Screw or nut with a thread a pitch of which varies and tool to produce said screw or nut

摘要

The distribution of load stresses on threads engaged with a standard screw or nut is very unequal. Indeed, the first threads in engagement support a large majority of the load. So if the load is too important, the threads give way and the function is not provided any more by the screw or the nut. In the prior art, threads are known whose depth or pitch varies a lot in order to cause a self-clamping. In particular, the invention aims at optimizing the resistance and the fatigue resistance of the screws by distributing the load at the very best on their threads without causing this self-clamping. It was shown that the control of the pitch variation, within a chosen pitch tolerance, makes it possible to control the stress distribution on the threads. It is possible to determine a different variation for each load case encountered.

主权项

1. Screw or nut provided with a thread whose pitch varies within a preset range, between a minimum and a maximum,
the range belonging to a fixed tolerance, the pitch decreasing and increasing in a controlled way, wherein at least one of, the pitch decreases over a plurality of threads according to two different slopes, one of said slopes being stronger than the other slope; or the pitch increases over a plurality of threads according to two different slopes, one of said slopes being stronger than the other slope; and wherein along the screw or nut, starting from a first end, the pitch has a variation that decreases then increases, before and after the variation, the pitch has a first constant value, after decreasing, and before increasing, the pitch has a second constant value close to a minimum of the tolerance.