Writer: Eric Bearing Limited
KOYO bearing bush can also be called KOYO sliding bearing. During the work, it is mainly to form an oil film gap with the journal, and a very thin oil film plays a role in lubrication during relative movement. If the lubrication is not good, it may cause direct contact between the shaft and the bearing bush, causing friction, and the high temperature generated by the friction will cause damage to the bearing bush. Although the KOYO bearing bush is made of high temperature resistant copper alloy material, the friction and high temperature generated by direct contact can still damage it. Therefore, the gap between the bearing bush and the shaft determines the accuracy of the sliding bearing, while the processing of the shaft and the bearing bush It is the key to ensure bearing accuracy.
1. The characteristics of large diameter, thin wall bearing
Large-diameter and thin-walled bearings generally refer to sets of small radial rigidity with bore diameter ≥560mm and wall thickness ≤25mm.
Main technical indicators: dimensional tolerance of outer circle and inner hole;
Roundness error of outer circle and inner hole;
Concentricity error of inner and outer circles;
The perpendicularity error between the end face and the inner hole.
Due to the limitation of this type of KOYO bearing structure. The most common problem in the manufacturing process is that the machining accuracy of the bearing bush is not up to the drawing requirements due to the influence of cutting heat, cutting force and clamping deformation. The usual process is rough turning-cutting-milling joint surface-combination-half Although the machining process of finishing turning and finishing turning is basically the same, if the specific processing parameters and methods are not selected properly, the processing quality obtained may be completely different.
2. Deformation analysis of KOYO bearing
The processing deformation and storage deformation of the bearing bush exist simultaneously, and the processing deformation is mainly affected by the clamping force and the cutting force. The storage deformation is more artificial.
3. Optimization of processing technology
(1) Reasonably choose machining tools and cutting amount
a. Selection of cutting tools
The raw material of the bearing bush is generally aluminum bronze ZCuA110Fe3, in which the main alloying element Al content is 8.5%~11.0%, Fe content is 2.0%~4.0%, which has high mechanical properties. Good wear resistance and corrosion resistance, tensile strength crb≥490MPa, yield strength s≥l80MPa, elongation ≥13%, it is a free-cutting alloy, you can choose ordinary high-speed steel or cemented carbide tools. The cutting tool must be sharp. Larger rake angles and entering angles can be used. KOYO 6202-2RS bearings online , pls click here :
b. Selection of cutting amount
In order to reduce the vibration and deformation of the workpiece, the cutting force and cutting heat on the workpiece should be made as small as possible. For this reason, a higher cutting speed, a smaller cutting depth and feed rate should be selected during cutting.
(2) The influence of clamping force on deformation
a. Workpiece installation
The use of horizontal lathe processing requires a process chuck and a stress relief groove to be turned. The workpiece is clamped axially, and the inner and outer circles and one end face are processed in one clamping, which minimizes the radial deformation of the clamping influences.
b. If the workpiece must be clamped radially, in order to reduce clamping deformation, increase the number of jaws and increase the contact area. Auxiliary supports can also be added when necessary.
(3) Control of cutting heat
The cutting heat generated during the cutting process is inevitable. This heat not only affects the deformation of the workpiece, but also has a great impact on the durability of the tool. For this reason, sufficient cutting fluid must be used during machining. Emulsions with a small concentration can be selected when roughing, and emulsions with a larger concentration can be used for finishing.
4. KOYO bearing deformation repair
Due to the influence of cutting stress during KOYO bearing processing and the restriction of tooling during operation and placement, deformation is inevitable. Through many years of practice, it is found that most of the deformation is the reduction of the tile diameter on the split surface. After being installed on the bearing seat, the bush mouth will be in a reduced diameter state, which will cause the contact area between the outer diameter of the bearing bush and the bearing seat hole to fail to meet the requirements.
In view of the above-mentioned deformation, in the actual production process, a hydraulic machine is generally used to repair it with wooden tooling.
First install the bearing on the shaft, add square wood on the top surface of the KOYO bearing, and add the thickness of the gasket according to the material and deformation. Gradually load the pressure of the hydraulic press, remove the workpiece after unloading, check the diameter of the tile mouth, and check whether the shape needs to be re-calibrated according to the actual measurement results.