Spring devices – Coil – Conical
Patent
1974-06-03
1976-06-22
Marbert, James B.
Spring devices
Coil
Conical
F16F 112
Patent
active
039647366
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a helical extension spring with a spring body and two eyelets or loops formed integrally with the body, the free ends of the eyelets touching the two end coils of the spring body; the invention also relates to a method of making such spring.
In the known helical extension springs, the eyelets on the spring body are manufactured by bending a half coil up to two coils of the spring body to form each eyelet. Insofar as such eyelets bear upon the spring body with a pre-stress, the pre-stress forces in the eyelets which are formed of a half loop attain in the maximum case the value of the pre-stress forces which can be produced with conventional coiling and winding methods in the spring body; the pre-stress forces in eyelets consisting of one to two coils are, by comparison, even smaller. It is to be understood that "pre-stress force" means that force which acts in the direction along the longitudinal axis of the spring, such force causing a lifting-off of the wire ends or full eyelet coils from the adjacent end coil of the spring body. In both cases the pre-stress forces are purely accidentally created and there is no teaching in the state of the art of spring manufacture according to which this pre-stress force may be utilized for the attainment of any particular effects. Many times these pre-stress forces are almost zero, and furthermore there are many cases in which the complete loops or eyelets or the wire ends lie at a predetermined accurate distance from the spring body. This is especially the case with loops or eyelets which are formed from a half coil of the spring body.
It is well-known that in all helical extension springs with eyelets or loops which are manufactured in the above-described manner from the coils of the spring body, or with loops or hooks having other forms and starting on the coil-diameter of the cylindrical spring body, with large stress ranges the loops or eyelets always break first at their roots, that is their beginnings.
In the conventional design of such helical extension springs, considering present-day know-how in the spring manufacturing art, the alternating bending stress at the eyelet-root is always approximately 1.5 times as big as the bending fatigue strength of the spring-wire when the spring body is stressed up to its torsional fatigue strength. As a result, the much larger wire length of the spring body, in comparison to the length of the wire in the loop or eyelet, can never be used to its full working capacity. The only way in which the spring body of a conventional helical tension spring can be employed to its full fatigue strength is by making the end coils on the spring body with a coil diameter which is approximately two-thirds of the coil diameters of the remaining coils of the spring body, and make the eyelet or loop of the spring with such decreased diameter. Such construction, however, cannot be used in springs which already have a small ratio of coil diameter to wire diameter (the so-called spring index). With larger values of this ratio, a few coils are necessary to effect the transition from the spring body diameter to the smaller end coil diameter. These understressed end coils unneccesarily increase the total lengths (not only the initial length but also the loaded lengths) of the spring.
In helical extension springs which are manufactured in a prior process suggested by me and known as twist winding, very large wound-in pre-stresses, never before achieved in mass production are present in the spring body; in such springs the until now known eyelets or loops would be disadvantageous, as they already have a considerable spring deflection before the coils of the spring body lift off from each other. The advantage of these springs, however, consists in the fact that they save considerable space if the minimum operational forces are larger than the initial forces available with conventional manufacturing methods. This advantage, however, is decreased if through the springing of the eyelets or loops there is already formed a spring d
REFERENCES:
patent: 924724 (1909-06-01), Benson
patent: 2040656 (1936-05-01), Kirstein
patent: 2524293 (1950-10-01), Lindstrom
patent: 3292884 (1966-12-01), Scheldorf
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