Different Types And Application Characteristics Of Radial Bearings

The function of the radial bearing is to bear the weight of the rotor and other additional radial forces, keep the rotation center of the rotor in line with the center of the compressor cylinder, and operate normally at a certain speed. The thrust bearing is used to bear the axial force of the rotor, limit the axial movement of the rotor, and keep the axial position of the rotor in the compressor cylinder. Centrifugal compressor speed is very high, their radial bearing linear velocity is generally above 50 Mn / s, thrust bearing linear velocity is generally above 80 n / s, all belong to high speed sliding bearing.

Working principle of radial bearing
During the operation of radial bearing, a thin oil film will be formed between bearing and journal, which can make the shaft float. In the running process of radial bearing, because the journal keeps turning, the journal will bring the lubricating oil between the collar and the bearing, forming a thin oil film from the surface. This kind of eccentric journal bearing does not make the rotor concentric with the center of the journal.
Different types and application characteristics of radial bearings
The radial bearings commonly used in centrifugal compressor include round bush bearing, elliptical bush bearing, multi oil wedge fixed bearing and tilting bush bearing. The advantage of the bearing is simple structure, but the high-speed stability is poor, now it is rarely used. Compared with round bush bearing, elliptical bush bearing has the following advantages: firstly, it has good stability. If the shaft shakes up and down, such as upward, the upper boundary becomes smaller, the oil film K force becomes larger, the lower clearance becomes larger, and the oil film pressure becomes smaller. The resultant force change of the two parts will push the journal back to the original position, so that the shaft runs stably; secondly, due to the large side clearance, the axial flow will increase The oil output is large, the heat dissipation is good, and the temperature of the bearing is low; however, the bearing has low bearing capacity. Due to the production of upper and lower oil films, the power consumption is large, and the anti vibration performance in the vertical direction is good, but the anti vibration performance in the horizontal direction is poor. Multi oil wedge fixed bearing has the advantages of good anti vibration performance in all directions, low bearing temperature rise, and less oil film oscillation, so it is often used in old compressors. Compared with other bearings, tilting pad bearing has the advantages that each pad can swing freely and form the best oil wedge in any case. It has very good high-speed stability and is not easy to produce oil film oscillation. It is widely used in centrifugal compressors. Tilting pad bearing is mainly composed of bearing body, oil seals on both sides and pad (as shown in the figure below). This kind of bearing pad generally uses five pads, each pad can swing freely. Five tiles are evenly distributed around the journal, each of which can swing around its own fulcrum. There is a normal bearing clearance between the pad and the journal. Generally, the clearance value is 1.5% - 2% of the diameter. The outer diameter of each pad is less than the inner diameter of the bearing body, and the back arc of the pad contacts the bottom line of the bearing bore. It is equivalent to a fulcrum. When the unit speed, load and other operating conditions change, the pad can swing freely on the support surface of the bearing body, and automatically adjust the pad position to form the most stable bearing Better lubricating oil wedge. In order to prevent the pad and journal from rotating along the circumference, each pad is positioned with a screw installed on the bearing body. In most cases, the positioning screw is in the middle of the pad. In order to prevent the pad from moving along the axial and radial direction, the pad is installed in the T-shaped groove in the bearing body. Generally, 20 steel or 25 copper is used for the tile, and Babbitt alloy is poured on the tile, and the alloy thickness is generally 0.8-2.5mm. In order to ensure the close fit between Babbitt alloy and tile block, the groove can be prefabricated on the tile block. The upper and lower half horizontal split bearing body is installed in the bearing seat. In order to prevent the bearing body from rotating, a radial locating pin is installed to prevent the bearing body from rotating. The number of oil inlets of bearings is different. Some bearings have only one oil inlet hole, and some bearings have oil inlet holes between pads, but they are always arranged in the place where the oil film is not damaged. The lubricating oil is generally discharged along the axial direction. There are grooves at both ends of the bearing body, and the oil drainage holes are connected with it. The lubricating oil is concentrated in the groove and flows back to the bearing box through the oil drainage holes.
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