GB2332503A

GB2332503A - Tunnel kilns

Info

Publication number: GB2332503A
Application number: GB9726755A
Authority: GB
Inventors: Jack Beaumont
Original assignee: JACK BEAUMONT KILNS Ltd
Current assignee: JACK BEAUMONT KILNS Ltd
Priority date: 1997-12-19
Filing date: 1997-12-19
Publication date: 1999-06-23
Anticipated expiration: 2017-12-19
Also published as: GB2332503B; GB9726755D0; GB2332503A9

Abstract

A heating apparatus includes a cavity or tunnel (12) bounded by side walls (14), a roof (16) and a base or hearth (18). At least a part of the cavity (12) may be heated, to fire articles passing therethrough. Carriers (30) are provided for supporting articles to be conveyed through the cavity (12). A conveyor mechanism (36, 38, 40) for the carriers (30) has a path of movement remote from the cavity (12).

Description

1 1 2332503 Heating Apparatus The invention relates to a heating apparatus

and particularly to a tunnel type heating apparatus or tunnel kiln for heat treating firable materials.

Kilns are used for firing ceramic articles including tableware, sanitary ware and technical ceramics such as those use in vehicle components. Kilns are also used for firing heavy clay wares and powders or slurries fired in saggars, and may be used for heat treating metals, such as stainless steels and high melting point alloys.

Tunnel type kilns are of elongate construction and are heated continuously while articles to be fired are moved through the kiln by conveying apparatus such as a conveyor belt or a kiln car running on tracks.

Tunnel type kilns suffer from certain problems associated with the conveying apparatus, particularly where the temperatures are high. The conveying apparatus traditionally includes alloy belts, but such belts cannot withstand high temperatures over about 1,1001C. At these temperatures, the parts of the conveying apparatus exposed to the high temperature regions of the kiln must consist of refractory materials such as ceramic fibres. Any parts of the conveying apparatus not made of highly heat-resistant materials must be continuously cooled in order to function effectively. The systems for cooling tend to be elaborate and wasteful of energy.

According to the present invention there is provided heating apparatus including means defining a cavity, means for heating at least part of the cavity, and means for conveying articles through the cavity, the conveying means providing article support means having a path of movement through the cavity and means for moving the support means having a path of movement remote from the cavity.

2 1 Preferably the cavity defining means includes a wall, the path of movement of the means for moving the support means being to the side of the wall remote from the cavity. Preferably the support means are movable relative to the wall. Preferably the wall defines a base of the cavity.

A plurality of the article support means, preferably two, may be provided. The or each article support means may comprise a plurality of heat resistant elements longitudinally adjacent one another and supported on respective carriers. The article support means may be spaced apart across the width of the cavity.

Preferably each carrier extends through a slot formed in the wall to extend throughout the length thereof, the carrier connecting the article support means with the means for moving the support means. Each carrier may include a neck which locates with minimum clearance through one part of a respective slot, and may include a baffle which locates in a recessed part of the slot. A seal may be provided between the baffle and a shoulder defining the recessed part of the slot.

Preferably the article support means support the article above the wall and preferably also above the means for moving the support means.

The or each article support means may be formed of a ceramics material, preferably corderite or mullite. Preferably also the wall is thermally insulating and heat resistant. The means defining the elongate cavity may include further walls formed of heat resistant and thermally insulating material, for example ceramic fibres.

The heating means may be provided at least partly within the wall, The heating means may include electric heating means, gas heating means, oil heating means or a combination of these.

The means for moving the support means may comprise an endless 1 3 drive, which may include one or more chains or belts.

An embodiment of the invention will now be described for the purposes of illustration only with reference to the accompanying drawings in which:

Fig. 1 is a diagrammatic side view of a tunnel kiln according to a first embodiment of the invention; Fig. 2 is a diagrammatic cross-section through the tunnel kiln of Fig. 1; and Fig. 3 is a diagrammatic cross-section of a part of a tunnel kiln according to a second embodiment of the invention.

Referring to the drawings, a tunnel kiln 10 includes an elongate cavity or tunnel 12 through which articles to be fired are conveyed. The articles to be fired are not shown in the drawings. The tunnel 12 is bounded by side walls 14, a roof 16 and a base or hearth 18, all including layers of heat resistant insulating material such as ceramic fibres. The side walls 14 and the roof 16 also include outer metal cladding 20.

The kiln 10 includes a preliminary firing zone 22, a main firing zone 24 and a cooling zone 26, for firing articles conveyed through the tunnel kiln 10 according to a predetermined firing cycle.

The kiln 10 includes two rows of carriers 30 for supporting articles as they are conveyed through the tunnel 12. Each row consists of a plurality of carriers 30 formed longitudinally adjacent one another to constitute an endless conveyor for the articles. The carriers 30 are closely adjacent one another as they are conveyed through the tunnel 12 but are able to articulate away from one another at the ends of the kiln, as illustrated in Fig. 1. A number of planar rectangular batts 28 are rested on the carriers 30 to span the rows of carriers and form a flat surface on which the articles may be rested. The batts 28 are placed on the carriers 30 at an inlet end 29 of the kiln 10 and removed at an 4 outlet end 3 1. The batts 2 8 and carriers 3 0 are made of a refractory material such as corderite.

Each carrier 30 includes an upper supporting portion 32 which travels through the tunnel 12 as the carrier 30 is conveyed through the kiln 10. Each upper supporting portion 32 is mounted on a narrow stem 34 which extends through a slot 3 5 formed in the hearth 18 to extend throughout the length thereof. The stems 34 of the carriers 30 are mounted at their lower ends on respective endless chains 36 forming part of a conveyor mechanism which includes gear wheels 38 and 40. One set of the gear wheels is driven, by means which are not illustrated, to move the chains 36 along the length of the kiln 10 underneath the tunnel 12. This moves the batts 28 on the carriers 30, together with any supported articles, consecutively through the pre-heating, heating and cooling zones of the kiln 10.

The narrow stems 34 of the carriers 30 fit closely into the respective slots 35 in order to minimise the transfer of heat from the cavity 12 to the conveyor mechanism. Each stem 34 also includes a projection 42, which acts as a baffle to further reduce heat transfer from the heated cavity 12. The projections 42 is accommodated by an undercut shoulder 43 in the slot 35.

The tunnel 12 in the firing zones is heated by heating means provided within the fixed hearth 18, the heating means not being illustrated in the drawings. The heating means may include gas or oil burners or electrical elements. The gas or oil and air or the electrical wiring is brought into the hearth from below. Additional heating is provided by electrical heating elements 44 provided at an upper region of the tunnel 12 within the firing zones.

Heat may be drawn from the tunnel 12 in the cooling zone 26 and directed into the tunnel 12 in the heating zones 22 and 24.

There is thus provided a tunnel kiln in which only the upper parts of th carriers 30 (and if applicable the batts 28) are heated within the tunnel 12 in the firing zones. The conveying mechanism, including the chains 36 and the gear wheels 38 and 40 is insulated from the heated cavity in the firing zones by the fixed hearth 18. Thus only a small quantity of material is repeatedly subjected to heating and cooling as the carriers repeatedly pass through the heating and cooling zones and along the relatively cool underside the apparatus. If the articles to be fired are relatively large or flat, as is the case with tiles, the batts may not be necessary and the articles may be rested directly on the carriers, further reducing the quantity of material to be heated and cooled.

Because the conveying mechanism is insulated from the heated cavity in the firing zones 22 and 24 by the hearth 18, it need not be manufactured from highly heat resistant material and may not require cooling.

A further advantage of the above described kiln is that heating means may be provided within the fixed hearth 18. It is advantageous to heat the tunnel 12 from below, but this is not possible with many prior art designs where conveyors or kiln cars move through the tunnel.

Additionally the kiln overcomes the problem associated with prior art designs which include supports made of ceramic fibres. When these supports are conveyed through the tunnel, the fibres give out dust as they are moved, particularly if burners are blown across the fibres. The dust contaminates the articles being fired.

Various modifications may be made to the above kiln while still falling within the scope of the invention. The carriers 30 need not be manufactured from corderite but may be made from any refractory material which is flame resistant and able to withstand thermal shock. Preferably the material should also be relatively light and suitable materials include silicon carbide, mullite or heat resistant alloys.

6 The conveying mechanism need not include chains and may use, for example, cables or a belt.

Oil or gas burners may be provided instead of or in addition to the electrical heating elements 44.

Further modifications may be made to minimise heat loss via the slots 3 5. If there is to be a reducing atmosphere inside the kiln, the tunnel 12 should be scaled from the atmosphere to prevent gases escaping and burning on reaction with oxygen in the atmosphere. A rubbing seal may be provided by including a soft ceramic fibre zone on each carrier 30, preferably on an upper part of the projection 42 to contact the bottom of the undercut shoulder 43 in the slot 35. An additional projection similar to the projection 42 may be included above the hearth 18 to provide further sealing.

Fig. 3 shows an alternative embodiment in which each carrier 30 includes a downwardly extending leg 46 which runs in a trough 48 filled with sand, gravel or a similar material 50. The legs 46 of adjacent carriers 30 are able to articulate as the carriers are conveyed around the ends of the conveyor. However, as the carriers 30 are transported through the tunnel 12, the legs 46 are closely adjacent to one another and form a continuous barrier. This barrier ensures that any hot air or gases from the heated tunnel 12 must past through the sand or gravel 50 in order to reach the conveying mechanism and the external atmosphere. Thus, the cavity 12 is effectively sealed.

More than two heating zones may be provided, in order that a more precise firing cycle may be followed. The apparatus may have up to about seven heating zones. The length of the heating section could be anything between about 3-4m and 40-50m.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable

7 feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

19 Clafins 1. Heating apparatus including means defining a cavity, means for heating at least part of the cavity, and means for conveying articles through the cavity, the conveying means providing article support means having a path of movement through the cavity and means for moving the support means having a path of movement remote from the cavity.

2. Heating apparatus according to claim 1 wherein the cavity defining means includes a wall, the path of movement of the means for moving the support means being to the side of the wall remote from the cavity.

3. Heating apparatus according to claim 2 wherein the support means are movable relative to the wall.

4. Heating apparatus according to claim 2 or claim 3 wherein the wall defines a base of the cavity.

5. Heating apparatus according to any preceding claim wherein the heating apparatus including a plurality of the article support means.

6. Heating apparatus according to any preceding claim wherein the or each article support means comprises a plurality of heat resistant elements longitudinally adjacent one another and supported on respective carriers.

7. Heating apparatus according to any preceding claim wherein the article support means are spaced apart across the width of the cavity.

8. Heating apparatus according to claim 6 when appended to claim 2, wherein each carrier extends through a slot formed in the wall to extend throughout the length thereof, the carrier connecting the article support means with the means for moving the support means.

q 9. Heating apparatus according to claim 8 wherein each carrier includes a neck which locates with minimum clearance through one part of a respective slot.

10. Heating apparatus according to claim 9 wherein each carrier further includes a baffle which locates in a recessed part of the slot.

11. Heating apparatus according to claim 10 wherein a seal is provided between the baffle and a shoulder defining the recessed part of the slot.

12. Heating apparatus according to claim 2 or any of claims 3 to 11 when appended to claim 2, wherein the article support means support the article above the wall and also above the means for moving the support means.

13. Heating apparatus according to any preceding claim wherein the or each article support means may be formed of a ceramics material.

14. Heating apparatus according to claim 2 or any of claims 3 to 13 when appended to claim 2 wherein the wall is thermally insulating and heat resistant.

15. Heating apparatus according to claim 14 wherein the means defining the elongate cavity includes further walls formed of heat resistant and thermally insulating material.

16. Heating apparatus according to claim 2 or any of claims 3 to 15 when appended to claim 2 wherein the heating means are provided at least partly within the wall.

17. Heating apparatus according to any preceding claim wherein the heating means includes electric heating means, gas heating means, oil heating means or a combination of these.

18. Heating apparatus according to any preceding claim wherein the means for moving the support means comprises an endless drive.

19. Heating apparatus substantially as herein described with reference to the drawings.

20. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.