Current status of research and development and application of typical mills at home and abroad

From the earliest grinding of grain winch, roller milling, to ball mills, Raymond mills, vertical mills (disc mills), etc., grinding mills have experienced hundreds of years of development. The mill is constantly updated and the grinding form is ever-changing. Here are a few common grinding equipment.

1 , ball mill
There are many types of ball mills. At present, the world's largest ball mill suppliers include Denmark's FFE Minerals, Australia's OUTAKUMP and ANI, Finland's Metso Minerals, Germany's Krupp and Japan's Kawasaki Heavy Industries. The schematic diagram and working diagram of the ball mill are shown in Figure 1.1 and Figure 1.2, which consist of the feeding part, the discharging part, the rotating part and the transmission part. When grinding, the material to be ground enters the rotating circular drum of the ball mill. Under the action of inertia, centrifugal force and friction, the grinding body adheres to the liner inside the drum, and is brought to a high position by the rotating drum to reach a certain height. When it is thrown off due to its own gravity, the falling abrasive body will crush the material in the drum to achieve the grinding effect, which also makes the ball mill relatively noisy during the grinding process.

The ball mill has a relatively simple structure and is convenient to operate, but the biggest problem is that it consumes a lot of energy, and it often has a boring phenomenon, low work efficiency, bulky body (total weight up to several hundred tons or more), large floor space, configuration Expensive, high production costs. Although the ball mill is one of the key equipments of the mine, in the initial construction process, the ball mill and its supporting equipment and their infrastructure investment account for about 50% of the total investment; and during the production, the material consumption and power consumption of the ball mill It also accounts for more than 50% of the total burn-in consumption. Studies have shown that the mechanical efficiency of ball mills is only about 2% to 5%. Based on the disadvantages of high energy consumption and high cost of ball mills, designers are more eager to design an efficient and energy-saving grinding equipment.

2 , Raymond Mill
Raymond mill is also known as a suspension roller disc mill, and its mechanism is shown in Figure 1.3. The working principle is that the main motor is driven to rotate the central shaft through the reducer, and the upper end of the central shaft is connected with the plum blossom frame, and the grinding roller is connected with the plum blossom frame through the horizontal hinge to form a swinging fulcrum. When the plum blossom frame drives the grinding roller to rotate, the grinding roller is in the centrifugal force. Under the action, it will be tightly pressed on the grinding ring. Under the action of friction, the grinding roller will rotate and pulverize the material. The blade for shoveling the material is installed in the lower part of the plum blossom frame. During the work, the grinding roller rotates together with the blade, throws the material shovel, and fills the material between the grinding roller and the grinding ring to form a material. The layer, the layer will be subjected to the outward centrifugal force (ie, the pressing force) when the grinding roller revolves, thereby pulverizing the material.
Some of the shortcomings of the traditional Raymond mill have affected its wide application, mainly in the following aspects.
(1) The product has a large particle size . The grinding size of the traditional Raymond mill is generally around 400 mesh. It can only occupy the low-end market in the grinding industry, and does not meet the future development direction of the ultra-fineness of the powder industry;
(2) The grinding roller suspension point is generally high . Under the action of centrifugal force, the grinding roller rolls on the grinding ring, and at the same time, the grinding ring is squeezed. When the material is ground, the structure is easy to make the grinding machine produce Vibration, affecting the milling performance of the mill;
(3) During the installation process of the mill, when the grinding ring is too small, the grinding roller is pressed inward during the working process so that the grinding roller shaft is inclined, and the working surface of the grinding ring and the grinding roller will be at a certain angle, destroying the material layer and affecting The working efficiency of the mill ;
(4) The particle size distribution of the material after Raymond grinding is not concentrated , which brings trouble to the subsequent product processing;
(5) Raymond mill has small output, high energy consumption, and short life of key components , which need to be replaced frequently, which leads to increased cost and great inconvenience in production.

In order to solve these problems, many manufacturers and developers are trying to improve, but because these defects are determined by the structural characteristics of Raymond mill, although some improvements have been made to these problems, the results are not satisfactory, and New mills are beginning to dominate the market, and some companies with limited size and weak R&D capabilities are more inclined to new milling equipment.

3 , vertical mill
Vertical mill, also known as disc roller mill, has a history of 100 years. With the development of science and technology and the continuous experience of production practice, the wear resistance of the vertical mill grinding machine has been continuously improved. Improvements, the structural form of the grinding roller and the grinding disc are continuously improved, which makes the grinding method of the vertical mill more reasonable and develops rapidly in the grinding industry.
A vertical mill is a device that breaks the material to be ground by relative rolling between the disc and the grinding roller. The material enters the inside of the mill through the discharge pipe and falls into the center of the rotary grinding disc. Due to the centrifugal force of the rotating grinding disc, it moves to the edge of the grinding disc. When the material to be ground enters the grinding zone of the grinding roller and the grinding disc, it will be bitten into the grinding machine. The roller is pulverized between the grinding disc and the grinding disc. As the material advances toward the outer edge, the airflow is rotated up by the high speed, and the large particles will fall back into the grinding disc for re-grinding, and the small particles pass through the separator on the upper part of the mill. The discharge port is collected.
By the year 2000, in the selection of various types of cement grinding equipment in the world, the selection rate of vertical mills has occupied about 30%, that is, cement grinding accounts for 15%, raw material grinding accounts for 35%, coal Grinding accounts for 60%, and it has also started in the field of slag grinding. For example, vertical grinding is the preferred grinding equipment in the cement industry, almost completely replacing the traditional ball mill. Table 1 shows the selection of vertical mills in various fields.

Vertical mills have the following advantages:
(1) Low energy consumption and high efficiency . The grinding power consumption is 35%-50% lower than that of the conventional ball mill of the same output.
(2) Strong drying ability. It can dry materials with water content up to 20%, eliminating material drying equipment.
( 3) The size of the grinding material is large and the crushing is relatively high . The grinding depth of the vertical mill can reach 4%-5% of the diameter of the grinding roller.
(4) The grinding process is simple, the floor space is small, and the quality is light . The vertical grinding machine has a simple grinding process and a compact structure. The entire grinding system covers an area of ​​about 60% to 70% of the ball mill, and the building space is about 50%-60% of the ball mill grinding system, with the same capacity. Compared to ball mills in production, vertical mills are lighter in weight.
(5) Wear parts are small in wear and long in life . The grinding roller system of the vertical mill is equipped with a limit device, so that there is no direct contact between the roller sleeve and the wear liner, so the wear parts are less worn and the wearing parts have a long service life.
(6) Less dust, low noise and comfortable operating environment. The vertical mill has a low noise of only 80-85dB and a noise level of about 20% lower than that of a ball mill.
(7) Easy maintenance.

Vertical mills are accelerating in the world today. Vertical mills that are at the forefront of the world's development include Germany's Extraordinary, Loesche, Burleys, Denmark's Smith, and Japan's Ube. Figure 1.4 shows the structure of two different types of vertical mills. Although the vertical mills produced by various companies have different structural forms, the grinding principle of all vertical mills is the same.
The rise and development of vertical mills in China's grinding industry is about 20 to 30 years later than in developed countries. The development level of vertical mills in China today is equivalent to the level of developed countries in the 1990s.

Table 1.2 shows the selection of vertical mills for new cement projects in China from 2000 to 2012. It can be seen that the application of vertical mills in China's cement industry has just started in 2000, and all vertical mills are imported from abroad. This domestic vertical mill relied on foreign imports until 2007, when it was broken by domestic vertical mills.

In recent years, the development of domestic vertical mills has been particularly rapid, such as the HRM vertical mill independently developed by Hefei Institute, the MLS vertical mill introduced by Shenyang Heavy Machinery Group, and the LM vertical roller mill developed by Dawn Heavy Industry based on foreign products. , MTW European version of the mill, etc., its grinding performance is much higher than the domestically developed mills, has largely replaced the market share of imported vertical mills. Up to now, the domestic vertical mill has accounted for more than 90% of the cement industry in China. It has improved the selection rate of vertical grinding in China's grinding industry, and has made important contributions to the promotion of vertical grinding in China's cement industry.