First, determine the basic principles of the crushing process

The basic purpose of crushing ore is to achieve a certain particle size requirement for ore, raw materials or fuel. In ore dressing , the purpose of crushing ore is: (1) supply the most reasonable ore feeding size such as rod grinding, ball milling, self-grinding, or provide qualified grinding medium for self-grinding and gravel grinding; (2) embedding coarse particles preliminary cloth mineral monomer dissociation, for sorting coarse fraction with a dressing method, such as heavy media option, jigging, magnetic separation, and washing the dry and the like; (3) the high-grade iron ore reaches certain requirements Granularity for direct smelting and the like.

Different purposes require different particle sizes, and thus there are many types of crushing processes.

(1) Fragmentation section

The crushing section is the most basic unit of the crushing process. Different crushing stages and different combinations of crusher and sieve have different crushing processes.

The crushing section is composed of the crushing operation entered by the screening operation and the product on the screen. Individual crushing sections may not include screening operations or both screening operations.

The basic form of the crushing section is as shown in Figure 3-1, (a) is the crushing section of a single crushing operation; (b) is the crushing section with pre-screening operation; (c) is marked with inspection The crushing section of the operation; (d) and (e) are crushing sections with pre-screening and inspection screening operations, the only difference being that the former is pre-screened and the screening is carried out on different sieves, the latter It is carried out on the same sieve, so the type (e) can be regarded as a change of the type (d). Therefore, the fracture section actually has only four forms.

The two or more stages of the crushing process are various combinations of forms of different crushing sections, so there are many possible solutions. However, a reasonable crushing process can be determined based on the number of crushing stages required, as well as the necessity of applying pre-screening and screening.

(2) Determination of the number of broken sections

The number of crushing stages required depends on the maximum particle size of the ore, the required final crushed product size, and the crushing ratio that can be achieved in each crushing section, that is, depending on the required total crushing ratio and the crushing ratio of each section. The maximum grain size in the ore is related to the occurrence conditions of the ore, the scale of the mine, the mining method, and the transportation and handling methods of the ore. When open-pit mining, it depends mainly on the size of the mine and the volume of the loading shovel, generally 500~1300 mm. When mining underground, it depends mainly on the mine size and mining method, generally 300~600 mm.

The size of the broken final product varies depending on the purpose of the crush. For example, the feeding requirements of the self-grinding machine !%% & $%% mm, the particle size of the iron-rich ore smelting in the blast furnace is divided into two levels of 500~1300 mm, and the reasonable feeding size of the rod mill is 300~600 mm. The ball mill has a reasonable ore size of 300~500 mm. The reasonable final crushed product size depends mainly on the requirements of the process and the results of technical and economic comparisons.

When determining the optimum particle size of the ball mill (ie, the final crushed product size), the total technical and economic effects of crushing and grinding should be considered. The larger the particle size of the crushed product, the higher the crusher's production capacity and the lower the crushing cost; however, the grinding mill's production capacity will be reduced and the grinding cost will increase. On the contrary, the smaller the particle size of the crushed ore, the smaller the production capacity of the crusher and the higher the cost of crushing; but the production capacity of the grinding machine will increase and the grinding cost can be reduced. Therefore, the crushing and grinding should be considered comprehensively, and the particle size which minimizes the total cost should be selected as the suitable crushing final product particle size. Practice has proved that the most suitable ore feeding size of the grinding machine is 10~25 mm. As the production scale of the concentrator is larger, the grain size of the mill is reduced, and the economic effect is greater.

On the other hand, when determining the final crushed product particle size, it must be considered that the actual crushed product particle size that can be achieved by the crusher to be selected must not exceed the allowable discharge port adjustment range, so that a smaller crush can be obtained with the permission of the equipment. Product size.

The crushing ratio of each crushing section depends on the type of crusher, the type of crushing section, the hardness of the treated vermiculite, and the like. The crushing that can be achieved by the common crusher is shown in Table 3-1. When the hard ore is treated, the crushing ratio is small; when the soft ore is processed, the crushing ratio is large.

(3) Determination of the application of pre-screening and inspection screening

The pre-screening is to pre-screen the qualified grain size before the ore enters the crushing section, which can reduce the amount of minerals entering the crusher and increase the production capacity of the crusher; at the same time, it can prevent over-grinding of the rich ore. When dealing with ore with higher water content and more fine ore, the wet mineral powder will block the crushing chamber of the crusher and significantly reduce the crusher's production capacity. The use of pre-screening to remove wet and fine mineral powder can cause more normal working conditions for the crusher. Therefore, the application of the pre-screening is mainly determined based on the content of the fine-grained grade in the ore (less than the fraction of the width of the discharge port of the crusher). The higher the fine fraction content, the more advantageous it is to use pre-screening. Studies have shown that technically and economically, pre-screening favorable ore is used, wherein the limit content of fine-grain grade is related to the crushing ratio of the crusher, and the relationship is shown in Table 3-2. When the ore size characteristics are straight, under the conditions of various crushing ratios, the content of the fine fraction exceeds the above limit value (that is, it is advantageous to use the limit content of the pre-screening). Also shown in Table 3-2.

From this, it can be seen that when the ore size characteristic is a straight line, it is always advantageous to use pre-screening regardless of the crushing ratio. In most cases, the grain size characteristics of the ore are concave, so pre-screening before crushing is economically cost-effective. However, due to the need to increase the height of the plant by pre-screening, when the production capacity of the coarse crusher is sufficient, or when the direct filling is used, the pre-screening may not be provided. The fine fraction content in the second crushing section and the third crushing section is mainly determined by the grain size characteristics of the tantalum ore in the previous section of the crusher. According to the actual measurement, the grain size characteristic curves of various coarse crushers and medium crushers are mostly concave, that is to say, the fine particles are mostly, so the second crushing section and the third crushing section are pre-screened. necessary. Only when there is a surplus in the production capacity of the selected crusher, it is not necessary to pre-screen before the crushing.

The purpose of screening is to control the particle size of the crushed product and to maximize the production capacity of the crusher. Because some crushing products of various crushers have a coarse fraction which is larger than the width of the discharge port, for example, when the short-head cone crusher breaks the medium-breakable ore, the product is larger than the discharge port width. The particle size is 60%, the maximum particle size is 2.2~2.7 times of the discharge port, and even worse when crushing the difficult ore. The content of coarse fraction (greater than the size of the discharge port) and the maximum relative particle size (ie the ratio of the maximum particle to the size of the discharge port) in the crushed products of various crushers are shown in Table (3-3).

After inspection and screening, the unqualified grain size is returned to the crusher, just as the closed loop of the grinding machine and the classifier is beneficial to improve the grinding efficiency. The inspection of the screening can improve the production capacity of the crusher. However, the use of inspection screening will increase the investment and complicate the equipment configuration of the crushing workshop. Therefore, inspection and screening are generally used only in the last crushing section, and combined with the pre-screening to form a pre-inspection screening closed loop.

This leads to two conclusions: (1) Pre-screening is necessary in each crushing section; inspection screening is generally only used in the last crushing section. (2) The number of broken sections is usually 2 to 3 sections.

Second, the common crushing process

(1) Two-stage crushing process

The two-stage crushing process has two types of open circuit and two sections and one closed circuit, as shown in Figure 3-2.

The crushed product obtained by the two-stage open crushing process has a coarse particle size and is only used in a simple small ore dressing plant or an industrial test plant. The first stage may not be pre-screened. In this case, when the mud and water in the ore are high, a small concentrator can also be used in order to make the production work normally.

The small ore dressing plant handles the ore mining with small granularity in the underground mining, and the second section adopts the two-stage closed-circuit crushing process when the relatively large crushing impact crusher is used.

(2) Three-stage crushing process

The basic types of the three-stage crushing process are: three-stage open circuit and three-stage one closed circuit, as shown in Figure 3-3. The three-stage and one-closed crushing process has been widely used as a preparation for grinding. Whether it is underground or open-pit mining ore, as long as the raw ore is not high in mud, it can be effectively adapted. Therefore, concentrators of different scales can be used.

Compared with the three-stage and one-closed process, the three-stage open-circuit crushing process has a coarser particle size, but it can simplify the equipment configuration of the crushing plant and save capital investment. Therefore, this process can be used when the grain size of the ore dressing is not strict and the rough grinding of the grinding section is carried out by rod grinding, and when the muddy ore having a high water content is treated and subject to terrain limitation. When dealing with ore with a high moisture content, it is not as easy to block the screen and the crushing chamber as the three-stage closed circuit process. The three-stage open-circuit and rod-grinding crushing process eliminates the need for complex closed-circuit screening and return product transportation operations; and the rod mill is less affected by the ore-grain size change, and the ore-mining particle size is uniform, which can ensure the lower-stage grinding operation. The operation is stable; at the same time, the production process produces less dust, which can improve the sanitary conditions. When the required mineral products coarser grinding (reselection plant) or brittle process (tungsten, tin ore), when a large proportion (lead ore) minerals, this process may be employed. Only in dealing with extremely hard ore and very large-scale concentrating plants, in order to reduce the crushing ratio of each section or increase the total crushing ratio, the four-stage crushing process is considered.
(3) The crushing process with washing operation

When the ore contains more than 5-10% of mud (-3 mm) and the water content is more than 5~8%, the fine-grained grade will bond into a mass, which will deteriorate the production conditions of the crushing process, such as causing the crushing chamber of the crusher. The screen hole of the screening machine is clogged, equipment accidents occur, and the storage and transportation equipment is blocked and leaked. In severe cases, production cannot be carried out. At this point, the washing facility should be added to the crushing process. Increasing the washing facilities will not only fully utilize the potential of the equipment, but also make the production work normally. Improving labor intensity, but also improve the recovery of useful metals, expanded use of resources.

The washing operation is generally set before and after coarse crushing, depending on factors such as the ore size, water content and structure of the washing equipment. Commonly used washing equipments include washing sieves (grid sieves, vibrating screens, cylindrical sieves), tank washing machines, cylinder washing machines, and the like. The net mine after washing, some need to be broken, and some can be used as qualified grain grade. The washed mud can be discarded if the grade is close to the tailings grade; if the grade is close to the original grade, it needs to be sorted. Due to the difference in the nature of the ore, the way of washing and the treatment of fine mud are different, and the process is diverse. Skarn ore deposit copper, 6 to 11% clay, 8% water content, which washing procedure shown in Figure 3-4, a three-stage crushing process is closed. In order to enable the crusher to be safely and normally produced, the first washing is carried out on a sieve, and the product is sieved for coarse crushing, and the sieved product is washed into a vibrating screen. After the second washing, the product on the sieve enters the medium crushing. The sieved product is graded and delimed into the spiral classifier. The classified sand returning is combined with the final crushed product. The graded overflow is buffered by the thickener, and after dehydration, it is separately fine. Mud grinding, flotation.

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