REFRACTORY CONTAINER MADE OF A CERAMIC MATERIAL, GREEN BODY FOR SUCH A CONTAINER, AND METHOD FOR THE MANUFACTURE OF A REFRACTORY CONTAINER MADE OF A CERAMIC MATERIAL AND OF A GREEN BODY PROVIDED FOR THIS PURPOSE

Abstract

The invention relates to a refractory container 1 for use in a furnace for heat treatment of workpieces, comprising a mat 5 of long fibers that are embedded in a ceramic shell, with the mat 5 being shaped into a container that forms a receiving space for workpieces, and to a green body of such a container 1. Furthermore, advantageous uses of the container 1 as well as a method for manufacturing a green body or container 1 according to the invention are specified.

Claims

1. A refractory container (1) for use in a furnace for heat treatment of workpieces, comprising a mat (5) of long fibers that are embedded in a ceramic shell, with the mat (5) being shaped into a container forming a receiving space for workpieces, characterized in that the mat (5) forms support structures and retaining structures, with the support structures having at least 50% greater flexural strength than the retaining structures.

2. The container (1) as set forth in claim 1, characterized in that the container (1) forms a plurality of openings (7) through which fluid can pass.

3. The container (1) as set forth in claim 1, characterized in that the support structures form a grid with a first mesh size and the retaining structures form a grid with a second mesh size, with the first and the second mesh sizes being different from one another.

4. The container (1) as set forth in claim 3, characterized in that the first mesh size is at least twice as large as the second mesh size, preferably at least three times as large, and especially preferably at least four times as large.

5. The container (1) as set forth in claim 1, characterized in that a first number of long fibers are embedded in the cross section of the support structures, and a second number of long fibers are embedded in the cross section of the retaining structures, with the first number being at least 50% greater, preferably at least 75% greater, particularly at least 100% greater than the second number.

6. The container (1) as set forth in claim 1, characterized in that a first type of long fiber is embedded in the cross section of the support structures, and a second type of long fiber is embedded in the cross section of the retaining structures, with the tensile strength of the first type of long fiber being at least 20% greater, preferably at least 30% greater, particularly at least 40% greater than the tensile strength of the second type.

7. The container (1) as set forth in claim 1, characterized in that a first type of long fiber is embedded in the cross section of the support structures, and a second type of long fiber is embedded in the cross section of the retaining structures, with the fiber weight of the first type of fiber being greater than the fiber weight of the second type of fiber, preferred the fiber weight of the first type of fiber is at least twice as great, more preferred at least three times as great, and especially preferred at least four times as great as the fiber weight of the second type of fiber.

8. The container (1) as set forth in claim 1, characterized in that the shell of the long fibers embedded in the support structures has different mechanical properties than the shell of the long fibers embedded in the retaining structures.

9. The container (1) as set forth in claim 1, characterized in that the mat (5) forms at least one kink-free surface, with the support structures in this area extending in two crossed main directions A and A and the retaining structures in this area extending in two main directions B and B.

10. The container (1) as set forth in claim 9, characterized in that the main directions A and B as well as A and B coincide or are different.

11. The container (1) as set forth in claim 1, characterized in that the mat (5) is embodied as a scrim of long fibers.

12. The container (1) as set forth in claim 1, wherein the mat (5) forms an edge, characterized in that the container (1) forms a collar (6) that mechanically reinforces the edge.

13. The container (1) as set forth in claim 12, characterized in that the collar (6) comprises a plurality of long fibers that are embedded in a ceramic shell.

14. The container (1) as set forth in claim 13, characterized in that the fibers in the collar are oriented substantially along the edge of the mat (5).

15. The container (1) as set forth in claim 13, characterized in that the long fibers in the collar (7) form a scrim.

16. A green body (2) for a refractory container (1) as set forth in claim 1, comprising a mat (5) of long fibers that is infiltrated with a ceramic slurry.

17. A method for using a container (1) as set forth in claim 1, characterized in that the container (1) is used in a sintering furnace or in a hardening furnace.

18. The method as set forth in claim 17, characterized in that the container (1) receives one or more metallic workpieces.

19. A method for manufacturing a green body (2) comprising a mat (5) for forming a refractory container (1) for use in a furnace for heat treatment of workpieces, characterized in that the mat (5) forms precursors of support structures and precursors of retaining structures, with the method comprising the following steps: a. infiltration of long fibers with a slurry that is suitable for forming a ceramic shell, b. forming of a mat (5) from long fibers, with the mat (5) forming precursors of support structures and retaining structures, and with the precursors of the support structures differing from the precursors of the retaining structures in at least one of the following features: i. the long fibers forming the precursors of the support structures are infiltrated with a first slurry, and the long fibers forming the precursors of the retaining structures are infiltrated with a second slurry, with the first and second slurries being different from each other, ii. a first number of long fibers are embedded in the cross section of the precursors of the support structures, and a second number of long fibers are embedded in the cross section of the precursors of the retaining structures, with the first number being at least 50% greater, preferably at least 75% greater, particularly at least 100% greater than the second number, or iii. a first type of long fiber is embedded in the cross section of the precursors of the support structures, and a second type of long fiber is embedded in the cross section of the precursors of the retaining structures, with the tensile strength of the first type of long fiber being at least 20% greater, preferably at least 30% greater, particularly at least 40% greater than the tensile strength of the second type, c. shaping of the mat (5) of infiltrated long fibers into a container that forms a receiving space for workpieces, and d. drying of the shaped mat.

20. The method as set forth in claim 19, characterized in that the mat (5) is embodied as a scrim.

21. The method as set forth in claim 19, characterized in that the mat (5) shaped into a container forms a plurality of openings (7) through which fluid can pass.

22. The method as set forth in claim 19, characterized in that the precursors of the support structures form a grid with a first mesh size and the precursors of the retaining structures form a grid with a second mesh size, with the first and the second mesh sizes being different from one another.

23. The method as set forth in claim 19, characterized in that the precursors of the retaining structures are formed substantially completely in one method step, and the precursors of the support structures are formed substantially completely in a separate method step.

24. The method as set forth in claim 23, characterized in that a drying step is carried out between the method steps for forming the precursors of the support structures and the precursors of the retaining structures in which at least partial drying of the slurry takes place in the infiltrated precursor of the support or retaining structures that have already been produced.

25. The method as set forth in claim 19, characterized in that, in order to shape the mat (5) of infiltrated long fibers into a container forming a receiving space for workpieces, one of the following process steps is advantageously carried out: a. winding of the long fibers onto a yarn package, b. placement of a mat (5) of infiltrated long fibers onto a mold body.

26. The method as set forth in claim 25 step a, characterized in that the mat (5) formed on the yarn package is divided into at least two parts that preferably have substantially the same shape.

27. The method as set forth in claim 25 step a, characterized in that the yarn package is a cuboid that is rotated about one of its space diagonals during the winding of the long fibers.

28. The method as set forth in claim 25 step a, characterized in that the winding body is an ellipsoid that is rotated about its axis of symmetry during the winding of the long fibers.

29. The method as set forth in claim 25 step a, characterized in that the yarn package is rotated about more than one axis of rotation during the winding of the long fibers.

30. The method as set forth in claim 19, characterized in that the shaped mat (5) forms an edge and, in an additional method step, a collar (7) is integrally formed on the edge of the shaped mat (5).

31. The method as set forth in claim 30, characterized in that the collar (7) is integrally formed prior to the drying of the mat (5).

32. The method as set forth in claim 30, characterized in that the collar (7) is integrally formed on the mat (5) by winding a long fiber that is infiltrated with a slurry that is suitable for forming a ceramic shell multiple times around the shaped container along its edge.

33. The method as set forth in claim 30, characterized in that, in order to form the collar (7), the shaped mat (5) is rotated about at least one axis.

34. A method for manufacturing a refractory container (1) for use in a furnace for heat treatment of workpieces, comprising the following method steps: a. manufacturing of a green body (2) as set forth in the method of claim 18, and b. sintering of the green body (2).

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0125] It should be noted that the features of the specified developments and advantageous embodiments as well as of the appended claims can be freely combined within the scope of what is technically possible even if this is not explicitly stated in the text. This also applies particularly beyond the limits of the claim categories of device and method.

[0126] Additional advantages and features of the green body and container according to the invention, of the use thereof, and of the manufacturing method according to the invention follow from the following exemplary embodiments, which are explained in greater detail with reference to the drawing.

[0127] FIG. 1 shows a top view of an enlarged cutout of a mat that is embodied as a scrim for forming a green body according to the invention, and

[0128] FIG. 2 shows a perspective view of an inventive green body or container according to a first exemplary embodiment.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0129] For the exemplary embodiment of the method according to the invention, a slurry is prepared on the basis of a high-purity micronized aluminum oxide, with the proportion of Al.sub.2O.sub.3 with respect to the total weight of the micronized aluminum oxide being about 99.8% by weight. The proportion of -Al.sub.2O.sub.3 is at least 95%. The particle size distribution of the micronized aluminum oxide is monomodal and can be characterized by d10=0.1 to 0.4 micrometers, d50=0.5 to 0.8 micrometers, and d90=1.5 to 3 micrometers. The particle size distribution has a maximum between 0.1 and 0.4 micrometers.

[0130] The slurry is prepared from the aforementioned micronized aluminum oxide, water, and a carboxylic acid-based plasticizer, with the weight proportion of aluminum oxide in the slurry being about 80%. Furthermore, the carboxylic acid-based plasticizer is added in aqueous form in a weight proportion of about 2 to 3%. Water is added as the remaining component. All three components are intermixed thoroughly until a highly viscous suspension is obtained. Milling during mixing is not required.

[0131] A plurality of Nextel 610-type continuous multifilament fibers (3,000 denier, 10,000 denier, or 20,000 denier fiber weight) are unwound from supply packages by means of an unwinding device and assembled into a roving.

[0132] The roving obtained in this way is fed to a slurry bath, to which a sufficient quantity of the aforedescribed slurry is also fed at the same time. As the roving passes through the slurry bath, it is infiltrated, resulting in an intensive penetration of the roving with the slurry that lo also extends particularly to the region between the fibers of the roving consisting of a bundle of multifilament fibers. Additional deflections of the roving in the sludge bath over cylinders with a smooth surface ensure complete infiltration.

[0133] The infiltrated roving is then passed through a plurality of successive mechanical apertures. The minimum cross section of the apertures used is selected such that it is greater than the minimum cross section of the rovings that is obtained with an optimum volume ratio of the multifilament fibers.

[0134] After passing through the plurality of mechanical apertures, the infiltrated roving is fed to a CNC-controlled winding station, in which the infiltrated roving is automatically wound onto a cylindrical yarn package. By controlling the rotational movement, the angle between the axis of rotation of the yarn package and the direction of movement of the roving being supplied, and a translational movement of the yarn package on a plane perpendicular to the direction of movement of the roving, complex winding patterns can be produced on the surface of the yarn package by means of the CNC-controlled winding machine. In a first step, the infiltrated roving is wound onto the lateral surface of the yarn package in such a way that a first rectangular grid with a first mesh width is obtained that is in the range of approximately 2 to 15 millimeters, preferably 10 millimeters. The width of the webs 3 of the grid is in the range of 2 millimeters, and the cross section of the webs 3 is in the range of 4 square millimeters.

[0135] In a second step, the infiltrated roving is wound onto the lateral surface of the first grid formed on the lateral surface of the yarn package, resulting in a second rectangular grid with a second mesh size that is in the range of about 10 to 70 millimeters, preferably 40 millimeters. The width of the webs 4 of the grid is in the range of 5 millimeters, and the cross section of the webs is in the range of 20 square millimeters.

[0136] The infiltrated roving is wound onto the yarn package such that the first grid and the second grid are inclined relative to each other, meaning that the main directions A and B and A and B of the first and second grid are inclined toward one another.

[0137] The different widths and cross-sectional areas of the webs 3, 4 of the first and the second grid are determined by different numbers of rovings wound next to one another and over one another on the circumference of the cylinder.

[0138] The shape of the cross-sectional areas of the webs of both the first and the second grid is approximately rectangular.

[0139] The webs 3 of the first grid form the precursors of the retaining structures.

[0140] The webs 4 of the second grid form the precursors of the support structures.

[0141] FIG. 1 shows a top view of the position of the second grid on a mat 5 produced in this way. In the ready-to-use container 1, the retaining structures form a support for the workpieces to be received by the container 1, and the support structures lie on the side of the retaining structures facing away from the support.

[0142] If a scrim of sufficient strength is completed in which the precursor structures are formed as required, so that the scrim constitutes a mat in the sense of the present invention, then this is separated from the continuous roving and cut open along a line of intersection that runs parallel to the axis of symmetry of the yarn package, so that the infiltrated scrim that is wound onto the yarn package can be removed from same and placed on a flat surface for further processing, for example.

[0143] Due to its grid structure, the mat 5 made in this way from long fibers thus forms a plurality of openings 7 through which fluid can pass, as can be seen from FIG. 1.

[0144] The resulting mat 5, which can still be deformed within wide limits before it is (slightly) dried, is then placed on a mold body that represents a negative mold for the receiving space of the container to be formed. Such a mold body can be a cuboid with two square upper surfaces, for example, with the mat 5 being deposited on one of these upper surfaces. The still shapeable mat 5 is then molded on the four side surfaces of the cuboid.

[0145] Any supernatant of the still wet mat 5 is then removed.

[0146] Such a supernatant can be minimized by properly cutting the mat 5 removed from the surface of the yarn package before depositing it on the mold body.

[0147] In an additional method step, a collar 6 is formed on the edge of the shaped mat 5 while the shaped mat 5 is still on the mold body. This collar 6 is formed prior to the drying of the infiltrated shaped mat 5.

[0148] To do this, the long fiber already used to form the mat 5 and infiltrated with the same slurry is wound several times around the shaped mat 5 on the mold body along its edge, which mat 5 already forms a receiving space for one or more workpieces. The mold body with the shaped mat 5 on it is repeatedly rotated for this purpose about at least one axis perpendicular to the square upper surface of the mold body. A collar 6 is thus produced in the form of a multilayer scrim from the long fiber that is infiltrated with the slurry.

[0149] The mat 5 that is located on the mold body and has been provided in this way with a collar 6 on its edge then undergoes a drying step. The drying can be carried out in ambient conditions, but it can also be accelerated through the use of microwaves or infrared radiation, the supplying of heat, or through removal of atmospheric moisture from the ambient air.

[0150] If a green body 2 according to the invention formed three-dimensionally in this manner in the form of a tray for a container 1 according to the invention is sufficiently dried as to have sufficient mechanical stability, the resulting three-dimensionally shaped, inherently stable green body 2 can be fed to a suitable sintering device. This can be a chamber furnace, for example, in which the green body 2 is sintered at a temperature of about 1200 C. for about one hour.

[0151] The resulting container 1 is removed from the sintering device and, after sufficient coolingwhich, in turn, can be accelerated in a cooling stationcan be provided for its intended use, for example as a sintered basket for receiving a plurality of metallic sintered bodies that are to be thermally treated.

[0152] FIG. 2 shows such a container 1 shaped as a tray or the preceding green body 1, with supporting structures or retaining structures formed being indicated only schematically by their associated webs 3 and 4. The retaining structures form the support surface for the workpieces, whereas the support structures lie on the outer surfaces of the container.

[0153] In a second exemplary embodiment, after infiltration with the aforedescribed slurry, the continuous long fiber described above is wound onto a cuboid yarn package that is rotated about one of its space diagonals for this purpose. The infiltrated long fiber is guided such that the two grids are formed which are superimposed and inclined toward one another and have different mesh sizes and web widths/cross sections according to the first embodiment.

[0154] In the case of the variant of the method according to lit. a., the mat is already shaped during its manufacture such that it immediately has a shape in which itoptionally after a certain post-processing, especially when the green body in the dried stateforms a receiving space for workpieces.

[0155] In this variant of the method, the mat formed on the yarn package is divided after at least partial drying into two parts having substantially the same shape, so that two green bodies according to the invention are simultaneously obtained for two containers according to the invention which, in turn, can be shaped like a tray.

[0156] In a third exemplary embodiment, an ellipsoid is used as the yarn package in an otherwise identical variant of the method and is rotated about its axis of symmetry during the winding of the long fibers. After at least partial drying, the resulting mat is broken down into two identically shaped green bodies, preferably by means of a cut that is guided on a plane that is parallel to the axis of symmetry of the ellipsoid or on a plane along which the axis of symmetry of the ellipsoid extends. In this exemplary embodiment, two identically shaped cup-shaped green bodies or containers can be obtained.