The invention relates to spring assemblies and particularly to a method of installing a spring assembly in an apparatus having first and second parts which, in use, are to be urged together by the spring assembly.

The invention is particularly, though not exclusively, concerned with an apparatus comprising a letter plate assembly comprising a frame, for example to be mounted, in use, over an opening for letters in a door, and a cover flap, which, in use, is normally urged into a closed position against the frame.

Such letter plate assemblies are well known and the two parts are generally urged together by one or more torsion springs. Assembling the components, with the necessary degree of preloading of the, or each, torsion spring, can be time consuming and expensive.

The invention provides a method of installing a spring assembly in an apparatus having first and second parts which, in use, have to be urged together by the spring assembly, comprising the steps of inserting a first end of the spring assembly into the first part, rotating the second end of the spring assembly to preload a torsion spring of the spring assembly, and then attaching the second end of the spring assembly to the second part. A winding member may be used to rotate the second end of the spring assembly.

A trigger may be provided to maintain the second end of the spring assembly in its wound condition prior to its attachment to the second part. The spring assembly may be inserted into a socket in the first part.

A compression spring may be inserted into the socket before insertion of the spring assembly, such that the spring assembly can be moved inwardly against the action of the compression spring before the second end of the spring assembly is attached to the second part. The second part of the spring assembly may be attached to the second part by permitting the second end of the spring assembly to move into a socket in the second part under the influence of the compression spring, after release of the trigger. The first and second ends of the spring assembly may comprise bosses connected to the ends of the torsion spring.

The boss forming the first end of the spring assembly may be shaped such that it can slide into the socket in the first part but cannot rotate with respect to the first part.

The boss forming the second end of the spring assembly may be provided with a hole which engages with a pin of the trigger.

The boss forming the second end of the spring assembly may be provided with a formation shaped to engage a mating formation on the winding member.

The formation on the boss may be shaped to mate with the socket in the second part.

The first part may have first and second ends, each end having a spring assembly as defined above.

The first part may comprise a cover flap of a letter plate assembly, the second part comprising a frame of the letter plate assembly. The invention includes an apparatus comprising first and second parts, the parts being urged together by a spring assembly installed using the method defined above.

By way of example, a specific embodiment of the invention will now be described, with reference to the accompanying drawings, in which:

Figure 1 shows a first step in a method according to the invention, namely the insertion of a compression spring into a cover flap of a letter plate assembly;

Figure 2a is an exploded view of a torsion spring device used in the embodiment of the invention; Figure 2b shows a second step in the method, namely the assembly of the torsion spring device;

Figure 3 shows a third step of the method including more details of the cover flap; and

Figures 4-10 show further steps in the method, the frame of the letter plate assembly being shown in Figures 8, 9 and 10.

This embodiment of the invention relates to a letter plate assembly comprising a cover flap 10 which in use is urged against a frame 1 1 (see Figures 8, 9 and 10) by a spring assembly.

The frame 1 1 has a slot 12 therethrough. In use, the frame 11 is mounted on a door with the slot 12 in register with a slot in the door to receive letters. In Figures 8, 9 and 10, the cover flap 10 is shown in a raised position, to expose the slot 12, so that letters can be inserted, but the flap 10 is normally urged against the frame 1 1 by a torsion spring 13 (see Figures 2a and 2b) so that the slot 12 is closed.

This embodiment of the invention is concerned with the assembly of the components, such that the torsion spring 13 has the desired preloading, to hold the flap 10 closed against the frame 1 1.

There is a spring assembly at each end of the letter plate assembly but as the spring assemblies are mirror images of one another, only one spring assembly will be described in detail with reference to Figures 1 , 2a, 2b and 3.

At each end of the flap 10 there is a socket 14 to receive the spring assembly, the spring assembly being shown in detail in Figures 2a and 2b. The first step in assembling the product is to insert a compression spring 15 into the socket 14.

The spring assembly comprises boss members 16 and 17 each having a protruding peg 18 to act as a guide for the torsion spring 13. The boss 16 has a keyway 19 thereon projecting radially therefrom and the boss 17 has a square cross-section peg 20 extending axially therefrom.

The projecting ends 21 of the torsion spring 13 are turned over through 90° at 22.

When the components shown in Figure 2a are assembled together, as shown in Figure 2b, the ends 21 of the torsion spring 13 extend into sockets within the bosses 16 and 17, the inner parts of the bosses 16,17 being shaped to trap the overturned ends 22 of the torsion spring 13 so that the bosses 16, 17 cannot rotate with respect to the ends of the torsion spring 13. In other words, if boss 17 is rotated with respect to boss 16, the torsion spring 13 will tighten.

In the next stage of the assembly process, shown in Figure 3, the spring assembly is inserted into the socket 14 of the flap 10. As seen in Figure 3, the socket 14 has a recess 23 to receive the keyway 19 of the inner boss 16 so that once the spring assembly has been inserted into the socket 14, the boss 16 cannot rotate with respect to the cover flap 10. However, the outer boss 17 is free to rotate with respect to the flap 10, such rotation causing loading of the spring 13. In the next step of the method, shown in Figure 4, the spring 13 is preloaded by attaching a winding wheel 24 and turning the winding wheel clockwise through 270°. The winding wheel 24 has a square socket, not visible in the figures, which fits over the square cross-section projection 20 so that rotation of the winding wheel rotates the boss 17.

In the next step, shown in Figure 5, an L-shaped trigger 25 is inserted. The trigger 25 has a pin not visible in the figures which is inserted into a hole 26 in the boss 17 to hold the boss 17 in the position to which it has been rotated by use of the winding wheel 24.

In the sixth step, shown in Figure 6, the winding wheel 24 has been removed but the boss 17 is retained in position by the trigger 25 so that the torsion spring 13 cannot unwind. The next step, as shown in Figure 7, is to repeat the first six steps with the other end of the flap, so at this point the flap 10 has two preloaded spring assemblies, one at each end, the preloading of the spring assemblies each being maintained by an associated trigger 25.

The flap assembly is then fitted into position on the frame 1 1. At each end of the frame 11 there is a square aperture and when the flap 10 is positioned against the frame 11 as shown in Figure 8, the square apertures in the frame are in register with the square bosses 20 of the respective spring assemblies.

Before the flap 10 is placed in position, the bosses 20 project outwardly. As shown in Figure 8, the triggers 25 are moved towards one another, in the direction of the arrows 27.

This moves the bosses 20 inwardly with respect to the flap, each spring assembly as a whole moving inwardly against the action of the associated compression spring 15 at the inner end of the associated socket 14.

This inner movement is possible because there is a slot 28 in the associated socket 14, as shown in Figure 5. In the next step, shown in Figure 9, the triggers 25 are moved outwardly again, in the direction of the arrows 29 so that the bosses 20 enter the square apertures at each end of the frame.

Finally, as shown in Figure 10, the triggers can be removed and the flap 10 then closes against the frame 1 1 under the influence of the energy stored in the torsion springs 13.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.