GB2036446A

GB2036446A - Permanent Magnet for Security Systems

Info

Publication number: GB2036446A
Application number: GB7938444A
Authority: GB
Original assignee: GKN Fasteners Ltd
Current assignee: GKN Fasteners Ltd
Priority date: 1978-11-25
Filing date: 1979-11-06
Publication date: 1980-06-25

Abstract

A magnet assembly for use in a security system of the kind incorporating an electrical circuit including an alarm and a set of magnetically operable electrical contacts responsive to the open or closed condition of the door or window, has a magnet assembly for operating the contact set constituted by an injection moulded unit 11 of a composite magnetic-plastics material. The selected material is a composite of nylon type 610 and a barium ferrite. A removeable end flange 12 facilitates mounting in a variety of ways. <IMAGE>

Description

SPECIFICATION Security System Magnet The invention relates to magnet assemblies for security systems.

One type of security system for doors or windows incorporates an electrical circuit including an alarm bell and a set of electrical contacts responsive to the open or closed condition of the door or window. The electrical contact set may be a magnetic read contact set, set into a door frame or window frame in which case the door or window is provided with a magnet assembly which comes into close proximity with the contact set when the door or window is closed but moves away from the contact set when the door or window is opened.

The contact set is such that the ccntacts are closed when the door or window is-closed due to the proximity of the magnet but the contacts are automatically opened as the door or window is opened. In this way it is possible for the contact set to signal that the door or window has been opened and to sound the alarm.

In a modification of this arrangement, the electrical contact set is surface mounted on the door or window frame, in which case surface mounting of the magnet is also required.

The invention is concerned with an improved magnet assembly for use in such a system.

According to one aspect of the present invention there is provided a magnet assembly for use in a security system and comprising an injection moulded unit constituted by a composite magnet-plastics material.

The magnet assembly may incorporate a magnet body having a flange on one end thereof.

The flange may be joined to the main body by a weakened break-away section so that the magnet unit can be used without the flange.

According to a second aspect of the invention there is provided a magnet assembly for use in a security system and comprising an injection moulded unit constituted by a composite magnetic-plastics material, the unit being elongated, being adapted for mounting in a support aperture by a removeable end flange on the unit and being adapted for surface mounting after removal of the flange by having a longitudinally extending mounting face and at least one transverse mounting hole through the unit.

According to a third aspect of the invention there is provided a magnet assembly for use in a security system and comprising an injection moulded unit constituted by a composite magnetic-plastics material, the unit being elongated, being adapted for mounting in a support aperture by a locking formation adapted to removeably receive an end flange and being adapted for surface mounting without the flange by having a longitudinally extending mounting face and at least one transverse mounting hole through the unit.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross-section through a complete magnet assembly in position in a door; Figure 2 is a corresponding view of a magnet assembly used without the flange; Figure 3 is a side elevation of a second embodiment of the invention; Figure 4 is a section on line IV--IV of Figure 3; Figure 5 is an end view of the unit shown in Figures 3 and 4; and Figure 6 is a view corresponding to Figure 4 but showing an alternative mounting arrangement for a flange.

The magnet assembly shown in Figure 1 is a moulding of a composite material constituted by 20% of nylon type 610 and 80% of a barium ferrite in finely divided form.

The moulding, as shown in Figure 1, incorporates a primary magnet unit 11 which is generally cylindrical but incorporates a slight taper, partly to facilitate moulding but also for another purpose to be described. At the larger diameter end of the primary magnet unit 11, there is a rectangular flange 12. The flange 12 is joined to the primary magnet unit 11 by a weakened portion 13 which is formed by providing an annular notch 14. This enables the flange 12 to be broken away from the primary magnet unit 11 as is shown in the arrangement of Figure 2.

Returning again to Figure 1 , the magnet assembly is shown mounted in a door 1 5. Prior to mounting the magnet assembly, a hole 1 6 is drilled in the door from one end 17 and the diameter of this hole is selected so as to be greater than the smaller diameter of the generally cylindrical primary magnet portion 11 but slightly smaller in diameter than the largest diameter thereof. In order to fix the magnet assembly in position, it is merely necessary to engage the free end (remote from the flange 1 2) of the assembly in the hole 16 and force or hammer the assembly into a wedged position in the hole as shown. In order to facilitate securing of the magnet assembly, the cylindrical portion may be provided with longitudinal external ribs to assist engagement between the hole in the door and the magnet assembly.

The material of the magnet assembly is magnetized during manufacture (by provision of a magnetic field during the moulding operation) in an axial direction as indicated by arrow 1 8. Thus a magnetic pole is provided adjacent the edge of the door. In use, a magnetic reed contact set incorporated in a security circuit is arranged in the fixed door frame in such a position that it lies adjacent the magnet assembly when the door is closed. Opening and closing of the door actuates the contact set which in turn causes an alarm to be sounded or another suitable warning to be given.

One purpose of the flange 12 is to ensure a tidy appearance to the door in the vicinity of the magnet assembly in that it completely closes off and hides any local damage around the edges of the hole 1 6. The flange may also if desired, be used to assist in mounting the magnet assembly to the door by means of non-magnetic fasteners such as brass screws.

It is important to provide a substantial magnetic field over a sufficient area adjacent the edge of the door to cater for slight misalignment between the magnet assembly and the contact set. The notch 1 4 tends to prevent the magnetic circuit from remaining in the flange 12 and in this way provides a substantial area with a significant magnetic field.

Figure 2 shows an alternative arrangement which can be used where it is desired to completely seal the magnet within the door.

Starting from a magnet assembly as shown in Figure 1 and a door with a similar hole to the hole 16, the magnet assembly is tapped in to the hole beyond the stage shown in Figure 1 so that the flange 12 breaks off and the primary magnet unit 11 becomes slightly recessed in the door. The recess is then filled with a conventional filler material 19 so that when it is painted or stained the magnet assembly is completely hidden. With the Figure 2 arrangement, care must be taken to ensure that the door is a reasonably close fit in its frame so that the contact set and the magnet unit are sufficiently close together for the magnet to operate the contact set.

The arrangement shown in Figures 3, 4 and 5 differs from that shown in Figures 1 and 2 primarily in that the cross-sectional shape of the magnet, including its flange, is square instead of being circuit. The square section unit can still be mounted in a circular drilled hole either in the way shown in Figure 1 or as shown in Figure 2. The drilled circular mounting aperture can be made of such a diameter that the corners of the square section unit are a tight fit in the aperture.

The square section also provides a flat mounting face 21 for the unit. When it is desired to surface mount the unit, the square section flange 22 is broken from the main body of the unit around the notch 23. The unit can then be mounted flush against a door or window or frame by means of two countersunk screws (not shown) inserted in transverse mounting holes 24. In order to save unnecessary material, the unit is provided with openings 25, 26 and 27 from the direction of the mounting face 21.

When installed in or on a door or window or frame, the magnet unit of Figures 3 to 5 cooperates with the other parts of a security system as described with reference to Figure 1 and Figure 2.

Instead of moulding the flange 27 as part of the unit shown in Figures 3 to 5, the flange could be a separate moulding which can be secured to the main unit by interlocking formations such as is shown for example in Figure 6. In the Figure 6 embodiment, the flange may be formed of the same nylon-ferrite composite as the main body of the unit or alternatively may be moulded from nylon or other non-magnetic material. When the same material is used for the body of the unit and the flange, these components could be formed in adjacent cavities in a mould and maintained in a joined together condition by sprues. This ensures that the flange is always available when the unit is to be used. The operator simply breaks the two units apart at the sprues and then either discards the flange or attaches it to the main body in the manner shown in Figure 6.

In greater detail, rectangular flange 32 has a central cylindrical projection 33 which is a tight fit in a corresponding aperture in the end face of the main magnet moulding. In order to provide a sufficiently thick end wall in Figure 6, the arrangement of mounting holes 34 and opening 35 has been altered as compared with Figures 3 to 5.

The arrangement of Figures 3 to 5 provides in a single moulding a magnet unit which can be mounted in any of the ways conventionally required for a magnet unit in a security system.

This versatile unit reduces the stock which has to be carried by a security system installer and also reduces the cost of the unit compared with conventional units which normally comprise separate magnets and housings.

Claims

1. A magnet assembly for use in a security system and comprising an injection moulded unit constituted by a composite magnetic-plastics material.

2. An assembly as claimed in Claim 1 incorporating a magnet body having a flange on one end thereof.

3. An assembly as claimed in Claim 2 in which the flange is joined to the main body by a weakened break-away section so that the magnet unit can be used without the flange.

4. A magnet assembly for use in a security system and comprising an injection moulded unit constituted by a composite magnetic-plastics material, the unit being elongated, being adapted for mounting in a support aperture by a removeable end flange on the unit and being adapted for surface mounting after removal of the flange by having a longitudinally extending mounting face and at least one transverse mounting hole through the unit.

5. A magnet assembly for use in a security system and comprising an injection moulded unit constituted by a composite magnetic-plastics material, the unit being elongated for mounting in a support aperture by a locking formation adapted to removeably receive an end flange and being adapted for surface mounting without the flange by having a longitudinally extending mounting face and at least one transverse mounting hole through the unit.

6. A magnetic assembly for use in a security system substantially as described with reference to and as illustrated by Figure 1 or Figure 2 of the accompanying drawings.

7. A magnet assembly for use in a security system substantially as described with reference to and as illustrated by Figures 3 to 5 or Figures 3 to 5 modified by Figure 6 of the accompanying drawings.