DE2319176B2 - Method and device for producing ceramic bodies - Google Patents

Description

40

The invention relates to a method for producing extruded ceramic bodies, the preferably have a flat contact side on the dry support, with little bending deformation while drying.

Known methods of this type are the re-pressing of dried, extruded shaped articles on punch presses or the so-called dry pressing with reduced moisture content on extrusion presses. In both processes, the cause of the lack of dimensional stability, namely the shrinkage of the ceramic blank during drying, is partially eliminated by keeping the material moisture very low during pressing. The strongest dryness shrinkage of about 6 to 10% occurs with a high mixing water content, which is usually between 15 to 25%. If the mixing water content is lower, the shrinkage is often only a fraction of it. The disadvantages of repressing procedure are in particular the necessary additional pressing on stamp presses, the drawbacks ⁶ S in dry compaction, are in high power consumption and machine wear and in the still poor shape retention.

In the usual processes, the pressed, plastic blank is placed on frames, frames, conveyor belts, Rolls or the like placed on which he is in the drying room is brought. Because the drying air is the contact surface = The lower surface of the blank cannot flow around 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 this compresses and shortens the still plastic underside. If in the further course During the drying process, the underside also shrinks, the already solidified upper side cannot be compressed more so that the underside is excessively shortened. The consequence of this is that the Ceramic body bends downwards at the edges when it dries out and arches up in the middle. This deformation is particularly strong in the case of flatter, plate-like bodies, since here the slowly drying one Bottom is relatively large. With more cubic bodies, the deformation is slight. An additional Deformation can also occur when the ceramic briquettes are fired, as often both Material softening and uneven firing shrinkage provide the conditions for this.

In order to ensure the best possible dimensional stability, two or more bodies of the desired shape with predetermined breaking points combined to form a more cubic body and is extruded in one piece and after drying or firing into the individual desired Body parted. The best possible symmetry of the composite cross-section favors the dimensional stability when drying and firing additionally. This method is z. B. applied in manufacturing of split tiles, in which intermediate webs are separated out as waste, or of brick shells for lintels. The disadvantages of this method are that for dividing the assembled body another operation is required and that many cross-sections are not available for assembly suitable for larger cross-sections.

Further methods of improving the dimensional stability during manufacture consist in the support surfaces of the blank on the frame approximately linear or punctiform or during the To change the drying process, so that the flow around and drying out the underside of the blank improves will.

What all processes have in common is the still inadequate shape retention and sometimes extraordinary high effort that is necessary to improve them. How great the difficulties are Ensuring good shape retention in the manufacture of ceramic bodies is clearly part of the DlN 456, "roof tiles", according to which z. B. the wings of beaver tails (size 155 χ 375 mm) 1st choice 6 mm and the wingedness of hollow sockets (size 235 χ 400 mm) may even be 12 mm.

The invention is based on the object of maintaining the shape, in particular winginess, longitudinal bending and Transverse bending of extruded ceramic bodies, without major manufacturing effort to improve.

According to the invention this object is achieved in that the mass strand in the mouthpiece and / or on Mouthpiece exit and / or, after leaving the mouthpiece, one of the bending deformations during drying counteracting preload is issued before the

Drying the body takes place. In practice this can Bias z. B. be generated in that the ceramic mass strand after exiting the The mouthpiece is bent upwards in the longitudinal direction, i.e. opposite to the bend, which is without bias would result on drying, and then the strand of mass is bent straight.

The invention also has an apparatus for performing the method described in various ways Embodiments to the subject. In one embodiment, the mouthpiece is around a Angle arranged inclined to the press head, and there is one between a belt table and the mouthpiece Curved roller conveyor arranged. By then straightening the strand on the The belt table is subject to compression in the lower zone of the strand and tensile prestress in the upper zone which counteract the undesirable downward bending during drying. The amount of bias can be achieved by varying the angle of inclination *> of the mouthpiece and by varying the string curvature be changed accordingly on the roller conveyor, so that except for downward curved or straight upward curved ceramic bodies can also be produced. The one for the greatest possible shape-retaining ^ 5 The necessary angle of inclination or the necessary strand curvature can be achieved through a few production attempts can be easily ascertained.

In another embodiment of the invention A belt table is arranged immediately after the inclined mouthpiece. on such a device does not have a curved roller conveyor. The strand will Slightly kinked immediately at the exit from the inclined mouthpiece, which is a very short but strongly curved one Roller conveyor equals.

In a particularly advantageous embodiment, the device according to the invention is provided with a mouthpiece marked whose lower inlet angle is greater than the upper inlet angle. With such a In the embodiment of the mouthpiece, the strand of material runs faster at the bottom than at the top.

In a modification of this embodiment of the invention The device is an adjustable brake in the area of the upper, smaller inlet angle arranged. A similar effect is achieved on such a device because the strand speed on the upper side is reduced by braking. The brakes, which cover the entire width of the Mouthpiece should reach, are adjustable, so that the preload necessary for the greatest possible dimensional stability or the exact brake setting can be determined through a few production tests.

Another way of generating pre-tensioning of the strand in the mouthpiece is to use the mouthpiece to be arranged off-center on the compression head, so that compression pressure and material speed are already on Mouth back entry are accordingly asymmetrical.

In a corresponding manner, such as a vertical bias, so a bias around the transverse axis of the Strand, can be generated, it is also possible to apply a lateral prestress around the vertical axis or a Generate transverse prestress around the longitudinal axis of the strand.

The advantages of the method according to the invention are that the dimensional stability of ceramic Bodies can be greatly improved at minimal cost. So can with the procedure ο! ■■■ :? particular difficulty ceramic plates in the dimensions of about 220 χ 380 mm can be produced, their longitudinal and transverse bending less than 0.5 mm is.

The devices necessary for applying the method can also be used in almost all cases can be retrofitted to the existing machines or mouthpieces without difficulty.

In the drawing, exemplary embodiments of the device according to the invention are shown.

F i g. 1 shows a side view of a device for carrying out the method according to the invention in FIG one embodiment. A mouthpiece 9 is attached to a press head 11 at an angle 10. A ceramic strand 12 runs on a curved roller conveyor 13 to a belt table 14 which by straightening the strand in a lower zone 15 of the same a compressive bias and a tensile prestress is generated in an upper zone 16 thereof.

F i g. 2 again shows a side view of a modified embodiment of a device for Implementation of the method according to the invention. In this embodiment, the roller conveyor 13 is omitted Embodiment according to FIG. 1. Rather, the strand 12 arrives immediately after it emerges from the mouthpiece 9 on a belt table 14. The strand 12 is given a slight kink 17.

F i g. 3 shows in cross section a modified embodiment of a mouthpiece 9 for devices for carrying out the method according to the invention. The lower inlet angle 18 of the mouthpiece 9 is larger than the upper run-in angle 19. By an adjustable brake 20, the effect of the upper, smaller Inlet angle 19 can still be reinforced in an adjustable manner.

1 sheet of drawings

Claims (6)

Patent claims: 1. A method for producing extruded ceramic body, which is preferably a flat Have the contact side on the drying surface, with little bending deformation during drying, d a through characterized in that the mass strand in the mouthpiece and / or at the mouthpiece outlet and / or, after leaving the mouthpiece, one which counteracts the bending deformation during drying Bias is applied before the drying of the body occurs 2. The method according to claim 1, characterized in that the mass strand one of the bending deformation opposite deformation is given during drying and then the mass strand is straightened. 3. Device for performing the method according to claim 1 or 2, characterized in that that the mouthpiece (9) is arranged inclined at an angle (10) to the press head (11) and that between a belt table (14) and the mouthpiece (9) is a curved roller conveyor (13) is arranged. 4. Device for performing the method according to claim 1 or 2, characterized in that that a belt table (14) is arranged immediately following the inclined mouthpiece (9). 5. Apparatus for performing the method according to claim 1, characterized by a mouthpiece (9), the lower inlet angle (18) of which is greater than the upper inlet angle (19). 6. Apparatus according to claim 5, characterized in that in the region of the upper, smaller inlet angle (19) an adjustable brake (20) is arranged.