DE2315875A1 - PROCESS FOR MANUFACTURING THIN-WALLED SHAPED BODIES FROM POWDERED CLAY-FREE RAW MATERIALS - Google Patents

Description

Process for producing thin-walled molded articles from powdery Clay-free raw materials The invention relates to a method for producing thin-walled raw materials Moldings made from powdered raw materials, which are either completely or only very slightly contain plastic parts. It allows moldings to be produced in the so-called dry pressing processes could not be produced at all and those in the isostatic pressing process or with the aid of the slip casting process in plaster of paris either do not form either or only under uneconomical conditions could be manufactured. the made according to this invention Shaped bodies are generally then subjected to a sintering process, a polycrystalline solid from the molded body consisting of powders will.

Powder is often required in oxide ceramics and powder metallurgy are processed to moldings that have no or only very low plastic proportions contain. Of the shaping processes available in this technology come for thin-walled cylindrical parts, thin-walled parts with a conical shape or thin-walled parts with different diameters, e.g. B. pipes with sockets, only a few molding processes in question. Unless they are constant cylindrical parts Extrusion may be considered.

For this, however, the addition of plasticizers is necessary. However, there are powder metallurgical and oxide ceramic materials that can be made from for various reasons not the plasticizing quantities necessary for extrusion can add. So z. B. many oxide ceramic products if too much is added Plasticizers are no longer tight during the subsequent ceramic firing. - The dry pressing process, which is otherwise used in oxide ceramics and powder metallurgy one of the most economical using presses similar to tabletting machines Form geoing process cannot be used for thin-walled parts either, because the dry powder is not in the tight Matrix spaces evenly trickle in enough.

Granulations of these powders, e.g. B. in the spray-drying process, do not provide any remedy. -When isostatic pressing in rubber dies or in one cylindrical die space between a solid steel core and a rubber die the same filling difficulties arise as mentioned for dry pressing have been.

Economically more favorable working speeds are therefore not to reach. In addition, these narrow die spaces can be filled evenly not yet achieved. -For oxide ceramic or powder metallurgical production Such parts have only been available using the slip casting process. An aqueous suspension of the powder in question is poured into a plaster mold, whereby the gypsum removes the water from the suspension, so that after some time a corresponding moldings of the plaster mold can be taken. This procedure is but very wage-intensive, in addition, the plaster of paris molds used only hold for one relatively small number of items.

Such thin-walled parts have also been proposed as a result to realize that initially parts with greater wall thickness are produced and these are then sanded down on grinding machines. Apart from the grinding Machining of powder metallurgical or oxide ceramic parts is very labor intensive is and therefore expensive, this process is forbidden for the production of molded parts the end more valuable raw materials. Are z. 3. Shaped body required, the oxides of the rare Contain earth and with each other and with other constituents of the ceramic react to the sealing burning process, the raw materials used can be extracted from the abrasive material not or at least not recover it economically.

But this would drastically reduce the grinding process more expensive.

3 for magnetic ceramic materials, especially for ferrite permanent magnets, which should have a magnetic preferred position, it is already known the ceramic Powder in the form of an aqueous suspension, a so-called slurry, into the die space bring in. The aqueous slurry allows the powder particles through align a magnetic field relatively frictionless. By subsequent pressing between the rigid upper and lower punches, the water becomes after the alignment through filters located in the upper and / or lower stamp from the sludge and thus removed from the die space.

The compacts or moldings produced by this process however, do not have a thin wall thickness.

According to the invention, thin-walled moldings are made from powdery, non-plastic raw materials, such as those used in powder metallurgy and oxide ceramics processed, produced according to the following process: the aqueous suspension the Powder is injected into the die space of the press tool via one or more injection needles injected. The suspension z. 3. from the powder and water to be processed can exist, is taken for this purpose from a storage container, where they through a stirrer or other means is kept in constant motion to prevent sedimentation to avoid powder particles in the aqueous slurry. The feeding of the reservoir to the hypodermic needle or to the hypodermic needles via dosing pumps, as is already known. For the purpose of injecting the suspension the injection needles are stirred into the die space and, if necessary, d. H. if this is necessary for an even distribution of the suspension in the sodium chamber is moved in the die space during the injection process.

After the injection has ended, the dosed amount of suspension should be used moves the hypodermic needles out of the die space. The whole sequence of movements For the injection it is expedient to use a device such as that used in the filling shoes on automatic presses is similar. The dimensions of the hypodermic needles to choose are determined on the one hand by the sodium space dimensions, on the other hand by the grain size of the powder used. When using aluminum oxide powders for the production injection needles made of steel, as used in medicine, with clearances of about 0.1 mm and 0.01 mm has proven itself, since these powders have grain sizes of 1 1um and less.

In the illustration of FIG. 1, there is an injection needle on the right-hand side shown in filling position. In the representation of Figure 1 and Figure 2 are the Matrix spaces into which the suspension is injected are denoted by 1. In the Representation of FIG. 1, this die space is annular, in the representation of FIG FIG. 2, this die space is annular and conical. Inside this Marizen room, At the same time, forming its inner wall, there is steel part 2. The die space is limited to the outside by the rubber-elastic part 3.

The injection needle is denoted by 4. The core of the die 2 contains Bores and channels, which the die space delimiting surface 5 with a water drainage connect, in which a pump can be switched on. These holes and channels are denoted by 6.

The surface 5 is covered by a filter that is permeable to water, however, it is impermeable to the powder particles of the suspension.

After completion of the filling process is to the water drain} in the the channels and bores 6 open, a negative pressure is applied. This will make the water the suspension through the filter which rests against the surface 5; withdrawn. Afterward the upper punch 7, which carries the rubber layer 8 on its underside, is from above moves onto the press cavity and closes it. The compression takes place by that located in the cavity 9 of the rubber-elastic outer part 5 of the die hydrostatic fluid, e.g. B. water, with known methods is pressurized.

The closing force with which the upper punch 7 is applied to the die rests, chosen so that the die space during the entire compression process remains closed.

The two just described processes of dehydration from the Suspension and compaction of the powder can also be combined in one operation will. For this purpose, the upper punch is used after the suspension has been injected into the die space 7 with its rubber-elastic pad 8 placed on the die and the necessary Closing force generated. Then the hydrostatic liquid located in the space 9 becomes pressurized, causing the water from the suspension to pass through the filter is expressed.

It has been shown that this way of expressing the zßcup without that a negative pressure needs to be applied to the bores and channels 6, by all means sufficient.

After the rupture process has ended, the hydrostatic fluid becomes depressurized again in room 9. For removing the compact from the die space the upper punch 7 is first lifted from the die. With simply cylindrical Shape of the shaped body, as it corresponds to the arrangement of Figure 1, can Molded body after the pressure fluid located in space 9 has been relieved by the Ejector 10 can be lifted out of the die.

A major advantage of the shaping process according to the invention is that not only cylindrical parts are produced can, but also parts of a conical shape or tubes that have a Wear sleeve.

As an example of the manufacture of such intricately shaped parts According to the invention, a part of a conical shape is explained with reference to FIG. the injection of the suspension into the cavity of the die 1 through the injection needle 4 takes place as described above5 only it should be noted that for the production of a uniform filling the injection needle 4 parallel to the line of fall of the die cavity forming cone is performed.

The removal of the suspension liquid and the compression of the Powder is carried out according to the procedure described above. To remove the Molded body from the press cavity after lifting the upper punch 7 is, however, before the outward movement of the part 10, the hydrostatic liquid located in the space 9 placed under a slight negative pressure. This becomes the die space 1 after externally delimiting area made of rubber-elastic material, which belongs to part 5, moved outwards. It is straightforward by suitably dimensioning the negative pressure possible to deform the part 5 so far outward that the ejector 10 the molded body can lift out of the die cavity> without hitting the part 3. To this In this way it is possible to remove even non-cylindrical parts from the press undamaged.

The filter lying against the surface 5 is expediently made made of paper, plastic or non-woven material. It is particularly cheap to use this filter before Injection of the suspension each time.

This can be done fully automatically immediately after a compact has been ejected done by a device. By choosing a suitable filter material it can always be achieved that this filter after the compaction of the powder Moving the molded body out of the die space remains adhering to the molded body. line separation problems that may otherwise arise between the molding and the die wall be avoided in this way.

As thin-walled parts in the context of this invention are parts with a Wall thickness that is less than half the height of the parts.

For parts that have different heights within the same part the highest occurring height must be taken as a basis. For parts that are different Have wall thickness, the smallest wall thickness that occurs is for this definition use.

Claims (2)

Expectations 1) kerfahren for the production of thin-walled moldings from powdery non-plastic raw materials, characterized in that the powder is a suspension (Slurry) is injected into a die space> the suspension liquid discharged through a boundary wall of the die space and a filter layer is the compression of the powder to form a molded body by means of hydrostatic pressure takes place on another boundary wall of a die space and the molded body is moved out of the die space after the hydrostatic pressure has been reduced. 2) Method according to claim 1, characterized in that the below die wall moved by hydrostatic pressure after the powder has been compacted into one Molding by creating a negative pressure in the hydrostatic fluid like this is far removed from the molding that it can be moved out of the die space can. )) Method according to one of claims 1 or 2, characterized in that that the filter layer is inserted before the injection of the suspension and when removing it of the molding from the die space remains on the molding. L e r s e i t e