The crushing process generally includes crushing, pre-screening and screening of the screening operations, and if necessary, washing or pre-selection operations. A crushing operation and a screening operation form a crushing section, and each crushing section combines to form a crushing and screening process. Therefore, the crushing and screening process needs to solve the problems of the number of broken sections, whether to apply pre-screening or inspection screening, and washing and pre-selection.
Determination of the number of broken sections
The task of crushing and screening operations is to provide suitable ore-feeding grain size for grinding operations; or to provide suitable grain size for sorting, smelting, construction, etc. directly. Therefore, the number of crushing stages depends mainly on the maximum particle size of the ore and the particle size of the crushed final product, that is, depending on the required total crushing ratio. The maximum grain size of the ore is related to the mine size, mining method and scraping equipment, see Table 7-3-2. At the time of design, the two majors should jointly propose the granularity that is considered reasonable. The particle size of the final product to be crushed depends on the application. Refer to Table 7 -3-3 and Table 7-3-4.
Table 7-3-2 shows that the maximum ore size range typically supplied mine beneficiation plant is 200-1400mm, to a particle size range of less than 20-10mm mine mill according to a suitable, conventional crushing process for a range of total reduction ratios of from 10 to 140 ,which is:
And various crusher ratio in a range of different operating conditions the maximum of only 8 to 40, the metal mine crusher used only 4 to 8 [Table 7-3-5]. It can be seen that even if the minimum total crushing ratio is 10, it is not possible to use only one crushing process. Therefore, the total crushing ratio should be divided into two or three stages according to the nature of the ore and the performance of the crusher. The total crushing ratio is equal to the product of the crushing ratio of each section. example
B Pre-screening and screening application conditions for screening
The basic form of the possible unit flow for the crushing process is shown in Figure 7-3-1. In the figure, [2] only the crushing operation, (b) consists of pre-screening and crushing operations, (c) consists of inspection screening and crushing operations; (d) and [e] consist of pre-screening and inspection screening. (a) [b] type is called open crushing process, (c) (d) (e) is closed circuit crushing process. The process can be arbitrarily combined to produce two-stage open and closed crushing process and three-stage open and closed crushing. Process.
Figure 7-3-1 Unit crushing flowchart
Pre-screening can be used to pre-screen fine particles, which can prevent the ore from being crushed and can increase the crusher's production capacity. When dealing with medium-fragile and brittle ore, it is suitable to use pre-screening because of the high fine-grain content in the ore; when the ore contains more mud and water (water content is about 30 ~ 50), Pre-screening plays a role in preventing the clogging of the crusher. However, pre-screening requires an increase in plant height and infrastructure investment. Therefore, when the production capacity of the coarse and medium crushers is sufficient, no pre-screening may be provided; When the crusher is used to fill the mine, it is generally not pre-screened.
The purpose of screening is to control the particle size of the crushed product and to fully utilize the crusher's production capacity. In addition, there are too large particles in the ore discharge products of various crushers that are larger than the discharge port, and the content thereof is relatively high. In order to achieve the particle size requirement of the crushed final product, it is necessary to set up the inspection sieve and the crusher to form a closed circuit. The excessive particle content (β) and the relatively large particle size Z (ratio of the maximum size of the ore discharge to the size of the discharge port) of various crushers are shown in Table 7-3-6.
For large-scale concentrating plants, sometimes it is not necessary to check the sieving, but the particle size of the finely divided product is relaxed to 25 ~ 30mm, and the product is fed into the rod mill, which is equivalent to adding a rod mill as a fine four-stage open-circuit crushing process.
Application conditions of C washing operation
When the ore contains more mud (>6%) and water (>5%), it is easy to block the silo, funnel and crushing and screening equipment . In order to make the equipment operate normally, the washing operation should be considered; The sorting effect is generally required to be washed before hand selection, photoelectric selection, heavy medium dressing, etc. In addition, some ores, such as gold deposits, need to be screened before sorting, and it is a very important preparation operation; the deposition type iron ore and manganese weathering sedimentary rock, calcium phosphate, washing is the primary means of dressing, after washing off the mud, to obtain useful minerals enriched product passing.
The choice of washing method is related to the type and proportion of clay contained in the ore and its plasticity, swelling and permeability. Refer to Table 7-3-7 for classification of ore washability.
It can be seen from Table 7-3-7 that the clay is classified into three types: easy washable, medium washable and difficult to wash. The design should be combined with the deposit conditions, mineral composition, physical properties of the ore and Washability, reference to domestic and foreign related practices to rationally choose washing methods and washing equipment.
After the ore has been washed, in addition to the washed ore, there is still a need for treatment. Due to the different nature of the mud mine and the sand mine, the slime after washing is generally treated separately, which can improve the selection effect. However, for smaller concentrators, the concentrator with less mud can combine the mud and sand mines.
Due to the complicated process, difficulty in management and increase of capital investment due to the use of washing operations, necessary tests should be carried out before design and comparison of the schemes can be carried out to determine whether or not to use washing. In addition to the washing program, the medium-shredded heavy-duty vibrating screen can be used to screen the powder ore directly into the powder ore bin, or the self-grinding or semi-self-grinding scheme can be adopted to make the optimal decision after comparison.
(2) Calculation of crushing and screening process
The purpose of the crushing and screening process calculation is to determine the absolute ore (ie, yield qi) and relative ore (ie, yield γ1) of each crushed and sieved product. Sometimes it is necessary to determine the particle size and particle size of the crushing and screening process. Composition, providing a basis for equipment selection.
In the process calculation, the principle of ignoring a small amount of mechanical loss and other losses, following the amount of ore entering each operation and the amount of ore discharged from each operation are equal, and qi and γ1 are obtained according to the established equilibrium equation.
A process calculation required raw data
The calculation of the crushing and screening process requires the following raw materials: the production capacity of the ore dressing plant (or crushing and screening plant) according to the original ore; the physical properties of the ore, mainly the crushability (or hardness) of the ore, the loose density, and the moisture content of the mud. Etc.; ore size characteristics; particle size characteristics of the crusher products; maximum particle size of the ore and the maximum particle size of the final product; screening efficiency of each segment of the screening operation.
The particle size characteristics of the raw ore and the crusher of each section can be directly determined by industrial tests, or the actual particle size characteristic curve of the concentrator of the treated ore can be borrowed, or the typical particle size characteristic curve can be used, as shown in Fig. 7 - 3 - 2, 7 - 3 - 3, 7 - 3 - 4, 7 - 3 - 5 are shown.
The screening efficiency of each screening operation shall be reasonably determined based on actual data. The screening efficiency of the pre-screening of the coarse and medium crushing pre-screening is generally 50% to 60%; the screening efficiency of the medium and fine crushing pre-screening and screening screening vibrating screen is 80%~ 85%. The correct selection of screening efficiency and mesh size has a great influence on the production capacity of the sieve. The mesh size and mesh shape are related to the shape of the material. The pre-screening mesh size is generally selected between the crusher discharge port and the maximum particle size of the crushed product, but the fixed bar screen mesh hole cannot be less than 50 mm. If the sieve hole is square hole, it is generally 1.2 times the maximum particle size [dmax] of the crushed product. At this time, the crusher discharge port is generally not greater than 0.8 dmax, otherwise, the closed loop amount will be increased.
B Process calculation steps
(1) Determine the working system and calculate the hourly production capacity of the crushing workshop;
(2) Calculate the total crushing ratio and the crushing ratio of the sub-equipment;
(3) Calculating the maximum particle size of each segment of the broken product;
(4) Calculate the width of the discharge port of each section of the crusher [b] Calculate the discharge port of the open crusher according to bdmax/Z, as described above for the closed circuit breaker;
(5) determining the mesh size and screening efficiency of each section of the sieve;
(6) Calculating the ore content and yield of each product;
(7) Flow chart for drawing quantities.
C unit unit flow calculation method (see Table 7-3-8)
D crushing and screening process calculation example
The crushing and screening process is developed and calculated according to the following conditions. Original conditions containing copper pyrite processing
The stone ore dressing plant has a treatment capacity of 1.32 Mt/a according to the original ore. The maximum grain size of the ore mine is 1000mm. The ore loose density is 1.8 t/m3, and the ore has a hardness of 8~10. It is a medium hard ore; raw ore and broken. The particle size characteristics of the machine product are based on a typical particle size characteristic curve; a conventional grinding process is required.
(1) Determining the working system Calculating the production capacity of the crushing workshop The crushing workshop is consistent with the mining work system. The continuous working system is adopted, and the annual working rate is 365 days, and the equipment operating rate is 68%. Therefore, the annual equipment operation is 330d, 3 shifts per day, 6 hours per shift, so the crushing workshop production capacity is:
(2) Calculate the total crushing ratio and distribute the crushing ratio of each section. Since the crushed product is fed into the ball mill, it is determined that the final crushed product has a particle size of 12 mm.
Total crushing ratio:
According to the total crushing ratio, a three-stage closed circuit (bbd) is used, as shown in Fig. 7-3-6. And preliminary drafting, the first section selects the jaw crusher , the second section uses the standard cone crusher, and the third section uses the short cone cone crusher. The split ratios of each section are assigned as follows:
(3) Calculate the particle size of each segment of the broken product.
(4) Calculate the width of the discharge port of each section of the crusher (b) The discharge port of the open crusher should ensure that the maximum grain size of the discharge port does not exceed the product grain size required in this paragraph, calculated as b=dmax/Z. The width of the discharge port of the closed crusher is calculated as b=0.8d11. The Z value is taken according to Table 7-3-6.
(5) Determine the mesh size and screening efficiency of each section of the sieve. The first and second sections are pre-screened using a rod sieve, and the sieve size is a1=180mm, a2=50mm, and the screening efficiency is E1. =E2=60%. The third stage pre-screening and inspection screening adopts a vibrating screen, the sieve hole a3 = 1.2d11 = 14.4mm (take 15), and the screening efficiency E3 = 80%.
(6) Calculate the ore and yield of each product.
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