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Characteristic values of
springs
Characteristic curve/spring rate of springs
We can obtain the characteristic curve of a
spring by producing a forces/travel diagram.
The spring rate is the ratio between the
effective force and the spring travel. The unit
of measurement for the spring rate is N/mm.
It informs us whether a spring is hard or soft.
If the spring rate remains the same
throughout the entire spring travel, the spring
has a linear characteristic curve.
A soft spring has a flat characteristic curve
while a hard spring has a steep curve.
A coil spring is harder due to:
• a greater wire diameter
• a smaller spring diameter
• a lower number of coils
Principles
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If the spring rate becomes greater as the
spring travel increases, the spring has a
progressive characteristic curve.
Coil springs with a progressive characteristic
curve can be recognised as follows:
a) uneven coil pitch
b) conical coil shape
c) conical wire diameter
d) combination of two spring elements
(example, see next page)
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Spring travel s
Resilience F
Linear characteristic curve
Hard spring
Progressive characteristic
curve
a
b
c
Linear characteristic curve
Soft spring