Process characteristics of crushing and grinding
The crushed material is common to see the phenomenon, but the crushing work beneficiation plant must analyze the following matters, in order to understand its purpose and process characteristics.
First, dissociation and over-grinding
The results of the mineral phase identification indicate that the most useful minerals and gangues in the ore are closely connected together. If you do not dissociate them first, any beneficiation method will not be able to enrich them. After the ore is broken, as the particle size becomes finer and the interface between different minerals is cracked, the various minerals that have been born together have a certain degree of separation. In the broken ore, some particles only contain A kind of mineral, called monomer dissociation particles; other particles are still born of several minerals, called continuous grains. The degree of dissociation of a mineral is the ratio of the number of monomer dissociated particles of the mineral to the sum of the number of consecutive particles containing the mineral and the number of monomer dissociated particles of the mineral, expressed as a percentage. The inspection of mineral processing products indicates that the concentrate grade is low, the tailings grade is high and the medium ore yield is large, which is often caused by insufficient dissociation. Therefore, crushing and grinding are indispensable tasks before the selection. It prepares the selected materials with sufficient dissociation of useful minerals for the sorting operation. As far as the mineral structure is concerned, except for a few extremely coarse-grained ores, only a large amount of monomer dissociation particles are obtained by using the crushed ore, and generally it is necessary to undergo grinding to obtain a sufficiently high degree of dissociation. The role of crushing ore is usually to prepare the feed for grinding, and the grinding is the final step to achieve full dissociation.
The grinding product is too thick, and the concentrate grade and recovery rate are poor due to insufficient dissociation. If it is too fine, it is not necessary, and it even causes harm. Because the broken ore will produce fine particles that are difficult to select. If there are more such particles, which is unfavorable for production, it is that the ore is excessively crushed. The hazards of over-grinding are: more difficult to control fine particles, poor grade and recovery rate, increased wear of the machine, reduced processing capacity of the equipment, and increased unprofitable power consumption of broken ore. The occurrence of over-grinding is serious in the grinding process, but it has appeared since the crushing. Therefore, when starting to break the ore, it is necessary to prevent over-crushing and to abide by the "no unnecessary breaking" rule. Processing brittle tungsten ore, tin ore gravity concentration plant, but must pay attention to this issue. The reason for the smashing is usually:
1. The grinding degree exceeds the optimum particle size.
2. The equipment used is not suitable for the nature of the ore, and it is easy to mud.
3. Operating conditions are not good.
4. The crushing and grinding process is unreasonable.
For each specific situation, a thorough examination is required to determine the cause of the smash.
Second, the crushing ratio and broken in stages
During the crushing and grinding process, the particle size of the raw material is reduced. The crushing ratio is the ratio of the original material particle size to the product particle size. It indicates the multiple of the particle size reduction of the raw material after crushing. Since the power consumption and productivity of the crusher and the grinding machine are related to the crushing ratio, it is a measure. A quantitative indicator of the crushing and grinding process.
The calculation method of the crushing ratio has the following types, each having a certain purpose:
1. Determine the ratio of the maximum particle size of the material before crushing to the maximum particle size after crushing.
Where i is the breaking ratio;
Maximum D - diameter of the largest block of material before crushing, mm;
d Minimum - Maximum tranches after crushed material diameter, mm; [Next]
The maximum block diameter can be found from the cumulative percentage curve on the screen. The particle size corresponding to 5% or 20% in the curve is the diameter of the largest block, which is the width of the square mesh through which 95% or 80% of the mineral material can pass. Many experiences have shown that the largest block in the material accounts for about 5% or 20%. Due to the different technical habits of different countries, the width of the mesh hole that 80% of the materials taken by the United Kingdom and the United States can pass is the diameter of the largest block. % The width of the mesh that can pass, as in the Soviet Union. This calculation is commonly used in design because the width of the ore feeder of the crusher is chosen according to the maximum block diameter.
2. Determine the ratio of the effective width of the ore feeder to the width of the discharge port.
Where B is the width of the ore feeder of the crusher, in millimeters;
S — The width of the discharge opening of the crusher, in millimeters.
Because the diameter of the largest nugget fed into the crusher should be about 15% smaller than the width of the crusher, it can be clamped by the crusher, so 0.85B in the above formula is the effective width of the miner's ore feeder. . For the coarse crusher, the maximum width of the discharge port is taken; for the center and fine crusher, the minimum width is taken. This kind of calculation is very useful in production, because it is impossible to perform screening analysis on a large number of mineral materials frequently in production. However, as long as the width of the ore feeder and the discharge port of the crusher is known, it can be estimated by the above formula. The crushing ratio is similar to the task of the crusher.
3. Determine with average granularity
Where D average - the average diameter of the material before crushing, mm;
d average - the average diameter of the broken material, in millimeters.
The materials before and after the crushing are statistical aggregates composed of several groups of particles, and only the average diameter can represent them. The crushing ratio calculated by this method can more accurately reflect the degree of fracture, so it is used in theoretical research.
In recent years, the ore size of the ore is very large. The largest block in the open pit can reach 1200 to 1500 mm, and the largest block in the pit is also about 200-600 mm. The particle size is usually very fine, usually below 0.1 mm. For example, the original ore of 1500 mm in diameter is crushed to an input particle size of 0.1 mm, and the crushing ratio is as high as 15,000. The crusher and grinding machine currently used are due to the structural relationship. Can work effectively within a certain range of crushing ratios. Therefore, it is impossible to break the coarse aggregates into very fine particles at a time, usually by sequentially connecting the crusher and the grinding machine suitable for processing various particle sizes in series to form a crushing and grinding process to ensure the required high crushing ratio. . In the process, each crushing device only fulfills part of the entire process, forming a crushing and grinding stage. The “segment†on the beneficiation is divided according to the particle size to be treated. From the grain size of the ore and product, the crushing and grinding stages are roughly divided into stages. The maximum block diameter of the product is the largest block diameter D (maximum) mm max (mm) )
Crushed mine: coarse crush 1500~300 350~100
Medium broken 350~100 100~40
Finely broken 100~40 30~5
Grinding: a section of grinding 1~0.3
Two-stage grinding 0.1~0.07 (or finer)
In the modern large-scale concentrating plant, it is useful to break the four sections. The first two sections are coarsely divided. The third section is medium-sized and the fourth section is finely divided. A few concentrators are useful for three-stage grinding. The above division method is approximate and only roughly explains the situation.
The crushing ratio of the entire crushing and grinding process is called the total crushing ratio (i), and the crushing ratio (i 1 , i 2 ... i n ) of each stage is called a partial crushing ratio. Let D is the maximum diameter of the largest block ore, crushed D is the final product in the maximum particle diameter, d 1, d 2 ...... d n-1, d n is the first section, second section ...... n-th stage crushing product Maximum particle diameter, then,
It can be seen that the purpose of crushing and grinding is to produce the selected materials which are fully dissociated but lightly pulverized. Its process feature is that several pieces of suitable equipment are connected in series to gradually break the ore fraction into the specified inclusion size.
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