The primary coal mine resources are concentrated underground, so coal mining work needs to be done underground. Compared with machinery and equipment for other construction work, the working environment of coal mine machinery is even harsher. The underground contains a lot of dust, noise, water vapor, and a large amount of acidic gas or liquid. The machinery must withstand a lot of environmental pressure during operation. The most common parts are mechanical gears in the entire coal mine machinery and equipment. Automatic gears are often in a long-term working state and have been subjected to considerable working pressure and environmental pressure, so various failures, especially broken gear—tooth problems. The maintenance of these gear failures is complicated, which directly affects the smooth progress of the entire mining work. Therefore, it is necessary to actively study the reasons for the loss of coal mine machinery and equipment and apply effective preventive measures to ensure that the machinery and equipment can operate normally and related work can be carried out smoothly.
1. The main reasons for broken teeth of mechanical gears
During the operation of mechanical equipment, the problem of broken teeth of mechanical gears will inevitably occur. Generally speaking, the gears that often have issues are heavy-duty gears in the working transmission system. Many. For example, the last stage gear in the reducer of the road header often suffers from broken teeth. Such gears have a huge torque during operation and are often subjected to various super-strong pressure shocks, so the tooth roots of the gears often bear concentrated solid force. Under the influence of long-term pressure, the origins of the gears are powerful. Broken teeth are prone to problems. In addition, as the bending stress on the gear increases, the service life of the gear will gradually decrease. Because of this, actively exploring and applying methods to reduce the bending stress of broken teeth can increase the service life of gears to a certain extent and effectively prevent the problem of broken teeth of mechanical gears. According to the analysis of the actual work situation, many factors cause the issue of broken teeth in mechanical gears. There are three main influencing factors:
1.1 Causes of broken teeth due to fatigue
The so-called fatigue tooth breaking problem is the phenomenon of mechanical gear breaking, and the entire gear will break according to the extension direction of the automatic teeth. Once the area of the mechanical gear is large, the end of the mechanical gear will die. Generally speaking, under the direct influence of the load force, the automatic helical teeth are prone to the problem of inclined cracking. Fatigue tooth breakage is a concave cracking curve that often occurs on gears used for overall quenching work. Or produce a concave step-shaped cracking curve caused by surface oxidation treatment. Once these two types of fatigue tooth breaking problems occur, the staff can identify the specific crack location and observe the gear tooth breaking process. The applied pressure is the main reason for the fatigue and tooth breakage of mechanical gears. The gears have been in operation for a long time. If the bending stress at the root of the teeth exceeds the bearing capacity of the gears, serious problems will occur. Fatigue, injury problems. If things go on like this, the gear’s root will suffer fatigue damage due to the tension problem. The crack will lengthen or deepen with the increase of time until it finally breaks completely, and the mechanical equipment no longer operates.
Specifically, the fatigue tooth breaking problem can be divided into two types: the low cycle fatigue tooth breaking issue and the high cycle fatigue tooth breaking issue. Common cycle fatigue tooth breakage is widespread because mechanical gears are always in cyclic operation under the influence of bending stress, so breakage occurs. In addition, when the automatic gear is under pressure, there has been a certain amount of damage inside the gear in the early stage. During the bending stress process, the gear’s internal bearing capacity will gradually change. As the gear’s working time becomes longer, the gear elasticity of the raw material will worsen. Then there will be severe deformation problems, and cracks will gradually appear. A rigid low-cycle fatigue fracture surface will be formed in the long run.
All in all, many factors lead to the problem of low-cycle fatigue tooth breakage in mechanical gears. The load force of the gears and the quality of the materials of the computerized facilities are all critical influencing factors. The high cycle fatigue gear tooth breakage problem occurs because the gears are subjected to more stress cycles than their actual bearing capacity. The pressure at the root of the mechanical gear far exceeds its actual bearing capacity. Generally speaking, this kind of problem will not appear in the early stage of work, and with the increase in gear usage time, the potential accumulated loss will become more serious. Under the influence of cyclic load force for a long time, mechanical gears will naturally occur due to stress concentration. Damage, if the number of stress cycles is too many, serious cracks will appear at the root of the mechanical gear, and then the problem of high cycle fatigue tooth breakage will occur. Specifically, suppose the entire mechanical working environment is relatively stable. In that case, the load stress does not change much, and the gear quality is high, then the automatic gear will suffer from high-cycle fatigue and tooth breakage during long-term operation.
1.2 Reasons for static broken teeth
There are many reasons for the problem of eccentric load and broken teeth in mechanical gears. The main reason is that the primary and auxiliary machine protection malfunctions are caused by the load not being evenly distributed with the contact line. Specifically, many factors cause the problem of eccentric load and broken teeth in mechanical gears. Temperature changes, pressure changes, flow changes, or valve position deviations can all cause this problem. During the operation of mining machinery and equipment, if the rigidity of the casing and shaft of the machinery equipment is relatively poor, the issue of eccentric load and broken teeth will often occur. In addition, in the entire mechanical operation system, a thermometer is usually installed, and the staff can observe the machine’s working condition according to the temperature displayed by the thermometer. Once the temperature indicated by the thermometer is abnormal, the mechanical gear likely has a problem of eccentric load and broken teeth. If the gear is offset between the two shafts, the pressure on the automatic gear will be too enormous. Once deformation or operation problems occur, the load capacity of the entire mechanical gear will not reach the working standard, and the load will not be able to get to the contact line of the gear. The distribution of the gears is the same. Once the eccentric load problem occurs, the two shafts of the gear will be deformed in opposite directions, and the entire gear will be gradually impaired, resulting in a fracture problem. During the mining work, the mining machinery and equipment often have the problem of eccentric load and broken teeth, which will seriously affect the whole work process. The impact of abnormal load broken teeth on mechanical equipment is enormous; the bearing capacity of the surfaces of the two mechanical gears will change, the correct position of the gears is seriously deformed, and the tooth roots at the end of the gears need to bear a sizeable bending force. Withstands up to 3 to 7 times more stress than without eccentric loading. In short, if the mechanical equipment has the problem of abnormal load and broken teeth during the operation, it will seriously affect the regular operation of the mechanical equipment and even damage the entire kit. It can be seen that it is necessary to actively study the reasons for the eccentric load of broken teeth, try to alleviate the abnormal load of broken teeth problem as much as possible, reduce the impact of this problem on routine work, and improve the safety of mechanical operation.
1.3 Reasons for the issue of static broken teeth
During the mining work, the working environment is impoverished, and the operating equipment is not perfect, so the gears on the mining machinery and equipment often have the problem of static broken teeth. The principle of the static tooth breaking problem is also straightforward. The external load of the mining machinery gear suddenly increases, far beyond the range that the mechanical gear can bear, and the static tooth breaking problem occurs in gear. Specifically, during the construction of the coal mine, if the coal mining machinery accidentally touches relatively solid rocks or other solid objects, the resistance of the entire cutting work will increase in an instant; if the workers are not skilled in the operation For related machinery, the uneven surface of the working floor may cause the problem of the shearer drum cutting the hydraulic support top beam, or the issue of the shovel plate in front of the scraper conveyor on the coal mining face, which will lead to cutting resistance. Rapid increase, which makes the shearer drum bear more excellent resistance and cannot usually work, then increasing the moment of inertia of the system parts in the cutting rocker arm will directly act on the gear teeth of the loaded gear. At this moment, the mechanical wheel’s pressure and dynamic torque on the teeth are much higher than the torque transmitted by the cutting motor. Under the severe influence of such a significant impact force, the bearing capacity of the mechanical gear will reach the limit, and the problem of brittle fracture of the gear teeth will occur.
2. 7 tips to avoid gear tooth break in coal mine machinery
2.1 Estimate the load force on the mechanical gear in advance
In fact, during the operation of mining machinery, the load force on the mechanical gear is constantly changing. It is necessary to estimate the load capacity of the automatic equipment in advance so that the gear’s strength and specific service life can be studied in depth. Many factors affect the gear load in the working process, and some external force factors are unavoidable, so there is no clear and effective calculation method. The commonly used methods in the actual work process are statistical, analogy, or new calculation. Relevant designers further develop technical solutions for estimating a load of mechanical gears according to the actual work situation, improve the accuracy of calculation data, and then design effective A-specific solutions to prevent the problem of broken teeth in mechanical gears.
2.2 Strengthen the rigidity of the mechanical gear housing and shaft
Based on the analysis of the reasons for broken teeth of mechanical gears, it is found that to avoid the problem of gears with eccentric load and broken teeth as much as possible, it is necessary to continuously strengthen the rigidity of the mechanical gear casing and shaft, and install the steel casing on the mining machinery gears: Cast iron or welded mechanical housing. In addition, it is possible to strengthen the rib plate on the automatic gear casing and strengthen the shaft hole boss to meet the actual demand standard of the shaft volume as much as possible.
2.3 Install overload protection device for broken teeth
There are more and more existing overload tooth-breaking protection devices. The most common are shear pin type couplings and friction disc type coupling clutches. The cutting torque of these devices is tremendous. Once the pressure on the mechanical gear is found, If it is more significant than its bearing capacity, the clutch will directly cut off the fuse to protect the related parts and prevent seriously broken teeth.
2.4 Active application of variable gears
If you want to increase the elasticity of the gears, you can constantly adjust the modulus of the gears. However, this method has excellent limitations in operation. Once the process of related mechanical equipment is carried out in the well, the entire space is entirely restricted, and the size of the mining machinery has to be reduced, which means that it is impossible to increase the mold of the gear. Number. To effectively solve this problem, it is necessary to actively apply to shift gears to improve the stability and safety of work continuously.
2.5 Continuously improve the precision and installation level of gear manufacturing:
Generally speaking, the contact accuracy of the manufactured gears must be as high as eight, so when making mechanical gears, it is necessary to pay attention to the processing of the root of the gears and complete the grinding work according to the manufacturing requirements to ensure that the stress on the gears will not be completely concentrated. . When installing mechanical gears, it is necessary to ensure that the angle of the bearing meets the installation requirements, leaving a corresponding tooth gap to reduce the bending stress on the root of the tooth, thereby effectively preventing the mechanical gear from breaking.
2.6 Maintenance of mechanical gears according to tooth length direction
The drum-shaped trimming according to the tooth length direction can make the side of the gear form a waist drum shape along the tooth length direction, and the broken tooth profile will gradually show an open line shape, which can effectively alleviate the problem of gear eccentric load.
2.7 Strengthen the management of the construction site and improve the management level
To effectively prevent the problem of broken teeth of mechanical gears, it is necessary to strengthen the management of construction sites and improve the management level. First, improve the technical level and operation ability of the staff to ensure that the mechanical operation will not cause the problem of gear breakage due to improper operation. Second, clarify the responsibilities of each staff member, clean up construction waste in time, and protect the construction environment. Third, the staff must check and maintain the mining machines in time and take defensive measures in advance to ensure the smooth progress of the work.
