GB2172950A - Self-locking threading and method of forming it - Google Patents

Abstract

A self-locking thread of uniform pitch suitable for provision on a screw, bolt, nut or tapped hole is asymmetric, the flanks of each thread being respectively at a 30 degree angle and an angle of less than 30 degrees. A bolt, nut, etc provided with this self-locking threading, is then mated with a symmetrically threaded 60 degree mating part whereby locking is effected. <IMAGE>

Description

SPECIFICATION Self-locking threading and method of forming the same This invention relates to the field of self-locking threads. More particularly, this invention relates to a new and improved self-locking thread suitable for use on bolts, screws, nuts and the like.

Standard mass produced free spinning nuts and bolts, although adequate for many applications, suffer from detrimental self-loosening in many environments. In particular, fastening applications under adverse conditions such as vibration or shock can often lead to dangerous results. Manufacturers have become acutely aware of the unreliability of standard screws in view of the increasing prevalence of expensive lawsuits stemming from the self-loosening phenomenon.

As a consequence, therefor, self-locking threads on nuts, bolts, and the like have been gaining popularity in the building and manufacturing trades. Todays market feature an enormous array of self-locking fasteners. See Product Engineering Magazine, Aprii, 1979 and December 1978. Included among these selflocking devices are screws and bolts (lockscrews) which utilize many novel and often times complicated thread forms used in conjunction with a standard nut. Other bolts and screws employ plastic inserts (i.e., nylon) or plastic patches as well as pre-applied adhesive (i.e., epoxy) and highly viscous fluid coatings.

Special lock nuts and washers are also utilized with either standard thread screws or specially threaded screws. These nuts and washers also come in a wide variety of designs.

Unfortunately, many problems have arisen in the application, cost and manufacture of the current self-locking fastener devices. For example, manufacturing costs and hence retail costs are often prohibitively expensive due to the complicated thread design and initially expensive tooling. Also, application of these devices can involve expensive and time consuming labor because of the extra steps involved in the more complicated designs and adhesive types.

Other problems include limited or absence of reusability, damage to the standard mating part, limited sizing of fasteners, locking taking place only on the thread peak and not the thread flank, locking taking place on only a small portion of the screw stem and finally, the fact that many current devices employ e,:- pensive secondary locking means such as lociewashers, epoxy patches, locking compounds, etc.

According to the present invention there is provided a self-locking threading comprising: a plurality of threads of equal pitch, said threads having side portions defined as thread flanks, each pair of said tread flanks having two bisecting angles therebetween, each of said bisecting angles uniformly alternating between angles of 30 degrees and angles of less than 30 degrees.

The novel self-locking thread system is applied to nuts, bolts, screws and the like and offers simplicity in manufacture, reusibility and reliability in application and hence, economy of use and production.

The American standard thread form has a uniform 60 degree angle between adjoining threads. The novel self-locking threads of the present invention uniformly decreases this angle to slightly less than 60 degrees. This uniform decrease is accomplished by bisecting the angle between adjoining thread flanks and alternating each bisected angle with a 30 degree angle and an angle of less than 30 degrees. A bolt, nut or the like having this special threading is then used in conjunction with a standard mating part. This unique combination creates a strong wedging action between the thread flanks of the communicating nuts and screws.

The simple construction of the present invention affords many advantages and improvements over prior art self-locking fasteners.

The self-locking thread devices of the present invention have tremendous manufacturing features. They cost much less to produce than complicated prior art self-locking thread designs. No special machines are required for manufacture and the threads of the present invention are easily adapted to most assemblies. The fasteners of the present invention are ideal for high temperature, high vibration environments. They eliminate the need for other locking means such as lockwashers, adhesive patches, plastic inserts, etc. and create a lasting hold since the locking takes place on the thread flank and along every thread for 360 degrees. Finally, their reusability and use in conjunction with standard thread mating parts substantially lowers applicaton costs.

Many other advantages will be evident from the description.

The above discussed and other advantage of the present invention will be apparent to and understood by those skilled in the art from the following detailed description and drawings.

Referring now to the drawings, wherein like elements are numbered alike in the several figures: Figure 1 is a cross-sectional elevation view of a standard American thread in accordance with the prior art.

Figure 2 is a cross-sectional elevation view of a screw or the like with a self-locking thread in accordance with the present invention.

Figure 3 is a cross-sectional elevation view of a nut or tapped hole with the self-locking thread similar to Fig. 2.

Figure 4A is a cross-sectional elevation view of a screw or the like, similar to Fig. 2, in conjunction with a standard threaded nut in a free spinning condition.

Figure 4B is a cross-sectional elevation view, similar to Fig. 4A, but in a locked condition.

Figure 4C is an enlarged view of a section of the locked threads of Fig. 4B.

Figure 5A is a cross-sectional elevation view of a nut or tapped hole, similar to Fig. 3, in conjunction with a standard threaded screw or the like in a free spinning condition.

Figure 5B is a cross-sectional elevation view, similar to Fig. 5A, but in a locked condition.

Referring first to Fig. 1, a standard American thread 10 in accordance with the prior art is shown. The angle X between the thread flanks 12 is a standardized and uniform 60 degrees. Of course, Fig. 1 is representative of only two individual threads while an actual bolt or screw would have many additional threads running in either direction. The structure of the standard thread 10 is equally applicable to a standard nut or tapped hole wherein the thread peaks and valleys are simply reversed to allow threadabie communication with a mating part.

In Figs. 2 and 3, the self-locking threads of the present invention are shown respectively on a screw or the like and on a nut or tapped hole. The present invention has a thread configuration similar to that in the prior art except that the angle between the thread flanks 12' is less than 60 degrees. Actually, the right side of the thread remains identical to the standard thread above. Thus, the angle x/2 defining the right side of the thread of the present invention is equal to 1/2 of 60 degrees or 30 degrees. Conversely, the left side of the thread in Fig. 2 is modified to somewhat less than 1/2 of 60 degrees or less than 30 degrees. Like a standard thread, the pitch between threads of the present invention is constant. Similarly, the height and overall sizing of the threads will vary with the particular use as in the standard devices.The selflocking threads of the present invention are extremely economical to manufacture, since, like the standard thread, they are easily mass produced and designed for use in conjunction with standard thread mating parts.

In a preferred embodiment, a screw or bolt as shown in Fig. 2 has a plurality of circular, uniform threads of equal pitch with a conventional head located at one end. These specially threaded screws are capable of mating or communicating with a standard receiver (i.e., nut) to achieve a lock fit. Adjoining threads are separated by alternating angles of 30 degrees and less than 30 degrees, respectively.

Preferably, the angle less than 30 degrees will be from about 29.5 degrees to about 10.0 degrees. Similarly, a preferred embodiment of a nut or tapped hole as shown in Fig. 3 has an inverse dimensional relationship reiative to the screw of Fig. 2 thereby providing suitable communication with a standard screw or bolt.

The ease of application and novel self-locking mechanism is clearly seen in Figs. 4A, 4B, 4C, 5A and 5B. In Fig. 4A, a bolt or screw 14 having the self-locking thread of the present invention is shown after insertion through a plate 16 and into a receiver, which in this case is a standard 60 degree nut 18. At this point, the bolt 14 freely spins inside the nut 18. An important feature of the present invention is that locking takes place only during the last turn of the fastener. In Fig. 4B, the bolt head 20 has engaged the plate 16 and each of the thread flanks 12' are securely locked into the nut 18.

During that last turn of the bolt 14, the thread flanks 12' having alternating angles of less than 30 degrees encounter the standard 30 degree angle thread flanks 12. The differences in angular position causes the two respective flanks 12 and 12' to wedgedly engage and lock. In practice, the thread flanks will undergo a slight amount of deformation or deflection. This wedged locking is clearly shown in Fig. 4C. Note that a space 22 is forced between the flanks having 30 degree angles. As previously stated, in a preferred embodiment the alternating angle which is less than 30 degrees should be between 29.5 degrees and 10 degrees in order to achieve maximum self-iocking.

Referring now to Figs. 5A and 5B, a nut or tapped hole 18 is shown having the novel self-locking threads of the present invention.

This nut 18 is then mated with a standard bolt or screw 14. As discussed above, upon the final turn, the flanks 12 and 12', each having alternating angles of 30 degrees and less than 30 degrees, respectively, wedgedly engage and lock. Thus, a clear advantage of the present invention over the prior art is that every thread coming into contact with the nut or tapped hole is locked for 360 degrees.

Note that secure locking is achieved by wedgedly fixing alternating thread flanks 12' with a corresponding thread flank in the mating part. The corresponding flanks which are not wedged have small gaps 22 therebetween. Unlike many prior art self-locking mechanism, the nuts, bolts and the like of the present invention are reusable and therefore extremely economical. As already discussed, the ease of manufacture also adds to overall economy.

Claims (10)

1. A self-locking threading comprising: a plurality of threads of equal pitch said threads having side portions defined as thread flanks, each pair of said thread flanks having two bisecting angles therebetween, each of said bisecting angles uniformly alternating between angles of 30 degrees and angles of less than 30 degrees.

2. A self-locking threading as claimed in claim 1, wherein: said alternating angle of less than 30 degrees is between about 29.5. degrees and about 10 degrees.

3. A self-locking threading as claimed in claim 1, wherein: said self-locking threading is incorporated on a screw or bolt.

4. A self-locking threading as claimed in claim 1, wherein: said threading is incorporated on a receiver.

5. A self-locking threading as claimed in claim 4, wherein: said receiver is a nut or tapped hole.

6. A method of forming a self-locking connection including the steps of: providing a first connector having a plurality of uniform threads of equal pitch, said threads having side portions defined as thread flanks, each pair of said thread flanks having two bisecting angles therebetween each of said bisecting angles uniformly alternating between angles of 30 degrees and angles of less than 30 degrees; and threadibly communicating said first connector to a second connector said second connector having a plurality of uniform threads of equal pitch having an angle between said threads equal to 60 degrees.

7. A method as claimed in claim 6, wherein: said first connector is a screw or bolt; and said connector is a receiver for said screw.

8. A method as claimed in claim 6, wherein: said first connector is a receiver for a screw or bolt; and said second connector is a nut or boit.

9. A self-locking threading substantially as hereinbefore described and as illustrated in the accompanying drawings.

10. A method for forming a self-locking connection substantially as hereinbefore described and as illustrated in the accompanying drawings.