HOLLOW CYLINDER OF CERAMIC MATERIAL, A METHOD FOR THE PRODUCTION THEREOF AND USE THEREOF

Abstract

A method for producing a round tube from a ceramic material or a glass-ceramic material or mixtures thereof is described. The method comprises introducing a silicate-ceramic, oxide-ceramic and/or non-oxide-ceramic material-forming agent into a melting vessel, which has along a longitudinal axis a tubular wall which defines a tubular cavity, wherein the melting vessel rotates about its longitudinal axis. A uniform layer of the ceramic and/or glass-ceramic material-forming agents is thereby formed, lying on the inner side of the wall, by means of centrifugal forces generated by rotation and is heated by means of a heat source arranged in the inner cavity of the melting vessel until at least the inner side of the layer of material-forming agents has melted. Such tubes can be used for various industrial purposes.

Claims

1.-11. (canceled)

12. A method for manufacturing a hollow cylinder from a ceramic material or a glass-ceramic material or mixtures thereof, comprising: introducing at least one of a silicate-ceramic, oxide-ceramic, and non-oxide-ceramic base material having a grain size of 0.5 m to 2 mm into a melting crucible which has a tube-shaped wall that defines a tube-shaped hollow space; rotating the melting crucible around its central longitudinal axis, to cause a uniform layer of the base material to form on the tube-shaped wall due to rotation-generated centrifugal forces, the uniform layer forming a hollow cylinder having an interior face and an exterior face, the exterior face being adjacent the tube-shaped wall of the crucible, and the interior face defining an interior hollow space; superheating the base material by a heat source located an the interior hollow space, until at least the interior face of the hollow cylinder is fused, but the exterior face is not fused; and cooling the fused interior face of the hollow cylinder at a cooling rate greater than 5 K/min.

13. The method of claim 12 wherein the base material is selected from the group of ceramic materials consisting of Al.sub.2O.sub.3, ZrO.sub.2, ZrSiO.sub.4, BaO, SiC, SiN, BN, BeO, TiO.sub.2, barium titanate, aluminum titanate, MgO, SiO.sub.2, CaO, and mixtures thereof.

14. The method of claim 12 wherein the base material is selected from the group of ceramic materials consisting of AZS materials from the ternary system Al.sub.2O.sub.3ZrO.sub.2SiO.sub.2.

15. The method of claim 12 wherein the base material has a grain size of 1 m to 1 mm.

16. The method of claim 12 wherein the base material is comprised of 5-28 wt. % SiO.sub.2, 34.5-72 wt. % Al.sub.2O.sub.3, and 5-50.7 wt. % ZrO.sub.2.

17. The method of claim 12 wherein the heat source is a resistance heater or an electric arc located in the interior hollow space of the hollow cylinder.

18. A hollow cylinder made by introducing at least one of a silicate-ceramic, oxide-ceramic, and non-oxide-ceramic base material having a grain size of 0.5 m to 2 mm into a melting crucible which has a tube-shaped wall that defines a tube-shaped hollow space; rotating the melting crucible around its central longitudinal axis, to cause a uniform layer of the base material to form on the tube-shaped wall due to rotation-generated centrifugal forces, the uniform layer forming a hollow cylinder having an interior face and an exterior face, the exterior face being adjacent the tube-shaped wall of the crucible, and the interior face defining an interior hollow space; superheating the base material by a heat source located in the interior hollow space, until at least the interior face of the hollow cylinder is fused, but the exterior face is not fused; and cooling the fused interior face of the hollow cylinder at a cooling rate greater than 5 K/min.

19. A hollow cylinder having an interior face and an exterior face, the interior face defining an interior hollow space, the hollow cylinder comprised of at least one of a silicate-ceramic, oxide-ceramic, and non-oxide-ceramic base material having a grain size of 0.5 m to 2 mm, the interior face of the hollow cylinder being fused, but the exterior face is not fused.

20. The hollow cylinder of claim 19, wherein the base material is selected from the group of ceramic materials consisting of Al.sub.2O.sub.3, ZrO.sub.2, ZrSiO.sub.4, BaO, SiC, SiN, BN, BeO, TiO.sub.2, barium titanate, aluminum titanate, MgO, SiO.sub.2, CaO, and mixtures thereof.

21. The hollow cylinder of claim 19 wherein the base material is selected from the group of ceramic materials consisting of AZS materials from the ternary system Al.sub.20.sub.3ZrO.sub.2SiO.sub.2.

22. The hollow cylinder of claim 19 wherein the base material has a grain size of 1 m to 1 mm.

23. The hollow cylinder of claim 19 wherein the base material is comprised of 5-28 wt. % SiO.sub.2, 34.5-72 wt. % Al.sub.2O.sub.3, and 5-50.7 wt. % ZrO.sub.2.

24. The hollow cylinder of claim 19 wherein the interior face and the exterior face of the hollow cylinder define a wall thickness, the wall thickness having a density that is at least 99% of a theoretical density of compact material on the interior face and at most 95% of the theoretical density on the exterior face, and wherein density from the interior face to the exterior face changes in stages or as a gradient.

25. The hollow cylinder of claim 19 wherein the hollow cylinder contains one of corrosion aggressive gasses at temperatures above 1100 C., cement, melted glass, molten metal pyrolyzing materials at a temperature above 1450 C., oxidizing atmosphere, halogen-containing atmosphere and flue gases.

26. The hollow cylinder of claim 19, also comprising a glass manufacturing apparatus the hollow cylinder serving as at least one of a feeder element and an outflow pipe in the glass manufacturing apparatus.

27. The hollow cylinder of claim 19 also comprising a glass furnace in which the hollow cylinder is a component.

28. The hollow cylinder of claim 19 also comprising a rotary furnace in which the hollow cylinder is a component.

Description

[0037] The invention is explained in more detail in the following examples.

[0038] FIG. 1 shows one arrangement for executing the method for producing tubes according to the invention. Here a furnace-shaped melting crucible (2) is located in a turning machine (1) so that it rotates. The ceramic-producing material is introduced into the hollow space inside the melting crucible (2) using filling equipment (4) and a filling lance (6) and is distributed uniformly over the inner wall of the melting crucible (2) by means of rotation, as shown schematically (3). After a heat source is switched on (ignition of an electric arc in this case), the material adhering to the wall due to centrifugal force is fused from the inside out. The fusing process is complete when the heat flow passing through the cooling water reaches a stationary value and no longer changes. Because at that point a status is achieved in which the inside of the tube is completely fused, the part following it is baked solid through a ceramic sintering process, and the part located outside on the wall of the melting crucible is still granular, the finished tube can be removed after cooling with no further processing required.

[0039] The ignition lances (7) are equipped with graphite electrodes on the lance tips that are pulled apart from each other after the electric arc is ignited and then form the electrodes on the furnace crucible ends between which the electric arc operates. The filling lance (6) is an ignition lance (7) with no graphite electrode on the tip. Here there is a defined opening for it, through which the raw material powder is distributed evenly over the length of the furnace space. The filling lance (6) is moved in the furnace crucible in the same manner and form as the ignition lances (7) and is replaced by the ignition lances (7) for the purpose of ignition.

[0040] FIG. 2 shows a typical spread of the crystalline grain size distribution on the finished tube as a function of wall thickness. It shows that the crystal grain size increases from the inside outward and then drops significantly back down in the sintering area. The relationship between density and porosity of the tube wall is shown in FIGS. 3a and 3b. In them, a high density in the melting area shows low porosity and a low density in the sintering area shows high porosity. Because of the high density and low porosity, the insides of tubes according to the invention exhibit high gas-tightness.

LIST OF REFERENCE INDICATORS

[0041] 1 Glass rotating machine [0042] 2 Furnace crucible [0043] 3 Material packing in the furnace crucible [0044] 4 Filling equipment [0045] 5 Cooling water equipment [0046] 6 Movable filling lances [0047] 7 Movable ignition lances with electrodes