GB2126158A

GB2126158A - Producing ceramic articles

Info

Publication number: GB2126158A
Application number: GB08321965A
Authority: GB
Inventors: Dagmar Hulsenberg; Wolfgang Gernlein; Horst-Gunter Kruger; Ulrich Knye
Original assignee: THURINGIA SONNEBERG VEB
Current assignee: THURINGIA SONNEBERG VEB
Priority date: 1982-08-20
Filing date: 1983-08-16
Publication date: 1984-03-21
Also published as: GB8321965D0; CS557083A1; IT1159497B; DD211243A3; FR2531900B1; DE3329675A1; IT8367876A0; FR2531900A1; GB2126158B; CS246595B1

Abstract

A process for the production of a ceramic sheet or shaped body from a ceramic suspension by removal of the dispersion agent is described wherein a ceramic suspension is subjected in a mould 2 by means of two plungers 3, 4 forming an anode and a cathode and a source of voltage 5 to pressure and the action of an electric field, the dispersion agent being simultaneously removed via plungers 4 to dehydrate the ceramic suspension. <IMAGE>

Description

SP ECIFICATION Process and device for the production of a ceramic massive sheet or formed body The present invention is concerned with a process and a device for the production of a ceramic massive sheet or of a formed body from a ceramic suspension by dehydration.

It is known to produce ceramic massive sheets from a suspension by passing the suspension by means of membrane pumps to filter presses and dehydrating in the filter presses. The filter cake thus obtained is homogenised in vacuum presses, drawn into troughs and cut up into massive sheets. If formed bodies are to be made therefrom, for example plates or cups, then these massive sheets are worked up on so-called roller machines.

Because of the many working steps involved, this method of operation requires a high expenditure of technology, investment, labour and transport, as well as storage capacity. The filter presses are operated discontinuously and are, therefore, not very suitable for the construction of automated finishing sections.

In order to make this process better automatable, it is known to carry out dehydration by means of spray driers, membrane pumps being used for supplying the spray driers, dehydration taking place by the evaporation of water in the spray drier. Subsequently, in a mixing plant, sufficient water or suspension is added to the granulate to give a plastically shapable mass.

Further working up then takes place as in the case of the above-described process. By means of the spray driers, labour is admittedly saved in comparison with the filter press operation but, due to the evaporation of water, there is a very high consumption of energy. Spray driers are technically very laborious and expensive and the use thereof necessitates additional technical measures for the stationing thereof.

For the production of massive sheets or of ceramic formed bodies from a suspension, it is also known in the ceramic industry to use an electrophoresis process. Thus, for example, Federal Republic of Germany Patent Specification No.

26 179 98 describes two opposite-lying rotatable cylinders, which are connected as anodes and are associated with a counterelectrode which is arranged opposite to the cylinder surfaces in one of two prismatic chambers having a curvilinear, Vshaped cross-section. Via a feed pipe, slurry is pumped from a storage container into the intermediate chambers formed by the V-shaped counter electrode and the cylinder walls, where electrophoretic deposition takes place on the outer surfaces of the cylinders.

The endless massive band produced by this process is either worked up by means of cutting press or punch devices to give a ceramic formed body or is further worked up in a vacuum press in known manner. However, high machine-technical expense also results herefrom.

Furthermore, from Federal Republic of Germany Patent Specification No. 27 12 318 it is known to arrange in a container filied with suspension two opposed electrodes connected as anodes, between which an auxiliary electrode can be introduced as a cathode. The deposition of solid material takes place on both electrodes connected as anodes which essentially have the shape of the shaped body to be produced. After sufficient accumulation of material on the electrodes, the auxiliary electrode is removed and, by bringing close together both electrodes, the two layers of material are pressed together to give a formed body.

The previously known electrophoretic processes have the common disadvantage that, as the operation progresses, the proportion of solids in the suspension decreases, the deposition procedure on the electrodes thereby being retarded and thus the efficiency of the process decreases very considerably. In order to overcome this disadvantage and in order always to keep constant the solids content in the suspension, a continuous feed in of solids is necessary. For the supply of solids, already prepared mass is again required so that the ratio of expense and result and thus the degree of working of the process is impaired.

Finally, there is known the so-called RAM process for the shaping of ceramic masses. In this process, for the shaping of ceramic products, there are used hard, permeable plungers of special gypsum through which pass strips of cotton. The porous plungers are introduced into metal housings and permit a reduction of the water content during shaping. The unfinished pieces are removed from the mould by applying pressurised air through the cotton strips. This process is very time-consuming and hitherto has not been used in practice.

It is an object of the present invention to save process steps, to simplify the technological process in the production of massive sheets, to reduce the specific energy consumption, to ensure an almost quantitative deposition of the solid material and not to reduce the solids content of the starting suspension during the deposition.

Thus, according to the present invention, there is provided a process for the production of a ceramic massive sheet or shaped body from a ceramic suspension by removal of the dispersion agent, wherein a ceramic suspension is subjected in a mould, by means of two plungers forming an anode and a cathode and a source of voltage, to pressure and the action of an electric field, the dispersion agent being simultaneously removed via one of the plungers to dehydrate the ceramic suspension.

With this combination of electrokinetic working principles and mechanical action, the dehydration of ceramic suspensions is achieved in a substantially shorter time than in the case of the previously known processes.

According to the process of the present invention, the electric field action can be produced by applying a direct or impulse voltage.

The effective electric field strength is preferably controllable via the stroke of one of the plungers and/or externally by a change of voltage.

A thinning agent is preferably added to the ceramic suspension, the proportion of monovalent cations introduced thereby strengthening the electro-osmosis effect and the total amount of dispersion agent to be removed is smaller.

According to a preferred feature of the present invention, the dispersion agent removed is recycled to the working up process.

According to yet another preferred feature, an under-pressure is applied to the plunger which is permeable to the dispersion agent.

Furthermore, the suspension can be heated for the purpose of shortening the reaction time, heat thereby being supplied either before dehydration in the form of a preheating or during the dehydration by the introduced electrical energy.

The present invention also provides a device for carrying out the process, which device comprises a mould in which are arranged plungers lying opposite one another, at least one of which is movable and at least one of which is permeable to the dispersion agent, one plunger forming an anode and the other a cathode.

The plunger conducting\away the dispersion agent is preferably made of an electricallyconductive sintered material or of a nonconductive material with open porosity in combination with an electrically conductive material or of a metallic holed plate in combination with a filter fabric or with an electrically conductive fabric.

The plunger which does not conduct away the dispersion agent can be made of a metallic material or of an electrically conductive, gaspermeable material or of a gas-permeable work material in combination with an electrically conductive material.

Finally, according to a further preferred feature, the mould is covered on its inner surface coming into contact with the suspension with an electrically non-conductive material or is made entirely of an electrically non-conductive material.

By means of the direct coupling of working up and shaping, process steps are saved and thus the technological process is simplified, a better adaptability to the production process thereby being achieved. The energy consumption in comparison with conventional processes is decisively reduced. An important advantage of the present invention is that a complete deposition of the solid particles from the suspension is achieved. A high economy of the process thereby results and the ratio between expenditure and result is fundamentally improved.

The moisture content of the massive bodies produced can be adjusted in any desired manner.

When the dispersion agent is recycled, a closed circuit is obtained which prevents impairment of the environment. Finally, the process permits the production of a low texture body which is of importance for further working up because, in this way, distortion during drying and firing is avoided, which results in an improvement of the quality and a reduction of waste.

The present invention will now be described in more detail, by way of a specific example and with reference to the accompanying drawing, which schematically illustrates the device of the present invention.

A suspension 1 is placed in a mould 2 between two plungers 3 and 4 forming an anode and a cathode, these plungers 3 and 4 being connected with a source of voltage 5. Upon moving the plungers 3 and 4 towards one another, the suspension 1 is subjected to pressure and to the action of an electrical field. Through the plunger 4, which is permeable to the dispersion agent, the dispersion agent is removed and again returned to the working up process. During this procedure, the solid particles are completely separated out from the suspension and a massive sheet results with a residual moisture content necessary for shaping, which sheet can be further worked up on a roller machine to give a formed body.

The electrical field strength can be controlled via the stroke of the plunger 3 and/or from outside by a change of voltage.

The two plungers 3 and 4 can also be constructed as shaping plungers so that, without subsequent shaping, a shaped body can be produced with a moisture content of 18 + 3% by weight.

The dehydration of the body by the electroosmosis can be so influenced by the electrical field strength that the stage of "leather hard drying" can be substantially by-passed.

According to another feature of the present invention, a non-plastic substance, such as aluminium oxide, titanium dioxide, barium titanate or the like, can be dispersed in water with the addition of a binding agent, for example latex, with the help of a thinning agent and subsequently introduced into the device according to the present invention. After application of a direct voltage and moving the plungers 3 and 4 towards one another, a solid body is obtained. The ceramic unfinished piece can subsequently be subjected to shaping, for example by stretching or pulling, or can also be used directly.

Claims

1. Process for the production of a ceramic massive sheet or shaped body from a ceramic suspension by removal of the dispersion agent, wherein a ceramic suspension is subjected in a mould, by means of two plungers forming an anode and a cathode and a source of voltage, to pressure and the action of an electric field, the dispersion agent being simultaneously removed via one of the plungers to dehydrate the ceramic suspension.

2. Process according to claim 1 , wherein a direct or impulse voltage is applied for the production of the electric field action.

3. Process according to claim 1 or 2, wherein the effective electric field strength is controllable via the stroke of one of the plungers and/or from outside by a change of voltage.

4. Process according to any of the preceding claims, wherein a thinning agent is added to the ceramic suspension.

5. Process according to any of the preceding claims, wherein the dipsersion agent running off is recycled to the working up process.

6. Process according to any of the preceding claims, wherein an underpressre is applied to the plunger through which the dispersion agent is removed.

7. Process according to any of the preceding claims, wherein the suspension is heated before the dehydration by preheating or during the dehydration by the applied electrical energy.

8. Process according to any of claims 1 to 7 for the production of a ceramic massive sheet or shaped body from a ceramic suspension, substantially as hereinbefore described and exemplified.

9. Device for carrying out the process according to any of claims 1 to 8, which comprises a mould in which are arranged plungers lying opposite one another, at least one of which is movable and at least one of which is permeable to the dispersion agent, one plunger forming an anode and the other a cathode.

1 0. Device according to claim 9, wherein one of the plungers is made of an electrically conductive sintering material or of a nonconductive material with open porosity in combination with an electrically conductive material or of a metallic holed plate in combination with a filter fabric or with an electrically conductive fabric and the other plunger is made of a metallic material or of an electrically conductive, gas-permeable material or of a gaspermeable material in combination with an electrically conductive material.

11. Device according to claim 9 or 10, wherein the mould is covered on its inner surface coming into contact with the suspension with an electrically non-conductive material or is made completely of an electrically non-conductive material.

12. Device according to any of claims 9 to 11, substantially as hereinbefore described and exemplified and with reference to the 'accompanying drawing.

13. A ceramic massive sheet or shaped body, whenever produced by the process according to any of claims 1 to 8 or by the use of the device according to any of claims 9 to 12.