Liners play a role of protecting the cylinder and transferring energy with the aim of crushing minerals in grinding mill. Based on this, the design and manufacture of liners should be capable of protecting the mill cylinder from breaking and transferring energy efficiently. Those liners with reasonable design structure, correct material selection and rational manufacturing process can achieve the target of safe use,wear resistance and impact resistance.The four key issues in the design and manufacture of mill liners are to understand attributes and parameters of minerals deeply, to design superior wear-resistance materials, to design more reasonable manufacturing process and to calculate more accurate structural parameters.Only the design of structure, material and process for liners achieve not only the orientation goal but also the qualitative goal, can the liners be in a good state. Deeply understand the mechanism of minerals and materials, improve the accuracy of process parameters, avoid the quality shortcomings in the manufacturing process, and take good charge of each link.
SAG/AG Mill Liner Comprehensive Analysis On Design And Manufacture
The grinding process, mill specifications and its types are all determined by mineral attributes and customer’s requirements for output. As a medium of transmitting energy, liner affects the efficiency and performance of crushing and grinding. Therefore, it is significantly important to design reasonable structure for liners with the unreasonable one will cause a series of problems including facture, life reduction and failure to meet expected output etc.
✔ Master mineral properties
We have carried out experimental analysis of minerals when selecting grinding mill. Based on the test report of beneficiation process and minerals’ laboratory analysis, as well as the simulation calculation results from JKSimMet, we have mastered JK parameters including A×b, ta, BWi, Ai etc., and understood the minerals properties, providing a basis for the design of liner structure.
✔ Structural design of liners
According to the requirements of mineral and grinding millassembly, the size of energy that liners needs to transfer is determined, and the structure of liner board is calculated. DEM and Mill Traj are adopted to simulate the structure of liners. Most of the traditional design methods are no more than comparison, borrowing without careful design, and the parameters determined by the simulation of DEM are used as the basis of the design. The design of liners cannot achieve the most ideal state at one time. The user will adjust the influence of factors such as grinding medium filling according to the change of output. The design of liners structure needs to be followed up, analyzed and summarized for a certain period of time so as to gradually perfect to achieve the ideal state.
Ideal design structure consists of theoretical calculation, verification of grinding mill software, practical experience reference and follow-up verification summary.
When it comes to material selection of liners, reasonable matrix structure and strengthening mechanism of structure are selected according to the type of grinding mill, mineral properties and the properties of grinding medium. The expected micro-structure and comprehensive properties are fulfilled by control of phase transformation process through heat treatment. Therefore，the expected results are achieved. The basic consideration gives priority to the strength and toughness of the material when selecting liners material for grinding mill in order to avoid the liners breaking in use, and the wear resistance of the material is secondly considered. When collision of waterfall load takes place in the large diameter AG and SAG mill, the liners will suffer great impaction and the risk of fracture increases. Therefore, the material selection of liners must be in line with the actual conditions of the grinding mill working conditions, and the matching of strength and toughness of material is a basic criterion.
The grinding mill does not add grinding body, and the material subject less impact to the liners during the operation of the AG mill. Considering that, material of martensitic CrMo alloy cast iron with hardness higher than HRC50 and superior wear resistance is selected, which can improve the service life of liners and reduce downtime. For those large SAG mill, a small amount of abrasive is added to increase productivity, which leads to greater damage to the liners and a risk of fracture. Therefore, pearlite CrMo alloy steel is the preferred material for liners of large AG mill, which has excellent matching of strength and toughness, offering lining plate with strong impact resistance and good wear resistance.
SAG mill mainly conduct production and operation by utilizing the principle of impact crushing of abrasive to minerals. The filling rate of the grinding body in the grinding mill is generally in the range of 8-15%. Especially for iron ore where the minerals are difficult to crush，so the diameter of the filling grinding body reaches 120 or larger. Under this condition, the liners suffer strong impaction from the abrasive body，what’s more ,the direct impact of the abrasive body on the liners will cause the liners to break if the design of the liners is unreasonable. Therefore, pearlite CrMo alloy steel is also needed for SAG mill liners.
The ball mill mainly grinds the material crushed by crusher, AG mill or SAG mill. Generally, the feed size is less than 12 mm, and the filling diameter of the grinding body is less than 60 mm. Meanwhile, the impact of the grinding body on the liner is small, and the hardness of the liners directly affects the use effect. The martensitic CrMo alloy cast iron, which has hardness close to that of the abrasive body,good friction pairs as well as long service life, meets the requirement of this working condition. It is relatively safe to adopt pearlite CrMo alloy steel for ball mills with D7 m or under special working conditions.
Rubber liners has been used in ball mill for a long time. Some cases of rubber and wear-resistant steel composite liners used in SAG mill also exist. However, rubber or composite liners has strict requirements on working conditions. The amount of ore treated by the mill will be affected, so the application scope is small and cannot be widely promoted due to the characteristics of rubber including absorbing impact energy, easy scratch and fatigue. However, it is a successful case where some liners not directly involved in grinding at inner ring of the inlet and outlet of feed end of large grinding mill are transformed into rubber liners. In addition, the rubber liner saves electricity, although there is no data to support this view.
The liners of self-grinding and AG mill rarely wears uniformly along the whole length of the cylinder. Moreover, the places where the wear is greatest are usually uncertain. Some are at the feed head, and some are in the middle. This is a systematic problem without rules to follow. Considering what is mentioned above, we shall constantly optimize the structure and adjust the performance of materials in different parts so as to make them have the same life cycle and then achieve the ideal using effect according to the using experience of liners.
The purpose of casting process design is to form dense defect-free castings to eliminate casting defects which result in casting fracture and non-wear resistance. Remove slag, inclusions, gas, sulfur, phosphorus to achieve the correct composition and purity of molten steel; The grain is refined by modifying the molten steel, and the casting defects, temperature field and as-cast microstructure are simulated and analyzed by Procast, so as to eliminate micro-porosity and improve the wear resistance of liners.
Adjust organization and performance structure of castings by reasonable heat treatment process is a powerful match to obtain ideal castings. Meanwhile, select the most appropriate process parameters of heat treatment such as heating temperature, holding time and cooling rate help fulfill the ideal organization and performance.
