Its function is to transfer the weight and load of the vehicle body to the wheel set, lubricate the journal, reduce friction and reduce running resistance. Axle box devices are divided into sliding bearing axle box devices and rolling bearing axle box devices according to the type of bearing used. The early rolling stock used the sliding bearing axle box device. The rolling bearing axle box device was tried in the early 20th century, and has gradually replaced the sliding bearing axle box device. Rolling bearing axle box device has been adopted for passenger cars, diesel locomotives and electric locomotives of China Railway, and some freight cars have been adopted.
The axle box of the freight car is installed on the outside of the wheel and is composed of axle box, axle box cover, bearing bush, bearing bush backing plate, oil lubrication device and dust plate. The axle box on the driving wheel and guide wheel of steam locomotive is installed on the inner side of the wheel, and the oil box is used to supply oil to lubricate the journal. Other parts are the same as the above parts.
The parts that bear load and store shaft oil are used to contain journal and other parts. In the early stage, it was made of cast iron and generally made of cast steel. The axle box body not only transmits the load from the frame to the journal, but also bears the load supported by the jack from the bottom when repairing and replacing the bearing, so it should have sufficient strength. The axle box body and the axle box cover must be closely fitted to avoid oil leakage and prevent rainwater and dust from entering. The axle box body has two types: guide frame type and no guide frame type.
The bearing bush rubs with the journal and transfers all the load borne by the axle box body to the journal, which is composed of the ina bearing body and a layer of antifriction alloy on its surface. In the early stage, the tile body was cast with copper alloy, and then steel backing copper lining was used. It was made of nodular cast iron in China. The antifriction bearing alloy used in Chinese railway vehicles, commonly known as white alloy, is lead antimony tin alloy. This alloy is easy to scrape and grind, has good compressive, antifriction and heat resistance, and is easy to cast. In recent years, in order to prevent the bearing bush from being scrapped prematurely and avoid burning the shaft, the front end of the bearing bush of freight cars with more than 50 tons is inlaid with plastic pads.
Parts installed between axle box body and bearing bush for load transfer. Its upper surface is arc-shaped to improve the load distribution on the surface of white alloy. When replacing the bearing bush, remove the backing plate first to reduce the lifting height of the jack.
A device that supplies shaft oil between bearing bush and journal to reduce friction. It is composed of oil roll, wooden front pillow and rear baffle, which is installed in the axle box. The oil roll is filled with shaft oil (lubricating oil) and is in contact with the lower part of the journal. When the vehicle is running, the journal rotates, bringing the shaft oil between the bearing bush and the journal to form an oil film, which changes the dry friction into liquid friction. Early oil rolls were mostly made of cotton wool, and some used oil brushes. In recent years, China’s rolling stock has been converted to foam rolls wrapped with foam plastic. The wooden front pillow is used to replace the oil roll at the outer end of the journal and prevent the oil roll from moving outward. The rear baffle is used to prevent shaft oil from overflowing from the rear end of the journal.
Its function is the same as that of the axle box cover, so it is also called the axle box back cover. Located in the interlayer of the rear wall of the shaft box, it is mostly wooden. The wooden dust-proof plate has poor sealing performance and often leaks shaft oil. In recent years, it has gradually changed to rubber dust-proof plate.
Advantages of rolling bearing axle box device
Compared with the sliding bearing axle box device, the rolling bearing axle box device can reduce the running resistance NSK bearing force of locomotive and vehicle by about 10% and the starting resistance by more than 80%, which can not only save power consumption, improve the running speed, but also improve the traction weight of the train. The traveling clearance of each component of the device is small, which is conducive to improving the running quality of locomotives and vehicles. It has a small failure rate in operation and can reduce the labor and material consumption of maintenance work. Therefore, although the manufacturing cost of rolling bearing axle box device is much higher than that of sliding bearing axle box device, it is still widely used.
The rolling bearing axle box device is usually composed of shaft box, front and rear axle box covers, rolling bearings, sealing devices and other parts. There are three kinds of rolling bearings used: cylindrical, conical and spherical. Among them, spherical rolling bearings bear better axial load, but the required size is large, which is not conducive to reducing the unsprung weight, high manufacturing cost and inconvenient maintenance. Therefore, they are less used in recent years.
Cylindrical rolling bearing axle box device is adopted on passenger cars in China Railway, and it is also mainly used on diesel locomotives and electric locomotives. On passenger cars, the axial force is borne by the retaining edge on the inner and outer rings of the bearing, while on locomotives, the bearing generally does not have a retaining edge, and the axial force is borne by the ball bearing installed at the shaft end. In addition to the cylindrical rolling bearing axle box device used in some freight cars, the sealed conical rolling bearing axle box device is mainly used in new freight cars. Both ends of the tapered rolling bearing are equipped with sealing devices. The outer ring is a bearing saddle, which is installed in the guide frame of the bogie side frame to transfer the load. There is no shaft box outside the bearing. Therefore, this structure is called “axle box free bearing device”. Rolling bearings are lubricated with grease, so it is not necessary to open the cover frequently for refueling or inspection.
Fag bearings and axle boxes need long-term maintenance during the use of bearings. Because this not only lengthens the service life of the bearing itself, but also allows businesses to reduce expenses.
The maintenance of fag bearing axle box is generally easier than that of sliding bearing axle box, there is no need to change tiles and refuel frequently, and there are fewer combustion shaft accidents. However, do not be careless. If the bearing is damaged and causes the combustion shaft, it is inconvenient to deal with it in the middle of operation, so you have to replace the wheel set or dump the car. Therefore, vehicle maintenance personnel need to regularly check the axle temperature, check the axle box for cracks, oil rejection, loose bolts, etc. The temperature of the bearing is mainly generated by the heat generated by the rolling friction between the roller and the inner and outer ring raceway, the sliding friction between the roller and the cage, the sliding friction between the end of the roller and the retaining edge of the inner and outer ring, and the friction between the roller and lubricating grease. Its temperature is generally relatively low.
Axle box temperature is related to many factors, such as load on fag bearing, operating speed, line state, air temperature, wind speed, continuous operation time, quantity and state of lubricating grease, etc. Two to three hours after the vehicle starts, the bearing temperature tends to be stable. The heat generated by bearing rotation friction is close to the balance with the heat generated by NTN bearing on the outer surface of axle box. In cold areas in the north, the axle box surface dissipates heat quickly The temperature difference between the top of the axle box and the inside of the bearing is 30 to 40 degrees, while in the hot season in the south, the temperature difference between the top of the axle box and the inside of the bearing is only about 100 degrees. Usually in summer, the axle box temperature on the sunny side is much higher than that on the sunny side.
Under normal conditions, the top of the axle box of fag bearing is only about 15-x-300c higher than the air temperature. If the top temperature of individual axle boxes in the same vehicle is more than four Baidu higher than the air temperature, it is an abnormal phenomenon, and the cause shall be found out. Since there are few factors affecting the bearing temperature, especially the train speed, grease quality and bearing clearance have a great impact on the bearing temperature, the calculation formula of the bearing allowable temperature cannot be provided at present. Generally, the external temperature + 40 can be used as the bearing allowable temperature and measured at the top of the axle box. For the spare wheel set equipped with roller bearing axle box, rotate the axle box every half a month or so to prevent the bearing from rusting.