Page 11 - Layout 1

the stem, so as the gate moves, the bellows By comparison, a pogo pin (a spring-loaded pin
expands or contracts to keep fluids from leaking out inside a sleeve) requires much more compression
of the stem. Two examples include pressure-relief before it starts to conduct electricity. Similarly, a
valves for overpressure in fuel systems, and inlet bellows in a contact assembly can withstand
valves for transferring hazardous fluids (both of vibration, angular offset or displacement better than
which have very low tolerance for fluid leakage). a pogo pin, and bellows can be made in any size.
Similarly, in valve applications involving cryogenic
fluids, the use of a bellows can ensure a hermetic Primary manufacturing techniques
seal (while packing and O-rings may be susceptible In general, metal bellows are produced using one of
to shrinkage under those extremely low three main techniques those being electrodeposition
temperatures). (also called electroforming), edge welding and
5. Volume compensation and fluid power hydroforming. Each technique has certain
applications: Bellows serve multiple roles in these advantages and disadvantages. In terms of the
applications. For instance, they can be used as materials that can be used and also the bellows
hydraulic dampeners (to bridge the gap between dimensions it is able to manufacture, and the
two shafts or hoses and dampen the impact of performance characteristics and engineering
vibration between them), as flexible seals to allow capabilities of the finished bellows it can produce.
for the adjustment of the dampening rate, and as Among these manufacturing techniques,
volume compensators to alleviate temperature- electrodeposition and edge welding are discussed
related volume changes in a fluid. Cryogenic volume below, since these two techniques offer
compensation is a typical example. Bellows can demonstrable advantages over hydroforming.
often provide a better solution to venting an Electrodeposited bellows: Electrodeposited
overpressure or high-pressure situation to the bellows are extremely rugged and lightweight. They
atmosphere. are produced by plating metal (most often nickel,
6. Mechanical seals: Thanks to their flexibility copper, gold and silver or a combination of these)
and ability to compress or extend in a predictable onto a precision-machined, bellows-shaped form or
way in response to pressure or temperature aluminum mandrel. The edges are trimmed, and
changes, bellows can function as flexible seals or the mandrel is chemically dissolved. Silver, copper
metal membranes to seal shafts that rotate or move and gold are also available as surface finishes if
in an axial direction. A bellows may be used to seal needed, to reduce corrosion risk or improve media
a shaft on an actuator to prevent contamination compatibility.
from scoring the shaft and thus provide prolonged This electrodepostion process allows the
operational life. manufacture of bellows with precisely controlled
7. Electrical contacts: The metallic construction wall thickness (as thin as 0.0051mm), and with
of the bellows provides good electrical conductivity. the smallest possible diameters (as small as
Metal bellows provide a useful function in contact 0.051mm). At these dimensions, the resulting tiny
assemblies that transmit a small current and deliver bellows are extremely sensitive — up to 25 times
a defined force against the opposing contact more sensitive than hydroformed bellows — and
surface. A bellows provides a sensitive, reliable thus are able to provide very large deflections in
mechanism, which will start conducting electricity response to the application of very small forces (as
as soon as it touches the opposing surface. small as 4 grams).

July 2020 • INDUSTRIAL TECHNOLOGY EXTRA! • p11