CA1045963A - Self-locking fasteners - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A self locking fastener is described. The fastener is generally C-shaped in transverse cross-section and is radially compressed when fitted with an opening in use. Outwardly projecting barbs on the fastener mechanically engage the inner wall of the opening. Movement tending to remove the fastener imposes mechanical shear forces on the barbs,which forces tend to resist removal of the fastener.
In one aspect of the invention the fastener is fitted to a screw body to form a self-locking set screw. In another aspect, the fastener is in the form of a spring pin.

Description

~963 T~is invention relates to self-locking fasteners~

Grub screws,locking screws, and the like, are commonly used to lock a machine part in place. In many cases, a locking screw is simply tightened so that it is : :
unlikely to work loose. In other cases where the screw .
may be subjected to relatively large temperature variations, ~ ~.
or to mechanical vibration, the locking screw is manufactured with a peripheral deformation such that when the screw is fed into a threaded openin~ in a work piece, there is ~
frictional resistance to turning which tends to prevent ~:
release of the screw. However, the force required to enter .:
the screw is not sufficiently different from the force required to remove it from the openin~ and the screw can be ::
removed without excessive damage to the opening.

Unfortunately, after the screw has been removed `.
several times this ~rictional resistance disappears and a new set screw must be used. Further, conventional friction~
.
locked set screws must be lubricated to prevent seizure. :~
This diminishes the friction and reduces lock-effect. In : 20 critical applicatiGns friction locked set screws or other fasteners are not acceptable and locking elements based on metallic shear principles (locking w.ire, cotter pins, tub washers, etc.) must be used.

It is an object of the present invention to provide an improved self-locking fastener based on the metallic shear principle.

In its broadest aspect the present invention provides a fastener for locking a first component to a ~ .
second component, the fastener being adapted to be located in an opening in one of the components, which opening is ~
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;` ~04S~363 cylindrical in shape and extends about a longitudinal axis, and the fastener being adapted to engage the other component. The fastener has a generally C-shaped transverse cross-section and is adapted to be fitted into said openlng with said cross-section disposed transversely with respect to said longitudinal axis of `-~
the opening. The fastener is made of a resilient material and is radially compressed when located in said opening so that at least part of the fastener is ~ ~-resiliently urged against an inner wall of the opening.
A plurality of outwardly projecting barbs are provided on the said part of the fastener for mechanical engage-ment with the inner wall of the opening. In use, move- `
ment tending to remove the fastener from said opening imposes on said barbs, mechanical shear forces tending to resist such removal of the fastener.

In one aspect, the present invention provides a self-locking screw which includes a first component in the form of a screw for insertion in an opening in a , second component, and a fastener secured to the screw component. The screw component has external screw threads and extends about a longitudinal axis and the opening in a second component is defined by an inner wall having internal screw threads complementary to said external screws threads of the screw component. The fastener has a generally C-shaped transverse cross-section and has a ~irst end secured to an outer portion o~ said screw component, and a second end remote from said first end.
The fastener is made of a resilient material and is arranged to extend generally transversely of and to curve around said longi~udinal axis of the screw component such J~)45~63 that at least a part of the fastener is resiliently ~ .
urged against said inner wall of the opening in said second cornponent when -the screw component is located in said opening in use. A plurality of outwardly projecting barbs are provided on said part of the fastener for mechanical engagement with the inner wall of the opening. In use, movement tending to remove the screw component from said opening imposes on said barbs of the fastener, mechanical shear forces tending to resist such removal of the screw c~mponent.

In another of its aspects, the invention provides a spring pin ~astener for locking a first component to a second component. The fastener is :~
adaptea to be located in an opening in one of said components, which opening is cylindrical in shape and extends about a longitudinal axis, and the fastener is adapted to engage the other component. The ~ :
fastener has a generally C-shaped transverse cross-section .
and is of elongate form, defining a hollow, generally-cylindrically pin formed with an axial slot. The fastener is made of a resilient material and is dimensioned such that it is radially compressed when located in said opening, whereby the outer surface of the fastener is resiliently urged against the inner wall of said opening. A plurallty o outwardly projècting barbs are provided on the said part of the fastener for mechanical engagement with the inner wall of the opening. In use, movement tending to remove the astener from the said opening imposes on said barbs, mechanical shear forces tending to resist such removal 3b of the fastener.

~ 5~:i3 It should at this point be noted that the expression "C-shaped" as used in this specification and in the claims includes any interrupted circular shape.
The invention will be better understood by reference to the accompanying drawings which illustrate various embodiments of the invention. In the drawings:-Fig. 1 is a diagrammatic view which illustrates the principle of operation of a fastener according to the invention;
Fig. 2 is a plan view of a practical form of fastener for use in a set screw;
Fig. 3 is a transverse sectional view on line III-III of Fig. 2;
Fig. 4 is a plan view of a set screw having spot-welded thereto a fastener of the form shown in Figs.

2 and 3;
Fig. 5 is a transverse sectional view on line V-V of Fig. 4;
' 20 Fig. 6 is an isometric view of a set screw ; having a fastener spot-welded thereto in somewhat diferent fashion;
Fig. 7 i.s a view similar to Fig. 6 in which the astener is secured to the screw by spring pins;
Fig. 8 is an isometric view of a set screw having an integral fastener;
Fig. 9 is an isometric view o a self-locking fastener in the form of a spring pin according to the invention;
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Figs. 10 ana 11 are isometric side views of other types of spring pin fasteners;

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~045~3 Figs. 12 to 14 are views similar to Figs. 9 to 11 respectively and illustrate modiications of the fasteners shown in the latter figures;
Fig. 15 is a partial section of a hexagonal nut ' locked with a spring pin fastener;
Fig. 16 shows the nut of Fig. 15 before installa- ~-tion of the spring pin fastener.
Fig. 17 is a partial cross-section of a hexagonal bolt head locked with a spring pin fastener;
Fig. 18 is an isometric view of a locked nut illustrated in Fig. 15;
Fig. 19 is an isometric view''of a locked bolt illustrated in Fig. 17;
Fig. 20 is an isometric view of an installed socket head cap screw locked by a spring pin fastener;
Fig. 21 is an isometric view, partly broken away, of a socket head cap screw, similar to that shown in Fig. 20, 'installed in a counter-bored hole;
Fig 22 is a plan view and Fig. 23 is a cross ,~
section on line X-X of Fig. 21;
Fig. 24 is a side elevation of a punch for use in ' ''~
fitting certain of the spring pin fasteners of the invention;
Fig. 2S is a plan view of a hexagonal nut locXed `
with a spring pin Eastener arranged in an oblique position;
F.~g. 26 is a side view, partly in section, of the nut of Fig. 25; and Fig. 27 shows a punch for use in fitting the ,~
spring pin in the arrangement of Figs. 25 and 26.

Reference will first be made to Fig. 1 in explaining the principle'of operation of a fastener according to the invention~ Fig. 1 may be considered as a diagrammatic plan ~5!~3 view. A fastener is indicated at 20 and is shown fitted in a cylindrical opening 22 in a component 24. Opening 22 has a longi-tudinal axis 26 which extends normal to the plane of Fig. 1. The fastener 20 i9 coupled to another component (not sho~n) and serves to lock the two components together.
The fastener 20 has a generally C-shaped trans-verse cross-section and is fitted into said opening 22 with its said cross-section disposed transversely with respect to the longitudinal axis 26 of opening 22. The fastener is made of a resilient material and, in its unfitted condition, is of somewhat larger diameter than the diameter of opening 22. Accordingly, the fastener is radially compressed when fitted in the opening so that its outer wall is resiliently urged against the inner wall of the opening. A plurality of outwardly projecting barbs 28 are provided on the outer wall of the fastener for mechanical engagement with the inner wall of the opening.
In use, movement tending to remove the fastener from the opening imposes mechanical shear forces on the barbs, which forces tend to resist removal of the fastener.
Referenae will now be made to the remaining figures of the drawings which illustrate the various practical embodiments of the invention. In the embodiments of Figs. 2 to 8, the fastener forms part of a set screw and serves to lock the screw in a screw-threaded opening in a component which the screw is to be attached.
Figs. 2 and 3 show the fastener prior to attach-ment to a set screw. The fastener is generally indicated at 30. In Figs. 4 and 5, the fastener 30 is shown fitted to the outer end face 32 of a screw 34 having a thread 35, 104~i~63 to form a self-locking set screw. The screw 34 is made Erom a ~errous metal and has a hexagon~l through-socket 36 in its upper surface. The soc~et may ~e blind in the case of long screws.
As can be seen from Figs. 2 and 4, the fastener 30 is generally C-shaped, having a first end portion 38 by which the fastener is attached to the set screw 34, and a second, free end portion 40. The free end portion 40 is shaped to define a pair of projections having vertical edges 42 at the outer end of the fastener. As can be seen from Figs. 3 and 5, the adjacent portion of the fastener indicated at 44, is somewhat thickened.
The outer face 46 of this portion is tapered and the inner face 48 is flat so tha~ a tool can be engaged with the outer end portion of the fastener for the purpose of re~
leasing the same in the event that the set screw is to { be removed from an opening in which it is fitted. A
suitable tool for this purpose is desaribed in U.S. Patent No. 3,662,804. ;
Adjacent said thickened portion 44 of the fastener is a series of outwardly projecting barbs 48 which extend around a substantial portion of the curved outer surface of the fastener. As can be seen from Figs. 2 and 4 r the barbs are angled towards the free outer end portion 40 of the fastener.
Referring now to Figs. 4 and 5, the fastener 30 is spot-welded to the upper surface 32 of the screw 34 along a spot-welded area generally indicated at 50. Although this area is shown as continuous in Fig. 4, it is, of course, to be understood that the weld area could be interruPted if ?
required for practical reasons. The shape of the fastener ~04S9~;3 30 is such as to permit it to be spot-welded in any orientation with respect to the hexagonal shape of the socket 36 or to the start of the thread 35 of the screw 3A. In any event, a clearance C (Fig. 5) is present between the screw and the remainder of the fastener remote from end portion 38 to allow movement of the fastener with respect to the screw. .

In Fig. 4, the minor (root) diameter of the thread of the screw is indicated in dotted outline at . 10 52. It will be noted that the fastener 30 is positioned on the screw such that its outer end portion 40 and the barbs 48 project outwardly of the said minor diameter.
Accordingly, when the set screw 34 is screwed into a complementarily internally screw threaded opening in a machine part or other component, the vertical edges 42 at the outer end portion 40 of the fastener and the barbs 48 engage the crests o the internal thread of the opening. The positions of the vertical edges 42 and the angled configuration o~ the barbs 48are such that the internal thread in the opening deflects the fastener 30 inwardly as the set screw is screwed into the opening, but the edges and barbs do not mechanically engage in the thread. When the set screw reaches its fully in position, the edges 42 and the barbs 44 ancho.r into the crests of the thread, providing a mechanical engagement with the said threads. Any movement of the screw in the anti-clockwise direction tending to unscrew the same imposes mechanical shear forces on the said edges 42 and barbs 48, said forces tending to resist such removal of the fasteners. In other words, the straight edges 42 and the barbs 48 cut into the crests of the internal threads.

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9S;3 This anchoring ef fect is increased by the asperitie~ ;
at the crests of the internal threaa u.sually left over from the tap drilling operation by which the thread was ormed.

The number and shape of the barbs 48 may ~;
vary within practical die limitations.Generally speaXing, the more barbs provided, the better is the anchoring effect.

An advantage of making the self-locking fastener 30 separately from the screw facilitates production of ~;

the fastener, for example, by press-punching or by-sintering techniques using metal powder. The fastener can be hardened prior to spot welding, which obviates the need to harden the whole assembly of the screw and fastener. A
further advantage of making the fastener separately i5 that it can be made o~ a non-corrosive metal. In outdoor ser~ice, the fastener would never corrode and the set screw would be efEectively locked until the screw itself disintegrated due to corrosion. Further, a separately -produced fastener can be attached to any commercial set ~
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screw of appropriate type to convert the screw into a self-locking set screw. Attachment of the fa~tener to the screw by spot welding is particularly attractive from this point o view.
Fig. 6 ~shows a set scxew made from a non-ferrous steel, modified by the addition of a self-locking fastener o~ the type shown in Figs. 2 and 3, in which the fastener is attached by thrée spaced welds. Primed reference numerals ;-have been used in Fig. 6 to denote parts which correspond with the previous figures. The three spot welds are indicated at 54.

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Fig. 7 is similar to Fig. 6. Double primed reference numerals have been used in Fig. 7 to denote parts which correspond with Figs. 2 to 5. In this case, the fastener 30" i9 secured to the upper surface 32"
of the screw 34" by three self-locking spring pins 56 which, in effect, act as nails, passing through aligned openings in the fastener and set-screw. The pins 56 may be of any of the forms shown in Figs. 12, 13 and 14, and will more specifically be described in ~ -connection with those figures.

Fig. 8 shows a set screw formed with an integral self-locking fastener. The body of the screw is indicated at 58 and the integral fastener portion is denoted 60.
It will be seen that the fastener portion 60 is very similar in coniguration to the fastener 30 of Figs. 2 and

3. A series o barbs 62 are provided on the fastener and the outer end of the fastener portion is provided with projections 64. It will, however, be noted that the barbs 62 and projections 64, in contrast to the previous figures, have the shape of the external thread on the set screw body 58. It will, of course, be appreciated that the edges are of this form because the fastener portion 60 is machined from the ~ screw body. Referring fi.nally to Fig. 8, it should be noted that the gap between the fastener portion 60 and the - set screw body 58 is substantially greater than the clearance C referred to in connection with Figs. 4 and 5. Accordingly, the set screw o~ Fig. B will be somewhat longer than the self-locking screws of the previous figures.

In describing Figs. 2 to 8, reference has been made to set screws. However, it is to be understood that ~O~

similar arrangements could be employed for screws Por other purposes ~e.g. pipe plugs) and that such screws would be of similar appearance to the se~ screws shown.
Reference will now be made to Figs. 9 to 27 of the drawings in connection with self-Iocking fasteners in the form of spring pins according to the invention.
Figs. 9 to 11 show three different spring pin fasteners according to the invention. Like reference numerals have been used in the respective figures to denote like parts. In each case, the ~astener includes a body 66 which has a generally C~shaped cross-section defining a hollow generally cylindrical pin formed with an axial slot 68. A series of barbs 70 are provided on the external surface of each body 66. In each case, the fastener body 66 is of slightly larger diameter than the opening in which it is to be fitted. Accordingly, each fastener is orce-itted into the opening and is radially compressed in its fitted condition. The barbs 70 scrape the inner wall of the opening as the pin enters the latter.
In use, movement tending to remove the fastener from the `
opening imposes mechanical shear forces on the barbs, which forces tend to resist such removal. Further, removal of such a fastener either aeliberately or as a result of vibration or thermal cycling would make the barbs spread.
As a result, the fastener would tend to adopt a larger ;
diameter increasing the retaining force.
It will be noted that in Figs. 9 to 11, the barbs 70 axe angled with respect to the longitudinal access of the fastener in order to facilitate insertion of the fastener into an opening. However, it is to be understood that the number of barbs and their location may be varied ''' '~ .

~0~5963 f~om the sp~cific arrangements shown in Figs. 9, 10 and 11.

Figs. 12, 13 and 14 show fasteners having body portions 66' basically similar to the body portions 66 of the fasteners shown in Figs. 9, 10 and 11 respectively.
However, in Figs. 12, 13 and 14, each Eastener includes a flange 72 at its upper end including an angled gap 73 at the position of the slot 68' in the body portion 66' of the fastener. The fasteners 56 of Fig. 7 may be of any ;
of the forms shown in Figs. 12 to 14.
Fig. 15 shows how a spring pin fastener according to the invention may be used to lock a nut 74 to a joint surface 76. The nut 74 (shown in isolation in Fig. 16) is modified by the provision of an axial opening 78 aajacent one of its corners. Opening 78 is countersunk at its lower end (79). The opening 78 may be drilled or moulded in during manufacture of the nut. The spring pin fastener i9 generally denoted 80 in Fig. 15 and may be of any of the forms shown in Figs. 12 to 14. The fastener may be factory pre-installed in the axial opening 78 or the fastener may be supplied separately for insertion by the i~ user. The fastener is then inserted as will now be described:-Fig. 24 shows a punch 82 having a shank 84 and a handle portion 86 which meet at a shoulder 88. This ;, punch is used to instalI the spring pin fastener 80 in ~I the nut 74 of Fig. 15. The punch is inserted into the ; opening 78 in the nut and is driven into the opening ; until shoulder 88 comes to rest on top of a nut. This forms a punched hole in the joint surface 76. The depth of the hole is controlled by abutment of the shoulder 88 ' ~
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3L0~L5i963 of the punch with the upper surface of the nut. The lower end of the shank 84 of the punch is formed to define a sharp end 90 designed to displace the maximum amount of metal from the joint surface so as to form a bulge 92 indicated in Fig. 15. This bulge expands into the countersunk lower end 79 of opening 78 referred to above. This bulge provides maximum contact between the nut and joint surface and maximum shear resistance to removal of the nut. In any event, the fastener 80 is hammered into the opening 78 until its lower end is ~ully engaged in ~he indentation formed by the punch. As shown in Fig. 18, the flange 72 at the upper end of the fastener 80 is preferably spaced above the upper surface of the nut at this time to permit engagement of the flange by the tool in the event that the fastener is to be removed.
To maximize the resistance to removal of the nut, its lower face ~4 is preferably made flat as shown in Fig. 16 in contrast to the chamfered lower surface conventionally provided on a nut. ;
The location of the spring pin fastener 80 adjacent the corner of the nut (see Fig. 18~ is such that the nut can conveniently be engaged by a socket wrench ,7 without inter~erence by the fastener.
It will be appreciated that a nut of the form shown in Figs. 15, 16 and 18 may be manufactured simply and economically by sintering at high temperature and pressure ~rom poWdered metals. The only additional operation required to form a nut is tapping of the main `~
axial bore.

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~V459~i3 Fig. 17 shows a ~olt having a head 96 and a shank 98 received in an opening in a component 100.
The bolt head is provided with an axial opening 102 similar to opening 78 in the nut o Figs. 15 and 16 and a spring pin fastener 104 i~ inserted into the opening in similar fashion to the fastener 80 of the previous figures. Pin 104 may be similar to pin 80 and may be installed in similar fashion. It should, however, be noted that the bolt shown in Fig. 17 cannot conveniently be manufactured by the sintering method referred to in connection with the nut. Consequently, the bolt of Fig.
17 would have to be manufactured by conventional methods and subsequently drilled and countersunk to form the opening 102.

Figs. 15 to 19 illustrate how nuts and bolts can be efficiently locked using the spring pin fasteners of the invention. Figs. 18 and 19 show, in isometric perspective, the spring pin fasteners in their installed positions locking a nut (Fig. 18) and a bolt (Fig, 19).
The fasteners are each positioned such that the slot in the fastener (reference 68' in Figs. 12 to 14) and hence the gap 73 in ~lange 72 faces in the direction o~
tightening of the nut or bolt as the case may be. The flanges 72 at the upper ends o~ the ~asten~rs should not project above the nuts sufficiently to interfere with use of a socket wrench.

Fig, 20 is an isometric view of a socket head cap screw 106 formed with a peripheral series of axial teeth 108. A spring pin fastener 110, which may be of any of the forms shown in Figs. 12 to 14, is fitted into an opening in a machine part 112 to which the screw 106 , 15 , , . . . , ~ . . .

~0459~i3 is to be locked. The fastener 110 has a flange 72 at its upper end which is formed wi~h an angled gap 74 of a shape complementary to the shape o the teeth 108.
The gap 73 is positioned to enyage one of the teeth, whereby the screw 106 is locked against turning.
Fig. 21 shows the cap head screw 106 of Fig.
20 located in a hole 118 in the machine part 112. As in Fig. 20, the screw 106 is locked by a fastener 110 arranged as in Fig. 20. A contersunk portion 120 (See Fig. 23)- is provided at the lower end of the hole ;
118 in the machine part 112. This countersunk portion provides clearance to permit removal of the spring pin fastener at appropriate times. This may be effected by a screwdriver, a small crowbar or by a special tool ; `
as referred to above.
Figs. 25 and 26 show respectively a plan view , and a partially sectioned side elevation of a nut 122 formed with a hole 124 which extends obliquely from one ~`
corner of the nut and penetrates the axial bore 126 of the nut. It will be noted that the hole 124 will not weaken the nut because the hole is located in the upper ;~ portion of the nut, whereas it is the lower portion which ~;
carries the load. A punch such as that shown at 128 in Fig. 27 i5 inserted into the hole 24 and is used to provide an indentation in the bolt or other threaded component inserted into the bore 12b of the nut. A
spring pin astener such as that indicated at 130 is .
then inserted into the hole 124 and driven home into the ~
indentation formed by the punch 128. ~ `
Although in the embodiments of Figs. 9 to 27 reference has been made to a single spring pin fastener ~04S963 only for locking a bolt or nut, it is of course, to be understood that more than one such fastener could be employed in a single nut or bolt head if required. Further, although the drawings show hexagonal nuts and bolt heads, it is to be understood that other ~orms of nuts (e.g. square, rectangular, round) may be manufactured with one or more axial or inclined openings.
This ~ethod of locking a nut or bolt described above avoids the need for substantial lateral clearance around the nut or bolt head required when nuts or bolts are locked by conventional methods employing cotter pins or locking wire. In turn, this allows nuts and bolts to be located closer together than otherwise would be possible, permitting overall weight and size reductions.
Self-locking screws and spring pin fasteners such as those described above have the advantage that they can be of shorter length than conventional self-locking screws and spring pins. This permits design of lighter and less bulky equipment than is currently possible. For 20 example, in nuclear plants the predominant shape is a tube and its joint, either in-line joint or "T" joint. Joînts must be reliably locked because of vibratory or varying temperature services. Presently used locking methods require substantial lateral workin~ clearance for use of tools and hands. To lock nuts, bolts or screws with locking wire, or cotter pins, space at the side of the fasteners must be available to drill a hole with an electrlc drill. For example, to lock the cap screw with a locking wire a side clearance for both hands and pliers, 3~ to twist the wires, must be available. Self-locking screws and spring pins, according to the invention, being very .. ~ .......................................... . . .
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~0459~3 short, permit the use of much thinner tubes and slimmer joints.
The quality inspection of locked screws according to the invention, would be ~asy, instant and -~
meaningful. By contrast, it is dif~icult to inspect the installation and locking integrity of nuts, bolts or screws either locked with locking wire or with cotter pins without removing the locking element first - to test the ~ , torque - or to use dental mirror to inspect proper locks in inaccessible spots.
Finally, it should be noted that fasteners according to the invention can be locked or unlocked from a distance. The remote handling of set screws is possible by means of a tool dlsclosed in U.S. Patent No. 3,662,804.
A similarly constructed tool may be used or remote installation or removal of proposed spring pin fasteners.
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Remote handling becomes an important feature when dealing with hostile environments such as radiation, high-or-low temperature, vacuum, oxygen-less space, inaccessible spaces, `

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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fastener for locking a first component to a second component, the fastener being adapted to be located in an opening in one of the components, which opening is cylindrical in shape and extends about a longitudinal axis, and the fastener being adapted to engage the other compon-ent, wherein the fastener has a generally C-shaped trans-verse cross-section and is of elongate form, defining a hollow, generally cylindrical pin formed with an axial slot and extending about a longitudinal axis, said pin being adapted to be fitted into said opening with said cross-section disposed transversely with respect to said longi-tudinal axis of the opening, wherein the fastener is made of a resilient material and is radially compressed when located in said opening so that at least part of the fastener is re-siliently urged against an inner wall of the opening, said part of the fastener having an exterior surface which is imperforate and which includes a plurality of outwardly pro-jecting barbs which are integrally formed in said surface for mechanical engagement with said inner wall of the opening, each said barb defining an elongate edge which.
mechanically engages said inner wall of the opening in use and which is disposed at an acute angle with respect to the longitudinal axis of said pin, whereby, in use, movement tending to remove the fastener from said opening imposes on said barbs mechanical shear forces tending to resist such removal of the fastener.

2. A fastener as claimed in claim 1, wherein said cylindrical pin is formed at one end with an integral flange having an outer circumferential edge, said flange being shaped to define a first gap aligned with said slot and having opposed side edges arranged in a V-configuration, and a second gap disposed in a generally diametrically opposed position to said first gap, said gaps opening into said circumferential edge of the flange and defining with said edge four angular formations for engagement with a com-ponent to be locked by said fastener.