ANALYSIS OF THE IMPROVED LINING DESIGN OF BALL MILL DRUMS

ABSTRACT

In this scientific paper, a significant role in the study of the main causes of factors affecting the failure of ball mills is played by the rate of slip on the surfaces of coatings at the expense of the friction forces that occur between the coating and the load current. Changing the slip rate has a major effect on the quality characteristics of the decay processes that determine the decay intensity. A change in the value of a certain pressure mainly only leads to a change in the intensity of Decay. The decay of Mill drum protectors will have different values depending on the location of the covers. In addition, this article shows the types of ore milling mills operating in hydrometallurgical plants under the Navoi mining and Metallurgical Combine JSC and their share, failure cases and coating failures. Based on the experiment conducted, coatings of improved new construction for the cylindrical part of their drum were proposed in order to reduce the duration of interruptions of ball mills, and the results obtained on their effectiveness were presented.

АННОТАЦИЯ

В данной научной работе значительную роль в изучении основных причин возникновения факторов, влияющих на выход из строя шаровых мельниц, играет скорость скольжения по поверхностям покрытий за счет сил трения, возникающих между покрытием и током нагрузки. Изменение скорости скольжения оказывает существенное влияние на качественные характеристики процессов затухания, которые определяют интенсивность затухания. Изменение величины определенного давления в основном приводит только к изменению интенсивности затухания. Степень износа защитных элементов барабана мельницы будет различной в зависимости от расположения крышек. Кроме того, в этой статье приведены типы мельниц для измельчения руды, работающих на гидрометаллургических предприятиях АО "Навоийский горно-металлургический комбинат", их доля, случаи поломок и повреждения покрытия. На основании проведенного эксперимента были предложены покрытия улучшенной новой конструкции для цилиндрической части их барабана, чтобы сократить продолжительность простоев шаровых мельниц, и представлены результаты, полученные в отношении их эффективности.

Keywords: ball mill, plating, coefficient, failure, efficiency, size, working member, improved, base, durability, working duration, element, bulge, lifters.

Ключевые слова: шаровая мельница, покрытие, коэффициент, отказ, эффективность, размер, рабочий орган, усовершенствованный, основание, долговечность, продолжительность работы, элемент, выпуклость, лифтеры.

Introduction

Purposes: increase the productivity of ball mills.

Research objectives: increasing the service life of lining drums of ball mills.

For the purpose of studying the operating mode of the mill, the speed of rotation of the drum, the forces affecting the coatings and the factors affecting their decay, the workshops of the 2nd hydrometallurgical plant owned by the Navoi mining and Metallurgical Combine JSC with the MMs were selected as the object of research. The plant has a total of 33 MMS type Mills with 27 MMS-7000x2300 and 6 MMS-9000x3000 Mills. The capacity of the workshops is 53 million tons of ore per year. The strength limit of the milled ores takes up to f<10÷14 on the Protodyakonov scale.

The study and analysis of the milling process in ball mills, when considering the decay of coatings on it, initially begins with the sequential installation of coatings along the inner surface of the mill drum [1].

In order to improve mill productivity, improve the efficiency of primary milling and reduce the timing of interruptions, rubber metal coatings made in India were installed and tested in self-propelled Mills of the MMS-7000x2300 type. The abrasion resistance and abrasion rate of the coatings were measured. This type of coating kit has been in use for five months. When using rubber metal coatings, the following disadvantages were identified: the high degree of decay of the risers, the observation of a fracture condition in the coatings, the formation of deformation in the drum during the movement of the load. It can be seen from this that the MMs-7000x2300 self-propelled mill under study shows that the use of rubber metal coatings is ineffective. When using this type of coating, the costs will be very large. That is, the coatings are produced in a remote Indian country and take months for the coatings to reach us. This causes the mills to fail for a long time [2;3;4].

For this reason, metal coatings made of 110g13l steel are currently being used. This type of Steel has been monitored for years to determine the time of operation of the coatings as well as its advantage. Taking into account the performance of the coatings, the volume of the product to be milled, data was collected, which was studied in intermediate inspections of the erasures on working surfaces. The main reason for the replacement of coatings made of 110g13l steel in Mills is the erosion of their risers [5; 6].

Materials and methods

Research has shown that changes in their elements during the use of self-propelled mill drum coatings have been found to change the friction forces acting on them and increase the quality of milling and the duration of the coating's operation cycle.

The energy loss of a mill working with eroded coatings during the milling process will be 25-30% higher than a mill where new coatings are installed. The operation practice of the MMs-7000x2300 self-propelled mill has shown that due to the decay of its coatings, interruptions last for almost 10 days, and the productivity of the mill decreases by 20-22% in exchange for the decay of coatings and their replacement with a new one.

Figure 1. Overview of the coating of the cylindrical part of the MMS-7000x2300 mill drum

There are currently several types of ball mill drum covers, and the standard manufactured coating shown in Figure 1 above is used for the cylindrical part of the MMS-7000x2300 mill drum in all hydrometallurgical plants under Navoi Mining Metallurgical Combine JSC.

Results and discussion

The cylindrical part of the mill drum as well as the hole (hatch) in the cylindrical part of the drum as a solution to the problem in the covers, at the cost of changing the height of the transverse bulge in the middle part of the cover from 165 mm to 95 mm, as well as increasing their resistance to decay by removing, it was found that the efficiency of milling operations of ball mills could be improved, and improved types of coating structures were developed.

In the process of operation of standard coatings on the cylindrical part of the mill drum as well as the hole (hatch) in the cylindrical part of the drum, the penetration of metal spheres and rocks between its ribs caused slip and friction forces to occur, which led to a deterioration in the quality of milling and a decrease in the efficiency of the mill.

The improved cladding structure differs from the previous cladding structure in that it has no ribs and the size of the relief in the middle of the cladding, giving it a bar-like appearance. The material of the improved cladding was left unchanged, namely, it is made of steel grade 110G13L.

In the newly developed improved design of the ball mill drum lining, it was proposed to change the dimensions of the central bulge, which differs from the standard lining elements, and to remove the transverse risers and two ribs  located at an angle of α=25-35º to the transverse bulge. The appearance and dimensions of the improved lining design are presented in Figure 2.

Figure 2. General view of the improved coating for the cylindrical part of the MMS-7000x2300 mill drum without ribs and with reduced relief

In the process of manufacturing the improved linings of the cylindrical part of the drum of the self-propelled mill, the length of the sides of the lining is 888 mm by 842 mm. The width of the base part of the lining is 538 mm, and the upper part is 488 mm. The thickness of its base plate is 75 mm, the height of the transverse risers on both sides is 265 mm, the thickness of the lower part of the risers is 100 mm, and the thickness of their upper parts is 75 mm, the height from the lower part of the base plate to the upper part of the transverse relief in the middle of the lining is 95 mm, and the thickness of the upper part of the relief is 90 mm, and its appearance is shown in Figure 2 above.

Conclusion

In the process of preparing the improved coatings, the height of the two side risers located above the plate part remained unchanged at 265 mm, the height of the relief above the plate was reduced from 165 mm to 95 mm, and the removal of the transverse risers and two ribs located at an angle of α=25-35º to the transverse relief increased the service life of the coating and the efficiency of the mill.

As a result of the introduction of the developed coatings of the new design in the MMS-7000x2300 mills, the coatings of the cylindrical part of the mill drum and the holes (manholes) in the cylindrical part of the proposed improved new design have a 25% higher corrosion resistance compared to the previously used coatings. It was also achieved a reduction in the downtime of each mill by 2-3% per year and a 22% reduction in the need for coatings.

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