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Home - News - The principle of oil seal and precautions for sealing!

The principle of oil seal and precautions for sealing!

March 20, 2023

There is an oil film controlled by the oil seal edge between the oil seal and the shaft, and this oil film has fluid lubrication characteristics. Under the effect of the surface tension of the liquid, the rigidity of the oil film just makes the oil film and the air contact end form a crescent surface, which prevents the leakage of the working medium and realizes the sealing of the rotating shaft. The sealing ability of the oil seal depends on the thickness of the oil film on the sealing surface. If the thickness is too large, the oil seal will leak; if the thickness is too small, dry friction may occur, causing wear of the oil seal and shaft; if there is no oil film between the sealing lip and the shaft, it will easily cause heat and wear .

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Therefore, when installing, you must apply some oil on the sealing ring, and at the same time ensure that the skeleton oil seal is perpendicular to the axis line. If it is not vertical, the sealing lip of the oil seal will drain the lubricating oil from the shaft, and it will also cause excessive sealing of the sealing lip. wear and tear. During operation, the lubricant in the casing seeps out a little to achieve the ideal state of forming an oil film on the sealing surface.


Matters needing attention when assembling the skeleton oil seal:


1. Receive a fixed number of oil seals.


2. From oil seal collection to assembly, it must be kept clean.


3. Before assembly, check the oil seal and measure whether the size of each part of the oil seal is consistent with the size of the shaft and cavity. Before installing the oil seal, first compare the size of the shaft diameter with the inner diameter of the oil seal to ensure that they match. The size of the cavity should be compatible with the width of the outer diameter of the oil seal. Check whether the lip of the oil seal is damaged or deformed, and whether the spring has fallen off or rusted. Prevent the oil seal from being placed flat during transportation, and being affected by external force extrusion and impact, which will damage its roundness.


4. Do a good job of machining inspection procedures before assembly. Measure whether the dimensions of the cavity and the shaft are correct. Especially the inner chamfer. There must be no slope. Assembling parts, there should be no burrs, sand, iron filings and other sundries at the part where the shaft is installed (chamfering), which will cause irregular damage to the lip of the oil seal. It is recommended that the chamfering part should use r angle.



5. In terms of operating skills, you can feel with your hands whether it is smooth and round.


6. Before the oil seal is installed, do not tear off the wrapping paper too early to prevent debris from adhering to the surface of the oil seal and being brought into the work.


7. Before installing the machine, the oil seal should be coated with lithium-based ester with molybdenum disulfide in an appropriate amount between the lips, so as to prevent the dry grinding of the lips when the shaft is started instantly and affect the interference of the lips. As soon as possible, assemble. If the oil seal seat installed with the oil seal is not installed immediately, it is recommended to cover it with a cloth to prevent foreign matter from adhering to the oil seal. Hands or tools applied with lithium-based grease must be clean.


8. The oil seal should be installed flat, and there should be no tilting phenomenon. It is recommended to use hydraulic equipment or socket tools for installation. The pressure should not be too great, and the speed should be even and slow.


9. For the machine with oil seal installed this time, mark it for easy tracking, and pay attention to the whole process.



The skeleton oil seal is relatively simple, and generally consists of three parts: oil seal body, reinforced skeleton and self-tightening coil spring. The sealing body is divided into bottom, waist, cutting edge and sealing lip according to different parts. Usually, the inner diameter of the skeleton oil seal in the free state is smaller than the shaft diameter, that is, it has a certain "interference". Therefore, when the oil seal is installed on the oil seal seat and the shaft, the pressure of the oil seal cutting edge and the contraction force of the self-tightening coil spring will produce a certain radial tightening force on the shaft. After a period of operation, the pressure will decrease rapidly or even disappear. , Therefore, adding a spring can compensate the self-tightening force of the oil seal at any time.