The clearance of sliding bearings is generally 0.01 to 0.02 millimeters. The range of values for the clearance of sliding bearings is determined based on the accuracy of the parts they are used in. For example, the accuracy of the main bearing fit between the grinding machine and the lathe indexing head is H7/g6, and the accuracy of the bearing fit for agricultural machinery is H11/d11.
Diagram of clearance of sliding bearings
There are two types of clearances for sliding bearings: radial clearance and axial clearance. Radial clearance is divided into top clearance and side clearance; Axial clearance is also known as axial play. The reason why sliding bearings need to have a certain radial clearance is for the following purposes: radial clearance is the minimum condition for achieving active connection between the shaft and the bearing; Secondly, radial clearance is the guarantee for the operational accuracy of the control shaft.
Of course, the smaller the radial clearance, the higher the operating accuracy of the shaft, but the radial clearance cannot be reduced arbitrarily. If the radial clearance is too small, it is not only difficult to form a lubricating oil film, but it may also lead to accidents such as bearing burning and shaft holding; Thirdly, radial clearance is an important condition for the formation of liquid lubrication, especially in dynamic pressure bearings, where the formation of lubricating oil film mainly relies on the wedge-shaped clearance between the shaft and the bearing. The radial clearance is divided into top clearance and side clearance, with the former having a value about twice that of the latter.
Diagram of Gap and Pressure Load
These two clearances are necessary for the wedge-shaped oil film formed between the journal and the bearing. There should be a certain axial clearance, which refers to the clearance in the axial direction, and is divided into thrust clearance and expansion clearance. The thrust clearance is a clearance left for the thrust bearing to allow for some axial movement. Expansion clearance is the clearance left for bearings to ensure free expansion of the shaft with radial load.
The size of the gap is related to the accuracy of the machine during operation. The smaller the radial gap, the higher the accuracy, but reducing the gap to a certain extent cannot guarantee liquid lubrication. If the gap is too large, it will cause jumping during rotation and cannot form a stable oil film lubrication. Therefore, the radial clearance value cannot be arbitrarily specified and should comply with the requirements of the machine technical documents. The radial clearance of sliding bearings is very important, both too large and too small are extremely harmful.
Radial clearance of sliding bearings
Excessive clearance makes it difficult to form a lubricating oil film in the bearing, which cannot guarantee liquid lubrication and can reduce the accuracy of machine operation, even causing severe vibration and noise, and in severe cases, can lead to accidents; If the gap is too small, it is difficult to form a lubricating oil film, and high heat can also be generated. In severe cases, accidents can also occur.
Sliding bearings should have axial clearance to allow for free expansion and contraction of the shaft during temperature changes. Generally speaking, in order to improve the accuracy of shaft operation, it is advisable to have a smaller axial clearance. But it cannot be too small either. If the axial clearance is too small, it may cause bite or even damage the bearings during high heat during operation, leading to accidents.
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