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Metal Bellows Designs:
Spring Rate and Elasticity
A FlexCom metallic expansion
joint, typically made from stainless steel, is a necessity
in applications requiring tolerance of very high pressure (up to
300psi) or temperature (up to 2500F) loads, or in applications
involving the transfer of liquids through the joint and its
surrounding piping. A metal
bellows is often one of the most sensitive components in
the system, called upon to reliably negotiate a wide range of
challenging load requirements.
Engineering
an optimum joint stiffness (or “spring rate”) is essential when
designing a metal bellows for a specific and demanding
application. Steel offers significantly greater thermal,
pressure load and thrust resistances than does a
fabric
expansion joint, but its strength comes at a price: the
stiffness of metal limits the joint’s ability to isolate
vibrations along the surrounding pipe work. In addition, a
higher spring rate also generally makes the joint a much more
resistant compensator of movement. The key to building an
effective metal expansion joint, therefore, is to
carefully engineer the joint’s spring rate.
This balance is unique to each individual application. FlexCom
engineers,
custom designing each metal bellows to meet the unique
specifications of our customers' applications, accomplish this
optimization by carefully selecting:
Bellows Design. FlexCom's
many available types of metal bellows designs (including Single,
Single Tied, Universal, Dual/Universal Tied, Hinged Universal,
Slotted Hinged and Gimbal designs) each offer varying balances
of stiffness, movement compensation and heat/pressure load
resistance.
Steel Ply Count. Rather than
building the bellows from a single ply of heavy steel, we can
reduce the joint stiffness - without sacrificing load tolerance
- by designing it instead using multiple plys of thinner metal.
Steel Grades. Joint
elasticity can be increased by delicately varying the grades of
stainless steel used in the metal bellows. By opting for the
most appropriate metallic grades, our engineers build the most
suitable and cost effective metallic expansion joints
possible with available materials.
Joint Size. A larger bellows
generally is a less stiff one. Depending on the needs of the
application, we can often increase the bellows elasticity simply
by increasing its size.
External Support. For
specific metal bellows designs, we can eliminate pressure
thrust by adding external tie rods to the joint. Fixed pipe
anchors also offer an excellent management solution for pressure
thrust forces.
By selectively balancing these various design and construction
elements, FlexCom can create the perfect metallic expansion
joint needed to fit your specific needs. Don't settle for an
approximate joint solution when FlexCom can provide you with an
exact one, customized to your application - saving you money and
substantially reducing wear and tear on your ductwork and
surrounding components.
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