Impact crusher structure, working principle and features

1. Impact crusher structure

  • 1.1 Impact crushers can be divided into two types according to the number of rotors: single-rotor and double-rotor impact crushers.
  • 1.2 The structure of the single rotor impact crusher (Figure 1) is relatively simple and consists mainly of the rotor 5 (strike plate 4), the impact plate 7 and the machine body. The rotor is fixed to the main shaft. In the cylindrical rotor is equipped with three (or several) strike plate (plate hammer), strike plate and rotor are more rigid connection, and the strike plate is made of wear-resistant high manganese steel (or other alloy steel).
  • 1.3 One end of the impact plate is hinged on the upper body 3 by the suspension shaft, and the other end is supported by the tie bolt on the conical washer of the upper body using the spherical washer, so the impact plate is freely suspended inside the machine. When the non-crushing objects enters impact crusher, the impact plate is subject to a large reaction force, forcing the tie bolt (compression spherical washer) “automatically” back to lift, so that the non-crushing objects discharged to ensure the safety of the equipment, this is the impact crusher safety device. In addition, adjusting the nut above the tie rod bolt can change the size of the gap between the strike plate and the impact plate.
  • 1.4 The body is divided into two parts, upper and lower body, along the axis. The upper body is equipped with inspection holes for maintenance and observation. The lower body is fixed to the foundation with foot bolts. The inner surface of the body is equipped with a protective liner of replaceable wear-resistant material to protect the body from abrasion. The chain curtain installed at the feed opening of the crusher (near the first stage impact plate) is a protective measure to prevent the ore from flying out during the crushing process of the machine.
  • 1.5 Double-rotor impact crushers, depending on the rotor rotation direction and rotor configuration position, are further divided into the following three types (as shown in Figure 2).
  • 1.5.1 Two rotor reversal rotation impact crusher (Figure 2 a). The two rotors move in opposite directions, equivalent to two parallel configurations of single-rotor impact crushers in parallel. The two rotors form separate crushing cavities with the impact plate for split-cavity crushing. This type of crusher has high production capacity and can crush large size ore, and the horizontal configuration of the two rotors can reduce the height of the machine, so it can be used as a coarse and medium crushing crusher for large mines.

    1.5.2. Impact crusher with two rotors rotating in the same direction (Figure 2 b). The two rotors move in the same direction, which is equivalent to the tandem use of two single-rotor impact crushers with parallel devices, and the two rotors form two crushing chambers. The first rotor is equivalent to coarse crushing and the second rotor is equivalent to fine crushing, i.e. one impact crusher can be used as coarse crushing and medium and fine crushing equipment at the same time. The crusher has a large crushing ratio and high production capacity, but consumes more power.

    1.5.3. Impact crusher with two rotors rotating in the same direction (Figure 2 c). The two rotors are configured according to a certain height difference, with one rotor positioned slightly higher for coarse crushing of the ore and the other rotor positioned slightly lower for fine crushing of the ore. This kind of crusher is to make use of expanding the working angle of the rotor and adopting the principle of splitting cavity (crushing cavity) to focus on impact crushing, which makes the two rotors give full play to coarse crushing and fine crushing. Therefore, this kind of equipment has a large crushing ratio, high production capacity, uniform product size, and the two rotors are in a high differential configuration, which can reduce the defects of missing large particles that do not meet the required product size.

  • 1.6 The following is an example of a domestic Φ1250×1250 double rotor impact crusher with a certain height difference configuration (Figure 3) to introduce its structure in detail, the characteristics of this crusher are
  • 1.6.1. The two rotors have a certain height difference (the angle between the center line of the two rotors and the horizontal line is 12°), which enlarges the working angle of the rotors and makes it possible for the first rotor to have the possibility of forced ore feeding and the second rotor to have the possibility of increasing the linear speed, resulting in sufficient crushing of the ore to obtain the final product size requirement.

    1.6.2. The two rotors moving in the same direction with the first and second stage impact plates form the coarse crushing and fine crushing cavities respectively. The first stage rotor and impact plate crush the ore from -850 mm to about 100 mm and feed it into the fine crushing chamber; the second stage rotor and the second stage impact plate continue to crush the material to -20 mm and discharge it through the discharge grate at the lower part of the crusher.

    1.6.3. The two rotors are equipped with different number of hammer heads, different hammer head heights and hammer head shapes, as well as two rotors with different linear velocities, their situation is generally as follows: the first rotor is fixed with 4 rows of hammer heads totaling eight plate hammers, crushing the large pieces of ore entering the crusher at a linear speed of about 38 m/s; The second rotor is fixed with 6 rows of hammer heads and 12 rows of plate hammers, which continue to crush the incoming material of about 100 mm into the required product size at a linear speed of about 50 m/s.

    1.6.4. In order to ensure the quality (particle size) of the crushed product, additional discharge grate plates are installed at the discharge of each of the two rotors.

  • 1.7 Key parts of the impact crusher
  • As can be seen from Figure 3, the rotor, plate hammer and impact plate are the main body of the impact crusher.

    1.7.1 Rotor: It is the most important working part of the impact crusher and must have sufficient weight to suit the needs of crushing large pieces of ore. Therefore, the rotor of large impact crusher, generally adopts the monolithic cast steel structure. This integral rotor is not only heavier and more durable, but also easier to place the strike plate. Sometimes several pieces of cast steel or steel plates are also used to form the rotor of the disc stacking type. This combined type of rotor is easy to manufacture and easy to get balanced. Smaller crushers are made of cast iron, or hollow rotors welded with steel plates, but they are less strong and sturdy.

    1.7.2 Plate hammer: also known as the strike plate, is the most easily worn working part of the impact crusher, much more serious than other crushers. The wear degree and service life of the plate hammer is directly related to the material of the plate hammer, the hardness of the ore, the linear speed of the plate hammer (rotor circumferential speed), the structure type of the plate hammer and other factors, of which the material of the plate hammer is the main factor in determining the degree of wear. Plate hammer material is currently used with high manganese steel or high chrome alloy steel.

    The plate hammer is fixed on top of the rotor by
    A. Screw fixing. This fixing method, not only the screw exposed to the striking surface, very easy to damage, and the screw is subject to large shear, once the shear will cause serious accidents.

    B.Pressure plate fixing. Plate hammer from the side into the groove of the rotor, the ends by the pressure plate. But this way of fixing the plate hammer is not strong enough, the work of the plate hammer is easy to loosen, this is because the plate hammer manufacturing processing requirements are very high and high manganese steel and other alloy materials are not easy to process.

    C.Wedge fixing. The use of wedge plate hammer fixed in the rotor way, work under the action of centrifugal force, this fixed way more and more solid, and reliable work, removal and replacement is more convenient. This is a better way of fixing the plate hammer at present, and almost all manufacturers are adopting this fixing method.

    The number of plate hammer is related to the diameter of the rotor specification. Generally speaking, when the diameter of rotor specification is less than 1 meter, three plate hammers can be used; when the diameter is 1-1.5 meters, 4-6 plate hammers can be used; when the diameter is 1.5-2.0 meters, 6-10 plate hammers can be used. For processing harder ore, or larger crushing ratio, the number of plate hammer should be more.

    1.7.3 Impact plate: The structure of the impact plate has a great influence on the crushing efficiency of the crusher. The impact plate is mainly in the form of a bending or arc-shaped structure. The bent impact plate (see Figure 1) is simple in structure, but does not guarantee the most efficient impact crushing of the ore. The arc-shaped impact plate (see Figure 3) is more commonly used in the form of an involute, which is characterized by a high crushing efficiency as the ore is impacted in a vertical direction at all points of the impact plate.

    1.7.4 In addition, the impact plate can also be made into the form of impact fence and impact roller. This structure can mainly play a screening role, improve the production capacity of the crusher, less over-crushing phenomenon, and reduce power consumption.

    1.7.5 One end of the first stage and second stage impact plate is hinged on both sides of the upper body through the suspension shaft, and the other end is supported by the tie bolt (or adjusting spring) on the body respectively.

    1.7.6 By changing the position of the impact plate, the particle size of the coarse crushing chamber and the fine crushing chamber can be adjusted. The square cross-sectional shaft hanging from the impact plate is connected to the connecting rod and compression spring mounted on both sides of the machine body.

  • 1.8 Both ends of the rotor are supported on the lower body by double-row radial spherical rolling bearings. Due to the high circumferential speed of the rotor, the bearings need to be lubricated with molybdenum disulfide grease. Several inspection holes (observation holes) are opened on the body for installation, inspection and maintenance.
  • 1.9 The transmission device of the crusher is driven by two motors, through the flexible coupling, hydraulic coupling and v-belt device, respectively, to drive the two rotors for the same direction of rotary motion. The use of hydraulic coupling can make the motor become a light load start, reduce the torsional vibration and load pulsation during operation, and can prevent the motor and crusher from overload and protect the motor and crusher from damage.
  • 2. Impact crusher working principle

    Impact crushers are machines and equipment that use impact energy to crush ore. In terms of the form of mechanical energy, the crusher that applies the principle of “free” crushing by impact force is superior to the crusher that uses the principle of crushing by static pressure. The jaw crushers, cone crushers are basically based on the principle of extrusion crushing, while impact crushers use the principle of impact “free” crushing to crush the ore. As shown in Figure 2-4-4, when the ore enters the crusher, it is mainly impacted by the high-speed rotating percussion plate, and the ore is selectively crushed along the laminae and joints. After being impacted, the ore gains huge kinetic energy and is thrown to the first impact plate at a high speed along the tangential direction of the impact plate, and then the ore is crushed again by the impact of the impact plate. The crushed material is also thrown to the second stage impact plate at a high speed and is crushed again, resulting in an “interlocking” crushing action of the ore (material) in the impact crusher. When the ore is in the round trip between the strike plate and the impact plate, there are many times between the ore (material) impact with each other. This process is repeated until the size of the crushed material is smaller than the gap between the striking plate and the impact plate, then it is discharged from the lower part of the crusher, which is the size of the crushed product.

    3. Impact crusher features

    Although the impact crusher appeared late, the development is very fast, at present, it has been widely used in the medium and fine crushing industries of cement, construction materials, coal and chemical and mineral processing, etc, it also can be used as coarse crushing equipment for ore.

    The reason why the impact crusher is developing so rapidly is mainly because it has the following important characteristics.

  • The crushing ratio is very large. Generally, the maximum crushing ratio of the crusher is not more than 10, while the crushing ratio of the impact crusher is generally 30-40, and the maximum is 150. Therefore, the current three-stage crushing process can be completed with one or two-stage impact crusher, which greatly simplifies the production process and saves investment costs.
  • High crushing efficiency and low power consumption. Because the impact strength of general ore is much smaller than the compressive strength, at the same time, because the ore is cracked first along the junctional partition interface and fragile organization after the high-speed action and multiple impacts of the striking plate, the crushing efficiency of this type of crusher is high and the electric power consumption is low.
  • Uniform product size and less over-crushing phenomenon. This kind of crusher uses kinetic energy to crush the ore, and the size of kinetic energy of each piece of ore is proportional to the mass of the piece of ore. Therefore, in the crushing process, the large pieces of ore are crushed to a greater extent, but the smaller particles of ore, under certain conditions, are not crushed, so the crushed product size is uniform, less over-crushing phenomenon.
  • Can be selectively broken. In the process of impact crushing, useful minerals and gangues are first broken along the joint surface to facilitate the separation of the monomers from the minerals, especially for the useful minerals with coarse grains (such as tungsten ore, etc.), this is even more significant.
  • Great adaptability. This crusher can crush brittle, fibrous and medium-hard ores, and is particularly suitable for crushing brittle ores such as limestone. Therefore, the impact crusher is very suitable for the cement and chemical industries.
  • The equipment is small in size, light in weight, simple in structure, easy to manufacture and convenient to maintain.
  • Based on these obvious advantages of the impact crusher, it is widely used and developed in various countries. However, the main disadvantage of the impact crusher is that when crushing hard ore, the wear of its plate hammer (strike plate) and impact plate is large. In addition, the impact crusher is a machine that rotates at high speed and relies on impact to crush ore, which requires high precision in parts processing and static and dynamic balancing in order to prolong the use time.

    The specification of the impact crusher is expressed by the rotor diameter D (actually the diameter of the circumference drawn on the end of the plate hammer) X rotor length L. For example, Φ1250×1000 single rotor impact crusher, indicates a rotor diameter of 1250 mm and a rotor length of 1000 mm.

    4. Technical parameters of impact crusher