Some Common Sense About Bellows

Release time:

2022-06-30

There are two types of plastic corrugated tubing: one is completely airtight and watertight, used for applications such as propellant transport in launch vehicles, gas lines, and water heaters; the other is made by continuously wrapping it with adhesive tape. The commonly used wrapped corrugated tubing is employed to protect cables—for example, in IC card phones and machine tools—while the corrugated tubing used in table lamps has steel wires embedded during the manufacturing process.

　　Plastic Bellows There are two types: one is completely airtight and watertight, such as the propellant tanks used in launch vehicles, gas appliances, and water heaters; the other involves continuous wrapping with adhesive tape. Commonly used corrugated tubing is employed to protect cables—for example, in SIM-card phones and machine tools—while the corrugated tubing used in table lamps has steel wires embedded during the manufacturing process.

　　Plastic corrugated pipes classified by forming process:

　　(1) Hydraulic forming is a commonly used method for manufacturing bellows. In this process, liquid pressure inside the tube blank causes it to expand within a constraint ring until it yields circumferentially; the tube blank is then compressed to the desired length. This method is typically employed for bellows with small diameters.

　　(2) The roll-forming process for corrugated pipes is primarily used to manufacture large-diameter corrugated pipes. It relies on forming wheels that roll and shape the pipe blank. This process can produce single-wave corrugations, and some equipment can even form several waves in a single pass.

　　(3) Mechanically expanded bellows are formed one by one into a corrugated shape using an internal expanding fixture inside the tube blank. After initial shaping, they undergo customized finishing through both internal and external matte treatments.

　　(4) Welded bellows for excessively high wave heights or special wave shapes Bellows The stamping-welding process is often employed. When the material’s elongation makes integral forming impractical, or when the complex wave pattern makes integral forming particularly difficult, welding is commonly used instead. Since this type of bellows cannot withstand internal pressure, it is not suitable for use as the flexible section of expansion joints.

　　(5) The deposition-formed bellows process involves depositing the bellows material onto a core mold via electrodeposition, after which the core mold is melted away. This bellows material is a highly flexible, pure nickel metal with a non-porous structure. As a result, it can withstand high vacuum conditions and is weldable. However, this type of bellows is not suitable for use in the flexible sections of expansion joints due to its high cost and the fact that it is made entirely of nickel.

　　Plastic corrugated pipes classified by number of layers:

　　(1) Single-layer bellows with displacement compensation under static loads adopt a single-layer bellows configuration, which is simple to manufacture and low in cost. Provided that the design requirements for pressure-bearing capacity, compensation amount, stiffness, and fatigue life are met, single-layer bellows should be given priority.

　　(2) For bellows used to withstand alternating loads or in more critical piping applications, multi-layer bellows with two or more layers are employed. Compared to single-layer bellows, these multi-layer bellows exhibit lower stiffness and superior fatigue resistance at the same load-carrying capacity.

　　Bellows are widely used in instrumentation, with their primary function being to convert pressure into displacement or force, serving as the sensing element in pressure-measuring instruments. Bellows have thin walls and high sensitivity, and their measurement range spans from tens of pascals to tens of megapascals. In addition, bellows can also be used as sealing and isolating components to separate two media or prevent harmful fluids from entering the measuring section of a device.

　　Bellows can also serve as compensating elements, using their variable volume to offset temperature-induced errors in instruments. Occasionally, they are employed as flexible connections between two components. Bellows According to the constituent materials, bellows can be classified into metallic bellows and non-metallic bellows. According to their structure, they can be divided into single-layer and multi-layer types. Single-layer bellows are widely used. Multi-layer bellows offer high strength, excellent durability, and low stress, making them suitable for critical measurements.

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