Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having structure to restrict rotation of threaded – mating... – Comprising a thread lock
Patent
1992-12-18
1994-10-25
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having structure to restrict rotation of threaded, mating...
Comprising a thread lock
411412, 72469, F16B 3504, F16B 3930, B29D 1700
Patent
active
053583663
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a fastening screw, and more particularly to a fastening screw for preventing loosening thereof after tightened and having a locking function, and a thread rolling die for forming such screw.
BACKGROUND OF THE INVENTION
A fastening screw is used in a variety of industrial fields since it can be used for connecting a plurality of members with ease. Particularly, a tapping screw immediately fastens steel plates or synthetic resin material only with forming a pre-drilled hole and without forming an internal thread to the material. That is, no tapping operation or tool like a screw tap is required to form the thread. Therefore, the tapping screw is widely used in manufacturing household electric appliances, automobiles and the like.
Meanwhile, in this kind of screw, generally, torque for loosening the screw is small and the screw is susceptible to inverse rotation or loosening due to vibration after tightened.
To solve the problem, a spring washer, double nuts or the like are applied when bolts and nuts are used. Further, when the tapping screw is adapted, a locking washer or bonding agent is preferably adapted.
However, with the conventional countermeasures described above, separate parts from the screw such as spring washers, another nut, other washers, and bonding agents are required, which increases costs and manhour for fastening work. Moreover, when the tapping screw is used, plastic deformation of an internal thread material loosens the screw even though the screw does not rotate. Therefore, with only the above method, the loosening can not be prevented securely, which provides another problem in this respect.
The present invention has been accomplished to eliminate the above drawbacks and the object thereof is to provide a screw, and a thread rolling die for manufacturing the screw.
DISCLOSURE OF THE INVENTION
To accomplish the object described above, the screw according to the present invention adopts a main thread to be screwed in; and a sub-thread formed in the direction opposite to the main thread, the sub-thread having an external diameter smaller than that of the main thread and larger than a diameter of a pre-drilled hole of a mating member, and a slant surface of said sub-thread on a screw-loosening side has a sharp slope and that on a screw-tightening side has a gentle slope.
In the above structure, the external diameter of the sub-thread may be substantially the same as the diameter of the pre-drilled hole.
A nut according to the present invention is used for the above screw and no internal thread is formed in the pre-drilled hole of the nut.
Further, the thread rolling die according to the present invention has a structure in which a thread groove for a main thread and that of a sub-thread are formed, and the thread groove for the sub thread formed in the direction opposite to the thread groove for the main thread and shallower than that of the main thread, and a slant surface of the thread groove for the sub-thread on a screw-loosening side has a sharp slope and that on a screw-tightening side has a gentle slope.
The present invention with the above structure works as described below.
When tightened, the screw screws in by the main thread having a larger diameter. The sub-thread is formed in the direction opposite to the main thread and has an external diameter smaller than that of the main thread and larger than the diameter of the pre-drilled hole and the inclination of the slant surface of the sub-thread is gentler on the tightening side, which permits the screw to advance in the direction opposite to the sub-thread.
When the screw is subject to a torque in the loosening direction after tightened, the torque works to tighten the sub-thread. Moreover, since the slant surface of the thread is steep, the sub-thread resists the return of the screw as if the sub-thread eats into the pre-drilled hole, which prevents the screw from being loosened.
If fastened material, to which the pre-drilled hole is formed, is provided with toughness, inn
REFERENCES:
patent: 2908309 (1959-10-01), Brill
patent: 3818749 (1974-06-01), Yankee et al.
patent: 5133630 (1992-07-01), Hughes
patent: 5273383 (1993-12-01), Hughes
Kabushiki Kaisha Suzuki Rashi Seisakusho
O S G Corporation
Wilson Neill R.
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