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friction failure
The materials used in the friction pair have poor wear resistance, large friction coefficient, and excessive end face specific pressure. When the sealing surface enters the solid particle impurities, the friction surface is worn, and the liquid film between the end faces is difficult to form and maintain, resulting in seal failure.
stress causes failure
(1) High pressure and pressure fluctuation cause mechanical seal failure
When the pressure in the sealing chamber exceeds the required pressure, the pressure ratio of the sealing end face is too large, the liquid film is difficult to form, the end face is severely worn, and the heat generation is too much. It will also deform the sealing parts. For the seal under high pressure conditions, methods should be adopted to make the end face reasonable and reduce deformation; strengthen cooling and solidification and lubrication measures; use a balanced seal and a smaller load factor; adopt a multi-face sealing structure, etc.
The fluctuation of the working pressure will affect the elastic deformation of the sealing parts and affect the sealing effect. Significant leakage occurs when the pressure varies greatly. Measures such as WC on WC friction pair should be used to reduce the influence of pressure fluctuations.
(2) Failure due to vacuum state
Vacuum will cause seal dry friction, air leakage and other phenomena. Practice has proved that the coefficient of friction is usually a few percent in semi-wet friction, and a few tenths in semi-dry friction and dry friction. That is, the heat released by dry friction is ten times or more than that of lubrication, which aggravates the wear of seals. As the surface is damaged, the surface temperature rises, and the mechanical properties of the material change, so that the severe wear process increases and the wear speed increases, resulting in thermal cracking or burning of the sealing ring, and then the equipment cannot work normally. In order to solve this problem, double-face sealing should be adopted, and sealing liquid should be injected to ensure lubrication and improve sealing performance, and change gas-phase sealing to liquid-phase sealing.
Failure due to incompatibility of sealing form or sealing material with sealing conditions
If the sealing material is not properly selected, the seal can be easily damaged by corrosion, high pressure, high speed or overheating. When the mechanical seal is used in corrosive medium, because the seal is subjected to chemical and electrochemical corrosion, the friction pair should be made of materials that are both corrosion-resistant and wear-resistant. In strong corrosive medium, bellows can be selected for high-pressure medium. Generally, when the double-end balanced structure or the multi-end series sealing device is used for high temperature, the parts should be subjected to stable heat treatment, and each part should be made of materials with similar expansion coefficients. Mechanical seals for high-speed rotating equipment should be used as much as possible Reduce rotating parts.
