GB2024386A

GB2024386A - Improved furniture for a tunnel kiln and a method of operating the kiln

Info

Publication number: GB2024386A
Application number: GB7917312A
Authority: GB
Original assignee: KERAMIK WTB VEB
Current assignee: KERAMIK WTB VEB
Priority date: 1978-05-22
Filing date: 1979-05-17
Publication date: 1980-01-09
Also published as: DE2906387A1; DD143714A3

Abstract

On the refractory platform (8) of a tunnel kiln carriage an open framework is constructed to support two rows of articles (11) to be fired. The framework comprises three longitudinal rows of columns each built out of similar, superimposed elements (3) which have a dovetail tongue-and-groove interconnection and each of which has two side shelves in which upwardly-opening recesses are formed to receive lugs projecting from the peripheries of the plate-like carrying elements (1) which bridge the columns. The shelves of the column members of the central row project laterally of the carriage and those of the outer rows longitudinally, the arrangement being such that the carrying elements (1) can be lifted out of the framework individually laterally of the carriage (8). <IMAGE>

Description

SPECIFICATION Improved furniture for a tunnel kiln and a method of operating the kiln This invention relates to improved furniture for a tunnel kiln and to a method of operating a kiln provided with such furniture.

The firing of glazed ceramic flat articles is effected predominantly in tunnel kilns with a length of 20 to 120 m with square or rectangular occupied cross-sections, the occupied width to the occupied height being in the ratio of 1:1 to 1:5. The dwell of the articles in the kiln amounts to about 24 to 40 hours for the firing of porcelain and 20 to 25 hours for earthenware or WC ware.

This results primarily from the permissible loading of the kiln with the articles and the furniture which supports them. Plate-shaped capsules are used as supports for flat crockery, the edge of a capsule sometimes being provided with slits or recesses to improve heat transfer, gas exchange and mechanical strength. The plate-shaped capsules are stacked one above the other to improve the utilisation of the available space. The volume of furniture to articles being fired is in the ratio of 6:1 to 10:1 which leads to a high energy consumption during the firing of flat crockery.

The energy consumption figures for firing porcelain are 7 to 1 2 kWh/kg and the kiln furniture costs amount to 20 to 60% of the total process costs depending on material and thermal loading.

A further disadvantage is the durability of the capsules which is limited by their complicated geometrical formation.

An acceleration of the process times for the.

firing is not possible because considerable differences in temperature would arise throughout the closed, compact construction and lead to a premature failure of the plate-shaped capsules.

It is, however, known to fire flat crockery not in conventional plate-shaped capsules.

A number of methods are known in which special supports which can be stacked render possible a multi-stage firing of flat crockery without capsules. These suffer from disadvantages to a greater or lesser extent, however, and can only be used for the fast firing of flat crockery with restrictions or are unsuitable for this. The shortcomings of these known supports from the point of view of use for the fast firing of flat crockery are to be seen in: -the lack of an integrated support for the whole batch of plates, -inadequate stability of the support furniture, -too complicated a construction of the furniture with consequent difficulties in production. Also it is necessary to unstack the furniture when inserting and removing the crockery.

Kiln furniture is known, which has a shelf construction. Poor loading of the oven results and this furniture is unsuitable for the fast firing of flat crockerv in tunnel kilns because of its geometry which results in alternating temperature stress.

A method is known according to which tlat crockery, such as porcelain, is fired in a continuous-heating kiln standing freely in a row, in which case kiln times of 1 to 3 hours are possible.

In this case, the kiln furniture costs can be reduced decisively but the quality of the products is not satisfactory because deformation can only be avoided with difficulty and a satisfactory glaze surface can only be achieved with difficulty.

Methods are also known according to which flat crockery articles are stacked at a short distance above one another by means of light and thin-walled supports in a continuous-heating kiln.

The operation of emptying and charging is laborious and expensive.

An object of the present invention is to provide improved kiln furniture necessary to carry out an improved method of operation which will secure the advantages of a tunnel kiln with regard to the quality of the products, labour organisation and storage, but decisively reduce the cost of the furniture, energy consumption and waste, and overcome the disadvantages of the known prior art.

According to one aspect of the invention there is provided furniture for a tunnel kiln comprising spaced-apart columns between which plate-like carrying elements are supported in rows longitudinally of the kiln carriage with the elements in each row in vertically spaced relation to provide an open framework from which the elements are individually removable laterally of the carriage.

Each column is preferably built from similar, superimposed members each having a dovetail shaped upper portion and a correspondingly shaped groove in its lower portion to receive the upper portion of a subjacent member, each member additionally having lateral shelves in which upwardly-opening recesses are provided to receive a lug on the periphery of a respective carrying element.In this arrangement the axes of the dovetail portion, the groove and the shelves of each member are preferably parallel and three rows of columns are provided on the carriage, the shelves of the members of the central row extending laterally of the carriage so that the central row of columns supports two longitudinal rows of carrying elements and the shelves of the members of the outer rows of coiumns extending longitudinally of the carriage so that two adjacent columns of each outer row support carrying elements of the same longitudinal row between th?m The members of any one of said columns are preferably formed with vertical bores which are in register when the members are vertically aligned to permit a locking rod to be passed through the centre of each column.

Each plate-like carrying element preferably has a circular, elliptical or polygonal periphery from which three lugs project in equi-angularly spaced relation to locate in respective shelf recesses of the column members.

The columns of a central row or rows may be fixed relative to the carriage but the columns of outer rows may be free-standing on the carriage so as to be individually or jointly displaceable relative to the carriage.

In accordance with another aspect of the present invention there is provided a method of firing glazed ceramic flat articles in a tunnel kiln provided with the furniture described in the five preceding paragraphs, wherein the articles are caused to travel through the tunnel kiln within a period of from 6 to 18 hours, and the temperature curve is effected with heating and cooling times of:: 20 to 10000C 220 to 650K/h 1 000 to 1 1 00 C 85to 200K/h 1100 to final firing temperature 80 to 250 K/h Isothermal process time at final firing temperature 0.5 to 6 hours Final temperature to transformation range 330 to 1000 K/h Transformation range to exit from kiln 130 to 400 K/h Preferably the articles are caused to travel through the tunnel 'kiln within a period of from 9.5 to 14 hours.

The carrying elements are adapted in their dimensions to the individual goods being fired.

The conventional occupied height of up to 1.2 m can be retained. In width, however, when only two rows are provided preferably an occupied width of 450 to 650 mm is provided.

For larger occupied widths, the firing frames are disposed in a plurality of longitudinal rows on the tunnel kiln carriage, either directly on the platform or on superstructures, two central rows of columns being fixed and lateral ones being moveable. The movable rows of columns are not joined together and are separately movable.

The flat crockery is only inserted or removed from the sides of the carriage. As a result, a minimum tier clearance is possible.

As a result of the construction of the kiln furniture as described, the possibility of heat transfer both by convection as a result of intensive flow through the charge and also by radiation by an increase in the radiation surfaces and the emission coefficient is favoured in such a manner that temperature differences between the furniture and the crockery are largely avoided.

The simplified geometry of the furniture leads to a considerably improved durability which is a prerequisite for rapid firing. The course of firing for the fast firing of porcelain with a final firing temperature of 1 3800C and a transformation region of 7000C with a kiln time of 12 hours is rendered possible by the arrangement of the supporting elements and of the flat articles. When firing other ceramic materials, such as earthenware or vitreous china, the course of the firing should be altered according to the required final firing temperature and cooling down in the transformation region.

The technical and economic advantages of the method using the kiln furniture of the invention lie in the simplification of the filling and emptying of the kiln, and expensive capsule transfer, separating and stacking installations are eliminated. On the other hand, in comparison with the former technology using plate-shaped capsules, an increase in the performance of the kilns oi up to 150% is achieved as well as a reduction in the furniture costs to 30% and a reduction in the energy consumption to about 70%.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a carrying element in plan view, Figure 2 shows in front view a member from which a column is constructed, Figure 3 is a side view of the member of Figure 2, Figure 4 is a plan view of a tunnel-kiln carriage provided with the furniture of the present invention, Figure 5 is a sectional elevation taken on the line A-A of Figure 4, and Figure 6 is a graph of the course of the firing.

A carrying element 1 has equi-angularly spaced around its periphery lugs 2 which are insertable in recesses 7 in shelves 6 on opposite sides of a member 3. This arrangement ensures that a defective carrying element 1 can be replayed without dismounting the whole framework. The shape of the carrying element 1 illustrated can be varied, for example it may be round, oval or polygonal. The member 3 has a dovetail shaped upper portion 4 and a correspondingly shaped groove 5 in its bottom portion so that members 3 can be superimposed to form columns 9,10 occupying the height available in the kiln. The dovetail portions are so designed that the load is received in the middle of the column 9 or 10. The lowest members 3 of each column are either stuck with a suitable refractory material placed freestanding or let in to recesses in the refractory platform 8 of the kiln carriage so that the lowermost carrying elements 1 can be inserted.

The inner supporting columns 9 and outer supporting columns 10 are built up from an appropriate number of members 3 connected to one another only by the dovetail portions' 4 and dovetail grroves 5. The inner supporting columns 9 are turned through 900 in relation to the outer supporting columns 10. The introduction of the carrying elements 1 into the members 3 is effected by introducing the lugs 2 over the shelves 6 and subsequently lowering the lugs 2 into the recesses 7. During initial construction, an alternate stacking of members 3 and carrying elements 1 is necessary.

The ceramic flat articles 11 to be fired are introduced into or removed from the framework from the sides of the platform 8 without unstacking of the framework being necessary. The shelves 6 render possible the individual replacement of carrying elements 1 in an already built construction.

If desired each member 3 may be formed with a vertical central bore (not shown) and when the bores of all the members 3 forming a column 9 or 10 are aligned a locking rod (not shown) may be passed through them to maintain the vertical alignment of the members 3.

In an alternative embodiment of the invention (not illustrated) four longitudinal rows of columns are provided in laterally spaced relation on the carriage platform 8, the columns of the two central rows being fixed to the carriage platform 8 but the columns of the outer rows being individually or jointly movable relative to the carriage platform 8.

Claims

1. Furniture for a tunnel kiln comprising spacedapart columns between which plate-like carrying elements are supported in rows longitudinally of the kiln carriage with the elements in each row in vertically spaced relation to provide an open framework from which the elements are individually removeable laterally of the carriage.

2. Furniture as claimed in claim 1, wherein each column is built from similar, superimposed members each having a dovetail shaped upper portion and a correspondingly shaped groove in its lower portion to receive the upper portion of a subjacent member, each member additionally having lateral shelves in which upwardly-opening recesses are provided to receive a lug on the periphery of a respective carrying element.

3. Furniture as claimed in claim 2, wherein the axes of the dovetail portion, the groove and the shelves of each member are parallel and wherein three rows of columns are provided on the carriage, the shelves of the members of the central row extending laterally of the carriage so that the central row of columns supports two longitudinal rows of carrying elements and the shelves of the members of the outer rows of columns extending longitudinally of the carriage so that two adjacent columns of each outer row support carrying elements of the same longitudinal row between them.

4. Furniture as claimed in claim 2 or claim 3, wherein the members of any one of said columns are formed with vertical bores which are in register when the members are vertically aligned to permit a locking rod to be passed through the centre of each column.

5. Furniture as claimed in any preceding claim, wherein each plate-like carrying element has a circular, elliptical or polygonal periphery from which three lugs project in equi-angularly spaced relation to locate in respective shelf-recesses of the column members.

6. Furniture as claimed in any preceding claim, wherein the columns of a central row or rows are fixed relative to the carriage but the columns of outer rows are free-standing on the carriage so as to be individually or jointly displaceable relative to the carriage.:

7. Furniture for a tunnel kiln carriage substantially as herein described with reference to and as shown in the accompanying diagrammatic drawings.

8. A method of firing glazed ceramic flat articles in a tunnel kiln provided with the furniture claimed in any one of the preceding claims, wherein the articles are caused to travel through the tunnel kiln within a period of from 6 to 1 8 hours, and the temperature curve is effected with heating and cooling times of: 20 to 10000C 220to 650K/h 1000to11000C 85 to 200K/h 1100 to final firing temperature 80 to 250 K/h Isothermal process time at final firing temperature 0.5 to 6 hours Final temperature to transformation range 330 to 1000 K/h Transformation range to exit from kiln 130 to 400 K/h

8. A method of firing glazed ceramic flat articles in a tunnel kiln provided with the furniture claimed in any one of the preceding claims, wherein the articles are caused to travel through the tunnel kiln within a period of from 6 to 1 8 hours, and the temperature curve is effected with heating and cooling times of: 20 to 10000C 220to 650K/h 1000to11000C 85to 200K/h 1100 to final firing temperature 80 to 250 K/h Isothermal process time at final firing temperature 0.5 to 6 hours Final temperature to transformation range 330 to 1000 K/h Transformation range to exit from kiln 130 to 400 K/h

9. A method as claimed in claim 8, wherein the articles are caused to travel through the tunnel kiln within a period of from

9.5 to 14 hours.

10. A method of firing glazed ceramic flat articles in a tunnel kiln provided with the furniture claimed in any one of claims 1 to 7 substantially as hereinbefore described.

New claims or amendments to claims filed on 14/9/79.

Superseded claims 5 and 8.

New and amended claims

5. Furniture as claimed in any preceding claim, wherein each plate-like carrying element has a circular, elliptical or polygonal periphery from which three lugs project in right-angularly spaced relation to locate in respective shelf-recesses of the column members.