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Basic
Considerations
Good spring design depends upon
many factors in addition to
dimensional and load
requirements. One factor is
environment. How hot or cold
will it be? Will the spring be
exposed to corrosion? Another is
required life. How long must the
spring survive without breaking
or experiencing excessive
permanent set? After considering
all the factors that could
affect performance, we can
design a spring that will give
the greatest possible value to
the spring user.
Often insufficient space is
allowed for springs in newly
designed equipment. This can
force the use of costly, high
stressed, close tolerance
springs, which increase the risk
of early failure. We can save
you time and money by helping
you design a spring before you
are committed to a final design.
Spring Life
As with most components, no
matter how much time and effort
is spent to ensure long life, it
is practically impossible to
guarantee that there will be no
failures in a given production
lot of springs. In addition to
breakage, loss of load and
distortion may also be failures.
Predicting spring life is not an
exact science. Nevertheless,
spring life can be extended by
careful design and selection of
material, as well as quality
control of both material and
production.
Corrosion
One of the most neglected
factors that can adversely
affect spring performance is
corrosion. Often microscopic
corrosion is the origin of
spring failure, but its presence
goes undetected, and the cause
of failure is attributed to
something else.
Springs made of uncoated steel
must be given some kind of
corrosion protection, even
during manufacturing, shipping,
and storage. The degree of
protection required after
installation is another matter
and depends upon the nature of
the application. We can help you
with this problem if we know the
environment in which the spring
will be operating.
Tolerances
Since it is an economic
consideration, specified
tolerances should be generous
enough to permit the fabrication
of acceptable springs by
ordinary production methods.
Also, it,s smart to apply
tolerances only on functional
requirements and dimensions.
This gives us an opportunity to
compensate for variations in the
size and mechanical properties
of all spring materials.
If your standard drawing forms
have tolerance boxes for
machined dimensions, they are
almost sure to be impractical
for springs. We suggest you
delete them and apply realistic
tolerances to spring
requirements.
Burrs
Some draftsmen include a note on
all drawings reading, "Remove
all burrs." This can result in
additional cost without adding
value to the part. Burrs are
produced, to some degree or
other, by many of the operations
used in manufacturing springs.
Burrs created in the cutting-off
operation are often harmless and
it would be unwise to pay for
their removal. Burrs arising
from other operations may
sometimes be controlled within
limits as to size, shape, and
location. If we can agree upon
such limits, they may be a
chance for significant savings.
Hydrogen Embrittlement
Whenever a carbon steel is
pickled in preparation for
plating or during some
electroplating processes,
hydrogen can become absorbed
into the material. While cracks
can develop in the pickling or
plating bath, more often then
they appear when the plated
springs are in service.
The hazard of hydrogen
embrittlement becomes more acute
when there is (1) high stress
concentration, (2) high Rockwell
hardness, or (3) high carbon
content. Tempered materials are
particularly susceptible.
To relieve embrittlement, the
springs must be baked
immediately after plating to
drive the hydrogen out of the
material.
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