Factors Affecting Design extension springs0 pages

factors affecting design

SYMBOLS >

W = Spring material width
T = Spring material thickness
L =Spring length (reference only)
J = Minimum extension for constantforce
H = Off-setdistance
D2= Storage drum diameter
D1= Outside diameter of spring when fully wound on storage drum >
RECOMMENDED DISTANCEBETWEEN DRUM FLANGES
EQUALS SPRING WIDTH (W+1) to 3mm
SEE DETAILS OFSPRING ENDS

Fatigue Life Stability

The fatigue life has a directeffecton the size of the spring and themaximum load available in the leastspace.A comparison of various
chartvalues illustrates the effectfatigue requirements have on the
size of the spring.For any application the required number of cycles
or reversals,should be estimated for the life of the equipmentor a
replacementschedule.The fatigue life of a spring can be defined as either a full or partialextraction and retraction of the spring i.e.the spring can be
exercised over its whole length and achieve the average life
expectation,however if itis exercised over any one section of the
spring repeatedly then thatsection can be expected to fatigue when
the total number of cycles approaches the life predicted for the
spring.Fatigue Life is nottime dependantunder normal operatingcircumstances;itis solely dependenton the number of operations.However pollutants even in low concentrations can have the effectofshortening the fatigue life through corrosion or chemical attack,
please refer to the statements regarding uses and misuses of
Spiroflex springs in our brochure and web site and refer to Spiroflex
if in doubt. The free end of the extension
spring should be guided to
preventthe spring from
wandering off the drum.The spring should be firmly
attached to the moveable member (see diagrams). >
Held flat or

TYPES OF MOUNTING

Drum Mounting

The Spiroflex spring will be held on the drum by its inherent
gripping action.No other fixing is required,provided there is
sufficientspring material remaining on the drum when fully
extended.An exception to this is when the mechanism does nothave
its own limiting stops,in which case we recommend the inner end
be secured to the drum by the holes provided (drum should be
stepped see diagram). >

Extension Spring used in conjunction with Idler Pulley

The Spiroflex spring can be used with an idler pulley provided itis
positioned to suitthe natural curvature of the spring (see diagram).
Extension springs should notnormally be bentback or reverse
wound,as this will permanently damage the spring. >

Cavity Mounting

A low costmounting arrangementis the Spiroflex spring coil seated
in a cavity the obvious disadvantage is the friction between the
spring coil and the cavity surface.We would recommend the cavity to
be lined with a low friction material.Another method is to use the
free coil force againsta moveable member. >
INCORRECTCORRECT

Multiple Mounting

Various standard methods of multiple mounting are shown below.Springs can also be laminated to provide an increase in force orfatigue life in a minimum space.Please apply to Spiroflex Sales
Departmentfor further details.To discuss your needs please call our Technical Sales Departmentwho will be pleased to help. >

Speed and Acceleration

There is almostno limitto the speed or acceleration to which the
spring will coil and uncoil.However,tests should be carried outto
satisfy yourself the spring will perform satisfactorily under your
conditions. >
Issue No.1 (Ext_spr_A/eng) size="-4">