Just as we say that the sieve is used as the main equipment when crushing, the grinding is also the same. The grading equipment associated with it is particularly important in the process of grinding. The working efficiency of the grading equipment directly affects the efficiency and indicators of grinding, but Different from crushing and sieving, the ability of crushing and screening in general design will be too large, even exceeding 50% of the capacity is a reasonable range, and the grinding classification is relatively accurate, and it is necessary to make strict calculation according to the characteristics of ore and the amount of processing. . So how do you choose a grinding and grading equipment?
There are many types of grinding equipment . According to the grinding medium, it can be divided into self-grinding machine , ball mill , rod mill and gravel mill. According to the mining method, it can be divided into lattice mill, overflow mill and peripheral mine, and of course More popular, vertical mixing mill for secondary fine grinding. The grading equipment used in conjunction with the mill mainly includes a linear sieve, a high frequency sieve, a classifier, a cyclone, and the like.
At present, the most used in the gold selection plant is the ball mill with classifier and cyclone. The coarse concentrate and the medium mine are re-grinded with the use of vertical mixing mill. With the continuous expansion of the scale of the plant, there are several large domestic ones. Gold companies also use self-grinding mills as a section of grinding, but self-grinding mills are intermediate equipment between crushing and grinding, so I won't go into details here.
The scale of the early gold plant was basically below 500t/d, almost all of them were matched with the classifier. It is worth noting that the ball mill is a standard equipment. Each manufacturer has a uniform model, although the appearance and foundation are slightly different, and the classifier is Undertake the role of inspection and grading, and also undertake the role of coarse sand lifting, simply speaking, it has the dual functions of sieve and conveyor belt, so the diameter (processing capacity) of the classifier is a standard parameter, and its length is based on grinding. The length of the machine is determined, and the feeding mode of the mill (drum feeding, snail feeding) is different, and the lifting height requirements of the classifier are also different. At the same time, the maximum installation angle of the classifier is also limited. Therefore, the length of the classifier needs to be calculated in detail according to various factors, and finally the order specification is issued to the equipment manufacturer. In addition, the head discharge port of the classifier and the feed port of the overflow end are all opened after the on-site installation, and there is no standard position. It is worth mentioning that both the ball mill and the classifier impeller are rotating, and the direction of rotation must be opposite, and the same and opposite are wrong. For different grinding fineness requirements, the selection of classifiers is also different. The classifiers are divided into two types: high-grade classifiers and sunken classifiers. For grinding fineness of -0.074mm, which accounts for less than 70%, We choose the sorghum classifier, and for the case where the fineness requirement is above 70%, we choose the sinking classifier, but the sunken classifier configuration is more difficult, so it is rare in the general plant selection. The two sections of the grinding are graded, and the second section is replaced by a cyclone.
Drum type feeding method
Snail-shaped feeding method
Then why do small-scale plants rarely use cyclones as a grading device? In fact, this principle is very simple. Although most of the particles in the ball mill are below 0.5mm, there are still a small amount of coarse particles above 10mm, and the small diameter. The corresponding sand sluice nozzle of the cyclone is also small, so it is extremely unstable to select a cyclone as a grading device of less than 300t/d, but the maximum processing capacity of the classifier is about 1500t/d (3m). Double helix classifier), and the processing capacity of the mill may far exceed this level, so when the single series of work is large, the cyclone must be selected as the classifying device. Of course, in order to ensure the continuity of production, the choice of cyclone is generally considered to be standby, that is, a cyclone group usually has 1-2 heads that are not in working condition and temporarily open when parts need to be replaced. In addition to the influence of the ore pressure and concentration on the index of the cyclone classification, the structure of the cyclone itself is also very important. Generally speaking, the smaller the cone angle of the cyclone, the higher the fineness of the classification, and vice versa. It is thick, so the choice of cyclone in a grade of grinding and regrind is different and needs careful consideration.
For the choice of lattice type or overflow ball mill, it is recommended in the design manual. The grinding fineness requirement is to select the lattice type ball mill when -0.074mm accounts for 70% or less, and the overflow type ball mill when more than 70%. Professor Hu Yongping from Beijing University of Science and Technology, a famous mineral processing expert in China, once said that in the case of 1000t/d, it is reasonable to choose a single mill to reach -0.074mm and 70% or more. When processing at 1000t/d or above, In order to make the grinding fineness reach -0.074mm and account for more than 70%, two-stage grinding should be used, that is, the lattice grinding machine and the overflow grinding machine are used together. However, with the development of large-scale equipment, more and more enterprises like to use the overflow ball mill to complete the grinding operation in a section of grinding. This saves the site and reduces the labor intensity, but it is not reasonable in energy consumption. After all, the same type of overflow grinding treatment capacity is only about 90% of the lattice grinding.
Some complex refractory gold mines need to re-grind coarse ore concentrates to obtain higher grades or recovery rates. The working principle of vertical agitator mills determines that the milling effect is better and the higher fineness is obtained. Degree, while its energy consumption is reduced by nearly 60% compared with the horizontal milling machine of the same capacity, it should be the first choice for regrind equipment, but the bottom feeding, the upper overflow has caused the problem of unstable or easy to block the ore, so currently In the gold enterprises, there is no good promotion. The general enterprises are equipped with small overflow mills as regrind equipment.
As a mining powerhouse, China is also at the forefront of the world in the manufacture of grinding and grading equipment. CITIC Heavy Industry's grinding machinery is the world's number one, and Weihai Haiwang's cyclone has maintained the number one sales volume in the world for many years. For the mineral processing workers, this is something to be proud of and proud of.
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