A gap appearing at one or both end faces indicates that the distance between the two end faces is too large, and when the two end faces are forcibly closed, a gap is formed. A common cause of end face separation is sudden evaporation of the medium in mechanical seals. For example, water, especially in hot water systems or liquids containing condensate, expands when evaporating, causing the two end faces to separate. The occurrence of air pockets in the pump combined with blocking of the sealing element can also cause the seal end faces to separate. In this case, it is not due to vibration and misalignment of the coupling, as that is not enough to cause the end faces to separate.
Reducing the temperature of the end faces is a commonly used method to prevent end face damage caused by rapid evaporation of the medium. At the same time, using materials with good thermal conductivity, such as pairing nickel-based hard alloys with copper-impregnated graphite, and adopting balanced mechanical seals, using specially corrosion-resistant mechanical seals to cover them from outside injection for cooling, or directly cooling the seal inside the cavity, etc., are all very effective in reducing the temperature of the sealing end faces.
A failed mechanical seal often leaves very fine radial cracks or radial cracks with water trace or even cracks on the friction pair end faces. This is due to overheating of the seal, especially ceramic and hard alloy sealing surfaces tend to produce this type of damage. Poor lubrication of the medium, overload, high operating temperature, high line speed, improper combination of pairing materials, any one of these factors, or a combination of several factors can produce excessive friction heat, and if the friction heat is not released in time, it will produce thermal cracks, resulting in excessive wear and high leakage. To solve the problem of seal overheating, in addition to changing the end face area and reducing the load, stationary seal can be used with guide sleeves to force cooling circulation fluid to guide the seal face, or fluid power grooves can be opened on the seal face to solve the problem. A large number of small thermal spots and isolated color-changing areas on the friction end face indicate that the seal element is deformed and distorted under high pressure and heat. General calculation methods for end face thermal deformation are not allowed, and finite element method calculations should be used to improve the design of the sealing ring.
Mechanical seal rings coated with hard materials, whether ceramic or hard alloy, for shipboard safematic mechanical seals or others, may have scaling or peeling on the lower layer of the substrate under thermal loads, indicating dry friction in the seal.
The maximum shaft bend should be less than 0.07mm. The runout inspection of the seal cavity surface, and the runout of the seal cavity surface should not exceed 0.13mm.
If the seal cavity surface is not perpendicular to the shaft, it may cause mechanical seal failure. Because the seal cover is fixed on the seal cover by bolts, if the seal cavity runout is too large, the installation of the cover will be tilted, and the seal static ring will be tilted, causing the entire seal to shake abnormally.
The wear of the auxiliary seal between the mechanical seal and the shaft or the sleeve will also be aggravated, and the abnormal shaking of the seal will also cause wear and fatigue of metal bellows or drive pins, resulting in premature seal failure.