Field

The present invention relates to a vacuum furnace device not requiring water for the use of cooling.

Background

Known vacuum furnace devices, such as the one shown in Figure 1, comprise an inner furnace chamber and an outer furnace vessel. The outer furnace vessel is disposed around the inner furnace chamber and defines a space to be evacuated to form a vacuum. Heaters provided within the inner furnace chamber raise the internal temperature of the furnace to over 1000°C, and as such methods are known to cool the surrounding area to ensure that the furnace is safe for use in settings such as factories. Power to the heaters is provided by power lead-ins (PLIs), which are disposed through the inner furnace chamber, space to be evacuated and outer furnace vessel.

The vacuum created in the vessel provides a cooling effect, eliminating heat transfer by convection and only allowing heat transfer by conduction through the body of the furnace and along the structures containing the PLIs, as well as some via radiation. The PLIs also heat up due to the flow of electricity therethrough. In order to provide further cooling in response to heat transfer from the inner furnace chamber via radiation and via conduction, the known solution is to provide a water jacket within the outer furnace vessel. A water feed provides water between two adjacent walls of the outer furnace vessel, whilst a water return vents the water to a tank connected to a heat exchanger or to a drain. The water vessel has a large surface area, acting as a cooling area in addition to cooling the PLIs.

The inner furnace chamber is also provided with layers of insulation made of graphite. Graphite is preferred as it absorbs water at a slow rate, meaning any water leakage from the water jacket or absorbed from the air during repressurisation of the space to be evacuated will not result in quick failure of the device. However, graphite is not as thermally efficient as other insulators such as ceramic. However, ceramic has been avoided for use in inner furnace chamber insulation, as it absorbs water at a fast rate, meaning any water absorption will result in a quicker failure of the component.

This is of particular importance when venting chambers back to atmospheric pressure, wherein the water cooled jacket causes condensation within the space to be evacuated. This can cause a ceramic insulated device to absorb water, which expands upon repressurisation of the device, resulting in the ceramic fibre board bursting. As such, graphite is preferred for the use of vacuum furnace insulation.

However, graphite poses its own limitations, including that upon an air leak into the chamber, consistent air flow can cause the graphite to turn to powder, resulting in decreased thermal efficiency and failure of the device. Reconditioning of the device is rendered difficult by the presence of the graphite powder.

The present invention seeks to overcome or at least mitigate the problems of these known devices.

Summary

A first aspect of the invention provides a vacuum furnace device comprising an inner furnace chamber; an outer furnace vessel, the outer furnace vessel being disposed around the inner furnace chamber and defining a space to be evacuated; at least one heating element provided within the inner furnace chamber; and at least one power supply for supplying power to at least one of the heating elements, each power supply comprising an interior power supply part and an exterior power supply part, the interior power supply part being located within the space to be evacuated and the exterior power supply part being located outside of the space to be evacuated; wherein the vacuum furnace device further comprises a gas cooling apparatus, the gas cooling apparatus comprising: at least one gas inlet located outside of the outer furnace vessel; at least one gas outlet located outside of the outer furnace vessel; a gas flow pathway fluidly connected to the gas inlet and to the gas outlet, the gas flow pathway being arranged to direct a flow of gas on to at least a part of the exterior power supply part.

The provision of such a gas cooling system allows for specific cooling of hot areas (i.e. the areas affected by conduction from the power supply) rather than generally cooling the entire area. Furthermore, using air rather than water allows for alternative insulating materials to be used throughout the vacuum furnace device. The lack of a water cooling system means a reduced risk of ceramic board rupture, and the single skinned jacket means the temperature external to the outer furnace vessel will be room temperature, resulting in a reduced risk of condensation forming upon repressurisation. The use of gas cooling over water cooling also provides other benefits, such as a lack of need for devices such as a heat exchanger or the need to provide extensive piping (as air can simply be vented into the atmosphere). Environmental benefits such as a reduced waste of water are provided as no water treatment is required due to the closed loop nature of the cooling system.

The interior power supply part and the exterior power supply part of the at least one power supply may be separated by a gas-tight seal, which may be disposed through the outer furnace vessel. Preferably, the gas flow pathway is arranged to direct a flow of gas on to the gas-tight seal.

The gas-tight seal allows the power supply to pass through the outer furnace vessel without air leakage into the space to be evacuated. The gas cooling system allows for cooling of specific regions identified to have a comparably higher level of heat energy, such as the gas-tight seals. Components such as these can absorb increased levels of heat energy due to heat conduction through the power supply parts and flow of electrical current generating heat through said power supply parts.

The gas used may be inert, such as a noble gas. Alternatively, it may be compressed air.

An inert gas gives the benefit of a reduction in reactivity with any of the materials of the device that it will come into contact with, increasing the lifespan on the device. Such a gas will also further reduce the amount of water present, due to a lack of water vapour that is present in air. However, such a gas may be harder to source and dispose of. Compressed air provides the benefit of a low level of reactivity, whilst being able to be sourced from and vented to the atmosphere.

A second aspect of the invention provides a vacuum furnace device comprising an inner furnace chamber; an outer furnace vessel, the outer furnace vessel being disposed around the inner furnace chamber and defining a space to be evacuated; at least one heating element provided within the inner furnace chamber; and at least one power supply for supplying power to at least one of the heating elements, each power supply comprising an interior power supply part and an exterior power supply part, the interior power supply part being located within the space to be evacuated and the exterior power supply part being located outside of the space to be evacuated; wherein the outer furnace vessel comprises a peripheral wall, the peripheral wall being spaced apart from the inner furnace chamber; and wherein the vacuum furnace device further comprises an insulation wall, the insulation wall being provided adjacent to the peripheral wall and spaced from the inner furnace chamber. Providing a second (peripheral) wall spaced apart from the insulation wall gives the benefit of providing an extra layer of protection in case of the failure of one of the internal components. In this formulation, if the insulation surrounding the inner furnace chamber were to burst or rupture, any debris would strike the peripheral wall and not puncture the insulation wall. As such, this increases safety of the user and prevents/ reduces the risk of rupture of the vacuum. Furthermore, the peripheral wall acts as a heat sink, drawing energy out of the system and ensuring it does not reach the insulation wall (which is contactable by the user).

At least one of the insulation wall and peripheral wall may be made of mild steel or stainless steel. The insulation wall is preferably made of mild steel, whilst the peripheral wall is preferably made of stainless steel.

Such materials provide the required material properties to withstand the pressure differential between the space to be evacuated and outside of the device. They also have the required properties, when used for the peripheral wall, to effectively protect the insulation wall from any debris.

The insulation wall may have a thickness in the range of 10mm to 80mm, preferably 10mm.

A third aspect of the invention provides a vacuum furnace device comprising an inner furnace chamber; and an outer furnace vessel, the outer furnace vessel being disposed around the inner furnace chamber and defining a space to be evacuated; wherein the inner furnace chamber comprises at least one wall of ceramic insulation.

This formulation provides better internal heat insulation than, for instance, a corresponding graphite insulation. Ceramic is also inert, which allows for greater stability and reliability of the insulation. The ceramic will not react with air when the vacuum chamber is repressurised, ensuring that the insulation wall has to be replaced less frequently.

The inner furnace chamber may have at least two walls of insulation, preferably an inner wall and an outer wall. The inner wall and outer wall are preferably disposed adjacent to each other, the thickness of the inner wall is preferably in the range of 25m to 80mm, and even more preferably is 77mm, whilst the thickness of the outer wall is preferably in the range of 25m to 80mm, and even more preferably is 60mm. Having at least two walls of insulation allows for differing formulations of insulation wall, such as differing materials, size or form, in order to increase the level of heat insulation. It can also be used to ensure an air-tight seal between the space to be evacuated and the inner furnace chamber. The absence of a gap between the inner and outer insulation walls eliminates any heat transfer between the walls via conduction or radiation.

The inner wall and outer wall may be made of the same or different insulation materials. At least one of the inner wall and the outer wall preferably comprises P1200R, P1000R and PROMAFORM® ceramic insulation.

As described above, microporous material provides optimum heat insulation. The specific microporous materials listed provide optimal material and heat insulation properties for the use, as well as being chemically inert. Using two different insulation materials allows for specific requirements for the different locations to be catered for.

Any one of the aspects of the invention provided may include at least one wall of graphite insulation.

Graphite provides benefits as described above, such as low water absorption.

From the centre of the inner furnace chamber to an outer surface of the outer furnace vessel in a horizontal direction, in any of the aspects of the invention provided, the ratio of the lengths of the inner furnace chamber and space to be evacuated may in the range of 1: 1 to 1:3, preferably 1 :2.

Providing a specific size of space to be evacuated as compared to the relative size of the outer furnace chamber balances the requirement of heat insulation and the device being an appropriate size for a factory environment.

It is understood that the three aspects of the invention can be combined in any way, to take advantage of synergistic effects thereof.

Brief Description of the Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 is a cross-section view of a vacuum furnace device with a water cooling system according to the known prior art;

Figure 2 is a view of the water cooling system of the known prior art of Figure 1;

Figure 3 is a cross-section view of a first embodiment of a vacuum furnace device according to the three aspects of the present invention;

Figure 4 is a cross-section view of a second embodiment of a vacuum furnace device according to the three aspects of the present invention;

Figure 5 is a diagrammatic view of exemplary embodiment according to the three aspects of the present invention;

Figure 6 is a heat transfer graph for an embodiment according to the three aspects of the present invention; and

Figure 7 is a heat transfer graph for a further embodiment according to the three aspects of the present invention.

Detailed Description of Embodiments

Figure 1 shows a vacuum furnace device 10 according to the prior art. This vacuum furnace device 10 comprises an inner furnace chamber 20, surrounded by an outer furnace vessel 50.

Heating elements 30 are provided within the inner furnace chamber 20, in order to heat the material placed within said inner furnace chamber 20. Due to the high temperatures produced by the heating elements 30 within the inner furnace chamber 20, various methods of cooling are known, as described below, to ensure any surface that a user could come into contact with is at a safe temperature. Heating elements 30 are often CFC heaters, but can also be graphite or tungsten mesh heaters. Multiple heaters spaced evenly around the outside of the interior of the inner furnace chamber 20 are often provided, to ensure a consistent heating of materials placed therein. Power to the heating elements 30 is provided by a power supply system 40, which will be discussed in further detail below. The inner furnace chamber 20 is often provided with insulation 22. This is commonly known to be made of graphite, due to its slow water absorption rate. The slow water absorption rate means that upon repressurisation of the vacuum furnace device 10, there will be little water absorbed by the insulation 22, reducing the risk of the water expanding, causing the insulation 22 to burst. The inner furnace chamber 20 can also be provided with features such as a water-cooled table 21 and associated ram 21a, a sealable lid and ventilation ports. The table 21 is where the mould for heating is placed. The insulation 22 forms the first part of heat insulation from inside the inner furnace chamber 20 to the outside of the device 10, reducing any heat transfer by radiation from the heating elements 30.

The space within the outer furnace vessel 50 forms a space to be evacuated 60, otherwise known as a vacuum chamber. This space to be evacuated 60 has an associated vacuum pump (not shown), that extracts air from the space to be evacuated 60 via a depressurisation port (not shown) located in the outer furnace vessel 50. Ventilation ports (also not shown) are also provided within the outer furnace vessel 50, in order to ensure that the space to be evacuated 60 can be repressurised. The space to be evacuated 60 provides the second barrier to heat transfer from the heating elements 30 to the outside of the device 10, by reducing the heat transfer via convection and conduction.

Power to the heating elements 30 is provided by power supply parts 42 (often referred to as "power lead-ins" or PLIs), to transfer power from a power source (not shown) to the heating elements 30. The power supply parts 42 are disposed both through the inner furnace chamber 20 and the outer furnace vessel 50. As such, some heat transfer via conduction still occurs, with heat passing through the power supply parts 42 from the inner furnace chamber 20 to the outer furnace vessel 50. In addition, the flow of electricity through the power supply parts 42 constantly heats said power supply parts 42. Power supply parts 42 are commonly standard electrical wiring, comprising graphite and copper elements, often with a bar formation or with a threaded or bolted connection.

The outer furnace vessel 50 is provided with an inner wall 52 and outer wall 54. As a final method to combat heat transfer, and to solve the problems associated with heat transfer caused by the power supply parts 42, a water cooling system 70 is provided to cool the outer furnace vessels 50. Water 72 is provided between inner wall 52 and outer wall 54 via water feed 74 and water return 76. In some embodiments, this water cooling system 70 is an open loop system, whereby the water feed 74 is connected to a water source and the water return 76 is connected to a drain. However, this is considered expensive and environmentally wasteful. As such, in alternative embodiments, the water cooling system 70 is provided as a closed loop system, whereby the water feed 74 and water return 76 are both connected to a water tank or reserve (not shown) and a heat exchanger (also not shown) for cooling the water 72.

Figure 2 shows a view of the whole system, in order to show in greater detail this water cooling system 70. The constant supply of cool water 72 between the inner wall 52 and outer wall 54 of the outer furnace vessel 50 provides additional cooling, ensuring that the outside surface of the device 10 is safe to touch when in a factory setting. The water 72 is also fed over the power supply parts 42, reducing heat transfer as discussed previously. The water cooling system 70 is often referred to as a water jacket in relation to outer furnace vessel 50.

However, as discussed above, this system poses numerous problems that are solved by the current invention.

The three aspects of the present invention will now be fully discussed in relation to Figures 3 to 7. The three separate concepts are each individually inventive but can be combined to assist one another in solving the inter-related problems of reducing temperature of the outside of the outer furnace vessel 50 and the power supply parts 42. As such, the three aspects of the invention have a synergistic effect which shall be discussed in greater detail below. These three aspects are:

• the use of compressed gas to cool specific hot points, particularly around the power supply parts;

• the use of an inner insulation skin to protect the outer furnace vessel from a breach event and to keep the temperature down; and

• the use of ceramic as interior insulation.

These aspects will be discussed individually and as a combination below. All three of these aspects help enable water to be removed from the system.

Any component consistent between the prior art device and an embodiment of the current invention will be accorded the same reference numeral. Any altered component will be accorded a reference numeral of the prior art device plus "100".

A vacuum furnace device 110 is provided comprising an inner furnace chamber 120, with an outer furnace vessel 150 disposed around said inner furnace chamber 120. As in the prior art device 10, a space to be evacuated 160 is formed therebetween. The inner furnace chamber 120 is formed of at least two walls of insulation and includes table 121 (which is moved by associated ram 121a). The table 121 is solid, due to the lack of water present in the known vacuum furnace device 10 resulting in no water-cooling channels needed in the table 121.

In a preferred embodiment shown in Figures 4 and 5, the inner furnace chamber 120 is formed of two walls of insulation, an inner wall 122 and an outer wall 124. These walls of insulation are of different microporous materials. A preferred material is a combination of P1200R, P1000R and PROMAFORM® ceramic insulation. Ceramic is preferred, especially for the outer wall 124, as air cooling (which will be discussed further later) will not result in the insulation deteriorating. Ceramic is also made possible by removing the water from the system.

The inner wall 122 has a thicknesses of 77mm, whilst the outer wall 124 has a thickness of 60mm, but these can alternatively be in the ranges of 25mm to 80mm respectively. This provides an adequate level of heat insulation, as shown in Figures 6 and 7, which will be discussed in further detail below.

In an alternative embodiment shown in Figure 3, there are three walls of insulation in some areas of the inner furnace chamber 120 wall. In this embodiment, top and bottom walls of the inner furnace chamber 120 are formed of three layers of microporous insulation. The side walls are formed of two layers of microporous insulation, the inner wall 122 and outer wall 124. Due to appropriate insulation only being available in sheet form, the inner wall 122 and outer wall 124 are formed of multiple layers of microporous insulation arranged back-to-back. The table 121 is formed of two or three layers of insulation.

The inner furnace chamber 120 is split into an upper heating zone 126 and lower heating zone 128. These zones 126, 128 are separated by a dividing layer 127 of microporous insulation. The inner furnace chamber 120 is encased in a stainless steel casing to help retain insulation integrity.

Outer furnace vessel 150 is provided with a peripheral wall 152 and an insulation wall 154. The peripheral wall provides protection for the insulation wall 154 in case of breach of at least part of the inner furnace chamber 120. This is more necessary if utilising a ceramic insulation (as discussed above) in combination with gas cooling (which will be discussed in further detail below), as any water vapour in the compressed gas may cause the ceramic to burst under repressurisation. As such, the provision of the peripheral wall 152 has a synergistic and beneficial effect with the other aspects of the current invention.

The peripheral wall 152 is made of stainless steel, whilst the insulation wall 154 is made of mild steel. However, either may also be made from stainless steel or mild steel. They form a gap 156 provided between them along at least part of the length of the peripheral wall 152 and insulation wall 154. This gap 156 provides additional protection from any shards of insulation material that may puncture the outer insulation wall 154. As such, the safety of the system 110 is increased by reducing the chance of the puncturing of the outer furnace vessel 150 surrounding the space to be evacuated 160 and the unexpected repressurisation of the device 110.

The ratio of the thicknesses of the peripheral wall 152, insulation wall 154 and gap 156 is in the range of approximately 1: 1 :2 to 1 :2: 10.

As in the prior art device 10, the heating elements 30 provided in the inner furnace chamber 120 are supplied power from a power source (not shown) via power supply parts 42. These power supply parts comprise an inner part 143 and an outer part 145. The inner part 143 is located within the space to be evacuated 160, while the outer part 145 is located outside of the space to be evacuated 160. The inner part 143 and outer part 145 of the power supply parts 42 are connected at the location where the power supply part passes through the outer furnace vessel 150. A seal 147 is provided to prevent air leakage from the atmosphere outside of the outer furnace vessel 150 into the space to be evacuated 160.

The seals 147 experience an increased amount of heat, via the conduction through the power supply parts 42 as discussed earlier, in addition to the heat generated by the electric current flowing through the power supply parts 42. A gas cooling system 170 is provided to cool the seals 147and, optionally, other parts of the outer furnace vessel 150.

The gas cooling system 170 comprises a generator (not shown) for pumping gas 172 into the vacuum furnace device 110 via a gas inlet 174. A gas flow pathway 178 is connected to this inlet 174 and is directed to direct a flow of gas onto the targeted area. The gas then exits the system via a gas outlet 176, either into the atmosphere or back into the system.

The gas 172 used is an inert gas, such as a noble gas or compressed air. An inert gas provides the benefit of a reduced level of reactivity with any insulation materials, whilst compressed air is easy to source and to dispose of once used (as it is simply vented into the atmosphere).

The inner furnace chamber 120 and outer furnace chamber 150 sit in a melt chamber of the furnace. A mould chamber sits below the melt chamber, which is divided by a vacuum valve from the melt chamber, such that both melt and mould chambers can independently be kept under vacuum while the product is loaded into or out of the mould chamber. The gas cooling system 170 operates in the mould chamber to speed up the cooling phase of the product. As the mould is lowered from the melt chamber into the mould chamber and the vacuum valve closes between the two chambers, the cooling cycle is initiated. A vacuum sealed motor and fan recirculates the gas 172 through the mould chamber and over a heat exchanger.

The three aspects of the invention described above each have individual benefits, but it should be understood that in any combination thereof they provide a synergistic benefit.

They each assist with an aspect of removing water from a vacuum furnace device. Appropriate ceramic insulation allows for an area heat problem across the outer furnace vessel 150 to instead become a point heat problem at the seals 147. Therefore, gas cooling system 170 can be used instead of water cooling system 70, as a point problem is present rather than an area problem. Synergistically, the use of the gas cooling system 170 over the water cooling system 70 allows for the use of ceramic insulation over the likes of graphite. Finally, the presence of a peripheral wall 152 in addition to the insulation wall 154 in the outer furnace vessel 150 increases the safety of the vessel 150 in case of ceramic insulation failure.

Figures 6 and 7 provide examples of heat insulation over preferred embodiments. Specifically, they show the preferred levels of heat transfer using the above referenced aspects of the invention in combination. The left hand side refers to the inner surface of the inner furnace chamber 120, whilst the right had side refers to outer surface of the outer furnace vessel 150. The graphs thus show the heat insulation occurring when travelling outwards from the centre of the vacuum furnace device 110.

Figure 6 shows a heat transfer graph for an embodiment of vacuum furnace device 110 according to all three of the invention. As can be seen, the inner wall 122 and outer wall 124 of the inner furnace chamber 120 provide good levels of heat insulation, whilst the presence of the space to be evacuated 160 provides an additional level of heat insulation. It can also be seen that the peripheral wall 152 and insulation wall 154 of the outer furnace vessel 150 provide little thermal insulation benefit, but the gap 156 therebetween does offer such a benefit.

The embodiment shown in Figure 7 has a thicker peripheral wall 152 made of a ceramic material, with no gap 156 present between the peripheral wall 152 and insulation wall 154. In this embodiment, the peripheral wall provides a greater level of thermal insulation in place of the absent gap 156.