GB2351538A

GB2351538A - Self-plugging blind rivet

Info

Publication number: GB2351538A
Application number: GB9915153A
Authority: GB
Inventors: D R Smith; Stephen John Morris; Stanley Brian Bourne
Original assignee: Newfrey LLC
Current assignee: Newfrey LLC
Priority date: 1999-06-30
Filing date: 1999-06-30
Publication date: 2001-01-03
Anticipated expiration: 2019-06-30
Also published as: GB9915153D0; GB2351538B

Abstract

The rivet includes a shell body (2) within which is situated a stem. The stem has a head (16) which, when the rivet is set, deforms the body (2). The stem includes a shank (14) having axial recesses (20) formed therein. The axial recesses (20) include protrusions (22) for co-operating with the deformed material of the body (2) when the rivet is set. The co-operation between the material of the deformed shell (2) and the protrusions (22) prevent recoil of the stem head (16) when the rivet is set.

Description

2351538 SELF-PLUGGING BLIND RIVET The present invention relates to a self

-plugging blind rivet for securing together apertured members when the rivet is set, the rivet comprising; a tubular shell having a tail end face at one end and a pre-formed radially enlarged head at the other end; a stem having a shank which extends through the shell, and a head adjacent the tail end face of the shell; the stem being formed with a plurality of axial recesses.

A rivet of this known type is disclosed, for example in W098/23872. The rivet described in this document is used to clamp together two or more apertured members. The rivet stem has axial recesses into which the shell material is forced during the assembly of the shell to the stem. This forms at the tail end of the rivet a thickened portion of shell material that by virtue of the forming process is also work hardened designed to give a retained stem portion. The rivet stem when inserted into a rivet setting tool is subjected to an applied axial load such that on setting the rivet, this axial loading is transferred to the shell, the shell deforms at a position below the thickened portion and the apertured workpiece to produce an enlarged blind side spread and hence permitting a strong clamping of the apertured members by the set rivet.

However, it has been found that W098/23872 itself creates problems with the effective setting of the rivet.

In order to set the rivet, as is known in the art, an axial loading force is applied to the shell by way of gripping the shank of the stem and axially pulling this so that the head of the stem which abuts the tail end of the shell, compressively loads the shell. As the shell deforms, the material of the deforming shell flows BR8666UK 2 radially outwards to form a setting head on the blind side of the workpiece. However, once the f low of the shell material has reached a compressive limit, a breakneck formed on the shank of the stem which provides an area of weakness on the stem breaks in order to leave the rivet in this set position.

When the breaking of the shank of the stem takes place, however, there is a sudden release of strain energy.

This sudden release of energy often causes the head of the stem to move in the opposite direction to that which it was previously pulled and therefore the head of the stem and the remaining part of the shank of the stem which is within the shell may move away from the shell in a direction from the enlarged head towards the tail end face thereof.

Even if this so-called recoil movement is minimal, it has the propensity to leave a small gap between the recesses and their associated shell material.

Furthermore, because the head of the stem has moved slightly out of the tail end face of the shell, this means there is a slight hole within the rivet between the inner periphery of the shell and the outer periphery of the stem and head.

It is possible for water or other moisture to pass through this hole and sit within the gap created in the recesses.

If the stem and/or the shell of the rivet are formed from a ferrous material, then there is the propensity for the rivet to rust and therefore eventually corrode.

It is therefore an object of the present invention to at least alleviate the aforementioned shortcomings by BR8666UK 3 providing a self -plugging blind rivet according to the opening paragraph above, the rivet characterised by each of the axial recesses having a protrusion formed therein such that each axial recess is discontinuous, and wherein the rivet is set by placing the shell under axial compression loading such that the shell remains in place in a region adjacent the axial recess of the stem, and the shell at least partially occupies each recess and also at least partially surrounds each protrusion.

The provision of a lateral protrusion within the recess allows the deforming shell material to effectively surround the protrusion. This creates a form of detent between the recess and the shell material which flows into the recess. Such a detent prevents relative movement between the stem and the shell when the breakneck of the stem shears. This in turn means that the head of the stem is prevented from moving away from the tail end face of the shell when the breakneck shears and hence prevents the influx of water or moisture to the rivet.

Preferably, the plurality of axial recesses are generally circumferentially spaced around the periphery of the stem. By spreading the distribution of the recesses around the periphery, a uniform setting force is likely to be distributed about the stem and the shell.

Advantageously, the protrusions comprise bar members 30 which extend generally across the circumferential width of the recesses. The use of such bar members extending the whole way across the width of the recesses creates a highly effective barrier to the influx of water. Also, this allows for a good holding force to be achieved between the deformed shell and the stem. In a preferred embodiment each recess has one corresponding bar member therein.

BR8666UK 4 It is also desirable for the deformed shell to axially straddle the protrusion when the rivet is set. This again allows for a good holding force between the shell 5 and the stem.

Preferably, the circumferential width across any recess is between 25% and 75% of the circumferential width of the land areas between and defining the recesses.

Furthermore, this may be between 45% and 55% of the circumferential width of the land areas in a preferred embodiment.

Preferably, the stem comprises a first end portion, pintail and a breakneck provided between the first stem portion and the pintail; the first end portion being on the stem head side of the breakneck and the entire first end portion being retained in the rivet shell and of larger diameter than the pintail such that, when the rivet is set the larger diameter of the first end portion cannot pass through a hole in the nose of a tool for setting a rivet and the pintail breaks off at the rivet head.

The present invention will now be described, by way of example only and with reference to the accompanying drawings, of which; Figure 1 is a longitudinal section through the shell of the rivet before assembly; Figure 2 is a side elevation of the stem of a rivet before assembly; Figure 3 is a section along the line -XX1 of Figure 2; BR8666UK Figure 4 is a part sectional view of the assembled rivet comprising the shell of Figure 1 and the stem of Figure 2; Figure 5 is a schematic perspective view of the stem of Figure 2; Figure 6 is an enlarged perspective view of the stem of Figure 5; Figure 7 is a perspective view of the stem of Figure 6, including a breakneck; Figure 8 shows a sectional view of a set rivet in accordance with the present invention, which is clamping together two apertured members, and; Figure 9 is a sectional view of a rivet in accordance with the present invention and part of a rivet setting tool showing how a rivet is set.

Referring firstly to Figure 1. The shell comprises a hollow tubular body (2) having a concentric cylindrical bore (4) and one end of the tubular body (2) terminates 2S in a radially enlarged head (6). The opposite end, the tail end (8) of the tubular body (2), is flat and is at right angles to the shell axis (10).

Referring now to Figure 2, it can be seen that the stem shown generally as (12) comprises a solid tubular shank (14) which terminates at one end in a radially enlarged head (16). The shank (14) has a breakneck (18) formed therein. The breakneck (18) is formed, in known manner, as an annular recess along the shank (14).

The stem (12) also includes a plurality of axial recesses, in this example four recesses (20). In the BR8666UK 6 example shown in Figure 2, each recess (20) includes a protrusion, here a projection (22) which, in this example is a pin having a height such that it sits flush with the outer periphery of the stem shank (14).

Referring also to Figure 3 it can be seen that in the example of Figure 2 there are four such axial recesses (20) formed peripherally in a cruciform arrangement. it can also be seen from Figure 3 that the centre of each axial recess includes a projection (22) (although only one such projection (22) has been referenced in Figure 3).

From Figures 2 and 3 it will be understood that the axial recesses (20) are formed by removing a quantityof material from the shank (14) such that the recesses (20) are of reduced diameter compared to the parts of the shank (14) which do not carry recesses (20) therein.

This can be seen most clearly from Figure 3 wherein the bases of each of the recesses (20) are clearly radially nearer the centre of the circular shank (14) than the lands which do not carry recesses.

Finally, as will be explained further below the central 25 axis of the stem (12) is also labelled as (10) (see Figure 2) because the stem (12) fits within the body (2) of the shell.

Figure 4 shows the assembled rivet wherein the stem (12) 30 is inserted into the shell (2. The central axes are concentric and this is shown as axis (10) in Figure 4.

Those skilled in the art will readily appreciate that in order to set the rivet axial load is applied to the body (2) once the body (2) has been passed through the apertured members (that is those members which are to be clamped together) such that the head (16) abuts one of BR8666UK 7 the members. When axial loading is applied to the stem (14), in known manner, the stem head (16) is pulled back in the direction of this force which thereby causes deformation of the shell body (2). Before describing the deformation process further, Figures 5, 6 and 7 show alternative arrangements of the stem (12). In these alternative arrangements it can be seen that the projection (22) has been replaced by a bar member (24). Although two different types of protrusion; a projection (22) and a bar member (24), are disclosed, those skilled in the art will appreciate that other suitable types of projection are equally efficacious in the present invention.

Referring now to Figure 8 it can be seen how the rivet is set in order to clamp together two apertured members (26) and (28).

An axial force has been applied to the stem shank (14) in the direction of the arrow shown as A. Although in Figure 8 it can be seen that the stem shank (14) has sheared at the breakneck (18), the setting of the rivet can readily be understood.

As the axial force in the direction of arrow A is increased, the stem head (16) pushes the body (2) in the direction of the arrow A. Because the material of the shell (2) is deformable (as is known in the art) the material deforms to compress axially, yet spread radially. The deformed material can easily be seen at reference (30). Because the recesses (20) carry, in this example, the bar member (24) which extends across the circumferential width of each recess (20), the deforming material (30) also surrounds (and in this example straddles both sides of) the bar (24).

BR8666UK 8 As a further force is applied to the stem (14) in the direction of arrow A, then once the deforming material (30) can deform no further and create a radially enlarged head to clamp the apertured members (26, 28) together tightly, then further force applied to the shank (14) will cause the shank (14) to break at the breakneck (18) in known manner. As the shank (14) breaks, the axial strain felt by the stem will be relieved. However, because the bar members (24) are straddled by deformed material (30) of the shell (2), then there will be no recoil of the stem head (16) in the direction of arrow B as shown in Figure 8 (recoil in the direction of arrow B follows from basic physical principles stating that to every action there is an equal and an opposite reaction).

Because there will be no recoil of stem head (16), then the abutment of the stem head (16) to the tail end (8) of the shell (2) remains tight thereby preventing influx of any water or moisture between the stem head (16) and tail end (8) of shell (2).

Thus, by provision of the bar members (24) (or indeed any style of projection such as pin (22)) then influx of water or moisture into the rivet is prevented.

It will be apparent to those skilled in the art from the foregoing that the purpose of a protrusion formed within the axial recess (20) of the stem is to allow the axial recess to be discontinuous, that is the contour surface of the axial recess must not be smooth. As long as there is no smooth (i. e. discontinuous) contour surface of the axial recess (20), then deformed material (30) of the shell (2) will be able to create an effective clamp with the stem.

Those skilled in the art will further appreciate that there is no necessity for the deformed material (30) of BR8666UK 9 the shell (2) to fully occupy the recesses (20) only partial occupation of the recesses (20) will be adequate so long as the protrusion of the recess is in contact with the deformed material thereby to create an effective clamp between the stem (14) and the shell (2). Following on from this reasoning, it will be understood that there is no need for total surrounding of each protrusion (22/24) by the deformed material (30) only partial surrounding will suffice in order to prevent recoil of the stem head (16) when the stem (14) shears about breakneck (18).

Although in the above examples four circumferentially spaced axial recesses (20) have been disclosed, the invention has been found to work with any number of recesses and they need not be circumferentially spaced when there are a plurality of such recesses. For example, only one recess or two axially separated yet longitudinally in line at recesses will suffice.

Thus can be seen particularly from Figure 8, it is advantageous for the stem to be of increased diameter in a region adjacent to stem head (16) as compared to the remainder of the stem shank (14). This is to allow for a setting tool to grip the stem shank (14), as can be seen from Figure 9. In Figure 9 it is shown how a rivet setting tool (part of which is shown at 32) is effective to grasp the shank (14) of the stem (12) and pull the stem (12) in the direction of arrow A (refer also to Figure 8).

The setting tool (32) includes a plurality of jaws (34) which are arranged to grasp the stem shank (14) in known manner.

The front end of the setting tool (32) abuts the radially enlarged head (6) of the shell (2)in order to maintain BR8666UK tight abutment between the head (6) and one of the apertured members for clamping (28).

It can be seen from Figure 9 that shearing of the shank (14) occurs at the breakneck (18) and that the position of the breakneck (18) along the actual length of the shank (14) has been chosen so that the breaking of the shank (14) occurs at position 36 which is flush with the end of the enlarged head 6. In this way there is solid stem material within the entire rivet once it has been set. Those skilled in the art will appreciate that the choice of position of the breakneck (18) is achieved in known manner, but is not germane to the present invention so will not be described any further herein.

It has been found that the circumferential width across any recess is preferably between 25% and 70%, and even more preferably between 45% and 55%, of the circumferential width of the land areas between and defining the recesses (20). These relative areas of land and recess have been chosen to allow an appropriate amount of deformed material (30) to enter the recesses (20) and so be able to achieve the aims of the present invention.

It will be understood that not every recess (20) need have an associated projection (22). Some of the recesses (20) can be formed without such an associated projection (22).

BR8666UK 11

Claims

1. A self-plugging blind rivet for securing together apertured members when the rivet is set, the rivet comprising; a tubular shell having a tail end face at one end and a pre-formed radially enlarged head at the other end; a stem having a shank which extends through the shell and a head adjacent the tail end face of the shell; the stem being formed with a plurality of axial recesses, the rivet characterised by:

is each of the axial recesses having a protrusion formed therein so that each axial recesses is discontinuous, and wherein the rivet is set by placing the shell under axial compression loading such that the shell deforms in a region adjacent the axial recesses of the stem and the deformed shell at least partially occupies each recess and also at least partially surrounds each protrusion.

2. A self-plugging blind rivet according to claim 1 wherein the plurality of axial recesses are generally circumferentially spaced around the periphery of the stem.

3. A selfplugging blind rivet according to claim 1 or claim 2 wherein the protrusions comprise bar members which extend generally across the circumferential width of the recesses.

4. A self-plugging blind rivet according to claim 2 wherein each recess has one corresponding bar member therein.

BR8666UK 12

5. A self -plugging blind rivet according to any one of the preceding claimed wherein the deformed shell axially straddles the protrusion when the rivet is set.

6. A self-plugging blind rivet according to any one of the preceding claims wherein the stem is of increased diameter in a region adjacent the stem head as compared to the remainder of the stem shank.

7. A self-plugging blind rivet according to any one of the preceding claims wherein the circumferential width across any recess is between 25% and 75% of the circumferential width of the land areas between and defining the recesses.

is

8. A self-plugging blind rivet according to any one of the claims 1-6 wherein the circumferential width across any recess is between 45% and 55% of the circumferential width of the land areas between and defining the recesses.

9. A self-plugging blind rivet according to any one of the preceding claims wherein the stem comprises a first stem portion, a pintail and a breakneck provided between the first stem portion and the pintail; the first stem portion being on the stem head side of the breakneck and the entire first stem portion being retained in the rivet shell and of larger diameter than the pintail such that, when the rivet is set, the larger diameter of the first stem portion cannot pass through a hcle in the nose of a tool for setting the rivet and the pintail breaks off at the rivet head.

10. A self-plugging blind rivet substantially as hereinbefore described with reference to the accompanying drawings.

BR8666UK