Our customer is a gold concentrator. The design capacity of the gold concentrator is 2 000 t / D, and the general hardness coefficient of the ore is 8-10. The ore belongs to the high-temperature hydrothermal altered rock type gold ore occurring in the compressional structural fracture zone of mylonite. The content of arsenic and carbon in the ore is high. Most of the gold grains are dispersed in the arsenopyrite in the form of micro and ultramicro dispersion and then contained in gangue minerals such as sericite, chlorite, and quartz.
They have a set of Φ6.0m x 3.0m SAG Mill, a set of Φ7.3m x 4.27m Ball Mill, and a set of Fx-500 hydrocyclone group. After one year’s operation, the mill liners of the semi-autogenous mill must be replaced after 4 months of service, and the liner of the ball mill must be replaced after 7 months of service. Under the premise of the unchanged medium system and operating conditions, the wear of mill liner will affect the lifting height of the steel ball, resulting in the reduction of grinding efficiency and the treatment capacity to 1 800 t / d.
Characteristics of liner wear of semi-autogenous mill
The semi-autogenous mill has the characteristics of impact damage and grinding. There are a lot of steel balls (grinding medium), block materials and slurry in the semi-autogenous mill. The working condition is very bad. In order to protect the mill barrel from the direct wear of slurry and steel ball, the semi-autogenous mill has the characteristics of impact damage and grinding. The lining plates are all installed inside. The lining plates are cast into one-piece wear-resistant lining plates made of arc-shaped bottom plates and convex lifting ribs, which are fixed on the mill barrel, and both ends by bolts. After the grinding medium and materials are continuously lifted by the lifting ribs at the connection of the lining plate, the materials are thrown and dropped each other to realize the self grinding function of the semi-autogenous mill. This kind of grinding form determines that the lining plate and lifting strip will wear continuously. After the lining plate and lifting bar wear, not only the shape changes but also affects the height of material lifting inside the mill, resulting in energy loss, thus reducing the grinding efficiency.
Characteristics of liner wear of the ball mill
In the working process of the ball mill, the material and steel ball has relative sliding and rolling on the lining plate, which makes the lining plate subject to extrusion and rolling. In addition, compared with the lining plate of the semi-autogenous mill, the lifting effect of the ball mill lining plate is relatively weak, and the addition of steel ball is relatively more. The material in the ball mill is mainly in the rolling process, and the wear of the lining plate is mainly caused by the wear of mixed materials when it falls The shape of body liner has a great influence on the operation of the ball mill. At present, tower connection and waveform are often used. There are several kinds of liners, such as convex, smooth, and ladder-shaped. The wave crest design of the liner is helpful to extend the distance of falling, and the grinding effect is strong. So as to improve the service life of the lining plate.
SAG Mill Liners transformation scheme and effect
Dimension, installation form, and wear condition of original SAG mill liners
The original cylinder liner of the semi-autogenous mill is divided into high rib liner and low rib liner. As shown in the figure, the lifting strip of high rib liner is symmetrical double chamfering design, the lifting strip of low rib liner is single chamfering design, the convex part of the liner is lifting strip, and the angle of double chamfering of the high rib is 55 ° and 25 °. The chamfering of low reinforcement is 25 ° and the height of the lifting strip is 150 mm and 80 mm, and the thickness of the liner plate is 70 mm.
After 3 months of production, the wear of the cylinder liner was mainly caused by the decrease of lifting bar, and the wear of the head surface of the lifting strip was inclined, with the slope angle greater than 60 ° resulting in excessive smoothness and the decline of lifting capacity, resulting in the decline of grinding efficiency and the fracture of part of the lifting bar. However, when the liner was scrapped, the wear of the lifting strip on the back spherical surface was relatively small, and the plate part of the liner did not wear through.
The size and shape of the reformed SAG Mill Liners
According to the analysis of the wear condition of the original liner and the motion track of the ball of the semi-autogenous mill, the cylinder liner is improved: the height of the lifting strip is increased from 150 mm and 80 mm to 170 mm and 100 mm. Considering that increasing the height of the lifting strip will increase the original weight of the rear lining plate, we try to improve the back spherical surface and the plate part with less wear of the lining plate. The thickness of the plate part of the lining plate is reduced from 70 mm to 60 mm. As shown in Figure 2, the asymmetric cone design scheme is adopted for the liner lifting strip, and the weight removed is subsidized to the lifting strip. After the modification, the theoretical total weight of the liner of a mill is increased by about 100 kg (the total weight of the liner is 36620 kg after modification), and the service life of the liner is extended from 2800 h to 4300 H.
Grid Plates Redesign
According to the practice and observation, the accumulation of intractable rocks in the semi-autogenous mill is also an important reason for the decline of grinding efficiency. These hard rocks accumulate continuously in the mill and can not be discharged in time, which will affect the composition of ore particle size while increasing the invalid filling rate. In the complete lining plate of the semi-autogenous mill, the grid plate is composed of a central grid plate and a peripheral grid plate. The grid plays a dual important role, one is to prevent the grinding medium from overflowing the grinding medium, steel ball, or large ore, and the other is the classification of grinding products. The grid joint of the peripheral grid plate is the weakest part of the overall design strength. The normal operation of the semi-autogenous mill will be affected rapidly after the grid-gap is broken. After a long time summary, our engineers have made corresponding improvements, as shown in Figure 3.
- In order to enhance the discharge of the semi-autogenous mill, reduce the invalid filling rate and improve the processing capacity of the semi-autogenous mill, the mesh size of the grid plate is increased from 20 mm to 30 mm, and the materials below 30 mm are forced to be discharged in time. Through production practice, the processing capacity is increased from 75 t / h to 120 t / h.
- In order to reduce the impact and wear on the grid joints, it has been proved by a large number of practices that heightening the blocking bulge on the surface of the grid plate can effectively prevent the falling grinding ball from directly hitting the grid joint of the grid plate and causing the grid joint fracture. The weight of a set of outer ring lattice plate is increased by 864 kg (the total weight of the modified grid plate is 12400 kg) when the original design height is increased from 150 mm to 210 mm. After improvement, the service life of the lattice plate can be obviously prolonged.
Φ7.3m x 4.27m Ball Mill Mill Liners Redesign
The liner plate of overflow type ball mill was originally designed as a single wave peak structure, as shown in Fig. 4. Due to the large distance between the adjacent wave peaks, the mill with this design structure has a large amount of ball storage. A large number of grinding balls are separated after lifting, which is not conducive to the play of the grinding function of the mill powder, and the sliding ball phenomenon of the grinding ball during the lifting process leads to the rapid wear of the liner. The cylinder liner of this design structure is generally used in grid type ball mill and a section of operation. When the ball mill works in the second stage of the grinding process, the design of the cylinder liner should highlight its grinding function. At this time, the double wave crest design structure should be adopted for the cylinder liner. At this time, during the operation of the mill, a large number of grinding balls in the mill run in the form of falling contact, so as to realize the powder grinding of the grinding materials. The structure of the double wave crest design is shown in Figure 4. The weight of liner increases by 9 kg after changing from a single wave crest design structure to a double wave crest design structure. The weight of the cylinder liner of the whole machine is increased by 2 016 kg (the total weight of the liner is 48160 kg after modification).
Transformation of end liner
The end liner of the overflow ball mill was originally designed as a two-stage split structure. Due to the influence of the material level in the ball mill, the strong wear zone of the ball mill end liner is generally located in the middle and lower part of the inner ring end liner and the outer ring end liner. However, the upper part of the inner ring end liner is not worn. The design structure of two-stage segmentation forces the inner ring end liner to be scrapped and replaced after the lower part is worn, which leads to the increase in the use cost of the lining plate. When the end liner of the ball mill adopts the design structure of the three-stage division, only the middle and lower part of the inner ring liner and outer ring end liner needs to be replaced after the end liner is worn and scrapped. The upper part of the inner ring end liner can be used for a long time without replacement. The specific scheme is shown in Figure 5.
After the transformation, after 10 months of production practice, the main process indexes of the grinding system before and after the transformation are compared and analyzed, and the results are shown in Table 1.
|Table 1 Grinding index comparison|
|Before transformation||After transformation|
|Production Capacity / (t /h)||75||120|
|SAG Mill Liners Working Life/h||≤2800||≤4300|
|Ball Mill Liners Working Life/h||≤5000||≤7200|
|Discharge fineness of SAG Mill/ %||35. 53||30. 38|
|Discharge fineness of ball Mill/ %||47. 26||43. 55|
|Sand settling fineness of Hydrocyclone / %||19. 26||14. 32|
|Overflow fineness of hydro cyclone /%||75. 77||75. 21|
|Classification efficiency /%||52||55|
|Return sand ratio of ball mill /%||105||120|
The comparison results in Table 1 show that the service life of semi-autogenous mill liner is increased from 2800 h to 4300 h, the service life of ball mill liner is increased from 5000 h to 7200 h, the production capacity is increased by 50%, and the discharge fineness of SAG mill is reduced by 3.71%. According to the above assessment results, the service life of the mill liners is prolonged, and the grinding efficiency is obviously improved. The transformation achieves the expected effect.