GB2450799A

GB2450799A - Fire resistant door

Info

Publication number: GB2450799A
Application number: GB0812130A
Authority: GB
Inventors: Martin Ellis; Wohciech Srokowski
Original assignee: Jeld Wen UK Ltd; Jeld Wen Inc
Current assignee: Jeld Wen UK Ltd; Jeld Wen Inc
Priority date: 2007-07-04
Filing date: 2008-07-02
Publication date: 2009-01-07
Anticipated expiration: 2028-07-02
Also published as: GB2450728B; GB2450728A; GB2450799B; GB0812130D0; GB0712962D0

Abstract

A fire resistant door has a core 16 comprising magnesium oxide board and a cellulosic fibre material sheet, the core being surrounded by frame components 20 and covered on at least one side by a door skin 12, 14 which is attached to the frame components. The core 16 may further comprise cellulosic fibre material sheets 30a, 30b between which the magnesium oxide board 32 is sandwiched. These sheets may comprise depressions that accommodate inwardly moulded regions of the door skin. As an alternative to the magnesium oxide board, surfaces of the depressions and/or the moulded regions can be covered by an intumescent material. Fire resistant doors with thicknesses as little as 35mm may be manufactured.

Description

FIRE RESISTANT DOORS

Invention Background

Fire resisting doors intended for use in various markets and to suit various fire resistance periods (as defined under applicable Standards and legislative requirements) have traditionally relied on thickness (bulk) of the door leaf to resist passage of fire. A thicker door will not only take longer to burn through and provide better insulation, but will also be more resistant to warping when exposed to differential heating/drying/steam evolution. This is particularly the case with doors made from cellulosic fibre products such as natural wood, chipboard, particleboard, hardboard, fibreboard and the like. Excessive warping will lead to gaps opening up between components of the door and/or between the door leaf and the surrounding frame components, allowing smoke and flame penetration.

Once a gap has opened up, localised burning and erosion can become intense, as the oxygen supply is usually richest at gaps or component edge/corner regions. Complete failure and collapse of the door leaf often rapidly follows. This tendency can be counteracted to some extent by incorporating intumescent seals in the vulnerable joint areas. Such seals are often mandatory between the door leaf and door frame. However a thin door can warp rapidly to such an extent that the edge seals will fail. The temperature at the face of the door not exposed to the fire can quickly rise to the point where there is danger of spontaneous combustion, if the door leaf is too thin.

Thus although in the European Union national legislation, building regulations and standards have not to date been fully harmonised, there is a harmonised method of testing and classification for fire resistant doorsets for buildings. The test results are expressed as the time taken for fire penetration of the doorset (integrity requirement), and the time taken for the face of the doorset not exposed to the fire to exceed a maximum allowed temperature (insulation requirement). For example, an "EI3O" rating means in effect that for the doorset concerned, both the integrity and insulation requirements were maintained during the EN standard test procedure for 30 minutes. In the UK there is also still a British Standard performance test for fire doorsets: BS476 part 22. Fire doors which meet this standard are again rated in the number of minutes of protection deemed to be provided, commonly abbreviated to the prefix FD, followed by the number of minutes of fire protection, for example FD3O, FD6O. National laws, building codes, etc, specif' different fire resistance ratings according to the EN and/or other (e.g. national) tests, depending upon the building use and layout, and also being able to take account of different national building styles and Occupancy patterns.

In the UK natural wood or cellulosjc fibre doors which rely on their bulk for fire resistance have for many years been manufactured to a thickness of 44mm so as to achieve a fire rating of 30 minutes, the base level for most UK fire door requirements. Some continental European designs for flush (flat faced) fire resistant doors of this general kind (in France, for example) have thicknesses down to 40mm, but doors significantly thinner than this (and hence possibly lighter, more materially efficient and easier to transport, install, maintain and use), have not met the fire resisting test standards.

The present applicants have previously developed a flush door only 35mm thick which still provides an FD3O fire resistance rating. The door has a core formed from flaxboard, which has been found to be less prone to warping than other cellulosic fibre materials when exposed to fire. The reasons for this are not precisely known, but it is thought that the higher silica content of flax fibre compared to other natural cellulosic fibre materials makes it less likely to burn through. The random arrangement of the flax fibres provides good dimensional stability when exposed to fire. However the same construction is not suitable for moulded doors, in which the core material must be routed out to accommodate inwardly projecting mouldings in the overlying door skins. The routing reduces the available thickness of the fire resisting core material, typically to 6mm on a 35mm thick door, with the result that the finished door does not pass the FD3O test. Also flax fibre supplies are limited and seasonally variable, leading to possible raw material supply problems in large scale manufacture.

There is an increasing demand for fire doors in many markets, including new-build and refurbished residential property in the UK and elsewhere. A growing proportion of such property consists of apartment buildings with three or more storeys (including or not including an occupied roof space), in which fire resistant doors must be provided not only between the common parts and each individual apartment, but must be used for most internal doors of each apartment too. Fire resistant doors must also be provided to protect stairwells of three or more storeys in houses, as well as in particular locations such as between an internal garage and the remainder of a dwelling. In many situations, such doors should preferably also provide adequate sound insulation, as set out in the building codes of many countries.

Magnesium oxide board is a material used in the construction industry to provide fire resistant linings in buildings, including partition walls, ceilings and as a decorative and fire resistant facing for doors. Magnesium oxide board usually includes (besides the magnesium oxide itself) glass fibre mesh or cloth, chopped strand matting or similar strengthening material, as well as binders and filler materials to improve mechanical strength or appearance.

is The present applicants have realised that magnesium oxide board may be used in forming the core of a fire resistant door which has many advantages over known fire resistant doors.

Summary of the Invention

According to a first aspect of the present invention there is provided a fire resistant door having a core comprising magnesium oxide board and a cellulosic fibre material sheet; the core being covered on either side by a door skin and being surrounded by frame components, to which the door skins are attached. The core may comprise at least two cellulosic fibre material sheets between which the magnesium oxide board is sandwiched.

The door skins are preferably made from a cellulosic fibre material such as hardboard or fibreboar4j, such as MDF. They may have a pattern embossed on their exposed face, for example a simulated wood grain effect. The door skins may comprise inwardly depressed and/or outwardly raised regions, to simulate a traditional panelled door in appearance.

Alternatively, the door skins may comprise plywood or wood veneer.

The cellulosic fibre material sheet(s) of the core may be unattached to the magnesium oxide board (for example being held in juxtaposition with the magnesium oxide board by some or all of the frame components, or by the door skins). Alternatively, the cellulosic fibre material sheet(s) of the core may be attached to the magnesium oxide board, for example by adhesive. The cellulosic fibre material sheet(s) may comprise chipboard or particleboard. A preferred material for the cellulosic fibre material sheets is wheat straw board.

Doors of the present invention may also comprise cores having two or more layers of magnesium oxide board, each magnesium oxide board being separated by one or more layers of cellulosic fibre material sheet such that the combined core forms a multilayer core.

Such a multilayer core may be further sandwiched between two outer layers of cellulosic fibre material sheet. Such a multilayer core provides the door with enhanced stability, fire resistance1 sound and thermal insulation properties compared to a door with only a single magnesium oxide board disposed within the core.

A face of a cellulosic fibre material sheet of the core may be positioned adjacent to a said door skin and comprise a depression which accommodates an inwardly extending moulded region of the door skin. The depression may be formed by routing. The door skin and the adjacent face of the core may be unattached. Preferably however, the door skin and the adjacent face of the core are attached to one another, for example by adhesive, such as a PVA adhesive. The attachment may be direct, or by one or more spacers or further sheets of material. These may improve sound or thermal insulation properties of the door, for example, as well as optionally providing a space for accommodating an inwardly extending moulded region of the door skin.

The thickness of the assembled door may be as low as 3 5mm, thereby providing a direct replacement for a standard non fire resistant door as used in the UK, without the need to modify the door frame, lining or casing. (These three terms are regional variations describing the same thing: the main structural components covering the door opening reveals, on which the door leaf is usually hung. In the rest of this document the term "frame" will be used). Existing buildings can therefore be more readily upgraded to provide improved fire precautions. A thinner fire resistant door in new build property also means narrower door frames and in turn thinner partition walls in which the door frames are situated. This not only provides a saving in materials for the door frames and wall studs, but also liberates valuable floor space within the building, along the entire length of each partition wall. Edges of the door may incorporate intumescent seals so that there is no need to fit separate seals to the door frame in upgrade applications. Alternatively, intumescent seals can be fitted to or in the frame, at the choice of the manufacturer or installer.

Such doors may be manufactured using relatively conventional processes. Components to be adhesively attached to each other can be coated with adhesive (e.g. PVA adhesive) on their mating faces. A first door skin is laid out, outer face downwards, and the adhesive coated components (e.g. stiles, rails, spacers (where present), core cellulosic fibre material sheet(s) (where present), magnesium oxide board, further core cellulosic fibre material to sheet(s) (where present), and further spacers (where present) are laid up successively on the upwardly facing inner face of the door skin. A pair of further door skins positioned outer face to outer face is then placed on top of the assembled stack, followed by further adhesive coated components and further outer face to outer face pairs of door skins. The process is repeated until a stack of the desired height (e.g. 30 doors) is formed. The stack is topped off with a final door skin, outer face uppermost, and the completed stack is transferred to a press and left for the adhesive to cure. Depending upon the type of adhesive used, if desired, the press may be heated so as to reduce cure times. The unified doors so formed are removed from the press for further finishing such as edge trimming, primer/paint/varnish application, marking with fire certification and serial number, installation of door furniture or assembly into door sets, as is conventional.

Variants and modifications of the above assembly process are readily possible. For example, the various core components may be preassembled using a stacking and press curing process similar to that described above for the complete door assemblies. Edges of the magnesium oxide board and/or edges of other core components may be received in grooves formed in the frame components.

The magnesium oxide board is non flammable and serves to stabilise and increase the fire resistance of any other core components used, thereby improving the fire resistance of the complete door. Other core components such as cellulosic fibre material sheets burn slowly and are easily routable compared with magnesium oxide board, but are still flammable.

Where cellulosjc fibre material sheets with moulded door skin accommodating depressions are used, the cellulosic fibre material sheets are easily routable in creating the depressions and the magnesium oxide board is particularly beneficial in providing the necessary fire/flame resistance and mechanical strength at the depressions in the thin sections of down to 5mm or less. In the extreme, the depressions may be formed (e.g. routed) through the entire thickness of the cellulosic fibre material sheets. The door therefore always has high fire resistance core at the thin or thick door sections due to the presence of magnesium oxide board throughout the core of the door leaf.

Interposing one or more magnesium oxide board layers in between sheets of cellulosic fibre material provides a fire resistant door core with alternate mechanically strong layers of incombustible and slow burning bulk material that is easily routed to conform with door skin depressions yet is cheaper to produce and simpler to shape (rout) than a door with a core composed solely of magnesium oxide board.

Cellulosic fibre material sheets typically absorb water. A fire resistant door may be exposed to wet environments by, for example, from sprinklers or fire hoses. If water manages to penetrate the door skins, the core may swell from absorption of water and deform the door, possibly creating unwanted gaps about the door periphery. Magnesium oxide board is waterproof and resistant to deformation in wet environments. Therefore a core comprising one or more layers of magnesium oxide board would serve to help maintain the structure of the door in such wet conditions.

Further preferred features and advantages of the invention are described below with reference to illustrative embodiments shown in the drawings.

Brief Description of the Drawings

Figure 1 is a front view of a moulded door embodying the invention; Figures 2 and 3 are, respectively, left and right side views of the door of Figure 1; Figure 2A is a partial cross-section on line C-C in Figure 1, Figures 4 and 5 are, respectively, cross-sectional views on lines IV-IV and V-V in Figure 1; Figures 4A and 5A are enlarged views of portions of Figures 4 and 5; Figures 6 and 7 are, respectively, front and side views of a core assembly used in the door of Figure I; Figure 7A is an enlarged view of a portion of Figure 7; Figure 8 is a front view of an alternative core, embodying the invention, and Figure 9 is a sectional view taken on line B-B in Figure 8, shown on an enlarged scale.

Figure 10 is a sectional view of an alternative core with two magnesium oxide board core layers.

Description of the Illustrative Embodiments

i 0 The door leaf 10 shown in Figures 1 -5, 2A, 4A and 5A comprises a pair of opposed door skins 12, 14 secured on opposite sides of a core assembly 16. Left 18a and right 18b stiles and double header and footer rails 20 (indicated in dotted lines in Figure 1) are adhesively secured between adjacent peripheral edges of the door skins 12, 14, to surround and enclose the core assembly 16. Together the stiles and rails form components which make up a is peripheral frame for the door 10. The left hand edge of the door leaf is mortised at 13 for receiving hinges. The right hand edge is drilled and mortised at 15 for receiving a mortise latch. Intumescent sealing strips 22 are secured in longitudinal recesses formed in the exposed faces of the stiles I 8a, I 8b and outermost header rail 20. Alternatively the intumescent seals may be accommodated in the door frame in which the door leaf is to be hung. Suitable intumescent sealing strips are readily available commercially, for example from Lorient Polyproducts UK (www.lorientuk.com). The core 16 may be adhesively secured to one or both of the door skins 12, 14 or alternatively may be trapped between the door skins and within the peripheral frame, without use of any adhesive between the core and surrounding components. In alternative embodiments (not shown) edges of the core 16 or edges of selected sheet materials making up the core may be received in grooves in the adjacent inner side faces of the peripheral frame. The stiles 18a, 18b and rails 20 may be formed from softwood, and the door skins 12, 14 from moulded wood fibre. In the case of flush doors, the door skins may also be formed from plywood, with a suitable wood veneer outer surface. However, in the door as illustrated, the door skins 12, 14 are moulded to include inwardly depressed regions 24 so as to simulate a traditional panelled door. As best shown in Figure 2A, groves 28 are routed in the faces of the core 16, forming relieved areas to accommodate the inwardly depressed door skin regions 24. As an alternative to routing, the grooves 28 may be formed in any other suitable way, e.g. moulded into the chipboard as it is formed.

The core 16 is best shown in Figures 6, 7 and 7A. It comprises a pair of cellulosic fibre material sheets 30a, 30b, preferably chipboard sheets, between which a sheet 32 of magnesium oxide board material is sandwiched. A core 16 of the present invention may also be formed from a single magnesium oxide board layer 32 and a single cellulosic fibre material sheet 30a. Magnesium oxide board is readily available commercially, for example from Dezhou Lingmei Industry & Trade Co., Ltd., China (www.dzlmgm.com). The sheets io making up the core can be inserted into the central cavity within the door 10 without being secured to each other. However it is preferred that the cellulosic fibre material sheets 30a, 30b are adhesively secured to the magnesium oxide board, either as the core is built up within the door central cavity, or at an earlier stage to form a preassembled core, as described above. The exposed faces of the cellulosic fibre material sheets 30a, 30b have the grooves 28 routed in them, laid out in rectangular configuration, enclosing "islands" of unrouted material. The cellulosic fibre material sheets contribute to the mechanical strength, fire resistance (by providing bulk material that takes some time to burn through) and sound and thermal insulation properties of the door. The magnesium oxide board helps to maintain the cellulosic fibre material sheets dimensionally stable when exposed to fire, as well as resisting the passage of the fire. The magnesium oxide board serves to protect the particularly vulnerable relieved areas of the cellulosic fibre material sheets.

The overall thickness of the assembled door leaf shown in Figures 1 -5 may be 35mm. The thickness of the magnesium oxide board may be 5mm, the thickness of each cellulosic fibre material sheet 30a, 30b e.g. as shown in Figures 7 and 7a may be 11.5mm; the door skins making up the remaining thickness of the door leaf (i.e. 3.5mm each).

A door substantially as described above with reference to Figure 1 has comfortably passed the FD3O test (BS476: Part 22: 1987, Clause 6); in fact lasting over 40 minutes before failure.

Another core construction is shown in Figures 8 and 9. The core 216 shown is similar to the core 16 in Figures 6 and 7, except that spacer pads 210 are secured to the "islands" at the centres of the routed grooves. The core may therefore be correspondingly thinner. Other positions and configurations of the spacers are also possible. The outer faces of the spacers 210 are secured to the corresponding panel parts of the door skins 12, 14, as best shown in Figure 9. The spacers 210 may be formed from cellulosic fibre material such as wood, plywood, chipboard, particleboard, hardboard or MDF. Alternatively, they may be formed from magnesium oxide board, expanded polystyrene, flame retardant (e.g. graphite loaded) polyurethane foam, compressed mineral wool blanket with a thermosetting polymer binder, io or any other suitable material, depending upon the strength, resiliency, sound/thermal insulation and fire resistance properties required for the spacer blocks. These blocks reduce the depth of the grooves in the core sheets 30a, 30b necessary to accommodate a given depth of the inwardly depressed regions 24 in the door skins 12, 14. In some embodiments the grooves 228 in the faces of the core may be omitted altogether; the blocks 210 providing the necessary clearance between the core and the door skins to accommodate the depressed door skin regions 24. In other embodiments, one or other of the cellulosic fibre material core sheets 30a, 30b may be omitted, with the corresponding spacers being of the necessary thickness for securing between the magnesium oxide board 32, the one sheet of cellulosic fibre material core sheets 30a, 30b and the door skin(s). The core may incorporate one or more further layers of material, e.g. for improved thermal and sound insulation. Different features of the various embodiments disclosed herein may be combined in ways not specifically illustrated.

Figure 10 shows a door of the present invention similar in structure to that of Figures Ito 5 wherein the core comprises two layers magnesium oxide board 32, the boards being separated by a central layer of cellulosic fibre material sheet 30c and further sandwiched between two outer layers of cellulosic fibre material sheet 30a and 30b. I0

Claims

1. A fire resistant door having a core comprising magnesium oxide board and a cellulosic fibre material sheet; the core being covered on either side by a door skin and being s surrounded by frame components, to which the door skins are attached.

2. A fire resistant door as defined in claim I, in which the door skin(s) is/are made from a cellulosjc fibre material.

3. A fire resistant door as defined in any preceding claim, in which the door skin has a pattern embossed on its exposed face.

4. A fire resistant door as defined in any preceding claim, in which the door skin comprises inwardly depressed and/or outwardly raised regions.

5. A fire resistant door as defined in any of claims I -3, in which the door skin comprises plywood or wood veneer.

6. A fire resistant door as defined in any preceding claim, in which edges of the magnesium oxide board and/or edges of other core components are received in grooves formed in the frame components

7. A fire resistant door as defined in any preceding claim, in which the core comprises at least two cellulosic fibre material sheets between which the magnesium oxide board is sandwiched.

8. A fire resistant door as defined in any preceding claim, in which the cellulosic fibre material sheet(s) of the core are unattached to the magnesium oxide board.

9. A fire resistant door as defined in any of claims I to 7, in which the cellulosjc fibre material sheet(s) of the core are attached to the magnesium oxide board.

II

10. A fire resistant door as defined in any preceding claim, in which the cellulosic fibre material sheet(s) comprise(s) one or both of chipboard and particleboard.

II. A fire resistant door as defined in any preceding claim, in which a face of a said cellulosic fibre material sheet of the core is positioned adjacent to a said door skin and comprises a depression which accommodates an inwardly extending moulded region of the door skin.

12. A fire resistant door as defined in claim II, in which the depression is formed by routing.

13. A fire resistant door as defined in any preceding claim, in which each door skin is unattached to the adjacent face of the core.

14. A fire resistant door as defined in any of claims 1 -12, in which each door skin is attached to the adjacent face of the core.

15. A fire resistant door as defined in claim 14, in which the attachment is by one or more spacers or further sheets of material.

16. A fire resistant door as defined in any preceding claim, in which the thickness of the assembled door is substantially 35mm.

17. A fire resistant door as defined in any preceding claim, in which edges of the door incorporate intumescent seals.

18. A fire resistant door as claimed in any preceding claim wherein the core comprises two or more magnesium oxide board layers with one or more cellulosic fibre material sheets disposed between the magnesium oxide board layers.

19. A fire resistant door substantially as described with reference to or as shown in any of Figures I -7A; or Figures 1 -5A, 8 and 9; or Figures 1 -5 and 10.

20. A core for a fire resistant door as described in any preceding claim.

21. A core for a fire resistant door substantially as described with reference to or as shown in any of Figures 2A, 4, 4A, 5, 5A, 6, 7, 7A, 8, 9, and 10.