WO1983002251A1

WO1983002251A1 - Device for molding ceramic objects, implementation and utilization method thereof

Info

Publication number: WO1983002251A1
Application number: PCT/CH1982/000136
Authority: WO
Inventors: Söhne Drabert; Reinhard Meyer; Fritz Drabert
Original assignee: Drabert Soehne; Reinhard Meyer
Priority date: 1981-12-23
Filing date: 1982-12-21
Publication date: 1983-07-07

Abstract

The ceramic molded objects are manufactured by means of a mold formed in a single piece or at least two parts. After introducing a plastic ceramic mass, the object being formed is subjected to a depression in order to evacuate the liquid. The mold (1), respectively its portions (7, 8), are comprised of at least two porous layers (2, 5), a first metal layer (2) delimiting the mold cavity (4), a second layer (5) forming a bedding for the first layer (2). In order to create the depression, the mold with the object to be molded is arranged in a box (11) inside (12) which a vacuum is generated.

Description

Apparatus for molding ceramic moldings and method for producing and operating the same.

The invention relates to a device for molding. ceramic moldings by means of a one-piece mold or a mold consisting of at least two molded parts, into the mold cavity of which a plastic ceramic mass is introduced, which has pores for draining off the liquid contained in the ceramic mass, and a method for producing and operating the device.

For the production of ceramic moldings, it is known to use molds made of plaster. The mold made of plaster has two tasks to do, on the one hand to withdraw so much liquid from the ceramic mass, which is introduced into the mold by casting, turning or pressing, that it takes on a leather-hard consistency that unloads from the molding tool without damaging the molding, and on the other hand to ensure the exact, repeatable shape accuracy over as large a number as possible.

However, gypsum is not an ideal building material for molds. Its resistance to breakage and abrasion is low. This is further reduced by the constant change of fluid intake and release (drying). If heat is used to accelerate the drying process, molds made of gypsum will rot even faster. There has therefore been no shortage of attempts to replace the building material gypsum with other materials which probably have the good properties of the gypsum - the possibility of rapid fluid withdrawal - but not its disadvantages. Are known molding tools made of metal in powder form, such as copper and aluminum, thermosetting plastics as binders serve ^• (CH-PS 514 412). The porosity that serves to absorb liquid is achieved by the evolution of gas when the plastic hardens.

If, however, molds are to withstand the high pressures that occur during injection molding, the strength, but above all ^" but the fatigue strength of plastic-bound materials, is no longer sufficient, even if additional measures are taken to avoid high pressures or high pressure gradients. It is also practically not possible to maintain a pore fineness with values of about 0.001 mm with certainty, but this fineness is so important for the life of a mold because the smallest solid particles of ceramic mass have dimensions of about 0.002 - 0.003 mm and must be prevented by the smaller pores from penetrating in. If this is not the case, the pores of the molding tool become blocked and can then no longer fulfill their task of withdrawing liquid.

This is where the invention comes in, based on the task

OMPI lies in designing a device of the type described in the introduction in such a way that the useful life of the molding tool when the ceramic materials are introduced into the molding tool can be effectively increased and the operation can be guaranteed over a longer period of time with little maintenance.

This object is achieved according to the invention in that the molding tool or its molded parts has or have at least two injection points, such that the distance from these points to the outermost parts of the mold cavity is at most equal to the distance to the center of the mold cavity .

The invention also relates to a method for producing the device according to the invention with a model, in which the first layer or the second layer is first formed, the first layer being flame-sprayed onto the model using a release agent or the second layer being formed with a a model enlarged by the wall thickness of the first layer is formed, the first layer being embedded in the second layer or flame-sprayed onto the second layer, and a method for operating the device in which the molding tool during and / or after insertion the ceramic mass is exposed to a negative pressure. ^•

The invention is illustrated in the accompanying drawing using some embodiments and described below. Show it:

OMPI 1 shows a section through a schematically illustrated device for shaping ceramic moldings by screwing in using a one-piece molding tool,

Fig. 2 shows a section through a schematically illustrated device for molding ceramic moldings using a two-part mold and

3 shows a section through a schematically illustrated device for the injection molding of ceramic moldings by means of a two-part molding tool.

The device shown in FIG. 1 has a one-piece molding tool 1, the wall parts of which consist of two layers, a first metallic layer 2, the surface 3 of which delimits a mold cavity 4, and a second layer 5, which is a backfill for the first metallic Layer 2 forms. It may be desirable to improve the adhesion of the two layers 2, 5 by means of anchors 6, only two of which are shown. The anchors 6 lie in the first metallic layer 2 and protrude into the second layer 5.

It is essential that the first metallic layer 2 can be reliably produced with a pore size of approximately 0.001 mm, while the second layer 5 is also porous, but its pores can be significantly larger than that of the layer 2. Has been particularly suitable for the production of the first

• gt3 & EA OH _. Layer 2 the flame spraying of metals or metal alloys, they are rust-proof and abrasion-resistant and can also be processed economically.

The mold 1 shown in FIG. 2 has two mold parts 7, 8, the parting line 9 of which lies in the plane of symmetry of the mold. The molding tool 1 according to Fig. 2, i.e. the molded parts 7, 8 also consist of the first metallic porous layer 2 and the porous second layer 5 as backfill.

As can be seen from FIGS. 1 and 2, the molding tool 1 has a supporting flange 10, by means of which it is supported on a vacuum box 11. The interior 12 of the vacuum box 11 is connected to a vacuum pump (not shown) via a vacuum line 13, in which a vacuum tap 14 is arranged. So that there is a sufficient seal between the mold 1 and the vacuum box 11, the mold 1 is sealed at the parts protruding from the vacuum box 11 with a lacquer layer 15, so that the flow of room air through the porous second layer is prevented. The gap between the mold 1 and the vacuum box 11 is also sealed by means of an O-ring seal 16. In the two-part mold 1 according to FIG. 2, a further elastic O-ring 17 is arranged, which holds the two mold parts 7, 8 together with the O-ring 16.

FIG. 3 shows a further molding tool 1, which consists of two molded parts 7, 8. The molded parts 7, 8 consist of the first, metallic and fine-porous layer 2 and of the likewise porous

^OMPI second layer 5. Since the molding tool according to FIG. 3 is used for the injection molding of moldings, it has at least one injection point with an insert 18 with an injection channel 19, through which the ceramic mass enters the molding unit with high pressure, for example 160 bar ¬ tool 1 is pressed. It is important here that so many injection points - two are shown in FIG. 3 - are provided that the distance to the most distant parts of the mold cavity 4 is equal to or smaller than the distance to the center of the mold cavity 4, so that the stress of the mold 1 can be kept low.

With regard to the choice of the metal or metal alloy to be used for the first layer 2 of the molding tool 1, the maximum pressures and the frequencies under which the pressures take effect must be taken into account. Zinc is sufficient, for example, for screw-in and casting molds according to FIGS. 1 and 2 without large pressure drops. It can be flame-sprayed with the desired pore fineness, it is rust-free and low in price, it can be processed easily, and the melting temperature is so low that two wooden models can be used as the material for the production of the first layer. the surface of which is expediently coated with a release agent, for example Graphite. The disadvantage of zinc is the low breaking strength, which, however, does not have a disadvantageous effect in the aforementioned areas of screwing and casting.

Bronze can be used as a further material. The necessary pore fineness can also be produced by flame spraying, it is rustproof and

OMPI has a higher breaking strength than zinc.

However, if molding tools 1 according to FIG. 3 are used for transfer molding, alloys of chromium-nickel, optionally with additions of tungsten or manganese, are required as the first layer. Since the melting temperature of these metals is very high, both temperature resistance and shrinkage must be taken into account when selecting the material of the material.

In the case of the molding tools 1, the first layer 2 of which consists of flame-sprayed zinc, the second layer 5 can be introduced in the form of a backfill as long as the first layer 2 lies on the wooden model. The second layer can consist of quartz sand with a grain size of approximately 0.8-1.2 mm and a self-curing plastic binder, the weight ratio being 20 parts quartz sand to 1 part binder. When introducing the second layer 5, care must be taken to ensure that the fine channels of the flame-sprayed metal layer are not blocked by the binder of the backfill and are therefore ineffective. For this reason, the side of the first layer 2 facing the second layer 5 is also coated with a low-viscosity release agent, for example wax dissolved in gasoline. If the second layer 5 is introduced, its binder does not adhere to the metal layer. In order to remove the separating agent from the fine-pored channels of the first layer 2, after the second layer 5 has completely hardened, a low-viscosity hydrocarbon, for example gasoline, is pressed through the wall of the first layer 2 and through subsequent ones Warm air dried.

3, the first layer 2 adheres firmly to the second layer 5 if the latter consists of a fired profile body consisting of corundum or silicon carbide and a flux. The fired profile body takes on the role of backfilling; in the case of a backfill with a plastic binding, this would partially gasify under the high temperatures of Chromnicke1 flame spraying and completely lose the binding power.

The high load on the molding tool according to FIG. 3 during transfer molding results from the transfer molding cycle. In this case, the two mold halves 7, 8 are first closed. Arrows A show schematically that both mold halves 7, 8 are sucked off by suppressing, e.g. with 600 - 700 Torr. Now, the ceramic mass is injected into the mold cavity 4 under high pressure. Liquid is sucked out of the mass until it is leather hard. Then they drive

Mold halves 7, 8 apart; Instead of the underpressure, an overpressure schematically represented by arrows B is generated, as a result of which the molding is easily detached from the molded parts 7, 8. An unillustrated unloading device then grabs suction cups after shaping and removes them from the mold 1. At the parting line 9, pore-free metal plates 20 can be used to save flame-sprayed material. These are sandblasted on the side facing the second layer 5 before being inserted into the mold, coated with liquid plastic binder, inserted into the mold and

O PI then only the second layer 5 is introduced.

1 and 2, the screwing or casting takes place outside the vacuum boxes 11. After screwing or casting, the molds are hung in the vacuum boxes 11 and the tap 14 in the supply line 13 to the vacuum pump is opened. This shortens the time to leather hardness, which significantly reduces the number of tools in circulation.

In the case of the molds described, it is achieved that the fine-pored, flame-sprayed first metallic layer means that no ceramic particles can enter the backfill, so that a very substantial increase in the service life of the mold can be expected, since the necessary breaking strength can also be achieved .

Claims

1. Device for molding ceramic moldings by means of a one-piece mold or a mold consisting of at least two mold parts, into the mold cavity of which a plastic ceramic mass is introduced, which has pores for draining off the liquid contained in the ceramic mass, characterized in that the molding tool ( 1) or its molded parts (7, 8) at least zv / ei injection points (18, 19), such that the distance from these points to the outermost parts of the mold cavity (4) is at most equal to that Distance to the center of the mold cavity.

2. Device according to claim 1, characterized in that the molding tool (1) or its

Molded parts (7, 8) are or are made up of at least two porous layers (2, 5), of which the first layer (2) delimiting the mold cavity (4) is a metal layer, the pores with a smaller opening than the smallest Ab ¬ measurements of the solid particles of the ceramic mass.

3. Device according to claim 1, characterized in that the first layer (2) is a dimensionally stable, porous metal shell.

4. The device according to claim 1 or 2, characterized in that the first layer (2) made of a flame-sprayed material, for example zinc, bronze or chromium-nickel alloys, if there is addition of manganese and / or tungsten.

5. Device according to one of claims 1 to 4, characterized in that the surface of the first metal layer (2) defining the mold cavity (4) is smoothed.

6. Device according to one of claims 1 to 5, characterized in that the first layer (2) is connected to the second layer (5) forming a bedding or backfilling, e.g. by means of anchors (6) arranged on the back of the first layer (2).

7. Device according to one of claims 1 to 6, characterized in that the first layer (2) has a thin metallic coating, e.g. of 0.3-2 mm, which is flame-sprayed on the second layer (5) formed as a fired ceramic profile shape.

8. The method for producing the device according to one of claims 1-7 with a model, characterized in that first the first layer (2) or the second layer (5) is formed, the first layer (2) under Ver¬ using a release agent, flame-sprayed onto the model or the second layer (5) is formed with a model enlarged by the wall thickness of the first layer (2), the first layer (2) being inserted into the second layer (5) ¬ is bedded or flame-sprayed onto the second layer (5).

9. The method according to claim 8, characterized in that graphite is used as the release agent.

10. Method of operating the device after

Claim 1, characterized in that the molding tool (1) is exposed to a negative pressure during and / or after the ceramic material has been introduced.