Grinding equipment and application (2)

The transmission mode can be divided into: (1) edge drive (Fig. 6a, b, c, d, i, j); (2) center drive (Fig. 6c, d, h); (3) idler Drive (Figure 6, e, f).
According to the transmission torque, the transmission mode can be divided into: (1) gear transmission (Fig. 6a, b, c, d, i, j); (2) friction transmission (Fig. 6e), f, g); (3) ring motor ( Gearless transmission. For small size mills, squirrel-cage asynchronous motors (or slip-ring asynchronous motors) are usually used to drive the mill through the reducer and the open gear. The advantage is that the motor is cheap, safe and reliable; the disadvantage is that a speed reducer is needed. For medium and large mills, such as China's D × L ≥ 2.7 × 3.6 m mill, low-speed synchronous motor drive. The utility model has the advantages that the speed reducer is not used, the floor space is small, the starting torque of the synchronous motor is large, and the power factor of the power grid can be improved; the disadvantage is that the motor requires an additional excitation device and is expensive. The use of a friction-driven roller device, which is simpler than a gear, has been limited to small-sized mills in the past, but is now also used for transmissions of larger mills (Fig. 7). In the 1970s, the mill began to use a ring motor drive. The advantages are: (1) The reducer and gear are eliminated. The mill cylinder itself is the rotor of the motor, which can realize stepless speed regulation and greatly reduce noise; (2) the efficiency of the motor is improved; (3) the structure is compact and the floor space is small. An application example of a ring motor drive mill manufactured by West Germany Siemens.

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The center drive (Fig. 6h) is the drive connecting tube of the drive motor through the reducer and the coupling to drive the hollow journal, which directly drives the mill barrel. A plurality of orifices are formed around the transmission nozzle for the mine to discharge. The reducer can be used with symmetrical and planetary gear reduction gearboxes. The transmission efficiency of this type of transmission is higher than that of the edge transmission, generally 0.92~0.95, up to 0.99 (the efficiency of the edge transmission mode is generally less than 0.90), compact structure, reliable operation, and the service life is up to 30 years. . This type of transmission is mostly used in multi-barrel tube mills and rod- ball mills in cement plants (rough grinding bin picking, fine grinding bin grinding balls). The mill is divided into two types: "left-handed" and "right-handed". From the discharge port of the mill to the feed port, the direction of rotation of the mill is clockwise, which is called "right-handed", otherwise it is called "left-handed".
When the mill installation power is large, for example, more than 1500 kW, it is better to use a dual motor drive. Dual motor drives are available with dual synchronous motors (Figure 6b) or dual asynchronous motors. (Fig. 6c), when the double synchronous motor is driven, two synchronous motors are arranged symmetrically, and directly pass through the two pinion gears, and simultaneously drive the large gear ring mounted on the discharge end of the cylinder (some large ring gears are also mounted on the hollow shaft) The extension of the neck causes the mill to rotate. In this way, the transmission requires a special coupling, or one of the motors should have a rotatable stator to make a relatively precise adjustment of the angle of the rotor to balance the load between the two motors. A dynamic load balancing control system (a common load distribution regulator) is used to correct the load swing between the two motors. Two squirrel-cage motors are used to drive the same mill through the clutch, and the equipment cost is lower than that of the two wound-wire motors. This squirrel cage motor is the same as the double synchronous motor drive mill. Each time a motor is started, the mill reaches the running speed under the load balance control of the clutch.
Figure 7 shows the transmission of the world's largest ball mill D × L = 6.5 × 9.65 m; it is characterized by a combination of a ring motor and a roller, which is currently installed in Sidva, Norway. Lange (Sydvarangers) iron ore beneficiation plant. The advantages of this mill are: (1) using a ring motor drive, the rotor to stator gap is 13 mm, error ± 1.5 mm; low noise, motor efficiency up to 95%; (2) using roller drive (cylinder pressure pad bearing ), so that the stress distribution of the cylinder is reasonable (see Figure 7b); the size and type of the inlet and discharge openings can be designed as needed without being limited by the simplified load. The transmission mode of the roller bearing can adjust the gap between the rotor and the stator to facilitate lubrication; (3) Adopt computer automatic control to increase the processing capacity of the mill and optimize production. The mill was put into operation in 1981 to 1987, and the treatment of iron ore reached 20 million tons. Compared with the small-scale mill, the steel consumption is reduced by 14% according to the raw ore treatment volume, and the single consumption of the liner is 33% lower. Reduced by 22.7%. [next]
Main bearing and lubrication system. The main bearing of the mill mainly bears the weight of the medium and material in the whole mill and the cylinder. Because of the low rotation speed of the mill, sliding bearings are usually used. This type of sliding bearing is different from a general sliding bearing in that a semi-circular bearing bush is formed in the lower half of the bearing, and a hollow bearing cap is in the upper half, and the bearing has a large diameter and a short length. Due to the large length and load of the mill barrel, the cylinder will have a certain deflection; therefore, the sliding bearing of the large mill is made self-aligning. The main bearing is generally composed of a bearing bush, a bearing housing, a bearing cap and a lubrication system. Bearing usually used Pap alloy casting, some also with bronze and other materials. The main bearing is one of the key components of the mill, so lubrication is an important issue. The simplest method of lubrication is to use oil cup drip lubrication for small mills. A more complete method is to use the dynamic oil film lubrication of the thin oil circulation system and the static pressure oil film lubrication. The latter method uses a high pressure oil pump with a pressure of about 700 kPa (70 atmospheres) to inject oil into the bearing inlet to form an oil film layer having a thickness of about 0.2 mm between the bearing pad and the journal. Even if the journal stops rotating, this oil film is still present, thereby avoiding metal friction to reduce friction loss. For example, the ball mill of Harding Company of the United States uses a dynamic pressure oil film lubrication method when the main bearing diameter is less than 1.2 meters; when the bearing diameter is larger than 1.2 meters, it is lubricated with a static pressure oil film. The main bearing of the mill is sometimes equipped with a water cooling device. The cooling water can take away the heat generated by the journal and the bearing bush during operation, so that the lubricating oil is cooled, keeping the bearing bush from heating, and ensuring the safe operation of the grinding machine.
(3) Rod mill The structure of the rod mill is basically the same as that of the ball mill. The main difference is that the rod mill does not use a grid plate for ore discharge, but uses an open type, overflow type or peripheral type of discharge device.
The medium used in the rod mill is a round steel rod that is 10 to 15% shorter than the length of the cylinder. In order to prevent the steel bar from tilting during the operation of the mill, the end cap liners at both ends of the cylinder are usually formed as straight end faces perpendicular to the axis of the mill, and the length to diameter ratio of the mill cylinder should be maintained at 1.5 to 2.0. Rod mills use non-smooth liners such as corrugated or stepped shapes. The diameter of the hollow journal of the discharge end is much larger than that of the overflow ball mill of the same specification, in order to speed up the passage of the slurry through the mill. When the rod mill is in operation, the steel rods in the cylinder are in line contact, and the material with a larger particle size is first pulverized. When the steel rod is driven to rise, the coarse particles are often clamped between the rod and the rod, and the fine particles are easily leaked from the gap of the rod with the slurry, so there is a "screening classification" between the rod and the rod. In order to make the rod mill have a strong desire for "selective grinding".
The structural feature of the end cap and hollow journal of the ore-mining end of the open-type rod mill is that there is no hollow journal at the discharge end of the mill, but a large flared overflow port is opened in the center of the discharge end. In order to prevent the slurry splash and the steel rod from sliding out of the mill barrel, the discharge port is blocked by a fixed conical cover, and the slurry overflows through the annular space between the flared overflow and the cover. [next]
The peripheral mine-type rod mill is divided into two types: the end of the cylinder (the end of the discharge) and the type of the middle of the cylinder. Except for different mining methods, the other structures are basically the same as the overflow ball mill. In view of the advantages of such a rod mill, it has high grinding efficiency, energy saving and product quality. It has been applied in some industrial production in China. Can be used as dry, wet grinding and wet grinding operations. During the wetting and grinding process, the grinding concentration can reach 87~92%, and the pellet operation is commonly used.
(4) Tube Mill The remarkable feature of the tube mill is that the length of the barrel is much larger than the simplified diameter, usually L/D = 2.5~6. Since the barrel is very long, the material is also ground in the barrel for a long time, and a very fine grinding product can be obtained. When the mill cylinder is divided into two, three or four different length chambers by the partition plate, it is called a multi-chamber (chamber) tube mill. Multi-barrel tube mills are mostly used in cement plants.
Figure 8 is a structural view of a three-barrel tube mill. The structure of the cylinder, the discharge mode, the transmission device, the main bearing and the lubrication system of this type of mill is basically the same as that of the ball mill, but the casing lining, the compartment plate and the grinding machine of the mill have obvious differences.

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The lining material should generally be selected according to the force conditions and effects of the lining in each of the cylinders. When a tube mill, two bins (bins kibble) generally loaded balls or large diameter steel rod, plate by the impact force, good abrasion resistance should be used in high-manganese steel or rubber liner. Third, the four-cylinder (fine grinding bin) grinding media mostly use small balls or grinding segments, the lining plate is less impact, mainly for grinding, commonly used alloy white cast iron. For the fine grinding chamber of the wet tube mill, the rubber liner is used, which has better service life and economic effect than the alloy liner. The simplified lining should be determined according to the nature of the material, the feed size, the mill speed and the pulverization of each bin. The working surface shape of the multi-barrel tube mill liner is mainly used in the following types: the corrugated liner is used for the barn of the baseball mill (a silo); the rib liner is lifted by the rib surface. Strong ability, mostly used in multi-barrel tube mill ball: Trapezoidal liner, tube mill bar and ball bin can be used. The working surface of the parallel lining plate is smooth, and the grinding ball (segment) has poor ability. It is often used for the fine grinding bin of the tube mill. The square bead rubber lining plate has strong lifting ability for the grinding medium, and the impact of the medium is large. In the coarse grinding bin; the asymmetric "K" type bead rubber lining, because the lifting surface is a combination curve of straight line and arc, the ability to lift the grinding ball is weak, the impact of the grinding ball is small, generally suitable for fine Grinding the warehouse.
Due to the difference in the function of each bin, the design and selection of the liner liner in the tube mill is very important.
The function of the compartment plate is to divide the cylinder into several compartments. The first chamber is used for rough grinding of the material and the last two chambers are used for fine grinding of the material. The compartment board is divided into a single layer and a double layer. The single-layer compartment board is composed of a number of fan-shaped slabs, which are joined together by a central circular plate. It is similar to the construction of the discharge grid plate of the short cylindrical ball mill and is used as a separator plate for the second and third chambers of the mill. The double compartment panels are also available in transitional and lift styles. The transitional warehouse type double compartment panel is composed of a ring fixing ring, a blind plate, a raft plate and a center circular plate. When the slurry surface in the first chamber of the tube mill is higher than the annular fixed ring, the slurry flows into the middle of the double-storage partition, so it should be shut down at regular intervals. This double compartment panel is only used in wet raw baseball mills. The pupil size and pupil arrangement of the compartment board should be determined on a case-by-case basis. The pupil width of the compartment board is generally 8 to 15 mm for a warehouse, 6 to 10 mm for a second warehouse, and 6 to 8 mm for a three warehouse. The compartment board is generally composed of 6~12 fan-shaped slabs. The arrangement of the boring holes on the sector plate is similar to that of the ball mill platoon plate, that is, concentric circular, inclined and radial.
The feeding device of the dry tube mill mainly includes three kinds of disc feeders, belt feeders and electromagnetic vibrating feeders. The disc feeder is fed according to the volumetric method, and the feeding amount is generally about 5%. However, the structure is simple, the manufacturing is easy, and the feeding amount can be conveniently controlled, so it is suitable for each of the larger particle sizes. Dry material; for wet and viscous materials, it is not suitable for use because it is easy to block at the discharge chute. The electromagnetic vibrating feeder is a new dosing device. Currently, mineral processing, metallurgy, chemicals, building materials, coal and other industries, has received relatively wide range of applications. The electromagnetic vibrating feeder can transport loose granular materials, transport block materials of 400~500 mm, and transport various powder materials. A belt feeder is a device that controls the amount of feed by weight. When it is used for fine-grained materials, the error of the feeding amount is generally not more than 1%; this feeder is suitable for feeding small pieces of coarse particles or various powdery dry materials. [next]
When the tube mill is used in the open flow (road) system, a larger aspect ratio is selected, generally L=(3.5~6.0)D; when used as a closed flow (road) system, a smaller aspect ratio is selected. L = (2.5 ~ 3.5) D. The length of each bin (chamber) of the multi-barrel tube mill is determined according to the actual situation. However, in many cases, the last chamber (fine grinding bin) of the mill has the longest length, and each bin (chamber) occupies a percentage of the effective length of the cylinder.
Grinding media commonly used in cement mills are grinding balls, steel bars and grinding segments. The diameter of the grinding ball commonly used in tube mills is 30 to 100 mm. The steel bar is only used in the first bin of the wet baseball mill. The diameter of the steel bar is usually 50-80 mm, and its length is about 30-100 mm shorter than the length of the bin. The steel segments are often of a short conical shape, and are commonly used: ф15×20, ф18×22, and ф25×30 mm (diameter×length). The specifications of the grinding media of each bin should be determined according to the specific conditions such as the size of the feedstock, the grindability of the material and the fineness requirements of the product. When the feed size is small and the wearability is good, the one-barrel of the multi-barrel tube mill can generally use the grinding ball with a diameter of 60-100 mm, the second bin adopts the 30-60 mm, the bar of the rod mill (a warehouse) ) A steel rod of 50 to 70 mm can be used, a grinding ball of 30 to 50 mm can be used for the second position, a three or four position, a tube mill for the grinding section, and a baseball mill with a grinding ball of less than 30 mm. When the feed size is large (maximum particle size is greater than 30 mm) and the grindability is poor (for example, a mixture of large clinker and slag), the maximum ball diameter of a tube mill can be 110 mm. The diameter is about 90 mm. Grinding ball materials are mostly made of carbon steel, alloy steel, alloy cast iron or manganese steel. Steel bars are usually rolled from 45 medium carbon steel or 70 high carbon steel.
(5) Self-grinding machine Self-grinding machine is also called medium-free grinding machine, which is characterized by using the treated ore (material) itself as the grinding medium. Usually, the largest lump ore that is fed into the self-grinding mill is 300-350 mm; in the mill, the 100 mm dry nugget acts as a grinding medium, and the less than 80-mm mm ore has poor grinding ability, which is not easy. For the large ore grinding, this part of the material is usually called "hard-to-grind particles"; in order to grind this part of the material, sometimes a large steel ball of about 4 to 8% of the mill volume is added to the self-grinding machine. Self-grinding. Self-grinding mills are divided into dry and wet.
The largest dry-type self-grinding machine currently produced abroad is D×L=10.5×2.05 m and the drive motor is 4500 kW; they are installed in Quebec and Mauritania, Canada, for the treatment of iron ore; The largest wet self-grinding mill is D×L=10.97×4.6 meters and the transmission power is 2×4480 kW. They are installed in Hiben and B.Col-umbia in the United States to treat the iron shale. And copper ore. [next]
A dry self-grinding machine dry self-grinding machine is basically the same as the ball mill, but compared with the ball mill, it has its remarkable characteristics, that is, the dry self-grinding machine has a large diameter and a short length (Fig. 9 The diameter ratio (L/D) is generally about 0.3 to 0.35, which is determined by the nature of the ore itself. Since the ore density is much smaller than the grinding medium, in order to obtain the impact and grinding force equivalent to the metal medium, the simplified diameter of the self-grinding machine needs to be designed to be larger. The cylinder is therefore short, mainly to prevent the occurrence of "segregation" of ore during the self-grinding process (large ore is concentrated at one end and small ore is concentrated at the other end). In addition, the cylinder is shorter, which can reduce the resistance loss when the wind flows through the cylinder, and increase the wind carrying capacity (the amount of dry material carried per hour per cubic meter of air volume). When “segregation” occurs in the production of the mill, the more ore in the middle of the cylinder (such as less than 80 and 20 mm), not only significantly reduces the grinding efficiency, but also causes the mill to “swell”. . The hollow journal of the two ends of the self-grinding cylinder has a large diameter and a short length. Usually, the inner diameter of the hollow journal is about twice the maximum feeding size. The large diameter is to adapt to the self-grinding machine to give a large amount of ore, and at the same time to facilitate the flow of materials. The self-grinding cylinder is equipped with a “B” type lifting lining. Its main function is to raise the ore and prevent the large ore from sliding downwards, and at the same time it acts as a sharp point when colliding with the falling ore. Figure 10 shows how it works.
The end caps of the dry self-grinding mill are arranged perpendicular to the cross section of the cylinder. The structural shape of the end cap liner is quite special (see Figure 9). A part of the end cap lining plate is a smooth lining plate, and two lining plates having a cross-sectional shape similar to a triangle, that is, a crest lining plate, are respectively disposed at the hollow journals near the both ends. Its function is to throw the ore near the two ends of the barrel to the center, which helps the ore in the mill to be evenly mixed to reduce the "segregation" of the ore; in addition, the end cap and the end cap of the ore end cap The two peaks have a wedge and "compact" effect on the ore at the bottom of the cylinder, which is conducive to the fragmentation of the ore.

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The self-grinding machine uses an electric motor to pass through the peripheral gear of the pinion and the large ring gear, and the large ring gear is mounted on the cylinder near the grinding end.
Since the self-grinding machine has a large size and a heavy load, the main bearing is lubricated by a static pressure oil film type. The dry self-grinding relies on the wind to transport the material. According to the characteristics of the air passage system, it is divided into two types: the open flow system (Fig. 11) and the closed flow system (Fig. 12). The former air passage system is simple and suitable for small-size self-grinding machines. For example, a self-grinding mill with a diameter of less than 4.0 meters. Practice has proved that the correct design, selection, installation and operation of the air duct system and equipment is the key to ensure that the dry self-grinding machine has high yield, stable production, reduced dust and reduced wear. [next]

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