GB2149074A - Tunnel kilns - Google Patents

Abstract

The bogies 17 for conveying wares through a tunnel kiln 11 run on tracks 16 outside the kiln and support light-weight ware decks 19 within the kiln by means of members 18 passing through slots 12. The kiln is in the form of a rectangular tube interrupted solely by the slots. The slots are sealed by sliding seals between the positions where the members (8) penetrate the slots. These seals may be under compression to form the seal and this can be eased when the bogies are stepped along the kiln. <IMAGE>

Description

SPECIFICATION Tunnel kilns FIELD OF THE INVENTION The present invention relates to tunnel kilns for firing wares at high temperatures such as 1 200 C.

BACKGROUND OF THE INVENTION Ceramics are fired in tunnel kilns at high temperatures. They are loaded onto wheeled cars and sent through the tunnel kilns through doors or screens. The kilns are of a steel frame construction lined internally with suitable thermal insulation. It is difficuit to get an even temperature distribution below and above the decks of the cars and there is a chilling effect from below the decks. Therefore the cars are massive with thermal insulation and have to have labyrinth seals between the decks and the walls of the kiln. These seals tend to be leaky and this can result in random chilling and cracking of the wares. Moreover fitting the seals is a time-consuming and expensive operation, as is the maintenance thereof.

The present invention aims at eliminating the need for labyrinth seals, whilst also improving the performance and reducing the overall cost of a tunnel kiln.

SUMMARY OF THE INVENTION The present invention provides a tunnel kiln for firing wares at high temperatures-wherein the kiln is formed as a complete tube of thermally insulating material interrupted only by means of slots with tracks for ware supporting members outside the wall, and the ware supporting members passing through the slots with the slots being sealed by sliding seals between where the members penetrate the slots.

The sliding seals in kilns where the ware is stepped forward rather than progressing smoothly can be arranged to be backed off during motion by a camming mechanism. The seals are preferably outside the kiln walls. It is preferred that the ware supporting members are suspended from the top or above of the kiln since then any cold air seeping through the sliding seals will enter the kiln at its hottest part and be rapidly heated up before it can contact the wares. Other advantages of suspended ware supporting means are that they are less prone to damage in that the trolley parts are outside the kiln and thus not subjected to heat damage and in that they are subjected to less mechanical rough treatment; indeed the decks of the means can be relatively light and thus will absorb less heat.It is thought that the decks of the means are best of a recrystallized silicon carbide or a similar refractory. The support means can be smaller, lighter and less expensive than the normal cars.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic section through a kiln embodying the invention, Figure 2 is a schematic axial section through the kiln of Fig. 1, and Figure 3 is a detail view showing the sealing of slots shown in Fig. 1.

BEST MODE OF PERFORMING THE INVEN TION The embodiment now to be described is by way of example.

The kiln proper 11 is made in the form of a complete rectangular tube interrupted only by slots 1 2 in a roof 14 of the tube. The method of construction is an external steel framework 1 5 clad internally with thermal insulating material. At least one rail 1 6 is associated with the or each slot and the weight of each rail is preferably taken down the sides of the framework in as near a direct compression force as possible.A ware supporting bogie 17, or more accurately a continuous succession of bogies, runs on these rails and is thus outside the kiln except for depending members 1 8 which pass through the slots, and then support ware decks 1 9. The members are of a heat-resistant steel covered with thermal insulation and recieve the ware decks in a manner similar to oven trays; the ware decks are of recrystallized silicon carbide. Substantially all of the section of the kiln is usable and there is no need to seal the ware decks to each other and to the walls of the kiln as is done with standard ware cars.It will be appreciated that there is a great advantage at the end of a production run in that it is not necessary to pass empty but sealed cars through the kiln ending up with a lot of empty, hot and therefore unusable, cars but instead merely at worst pass empty bogies along the outside of the kiln and these bogies are immediately reusable. If two slots are used as shown, it is of course necessary to support the part of the kiln roof between the slots and the bogie would either have to be in two synchronised halves or joined only by means of using Ushaped members.

The slots are of T-section as shown in Fig.

3 and T-shaped seals 21 are fitted in these slots between the members. On the outside of these seals are fitted backing plates 22. These seals are designed to that they fit together with a force-fit but nevertheless since they have to slide when the bogies are moved they tend to be slightly leaky.

An intermittent drive 23 is provided to push the succession of bogies through the kiln as shown in Fig. 2. Associated with the drive is a cam bar 24 associated with each slot. This cam bar on the return motion of the drive when the bogies are held by fixed stops pushes down on the backing plates to make the seals highly effective.

Other ways of achieving the sealing pressure are possible. For example the rails 1 6 can have depressions defining stations for the bogies. When the succession of bogies is driven forward, all the bogies lift simultaneously and then drop when they reach the next station. Seals carried by the bogies would then be released for movement and remade when the bogies' wheels entered the depressions. Another way would be to have the roof of the kiln (and maybe some of the side walls) raisable by means of jacks from the rest with a seal between the two parts with bogie wheel axles travelling along the seal and when the roof is lowered the seal is remade and also forms itself around the axles.

It will be appreciated that by divorcing the need for the cars to be thermally insulating and form a thermal barrier, there is no need for the ware decks to be massive and there is no need for seals between the decks and between the decks and the kiln.

The decks would be fed into and removed from the kiln through a double-door air-lock if needed. The doors could be sliding doors, guillotine doors or any other suitable type of door. Horizontally sliding doors are the best as they give fewer problems. Either the ware decks can be shorter than the bogies to allow the doors to close with the ware decks passing through the inner door and the kiln on a continuous sealed stream of bogies with auxiliary drive means to feed further bogies into, or remove bogies leaving the kiln from, the air locks through the outer doors; or if the ware decks are as long as the bogies, the drive means must be such that bogies in the entry air lock, or leaving the kiln into the discharge air lock, are given that much extra travel to space the decks apart to allow the inner doors to close.

Claims (7)

1. A tunnel kiln for firing wares at high temperature wherein the kiln is formed as a complete tube of thermally insulating material interrupted only by means of slots with tracks for ware supporting members outside the kiln's wall, and the ware supporting members passing through the slots with the slots being sealed by sliding seals between where the members penetrate the slots.

2. A kiln according to claim 1 wherein the ware supporting members are bogies with ware decks mounted from the bogies by means of members passing through the slots.

3. A kiln according to claim 2 with a track for the bogies on or above the kiln with the members passing downwardly through the top of the kiln by means of the slots which are in the top of the kiln.

4. A kiln according to any one of the preceding claims wherein the ware decks are of recrystallised silicon carbide and are of light weight.

5. A kiln according to any one of the preceding claims having an intermittent bogie drive and means for compressing the seals when the bogies are not being driven but easing off the seals when the bogies are being driven.

6. A kiln according to any one of the preceding claims having doors at each end to minimise heat loss.

7. A tunnel kiln substantially as herein described with reference to the accompanying drawings.