BACKGROUND TO THE INVENTION

This invention relates to a lock guard for use in a security screen door, in particular, a conventional metal framed door which incorporates a spline channel. Security screen doors resist intruders by the use of metal lattice screens and locks. The screen allows circulation of air while preventing access to the interior of a building by insects. The lock usually includes a mechanism for locking the door from inside the building without the key, commonly known as a snib. A barrier plate is normally attached inside the door to prevent access to the snib from outside the building. These plates are welded or screwed in position adjacent the lock, which requires additional time and labour costs during assembly of the doors.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved barrier against access to the snib in a security screen door, or at least to provide an alternative to existing barriers. In a first aspect the invention resides in a lock guard for use on a security screen door or similar, including: a planar section for inhibiting access to the lock, a tongue extending transversely from one edge of the planar section, and a projection extending transversely from the tongue, adapted to engage a wall of a spline channel of a frame of the door. The tongue preferably extends from the edge of the planar section at an acute angle, preferably in the range of 70° to 85°. The tongue preferably extends the full length of the edge of the planar section. A lock guard of this kind may be snapped into position within the spline channel. The projection is preferably adapted to engage with a serrated wall of the spline channel. The projection may be formed as a barb and preferably a continuous linear barb along the tongue. The barb is preferably adapted to insert into a groove in the wall of the spline channel. In a further aspect, the invention resides in a method of forming and positioning a lock guard for a security screen door, including: forming a lock guard having a planar section, a tongue extending from the planar section, and a barb on the tongue, positioning the lock guard with the tongue ,and linear barb aligned with a spline channel of a door frame, and urging the barb and tongue into the spline channel so that the lock guard is snapped into position. The invention also resides in a door frame or a security screen door that incorporates a lock guard as defined above.

BRIEF DESCRIP TION OF THE DRAWINGS

Preferred embodiments of the invention will be described with respect to the accompanying drawings of which: FIG. 1 is a top view of a lock guard, FIG. 2 is a side view of the lock guard of FIG. 1 with FIG. 2A showing representative dimensions and angles of a ledge and barb arrangement, FIG. 3 is a lower isometric view of the lock guard in FIG. 1; FIG. 4 is an isometric view of the positioning of a lock guard relative to a section ofa door, FIG. 5 shows the arrangement of FIG. 4 with a lock guard advanced towards its operative position, FIG. 6 shows the arrangement of FIG. 5 further advanced into operating position, and FIGS. 7 to 9 show side views of the process of FIGS. 4 to 6.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings it will be appreciated that the invention can be implemented in a variety of ways for a range of different screen doors. In FIG. 1, there is seen a lock guard 10 having a front edge 11, rear edge 12 and side edges 13, 14. A transverse tongue 16 is shown in hidden detail behind a substantially planar section 17. The planar section is dimensioned to provide adequate coverage as a guard against access to a lock located inside the door. The lock guard may be formed from any suitable material but is preferably formed from metal, such as aluminium, or a plastic or polycarbonate material. FIG. 2 shows the embodiment of FIG. 1 in side view. Planar section 17 extends away from side edge 13. At its' front edge 11, the planar section is continuous with the tongue 16 which is shown projecting from the planar section at an acute angle. That is, the tongue 16 extends at an angle less than 90° and preferably 70 to 80° in a fashion that creates a slight return. The tongue 16 has a transverse barb 18 which projects in a direction towards the planar section. Typical angles and dimensions are shown in FIG. 2A wherein the acute angle is around 80°. The barb has an outer angle of approximately 30° relative to an axis parallel to the planar section 17 and the barb point is formed by a 35° truncation of the outer edge of the barb. A preferred size for the planar section is around 240mm long by 100mm wide. The tongue may extend approximately 12.5mm inwardly. FIG. 3 shows a lower isometric view of the arrangement of FIGS. 1 and 2. In FIG. 4, a lock guard 10 is positioned relative to a section of a screen door comprising a frame member 20 and security screen infill material 21 forming a mesh. The frame member 20 is formed with an internal channel 22 and inner projecting ledge 23 which supports a spline channel 24. The spline channel 24 has serrated or ribbed walls. The lock guard is structured to snap into position with the tongue and barb inserted into the spline channel and an outer edge of the planar section abutting, at least in part, the infill material. The tongue 16 is lined up with the spline channel 24 and the rear edge 12 is positioned inwardly of the frame member 20. The infill material 21 is preferably of rigid material formed as a series of interconnected components in a repeating pattern to provide apertures for air movement while excluding intruders. A fine mesh material may be overlaid on the rigid web. In FIG. 5, the arrangement of FIG. 4 has been advanced so that the tongue 16 and barb 18 are entered into the spline channel 24. Beyond this point the planar section may begin to flex and be partly deformed by application of manual force. The tongue and barb - A -

are preferably relatively rigid. This provides tension in the lock guard and allows a snap action when the guard is installed. This process is continued until the arrangement of FIG. 6 is obtained as the tongue 16 and barb 18 snap into position in the spline channel with the barb locking against one or more of the grooves 26. The rear edge 12 has also advanced into abutting contact with the infill material 21 to provide a locking action which will be further described below. FIGS. 7, 8 and 9 show a sideway view of the process of FIGS. 4 to 6. The lock guard 10 is aligned in FIG. 7 with the tongue 16 positioned above the spline channel 24 and the rear edge 12 of the lock guard clear of the infill material 21. The lock guard 10 is advanced in FIG. 8 so that the tongue 16 and barb 18 are positioned in the spline channel 24 and the rear edge 12 abuts the infill material 21. In FIG. 9, the lock guard 10 has been snapped into position so that the barb 18 is urged against a rib of the spline channel 24. The rear edge 12 is forced against the infill material 21 so that the linear barb engages with the rib or serrated edge of the spline channel. When fully engaged, competing forces are generated between the barb 18, particularly the barb point, an upper outer corner 28 of the tongue and the rear edge 12 of the lock guard being forced against the infill material 21. It is intended to be difficult and preferably impossible to interfere with the lock guard through the infill material from outside the door. If necessary however, the lock guard may be adjusted or removed from inside the door by applying force to the middle of the planar section and directed towards the infill material and an outwardly directed force at point 30 to disengage the barb and free the lock guard. Throughout the specification, the aim has been to describe preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Various modifications and changes can be made without departing from the scope of the invention.