The Right Metal Bellows for the Job

Written by Wall Street News on September 30, 2018. Posted in Exhaust flex joint purpose, Pipe expansion joint, What can bellows be made of

Anyone knows what a fireplace bellows is, but for today’s industry, metal bellows are a totally different device, and have a wide range of uses with different metal types. The model and size of a bellows will be based on the job at hand and the types of metals being used, whether steel or brass or anything else. What are bellows use for? What can bellows be made of? How can one build a custom bellows?

The Basics of Bellows

Whether a standard model or a custom bellows, these devices are highly useful. According to Machine Design, a metal bellows is a compressible metal tube that is an odd combination of being flexible under pressure and needing to stand up to intense pressure without breaking, and they must be reliable over the long run during their service. They can be used as temperature sensors, hermetic seals, volume compensators, flexible connectors, and nearly anything else that a machine calls for. Custom bellows can be tailor for nearly any job with any sort of metal, pressure, temperature, or anything else, making them a flexible (literally and otherwise) tool for industry. Multi-ply bellows are often made with two or three tubes, but based on need, they may have as many as five. Because they are used so widely, metal bellows models are often specific in their composition and function, with a wide variety out there. They have several factors that will change from one model to another, and anyone making a custom bellows will keep them in mind as well.

The stress modes should be considered, such as swiveling, bending, torque, and speed of rotation, among others. Pressure deferential is important to note, that being the difference of pressure inside and outside the bellows, as well as maximum instantaneous pressure and whether high pressure will be applied inside or outside the bellows. Also, in fine detail, an engineer should note the amount of vibration or shock conditions that a bellows will experience during use so it does not break on the job. Highest and lowest temperature extremes should be noted, along with the lengths and types of the bellows ends.

Custom bellows design starts with an engineer or other industrial worker noting that an existing bellows could be upgraded, or if a machine is changed and now needs a bellows on it. If an existing model can do the job, there is no need for a custom bellows, but if not, an engineer can work on creating one. Consulting an experienced bellows engineer is recommended for those newer to the industry. Balancing flexibility versus rigidity is another factor that is determined by the assembly or device that needs a bellows, and may vary based on temperature, pressure, and the specific work being done.

The metals used as a bellows, or the metals that a bellows works with, can vary based on temperature, and in some conditions, only certain metals can stand up to workplace conditions. Steel, for example, has a melting point of 2,500 degrees Fahrenheit, but a new alloy, Hastelloy X, can be used in high temperature conditions such as in aerospace (its main use), but it is cost-friendly for commercial bellows for up to 1,600 degrees Fahrenheit use. In addition, for marine use, Marine Grade Stainless Steel can resist salt’s corrosive properties and is an alloy that includes molybdenum, an element that has a melting point of 4,748 degrees Fahrenheit. No matter what the job, a well designed custom bellows will have the right metal and the right properties for the work at hand.

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