Abstract:
A fastener comprises a body having an enlarged head at a first end, a tapered ramp at a second end, a cylindrical shank disposed between the enlarged head and the tapered ramp, internal threads, and a cylindrical passage formed through the body between the first and second ends. The fastener further includes a generally cylindrical corebolt having first and second threaded sections separated by a third non-threaded section, the corebolt disposed within the passage of the body and a sleeve having a generally cylindrical passage therethrough and movably disposed over a portion of the corebolt. A nut is in threaded engagement with the corebolt and is disposed adjacent an end of the sleeve. An interface between the corebolt and the nut is configured to resist relative rotation of the nut with respect to the corebolt until the sleeve is in abutment with a workpiece.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Pratt U.S. Provisional Application Ser. No. 61/534,495, filed on Sep. 14, 2011, and entitled “Fastener and Method of Installing Same.” 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to fasteners for assembly of two or more panels of a workpiece, and more particular to a blind fastener having an installed flushness that requires little, if any, post-installation shaving or filling. 
     2. Description of the Background 
     Exterior airframe joints are required to be flush to reduce aerodynamic drag. It is therefore desirable to prevent any portion of a mechanical fastener from protruding beyond a surface of an outer panel of a workpiece in which the fastener is installed. It is also preferred to prevent any portion of a fastener from being recessed within the workpiece or recessed as compared to the remainder of the fastener. Having all portions of the fastener and the surface of the outer panel of the workpiece in an even plane is referred to as the “flushness” of the fastener. It is further desired to minimize the visibility of mechanical fasteners on an aircraft&#39;s exterior in order to improve appearance. Such flushness and appearance goals are easily met with conventional fasteners such as solid rivets, lock bolts, and threaded pins with nuts. Many pull-type blind fasteners also exhibit acceptable installed flushness. However, threaded blind bolts have always suffered from the need to have a corebolt break-off location vary by as much as 0.103 inch so that, in some grip conditions, the corebolt either protrudes above the surface of the outer panel by this amount or, if the break-off location is positioned to never break above the exposed body head surface, the corebolt breaks low, thereby leaving a cavity up to 0.103 inch deep. In either case, the fastener oftentimes requires milling of the protruding corebolt or filling (potting) of the cavity to produce the desired level of aerodynamic flushness. 
     A need therefore exists for a threaded blind fastener that produces a predictable and consistent flush installation throughout the gripping range and that minimizes the need for post-installation milling or potting. 
     SUMMARY 
     According to one aspect of the present disclosure, a fastener includes a body having an enlarged head at a first end, a tapered ramp at a second end, a cylindrical shank disposed between the enlarged head and the tapered ramp, internal threads, and a cylindrical passage formed through the body between the first and second ends. The fastener further includes a generally cylindrical corebolt having first and second threaded sections separated by a third non-threaded section, the corebolt disposed within the passage of the body. A sleeve having a cylindrical passage therethrough is movably disposed over a portion of the corebolt and a nut is in threaded engagement with the corebolt and disposed adjacent an end of the sleeve. The fastener still further includes means for restricting relative rotation between the nut and the corebolt until the sleeve has formed a blind head against a workpiece. 
     According to another aspect of the present disclosure, a fastener includes a body having an enlarged head at a first end, a tapered ramp at a second end, a cylindrical shank disposed between the enlarged head and the tapered ramp, internal threads, and a cylindrical passage formed through the body between the first and second ends. The fastener further includes a generally cylindrical corebolt having first and second threaded sections separated by a third non-threaded section, the corebolt disposed within the passage of the body. A sleeve having a cylindrical passage therethrough is movably disposed over a portion of the body and a nut is in threaded engagement with the corebolt and disposed adjacent an end of the sleeve. An interface between the corebolt and the nut is configured to resist relative rotation of the nut with respect to the corebolt until the sleeve is in abutment with a workpiece. 
     According to a different aspect of the present disclosure, a method of installing a fastener in a workpiece includes the step of inserting a fastener into a workpiece. The fastener includes a body having an enlarged head at a first end, a tapered ramp at a second end, internal threads, a cylindrical shank disposed between the enlarged head and the tapered ramp, and a cylindrical passage formed through the body between the first and second ends. The fastener further includes a generally cylindrical corebolt having first and second threaded sections separated by a third non-threaded section, the corebolt being disposed within the passage of the body. A sleeve having a cylindrical passage therethrough is movably disposed over a portion of the corebolt and a nut is in threaded engagement with the corebolt and disposed adjacent an end of the sleeve. The method further includes the steps of restricting relative rotation between the corebolt and the nut and rotating the corebolt and the nut while rotationally restraining the body, until the sleeve has formed a blind head against the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a first embodiment of a fastener that may be used to connect two or more panels forming a workpiece, by a single operator or mechanic; 
         FIG. 2  is a cross-sectional view taken generally along the lines  2 - 2  of  FIG. 1  and depicting the fastener of  FIG. 1  having a body, a translating threaded corebolt disposed within the body and having a breaking groove, a sleeve disposed over the corebolt and adjacent a tapered ramp of the body, and a nut disposed adjacent the sleeve; 
         FIG. 3  is a isometric view of the fastener of  FIG. 1  inserted into aligned apertures of two or more panels forming a workpiece, wherein a thickness of the workpiece corresponds to a minimum grip condition; 
         FIG. 4  is a side elevational view of  FIG. 3  showing the body and corebolt in phantom to illustrate how the fastener fits within the workpiece corresponding to minimum grip condition before installation; 
         FIG. 5  is a side elevational view similar to that of  FIG. 4  after an installation tool has been activated to rotate the corebolt such that the corebolt moves inwardly toward the workpiece, thereby pushing the sleeve inwardly against the workpiece; 
         FIG. 6  is a cross-sectional view taken generally along the lines  6 - 6  of  FIG. 5  and showing the installation phase of  FIG. 5 ; 
         FIG. 7A  is a side elevational view similar to that of  FIG. 5  and showing the body (in phantom) within the workpiece, wherein a thickness of the workpiece corresponds to a maximum grip condition; 
         FIG. 7B  is a cross-sectional view similar to that of  FIG. 6  and showing the installation phase and grip condition of  FIG. 7A ; 
         FIG. 8  is a cross-sectional view similar to that of  FIG. 7B  and showing the installation phase of  FIG. 7A  in a maximum grip condition after the pintail has separated; 
         FIG. 9A  is a top isometric view of a body for use with any of the fasteners disclosed herein; 
         FIG. 9B  is a cross-sectional view taken generally along the lines  9 B- 9 B of  FIG. 9A ; 
         FIG. 10A  is an isometric view of a nut for use with any of the fasteners disclosed herein; 
         FIG. 10B  is a cross-sectional view taken generally along the lines  10 B- 10 B of  FIG. 10A ; 
         FIG. 11A  is an isometric view of a corebolt for use with any of the fasteners disclosed herein; 
         FIG. 11B  is a side elevational view of the corebolt of  FIG. 11A ; 
         FIG. 12A  is a bottom isometric view of a frangible wrenching element for use in a further embodiment of a fastener; 
         FIG. 12B  is a cross-sectional view taken generally along the lines  12 B- 12 B of  FIG. 12A ; 
         FIG. 13  is an isometric view of a further embodiment of a fastener, with a body and sleeve having been removed therefrom; and 
         FIG. 14  is a cross-sectional view taken generally along the lines  14 - 14  of  FIG. 13 . 
     
    
    
     Other aspects and advantages of the present disclosure will become apparent upon consideration of the following detailed description, wherein similar structures have like or similar reference numerals. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a first embodiment of a fastener or blind bolt  30  in accordance with the present disclosure includes a generally cylindrical body  32  having a passage  34  disposed through a central portion of the body  32 . Also referring to  FIGS. 9A and 9B , an inner surface  36  of a wall  38  forming the passage  34  includes a non-threaded portion  40  at a first end  42  of the body  32  and a threaded portion  44  at a second end  46  of the body  32 . The non-threaded and threaded portions  40 ,  44  are separated by a shoulder portion  50 . The body  32  further includes a tapered ramp  52  disposed on an outer surface of the body  32  at the first end  42  and an enlarged head  54  is disposed at the second end  46  of the body  32 . As best seen in  FIG. 9A , a recess  56  with outwardly extending recesses  58  is disposed within the enlarged head  54 , as will be discussed in greater detail hereinafter. 
     A generally cylindrical corebolt  70 , as best seen in  FIGS. 1 ,  2 ,  11 A, and  11 B, is concentrically disposed within the passage  34  of the body  32 . As best seen in  FIGS. 11A and 11B , the corebolt  70  includes first and second end portions  73 ,  74  that are threaded and a central portion  76  disposed between the first and second end portions  73 ,  74  that is unthreaded. Each of the first and second end portions  73 ,  74  includes opposing flats  78 ,  80 , respectively. The threading of the first end portion  73  terminates at a shoulder portion  82  and a circumferential break groove  84  is disposed in a central portion of the corebolt  70  within the threading of the second end portion  74 . The second end portion  74  forms a pintail  86  that terminates at the break groove  84  and which is discarded upon completion of installation, as will be discussed in greater detail hereinafter. 
     Now referring to  FIGS. 1 and 2 , the fastener  30  further includes a deformable cylindrical sleeve  100  having a throughbore  102 . An inner surface  104  forming the throughbore  102  is generally cylindrical, although counterbores or internal tapered bores may also be incorporated as required by the specific application. A first end  106  of the sleeve  100  is positioned around the first portion  73  of the corebolt adjacent a nut  108  and a second end  110  of the sleeve  100  is positioned adjacent the first end  42  of the body  32 . As seen in  FIGS. 1 ,  2 ,  10 A, and  10 B, the nut  108  includes an inner cylindrical surface  112  forming a throughbore  114  and the nut  108  includes first and second ends  116 ,  118  with the entire surface  112  being threaded except at the second end  118 . The nut  108  is in threaded engagement with the first end portion  73  of the corebolt  70  with the second end  118  of the nut  108  bearing against the sleeve  100 . The nut  108  is secured to the first end portion  73  of the corebolt  74  such that a predetermined level of torque is required to begin threading the corebolt  70  through the nut  108 . 
     The nut  108  includes means for restricting relative motion between the nut  108  and the corebolt  70 . An example of such means includes crimping of the nut  108  to remove any gaps between opposing threads, thereby preventing rotation of the corebolt  70  and nut  108  with respect to one another until a predetermined level of torque is applied. In another embodiment, the means includes a portion of material  120  from the nut  108  displaced into one or more non-helical grooves  121  ( FIG. 11B ) within the threaded region of the corebolt  70 , for example, at a point just prior to the threading on the first end portion  73  (such as adjacent the non-threaded portion  40 ). The crimping of the nut  108  and/or displacement of a portion of material  120  from the nut  108  into the groove(s)  121  is sufficient to delay the onset of rotation relative to the corebolt and cause interference between the threaded first end portion  73  and the nut  108  due to mechanical distortion of the nut  108 . Other optional means include, but are not limited to, a chemical adhesive (see  122  in  FIG. 14 ) disposed in the threading of the first end portion  73  adjacent the nut  108  (or in the threading of the nut  108 ), chemical threadlockers, dimensional interference (see  124  in  FIG. 11B ) between the threads of one or both of the nut  108  and the corebolt  70  where the nut  108  is disposed on the corebolt  70  to prevent movement of the nut  108  along the corebolt  70 , and/or a deformation of the thread in the corebolt  70  and/or the nut  108  (see, for example,  126  in  FIG. 11B ) where the nut  108  is attached to the corebolt  70 . The deformation seen in  FIG. 10B  can be formed through crimping or by any other manner known in the art. 
       FIGS. 3 and 4  depict the fastener  30  of  FIGS. 1 and 2  inserted into two or more panels forming a workpiece  130 , wherein a thickness of the workpiece  130  corresponds to a minimum grip condition. The fasteners  30  disclosed herein can be inserted within and suitably installed within workpieces  130  having thicknesses ranging between a minimum grip thickness and a maximum grip thickness wherein maximum grip is generally defined as 1/16-inch more than minimum grip for a particular length fastener. When a minimum grip condition is referenced, it is meant that the fastener  30  is installed within a workpiece  130  having the minimum grip thickness for a particular length fastener. Similarly, when a maximum grip condition is referenced, it is meant that the fastener  30  is installed within a workpiece  130  having a maximum grip thickness.  FIGS. 5 and 6  depict the fastener  30  of  FIGS. 1 and 2  as the fastener  30  is installed within the workpiece  130  and prior to detachment of the pintail  86  of the corebolt  70 . The fastener  30  is installed using blind bolt installation tools as are known in the art. The workpiece  130  is generally comprised of two or more sheets, or panels of material, or two or more structural elements. Before installation of the fastener  30  within the workpiece  130 , the fastener  30  is inserted into aligned apertures in the panels forming the workpiece  130  (see  FIGS. 3 and 4 ). The corebolt  70  is thereafter rotated while the body  32  is rotationally restrained, thereby causing the nut  108  to move toward the workpiece  130 . Movement of the nut  108  toward the workpiece  130  forces the sleeve  100  up the tapered ramp  52  disposed at the first end  42  of the body  32  and along a shank  140  of the body  32  into contact with an inner surface  142  of the workpiece  130 , as seen in  FIGS. 5 and 6 . Further rotation of the corebolt  70  compresses the sleeve  100  against the workpiece  130  to form a blind head  144 , as further seen in  FIGS. 5 and 6 . The torque required to continue rotation of the corebolt  70  greatly increases after the blind head  144  has been completely formed and compressed against the workpiece  130 . 
     Further rotation of the corebolt  70  causes the second end portion  74  of the corebolt  70  to thread through the nut  108 , while the second end  118  of the nut  108  remains stationary against the first end  106  of the sleeve  100 . Threading of the corebolt  100  through the nut  108  continues until the shoulder portion  82  of the corebolt  70  abuts the shoulder portion  50  of the body  32 , as seen in  FIGS. 7 and 8 , whereupon the torque required to continue threading the corebolt  70  through the body  32  and the nut  108  exceeds the failure torque at the break groove  84  and causes the pintail  86  to break free from the fastener  30 . Referring to  FIGS. 2 ,  8 ,  9 B, and  11 B, a distance X between the shoulder  50  of the body  32  and an outer surface  145  of the enlarged head  54  of the body  32  is approximately equal to or slightly less than a distance Y between the shoulder portion  82  and the break groove  84  of the corebolt  70 . During installation, when the shoulder portion  82  of the corebolt  70  abuts the shoulder  50  of the body  32 , the corebolt  70  stops advancing and the pintail  86  breaks off flush with, or slightly above, the outer surface  145  of the enlarged head  54 . 
     During installation of the fastener  30 , the body  32  is restrained from rotating with the corebolt  70  such that the corebolt  70  will advance upwardly through the body  32 . As described above, the body  32  is rotationally restrained through engagement of the outwardly extending recesses  58  in the enlarged head  54  of the body  32  by protrusions on a non-rotation component of the installation tool, as is well known in the art. Other means for rotationally restraining may be employed, including but not limited to, a separate disposable drive nut, as taught in U.S. Pat. No. 4,967,463, a frangible wrenching member, as taught in U.S. Pat. No. 2,282,711, or simply relying on a press fit between the shank  140  of the body  32  and apertures in the workpiece  130 . 
     In an alternative embodiment, as seen in  FIGS. 12A and 12B , similar to the embodiment of  FIGS. 1 and 2 , the body  32  is replaced by an element  200  having a body  202  similar to the body  32  and an integral frangible wrenching element  204  that may be broken off after installation. The frangible wrenching element  204  is formed as a frangible nut that includes a wrenching region  206  that is used to rotationally restrain the body  202  during installation. The wrenching element  204  may include a break groove  208  sized to allow the wrenching element  204  to be severed from the body  202  upon completion of installation. For example, the wrenching element  204  may be removed after installation with a standard wrench or by twisting the installation tool. The break groove  208  would need to be sized to withstand the reaction torque of installation (which is approximately equal to the torque required to bring the sleeve  100  in contact with the workpiece  130 ). 
       FIGS. 13 and 14  depict a further alternative embodiment of the corebolt and nut that is similar to the embodiment of  FIGS. 1 and 2 , except that the nut  108  is attached to the corebolt  70  in a different manner. In particular, an area of reduced diameter  220  is disposed between the first end portion  73  and the central non-threaded portion  76  of the corebolt  70 . The nut  108  is deformed at one or more deformations  222  into the area of reduced diameter  220  to retain the nut  108  on the corebolt  70  and prevent rotational movement of the nut  108  with respect to the corebolt  70 . 
     Any of the embodiments described herein may be modified to include any of the structures or methodologies disclosed in connection with other embodiments or disclosed generally herein. 
     Further, although directional terminology, such as upper, lower, etc. may be used throughout the present specification, it should be understood that such terms are not limiting and are only utilized herein to convey the orientation of different elements with respect to one another. 
     Numerous modifications to the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out same. The exclusive rights to all modifications which come within the scope of the appended claims are reserved.