GB2236583A

GB2236583A - Support base for ceramic material to be fired

Info

Publication number: GB2236583A
Application number: GB9015590A
Authority: GB
Inventors: Dieter Seltmann
Original assignee: Riedhammer GmbH and Co KG
Current assignee: Riedhammer GmbH and Co KG
Priority date: 1989-07-17
Filing date: 1990-07-16
Publication date: 1991-04-10
Anticipated expiration: 2010-07-16
Also published as: IT9020952A0; IT9020952A1; PT94730B; FR2649785A1; GB2236583B; ES2023073A6; GB9015590D0; FR2649785B1; DE3923564C1; IT1243346B; PT94730A

Abstract

Support base for ceramic material (26) to be fired, consisting of a multiplicity of elements (10) which are dimensionally stable above the maximum firing temperature and which each consist of a lower, foot section (12) standing on a base (20) and of an upward-extending, pin-type section (14) whose end faces (24) serving as placing surface for the material (26) to be fired are mutually aligned, at least the foot sections (12) of the elements (10) being fixed in position relative to one another and free spaces (28) remaining between the upper sections (14). <IMAGE>

Description

Support base for ceramic material to be fired

Description

Ceramic material to be fired, in particular fine ceramic products such as porcelain, is made up on ap propriate support bases or so-called firing aids and fired in a continuous kiln such as a tunnel kiln or in a is discontinuous kiln such as a bogie hearth kiln.

For arranging the firing material at different levels one above the other, firing aids consisting of plates and webs are used which, when assembled, form a kind of structure for taking up the firing material.

Apart from the fact that such structures are not very stable mechanically and frequently collapse when trans ported on kiln bogies through a kiln, automatic placing and removing of the ceramic products is virtually impossible.

This also applies to the use of so-called sag gers, whose dimensions are adapted to the particular firing material.

With the development of quick-firing kilns, "single-layer" firing has been adopted, that is to say the articles are arranged side by side and no longer on top of one another. Then, only appropriate support bases are still required. Typical dimensions of the kiln channel of such a quick-firing kiln are: 3 to 5 m width, to 50 cm height. The problem then arises that integral support bases having the said widths are not available, that is to say the support base for the firing material must be assembled from a plurality of individual bases.

As a result, edges and shoulders are formed in the area of contact between the individual bases, so that the firing material no longer has an absolutely planar resting surf ace. Furthermore, in the case of bases of large area. there is an increased risk of thermal stres ses on passage through the kiln.

German Offenlegungsschrift 2,844,281 has dis closed a base for ceramic firing material, which has a structure similar to that of a comb, the comb backbones being inserted into grooves in webs which rest on the floor of the kiln bogie. The arrangement of the "comb teeth" should here be such that their free ends are located in a horizontal plane. A disadvantage is the complicated structure and the low mechanical stability of the arrangement. Moreover, the spacing of the individual rows of the support columns must be adjusted individually as a function of the material which is to be fired.

is In German Offenlegungsschrift 3,516,490 dividing the purely ceramic firing aids into a fired ceramic component and a f ibre component is suggested. In this case, the fired segment-like base bodies are to be arranged in a stable position in grooves, slots or other depressions in the fibre mat. The firing material is then placed onto the surf ace of the base bodies. Eventhough such a f iring aid can also be used for quick-f iring kilns of the type mentioned at the outset, a not insignificant disadvantage of the known arrangement is that the firing aids and especially the arrangement of the base bodies in the fibre mat must be carried out individually. that is to say when different firing materials are.placed, the base bodies must in each case be displaced accordingly.

Even if as suggested in German Offenlegungsschrift 3,516,490 such a displacement of the base bodies can be automated using a robot, this still involves an essential disadvantage of the known proposal. since every displace ment costs time and money and there is a risk of mechani cal destruction of the base bodies.

In the light of this the invention is based on the object of providing a firing aid, or.a support base, for ceramic firing material, by means of which the dis advantages described are overcome. In particular, the support base should be designed in such a way that it allows universal application and hence automatic placing and removing, independently of the particular firing material being placed.

The invention is based on the f inding that the disadvantages described can be overcome now by assembling large-area support bases, known from the state of the art, from a multiplicity of mosaic-like elements which, although they are fixed in position relative to one another, still allow a certain mobility relative to one another.

In this way, thermal changes in length are transmitted to small mosaic-like sections which are readily controllable technically.

In addition, the invention has recognised that.

by mosaic-like assembling of a support base, the indivi dual mosaic elements can be designed in such a way that a kind of "bed of nails" is formed, with the advantage that the kiln gases can pass through between the indivi dual, vertically upward-projecting webs. In this way, the firing material placed in one layer is subjected to a uniform flow of kiln gases all around and is thus heated and fired not only more quickly but also more uniformly.

The "cold feet" of the firing material, frequently observed with conventional firing technology using usual firing aids, are avoided. Those sections of the firing material which are less thoroughly sintered are called "cold feet" by the ceramics specialist. This concerns, for example, the lower sections of a firing material which stood directly on the kiln plateau in the middle of a kiln bogie and was therefore less accessible to the kiln gases.

In its most general embodiment, the invention accordingly describes a support base for ceramic material to be f ired, consisting of a multiplicity of elements which are dimensionally stable above the maximum firing temperature and which each consist of a lower, f oot section standing on a base and of an upward-extending.

pin-type section, whose end f aces serving as placing surfaces for the material to be fired are mutually aligned, at least the foot sections of the elements being fixed in position relative to one another and free spaces remaining between the upper sections.

An important feature of the invention is repre sented by the mosaic-like structure of a support base consisting of individual elements. It is also important, however. that these elements are formed essentially in two parts and consist of a lower foot section, which essentially serves to fix each element in position, whereas the upper section forms, on the one hand, a (part) placing area for the material to be fired, but simultaneously also allows, owing to its shape, the formation of a free space for passing the kiln gases through.

is The design of the foot sections and the make-up of the individual elements relative to one another can be effected in various ways. The foot sections and hence the elements can have direct mutual contact. In this case.. a polygonal cross-sectional area. for example in the form of a honeycomb, is suggested. The six faces of the foot section are then each in contact with corresponding faces of the adjacent six further elements. This results quasi in an "in situll fixing of the elements in position rela tive to one another. Of course. such an allocation can.

for example, also be achieved in the case of a square or circular cross-section, but a cross-sectional form of the elements is preferred in which a more or less closed surface is formed overall.

Equally. it would also be possible. however. to arrange the foot sections in corresponding seats of a holding device of a temperature-resistant material. This holding device can be a ceramic plate or mat, in parti cular a ceramic fibre mat. In contrast to the embodiment according to German Offenlegungsschrift 3r516r490y however,, the individual elements should now be arranged here at random side by side in a uniform distribution.

and this will be explained in more detail below.

The upper sections can more or less have any desired cross-sectional shape. It is important. however, that their cross-sections are selected such that a free space remains in each case between adjacent sections. so that a kind of channel system, through which the kiln gases can pass free and unhindered, remains underneath the material to be fired even after an object to be fired has been placed. In this way, it is ensured that the kiln can be operated exclusively with top burners.

Since it cannot be excluded that, during the ,kiln campaign", parts of the material being fired will spall at some time or impurities, for example from the burners, are passed onto the material being fired, it is proposed that the free space between the upper sections of the elements directly above the foot sections be filled with a temperature-resistant material, for example is a ceramic fibre mat, so that such foreign particles drop onto this mat and cannot penetrate between the faces of adjacent foot sections.

The foreign particles thus lying on the fibre mat can later be easily extracted outside the kiln.

On their passage through the kiln, the elements are subjected to different temperatures. In order to.

prevent mechanical stresses between the foot sections of the individual elements,, it is proposed to make the elements, entirely or at least the foot sections of the elements, from a material having a low coefficient of thermal expansion. Since,, however,, no material exists which is virtually free of thermal expansion, the inven tion proposes, in an advantageous embodiment. to provide expansion joints between the foot sections of individual elements or groups of elements and. if appropriate. to fill these with a temperature-resistant. reversibly compressible material such as a ceramic fibre mat. In this case. the expansion joints should be as narrow as possible, so that the overall stability of the elements relative to one another is not endangered.

The selection of material for the elements is also determined by the tasks to be fulfilled by the individual sections. Thus. it is proposed to form the foot sections of the elements from a heat-insulating material and to form the upper, pin-type sections of the elements from a heat-conducting material. In this way, an additional thermal insulation downwards, in the direction of the conveying means, for example the kiln bogie, is achieved, whereas the pin-type upper sections of the elements are intended, as easily as possible, to absorb the heat passing through in between and to transfer it to the material to be f ired. For this reason, it is also proposed to form the pin-type sections as hollow bodies.

Materials which can be used are inter alia alumina,, silicon carbide. recrystallized silicon carbide, SiSiC, zirconium dioxide or titanium dioxide. The indivi dual elements can be cast or pressed. Pressed parts have the advantage of a high density and hence reduced thermal is expansion.

The individual elements are then arranged once and for all piece by piece and side by side, for example on a kiln bogie in a corresponding edge-side seat. The height of the elements and the cross-sectional area of the upper sections here depend in particular on the material which is to be fired. In the case of porcelain, a height of the complete elements of between 5 and 15 cm is suitable, the foot section in each case amounting to approximately half the total height. In the case of circular cross-section, the diameter of the upper sec tions of the elements should be between about 0.5 and 1.5 cm, the free mutual spacing of the upper sections preferably being between 0.3 and 1.0 cm, so that any desired firing material can readily be placed upon a support base designed according to the invention.

In order to prevent bonding or sintering between the material being fired and the support faces of the elements,, it can be advantageous to provide the end faces of the elements with a separating agent which is, for example, sprinkled on, sprayed on or stuck on before each new kiln cycle.

Further features can be taken from the features of the subclaims and from the other application documents.

The invention is explained below by reference to various graphically represented illustrative examples the f igures being highly diagrammatic for the sake of better clarity. In the drawings:

Figure la: shows a side view of anIndividual element, Figure lb: shows a plan view of the element according to Figure la.

Figure 2: shows a perspective view of a support base consisting of a multiplicity of elements, Figure 3: shows a longitudinal section through another embodiment of a support base, with the material to be fired being placed thereon.

Figure 4: shows a vertical section through a quick-f iring kiln with a kiln bogie having a support base resting thereon, and Figure 5: shows an alternative embodiment of a support base.

Identical components or or components having the same action are shown with the same reference numerals in the figures.

The element 10 according to Figures la. b con sists of a lower foot section 12 having a hexagonal, honeycomb-like cross-section and an upper, web-like section 14 having a circular cross-section. It can be seen from Figure lb that the cross-sectional area of the foot section 12 is greater than the cross-sectional area of the upper section 14. The upper section 14 is made as a hollow cylinder, whereas the foot section 12 is of solid design.

A multiplicity of the elements 10 is - as Figure 2 shows - assembled to form a support base, each of the six faces of the foot section 12 being in contact with a face of an adjacent element 10, so that the overall result is a honeycomb-like make-up of the foot sections 12 within a frame 18 with the base 20. The box-shaped frame 18 with the base 20 consists of a temperature resistant material. for example SiC or A1,03. However,, the parts can also be made of temperature-resistant ceramic fibre materials.

As a result of the fact that the elements 10 are all of the same construction, the foot sections 12 form a more or less closed base 22 between them, f rom which the web-like sections 14 project upwards. The upper end faces 24 of the elements 10 here extend in one plane and serve as the support surface for the ceramic material 26 which is to be f ired (Figure 3). Even with the f iring material 26 placed. a free space 28 always remains between the web-type sections 14. It is important that the free space 28 is open horizontally from the front to the back and from the right to the left, so that the kiln gases can freely pass through the free space 28 when the support base is pushed, f or example on a kiln bogie, through a quick-f iring kiln. In this way, the f iring is material 26 is subjected to the combustion gases not only from above but in the same way also from below, so that particularly intensive and uniform heat treatment of the f iring material 26 is achieved. The combustion gases uniformly flow around the material virtually on all sides.

The dimensions of the elRments 10 and especially the free mutual spacing of the upper sections 14 is selected specifically to the application, and in parti cular in such a way that both small and large parts can be placed securely on the end faces 24 of adjacent ele ments 10. The spacing of the elements is here selected to be so narrow that, even if the parts are placed auto matically, at least three support points (end faces 24) are always available for the particular article. For example, in a kiln for f iring porcelain, the design of the shape and size of the elements will therefore be determined by the smallest parts which are to be fired, for example egg cups, and the result of this is that larger parts, such as plates, cups or coffee pots can then readily be placed securely on the elements 10, since they rest on a correspondingly larger number of elements 10.

Depending on which material the foot sections 12, in particular, consist of, thermal expansions of the matrix material can occuri especially in the region of the firing zone of the kiln. Because of the two-dimen sional arrangement of the elements 10 relative to one another. mechanical stresses between adjacent elements 10 might then arise, depending on the level of the tempera tures there. For this reason. it is proposed to provide an expansion joint, for example between every Sth or 10th row of elements 10. where, for example, a compressible ceramic fibre mat is inserted, so that the expansions can readily be absorbed easily. Equally, it is also possible to provide a corresponding expansion joint, for example, all around in the region of the frame 18.

Figure 3 shows an embodiment of a support base 16, in which a ceramic fibre mat 32 lies on the end faces 30 of the foot sections 12 between the upper sections 14.

their height being less than the height of the web-like sections 14, so that the latter freely project upwards beyond the fibre mat 32. The fibre mat 32 is intended to prevent any foreign particles. which arise, for example, by spalling of the material 26 being fired, from being able to drop directly onto the foot parts 12 or into the contact region of adjacent elements 10 and cause mechani cal stresses there between the elements 10. Such foregin particles will then fall onto the surface of the fibre mat 32 and, after the support base 16 has been moved out of the kiln end. they can readily be swept of f or ex tracted. At the same time, the fibre mat serves for thermal insulation in the direction of the floor 20.

Figure 4 shows the arrangement of a support base 16 on a kiln bogie 32, the edge of which is sealed against the walls 34, 36 of the kiln 38 by appropriate recesses. It can also be seen from the figure that burners 40 are arranged in the side walls 34, 36, the burners 40 being located approximately at the level of the material 26 being fired. that is to say the kiln is run exclusively with so-called top burners. Bottom burners, that is to say burners which are located under neath the material being fired, can be omitted owing to the design according to the invention of the support bases 16. since heat transfer via the free spaces 28 is ensured even in the region underneath the material 26 being fired. As a result. the kiln structure is simpli fied overall and the t hermal energy required is reduced.

The support base 16 shown in Figure 5 differs from that according to Figure 2 in that the foot sections 12 of the elements 10 are not placed directly against each other and hence fixed in their position, but are inserted into corresponding seats 42 of a ceramic fibre mat 44. In this case, a f ibre mat of relatively high density is preferably selected, in order to ensure secure positioning of the elements 10. In this embodiment, a separate f ibre mat 32, as shown in Figure 3, can be omitted. In other respects, however, the same advantages is as described above can be achieved by means of the sup port base according to Figure 5, and in particular a free space which allows free horizontal passage and through which the kiln gases can pass, is again created between the upper, web-like sections 14. in order to heat the firing material 26 also from below.

If this is desired, a single support base 16 can be provided on one kiln bogie. Equally, it is also pos sible,, however,, to make up different support bases, quasi.

as modules, and to arrange - these in turn directly op posite one another.

Claims

Patent Claims

Support base for ceramic material (26) to be fired, consisting of a multiplicity of elements (10) which are dimensionally stable above the maximum firing temperature and which each consist of a lower, foot section (12) standing on a base (20) and of an upwardextending, pin-type section (14) whose end faces (24) serving as placing surface for the material (26) to be fired are mutually aligned, at least the foot sections (12) of the elements (10) being fixed in position relative to one another and free spaces (28) remaining between the upper sections (14).
2. Support base according to Claim 1, wherein the foot sections (12) of the elements (10) have a greater cross-sectional area than each of the associated upper sections (14).
3. Support base according to Claim 1 or 2, wherein the foot sections (12) and/or the upper sections (14) have a polygonal cross-sectional area.
4. Support base according to Claim 3. wherein the foot sections (12) and/or the upper sections (14) have a honeycomb-like cross-section.
5. Support base according to one of Claims 1 to 4, wherein the upper sections (14) have a circular crosssection.
6. Support base according to one of Claims 1'to 5, wherein the foot sections (12) of the elements (10) are in mutual contact.
7. Support base according to one of Claims 1 to 6. wherein expansion joints are provided between the foot sections (12) of the individual elements (10) or groups of elements (10).
8. Support base according to Claim 7, wherein the expansion joints are filled with a temperature-resistant, reversibly compressible material.
9. Support base according to Claim 81 wherein the expansion joints are filled with a ceramic fibre material.
10. Support base according to one of Claims 1 to 5, wherein the foot sections (12) are fixed in position in corresponding seats (42) of a holding device (44) of temperature-resistant material.
11. Support base according to Claim 10. wherein the holding device (44) consists of a ceramic plate or mat.
12. Support base according to Claim 11, wherein the holding device (44) consists of a ceramic fibre mat.
13. Support base according to one of Claims 1 to 12. wherein the free space (28) between the upper, pin-type sections (14) is filled, in the region adjoining the foot sections (12), with a temperature-resistant material (32), above which the elements (10) project upwards (in the direction of the material to be placed).
14. Support base according to Claim 13. wherein the free space (28) is partially filled by a ceramic fibre material.
15. Support base according to one of Claims 1 to 14. wherein the foot sections (12) of the elementt (10) consist of a heat-insulating material and the upper, pintype sections (14) consist of a heat-conducting material.
16. Support base according to one of Claims 1 to 15, wherein the elements (10) are each constructed in two parts and the upper, pin- type section (14) is positively joined to the associated foot part (12).
17. Support base according to one of Claims 1 to 16. wherein at least the upper, pin-type sections (14) are constructed as hollow bodies.
18. Support base according to one of Claims 1 to 17. wherein the elements (10) consist wholly or partially of a ceramic, 'high temperatureresistant material such as A12031 SiCs, recrystallized SiC, SiSiC, Zr02 or T'02 -
19. Support base according to one of Claims 1 to 18, wherein the elements (10) are cast or pressed parts.
20. Support base according to one of Claims 1 to 19. wherein the end f aces (24) of the elements (10) are coated with a material which forms a temperature-resistant layer separating them from the ceramic firing material (26) placed thereon.
21. Support base according to one of Claims 1 to 20, A wherein the end faces (24) form different surface levels for.several elements (10) (element groups).
22. Use of a support base according to one of Claims 1 to 21 as a placing base for porcelain in ceramic sharpfiring kilns.

Published 1991 at Ihe Patent Office. State House. 66/71 High Holborn. London WC I R 41P. Further copies rriky be obtained from Sales Branch. Unit 6. Nine Mile Point Cwm(elinfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques lid. St MarY Cray. Kent.