GB2198801A

GB2198801A - Locking fastener

Info

Publication number: GB2198801A
Application number: GB08727726A
Authority: GB
Inventors: George Manoogian
Original assignee: Masco Industries Inc
Current assignee: Masco Industries Inc
Priority date: 1986-12-19
Filing date: 1987-11-26
Publication date: 1988-06-22
Anticipated expiration: 2007-11-26
Also published as: CA1302131C; GB2198801B; DE3743010C2; GB8727726D0; JPS63176810A; DE3743010A1

Description

l> i is 11 LOCKING FASTENER2198801

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fasteners and, in particular, to vibration resistant locking fasteners which utilize a series of deformed threads to retard release of the fastener.

11. Description of the Prior Art

Interference fits between a male fastener member, such as a bolt or screw, and its receiving member has long been utilized to increase the torque necessary to remove the fastener thereby preventing inadvertent removal due to vibration. Initially,, additional elements such as lock washers and the like were utilized which increased manufacturing and, assembly costs. Non-circular thread forms and variable pitch threads have also been utilized to increase the torque necessary to remove the fastener. However, such configurations require special tooling and manufacturing steps to complete the fastener.

Deformation of the thread crests has also been utilized to create the interference fit between the fastener and the nut. Generally, a male fastener with a standard thread form is utilized in conjunction with a nut with deformed or truncated thread forms such that as the nut is mounted to the bolt, the thread crests are gradually. deformed to create the interference. Usually, however, such fasteners are only usable once since the deformation cannot be reversed. Truncation of the thread forms of the male fasterier have also been utilized to create an interference fit. Such devices are advantageous a 2 because they may be used with standard fastening nuts or a tapped hole. However, these types of fasteners are dependent upon variable thread forms over the entire length of the fastener or over the initial convolutions. Because of the variable nature of the deformation, manufacturing costs are substantially increased.

SUKY1ARY OF THE PRESENT INVENTION The present invention overcomes the disadvantages of the prior known locking fasteners by providing a device which is simple and cost effective to manufacture yet provides the necessary interference fit to prevent release due to vibration.

The fastener according to the present invention includes three zones of thread forms to create the necessary interference fit. The first and third zones comprise standard thread forms to, respectively, facilitate assembly with the female or mating part and to meet the overall thread length specifications for the fastener. The second or intermediate zone includes a plurality of deformed thread crests designed to cooperate with the standard thread forms of the mating member to establish An interference fit. Preferably, the intermediate zone consists of two to eight consecutive thread convolutions depending upon the torque requirements. The deformed thread crest's are partially flattened concentric with the main body of the threaded member. The percentage of deformation is dependent upon the prevailing torque requirements of the part.

Deformation of the thread crests is conducted in such a manner as to maintain the overall volume of the thread. In this fashion, as the fastener is mated with the receiving member, the thread crests are reshaped in 0- 4 th 3 is accordance with the configuration of the receiving thread form thereby forming a snug interference fit.

Other objects, features, and advantages of the present invention will be apparent from the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The present inention will be more fully understood by reference to the following detailed description of a preferred embodiment of the present invention when read in conjunction with the accompanying drawing, in which like reference characters refer to like parts throughout the views and in which:

FIGURE 1 is a side perspective, partly in section of a fastener constructed in accordance with the present invention; FIGURE 2 is a partial sectional view of a portion of the threads of the fastener of the present invention; and FIGURE 3' is a partial sectional view of a portion of the threads of the fastener in conjunction with a mating -f astener.

MED DETAILED DESCRIPTION OF A PREFTEMBODIMENT OF THE PRESENT INVERTION

Referring f irst to Figure 1, there is shown a locking, fastener 10 embodying the present invention and generally comprising a head 12 of any known configuration and a shank or male threaded portion 14 having a helical thread form. Preferably, the thread form includes a substantially uniform axial thread pitch. In addition, each thread convolution includes a crest 16 and a root 18 wherein the root diameter along the length of the threaded portion 14 is uniform. The fastener 10 is adapted to be 4 received in a threaded female member 20 having a standard helical thread form with conventional crest 22 and root 24 cross-sectional configurations (Fig. 3). Examples of such female receiving members include conventional fastening nuts and tapped bore holes.

The male threaded member 14 includes three thread zones along its length. The f irst zone A acts as an engagement zone to facilitate mating of the male member 14 with the female member 20 as is well known. Preferably, the engagement zone A includes at least one convolution of standard helical thread forms although this number may be increased depending upon the specifications for the fastener.

Intermediate thread zone B includes a plurality of subsequent thread convolutions and provides the fastener 10 with its vibration-resistant prevailing torque characteristics. The thread crests of the intermediate zone threads 30 arre uniformly flattened parallel to or concentric with the roots 18 of the member 14. As is best shown in Fig. 2, the crests 32 of the threads 30 have a substantially rectangular cross-sectional configuration with a flat outer surface 34 and side walls 36 which extend inwardly perpendicular to the flat outer surface 34 to engage the standard sloped surfaces 38 of the thread form 30. Deformation of the thread crests 32 is conducted in such a manner as to substantially maintain the overall, volume of the individual threads 30 such that as the fastener 10 is mated with a receiving member, the thread crests 32 are re-shaped in accordance with the receiving thread form. In the preferred embodiment of the invention, each of the threads 30 in the intermediate zone B are uniformly flattened such that the outer surfaces 34 of each thread convolution are even with each other and all equidistant from the root surface 18. Moreover, the to A -1 outer surface diameter 34 is preferably between 90% and 98% of the diameter of the fully formed thread crests depending upon the torque requirements for the fastener. In addition, the intermediate zone B consists of two to eight consecutive thread convolutions depending upon the prevailing torque requirements specified for the fastener 10.

Referring again to Fig. 1, the third thread zone C also consists of a plurality of standard helical thread forms through the terminal convolutions of the fastener 10. The number of thread convolutions of zone C is dependent upon the overall thread length requirements for the fastener 10. The third thread zone C terminates with the bolt head 12.

Referring now to Fig. 3, the interference fit is created upon inserting the male fastener 10 within the female receiving member 20. Over the first few rotations of the threaded member 14 the threads of zone A cooperate with the thread forms of the female member 20 in a conventional manner. As the flattened threads 30 of zone B engage the female member 20 the rectangular crests 32 are deformed by the interaction thereof to substantially conform to the configuration of the root 24. However, because conventional thread forms are provided with a Certain amount of leeway space to allow smooth coupling, the deformed crests of the present invention eliminate this space to create the interference fit. As is shown in Fig. 3, a portion of the conventional leeway space 40 is eliminated in the area of the flattened thread crest 32 such that the thread crest 32 -simultaneously contacts opposing surfaces of the female thread form. Moreover, because of the uni-directional interaction of the male member 14 within the female member 20, the. thread crest 32 is deformed in such a manner that the leading edge 42 of 6 the thread 30 is in full contact with the female thread form while only the crest portion 32 of the trailing edge 44 is in contact with the female thread form thereby creating the interference fit. As has been noted above, the prevailing torque of the fastener 10 can be altered by varying the degree of deformation of the thread crests 32.

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Claims

1. A male threaded member having a unif orm axial thread pitch and root diameter throughout the major portion of its length, said member comprising:

a thread zone having a plurality of thread convolutions with thread crests uniformly flattened concentric with the thread roots along said thre ' ad zone, said flattened thread crests having a substantially rectangular cross-sectional configuration.

2. The male threaded member as def ined in claim 1 wherein said thread zone is an intermediate thread zone disposed between two thread zones of standard helical thread forms.

3. The male threaded member as def ined in claim 2 wherein the diameter of the flattened thread crests of said intermediate thread zone is uniform along the length of said thread zone.

4. The male threaded member as def ined in claim 2 wherein one of said two threaded zones of standard helical thread forms is an engagement zone of at least the initial complete convolution of the thread to facilitate engagement of the male member with a threaded female receiving member.

5. The male threaded member as def ined in claim 2 wherein one of said two threaded zones of standard helical thread forms terminates with head means f or rotating the male threaded member.

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6. In a locking fastener adapted to be received in a threaded female member having a standard helical thread form, a male threaded member having a uniform axial thread pitch and consisting of three axial thread zones along its length, including: a first engagement zone of standard helical thread forms extending th2ough at least the initial complete convolution of the thread; an intermediate zone extending through subsequent convolutions of the thread, the crests of said intermediate zone threads being uniformly flattened concentric with the thread roots along said intermediate zone thereby causing interference between the male member and female member; and a third zone of standard helical thread forms extending through the terminal convolutions of the thread of said male threaded member.

7. The fastener as def ined in claim 6 wherein said third thread zone terminates with head means for rotating said male threaded member.

8. The fastener as defined in claim 6 wherein said intermediate thread zone comprises a plurality of consecutive thread convolutions whereby the number of' thread convolutions in said intermediate thread zone is directly proportional to the prevailing torque requirements of the fastener.

9. The fastener as defined in claim 6 wherein the diameter of the flattened thread crests of said intermediate thread zone is uniform along the length of said thread zone, said diameter being between.90 and.98 -14 9 9 is of the crest diameter of said standard helical thread forms, whereby the diameter of said flattened thread crests is directly proportional to the prevailing torque requirements of the fastener.

10. The fastener as defined in claim 6 wherein said flattened thread crests of said intermediate thread zone have a substantially rectangular cross-sectional configuration.

11. In a locking fastener adapted to be received in a threaded female member having a standard helical thread form, a male threaded member having a uniform axial thread pitch and root diameter throughout the naj or portion of its length, said male threaded member comprising three axial thread zones along its length including: a f irst engagement zone of standard helical thread forms extending through at least the initial complete convolution of the thread; an intermediate zone extending through subsequent convolutions of the thread, the crests of said intermediate zone threads being uniformly flattened concentric with the thread roots along said intermediate thread zone, said flattened thread crests having a substantially rectangular cross-sectional configuration wherein the outer diameter of said flattened thread crests, is uniform along the length of said intermediate thread zone; and a third zone of standard helical thread forms extending through the terminal convolutions of the thread of said male threaded nember.

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12. The fastener as defined in claim 11 wherein said third thread zone terminates with head means for rotating said male threaded member.

13. A locking fastener substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

1 Published 1988 at The Peter Office, State House, 66'7TH19' Ho Tborr, Londin WClR 4TP Further copies may be obtained from The Patent Office, Sales Branch. St Mary Cray. Orpington. Rent BRS 3RD PrinLed by Multiplex techniques ltd, St MaTy Cray. Kent. Con. 1/87