Compression springs are the most common type of
spring used in the engineering industry. They are open coiled springs which are relatively
easy to design and manufacture.
Compression springs can be made from round or
square wire, although round is considerably cheaper and easier to manufacture. We keep a
vast selection of material sizes and types in stock, from standard spring steels to nickel
alloys, all of which can be used to manufacture compression springs.
The performance of a compression spring depends
on the following factors:
Wire size -
Increasing the wire size of a compression spring will make the spring stronger. We stock
all the standard wire sizes and also a large range of non-standard wire sizes for specific
requirements. A list of standard sizes is given in our technical help section here.
Diameter - As the diameter of the
spring increases the strength (rate) will decrease. Also, when a compression spring is
compressed the diameter will increase slightly. To avoid the spring jamming, if the spring
is to work over a rod or inside a hole, specify the size of rod or the hole it is to go
Number of coils - The number of active
coils is inversely proportional to the rate of a compression spring. This means a large
number of coils will result in a fairly weak spring and a small number of coils will give
a relatively strong spring. The total coils is dependant on the type of end given to the
spring (see below). Springs with closed or closed and ground ends will usually have one
inactive coil at each end.
Length - It is usual to specify the
free length required. The solid length (fully compressed length) can easily be calculated
or, if required, the working length for a specified load.
Rate - The rate (strength) of the
spring depends on all of the above factors and can easily be calculated. However,
sometimes the rate is the starting point from which the design can be based. This is
particularly useful if the forces at particular working lengths are critical. Rate is
defined as the force that has to be applied to the spring in order to produce a unit
deflection, and is measured in either Newtons per mm (N/mm) or pounds per inch (lb/in).
End types - There are three basic
types of end finish for compression springs:
and not ground.
and not ground.
and ground (ECG).
The most common type of end finish is the
closed and ground end which is the most stable type as it provides a much greater area for
the spring to exert it's force onto.
Hand - This is the direction in which the
coils are wound (clockwise or anticlockwise) and is illustrated in these
diagrams. It is actually quite obvious what hand a spring is
once you learn to recognise it: A Right-Hand wound spring is like a
corkscrew and would screw down when twisted clockwise, a Left-Hand
wound spring is the opposite.
Index - This is the ratio of the
mean diameter to the wire diameter. A low index indicates a tightly wound spring (a
relatively large wire size wound around a relatively small diameter mandrel giving a high
rate). The British Standard for compression springs (BS1726 part 1) does not give
tolerances for springs whose index is less than 3.5 or greater than 16 but even so, a
spring should ideally have an index of between 5 and 10.
Stresses - When a compression
spring is compressed the active coils are stressed in torsion. There is a physical limit
to the torsional stress that any material can withstand and it is this maximum stress
limit which constrains the maximum force which can be obtained from a spring. It is an
easy for our design programs to calculate these stress levels for your spring ensuring
that the spring performs well during use. For more information contact
our design department.
Spring Nests - In certain
situations it is often necessary to incorporate a nest of springs where one spring is
placed inside another. This is of particular use where space is limited such as engine
valve springs. Again, if you require further information please contact
our design department.
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