CH629414A5 - Process and apparatus for producing extruded ceramic articles - Google Patents

Description

The invention relates to a method for producing extruded ceramic bodies, in particular plate-shaped bodies.

Known methods of this type are the re-pressing of dried, extruded moldings on stamp presses or the so-called dry pressing with reduced moisture content on extrusion presses. In both processes, the cause of insufficient dimensional stability, namely the shrinkage of the ceramic blank when drying, is partially eliminated by keeping the material moisture very low during pressing. The greatest dry shrinkage of about 6 to 10% is in fact present with a high mixing water content, which is usually between 15 to 25%. With a lower mixing water content, the shrinkage is often only a fraction of this. The disadvantages of the repressing process are, in particular, the additionally required pressing process on stamp presses, the disadvantages of dry pressing are the high power consumption and machine wear and the still poor shape retention.

In the usual processes, the pressed, plastic blank is placed on frames, frames, conveyor belts, rollers or the like. on which it is brought to the drying plant. Since the drying air cannot flow around the contact surface = bottom surface of the blank as well as the other surfaces, in particular the surface, the top of the blank dries earlier, begins to shrink and becomes leather-hard, while the underside, which is still plastic, is compressed and shortened. If in the further course of the drying process the underside also shrinks, the already solidified top can no longer be compressed, so that the underside is shortened excessively. The consequence of this is that the ceramic body bends downwards at the edges during final drying and bulges upwards in the middle. This deformation is particularly pronounced in the case of flatter, plate-like bodies, since the slowly drying underside is relatively large here. With more cubic bodies, the deformation is slight.

An additional deformation can also occur when the ceramic moldings burn, since here both material softening and uneven burning shrinkage provide the prerequisites for this.

In order to ensure the best possible shape retention, in a conventional method two or more bodies of the desired shape with predetermined breaking points are assembled to form a more cubic body and extruded in one piece and, after drying or firing, divided into the individual desired bodies. The best possible symmetry of the assembled cross-section also favors the shape retention during drying and during firing. This method is e.g. used in the production of split panels, in which intermediate webs are separated as waste, or in brick shells for window lintels. The disadvantages of this method are that a further operation is required to cut the assembled bodies and that many cross sections are not suitable for assembling larger cross sections.

Further methods for improving the dimensional stability during production are to design the contact surfaces of the blank on the frame to be approximately linear or punctiform or to change them during the drying process, so that the flow around and drying out of the underside of the blank is improved.

Common to all methods is the still poor shape retention or the sometimes extremely high effort required to improve them. How serious the difficulties are in ensuring good shape retention in the production of ceramic bodies is clearly evident from DIN 456, «Roof Tiles», according to which e.g. the winging of beaver tails (size 155 x 375 mm) I. Choice 6 mm and the winging of hollow pans (size 235 x 400 mm) may even be 12 mm.

From «Consultation room for ceramic-glass-enamel» p. 252 to 254 from May 20, 1957 and p. 280 to 283 from May 5, 1957, it is known to influence the strand before it emerges from the mouthpiece. Such measures, however, only allow the errors which arise during the pressing itself to be eliminated and thereby to obtain a symmetrically running strand.

From DE-PS 2 319 176 of the applicant, a method for producing extruded ceramic bodies, which preferably have a flat support side on the dry base, with little bending deformation during drying is known, in which the mass strand exits at the mouthpiece and / or after Leaving the mouthpiece is given a pre-tension which counteracts the bending deformation during drying before the drying of the body takes place. This method still proves to be advantageous for ceramic bodies down to a thickness of approximately 20 to 25 mm.

The invention has for its object to significantly improve the shape retention, in particular the longitudinal bend and the transverse bend of extruded ceramic bodies, without great manufacturing outlay, in particular also for plate-shaped bodies below the mentioned thickness of approximately 20 to 25 mm.

According to the invention, this object is achieved in that an agent which prevents the evaporation of the mixing water is applied in whole or in part to the surface of the mass strand. This means can e.g. from oil, paint, fat or e.g. consist of oil, paint or fat emulsified in water or another liquid. In a further advantageous refinement of the invention, the thickness of a coherent layer can be varied, so that the strength of the impediment to evaporation is thereby also reduced

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629 414

is varied. In another, particularly advantageous embodiment of the method according to the invention, the concentration of the material of an applied layer is varied, so that the thickness of the impediment to evaporation can be varied while the thickness of the layer remains the same. 5

The invention also relates to a device for performing the described method. It consists in the fact that behind the mouthpiece of a press a sponge attached to a holder has at least one finely adjustable drip tap with liquid, e.g. with oil,

Paint, grease or a corresponding emulsion, can be applied. The device required to carry out the method according to the invention can be used in almost all of them

Cases can be retrofitted to existing machines without difficulty.

In the drawing, an embodiment of the device according to the invention is shown.

The only figure of the drawing shows this device in side view. Behind a mouthpiece 1, a sponge 3 is attached to an adjustable holder 2. The holder 2 is set such that the sponge 3 touches the mass strand 4 coming from the mouthpiece 1 as evenly as possible. The sponge 3 is supplied with a liquid 6 from a container 7 via a finely adjustable drip tap 5.

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Claims (5)

629 414 PATENT CLAIMS 1. A process for the production of extruded ceramic bodies, in particular plate-shaped bodies, characterized in that an agent which prevents the evaporation of the mixing water is applied in whole or in part to the surface of the mass strand (4). 2. The method according to claim 1, characterized in that a coherent layer is applied in different thickness. 3. The method according to claim 1, characterized in that the strength of the impediment to evaporation is changed while maintaining the thickness of an applied layer by appropriate concentration of the material of the layer. 4. The method according to any one of claims 1 to 3, characterized in that the evaporation of the mixing water hindering agent oil, paint or fat or in a liquid, e.g. in water, emulsified oil, paint or fat. 5. Device for performing the method according to one of claims 1 to 4, characterized in that behind the mouthpiece (1) of a press a sponge (3) attached to a holder (2) via at least one finely adjustable drip tap (5) with liquid is acted upon.