Graduated-load spring washer system for screws and threaded fasteners

Claim 1

A graduated-load spring washer system for screws and threaded fasteners to maintain a tailored preload and screw-locking force on a sandwiched joint to prevent loosening before, during and after joint thickness changes caused by material stress relaxation, creep and wear, comprising: a. A threaded fastener means and a graduated-load spring washer; b. said threaded fastener means, having a head, being operable to apply compressive load forces to said graduated-load spring washer and said sandwiched joint when tightened; c. said graduated-load spring washer comprising a deflection coil spring of slightly less than one coil; d. said coil spring having an upper surface that is in contact with the outer circumference of the head of said fastener means throughout the tightening process whereby the contact between the head and said upper surface of the coil spring is spaced inwardly from the outer circumference of the coil spring; e. said coil spring having a lower surface that provides a gap between the lower surface of said coil spring and the surface of said sandwiched joint, said lower surface pressed flat against said surface of said sandwiched joint when said graduated-load spring washer is fully compressed; f. said coil spring having an outer peripheral surface and an inner peripheral surface, said outer peripheral surface determining the greater thickness of said graduated-load spring washer; g. the opposite ends of said slightly less than one coil spring having a specially contoured configuration which prevents marring and minimizes damage of external surfaces of the sandwiched joint; wherein a precise preloading of force is applied by said threaded fastener means to said graduated-load spring washer at a position directly below said outer circumference of said head of said threaded fastener means and onto said upper surface of said graduated-load spring washer when said threaded fastener is tightened to flatten said graduated-load spring washer coil against the sandwiched joint, thereby maintaining a large anti-unscrewing force, spring force and centering force applied in opposition to forces that cause joint separation, thus keeping the sandwiched joint compressively loaded although large joint-thickness changes occur; and without degrading fatigue capability of the fastener means or causing structural configuration changes that make the fastener means susceptible to overload failure.