grinding unit and steel ball gradingDate: 2019-07-08 Views:
1. Grinding unit grinding system includes open-circuit grinding and closed-circuit grinding system.
The two operation methods are basically similar. Closed-circuit systems are relatively dynamic and complex, but the closed-circuit grinding method is fully applicable to open-circuit grinding. As we all know, there are many factors affecting the quality of mill production, including three major aspects, one is the nature of materials, there are grinding grain size, easy to grind, finished product size, material temperature, moisture, grinding aid, etc.; In terms of parameters, there are ball forging grading, loading, material flow rate in the mill, cooling, ventilation; third, mechanical structure, length to diameter ratio, position, lining form, raft form, boring size, classifier Performance, dust collection, etc.
2. The particle size of the grinding is not as small as possible.
In the actual production, when the average particle size of the grinding mill is reduced to less than 10 mm, the increase in the mill output is not obvious. In the past, everyone thought that the energy required to grind a ton of material was more than 20 times the energy required to break a ton of material. Now it seems that this theory is not completely correct. A mill has two functions, one is crushing and the other is grinding. The reason is that when the grinding material is smaller than a certain particle size, even if the grinding grain size is further reduced, the effect of increasing the yield is not obvious. Especially for closed-circuit systems, the tube mill is set to at least two bins. The 20 times mentioned above refers to the grinding bin, which is broken rather than ground. When the material is smaller than a certain particle size, as long as the grading of a warehouse is reasonable and the warehouse length is in place, the material entering the second warehouse can fully meet the required particle size requirements.
3. Steel ball grading
3.1 Broken bin grades Many cement manufacturers use the formula 28 3√D to determine the maximum ball diameter of a warehouse. Imagine the same grinding machine with Φ3.0m, Φ3.5m, Φ3.8m, Φ4.2m. The diameter of the mill is different, the height of the ball is different, and the potential energy generated is completely different. It can be seen from the test that when a ball of Φ30 mm (Φ70) is freely dropped from a height of 40 cm, its potential energy can completely crush a clinker particle having a diameter of 10 mm (25). Then, how should a level of grading should be determined? According to many years of practical experience of many manufacturers, a warehouse is graded at level 3 or level 2 or even level 1. At present, many manufacturers have a large ball warehouse with at least 4 or more balls, and even have as many as 6 levels. The reason is that large blocks are broken with large balls, and small blocks are broken with small balls. Others believe that the flow rate of a warehouse can be controlled by ball, so that the particle size of the material entering the second bin or the grinding bin can meet the artificial requirements. This is not the case. For example, in the production, the phenomenon of mixing in the warehouse is often encountered. After opening the large ball bin, neither the small ball nor the small forging can be seen. When you take the big ball out of the warehouse one by one, you will find that the ball is at the bottom of the bin and the ball diameter is gradually reduced from top to bottom. It is not difficult to imagine that the vast majority of the balls that are brought to the highest position during operation are the smallest balls. By analogy, most of the largest balls have the lowest height during the grinding process. A Φ50mm ball has a potential energy that is not as good as a Φ30mm ball. However, the weight of a Φ50mm ball is equivalent to two Φ30mm balls, or three Φ25mm balls, or four Φ20mm balls. If a Φ50mm ball is replaced by two Φ30mm balls, or three Φ25mm balls, the surface area of the ball will gradually increase, and the number of impacting materials per unit time and space will increase, and the impact energy will be greatly improved. Thus, it is sufficient to use a ball of Φ30mm and Φ25mm and a part of a ball of Φ20mm in one bin. As for the grading of a warehouse to control the flow rate of the material, or to achieve the grinding effect, the possibility is very small, mainly to control the gradation. In addition, the ball diameter must match the form of the lining: the lifting lining has a high ball, the impact force is large, and the ball diameter can be smaller; for a new lining and an old lining of a warehouse, it is also treated differently. Under the premise of sufficient impact energy, the ball diameter should be the smallest, so as to increase the number of steel balls, so that the number of impacts of the steel balls on the material increases, thereby achieving the purpose of improving the grinding efficiency.
3.2 Grading of the grinding bins It is worthwhile to explore whether the two bins are good or forged. 95% of the cement grinding bins or grinding bins in foreign countries use balls. In fact, it is better to use the ball than to use it. In the grinding process, the ball is point contact and the forging is line contact. In theory, it is better to use the forging ratio ball. However, even if the forging gradation is adjusted to a reasonable state in the system, the holding time will not be too long. Long, the reason is that the forged two ends have a wheel angle, especially the poor quality of the forging, the wheel angle is vulnerable, and the void ratio between forging and forging will change significantly. When the ball is used, the wear changes are small, and after being adjusted to the optimum state, it can be maintained for more than half a month, and the range is wide. It is well known that a reasonable internal flow rate determines a reasonable fineness of grinding, a reasonable grinding fineness determines a reasonable cyclic load, and a reasonable cyclic load determines a reasonable cement particle gradation, and also determines the Taiwanese production. In addition, the second warehouse should maximize the surface area of the ball, so that the surface area per ton of grinding body can reach more than 50m2; the grading of the ball should not exceed three levels, the grading of the ball is too much, the flow rate is difficult to control, affecting the grinding efficiency. .
4. Make up the ball and add the ball
It is very important to make up the ball in the production process. When to make up the ball, there must be a basis and not blind. The simplest method is to analyze and judge the three fineness of grinding, returning and finished products, and sieve the results with three finenesses of 30μm, 45μm, 60μm and 80μm, and analyze the results according to the results. For example, if the 30μm particle content in the grinding is low and the content is 80μm, it means that the flow rate in the mill is too fast, the filling rate of the second bin is low, the filling rate of a bin is too high or the ventilation inside the mill is too large, or the grinding capacity of the Ercang abrasive body. difference. In the daily control process, it is necessary to control the grading relationship of 30μm, 45μm, 60μm and 80μm in the grinding. For closed-circuit grinding systems, if the required particles are not present in the grinding, even if the efficiency of the classifier is high, it is useless. For the general mill, first analyze the results of the 45μm in the grinding, and then observe the particle composition and particle distribution of the grinding sieve, and also observe the particle distribution of the recycled material, because the return material can be regarded as concentrated. The grinding can be seen more intuitively. If the fineness of the grinding is too fine, the flow rate in the grinding is too slow, but the fineness is too fine, and the particle grading is not necessarily reasonable. The amount of replenishment of the abrasive body can generally be determined by the change in the mill current. For a mill, adding one ton of ball to a warehouse is equivalent to increasing the current. Adding one ton of grinding body to the second bin is equivalent to increasing the current. We can summarize it through empirical data. Under normal current conditions, the ratio of the large ball bin to the small ball bin is determined according to the particle distribution of the ground material; under abnormal conditions, the ball is added according to the feeling. If you are not sure when adding the ball, it is best not to add the big ball and the small ball at the same time, first add the small ball; when the small ball or small forging is added, run one or two shifts to see the current and the three fineness changes. In the case, add a big ball from the grinding head. If the mill current is normal, or the change is not large, the flow rate in the mill is too fast, there may be the following reasons:
(1) The load of Ercang is less;
(2) The ball of Ercang is unreasonable, resulting in excessive void ratio between the grinding bodies;
(3) The load of a warehouse is excessive;
(4) The wind speed in the mill is too large;
(5) Excessive amount of grinding aid. If the current of the mill does not change much, but the flow rate of the mill is slow and the output is low, it may be that the load of the second bin is too large, the load of one bin is too small, the wind speed in the mill is too small, and the amount of the grinding aid is less.
5. Loading of the grinding body
In the grinding process, appropriately increasing the filling rate (abrasive load) has a certain effect on increasing the yield, and to some extent, the grinding efficiency of the mill can be improved. However, the filling rate of the grinding body is not as high as possible. Especially for a mill with a smaller diameter, if the filling rate of a warehouse is too large, the potential energy of the large ball in the large ball bin is bound to be lowered. The increase in the loading of the grinding body is sometimes an illusion. It is not necessarily a good thing. It has a great relationship with the working surface of the grinding liner. As the working surface of the liner wears, the loading of the mill will gradually increase. Increase, however, the grinding efficiency may not be improved. In order to maximize the loading of the mill under normal conditions, the following must be done: (1) make the weight of each lining the lightest;
(2) The contact surface between the sliding bearing surface and the hollow shaft should be reasonable, and the braking phenomenon cannot be generated by the shaft.
(4) The actual power of the motor and the pressure drop generated by the line, the large pressure drop has a great influence on the loading of the grinding body. These problems are management issues in daily production. The main purpose of solving these problems is to minimize the starting current.
6. Grinding only works on coarse grade particles
The phrase “grinding only works on coarse particles” is the essence of grinding theory. The finer materials produced in a warehouse are broken or crushed. The return material entering from the grinding head passes through a warehouse from the gap of the ball and passes through the compartment board to enter the second warehouse. The grinding in the second warehouse The body only has grinding, no crushing, or less effect on material crushing. The small grinding body is driven by the mill cylinder, and the moving state is turbulent, rolling and sliding. The small abrasive body grinds and peels off the material particles during sloping and swaying. If there is a large particle that is not a recycled particle, it can be called a primary particle, and the particle moves from the partition plate to the finishing tail. For open-circuit grinding, it is required to be less than 45μm or even smaller when moving to the end of the grinding; for closed-circuit grinding, it is not required to be less than 45μm from the beginning of grinding to the grinding, and it is only required to peel off the surface of the original particles. Most of the portion peeled off from the surface of the particles is particles of 32 μm or less. When the original particles enter the mill once or twice, as the volume becomes smaller, the difficulty of peeling and grinding becomes larger and larger, because the particles are small, and the degree of softening increases. When the particles are small to a certain size, It is completely softened, and any object is the same. Generally speaking, the more large particles entering the mill bin, the higher the efficiency of grinding. In order to increase the amount of large particles in the mill, it is necessary to increase the cyclic load appropriately. More importantly, the classifier used has a high degree of selectivity for a particular particle within a certain range.