ANALYSIS OF THE HARDNESS AND CHEMICAL COMPOSITION OF METALS USED IN MILL LININGS

ABSTRACT

This article examines the hardness indicators and chemical composition of metals used in mill liners, focusing on their wear resistance during ore grinding. The study identifies the main types of liner wear, including direct abrasive, impact-abrasive, and fatigue wear, which depend on the physical and mechanical properties of rocks, such as density, hardness, and plasticity. The analysis highlights the role of different alloyed steels and cast irons, including manganese steel, chromium-alloyed, chromium-molybdenum, nickel-hardened, and white cast irons. Their hardness values and microstructures are compared, demonstrating how material selection affects durability under abrasive and impact conditions. The results show that improving liner design and choosing suitable alloys can reduce downtime caused by frequent replacements and extend the service life of mills. Thus, the article emphasizes the importance of material properties in optimizing the efficiency of ball mill operations in mineral processing plants.

АННОТАЦИЯ

В статье рассматриваются показатели твердости и химический состав металлов, используемых в футеровках мельниц, с акцентом на их износостойкость при измельчении руды. Выделены основные виды износа футеровок: прямой абразивный, ударно-абразивный и усталостный, которые зависят от физико-механических свойств горных пород, таких как плотность, твердость и пластичность. Проведен анализ различных легированных сталей и чугунов, включая марганцовистую сталь, хромистые, хромомолибденовые, никелевые и белые чугуны. Сравнены их показатели твердости и микроструктуры, показана зависимость долговечности от выбора материала в условиях абразивного и ударного воздействия. Результаты показывают, что совершенствование конструкции футеровок и правильный выбор сплавов позволяют сократить простои, вызванные заменой деталей, и увеличить срок службы мельниц. Таким образом, статья подчеркивает значимость свойств материалов для повышения эффективности работы шаровых мельниц в обогатительных фабриках.

Keywords: mill liners, wear resistance, hardness, alloyed steel, cast iron, abrasive wear, impact-abrasive wear, fatigue wear, mineral processing, grinding efficiency.

Ключевые слова: футеровки мельниц, износостойкость, твердость, легированная сталь, чугун, абразивный износ, ударно-абразивный износ, усталостный износ, обогащение руд, эффективность измельчения.

Introduction

 When grinding rocks, mill coatings are of great importance, the destruction of which is largely determined by the physical and mechanical properties of the rocks. Physical properties such as density, viscosity, porosity, moisture, as well as mechanical properties such as hardness, plasticity, and softness significantly affect the service life of coatings. Coating wear is divided into three types: abrasive, impact-abrasive, and fatigue wear.

The main reasons for the wear of coatings during the grinding of rocks with mills are determined by the physical and mechanical properties of these rocks. The physical properties of rocks include their density, viscosity, porosity, moisture content, and others. Its mechanical properties include hardness, softening, degree of softness, plasticity, and so on.

The operating mode of the mill, the hardness of the coating material and rock, significantly affect the shape of the coating. Coating wear can be divided into three main types:

- direct abrasive wear - in which high-hardness rocks move intensively with the drum, the hardness of the rocks exceeds the hardness of the coating material, and the rocks have a cutting effect on the metal. In cascade milling mode, flat and corrugated coatings are used for crushing hard rocks. In this case, the hardness of crushable metal ores is -1000 HV;

- impact-abrasive weathering - in this case, the hardness of the rocks is greater than the coating material, when the mill operates in a cascade or waterfall mode, the crushed rocks move practically without slipping, under the action of moving balls, the rocks create plastic deformation on the coating material without exerting a cutting effect;

- Fatigue (aging) weathering - the phenomenon of elastic deformation occurs between rock, metal balls, and coatings during the crushing of soft rocks (hardness 135 HV) in cascade and cascade modes of the mill. This causes wear on the surface of the coatings.

Methods

The article analyzed the chemical composition and hardness indicators of various metal coatings. The microstructure and hardness indicators of manganese steel, chromium alloy steel, chromium-molybdenum alloys, nickel-based hard steel, and ferrous steel were compared using graphs.

Results

The following figures show the hardness indicators and chemical compositions of metals used for spare parts and coatings of grinding mills at processing plants in the mining industry.

Under the influence of small forces of ores and mill balls on manganese steel, HB can reach a hardness of 300-400, and under the influence of large forces, HB can reach a hardness of 500-800. Under the influence of forces, the strength layer of the coating surfaces reaches 10-20 mm. Its graph is shown in Figure 1 below.

Figure 1. Chemical composition of manganese steel

Chromium alloy cast irons are divided into high, medium, and low chromium alloy cast irons. The microhardness of materials with such composition is HV1300-1800, and the resistance of ball mills to impacts and destruction is high. The graph of the dependence of the material is shown in Figure 2 below.

Figure 2. Chromium-doped chemical composition

The microstructure of the chromium-molybdenum alloyed coating material is pearlitic and martensitic, with a hardness of HB 325-400. Coatings of this type are resistant to impact and destruction under the action of load forces on the surface layer. The graph of the dependence of the material is shown in Figure 3 below.

Figure 3. Chromium-molybdenum doped chemical composition

The base of nickel-hard steel is white cast iron, the surface of which is alloyed with nickel and chromium. Small weathering occurs as a result of slippage during the grinding of dry and wet ores. Nickel hard steel coatings are effectively used in environments with abrasive and wear. The graph of the dependence of the material is shown in Fig. 4.

Figure 4. Chemical composition of nickel-hard steel coating

White steel is used for small impact interactions. The microstructure consists of martensite, carbide, and austenite, and the chemical dependence of the material is shown in Figure 5 below.

Figure 5. Chemical composition of white-iron steel coating

The study of the decrease in the service life of metal balls under the influence of impacts and slippage, as well as the occurrence of abrasive wear as a result of the impact of ores on mill coatings, stopping times due to the processes of replacing coatings installed on the mill drum, is relevant.

Issues of improving the design of armored plates the main reason for the decrease in the coefficient of technical operation of drum mills is the intensive wear of the coatings and premature repair of the planned service life.

Discussion

The obtained results show that the wear of coatings is influenced not only by the hardness of the rocks, but also by the coating material, microstructure, and alloying elements. Various metal coatings are suitable for certain operating modes. Therefore, in the mining industry, it is important to improve the selection of materials and the design of the coating to ensure the effective operation of mills.

Conclusion

The service life of mill linings depends on their material, chemical composition, and interaction with rocks. The use of high-alloy steel and cast iron increases resistance to abrasive and impact corrosion. The optimal choice of coatings determines not only their strength, but also the overall efficiency of the mills. Thus, improving the coating design and selecting the appropriate material is one of the key factors in increasing production efficiency in the mining industry.

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