What is Metal Bellows?
This post will talk these points as below:
2, Characteristics when Production
3, Material of Bellows
4, The structure and varieties of metal bellows( Updated 9th, April, 2020）
5, The Application of Metal Bellows ( Updated 9th, April, 2020）
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Metal Bellow is a kind of tube-shell accessories, which with good flexible, thin wall thickness, transverse wave, and well-sealed characteristic. The bellows are widely used in Machinery, Instrumentation, Petroleum, Chemical Industry, Electric, Heating, Locomotive, Shipbuilding, Nuclear Industry, Aerospace, Experimental Research.
Generally, there are 3 kinds of metal bellows, such as metal bellows, expansion joint bellows and metal corrugated hose. With the advancement of technologies such as metal pressure processing and the application of various structural bellows, there’re accordingly produced many methods of manufacturing bellows. These manufacturing methods, for example, hydro-formed, welded-formed and Electrodeposition, other methods such as rubber and mechanical bulging are not we discussed. Each method has its own feature. For example, hydro-formed bellows have better overall performance; Roll-formed bellows are suitable for bigger diameter; welded bellows have a better elastic characteristic, And Electrodeposition-formed bellows are suitable for ultra-high precision and small diameter.
2, Characteristics when Production
- a，Professional Produced.
- c，High quality
- d， Required strict technology
3, Material of Bellows
The performance of bellows’ is mainly based on the material quality of bellows. Whether the performance of the bellows can meet the design requirements largely depends on the manufacturing quality of these materials. Out of shape’s material, uneven welded technology, irregular wave after formed, and other damage can result in partial stress, these finally shorten the life-time of bellows. So when designing, the designer should firstly considerate the points of material:
- The Bellows must be compatible with the connected medium and parts. Because the wall thickness is very thin, it is easy to destroy the integrity of the bellows due to corrosion and stress corrosion. The cleaning medium and cleaning process must be carefully studied, as cleaning and inspection are particularly difficult inside the corrugated areas of the bellows.
- The working temperature of the metal bellows is about -253 ~ 600 C. So the materials for metal bellows must be sufficient thermal stability to bear the high temperature. When the operating temperature increases, the elastic modulus of the material decreases, which results in a reduction of the stiffness, pressure resistance and lifetime of the metal bellows. While when low temperature operating, the bellows need to be well performance too. At low temperatures, the brittleness of the material is very sensitive to surface defects, so the surface quality of the material should be strictly controlled.
- c，Lifetime and stress
- The pressure capacity of the bellows is limited by the yield strength of the material, and the number of fatigue cycles is limited by the fatigue life and structural stability of the material. Bellows that require high life should be designed to work within the elastic range, such as bellows for instrument components and axis seals.
- d, Manufacturing Technology
- The materials used for bellows require good plasticity and welding performance. Bellows with smaller diameters are usually manufactured with seamless pipes, while diameter larger than 25MM can be formed by sheet or strip into a cylinder and then longitudinally welded to form bellows.
- Additional considerations for materials: How to choose the material used for the bellows? (whether it is a pipe, strip or sheet materials), the thickness tolerance should be taken into consideration, according to the performance requirements of the bellows. When the stiffness is not the main performance requirement, the wall thickness tolerance can be ± 10%; When the stiffness requirement is strict, the wall thickness tolerance is ± 5%. The grain size of the bellows material before forming should be less than 35um, and the unevenness of the grain is not more than 2
- The materials used to make bellows are mainly stainless steel, tin bronze and beryllium bronze.
- Austenitic stainless steel（1Cr18Ni9Ti、0Cr18Ni9、00Cr17Ni14Mo2）has good mechanical properties and corrosion resistance, and the bellows made of Austenitic stainless steel are mostly used for isolation media or sealing elements.
- Tin bronze（QSn6.5-0.1、QSn6.5-0.4）has fine elasticity, good process performance, high fatigue strength, small elastic temperature coefficient, and bellows made by tin bronze are often used in instruments and meters;
- Beryllium bronze（QBe2)has good process performance, high elasticity and flexible, low hysteresis, good corrosion resistance, high fatigue strength, small elastic temperature coefficient, and bellows made by beryllium bronze are generally used for higher occasions;
- Brass（H80）has good flexible and process performance, but has poor elasticity and large hysteresis. The bellows made by brass are often conjunction with springs and are generally used for occasions with low requirements
- In addition to the above commonly used materials, there are more materials, such as elastic alloyNi36CrTiA1(3J1)、Inconel 718。
- The inspection and acceptance of materials shall meet relevant standards. for example, quality certification, the material must be accurate and traceable.
Next blog about:
>>The Structure of Metal Bellows:
>>The Application of Metal Bellows