Coal hammer crusher is important equipment for crushing large raw coal. Its stable operation plays an important role in ensuring the raw coal conveying efficiency of the underground coal mine. We can put forward the corresponding solutions via analyzing the main fault sources and common faults of coal hammer mill crushers. Then improve the hammer coal mill crusher’s operation reliability, reduce the maintenance difficulty, and make sure the smooth progress of coal mining.
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According to the working principle, coal crusher can be divided into two types: hammer crusher and jaw crusher. The hammer mill crushers have large processing capacity that max capacity is 4000tph. So the coal plant mainly uses hammer crushers to crushing raw coal. The power of the hammer crusher general is 90 ~ 400kw, which mainly depends on the rotating parts to drive the hammer up. Then crush the lump coal to the particle size which is easy to transport by the impact force of the hammer falling.
As important equipment of the underground coal mine transportation system, a coal hammer crusher is usually installed in the middle of the climbing section. The large piece of raw coal is transported to the transfer machine by the scraper conveyor and then guided into the hammer crusher by the transfer machine. The coal is crushed into small pieces by a hammer coal crusher and then transported to the ground coal yard.
Hammer coal crusher structure
The coal hammer mill crusher is composed of a bottom groove, crushing frame, hammer shaft, driving and adjusting device, and lubricating system. It has no transshipment function which needs after connecting the crushing bottom groove and connecting slot. Then uses the transshipment machine. The hammer impact crusher frame body is located on the upper part of the bottom groove and installs a crushing hammer shaft in the middle of the frame body. The mechanism is that the hammer shaft is lifted to a certain height through the transmission device which increases the gravitational potential energy. After falling, the hammerhead impacts and squeezes the raw coal at the bottom trough, crushing it to smaller particle sizes. The small coal particle is convenient for continuous conveying by the transfer machine.
Coal crusher power
According to the power of the equipment, the underground coal hammer crusher adopts two different transmission forms: pulley and retarder. In general, the belt pulley transmission is only used for power below 250kw. The power greater than 250kw is through the reducer.
Analyze fault for the large-scale, high-power hammer mill crusher, it can’t diagnose specific faults. If the equipment fault is considered to be caused by the damage of a single component, the diagnosis is too one-sided. The test results may be biased, and the subsequent maintenance of the equipment may not achieve the desired repair effect. Therefore, the failure of a high-power hammer crusher should be considered from various factors, such as the design, processing, installation, commissioning and use.
(1) Defects in design and processing
The design should ensure the stability of the structure and the good dynamic characteristics of the equipment. The unreasonable mechanical structure will lead to the local stress concentration and affect the dynamic characteristics of the equipment. Then they may lead to forced vibration or self-excited vibration and other undesirable phenomena. In addition, the common design and manufacture defects include working speed and the material of the spare part can not meet the design requirements, machining accuracy is too low, poor moving cone balance performance, etc.
(2) Installation, debugging, maintenance
The hammer crusher installation, commissioning and maintenance stage may occur crusher parts installation dislocation. The transmission system with the shafting and installation location is not appropriate. The overall equipment geometric parameter adjustment is not good. The installation position of the dynamic cone is not reasonable. All the problems may lead to the equipment large load and poor stability in operation.
3) Operating mistake
In the process of man-made operation, the equipment abnormal opening, closed and adjusted speed improperly. The equipment operated beyond the designed working condition for a long time. Lack of maintenance. Lubrication between the components was insufficient. These also cause the failure of the hammer crusher.
(4) Parts wear and deformation
The coal hammer crusher operates for a long time, the parts are easy to wear and deformation. Individual parts may be shaken off, crack or even damage. The dynamic cone changes, spare parts will also be affected by the external environment caused by pitting or corrosion. Or with other parts wear each other. Or affected by vibration which causes uneven settlement of the ground where the equipment is located. At the same time, the increase of clearance between some spare parts, losing fit surface and lowering of fit surface friction will affect the normal work of the hammer mill.
5 Analysis of common faults
According to mine production practice, the malfunctions of the hammer coal crusher are divided into the following types.
Movable cone unbalance
The vibration and the movement of the dynamic cone in the operation of the hammer crusher will cause the dynamic cone ware. Then lead to the eccentricity of the center of gravity of the dynamic cone and the unbalance of the dynamic cone. The problems caused by the unbalance of the movable cone are as follows:
- The dynamic cone produces the eccentric distance and changes the rotor stress condition which causes its stress not to be even, the dynamic cone repeatedly bends in the rotating movement process. When the fatigue limit is reached, it may occur damage or even fracture.
- The violent vibration causes noise, which disturbs the external environment.
- During the working process, the rotor will be deflected due to uneven force, which will cause friction with the bearing or other adjacent parts. It not only causes the wear and tear of the parts in the equipment but also affects the working efficiency of the equipment. This is more serious security risks, should strengthen inspection and timely disposal.
The rotor misalignment is the main cause of all kinds of mechanical failures, as shown in Fig. 1.
In the rotor system which connects with coupler, misalignment between the two rotors will cause the coupler to deflect. The bearing affected will shorten the service life, affect the stability of oil film, the operation is not smooth. We should increase the monitoring of rotor misalignment faults and focus on the detection of vibration amplitude and phase stability.
Rotor rub-impact, shaft misalignment
The rotor system is affected by factors such as misalignment of the rotor, bending of the shaft, loosening of the foundation, wear of the bearing, improper assembly, etc. It will rub-impact with bearings. Although the torque of the rotor can be balanced when the equipment is running, the speed is greatly affected. The rotor system is unstable, and the overall stability of the equipment decreases.
The main performance: one is the rotor system vibration, the other is the impact of rub-impact on the rotor itself. The combination of the two results in more complex adverse reactions, such as phase reverse displacement and axial trajectory diffusion or turbulence. In the design stage, in order to ensure the stability of the equipment, the gap between the rotating parts and the adjacent parts is relatively small, and the probability of the rub-impact phenomenon is more easily increased.
Oil Whirl is a phenomenon that the rotor of the transmission system moves the wedge oil film around the center of the bearing bush according to the average velocity of oil due to vibration and rotation fluctuation. The main characteristics are the smooth phase. It is obviously affected by lubricating oil characteristics. The trajectory presents a double – ring ellipse. The subharmonic generated by the vibration will change with the increase of the rotational speed.
Loose foundation and crankshaft bearing
Hammer crusher is rotating vibration equipment. The foundation and fixed foundation bolt vibration during the crusher machine operating. It is easy to cause the bolt loose. At the same time, the bearing pedestal will be loose because of vibration. Vibration amplitude is large, mainly acting in the vertical direction. In order to determine the foundation and bearing pedestal looseness, the vertical vibration signals are detected and compared with the vibration signals of crusher and foundation bolt. If the foundation and the bearing seat are looser, there will be a big difference between the two vibration signals, which should be handled in time to avoid accidents.
The coal hammer crusher is the key equipment for crushing large raw coal in the underground coal. The machine is an important part of the raw coal transportation system. The common problems are design Defects, installation, debugging and maintenance problems, parts wear and deformation, movable cone unbalance, rotor rub-impact, shaft misalignment, etc.