DE102005060304B4 - Process for the production of molded articles from non-silicate technical ceramics - Google Patents

Abstract

...A method of producing non-silicate engineering ceramic moldings wherein an aqueous slurry of silicon carbide, colloidal carbon, adjuvants and a liquid medium is formed, the slurry being poured into a mold to form a blank and the blank in contact with liquid after demolding and drying or gaseous silicon is heated and for the slurry powdery silicon carbide with a virtually continuous particle size distribution with a maximum particle size of about 250 microns and silicon carbide in an amount of at least 70 wt .-%, colloidal carbon in a proportion of 5 to 15 wt .-% and water is used in a proportion of less than 25 wt .-%, wherein the silicon carbide distributed on grain bands of a particle size distribution as follows: <5 μm: 15 vol.% ± 10 vol.%, 5 to 10 μm: 15 vol.% ± 5 vol.%, 10 to 20 μm: 15 vol.% ± 5 vol.%, 20 to 40 μm: 15 vol.% ± 5 vol.%, 40 to 65 μm: 10 vol.% ± 5 vol.%, 65 to 100 ...

Description

The The invention relates to a method for producing non-silicate Technical ceramics according to the preamble of claim 1.

in the Field of silicate ceramics, especially sanitary ceramics, is the Schlickerdruckguß meanwhile a manufacturing process, especially in mass production proven Has. A corresponding development regarding technical ceramics there is not any. Like H. Rump in Ber. DKG 71 (1994) no. 11-12 / 94 reported can be for the unpressurised casting in slips suitable slip by die casting not without process more, because in die casting the blank at the removal from the mold due to the process, wetter and therefore less stable than in non-pressurized casting, except that at the synthetic, inelastic raw materials for the oxidic and non-oxidic technical ceramics auxiliaries are added to the processing properties to recapture traditional ceramics. In addition, the detachment of the Blanks from the mold a problem. For this purpose, H. Rump provided the detachment of the cullet by respective application of microcellulose facilitate. It is essential, however, above all, that the achievable density, the crucial for the oxidation resistance of silicon carbide is lower than that of the non-pressure cast Is comparative patterns. Here also no bimodal grain distribution helps farther apart fine and coarse grain fractions, this leads rather too unfavorable Processing properties.

Out Wolfgang Kollenberg, Technical Ceramics, Vulkan-Verlag Essen, 2004, Page 393 is known to be in the field of technical ceramics reinforced for about 15 years Efforts are recognizable in the die casting technology in the Use oxide and non-oxide ceramics sensibly. A diverse number on R & D projects employee or busy with this objective. The firmness of the greenlings is after die casting usually too low and led to the Handling to difficulties. Quality-reducing is also the Effect of rinsing the fine and finest grain fraction during the stripping process of the formed cullet from the mold wall. To these phenomena it was necessary to add selected organic additives. A gapless Particle size distribution elevated Although advantageous the density and improves the capillary action Use of plaster molds. The filtration in connection with die casting is However, this negatively influenced and therefore the addition of regarded as necessary for suitable additive strengthening agents.

Out US Pat. No. 3,725,015 It is known to produce flat, refractory plates by dry pressing ceramic borocarbon-based powders. For curved objects, however, uniaxial dry pressing is unsuitable because of the problem of evenly filling curved molds with the ceramic powder.

Out US 3 442 994 A It is known, when using oxidic materials which soften at high temperatures, to press flat plate blanks, which then form during the ceramic firing of a curved kiln furniture.

Out US Pat. No. 6,609,452 B1 For example, reaction-bonded silicon carbide ballistic reinforcements are known, which are elaborately made by pressure casting in plaster molds or vibratory casting in combination with slip hardening by freezing.

Out DE 42 43 864 C2 a process for the production of moldings of silicon carbide is known, in which a slip with a virtually continuous particle size distribution is poured without pressure in plaster molds as hollow or solid cast.

task The invention is a method for producing moldings Non - silicate technical ceramics according to the generic term of the To claim 1, the die casting with a hassle-free Removal of the blanks and the achievement of densities as in the unpressurized to water in plaster molds.

This object is achieved according to the features of claim 1. Surprisingly, it has been found that a slurry of powdered silicon carbide having a virtually continuous particle size distribution with a maximum particle size of about 250 microns, preferably 150 microns, and silicon carbide in a proportion of at least 70 wt .-%, colloidal carbon in a proportion of 5 to 15 wt .-% and water in a proportion of less than 25 wt .-%, wherein the silicon carbide distributed on grain bands of a particle size distribution as follows: <5 μm: 15 vol.% ± 10 vol.%, 5 to 10 μm: 15 vol.% ± 5 vol.%, 10 to 20 μm: 15 vol.% ± 5 vol.%, 20 to 40 μm: 15 vol.% ± 5 vol.%, 40 to 65 μm: 10 vol.% ± 5 vol.%, 65 to 100 μm: 10 vol.% ± 5 vol.%, > 100 μm: 20 vol.% ± 15 vol.%, suitable to be processed by die casting, without the problems previously encountered in die casting arise in terms of mold releasability and the achievement of a density as in non-pressure casting. This results in the desired by the die casting benefits in terms of mass production capability and precision in the production of complex components, such as in relation to required tight wall thickness tolerances.

Except moldings Die-cast, silicon-infiltrated silicon carbide also can moldings boron carbide containing reaction bonded silicon carbide thereby be prepared that in the slip the SiC fractions> 40 microns at least partially replaced by appropriate Borcarbidkörnungen.

In Shape of curved Slabs are particularly suitable due to the boron carbide-containing material its mechanical properties and low density for making ceramic inserts in bulletproof vests.

Conveniently, is the maximum grain size of the silicon carbide or the boron carbide 150 microns.

colloidal Carbon is preferably used in a proportion of 8 to 12 wt .-% and with a particle size <3 microns. The slip can as auxiliaries 0.1 to 1.0% by weight of plasticizer and 0.3 to 1.5% by weight Binder be added. As a binder, a polysaccharide can be added become.

The slurry is expediently adjusted to a pH of> 8 and a weight per liter above 2000 g and a blank having a density of> 2.0 g / cm ^{3 is} produced. Silicon carbide and optionally boron carbide can be used with a progressively increasing distribution density in the selected grain size spectrum. Silicon carbide and, if appropriate, boron carbide are expediently used with a distribution density determined according to Litzow in the selected particle size spectrum.

silicon carbide can be in grain size range from 0.1 to 30 μm with a proportion of 45 to 65 vol .-%, in the particle size range of 30 to 100 microns with a Proportion of 20 to 35 vol .-% and in the particle size range above 100 microns with a share of 15 to 30 vol .-% can be used, optionally with silicon carbide with a grain size> 40 microns by boron carbide is replaced. Here, silicon carbide in the particle size range of 0.1 to 30 μm with a proportion of 46 to 56% by volume, in the particle size range from 30 to 100 μm, with one fraction from 22 to 30 vol .-% and in the particle size range over 100 microns with a share of 18 to 25 vol .-% is used, optionally with silicon carbide a grain size> 40 microns by boron carbide is replaced.

The smallest grain size can at 0.1 μm are at least 0.2 microns are preferred. In modification of the described, seamless Particle size distribution for silicon and optionally boron carbide, the particle size distribution may also be optional small gaps but then less than a tenth of the gaps adjacent Grain sizes are, So that the Particle size distribution thereby still practically complete remains.

silicon carbide and optionally boron carbide also by carbon up to 15% by volume and / or hard materials (nitrides, Boride, silicides) up to 8 vol .-% in each case based on the shaped body, partially be replaced, the proportion of carbon and / or hard materials a grain size spectrum corresponding to that of the silicon or boron carbide or in each case replaced certain grain fractions thereof.

Example 1:

From 10% by weight of colloidal carbon having a particle size <3 μm and silicon carbide abrasive grains F1200 (1-7 μm): 10% by weight, F800 (2-14 μm): 18% by weight, F400 (8-32 μm ): 23 wt%, F280 (22-59 μm): 9 wt%, and F100 (75-212 μm): 30 wt% was an aqueous dispersed slurry rode.

The mixture of the SiC fractions results in a silicon carbide grain mixture having the following particle size distribution: <5 μm: 14.0 vol.%, 5 to 10 μm: 17.5 vol.%, 10 to 20 μm: 20.0 vol.%, 20 to 40 μm: 11.0 vol.%, 40 to 65 μm: 5.5 vol.%, 65 to 100 μm: 11.5% by volume > 100 μm: 20.5% by volume

On 100 parts by weight of solid were 21 parts by weight of water and each 1 part by weight of organic wetting and binding agents added. The slip became a curved plate at a slip pressure of 40 bar with the dimensions 295 mm × 245 mm × 10 mm pressed. The die casting machine is one for the manufacture of sanitary ware common. It is also the case for the mold used material, a porous polymethacrylate, to a such as die-casting of sanitary ware is used.

The die-cast plate settled demold easily. After drying and for the production of reaction-bonded SiC usual Silicon infiltration thus became a SiSiC insert for a bulletproof vest receive.

Example 2:

From 7% by weight of colloidal carbon having a particle size <3 μm, silicon carbide abrasive grains F1200 (1-7 μm): 13% by weight, F800 (2-14 μm): 18% by weight, F400 (8-32 μm ): 23 wt% and boron carbide abrasive grains F240 (28-70 μm): 9 wt% and F100 (75-212 μm): 30 wt% was prepared into an aqueous dispersed slurry. The mixture of the SiC / B ₄ C fractions results in a grain mixture of the carbides with the following particle size distribution: <5 μm: 14.5 vol.%, 5 to 10 μm: 15.5 vol.%, 10 to 20 μm: 17.5 vol.%, 20 to 40 μm: 6.5% by volume, 40 to 65 μm: 10.0 vol.%, 65 to 100 μm: 13.0% by volume > 100 μm: 23.0% by volume

On 100 parts by weight of solid were 23 parts by weight of water and each 1 part by weight of organic wetting and binding agents added. All Further steps were carried out as in Example 1. The result was a ceramic insert of a boron carbide silicon carbide silicon ceramic.

Claims (11)

A method of producing non-silicate engineering ceramic moldings wherein an aqueous slurry of silicon carbide, colloidal carbon, adjuvants and a liquid medium is formed, the slurry being poured into a mold to form a blank and the blank in contact with liquid after demolding and drying or gaseous silicon is heated and for the slurry powdery silicon carbide with a virtually continuous particle size distribution with a maximum particle size of about 250 microns and silicon carbide in an amount of at least 70 wt .-%, colloidal carbon in a proportion of 5 to 15 wt .-% and water is used in a proportion of less than 25 wt .-%, wherein the silicon carbide distributed on grain bands of a particle size distribution as follows: <5 μm: 15 vol.% ± 10 vol.%, 5 to 10 μm: 15 vol.% ± 5 vol.%, 10 to 20 μm: 15 vol.% ± 5 vol.%, 20 to 40 μm: 15 vol.% ± 5 vol.%, 40 to 65 μm: 10 vol.% ± 5 vol.%, 65 to 100 μm: 10 vol.% ± 5 vol.%, > 100 μm: 20 vol.% ± 15 vol.%, characterized in that the slurry for forming the blank is poured into a die and pressed at a slip pressure, wherein a porous polymethacrylate is used as the material for the mold. Method according to claim 1, characterized in that that the maximum grain size of the silicon carbide 150 microns. Method according to claim 1 or 2, characterized that the SiC fractions> 40 microns at least partially replaced by corresponding Borcarbidkörnungen. Method according to one of claims 1 to 3, characterized that colloidal carbon in a proportion of 5 to 10 wt.% and used with a particle size <3 microns becomes. Method according to one of claims 1 to 4, characterized 0.1 to 1.0 wt .-% liquefier and 0.5 to 1.5 wt .-% binder can be added. Method according to claim 5, characterized in that that a polysaccharide is added as a binder. Method according to one of claims 1 to 6, characterized in that the slurry is adjusted to a ph value> 8 and a liter weight above 2000 g and a blank having a density> 2.0 g / cm ^{3 is} produced. Method according to one of claims 1 to 7, characterized that silicon carbide in the particle size range from 0.1 to 30 μm with a proportion of 45 to 65 vol .-%, in the particle size range of 30 to 100 microns with a Proportion of 20 to 35 vol .-% and in the particle size range above 100 microns with a share of 15 to 30 vol .-% is used, optionally with silicon carbide a grain size> 40 microns by Borcabid is replaced. Method according to claim 8, characterized in that that silicon carbide in the particle size range from 0.1 to 30 μm with a proportion of 46 to 56 vol .-%, in the particle size range of 30 to 100 microns with a Proportion of 22 to 30% by volume and in the particle size range above 100 μm with a proportion of 18 to 25 vol .-% is used, optionally with silicon carbide a grain size> 40 microns by boron carbide is replaced. Method according to one of claims 1 to 9, characterized that the silicon carbide and optionally boron carbide by carbon up to 15% by volume and / or hard materials up to 8% by volume, in each case obtained on the molding, partially replaced, the proportion of carbon and / or Hard materials a grain size spectrum corresponding to that of the silicon or boron carbide or in each case replaced certain grain fractions of the silicon or boron carbide. Method according to one of claims 1 to 10, characterized that ballistic reinforcements, especially inserts for bulletproof West, are made.