Improvements in insulated metal doors

Abstract

The invention is an improved metal door that includes an insulating layer to minimise or prevent unwanted ingress or loss of heat. Key components of the door of the present invention are connected to each other in such a way as to accommodate movement, and in particular, expansion or contraction, of the two outer panels of the metal door, primarily along its vertical dimension via a pair of opposing stiles on the left and right side edges of the door. This is achieved without compromising the overall integrity of the door as the pair of opposing stiles comprises a first elongate structure associated with a first outer metal panel and a second elongate structure associated with a second metal panel. The two elongate structures are connected such that they can slidably move along their vertical length with respect to each other. The door also comprises a pair of opposing bars defining respective top and bottom edges of the door and each bar contains an element connected to the first and second metal panels and elongate structures of the opposing stiles. The elements of the opposed bars can move pivotally with respect to each other. By allowing the components of the door to move relative to each other in response to expansion or contraction, stress on the components can be minimised and the door may therefore be less prone to temperature-related damage or failure.

Description

IMPROVEMENTS IN INSULATED METAL DOORSSTATEMENT OF CORRESPONDING APPLICATIONSThis application is based on New Zealand Patent Application No. 778362, filed on 22 July 2021, and the entire contents thereof are incorporated herein by reference.FIELD OF INVENTIONThe present invention relates to insulated metal doors. The invention has particular application to aluminium doors, such as those intended for installation in entranceways to buildings. However, the invention may also have application to doors formed from other metals or installed in other parts of buildings.BACKGROUND TO THE INVENTIONAluminium doors are known in the art and are often preferred for construction of buildings by virtue of their sleek and elegant appearance, relatively minimal weight, ease of manufacture, structural integrity, and for other functional and aesthetic advantages.Aluminium doors may commonly be formed as a shell of two parallel aluminium sheets. These may be connected to one or more intermediary sheets of a different material forming the internal structure of the door. For instance, a sheet of plywood may be sandwiched between and connected or otherwise affixed to the aluminium sheets.Aluminium is a thermally conductive material and as such, an uninsulated aluminium door may lead to unwanted ingress or egress (as the case may be) of heat into or out of a building. This may undermine the efficacy of central heating in winter, or of air conditioning in summer.Therefore, an intermediary sheet, in the form of an insulating layer of a material having relatively low thermal conductivity, may be provided. This is typically in the form of one or more sheets of polystyrene or polyurethane foam or the like rigidly connected to the interior structure of the door, through the use of a bonding agent such as industrial-strength adhesive.The connection between the intermediary sheets and aluminium sheets is typically rigid; the industrial-strength adhesive that is typically used is applied continuously or intermittently to the contact surfaces of the respective sheets, bonding them together. This means that the sheets are not free to move relative to each other.The door may typically also comprise additional components such as “caps” connected to the edges and / or corners of the respective sheets. Ancillary components, such as hinges, handles and / or locks, may be attached directly or indirectly to the sheet(s) by common techniques such as welding, adhesive, screws or other fastening means.The rigid connections between the aluminium sheets and the intermediary sheets of the door (such as the plywood sheet and / or polystyrene sheet) as well as other components of the door may commonly lead to functional problems and damage to, or even failure of, the door.Aluminium has a relatively high thermal coefficient of expansion; that is to say, it tends to expand and contract by a significant amount in response to changes in temperature, meaning the length and / or width dimensions of the aluminium sheets may change by a relatively significant amount.The intermediary sheets forming the door tend to have a different thermal coefficient of expansion to that of the aluminium sheets. For example, the plywood sheet may expand or contract by significantly less (potentially up to ten times less) than the aluminium sheets, and the polystyrene sheet may expand or contract by significantly more (such as up to three times more) than the aluminium sheets.The relative expansion of the respective aluminium and intermediary sheets by differing amounts may often result in damage to, or failure of, the overall door structure. This may be exacerbated by the fact that the adhesive connecting the individual sheets of the door may tend to soften and weaken as temperature increases.A particularly common problem is the aluminium sheets bowing or warping as they expand, overcoming the adhesive bond and forming a “bubble” protruding away from the intermediary sheet to accommodate their expansion relative to the plywood sheet. Where a polystyrene insulating sheet is used, this may rupture or otherwise fail as it attempts to expand away from the aluminium sheet.The caps at the edges and / or corners of the door may also be damaged by the stresses generated as a result of the unequal expansion of the aluminium sheets; as may other components of the door. Ancillary components, such as handles, hinges or locks, may be displaced out of alignment and thus not be able to function properly. This may prevent the door from closing and / or locking properly, which may compromise the security of the building in which the door is installed. Such damage often ultimately requires the door to be repaired or replaced.This problem may be further exacerbated if the aluminium sheets forming the respective interior and exterior sides of the door are exposed to significantly different temperatures, such that there is a significant temperature differential between the two sheets. In such cases, one of the sheets may expand relative to the other. For example, the exterior sheet, if exposed to direct sunlight, becomes very hot and could expand, potentially leading to bowing or warping of that sheet relative to the interior sheet. This may place additional stress on the door structure, and hence exacerbate the damage to the components of the door.OBJECT OF THE INVENTIONIt is an object of the invention to provide a door that is effectively thermally insulated and hence eliminates or minimises conductive heat transfer through the door.Alternatively, it is an object of the invention to provide a door that allows for the expansion or contraction of its exterior panel while absorbing the resulting dimensional change of the panel and allowing the other components of the door to remain substantially stationary and free of applied stresses or forces.Alternatively, it is an object of the invention to provide a door that is robust and at reduced risk of damage or failure due to temperature changes.Alternatively, it is an object of the invention to provide a door that is robust and at reduced risk of damage or failure in the event of a significant temperature differential between the exterior and interior panels of the door.Alternatively, it is an object of the invention to address the foregoing problems with the prior art.Alternatively, it is an object of the invention to, at the very least, provide the public with a useful choice.SUMMARY OF THE INVENTIONAccording to one aspect of the invention, there is provided an insulated metal door, comprising:a first outer panel and a second outer panel;an inner panel disposed between the first outer panel and a second outer panel;an insulating layer disposed between the inner panel and one of the first and second outer panels;a pair of opposing stiles defining respective left and right side edges of the door, wherein each stile comprises a first elongate structure associated with the first outer panel and a second elongatestructure associated with the second outer panel, wherein the first elongate structure is connected to the second elongate structure such that they are able to move with respect to each other,a pair of opposing bars defining respective top and bottom edges of the door, wherein each bar comprises a first element associated with the first outer panel and the first elongate structure of the stile and a second element associated with the second outer panel and the second elongate structure of the stile, wherein the first element is connected to the second element such that they are able to move with respect to each other.According to another aspect of the invention, there is provided a kit set for an insulated metal door, comprising:a first outer panel and a second outer panel;an inner panel disposed between the first outer panel and a second outer panel;an insulating layer disposed between the inner panel and one of the first and second outer panels;a pair of opposing stiles defining respective left and right side edges of the door, wherein each stile comprises a first elongate structure associated with the first outer panel and a second elongate structure associated with the second outer panel, wherein the first elongate structure is slideably movable relative to the second elongate structure;a pair of opposing bars defining respective top and bottom edges of the door, wherein each bar comprises a first element associated with the first outer panel and the first elongate structure of the stile and a second element associated with the second outer panel and the second elongate structure of the stile, wherein the first and second elements are pivotally linked to each other.According to yet another aspect of the present invention, there is provided a method of manufacturing an insulated metal door, the method including the steps of:• providing a first outer panel;• providing an insulating layer proximate the first outer panel;• bonding an inner panel to the insulating layer;• providing a pair of opposing stiles defining respective left and right side edges of the door, to the first outer panel, wherein each stile comprises a first elongate structure associated with the first outer panel and a second elongate structure associated with a second outer panel, wherein the first elongate structure is slidably movable relative to the second elongate structure;• providing a pair of opposing bars defining respective top and bottom edges of the door, to the first outer panel, wherein each bar comprises a first element associated with the first outer panel and the first elongate structure of the stile and a second element associated with the second outer panel and the second elongate structure of the stile, wherein the first and second elements are pivotally linked to each other; and• providing the second outer panel and fixing same to the pair of opposing stiles and bars.The invention is an improved metal door that includes an insulating layer to minimise or prevent unwanted ingress or loss of heat. Key components of the door of the present invention are connected to each other in such a way as to accommodate movement, and in particular, expansion or contraction, of the outer panels of the door, primarily along its vertical dimension. This is achieved without compromising the overall integrity of the door. The door may therefore be less prone to temperature-related damage or failure.It will be understood that the present invention has particular application to insulated aluminium doors, which are commonly used in buildings.The use of aluminium is preferred due to the relative ease with which aluminium can be worked; in particular, its suitability to manufacturing processes such as extrusion, machining and pressing which may be involved in forming the panels of the present invention. Furthermore, aluminium is able to withstand sufficiently high temperatures (in the region of 200°C) to enable the panels to be powder-coated, which is a common finishing treatment.Accordingly, the metal panels preferably comprise aluminium panels and reference to this effect shall now be made throughout the remainder of this specification.However, this is not intended to be limiting. It will be appreciated that the present invention may also have application to doors formed from other metals which have relatively high thermal conductivity and which have components that are prone to expansion and contraction, relative to other components, due to changes in temperature.A panel should be understood to mean a flat sheet, preferably rectangular in plan view and which is the typical shape of a door. Thus, a panel has an elongate dimension and a width dimension.The plurality of aluminium panels should be understood to be orientated such that their elongate dimensions are substantially vertical in use. In use, the door will be hinged to the door frame with which it is to be used along an edge of the elongate dimension.The door includes at least a first outer panel and a second outer panel. Each panel will be understood to have two sides or faces (the interior and exterior surfaces) as well as opposing pairs of edges.“Outer panels” should be understood to mean those which define the overall external structure and dimensions of the door, that is to say, one side of each panel forms the exterior or external surface of the door, i.e. the surfaces which are exposed to environmental elements, i.e. weather, in use andwhich may be directly contacted by a user. The other side forms the interior or internal surface of the panels.In exemplary embodiments of the invention, the first outer panel is the external, outward facing side of the door. It will be understood that this is the side that faces the exterior of the building and is exposed to environmental elements. In these embodiments, it will be understood that the second outer panel should be understood to be the internal, inward facing side of the door. This is the side that faces the interior of the building.However, it should be appreciated that in some instances the door may be mounted as an internal door and as such both outer surfaces may face rooms or hallways.These respective first and second outer panels shall be referred respectively to as the exterior and interior panels of the door.In some embodiments of the invention, an additional coating or finishing layers may be applied to the exterior and / or interior panels. For example, a coat of paint, varnish or similar finishing material may be applied to their respective exterior surfaces.Alternatively, or in addition, an additional layer or “skin” of material may be applied to the exterior surface of the exterior and / or interior panels, such as for decorative purposes. This “decorative” skin may be formed from a rigid, semi-rigid or flexible material, such as a thin sheet of metal or a suitable plastics material. The skin may be patterned, textured or moulded as desired for aesthetic appearances. Preferably in this embodiment, the skin has a thermal co-efficient of expansion that corresponds to that of the panel to which it is applied. The exterior surfaces of the first and / or second panels may comprise attachment means, for example grooves or similar snap-lock fittings, configured to enable attachment of the skin. This may allow the skin to sit flush against the exterior surface of the first and / or second panels when the door is assembled.In some embodiments, small plates of aluminium, or appropriate pieces of aluminium extrusion, may be applied to the exterior or interior surfaces of the exterior and interior panels to provide additional structural integrity for the mounting of door hardware. For example, an aluminium plate may be provided to the top corner of the door, proximate the hinging edge, for attachment of a selfcloser mechanism. Similarly, an aluminium plate may be provided to the centre of the door, proximate its non-hinging edge, to allow fitting of handles and / or locks. In these embodiments, the aluminium plate used for the hardware may be fixed in place with high strength adhesive or mechanical fasteners, such as screws or the like.In a preferred embodiment, the exterior and interior panels are each comprised of a single unitary structure in the form of a panel having dimensions corresponding substantially to the overall desired dimensions of the door. Reference to this effect shall be made throughout the remainder of the specification. However, this is not intended to be limiting and it will be understood that in some embodiments, one or both of the exterior and interior panels may be comprised of two or more panels. For instance, the interior panel may be formed from an upper section and a lower section, or even from four or eight sections. The skilled person will readily envisage appropriate means by which such panels may be connected to each other to form the exterior and interior panels respectively. However, it will be appreciated that this may complicate manufacture and assembly of the door.Preferably, the exterior and interior panels are configured as aluminium sheets. In particular, when assembled, the door preferably does not require transverse reinforcing elements between the first and second panels such as internal “ribbing”. This may be achieved by selecting panels having appropriate dimensions and / or structural properties.For instance, one or both of the exterior and interior panels may be manufactured to have a “honeycomb” cross-section, or may have a corrugated cross-section comprising linear flutes formedby extrusion or rolling and covered by a flat exterior skin. The skilled person may envisage other suitable configurations for the panels.It will be understood that the exterior and interior panels of the door are parallel to and laterally spaced from one another, such that they do not directly contact one another in use.The door includes an inner skin disposed between the exterior panel and the interior panel.Preferably, the inner skin is configured as aluminium sheet. Even more preferably, the inner skin is configured from aluminium sheet that is thinner than that used for the exterior and / or interior panels of the door.Preferably, the inner skin is held in a fixed position relative to the exterior panel through the use of a spacing structure.Preferably, the spacing structure is in the form of one or more corrugated stiffening ribs. The stiffening ribs are a formed profile that may be configured as an aluminium extrusion bonded to the inner surface of the exterior panel and the surface of the inner skin that faces the inner surface of the exterior panel. The aluminium extrusion may be roll-formed or alternatively pressed from aluminium sheet. In this embodiment, the exterior panel and inner skin together assume a honeycomb-like structure in profile. While it is preferred that the stiffening ribs be positioned between the exterior panel of the door and the inner skin for superior insulation performance, it should be appreciated that in some embodiments of the invention, the stiffening ribs could be integrated with the insulating layer such that it is positioned between the interior panel of the door and the inner skin.In exemplary embodiments, the bonding between the corrugated stiffening ribs and the surface of the inner skin is achieved through the use of high strength adhesives and the like such as will bereadily apparent to persons skilled in the art. Alternatively, mechanical fasteners such as screws, bolts or rivets may be used.The use of stiffening ribs helps with increasing the overall rigidity of the door, particularly in respect of the exterior panel. In preferred embodiments of the invention, this is the side of the door that is most likely to experience dimensional changes and movement as a result of environment thermal changes. Heat loss is limited due to the insulating layer being located proximate the interior side of the door.The insulating layer should be understood to be a layer that acts as a thermal break between the aluminium panels to prevent or minimise conductive heat transfer from one panel to another.Preferably, the insulating layer is formed from a material having relatively low thermal conductivity. In particular, the thermal conductivity of the insulating layer is preferably significantly lower than that of the aluminium panels forming the exterior and interior panels of the door respectively.Preferably, the insulating layer is resilient, i.e. able to be deformed to an extent but return to its original shape with little or no loss of structural integrity.In some embodiments, the insulating layer is formed from plastics foam such as polyurethane or polyvinyl chloride. For example, the insulating layer is formed from polymeric closed cell foam such as STYROFOAM™. Such material is lightweight, cost effective and easily sourced.The inventors have found that a particularly effective insulating material for use with the invention is polyisocyanurate (PIR), a type of plastics material in foam form. It has relatively good integrity compared to many other plastic foams, particularly in respect of resistance to penetration damage which can be helpful during manufacture. Additionally, it has a low co-efficient of friction compared to many other plastic foams. However, this example is not intended to be limiting and personsskilled in the art will readily identify other materials suitable for use as the insulating layer of the door.Preferably, the insulating layer is provided by a single sheet of insulating material. This may be conducive to the ease of manufacture and assembly of the invention, as well as its insulating efficacy. However, in some embodiments of the invention, the insulating layer may be provided by two or more sheets of insulating material that have been bonded or otherwise secured together to form a unitary structure.Preferably, the insulating layer is disposed across substantially the entire surface of the inner skin, thus substantially filling the space between it and the interior panel. This may maximise the efficacy of the insulating layer at minimising conductive heat transfer through the door. However, in some embodiments the insulating layer may be disposed across only a portion of the surface area of the inner panel.Preferably, the insulating layer abuts and contacts the interior surfaces of the interior panel. In some examples, the insulating layer is bonded to the interior panel using the likes of high strength adhesive as a coating across one or both of the respective contact surfaces. Alternatively, the adhesive may be coated or applied at regular intervals along the contact surfaces.Preferably, the insulating layer is only bonded to the interior panel substantially at the horizontal centre line of the door. It should be understood that any vertical movement, i.e. expansion and contraction of the aluminium interior panel tends to be away from the centre, and towards its edges. This means that there is less movement of the centre portion of the inner panel relative to the rest of the interior panel.This arrangement allows for some movement of the interior panel relative to the inner skin of the door. It will be appreciated that any movement of the interior panel may also result in movement of the insulating layer relative to the inner skin.As previously noted, the preferred material of choice for the insulating layer, PIR, has a low coefficient of friction relative to many other types of plastic foam. As such, it is relatively slippery and contributes towards the ability of the insulating layer being able to slide or otherwise move relative to the inner skin. However, as noted above, other plastic foams may be used and in such instances, the surface of the insulating layer that contacts the inner skin may be coated with a material that helps reduce its co-efficient of friction, thereby better facilitating any sliding movement.The door includes a pair of stiles, wherein the stiles define the left and right sides of the door.Preferably, the stiles are configured as extrusions of aluminium. The use of aluminium for the stiles may be advantageous as it may mean the stiles has the same coefficient of thermal expansion as the bars (discussed below) and aluminium panels of the door. Aluminium is also able to withstand sufficiently high temperatures (in the region of 200°C) to enable the stiles to be powder-coated, which is a common finishing treatment for such components.However, other materials meeting the above discussed parameters may also be suitable for the stile; specifically, materials having a coefficient of thermal expansion relatively similar to the aluminium panels, and which are able to be powder-coated.Each stile comprises a first elongate structure and a second elongate structure, each running the length, or at least a substantial portion of the length, of the respective stiles. The first elongate structure is associated with the exterior panel and the second elongate structure is associated with the interior panel. Preferably the respective panels are secured to their respective elongatestructures through the use of high strength adhesives or appropriate mechanical fasteners such as screws or the like.The first elongate structure is connected to the second elongate structure such that they are able to move with respect to each other.Preferably, the first elongate structure includes a C-channel or similar feature running its vertical length, or at least a substantial portion of its vertical length, and the second elongate structure is provided with a complementary protrusion or rail. However, it should be appreciated that this arrangement may be reversed, such that it is the first elongate structure that is provided with the protrusion or rail and the second elongate structure is provided with the C-channel or similar structure.Preferably the surfaces of the C-channel that in use may contact the complementary protrusion or rail includes a liner or coating of a material having low thermal conductivity relative to aluminium. Even more preferably, the liner or coating is extruded, moulded or otherwise configured from a plastics material. In preferred embodiments of the invention, the plastics material is from the polyketone family. A polyketone is a type of thermoplastic polymer that is hardwearing and robust while being resistant to softening at the typical temperatures that the door may experience in use, important properties for the functioning of the invention. However, this is not meant to be limiting and persons skilled in the art will identify other types of plastics material suitable for use in the invention that have the desired hardwearing, robust and heat resistance properties.The door includes a pair of opposing bars defining its respective top and bottom edges.Preferably, the opposing bars are configured as extrusions of aluminium. The use of aluminium for the bar may be advantageous as it may mean the bar has the same coefficient of thermal expansion as the stiles and aluminium panels. Aluminium is also able to withstand sufficiently hightemperatures (in the region of 200°C) to enable the bar to be powder-coated, which is a common finishing treatment for such components.However, other materials meeting the above discussed parameters may also be suitable for the bar; specifically, materials having a coefficient of thermal expansion relatively similar to the aluminium panels, and which are able to be powder-coated.Each opposing bar comprises a first element associated with the first outer panel and the first elongate structure of the stile and a second element associated with the second outer panel and the second elongate structure of the stile.Preferably, each of the first and second elements include a horizontal bar and a depending flange. The horizontal bar and depending flange may be separate components, secured to each other through the use of appropriate fasteners, or alternatively may be formed as a single extrusion of aluminium.Preferably, the depending flange may be configured with a surface to receive an edge of the panel with which it is to be associated. Even more preferably, the depending flange may be provided with a recess complementary to ribs provided to the edge of the panel with which it is to be associated.Preferably, the respective first and second elements of each opposing bar are connected to the respective first and second elongate structures of each stile with fasteners, such as screws, bolts or rivets. Alternatively, they may be welded or secured through the use of high strength adhesives.The first element is connected to the second element such that they are able to move with respect to each other.Preferably, the first element is connected to the second element via a connector having low thermal conductivity. Even more preferably, the connector is configured from a plastics material, such as apolyketone, as previously described in respect of the liner of the C-channel. However, other appropriate hardwearing and robust plastics material that has some resistance to softening may be used.In some embodiments, any potential contact surfaces between the first and second elements may be coated with a material having low thermal conductivity. For example, the contact surfaces may be coated with plastic or rubber. This has the effect of minimising thermal conductively across the respective elements.The use of at least two components to form each stile and opposing bar allows each to accommodate some movement of the exterior and / or interior panels with which each is associated, while minimising the stresses that may be applied to the other components of the door as a result of the movement. In other words, a change in length and / or width of the exterior or interior panels, such as may arise when there is a significant temperature differential between the respective panels, is accommodated without affecting the appearance and / or structural integrity of the door.The invention has been found to be relatively resistant to deformation arising from repeated thermal expansion. During testing, where heat is applied via an 8 kiloWatt infrared heater to one side of a door, formed in accordance with an exemplary embodiment of the invention, such that that side of the door attains a temperature up to 70° Celsius (the expected maximum range of operating temperature in New Zealand), the other side (the cold side) has been found to remain at a temperature between 28° to 31° Celsius when measured at the centre of the door.Furthermore, the cold side of the door is substantially flat in all directions, with minimal bowing. The structural integrity of the bonding means is uncompromised with no delamination or failure of the adhesive.Further aspects and advantages of the invention, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the ensuing description which provides at least one example of a practical application of the invention.BRIEF DESCRIPTION OF FIGURESFurther aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:Figure 1        is a cross-sectional view of an insulated metal door according to a preferredembodiment of the present invention;Figure 2        is a detail isometric view of the top corner of the insulated metal door of Figure 1;Figure 3        is an isometric view of a top bar for the insulated metal door of Figures 1 and 2;Figure 4A      is an end view of the top bar of Figure 3 in a first condition; andFigure 4B      is an end view of the top bar of Figure 3 in a second condition.Throughout the drawings, like features are assigned a like numeral.DETAILED DESCRIPTION OF FIGURESFigure 1 shows a cross-section of an insulated metal door (generally indicated by 100) according to a preferred embodiment of the present invention.The door 100 of this embodiment comprises two aluminium panels 102, 104 laterally spaced from one another and forming the respective outer surfaces of the door. When mounted as an exterior door to a building, one surface faces the exterior of the building, i.e. is the exterior side of the door, and the other surface faces the interior of the building, i.e. is the interior side of the door.These panels shall be referred to as the exterior 102 and interior panels 104 of the door 100 as appropriate. However, it will be appreciated in some instances the door may be mounted as an internal door and as such both outer surfaces may face adjacent rooms or hallways. In these cases, the panel referred to as the exterior panel faces the cooler of the two rooms and / or hallway.It should be noted that in the following description, any thicknesses recited for any of the components of the door discussed herein are not meant to be limiting and variations from these, for example due to availability of materials or the intended end use of the door, will be readily envisaged by persons skilled in the art.In the illustrated example, each of the exterior 102 and interior panels 104 are formed from 1.6 to 2.0 millimetres thick aluminium sheet. Preferably, the panels are of the same thickness for ease of manufacture or reducing inventory requirements. However, in some alternate examples, one of the panels forming the exterior and interior sides of the door 100 respectively may be thicker than the other. This could be desirable, for example, when one side of the door is likely to experience greater wear than the other, and thus requires increased structural integrity. However, it will be appreciated that attention may then need to be paid to the hanging of the door to ensure that the thicker panel is orientated correctly.Provided between the exterior 102 and interior panels 104 is an inner skin 106, comprised of a further aluminium panel. As this inner skin is not exposed or visible when the door 100 is assembled, and thus is not exposed to user wear or inclement weather, it may be thinner than the panels forming the outer surfaces of the door.In the illustrated example, the inner skin is 0.45 millimetre aluminium sheet in contrast to the 1.6 to 2.0 millimetre thick aluminium sheet used for the panels 102, 104 forming the outer surfaces of the door 100.As previously noted, it should be appreciated that the thicknesses referred to herein are cited as examples only; aluminium sheets may be of greater or lesser thicknesses, depending on availability of materials, building specifications, and / or intended use. Of course, if the sheet is thicker, then this may affect the overall weight of the door and thus the hanging fittings may need to be appropriately engineered.The inner skin 106 is set and held inwards of the exterior panel 102 of the door 100 through the use of a ribbed or similar structure 108. This structure may be formed from one or more formed profiles of aluminium which have been adhesively bonded or otherwise secured, for example with mechanical fasteners, to the exterior panel and the inner skin. Both the inner skin and ribs contribute to the overall rigidity and structural integrity of the door, particularly in respect of the exterior side of the door, which is likely to undergo the most thermal change.The ribbed structure 108 forms approximately a third of the thickness of the door 100. The substantial portion of the remaining thickness of the door is formed by an insulating layer 110. This insulating layer 110 is disposed between the interior panel 104 of the door 100 and the inner skin 106 and is bonded to the interior panel 104 through the use of an appropriate adhesive. This arrangement allows the inner skin of the door to slide past the insulating layer should the length of the interior panel change due to heat-related expansion and contraction.It should be appreciated that the relative thickness of the respective ribbed structure 108 and the insulating layer 110 may vary from that described, depending on availability of materials and / or end use of the door. For example, where insulation properties are less important, the insulating layer may be reduced relative to the ribbed structure. Alternatively, if there are constraints on the availability of the substrate from which the ribbed material is formed, this may be reduced relative to the insulating layer; material for the latter is likely to be cheaper to source.In the illustrated example, the material used for the insulating layer 110 is polyisocyanurate (PIR) foam which has a relatively low co-efficient of friction, which aids in the sliding movement between it and the inner skin 106. However, in some embodiments not shown, other plastic foams could be used, and these could have a layer of film or material applied to the surface that in use contacts the inner skin so as to decrease the co-efficient of friction.This placement of the insulating layer 110, relative to the interior panel 104, serves to help keep the temperature of the interior side of the door 100 at a similar temperature to that of the interior of the house. It also helps ensure even temperature across the entire surface of the exterior panel 102 of the door.The respective left and right sides of the door 100 are defined by stiles 112, 114 that run the entire vertical length of the door. Each stile is made up of two distinct elongate structures 112a, 112b, 114a, 114b, each associated with a respective panel of the door. The thickness of each stile substantially corresponds to the combined thickness of the ribbed structure 108 and insulating layer 110.Th stile 114 is best seen in Figure 2, which is an isometric view of a top corner of the door 100 from its exterior side. The respective elongate structures 114a, 114b of the stile 114 are secured to the exterior panel 102 and interior panels 104 respectively through the use of appropriate bonding means, whether a high strength adhesive or even fasteners such as screws or rivets. This means the exterior and interior panels of the door each bear part of the stiles.Each of the elongate structures 114a, 114b are configured with complementary fittings such that they can be connected to each other to form a complete stile 114. A significant aspect of the invention is that this connection is such that it allows vertical movement of the elongate structures, and therefore the panel 102, 104 to which it is attached, relative to each other.In the illustrated embodiment, it can be seen that one elongate structure 114b is provided with a recessed channel 116 running its vertical length. A length of plastics material 118, preferably comprised of a polyketone, is provided as a liner to the channel. This type of plastic is hardwearing and robust while still resistant to softening even at the upper ranges of the temperatures that the door may experience if it was exposed to sunlight for extended periods of time.The other elongate structure 114a forming the stile 114 is provided with a flange 120 running its vertical length, the flange having a profile that is substantially complementary to that of the channel 116 of the opposing elongate structure 114b. These two parts, the channel and flange interlock with each other in this manner.Any vertical movement of one of the interior 104 and exterior 102 panels relative to the other of the panels is allowed through the use of the plastic liner 118. Depending on the density of the plastic liner, and the clearances in assembly, some horizontal movement of the respective panels may also be accommodated. Furthermore, the use of a plastic liner for the channel 116 serves as a thermal break and helps stop or minimise thermal conduction from one side of the door 100 to the other.In Figure 2, it will be observed that, in contrast to the stile 114, the ribs 108 and insulation layer (not shown in this figure for sake of clarity) do not reach the full height of the exterior 102 and interior panels 104 of the door 100. This is to leave sufficient clearance for the bar (not shown) that forms the top edge of the door. Although not shown here, the bottom of the door is configured in a similar manner, to ensure clearance for the bar that forms the bottom edge of the door.An embodiment of the top bar 122 is shown in an isometric view in Figure 3. As can be seen, the top bar is formed from two distinct elements 122a, 122b. Each element is comprised of a substantially horizontal bar, which together substantially correspond to the overall width of the door (not shown), and which forms the uppermost portion of the top bar. From this horizontal bar, a flange 124a, 124b depends downwards and serves as a stiffener for the overall top bar.In the illustrated embodiment, the stiffener 124a, 124b is a separate skirt structure that is secured to their respective horizontal bar 122a, 122b through the use of fasteners (not shown here). Fasteners that may be used for this purpose could be the likes of screws, bolts or rivets, or bonding agents such as a high strength adhesive. However, in other embodiments, not shown here, the horizontal bar and skirt may be configured as an integral structure, for example as a single extrusion of aluminium.Each horizontal bar 122a, 122b is associated with a respective panel (not shown) of the door (not shown) and its associated stile (not shown). The apertures 126 visible at the ends of each horizontal bar are for the use of screws or the like which connect the element to the respective stile.Turning now to Figures 4A and 4B, which show the top bar 122 forming the top edge of the door and depict the cross-sectional profile of the horizontal bars 122a, 122b. The movement of each horizontal bar forming the top bar respective to each other can be appreciated.Dealing first with the horizontal bar 122a, 122b of the cross-sectional profile, the recesses 128a, 128b provided for the fasteners (not shown) connecting the horizontal bars to their respective skirts 124a, 124b can be seen. Although not visible here, in use, the fasteners enter at the top of the horizontal bar via the apertures 126 shown in Figure 3.Also visible is the position of the skirts 124a, 124b, which are disposed inwards of the front edges of the horizontal bars 122a, 122b. This creates contact surfaces 130a, 130b against which the top edge of the respective exterior and interior panels 102, 104 is located in use. The skirts include channels 138 running the horizontal length of the contact surfaces; these provide some weight reduction and also form glue traps. Any excess adhesive used to bond the respective components may collect in the channels such that it does not exit the interior surfaces of the door.On the rear edge of the horizontal bars 122a, 122b and skirts 124a, 124b are provided recesses into which a pair of connectors 132, 134 of a suitable hardwearing and robust plastics material, preferably of polyketone, are fitted. The recesses are contoured to minimise any lateral displacement as the connector pivots in response to any vertical movement of the respective exterior and interior panels 102, 104. These connectors link the respective horizontal bars to each other. The use of plastics material for the connectors means that this is in a way that prohibits or at least minimises any thermal conduction from one side of the door (not shown) to the other. This reduces heat loss.The underside of the horizontal bars 122a, 122b are recessed 136a, 136b, to allow the fitting of a plastic or rubber gasket (not shown). This gasket contacts the top and bottom ends of the stiles (not visible in Figures 4a and 4b). Depending on the length of the gasket, it may also contact the insulating layer (not shown) and / or the inner skin (not shown) and / or ribbed structure (not shown). The gasket serves as a further thermal break, such that there is no metal-to-metal contact between the interior panel and the exterior panel.As previously noted, thermal expansion and contraction of the exterior and / or interior panels 102, 104 occurs in a direction away from the centre of the panels, towards their edges. As it does so, the upper edges of the respective exterior and / or interior panels biases against the horizontal bars 122a, 122b, urging them upwards. The connectors 132, 134 rotate or pivot slightly to permit this movement. Similarly, the expansion of one of the panels relative to the other also causes movement of the elongate structure of the stile (not shown) that is associated with that panel. It is able to move along the structure that connects the respective elongate structures. The use of plastic connectors for both the stiles and the top and bottom bars mean that the exterior panel is thermally isolated from the interior panel of the door. This helps minimise thermal losses.In Figure 4a, the top bar is shown 122 as it would appear if the panel 104 associated with the contact surface 130b has expanded (or if the panel 102 associated with the contact surface 130a has contracted). In Figure 4b, the arrangement is reversed.Although only the top bar 122 is shown here, it will be appreciated that the bottom bar of the door is arranged in a similar fashion. In this manner thermal expansion and contraction, and the resulting changes in the vertical dimensions of the aluminium sheets forming the exterior and interior panels of the door, can be accommodated without comprising the structural integrity of the door, particularly in relation to any hardware fitted to the door, such as handles and locks.Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features. Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the invention as claimed herein and withoutdiminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present claims.Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the claims as defined herein.

Claims

CLAIMS1.       An insulated metal door, comprising:a first outer metal panel and a second outer metal panel;an inner panel disposed between the first outer metal panel and the second outer metal panel;an insulating layer disposed between the inner panel and one of the first and second outer metal panels;a pair of opposing stiles defining respective left and right side edges of the door, wherein each stile comprises a first elongate structure associated with the first outer metal panel and a second elongate structure associated with the second outer metal panel, wherein the first elongate structure is connected to the second elongate structure such that they are slidably moveable with respect to each other along their vertical length,a pair of opposing bars defining respective top and bottom edges of the door, wherein each bar comprises a first element associated with the first outer metal panel and the first elongate structure of the stile and a second element associated with the second outer metal panel and the second elongate structure of the stile, wherein the first element is connected to the second element such that they are able to pivotally move with respect to each other.

2.      The insulated metal door of claim 1, wherein the inner panel is held in a fixed position relativeto the first outer metal panel through the use of a spacing structure.

3.     The insulated metal door of claim 2, wherein the spacing structure is one or more corrugatedstiffening ribs.

4.     The insulated metal door of any one of claims 1 to 3, wherein the insulating layer is disposedbetween the inner panel and the second outer metal panel.

5.     The insulated metal door of claim 4, wherein the insulating layer is bonded to the secondouter metal panel along a horizontal centre line.

6.     The insulated metal door of any one of claims 1 to 5, wherein the first elongate structure andsecond elongate structure run the length of the respective opposing stiles.

7.     The insulated metal door as claimed in any one of claims 1 to 6, wherein the first elongatestructure and second elongate structure each have a contact surface complementary to the other of the first elongate structure and second elongate structure.

8.     The insulated metal door as claimed in claim 7, wherein at least one of the contact surfacesof the first elongate structure and second elongate structure is provided with a liner or coating of a material having low thermal conductivity relative to aluminium.

9.     The insulated metal door as claimed in either claim 7 or claim 8, wherein the liner or coatingis configured from a polyketone.

10. The insulated metal door of any one of claims 1 to 9, wherein the first elongate structure and second elongate structure are complementary C-channels and rails.

11. The insulated metal door of any one of claims 1 to 10, wherein the first element of the opposing bars is provided with a depending flange configured with a surface to receive a top and bottom edge of the first outer metal panel.

12. The insulated metal door of any one of claims 1 to 11, wherein the second element of the opposing bars is provided with a depending flange configured with a surface to receive a top and bottom edge of the second outer metal panel.

13. The insulated metal door of any one of claims 1 to 12, wherein the first element of each opposing bar is pivotally connected to the second element of each opposing bar via a connector.

14. The insulated metal door as claimed in claim 13, wherein the connector is configured from a material having low thermal conductivity relative to aluminium.

15. The insulated metal door as claimed in either claim 13 or claim 14, wherein the connector is configured from a polyketone.

16. The insulated metal door of any one of claims 1 to 15, wherein:a) the inner and outer metal panels are sheets of aluminium; and / orb) the pair of opposing stiles are extrusions of aluminium; and / orc) the pair of opposing bars are extrusions of aluminium; and / ord) the insulating layer is polyisocyanurate.

17. A kit set for an insulated metal door, comprising:a first outer metal panel and a second outer metal panel;an inner panel disposed between the first outer metal panel and the second outer metal panel;an insulating layer disposed between the inner panel and one of the first and second outer metal panels;a pair of opposing stiles defining respective left and right side edges of the door, wherein each stile comprises a first elongate structure associated with the first outer metal panel and asecond elongate structure associated with the second outer metal panel, wherein the first elongate structure is slideably movable relative to the second elongate structure;a pair of opposing bars defining respective top and bottom edges of the door, wherein each bar comprises a first element associated with the first outer metal panel and the first elongate structure of the stile and a second element associated with the second outer metal panel and the second elongate structure of the stile, wherein the first and second elements are pivotally linked to each other.

18. The kit set as claimed in claim 17, wherein the kit set also includes a spacing structure configured to hold the inner panel in a fixed position relative to the first outer metal panel.

19. A method of manufacturing an insulated metal door, the method including the steps of:• providing a first outer metal panel;• providing an insulating layer proximate the first outer metal panel;• bonding an inner panel to the insulating layer;• providing a pair of opposing stiles defining respective left and right side edges of the door, to the first outer metal panel, wherein each stile comprises a first elongate structure associated with the first outer metal panel and a second elongate structure associated with a second outer metal panel, wherein the first elongate structure is slidably movable relative to the second elongate structure;• providing a pair of opposing bars defining respective top and bottom edges of the door, to the first outer metal panel, wherein each bar comprises a first element associated with the first outer metal panel and the first elongate structure of the stile and a second element associated with the second outer metal panel and the secondelongate structure of the stile, wherein the first and second elements are pivotally linked to each other; and• providing the second outer metal panel and fixing same to the pair of opposing stiles and bars.114b114a

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