Vehicle wheelsets and their wear
Wheel set is one of the important parts in the running gear of metro vehicles. Because it bears large static and dynamic loads, each component must have sufficient strength and Factor of safety. With the rapid development of wheel rail technology and the reasonable matching of wheel rail hardness, integral rolled steel wheels have been widely used in subway vehicles. The integral rolling steel wheel eliminates the traditional inlayable tire, which is integrated with the wheel center and has high strength, high hardness, and good wear and heat resistance. However, due to the lack of tire, the wheel diameter reaches the limit, and the wheel center must be replaced as a whole. The vehicle is guided by wheel sets when passing through curves. The more curves there are, the smaller the radius. The more contact the wheel rims of the wheel sets have with the steel rails, the more severe the wear of the wheel rims. The design of subway lines is constrained by factors such as urban terrain, geology, underground pipelines, building distribution, construction conditions, and convenient transportation, resulting in many small radius curves.
The regulations for the overall rolled steel wheels used in subway vehicles stipulate that the new wheel diameter is 840mm, with a limit of 770mm. In addition, AC transmission power vehicles have strict regulations on the diameter difference of each wheel, with the difference between the diameters of two coaxial wheels not exceeding 1mm, the diameter difference of each wheel of the same power car bogie not exceeding 2mm, the diameter difference of each wheel of the same car not exceeding 4mm, and the thickness of the wheel flange being 32-26mm. The quality of its tread is of great importance to the smoothness and safety of operation. If the tread of a pair of wheels is punctured or the wheel flange reaches the limit, a non falling wheel lathe should be used to process the wheels of one car, with a unilateral cutting amount of 25mm each time. Based on this cutting amount, it can be inferred that the new wheel Z needs to be machined three times to reach the limit. Once the limit is reached, the bogie must be disassembled and the wheel set sent to the factory for replacement of the wheel cake. It goes without saying that a large amount of manpower and expenses have been spent. For a rolling stock depot, ensuring vehicle maintenance and stopping time is the key to normal operation. However, excessive repair distance inevitably leads to prolonged maintenance and stopping time, reduced vehicle utilization, and tight vehicle usage. At the same time, it also makes it difficult to turnover spare parts for wheel sets. A 6-car subway vehicle has 24 pairs of wheels, requiring more wheel set spare parts for replacement. Once the supply of spare parts is not available, the vehicle will be in a state of waiting for repair, unable to go online normally, and it will also cause tension in the use of garage tracks. Maintenance downtime and spare parts turnover are crucial for the depot. Maintenance is timely, and faulty vehicles must be rushed out of the warehouse according to the plan. Only in this way can safety, quality, site, and operation be orderly and controllable.
At present, the repair of DF4D, DF11 and DF11G locomotives in the Motive power depot often encounters that the spare parts for integral rolled steel wheels cannot keep up with the limit of wheel diameter, and even the manufacturers cannot supply them. Some subway operating companies have already encountered issues with wheel flange processing on lines with small curve radii. At the same time, the track and wheel are a pair of friction pairs, and reducing the wear of the wheel flange also requires considering the wear of the steel rail. If the steel rail is worn to the limit and replaced, it is also a significant investment in economy. In order to solve the problem of wheel flange and rail wear and ensure the service life of the wheel set for one repair period (about 12 years), it is necessary to install a wheel flange lubrication system in subway vehicles to reduce wheel flange wear.
Working principle of wheel flange lubrication system
The wheel flange lubrication system is divided into two types: single line and double line. The oil and gas mixture shown in Figure 1 directly enters the nozzle, which is called a single line. As shown in Figure 2, each nozzle needs to be connected to a separate oil and gas pipe, and a connection block is required in front of each nozzle, which is referred to as a dual line.
Figure 1 Single line wheel flange lubrication system
Figure 2 Dual Line Lubrication System
The dual line lubrication system is composed of a controller, an electric control valve, a grease tank, and a nozzle. The compressed air through the electric control valve is output in two ways, and the quantitative grease is pressed into the nozzle through the grease tank and nozzle inlet; Another way of compressed air enters the air inlet of the nozzle, atomizing the grease inside the nozzle and spraying it out. This type of lubrication system is widely used on Locomotive, such as HB device. This system uses locomotive air source to spray JH type special graphite grease in grease storage tank to the root of wheel flange intermittently through the nozzle, so as to reduce harmful wear between vehicle wheel flange and rail. The electronic controller is a key component for achieving automatic control of the system. The HB-2 model can set the distance between two fuel injections on the electronic controller, with each injection time of 2 seconds. In 2000, the Institute of Metallurgy of the Chinese Academy of Railway Sciences designed and developed a device that can control the wheel rail lubrication system to achieve automatic timed grease spraying control (the new HB-3 wheel rail lubrication device). This electronic controller implements the timed grease spraying mode of the system, utilizing the line section information provided by the locomotive's on-board ground data to develop corresponding software. It can be used in conjunction with curve sensors, and can achieve multiple lubrication forms, with intelligent lubrication function for curves. It can correctly identify line sections (straight, left, and right curves), and adopt different grease spraying control modes for straight and curve sections. Through the above measures, locomotive and vehicle can maintain a more reasonable lubrication state when passing through curves, further reducing wheel flange wear, and also reducing rail wear in curve sections. In addition, a water separation filter has been installed on the basis of the HB-2 model, reducing the failure rate of the nozzle and electric air valve; A new type of grease tank has been designed to improve installation reliability.
The single line wheel flange lubrication system shown in Figure 1 consists of a pneumatic pump, an air solenoid valve, an oil air distributor, a nozzle, and a control device. The pneumatic plunger pump uses the compressed air of the vehicle to inject lubricant into the oil gas mixing block. The lubricant and compressed air are mixed in the oil gas mixing block, and with the help of compressed air, they are distributed through the distributor and sent to the nozzle, which is directly sprayed onto the wheel flange (Figure 3).
Figure 3 Lubricant sprayed from the nozzle onto the wheel flange
As the speed of the vehicle increases, the centrifugal force generated around the wheel rims thickens the lubricating film, and the lubricant is easily thrown out under the centrifugal force. Experiments have shown that when the particle diameter is greater than 0.4mm, centrifugal force will cause the lubricant to splash. If the lubrication system has a high injection speed and a small particle diameter, the lubricant will not splash. Avoiding lubricant splashing not only reduces lubricant consumption, but also avoids lubricant pollution to vehicles and the route. The test conducted by the Deutsche Bundesbahn Bureau shows that when the diameter of the lubricant particles sprayed is less than 0.4 mm and the vehicle speed reaches 300 km/h, no excess lubricant is found on the rail after 40 consecutive injections. In addition, the surface pressure between the wheels and rails is extremely high, and the pressure resistance of the lubricant must be good. The lubricant must contain a high proportion of solid extreme pressure additives?, Such as fine graphite. In a single line lubrication system, the intermediate pipeline between the pump and nozzle contains approximately 10% lubricant and 90% compressed air, which allows compressed air to form a fine oil film layer on the lubricant during the spraying process. Under the action of compressed air, a lubricant with a high proportion of pressure resistant solid particles is added and sprayed onto the wheel flange at a high speed of 150-200m/s to ensure that the sprayed lubricant can break through the air flow and driving wind around the wheels and finely cover the wheel flange of the vehicle at high speed. The thickness of the oil film sprayed onto the wheel flange reaches 0.001mm, with a width of 10-15mm. A lubricant amount of 10-30mm3 is sprayed onto the wheel flange in Z fine particles within a few seconds. If the pneumatic pump adopts a quantitative pump, the longer the injection time, the finer the particles, but the compressed air capacity is limited. Therefore, the injection is not continuous, but once every other period of time, lasting for 6-10 seconds. The spraying interval of lubricants can depend on time or distance traveled; When the vehicle is in a bend, a bend sensor or on-board ground data system can be used to provide the position of the bend. At this time, the spray dose on the outer edge of the curve should be appropriately increased. Stop working when the vehicle's speed drops below a certain value, ensuring that the lubrication system does not work when the vehicle is parked or parked.
With the improvement of automation, the controller of the lubrication system has been based on microprocessors, optimizing the lubrication cycle Z based on distance, speed, curve, or any combination. By programming, lubrication can be avoided during sandblasting, braking, and low-speed operation. When the locomotive is in a bend, the curve sensor can sense and increase the lubrication of the wheels on the outside of the bend.
China's railway system has developed a wheel rail solid lubrication device, which consists of a wheel rail solid lubrication rod and a lubricating rod bearing and fixing mechanism. It has the characteristics of low operating cost, reducing locomotive flange wear, improving the adhesion stability of locomotive driving wheel tread, convenient installation, use and maintenance, and low pollution, and can meet the requirements of Locomotive operation. Jinan West Motive power depot uses the gravity type dry flange lubrication device on NDS locomotives. After six years of operation, it shows that the gravity type solid (dry) flange lubrication device is simple and reliable in design, free of maintenance, easy to manage, and low in cost. The dry lubricant has strong adhesion, easy film formation, extreme pressure resistance, and good long-term effect. The wear reduction effect is very prominent. The wear rate of the wheel flange is reduced from 0.37mm/10000km to 0.18mm/10000km.
Effect of using a rim lubrication system
The wheel flange lubrication system is compact and simple, with high economic benefits.
(1) Rim wear is greatly reduced, greatly extending the service life of wheels and tracks. After investigation, the Technical Center of the Deutsche Bundesbahn Bureau found that in practical application, on a line with many curves, the distance that locomotive wheels could travel before the next grinding cycle was only 10000 to 20000 km, but after the installation and use of wheel flange lubrication equipment, the distance could be increased to 100000 to 200000 km under the same line conditions. At present, after using high-performance wheel flange lubrication equipment, the distance traveled by the locomotive has reached 400000 km or even more before the next grinding cycle.
(2) Reduced noise, especially on bends and turnouts. The noise generated by vehicles during driving can reach 100dB in the past, and even higher when driving in curves and tunnels; And when the subway passes through cities or residential areas, the noise directly affects the comfort of passengers and disturbs the residents along the line. The use of high-performance wheel flange lubrication system not only reduces wear between wheels and tracks, but also reduces noise. The measurement results in Budapest, Hungary show that the use of a high-performance wheel flange lubrication system reduces the noise level by 30dB, reduces the squeaking and piercing noise of the original vehicle during operation, and also avoids sparks rubbing between the wheels and the track during cornering.
(3) Reduce operational resistance and reduce the probability of train derailment. Excessive friction between the wheel flange and rail angle can easily cause the train wheels to climb off the track. After using flange lubrication, the roughness of the rail angle is reduced and the frictional resistance is reduced.
(4) The lubricants used in wheel flange lubrication systems nowadays are generally biodegradable synthetic oils, which are mobile lipids. In addition, adding a high proportion of solid particle components, such as graphite disulfide aluminum powder, to the synthetic oil can significantly improve the wear resistance of the wheel flange without increasing environmental pollution.
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2023-07-18