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MW INDUSTRIES INC., IS THE MARKET LEADER OF
HIGHLY ENGINEERED COMPRESSION SPRING SOLUTIONS
FOR OEM AND MRO APPLICATIONS
Take a look at any industrial or consumer product with moving parts; there’s a good chance you’ll find a spring
that is somehow integral to that design. Compression springs are among the most common types of springs,
although many designs also incorporate extension, torsion, and specialty springs.
Compression springs vary widely to accommodate the different environmental, geometric, and dynamic
requirements of their varied applications. Many designers assume that they will need to have a spring custom-
designed for their needs. In reality, spring manufacturers stock a dizzying array of spring types, sizes, and
constructions. Designers can often find springs in stock that meet their application needs and avoid the cost of
custom design. This can be particularly useful in cases where lead times are short, or designers might want to try
more than one spring solution.
So, the first step in designing with springs is to identify the specific needs of your application. As it pertains
to springs, you’ll need to ask yourself what force the spring needs to supply or withstand, how much and how
frequently the spring needs to deflect, what space the spring needs to fit into, what environment the spring will
be used in, and how the spring will be installed.
Finding the force
Defining the forces on the spring in your design is a good starting point for determining the spring you need.
Compression springs react against compressing forces. Whether they are assisting in the opening of a heavy-duty
die or maintaining pressure on a gasket in a tiny valve, it’s vital to know the force they have to exert or resist.
You probably already have a feel for the magnitude of this force based on the weight of your die, the durometer
of your gasket, or other application-specific forces. Just remember that a compression spring only reacts the
component of the force that is aligned with its axis.
Next, translate the required force into a spring configuration. Ideal springs operate according to Hooke’s Law:
F = -kx
where F is the reacting force of the spring, and x is the spring deflection, and k is the spring constant in lb/
in or N/mm. The presence of the negative sign indicates
that the spring supplies more reactive force the more it is
deflected. The linear nature of k holds as long as the spring
is within its elastic limit, and higher values of k represent
stiffer springs.
The spring constant, k, in turn, depends on the spring’s
physical attributes:
k = G×d4 ÷ [8×D3×na]
where na is the number of active coils, d is the spring
wire diameter, and D is the spring coil’s mean diameter,
calculated by subtracting d from the coil’s outer diameter.
G is the material’s shear modulus, calculated from the
more commonly stated elastic or Young’s modulus by:
G = E ÷ 2(1 + ν)
where E is the Young’s modulus and ν is the material’s
Poisson’s ratio.
These equations address the spring constant for the
most common type of compression spring, the coil design.
For wave springs, spring constant calculations must also
Basics of Design:
Designing with
Compression Springs
Presented by
The spring constant, k, relates the force
on a spring to its deflection. It is usually
taken as linear between 15 and 85% of full
deflection, and depends on material and
geometric properties.
Load (P)
PI
Deflection (f)
