GB2538045A

GB2538045A - Improvements to letter-plates

Info

Publication number: GB2538045A
Application number: GB1504429.0A
Authority: GB
Inventors: Mcloughlin John
Original assignee: UAP Ltd
Current assignee: UAP Ltd
Priority date: 2015-03-17
Filing date: 2015-03-17
Publication date: 2016-11-09
Anticipated expiration: 2035-03-17
Also published as: GB201504429D0; GB2538045B

Abstract

A letter-plate 1 comprises a pair of frames 2, 3 fitted on opposing sides 6, 7 of a door 4. At least one sleeve 9, 10 passes through an aperture 5 in the door between the frames. At least one of the frames is provided with a flap 12 that is pivotally mounted thereto by a hinge pivot comprising a plastics rod 15. The plastics rod is located in a channel 16 defined by the flap and has an end 17 located in a channel 18 defined by the frame so that in use the flap hangs downwards to cover the aperture in the door until raised. A bridge 19 is formed by a length of the rod between the channel in the frame and the channel defined by the flap. This bridge is covered by a metal jacket 20 in order to maintain the structural integrity of the bridge 19 in the event of a fire. A metal pin 23 (figures 7a, 7b, not shown) may be incorporated into the plastics rod spanning that part of the rod defining the bridge. In use, during a fire the metal jacket and optional metal pin enable a flap 12 to remain in position covering the aperture 5 for a longer period of time than would otherwise be the case.

Description

IMPROVEMENTS TO LETTER-PLATES The present invention relates to letter-plates.

Conventionally a letter-plate comprises a pair of frames with inter-engaging sleeves that are fitted together through both sides of an aperture cut into a door to accommodate same. The letter-plate finishes the aperture and provides one or more flaps and/or brushes to cover the framed aperture and thereby protect the space on, for example, an interior side of the door from the weather on the exterior side of the door whilst enabling letters and small packets to be pushed through the framed aperture. Usually a spring-loaded flap that is biased into a closed position covering the aperture is used on the exterior side of the door and a second flap or brushes are used to cover the aperture on the interior side of the door.

Most letter-plates are made of elements that are comprised of metal or of plastics. In particular, the frames and the flaps are usually metal but the inter-engaging sleeves are of plastics. In addition, the flaps are often provided with a plastics hinge pivot that doubles both as a torsional spring, in order to provide the required closing force to prevent the flaps from rattling in the wind and to assist in draught exclusion, and as a pivot that holds the flap in axial alignment with the supporting frame to allow a free radial opening/closing movement. Such plastics hinge pivots comprise a plastics rod which is twisted when the flap is opened. They usually have excellent fatigue properties so that they can continue to operate over many years of service. However, in a fire or during fire testing the interior flap usually falls off the letter-plate very quickly, typically within a couple of minutes, because the plastics rod melts. Its melting point is usually around i6o°C and this temperature is reached very quickly if the fire is close to the door. The inter-engaging frames through the aperture are then directly open to the heat and flames and soon start to melt too.

In order to check fires, usually doors are made from fire-rated materials. It is, however, important to prevent the aperture through the letter-plate from providing a conduit for flames and smoke to escape and for air from the exterior of a building to fuel a fire within, especially once the interior flap has fallen away. To this end the letter-plate may be provided with an intumescent insert that can close the aperture if the need arises. This insert is usually located around the exterior of the outer of the two inter-engaging sleeves that are fitted through the aperture. If this insert becomes sufficiently hot, for example in the case of a fire occurring on the interior side o of the letter-plate, then it swells, collapsing the by now heat-softened inter-engaging plastics sleeves inwards in order to close off the aperture.

However, there is inevitably a time lag during which the intumescent insert is expanding sufficiently to close off the aperture completely. During this period the exterior flap and frame may also be exposed to the heat and flames and the exterior flap may fall away if its plastics pivot melts thereby removing the remaining impediment to the flow of air, flames and smoke through the aperture until the intumescent insert closes off the aperture, which may not occur fully in any event if the inter-engaging sleeves are not sufficiently softened by the heat. Inevitably, because of the highly complex and variable nature of flame propagation, plastics melting temperatures and intumescent expansion times and rate, the time it takes for an intumescent insert to become fully operational is variable. That means, in practice, that some letter-plates survive a fire without their front frame and flap being compromised while others lose the exterior flap before the intumescent insert fully closes the aperture in the door.

It is an object of the present invention to provide a letter-plate that overcomes or substantially mitigates the aforementioned problems.

According to the present invention there is provided a letter-plate comprising a pair of frames that are adapted to be fitted respectively on opposing sides of a door and at least one sleeve that is adapted to locate through an aperture in the door, at least one of the frames being provided with a flap that is pivotally mounted thereto by a hinge pivot comprising a plastics rod that is located in a channel defined by the flap and that has an end that is located in a channel defined by said one frame whereby in use the flap hangs downwards to cover the sleeve and thereby the aperture in the door until raised, a bridge being formed by a length of the rod between the channel in the frame and the channel defined by the flap, which bridge is covered by a metal jacket.

Preferably, the metal jacket covers the end of the rod that is located in the channel in the frame.

Preferably also, a metal pin is inserted into a blind bore formed in the end of the rod such that it spans that part of the rod defining the bridge.

Preferably also, a pair of inter-engaging plastics sleeves are provided that slide one within the other and that are both structurally weakened at their corners, the intumescent insert being provided around the exterior of the outer sleeve.

Preferred additional features of the invention are described in the dependent claims appended hereto.

The present invention will now be described by way of example with 25 reference to the accompanying drawings, in which:-Fig. 1 is a schematic cross-section through a letter-plate according to the present invention when fitted through an aperture formed in a door; Fig. 2 is a perspective, exploded view of the exterior side of the letter-plate shown in Fig. 1, the brush seal shown in Fig. 1 being omitted; Fig. 3 is a perspective exploded view of the hinge pivot shown in Fig. 2 but to an enlarged scale along with a metal jacket for use therewith; Fig. 4 is a view similar to Fig. 3 but showing the metal jacket in 5 position over the end of the hinge pivot; Figs. 5 and 6 respectively show the hinge pivot and metal jacket after insertion into a channel provided in a flap of the letter-plate as shown in Figs. 1 and 2 and with the flap attached to the letter-plate; Figs. 7a and 7b are longitudinal cross-sectional views of one end of the hinge pivot shown in Figs. 5 and 6 when modified by the provision of an internal metal pin, the pin being shown prior to its location into the hinge pivot in Fig. 7a and when embedded in the hinge pivot in Fig. 7b; and Fig. 8 is a back view of the exterior side of the letter-plate with a ringed detail shown to an enlarged scale.

A letter-plate 1 comprises a pair of rectangular frames 2, 3 that are adapted to be fitted respectively one opposing sides of a door 4 around a rectangular aperture 5 cut into the door 4. The frames 2 and 3 surround the edges of the aperture 5 and are adapted to lie adjacent an interior side 6 and an exterior side 7 of the door 4 respectively. In Fig. 1 the frames 2 and 3 are shown fastened to the door by screws 8 but in other embodiments they may be screwed directly to one another through two or more bores made through the door 4 on either side of the aperture 5. Respectively attached to each frame 2, 3 or integrally formed therewith is a sleeve 9, 10 that extends at right angles to the frame 2, 3. The sleeves 9, 10 project into the aperture 5 in the door 4 and thereby cover and shield the interior of the door structure, for example to prevent the ingress of rainwater and to facilitate the passage of mail through the door. It is usual for letter-plates to comprise two sleeves 9, lo so that they can inter-engage by sliding one within the other in order that the letter-plate 1 can be adapted to fit doors of different thicknesses. In the present case, the sleeve 9 of the exterior frame 2 fits around the outside of the sleeve 10 of the interior frame 3 but in other letter-plates the opposite may be the case. In addition, it will be appreciated that a letter-plate could be customized to fit a particular door in which case only one sleeve may be required.

Arranged around the exterior of the outer sleeve 10 is one or more intumescent inserts 11. These inserts 11 are usually made from a graphite-based material backed with glass scrim and are designed to swell when 10 heated sufficient to crush the sleeves 9 and 10 to close-off the aperture 5.

Each of the frames 2, 3 is also provided with a rectangular flap 12 that is hinged along its uppermost side to the frame 2, 3 beneath a protective overhang 13 such that in use it hangs downwards to cover the sleeves 9, 10 and thereby the aperture 5. The flaps 12 pivot outwardly of the door 4 to enable letters and small packets to be posted through the aperture 5. Flaps 12 may be provided on both sides of the door for aesthetic purposes but generally at least one flap 12 is preferably provided on the external side of the door to prevent wind and rain from entering the aperture 5. The exterior frame 3 may also be provided with a brush seal 14 that also covers the aperture 5 in the door 4, as shown in Fig. 1. As an alternative or in addition, a similar brush seal may be provided on the interior frame 2. The brush seal 14 comprises a pair of brushes that overlap centrally of the aperture 5 in order to reduce draughts through the aperture 5 while still enabling mail to be readily posted through the letter-plate 1.

The exterior flap 12 is pivotally-mounted to its frame 3 at one side of the flap 12 by at least one hinge pivot comprising a plastics rod 15. The pivot at the other side of the flap is usually a metal barrel hinge or similar. The rod 15 doubles both as a torsional spring and as a pivot at one side of the flap 12 as described above. The interior flap 12 may also be provided with a similar arrangement. The rod 15 is located in a channel 16 defined by the flap 12 and has an enlarged end 17 that is located in a channel 18 defined by the respective frame 2, 3. It will be appreciated that a bridge 19 is formed by a small length of the rod 15 between its main body within the channel 16 and its end 17 located within the channel 18. This bridge 19, if exposed, would be vulnerable to heat in the event of a fire. Accordingly, in accordance with the invention the bridge 19 of at least one of the flaps 12, which is preferably that on the external side 7 of the door 4, is covered by a metal jacket 20. The jacket 20 is preferably secured to the end of the rod 15 within the channel 18 and preferably also covers the enlarged end 17 of the rod 15 in the channel 18 in addition. The jacket zo is therefore adapted to fit within the channel 18 in o a non-rotational manner so that it does not rotate when the flap 12 is raised or lowered relative to the frame 2, 3 so that the rod 15 is twisted when this occurs. For this purpose the end of the metal jacket 20 in the channel 18 is enlarged, as at 21, to cover the end 17 of the rod 15 and to fit into a correspondingly shaped recess in the channel 18 such that the jacket zo cannot rotate within the channel 18.

As shown in Figs. 2 and 3, the metal jacket 20 may be split longitudinally into two parts that are fitted together around the plastics rod 15. Alternatively, the jacket zo may be in the form of a blind tube that is 20 fitted over the end of the rod 15 and then secured thereto.

In the event of a fire, the jacket 20 maintains the structural integrity of the hinge, in particular across the bridge 19 even when the underlying plastics rod 15 has softened or melted in the heat of the fire so that the flap 12 can remain in position covering the aperture 5. It is intended that the jacket 20 will protect the bridge 19 for at least a sufficient length of time until the intumescent insert if can operate to fully close-off the aperture 5. This is described further below.

In addition to the jacket 20, the bridge 19 may be further protected by a metal pin 22. The pin 22 may be inserted in a blind channel formed in the end of the rod 15 that is located in the channel 18 or it may be embedded in this end of the rod 15 by being moulded in situ when the rod 15 is -7 -manufactured. As shown in Figs. 7a and 7b, advantageously the metal pin 22 has a head 23 that is countersunk into the end of the rod 15. The head 23 prevents the pin 22 from falling out the channel 18 should the rod 15 melt in the heat of a fire. The metal pin 22 preferably has a diameter of at least 1.0 5 mm and more preferably a diameter of around 1.2 mm. It has a length that is preferably 15 mm in order that the pin 22 spans the adjacent bridge 19. The head 23 of the pin 22 preferably has a diameter of 2 OMM and may be up to 1.0 mm in depth. The provision of a pin 22 considerably strengthens the end of the rod 15 and provides a back-up hinge to prevent the flap 12 from falling 10 away even if the structural integrity of the rod 15 and the metal jacket 20 is compromised.

As described above, in the event of a fire, the intumescent insert 11 swells. As it is constrained by the edges of the apertures 5 in the door 4 it acts in the opposite direction to collapse the by now heat-softened inter-engaging plastics sleeves 9, 10 inwards in order to close off the aperture 5. However, the sleeves 9, io may not collapse evenly because of their rectangular shape. It has been found that the corners of the sleeves 9, in create an unwanted rigidity leading to localised resistance to the crushing force of the insert 11.

This may slow the time taken for the insert 11 to swell sufficiently to close of the aperture 5 and in some cases the aperture 5 may not be completely closed off. It is therefore important and advantageous for the collapse of the sleeves 9, io to occur in as rapid and predictable a manner as possible. To this end, the sleeves 9, 10 are preferably weakened at their corners 24, as shown in Fig. 8. The weakening is preferably accomplished by thinning of the thickness of the sleeves 9, 10 adjacent their corners. This can be done during moulding or by cutting away parts of the sleeves 9, 10. Preferably, the weakening takes the form of channels 25 in the body of the sleeve 9, 10. These channels 25 may extend longitudinally along the length of each sleeve 9, 10 adjacent its corners 24, as shown in Fig. 8, or a plurality of channels may run at least partially around the perimeter of the sleeve 9, 10 adjacent its corners. The channels 25 weaken the structure of each sleeve 9, 10 and also define the location of collapse of the sleeve 9, 10 thereby accelerating its -8 -collapse leading to a more rapid and predictable collapse pattern. In turn this protects the exterior flap 12 more effectively from the heat of a fire that may otherwise compromise the rod 15 leading to a loss of the front flap 12 before the aperture 5 has been fully closed off.

Claims

CLAIMS1. A letter-plate comprising a pair of frames that are adapted to be fitted respectively on opposing sides of a door and at least one sleeve that is adapted to locate through an aperture in the door, at least one of the frames being provided with a flap that is pivotally mounted thereto by a hinge pivot comprising a plastics rod that is located in a channel defined by the flap and that has an end that is located in a channel defined by said one frame whereby in use the flap hangs downwards to cover the sleeve and thereby the aperture in the door until raised, a bridge being formed by a length of the rod between the channel in the frame and the channel defined by the flap, which bridge is covered by a metal jacket.
2. A letter-plate as claimed in Claim 1, wherein the metal jacket covers the end of the rod that is located in the channel in the frame.
3. A letter-plate as claimed in Claim 1 or Claim 2, wherein the metal jacket is secured to the rod.
4. A letter-plate as claimed in Claim 3, wherein the jacket is located in the channel in the frame in a non-rotational manner so that it does not rotate when the flap is raised or lowered relative to the frame.
5. A letter-plate as claimed in any of Claims 1 to 4, wherein the metal jacket is split longitudinally into two parts that are fitted together around the plastics rod.
6. A letter-plate as claimed in any of Claims 1 to 5, wherein a metal pin is located in the end of the rod such that it spans that part of the rod defining the bridge.

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7. A letter-plate as claimed in Claim 6, wherein the metal pin has an enlarged head that is countersunk into the end of the rod.
8. A letter-plate as claimed in Claim 6 or Claim 7, wherein the metal pin has a diameter of at least 1.0 mm.
9. A letter-plate as claimed in any of Claims i to 8, wherein an intumescent insert is provided around the exterior of the sleeve.
10. A letter-plate as claimed in Claim 9, wherein the sleeve has a cross-sectional profile that is substantially rectangular and that is structurally weakened at its corners.A letter-plate as claimed in Claim 9 or Claim 10, wherein a pair of inter-engaging plastics sleeves are provided that slide one within the other and that are both structurally weakened at their corners, the intumescent insert being provided around the exterior of the outer sleeve. 12. 13. 14. 15.A letter-plate as claimed in Claim 10 or Claim it, wherein the or each sleeve is weakened by thinning of the thickness of the sleeve.A letter-plate as claimed in Claim 12 wherein the or each sleeve is weakened by the provision of channels in the body of the sleeve that run longitudinally along the length of the sleeve adjacent its corners.A letter-plate as claimed in Claim 12 wherein the or each sleeve is weakened by the provision of channels in the body of the sleeve that run at least partially around its perimeter adjacent its corners.A letter-plate substantially as described herein with reference to the accompanying drawings.