March 23rd, 2020
Numerous industries have been maximising different types of sealers for machines and other types of assembly. For instance, an O-ring is a mechanical gasket designed to be seated in a groove and compressed during assembly of two or more parts. Another example of a sealer is a washer, which is often used to distribute the load of a threaded fastener or serve as a spacer.
After repetitive use of a machine or parts, the seal used for them might fail due to different reasons. One, you should consider finding the root cause of the seal failure. Some factors that you may consider when starting a failure analysis include the hardware information, the way a seal is installed, application conditions, and the lifespan of the seal.
With the mentioned factors, your failure analysis will be much easier than ever before. Through the following basic failure diagnostics, you can easily reduce downtime and costly seal replacements.
The compression set of every material varies depending on its properties, lifespan and surrounding temperature. For seals, compression is defined as their ability to return to their original shape after the force applied to them is removed. If the seal has zero percent compression set, then it indicates that no permanent deformation has occurred. Meanwhile, a 100% compression set means that the seal no longer applies a force on the mating surface. Altogether, a compound with a low percentage of compression set means that the material is more resilient.
There are numerous potential factors that can affect the compression set of a compound. These factors include poor material properties, improper glands, fluid incompatibility, and higher than recommended temperature exposure for the material.
Extrusion and Nibbling
While the compression set is directly affected by the material properties and the surrounding environment, the occurrence of extrusion and nibbling shares a different story. This failure mode happens whenever a seal material deforms into the space between the bore and the outside of the tube, which can be referred to as the extrusion gap. It can also occur due to gland overfill. Gland overfill happens when the deformation from the seal compression fills the entire groove and then lips over into the extrusion gap.
The absence of extrusion gap on face seals makes them safe from the risk of this failure mode. On the other hand, radial seals can experience extrusion. Fortunately, the extrusion in radial seals can be remedied by reducing the clearance gap or by adding a back-up ring.
A lot of factors can affect seal extrusion damage. These factors include the magnitude of the differential pressure, radial extrusion gap clearance, defects at the extrusion gap corner, temperature, hydraulic pressure shock, and many more.
When an O-Ring is sliding and rolling in the groove, then it experiences spiral failure. This failure is often found on long stroke hydraulic piston seals and rod seals. Most of the time, this occurs in dynamic reciprocating O-Ring applications. The installation of O-Ring can also cause spiral failure right away. The root cause of spiral failure can be difficult to pinpoint. However, some factors that contribute to spiral failure include uneven surface finish, poor lubrication, side loading, eccentricity, improper installation, and many more. When spiral failure occurs, a series of deep spiral cuts will be present on the surface of the seal.
Knowing this basic failure diagnostics can help you determine and prevent impending seal failure ahead of time. To know more about seal failures, you can visit us at Gasketech. We manufacture and supply gaskets and sealing washers, extrusions, and mouldings for all industries.
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