GB2063434A - A Furnace, for Example, for Heating Ceramic Objects - Google Patents

Abstract

The furnace has a furnace space (4) and at least one burner (13, 14) providing flame or hot combustion gases to the furnace space. A gap (24) is provided as an outflow opening for combustion gases from the furnace space (4). This gap (24) acts as a throttle so that the pressure within the furnace space builds up. This prevents the formation of cracks in ceramic objects during heating in the furnace space. In addition, the combustion gases are confined to flow through conduits (25, 26) defined between panels (20, 21) of heat transmitting material and the inner surface of the furnace space. Heat from the gases within the conduits (25, 26) is thus supplied to the furnace space (4) such that the heating up period is short. <IMAGE>

Description

SPECIFICATION A Furnace For Example For Heating Ceramic Objects The present invention relates to a furnace, for example, for heating ceramic objects.

Furnaces are known in which the furnace space or the space for the objects is heated by means of a flame from a burner. The flame produced or exhaust gases from said flame are removed from the furnace space through outlet openings in the furnace space. The disadvantage of such a furnace is that the heating-up period for the furnace is long. It takes about 4 hours to heat a known furnace to 11 50 C. It is desirable to be able to heat the furnace in a considerably shorter time and to a temperature exceeding 1 3000C.

However, such rapid heating has the drawback that a ceramic object placed in the space for objects has a tendency to crack with such rapid heating.

It is an object of the present invention to provide a furnace in which rapid heating to a temperature of 1 3000C or over can be achieved.

According to the present invention there is provided a furnace comprising at least one burner located such that the flame or combustion gases produced thereby are supplied to the furnace space, wherein the furnace space is provided with one or more outflow openings acting as throttles.

The size of the outflow openings can be adjusted by suitable means.

Preferably, the or each burner is arranged such that it will not be extinguished when a pressure is created in the furnace space.

A deflection member may be arranged in front of the burner so that the flame from the burner or exhaust gases produced are supplied to as great a part as possible of the furnace space.

The or each outflow opening is preferably connected to an outlet conduit or channel connecting the outflow openings to a chimney or chimney pot.

The inner surface defining the furnace space may have panels spaced therefrom such that between each panel and the inner surface a flow channel is formed for exhaust gases. The flow channel is in communication with an outlet conduit or a chimney or chimney pot. Gas to said channel(s) is supplied from the furnace space through holes in said panels or through one or more gaps formed by the edge of one panel and the opposite part of the inner surface. The height of the gap may be regulated, for instance, by some suitable mechanism and by said panel preferably consisting of more than one part.

The distance between a panel and the opposite part of the inner surface may also be adjustable.

The panels are made of a material which makes the panels themselves heat-conducting so that heat can be transmitted to the furnace space from exhaust gases in said channels.

It is advisable to arrange a gap close to the wall of the furnace space opposite the wall containing the burner. The gap should preferably be arranged at the bottom of the furnace space. Thus, after passing through the gap the exhaust gases will pass through channels along side wall(s) and through channels in the top of the furnace space to an outlet channel which means that the heat from the exhaust gases leaving the furnace space will be exploited maximally to heat the furnace space.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a furnace according to the present invention, Figures 2a and 2b show alternative methods of attaching wall elements within the furnace space, Figure 3 shows a cross section of a wall, and Figure 4 shows a second embodiment of a burner for the furnace.

The furnace illustrated in the Figures has a frame 1 of iron or the like for supporting a parallelepiped furnace body. The frame 1 holds together the furnace body which is formed by an outer wall layer 2 and an inner wall layer 3, both layers being of material which is heat-insulating.

The outer layer 2 is of stones having a thickness of ca. 25 mm. Said stones are marketed by Hoganas AB under the trade name Ceraform and are described in the Hoganas catalogue from 1976 on page 1. The inner layer 3 is also made of stones, plates or layers of heat-insulating material and has a thickness of 75 mm. The stones are marketed under the trade name Porisil G. These stones are manufactured by Hoganas AB. A furnace space 4 to receive objects to be heated is defined within the furnace body. Access can be gained to the space 4 by means of a door 5, also made of heat-insulating material. The door 5 is provided with hinges 6 and a locking mechanism 8 of known type. There is a plug 7 in the furnace door, which can be removed in order to provide a eep-hole. The plug must also be of heat-insulating material.The furnace space 4 has an aperture 9 at the top, which is in communication with an outlet channel 11 formed by a unit 10. The unit 10 contains a throttle 12 in the form of a damper or the like which can be moved transversely, thus completely closing the outlet channel 11. The righthand, short wall of the furnace contains a burner 13, 14 with a horizontal section 13 and a vertical section 14. The horizontal part 13 contains a sparking plug 1 5 by means of which a spark can be electrically produced to ignite the combustion gas. The vertical part 14 of the burner includes a channel 1 6 for connection to a source supplying a gas mixture containing acetylene and air.This gas mixture is supplied through the channel 1 6 to a space in front of the sparking plug 15, which space has a conical inner wall 1 7. This inner wall 17 is in communication with an aperture 18, conical in shape, which extends through said short wall. In front of the aperture 18 is a deflecting wall or member 19, preferably at a distance of 5 cm. The wall 19 has a thickness of 12 mm and a height such that flame or gas jet from the burner is deflected as advantageously as possible in the furnace space 14 so that the jet is spread as much as possible in this space. The height of the deflecting wall may be varied.

However, it is advisable for it to be such that an object placed in the space does not come into direct contact with flame or gas jet. The wall 1 9 should have good heat-transfer properties and is preferably of the type described in catalogues from Hoganas, i.e. containing silicon carbide.

Walls of the type mentioned usually go under the designation SIC. The distance from the wall to the aperture 18 can be made adjustable. The wall 19 is preferably secured in two grooves arranged opposite each other in the longitudinal walls of the furnace. Below the top of the furnace, at a distance of 2 cm, for instance, is an inner ceiling in the form of a wall panel 20 of the same material as the wall 1 9. The distance of the wall panel 20 from the top of the furnace may of course be varied. The wall panel 20 is preferably secured in grooves arranged opposite each other in the longitudinal walls. In front of the short wall opposite that containing the burner is a side wall panel 21, preferably arranged at a distance of 1 cm from the inner surface of the short wall, but this distance may of course be varied as desired.

The side wall panel 21 is secured in grooves 32 opposite each other in the longitudinal inner walls of the furnace. The side wall 21 is manufactured of the same material as wall 19 and may be retained in the groove 32 by two spacers 33 and 34 as shown in Figure 2a or by a spacer 35 as shown in Figure 2b. The wall 19 and wall panel 20 are preferably secured as shown in Figures 2a or 2b. The lower edge 22 of the wall panel 21 is spaced from the bottom 23 of the furnace, so that a gap 24 is formed. This gap may suitably be 1 cm high but it should be obvious that the height can be adjusted or varied to the desired value. The gap may initially be given a certain height, but if the side walls consist of two wall elements it should be clear that the height of the gap can be varied in one way or another by mechanical means as desired.

The gap need not be arranged within the furnace space but can be arranged at other locations. In particular, the gap may be replaced by apertures arranged either in the side wall panel 21 or the wall panel 20.

Between the inner surface of the short wall shown on the left in Figure 1 and the side wall panel 21 a vertical channel 25 is formed, which is in communication with a channel 26 formed by the inner surface of the top wall of the furnace body and the wall panel 20. The channel 26 is also in communication with the aperture 9 and the outlet channel 11.

A panel corresponding to the panel 21 may also be placed in front of the inner surface of a longitudinal wall of the furnace body so that another vertical channel is provided for outflow of the combustion gases.

The furnace described above functions as follows: An object, such as a ceramic object, is inserted in the furnace space 4. Thereafter a suitable mixture of gas is supplied through channel 1 6. The gas mixture is ignited by means of a spark from the sparking plug 15. The flame or combustion gas flowing out through the aperture 18 is deflected upwards and passes along the inner surface of the wall panel 20, down towards the object and down to the gap 24. Since the gap24 has a throttling action, the amount of combustion gas flowing out is limited, which results in pressure being built up within the furnace space 4 so that the temperature therein increases extremely rapidly. The fact that pressure is built up also prevents the formation of cracks in the ceramic object due to the rapid heating.The combustion gas flows from the gap 24 through the vertical channel 25, resulting in heat being transferred from the gas to the furnace space by the side wall panel 21. From the channel 25 the combustion gas flows on through the channel 26 to the apertur.e 9, to pass out through the outlet channel 11. During its passage through the channel 26 heat is also transmitted through the wall panel 20 to the furnace space 4 from the combustion gas flowing in the channel 26. The pressure in the gas mixture supplied to the aperture 1 8 from the channel 1 6 is selected so that the gas pressure built up inside the furnace space is not able to extinguish the flame produced in the burner.With a furnace according to the present invention it has been possible to achieve a temperature of 1 3000C in a time of 2 hours and 10 minutes. If a temperature of only 9000C is required, a heating up period of only 1 hour is sufficient.

Figure 4 shows an alternative burner which is suitable for use with a furnace according to the present invention. This burner consists of a cylindrical pipe 27 with a bottom 28. A sparking plug 1 5 is located in the bottom. In the cylindrical pipe 27 is a conical unit 29, the wall of which is formed of sintered particles of bronze, for instance, the sintered particles being so sintered to each other that no straight throughflow channels are formed. The cylindrical pipe 27 with its bottom 28, together with the conical unit 29, forms a closed space 30. A gas mixture consisting of acetylene and air is supplied to this space from a connection pipe 31.

The present invention is not limited to the embodiments described above. In all the possible embodiments a gas jet or several gas jets is supplied to a furnace space and the gas jet or combustion gases formed is allowed to leave the furnace space through a throttle arranged to enable a build up of a pressure in the furnace space as quickly as possible, the throttling being regulated in accordance with the effect of the energy supplied from the burner or burners. The dimensioning of channels 25 and 26 has some relevance to the building up of the desired pressure in the furnace space. This is also the case with the throttle 12 of the unit 10. Another important feature of the present invention is that the remaining thermal energy from the combustion gases after passage through the throttle is utilized to heat the furnace space.

In Figure 4 the gas is allowed to pass through the cone before being ignited. It is no doubt clear that it may also be allowed to pass through a cylindrical body of ceramic material, preferably of porcelain type, before being ignited, the cylindrical body being provided with a number of axial apertures. A suitable body is marketed by the company BP.

Claims (18)

Claims

1. A furnace comprising at least one burner located such that the flame or combustion gases produced thereby are supplied to the furnace space, wherein the furnace space is provided with one or more outflow openings acting as throttles.

2. A furnace as claimed in claim 1, wherein the or each outflow opening and the or each burner are so arranged that as high a temperature as possible is reached within the furnace space in the shortest possible time.

3. A furnace as claimed in claim 1 or 2, wherein the or each outflow opening is arranged such that a sufficient pressure is achieved in the furnace space to eliminate the formation of cracks in ceramic objects placed therein.

4. A furnace as claimed in any preceding claim, wherein the or each said outflow opening is adjustable.

5. A furnace as claimed in any preceding claim, wherein the or each said burner is adjustable.

6. A furnace as claimed in any preceding claim, arranged such that heat from flame or combustion gas is supplied to said furnace space after passage through the or each outflow opening.

7. A furnace as claimed in claim 6, wherein the or each outflow opening is in communication with one or more conduits for gas, the or each said conduit extending adjacent the inner surface of the furnace space to an outlet channel.

8. A furnace as claimed in claim 7, wherein said outlet channel is provided with an adjustable throttle.

9. A furnace as claimed in claim 8, wherein said adjustable throttle can close the outlet channel.

10. A furnace as claimed in claim 7, 8 or 9, wherein a plurality of said conduits are provided, each of said conduit being defined by a wall element spaced from the inner surface of a wall defining the furnace space.

11. A furnace as claimed in claim 10, wherein said wall elements are made of heat transmitting material.

12. A furnace as claimed in claim 10 or 11, wherein the or each said outflow opening consists of a hole passing through a wall element.

13. A furnace as claimed in claim 10 or 11, wherein the or each said outflow opening is formed by a gap between the edge of a wall element and part of the inner surface defining the furnace space.

14. A furnace as claimed in any preceding claim, wherein a deflection member or wall is arranged in front of the burner flame such that the flame is deflected away from the direction of an object in the furnace space as seen from the burner.

1 5. A furnace as claimed in claim 14, wherein said deflection member is made of heat transmitting material.

16. A furnace as claimed in any preceding claim, wherein the burner and the or each said outflow opening are arranged in or in the vicinity of two opposing walls defining the furnace space.

17. A furnace as claimed in any preceding claim, wherein the burner is arranged such that it cannot be extinguished by pressure arising in the furnace space.

18. A furnace substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.