Bellows are categorized into metal and non-metallic types, each designed for specific applications. Metal bellows include varieties such as formed, edge-welded, and electroformed, suited for handling pressure changes. Non-metallic bellows, made from materials like rubber, fabric, and plastic, offer durability in harsh environments.
Key Takeaways
- Metal bellows types: formed, edge-welded, electroformed, machined, deposited.
- Non-metallic bellows materials: rubber, fabric, durable plastics.
- Selection criteria: material, operating environment, size, performance criteria and cost.
Types of Bellows
Formed or Convoluted Bellows
Formed or convoluted bellows are made by reshaping a metal tube into a corrugated, cylindrical shape using various techniques.
One common technique is hydroforming. Here, the metal tube is placed inside a die cavity that has the shape of the final bellows. High-pressure water is then injected into the tube, causing it to expand and conform to the die’s interior, thus forming the desired corrugated pattern.
Another technique is cold forming. This method does not require heat and involves physically manipulating the metal tube at room temperature. Techniques in cold forming include rolling the tube with external rollers to create the convolutions or using internal punches that push outward to form the corrugated shape.
Edge-Welded Bellows
Edge-welded bellows are made by welding stamped metal diaphragms together at both their inner and outer edges. These diaphragms are thin, circular pieces of metal that, when connected, form corrugations known as convolutions. The process begins by welding the inner edges of the diaphragms, followed by connecting the outer edges. This method builds up the bellows into a flexible, accordion-like structure.
This type of bellows falls under the category of metal bellows, and they are highly valued for their precision and sturdiness. Their design provides significant flexibility and strength, which are essential for applications that need precise motion control and tight seals. The use of stamped metal ensures each convolution is uniform, which increases the overall effectiveness and dependability of the bellows.
Electroformed Bellows
Electroformed bellows are created through a precise method known as electroforming. In this process, metals like nickel or copper are used. The metal starts in an electrolytic solution as ions. When an electric current is applied, these ions move and attach to a mandrel, which is a model or form used to shape the bellows. This forms a thin, even layer of metal over the mandrel.
The thickness of the metal layer is crucial and is controlled with precision. This is to ensure that the final product has the necessary strength and durability. Once the desired thickness is achieved, the next step involves the careful removal of the mandrel. This step is delicate because the mandrel holds the bellows in the correct shape and configuration.
Removing the mandrel without damaging the bellows is essential. This ensures that the intricate designs and specific dimensions are preserved. The end product is a seamless metal bellows that is robust and accurate in dimensions.
Machined Bellows
Machined bellows are formed by mechanically manipulating metal tubes into specific shapes called convolutions. This is done using equipment designed for this purpose, involving either rolling or pressing the tubes. They use dies and forming machines to craft the precise, intricate shapes needed for the bellows to function effectively.
This method contrasts with hydroforming, where bellows are shaped by applying hydraulic pressure inside a mold to expand the metal into the desired form. In machined bellows manufacturing, direct mechanical force is applied, allowing for tighter control over the dimensions and flexibility of the final product.
Deposited Bellows
Deposited bellows are fabricated by coating a mandrel, often made of aluminum, with metal. The mandrel is then removed, revealing a detailed bellows structure. Two primary methods are used: electrodeposition and chemical deposition.
Electrodeposited bellows, also known as electroplated bellows, employ a nickel-cobalt alloy. This technique results in thin, strong walls ideal for small, precise components. Such bellows can be designed with very small diameters, starting from 1.6 mm, tailored for specific, detailed applications.
Chemical deposition, in contrast, allows for bellows with varied wall thicknesses. This adaptability makes it possible to produce larger bellows, with diameters reaching up to 177.8 mm. This method suits larger or more complex systems, providing greater flexibility in design and application.
Types of Non-Metallic Bellows
Rubber Bellows
Rubber bellows, typically made from rubber or silicone, are flexible, cylindrical devices. Their accordion-like design allows them to stretch and compress, ensuring a secure, tight seal. This sealing capability is crucial in protecting against environmental contaminants like dust and water. The design features annular convolutions that enhance their functionality in various settings.
Fabric and Plastic Bellows
Fabric bellows are primarily made from woven materials such as nylon, polyester, fiberglass, or Nomex. These fabrics often receive coatings like polyurethane or aluminized finishes, which significantly boost their durability and environmental resistance. Their design is particularly beneficial in scenarios requiring high flexibility and resistance to heat, making them suitable for protective and insulative applications.
Contrastingly, plastic bellows are crafted from durable plastics such as PVC or silicone rubber. Known for their impressive elasticity, these bellows excel in environments that demand resilience to a broad spectrum of temperatures and chemical interactions. Their adaptability makes them indispensable in applications where components need safeguarding against various physical and chemical stressors.
How do I choose a bellows
Material Selection:
- Stainless Steel: Offers excellent corrosion resistance, high strength, and durability, making it suitable for harsh environments and high-pressure applications.
- Aluminum: Lightweight and cost-effective, aluminum bellows are often used in low-pressure and temperature applications.
- Brass: Provides good corrosion resistance and is commonly used in low-pressure systems.
- Inconel: A nickel-chromium alloy with exceptional resistance to high temperatures, oxidation, and corrosion, making it suitable for extreme environments.
- Hastelloy: Another nickel-based alloy with superior resistance to chemical attacks, often used in the chemical and petrochemical industries.
Operating Environment:
- Temperature Range: Bellows must be able to withstand the expected temperature extremes without degradation or failure.
- Chemical Exposure: Certain materials may be more resistant to specific chemicals or corrosive environments than others.
- Vibration: Bellows used in applications with high vibration levels may require additional reinforcement or specific designs to prevent fatigue failure.
- Outdoor Conditions: Bellows exposed to outdoor environments may need to be resistant to UV radiation, moisture, or other environmental factors.
Size and Dimensions:
- Diameter: The inner and outer diameters of the bellows must be compatible with the connected components and available space.
- Stroke Length: The maximum allowable linear or angular movement the bellows can accommodate without overstressing or buckling.
- Configuration: Bellows can be round, rectangular, U-shaped, or custom-designed to fit specific geometries or clearances.
Performance Criteria:
- Pressure Rating: The maximum pressure (positive or negative) the bellows can withstand without failure or excessive deformation.
- Spring Rate: The force required to compress or extend the bellows, which affects its flexibility and responsiveness.
- Cycle Life: The number of compression/extension cycles the bellows can endure before failure, important for dynamic applications.
- Flexibility: The ability of the bellows to accommodate misalignment or movement without excessive stress or fatigue.
Cost and Availability:
- Budget Constraints: Different materials and designs can vary significantly in cost, requiring a balance between performance and budget.
- Lead Times: Certain bellows types or custom designs may have longer lead times, which could impact project timelines.
- Availability: Some materials or configurations may be more readily available from suppliers, affecting procurement and maintenance considerations.
Conclusion
When deciding on the appropriate bellows for your needs, consider the specific demands of your application. Metallic bellows are suited for high-temperature, industrial settings due to their durability, while non-metallic bellows are preferable for applications requiring greater flexibility. It’s crucial to evaluate aspects such as temperature, pressure, and chemical exposure before making a selection.
For optimal functionality and extended lifespan of your bellows, consulting with an expert is highly recommended. Reach out today to ensure you choose the best solution tailored to your system’s requirements.
