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Causes And Analysis Of Seal Failure
- Oct 26, 2018 -

(1) There are three main reasons for seal failure:

1, the sealing surface is open

When repairing mechanical seals, 85% of seal failures are not caused by wear, but are leaked before wear.

When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of the liquid pressure. After the sealing surface is closed, the solid particles are embedded on the surface of the soft ring (usually the right ink ring), which actually becomes a " The grinding wheel will damage the hard ring surface.

Since the moving ring or the rubber ring is fastened on the shaft (sleeve), when the shaft is strung, the moving ring cannot be timely fitted, and the sealing surface is opened, and the hysteresis of the sealing surface is closed, so that the solid particles enter the sealing surface. .

At the same time, there are solid particles between the shaft (sleeve) and the sliding member, which affects the sliding of the rubber ring or the moving ring (relative to the dynamic sealing point, common faults). In addition, the medium will also produce crystals in the friction zone between the rubber ring and the shaft (sleeve), and there will also be solid matter in the spring, which will open the sealing surface.

2 overheating

Because the heat is generated on the sealing surface, the rubber ring should be used at a lower temperature than the design specifications. Fluororubber and PTFE are used at 216 ° C, but nitrile rubber is used at 162 ° C. Although they can withstand higher temperatures, the rubber ring has continued to cure due to the higher heat generated by the sealing surface. The danger of eventually losing flexibility and leaking. (Cold zone considers cold brittleness) The crystallization of the medium due to heat, such as carbon formation, between the sealing surfaces causes the sliding parts to stick and the sealing surface to condense. Moreover, some polymers are coked due to overheating, and some fluids lose lubrication or even flash fire due to overheating.

In addition to changing the condition of the medium, it can also increase its corrosion rate. Causes deformation of metal parts, cracking of the alloy surface, and cracks in some coatings. The design should use a balanced mechanical seal to reduce the specific pressure to prevent overheating.

3 out of tolerance

Proper assembly tolerances are necessary to install the mechanical seal. The shaft (sleeve) must have the proper surface finish and the correct dimensions, but the manufacturer rarely provides tolerance data, which is critical for installation. of. (reliance on experience and common sense)

The dimensional accuracy and shape tolerance of the mechanical seal must meet the drawing requirements, and the tolerance will cause the seal to fail prematurely.