Compressor thrust bearing

Kingsbury-type thrust bearings can self-align automatically during rotor operation, while Michel-type ones are less capable of doing so! Kingbury is currently being used in both turbines and compressors.

In the Michel design, no attention was paid to the appropriate form of designation. In compressors of the Kingsbury type, the thrust bearings benefit from the automatic leveling capability of their wedge-shaped structures; many improvements have been made over time. It seems that this technology was introduced by Shaanxi Gas Turbine to a Nordic country – it was first used on thrust bearings, and later variants were developed for radial bearing shells as well, enabling automatic centering. In the past, centering was achieved through grinding and the use of shims behind the bearings; around the year 2000, machining was used to ensure precision. Nowadays, this technology is widely used in both turbines and compressors. It’s likely that the patent protection period for it has expired, and independent manufacturing of such components has become fully possible

This post was last edited by lovestory on 2010-12-16 02:57. Compared to Mitchell-type bearings, Kingsbury bearings offer greater flexibility in adjustment, more even load distribution, and a stronger ability to compensate for rotor misalignment and deflection; however, they have a more complex structure and larger axial dimensions. It seems that the application of these two is not clearly distinguished these days; they are found in both compressors and turbines. Mitchell-Douglas for large steam turbines, and Kingsbury-Douglas for small ones. Personally, from the perspective of a maintenance worker. Mitchell is simple, direct, easy to install, and easy to maintain. The Kingsbury is complex to install, and if not handled carefully, the measured thrust clearance can be inaccurate, as the floating block tends to get stuck, resulting in false values for the thrust clearance.

Each has its own characteristics, and there is no mandatory specification regarding where they should be used. However, nowadays, both centrifuges and steam turbines use Kingsbury bearings

Each has its advantages and disadvantages! As for where it is used, it depends on the requirements; our turbines and compressors use Kingsbury bearings!

1. Mitchell-type thrust bearings can be disassembled and assembled as a whole, and are mainly used in compressors with cylindrical cylinders. In Mitchell thrust bearings, there is a positioning pin between the thrust block and the base ring (in some cases, steel balls or cutting edges are used for contact); when the thrust block is subjected to thrust forces, its position can be automatically adjusted to create an optimal oil wedge. On both sides of the thrust disc, there are primary thrust bearings and secondary thrust bearings. Under normal conditions, the axial force of the rotor is transmitted to the main thrust pads through the thrust disc via the oil film, and then to the bearing housing through the base ring. Reverse axial thrust may occur during startup or load rejection, and this thrust will be absorbed by the auxiliary thrust pads. Babbitt is cast on the surface of the tile, with a thickness that should be less than the minimum axial clearance between the moving and stationary parts of the compressor. This is because once the babbitt melts, the thrust disc is still supported by the steel ring, preventing damage to the moving and stationary parts inside the compressor in the short term; generally, the thickness of the babbitt ranges from 1 to 1.5 mm. The axial position of the thrust disc is determined by the thrust bearings, that is, it is set by the position between the thrust disc and the thrust pads. Therefore, determine the length of the spacer sleeve based on the dimensions of the flow passage part of the compressor, and do not change it during maintenance. If it is necessary to replace the thrust plate, attention should be paid to whether there is any change in the thickness of the new thrust plate; if there is a change, the length of the spacers must be adjusted again to ensure the accurate axial position of the rotor within the cylinder. A gap is left between the thrust disc and the bearing shells, which allows an oil wedge to be formed between them in order to withstand the axial thrust of the rotor. This clearance is usually referred to as the thrust clearance or the amount of axial movement of the rotor (which is different from the axial movement of the rotor when no thrust bearings are in place). There is also a structure similar to this, known as a single-mounted thrust bearing; in this type of thrust bearing, the thrust plates are fixed by means of pin holes on their back side, which engage with pins on the support ring, thereby preventing the plates from rotating along with the thrust disc. The pivot of the wafer is eccentric; upon oil entry, it tilts slightly, creating an oil wedge. There are generally 8 to 16 tiles. These bearings are commonly used in the bearing shells of turbo compressors and large steam turbines. 2. * The common feature of Kingsbury bearings and Mitchell bearings is their multi-block design; there is a pivot point beneath the thrust block, which is usually located away from the center of that thrust block. The thrust block can swing around this pivot point, thereby creating an optimal oil film in response to changes in load and rotational speed. In Mitchell bearings, the thrust block is in direct contact with the base ring, and they are of single-layer design ； The Kingsbury bearing consists of an upper leveler block and a lower leveler block beneath the thrust block, with the base ring coming next, meaning it is structured in three layers. Figure 8-15 shows the thrust bearing of the air compressor, which uses a Kingsbury bearing. The thrust pad is fitted with an upper level block, a lower level block, and a base ring; they are in contact through spherical pivot points, which ensures that the thrust pad and level blocks can move freely, allowing for even load distribution. The thrust pads are made of carbon steel, with babbitt cast on their surface. A support block made of tool steel, with a hardness of HRC 50–60, is embedded within the thrust pad; this support block comes into contact with the upper level block. The upper level block is positioned in the circumferential direction using an adjustment screw; both the upper and lower level blocks are typically manufactured by precision casting, and can be made from the wear-resistant material QT40-10. The lower leveling block is fitted into the groove of the base ring, with its cutting edge in contact with the base ring. The upper level block is positioned using screws. To prevent the base ring from rotating, a anti-rotation pin key is provided on it. The axial play of the rotor allows lubricating oil to enter from between the bearing housing and the casing, pass through the oil grooves machined on the back of the base ring, and then enter between the thrust plate and the thrust blocks via the gap between the base ring and the journal. As the thrust disc rotates, oil is flung out due to centrifugal force and is discharged through the oil outlet located above the bearing housing. ( Z9 q# W7 H) m6 j* ` The Kingsbury bearing is characterized by even load distribution, flexible adjustment, the ability to compensate for rotor misalignment and skew, as well as the capability to rotate in reverse; it possesses excellent skills in distributing and reducing loads. However, it has a large axial dimension and a complex structure. It is mostly used in centrifugal compressors. Adjust using shims.

Could you upload the structural diagrams of the two types of bearings? That looks more intuitive!