BELLOW

A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest

type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather

sides enclosing an approximately airtight cavity which can be expanded and contracted by operating

the handles, and fitted with a valve allowing air to fill the cavity when expanded, and with a tube

through which the air is forced out in a stream when the cavity is compressed.[1] It has many

applications, in particular blowing on a fire to supply it with air.

Hand-made English fireplace bellows

The term "bellows" is used by extension for a flexible bag whose volume can be changed by

compression or expansion, but not used to deliver air. For example, the light-tight (but not airtight)

bag allowing the distance between the lens and film of a folding photographic camera to be varied is

called a bellows.

Metal bellows are elastic vessels that can be compressed when pressure is applied to the outside

of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will

return to its original shape (provided the material has not been stressed past its yield strength).

Bellows technology of the 20th and 21st century is centered on metal bellows. These high-

technology products bear little resemblance to the original leather bellows used traditionally

in fireplaces and forges.

There are three main types of metal bellows - formed, welded and electroformed.

Formed bellows are produced by reworking tubes, normally produced by deep drawing, with a

variety of processes, including cold forming(rolling), and hydroforming. They are also called

convoluted bellows or sylphons.

Welded bellows (also called edge-welded, or diaphragm bellows) are manufactured by welding a

number of individually formed diaphragms to each other. The comparison between the two bellows

types generally centers around cost and performance. Hydroformedbellows generally have a

high tooling cost, but, when mass-produced, may have a lower piece price. However, hydroformed

bellows have lower performance characteristics due to relatively thick walls and high stiffness.

Welded metal bellows are produced with a lower initial tooling cost and maintain higher performance

characteristics. The drawback of welded bellows is the reduced metal strength at weld joints, caused

by the high temperature of welding.

Electroformed bellows are produced by plating (electroforming) a metal layer onto a model

(mandrel), and subsequently removing the mandrel. They can be produced with modest tooling

costs and with thin walls (25 micrometres or less), providing such bellows with high sensitivity and

precision in many exacting applications.[1]

Another area of comparison is in metals of construction. Hydroformed and rolled bellows are limited

to metals with high plastic elongation characteristics, whereas welded bellows may be fabricated

from a wider variety of standard and exotic alloys, such as stainless steel andtitanium, as well as

other high-strength, corrosion-resistant materials. Electroformed bellows can be produced of nickel,

its high-strength alloys, and copper.