GB2425159A

GB2425159A - Tamper evident fasteners

Info

Publication number: GB2425159A
Application number: GB0507733A
Authority: GB
Inventors: John Ian Potter; Graeme Lindsay Jonath Paterson
Original assignee: Guidance Control Systems Ltd
Current assignee: Guidance Control Systems Ltd
Priority date: 2005-04-16
Filing date: 2005-04-16
Publication date: 2006-10-18
Anticipated expiration: 2025-04-16
Also published as: GB0507733D0; GB2425159B

Abstract

A tamper evident fastener such as a rivet comprises a rigid member 2 having at least one engaging means such as a barb 4. The rigid member 2 is connected to a head portion or flange 6 by a weakened region 8, 10 which will break if tampered with.

Description

TITLE

New fasteners

DESCRIPTION

Technical Field

The present invention relates to tamper-evident rivets, and in particular to tamper- evident rivets that may be used, for example, to secure together parts of a container or housing and that provide a clear visual indication if an attempt is made to open the container or housing.

Summary of the Invention

The present invention provides a tamper-evident rivet that can be used to secure together two component parts of a container or housing, for example. The rivet is intended to break if an attempt is made to force the component parts open or if the rivet itself is otherwise interfered with. The rivet comprises a rigid member having at least one engaging means and a head portion, wherein the rigid member is connected to the head portion by a weakened region.

The at least one engaging means can be a barb that engages with a corresponding locating means provided on one of the component parts of the container or housing. It is generally preferred that the rigid member contains two barbs, each barb extending in a direction back towards the head portion. However, it will be readily understood that the at least one engaging means can have any suitable construction. Alternatives may include a recess for receiving a locating means (such a projection or barb) provided on one of the component parts of the container or housing, or a retractable or spring-loaded projection that is received in a recess or behind a shoulder provided on one of the component parts of the container or housing.

The head portion is preferably a flange extending radially outwardly from an end of the rigid member. The flange can include alignment means su'h as a projection, recess or tab or can be formed with a particular nonsymmetrical shape so that the rivet may only be located in a particular orientation where the at least one engaging means and the corresponding locating means are properly aligned. For example, the flange may be rectangular-shaped and is received in a corresponding rectangular- shaped recess in the outer surface of one of the two component parts so that the at least one engaging means of the rivet is aligned with the locating means provided in the other of the two component parts. The alignment means and/or the shaped recess also prevent the head portion from being able to rotate.

The weakened region can be a continuous weak section defined, for example, by a line of reduced thickness in the head portion extending around the end of the rigid member. The line of reduced thickness can also extend around just part of the end of the rigid member. The rigid member can also be connected to the head portion by at least one frangible bridge, in a particularly preferred case, a series of perforations or slots are provided in the head portion around the end of the rigid member to define a number of weak sections of material or frangible bridges linking the head portion to the rigid member. The number, size and shape of the frangible bridges can be adjusted to provide the required strength and mechanical characteristics for a particular application. For example, in some circumstances it might be necessary for the frangible bridges to break when only a small amount of force is applied. In this case, the frangible bridges may be made weaker by altering their size and shape accordingly, or by reducing the total number of frangible bridges connecting the rigid member and the head portion together. Also, the frangible bridges may be adjusted to make them less resistant to applied rotational force and more resistant to applied axial force (that is where an attempt is made to force the two component parts of the container or housing apart) or vice versa.

It will be readily appreciated that the strength of the at least one engaging means is preferably greater than the total strength of the weakened region so that the weakened region will always break in preference to the engaging means.

In use, the rivet is inserted through an aperture provided in ofle of the two component parts of the container or housing. The rivet is orientated such that the at least one engaging means on the leading end of the rivet cooperates with a locating means provided on the other of the two component parts. The head portion is preferably in contact with the outer surface of the said one of the two component parts and can optionally be received in a recess in the outer surface surrounding the aperture as described above. The two component parts are therefore firmly secured together between the head portion and the at least one engaging means of the rivet.

The two component parts may only be unsecured by removing the rivet and this can only be achieved by separating the head portion from the rigid member by breaking the weakened region. If an attempt is made to pull the two component parts apart to gain access to the interior of the container or housing, for example, then the application of an axial force will cause the weakened region to break. If the rivet is broken then it cannot be reused and it will be obvious to the casual observer that tampering has taken place because the two component parts will no longer be secured together. The weakened region cannot be repaired without such a repair being immediately obvious. It will also be obvious to the casual observer if the weakened region is only partially broken (for example, if the application of the axial force is only sufficient to break some but not all of the frangible bridges) even though this will mean that the head portion is still retained on the rigid member and the two components parts are still secured together.

It may be appropriate for the rivet to be legitimately removed to allow access to the interior of the container or housing by an authorised person. In this case, it is generally preferred (although not essential) that the rigid member is provided with a shaped recess or a number of individual recesses. The recess or recesses are preferably formed in a face of the end of the rigid member within the area defined by the weakened region. To remove the rivet, a removal tool having a corresponding shaped projection or individual projections is used. The projection or individual projections are inserted into the shaped recess or individual recesses and the removal tool is then rotated. Alternatively, the face of the end of the rigid member is provided with a shaped projection or individual projections and the removal tool includes a corresponding shaped recess or individual recesses. An example of a simple removal tool might be a standard screwdriver having a flat or cross-head blade tip that is received in a corresponding recess in the face of the rigid member. Other more specialised removal tools can also be used. The head portion is unable to rotate (see above) and the application of the rotational force to the rigid member causes the weakened region to break. Rotation of the rigid member relative to the head portion through a predetermined angle (such as 90 , for example) preferably brings the at least one engaging means out of alignment with the corresponding locating means provided on the other of the two component parts so that the rivet can be withdrawn from the aperture.

The shaped recess or individual recesses may be tapered so that the removal tool grips the rigid member securely during the rotation and extraction process.

The removal tool may also be adapted to cut or break the weakened region. This can he in addition to, or instead of the use of any engagement between shaped projection(s) and recess(es).

When the rivet is located in position, it is generally preferred that only the head portion and the end of the rigid portion are visible from outside the housing or container. To further prevent the at least one engaging means from being tampered with, the rigid member can also include a blocking flange or thickened region located axially between the at least one engaging means and the head portion. The blocking flange obscures the engaging means from view and restricts access from outside the housing or container.

The rivet may be integrally formed of a rigid plastics material.

The use of an inexpensive single-use rivet allows the two component parts to be secured together in a quick and easy manner.

Drawings Figure 1 is a first view of a tamper-evident rivet in accordance with the present invention; Figure 2 is a second view of the tamperevident rivet of Figure 1; Figure 3 is a cross section view of the tamperevident rivet of Figure 1; and Figure 4 is a cross section view of housing having a base part and a lid part secured together by the tamper- evident rivet of Figure 1.

With reference to Figures 1 to 3, a tamper-evident rivet includes a rigid shaft 2. A pair of rearwardly extending barbs 4 are provided on a leading end of the shaft 2. The trailing end of the shaft 2 is connected to a rectangular-shaped flange 6 by a number of frangible bridges 8. The frangible bridges 8 are separated by a number of perforations or slots JO and together define a circular weakened region that extends around the base of the trailing end of the shaft 2.

The face of the trailing end of the shaft 2 includes a pattern of individual circular recesses 12.

The shaft 2 also includes a blocking flange 14 that is axially located between the barbs 4 and the flange 6. The blocking flange 14 is merely a region of increased diameter and its purpose is explained in more detail below.

With reference to Figure 4, the tamper-evident rivet is used to secure together a lid part 20 and a base part 22 of a housing where access to the interior is only permitted to authorised persons. One end of the base part 22 has an aperture 24 into which the rivet is inserted. The corresponding end of the lid part 20 includes a pair of engaging features 26 with inwardly extending shoulders 28 behind which the barbs 4 of the rivet can locate. The construction of the engaging features 26 is described in more detail below.

The base part 22 includes a recess 30 that surrounds the opening of the aperture 24 and which is shaped to receive the rectangular-shaped flange 6 of the rivet. Because both the flange 6 and the recess 30 are rectangular-shaped it means that the rivet can only be located in the aperture 24 in such a way that the barbs 4 are aligned with the shoulders 28 as shown in Figure 4. It also means that the flange 6 cannot rotate in the recess 30. If the flange 6 is square-shaped or circular, for example, then it could be provided with a tab that extends into a groove in a sidewall of the recess, or with a projection that is received in a hole in the base of the recess. Both of these alternative constructions would mean that the rivet could only be located in the aperture in one orientation to make sure that the barbs are properly aligned with the shoulders of the engaging features.

The engaging features 26 are formed as oppositely fttcing beads that extend along part of the inside surface of a sleeve 32 having a general oval-shaped cross section when viewed along its axis. The base part 22 also includes a sleeve 34 that surrounds the aperture 24 and overlaps with the sleeve 32.

In use, the lid part and base part 20 and 22 are brought into contact with each other and secured together using a rivet (although two or more rivets can be used as necessary). More particularly, the rivet is inserted into the aperture 24 in the base part 22, until the flange 6 is fully received in the recess 30 and the barbs 4 are firmly located behind the shoulders 28 of the engaging features 26 as shown in Figure 4.

The sleeve 34 surrounds the aperture 24 to enclose the rivet and protect against tampering from inside the housing in the unlikely event that the lid part and base part 20 and 22 are forced apart at a different location. The sleeve 34 also provides additional support to the rivet by providing an engagement overlap with the sleeve 32 on which the engaging features 26 are formed. This reduces the effect of any sideways forces applied to the rivet and concentrates any forces along (or around) the axis of the rivet.

Further protection against tampering from outside the housing is provided by the blocking flange 14, which in use is positioned just below the engaging features 26 and prevents a tool or the like from being inserted along the aperture (perhaps through the slots 10) and into the cavity between the engaging features in an attempt to free the barbs 4 from the shoulders 28.

If the lid part 20 and the base part 22 are pulled apart to try and gain access to the interior of the housing then this will cause some or all of the frangible bridges 8 to break. Although the rivet will not actually prevent unauthorised access to the interior of the housing, its main purpose is to provide evidence that tampering has occurred.

If all of the frangible bridges 8 are broken then the rivet will no longer secure the lid part and base part 20 and 22 together and this will be immediately obvious to the casual observer. Any attempt to mend the broken frangible bridges (which in any case will be almost impossible to achieve) can also be easily detected because the flange 6 and the frangible bridges 8 are clearly visible when the base part 22 is inspected. Such an inspection would also show if some but not all of the frangible bridges 8 have been broken if the base part and lid part 20 and 22 were pulled apart with insufficient force to facilitate the complete separation of the shaft 2 from the flange 6.

The rivet can be legitimately removed by an authorised person using a removal tool (not shown). The tool includes a number of projections corresponding to the paftern of circular recesses 12 provided in the face 2a of the trailing end of the shaft 2. The projections are received in the recesses 12 and the removal tool is rotated to impart a rotational force to the shaft 2. Because the flange 6 cannot rotate in the recess 30, the rotational lbrce causes the frangible bridges 8 to break. Rotation of the shaft 2 by 90 brings the barbs 4 out of alignment with the shoulders 28 of the engaging features 26 and, more particularly, into alignment with a part of the sleeve 32 along which the inwardly facing beads do not extend. The rivet can therefore be extracted from the aperture 24 and discarded.

Claims

1. A tamper-evident rivet comprising a rigid member having at least one engaging means and a head portion, wherein the rigid member is connected to the head portion by a weakened region.

2. A tamper-evident rivet according to claim 1, wherein the at least one engaging means is a barb.

3. A tamper-evident rivet according to claim I or claim 2, wherein the head portion is a flange.

4. A tamper-evident rivet according to any preceding claim, wherein the rigid member is connected to the head portion by at feast one frangible bridge.

5. A tamper-evident rivet according to any preceding claim, wherein the rigid member is provided with a shaped recess for receiving a corresponding shaped projection of a removal tool.

6. A tamper-evident rivet according to any preceding claim, wherein the head portion includes alignment means.

7. A tamper-evident rivet according to any of claims 3 to 6, wherein the flange is rectangular-shaped.

8. A tamper-evident rivet according to any preceding claim, wherein the rigid member further comprises a blocking flange located between the at least one engaging means and the head portion.

9. A tamper-evident rivet according to any preceding claim, integrally formed of a rigid plastics material.

10. A tamper-evident rivet substantially as herein described and with reference to the drawings.

Amendments to the claims have been filed as follows

3. A tamper-evident rivet according to claim 1 or claim 2, wherein the head portion is a flange.

4. A tamper-evident rivet according to any preceding claim, wherein the weakened region connecting the rigid member to the head portion comprises at least one frangible bridge.