Types of Metal Bellows

What Is Metal Bellows

Metal bellows are flexible, mechanical seals that consist of thin-walled, convoluted metal tubes. They are designed to compress, extend, or bend in response to pressure, temperature changes, or mechanical forces. Metal bellows can be made from a wide range of materials, including stainless steels, nickel alloys, and specialty metals like Beryllium copper, depending on the application requirements.

What is Formed Bellows

Formed bellows, also known as convoluted bellows, are created by cold-forming a metal tube into a corrugated shape using a stamping process. This process allows for the production of bellows with a precise spring rate and a variety of end configurations.

Formed bellows are cost-effective for high-volume applications and offer a wide range of design options to meet specific performance characteristics.

What is Welded

Welded bellows are manufactured by welding individual metal diaphragms together to form a bellows assembly. The welding process can be performed using various techniques, such as laser welding, micro-plasma welding, or resistance welding.

Welded bellows offer several advantages, including the ability to withstand higher pressures, greater flexibility in material selection, and the ability to create complex geometries. However, welded bellows may have lower tensile strength and shorter fatigue life compared to formed bellows due to the heat-affected zones created during the welding process.

What is Electroformed

Electroformed bellows are created by depositing metal onto a precision-machined mandrel through an electroplating process, followed by the removal of the mandrel. This process allows for the production of seamless, thin-walled bellows with excellent dimensional accuracy and surface finish.

Electroformed bellows are ideal for applications requiring high performance, such as aerospace systems, medical devices, and precision instruments. However, the electroforming process is more expensive and time-consuming compared to other bellows manufacturing methods, making it less suitable for high-volume applications.

Applications of Metal Bellows

• Manufacturing process: Formed bellows are cold-formed or hydroformed from a single piece of metal, while welded bellows are assembled from individually stamped diaphragms that are welded together.
• Size and length limitations: Formed bellows are typically limited to smaller diameters and shorter lengths due to the forming process, while welded bellows can be produced in much larger sizes and lengths.
• Material options: Formed bellows are usually made from high-elongation metals like brass or bronze, while welded bellows can be constructed from a wide variety of materials, including stainless steels, high-strength alloys, and exotic metals.
• Flexibility and spring rates: Welded bellows, particularly edge welded bellows, offer greater flexibility and lower spring rates compared to formed bellows, making them suitable for applications requiring significant axial displacement or angular movement.
• Pressure and vacuum capabilities: Welded bellows can withstand higher internal and external pressures, as well as deeper vacuum levels, compared to formed bellows due to their robust construction and leak-tight welds.
• Cost and lead times: Formed bellows are generally less expensive and have shorter lead times than welded bellows, as the forming process is simpler and more automated. However, the cost difference narrows for larger quantities or custom designs.

Metal Bellow Manufacture

The manufacturing process for metal bellows depends on the type of bellows being produced.

Formed bellows are typically manufactured using a stamping process, where a metal tube is cold-formed into a convoluted shape using a series of dies. This process allows for high-volume production and modest tooling costs.

Welded bellows are created by welding individual metal diaphragms together using techniques such as laser welding, micro-plasma welding, or resistance welding. The welding process enables the production of bellows with complex geometries and a wide range of materials.

Electroformed bellows are manufactured by depositing metal onto a precision-machined mandrel through an electroplating process, followed by the removal of the mandrel using chemical or mechanical means. This process allows for the creation of seamless, thin-walled bellows with excellent dimensional accuracy and surface finish.

Faqs

What Is the Best Material for Bellows

• Stainless steels: 304, 316, 321, and 17-7 PH stainless steels offer excellent corrosion resistance, strength, and flexibility.
• Nickel alloys: Inconel 625, Inconel 718, and Hastelloy C-276 provide superior high-temperature performance and corrosion resistance.
• Beryllium copper: This alloy offers excellent fatigue life, thermal conductivity, and electrical conductivity, making it suitable for applications in aerospace, electronics, and medical devices.

Other materials, such as titanium, Monel, and specialty alloys, may be used for specific applications with unique requirements.

What Are the Different Types of Expansion Bellows

• Axial expansion joints: These bellows allow for axial movement in piping systems due to thermal expansion or contraction.
• Lateral expansion joints: Also known as hinged or gimbal expansion joints, these bellows accommodate lateral movement in piping systems.
• Angular expansion joints: These bellows allow for angular movement in piping systems, accommodating misalignment or deflection.
• Universal expansion joints: These bellows combine the features of axial, lateral, and angular expansion joints, allowing for multi-plane movement in piping systems.