Metal deforming – By use of tool acting during relative rotation between tool... – During rotation of work
Reexamination Certificate
1999-03-31
2001-04-17
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of tool acting during relative rotation between tool...
During rotation of work
C411S311000, C470S010000
Reexamination Certificate
active
06216510
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a self-lock screw having a loosening preventive function and a method of producing the same and, more particularly, to a self-lock screw with the thread having a broad root so as to facilitate the elastic deformation of the flanks and enhance the locking effect and a method of producing the same.
BACKGROUND ART
A self-lock bolt with a slit formed along the crest portion of the thread and a method of producing the same are known, as described in, e.g., Japanese Patent Publication No. Hei 2-58016. In the bolt proposed in Japanese Patent Publication No. Hei 2-58016 is, the flanks of the bolt are pressed against the slit by the flanks of the nut so as to cause elastic deformation, and the bolt is kept from loosening by the pressing force of the elastic deformation. According to the method of producing such a self-lock bolt, a double-threaded screw having half a desired pitch is first formed by rolling, and the screw is then formed into a single-threaded screw having the desired pitch by rolling, thereby forming a slit along the crest portion of the thread.
When a slit is formed along the crest portion of the thread in this manner by a die similar to the one which is used for the roll forming of an ordinary screw, it is not always possible to produce a slit having an adequate depth. As a result, the rigidity on both sides of the slit becomes large and the amount of elastic deformation of the flanks becomes small, so that it is impossible to have an adequate locking effect (spring back effect) of the screw caused by the reaction of the elastic deformation.
To solve this problem, the present applicant proposed a method of producing a screw described in Japanese Patent Laid-Open No. Hei 7-139537. According to this method, in a first roll forming process, a thread groove having a small depth and a thread groove having a large depth are alternately arranged, and the thread groove having a large depth is formed into a slit in a second roll forming process. In this manner, it is possible to form a slit having an adequate depth.
However, the method of producing a screw disclosed in Japanese Patent Laid-Open No. Hei 7-139537 requires a special roll forming die for forming a thread groove having a small depth and a thread groove having a large depth which are alternately arranged, so that the cost of producing a roll forming die is disadvantageously increased. In addition, in the roll forming of a screw by such a die, since it is difficult to apply a uniform roll forming pressure, the production of a screw becomes difficult. Furthermore, since the depth of the slit becomes smaller than that produced by a conventional method, if the phase adjustment of the roll forming die and the groove of a screw is reversed, it is necessary to pay close attention to the phase adjustment. In this manner, the first roll forming process and the second roll forming process require skill of a high level and dexterity. Furthermore, the product yield is poor.
Accordingly, it is an object of the present invention to provide a self-lock screw with the thread having a broad root so as to form a deep slit without the need for skill of a high level or dexterity and facilitate the elastic deformation of the flanks which heightens the self-lock effect.
DISCLOSURE OF INVENTION
To achieve this end, a self-lock screw according to the present invention is provided with a slit which separates the flanks on both sides of a thread along the crest of the thread, and the vicinity of the root is formed as a broad bottomed concave portion in a shape given by inwardly scraping the extended surfaces of the flanks. Since the slit at the crest portion of the thread becomes deep by providing the broad bottomed concave portion in the vicinity of the root of the thread, the flanks are ready to be elastically deformed, so that the spring back effect is enhanced and the effect on preventing the screw from loosening is increased. In addition, it is possible to produce a self-lock screw of the standard dimension having a slit from a material for a screw of the standard dimension. Since it is possible to use a generally used material of the standard dimension without the need for a material of a specific dimension, it is possible to reduce the production cost.
In this self-lock screw, the broad bottomed concave portion is preferably approximately rectangular in a transverse section of the thread. The bottom surface of the broad bottomed concave portion can be flat in a transverse section of the thread.
In this self-lock screw, the bottom surface of the broad bottomed concave portion may be approximately arcuate in a transverse section of the thread. Alternatively, the bottom surface of the broad bottomed concave portion can be flat at the central portion and approximately arcuate in the vicinities of both end portions in a transverse section of the thread. In this manner, since the root portion of the thread has a wide area as a broad bottomed concave portion and the curvature changes comparatively gradually, the stress concentration on the root portion is unlikely to be caused, thereby reducing the possibility of stress breaking or fatigue breaking.
In this self-lock screw, the bottom surface of the slit may be approximately arcuate in a transverse section of the thread. Since the cross section of the slit is arcuate with the bottom portion largely scraped off, the flanks are further ready to be elastically deformed, so that the spring back effect is further enhanced. It is also possible to form the screw in such a manner as to have a slightly larger flank angle than an ordinary one, thereby enhancing the adaptability of the screw to a female screw having a tolerance.
A method of producing a self-lock screw provided in one aspect of the present invention comprises: a first roll forming process for forming double a desired number of thread grooves having half a desired pitch by rolling a screw material; and a second roll forming process for forming every other thread groove produced in the first roll forming process into a broad bottomed concave portion having a shape given by inwardly scraping the extended surfaces of the flanks, and assembling the double threads formed in the first roll forming process so as to form a single thread having a slit along the crest. Since a slit having a large depth is formed at the crest portion of the thread by forming a broad bottomed concave portion in the vicinity of the root of the thread in the second roll forming process, the elastic deformation of the flanks is facilitated, so that the spring back effect is enhanced and the effect on preventing the screw from loosening is increased. In addition, since it is possible to produce a self-lock screw of the standard dimension having a slit from a screw material having a diameter of the standard dimension. Since it is possible to use a generally used material of the standard dimension without the need for a material of a specific dimension, it is possible to reduce the production cost.
In the method of producing a self-lock screw, it is possible to set the flank angle of the thread formed in the first roll forming process to be smaller than the flank angle of the thread produced in the second roll forming process. In this manner, since the depth of the slit at the crest portion of the thread becomes even larger, the spring back effect of the flanks, i.e., the effect on preventing the screw from loosening is further increased.
In addition, in the first roll forming step in the method of producing a self-lock screw, it is also possible to form the thread in such a manner that the radius of curvature at the root portion is larger than the radius of curvature at the crest portion in the cross section of the thread. In this manner, the cross section of the slit has an arcuate shape given by largely scraping off the bottom portion of the slit, the flanks are further ready to be elastically formed, so that the spring back effect is further enhanced. It is also possible to form the screw in such a manner as to have a
Armstrong Westerman Hattori McLeland & Naughton LLP
Larson Lowell A.
The Holistic Environment Creators Co., Ltd.
LandOfFree
Method of producing self-lock screw does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing self-lock screw, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing self-lock screw will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2553901