LOW-TOLERANCE THREADED FASTENER

Abstract: A threaded fastener (10) is having a raised area or bump (16) on a thread flank. The flank can be positioned on the nut thread (12) or on the bolt thread (14). The bump (16) forces the mating threads at least on one flank to have near zero tolerances along the pitchline of the threads and thereby eliminating play. A threaded repair insert (60) having at least one raised area on a threaded surface (62) also is provided.

Description: LOW-TOLERANCE THREADED FASTENER Background of the Invention This invention relates generally to threaded fasteners such as nuts and bolts and more particularly to threaded fasteners having an improved thread and reduced tolerances and improved fastening. Threaded fasteners are well known to the art. One goal of threaded fasteners, particularly nut and bolt combinations, is to provide such a fastener that stays tightened and does not loosen in use. Generally accepted matching techniques result in tolerances between the nut an bolt threads and there is clearance or play which allows for movement between the elements. For example, a fastener or nut and bolt can loosen under load or vibration. There are several prior art systems that try to remedy this problem. First, locknuts are used with a nylon washer locked in at the end of the nut. When the nylon washer contacts the bolt, it tightens around the thread and locks the nut in position. Locknuts have disadvantages. The nylon portion of nut has no load carrying threads. Further, it requires more material to make the nut longer and the nylon washer and the nut must be made separately and then crimped together. The locknut of this type can be used only a few times, is not as resistant to heat and requires chemicals i.e. nylon. Deformed nuts have been used to overcome the loosening problem. These comprise nuts that are deformed out of the circular shape and made into rounded-off triangle shape. Then the bolt engages the threads, it contacts three points and the nut locks around the bolt. However, only heat-treated nuts can be used. To make the deliberate deformation requires an expensive manufacturing set-up. Further, the process is very slow. Also, the reaction of each individual nut is variable, which makes it difficult to predict or guarantee tolerances. Moreover, it can only be used with nuts. A spiral lock is a lock thread is a commercially available alternative. However, the spiral lock provides an interference on the outside diameter of the bolt. It is difficult to control the interference with accuracy. The surface of the bolt thread can cause galling of the nut and subsequent failure. Interference-fit threads are used which include a complete interference of the matching parts at the flanks to provide an interference or metal flow. However, based upon accepted machining practices, it is very difficult to produce, for example, class 5 threads (Federal Standard Screw-Thread Standards For Federal Services-Class 5 Interference Fit Screw Threads). Examples of prior art fastener technologies are disclosed in the following U.S. Patents: No. 1,369,156, to Woodward; No. 2,842,180, to Brown et al; No. 3,459,250 to Tabor; No. 3,661,194, MacFarlane et al.; No. 3,721,283, to Evan; No. 3,850,215, to Orlomoski; No. 3,927,503, to Wilson; No. 4,023,914, Holmes; No. 4,071,067, to Goldby; No. 4,396,321, Holmes; No. 4,846,614, to Steinbock; and No. 5,194,214, to Snyder et al. It would be advantageous, therefore, to develop a fastener that has close tolerances yet is resistant to loosening or play without the disadvantages of the prior art designs. Summary of the Invention It is among the principal objects of the present invention to provide a threaded fastener that is resistant to loosening. It is another object of the present invention to provide a threaded fastener that has very close tolerances and is resistant to loosening. Another object of the present invention to provide a threaded fastener that controls thread contact and tolerances along the thread pitchline. Another object of the present invention to provide a threaded fastener that controls thread contact and tolerances along the thread pitchline and by controlling width of contact. Still another object of the present invention is to provide such a threaded fastener that not only controls the pitch diameter of the respective threads to assure correct interference along the thread flank, but also controls the width of contact. It is still another object of the present invention to provide such a threaded fastener that can be manufactured and produced in a broad range of sizes. It is yet another object of the present invention to provide such a threaded fastener that is simple and economical to tool, versatile and well suited for its intended purposes. In accordance with the invention, a threaded fastener is provided having a raised area or bump on the thread flank. The bump forces the mating threads at least on one flank to have near zero tolerances along the pitchline of the threads and thereby eliminating play. Brief Description of the Drawings FIG. 1 is a diagrammatic representation of engaged standard prior art threaded fastener threads; FIG. 2 is a is a diagrammatic representation of a perfect thread; FIG. 3 is a diagrammatic representation of one embodiment of the novel threaded fastener threads of the present invention with the bump on the external threads of the nut; FIG. 4 is a diagrammatic representation of another embodiment of the novel threaded fastener threads of the present invention; FIG. 5 is a diagrammatic representation of another embodiment of the novel threaded fastener threads of the present invention; FIG. 6 is a diagrammatic representation of another embodiment of the novel threaded fastener threads of the present invention; FIG. 7 is a diagrammatic representation of another embodiment of the novel threaded fastener threads of the present invention with the bump on the external thread of a bolt; FIG. 8 is another diagrammatic representation of a normal bolt and nut combination under normal load; FIG. 9 is another diagrammatic representation of a normal bolt and nut combination under irregular load; FIG. 10 is another diagrammatic representation of a the embodiment of FIG. 6; FIG. 11 is another diagrammatic representation of a the embodiment of FIG. 6; FIG. 12 is another diagrammatic representation of a the embodiment of FIG. 6 illustrating zero play between the nut and bolt; FIG. 13 is another diagrammatic representation of a the embodiment of FIG. 6 under load; FIG. 14 illustrates a prior art thread repair insert; FIG. 15 illustrates the prior art wire insert of FIG.14 under a load condition; and FIG. 16 illustrates a thread repair insert of the present invention. Description of the Preferred Embodiment FIG. 1 illustrates a standard thread 1 with clearance C. FIG. 8 also illustrates the relationship and play between a normal nut thread 2 and bolt thread 3 As will be appreciated, there are significant clearances C between the respective threads. FIG. 9 illustrates a normal thread under irregular load conditions which significantly increases the clearance C between the nut and bold threads. The amount of clearance is determined by the tolerances set by the manufacturer. FIG. 2, by comparison, is an ideal or perfect thread having full flank contact at points 4 and 5. A perfect thread, however, would require the nut and bolt have identical pitch diameters without clearance. FIG. 3 illustrates one preferred embodiment of the threaded fastener of the present invention, indicated generally by reference numeral 10. The fastener includes a nut thread 12 and a bolt thread 14 As can be seen, the nut thread 12 is tooled with bump 16 on the flank of the thread. As seen in FIGS 10-13, the bump 16 urges the threads to one side so that there is full flank contact at point 20. The thread, with the bump, are formed by a thread tapping tool. As shown in FIG. 10, the contact area can be varied according to holding torque. The size of the bump 16 can be varied to increase the contact areas on the flanks, as shown in FIG. 4, which has an enlarged or wider bump 16. FIG. 12 illustrates a condition of "zero" play between the thread flanks as a result of the size and positioning of the bump 16. FIG. 13 illustrates the substantial contact between the flanks of the threads due to the positioning and size of bump 16, even under load conditions. FIG. 5 illustrates another embodiment of the thread of the threaded fastener of the present invention including a pair of spaced apart bumps 16A and 18B. As shown in FIG. 6, the right flank has 100% contact and at the left approximately 15% contact. The threaded nuts previously described can be formed by using a tape with a complementary indention which will create the desired bump on the thread flank when tooled. FIG. 7 illustrates another embodiment of the present invention wherein the bolt 22 has a bulge 24 formed on the thread flank. This thread is easily formed on a thread rolling machine with thread rolling dies in a cold forming process. These threads can be formed of a harder material than the nut so that the bump can "bite" into the softer metal. The inclusion of the bump on the bolt thread causes the threaded fastener to function the same way as previously described embodiments, with flush fit on the flanks at point 26. Thread repair inserts are known in the art. Generally, the worn threads are repaired by tapping the worn threads with a tap and then inserting an insert. The prior art inserts are indicated generally in FIGS. 14 and 15 by reference numeral 50. As can be seen in FIG. 14, the insert has threads on the other surface 52 and inner surface 52. Threaded surface 54, for example, engages the retapped threads of a nut, indicated generally at 56, while the other threaded surface 52 engages the threads of the bolt, for example. As shown with the prior art inserts of FIGS. 14 and 15, there is still considerable clearance C both in repose and under tightening pressure. On the other hand, a threaded insert of the present invention is indicated generally by reference numeral 60 in FIG. 16. Insert 60 has a first externally threaded surface 62 and a second externally threaded surface 64. Insert 60 is tooled with a bump 66 on one threaded flank surface and functions in the same way as the previously described bumps. When the insert is seated and torque applied, bump 66 urges the insert into a full flank contact as shown as points 68 in FIG. 16, thereby eliminating play. It will be appreciated that a bump 62 can be formed on either surface 62 or surface 64, or both. It will be appreciated from the foregoing that various changes and modifications may be made in the threaded fastener of the present invention without departing from the scope of the appended claims. Therefore the foregoing specification and accompanying drawings are intended to be illustrative only and should not be viewed in a limiting sense.

Claims: WHAT IS CLAIMED IS: 1. A threaded fastener comprising: an externally threaded bolt; a threaded nut engaged on said threaded bolt having internal threads disposed to engage the threads on the threaded bolt, said internal threads being tooled to include a raised area on a flank portion of said thread, said raised area disposed to increase the contact area between the flank portion of the internal threads and a flank portion of said bolt threads so as to decrease an area of clearance between the respective threads when engaged. 2. A threaded fastener comprising: a threaded nut having internal threads; a threaded bolt threadedly engaged within said threaded nut having external threads disposed to engage the threads on the inside the threaded nut, said external threads being tooled to include a raised area on a flank portion of said thread, said raised area disposed to increase the contact area between the flank portion of the internal threads and a flank portion of said external threads so as to decrease an area of clearance between the respective threads when engaged. 3. A method of creating a threaded fastener having an internally threaded nut and externally threaded bolt comprising: forming internal threads within said nut by tapping said nut with a threaded tap, said tap having an indentation formed on a thread flank therein so as to form a complementary bump on the threads formed by the tapping within the nut. 4. A thread repair insert comprising: a first externally threaded surface; a second externally threaded surface; at least one of said externally threaded surfaces being tooled to include a raised area on a flank portion of said thread, said raised area disposed to increase the contact area between the flank portion of the threads and a flank portion of threads engaged thereon so as to decrease an area of clearance between the last recited respective threads.

Inventors: JANITZKI BERNHARD M, JANITZKI, BERNHARD, M.
Applicants: JANITZKI BERNHARD M, JANITZKI, BERNHARD, M.
Application year: 1998
Main classification: F16B
IPC codes: B23G1, F16B37, F16B39