METHOD FOR PRUDUCING A CERAMIC MOULDED BODY

Abstract

The invention relates to a method for producing a ceramic moulded body, comprising the following steps: a) producing a green body containing ceramic material, binding agents and an organic pore forming agent; b) heating the green body to a temperature equal to or higher than the sublimation temperature of the pore forming agent; c) burning the green body to form a ceramic moulded body. According to the invention that the organic pore forming agent is selected from the group consisting of dicarboxylic acids and mixtures of dicarboxylic acids, the sublimation temperature being at least 80 k lower than the decomposition temperature.

Claims

1. A method for producing a ceramic molding comprising the steps of: a) producing a green body comprising ceramic material, binders and an organic pore former; b) heating the green body to a temperature equal to or above the sublimation temperature of the pore former; c) firing the green body to form a ceramic molding; characterized in that the organic pore former is selected from the group consisting of dicarboxylic acids, of which the sublimation temperature is at least 80 K below the decomposition temperature.

2. The method as claimed in claim 1, characterized in that the sublimation temperature is from 160 to 240 C., preferably 180 to 220 C.

3. The method as claimed in claim 2, characterized in that the pore former is fumaric acid.

4. The method as claimed in any of claims 1 to 3, characterized in that the proportion of pore former of the total weight of the green body in step a) of claim 1 is between 2 and 60% by weight, preferably 2 and 50% by weight, more preferably 10 and 50% by weight, more preferably 10 and 30% by weight, more preferably 15 and 20% by weight.

5. The method as claimed in any of claims 1 to 4, characterized in that the heating in step b) of claim 1 is conducted at a heating rate of 2 to 80 C./h, preferably 20 to 60 C./h.

6. The method as claimed in any of claims 1 to 5, characterized in that, prior to the heating in step b) of claim 1, additionally heating to a temperature below the sublimation temperature of the pore former, preferably 30 to 50 C., is carried out and the green body is maintained at this temperature preferably for 4 to 48 h.

7. The method as claimed in any of claims 1 to 6, characterized in that the ceramic molding is a tool composed of bonded abrasive.

8. The method as claimed in any of claims 1 to 7, characterized in that in addition a temporary binder is used during the production of the green body.

9. The method as claimed in claim 8, characterized in that the binder comprises polyglycols.

10. The method as claimed in claim 9, characterized in that the polyglycols are polyethylene glycols having a molar mass from 100 to 20 000, more preferably 200 to 10 000, more preferably 250 to 8000.

11. The method as claimed in claim 9 or 10, characterized in that the binder additionally comprises reactants able to esterify the polyglycols.

12. The method as claimed in claim 11, characterized in that the pore former is additionally used as reactant.

13. The method as claimed in claim 12, characterized in that the pore former is used as a solid in at least two different particle size fractions.

14. The method as claimed in claim 13, characterized in that the finer particle size fraction has a particle size from 1-100 m, preferably 1-30 m and more preferably 1-20 m.

Description

EXAMPLE 1

[0062] 2 identical abrasive bodies of dimensions 30020127 were produced from the following formulations.

[0063] Formulation 1 is a comparative example and formulation 2 is inventive. The ceramic binder used in this and all further examples is a mixture of 50% by weight frit 90158 (Ferro), 25 percent by weight clay and 25% by weight petalite.

TABLE-US-00001 1. Sintered corundum F100 20.8% Special fused alumina F100 62.5% Ceramic binder 16.7% Naphthalene 13.0% (powder ca. 200 m particle size) Dextrin powder 2.0% Water 2.8% Density after firing: 1.78 g/cm.sup.3 Modulus of elasticity: 29.0 GPa 2. Sintered corundum F100 20.8% Special fused alumina F100 62.5% Ceramic binder 16.7% Fumaric acid 16.1% (powder ca. 200 m particle size) PEG 300 3.0% PEG 6000 1.0% Density after firing: 1.77 g/cm.sup.3 Modulus of elasticity: 29.0 GPa

[0064] The abrasive body composition according to formulation 1 with naphthalene as pore former was compressed and subsequently dried at 80 C. in a drying oven equipped with thermal afterburning system and the naphthalene was debinded. The abrasive bodies were then fired at a maximum temperature of 950 C. in a ceramic kiln (Energo oven).

[0065] The abrasive body composition according to formulation 2 with fumaric acid as pore former was compressed and subsequently hardened/esterified at a maximum temperature of 165 C. for 24 h in a hardening oven (Reinhardt oven). The following hardness curve was applied.

[0066] The abrasive bodies were subsequently fired at a maximum temperature of 950 C. in a ceramic kiln (Energo oven). In the heating phase, the heating rate was ca. 30-50 C./h. In the heating phase the fumaric acid was debinded.

[0067] The abrasive bodies produced with the fumaric acid and naphthalene pore formers were compared by sanding on a grinding test stand (Blohm flat grinding machine). The grinding force (diagram 2), the G ratio (diagram 3), and the roughness (diagram 4) were measured in each case relative to the machined workpiece volumes.

[0068] The grinding forces caused by these abrasive bodies are almost identical.

[0069] The G ratio of the abrasive body produced with fumaric acid is somewhat greater and the grinding force somewhat lower.

[0070] The roughness of the abrasive body is also to be assessed as about the same.

[0071] Overall, it can be shown that the grinding performance of both abrasive bodies can be rated as equivalent.

EXAMPLE 2

[0072] Production of a highly porous test specimen (diameter 202, height 100 mm).

Formulation

[0073]

TABLE-US-00002 Special fused alumina F80 88.6% Ceramic binding 11.4% PEG 300 4.0% PEG 6000 3.0% Fumaric acid 40.0% (Granules 500-800 m) Density after firing: 1.39 g/cm.sup.3

[0074] The formulation components were homogeneously mixed and subsequently compressed. The disk was then debinded in a drying oven equipped with thermal afterburning system. The debinding curve included the heating at 50 C./h up to 200 C., maintaining the maximum temperature of 200 C. over 48 h and the natural cooling of the oven to room temperature. The strength was then fully sufficient to assemble the disk on the kiln car for ceramic firing. The abrasive bodies were then fired at a maximum temperature of 950 C. in a ceramic kiln (Energo oven).