The function of the gear transmission system of coal mine machinery is to transfer movement and power for the mining work of coal mine machinery. In order to ensure the working efficiency and working time of coal mine machinery, it is necessary to put forward requirements for the accuracy and stability of its gear transmission. According to the fault type analysis of coal mine machinery gear described above, the main factors affecting the life of the gear transmission system of coal mine machinery are determined as Internal factors include gear damage and load characteristics, and external factors include gear lubrication and other factors. The following will be analyzed according to the influence degree of the life of the coal mine mechanical gear transmission system.
Gear damage
The long-term overload operation of coal mine mechanical gear causes certain damage to it, which will seriously affect the working reliability of its gear transmission system, and the degree of damage will determine the normal working life of the coal mine mechanical gear transmission system. However, not all gear damage will cause gear transmission system failure, and the impact of various damages on the transmission is not completely independent, but there is a mutual relationship. The quality of gear transmission is the comprehensive result of all kinds of gear damage, and the influence of each other on the quality of gear transmission may be superimposed or offset.
There are many factors that cause gear damage. If we study all the influencing factors, it is not economic or necessary. Therefore, combined with the main fault types of coal mine mechanical gear, the causes of tooth fracture, pitting, gluing and wear, we can determine the influencing factors of gear damage on the life of gear transmission system as follows: the ratio of tooth crack width to tooth width; the maximum pitting area and tooth area Ratio; the ratio of the maximum size of pitting pit to the modulus value; the ratio of the maximum depth of pitting pit to the modulus value; the ratio of the area of gluing area to the area of gear teeth; the ratio of the depth of gluing groove to the modulus value; the ratio of the sum of the loss on both sides of worn tooth root to the normal modulus value.
Gear lubrication
The gear transmission system of coal mine machinery relies on the force generated when the gears mesh with each other to transmit the movement and power. The lubricating oil plays a key role in the bearing capacity and working life of the gears. The lubricating oil can not only form a layer of lubricating oil film in the process of gear meshing to avoid the tooth surface damage caused by the direct contact of the tooth surface, but also improve the transmission efficiency, reduce the temperature of the teeth Reduce vibration and noise, prevent gear from rusting and improve gear operation.
However, due to the poor working environment of coal mining machinery, the gear lubricating oil often deteriorates due to oxidation or mixing with moisture, mechanical impurities and other reasons, resulting in the change of lubricating viscosity, which is an important evaluation index of lubricating oil, and its change will have a serious impact on gear transmission.
1) Viscosity of lubricating oil
The relationship between the maximum contact stress of gear and its friction coefficient is positive correlation. Therefore, under the condition of good lubrication, the friction coefficient of gear surface can be reduced, and the maximum contact stress of gear surface can be reduced accordingly, which will help to improve the contact fatigue strength of gear.
The influence of different viscosity of lubricating oil on the thickness of oil film on the meshing surface can be seen from its change curve that the thickness of oil film and the viscosity of lubricating oil are also positively correlated. The curve between the viscosity of lubricating oil and the minimum film thickness shows a linear change, that is, the film thickness increases with the increase of the viscosity of lubricating oil. It can be seen from the above that the influence of lubricant viscosity on oil film thickness will determine the lubrication conditions of gear engagement.
At the same time, the temperature of gear lubricating oil film increases with the increase of viscosity, because the increase of lubricant viscosity will increase the friction force on the tooth surface in the process of meshing, so that the temperature increases. When the temperature of lubricating oil is high, it will lead to the increase of gear temperature, the decrease of gear side clearance, the increase of gear meshing stress and the shortening of gear life.
2) moisture content
Due to the large moisture content in the coal mine underground, there is often water mixed into the gear lubricating oil, which will produce chemical corrosion on the gear, rust on the gear surface, resulting in the reduction of the contact surface strength of the gear and shortening the working life of the gear transmission. The water and air in the lubricating oil act together with the metal ions formed by rust to accelerate the oxidation reaction of lubricating oil, make it emulsified and accelerate the corrosion and wear of gears.
Additives in lubricating oil, especially extreme pressure anti-wear agents, preservatives and other active agents, some of which are soluble in water, some of which precipitate with water, resulting in the failure of lubricating oil additives and affecting the lubrication effect of gears.
3) Mechanical impurities
Mechanical impurities in lubricating oil include carbon slag, dust and metal particles damaged and peeled off by gears in the process of coal mining. Mechanical impurities will have a serious impact on the formation of lubricating oil film, resulting in increased wear of gears, at the same time, it will block the oil filter and make the lubricating oil not effectively cleaned. Therefore, excessive mechanical impurities will lead to abnormal operation of gear transmission.
Load characteristics
The gear transmission system of Coal Mine Machinery Works for a long time. Under the action of repeated alternating stress, after a certain number of cycles, the gear will form fine cracks at its stress concentration, and the cracks will continue to expand, and finally the gear will break, that is, the gear will produce fatigue damage.
Every rotation of coal mine mechanical gear will cause certain damage to the gear, but the number of cycles can indirectly reflect the fatigue damage, so the average number of cycles of gear damage can be used as the basis for judging the damage degree. However, in the process of gear rotation, the actual cycle times are often seriously affected by external factors. Therefore, the design cycle times of gear are also used as the basis for judging the degree of damage. Therefore, the ratio of gear cycle times to its average cycle times and the ratio of gear cycle times to design cycle times are taken as the basis of judging gear fatigue damage.
Other factors
1) Machining error
The machining error will directly lead to the error of gear tooth shape, affect the stability of gear transmission, and reduce the working life of gear transmission.
2) Assembly error
Because of the assembly error, the gear transmission system will cause incomplete contact, different shafts and imbalance. If the meshing surface of the gear is not parallel, the wear of both ends of the gear will be inconsistent, which will cause the uneven force on the gear teeth during the meshing process, and affect the stability of its transmission. At the same time, the load on one side of the gear will be too large, which will cause the gear teeth to break seriously.
3) Impact load
Due to the inhomogeneity of coal seam, the gears of coal mine machinery will be subjected to additional nonlinear impact load in the working process. At the same time, when the speed of the gear transmission system changes suddenly, the gears will also be subjected to impact load, which will cause severe vibration and noise of the gears, and seriously affect the transmission performance of the gears.
4) Use and maintenance
Overload, overspeed and lack of oil in the gear drive of coal mine machinery will aggravate the damage of tooth surface, and the abnormal heating and abnormal noise in the process of gear drive will lead to serious fault of gear drive system if they are not checked and replaced in time.
