What is the clearance of plain bearings?
The clearance of plain bearings is usually 0.01 to 0.02 millimeters.The range of sliding bearing clearance according to the use of precision parts to determine, for example: grinder and lathe dividing head main bearing with the accuracy of H7/g6, agricultural machinery bearings with accuracy of H11/d11.The clearance of plain bearings consists of two kinds of radial clearance and axial clearance. The radial clearance is divided into the top clearance and the side clearance, and the axial clearance is also called the inter axis thrust.The reason to have a sliding bearing radial clearance of the following, first, radial clearance is movably connected with a bearing shaft to achieve the basic conditions;
To leave a certain axial clearance, which refers to the axis of the movement of the gap, but also divided into thrust gap and expansion gap. The thrust clearance is the clearance left for the thrust bearing to allow for axial movement. The expansion clearance is the clearance left to the bearing in accordance with the radial load in order to ensure the free expansion of the shaft. The size of the gap is related to the accuracy of the machine in operation, the smaller the radial clearance, the higher the accuracy, but the gap narrowed to a certain extent, it can not guarantee liquid lubrication. When the clearance is too large, it will generate pulsation in the rotation, and can not form a stable oil film lubrication. Therefore, the radial gap value can not be arbitrarily specified, should comply with the requirements of the machine technical documents. The radial clearance of plain bearings is very important, too large and too small to be extremely harmful. The gap is too large, the lubricating oil film bearing is formed, can not guarantee the liquid lubrication, and can reduce the operation of the machine precision, even violent vibration and noise, would cause serious accidents; the gap is too small, it is also difficult to form a lubricating oil film, will have a high fever, serious accident will occur. The sliding bearing should be provided with an axial clearance to allow the axle to flex freely when the temperature changes. Generally speaking, in order to improve the running accuracy of the shaft, the axial clearance is smaller. But not too small, axial clearance is too small, high heat occurs in the operation may produce bite phenomenon, or even damage bearings, accidents.
second, the radial clearance is the control shaft running accuracy. Of course, the smaller radial clearance, axial running accuracy is higher, but can not reduce the radial clearance and radial clearance is too small, not only difficult to form a lubricating oil film, and may cause the burnt axle accident; third, the radial clearance is an important condition for the formation of liquid lubrication, especially the dynamic pressure bearing, the formation of lubricating oil the film mainly depends on the wedge gap between the shaft and the bearing. The radial gap, the clearance between the top and the side gap, the former value is about two times of the latter. The two clearances are necessary for the formation of a wedge-shaped oil film between the journal and the bearing.
