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Views: 2455     Author: Site Editor     Publish Time: 2020-07-29      Origin: Site


Most industrial equipment needs to have good sealing to ensure the working efficiency of the equipment. Common seals include non contacting mechanical seal, spring seal, pump seal, elastomer bellows seal, gland packing, etc. Here are a few things you need to know when choosing the metal bellows mechanical seal.



Plate Shape

The shape of the plate affects bending, travel, and operating length. In a nested bellows, all plates in the bellows are the same, and their outlines can be nested during compression. The contour line also improves the ability of bellows to withstand high pressure. The nesting-ripple plate shape can also more effectively achieve maximum flexing, long (axial motion) stroke with short operating lengths and a low spring rate.




For the bellows with straight flat segments, the change of the micro-structure in the heat-affected zones will reduce the reliability of the weld joints. By theoretical analysis using linear, thin-shell theory, the result shows that the inclined bellows axis can greatly reduce the stress at the welding position and the heat-affected zones. The analysis shows that the stress at the weld is mainly bending stress, but the larger the inclination angle is, the smaller the bending stress is. This design principle has also been fully proved in the research conducted by a professional organization. When the inclination angle is 45°, the bending stress will be drawn away from the heat-affected zones. This increases the stiffness of the plate, increases reliability and reduces fatigue.



Weld Integrity

It is very important to use the most advanced manufacturing process to make bellows, and to ensure the integrity of the weld by preventing too large root gap caused by weld geometry, weld thickness and roll-over control. With helium mass spectrometry, the seal is evacuated internally and blanketed in helium. If there is no gap or material defect in the weld, the gas can not pass through the seal, and the sensor probe can not detect these gases, which proves that the sealing performance is good.



Plate Thickness (Thin Plate)

The thin plate can provide low spring stiffness, thus reducing the end load, unit load, heat generation and extending the seal life. The thicker bellows plate has higher spring stiffness and is more susceptible to metal fatigue. In the process of plate bending, plastic deformation will occur repeatedly, which will lead to fatigue and greatly shorten the seal life. Increasing the thickness of the plate, though easier to weld, will significantly increase its stiffness and the coefficient of elasticity of the bellows.



Controlling Vibrations

Not all bellows in the industry are equipped with vibration dampers, which help to prevent any potential damage caused by harmonic vibration caused by idling. In some seal designs, the damper is a built-in design that provides protection when required to prevent potentially damaging vibration.



Double-ply Bellows

The strength and flexibility of double-ply bellows are higher than that of single-ply bellows. The principle of the double-ply design is similar to the leaf spring used in light trucks and trailers. The spring rigidity of the double-ply bellows is obviously lower than that of the single-ply bellows with two times of the plate thickness.


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