Text version of the page

factors affecting design

Factors Affecting Design extension springs - 15944 EXTENSION SPRINGS

SYMBOLS

WTJD2D2D1H

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)