GB2326908A

GB2326908A - Fastener for superposed members

Info

Publication number: GB2326908A
Application number: GB9714151A
Authority: GB
Inventors: Derek Crutchley
Original assignee: Avdel Textron Ltd; Textron Fastening Systems Ltd
Current assignee: Avdel UK Ltd
Priority date: 1997-07-04
Filing date: 1997-07-04
Publication date: 1999-01-06
Also published as: GB9714151D0

Description

FASTENER The invention relates to a fastener, and more particularly to a fastener for insertion through aligned holes in superposed members to secure the members together.

In particular, the invention relates to a fastener of the type comprising a first part having a radially enlarged head at one end and an elongated shank protruding therefrom, and a bore extending axially completely through the head and shank, the interior of at least part of the bore carrying first engaging means; and a second part having a radially enlarged head at one end, and an elongated shank protruding therefrom, the exterior of at least part of the shank carrying second engaging means; the shank of the second part being insertable into the bore of the first part so that the first and second engaging means mutually engage.

One example of such a fastener is described in our earlier GB 1 538 423, and is commercially available in many countries under the Registered Trade Mark AVTAINER. In that example fastener, the first engaging means comprises a resilient sleeve and the second engaging means comprises one or more annular rigid barbs formed on the shank of the second part. In use of the fastener, the barbs engage in the resilient sleeve to prevent separation of the two parts of the placed fastener, and also to support tension strength within the placed fastener thereby to secure together the members joined together by the fastener. In practice, the first part is referred to as the shell and the second part as the pin.

GB 1 538 423 was filed in 1975 and described a fastener being used to secure a relatively thick low density plywood panel member to a steel frame member, a typical user application at that time. There is now a user requirement to be able to secure together members which are thinner, and are also stronger and support greater loads. There is thus a need to provide such a fastener which will satisfactorily secure together members of a reduced total thickness (known as the "grip" of the fastener), and at the same time support a greater tension load. It is clear that maximum tension load which can be supported by such a fastener depends to a certain extent upon the length of overlap of the first and second engaging means when in the fully engaged position. In the example type of fastener, this means that in practice a minimum number of barbs (which are spaced apart axially along part of the length of the shank) need to be engaged in the resilient sleeve. In GB 1 538 423 it was stated that the two parts of the fastener could be adequately locked together even if only one barb was in engagement. However, this is no longer true with the much higher tension loads which are required of present-day fasteners, which typically may need, say, the engagement of four barbs.

Furthermore, the length of the shell could not be greater than the minimum grip. However, the desired minimum grip may be too short to accommodate a first part with a resilient sleeve long enough to engage a sufficient number of annular barbs. Thus the problem is to provide a fastener which satisfies the conflicting design requirements of providing a reduced minimum grip at the same time as an increased minimum number of barbs to engage throughout the grip range.

A further requirement imposed by users of such fasteners is that the user need stock the minimum number of different sizes of fasteners or fastener parts to cover as large as possible a range of total workpiece thickness to the joined.

The present invention is intended to help solve these problems.

Accordingly, the present invention provides a fastener as set out in claim 1.

Preferred features of the invention are set out in claims 2, 3, 4 and 5. The invention also provides a combination comprising two or more fasteners, as set out in claim 6 and claim 7.

Specific embodiments of the invention, in the form of a fastener, and a combination of fasteners, will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 illustrates a fastener according to invention, with the two parts assembled together but not engaged; Figure 2 illustrates the fastener of Figure 1 used to secure members together at its maximum grip; Figure 3 illustrates the fastener of Figure 1 used to secure members together at its minimum grip; Figure 4 illustrates a prior art fastener about to be installed to secure members together at its maximum grip, including part of the placing tool; and Figure 5 illustrates the fastener of Figure 4 used to secure members together at its minimum grip.

The fastener of the present invention is best understood by comparison with the prior art fastener illustrated in Figures 4 and 5. This prior art fastener is fully described in our earlier GB 1 538 423, to which the reader is referred for further information. Briefly, referring to Figures 4 & 5 of the accompanying drawings, which show the fastener in somewhat simplified form, the fastener comprises a first part or shell 11 and a second part or pin 12. The shell 11 comprises a tubular steel outer member including a radially enlarged flange-like head 15 of low profile and a tubular elongated shank 16 protruding centrally from the head, the shank 16 and head 15 having a cylindrical bore extending completely through them. The tail end of the shank (i.e. the end remote from the head 15) is formed with an inwardly extending flange 18. The bore of the shank contains the first engaging means in the form of a sleeve 14 of nylon-66 material. This extends axially from the flange 18 nearly to the head end of the shank bore. The exterior diameter of the sleeve 14 is such that the sleeve is a push fit in the bore of the shank, and the interior diameter of the sleeve is somewhat less than that of the aperture defined inside the flange 18.

The second part or pin 12 is also of steel and comprises a radially enlarged low profile head 22 with a flat underhead surface and an elongated shank 23 extending from the head. The pin shank 23 is formed externally with a number of axially adjacent zones which are, in order starting at the head 22:- a plain portion 24; four annular barbs 25 (providing the second engaging means); a breakneck 26; and a pin tail 27 having pulling grooves 28 (shown part broken away in Figure 4 for convenience of illustration). The external diameter of the pin tail 27 is a sliding fit within the bore of the sleeve 14, and the maximum diameter of the barbs 25 is greater than the bore diameter. The form of the barbs is preferably as described in our earlier GB 1 600 490, which gives enhanced tension strength upon engagement.

By way of example, Figure 4 illustrates the use of the fastener to secure together two superposed members 29, 31 which have an aperture 32 through them which is of sufficient diameter to receive the shell shank 16, and one end of which is preferably provided with a small countersink or chamfer 33 to accommodate the radius profile where the shell shank 16 and head 15 meet. The pin shank is inserted through the aperture 32 from the end remote from the countersink 33 until the underside of the pin head 22 abuts the outer face of the member 31, and the majority of the length of the pin protrudes from the remote face of the other member 29 which carries the countersink 33. The shell 11 is then offered, shank 16 first, over the protruding end of the pin shank 23, until the shell shank 16 starts to enter the aperture 32 and the leading end of the nylon sleeve 14 abuts the nearest of the barbs 25 on the pin. The resistance to entry of the barb into the sleeve is such that further engagement by manual hand-pressure is impossible. If necessary the pin head 22 is maintained in contact with the member 31 by hand pressure.

A suitable pulling tool 34, such as those commercially available under the designation AVDEL (registered trade mark) Series 749 and Series 7572, is then applied to the projecting end of the pin tail 27. Essentially the tool 34 comprises a barrel 35 carrying at its front end an annular nosetip 36 including a forward projecting annular pin 37. Inside the barrel 35 are located pulling jaws 38 housed in a retractable collet 39. A pneumatic-hydraulic device (not shown) is provided to retract the collet 39 so that the jaws 38 engage the pull grooves 28 on the pin tail and exert an increasing pull on the pin tail. The reaction to the pull is applied through the front face of the nosetip 36 to the head 15 of the shell.

The tool 34 is actuated to engage and pull the jaws as just described, and the tool barrel 35 moves forwardly in relation to the jaws 38 and pin tail 27 so that the nose tip 36 forces the nylon sleeve 14 and the shell 11 forwards over the barbs 25.

The nose tip rim 37 supports the sleeve 14 to prevent it being pulled out of the shell shank 16. The shell head 15 abuts the member 29 and, in co-operation with the pin head 22 abutting the far side of the other member 31, clamps the members tightly together. Increasing pull on the pin tail 27 applied by the tool 34 eventually causes the pin to break at the breakneck 26, leaving the fastener installed to secure the members 29, 31 together. Figure 4 shows the position just before the break occurs.

The fastening system described above is well known and its operation is well understood.

As previously mentioned, the fastener of this example is provided with four barbs on the pin, and in order to provide sufficient tension strength in the installed fastener it is necessary that all four barbs engage on the nylon sleeve of the shell.

In practice, it is necessary to provide a fastener with a certain minimum grip range (i.e. a range of total thicknesses of members which identical fasteners will satisfactorily secure together). To this end, as illustrated in Figures 4 & 5, the nylon sleeve 14 in the shell is longer than the total axial extent of the barbs 25 on the pin. This gives a range of satisfactory grip thickness, the grip range being rather less than the excess of the length of the sleeve 14 over the total axial extent of the barbs 25. Figure 4 shows a fastener installed in about maximum grip.

Figure 5 shows a fastener identical with that in Figure 4, installed in the minimum grip. In both cases, all four barbs are embedded securely in the sleeve.

The maximum and minimum of the grip range could be increased together by making longer pins, i.e. having a longer plain portion 24 so that the barbs 25 are further from the head 22. However, the minimum grip cannot be reduced below the axial length of the shell shank 16 between the underface of head 15 and the remote end of the shank which is needed to contain the length of the nylon sleeve 14, unless the grip range is reduced, which is not acceptable in practice. Nor is it acceptable for the broken end of the pin at the breakneck 26 to protrude beyond the head 15 of the shell.

An example of the fastener according to the present invention is illustrated in Figures 1, 2 and 3. Like parts of this fastener to those of the prior art fastener illustrated in Figures 4 and 5 are denoted by like numerals. In Figure 1 the shell and pin of the fastener are shown partially assembled together, but the workpiece members to be clamped between their heads are omitted for the sake of clarity.

The first part or sleeve 11 of this fastener is identical with and interchangeable with that of the fastener of Figures 4 and 5, and need not be described further. The second part or pin 41 is similar to the pin 12 of the fastener of Figures 4 and 5 in so far as it comprises a shank 23 which is similar in form to the previous one, having a plain portion 47, four barbs 25, a breakneck 26 and a pin tail 27 carrying pulling grooves 28. The plain portion 47 in this fastener is somewhat shorter than the plain portion 24 in the fastener of Figures 4 and 5, but otherwise the pin shanks are substantially identical.

However, the head 42 of this pin is different. It comprises an annular workpiece-engaging zone in the form of a peripheral rim 43 which is spaced radially outwardly from the shank and is located axially spaced apart from the junction of the head 42 and shank 23. This provides an axially-extending annular space 44 around the shank 23 and adjacent to the head 42. As illustrated in Figure 1, the axial extent of this annular space is rather more than twice the pitch between adjacent barbs 25. This fastener is installed in the same way as the fastener illustrated in Figures 4 and 5, using the same tool and the same procedure as previously described.

Figure 2 shows the fastener of Figure 1 installed in its maximum grip, with barbs 25 on the pin embedded in the nylon sleeve 14 adjacent to the end of the sleeve abutting flange 18. The end of the shell shank 16 does not protrude beyond the outer face of the member 31.

Figure 3 shows the fastener installed at its minimum grip, with the barbs 25 embedded in the sleeve 14 adjacent the other end of the sleeve at the shell head end.

The remote end portion 45 of the shell shank 16 protrudes beyond the interface of the member 31, and is accommodated in the annular space 44 under the pin head 42. The precise length of the minimum grip distance can be adjusted by selecting the axial length of the annular space 44 and/or by selecting the axial length of the plain portion 47 of the pin, although the maximum grip distance is thereby similarly adjusted, so that the extent of the grip range cannot thereby be increased. It is important that, in the minimum grip, the tail end of the protruding portion 45 of the shell shank 16 does not abut the underside of the pin head 42, otherwise the clamping effect of the two heads of the fastener on the workpiece members will be diminished or lost. Accordingly, in Figure 3 a clearance gap is shown at 46, although in Figure 3 the extent of this is exaggerated for clarity of illustration.

Since both the prior art fastener and the fastener of this invention have identical and interchangeable shells 11, a combination of the two types of fastener, i.e. one or more pins of the prior art type, one or more pins according to the invention, and/or pins according to the invention having annular underhead spaces 44 of different lengths, together with sufficient shells, will enable the selection of the appropriate pin to provide fasteners which will operate over an enhanced range of grip thickness. Such an enhanced range is preferably, but not necessarily, continuous. Furthermore, the grip range may be adjusted (to increase or decrease both maximum and minimum grip together) as previously described by providing different pins having different lengths of plain shank under the head, i.e. in which the second engaging means (barbs 25) are spaced from the workpiece-engaging portion of the pin head (whether it is provided by the flat underhead of the prior art pin or the annular rim 43 of the pin according to the invention) by different distances.

The invention is not restricted to the details of the foregoing examples. For instance, in practice it would be preferable to provide a suitable seal between the pin head (12 or 42) and the workpiece.

The engaging means on the two fastener parts could be provided in a form other than the annular barbs and resilient sleeve described above. It would be possible to omit the pin tail 27 and breakneck 26, so that the pin becomes what is known as a "stump", and to engage the two parts of the fastener together by applying forces in opposite directions from opposite sides of the workpiece members to be secured together.

Claims

1. A fastener comprising: a first part having a radially enlarged head at one end, an elongated shank protruding therefrom, and a bore extending axially completely through the head and shank, the interior of at least part of the bore carrying first engaging means; and a second part having a radially enlarged head at one end, and an elongated shank protruding therefrom, the exterior of at least part of the shank carrying second engaging means; the shank of the second part being insertable into the bore of the first part from the end thereof remote from the head of the first part, so that the first and second engaging means mutually engage, thereby to secure together the first and second parts of the fastener and thus secure together workpieces clamped between the head of the first part and the head of the second part; in which the radially enlarged head of the first part has an annular workpieceengaging zone spaced radially outwardly from the shank and located axially spaced apart from the junction of the head and the shank, thereby to provide an axially-extending annular space around the shank and adjacent to the head to accommodate, if necessary, a portion of the shank of the second part protruding from the workpiece when the first and second parts are secured together as aforesaid.

2. A fastener as claimed in claim 1, in which at least one of the engaging means comprises a plurality of barbs mutually spaced apart along the direction of the axis of the part carrying them.

3. A fastener outlined in claim 2, in which the axial extent of the aforesaid annular space is equal to at least one barb pitch.

4. A fastener as claimed in claim 2, in which the axial extent of the aforesaid annular space is substantially equal to at least twice the barb pitch.

5. A fastener as claimed in any of the preceding claims, in which the shank of the second part of the fastener includes a pulling portion at the end thereof remote from the head, and beyond the second engaging means, such that the pulling portion protrudes from the bore, beyond the head of the first part, thereby enabling the first and second parts of the fastener to be pulled together, the pulling portion being thereafter detachable from the shank.

6. The combination of at least one fastener as aforesaid as claimed in any of the preceding claims, with at least one other fastener, the or each other fastener comprising a first part which is substantially identical with the first part of the or each fastener as aforesaid, and a modified second part which is generally similar to the second part of the or each fastener as aforesaid but has no axially-extending annular space as aforesaid or an axially-extending annular space as aforesaid which is substantially less in axial extent than that of the second part of the or each fastener as aforesaid, whereby any one of the substantially identical first parts may be engaged with any selected one of the second parts, thereby to enable the securing together as aforesaid of workpieces over an extended range of total thicknesses.

7. The combination as claimed in claim 6, including at least two fasteners as claimed in any of claims 1 to 5, the two fasteners having second parts in which the respective second engaging means are spaced axially along the shank from the annular workpieceengaging zone by different distances.

8. A fastener substantially as hereinbefore described with reference to, and illustrated in, Figures 1, 2 and 3 of the accompanying drawings.

9. The combination of at least one fastener as claimed in claim 8 with at least one other fastener substantially as hereinbefore described with reference to, and illustrated in, Figures 4 and 5 of the accompanying drawings.