GB2097083A - Blind rivet - Google Patents

Abstract

A sealable blind rivet is of the kind incorporating a tube 11 with a preformed flange 12 forming a head on one end. The end of the tube 11 opposite flange 12 is expanded by means of a head 24 which is pulled into the tube 11 by a mandrel 13. The pulling operation is terminated by breaking of the mandrel 13 at a reduced cross section region and only the remaining part of the mandrel 13 is shown. The head 24 tapers continuously from the large diameter outer end to a smaller diameter at the opposite end. The outer end of the head has a continuous circumferential sharp edge which bites into the metal of the tube to provide sealing therewith as well as mechanical retention of the head after braking of the mandrel 13. <IMAGE>

Description

SPECIFICATION Blind rivet The invention relates to blind rivets.

A typical blind rivet comprises a tube, an integral flange at one end of the tube, a mandrel extending through the tube, a head on the mandrel adjacent the end of the tube opposite the flange and a reduced cross section portion of mandrel close to the head. Generally, the diameter of the head is approximately equal to the outer diameter of the tube. In use, the head of the mandrel and the tube are inserted in apertures of sheets to be joined together until the flange contacts one of the sheets.

The mandrel is then pulled so that the head enters into and expands part of the tube to form a rivet head. The flange forms the other rivet head. Further pulling breaks off the mandrel at the reduced cross section portion, thus leaving a tubular blind rivet with the head closing off the tube. With conventional blind rivets, there is a possibility that the head may fall out of the rivet during the life of the rivet. For some applications this is not important but there are installations such as in electrical cabinets where a loose head could be an embarrassment. Perhaps more important, there are situations such as with cladding panels for buildings or for containers where the rivet assembly should be windproof, dustproof and rainproof and to achieve this it is important to retain the head within the rivet to seal the central hole in the rivet.

A proposal has been made in British Patent 949,003 to retain the head within a blind rivet assembly. In this patent the head is formed with a flat on one side thereof so that, when the rivet tube is expanded by pulling the head into it, the tube end tends to fold over the flat and over the end of the head to provide a mechanical retention of the head within the tube. However this asymmetric arrangement could still permit the head to be loosely retained within the tube and no actual seal is formed between the head and the rivet tube.

The objects of the present invention are to provide an improved sealable blind rivet, a riveted connection utilising such a rivet and a method of riveting with such a rivet wherein the mandrel head of the rivet is mechanically retained within the tube in sealing engagement therewith.

In accordance with a first aspect of the invention there is provided a sealable blind rivet adapted to be inserted through aligned holes of workpieces to be secured together by the rivet and comprising a deformable metal tube having an integral outwardly extending flange at one end thereof, an elongate metal mandrel extending through the tube, an enlarged head on the mandrel at one end thereof located adjacent that end of the tube remote from the flange, a reduced cross-section portion of mandrel below the head and a projecting mandrel stem extending out of the tube at said flange end thereof characterised in that the mandrel head is of frustoconical form tapering from an inner end adjacent the mandrel to an outer end, the diameters of both inner and outer ends being greater than the internal diameter of the tube, and the periphery of the outer end of the head providing an annular sharp edge whereby, in use, when the mandrel stem is pulled axially outwardly of the flanged end of the tube, the mandrel head is pulled into the other end of the tube to deform the metal thereof radially outwardly, the reduced cross-section portion ofthe mandrel is severed, and the rivet is set to secure the workpieces together with the mandrel head remaining in position in the tube; the sharp annular edge of the mandrel head engaging positively around its circumference with the inner wall of the deformed portion of the tube to seal the rivet and to mechanically prevent subsequent axial displacement of the mandrel head from the tube.

In accordance with a further aspect of the invention there is provided a riveted connection between workpieces comprising a sealed blind rivet set through aligned holes in the workpieces to secure them together, the set rivet comprising a metal tube having an integral flange at one end thereof, a mandrel portion within the tube and an enlarged head on the mandrel engaged within a radially outwardly deformed portion of the tube remote from the flanged end characterised in that the mandrel head is of frusto-conical form tapering from an inner end adjacent the mandrel portion to an outer end, the diameters of both inner and outer ends being greater than the undeformed internal diameter of the tube and the periphery of the outer end of the head having a sharp edge engaged positively around its circumference with the inner wall of the deformed portion of the tube to seal the rivet and to mechanically prevent axial displacement of the mandrel head from the tube.

In accordance with a yet further aspect of the invention there is provided a method of securing workpieces together by means of a sealable blind rivet inserted through aligned holes in the workpieces characterised in that the rivet comprises a deformable metal tube having an integral outwardly extending flange at one end thereof, an elongate metal mandrel extending through the tube, an enlarged head on the mandrel at one end thereof located adjacent that end of the tube remote from the flange, a reduced cross-section portion of mandrel below the head and a projecting mandrel stem extending out of the tube at said flange end wherein the mandrel head is of frusto-conical form tapering from an inner end adjacent the mandrel to an outer end, the diameters of both inner and outer ends being greater than the internal diameter of the tube, and the periphery of the outer end of the head providing an annular sharp edge; and further characterised in that the method comprises the steps of pulling the mandrel stem axially outwardly of the flanged end of the tube to pull the mandrel head into the other end of the tube to deform the metal thereof radially outwardly and to sever the reduced crosssection portion of the mandrel whereby the rivet is set to secure the workpieces together with the mandrel head remaining in position in the tube; the sharp annular edge of the mandrel head engaging positively around its circumference with the inner wall of the deformed portion of the tube to seal the rivet and to mechanically prevent subsequent axial displacement of the mandrel head from the tube.

An embodiment of the invention will now be described and compared with conventional com mercially available prior art rivets with reference to the accompanying drawings in which: Figure 1 shows a conventional commercially available blind rivet prior to installation in cross section; Figure 2 shows the blind rivet of Figure 1 after installation to rivet together two sheets of material; Figure 3 corresponds to Figure 2 but shows an embodiment of the invention; and Figure 4 corresponds to Figure 3 but showing the rivet of the invention.

The known rivet of Figures 1 and 2 comprises a circulartube 11 of ductile metal having an integral flange 12 at its lower end. A circular metal mandrel 13 extends through the tube and is a close fit therein.

Mandrel 13 carries a head 14 at one end of the mandrel and this head in Figure 1 lies against the end of the tube 11. The inner surface of the tube adjacent the head is rounded at 16 to provide a lead in for the head. The outer end of the upper surface of the tube is tapered at 15 partly to assist insertion of the rivet in a hole. Provision of this taper also helps to cause the tube to grip the mandrel by reducing the internal mandrel diameter just below rounded region 16. The head itself is generally barrel shaped with its largest diameter at the centre of the head and a taper in both directions from the centre. The mandrel 13 has a portion 17 of reduced cross section. This reduced cross section is formed by clenching the mandrel prior to assembly within the tube.

In use of the rivet, it is passed through holes in two or more sheets which are to be riveted together. The flange 12 is held firmly in contact with one of these sheets and the mandrel 13 is pulled to draw the head 14 into the tube 11, thus expanding the tube. Further pulling breaks offthe mandrel and leaves a completed rivet assembly as shown in Figure 2.

Immediately prior to breaking off of the mandrel, there is a large compressive load in region A below the mandrel head 14 and this tends to spread the tube to a diameter slightly larger than that of the head 14. This spreading tendency is the major cause of loosening the head within the tube.

Although the material of the tube is ductile, there is a slight tendency for the tube to have a degree of resilience and so tend to spring back slightly after the load has been removed when the mandrel breaks off. It is believed that the slight resilient recovery of the tube in region A when the mandrel load is removed can tend to loosen the head 14 within the tube.

Another factor tending to allow the head to be released from the tube is the way in which the tube deforms as the head is pulled through. When the mandrel has been pulled part way into the tube so that its largest diameter section is within the tube and the tube has thus expanded to the diameter of the head, further pulling of the head down into the tube will tend to expand a part of the tube immediately below the already expanded part. This lower part of the tube is naturally joined to the already expanded upper part of the tube so that as the lower part of the tube is expanded, it tends, very slightly, to open the upper part of the tube even further.

As a consequence of the loosening of the remaining part of the mandrel within the tube by relief of the loading at A and as a result of the tendency for the outer part of the tube to be of slightly increased diameter as compared with the inner or lower part of the tube, there is a tendency for the head to work free and drop out of the rivet.

An objective ofthe present invention is to modify the shape of the head from the conventional head 14 in order to provide a system in which the head of the installed rivet will notfall out and which will seal the rivet.

The embodiment of the invention as shown in Figures 3 and 4 corresponds in most respects to the prior art described with reference to Figures 1 and 2 and this description will not be repeated. However, the shape of the head 24 of Figure 3 differs materially from the head 14 of Figure 1. Head 24 has a slightly curved lower shoulder corresponding to that of the head 14 but the main body of the head has a straight conical taper from a largest diameter upper part 25 to a smaller diameter portion 26 near the lower end of the rivet adjacent the tube. The transition from the conical wall providing this taper to the flat upper surface of the rivet is a sharp continuous circumferential edge 27.

When the rivet of Figure 3 has been installed and the mandrel 13 pulled and broken off to produce the completed rivet assembly of Figure 4, a compressive load is built up at A as in the prior art and then released on breaking of the mandrel. However, the tendency for this head to fall out of the rivet is very much reduced as can be illustrated by the fact that tests show that in a typical rivet a load in excess of 50 kg is needed to remove the head from the rivet.

It is believed that the profile of the head produces this improved location within the tube in four ways.

Firstly, the largest diameter part of the head is well away from the region A of high compressive loading and the associated tendency to spread so the spreading action is unlikelyto release the head. Secondly, the latter part of the expansion of the tube is carried out by a gradual straight taper rather than the more sudden expansion of the prior art. The result of this is that the last part of the expansion at a given position along the length of the tube is very small so that the tendency to further expand an upper part of the tube as an immediateLy lower part of the tube is expanded is very much reduced. Any tendency to expand the upper part of the tube after the head has passed through can be within the elastic recovery limits ofthe material of the tube so that no significant taper occurs on the tube and in fact the upper part of the tube can have a slightly smaller diameter than the maximum diameter of the head due to this elastic recovery. By virtue of this situation, a slight disturbance of the head within the tube on release of the loads associated with the mandrel and the slight recovery of the rivet in region A is much less likely to release the head with the arrangement of Figure 4 than with the arrangement of Figure 2. Thirdly, due to the continuous taper of the head of the rivet, the whole of its outer surface can be in contact with the surface of the tube, thus holding it against inadvertant angular movement within the head which could also tend to release the head. A fourth factor assisting retention of the head of Figures 3 and 4 within the tube is the sharp upper edge 27 of the head which is in contrast to the tapered lead in the corresponding region of the known rivet. This sharp edge 27 provides positive circumferential engagement thereof with the inner wall of the deformed portion of the tube to mechanically prevent axial displacement of the head from the tube. The edge 27 "bites" into the metal of the tube under the action of the compressive loading at A to provide an annular seal of the head to the rivet as well as to provide the mechanical retention thereof.

Claims (6)

1. A sealable blind rivet adapted to be inserted through aligned holes of workpieces to be secured together by the rivet and comprising a deformable metal tube having an integral outwardly extending flange at one end thereof, an elongate metal mandrel extending through the tube, an enlarged head on the mandrel at one end thereof located adjacent that end of the tube remote from the flange, a reduced cross-section portion of mandrel below the head and a projecting mandrel stem extending out of the tube at said flange end thereof characterised in that the mandrel head is of frusto-conical form tapering from an inner end adjacent the mandrel to an outer end, the diameters of both inner and outer ends being greater than the internal diameter of the tube, and the periphery of the outer end of the head providing an annular sharp edge whereby, in use, when the mandrel stem is pulled axially outwardly of the flanged end of the tube, the mandrel head is pulled into the other end of the tube to deform the metal thereof radially outwardly, the reduced crosssection portion of the mandrel is severed, and the rivet is set to secure the workpieces together with the mandrel head remaining in position in the tube; the sharp annular edge of the mandrel head engaging positively around its circumference with the inner wall of the deformed portion of the tube to seal the rivet and to mechanically prevent subsequent axial displacement of the mandrel head from the tube.

2. A riveted connection between workpieces comprising a sealed blind rivet set through aligned holes in the workpieces to secure them together, the set rivet comprising a metal tube having an integral flange at one end thereof, a mandrel portion within the tube and an enlarged head on the mandrel engaged within a radially outwardly deformed portion of the tube remote from the flanged end characterised in that the mandrel head is of frusto-conical form tapering from an inner end adjacent the mandrel portion to an outer end, the diameters of both inner and outer ends being greater than the undeformed internal diameter of the tube and the periphery of the outer end of the head having a sharp edge engaged positively around its circumference with the inner wall of the deformed portion of the tube to seal the rivet and to mechanically prevent axial displacement of the mandrel head from the tube.

3. A method of securing workpieces together by means of a sealable blind rivet inserted through aligned holes in the workpieces characterised in that the rivet comprises a deformable metal tube having an integral outwardly extending flange at one end thereof, an elongate metal mandrel extending through the tube, an enlarged head on the mandrel at one end thereof located adjacent that end of the tube remote from the flange, a reduced cross-section portion of mandrel below the head and a projecting mandrel stem extending out of the tube head at said flange end wherein the mandrel head is of frustoconical form tapering from an inner end adjacent the mandrel to an outer end, the diameters of both inner and outer ends being greater than the internal diameter of the tube, and the periphery of the outer end of the head providing an annular sharp edge; and further characterised in that the method comprises the steps of pulling the mandrel stem axially outwardly of the flanged end of the tube to pull the mandrel head into the other end of the tube to deform the metal thereof radially outwardly and to sever the reduced cross-section portion of the mandrel whereby the rivet is set to secure the workpieces together with the mandrel head remaining in position in the tube; the sharp annular edge of the mandrel head engaging positively around its circumference with the inner wall of the deformed portion of the tube to seal the rivet and to mechanically prevent subsequent axial displacement of the mandrel head from the tube.

4. A sealable blind rivet constructed and arranged substantially as hereinbefore described with reference to and as shown in Figure 3 of the drawings.

5. A riveted connection between two workpieces constructed and arranged substantially as hereinbefore described with reference to and as shown in Figure 4 of the drawings.

6. A method of securing workpieces together by means of a sealable blind rivet substantially as hereinbefore described with reference to Figures 3 and 4 of the drawings.