EXTENSION SPRINGS
2Pages

factors affecting design EXTENSION SPRINGS SYMBOLS W = Spring material width T = Spring material thickness L = Spring length (reference only) J = Minimum extension for constant force H = Off-set distance D2 = Storage drum diameter D1 = Outside diameter of spring when fully wound on storage drum SEE DETAILS OF SPRING ENDS D1 RECOMMENDED DISTANCE BETWEEN DRUM FLANGES EQUALS SPRING WIDTH (W+1) to 3mm Fatigue Life The fatigue life has a direct effect on the size of the spring and the maximum load available in the least space. A comparison of various chart values illustrates the effect fatigue 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 equipment or a replacement schedule. The free end of the extension spring should be guided to Held flat prevent the spring from wandering off the drum. The spring should be firmly attached to the moveable member (see diagrams). The fatigue life of a spring can be defined as either a full or partial extraction and retraction of the spring i.e. the spring can be exercised over its whole length and achieve the average life expectation, however if it is exercised over any one section of the spring repeatedly then that section can be expected to fatigue when the total number of cycles approaches the life predicted for the spring. Fatigue Life is not time dependant under normal operating circumstances; it is solely dependent on the number of operations. However pollutants even in low concentrations can have the effect of shortening 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. Drum Mounting The Spiroflex spring will be held on the drum by its inherent gripping action. No other fixing is required, provided there is sufficient spring material remaining on the drum when fully extended. An exception to this is when the mechanism does not have 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 it is positioned to suit the natural curvature of the spring (see diagram). Extension springs should not normally be bent back or reverse wound, as this will permanently damage the spring. Cavity Mounting A low cost mounting arrangement is 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 against a moveable member. Multiple Mounting Various standard methods of multiple mounting are shown below. Speed and Acceleration There is almost no limit to the speed or acceleration to which the spring will coil and uncoil. However, tests should be carried out to satisfy yourself the spring will perform satisfactorily under your conditions. Springs can also be laminated to provide an increase in force or fatigue life in a minimum space. Please apply to Spiroflex Sales Department for further details. To discuss your needs please call our Technical Sales Department who will be pleased to help. Issue No. 1 (Ext_spr_A/eng)

EXTENSION SPRINGS factors affecting design Spring ends not tailed as shown SPRING MATERIAL Type 301 High Yield Stainless Steel Drum must be free running NOTE:- Drums not supplied How the spring is assembled on drum (not supplied) END B Outer end of spring to be first wrap on storage drum Spring as supplied resembles a tight roll of metal tape Methods of using extension springs MULTIPLE MOUNTINGS D1+30t Chart Extensions Less by (D1+30t) Chart Extensions less by (D1+30t+J) BACK TO BACK & TANDEM