GB2147399A

GB2147399A - Process for drying ceramic articles

Info

Publication number: GB2147399A
Application number: GB08423254A
Authority: GB
Inventors: Johannes Hirsch
Original assignee: KERAMIK WTB VEB
Current assignee: KERAMIK WTB VEB
Priority date: 1983-09-26
Filing date: 1984-09-14
Publication date: 1985-05-09
Also published as: GB8423254D0; DD219267A1; DE3428925A1

Abstract

Air which has a temperature of 20-30 DEG C and a relative humidity of up to 70%, is blown from below and above the entire surface of a ceramic article, which is dried in 30-50 minutes from a moisture content of about 22% to a residual humidity of about 1.5%, and so passes through an equivalent to the "leather-hard drying" and "white drying" stages which are otherwise required before firing. Preferably the drying air is a mixture of compressed air exiting pipes 8 through nozzles 6 and ambient air 14 entrained by the compressed air jets as they enter open-ended pipes 7. <IMAGE>

Description

SPECIFICATION Process for drying ceramic articles The invention concerns a process for drying ceramic articles in the "leather-hard drying" and "white drying" range within the ceramics industry.

Ceramic articles are subjected to a drying process prior to firing. This ensures that the material to be fired is of a high quality when it leaves the furnace.

In order to accelerate the drying stage it is carried out by applying heat at a temperature in the range 40-120"C.

This process, however, requires considerable heat energy input for vaporization or evaporation of moisture in the article and embraces the entire temperature range covered by "leather-hard drying" and "white drying". The drying process is determined by the nature of the raw materials used, the shape of the article to be produced, the external drying conditions and also the state and design of the drying installation. If the many parameters involved are not properly coordinated the quality of the articles dried can be reduced, leading to deformation and cracking.

References concerning conventional drying techniques include "Technologie der Feinkeramik" (Technology of Fine Ceramics) published by the Deutscher Verlag fu"r Grundstoffindustrie (Ger.Raw.Mat.lnd. Publishers), "Technologie der Grobkeramik" (Technology of Ordinary Ceramics) Vols. 2 and 3, published by the Verlag fu"r Bauwesen (Building Publishers), Berlin, "Trocknungstechnik" (Drying Technique) Vols. 1 and 2, published by Springer Berlin, and "Das Trocknen" (Drying), Published by Sauerländer.

An object of the invention is to considerably reduce energy consumption and also reduce the outlay on drying equipment by modifying the drying technology and using ambient air, i.e. the surrounding or room air as a drying agent.

In conventional convection drying processes the drying intensity is determined by external conditions, i.e. the temperature of the drying medium, the relative moisture of the said medium and also the speed at which it moves.

In the "leather-hard drying" temperature range of about 40"C, however, the main object is to enable the drying process to take place with the aforementioned three parameters very accurately adapted to one another, as the drying otherwise leads to a reduction in quality, resulting in deformation and finally cracking of the product. "White drying", on the other hand, is effected at higher temperatures, reaching about 1 20 C.

According to this invention there is provided a process for drying a ceramic article in the "leather-hard drying" and "white drying" field wherein drying is effected utilizing ambient air at a temperature of about 20-23"C and having a moisture content of up to about 70%, the drying medium moving a high speed within a drying apparatus incorporating a blower device.

By means of the invention the drying effect is obtained by fulfilling only one of the drying conditions, i.e. the speed of the medium. This is done by causing ambient air from the surroundings, as the drying medium, at its prevailing temperature to be taken in by suction by an air conveying means, then conveyed through a pipe with a blower device to a position immediately in front of the article.

The drying agent emerges from the piping via nozzles of the blower device at a high outlet speed, resulting in a considerable heat transfer coefficient at the point of impact. The air carried along by the propulsive jet of the nozzles is termed drying medium after the two currents have combined.

If a large number of nozzle apertures are provided in the zone of the article this ensures high drying intensity and a uniform removal of moisture after the drying medium has encountered the surface of the article, as well as ensuring tension-free removal of water from the surface of the article. The drying intensity may be increased by altering the distance of the nozzles from the article and thus the intensity of impact. In a preferred embodiment the transfer of material can also be influenced by the provision of interceptor pipes at different distances from the nozzle and by using different quantities of propulsive jet.

Preferably an exhaust air blower conveys the consumed drying medium from the drier into the atmosphere or returns it to the process as circulating air. Transport of articles through the dryer can be effected by a conventional device which conveys them from the feed point to the discharge point, the drying taking place simultaneously. The entire blowing apparatus, on the other hand, may be accommodated in a dryer frame in a permanent position but in such a way that it can be locally adjusted. The drying medium used in the invention is ambient air at a temperature of 20-300"C and with a relative humidity of up to about 70%. With this room temperature and with a high drying agent speed the articles, after being separated from a metal plaster mould, can be dried from their initial humidity of about 22% to a final humidity of about 1.5% within about 30-50 minutes.

The invention will be explained in greater detail with reference to the accompanying drawings by way of example only and in which: Figure 1 is a schematic plan diagram showing the drying process with cold air blown in, and Figure 2 is a part-sectional view of a cera mic plate conveying system incorporating a blower device.

As shown in the drawings, conveyor chains 3 having rockers 2 provided with a sufficiently free and flat supporting surface, are continuously conveyed in the direction 3.1 into and through the entire width of the dryer 4. Ceramic articles (plates) 1 are placed side by side on the said rockers 2. For drying purposes air 14 from the surroundings is conveyed by suction through the pipe connection 9 to the blower 10 and conveyed to the article 1 by means of the pipe 8, the aperture 22 and the blower device 5. In the pipe 8 and blower device 5 nozzle holes 6 are provided at short distances apart in the vicinity of the articles 1.

After the propulsive jet 21 leaves the nozzle aperture 6 it encounters interceptor pipes 7.

The pipe 8 and interceptor pipe 7 are installed in the dryer 4 above and below the rockers 2 loaded with articles 1. The pipe 8 and interceptor pipe 7 of the blower device 5 can be displaced in the vertical direction 20 if and when required. Air 14 conveyed through the pipe 8 from the blower 10 to the nozzles holes 6 moves in the form of propulsive jets 21 at a high "core speed" into the interceptor pipe 7; ambient air 14 being caused to be entrained within the pipes 7 by this movement and, after the two currents have combined, leaves the interceptor pipe 7 as drying medium 14, 21, at a still higher speed. The drying medium 14, 21, now encounters the entire surface of the article 1 and removes, at high heat transfer coefficients, moisture emitted by the article. In order to dry the article air 14 from the room is then taken in by suction via a multiplicity of apertures 1 3 or supplied by a ventilator and this air acts as the drying medium 14, 21, on the articles 1 passing through the dryer 4.

A fan 1 7 conveys the drying medium 14, 21, through apertures 15 via the pipe 16, 18, into the open, or else it is partly or wholly mixed as circulating air with the ambient air 14. The quantities can be regulated by means of dampers 11, 12 and 19.

Claims

1. A process for drying a ceramic article in the "leather-hard drying" and "white drying" field, wherein drying is effected utilizing ambient air, at a temperature of about 20-30"C and having a moisture content of up to about 70%, the drying medium moving a high speed within a drying apparatus incorporating a blower device.

2. A process as claimed in Claim 1, wherein the ambient air constituting the drying medium acts on a ceramic article vertically or obliquely and upon both sides thereof.

3. A process for drying a ceramic article substantially as herein described and illustrated with reference to the accompanying drawings.