Mechanical seals are divided into high-temperature resistant, low-temperature resistant, high-pressure resistant, corrosion-resistant, particle-resistant, and light hydrocarbon-resistant mechanical seals, depending on the working conditions and properties of the medium. Different structural types and materials of mechanical seals should be selected according to their different uses.
Such as centrifugal pumps, centrifuges, reactors, and compressors. Because the transmission shaft penetrates both inside and outside the equipment, there exists a circumferential gap between the shaft and the equipment. The medium inside the equipment leaks out through this gap. If the internal pressure of the equipment is lower than atmospheric pressure, air leaks into the equipment. Therefore, a shaft sealing device that prevents leakage must be installed. Due to the advantages of low leakage and long service life, mechanical seals are the main shaft sealing method for these devices worldwide.
When a gap appears on one or both end faces, it indicates that the distance between the two end faces is too large. When the two end faces are tightly pressed together, a gap will be produced. The common cause of end face separation is the sudden evaporation of the mechanical seal medium entering. For example, water, especially in hot water systems or liquids containing condensate, expands when evaporating, so that the two end faces are separated. Pump cavitation phenomena and the blockage of sealing elements may also cause end face gaps in mechanical seals for water pumps. In this case, not caused by vibration and coupling asymmetry, as this is not sufficient to cause end face gaps. Reducing the end face temperature is a common method to prevent end face damage caused by sudden evaporation of the medium. At the same time, it is also beneficial to use mechanical seal parts materials with good thermal conductivity as pairs, such as nickel-based hard alloys and copper-infiltrated graphite. In addition, the use of balanced mechanical seals, or the injection of a special corrosion-resistant mechanical seal gasket from the outside for liquid cooling or direct cooling of the seal in the cavity, etc., are very effective in reducing the temperature of the seal end face.
Failed mechanical seals' friction pairs usually leave very fine radial cracks or radial cracks with water bubbles, and even cracks. This is caused by overheating of the seal, especially ceramic and hard alloy sealing surfaces are prone to this type of damage. Any one of the factors such as poor medium lubrication, overload, high operating temperature, high line speed, improper matching of mechanical seal parts material pairs, or the combination of several factors can generate excessive frictional heat. If the frictional heat cannot be dissipated in time, it will cause thermal cracks in the mechanical seal, 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, a static seal can be used with a flow guide sleeve for forced circulation of cooling fluid to guide the flow of fluid towards the seal face or a fluid dynamic groove can be opened on the seal end face to solve the problem. There are many small hot spots and isolated discoloration areas on the frictional end face, indicating that the sealing element is deformed and distorted under high pressure and temperature. For the thermal deformation of the end face, the general calculation method is not allowed, and finite element method should be used to calculate in order to improve the design of the sealing ring.