Abstract:
There is provided a peel type blind rivet ( 22 ) for securement in an aperture of a workpiece, the rivet comprising a tubular shell ( 24 ) having a flange ( 26 ) at one thereof, this shell housing a mandrel stem ( 28 ) with a mandrel head ( 30 ) disposed at one end of the mandrel stem so as to abut a remote end of the tubular shell, the mandrel head ( 30 ) having a plurality of edges extending radially outwards therefrom which, in operation when the mandrel is subjected to a tensile load engage with the remote end of the shell so as to split the shell into a plurality of segments ( 40 ) to engage the blind side of the workpiece, whereby the stem of the mandrel further comprises at least one protrusion ( 38 ) about which the shell of the rivet body deforms during setting to retain the mandrel head ( 30 ) within the set rivet.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to a blind rivet, and more especially to a peel type blind rivet.  
         BACKGROUND OF INVENTION  
         [0002]    Blind rivets are set in an aperture in one or more application pieces from one side of the application piece. A blind rivet typically comprises an outer tubular shell flanged at one end, and a mandrel, having a stem and a radially enlarged head at one end of the shell. The periphery of the radially enlarged head of the mandrel is the same size or slightly smaller than the periphery of the rivet shell, so that both parts can be inserted together into the application piece(s) from the front side. The rivet shell is positioned in the aperture of the application piece(s) with the flanged end on the operator side, and the mandrel stem extends into the tubular shell so that its enlarged head is on the blind side of the application piece(s). During the rivet setting process, the flange of the rivet shell is supported by a setting tool, and the stem of the mandrel is subjected to tensile loading by the tool, and thereby pulled through the shell of the rivet until the enlarged head of the mandrel contacts the remote end face of the tubular shell of the rivet. Further tensile loading of the mandrel stem then causes the remote end of the shell to collapse in some way into contact with the blind side of the application piece(s). The manner of collapse of the remote end of the shell depends on the type of rivet. The application piece(s) are thereby firmly gripped between the collapsed remote end of the rivet shell and the front flange of the rivet shell.  
           [0003]    In a known peel type blind rivet, the enlarged mandrel head is typically provided with a number of edges, typically four edges, beneath the mandrel head. The effect of this is that during the setting process the remote end of the rivet shell is split into segments or petals (the number of segments or petals corresponding to the number of edges beneath the mandrel head). The segments or petals spread out on the blind side of the application piece(s) to make a broad bearing area onto the back face of the application piece(s). Therefore in peel type rivets the manner of collapse of the remote end of the shell is by splitting into segments or petals, which peel back into contact with the blind side of the application piece(s).  
           [0004]    In known peel type blind rivets, on completion of the setting process the tensile loading is at its highest causing the mandrel stem to break (it is usually necked to enhance this break). This results in a release of strain energy. The release of energy causes the mandrel head part, which was temporarily lodged in the end of the peeled back shell, to be dislodged from its position, and to move in the opposite direction to that which it was previously pulled. Therefore the mandrel head and the remaining part of the mandrel shank are ejected from the rivet shell.  
           [0005]    There are instances where the ejection of the mandrel head from the peel type blind rivet is undesirable. For example ejection would be undesirable where the rivet is being installed in the proximity of moving parts, or where electrical equipment is installed.  
           [0006]    It is known from GB-A-2351538, in another type of blind rivet (a self plugging blind rivet), to provide a means to retain the mandrel head in the set blind rivet. According to this reference the stem of the mandrel is provided with a plurality of axial recesses, and each recess has a protrusion or bar member formed on it. When the rivet is set the shell deforms in a region adjacent the recess and surrounds each protrusion or bar member.  
           [0007]    The present invention aims to provide a peel type blind rivet with means substantially to prevent the ejection of the mandrel head portion from the set shell, and means for retaining the mandrel head in the rivet shell body.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a peel type blind rivet for securement in an aperture in one or more application pieces, the rivet comprising:  
           [0009]    a tubular shell having a flanged front face and a remote end;  
           [0010]    a mandrel having an enlarged head end having a plurality of edges beneath the head, and a stem extending from the enlarged head, the stem being arranged to pass through the tubular shell so that the enlarged head of the mandrel is on the blind side of the application piece(s),  
           [0011]    the stem comprising one or more protrusions from a surface thereof;  
           [0012]    wherein during the setting process of the rivet the stem of the mandrel is subjected to tensile load whereby the edges beneath the enlarged head of the mandrel cause the remote end of the shell to split into a plurality of segments that engage the blind side of the application piece(s), and the shell of the rivet body deforms around the protrusion(s).  
           [0013]    The deformation of the rivet body shell around the protrusion means that the mandrel head is retained in the shell.  
           [0014]    Preferably a plurality of protrusions spaced around the periphery of the mandrel are provided. These may be at the same longitudinal location along the mandrel stem or spaced longitudinally along the stem. Preferably one or more pairs of diametrically opposed protrusions are provided.  
           [0015]    Preferably the mandrel stem comprises a pre-necked portion, whereby during the setting process of the rivet the stem of the mandrel is subjected to tensile load and the stem breaks at the said pre-necked portion. In this case there is an ensuing release of strain energy at the instant of mandrel break time, and it is an advantage of the invention that the mandrel head can be retained by the protrusions in the shell against the opposing force generally operating to urge it against the direction it was previously pulled prior to mandrel break.  
           [0016]    Preferably the portion of the mandrel stem between its enlarged head portion and its pre-necked portion defines a head-shaft portion, and the protrusion(s) are located on a surface of the head-shaft portion. Such a head-shaft portion is typically 3-5 mm long, preferably about 4 mm long. Such a head-shaft portion may be any shape in cross-section. In one preferred embodiment the head shaft portion is circular in cross-section. The remainder of the stem may be any shape in cross-section, but is preferably circular in cross-section. Where both the head-shaft portion and the remainder of the mandrel stem is circular in cross-section the head-shaft portion is preferably the same diameter as the remainder of the mandrel stem, but could be smaller, or even larger. In another preferred embodiment the head-shaft portion is rectilinear, preferably square, in cross-section. Advantages of a rectilinear, especially square cross-sectioned head shaft portion is lower cost tooling to manufacture the mandrel, and the fact that the edges of the rectilinear cross-sectioned head-shaft portion help to keep and guide the mandrel head in a central position in the rivet during setting. Where a square cross-sectioned head-shaft portion is used in combination with a remaining stem portion that is cylindrical, the longitudinal edges of the head-shaft portion are preferably in line with the sides of the cylindrical remaining stem portion.  
           [0017]    The protrusion on the stem of the mandrel may be any shape, as would be apparent to the man skilled in the art, to retain the mandrel head in the rivet body. In one embodiment the protrusion(s) comprises a bulge on a surface of the stem of the mandrel. Bulged protrusions are particularly appropriated for use with circular cross-sectioned mandrel stems, but can be used on any shaped mandrel stem. In another embodiment the protrusion(s) comprise a bar member extending across a surface of the mandrel head shaft or, stem, preferably in a direction perpendicular to the axis of the rivet. Bar-shaped protrusions are particularly appropriate for use with rectilinear-, especially square-cross-sectioned mandrel stems, but can be used on any shaped mandrel stem. Combinations of different shaped protrusions may also be used.  
           [0018]    Preferably two protrusions are provided, located in opposed positions around the mandrel stem periphery, for example in diametrically opposed positions.  
           [0019]    In another embodiment four protrusions are provided; a first pair of protrusions being located in opposed positions around the mandrel stem periphery in a first plane, and a second pair of protrusions being located in opposed positions around the mandrel stem periphery in a second plane, the second plane being 90° from the first plane. In this embodiment the second pair of protrusions is preferably longitudinally spaced from the first pair of protrusions along the stem of the mandrel.  
           [0020]    Indentations may also be provided around the periphery of the rivet mandrel stem, preferably between the protrusions. These preferably accept deformed shell material during the setting process.  
           [0021]    Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1A is a longitudinal section through a peel type blind rivet according to the prior art, prior to setting;  
         [0023]    [0023]FIG. 1B is a longitudinal section through the rivet of FIG. 1A, after setting;  
         [0024]    [0024]FIG. 2A is a longitudinal section through a first embodiment of peel type blind rivet according to the invention, prior to setting;  
         [0025]    [0025]FIG. 2B is a longitudinal section through the rivet of FIG. 2A, after setting;  
         [0026]    [0026]FIG. 2C is a cross-sectional view along line A-A of FIG. 2B;  
         [0027]    [0027]FIG. 3A is a longitudinal section through a second embodiment of peel type blind rivet according to the invention, prior to setting;  
         [0028]    [0028]FIG. 3B is a longitudinal section through the rivet of FIG. 3A, after setting;  
         [0029]    [0029]FIG. 3C is a cross-sectional view along line A-A of FIG. 3B;  
         [0030]    [0030]FIG. 3D is a cross-sectional view along line B-B of FIG. 3B;  
         [0031]    [0031]FIG. 4A is a longitudinal section through a third embodiment of peel type blind rivet according to the invention, prior to setting;  
         [0032]    [0032]FIG. 4B is a longitudinal section through the rivet of FIG. 4A, after setting;  
         [0033]    [0033]FIG. 4C is a cross-sectional view along line A-A of FIG. 4B;  
         [0034]    [0034]FIG. 5A is a longitudinal section through a fourth embodiment of peel type blind rivet according to the invention, prior to setting;  
         [0035]    [0035]FIG. 5B is a longitudinal section through the rivet of FIG. 5A, after setting;  
         [0036]    [0036]FIG. 5C is a cross-sectional view along line A-A of FIG. 5B; and  
         [0037]    [0037]FIG. 5D is a cross-sectional view along line B-B of FIG. 5B. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Referring to FIGS. 1A and 1B, these show a peel type rivet according to the prior art, before and after setting respectively. From FIG. 1A, it can be seen that the known rivet  2  comprises an outer cylindrical shell  4  having a flanged head  6 . The flanged head  6  is on the front operator side of the application pieces when the rivet is set. The rivet  2  also comprises a mandrel having a solid cylindrical stem  8  terminating at its remote end with an enlarged head  10 . The underside of the enlarged head  10  of the mandrel has four cut edges  12  (two are visible in FIG. 1). The stem  8  of the mandrel is pre-necked by the inclusion of four indented portions  14  around the circumference of the stem at a predetermined distance along the length of the stem  8 .  
         [0039]    [0039]FIG. 1B shows the rivet  2  of FIG. 1 after setting. The rivet  2  comprising the shell and mandrel is placed from the front into aligned apertures in two application pieces  16  and  18 , and then during the setting process a tensile load is applied to the mandrel stem  8  pulling it towards the front of the application pieces (i.e. downwards in the Figures). During this process the edges  12  beneath the mandrel head  10  cause the remote end of the shell  4  to split into four segments or petals  20 , which spread out against the blind side of the application pieces  16 ,  18 , whereby the pieces  16  and  18  are held together between the spread petals  20  and the shell flange  6 . On completion of the setting process, when the tensile loading is at its maximum, the mandrel stem  8  breaks at the pre-necked portion  14 , and the ensuing release of energy causes the mandrel head  10  to be ejected from the rivet body.  
         [0040]    FIGS.  2  to  5  show peel type blind rivets according to the invention.  
         [0041]    In FIG. 2A a blind rivet  22  according to a first embodiment is shown prior to setting. It comprises a tubular shell  24  having a flanged end  26 . A mandrel having a stem  28 , with a pre-necked portion  34 , and an enlarged head  30  the underside of which presents four cut edges  32 , is provided. The length of the mandrel stem between the enlarged head  30  and the pre-necked portion  34  defines a head-shaft portion  35 , which is about 4 mm long. The head shaft portion  35  is generally cylindrical, i.e. circular in cross-section and includes two protrusions in the form of diametrically opposed bulges  36  on the cylindrical surface of the head-shaft portion, and two diametrically opposed recesses  38  in the form of flat planes cut into the outer surface of the cylindrical head-shaft portion  35 . The two bulges  36  and the two recesses  38  are at the same longitudinal point along the head-shaft portion  35  circumferentially spaced between each other. The cylindrical head-shaft portion has the same diameter as the rest of the mandrel stem  28 .  
         [0042]    [0042]FIGS. 2B and 2C show the blind rivet of FIG. 2A after setting. As in the prior art rivet of FIG. 1, the edges  32  of the head  30  of the mandrel cause the remote end of the shell  24  to split into four petals  40  to spread along the blind side of the application pieces  16 ,  18 . In this case, however, the applied tensile force has also caused the material of the shell  24  to be deformed around each of the bulges  36  and into each of the indented recesses  38 . This deformation of the material of the shell  24  can be seen by comparing the forward sloping hashed section of FIG. 2C with the dotted outline. In FIG. 2C, and also in FIGS. 3C, 3D,  4 C,  5 C, and  5 D the forward sloping hashed section show the shell position after setting, and the dotted outline shows the shell position prior to setting.  
         [0043]    In contrast to the prior art, in this case, on completion of the setting process, when the tensile loading is at its maximum, the mandrel stem  28  breaks at the pre-necked portion  34  as before, but the ensuing release of energy is not able to eject the mandrel head  30  from the rivet body  24  since the head shaft portion connected to the mandrel head  30  is held firmly in place by the deformed shell material that has moved around the bulges  36  and into the indentations  38  of the mandrel stem  28 . Also the radially outward deformation at points  39  urges the shell  24  into close conformity with at least part of the inner surface of the apertures in application pieces  16 ,  18 .  
         [0044]    [0044]FIGS. 3A to  3 D show a second embodiment of rivet according to the invention. Like parts are given like reference numerals compared to the first embodiment of FIG. 2. In common with the FIG. 2 embodiment, the head-shaft portion  35 ′ of the mandrel stem  28  is generally cylindrical, i.e. circular in cross-section, and has the same diameter as the rest of the mandrel stem  28 . However, in addition to the bulges  36  and indentations  38  present in the first embodiment of rivet according to FIG. 2, the head shaft portion  35 ′ of the FIG. 3 embodiment also comprises a second pair of diametrically opposed bulges  46  and diametrically opposed indentations  48 . The second pair of bulges and indentations  46 ,  48  are longitudinally spaced from the first pair of bulges and indentations  36 ,  38 . Also the bulges  36  are in the same plane as the indentations  48  and the indentations  38  are in the same plane as the bulges  46 . Looking in particular at the cross-sectional views of FIGS. 3C and 3D it can be seen that material from the shell  24  is therefore urged outwards, and hence into conformity with the apertures in the application pieces  16 ,  18 , at four points  41  around the circumference of the head shaft portion  35 ′, and that shell material is urged around four bulges and into four indents. Securement of the mandrel head portion  30  and head shaft portion  35 ′ in the shell, and the rivet in the application pieces  16 ,  18 , is therefore enhanced compared to the embodiment of FIG. 2.  
         [0045]    FIGS.  4 A-C show a third embodiment of blind rivet according to the invention. As before like reference numerals refer to like parts compared to the earlier embodiments. In this case the head-shank portion  35 ″ of the mandrel is square in cross-section. It comprises two protrusions in the form of diametrically opposed bars  50  extending across opposed faces  51  of the square cross-sectioned head shank  35 ″. The bars  50  extend across the faces  51 , in a direction perpendicular to the axis of the mandrel. The two intervening faces of the square cross-sectioned head shank portion  35 ″ are referenced  52  in FIGS.  4 A-C. During the setting process shell material is deformed around the bars  50  and into the recesses presented by the faces  51  around the bars  50  and into the recesses presented by faces  52 . This material deformation thereby prevents ejection of the mandrel head  30  during the setting process. The material also deforms outwards at points  54  (see FIG. 46). The deformation at points  54  causes the rivet shell  24  to be urged into contact with the inner surface of the apertures in the application pieces  16 ,  18 .  
         [0046]    FIGS.  5 A-D show a fourth embodiment of blind rivet according to the invention. As before like reference numerals refer to like parts compared to the earlier embodiments. As in the embodiment of FIG. 4, the head-shank portion  35 ′″ of the mandrel is square in cross-section. However in this case it comprises not only the two diametrically opposed bars  50  extending across opposed flat faces  51  of the square cross-sectioned head shank  35 ′″, but also a second pair of diametrically opposed bars  56  extending across the other diametrically opposed flat faces  52  of the square cross-sectioned head shank  35 ′″ in a direction perpendicular to the rivet axis. Each pair of bars  50 ,  56  is longitudinally spaced from the other pair of bars  54 ,  56 . Looking in particular at the cross-sectional views of FIGS. 5C and 5D. it can be seen that material from the shell  24  is therefore urged outwards, and hence into conformity with the apertures in the application pieces  16 ,  18 , at four points  62  around the circumference of the head shaft portion  35 ′″, and that shell material is urged around four bars  50 ,  56 , and against the flat faces  51  and  52  around and between the bars  50  and  56 . Therefore securement of the mandrel head portion  30  and head shaft portion  35  in the shell  24 , and securement of the rivet shell  24  in the application pieces  16 ,  18  is enhanced compared to the embodiment of FIG. 4.  
         [0047]    While the above description constitutes the preferred embodiment(s), those skilled in the art will appreciate that the present invention is susceptible to other modifications and changes without departing from the proper scope and fair meaning of the following claims.