Qiming Machinery is a leader in the design, manufacture and supply of mill liners for mineral processing and quarrying industries. We offer our customers complete wear liner solutions for mills that increase performance, equipment availability and lower maintenance costs. Our mill liners are also tested to withstand the acidity level of different elements that may be present in the milling process. Longer milling life to your machine means fewer expenses and more profit or income to your company.
Qiming Machinery mill liners are subjected to different combinations of impact and abrasion, as they are used in SAG/AG, ball or rod mills. Our wear parts are manufactured to the highest standards of quality and delivery, ensuring high levels of reliability for our customers. Also, our mill liners wear parts add value to customers’ processes through customized designs.
Types Of Mill Liners
SAG/AG Mill Liners:
• Integrated and/or plate and lifter designs for head and shell liners
• Pulp lifters
• Filler rings
Ball Mill Liners:
• Single wave liners
• Modified single wave liners
• Double wave liners
• Shell liners
• Feed head liners
• Discharge end liners
Rod Mill Liners:
• Shell liners
• Head liners
• “Wedge” shell liners
Mill Liner Material Selection
The selection of the material of construction is a function of the application, abrasivity of ore, size of mill, corrosion environment, size of balls, mill speed, etc. liner design and material of construction are integral and cannot be chosen in isolation. A list of the primary material of construction is given, with the particular uses and strengths of each.
- Manganese Steel: This is used for grid liners, and generally smaller mills.Its great advantage is that it work hardens under stress, yet the substrate remains tough andcan withstand extreme impacting without fracture. Its primary disadvantage is that it spreads with impact, so solid liners begin to squeeze together and become extremely difficult to remove, and can damage a mill shell if the stress is allowed to build up to an extreme level.
- Low Carbon Chrome Moly Steel (300 to 370BHN): Was generally used for mill liners (AG,SAG and Ball) prior to the movement to higher carbon content steels. It has excellent wear characteristics with some impact resistance, generally now used for discharge grates where slightly better impact resistance is required compared to the higher carbon chrome moly steels or for thinner section liners.
- High Carbon Chrome Moly Steel (325 to 380BHN): This steel is now considered the main material used for SAG mill liners. There are a number of variations with either different carbon or chrome contents. The variations tend to have a bearing on the size of the liner and its section thickness. There is ongoing development within this area as the size of the liners are outstripping the properties provided by the standard high chrome moly steels.
- Nihard Iron (550BHN): The use of this type of material generally began with Rod Mills and Ball Mills, where impacts were considered low enough for this brittle yet highly abrasive resistant wear material to perform well. However, it is now considered obsolete in light of the use of high chrome irons and chrome moly white iron.
- High Chrome Irons (+600BHN) Cr Iron: It is considered to have superior wear abrasion characteristics, and is generally used in rod and ball mills. It is more cost competitive but more brittle than chrome moly white irons.
- Chrome Moly White Irons (600 to 700BHN) WI: This cast material is considered to be the ultimate developed and used to date for abrasion resistance in Milling. It is commonly used in cement mills and some of the largest Ball Mills in the world and where performance has not been bettered to date.
Longer Mill Life, Higher Profit
Our mill liners are also tested to withstand the acidity level of different elements that may be present in the milling process. Longer milling life to your machine means fewer expenses and more profit or income to your company.
Qiming Machinery can also be an issue. With the rubber formulated liners attached to your millers, it will not intervene with the grinding process, and thus, you are saving a lot of money with the maintenance.
Wear Out Mill Liners
To give our customers peace of mind, as you purchase liners from us, we will provide you the expected life duration of your liners. This will depend on your type of milling business, the number of grinding hours in a day and other factors that may affect the quality of your machine.
Entrust your business to the experienced team. Get in touch with us by getting a free quote from our website. Our team will get back to you with our advice and recommendations.
Analysis and treatment of mill liners problem of Ф 2.2m × 6.5m ball mill
We have a Russian customer, who has a cement clinker production line. One month after the ball mill was put into operation, the liner plate and step liner of the first bin was broken frequently. At most, 18 pieces were broken in one week, which needs to be replaced. It costs a lot.
Cause analysis and treatment
First of all, consider whether there is a problem with the lining quality. The material of damaged grinding head liner and step liner is zg40cr2mnsi2more, HRC hardness index is 48 ~ 50, impact toughness is ≥ 59 J / cm2. The factory inspection is qualified,
It has been used in other projects normally without any abnormal conditions such as fracture and breakage.
Secondly, check whether the grinding body gradation is reasonable, the hardness of steel ball HRC ≥ 58, the toughness ≥ 3 J / cm2, the damage rate ≤ 0.5%, and the basic indexes are within the design range. The grading in the mill is shown in Table 1. According to the conventional feed size range of 0 ~ 50 mm, the proportion of 0 ~ 25 mm material is about 70%, and the configuration is reasonable.
After drying, more than 95% of the iron slag and kaolin are in powder form, the fineness is 80 μ m, and the sieve residue is 20%; the particle size of some large materials is 20 mm ~ 35 mm. The fineness of the feed material is much smaller than that designed by the ball mill manufacturer.
|Grinding Media||First Cabin||Ф80 mm||3||High Chrome|
|Ф70 mm||5||High Chrome|
|Ф60 mm||4||High Chrome|
|Ф50 mm||2||High Chrome|
|Grinding Media||Second Cabin||Ф20 mm×20 mm||6||High Chrome|
|Ф16 mm×16 mm||10||High Chrome|
|Ф14 mm×14 mm||5||High Chrome|
The grinding sound of the mill is too clear and harsh. The grinding sound value of the electric ear is 158 dB, which is obviously higher than the normal 120 dB standard. It is fully explained that the mill load is too small, the feed quantity is too small, and the steel ball impacts the liner for a long time, resulting in fracture.
Based on the above analysis, the unreasonable grading of steel ball is the fundamental reason for the over grinding of the ball mill. Therefore, the steel ball gradation is adjusted, as shown in Table 2. At the same time, the feed rate was increased according to the grinding sound and grinding fineness. After adjustment, not only the per hour output increased to 20 ~ 25 t / h, but also the mill liner was not damaged frequently.
|Grinding Media||First Cabin||Ф60 mm||3||High Chrome|
|Ф50 mm||5||High Chrome|
|Ф40 mm||4||High Chrome|
|Ф30 mm||2||High Chrome|
|Grinding Media||Second Cabin||Ф20 mm×20 mm||6||High Chrome|
|Ф16 mm×16 mm||10||High Chrome|
|Ф14 mm×14 mm||5||High Chrome|
In the initial stage, the owner only provided the chemical composition and moisture content of the material but did not give the particle size of the material. According to the conventional data, the ball mill manufacturer designs the grading of the grinding body, and the mill liner is purchased by the general contractor. When finding out the causes, the general contractor failed to analyze the problems systematically and took it for granted that the quality of the lining plate was unqualified, and the change of raw materials was ignored. It was necessary to adjust the gradation and feed rate, and the effect was good after treatment.
Φ6.0m x 3.0m SAG Mill and Φ7.3m x 4.27m Ball Mill Mill Liners Redesign
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 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 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.