There are three main reasons for the failure of the sealing function of mechanical seals-

There are three main reasons for the failure of the sealing function of mechanical seals

　2016-11-23　　

(1) The sealing surface is open

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

　　 When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of liquid pressure. After the sealing surface is closed, these solid particles are embedded in the surface of the soft ring (usually the right ink ring). This is actually A 'grinding wheel' will damage the surface of the hard ring.

　　Because the moving ring or rubber ring is fastened to the shaft (sleeve), when the shaft moves in series, the moving ring cannot fit in time, so that the sealing surface opens, and the sealing surface is closed with a hysteresis, so that solid particles enter In the sealing surface.

　　 At the same time, there are solid particles between the shaft (sleeve) and the sliding parts, which affect the sliding of the rubber ring or the moving ring (relative to the dynamic seal point, common failure). In addition, the medium will also produce crystals at the friction between the rubber ring and the shaft (sleeve), and there will also be solid substances in the spring, which will cause the sealing surface to open. Mechanical seal

(2) Overheating

　　Because of the heat generated on the sealing surface, the temperature of the rubber ring should be lower than the design specification. The service temperature of fluorine rubber and polytetrafluoroethylene is 216℃, and the service temperature of nitrile rubber is 162℃. Although they can withstand higher temperatures, the heat generated by the sealing surface is higher, so the rubber ring continues to vulcanize The danger of eventually losing its elasticity and leaking. (Consider cold brittleness in cold zone)

　　The heat between the sealing surfaces will also cause the crystallization of the medium, such as carbon formation, causing the sliding parts to be stuck and the sealing surface to be condensed. Moreover, some polymers are coked due to overheating, and some fluids lose lubrication due to overheating, and even flash fire.

　　 Overheating can not only change the condition of the medium, but also increase its corrosion rate. Cause the deformation of metal parts, cracks on the alloy surface, and some cracks in the coating. The design should select a balanced mechanical seal to reduce the specific pressure and prevent overheating.

(3) Out of tolerance

　　 The correct assembly tolerance is necessary for the installation of mechanical seals. The shaft (shaft sleeve) must have the appropriate surface roughness and the correct size, but the manufacturer rarely provides tolerance data, which are all for installation. Is very critical. (Rely on experience and common sense)

　　 The dimensional accuracy and geometric tolerances of mechanical seals must meet the requirements of the drawings. Excess tolerance will cause premature seal failure.

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