AU2007203642B2 - A furnace - Google Patents

Description

S&FRef: 821260

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant Actual Inventor(s): Address for Service: Invention Title: Forever Glass Pty Ltd, an Australian company, ACN 116 549 412, of 8 Cheshire St, Wagga Wagga, New South Wales, 2650, Australia Peter Geddes Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) A furnace Associated Provisional Application Details: [33] Country:

AU

[31] Appl'n No(s): 2006904236 [32] Application Date: 04 Aug 2006 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c(896765_ I) 1 A Furnace Field of the Invention The present invention relates to a furnace and a method of evenly modulating the temperature of a product inside the furnace. In particular, the present invention relates to a furnace for evenly heating and cooling glass products.

Background of the Invention During the production of a glass product it is often necessary to raise and lower 1o the temperature of the glass at different stages of the production process. Conventional furnaces use infrared heating elements to increase the temperature of glass and ceramic products. Such infrared heating is used during the production of existing glass panels when applying surface coating, texturing or tempering the panel. Alternatively, such heating can be used to fuse recycled glass cullet broken bottle or window glass) for conversion into new glass panels.

A problem with conventional furnaces is that thermal gradients are often present in the glass product during temperature modulation due to uneven heating, whereby a temperature differential exists in the product. The thermal gradients can result in fracturing or warping of the glass, or alternatively the finished product may contain stresses resulting from uneven heating and cooling.

In order to reduce the occurrence of thermal gradients in the glass product, it is known to heat or cool the glass extremely slowly to each desired temperature. This results in greater uniformity of the local temperature at different areas of the glass product.

However, this is typically energy and time intensive and hence adds to the cost of manufacturing, and reduces the amount of glass that can be treated in a given period of time.

Object of the Invention It is an object of the present invention to overcome or ameliorate one or more of the above described disadvantages, or at least to provide a useful alternative to existing furnaces.

Summary of the Invention In a first aspect, the present invention provides a furnace comprising: 894308,I pla chamber adapted to receive a product, said product having first and second opposing surfaces; a heat generation element located in said chamber and adapted to heat a gas; a product support member adapted to support said first surface in a raised position s relative to a base portion of said chamber, such that a first clearance is provided between said first surface and the base portion, said product support member is defined by one or more ceramic batts having an interior cavity formed therein defining the first clearance; a second clearance is provided between the second surface of the product and an upper portion of the chamber; and a gas circulation fan mounted inside said chamber; wherein said gas circulation fan is adapted to circulate said gas inside said chamber such that said gas is directed through said first clearance in proximity to the first surface of the product, and said gas passes through the second clearance in proximity to the second surface of said product.

is In a second aspect, the present invention provides a furnace comprising: a chamber adapted to receive a glass product, said glass product having first and second opposing surfaces; a heat generation element located in said chamber and adapted to heat a gas; a product support member adapted to support said first surface in a raised position relative to a base portion of said chamber, such that a first clearance is provided between said first surface and the base portion, said product support member is defined by one or more ceramic batts having an interior cavity formed therein defining the first clearance; a second clearance is provided between the second surface of the glass product and an upper portion of the chamber; and a gas circulation fan mounted inside said chamber; wherein said gas circulation fan is adapted to circulate said gas inside said chamber such that said gas is directed through said first clearance in proximity to the first surface of the glass product, and said gas passes through the second clearance in proximity to the second surface of said glass product.

The product support member is preferably formed by one or more thin walled ceramic tile modules having an interior cavity formed therein defining the first clearance.

The product support member is preferably supported by one or more silicon carbide support beams.

A first gas deflector is preferably mounted inside the chamber, the first gas deflector being located adjacent to the gas circulation fan and adapted to deflect the gas into the first clearance.

A second gas deflector is preferably mounted on an opposing side of the chamber relative to the gas circulation fan, the second gas deflector being adapted to deflect the gas exiting from the first clearance to the second clearance.

A cooling fan is preferably adapted to introduce ambient air from outside the furnace s into the chamber.

A cooling air duct is preferably connected to the cooling fan, the duct having a plurality of apertures located along its length and the duct being mounted in the chamber.

A hot gas exhaust fan is preferably adapted to extract gas from the chamber.

A hot gas extraction duct is preferably connected to the exhaust fan, the hot gas extraction duct having a plurality of gas intake apertures located along its length and the duct being mounted in the chamber.

The gas is preferably recirculated in the chamber through a substantially circular flow path.

The furnace is preferably a continuous tunnel type furnace.

The product support member is preferably formed from a material having a high thermal conductivity.

A first separator preferably divides the first clearance into first and second vertically spaced gas flow passages.

A second separator preferably divides the second clearance into third and fourth vertically spaced gas flow passages.

The gas circulation fan is preferably adapted to direct the gas into the gas flow passages which are furthest from the product, the gas is subsequently deflected by the second gas deflector into the gas flow passages which are closest to the product.

In a third aspect, the present invention provides a method of uniformly heating and/or 2 cooling a glass product in a furnace chamber, said method including the steps of: positioning a support member in said furnace chamber, said support member is defined by one or more ceramic batts having an interior cavity formed therein defining a first clearance; positioning a first surface of said glass product on said support member such that the first clearance is located between a base portion of said furnace and said first surface; raising and/or lowering a gas temperature in said chamber; and circulating said gas inside said chamber such that said gas passes through said first clearance in proximity to the first surface of the glass product, and through a second 4 clearance located in an upper portion of said chamber in proximity to a second opposing surface of said glass product.

The step of circulating the gas inside the chamber preferably includes deflecting the gas off one or more deflector plates mounted in the walls of the chamber, such that the gas circulates inside the chamber in a generally circular flow path.

The step of raising the gas temperature preferably includes raising to a level up to and including 970C.

The method preferably includes the step of directing the gas through first and second vertically spaced gas flow passages formed by a separator positioned within the 1o first clearance.

The method preferably includes the step of directing the gas through third and fourth vertically spaced gas flow passages formed by a separator positioned within the second clearance.

The gas is preferably circulated from a gas circulation fan into the gas flow passages which are furthest from the product.

Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a sectional side view showing a furnace according to a first embodiment; Fig. 2 is a sectional side view showing the cooling system and hot air exhaust system of the furnace according to the first embodiment; Fig. 3 is a sectional side view showing the mounting arrangement of the gas circulation fan of the first embodiment; Fig. 4 is a top view of a support member according to the first embodiment; Fig. 5 is a side view of the support member shown in figure 4; Fig 6 is a graph showing temperature vs. time for a thermal modulation cycle during production of a glass product; Fig. 7 is a sectional side view of a furnace according to a second embodiment; Fig. 8 is a perspective view of a ceramic return air plenum according to the second embodiment; Fig. 9 is a perspective view of a cast ceramic fan impellor housing according to the second embodiment; 894308vI prw Fig. 10 is a perspective view of a cast nozzle according to the second embodiment; and Fig. 11 is a perspective view of a modular furnace according to the second embodiment.

Detailed Description of the Preferred Embodiments Fig. I shows a first embodiment of an electric furnace generally indicated by the to reference numeral 20, suitable for the high temperature processing of glass panels. The furnace 20 can be either a "batch furnace" or a "continuous tunnel furnace". In a batch furnace a single batch of products is fired during a given heating operation. Alternatively, in a continuous tunnel furnace, the glass product is moved through a tunnel at different stages of the heating/cooling process, and multiple products are fired at a given time, each being exposed to a different stage of the firing process.

The furnace 20 has opposing side walls 22a, 22b, a base 24 and a roof 26 which together define an internal chamber 28. The furnace 20 includes a number of infrared heating elements (not shown) which are distributed in the roof 26 and base 24.

A support 32 is provided in the furnace 20 for supporting a piece of glass 34, or other such product to be fired. As seen in Fig. 1, the support 32 is formed from a hollow batt 32 which is open at each end providing an air clearance therein through which air can pass. The batts 32 are typically 80mm thick with 50mm hollow sections and have a wall thickness of less than In the embodiment shown in Fig. 4, the batts 32 are arranged side to side in a modular arrangement. This provides a single, large support area which permits direct support of unfired glass cullet. (e.g broken bottle or window). Silicon carbide support beams 36 longitudinally support the hollow batts 32 and are placed in the base 24 of the chamber 28.

The support beams 36 are typically 3200mm long and have a 70mm x 3U section with a wall thickness of approx 12mm. For batch furnace 20 applications, the beams 36 are laid directly on the furnace hearth piers (not shown). For continuous tunnel furnaces 20 the beams are laid longitudinally on a powered trolley base.

The furnace 20 includes a number of air circulation fans 30 which are mounted in the side wall 22a. Fig. 3 shows the bearing arrangement for mounting each fan 30. The fans 30 have impellers 39 of a radial blade design having 6 blades 39a and a flat, 6 circular backing plate (4mm thick). The blades 39a are each 60mm long x 4mm thick and are welded to a centre boss of 50mm diameter with a 30mm bore.

Each impeller 39 has a nominal diameter of 130mm across the tips of the blades 39a. There are 8 air circulation impellers 39 fitted along the length of one side 22a of the furnace 20. Each of the impellers 39 is retained on its respective shaft 42 by a shaft key and high temperature ceramic cement. The circulation fan 30 components are made from high temperature alloy Sandvik 253MA or Incoloy 800H).

The eight fan impellers 39 are located in housings formed by high temperature cast refractory wall modules 40. These modules 40 are shown in figure 8, and are fitted 1o side by side at equal intervals along one internal sidewall 22a.

The impeller housing modules 40 are rectangular face blocks with the dimensions 410mm long x 230mm high x 126mm wide. Each module 40 has a cast cutout shape formed in the middle to accommodate the fan impeller 39. The modules 40 are finish coated and post-fired with a high alumina coating.

is The air inlet side of each housing module 40 accommodates a removable flat refractory tile 41 for shielding the front of the impellor. The refractory tile 41 is retained at each side in a notched groove cast into the housing module 40. Each of the eight tiles 41 has a 70mm diameter air inlet hole 41a cut out on the fan centre line.

Each circulation fan 30 has a shaft 42 (best seen in Fig 3) constructed from high temperature alloy Sandvik 253MA or Incolloy 800H). Each shaft 42 is diameter x 500mm long with a stepped 30mm diameter section at the hot zone end to accommodate the impeller 39. The shafts 42 are machined from solid round blanks and are hollow bored to reduce heat conduction. Upon final fitting the hollow shafts 42 are ram filled (plugged) with ceramic fibre wool 43. This significantly reduces shaft 42 temperature at the bearing support sections outside the furnace.

The fan shaft 42 bearings comprise full ceramic self aligning deep groove ball bearings 44a, 44b. The bearing centres are 55mm and 205mm from the cold end of the fan shaft 42. The bearings 44a, 44b are fitted into cast iron foot mounted split pillow blocks 46a, 46b. The bearing 44b closest to the furnace 20 is fixed to the fan shaft 42 by a screw lock while the bearing 44a furthest from the furnace is not fixed (floating).

The drive pulley 48 on the fan shaft 42 comprises a single row round section steel pulley with a pitch circle diameter of 90mm. The pulley 48 is fitted to the shaft 42 via a "Fenner" taper-lock bush.

Each of the fan shafts 42 is pulley driven from a common motor drive shaft (not shown) approximately 3200mm long x 50mm diameter. The motor drive shaft is located 894308vl pw 7 externally along the length of the furnace 20 below the main furnace chamber 28. The motor drive shaft is supported by bearings at each end and in the centre.

The drive transmission from the motor shaft (not shown) is effected via a round section "Durabelt" elastic belt rated at 230C. This high temperature belt includes a tempered stainless steel spring with a silicon jacket. The heat resistant spring provides the elasticity, and the flexiblejacket is under compression.

The motor drive shaft is fitted with 8 pulleys located such that their centre lines correspond to the respective drive pulleys 48. The motor drive shaft is orientated at a right angle relative to each of the drive pulleys 48. Each round section pulley drive belt is 1o twisted through 90 degrees. The motor drive shaft is powered by a 0.35kw single phase motor (not shown), and the motor is controlled by a variable voltage speed control. This enables the user to select an optimum circulation rate which is a compromise between acceptable temperature uniformity and maximum acceptable air velocity in the chamber 28.

As shown in Fig. 1, an air deflector 49a is located below the fans 30. The deflector 49a is connected to the furnace wall 22a and has a curved surface. A similar air deflector 49b is positioned on the opposing wall 22b.

An air cooling system 50 as seen in Fig. 2 comprises an external centrifugal fan 52 which is connected to a cylindrical air duct 54 which extends vertically down through the roof of the furnace 20 into the chamber 28, and which is connected via an elbow connector 55 to a horizontal distribution duct 56 located in the furnace chamber 28. The cooling fan 52 is a single scroll centrifugal fan/high pressure blower having a capacity of 200 CFM (5.66 Cubic metres per minute). The cooling fan 52 is mounted externally on the top of the furnace The cooling ducts 54, 56 are fabricated from 1100 IOOC grade high temperature alloy (Sandvik 253MA), and the horizontal distribution duct 56 is formed from a straight, full length (3100mm) round seamless pipe section of 89mm nominal bore (100mm OD). The duct 56 is mounted inside the furnace chamber 28 along the sidewall 22b opposite to the wall 22a which accommodates the air circulation fans 30. The horizontal duct 56 is positioned in the furnace 20 at a height slightly above the surface of the glass product 34.

The horizontal duct 56 has laser cut air entry holes 60 each of 35mm diameter along it's length at 55mm centres and the end of the duct 56 is blanked off. The horizontal duct 56 is mounted in the furnace 20 with the holes 60 facing in toward the centre of the furnace chamber 28.

X94308vl pr A butterfly valve 62 is located in the vertical duct section 54 between the connection to the centrifugal fan 52 and the elbow connector The furnace 20 includes a hot air exhaust system 64 also shown in Fig. 2 which is similar to the cooling system 50. The hot air exhaust system 64 includes a horizontal duct 66 which extracts hot air evenly from the furnace chamber 28. The hot air is extracted by a hot air exhaust fan 68 which is a centrifugal fan having a capacity of 200 CFM (5.66 Cubic metres per minute) and is located at the opposite end of the furnace chamber 28 to that where the external cooling fan 52 is located.

The hot air extraction fan impeller is a fabricated radial unit similar (but slightly 1o larger) to the internal circulation fans 30. It is constructed from high temperature alloy (1 100C grade Sandvik 253MA).

A butterfly valve 70 is incorporated into the vertical duct 72 near the exhaust fan 68. The bottom of the vertical duct 72 is fitted with a fabricated 90 degree elbow connector 73 which is subsequently connected to the horizontal duct 66. The vertical duct 66 is a straight full length (3100mm) round seamless pipe section of 89mm nominal bore (100mm OD), and is positioned in the furnace 20 at a height slightly below the centreline of the hollow support batt 32 which supports the glass product 34.

The horizontal duct 66 has laser cut air entry holes 74 each of 35mm diameter along it's length at 55mm centres and the end of the duct 66 is blanked off. The duct 66 is mounted in the furnace 20 such that the holes 74 face inwards toward the centre of the air clearance beneath the supporting batt 32.

Cast wall modules 80 as shown in Fig. 9 are present for internal support of cylindrical cooling and exhaust ducts 56, 66. The ducts 58, 66 are nestled into a number of the cast refractory modules 80 which are positioned in the sidewall 22b.

The cast refractory modules 80 are constructed of the same material (800kg/M3 density cast ceramic fibre) as the high temperature housing modules 40 described for the circulation fans 30. The modules 80 are finish coated and post-fired with a high alumina coating to ensure a hard abrasion resistant surface which will withstand the high air velocity of the circulation air.

The supports 32 are thin walled hollow ceramic tile modules, and the deflector 49a is integrally formed in the impeller housing module in another embodiment, the furnace 20 is a batch furnace. The batch furnace utilises a commercially available multi-stage temperature controller (not shown) which permits preset heating rates and temperatures for each stage of the temperature modulation process. The controller has preset event outputs which enable the cooling 894308I pfans 30 to be turned on or off, automatically as required. The controller has full communications protocols for remote operation from a computer which runs a temperature profiling software package.

In another embodiment, the furnace 20 is a continuous tunnel furnace 20. The continuous furnace 20 design incorporates a powered roller conveyor (not shown) using ceramic rollers.

The operation of the furnace 20 of the first embodiment will now be described. A glass panel 34 is generally heated to a number of different temperatures for different periods of time during a typical glass processing cycle. An example of such a process is io shown below and is graphically illustrated in figure 6.

Processing Stage Description Temperature Time Total Time 1 Initial reheat Heat to 550'C for 1 hour 1 hour 2 Stabilisation Hold at 550'C for 0.5 hour 1.5 hours 3 Final heating Heat to 970 0 C for 1 hour 2.5 hours 4 Fusing Hold at 970'C for 0.5 hour 3.0 hours Rapid cooling Cool to 550 0 C for 1 hour 4.0 hours 6 Annealing Hold at 550'C for 1.5 hours 5.5 hours 7 Final cooling Cool to 100 0 C for 4.5 hours 10 hours The glass panel 34 is initially loaded into the furnace 20, and is evenly supported from underneath by the supports 32.

The air temperature in the chamber 28 is increased to the desired level by the infrared heating elements. The fans 30 are operated to circulate the heated air throughout the chamber 28, as shown schematically by the arrows in figure 1. The air outputted by the fans 30 is deflected off the deflector 49a and forced into the air clearance 38. The drive motor for the fans 30 is controlled by a variable voltage speed control by the operator. The operator can determine the optimum circulation rate by selecting a compromise between acceptable temperature uniformity and maximum acceptable air velocity in the chamber 28.

The support 32 material has a high thermal conductivity, allowing heat transfer to occur between the air in the clearance 38 and the lower side of the glass plate 34. The air subsequently exits from the end of the clearance 38 and comes into contact with the air deflector 49b. The deflector 49b deflects the air upwardly and in a return direction towards the fans 30, through the upper part of the chamber 28. In this stage of the air 894308 pcirculation, the air comes in contact with the upper surface of the glass product 34. By repeated circulation of the air through the chamber 28, and in particular through the air clearance 38, a similar temperature is achieved at both the upper and lower surfaces of the glass product 34.

The air is repeatedly recirculated through the chamber 28 in a generally circular path as shown by the arrows in figure 1.

Cooling of the chamber 28 is required for example during stage 5 (rapid cooling) in the process shown in the above table. When the cooling fan 52 of the cooling system is operated and the butterfly valve 62 is switched to an open flow position, the flow of 1o ambient air from outside the furnace 20 commences. The ambient air enters the air duct 54 and is directed into the horizontal pipe 56. The ambient (cool) air is then ejected through each of the holes 60 spaced along the length of the horizontal pipe 56. The cool air at this stage is distributed evenly along the width of the chamber 28.

The cool air is circulated evenly through the chamber 28 in the manner described above by the cooling fans 30 and the deflectors 49a, 49b. The air circulation fans circulating the normally hot furnace air dilute and mix the incoming ambient air with the hot furnace air to evenly lower the chamber 28 temperature.

The extraction of hot air from the chamber 28 is also required at certain stages of the process, for example during stage 7 (final cooling) shown in the above table. The hot air exhaust fan 68 of the hot air exhaust system 64 is operated while the butterfly valve is open. Air from inside the chamber at an elevated temperature relative to the ambient air temperature is then drawn into the entry holes 74 along the length of horizontal duct 66.

The extracted air passes through the elbow connector 73 into the vertical duct 72 and subsequently out of the furnace 20. Similarly to the cooling system 50, the fans and deflectors 49a, 49b are used to circulate the air in the chamber 28 during and/or after the hot air extraction process.

In the embodiment where the furnace 20 is a continuous tunnel furnace 20, the various stages of the process (as shown in the table above) are translated into different sections of the furnace which have a finite length. Each section has a designated temperature. The total number of furnace sections is determined by establishing the shortest part of the process and then making up the length of each of the other longer process stages as multiples of the shortest part. The temperature control in this instance is different from that required for the batch furnace 20. Individual controllers are simply set to the maximum temperature required for the particular section.

894308vI pr- In this embodiment, in order to keep the glass 34 as uniform as possible in all directions, the movement through the tunnel furnace 20 is not "continuous" as such.

Instead the glass panels 34 are moved (indexed) from one furnace section to the next, and the sections are then sealed. Accordingly, each section is a Scompartment with individual forced circulation and is fitted with vertical opening doors.

This makes it easy to apply rapid cooling or heating to the individual glass panels 34 without affecting the temperature uniformity or integrity of heat patterns in an adjoining part ofthe furnace In this embodiment, the system of indexing the panels (i.e.stopping them in the 1o furnace), introduces the possibility of damage to the ceramic rollers. Accordingly, the glass panels 34 are "reciprocated" within each closed compartment, and as such they are continually stopped, and reversed, then stopped and reversed again. Thus the rollers are never resting long enough to get a permanent bend or "set" as a result of the high temperatures. The glass reverses and travels only about 300mm at each reciprocating Is motion which is enough to turn the rollers just a few revolutions. This indexing and reciprocating transport system also minimises the overall length of the continuous furnace, as without it the glass panels 34 would always be moving forward. The operator can determine the temperature in the furnace 20 by radiation pyrometers in each furnace section.

In this embodiment, a brake and a take up fluid coupling clutch are used such that the rollers are idle at the stationary load section until the operator engages the drive.

When the operator engages load section rollers, they rotate in directional unison and speed with the rest of the furnace rollers.

An advantage of the invention is that the air circulation provides even distribution of the heated air inside the chamber 28, such that an even thermal gradient is obtained across the upper and lower surfaces of the glass product 34.

A second embodiment 100 will now be described. Like reference numerals are used to indicate similar components. The furnace 100 of the second embodiment operates in a similar fashion to the first embodiment, however it permits an altered air flow path within the chamber 28.

As shown in Fig. 7, within the chamber 28, above the support 32, there are overhead silicon carbide beams 102. The beams 102 are shown in detail in Fig. 10. The beams 102 support thin section carbide tiles 104, thereby dividing the space between the support 32 and the roof of the chamber 28 into two air flow paths in the form of an upper 12 air passage 106 and a lower air passage 108, which are both located above the glass product.

Similarly a further upper air passage 110 and a further lower air passage 112 are located below the support 32.

Fig. 8 shows a return air plenum 120 having two curved air return surfaces 122, 124 which are shaped to provide a smooth change of direction for the circulating air. Air is initially expelled from the air circulation fans 30. The air then passes through the air passage which is furthest away from the glass product. That is, the air is initially directed to the passage 106 closest to the top of the chamber 28 and the passage 112 closest to the 1o base of the chamber 28. The air upon reaching the end of the chamber 28 is deflected by the two curved surfaces 122 and 124 of the air plenum 120 in the opposite direction toward, toward the fans 30. On this stroke, the air passes through the passages 110 and 108 which are closest to the glass product.

Circulation air is blown and directed both upward and downward within the fan impeller housing 40. The upward air is then directed across the underside of the roof elements within a cavity. The cavity is formed by placing a pair of silicon carbide beams across the chamber above the glass product level but well below the underside of the chamber 28 roof. The beams 102 are supported on brick piers at each side of the furnace 100. The beams 102 in turn are used to suspend all of the cast refractory air directing modules inboard of the piers at each side of the furnace 100.

In the second embodiment, each impeller 39 has a nominal diameter of 140mm across the tips of the blades 39a. There are 7 air circulation impellers 39 fitted along the length of one side 22a of the furnace 100. The actual number of impellors 39 can be varied, but 7 provides a chamber 28 length of approx 3150mm enabling a 3000 mm long glass slab to be produced.

All impellers 39 are retained on their shaft by a shaft key and high temperature ceramic cement.

To avoid the possibility of any vibration, the support frame for the direct coupled circulation fan 30 motor and the circulation fan shaft bearings 44a, 44b is constructed as a separate structure from the main kiln frame. The separate frame is heavily strengthened to avoid resonance.

The impellor housing modules 40 are rectangular face blocks with dimensions of 450mm long x 230mm high x 86mm wide. Each module 40 has a cast, dish shape (fiat in the middle), designed to accommodate the fan impeller, as shown in Fig. 9.

The modules are constructed from 800kg/M3 density cast ceramic fibre, finish coated and post-fired with a high alumina coating to ensure a hard abrasion resistant surface which will withstand the high air velocity of the circulation air.

894308vl p-r The air inlet side of each cast refractory impeller housing module 40 accommodates a cast refractory air inlet nozzle 140 as shown in Fig. 10. the inlet nozzle 140 is retained against the face of the fan impeller housing 40 by ceramic threaded anchors at each side.

The air inlet nozzles 140 are constructed from 800kg/M3 density cast ceramic fibre and similarly finish coated and post-fired with a high alumina coating. Each of the seven nozzles 140 has a 70mm diameter air hole cut-outs on the fan centre line, as shown in Fig. The batch furnace application utilises a commercially available PLC (programmable logic controller) with multiple thermocouple inputs and a corresponding number of multiple control outputs. The PLC has the facility to accept and retain preset 1o heating rates and temperatures for each stage of the process. The PLC also has preset event outputs which enable the cooling fans 52 to be turned on or off, as required by the process. Eg for rapid cooling from fusing temperature back down to annealing temperature and then slower fan assisted cooling back down to room temperature. The controller has full communications protocols for remote operation from a computer which Is may run a temperature profiling software package.

The kiln can be fitted with a variety of heating element types- depending on power loading and temperatures required. For most applications, conventional wire wound heating elements are used which are mounted on or within clear quartz tubes for support. Alternatively they can include wire wound elements cluster mounted on ceramic bobbins, and fitted up inside high temperature alloy tubes. Silicon carbide heating element rods can also be used where higher power densities are required. For very high power densities molybdenum disilicide heating elements are employed.

The heating elements are fitted both in the roof of the main furnace chamber 28 and also in the trolley underneath the hollow ceramic support batts 32.

As shown in Fig. 11, the furnace 100 is formed of a number of modular sections 160. Electric elements are fitted to each modular section 160 of the furnace or kiln 100.

The modular section 160 can be either single or multiphase, depending upon the size of the particular kiln width, length and height) The electrical supply to each modular section 160 is controlled initially by a contactor. This provides electromechanical isolation to each section at the end of the process and when the system is in an idle mode.

SCR type switching e.g. solid state relays can be used to control separate zones for top and bottom sections and separate zones along the length of the kiln. This provides the means of fine control over each of the element circuits.

9)4308vl pr The modular construction of the furnace 100 lends itself to heat zoning. Each modular section 160 represents a part of the overall main furnace 100 frame length and a similar part of the length of the trolley base. Each main furnace frame module is fitted with a set of elements (either single or multi-phase) in the roof and a matching trolley module below is fitted with a similar set of elements (either single or multiphase) of the same power. Generally, each set of elements will represent 3 circuits, which is ideal for 3 phase. Accordingly, for most applications there will be 6 circuits or zones of heating per modular (main frame trolley) section.

The furnace 100 may include 7 modules offering 42 heating zones all to referenced back to the closed loop PLC based control system.

The furnace 100 can be set up to operate during the heating cycle without air circulation during the heating cycle and with the fine degree of control offered by multizoning, even heating across the whole surface of the glass is assured. Alternatively the heat can be biased to either bottom or top by programming a deliberate offset into the control. A higher temperature will produce a clearer glass (more impurities are fired out) and so a heat bias to one side of the glass will produce a more homogenous (or clearer) glass on one side than the other, which may offer aesthetic advantages in the finished glass product.

When it is time to start cooling the glass product, the programmed heat bias is removed and the whole of the glass is quickly brought back to being the same temperature throughout by the combined use of forced air circulation and heating.

Either thermocouples or radiation pyrometers can be used to sense the temperature of the glass in each section. However, thermocouple sensing is acceptable for most applications.

Cool air from an external source is required to accelerate the natural cooling rate of the kiln or furnace 100. The cooling air inlet system comprises an external, centrifugal fan which blows cool room temperature air into a port in the side of the kiln or side of each kiln module. The inlet port generally comprises an extruded ceramic tube which is fitted into a drilled hole in the sidewall insulation. The tube is made long enough to pass through the entire insulation thickness and to then fit into a hole in the cast refractory air circulation.

The hole in the housing then turns 90 degrees and exits the housing into the kiln chamber so that the air blows out of the housing and across the face of the air circulation impeller 39. Since the cooling air will only be introduced when the air circulation fan is also running, it follows that the cooling air will be immediately drawn into the eye of the 894308vi prw air circulation fan, along with air returning from across the chamber The cooling air will be mixed with furnace air so that a homogenous but slightly lower temperature air is pushed back around the furnace.

The additional cooling air being forced into the chamber 28 would tend to increase the pressure in the chamber were it not for some exit ports which are also constructed into the chamber 28 sidewalls of the air circulation housing in the path of the exit air from the air circulation fan 39. These exit ports become the hot air exhaust ports.

The speed of the cooling fan motor for the furnace 100 or for each modular section 160 is controlled by a variable frequency controller which receives a control input 1o (generally 0-10V DC) from the main PLC controller which is controlling the furnace 100 air temperature.

If the furnace size is significant and is of modular construction such as shown in Fig. 11, then each modular section 160 is fitted with a cooling system, each controlled individually to the master program held by the PLC.

This system is designed to similarly remove air from the furnace 100 at a rate commensurate with the incoming cooling air. The hot air system is fitted to the same side of the furnace 100 or modular section 160 as the cooling air fan and circulation fan.

The external hot air exhaust fan is a small single centrifugal fan and blows air up through an external, vertical metal pipe. The pipe is waisted at the point where it passes the horizontal exhaust port (which protrudes from the side of the furnace 100 or modular section 160). The two pipes are joined at this point to form a simple venturi system.

The hot air exhaust system is designed more to capture the hot air being expelled from the chamber 28 and contain it, rather than suck it from the furnace 100. The hot air can be manifolded and used for waste heat recovery or can simply be piped to atmosphere.

The hot air exhaust fan motors can be speed controlled in the same way as the cooling fan motors are controlled.

A further advantage of the invention is that the even thermal gradient permits the temperature modulation operation and overall glass production to be carried out at an increased rate.

Another advantage of the present invention is that minimum energy is required for processing the glass product 34.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

X894308v prw

Claims (19)

1. A furnace comprising: a chamber adapted to receive a product, said product having first and second opposing s surfaces; a heat generation element located in said chamber and adapted to heat a gas; a product support member adapted to support said first surface in a raised position relative to a base portion of said chamber, such that a first clearance is provided between said first surface and the base portion, said product support member is defined by one or 1o more ceramic batts having an interior cavity formed therein defining the first clearance; a second clearance is provided between the second surface of the product and an upper portion of the chamber; and a gas circulation fan mounted inside said chamber; wherein said gas circulation fan is adapted to circulate said gas inside said chamber such that said gas is directed through said first clearance in proximity to the first surface of the product, and said gas passes through the second clearance in proximity to the second surface of said product.

2. A furnace comprising: a chamber adapted to receive a glass product, said glass product having first and second opposing surfaces; a heat generation element located in said chamber and adapted to heat a gas; a product support member adapted to support said first surface in a raised position relative to a base portion of said chamber, such that a first clearance is provided between said first surface and the base portion, said product support member is defined by one or more ceramic batts having an interior cavity formed therein defining the first clearance; a second clearance is provided between the second surface of the glass product and an upper portion of the chamber; and a gas circulation fan mounted inside said chamber; wherein said gas circulation fan is adapted to circulate said gas inside said chamber such that said gas is directed through said first clearance in proximity to the first surface of the glass product, and said gas passes through the second clearance in proximity to the second surface of said glass product. 17

3. The furnace of one of claims 1 or 2, wherein the product support member is formed by one or more thin walled ceramic tile modules having an interior cavity formed therein defining the first clearance.

4. The furnace of one of claims 1 or 2, wherein the product support member is supported by one or more silicon carbide support beams.

The furnace of one of claims 1 or 2, wherein a first gas deflector is mounted inside the chamber, the first gas deflector being located adjacent to the gas circulation fan and adapted to deflect the gas into said first clearance.

6. The furnace of claim 5, further comprising a second gas deflector mounted on an opposing side of the chamber relative to the gas circulation fan, the second gas deflector being adapted to deflect the gas exiting from the first clearance to an upper portion of the chamber.

7. The furnace of one of claims 1 or 2, further comprising a cooling fan adapted to introduce ambient air from outside the furnace into the chamber.

8. The furnace of claim 7, including a cooling air duct connected to the cooling fan, the duct having a plurality of apertures located along its length and the duct being mounted in the chamber.

9. The furnace of one of claims 1 or 2, further comprising a hot gas exhaust fan adapted to extract gas from the chamber.

The furnace of claim 9, wherein a hot gas extraction duct is connected to the exhaust fan, the hot gas extraction duct having a plurality of gas intake apertures located along its length and the duct being mounted in the chamber.

11. The furnace of claim 10, wherein the gas is recirculated in the chamber through a substantially circular flow path.

12. The furnace of any one of the preceding claims including a first separator which divides the first clearance into first and second vertically spaced gas flow passages.

13. The furnace of claim 12, including a second separator which divides the second clearance into third and fourth vertically spaced gas flow passages.

14. The furnace of claim 13, wherein the gas circulation fan is adapted to direct the gas into the gas flow passages which are furthest from the product, the gas is subsequently deflected by the second gas deflector into the gas flow passages which are closest to the 1o product.

A method of uniformly heating and/or cooling a glass product in a furnace chamber, said method including the steps of: positioning a support member in said furnace chamber, said support member is is defined by one or more ceramic batts having an interior cavity formed therein defining a first clearance; positioning a first surface of said glass product on said support member such that the first clearance is located between a base portion of said furnace and said first surface; raising and/or lowering a gas temperature in said chamber; and circulating said gas inside said chamber such that said gas passes through said first clearance in proximity to the first surface of the glass product, and through a second clearance located in an upper portion of said chamber in proximity to a second opposing surface of aid glass product.

16. The method of claim 15, wherein the step of circulating the gas inside the chamber includes deflecting the gas off one or more deflector plates mounted in the walls of the chamber, such that the gas circulates inside the chamber in a generally circular flow path.

17. The method of either of claims 15 or 16, wherein the step of raising the gas temperature includes raising to a level up to and including 970 0 C.

18. The method of any one of claims 15 to 17, including the step of directing the gas through first and second vertically spaced gas flow passages formed by a separator positioned within the first clearance.

19. The method of claim 18, including the step of directing the gas through third and fourth vertically spaced gas flow passages formed by a separator positioned within the second clearance. S A furnace substantially as hereinbefore described with reference to any one of the embodiments as that embodiment is shown in the accompanying drawings. Refire Glass Research Pty Limited By Patent Attorneys for the Applicant ©COTTERS Patent Trade Mark Attorneys