US 5,842,923 AGranted

Screw and method for its production

AssigneesMinebea Co., Ltd., Nissan Jidosha Kabushiki Kaisha

InventorsMasaharu Umemura, Takashi Yamamoto, Ryoichi Nakayama

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Abstract

The screw comprises a circular thread portion 2a formed in a base portion of the screw, in which a helical thread is formed at the same depth and at the same crest angle; a special non-circular thread portion 2b which follows the portion 2a and has its thread depth gradually vary so as to assume a polygonal shape in cross section and permit the crest portion of thread to reach its highest points A-J in a turn of the thread, the highest points A-J being equal in thread depth and crest angle to the thread of the portion 2a; the portion 2b has its crest angle gradually increase as the thread moves from the highest points A-J to its lowest points along the length of the thread; and, lines connecting axially adjacent ones of the highest points A-J are tilted from the axis of the screw at a predetermined angle so that the portion 2b assumes a twisted polygonal prism-like shape as a whole.

Claims8

Dependent claims

A method for producing a screw from a stepped-stock blank, said stepped-stock blank including a first portion for forming a circular threaded portion of said screw and a second portion for forming a special non-circular threaded portion of said screw, said second portion being smaller in cross section then said first portion, the method comprising the steps of:

rolling the first portion of said stepped-stock blank with a flat thread rolling die which includes a plurality of first rolling grooves having a predetermined depth to form the circular threaded portion of said screw;
and
rolling the second portion of said stepped-stock blank with the flat thread rolling die which includes a plurality of second rolling grooves gradually varying in depth to form the special non-circular threaded portion of said screw;
wherein said second rolling grooves have a plurality of deepest points being equal to the predetermined depth of said first rolling grooves;
wherein crest portions of both said first and second rolling grooves have the same height and lie in the same plane;
wherein a line passing through vertically adjacent deepest points of said second rolling grooves forms an inclination angle with respect to a line which is vertical in relation to said die;
and
wherein said second rolling grooves follow said first rolling grooves, both said first and second rolling grooves extending parallel to each other at a predetermined lead angle to cover the entire surface of said die.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/978,276Filed 28 Nov 1997 · continuation
Priority: JP 7-17143514 Jun 1995
Granted: 1 Dec 1998
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

B21H 3/027
External screw-threads ; Making dies for thread rolling: rolling of self-tapping screws
F16B 25/0047
Characterised by the geometry of the thread, the thread being a ridge wrapped around the shaft of the screw: the ridge being characterised by its…
F16B 25/0078
Characterised by geometric details of the screw: with a shaft of non-circular cross-section or other special geometric features of the shaft
F16B 25/0084
Characterised by geometric details of the screw: characterised by geometric details of the tip