CA1135087A - Blind fastener - Google Patents
Blind fastenerInfo
- Publication number
- CA1135087A CA1135087A CA000341448A CA341448A CA1135087A CA 1135087 A CA1135087 A CA 1135087A CA 000341448 A CA000341448 A CA 000341448A CA 341448 A CA341448 A CA 341448A CA 1135087 A CA1135087 A CA 1135087A
- Authority
- CA
- Canada
- Prior art keywords
- bolt
- nut
- thread
- locking zone
- blind fastener
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000011248 coating agent Substances 0.000 claims description 7
- 238000000576 coating method Methods 0.000 claims description 7
- 239000000314 lubricant Substances 0.000 claims description 7
- 230000013011 mating Effects 0.000 claims description 6
- 229910052793 cadmium Inorganic materials 0.000 claims description 3
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 claims description 3
- 238000005520 cutting process Methods 0.000 claims description 3
- 238000010079 rubber tapping Methods 0.000 claims description 3
- 229910052751 metal Inorganic materials 0.000 claims description 2
- 239000002184 metal Substances 0.000 claims description 2
- 238000007747 plating Methods 0.000 claims description 2
- 230000002311 subsequent effect Effects 0.000 claims 1
- 230000000295 complement effect Effects 0.000 abstract description 4
- 238000004519 manufacturing process Methods 0.000 description 6
- 230000002452 interceptive effect Effects 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000005489 elastic deformation Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B19/00—Bolts without screw-thread; Pins, including deformable elements; Rivets
- F16B19/04—Rivets; Spigots or the like fastened by riveting
- F16B19/08—Hollow rivets; Multi-part rivets
- F16B19/10—Hollow rivets; Multi-part rivets fastened by expanding mechanically
- F16B19/1027—Multi-part rivets
- F16B19/1036—Blind rivets
- F16B19/1045—Blind rivets fastened by a pull - mandrel or the like
- F16B19/1063—Blind rivets fastened by a pull - mandrel or the like with a sleeve or collar sliding over the hollow rivet body during the pulling operation
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B39/00—Locking of screws, bolts or nuts
- F16B39/22—Locking of screws, bolts or nuts in which the locking takes place during screwing down or tightening
- F16B39/28—Locking of screws, bolts or nuts in which the locking takes place during screwing down or tightening by special members on, or shape of, the nut or bolt
- F16B39/30—Locking exclusively by special shape of the screw-thread
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Dowels (AREA)
Abstract
Title of the invention:
"A BLIND FASTENER"
ABSTRACT OF THE DISCLOSURE
A three piece blind fastener comprising an externally threaded, headed, bolt having a breakneck for limiting the torque transmissible therethrough; a tubular nut having an elongate shank, a head and an internal thread complementary to that of the bolt; and a tubular sleeve which, by relatively turning the bole in threaded engagement with the nut, can be forced on to the shank of the nut and expanded thereby to form a blind head, has the complementary threads of both the nut and bolt modified for frictional self locking interengagement.
The bolt thread is modified by the provision of a cylindrical locking zone between the ends of the bolt thread, which zone has a diameter intermediate between the diameters of the crests of the threads of the bolt and the nut, and the thread of the nut is reamed to provide a truly cylindrical crest surface of smaller diameter than the locking zone of the bolt to give a controlled interference between the locking zone of the bolt and the nut thread which serves to lock the nut and bolt together.
P.261
"A BLIND FASTENER"
ABSTRACT OF THE DISCLOSURE
A three piece blind fastener comprising an externally threaded, headed, bolt having a breakneck for limiting the torque transmissible therethrough; a tubular nut having an elongate shank, a head and an internal thread complementary to that of the bolt; and a tubular sleeve which, by relatively turning the bole in threaded engagement with the nut, can be forced on to the shank of the nut and expanded thereby to form a blind head, has the complementary threads of both the nut and bolt modified for frictional self locking interengagement.
The bolt thread is modified by the provision of a cylindrical locking zone between the ends of the bolt thread, which zone has a diameter intermediate between the diameters of the crests of the threads of the bolt and the nut, and the thread of the nut is reamed to provide a truly cylindrical crest surface of smaller diameter than the locking zone of the bolt to give a controlled interference between the locking zone of the bolt and the nut thread which serves to lock the nut and bolt together.
P.261
Description
1135~8~7 "A BLIND FASTENER"
This invention relates to a self-locking blind fastener and more particularly to a blind fastener of the kind comprising three main parts, namely a screw-threaded headed bolt, a nut having a female screw thread for mating engagement with the thread of the bolt and having a shank and an enlarged head, the shank provid;ng a nose which tapers towards the end remote from the head and a sleeve which can be expanded to form a blind head by screwing the bolt through the nut so that the bolt head abuts the sleeve and forces it onto the tapered nose of the nut.
Priorto use, the parts are~ assembled, the bolt being inserted into the sleeve and then screwed into the end of the nut remote from the nut head until it projects from the head end of the nut. In use, the shank of the nut is inserted through aligned holes in workpiece sheets to be fastened together so that the head of the nut abuts one side of the work-piece and the tapered nose projects beyond the opposite side. The fastener is set by rotating the bolt relative to the nut so that, by virtue of the threaded engagement between the nut and bolt, the head of the bolt is advanced towards the shank of the nut, forcing the sleeve over the tapered nose and thereby causing the sleeve to be expanded to form a blind head which is held in abutment with the said opposite side of the workpiece by the bolt head.
In one ~orm of blind fastener of the type referred to, the stem of the bolt is provided with a breaker groove at which the diameter of the stem is reduced to a breakneck at which the stem will break when sub-P.261 1~3~h~
jected eo a predetermined torque. The breaker groove demarcates the bolt into a main part which includes the bolt head and adjacent threaded portion of ~he stem, and a break-off portion of the stem, remote from the bolt head. The break-off portion is arranged to project from the headend of the nut prior to setting the fastener so that the bolt can be gripped and rotated reiative to the nut to set the fastener. It will be appreciated that the torque required to turn the bolt relative to the nut increases as the expansible sleeve is forced further on to the shank of the nut and as any workpiece clamped between the head of the nut and the blind head formed by the expanded sleeve is compressed, and eventually the required torque exceeds that substainable by the breakneck so that the bolt stem breaks at the breakneck, leaving the main part of the bolt as an integral part of the set fastener, and the break-off portion is discarded.
1~ Blind fasteners of such a kind are used in the aerospace industry for the assembly of parts of aircraft and space vehicles, and, in recent years, there has arisen a demand for such fasteners to be pro-vided with self-locking threads in order to reduce the risk of the nut and bolt becoming unscrewed in use as can happen as a result of stress and vibration over prolonged periods of time.
Many kinds of self-locking thread arrangements have been proposed and used for nut and bolt type fasteners but few are suTtable for blind fasteners of the kind referred to above. There are two main reasons for this. First, the strength of the lock obtainable has to meet certain minimum requirements and it is also generally found that, the stronger P.261 ~3S~7 the lock required, the greater the force needed to engage the lock.
However, the amount of torque available for engaging the lock in blind fasteners of the kind referred to is limited to that which can be trans-mitted by the breakneck of the bolt which in turn has necessarily to be limited and controlled within a fairly precise range in order to ensure that the fastener can be set and clamp the members of a work piece to-gether sufficiently tightly?and for the bolt then to break at the break-neck so as to avoid over-tightening of the fastener which could result in failure of a different kind.
It will therefore be appreciated that while the torque required to engage the lock cannot be allowed to approach too closely to that re-quired to set the fastener and break the bolt, the necessarily lower torque required to overcome the lock, which represents the effectiveness of the lock, must be as high as possible. Moreover, Tn manufacturing the blind fasteners careful control must be exerted in order to ensure minimum variation between the various torque values concerned.
We have now devised a blind fastener of the kind referred to which effectively meets the requirements of the market for a self-locking capability and which can be manufactured to tolerances which are easily controlled ~o as to provide consistent performance as between one fastener and another.
According to the present invention there is provided a blind fastener compris;ng a screw-threaded, headed, bolt, a nut having a female screw-thread for matingly engaging the screw thread of the bolt and having a shank and an enlarged head, the shank of the nut providing a nose which tapers towards the end remote from the head of the nut; and P.2~1 ~13S~}8~7 1, a sleeve which can be forced onto the tapered nose of the shank of the nut by screwing the nut along the bolt towards the head thereof and thereby expanded to form a blind head, wherein the bolt has a sub-stantially cylindrical locking zone, the diameter of the bolt in the locking zone being intermediate between the crest diameter of the screw thread of the bolt and the crest diameter of the thread of the nut, the locking zone extending axially through a distance greater than the pitch of the thread;
at least that part of the nut thread which will, in use of the fastener, be traversed by the locking zone of the bolt having a crest the surface of which forms part of a truly cylindrical surface having a lesser diameter than the diameter of that helical strip upon the surface of the locking zone of the bolt with which the aforesaid crest surface will engage, whereby when the nut is screwed along the bolt to set the fastener the crest surface of the nut thread interferes to a predetermined extent with the locking zone along the helical strip and provides a con-trolled interference giv;ng a frictional lock between the nut and bolt.
The locking zone may be spaced from the head of the bolt by a distance equal to at least twice the pitch of the bolt thread.
The locking zone of the bolt may have a diameter equal to or slightly greater than the effective diameter of the bolt thread.
Preferably the diameter of the locking zone is not less than the effective diameter of the bolt thread.
Preferably, the interference bet~een the cres~ s~rface of the nut thread and the locking zone is such as to be insufficient to cause P.261 113S~B7 plastic deformation of the nut thread.
The said interference may be within the range 0.025 mm to 0.1016 mm and preferably is within the range 0.0381 mm to 0.0762 mm.
.
The truly cylindricalform of the crest surface of the said part of the nut thread may be formed by an accurate dimensioning operation performed subsequent to forming the thread of the nut.
The nut thread may be formed by a cutting or roll tapping operation and the said part thereof may be a subsequently reamed portion thereof.
The mating surfaces of the nut and or the bolt may have a lubricant coating thereon.
The lubricant coating may be a plating of a lubricant metal such as cadmium.
Preferably the locking zone is intermediate between the ends of the screw thread.
The locking zone may be formed as a cylindrical portion of sufficient diameter to interfere wlth the crest of the thread of the nut without causing appreciable plastic deformation of the thread of the nut.
Preferably, the locking zone of the bolt extends axially through a distance equal to at least twice and not greater than four times the pitch of the screw thread of the bolt.
A preferred form of the invention will now be described with reference to the accompanying drawings in which:-P.261 1135~7 Figure 1 is a sectional elevation of a blind fastener embodyingthe invention;
Figure 2 is an elevation of the bolt part of the fastener of Figure l;
Figure 3 is a sectional elevation of an assembly, illustrating the fastener of Figure 1 in use, and Figure 4 is an enlarged fragmentary elevation, partly in section, of the assembly of Figure 3.
Referring first to Figure 1 of the drawings, a blind fastener 10 comprises a nut 12, a bolt 14 and a sleeve 16.
The nut 12 comprises a hexagonal head 18 and an elongate shank 20 having an end portton 27 remote from the head and tapered away from the head to form a conical nose. The nut is, of course, tubular and Is formed with an internal screw thread 24 throughout the length of its bore.
The sleeve 16 is a tubular cylinder having an external diameter substantially equal to that of the shank of the nut and has a bore which is flared at both ends, the flared ends each reaching slightly greater internal diameter than the smallest diameter of the tapered nose 22 of the nut so that the nose 22 can easily enter either of the flared ends.
The bolt 14 has a head 30 at one end of diameter substantially equal to that of /the shank of the nut, and an elongate stem 32 of greater ax.l:al length P.261 1~3501~7 than the combined lengths of the nut 12 and sleeve 16. A break-off wrenching portion 34 of the bolt stem most remote from the head 30 is provided with a pair of diametrically opposed wrenching flats 36 whereby the bolt may be rotated, and the portion 34 is joined to the remainder of the stem 32 by a breakneck 38 at which the stem may be broken at a predetermined torque, enabling the wrenching portion 34 to be detached from the installed fastener as illustrated in Figure 3.
A screw thread 40 which is generally complementary to the screw thread 24 of the nut so as to matingly engage the nut thread, extends is throughout the length of the bolt stem 32, except in a locking zone 42 and over the surfaces of the breakneck and wrenching flats. The locking zone 42 is spaced from the head of the bolt by a distance approximately equal to the length of the sleeve 16. The locking zone 42 is in the form of an unthreaded cylindrical land accurately concentric with the axis of the bolt thread and having a diameter which iç greater than the crest diameter of the complementary thread of the nut and which is less than the diameter of the stem taken across the crest of the thread on the bolt. The land 42 extends axially through a distance which is equal to twice the pitch of the thread 40. It is not objectionable if 2n the surface of the land has a raised vestige of thread provided that the land has a helical path over which the mating thread of the nut can pass which path has a surface which is part of a cylinder concentric with the axis of the bolt thread~
Moreover, at least ~hat part of the thread 24 of the nut which, in use of the fastener, will be traversed by the locking zone of the bolt .
P.26~
has a fiattened crest. As shown in the drawings, the entire length of the nut thread has a flattened crest since this is more convenient to achieve in the manufacturing process than over a limited length of the thread. In particular, it is here stressed that the flattened crest of the nut thread is formed with precision so that the surface of the crest is part of a truly cylindrical surface.
The mating threads of the nut and bolt in this embodiment are basically of the form known as Unified National Fine and as is well known, the basic form of this thread has a flattened crest, although in normal manufacture it is usual to tolerate some rounding especially of the longitudinal edges of the crest.
However in forming the nut of the invention we take especial steps thread to ensure that the crest of ehe nut/is truly cylindrical and free from burrs and irregularitTes such as are normally formed in manufacture by tapping or thread rolling and to this end we first form the thread in a normal manner by means of a cutting tap, and then ream at least that portion which will be traversed by the locking zone of the bolt so as to remove a portion of the crest of the thread and leave a truly cylindrical crest surface.
Furthermore, the nut thread is reamed to a minor diameter such that the crest will interfere with the cylindrical surface of the land of the bolt to a predeter~ined extent within close tolerances. More specifically the amount of interference is arranged to be such that the deformation of the thread of the nut when engaged with the locking zone of the bol~ is within the elastic limit of the materTal of the nut so that the nut ~.261 ~135()8~ -g thread is not caused to undergo any plastic deformation.
Thus, in this embodiment, both the nut and the bolt are formed of steel, and the shank of the nut has a nominal external diameter of A
4.83 mm. The mating threads of the nut and bolt have the form of 6 - 40 UNF with an effective diameter for the bolt thread of 3.02 mm.
The cylindrical land of the locking zone of the bolt has a diameter which is made the same as (or can be very slightly greater than) the effective diameter, and the thread of the nut is reamed to a minor diameter so as to interfere with the land of the bolt and with a precision such that the interference is within the range of 0.038 mm to 0.076 mm.
Prior to use, the blind fastener 10 is assembled so that the cylindrical sleeve 16 is disposed on the stem of the bolt 14 adjacent the head 30, and the stem of the bolt is entered into threaded engage-ment with the nut 12 so that the conical nose 22 at the end of the nut 12 just reaches the nearer end of the locking zone 42 on the bolt. The wrenching portion 34 of the bolt then projects beyond the head 18 of the nut.
Referring to Figures 3 and 4, in use of the blind fastener 10, the bolt head 30, sleeve 16, and nut shank 20 are inserted through aligned holes in workpiece members 50, 52 to be joined together so that the head 18 of the nut abuts a surface of the member 50, and the head of the bolt, the sleeve and the conicat nose of the nut shank project beyond the face of the other member 52 remote from the head of the nut. The nut 12 and bolt 14 are then relatively rotated, conveniently using the wrenching P.261 1~3S~87 flats 36 of the bolt and hexagonal form of the head of the nut ~8 to obtain a suita~le grip~ so as to bri~ng the head 30 of the bolt nearer to the head ~8 of the nut. In doing so, tfie sleeve ]6 ts forced over the conical nose 22 of the nut shanR and tfiere~y expanded to form a blind head 54 whicn ab~ts the ad)acent face of the workp~ece member 52 and causes the two ~orRpiece ~embers to ~e ti~g~tly clamped ~etween the b`lind fiea~ 54 and tfie head ~8 of tfie nut.
Once che workpiece mem6ers 5~,52 are tigfitly clamped ~tween the head 18 of the nut and the blind head 54, the force required to rotate the bolt further relative to the nut exceeds that which can be sustained 6y the breakneck 38 and the bott stem breaks at the breakneck allowing the wrenching portion to be discarded, leaving the set fastener in the condition illustrated in Figure 3 In entering the bore of the nut, the locking zone of the bolt ]5 interferes with the thread of the nut, producing some elastic deformation of the nut. However, due to the close tolerances within which the locking zone and the reamed thread of the nut are formed, neither the locking zone nor the nut thread undergo any plastic deformation and no galling occurs The friction between the Interfering surfaces of the nut thread 2û and tfie locktng zone o6tained with the prescribed amount of interference for tfiis embod~ment ~namely o.a38 - û.076 mm) i5 low enough to enable the fastener to apply an adequate clamping pressure to the workpiece mem6ers which, as preYiously expla;ned, is limited by the torque trans-misstble by the breakneck, but sufficient to ensure that the fastener will not ~ecome unscrewed even under rigorous condittons of use.
P.26]
113~V87 ,..
Other similar fasteners have been made with dimenstons differing from those of the foregoing example. In all those tried, tt has been found that the dimensions of the fastener can be varied slightly but that the interference between the crest surface of the nut tfiread and the locking zone should always 6e ~ithin a broad range of 0.025 mm to 0.~016 mm. There is however, an overriding need to avoid the interference 6eing so great tha~ the bolt will break before the fastener has clamped the workpiece mem6ers together, and also the interference ought not to be so great that plastic deformation occurs at the interfering surfaces.
The friction between the interfertng surfaces reaches a maximum once the locking zone has entered fully into engagement with the nut thread and does not increase as the locking zone passes further along the nut thread.
Slmilarly, once the fastener has been set, the torque required to turn the bolt in a directlon to unscrew the bolt from the nut remains ~5 constant as long as the locking zone of the bolt is entirely within and engaged by the nut thread. Consequently, and especially in order to meet user requirements for a thread lock which maintains a predetermined strength of locking after the bolt has been unscrewed through up to two full turns, we arrange the locking zone of the bolt at a position so spaced from the head of the bolt that when the fastener is fully set, the locking zone has entered the nut and passed beyond at least two full turns of the nut thread.
In order that the transverse width across the flattened crest of the nut thread is great enowgh to have substantial resistance to plastic deformatton when tnterfered ~ith by the locking zone of the 601t, we P . 26 ~13SO~
arrange that the dianeters of the locking zone of the bolt and the crest of the nut thread are such as to interfere with each other at a diameter which is substantially the same as or slightly greater than the effective diameter of the bolt thread, 6ut not so great that the height of the crest of the nut thread above its root is so small as to render the nut thread of inadequate strength to strongly engage the thread of the bolt.
After manufacturing the parts of the blind fastener to the dimensions and tolerances referred to above, the parts are then provided with a coating in the form of an electrolytically deposited layer of cadmium to serve as both a lubricant coating on the surfaces of the frictionally engaging parts and the interfering parts and to act as a rust proofing coating.
- Although the bolt 14 of the self-locking blind fastener hereinbeforespecifically described and illustrated by way of example incorporates break-off portion and a torque-limiting means in the form of a breakneck which is adapted to transmit sufficient torque to engage the self-locking threads and set the fastener and to break when the torque applied exceeds a pre determ;ned value, It will be appreciated that Tt is not essential for the bolt of a self-locking blind fastener according to the invention to have these features since the fastener can be set and the threads brought into locking engagement without any need to limit the torque applied, or for the bolt to break. As previously explained, however, it is very desirable to have some means for limiting the torque which can be applied,in order to avoid over tightening the fastener: such torque limiting means can be incorporated in the tool used for se~ting P.261 1135(~t7 the fastener or in the fastener itself, as in the illustrated embodiment.
We prefer that the torque-limiting means be incorporated in the fastener, since this avoids relying upon proper adjustment of the tool used.
Furthermore the breaking-off at an appropriate position of the part of the bolt which is engaged by the tool when rotating the bolt, enables the set fastener to have a neat appearance without any portion of the bolt pro-jecting from the head of the nut.
It will of course be appreciated that when, as in the illustrated em60diment, the 601t of the self-locking blind fastener has a torque-limiting breakneck, then it is of particular importance to be able reliably to control the torque required to engage the locking threads and set the fastener in order that this torque shall not exceed that transmissible by t~e ~reakneck. The thread-locking arrangement incorporated in a fastener according to the invention is susceptible of close control in manufacture and is therefore particularly suitable for the particular kind of fastener having a bolt with a torque limiting breakneck.
P.261
This invention relates to a self-locking blind fastener and more particularly to a blind fastener of the kind comprising three main parts, namely a screw-threaded headed bolt, a nut having a female screw thread for mating engagement with the thread of the bolt and having a shank and an enlarged head, the shank provid;ng a nose which tapers towards the end remote from the head and a sleeve which can be expanded to form a blind head by screwing the bolt through the nut so that the bolt head abuts the sleeve and forces it onto the tapered nose of the nut.
Priorto use, the parts are~ assembled, the bolt being inserted into the sleeve and then screwed into the end of the nut remote from the nut head until it projects from the head end of the nut. In use, the shank of the nut is inserted through aligned holes in workpiece sheets to be fastened together so that the head of the nut abuts one side of the work-piece and the tapered nose projects beyond the opposite side. The fastener is set by rotating the bolt relative to the nut so that, by virtue of the threaded engagement between the nut and bolt, the head of the bolt is advanced towards the shank of the nut, forcing the sleeve over the tapered nose and thereby causing the sleeve to be expanded to form a blind head which is held in abutment with the said opposite side of the workpiece by the bolt head.
In one ~orm of blind fastener of the type referred to, the stem of the bolt is provided with a breaker groove at which the diameter of the stem is reduced to a breakneck at which the stem will break when sub-P.261 1~3~h~
jected eo a predetermined torque. The breaker groove demarcates the bolt into a main part which includes the bolt head and adjacent threaded portion of ~he stem, and a break-off portion of the stem, remote from the bolt head. The break-off portion is arranged to project from the headend of the nut prior to setting the fastener so that the bolt can be gripped and rotated reiative to the nut to set the fastener. It will be appreciated that the torque required to turn the bolt relative to the nut increases as the expansible sleeve is forced further on to the shank of the nut and as any workpiece clamped between the head of the nut and the blind head formed by the expanded sleeve is compressed, and eventually the required torque exceeds that substainable by the breakneck so that the bolt stem breaks at the breakneck, leaving the main part of the bolt as an integral part of the set fastener, and the break-off portion is discarded.
1~ Blind fasteners of such a kind are used in the aerospace industry for the assembly of parts of aircraft and space vehicles, and, in recent years, there has arisen a demand for such fasteners to be pro-vided with self-locking threads in order to reduce the risk of the nut and bolt becoming unscrewed in use as can happen as a result of stress and vibration over prolonged periods of time.
Many kinds of self-locking thread arrangements have been proposed and used for nut and bolt type fasteners but few are suTtable for blind fasteners of the kind referred to above. There are two main reasons for this. First, the strength of the lock obtainable has to meet certain minimum requirements and it is also generally found that, the stronger P.261 ~3S~7 the lock required, the greater the force needed to engage the lock.
However, the amount of torque available for engaging the lock in blind fasteners of the kind referred to is limited to that which can be trans-mitted by the breakneck of the bolt which in turn has necessarily to be limited and controlled within a fairly precise range in order to ensure that the fastener can be set and clamp the members of a work piece to-gether sufficiently tightly?and for the bolt then to break at the break-neck so as to avoid over-tightening of the fastener which could result in failure of a different kind.
It will therefore be appreciated that while the torque required to engage the lock cannot be allowed to approach too closely to that re-quired to set the fastener and break the bolt, the necessarily lower torque required to overcome the lock, which represents the effectiveness of the lock, must be as high as possible. Moreover, Tn manufacturing the blind fasteners careful control must be exerted in order to ensure minimum variation between the various torque values concerned.
We have now devised a blind fastener of the kind referred to which effectively meets the requirements of the market for a self-locking capability and which can be manufactured to tolerances which are easily controlled ~o as to provide consistent performance as between one fastener and another.
According to the present invention there is provided a blind fastener compris;ng a screw-threaded, headed, bolt, a nut having a female screw-thread for matingly engaging the screw thread of the bolt and having a shank and an enlarged head, the shank of the nut providing a nose which tapers towards the end remote from the head of the nut; and P.2~1 ~13S~}8~7 1, a sleeve which can be forced onto the tapered nose of the shank of the nut by screwing the nut along the bolt towards the head thereof and thereby expanded to form a blind head, wherein the bolt has a sub-stantially cylindrical locking zone, the diameter of the bolt in the locking zone being intermediate between the crest diameter of the screw thread of the bolt and the crest diameter of the thread of the nut, the locking zone extending axially through a distance greater than the pitch of the thread;
at least that part of the nut thread which will, in use of the fastener, be traversed by the locking zone of the bolt having a crest the surface of which forms part of a truly cylindrical surface having a lesser diameter than the diameter of that helical strip upon the surface of the locking zone of the bolt with which the aforesaid crest surface will engage, whereby when the nut is screwed along the bolt to set the fastener the crest surface of the nut thread interferes to a predetermined extent with the locking zone along the helical strip and provides a con-trolled interference giv;ng a frictional lock between the nut and bolt.
The locking zone may be spaced from the head of the bolt by a distance equal to at least twice the pitch of the bolt thread.
The locking zone of the bolt may have a diameter equal to or slightly greater than the effective diameter of the bolt thread.
Preferably the diameter of the locking zone is not less than the effective diameter of the bolt thread.
Preferably, the interference bet~een the cres~ s~rface of the nut thread and the locking zone is such as to be insufficient to cause P.261 113S~B7 plastic deformation of the nut thread.
The said interference may be within the range 0.025 mm to 0.1016 mm and preferably is within the range 0.0381 mm to 0.0762 mm.
.
The truly cylindricalform of the crest surface of the said part of the nut thread may be formed by an accurate dimensioning operation performed subsequent to forming the thread of the nut.
The nut thread may be formed by a cutting or roll tapping operation and the said part thereof may be a subsequently reamed portion thereof.
The mating surfaces of the nut and or the bolt may have a lubricant coating thereon.
The lubricant coating may be a plating of a lubricant metal such as cadmium.
Preferably the locking zone is intermediate between the ends of the screw thread.
The locking zone may be formed as a cylindrical portion of sufficient diameter to interfere wlth the crest of the thread of the nut without causing appreciable plastic deformation of the thread of the nut.
Preferably, the locking zone of the bolt extends axially through a distance equal to at least twice and not greater than four times the pitch of the screw thread of the bolt.
A preferred form of the invention will now be described with reference to the accompanying drawings in which:-P.261 1135~7 Figure 1 is a sectional elevation of a blind fastener embodyingthe invention;
Figure 2 is an elevation of the bolt part of the fastener of Figure l;
Figure 3 is a sectional elevation of an assembly, illustrating the fastener of Figure 1 in use, and Figure 4 is an enlarged fragmentary elevation, partly in section, of the assembly of Figure 3.
Referring first to Figure 1 of the drawings, a blind fastener 10 comprises a nut 12, a bolt 14 and a sleeve 16.
The nut 12 comprises a hexagonal head 18 and an elongate shank 20 having an end portton 27 remote from the head and tapered away from the head to form a conical nose. The nut is, of course, tubular and Is formed with an internal screw thread 24 throughout the length of its bore.
The sleeve 16 is a tubular cylinder having an external diameter substantially equal to that of the shank of the nut and has a bore which is flared at both ends, the flared ends each reaching slightly greater internal diameter than the smallest diameter of the tapered nose 22 of the nut so that the nose 22 can easily enter either of the flared ends.
The bolt 14 has a head 30 at one end of diameter substantially equal to that of /the shank of the nut, and an elongate stem 32 of greater ax.l:al length P.261 1~3501~7 than the combined lengths of the nut 12 and sleeve 16. A break-off wrenching portion 34 of the bolt stem most remote from the head 30 is provided with a pair of diametrically opposed wrenching flats 36 whereby the bolt may be rotated, and the portion 34 is joined to the remainder of the stem 32 by a breakneck 38 at which the stem may be broken at a predetermined torque, enabling the wrenching portion 34 to be detached from the installed fastener as illustrated in Figure 3.
A screw thread 40 which is generally complementary to the screw thread 24 of the nut so as to matingly engage the nut thread, extends is throughout the length of the bolt stem 32, except in a locking zone 42 and over the surfaces of the breakneck and wrenching flats. The locking zone 42 is spaced from the head of the bolt by a distance approximately equal to the length of the sleeve 16. The locking zone 42 is in the form of an unthreaded cylindrical land accurately concentric with the axis of the bolt thread and having a diameter which iç greater than the crest diameter of the complementary thread of the nut and which is less than the diameter of the stem taken across the crest of the thread on the bolt. The land 42 extends axially through a distance which is equal to twice the pitch of the thread 40. It is not objectionable if 2n the surface of the land has a raised vestige of thread provided that the land has a helical path over which the mating thread of the nut can pass which path has a surface which is part of a cylinder concentric with the axis of the bolt thread~
Moreover, at least ~hat part of the thread 24 of the nut which, in use of the fastener, will be traversed by the locking zone of the bolt .
P.26~
has a fiattened crest. As shown in the drawings, the entire length of the nut thread has a flattened crest since this is more convenient to achieve in the manufacturing process than over a limited length of the thread. In particular, it is here stressed that the flattened crest of the nut thread is formed with precision so that the surface of the crest is part of a truly cylindrical surface.
The mating threads of the nut and bolt in this embodiment are basically of the form known as Unified National Fine and as is well known, the basic form of this thread has a flattened crest, although in normal manufacture it is usual to tolerate some rounding especially of the longitudinal edges of the crest.
However in forming the nut of the invention we take especial steps thread to ensure that the crest of ehe nut/is truly cylindrical and free from burrs and irregularitTes such as are normally formed in manufacture by tapping or thread rolling and to this end we first form the thread in a normal manner by means of a cutting tap, and then ream at least that portion which will be traversed by the locking zone of the bolt so as to remove a portion of the crest of the thread and leave a truly cylindrical crest surface.
Furthermore, the nut thread is reamed to a minor diameter such that the crest will interfere with the cylindrical surface of the land of the bolt to a predeter~ined extent within close tolerances. More specifically the amount of interference is arranged to be such that the deformation of the thread of the nut when engaged with the locking zone of the bol~ is within the elastic limit of the materTal of the nut so that the nut ~.261 ~135()8~ -g thread is not caused to undergo any plastic deformation.
Thus, in this embodiment, both the nut and the bolt are formed of steel, and the shank of the nut has a nominal external diameter of A
4.83 mm. The mating threads of the nut and bolt have the form of 6 - 40 UNF with an effective diameter for the bolt thread of 3.02 mm.
The cylindrical land of the locking zone of the bolt has a diameter which is made the same as (or can be very slightly greater than) the effective diameter, and the thread of the nut is reamed to a minor diameter so as to interfere with the land of the bolt and with a precision such that the interference is within the range of 0.038 mm to 0.076 mm.
Prior to use, the blind fastener 10 is assembled so that the cylindrical sleeve 16 is disposed on the stem of the bolt 14 adjacent the head 30, and the stem of the bolt is entered into threaded engage-ment with the nut 12 so that the conical nose 22 at the end of the nut 12 just reaches the nearer end of the locking zone 42 on the bolt. The wrenching portion 34 of the bolt then projects beyond the head 18 of the nut.
Referring to Figures 3 and 4, in use of the blind fastener 10, the bolt head 30, sleeve 16, and nut shank 20 are inserted through aligned holes in workpiece members 50, 52 to be joined together so that the head 18 of the nut abuts a surface of the member 50, and the head of the bolt, the sleeve and the conicat nose of the nut shank project beyond the face of the other member 52 remote from the head of the nut. The nut 12 and bolt 14 are then relatively rotated, conveniently using the wrenching P.261 1~3S~87 flats 36 of the bolt and hexagonal form of the head of the nut ~8 to obtain a suita~le grip~ so as to bri~ng the head 30 of the bolt nearer to the head ~8 of the nut. In doing so, tfie sleeve ]6 ts forced over the conical nose 22 of the nut shanR and tfiere~y expanded to form a blind head 54 whicn ab~ts the ad)acent face of the workp~ece member 52 and causes the two ~orRpiece ~embers to ~e ti~g~tly clamped ~etween the b`lind fiea~ 54 and tfie head ~8 of tfie nut.
Once che workpiece mem6ers 5~,52 are tigfitly clamped ~tween the head 18 of the nut and the blind head 54, the force required to rotate the bolt further relative to the nut exceeds that which can be sustained 6y the breakneck 38 and the bott stem breaks at the breakneck allowing the wrenching portion to be discarded, leaving the set fastener in the condition illustrated in Figure 3 In entering the bore of the nut, the locking zone of the bolt ]5 interferes with the thread of the nut, producing some elastic deformation of the nut. However, due to the close tolerances within which the locking zone and the reamed thread of the nut are formed, neither the locking zone nor the nut thread undergo any plastic deformation and no galling occurs The friction between the Interfering surfaces of the nut thread 2û and tfie locktng zone o6tained with the prescribed amount of interference for tfiis embod~ment ~namely o.a38 - û.076 mm) i5 low enough to enable the fastener to apply an adequate clamping pressure to the workpiece mem6ers which, as preYiously expla;ned, is limited by the torque trans-misstble by the breakneck, but sufficient to ensure that the fastener will not ~ecome unscrewed even under rigorous condittons of use.
P.26]
113~V87 ,..
Other similar fasteners have been made with dimenstons differing from those of the foregoing example. In all those tried, tt has been found that the dimensions of the fastener can be varied slightly but that the interference between the crest surface of the nut tfiread and the locking zone should always 6e ~ithin a broad range of 0.025 mm to 0.~016 mm. There is however, an overriding need to avoid the interference 6eing so great tha~ the bolt will break before the fastener has clamped the workpiece mem6ers together, and also the interference ought not to be so great that plastic deformation occurs at the interfering surfaces.
The friction between the interfertng surfaces reaches a maximum once the locking zone has entered fully into engagement with the nut thread and does not increase as the locking zone passes further along the nut thread.
Slmilarly, once the fastener has been set, the torque required to turn the bolt in a directlon to unscrew the bolt from the nut remains ~5 constant as long as the locking zone of the bolt is entirely within and engaged by the nut thread. Consequently, and especially in order to meet user requirements for a thread lock which maintains a predetermined strength of locking after the bolt has been unscrewed through up to two full turns, we arrange the locking zone of the bolt at a position so spaced from the head of the bolt that when the fastener is fully set, the locking zone has entered the nut and passed beyond at least two full turns of the nut thread.
In order that the transverse width across the flattened crest of the nut thread is great enowgh to have substantial resistance to plastic deformatton when tnterfered ~ith by the locking zone of the 601t, we P . 26 ~13SO~
arrange that the dianeters of the locking zone of the bolt and the crest of the nut thread are such as to interfere with each other at a diameter which is substantially the same as or slightly greater than the effective diameter of the bolt thread, 6ut not so great that the height of the crest of the nut thread above its root is so small as to render the nut thread of inadequate strength to strongly engage the thread of the bolt.
After manufacturing the parts of the blind fastener to the dimensions and tolerances referred to above, the parts are then provided with a coating in the form of an electrolytically deposited layer of cadmium to serve as both a lubricant coating on the surfaces of the frictionally engaging parts and the interfering parts and to act as a rust proofing coating.
- Although the bolt 14 of the self-locking blind fastener hereinbeforespecifically described and illustrated by way of example incorporates break-off portion and a torque-limiting means in the form of a breakneck which is adapted to transmit sufficient torque to engage the self-locking threads and set the fastener and to break when the torque applied exceeds a pre determ;ned value, It will be appreciated that Tt is not essential for the bolt of a self-locking blind fastener according to the invention to have these features since the fastener can be set and the threads brought into locking engagement without any need to limit the torque applied, or for the bolt to break. As previously explained, however, it is very desirable to have some means for limiting the torque which can be applied,in order to avoid over tightening the fastener: such torque limiting means can be incorporated in the tool used for se~ting P.261 1135(~t7 the fastener or in the fastener itself, as in the illustrated embodiment.
We prefer that the torque-limiting means be incorporated in the fastener, since this avoids relying upon proper adjustment of the tool used.
Furthermore the breaking-off at an appropriate position of the part of the bolt which is engaged by the tool when rotating the bolt, enables the set fastener to have a neat appearance without any portion of the bolt pro-jecting from the head of the nut.
It will of course be appreciated that when, as in the illustrated em60diment, the 601t of the self-locking blind fastener has a torque-limiting breakneck, then it is of particular importance to be able reliably to control the torque required to engage the locking threads and set the fastener in order that this torque shall not exceed that transmissible by t~e ~reakneck. The thread-locking arrangement incorporated in a fastener according to the invention is susceptible of close control in manufacture and is therefore particularly suitable for the particular kind of fastener having a bolt with a torque limiting breakneck.
P.261
Claims (15)
1. A blind fastener comprising a screw-threaded, headed, bolt;
a nut having a shank, an enlarged head and a female screw-thread for matingly engaging the screw thread of the bolt, the shank of the nut providing a nose which tapers towards the end remote from the head of the nut; and a sleeve which can be forced onto the tapered nose of the shank of the nut by screwing the nut along the bolt towards the head of the bolt, and thereby expanded to form a blind head;
wherein the bolt has a substantially cylindrical locking zone, the diameter of the bolt in the locking zone being intermediate between the crest diameter of the screw thread of the bolt and the crest diameter of the thread of the nut, the locking zone extending axially through a distance greater than the pitch of the thread; and at least that part of the nut thread which will, in use of the fastener, be traversed by the locking zone of the bolt has a crest the surface of which forms part of a truly cylindrical surface having a lesser diameter than the diameter of that helical strip upon the surface of the locking zone of the bolt with which the aforesaid crest surface will engage, the arrangement being such that, when the nut is screwed along the bolt to set the fastener, a predetermined interference will occur between the crest surface of the nut thread and the locking zone along the helical strip and provide a frictional lock between the nut and bolt.
P.261
a nut having a shank, an enlarged head and a female screw-thread for matingly engaging the screw thread of the bolt, the shank of the nut providing a nose which tapers towards the end remote from the head of the nut; and a sleeve which can be forced onto the tapered nose of the shank of the nut by screwing the nut along the bolt towards the head of the bolt, and thereby expanded to form a blind head;
wherein the bolt has a substantially cylindrical locking zone, the diameter of the bolt in the locking zone being intermediate between the crest diameter of the screw thread of the bolt and the crest diameter of the thread of the nut, the locking zone extending axially through a distance greater than the pitch of the thread; and at least that part of the nut thread which will, in use of the fastener, be traversed by the locking zone of the bolt has a crest the surface of which forms part of a truly cylindrical surface having a lesser diameter than the diameter of that helical strip upon the surface of the locking zone of the bolt with which the aforesaid crest surface will engage, the arrangement being such that, when the nut is screwed along the bolt to set the fastener, a predetermined interference will occur between the crest surface of the nut thread and the locking zone along the helical strip and provide a frictional lock between the nut and bolt.
P.261
2. A blind fastener according to claim 1, wherein the locking zone is spaced from the head of the bolt by a distance equal to at least twice the pitch of the bolt thread.
3. A blind fastener according to claim 1, wherein the locking zone is intermediate between the ends of the screw thread of the bolt.
4. A blind fastener according to claim 1, wherein the locking zone of the bolt extends axially through a distance equal to at least twice and not greater than four times the pitch of the screw thread of the bolt.
5. A blind fastener according to claim 1, wherein the locking zone is a cylindrical portion accurately concentric with the axis of the thread of the bolt.
6. A blind fastener according to claim 1, wherein the diameter of the locking zone of the bolt is not less than the effective diameter of the bolt thread.
7. A blind fastener according to claim 1, wherein the locking zone of the bolt has a diameter equal to or slightly greater than the effective diameter of the bolt thread.
8. A blind fastener according to claim 1, wherein the interference between the crest surface of the nut thread and the locking zone is not sufficient to cause plastic deformation of the nut thread.
9. A blind fastener according to claim 1, wherein the interference is within the range 0.025 mm to 0.1016 mm.
10. A blind fastener according to claim 6, wherein the interference is within the range 0.0381 mm to 0.0762 mm.
P.261
P.261
11. A blind fastener according to claim 1, wherein the truly cylindrical form of the crest surface of the said part of the nut thread is formed by an accurate dimensioning operation performed sub-sequent to forming the thread of the nut.
12. A blind fastener according to claim 1, wherein the nut thread is formed by a cutting or roll tapping operation and the said part thereof is a subsequently reamed portion thereof.
13. A blind fastener according to claim 1, wherein the mating surfaces of the nut and or the bolt have a lubricant coating thereon.
14. A blind fastener according to claim 13, wherein the lubricant coating is a plating of a lubricant metal such as cadmium.
15. A blind fastener according to claim 1 wherein the bolt has a breakneck spaced away from the bolt head beyond the locking zone, the breakneck having a strength adequate to set the fastener but not to overtighten the fastener.
P.261
P.261
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB48026/78 | 1978-12-11 | ||
| GB7848026A GB2038978B (en) | 1978-12-11 | 1978-12-11 | Locking of blind fasteners |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1135087A true CA1135087A (en) | 1982-11-09 |
Family
ID=10501658
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000341448A Expired CA1135087A (en) | 1978-12-11 | 1979-12-07 | Blind fastener |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5582812A (en) |
| AU (1) | AU5363979A (en) |
| BR (1) | BR7907997A (en) |
| CA (1) | CA1135087A (en) |
| DE (1) | DE2948967A1 (en) |
| FR (1) | FR2444191A1 (en) |
| GB (1) | GB2038978B (en) |
| IT (1) | IT1120212B (en) |
| NL (1) | NL7908758A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103291719A (en) * | 2013-06-25 | 2013-09-11 | 贵州航天精工制造有限公司 | Self-plugging rivet |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3242009A1 (en) * | 1981-11-18 | 1983-06-09 | Avdel Ltd | BLIND FASTENERS AND METHOD FOR THE PRODUCTION THEREOF |
| GB8400345D0 (en) * | 1984-01-06 | 1984-02-08 | Avdel Ltd | Blind fastener |
| US4752169A (en) * | 1985-04-12 | 1988-06-21 | Monogram Industries, Inc. | Flush break blind bolt |
| GB2220721B (en) * | 1988-07-11 | 1992-02-12 | Austin Rover Group | A method of making threaded fasteners |
| US4900205A (en) * | 1988-08-15 | 1990-02-13 | Huck Manufacturing Co. | Blind fastener forming a blind head with a large effective area |
| JP2826269B2 (en) * | 1994-06-14 | 1998-11-18 | 大和ハウス工業株式会社 | Column / beam joint structure using one side bolt |
| JP2731352B2 (en) * | 1994-06-14 | 1998-03-25 | 大和ハウス工業株式会社 | Column / beam joint structure using one side bolt |
| JP4357158B2 (en) * | 2002-07-16 | 2009-11-04 | クラウン精密工業株式会社 | Structure of push rod of brake operating cylinder in vehicle brake device |
| DE102010035571A1 (en) | 2010-08-24 | 2012-03-01 | Siemens Aktiengesellschaft | Electric switch |
| CN103291727A (en) * | 2013-07-03 | 2013-09-11 | 许松林 | Anti-loosening cylindrical threaded part |
| JP6544766B2 (en) * | 2015-05-18 | 2019-07-17 | 株式会社ＮｅｊｉＬａｗ | Fastening device |
| DE102020129387A1 (en) | 2020-11-09 | 2022-05-12 | Bayerische Motoren Werke Aktiengesellschaft | Screw connection system and method for producing a screw connection using a screw connection system |
-
1978
- 1978-12-11 GB GB7848026A patent/GB2038978B/en not_active Expired
-
1979
- 1979-12-04 NL NL7908758A patent/NL7908758A/en not_active Application Discontinuation
- 1979-12-05 DE DE19792948967 patent/DE2948967A1/en not_active Withdrawn
- 1979-12-07 BR BR7907997A patent/BR7907997A/en unknown
- 1979-12-07 CA CA000341448A patent/CA1135087A/en not_active Expired
- 1979-12-10 AU AU53639/79A patent/AU5363979A/en not_active Abandoned
- 1979-12-10 FR FR7930213A patent/FR2444191A1/en not_active Withdrawn
- 1979-12-11 IT IT51052/79A patent/IT1120212B/en active
- 1979-12-11 JP JP15985979A patent/JPS5582812A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103291719A (en) * | 2013-06-25 | 2013-09-11 | 贵州航天精工制造有限公司 | Self-plugging rivet |
Also Published As
| Publication number | Publication date |
|---|---|
| DE2948967A1 (en) | 1980-06-19 |
| JPS5582812A (en) | 1980-06-21 |
| GB2038978B (en) | 1983-02-09 |
| NL7908758A (en) | 1980-06-13 |
| BR7907997A (en) | 1980-07-29 |
| IT7951052A0 (en) | 1979-12-11 |
| GB2038978A (en) | 1980-07-30 |
| AU5363979A (en) | 1980-06-19 |
| FR2444191A1 (en) | 1980-07-11 |
| IT1120212B (en) | 1986-03-19 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |