GB2504920A - A glass door for a gas fire with adhesive bonded glass and a convection path - Google Patents

Abstract

An outer door 10 for a gas fire comprises a ceramic glass panel 16 bonded to a sheet metal frame 11-14 using adhesives (fig 2, 26) with a layer of opaque sealant between the panel and the frame to obscure the adhesive and frame from view, or has an outer door 10 spaced from an inner door 8 to form a convection path (fig 4, 38). The door is made by screen printing the panel; applying sealant over the screen printed areas (fig 3, 32) where the glass will overlie the frame; allowing the sealant to cure fully; forming a frame with a flat surface; and bonding the panel to the frame using adhesives.

Description

A GAS FIRE AND A DOOR TIELEREFOR

The present invention relates to a door for gas fires and to an improved gas fire incorporating such a door. In particular, the invention relates to a door for a gas fire with an outer glass panel, providing improved efficiency and aesthetics to a gas fire. The invention also relates to a method of manufacturing the door.

There is a continuing desire to improve the efficiency of gas fires. There is also a desire to improve and update the aesthetics of fires. The present invention arose through a desire to provide a highly efficient gas fire with a door having no visible external fixings.

As fires become more efficient the temperatures reached within the combustion chamber increase. It is conventional to restrict or seal off the front aperture of the combustion chambers of high-efficiency gas fires with a 4-5mm thick sheet of ceramic glass. A further outer door or metal frame is then generally provided to obscure the edges of the firebox and inner door of the fire for aesthetic reasons.

The outer doors of gas fires typically comprise a metal frame, to obscure the more unsightly parts of the fire, and inner door, and with a central opening to allow radiant heat to emit and to allow the flame effect of the fire to be seen. Typically, the door is provided with supports or fixings through or around the frame to support the door on hinges and the like.

Occasionally, a glass panel glass is included in the outer door.

In order to mimic the appearance of flat screen televisions, there was a desire to produce a fire of this type where no external fittings are visible on the outside of an outer glass door, giving the outward appearance of a single piece of glass floating' in front of the fire.

According to the present invention there is provided a door for a gas fire as defined in the appended claim 1. The invention also provides a method for making the door according to appended claim 6, and a gas fire according to appended claim 12. Further advantageous features are recited in the associated dependent claims.

The door of claim 1 comprises a frame, and a glass panel bonded to the frame using adhesive. This provides a very clean' outward appearance, with no external fittings visible.

Rather than fitting the outer glass panel into a frame and/or attaching hinges by bolts or screws, it was hoped to achieve a clean outward appearance by simply bonding the glass panel to the outside of a metal frame which supported the hinges and fixing components of the door. This approach was new and untried, so numerous problems had to be overcome in developing the fire.

The high price of ceramic glass typically means that, where glass is used in an outer door, it is typically a less expensive toughened float glass. The heat experienced by the outer door is typically not so high as to cause problems for the glass of the outer door.

In development of the present invention, the high temperature generated by the fire caused problems with the glass door. The typical toughened float glass was found to deform and balloon' to unacceptable levels when subjected to the higher than normal temperatures.

This was unexpected since the temperatures measured at the outer door were within the ranges which should be tolerated by toughened glass. However, the large size (950mm x 688mm) of the glass door being used for this particular fire meant that the temperatures experienced by the middle of the outer door were considerably higher than those experienced at the edges. It was these temperature differences that were understood to cause the unacceptable ballooning of the central part of the outer door.

Thicker panels of toughened glass (6mm as opposed to 4mm) were tried, but were found not to overcome the problem, and the greater weight of the door due to the thicker glass was also deemed undesirable. The air gap between the inner and outer doors was also increased, but to no avail.

One known approach to overcoming the negative effects of high temperatures on an outer door is to remove a central portion of the glass in the outer door, but this approach is clearly inconsistent with the aim of providing a single clean glass panel in front of the fire. It was therefore decided, despite the significantly higher cost, to use ceramic glass for the outer door to try and overcome the deformation problem.

Ceramic glass is used for the inner doors of fires of this type primarily because it exhibits almost zero expansion even when exposed to temperatures in the region of 1000°C. This is obviously beneficial when the glass is being used in high temperature applications/environments. However, the total lack of expansion of the ceramic glass itself caused further problems which had to be overcome, as will be explained below.

Surprisingly, the initial trials with the ceramic glass sheet still showed unacceptable levels of ballooning in the centre of the glass door. The problem was determined to be a result of the metal frame expanding and/or bowing with the temperature rise even though the ceramic glass did not. The bond between the glass panel and the frame was so strong that the deformation of the metal frame caused a degree of deformation in the glass panel. Although this deformation was considerably less than when toughened float glass was used (around 3mm compared to around 12mm), it was still not considered acceptable.

To minimise the problem it was decided to remove some of the material and strengthening components from the metal frame. One benefit of bonding the glass panel to the entire surface of a frame rather than using bolts or similar is that the glass panel provides additional strength and rigidity to the frame. This allows material to be removed from the metal frame and thinner gauge metal to be used in its construction without a loss of strength and robustness of the door.

The initial frame was essentially a four piece steel frame comprising top, bottom, left and right pieces, each with a strengthening flange on the inside. When removing strengthening material it was decided to remove the, longer, horizontal strengthening flanges running across the top and bottom of the door frame. This was partly to because of the greater effect on the expansion of longer pieces of the frame, but it additionally helped to ensure that the maximum strength of the door remained at the vertical edges where the hinges and other closure fixes are provided. With the strengthening flanges removed, the remaining flat pieces of metal at the top and bottom of the frame were found to expand and bow less, thus reducing the deformation of the door. The deformation was further reduced by reducing the thickness of the metal used at the top and bottom of the frame from 1.5mm to 1 mm.

It was necessary to retain the thicker, 1.5mm, material and strengthening flange on the hinge side of the door, but it was possible to reduce the thickness of all other pieces of the door frame to 1mm and remove the horizontal strengthening flanges because of the extra strength and rigidity provided by the bonded glass panel. This configuration was found to reduce the ballooning of the door to acceptable levels.

Using a solid outer glass door instead of an open frame or cut-out glass panel also provides a convection path between the inner and outer doors that does not exist where an opening is provided in the centre of the outer door. This improves the convective heat output from the fire and counteracts the slight reduction in radiant heat output resulting from the inclusion of an additional glass panel in front of the fire. Convected air travels further into the room than radiant heat and additionally generates an air flow around the room to provide a more uniform overall temperature.

A further advantage of removing material from the metal frame, in particular removing horizontal strengthening flanges, was that the passage available for convection between the inter and outer glass doors could be made free from obstruction across the entire width of the door, thus maximising the convective air flow and resulting heat output. Having addressed the expansion problems, and due to the stable nature of ceramic glass, it was also possible to reduce the air gap between the inner and outer doors to optimise the convective air flow.

The increased convective air flow was beneficial in obtaining the maximum possible output from thc firc, but created very high temperatures immediately above the fire. Despite advice to the contrary, many people mount flat screen televisions above gas fires. The high temperatures generated by gas fires can be damaging to such wall mounted screens, and the especially high temperatures generated by the fire according to the present invention exacerbate this problem.

Furthermore, there was a risk that the high temperature air resulting from the convection path between the inner and outer doors could also cause discolouration and damage to wall coverings surrounding the fire in instances where the fire is not mounted within a hearth.

Previously, outer frames of similar fires have been provided with a small deflector to direct the hot air generated by the fire away from the wall. However, the present fire not only develops greater temperatures due to the convection between doors, but also omits the frame from the outer door in order to provide its clean appearance. It was therefore necessary to provide a separate deflector component as a part of the fire itself for wall mounted applications.

[he deflector is provided at the top of the fire and serves to direct the convection air horizontally into the room and keep it clear of the wall above the fire. A small gap is provided between the deflector and the wall to prevent conductive heat transfer from the deflector (which can get hot during use of the fire) and the wall. The deflector is provided as a sheet metal component attached to the top of the fire, with a flat piece of glass glued to the top to mimic the outer door of the fire and also to extend the overhang of the deflector.

This allowed the edge of the deflector to be extended outwards, to help in moving the convection air away from the wall, while also maintaining a smooth air flow by optimising the angle and spacing of the deflector.

The top deflector was found to be beneficial in directing the airflow away from the wall and reducing the temperature immediately above the fire. However, the temperatures were still too high to be able to recommend safe mounting of a flat screen television above the fire. It was possible to reduce the temperature to acceptable levels (typically less than 38°C/l00°F) where a mantle was present and with particular spacing of the various components. When wall mounting the fire without a mantle, it is recommended to include a further deflector component, or TV shield, on the wall between the fire and the television. Preferably, the television should be mounted at least 40mm above the shield to ensure that the temperatures experienced by the television remain within these acceptable levels.

The TV shield, like the top deflector, is provided as a metal component with a flat piece of glass glued to the top. In both cases, the direct bonding of the glass to the metal component has safety benefits because the glass is likely to remain attached to the metal even in the case of a breakage.

Another problem with using a ceramic glass with near zero expansion arose when it came to apply a screen printing to the glass panel.

Toughened float glass can be readily screen printed with high intensity colours. The level of adhesion between the print and the glass is also extremely high, so the printed finish is robust and durable. In contrast, it is difficult to apply a high intensity colour screen print to ceramic glass. This is due, at least in part, to the fact that the inks typically used tend to expand and contract at comparable rates to toughened glass. A conflict therefore arises with the near zero expansion of ceramic glass.

The adhesive used to bond the glass panel to the steel frame in the present invention is a silicone mbber adhesive, and needs to be applied in beads to provide its optimum adhesive strength. These beads would be visible through the outer glass panel if no printing were applied, which would obviously be undesirable.

The initial attempts to provide a screen printing on the ceramic glass sheet were unacceptable. The bond between the print and glass was insufficient, leading to the printing de-laminating in the areas where the adhesive was applied, leaving some of the print on the panel and the remainder on the adhesive beads. This problem was overcome by reducing the thickness of the screen print, but the resulting lower colour density meant that the beads of adhesive remained visible through the glass panel, which was not acceptable.

The above problem was overcome by applying a thin layer of silicone sealant over the screen printing in the area of the panel which was to overlie the metal frame. The colour of the silicone sealant was chosen to match the colour of the screen printing on the glass panel, typically black or white. Once the layer of silicone had fully cured, the silicone coated side of the panel was bonded to the metal frame as before to form the finished outer door.

This new technique was found to provide a suitable colour depth to fully obscure the adhesive beads, while also overcoming the problem with de-lamination of the printing.

It should be seen that the development process above involved overcoming a number of technical problems in order to achieve a satisfactory result.

* The usual glass considered for the purpose was found to be insufficient, so a more expensive, specialised, type of glass (ceramic glass) had to be used.

* The use of ceramic glass required modification of the frame, and also created problems with the colour intensity of screen printing, which had to be overcome.

* The problems with the colour density were exacerbated because of the need to obscure beads of adhesive between the glass panel and the metal frame. This problem does not arise with more traditional means of manufacture.

The final fire also provided a number of benefits over conventional fires, as set out below * The use of a single continuous glass panel for the outer door provided a convection air path between the inner and outer door that would not be present where a frame or an outer door with a central aperture were used.

* The convection was further improved by the removal of strengthening flanges on the door frame, made possible by the additional strength and rigidity obtained from bonding the glass panel directly to the metal framework.

* It is also envisaged that forced convection could be employed between the inner and outer doors. This would not only improve the convective heat transfer, but would also reduce the temperature of the outer panel to safer levels when the fire is in use.

These, and other, aspects of the invention will be better understood with reference to the accompanying figures, in which: Figure lisa perspective view of a fire according to an aspect of the present invention: Figure 2 is a schematic view of a frame from a door for a fire according to an aspect of the invention; Figure 3 is a schematic view of a glass panel from a door for a fire according to an aspect of the invention; Figure 4 is a schematic cross sectional view of a fire according to an aspect of the invention; and Figure 5 is a schematic cross sectional view of the fire of Figure 4 mounted for use.

The fire 1 shown in Figure 1 is a glass fronted gas fire for mounting in a fireplace or a hole in the wall. It comprises a firebox 2 which is closed off or sealed off at the front opening when in use by a hinged inner door 4. The inner door 4 comprises a ceramic glass panel 6 held in a steel frame 8. Inner doors of this type are known in glass fronted fires of this type, so no fUrther details will be provided here.

The fire 1 is a Conventionally Flued Fire (CF), which is connected to a chimney in use, but the design features described below would be equally applicable to glass fronted fires of other types, for example a Balanced Flue Fire (BF) where no chimney is required and the combustion products and air for the fire pass through common concentric tubes connected through an outside wall.

The fire 1 of Figure 1 also comprises a fUrther outer door 10, which is located outside and spaced from the inner door 4 when the doors 4,10 are closed. Both the inner door 4 and the outer door 10 are shown in an open position in Figure 1 for the sake of clarity, but would be fully closed when the fire 1 is in use.

The outer door 10 comprises a metal frame made up of first and second vertical frame parts 11,12 and two horizontal frame parts 14. The vertical and horizontal frame parts 11,12,14 are riveted together via small joining flanges 13 to form a complete frame. A single piece of ceramic glass 16 is bonded to the frame with adhesive as will be described in greater detail later.

The vertical frame parts 11,12 additionally comprise strengthening flanges 18 at both side edges of the outer door 10 to provide additional strength and, on the first vertical frame part 11, to provide mounting areas for the hinges 20 of the outer door 10. Significantly, no similar strengthening flanges are provided on the thinner horizontal frame parts 14. The first vertical frame parts 11 of the outer door 10 is formed from 1.5 mm thick steel plate, hereas the second vertical frame part 12 and the horizontal frame parts 14 are formed from 1mm thick steel plate. The thicker material of the first vertical frame part 11 is required predominantly for strength where the hinges 20 are mounted.

Magnets 22 are provided on the second vertical frame part 12 of the outer door 10 to maintain the outer door 10 in a closed position when the fire 1 is in use, and a convection air gap 24 isprovidcd around the outside of the firebox 2, as is known in gas fires of this type.

As mentioned above, the glass panel 16 of the outer door 10 is bonded to the frame parts 11,12,14 using an adhesive, specifically a high temperature silicone rubber adhesive such as PACTAN 7076 or PACTAN 6060. Other PACTAN adhesives or alternative adhesives with similar qualities could also be used. Figure 2 shows how the beads of adhesive 26 are applied to flat surfaces of the vertical and horizontal frame parts 11,12,14 ready for application of the ceramic glass panel 16. / Figure 2 shows the outside of the frame, i.e. the opposite side from that which is visible in Figure 1. On this side of the frame, the vertical frame parts 11,12 and the horizontal frame parts 14 provide a flat surface uninterrupted by features, fixings or changes in level to ensure that the flat glass panel 16 can be reliably bonded to the frame. The application of the adhesive in beads with spaces in-between is important in ensuring that the adhesive will cure/set properly, however the pattern of the beads 26 shown in Figure 2 is merely an

example.

Figure 3 shows the glass panel 16 ready to be bonded to the frame of Figure 2 in order to complete the outer door 10 of the fire 1. The panel 16 is provided with colouring in certain areas in order to obscure the beads of adhesive 26 that would otherwise be visible through the glass panel 16. As discussed earlier, problems were encountered during development -10 -when applying screen printing to the ceramic glass panel 16, so it was necessary to additionally add a layer of silicone sealant/adhesive, such as PACTAN 7076 or PACTAN 6060 or similar, to ensure that a necessary colour depthlintensity was achieved. The process will be briefly described with reference to Figure 3.

The panel 16 shown in Figure 3 shows three separate areas, a clear central area 28, and two oppositely hatched areas 30,32 located concentrically around the central area 28. The first step in applying colour to the panel 16 is to screen print a shade or colour of choice in the outermost hatched area 32. The screen printing will typically be black or white, although other colours could be used. The screen printing step may also incorporate a fade or stippling effect in the innermost hatched area 30 if desired.

After completing the screen printing process, the next step is to mask off the innermost hatched area 30 with masking tape. A few millimetres around the outer edge of the panel 16 may also be masked off if desired. A smooth thin layer of silicone sealant is then applied to the outermost hatched area 32 over the top of the screen printing before the masking tape is removed to leave clean lines at the edges of the sealant layer. The colour of the sealant should preferably be selected to match the screen printing, for example black sealant would be used for black printing, white sealant for white printing etc. The panel is then left in a clean dust-free environment, typically for around 24 hours, to allow the silicone sealant to cure. It is important that the silicone layer is properly cured because it is this that will be directly bonded to the frame of Figure 2 to make the outer door of the fire 1. Although the figures show the beads of adhesive 26 provided on the frame, it is quite possible, and perhaps even preferable, for the beads of adhesive 26 to instead be applied to the panel 16 after the thin silicone layer has cured.

Preparing the glass panel 16 in this way ensures that a clear central window 28 is provided, while the periphery of the panel 32, which will overlie the frame of Figure 2, is coloured so that the beads of adhesive 26 will not be visible.

Once the frame and the prepared glass panel 16 have been bonded together, it is important that the adhesive is left for as long as possible to cure/set completely. The bond between the glass panel 16 and the frame parts 12,14 is not simply a means of holding a glass panel 16 on/in the frame. The glass panel itself also provides greater strength to the door 10 as a whole. This allows the use of thinner material for three of the four frame parts 12,14, and the omission of the horizontal strengthening flanges. One key advantage of omitting these flanges will be explained with reference to Figure 4.

Figure 4 shows a cross-sectional view of a fire I similar to that of Figure 1. A convection air gap 24 is provided between the outside of the firebox 2 and an outer case 34 of the fire 1, as is known in fires of this type, to allow convection around the firebox 2 as shown by solid arrows 36. Unlike known fires, a further convection path is provided between the glass panel 6 of the inner door 4 and the glass panel 16 of the outer door 10. This secondary convection, indicated by broken arrows 38, scrubs' further heat from the glass panel 6 of the inner door 4 and contributes to a greater overall convective heat transfer from the fire 1.

This offsets a small loss in radiant heat transfer resulting from including a second solid glass panel 16 in front of the fire.

The new construction of the outer door 10, as discussed above, allows for the omission of horizontal strengthening flanges, which means that the secondary convection 38 is unimpeded by features on the inside of the outer door.

The fire 1 thus achieves an improved heat output which penetrates further into a room than radiant heat. This makes the resulting fire 1 highly efficient as well as being aesthetically desirable.

The transfer of convection air into the room is further improved by the inclusion of a deflector 40 positioned at the top of the fire I above the gap between the inner and outer doors 4,10. The deflector 40 comprises a bent sheet metal part, attached to the top of the fire, with a flat piece of glass glued to the top to mimic the outer door of the fire and also to extend the overhang. As can be seen in Figure 4, the deflector 40 directs both flows of convection air 36,38 away from the wall in which the fire is mounted and outward into the room.

An angle A of 1 go in the metal part of the deflector 40 has been found to be most effective, although other similar angles, i.e. 10°-25°, would likely achieve similar results. The deflector 40 extends away from the wall by around 50-70 mm, preferably around 55mm, to ensure that it redirects the secondary convection air 36 from between the inner and outer doors 4,10 without appearing too obtrusive.

Directing the hot convection air 36,38 away from the wall and into the room not only improves the effectiveness of the fire 1, but also serves to prevent damage to the wall and wall coverings above the fire 1. Figure 5 shows the fire 1 of Figure 4 installed as a so called Hole in the Wall' fireplace, i.e. without a hearth or other fire surround. A fire I may be installed in this way for purely aesthetic reasons, or it may be that there is insufficient space to provide a hearth around the fire 1. In either case, a problem can arise because the heat from the fire 1 will rise up the wall 42 in which it is mounted and cause damage to the wall coverings or, in extreme cases, to the fabric of the wall 42 itself The high heat output of the fire I of the present invention meant that this was a serious concern.

As mentioned above, the deflector 40 provided at the top of the fire 1 helps to mitigate this problem by directing the hot convection air away from the wall 42. Since the deflector 40 can get hot during use, because of the hot convection air 36,38, an air gap 44 is provided between the deflector 40 and the wall 42 to avoid problems of direct heat transfer.

Mounted above the fire 1 in Figure 5 is a flat screen television 46. Despite the inclusion of the deflector 40, hot air can be drawn back toward the wall 42 as it rises past the deflector 40 such that temperatures above the fife can remain quite high. High temperatures are damaging to electrical equipment, which is why it is not generally recommended to mount a flat screen television above a fire. To reduce this problem, a further deflector component, or TV shield 48, is provided on the wall 42 between the fire 1 and the television 46. The TV shield 48 is larger than, but similar in construction to, the deflector 40 at the top of the fire 1, and serves to direct any residual hot air above the deflector 40 away from the wall 42.

-13 -Figure 5 is not to scale, but the TV shield should be located 300-350mm above the top of the fire 1, and the television 46 should be at least 35-40mm above the TV shield 48. This allows the temperatures in the area around the television 46 to be maintained at acceptable levels.

The above description is intended only to clarifj various aspects of the invention by reference to certain preferred examples. It is not intended to limit the protection sought, as defined by the appended claims. The features and benefits described above equally apply to other types and designs of glass fronted gas fires, and various modifications may be made to the preferred embodiment of the invention while still remaining within the scope of the appended claims. For example, alternative materials and fixings, known to be suitable to a skilled person, may be used in various parts of the fire design. Also, although it is generally preferable to include a convection path around the flirebox, the benefits of the invention would also be present were such a convection path not provided.

Claims (15)

1. -14 -CLAIMS: 1. A door for a gas fire, the door comprising a frame and a glass panel bonded to the frame using adhesive.
2. 2. A door according to claim 1, wherein the frame is formed from sheet metal.
3. 3. A door according to claim 1 or 2, wherein the glass panel is a ceramic glass panel.
4. 4. A door according to any of claims 1 to 3, wherein a layer of opaque sealant is provided between the glass panel and the frame.
5. 5. A door according to any of the preceding claims, wherein the glass panel is bonded to a flat, planar, surface of the frame.
6. 6. A method of making a door for a gas fire, the method comprising the steps of: * applying a layer of opaque sealant to predefined areas of a glass panel; * forming a frame with a flat surface; and * bonding the glass panel to the flat surface of the frame using adhesive.
7. 7. A method according to claim 6, wherein the sealant is allowed to cure fully before the bonding the glass panel to the frame.
8. 8. A method according to claim 6 or 7, wherein the sealant is applied in areas of the glass which will overlie the frame.
9. 9. A method according to any of claims 6 to 8, further comprising the step of screen printing the glass prior to applying the layer of sealant.
10. 10. A method according to claim 9, wherein the layer of sealant is applied over the screen printing. -15-
11. 11. A door according to claim 4 or 5, made using a method according to any of claims 6 to 10.
12. 12. A gas fire comprising a firebox, an inner door to restrict the front opening of the firebox, and an outer door spaced from the inner door and providing a convection path between the inner door and outer door.
13. 13. A gas fire according to claim 12, fttrther comprising a deflector component positioned above the convection path between the inner and outer doors.
14. 14. A gas fire according to claim 12 or 13, wherein a fan is provided to increase convection in said convection path.
15. 15. A gas fire according to any of claims 12 to 14, wherein the outer door is a door according to any of claims ito 5 or 11.