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Mechanical seal failure analysis

Date:Feb 13, 2020

There are three main reasons for seal failure:


1. Sealing surface is open 85When repairing mechanical seals, 85% of seal failures are not caused by wear, but they have leaked before wear. As soon as 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), which actually becomes a " "Grinding wheels" can damage hard ring surfaces. Because the moving ring or rubber ring is fastened on the shaft (shaft sleeve), when the shaft moves in series, the moving ring cannot fit in time, and the sealing surface is opened, and the sealing surface lags behind, so that solid particles enter the sealing surface. . At the same time, there are solid particles between the shaft (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 generate crystals in the friction parts of the rubber ring and the shaft (shaft sleeve), and solid substances will also be stored in the spring, which will open the sealing surface.               

 

2. Overheating Because the sealing surface will generate heat, the operating temperature of the rubber ring should be lower than the design specification. The operating temperature of fluororubber and polytetrafluoroethylene is 216 ° C, and the operating temperature of nitrile rubber is 162 ° C. 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 elasticity and leaking. (The cold zone is considered to be cold and brittle.) The medium will also cause crystallization of the medium between the sealing surfaces, such as carbon, causing the sliding parts to be stuck and the sealing surfaces to be condensed. And some polymers are coked due to overheating, some fluids lose their lubrication due to overheating and even flash fire. Overheating can not only change the condition of the medium, but also increase its corrosion rate. Causes the deformation of metal parts, cracks on the alloy surface, and cracks in some coatings. The design should use 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 (sleeve) must have a suitable surface roughness and correct dimensions, but manufacturers rarely provide tolerance data. These data are required for installation Is critical. (Depending on experience and common sense)

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