Door frame

Abstract

A metal door frame is disclosed where the jambs and header include thermal breaks. They are each formed of a single, unitary piece, and a plurality of holes or apertures is formed along the length of

Description

FIELD OF THE INVENTION The present invention relates to metal door frames and insulated door panels. BACKGROUND ART Common metal doors and door frames are designed with thermal efficiency in mind, so as to minimise thermal leakage. This is increasingly important as building regulations stipulate that doors and door frames must provide increasing levels of thermal insulation so as to be able to achieve environmental targets; the measure of the rate of heat transfer through a building component is commonly called U-value, and that the slower or more difficult it is for heat to transfer through the component, the lower the U-value. Extreme differences in temperature and thermal forces between the interior of the building and its interior, such as during a fire, or where the door is to a refrigerated enclosure, may result in deformation due to thermal bow. A common approach to minimising thermal leakage is to fill the door with a thermally insulating material, and to include a thermal break in the design of the door frame so that the conduction of heat between the two sides of the door and frame is interrupted. There are many designs of such thermal breaks, but these generally comprise separate inner and outer door frames which are either physically separate, but connected by a separate thermally insulating element, as in US3191727 and US4594831, for example, or they are shaped so as to mechanically interlock, and are kept from making direct metal to metal contact with each other by a separate thermally insulated element or tape, as in WO 2018 / 026654 and US11993977. Such conventional designs, although providing an acceptable thermal break, require multiple manufacturing operations to make, are unwieldy to install and are often vulnerable to being broken into and therefore are not suitable for applications where security is important. There is a need for a design of metal door frame which addresses these deficiencies while providing a sufficient thermal break. SUMMARY OF THE INVENTION The present invention is predicated on the realisation that a sufficient thermal break can be created using a one-piece door frame of a particular shape and configuration. The present invention therefore provides a metal door frame for surrounding an opening in a wall into which a door fits, the frame comprising separate, elongate jambs and an elongate header configured for receiving side and top edges of a door, respectively, and for enclosing edges of the wall at the opening, in which the jambs and header are each formed in a single, unitary piece, and in which a plurality of holes is formed along the length of each of the jambs and the header. With such an arrangement, the holes form part of the thermal break, which can be added to as will be explained below, whilst the one-piece nature of the metal jambs and header mean that they are very much more secure against burglars and the like than are most two-piece designs. The frame is easily assembled and installed; the jambs, header, and threshold are welded together and installed into the wall aperture as one piece, which makes the frame very strong, and there is no need to try and align the two pieces of the jamb and header as with a conventional door frame. The jambs and header can be shaped on a press brake, stamped or extruded, depending on the nature of the material. The holes are preferably elongate in shape, and can be stamped out from the metal, before or after shaping, using a CNC punch. The holes are preferably aligned in at least one row along the lengths of the jambs and the header; alternatively they may be formed in two or more rows, and the rows of elongate holes may be offset. Where there is a single row of holes the total length of the holes is an important factor, since heat will be conducted from one side of the door frame to the other through the unbroken lengths of the jambs and header. The unbroken length must be small enough to provide a reasonable thermal break, but not so short as to compromise the security of the design. The total overall length of the holes in the jambs and header and the total unbroken length of the jambs and header to give the required U-value can be determined empirically, and depends on factors such as the particular metal and its thickness, and the size and shape of the holes, but we have found that designing the door frame so that the total length of the holes in the jambs and the header around the door frame are between about 40% and 60%, and preferably between about 45% and about 55%, of the total lengths of the jambs and the header gives a suitable compromise between low U-value and security. Preferably, the holes are formed in a channel, the channel containing a plastic material forming a thermal break. The channel may be shaped and sized so as to retain a strip of plastic material which is inset into the channel, and runs around the interior length of the door frame. As with most doors there are provisions for hinges on one jamb and locking plates / sockets on the other, opposite jamb, and the hinges and lock plates are preferably all on the jambs on the same side of the channel forming the thermal break. This puts the hinges and lock plates to one side of the thermal break, so that their contribution to the overall U-value of the door frame can be easily determined. The number and relative lengths and locations of the holes around the inside of the door frame can be varied, so long as the holes are not all close together, for example, which would compromise the strength and hence security of the frame at that point, and they need not be located symmetrically because this might not be possible having regard to the need to add hardware such as hinges and lock plates. The thermal simulation, from which a U-value is derived, calculates the door and frame as a complete unit. Therefore, the percentage area of holes relative to solid sections is important in determining U-value; so, provided that the relative cross-sectional areas of holes to solid sections is maintained the same, the holes can be located to suit the hardware positions. The jambs and the header may be shaped and configured to encase a cavity around the edges of the wall at the opening, the cavity containing thermally insulating material. This contributes to the U-value of the door frame. There may be a sill for location at the bottom of the opening, forming the bottom of the frame. The sill may not have any holes as these would form dirt traps and would be aesthetically unpleasing; because the sill is at the bottom of the door frame, and heat rises, the temperature of the sill will usually be lower than the temperatures of the jambs and header, so the sill would conduct less heat through the door frame, so it could be made without a thermal break and would still contribute to the security of the frame. The invention extends to a door frame as set out above in the form of a kit of parts, and the kit may also include a door. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example and with reference to the accompanying figures, in which; Figure 1 is a front view of a typical door and door frame; Figure 2 is a front view of an embodiment of a door frame in accordance with the invention, showing the jambs and header alongside as seen from within the door frame; Figures 3(a) and 3(b) are views along the line 3-3 in Figure 2 showing the jamb in cross-section and in perspective, respectively, and Figures 4(a) and 4(b) are views along the line 4-4 in Figure 2 showing the jamb in cross-section and in perspective, respectively. DETAILED DESCRIPTION OF THE EMBODIMENTS Figure 1 shows a door frame 2 comprising a header 4 at the top, a jamb 6 to one side for receiving the door hinges 8, and a second jamb 10 to the other side for receiving the locking plate 12; the header 4 and jambs 6,10 are separate but unitary, or one-piece, items that are shaped so as to fit inside the opening where the door is to be positioned and to surround the edges of the wall within which the door opening is formed. The door frame 2 is formed by locating each of the header and the jambs over the edges of the wall at the opening; the door frame illustrated has a simple (and constant), generally U-shaped crosssection, so that the abutting edges are shown with a mitre joint, but it will be understood that where the frame has a more complicated cross-section a square joint would be more appropriate. A door 14 is located in the frame 2, with a handle 16. It will be understood that the hinges 8 are fixed to both the jamb 6 and to the door 14, allowing the door 14 to be swung open or closed within the frame 2. Also, the handle 14 operates a locking mechanism (not shown, but within the door 14) which engages a latch (not shown) within the locking plate 12 to hold the door in the closed position, or disengages the latch from the locking plate to allow the door 14 to open. The door frame illustrated does not have a sill, but these are commonplace and typically are in the form of a flat plate which joins the lower ends of the jambs 6, 10 together. Figure 2 shows a door frame 20 in accordance with the invention, which comprises a header 24, a hinge jamb 26, a lock jamb 30 and a sill plate 34. The hinge jamb 26 is configured to receive hinges 28, and the lock jamb 30 is configured to receive a lock plate 32. All of these elements are single, unitary pieces of 2mm galvanised steel sheet; the header 24 and the jambs 26, 30 have been shaped in a press brake so as to have a generally constant, generally U-shaped cross-section (shown in more detail in Figures 3 and 4) forming a cavity which can be filled with thermal insulation material and then located within the edges of the wall within which the door opening is formed, and are shown fitted in a door opening; the header and jambs are welded together with square joints where the tops of the jambs abut the ends of the header. A sill plate 34, a metal plate, is welded to join the lower ends of the jambs together. A channel 44, shown more clearly in Figures 3a, 3b, 4a and 4b, is formed along the lengths of each of the header 24 and jambs 26, 30; the inner edge of this channel is discontinuous, being formed with alternating cutout portions C (or holes) and solid portions S. The cutouts C are stamped out of the sheet metal by a CNC punch during the process of forming the header 24 and the jambs 26,30, and have a width of about 10mm. The respective lengths of the cutouts C and of the solid portions S along the lengths of the header and jambs are chosen so as to give the assembled door frame structural integrity and sufficient strength to be secure against anyone attempting to break in, whilst also providing a frame which overall has a sufficiently low U-value to meet ever more demanding environmental targets; the particular lengths will also depend on the materials which are used (including the additional insulating materials described below), but we have found that for a standard UK-size door frame with a door frame which measures about 117mm from its inner face 40 to its outer face 42 made of 2mm steel plate, a ratio of about 1:1 of total length of cutouts C to total length of solid portions S gives an acceptably low U-value, whilst retaining sufficient strength in terms of attack resistance and durability. It will also be understood that the length, width and shape of the cutouts C can be varied as required - so as to mount hinges 28 and a lock plate 32, for example, or to allow for different materials. In our design the cavity within the inner and outer faces 40, 42 of the frame are filled with thermal insulating material such as that sold by Rockwool A / S under the trade mark Rockwool, and into the channel 44 is set a strip 46 of nylon 66 as a thermal break; the skilled person will understand that other materials may be used, and the lengths of the cutouts C adjusted so as to change the cross-sectional area of frame material in the channel 44 across which heat can be transferred to achieve the desired U-value. It will of course be understood that many variations may be made to the abovedescribed embodiment without departing from the scope of the present invention. For example, other materials may be used than those detailed, and the U-value of such a different arrangement can be reasonably easily determined. A metal door which fits in the frame may incorporate a similar thermal break design around its edges, to prevent heat transmission between the two metal faces of the door. The cutouts C are generally in the form of rectangular slots, but these could be replaced by alternatives such as repeated circular perforations or holes, or a combination of slots and perforations. Where different variations or alternative arrangements are described above, it should be understood that embodiments of the invention may incorporate such variations and / or alternatives in any suitable combination. -7-

Claims

1. A metal door frame for surrounding an opening in a wall into which a door fits, the frame comprising separate, elongate jambs and an elongate header configured for receiving side and top edges of a door, respectively, and for enclosing edges of the wall at the opening, in which the jambs and header are each formed in a single, unitary piece, and in which a plurality of holes is formed along the length of each of the jambs and the header.

2. A metal door frame according to Claim 1, in which the holes are elongate.

3. A metal door frame according to Claim 2, in which the holes are aligned in at least onerow along the lengths of the jambs and the header.

4. A metal door frame according to Claim 1, 2, or 3, in which the total length of the holes along the jambs and the header are between about 45% and about 55% of the total lengths of the jambs and the header.

5. A metal door frame according to any preceding Claim comprising a plurality of holes aligned along the lengths of the jambs and the header, in which the holes are formed in a channel, the channel containing a plastic material forming a thermal break.

6. A metal door frame according to Claim 6, further comprising hinges on one jamb and locking plates on the other jamb, the hinges and lock plates all being on the jambs on the same side of the channel.

7. A metal door frame according to any preceding Claim, in which the jambs and the header are shaped and configured to encase a cavity around the edges of the wall at the opening, the cavity containing thermally insulating material.

8. A metal door frame according to any preceding Claim, further comprising a sill for location at the bottom of the opening, forming the bottom of the frame.

9. A kit of parts for forming a door frame according to any preceding |Claim.

10. A kit of parts according to Claim 9, further comprising a door.Application No: GB2409106.8Examiner:Claire TreaseClaims searched: 1-10Date of search: 2 January 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-10 GB 2556064 A (ASSA ABLOY LTD) Figures 3 and 5 show a metal doorframe 5 with header and jambs, each formed as a unitary piece 501, 503, 504 comprising a plurality of slots 509. X 1-4, 6-10 GB 2620580 A (SIMON PETER EVERSHED) Figures 1 and 4 show a metal door frame 100 with header 110 and jambs 121, 122, each formed as a unitary piece comprising a plurality of slots 130. v A 1-4, 6-10 DE 202012002498 UI (VAITTINEN TEUVO) Figures 1-4 show a metal door frame 1 formed as a unitary piece comprising a plurality of slots 31. X 1-4, 6-10 EP 0655541 Al (DIERRE SPA) Figures 1-5 show a metal door frame 1 formed as a unitary piece comprising a plurality of slots 31, 32, 33. X 1-4, 6-10 RU17557U1 (RANNILA STEEL OY) Figures 1 and 4 show a metal door frame each part formed as a unitary piece 1 comprising a plurality of slots 2. X 1-5, 6, 8- BE827106 A 10 (ANON.) Figures 1, 2 show a metal doorframe 1 formed as a unitary piece comprising a plurality of holes 10.Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category'. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority' date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From E06B 0003 / 263 01 / 01 / 2006 E06B 0001 / 12 01 / 01 / 2006 E06B 0001 / 52 01 / 01 / 2006

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