reaction Mechanical seal for kettle Key points for manufacturer's design
As the reaction kettle is gradually developing towards high pressure and large diameter, and the rotating speed is lower than the mechanical seal used for the kettle, the following points should be paid attention to in the design: 1. As most reaction vessels are sealed with gas, the selection of materials should not only consider the corrosiveness of the medium, but also consider whether the material itself has leakage. When the diameter is large, the integral surface composite material shall be used; When the pressure is high, the matching material with high pv value and high mechanical strength should be used. When the medium pressure is below 10MPa, it is recommended to use cemented carbide or silicon carbide and carbon graphite materials for matching. When the medium pressure is greater than 10MPa, cemented carbide and cemented carbide, cemented carbide and copper alloy, silicon carbide and copper alloy are recommended. In addition to pressure and circumferential velocity, the selection of friction materials should also be considered comprehensively with all conditions such as shaft diameter, temperature, lubrication, cooling mode, etc.
For high pressure and large diameter seals, the end faces of friction pairs are easy to deform, especially with the increase of medium pressure, the starting torque tends to increase. Therefore, the seal ring shall be made of materials with high strength and good rigidity.
2. In the structural design of the mechanical seal for kettle, the high-pressure large diameter seal should be double-sided to ensure reliable sealing. Generally, the atmospheric end is sealed, and it is designed to be balanced due to the large pressure difference; Due to the effect of sealing fluid in the sealing cavity, the pressure difference on both sides of the sealing end face of the middle end seal is very small, so it can be designed as an unbalanced type; However, when the medium pressure in the kettle is unstable or the pressure of the sealing liquid in the sealing chamber is unstable during operation, which causes pressure fluctuations, it can also meet the requirements and should also be designed as a balanced type. In some imported equipment, the sealing under low pressure is also balanced. This is to reduce the friction heat on the end face and prevent the evaporation of the liquid film on the end face, so as to obtain a longer service life. When the pressure in the kettle exceeds 10MPa, it is recommended to use multi-stage mechanical seal device.
3. The determination of geometric dimensions shall fully consider the shape and support mode of seal ring in the design of mechanical seal for autoclave. The bending caused by pressure and the moment caused by eccentric force on the rotating center of the section will have a great impact on the sealing characteristics. Due to the limitation of the flange size of the kettle, the radial space of the fixing ring is generally not too large. Therefore, it is necessary to fully consider the ring shape, support mode, sealing ring position, etc., so its pressure resistance and deformation are small. In order to avoid deformation caused by pressure, thermal stress and unbalanced force, the shape should be symmetrical and simple as far as possible. It is also recommended to contact the back of the support method. Special attention shall be paid to the fillet R at the end boss connection. The fillet R shall be as large as possible, and other chamfers shall also take appropriate values, without sharp corners. The friction width varies with the shaft diameter and the appropriate strength coefficient.
