Self plugging blind rivet

Abstract: A self plugging blind rivet (i.e. one in which at least a portion of the stem remains in the shell after installation so that the shell bore is thereby plugged) has a stem having a shank (26) which is provided with an annular shoulder (38) which, when the stem is drawn into the shell, engages with an annular shoulder in the shell bore to deform material of the shell into the space between the stem shoulder (38) and a radially projecting locking ring on the stem shank, so as to look the stem into the shell. The locking ring of this rivet is formed of two part-circular portions (34, 34′) separated by gaps (36). These gaps allow deformed material of the shell to flow through them if necessary, thereby enabling the stem to be drawn further into the shell. This extends, at its lower end, the range of total thicknesses of workpiece which the rivet can satisfactorily join together.

Description: The present invention relates to a self plugging blind rivet. Self plugging blind rivets are known in a variety of forms, and generally comprise a tubular shell and a stem which extends through the bore of the tubular shell, the stem being pulled to expand the tubular shell and thereby set the rivet. At least a part of the stem acts as a plug which is left plugging the bore of the set rivet. The plug serves to close the bore and/or strengthen the rivet. Examples of such self plugging rivets can be found in U.S. Patents 3,047,181; 4,355,934 and 4,627,775. One of the practical requirements of such rivets is that a given design and size of rivet has as wide as possible a grip range, that is to say, as wide as possible a range of total workpiece thickness in which identical rivets can be set successfully. The present invention provides a self plugging blind rivet comprising: a tubular shell having a head at one end, an elongate shank portion expandible radially to form a blind head, and a bore extending through said head and said shank portion from said one end to the other end opposite thereto, wherein said bore has a shoulder at an intermediate portion thereof to form a locking portion of said bore on a side of said shoulder towards said one end, said locking portion having a diameter smaller than a diameter of said bore on a side of said shoulder towards said another end; a stem fitted in said bore of said tubular shell, said stem comprising a head positioned adjacent said other end of said shell, and a shank extending from said stem head toward said one end of said shell and beyond said one end of said shell, whereby a setting tool may grip said shank to set rivet; a breakneck formed on said shank, whereby said stem can rupture at said breakneck on completion of the setting of said rivet; a shoulder formed on said shank at a position between said breakneck and said stem head such that said shoulder may reach said locking portion during the setting of said rivet, said shoulder of said shank defining a swaging portion of said shank on a side thereof towards said stem head, said swaging portion having a diameter greater than that of said locking portion of said bore; and locking means formed on said shank at a position between said shoulder of said shank and said breakneck, said locking means comprising at least one projection extending radially from said shank and having a diameter which is not greater than that of said locking portion of said bore, whereby upon engagement of said shoulder of said shank with said shoulder of said bore during the setting of the rivet, material of said shell at said locking portion is caused to flow towards said locking means to lock said stem in said bore, wherein said locking means comprise an interrupted ring having at least two circumferentially extending ring portions projecting from said shank, each of said ring portions being circumferentially separated from adjacent ring portions by a reduced diameter gap, whereby said material of said shell which has been caused to flow towards said locking means may flow axially through said gaps. This provision for flow of the shell material through the gaps allows the stem to be pulled further into the shell if needed, thus extending downwardly the grip range of the rivet. Further features of the invention will become apparent from the accompanying claims. A specific embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Figure 1 is an axial section through a shell of the rivet before assembly; Figure 2 is a detail view of part of the rivet stem, illustrating the locking means; Figure 3 is a side view of the stem of the rivet, before assembly; Figure 4 shows the stem assembled to the shell; and Figure 5A through 5E show the rivet during successive phases of a setting operation. Referring to Figure 1, there is shown in section a tubular shell according to the present invention. The tubular shell 2 has an enlarged diameter head 4 at one end thereof and an elongate shank portion 6 extending from the head to the other end thereof. The shank portion 6 has a generally cylindrically-shaped outer periphery of a constant diameter appropriate to the size of the holes in the materials to be clamped by the rivet. A bore 8 extends through the tubular shell from the one end to the other end thereof. At a midportion along the length of the bore there is formed an annular shoulder 10, whereby the bore at a side of the shoulder towards the one end having the head 4 has a reduced diameter, compared to the portion 12 of the bore on the side of the shoulder towards the other end, thereby producing a locking portion 14 of the bore on the side of the shoulder towards the one end. This locking portion 14 has a constant diameter less than that of portion 12 and terminates at an outward taper portion 16 of the bore. This outward taper portion 16 tapers with a progressively increasing diameter toward the said one end of the shell. During setting, the shank portion 6 must expand radially outward to form the blind head. In this example the shank portion is provided with means for permitting such radially outward expansion, in the form of longitudinally extending weakened portions formed on the shank portion 6. In this example, these weakened portions comprise a plurality of axially extending slits 18 in the shank portion (only one is shown in Figure 4) extending from the other end of the shank portion to a point immediately adjacent the head 4. Preferably, there are three such slits 18 which are spaced circumferentially by 120°, however fewer or more such slits are possible. The tubular shell 2 is preferably an extruded aluminium piece produced on a four-station cold heading machine which extrudes the shell and the bore simultaneously. The slits 18 are then formed of the shell with the stem. It should be noted that the formation of the slits 18 displaces some material of the shell inwardly. This displaced material is used to create an interference fit between the stem and the shell, as well be described below. Referring to Figure 3, the stem 20 has a head 22 which is normally positioned adjacent the other end of the shell 2 (see Figure 4). The underside of the stem head 22 is radiused at 24 in order to promote the splitting of the shank portion 6 during setting. The shank 26 of the stem extends from the head to the opposite end 28 which may be sharpened to promote insertion of the stem into the workpiece. The stem generally has a constant diameter which is less than that of the locking portion 14 of the bore so that the stem can be inserted entirely through the bore 8 and be fitted in the position shown in Figure 4, where the stem head 22 is positioned adjacent the other end of the shell 2. The end 28 of the stem then extends from the shell so that it may be grasped by a conventional setting tool (not shown) for setting the rivet. A breakneck 30 is formed on the shank 26 at a position where it is desired for the stem to rupture at the end of the setting sequence. Between the breakneck 30 and the stem head 22 there is formed a locking means 32 for locking the ruptured stem in the shell after the setting operation. The locking means 32 comprises at least one projection extending radially from the stem and having a diameter which is not greater than that of the locking portion 14 of the bore. In the preferred embodiment, the locking means comprises an interrupted ring having two semi-annular ring portions 34 and 34′ which are circumferentially separated by a pair of reduced diameter gaps 36 (only one gap is shown). The radially outer edges of the ring portions 34 and 34′ lie on a circle which has a diameter which is substantially the same as that of the locking portion 14 to form a sliding fit therein, but can be slightly smaller so as to form a clearance fit. Between the locking means 32 and the stem head 22 there is provided the annular shoulder 38 and the stem head 22 has an enlarged diameter compared to the remainder of the shank 26, thereby forming a cylindrical swaging portion 40 of the stem. The swaging portion has diameter greater than that of the locking portion 14 of the shell, but not greater than that of the portion 12 of the shell bore 8. Preferably, the diameter if the swaging portion 40 is substantially the same as that of the portion 12 of the shell bore 8, so that the inward deformations of the shank portion 6 of the shell produced by the formation of the slits 18 create a friction fit for the swaging portion 40 within the shell. The stem can thus be held together prior to setting. The stem 20 is preferably made of steel and headed on a Wafios nail maker using a split die process which produces the breakneck 30 and the split ring portions 34, 34′. More particularly, the stem 20 is produced a high speed, split die, single blow wire nail press. Inserts in the split die form the multiple diameters required to produce the interrupted ring on the stem. As the moving side of the split die moves radially inward toward the rod like stem blank, material is displaced to form the interrupted ring portions 34 and 34′. The gaps 36 between the ring serpents facilitate the release of the parts from the stationary side of the die. Subsequently, a head punch forms the head 22, the radiused underside 24 and the swaging portion in the stem blank. The stem is then inserted within the shell and held therein by the interference fir between the bore of the shell and the swaging portion 40 of the stem. Prior to such assembly, the components may be heat-treated, plated and lubricated. Referring to Figure 5A, the assembled rivet is shown in section after insertion of the shank portion of the shell 2 in the aligned holes of workpieces 50A and 50B which are to be clamped. The swaging portion 40 of the stem 20 is then held in interference fit within the bore 8 of the shell while the interrupted ring portions 34 and 34′ are in a clearance fir within the portion 12 of the bore. Subsequently, a setting tool grips the end 28 of the stem shank 26, while an anvil thereof retains the head 4 of the shell, in a manner which is well known. This causes the stem to move to the right (as seen on Figure 5B) so that the stem head 22 enters the shank portion 6 of the shell. This results in the adjacent end of the shank portion splitting radially outward at the slits, due to the progressively increasing diameter of the radiused underside of the head 22. As the setting tool continues to pull the stem rightward relative to the shell, the split shank portion 6 continues to expand radially outward for setting the rivet. Simultaneously, the ring portions 34 and 34′ of the locking means enter the locking portion 14 of the shell bore. However, since the ring portions 34 and 34′ have a diameter which is not greater than that of the locking portion, the shell is not deformed thereby. Referring to Figure 5D, the annular shoulder 38 of the stem 20 eventually reaches the annular shoulder 10 of the shell. Since the swaging portion 40 has a diameter greater than that of the locking portion 14, the resistance of the stem to further rightward movement increases and any further such rightward movement must be accompanied by the deformation of the locking portion as the material thereof is forced to flow rightward ahead of the swaging portion 40. As it does so, it enters the annular space 42 between the annular shoulder 38 of the stem and the ring portions 34 and 34′, and so locks the stem in the shell. If the workpieces are thin, the stem must advance further to the right before the rivet is fully set and so a greater amount of the material of the locking portion is deformed during setting of the rivet. Some of this material ultimately flows through the gaps 36 to surround the split ring portions 34 and 34′. Finally, in the position of Figure 5E, the head 22 of the stem reaches a position where further rightward movement of the stem is prevented by the walls of the workpieces 50A and 50B so that further movement of the stem relative to the shell is prevented. At this time, the shank portion 6 of the shell is split to a position abutting the workpieces, so that the rivet is fully set. Moreover, since the material of the locking portion has been forced to flow into the annular space 40, and perhaps also through the gaps 36 and around the ring portions 34 and 34′, the stem is firmly locked within the shell. Additional force on the end 28 of the shank 26 of the stem causes the breakneck 30 to rupture for completing the setting operation. The provision of the gaps 36 through which the shell material may flow allows the stem to be pulled further into the shell, thus extending downwardly the grip range of the rivet. Furthermore, in very thin workpieces, excess material from the locking portion 14 can flow into the enlarged diameter region of the tapered portion 16, thereby avoiding premature stem breakage. The invention is not restricted to the details of the foregoing example. For instance, the tail of the shell shank need not be of a type which splits to form a blind head, but could be of any other type, e.g. one which radially expands by buckling, folding or bulbing to form a blind head. The shape of the ring portions 34, 34′ may be of any convenient form. For example, the radial height of each portion above the surface of the shank 26 may be a maximum at the mid-point of the ring portion whilst reducing progressively from the mid-point towards each end which is adjacent to, and blends into, one of the reduced diameter gaps 36.

Claims: A self plugging blind rivet comprising: a tubular shell (2) having a head (4) at one end, an elongate shank portion (6) expandible radially to form a blind head, and a bore (8) extending through said head (4) and said shank portion (6) from said one end to the other end opposite thereto, wherein said bore (8) has a shoulder (10) at an intermediate portion thereof to form a locking portion (14) of said bore (8) on the side of said shoulder (10) towards said one end, said locking portion (14) having a diameter smaller than a diameter of said bore on the side of said shoulder (10) towards the said other end; a stem (20) fitted in said bore (8) of said tubular shell (2), said stem (20) comprising a head (22) positioned adjacent said other end of said shell (2), and a shank (26) extending from said stem head (22) toward said one end of said shell and beyond (28) said one end of said shell, whereby a setting tool may grip said shank to set the rivet; a breakneck (30) formed on said shank (26), whereby said stem (20) can rupture at said breakneck (30) on completion of the setting of said rivet; a shoulder (38) formed on said shank (26) at a position between said breakneck (30) and said stem head (22) such that said shoulder (38) may reach said locking portion (14) during the setting of said rivet, said shoulder (38) of said shank (26) defining a swaging portion (40) of said shank (26) on a side thereof towards said stem head (22), said swaging portion (40) having a diameter greater than that of said locking portion (14) of said bore; and locking means (32) formed on said shank (26) at a position between said shoulder (38) of said shank (26) and said breakneck (30), said locking means comprising at least one projection (34, 34′) extending radially from said shank (26) and having a diameter which is not greater than that of said locking portion (14) of said bore, whereby upon engagement of said shoulder (38) of said shank (26) with said shoulder (10) of said bore (8) during the setting of the rivet, material of said shell (2) at said locking portion (14) is caused to flow towards said locking means (32) to lock said stem (20) in said bore (8), characterised in that said locking means (32) comprises an interrupted ring having at least two circumferentially extending ring portions (34, 34′) projecting from said shank (26), each of said ring portions (34, 34′) being circumferentially separated from adjacent ring portions (34, 34′) by a reduced diameter gap (36), whereby said material of said shell (2) which has been caused to flow towards said locking means (32) may flow axially through said gaps (36). The rivet of claim 1, wherein said bore (8) has an outward taper (16) from said locking portion (14) to said one end, whereby said material of said shell may enter the a space between said shell and said shank at said outward taper (16) during the setting of said rivet. The rivet of claim 1 or claim 2 wherein there are two of said ring portions. The rivet of any of the preceding claims, wherein said ring portions (34, 34′) are simultaneously formed in a single blow, split die, wire nail press. The rivet of any of the preceding claims, wherein the radially outer edges of the ring portions (34, 34′) lie on a circle which has a diameter which is substantially the same as, or slightly smaller than, the diameter of the locking portion (14) of the shell. The rivet of any claims 1 to 4, wherein the radial height of each ring portion (34, 34′) is at a maximum at the mid-point of the ring portion and reduces progressively towards each end of the ring portion which is adjacent one of the gaps (36). The rivet of any of the preceding claims, wherein said means for permitting said shank portion to expand comprise a plurality of axial slits (18) in said shank portion (6), said slits (18) extending from said other end towards said one end. The rivet of any of the preceding claims, wherein said swaging portion (40) of said shank (26) forms an interference fit with said bore (8) prior to setting of the rivet, so as to maintain said shell (2) and said stem (20) in an assembled state.

Inventors: CASTANEDA CARLOS, GETTEN STEVEN, CASTANEDA, CARLOS, GETTEN, STEVEN
Applicants: AERPAT AG, AERPAT A.G.
Application year: 1991
Main classification: F16B19
IPC codes: F16B19