Analysis on fault diagnosis technology of rocker gearbox of coal shearer

Wang Xiaopei

In order to further improve the start-up rate of the shearer in the fully mechanized mining face, considering that the shearer rocker gearbox is one of the weak links, based on the analysis of the shearer rocker gearbox structure, the fault types of the rocker gearbox are analyzed, the vibration signal characteristics corresponding to different faults of the rocker gearbox are analyzed, and effective diagnosis strategies are combined to accurately complete the diagnosis of rocker gearbox faults. Practical application shows that the gearbox fault diagnosis technology has good application effect.

The shearer is a key machine on a fully mechanized coal face, responsible for cutting the seam and bringing down coal. Against the current drive toward highly efficient and safe production, the high-intensity, high-power production requirements of the face demand better shearer performance. Practical experience shows that the shearer's ranging-arm gearbox is a relatively weak link and suffers frequent failures in production. Statistics indicate that ranging-arm gearbox failures account for as much as 34.2% of shearer failures. This figure already affects shearer availability and consequently the efficiency of face production.

This article focuses on the research on fault diagnosis technology of gearbox, the weak link of coal shearer.

01 Shearer rocker gearbox structure and failure analysis

Shearer rocker gearbox structure: An ordinary electric traction shearer consists of a cutting part, a traction part, an electrical control box, etc. The rocker gearbox of the shearer is an important part of the cutting part. As a key component of power transmission, it transmits the power of the cutting part motor to the cutting drum, thereby completing the tasks of coal dropping and coal loading. The three-dimensional structure of the shearer rocker gearbox is shown in Figure 1.

Figure1 Three-dimensional structure of shearer rocker gearbox

As shown in Figure 1, the inside of the shearer rocker gearbox is the power transmission system of the cutting part, which mainly includes two-stage spur gears and two-stage planetary gears. The above-mentioned gear train constitutes the reduction system of the rocker arm of the cutting part of the shearer, and includes a primary spur gear reduction gear train composed of two spur gears, a secondary spur gear reduction gear train composed of 6 spur gears, a primary planetary gear reduction gear train composed of 3 planetary gears, and a secondary planetary gear reduction gear train composed of 3 planetary gears.

Among them, the 4 gears in the middle of the secondary spur gear reduction gear train do not play the role of reduction, but only play the role of transmitting power. The main purpose is to increase the length of the rocker arm to adapt to the mining height requirements of the fully mechanized mining face. At the same time, the entire rocker arm gear is lubricated by splashing.

Rocker gearbox failure: According to the statistics of rocker gearbox failure types in the shearer cutting section in actual production, the frequent failures mainly include failures of the primary reduction spur gear and bearings in the high-speed zone, failures of the secondary planetary reduction gear train in the low-speed zone, and floating oil seals. Among them, the failure of the primary reduction spur gear and bearing in the high-speed zone accounts for 42% of all gearbox failures; the failure of the secondary planetary reduction gear train in the low-speed zone accounts for 30% of all gearbox failures; and the failure of the floating oil seal accounts for 29%.

The details are as follows:

1.High-speed zone first-level reduction spur gear system

Failures of primary reduction spur gears and bearings in the high-speed zone are mainly characterized by varying degrees of wear, pitting, scratches, or gluing on the gear tooth surfaces. The direct manifestation in actual production is that the gears in the high-speed area vibrate strongly and make loud noises, which leads to bearing failure. In the end, the failure needs to be eliminated by replacing the gears or bearings.

2. Secondary planetary reduction gear train in low speed zone

The failure of the secondary planetary reduction gear train in the low-speed zone is mainly manifested by the breakage of the planetary gear and the internal ring gear. The main reason for the above failure is that the planetary gear train has received a large impact or suffered excessive load for a long time.

3.Floating oil seal

The main manifestation of floating oil seal failure is that the floating seal is damaged. The main reason for the above failure is that the seal is damaged due to deterioration of hydraulic oil quality or fatigue damage, which causes hydraulic oil leakage in the rocker gearbox, which in turn induces other failures of gearbox gears or bearings.

This article focuses on the corresponding diagnosis and research on the faults of the primary reduction spur gear train in the high-speed zone and the secondary planetary reduction gear train in the low-speed zone of the rocker gearbox.

02 rocker gearbox fault diagnosis technology

Based on the different signal spectrum characteristics in response to different faults of the rocker gearbox, the fault type of the rocker gearbox is determined.

Analysis of rocker gearbox fault signal characteristics: Rocker gearbox faults can be subdivided into gear faults and roller bearing faults. The fault types of different components reflect different signal characteristics.

The failure modes of gears mainly include tooth surface wear, tooth surface gluing and scratches, tooth surface contact fatigue, broken teeth and bending fatigue. Different fault forms reflect different meshing frequencies in the vibration signals. In order to more accurately locate the fault type of the gear, it is necessary to analyze the additional pulses, implicit spectral lines and bearing vibrations in the vibration signals reflected by different fault types.

For roller bearings, in addition to vibrations caused by their own structures, faults are also the main cause of vibrations. When a rolling bearing is not well lubricated, is overloaded for a long time, or undergoes a sudden load change, defects such as peeling, cracks, or local damage may occur in the outer ring. Therefore, the vibration signal of a rolling bearing failure contains the vibration frequency of its own failure and the vibration frequency of the component itself. The roller bearing failures corresponding to different frequencies are shown in the table 1.

Rocker gearbox fault diagnosis strategy: On the basis of the different vibration signals corresponding to the different faults mentioned above, an effective diagnosis strategy can also accurately determine the fault type and location of the shearer rocker gearbox. Therefore, in the actual diagnosis process, different diagnosis strategies should be adopted according to the frequency of different faults. The specific introduction is as follows:

1) Use spectrum analysis method to diagnose the rotational frequency and its higher harmonics, gear meshing frequency and its higher harmonics;

2) Aiming at the modulation of the meshing frequency, it is diagnosed through a combination of spectrum and demodulation;

3) Aiming at the modulation of the gear's natural frequency, it diagnoses it by combining demodulation spectrum, refinement spectrum and frequency spectrum;

4) Aiming at the modulation of the natural frequency of the shearer rocker gearbox, it uses demodulation analysis, energy analysis, and a combination of time domain and frequency domain to diagnose it.

03 Coal shearer rocker gearbox fault diagnosis test

Based on the above-mentioned research on the fault diagnosis technology of the shearer rocker gearbox, taking the 7LS06 rocker gearbox as an example, sensors are set up on its key gears and bearings, and its vibration signals are collected to analyze whether there is a fault and determine the fault type. No obvious fault was found in the first-level spur gear train in the high-speed zone of the shearer rocker gearbox; an obvious fault frequency (193Hz) and its corresponding two harmonic frequencies appeared in the planetary gear train in the low-speed zone of the shearer rocker gearbox.

By comparing it with the corresponding natural frequency of the planetary gear train, it can be initially determined that a more serious fault has occurred at the head of the planetary gear. Moreover, through practical testing, it can be seen that after the surface temperature of the planetary gear head reaches 98°C and the planetary gear train is disassembled, it can be seen that the first-level planetary gear train is seriously damaged.

04 Conclusion

Coal shearers are key equipment in fully mechanized mining working faces. The stability and performance of the equipment directly determine the production efficiency and safety of fully mechanized mining working faces. As the weakest link of the rocker gearbox in the cutting part of the shearer, it is of great significance to obtain its fault type in advance and accurately locate it before repairing it quickly and accurately, ultimately improving the operating rate of the shearer. This paper specifically develops the fault vibration technology of the shearer rocker gearbox, and verifies the efficiency of the fault diagnosis technology through actual cases.

Through verification, it can be seen that this fault diagnosis technology can accurately and quickly complete the fault diagnosis of the rocker gearbox, and can be promoted and applied in actual production.

Source: "Machinery Management Development" 2022 07 issue

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