Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having structure to restrict rotation of threaded – mating... – Comprising a thread lock
Reexamination Certificate
2000-01-06
2003-06-03
Saether, Flemming (Department: 3679)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having structure to restrict rotation of threaded, mating...
Comprising a thread lock
C411S411000
Reexamination Certificate
active
06572315
ABSTRACT:
FIELD OF THE INVENTION
The following invention relates generally to fasteners. More particularly, this invention pertains to the field of fasteners having an exterior thread located peripherally about the shaft of the fastener, in which the thread spirals along a portion of the shaft. Most specifically, the thread, when taken in cross-section has a contour which increases in a dimension as it extends radially away from a root of the thread.
BACKGROUND OF THE INVENTION
Threaded fasteners are extremely old devices which exhibit superior holding properties over non-threaded fasteners primarily due to a higher coefficient of friction. This coefficient of friction is manifested along the inter-face of the threads to its connecting; environment. Fasteners where the threaded portion exhibits a dovetail when viewed in cross-section define one specie of threaded fastener.
The following patents reflect the state of the art of which applicant is aware and is included herewith to discharge applicant's avowed duty to disclose prior art. It is respectfully submitted, however, that none of these patents singly nor when combined in any conceivably permissible manner teach or render obvious the instant invention as set forth hereinafter.
Pat. No.
ISSUE DATE
INVENTOR
5,338,074
Aug. 16, 1994
Barringer, et al.
5,360,240
Nov. 1, 1994
Mott
5,379,505
Jan. 10, 1995
Reed
5,415,442
May 16, 1995
Klementich
5,417,532
May 23, 1995
Reed
5,454,605
Oct. 3, 1995
Mott
5,499,892
Mar. 19, 1996
Reed
While several of these patents teach the use of an element which appears to benefit from dovetail geometry, none provide interconnection between a threaded fastener and a correspondingly contoured bore in which the fastener meets with gradually increased resistance, providing an interference fit as the fastener becomes progressively engaged.
SUMMARY OF THE INVENTION
This invention is a new type of thread combination that has a special ability to self tighten while creating a radial clamping action. Normal straight threads do not have an ability to self tighten or an ability to clamp radially. Normal threads in fact create radial spreading force when tightened into a threaded bore or nut. This radial spreading force often overpowers the strength of the piece it is tightened into and causes the piece to crack. This is very common in cast iron and aluminum castings with tapped holes. The object of this invention is to provide a means wherein both of these limitations of normal threads are overcome. With this thread design applied to a tapered pipe lug and receiving hole in a casting, problems of over tightening the plug to obtain a seal which often results in a crack being formed in the side wall of the treaded hole will be eliminated.
The thread can also be applied to metal stitching pins used to repair cracked and damaged castings. One advantage over the prior art is that the old method which required a machined counterbore to be cut into the surface of the casting is eliminated. The present invention will make it much easier to repair thin wall castings that currently are very difficult to repair with hook thread style stitching pins.
The prior art also teaches crack repair utilizing either tapered threaded pins or straight threaded pins having a shoulder or abutment above the threads to halt the forward rotation of the pin thus causing it to tighten in the threaded bore. This new invention does not require either a shoulder or abutment.
The thread design in cross-section resembles that of an interlock wherein the thread cross-section of the crest or major outside surface of the thread tooth is wider than the cross-section of the root thread tooth. When installed into a similarly threaded bore, the interlock is perfected and clamping and radial drawing of the female threaded hole threads occurs, so that interlocking of the male screw threads and the female threaded bore threads are completed. This will have the effect of strengthening the threaded bore material as if there had not been a hole cut into it let alone the negative effect of having a standard, spreading fastener tightened into it. Reversal of the prior art spreading force will greatly increase the life of threaded holes which affects the life and serviceability of the part.
This invention utilizes a thread tooth profile that has the same side, root and crest surfaces parallel to each other but not necessarily to the length axis of the pin. It also uses a new concept of varying the pitch of either or both of the side flanks of the teeth. Changes to the pitch geometry of the threaded pin while maintaining a constant pitch within the threaded receiving hole by increasing either or both flank pitches can cause the threaded pin to be self-engaging as it is screwed into the receiving hole. This self-engagement will result in the threads of the pin being drawn deeper into the side wall of the threaded hole which when tightening occurs and, results in halting continued forward rotation (advancement) of the pin. The depth of installation can be controlled by slight changes to the width of the crest by changes to the pitch of upper and lower flanks of the thread teeth.
Different threaded products can be manufactured with predetermined effects based on desired outcome. Providing radial clamping force on certain threaded fasteners can have dramatic affects on the base material that they are threaded into. Spreading force causes cracks. Threaded holes that are too close to an edge are prone to cracking. Threaded holes in soft materials are prone to stripping. By using the present fastener, the forces engendered cause the material receiving the fastener to draw towards the fastener not away as in the prior art.
The instant invention is distinguished over the known prior art in a multiplicity of ways. As will be defined in the ensuing description of the preferred embodiment, the fastener is defined by a shaft or shank which may be cylindrical or tapered. A thread is spirally wound around the shaft. In section, the thread has a contour which diverges or bulges as it extends further outwardly from the shaft. Each section of the thread includes a root base, an upper flank and a lower flank which are girded on an outer exterior by a crest having a height. A root gap is interposed between adjacent teeth in line with the root base. The key to the instant invention involves the relationship of these various aspects of the fastener, one to the other and to its associated bore.
For example, assume the portion of the thread viewed in section appears as a dovetail. Each dovetail has an upper flank (nearer the fastener's driving head or “top”) and a lower flank. These threads are spirally formed about a shaft of the fastener. The upper flank preferably has a constant pitch whereas the lower flank has a pitch which varies along the length of the thread. By pitch it is meant thread density per unit length of shaft. In actuality, with a thread which is “dovetail” in section, the thickness of the thread will vary. More particularly, it is preferred that the pitch of the lower flank decreases as it goes from a “bottom” or second (lower) end of the fastener to the “top” or first (upper) end of the fastener. By “bottom” it is meant an end of the shaft remote from a driving end. This means that the distance between adjacent, vertically aligned lower flanks of the thread increases as it moves from a bottom of the shaft to a top of the shaft. In this example, it is preferred that the upper flank's pitch is held constant.
Two geometrical corollaries are obtained from the foregoing example. First, the root gap of the shaft that extends between facing upper and lower flanks will correspondingly increase in dimension from the top to bottom as successive root gaps are viewed from a top most portion (or first end of the threaded shaft) to a lower most or second end of the threaded shaft. Note that while the root gap increases, the root base decreases from top to bottom.
Second, the crest height which is defined by the outer wall of the crest that exists between each upper flank and
Kreten Bernhard
Saether Flemming
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