Abstract:
A blind fastener for insertion through an aperture in a workpiece, the fastener including a pin, a sleeve and an abutment member; wherein the abutment member can be removed from the sleeve so that the pin and sleeve can be forced out of the aperture, to remove the fastener therefrom, wherein the sleeve has a radially expanding head, which is received in a recess of the abutment member and wherein, prior to insertion of the fastener into the workpiece aperture, the abutment member is secured to the sleeve by deformation of part of the abutment member adjacent the recess over and into contact with the sleeve head.

Description:
RELATED/PRIORITY APPLICATION 
     This application is a National Phase filing regarding International Application No. PCT/GB2004/002042, which relies upon British Application Nos. 0311053.3 and 0311368.5 for priority. 
     TECHNICAL FIELD 
     The invention relates to a blind fastener, that is, one which can be installed by access to one side only of a workpiece. More particularly the invention relates to a blind fastener of the type comprising a pin, a sleeve, and an abutment member. In use of the fastener in a workpiece comprising two or more members to be secured together, the pin and sleeve are inserted through an aperture in the workpiece so that their remote end portions protrude beyond the remote or blind face of the workpiece. The application of axial compression to the sleeve by means of a pulling force on the pin with respect to the sleeve causes the protruding end portion of the sleeve to deform into a blind head which contacts the blind face of the workpiece. The workpiece is then compressed between the blind head and the abutment member and the abutment member is then secured to the pin e.g. by swaging, to secure the workpiece members together in the compressed condition. 
     BACKGROUND ART 
     There are alternative possible ways of providing the necessary mechanical engagement between the various component members of the fastener. The remote end of the pin may have a radially protruding head which contacts the end of the sleeve to apply compressive force to it, or the remote end of the pin may be in threaded engagement with the sleeve. 
     The abutment member is secured to the near end of the sleeve, to enable correct insertion of the fastener into the aperture through the workpiece. 
     One such fastener is that commercially available under the trade mark “HUCK BOM”, which is described in U.S. Pat. No. 2,527,307. In this fastener, the abutment is in the form of a radially enlarged head integral with the sleeve. 
     In use, it is sometimes found that it is necessary to remove a fastener which has been installed in a workpiece, e.g. for servicing or repairing the equipment of which the workpiece forms a part. It is extremely difficult to do this, since the abutment member is swaged on to the pin, and is integral with the sleeve. The pin is too hard to drill out. In any event, it is unacceptable for removal of the fastener to cause damage to the adjacent part of the workpiece. 
     The present invention is intended to provide a fastener of this type which can, if needed, be removed more easily and conveniently. 
     DISCLOSURE OF INVENTION 
     The invention provides, in one of its aspects, a blind fastener for insertion through an aperture in a workpiece, the fastener comprising a pin, a sleeve and an abutment member; the pin extending inside the sleeve and engaging therewith at or near a first end of the sleeve; the sleeve having a radially expandable portion; the abutment member being adjacent the second end of the sleeve and projecting radially therefrom and the pin extending beyond the abutment member; whereby, when the sleeve is inserted into a suitable aperture in a workpiece of suitable thickness with the expandable portion of the sleeve protruding beyond the blind or remote face of the workpiece, and when a progressively increasing pulling force is applied to the part of the pin extending beyond the abutment member, the pulling force being supported against the abutment member, so that axial compression is applied to the sleeve between the abutment member and its engagement with the pin, the radially expandable part of the sleeve to radially expand to form a blind head in abutment with the remote face of the workpiece; thereby to apply compression to the workpiece between the blind head and the abutment member; and thereafter the abutment member can be secured to the pin; in which the abutment member is removable secured to the sleeve by means sufficiently strong to allow handling of the assembled fastener to be inserted in the aperture in the workpiece and installed therein, but sufficiently weak to allow the abutment member to be removed from the sleeve so that the pin and sleeve can be forced out of the aperture on the workpiece, to remove the fastener therefrom. Further features of the invention are a fastener in which the sleeve and abutment member are separate members and the removable securing means comprises deformation of at least one of them into engagement with the other; a fastener in which the sleeve has a radially extending head, the rim being insufficiently strong to prevent the sleeve being driven through the aperture, the abutment member has a corresponding recess in which the sleeve head is received, and part of the abutment member adjacent the recess is deformed over and into contact with the sleeve head; and a fastener in which the abutment member is deformed as aforesaid at a plurality of positions spaced apart around the sleeve head. The invention includes a method of removing a fastener from a workpiece which has been installed in the workpiece as aforesaid, which method comprises removing the abutment member from the sleeve, and then removing the pin and the sleeve through the blind side of the aperture. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       A specific embodiment for the invention will now be described by way of example and with reference to the accompanying drawings, in which: 
         FIG. 1A  is an outside elevation of the pin; 
         FIG. 1B  is an axial section through the sleeve; 
         FIG. 1C  is an axial section through the abutment member; 
         FIG. 2A  shows those three parts assembled to form a fastener ready for installation; 
         FIG. 2B  is an enlargement of part of  FIG. 2A ; 
         FIG. 2C  is a plan view on  FIG. 2A ; 
         FIG. 3A  is a section through a fastener inserted in an aperture in a workpiece, ready for installation therein, together with an enlargement of a detail thereof; 
         FIGS. 3B and 3C  are similar to  FIG. 3A  but show other possible conditions which will be described below; 
         FIGS. 4A ,  4 B,  5 A,  5 B,  6 A and  6 B are similar to  FIG. 3A , and show successive stages of the installation of the fastener; and 
         FIGS. 7A ,  7 B,  7 D,  8 A,  8 B and  8 C show successive stages of the removal of an installed fastener from the workpiece,  FIG. 7C  being a section on the line C-C of  FIG. 7B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The pin, sleeve and abutment member all have circular symmetry. 
     The pin  11  ( FIG. 1A ) is of medium carbon alloy steel and comprises an elongated cylindrical shank  12  with an integral radially enlarged head  13  at one end of the shank, by means of which the pin engages with one end of the sleeve. Adjacent the head  13  the pin shank has a slightly oversize portion  20  formed with longitudinal ribs  30 . Next to this portion  20  is a plain portion  14 , followed by a locking groove portion  15  and then a breakneck  16  which is the weakest part of the pin. Next to this there is another plain portion  17 , followed by a pulling groove portion  18  which grooves are for engagement by the jaws of the fastener installation tool. 
     The sleeve  21  ( FIG. 1B ) is generally cylindrical and is made of low carbon steel. It has a through bore  22  of uniform diameter which is a sliding fit on the pin shank  12 , and a cylindrical shank  23  which is of uniform external diameter. At one end (the tail end) the sleeve shank has a flat end face  24  and at the other end (the head end) an integrally formed slightly radially enlarged head  25 . The sleeve head comprises a flange  26  having a conical underhead face  27 . As illustrated in  FIG. 1B , the head has a flat top face  29 . 
     The sleeve shank includes a radially expandable portion which is centred on a softened zone  19  which, as indicated in  FIG. 1B , in this example extends axially from a position about halfway along the length of the sleeve shank  21  to a position about three quarters of the way from the sleeve head  26  towards the sleeve tail  24 . In this example, this softened portion  19  is made softer than the remainder of the sleeve by band annealing. It has a through bore  22  which is an interference fit on enlarged portion  20  of the pin shank  12 . 
     The abutment member ( FIG. 1C ) is in the form of a collar  32  made of medium carbon steel. The peripheral edge of one end of the collar has a bevel  34 , whilst the other end has a radially projecting flange  35 . That end face  36  is flat, but is annular, since it is provided with a recess  37 , which is generally circular on the axis of the collar. The outer recess  37  is of a diameter and depth suitable to receive the head flange  26  of the sleeve, having an annular bottom face  41  which surrounds the recess  37 . The axial depth of the recess  37  is rather greater than the total axial thickness of the sleeve head  26 . 
     The pin, sleeve and collar are assembled together to form a fastener in the way illustrated in  FIGS. 2A ,  2 B and  2 C. The sleeve is assembled on the pin shank  12  so that the sleeve end face  24  abuts the annular face of the pin head  13 , there being an interference fit between the ribbed oversize portion  20  of the pin and the tail end portion of the sleeve  21  beyond the softened zone  19 . The collar  32  is then assembled on to the sleeve by inserting the sleeve head flange  26  into the collar recess  37  so that the sleeve head end face  29  contacts the annular face  41  of the collar recess. The sleeve and collar are then removably secured together by staking down the collar head adjacent the recess  37  at three positions around the periphery of the recess, to deform the head material at those positions over and into contact with the conical face  27  of the sleeve head, to form three lugs or projections  38 . The pin plain portion  17  protrudes from the end face of the collar  32 . 
     As illustrated in  FIG. 3A , the fastener is used to secure together two structural metal panels  42 ,  43  which have a cylindrical aperture  44  through them in which the sleeve  21  is a clearance fit. The total thickness of the workpiece formed by the panels  42  and  43  is rather more than half of the length of the sleeve shank  23 , so that the nearer end of the sleeve softened zone  19  indicated in  FIG. 1B  lies inside the remote face  46  of the workpiece when the underhead face  36  of the collar contacts the near face  45  of the workpiece. 
     As illustrated in the enlarged detail of  FIG. 3A , the staked lugs  38  which contact the sleeve head flange  26  are undisturbed and continue to hold the sleeve and collar together. 
     If however there is resistance to the insertion of the fastener sleeve into the aperture  44  on the workpiece (e.g. because the aperture  44  is undersize and produces an interference fit, or the two parts of the aperture  44  are mis-aligned not shown in  FIGS. 3B and 3C ), then it may be necessary to use force to insert the fastener, by axial force on the pin, as illustrated by the arrow B in  FIG. 3B , e.g. by applying hammer blows to the projecting tail end of the pin. It is possible that this maybe sufficient to deform the staking lugs  38  in the way shown at  39  in  FIG. 3B  and its enlargement. The sleeve moves so that its head  26  contacts the near face  45  of the workpiece, the radial extent of the head  26  and its strength being sufficient to hold the sleeve in this position. 
     If a very large axial force has to be applied to the pin to make the sleeve enter the aperture, it is possible that the retaining force between the pin and sleeve, due to the interference fit between them at portion  20  of the pin, may be overcome, so that the pin moves axially through the sleeve and the interference portion  20  protrudes from the tail end of the sleeve, as illustrated in  FIG. 3C . Provided that sufficient of the pin pulling groove position  18  remains outside the collar  32 , it would still be possible to install the fastener in the way to be described below, but this might require two successive actuations of the installation tool. 
     If the pin is pushed too far into the sleeve, it cannot be installed, and the pin can be knocked completely through the sleeve. The collar can then be lifted off (since its connection to the sleeve has already been broken), and the sleeve punched through and out of the workpiece aperture. Alternatively the uninstalled fastener can be extracted by gripping and pulling the pin or the sleeve. 
     A fastener which has been inserted in a workpiece in the normal way as illustrated in  FIG. 3A  is now installed by applying a progressively increasing pull to the protruding part of the pin  11  in relation to the sleeve  21 . This is done by means of a standard hydraulically-powered fastener placing tool, such as that commercially available under the designation AVDEL (Registered Trade Mark) Type 722, which is used for installing pin and collar type fasteners previously referred to. 
     The tool includes an annular anvil  47  ( FIG. 4A ) having an internal throat  48  shaped appropriately to swage the collar  32 . The tool also includes jaws  49  which engage with the pulling grooves in the portion  18  of the pin, and a hydraulic piston and cylinder device (not shown) for applying a progressively increasing retraction force to the jaws with respect to the anvil. Such tools and their manner of use are well known to those who use blind fasteners, and need not be described in detail here. 
     The tool is offered up to the protruding part of the pin, so that the outer end of the anvil throat contacts the top of the collar  32  around its bevel  34 , as illustrated in  FIG. 4A . The tool is then actuated so that its jaws engage the pulling groove portion  18  of the pin and exert a progressively increasing pull on it with respect to the anvil  47 . The reaction force is transmitted through the collar  32  to its end face  36  against the workpiece, and thence via the annular face  41  face of the collar to the sleeve head  25 . If, during insertion of the fastener into the aperture, the sleeve head  25  has moved away from the collar annular face  41 , it will be pulled back into contact with it. The sleeve is thus axially compressed between the face of the head flange  26  and its end face  24  in contact with the pin head  13 . The softened portion of the sleeve deforms by bulging outwardly, to progressively form a blind head in contact with rear face  46  of the workpiece. As the blind head progressively forms (See  FIG. 4B ), it exerts a compressive force on the rear face  46  of rear panel  43 , which urges the panels  42 ,  43  together (and so closes any gap which may exist between them) so that the panels are firmly in contact with each other and compressed together between the collar end face  36  and the blind head. The final form of the blind head, in this example, is illustrated at  49  in  FIG. 5A . 
     As the force applied by the tool further increases, the anvil  47  is pushed down over the exterior of the collar, so that the anvil throat  48  swages the collar  32  radially inwardly into the locking grooves  15  on the pin. The anvil stops with its lower face near the flange at the bottom of the collar. This position is illustrated in  FIG. 5B . 
     Further increase of the force applied by the tool causes the pin to break at the breakneck  16 , the broken off pin tail being pulled away by the jaws, leaving a broken surface  52 , as illustrated in  FIG. 6A . The tool is then removed, to leave the installed fastener, as illustrated in  FIG. 6B . 
     As previously mentioned, the fastener described above is advantageous in that an installed fastener can, if needed, be removed from the workpiece relatively easily. 
       FIG. 7A  shows a pair of bolt cropper blades  51  being offered up to the collar  32 . These are located fully over the swaged collar, on a diametrical plane thereof, and the tool actuated to force the blades together so that they substantially cut the collar in half, as illustrated in  FIGS. 7B and 7C . 
     The two halves of the collar may remain connected together by thin pieces of its material, in which case the two halves of the collar can be separated and removed by a hammer and chisel or a power chisel, leaving the pin and sleeve in the workpiece as shown in  FIG. 7D . 
     The pin and sleeve can then be removed from the workpiece, and this is conveniently done by using a single two-stage punch  52 , as illustrated in  FIGS. 8A ,  8 B and  8 C. The punch comprises a leading narrower part  53  of appropriate diameter to enter the sleeve and push the pin, and a following wider part  54  having a diameter appropriate to enter the workpiece aperture, joined to the narrower part  53  by an annular face  55  appropriate to contact the sleeve head face. As shown in  FIG. 8A , the punch portion  53  is offered up to the end of the fastener pin, and axial force applied by hammering, to break the interference fit between the pin and sleeve and drive the pin through the sleeve until the punch annular face contacts the sleeve head face  29 , as shown in  FIG. 8B  including its enlarged detail. Application of further force to the punch deforms the outer peripheral part of the sleeve head flange  26 , as shown in  FIG. 8C  and its enlarged detail (in some cases, the outer peripheral part may be sheared off). Further movement of the punch drives the sleeve and pin through the far end of the workpiece aperture, thus removing the installed fastener. 
     It will be apparent that, in order for the fastener to be installed and removed in the way described above, there must be the correct relationship between the various axial forces needed to separate various components. Thus, the axial force needed on the sleeve to separate it from the collar (by overcoming the staked lugs  38 , as described with reference to  FIG. 3B ) must be less than the axial force needed to overcome the interference engagement between the pin and sleeve (as described with reference to  FIGS. 3C and 8B ), which in turn must be less than the force needed to push the sleeve head through the aperture (as described with reference to  FIG. 8C ). 
     The three measured force values for an example fastener of sleeve outside diameter 10 mm are respectively 900 Newtons, 1900 Newtons, and between 6000 Newtons (for an aperture of maximum diameter in which sleeve head folds up,  FIG. 8C ) and 9000 Newtons (for an aperture of minimum diameter). 
     The invention is not restricted to the details of the foregoing example. For instance, the sleeve and the abutment collar could be releasably connected to each other by any convenient arrangement.