффективности производства.

Keywords: synthetic cast iron, induction crucible furnace, chemical composition, secondary raw materials, temperature, mechanical properties.

Ключевые слова: синтетический чугун, индукционная тигельная печь, химический состав, вторичное сырье, температура, механические свойства.

Introduction. Today, because of the rapid development of industrial sectors, the volume of various metallurgical wastes and secondary raw materials is increasing. Rational and efficient use of these resources not only increases economic efficiency, but also plays an important role in reducing environmental problems. In particular, the production of synthetic cast iron from secondary metallurgical waste is one of the current directions of modern technology. The production of synthetic cast iron based on the use of local secondary waste raw materials allows not only to reduce the use of fixed resources, but also to reduce production costs and minimize the negative impact on the environment. At the same time, there are several problems in the organization and improvement of these processes. Such issues as the variability of the chemical composition of secondary raw materials, harmful impurities and their influence on the quality of the finished product, technological aspects of the melting process, and energy consumption require serious scientific and practical solutions [1].

This article provides for the creation of a technology to produce synthetic cast iron based on local secondary waste raw materials, identifying existing problems, and developing proposals and recommendations for their elimination. The research results serve as a scientific and practical basis for the implementation of effective technological processes at industrial enterprises and the formation of an environmentally friendly production system. The research process was carried out at JSC ‘QUYUV-MEXANIKA ZAVODI’ using a medium-frequency induction crucible furnace of the company ‘OTTO JUNKER’ with a neutral coating with a capacity of 6 tons. Neutral coating properties of induction crucible furnaces (Table 1).

Table 1.

Neutral coating properties of induction crucible furnaces

Induction crucible furnaces are widely used in smelting processes in metallurgy. These furnaces are distinguished by high efficiency, allowing for energy savings and rapid and accurate control of the temperature regime. The preparation of the charge for an induction crucible furnace should be designed considering the optimal size of the pieces, not exceeding 300×300 mm², and ensuring the density of their placement in the furnace. The use of very small pieces leads to insufficiently high power, which increases the melting time and power consumption. With a decrease in the flow frequency, its penetration depth increases, which leads to a decrease in specific power. Therefore, when reducing the flow frequency, it is necessary to increase the volume of charge components. The charge must be protected from strong oxidation, as this can lead to poor electrical conductivity between individual parts. In each individual section of the charge, the electric current can be blocked, which increases the melting time and energy consumption. The denser the charge, the faster the melting occurs, and the less electricity is consumed. The process of smelting synthetic cast iron using secondary raw materials in an induction crucible furnace is shown in Figure 1, the chemical composition of secondary raw materials and the material balance are presented in Table 2.

Figure 1. Process of smelting synthetic cast iron using secondary raw materials in an induction crucible furnace

The use of inexpensive metal waste for smelting synthetic cast iron ensures a reduction in its cost by 25...35% compared to secondary smelting of ordinary cast iron. Today, synthetic cast iron is used to obtain various high-responsibility parts, such as locomotive shoes, crankshafts, cylinder blocks, internal combustion engine heads, wear-resistant castings, high-temperature castings, balances of local secondary raw materials, and chemical composition of charge materials (Table 2) [2].

Table 2.

Balance of materials and chemical composition of charge materials

Research methodology. Materials used in obtaining synthetic cast iron using local secondary raw material scrap. Steel scrap 70%, returned cast iron scrap 30%, and the material balance and charge materials for the smelting process were calculated. In the production of synthetic cast iron, electrode fragments of an electric arc furnace were used to increase the carbon content in the metal [3]. The consumption of charge materials for obtaining one ton of liquid cast iron is 1043.56 kg. For wheel pairs, wheel axles, and other similar parts used in railway transport, the chemical composition of carbon steel scrap of the secondary waste Al brand according to ГОСТ 10791-2011, EN 13262 is given in Table 3, and the chemical composition of cast iron scrap is given in Table 4 [4].

Table 3.

Chemical composition of secondary waste steel scrap

Table 4.

Chemical composition of reduced cast iron scrap

The following ferroalloys were used as alloying elements. Ferro silicomanganese (МнС17) is an alloy consisting of manganese, silicon, and iron, widely used in the metallurgical industry. МнС17 contains approximately 17% silicon (Si) and high manganese content. This alloy is of great importance in the production of steel and cast-iron alloys [5, 6]. Ferromanganese (ФМн75) is an alloy containing approximately 75% manganese (Mn), as well as iron (Fe) and small amounts of other elements (Si, C, S, P). It is used in metallurgy as an alloying and deoxidizing additive in the production of steel and cast iron. The chemical composition of ferro silicomanganese (МнС17) and ferromanganese (ФМн75) is presented in Table 5.

Table 5.

Chemical composition of ferroalloys

Results and discussion. The process of obtaining synthetic cast iron in an induction crucible furnace is carried out in the following order: when melting metal in an induction crucible furnace, the amount of steel residues should not exceed 40%. When comparing cast irons with the same chemical composition, the graphite of cast irons melted in charge containing more than 40% steel residues appears relatively finer and with improved mechanical properties.

Desulfurization technology using the SiCaAl briquette modifier material. The briquette modifier SiCaAl is a silicon charge material used in cast iron smelting instead of ФС45 ferrosilicon [7]. In addition to doping the metal with silicon, the briquette modifier SiCaAl acts as a purifier of the metal melt, purifying the liquid metal from sulfur and phosphorus, since it contains magnesium and up to 15% active alkaline earth and rare earth elements. After melting the charge, when the resulting melt occupies 1/3 - 2/3 of the total volume of the furnace, the briquette modifier SiCaAl is added. The rest of the charge is placed on them so that they completely cover the briquettes to ensure their most efficient use [8, 9]. After the entire charge is melted in the furnace, the slag is coated to prevent the reduction of sulfur and phosphorus. The used briquette modifier SiCaAl (Fig. 2) is shown, the number of briquettes depends on the process conditions and the requirements for the final product and can only be determined experimentally in each foundry.

Figure 2. Briquette modifier SiCaAl

The average consumption of the briquette modifier SiCaAl is 20 kg per 1 ton of molten metal. The application of the above-described technology of solution desulfurization using SiCaAl briquette modifiers allows for a reduction in the sulfur concentration in the metal. The chemical composition of the briquetted complex modifier SiCaAl is presented in Table 6.

Table 6.

Chemical composition of the briquetted (SiCaAl) complex modifier

In the research work, a new concept for the technology of cast iron smelting in induction crucible furnaces was proposed, which allows obtaining synthetic cast iron using steel waste in the composition of the metal charge. The composition of the charge should ensure that all elements after melting are close to the specified amount in the finished metal. Cast and intermediate cast irons, cast iron scraps, steel scraps, carburetors, and ferroalloys are used as initial charge materials. It is advisable to start the calculation of the metal charge by determining the number of alloying ferroalloys necessary for the inclusion of waste during the melting period, steel scrap, and additives during the technological period, ensuring that the composition of the liquid cast iron is close to the requirements. The method of melting synthetic cast iron in induction crucible furnaces consists in calculating the charge before melting, considering the proportion of carburetors, steel scrap, and ferroalloys. Melting begins with filling the induction furnace crucible with 10-30% of the total capacity of the reflected cast iron scrap. The returned cast iron, loaded with liquid metal, is heated to 1350 °C for 20-30 minutes, corresponding to the amount of scrap. Then electrode fragments from the electric arc furnace are added, the consumption rate of which is determined by the total charge calculation at a certain fraction of steel scrap.

The crucible furnace is started in the following order. All water-cooled elements of the furnace are switched on, then 2/3 of the capacitor-battery power is switched on, then the generator is switched on and the voltage in the generator is reduced from the nominal value to 0.7... 0.8 is set. They turn on the linear contactor on the inductor panel of the furnace and additionally connect the capacitors, adjusting the reactive inductive power of the inductor to cosφ=1. With automatic control, the power cycle is transferred to the automatic electrical mode regulator. During the melting process, short circuits initially occur when the pieces of the charge have insufficient contact areas. These short circuits lead to a change in the flux in the inductor circuit, so the melting process begins to use reduced power from the source. With a decrease in flow, the converter switches to maximum power.

Conclusion. Improvement of the technology for obtaining synthetic cast iron using local secondary waste raw materials is one of the urgent directions of modern industry. During the smelting of cast iron, the sulfur content should not exceed 0.0296. Otherwise, unstable results are obtained in terms of chemical composition and mechanical properties, and graphite in a distorted form is observed in the structure of cast iron. The research results showed that it is possible to make production processes more environmentally and economically efficient through the efficient use of available resources. The composition of processed metallurgical and industrial waste was thoroughly analyzed, the main problems arising during their smelting, including the presence of harmful impurities and instability of the composition, were identified, and practical recommendations for eliminating these problems were developed. Also, the use of energy-saving furnaces and advanced technological methods has increased production efficiency and made it possible to maintain the quality of finished products. The widespread use of local raw materials plays an important role in reducing production costs and ensuring environmental safety.

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