33 frequently asked questions take you to a comprehensive understanding of the ball mill

Before buying a ball mill, we need to understand the model, output, structure, etc., before the ball mill is put into operation, we should understand how to load the ball and the ratio of the medium, and consider how to improve the output and how to solve the problem of the ball mill. Where are we going to find the answers to all these questions? Today, Xiaobian summarized 33 common problems about the ball mill and shared them with you.

1. What are the types and significant characteristics of the mill?
A: According to the different grinding medium is divided into: the medium is steel ball, it is called ball mill; The medium for the steel rod is called the rod mill; The medium for gravel is called gravel mill; With its own ore as the medium is called the autogenous mill, and then add the right amount of steel ball to the autogenous mill, which constitutes the so-called semi-autogenous mill. According to the shape of the shell and the discharge method: the ball mill is divided into short cylindrical, tubular, conical overflow discharge and lattice discharge, the rod mill is divided into cylindrical overflow discharge and open low level discharge, and the self-grinding or semi-self-grinding machine is mainly short cylindrical shape.

2. What is the representation of mill specifications?
A: The expression method is: diameter × length, expressed by symbol as D×L, such as 2700×2100mm ball mill, then its diameter is 2700mm, the length is 2100mm.

3. What are the types and characteristics of the ball mill?
Answer: There are two kinds of ball mill commonly used in the selection plant: grid type and overflow type, the difference between them is no fan grid plate device in the overflow type ore discharge part, the slurry of overflow type ball mill is automatically discharged through the discharge port, and the grid type has a forced discharge effect due to the installation of grid plate, thereby increasing the processing capacity and reducing the ore over crushing.

4. What is the expression method of grinding fineness?
A: The fineness of the grinding product is usually screened with a 200-mesh screen of the standard screen, and is expressed as a percentage of the total product under the screen (the mesh is the number of screens in each inch of the screen layer, and is used to name the screen).

5. What is the definition and calculation method of the utilization coefficient of the mill?
A: The mill utilization factor is the average amount of raw ore that can be processed per cubic meter of the effective volume of the mill per unit time, expressed in tons /m³. That is, the mill utilization coefficient q=Q/V (ton /m³· hour).

6, the definition and expression of the production capacity of the mill?
A: The production capacity of the mill is the amount of raw ore that the mill can handle per unit time (hour) under certain conditions of giving ore and product particle size, expressed in tons/unit time.

7, what is the grinding efficiency? How many ways can it be expressed?
A: It refers to the amount of ore that can be processed per consumption of 1 kilowatt · hour (one degree) of electric energy, which is expressed in the following ways:
(1) Tons of raw ore processed per kilowatt hour of electricity consumed, that is, tons/degree.
(2) The tonnage of grinding products is calculated according to the specified level (usually 200 mesh) for each degree of electricity consumed.
③, according to the surface area tons/KWH of electricity to calculate.

8, what is the technical efficiency of the mill?
A: It refers to the ratio between the percentage of qualified grade content in the product obtained after grinding and the percentage of greater than qualified grade content originally contained in the feed ore.

9, what is the qualified grain grade?
A: The so-called qualified particle size is that the upper limit of its particle size should be less than the specified maximum particle size, and the lower limit of its particle size should be subtracted from the over-crushed part.

10, what is the passing capacity of the mill? How to calculate?
A: The passing capacity of the mill refers to the total amount of ore that can be passed per unit time, and its calculation method is: q=Q(1+c) in type V: q mill passing capacity, tons /m³. Q The productivity of the mill is calculated according to the raw ore, tons/hour. C sand return ratio, measured in multiple. V Effective volume of the mill, m³.

11. What is the grinding process of the ball mill for the ore?
A: When the mill spins at a certain speed, the centrifugal force is generated, so that the medium and the cylinder produce friction, and the same cylinder spins together, when it reaches a certain height, the centrifugal force of its own gravity, it is thrown down from the cylinder, thus crushing the ore. At the same time, due to the sliding phenomenon in the medium, the ore is also abrasive. Under the impact force and grinding force of the medium, the ore is crushed.

12. How many kinds of motion trajectories do the media have in the ball mill?
A: There are three kinds of motion trajectory: ①, sliding type (low speed operation); ②, drop type (normal speed); 3, centrifugal operation (medium and cylinder movement trajectory is consistent).

13, what is the movement law of the medium in the ball mill?
A: There are four main points:
(1) When the mill operates at a certain speed, the medium moves in a regular cycle under the action of centrifugal force and gravity;
(2) The movement path of the grinding medium in the cylinder is composed of the upward movement of the circular trajectory and the downward movement of the parabolic trajectory;
③, the height of each layer of media is different. The height of the outermost layer to the innermost layer of the medium decreases in turn;
4, the rotation period of each layer of media is different, the closer to the inner layer, the shorter the rotation period.

14, What are the components of the ball mill?
A: It is mainly composed of six parts, such as the barrel part, the feeding part, the discharging part, the transmission part, the bearing part and the lubrication system.

15. What are the components of the ore feeding part?
A: The ore feeding part is composed of the end cover of the hollow journal and the ore feeder and the inner sleeve of the shaft neck.

16, What are the types of ore feeder?
A: The ball mill in the concentrator uses three feeder types: drum type, spiral shape and combined feeder.

17. What are the components of ore discharge? (Grid type)
A: The ore discharge part is composed of the end cover of the hollow journal, the fan grid plate, the center liner plate and the inner sleeve of the shaft neck.

18. What are the working characteristics of the rod mill?
A: Its working characteristics are: it crushes the ore by crushing and grinding produced by the line contact of the steel rod. Therefore, it has a selective crushing effect, which reduces the over-crushing of the ore, and the product size is uniform.

19. What are the operating factors affecting the grinding and grading unit?
A: It can be broadly divided into the following three categories:
①, ore properties. Including hardness, mud content, feed size and required fineness of grinding products.
②, the structure of the mill. Including grinding machine type, specifications, speed, etc.
③, operating conditions. There are mainly grinding medium, pulp, concentration, sand return ratio and classification efficiency.

20, how to choose the shape of the grinding medium?
A: According to the purpose of grinding and the test shows that the spherical and P2 rod shaped medium grinding effect is the best; The collision of spherical medium in grinding is point contact, so the grinding efficiency is high, suitable for fine grinding, but compared with rod grinding, over-grinding phenomenon is serious, generally when the ore size is below 30mm, the product size is not less than 1mm, the use of rod grinding is higher efficiency.

21. What is the selection principle of grinding media material?
A: When selecting the medium material, it should be fully considered from the specific gravity, hardness, wear resistance, price, processing and manufacturing conditions of the material. At present, steel or iron materials are generally used. In production, steel is commonly used in large balls, iron is commonly used in small balls, steel is suitable for rough grinding, and iron is available for fine grinding. In recent years, rare earth medium manganese nodular cast iron balls have been successfully replaced by steel balls.

22, what is the size system of grinding media loading?
A: Its size according to the nature of the ore to determine the harder the ore, the coarser the size of the ore, the larger the size of the medium should be added to produce a larger impact grinding effect, and conversely, the smaller size of the medium can be used to enhance the grinding effect.

23, What is the definition of the medium filling coefficient and the relationship with the mill speed?
A: That is, the filling rate, which refers to the percentage of the grinding medium in the mill volume.

24, in the mill operation should pay attention to what?
A: In the mill operation should pay attention to the following aspects:
①, closed-circuit grinding should be appropriate cycle load;
②, the speed of the mill should be controlled properly;
③, the ball loading system should be reasonable;
4, grinding concentration should be appropriate.

25, What are the methods of loading proportion of the size of the ball mill grinding medium?
A: There are two main approaches:
1, according to the total feed size of the mill to load the ball, the principle is: the ball diameter and the feed size is suitable, the ball amount and the feed grade content is suitable.
(2) Simple method: the proportion of various balls is proportional to the diameter of the ball mill.

26. What is the impact of the amount of ball loading on the grinding process?
A: The amount of ball loading has a certain impact on the grinding efficiency, less ball loading, low mill efficiency, too much ball loading, and easy to interfere with the inner ball during operation, destroying the normal circulation of the ball. The efficiency of grinding (crushing) ore is also reduced. Practice has proved that the amount of ball loading is related to the speed of the mill. When the running speed of the mill is low, more balls can be installed, and when the speed is high, less balls can be installed.

27, why must the steel ball be loaded into the mill in a certain proportion according to the size?
Answer: The size and size of the steel ball are mainly executed by the physical and mechanical properties of the ore and the particle size composition of the ore. To deal with the ore with high hardness and coarse grain size, it is necessary to have a larger impact force and need to add a larger steel ball; The processing ore is soft and the feeding particle size is small, and the product particle size is required to be fine, so it should be mainly ground and can be loaded into a smaller steel ball. Production field ball mill into a variety of ball diameter balls. According to a certain proportion, to deal with the material composed of different sizes of ore particles. Theoretically speaking, only by ensuring that a certain proportion of various balls can be adapted to the particle size composition of the material to be ground, in order to achieve good grinding results.

28, if there are too few big balls or small balls in the mill, what will happen?
Answer: When the material size is larger or the hardness is larger, the proportion of large balls will appear coarse grinding products, which can not meet the fineness requirements. And the processing capacity is also limited, affecting the grinding efficiency. When dealing with materials with small ore size and low hardness, if the pellet ratio is small, coarser product size will also appear. The pellets should be properly supplemented and the proportion of pellets should be added to adapt to the nature of the treated ore to obtain better fineness of the product. Therefore, the proportion of ball loading must be strictly in accordance with the proportion to prevent the imbalance of the proportion.

29, how to improve the technical efficiency of the mill?
A: To improve the technical efficiency of the mill, it can be considered from the following aspects:
①, adopt closed circuit grinding process.
2, in the choice of equipment, coarse grinding should be used around the discharge of the rod mill, fine grinding should be used lattice ball mill.

30, the type of mill lubrication parts and lubricating oil? What about the period?
A:
1, size gear: 40-50# mechanical oil, add twice per shift, half a year to change the oil.
(2) Hollow bearings: half of 50# mechanical oil and half of 24# or 28# mechanical oil mixed, add once per shift, 3 months oil change.
3, pinion rolling bearing: calcium base grease drop T=90℃, added per shift, half a year oil change.
4, reducer gear and bearing: 40-50# mechanical oil, added per shift, 3 months oil change.
⑤, motor: calcium grease drop, T=120℃, half a year oil change.

31. What phenomenon occurs when the mill expands its stomach?
A: The following phenomena generally occur:
①, the main motor ammeter indicates that the current is declining;
②, the mill discharge ore spit out large, pulp gush;
③, the classifier overflow coarse phenomenon is serious, sand return significantly increased;
(4) The running sound of the mill is dull, and the sound of steel ball impact cannot be heard.

32. When the mill is bloated, how should it be handled in operation?
A: First of all, it is necessary to analyze the changes in the nature of the ore, the amount of ore, the amount of water, the amount of sand return, the overflow particle size, etc., is normal, and the following measures can be taken in operation:
①, reduce the ore feed of the mill or stop the ore feed in a short time;
(2) Adjust the water consumption, that is, strictly control the grinding concentration;
③, reasonable addition of grinding media.

33, the reason why the ball consumption of the ball mill is too high if the ball consumption of the ball mill is too high, the reasons should be found and solved in time, so as to save the cost of steel consumption and improve the grinding efficiency. The reasons for the high steel consumption are:
1) Steel ball quality Steel ball quality has a great relationship with ball consumption of ball mill, ordinary forged ball surface and internal wear resistance difference will be relatively large, the diameter reduction rate is not uniform during the grinding process, resulting in a large mismatch of steel ball grading in the mill, resulting in high ball consumption, and even affect the grinding efficiency and fineness; Cast steel ball quality is better, are cast with round steel, wear resistance is better, and the speed of ball diameter reduction is more balanced, will not cause gradation deviation;
2) Too many failed balls too many failed balls, the broken ball rate increases, will lead to the ball mill bearing capacity increase, improve power consumption, is also one of the reasons for high ball consumption;
3) High proportion of large diameter steel balls if the proportion of large diameter steel balls in the mill exceeds 70%, it will lead to the reduction of the area of the mill ball, we know that the grinding efficiency of the ball mill is obtained by the sum of the work done by each steel ball, too many large balls lead to many grinding balls do not play their maximum efficiency, resulting in the decline of the grinding efficiency of the ball mill is also an inevitable result.