Bellows: Hydro-Formed vs. Edge-Welded

Metal bellows have been in use for centuries. Over the years, they have been major components in sealing applications and demanding sensing for industries. They are the perfect solution for dealing with pressure or installation issues. Bellows can convert the changes in their internal and external pressures.

They can deflect elastically to respond and contain the force applied to them and, in turn, exert a reactive force. Metal bellows come in two types; hydro-formed and edge-welded. This article will delve deep into the two as it highlights their major differences.

What are Metal Bellows?

These are elastic vessels that can compress when you apply pressure to their exterior, or extend when put under a vacuum. When you release the vacuum or pressure, the metal elastic vessel can return to its original shape. However, this applies only if it did not stress past its yielding strength.

Edge-Welded

Since the 20th Century, these elastic metal vessels used have been centered on metal types, unlike the traditional types, which were originally leather and used in forges and fireplaces. The edge-welded kinds involve welding and stamping as necessary steps. The stamping process involves a set of ring-shaped diaphragms. The diaphragms are joined together on the inner and outer diameters using welds.

In most cases, edge-welded designs are used in medical devices, aircraft engines, and semiconductors. This is because they are the perfect fit for applications where size is a premium factor and cost is not a primary concern. In addition, their high level of precision makes them the most preferred for industrial applications. They are also perfect for risk reduction of operational or catastrophic equipment failure.

Hydro-Formed

Hydro-formed fall under the formed types, subclassified into cold-formed, electroformed, and hydro-formed. Hydro-formed allows the tube to expand slightly to accommodate the pressure, thermal movements, and vibrations. It is the perfect application in automotive, aerospace, pipe, and microelectromechanical systems.

Forming the hydro-formed types is a straightforward process. First, a segment of a metal tube is forced by hydraulic pressure against the mold until the bellow fully forms. When pressure is high inside the tube, the hydro-welded will expand.

The gadget allows for ease of expansion without damaging the pipes and any related parts. The tube manufacturers always aim to insert the expansion joints into the piping system. This helps absorb the heat growing in the pipe. After some time, the pipe heats up and cools, making a complete cycle for the device.

Comparison of Hydro-Formed vs. Edge-Welded

It is best to choose metal bellow that best suit your needs. High Vac Depot has the materials to help you achieve various media compatibility, temperature, and pressure requirements. It is evident that the edge-welded types’ applications are fast expanding, and now they are also applicable in the oil and gas, medical, semiconductor, instrumentation, and water industries.

High Vac Depot can provide perfectly welded end connections to help produce a complete assembly. Additionally, they can guide you to prepare the assembly and weld it yourself.

Material Construction of Edge-welded

Edge-welded type offer a wide range of materials you can choose from. In addition, they have specialty metals that can operate at temperatures as high as 800 degrees Fahrenheit. This makes them quite flexible for application across different industries. There are also ways to increase the sealing viability of these designs:

• Heat treating: this is done after the gadget’s core has been welded. The main aim of this process is to modify the characteristics of the material to provide higher pressure ratings, increased spring rates, and tensile strength.
• Double-ply bellows: this helps create flexibility and strength without any form of thickness. These types are used in services where more start-up torque strength is needed and in high-pressure situations.

Material Construction of Hydro-formed

Hydro-formed kinds are mostly limited to metals with high elongation properties like bronze and brass. However, these metals’ extension, formation, and integrity can easily be challenged when installed in corrosive or high-pressure applications. This is why working with High Vac Depot will ensure you achieve only the required temperature and pressures that the bellows can withstand for maximum output.

Operational Characteristics of Edge-Welded

Edge-welded types have the highest flexibility because of a thin individual metal diaphragm measuring in mils. This characteristic alone gives it a greater space allowance, range of motion, and flexibility. They also have great precision because of their spring rate. They can easily allow for the addition or subtraction of individual convolutions.

This, in turn, allows for a precise spring rate. When the spring rate is correct, it lightens the force affecting the faces, generating less heat and leading to a long legal cycle.

Operational Characteristics of Hydro-Formed

Hydro-formed has a high definitive rigidity because of thick, formed walls with existing stiffness. As a result, they have the highest spring rate compared to edge-welded types with a thicker convolution structure that negatively impacts precision loading. However, forming the hydro-formed can sometimes cause inconsistent wall thickness on the gadget units. This, in turn, can create hotspots and vulnerabilities for failure.

Cost of Manufacturing For Edge-Welded

Edge-welded ones are inexpensive compared to hydro-formed as you can produce them with lower initial tooling costs. However, the actual cost varies depending on the number of manufacturing materials and size. On the other hand, hydro-formed are also less expensive per unit when produced in high quantities.

Their manufacturing process has some cost benefits, but you must calculate them with the setup costs and higher tooling. Cost is essential in determining the type of bellow seal design to work with. However, it should not be a determining factor in the selection process.

Summing Up

Metal bellows have numerous applications. For example, some are used in space applications to provide reservoirs with potable water and accumulators to collect wastewater. Before settling on any bellows, you must do due diligence on the different manufacturers and identify what you need. Feel free to contact the experts at High Vac Depot for all of your questions and needs!