What Are The Wear Conditions Of Sealing Rings?
Sealing performance is one of the important properties of hydraulic cylinders. The damage caused by long-term wear of the sealing ring is one of the important reasons for oil leakage in hydraulic cylinders.
The sealing ring on the outer surface of the piston is used to isolate the two chambers and prevent leakage. When the hydraulic cylinder is working, the piston makes reciprocating linear motion in the cylinder barrel, and the sealing ring always rubs against the inner surface of the cylinder barrel. Under normal circumstances, its wear is uniform wear along the circumference, so it needs to be replaced regularly.
In engineering, due to various reasons, the sealing ring often has unilateral and local non-uniform wear, which causes the piston cylinder to need to replace the sealing ring due to leakage in a short time, which directly affects the working efficiency of the piston cylinder.
What Is The Reason For Uneven Wear Of The Sealing Ring?
Whether the seal ring wears evenly is mainly related to whether the piston and the cylinder are concentric. When the outer surface of the piston is completely concentric with the inner surface of the cylinder, the seal ring will wear evenly; when the outer surface of the piston is not completely concentric with the inner surface of the cylinder, the seal ring will wear unevenly.
Whether the piston and cylinder are concentric is mainly affected by the following factors:
1. During the manufacturing and assembly of the hydraulic cylinder, the coaxiality accuracy of the piston and cylinder itself affects whether the piston and cylinder can be concentric.
2. Related to the piston rod
The piston and the piston rod as a whole make reciprocating linear motion in the cylinder. Due to the requirements of the manufacturing process, the piston and the piston rod are generally manufactured separately, and then the two are fixed together by an appropriate connection method. There are many ways to connect the piston and the piston rod. Currently, the basic ones are rigid connections, that is, there can be no displacement between the relative connecting parts.
alt. Hydraulic Cylinder Structure Diagram
After the piston and the piston rod are connected, the following factors may cause the coaxiality error between the piston and the cylinder:
(1) The coaxiality error between the outer surface of the piston rod connection and the inner surface of the piston, see A in the figure above;
(2) The coaxiality error between the outer surface of the piston rod and the inner surface of the cylinder head, see B in the figure above;
(3) The coaxiality error between the inner surface of the cylinder and the outer surface of the cylinder head, see C in the figure above.
When the piston and the piston rod are rigidly connected, due to manufacturing and assembly errors, the above three reasons cause the piston axis and the cylinder axis to produce an angle, see the figure below (a).
At this time, the deformation on the sealing ring is unequal, and a non-uniformly distributed radial force is generated on the sealing ring along the circumference, as shown in the figure above (b).
The unevenly distributed radial force causes the positive pressure acting on the sealing ring to be unequal, which leads to unequal friction between the sealing ring and the inner surface of the cylinder along the circumferential direction, resulting in unequal wear and ultimately causing uneven wear of the sealing ring along the circumferential direction.
3. When the piston rod is connected to the driven load, the load will also affect the coaxiality of the piston and the cylinder.
It is precisely because of the errors caused by the above superposition that the piston and the cylinder are not coaxial, resulting in uneven wear of the sealing ring.
Summary
The non-uniform wear of the seal ring can be reduced by reducing the coaxiality error between the piston and the cylinder. The specific methods are:
1. Ensure the processing accuracy of related parts, such as the straightness of the piston rod, the processing accuracy of the piston sealing groove, and the coaxiality of the piston rod and the piston.
2. When assembling the hydraulic cylinder, try to ensure the concentricity of the cylinder barrel and the cylinder head, and the cylinder head and the piston rod, and avoid the deviation of the axis of the hydraulic cylinder from the direction of movement.
3. Another reason for the uneven wear of the piston and the piston rod with flexible connection is excessive tightening and clamping. Through the flexible connection, a large gap is maintained between the piston and the piston rod, and a large gap is also left between the two end faces of the piston and the two pressure plates. An O-ring (whose elastic coefficient is smaller than the elastic coefficient of the sealing ring on the outer surface of the piston) is configured between the piston and the piston rod. In addition to the sealing function between the piston and the piston rod, the O-ring can also eliminate the influence of the coaxiality of the outer surface of the piston and the inner surface of the cylinder caused by the connection error between the piston rod and the piston through its own deformation.
