Writer: Eric Bearing Limited
Bearing bush is an important part of KOYO bearing, and it is the contact part of sliding bearing and journal. Whether the structural design of the bearing bush is reasonable has a great influence on the performance of the bearing. It is a tile-like semi-cylindrical surface, which is very smooth. It is generally made of bronze, antifriction alloy and other wear-resistant materials. In special cases, it can be made of wood, engineering plastics or rubber. Sometimes in order to save valuable materials or structural needs, a layer of bearing alloy is often poured or rolled on the inner surface of the bearing bush, which is called a bearing lining. The bearing shell should have a certain strength and rigidity, be reliable in positioning in the bearing, easy to input lubricant, easy to dissipate heat, and easy to assemble, disassemble and adjust.
When KOYO bearings are working, a thin film of oil is required between the bearing bush and the rotating shaft for lubrication. If the lubrication is not good, there will be direct friction between the bearing bush and the rotating shaft, and the friction will generate high temperature. Although the bearing bush is made of special high-temperature alloy material, the high temperature generated by direct friction is still enough to burn it. Bearing bushes may also burn due to factors such as excessive load, high temperature, impurities in the lubricating oil or abnormal viscosity. The sliding bearing is damaged after burning the tile.
1. Common form and structure of KOYO bearing
Commonly used bearings have two structures, one-piece and split-type. According to different materials and manufacturing methods, monolithic bushes are divided into monolithic bushes and single-layer, double-layer or multi-layer rolled bushes. The non-metal monolithic bearing bush can be either an integral non-metal bushing or a steel bushing lined with non-metallic materials.
There are thick-walled bearings and thin-walled bearings. The thick-walled bearing bush is manufactured by casting method, and the inner surface can be attached with bearing lining. The bearing alloy is often poured on the inner surface of cast iron, steel or bronze bearing bush by centrifugal casting. In order to make the KOYO bearing alloy and the bearing shell adhere well, various forms of tenons, grooves or threads are often made on the inner surface of the bearing shell.
Because thin-walled bearings can be mass-produced by new technology such as continuous rolling of bimetallic plates, the quality is stable and the cost is low, but the rigidity of the bearing is small, and the inner surface of the bearing is no longer repaired during assembly. After the bearing is stressed, its shape is complete Depends on the shape of the bearing seat, therefore, both the bearing shell and the bearing seat require precision machining. Thin-walled bearings are widely used in automobile engines and diesel engines. KOYO 6309ZZCM bearings online , pls click here :
2. Positioning of KOYO bearing
The bearing shell and the bearing seat are not allowed to move relative to each other. In order to prevent the bearing shell from moving, flanges can be made at both ends for axial positioning, or it can be fixed on the bearing seat with a set screw or pin, or a positioning lip can be punched out on the split surface of the bearing shell for positioning use.
Oil hole and groove
In order to introduce lubricating oil into the entire friction surface, oil holes or grooves must be opened on the bearing bush or journal. For hydrodynamic radial bearings, there are two types of axial oil groove and circumferential oil groove to choose from.
Axial oil groove is divided into single axial oil groove and double axial oil groove. For integral radial bearings, when the journal rotates in one direction, the load direction does not change much. The single axial oil groove is best opened at the position of the largest oil film thickness to ensure that the lubricating oil enters the bearing from the place where the pressure is the least.
For split radial bearings, the axial oil groove is often opened at the bearing split surface (the split surface is at 90° to the load action line). If the journal rotates in both directions, a biaxial oil groove can be opened on the bearing split surface. Generally, the axial oil groove should be slightly shorter than the width of the bearing in order to leave a sealing surface at both ends of the bearing to prevent a large amount of lubricating oil from being lost from the end.
Circumferential oil groove is suitable for occasions where the load direction variation range exceeds 180°. It is standing in the middle of the bearing width and divides the bearing into two independent parts; when the width is the same, the bearing capacity of the bearing with circumferential oil groove is lower than that of the shaft. Bearing to the oil groove. For incomplete liquid lubrication of radial bearings.
3. Common materials of bearing bush
(1) Metal materials
a. Bearing alloys (Babbitt alloy, white alloy) are alloys composed of tin, lead, antimony, copper, etc.;
b. Copper alloys are divided into two types: bronze and brass;
c. Cast iron includes ordinary gray cast iron, ductile iron, etc.
(2) Powder metallurgy materials
A porous bearing material made of copper, iron, graphite and other powders after pressing and sintering.
(3) Non-metallic materials
There are plastic, hardwood, rubber, etc., of which plastic is the most used.
4. Material performance of bearing bush:
(1) Antifriction: The material pair has a lower friction coefficient.
(2) Wear resistance: The wear resistance of a material, usually expressed in terms of wear rate.
(3) Seizure resistance (gluing): The heat resistance and anti-adhesion properties of the material.
(4) Friction compliance: The ability of the material to compensate for the initial poor fit of the sliding surface of the bearing through elastoplastic deformation of the surface.
(5) Embedding: The material contains hard particles to embed, thereby reducing the performance of scratches or abrasive wear on the sliding surface of the bearing.
(6) Running-in: the ability (or properties) of the bearing bush and journal surface to form a consistent surface shape and roughness after a short-term light-load operation.
(7) In addition, it should have sufficient strength and corrosion resistance, good thermal conductivity, manufacturability and economy.