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Info Letter No. 84 - March/April 2004

by Fritz Ruoss


FED1+, FED2+, FED3+ Resonance System with external Mass

When entering an external mass, the software calculates resonance frequency of the spring-mass system (without attenuation). The mass of the spring itself is considered by adding 1/3 of spring mass to external mass. For tension springs with screwed bolts and hooks, you must add the mass of the screwed parts (oscillating spring end only) to the external mass.

Instead of an external mass, you have to input an external mass moment of inertia at the FED3+ software (torsion spring). For mass points on the free leg, mass moment is J = m * r.

Resonance curve shows the amplitude of the spring-mass system as function of the load cycle frequency (constrainting frequency fz). dy (fz) is the value for overshoot of the spring-mass system in % and .


FED - tau-d Diagram

For dynamic load, corrected shearing stress tauk1 and tauk2 is marked. For static load (tau1 and tau2), dynamic correction coefficient is not considered.


FED1,2,3,5,6,7,8: Permissible Shear Stress for Hot-coiled Springs

According to EN 13906, permissible shear stress for hot-coiled tension springs is 600 N/mm, and 840-250*log(d/20) for compression springs (formula from diagram). Until now, HEXAGON spring software used this values if "hot coiled spring" was selected at "Production" window. Permissible shear stress values are ok, if suitable materials were selected (hot-rolled spring steel wire to EN 10089). But if, for example, a stainless steel 1.4310 was selected, the values for permissible shear stress are too high compared with the ones calculated for cold-formed springs. So, HEXAGON spring programs now calculate both values (for cold and hot rolled springs), and use the lower one.


FED5 Shear Stress Diagrams

Tau-d diagram is new for FED5 (tensile strength and permissible shear stress as function of the wire diameter). The vertical line marks the spring travel between tauk1 and tauk2 (or tau1 and tau2 for static load) of the most stressed coil.

Another new diagram in FED5 is the shear stress (max) as function of the spring travel s (tau-s diagram).


FED7 Special Shape

FED7 calculates helical compression springs of any shape by dividing the spring into many cylindrical sections. At "Special Shape", FED7 generates the sections for often used shapes: conical spring, barrel spring and waisted spring. Now, the input windows for these special shapes are more comfortable.


SR1 Description of Clamping Plates

A new edit field has been added to describe every clamping plate by name.


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