Metering device for withdrawing and dispensing a melt and method for producing the metering device

Abstract

A metering device (10) for withdrawing and dispensing a melt consisting of or containing an oxide fibre reinforced oxide ceramic composite material.

Claims

1. A metering device for withdrawing and dispensing a melt, comprising: an oxide-fiber-reinforced oxide ceramic composite material comprising an oxide ceramic matrix, and having an open porosity of from 20% to 40%; wherein an inside surface and/or an outside surface of the metering device is coated with at least one coating, or is compacted; and a stopper configured to close an opening of the metering device, and comprising a material from the group SiC, or the material of the oxide ceramic matrix.

2. The device according to claim 1, wherein one or more coatings of a thickness d of 50 ?m?d?2 mm are disposed on the oxide-fiber-reinforced oxide ceramic composite material.

3. The device according to claim 1, wherein the oxide-fiber-reinforced oxide ceramic composite material comprises oxide ceramic fibers, formed from a member selected from the group consisting of Al.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, Y.sub.2O.sub.3, TiO.sub.2, Cao, MgO, Y.sub.2O.sub.3-stabilized ZrO.sub.2, and mixtures thereof, and/or the oxide-fiber-reinforced oxide ceramic composite material comprises an oxide ceramic matrix, formed from a member selected from the group consisting of Al.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, Y.sub.2O.sub.3, TiO.sub.2, Cao, MgO, Y.sub.2O.sub.3-stabilized ZrO.sub.2, and mixtures thereof.

4. The device according to claim 3, wherein the oxide ceramic matrix and the fibers consist of or comprise the same oxide ceramic material, or the main constituents of the oxide ceramic materials match.

5. The device according to claim 1, wherein the metal in the oxide-fiber-reinforced oxide ceramic composite material and the metal of the melt, or of a main constituent of the melt, is identical.

6. The device according to claim 1, wherein the open porosity of the device, or of the oxide-fiber-reinforced oxide ceramic composite material, is between 27% and 32%.

7. The device according to claim 3, wherein the density ? of the fibers is 2 g/cm.sup.3<?<6 g/cm.sup.3, and/or the fiber diameter is from 5 ?m to 20 ?m.

8. The device according to claim 1, further comprising a metallic structure inserted into the metering device; wherein the metallic structure has a rigid body and consists of the oxide-fiber-reinforced oxide ceramic composite material of the metering device.

9. The device according to claim 3, produced by winding the oxide ceramic fibers onto a die that replicates an internal geometry of the metering device, and/or by the use of textile mats, meshes, and fabrics from the oxide ceramic fibers.

10. The device according to claim 3, wherein the oxide ceramic fibers consist of endless fibers, or short fibers, or a combination thereof.

11. The device according to claim 1, wherein the device has a wall thickness W.sub.D of 1 mm?W.sub.D?20 mm, and/or the metering device comprises load-appropriate fiber reinforcements.

12. The device according to claim 1, further comprising flow aids provided on the inside surface of the metering device.

13. The device according to claim 1, wherein the stopper is hollow; and wherein a sensor is arranged inside the stopper.

14. The metering device according to claim 1, wherein the coating has a density of at least 95% of the theoretical density of the material of which the coating consists.

15. The metering device according to claim 3, wherein the density ? of the fibers is 3.0 g/cm.sup.3<?<4.0 g/cm.sup.3, and/or the fiber diameter is 10 ?m to 12 ?m.

16. The metering device according to claim 1, having a wall thickness W.sub.D of 1 mm?W.sub.D?3 mm, and/or the metering device has load-appropriate fiber reinforcements.

Description

(1) The drawing shows in:

(2) FIG. 1 an illustration of the principle of a metering device for withdrawing and dispensing a melt with separately drawn stopper,

(3) FIG. 2 a section from FIG. 1,

(4) FIG. 3 a variant of the illustration in FIG. 2 and

(5) FIG. 4 an illustration of the principle of a winding process.

(6) The figures show purely by way of example a metering device for withdrawing and dispensing a melt, in particular a metal melt, which is also referred to as a metering crucible or container 10 and in the following is called metering crucible for simplicity.

(7) The metering crucible 10 has on the withdrawing/dispensing side a mouth opening 14 closable using a stopper 12 and merging into a conical and then hollow-cylindrical section 16, 18.

(8) The external diameter of the stopper 12, more precisely in its distal section 20, matches the internal diameter of the spout or mouth opening 14. The mouth opening can accordingly be closed or freed by axial movement of the stopper 12.

(9) The metering crucible 10 consists of a fiber-reinforced oxide ceramic composite material of the previously described material(s).

(10) The porosity of the metering crucible 10 should be in the range of in particular between 27% and 32%.

(11) The stopper 12 can consist of an identical material to that of the metering crucible 10 or also for example of silicon carbide.

(12) If the stopper 12 is produced from an oxide ceramic composite material, it can thus be designed hollow and for example contain one or more sensors to check the process and where necessary control or regulate it.

(13) The metering crucible 10 is preferably produced by winding, although prepregs that can be laid onto a die replicating the internal geometry of the metering crucible 10, or a combination of these methods, can also be used.

(14) Fiber bundles, so-called rovings, are wound onto the winding core, where the individual fiber filaments should have diameters between 5 ?m and 20 ?m, in particular in the range between 10 ?m and 12 ?m. The density should be in the range between 2 g/cm.sup.3 and 6 g/cm.sup.3, preferably between 2.5 g/cm.sup.3 and 3.2 g/cm.sup.3.

(15) Before winding onto the winding core, the fiber bundles are passed through a slurry and thereby impregnated. The slurry contains the ceramic particles forming the matrix of the composite body.

(16) The proportion of ceramic particles can be 10% by volume to 50% by volume, in particular 20% by volume to 40% by volume, relative to the total volume of the slurry.

(17) In particular, a water-based slurry is used with preferably organic additives, for example polyols, polyvinyl alcohols or polyvinyl pyrrolidones, dispersion binders, preferably styrene acrylate dispersions.

(18) The slurry can contain at least 10% by wt. to 20% by wt., preferably at least 24% by wt., e.g. 21-35% by wt., of glycerin relative to the total weight of the ceramic particles.

(19) Both for the ceramic particles and for the fibers, a material in particular from the group Al.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, Y.sub.2O.sub.3, TiO.sub.2, CaO, MgO, Y.sub.2O.sub.3-stabilized ZrO.sub.2 is conceivable as the oxide ceramic.

(20) If an aluminum melt or an aluminum alloy melt is to be metered using the metering crucible 10, Al.sub.2O.sub.3 should be used as the material both for the matrix, i.e. accordingly the ceramic particles, and for the fibers.

(21) The slurry can contain if necessary additives such as ZrO.sub.2, where the proportion can be between 5% and 30%, in particular between 12% and 25% as a % by weight of the entire powder quantity of the ceramic metal oxide.

(22) The proportion by volume of the ceramic particles should be 20 to 50% by volume relative to the total volume of the slurry.

(23) The corresponding impregnated fiber bundles are now wound onto the winding core, then dried, in particular in the temperature range between 40? C. and 250? C., preferably in the range between 80? C. and 150? C. A body thus produced is divided and removed from the winding core. This is followed by sintering in the temperature range between 1000? C. and 1300? C., in particular between 1150? C. and 1250? C. If necessary reworking takes place and then use of the metering crucible 10 thus produced.

(24) The drying duration is temperature-dependent and is between 2 h and 48 h, preferably between 12 h and 24 h.

(25) Sintering is done over a temperature/time curve with various holding stages and durations, where the holding duration at the maximum temperature should be between 5 min and 24 h, preferably between 1 h and 12 h.

(26) Due to the winding technique used, the geometry of the metering crucible 10 can be varied to the required extent depending on the geometry of the winding core. This is illustrated in principle in FIGS. 2 and 3. There is thus the possibility of varying the opening angle of the conical section 16 to the required extent. In FIG. 2 the angle ?1 is smaller than the angle ?2 in FIG. 3. Furthermore, the length of the spout 14 can be varied, as is made clear by a comparison of FIGS. 2 and 3 in respect of the sections S1, S2. The length of the conical section 16 can also be varied (L1<L2).

(27) There is furthermore the possibility of varying the wall thickness of the component or of designing the end sections of the winding core such that flow aids are created inside the cones, as indicated purely in principle by FIG. 3.

(28) For example ribs can be formed, preferably in helical form. Wave structures can also be provided running concentrically about the longitudinal axis of the metering crucible, to affect to the required extent the flow behavior of the melt.

(29) In particular it is provided that the fiber volume content of the metering device is 35% to 50%, preferably 32% to 42%.

(30) The following must be set forth regarding the winding technique.

(31) Winding processes are used to produce rotation-symmetrical parts. The internal geometry of the object is predetermined by the so-called winding core on which the fibers impregnated with the matrix are laid.

(32) For the winding core, a distinction is made between reusable, lost, meltable and strippable cores. In the present case, the metering crucibles are removed from the core, such that the latter can be used again. For smaller components, meltable cores are frequently used, and strippable cores for components of larger diameter.

(33) Winding is usually performed with a winding machine matching a CNC lathe. The winding core is here clamped at one of its ends in a three-jaw chuck and at the other end mounted for example on a tailstock.

(34) To wind rovings, i.e. fiber bundles, which can for example comprise 100 or more individual fibers, so-called filaments, onto the winding core, they are unwound from a spool receptacle. Then the rovings can pass deflecting pulleys, by means of which the tension of the rovings is set. The fiber bundle is now passed through a thread eye over further deflecting pulleys and through a slurry bath of which the composition has been described above. After impregnation of the fibers, they are passed over one or more further deflecting pulleys, which likewise determine the thread tension and, by the number of revolutions, the winding speed and the length of the consumed fiber strand, centered by a thread eye, and laid on the winding core as it rotates. The thread tension also has a greater significance here. If it is too low, the fibers are not pressed onto the winding core to a sufficient extent. If the tension is too high, the slurry cannot penetrate sufficiently between the individual fiber filaments, and tearing of the roving might ensue.

(35) After the winding process, the wound fiber architecture is bonded using peel ply. This is intended to provide an even surface, compact it by displacing excess slurry and hence increase the fiber volume content, while additionally protecting the component.

(36) In circumferential winding, also called radial winding, the rovings are laid parallel, as can be seen in the illustration in FIG. 4. With cross-winding, the rovings are laid from one end to the other end, in order to provide a fiber reinforcement in the x and y directions too. The winding angle is measured from the laid fiber strand, against the rotation axis, and influences the absorption of axial loads.

(37) If a wound part has purely unidirectional circumferential windings, i.e. if the angle ? is around 90?, very high tensile strengths are achievable in the tangential orientation. If the winding angle is <45?, higher axial loads are absorbed. With reinforcement in the axial direction, i.e. with small winding angles, the problem arises during production that fixing of the roving at the end of the body is no longer possible.

(38) Various computation programs are available for coordination of the winding type, winding angle and number of layers (fiber requirement).

(39) After the winding process, the wound fiber architecture is bonded using a peel ply to obtain an even surface. Compaction is also achieved by displacing excess slurry, increasing the fiber volume content while the component is additionally protected. This is followed by drying and the sintering process.

(40) The following represents an example:

(41) Firstly, oxide ceramic prepregs are produced. To do so, fabric made from aluminum oxide fibers (>99% Al.sub.2O.sub.3) is impregnated with a water-based slurry containing oxide ceramic particles. The filament diameter is 10-12 ?m and the yarn fineness is 20,000 denier. The slurry has a solids content of 30% by volume, consisting of 80% by wt. Al.sub.2O.sub.3 particles and 20% by wt. ZrO.sub.2 particles. The mean particle size is 1 ?m. As a dispersant, 2% by weight of polyacrylic acid is added. After a reduction in the water content of the infiltrated fiber architecture, the resultant prepreg can be processed by cutting it to size and laying it onto a die replicating the internal contour of the metering crucible. After that, the die loaded with the prepreg is clamped into a winding device. Then the aluminum oxide fiber rovings (>99% Al.sub.2O.sub.3) of 20,000 denier yarn fineness are passed from a spool receptacle over deflecting pulleys and through an immersion bath, and laid on the rotating winding core. The rovings are centered by a thread eye. The thread tension is in the range from 10 to 90 N and is set using the deflecting pulleys. The slurry inside the immersion bath has a solids content of 32% by volume of ceramic particles relative to the total volume of the slurry, consisting of 80% Al.sub.2O.sub.3 particles and 20% ZrO.sub.2 particles. The mean particle size is 1 ?m. As a dispersant, 2% by weight of polyacrylic acid is added. The wound fiber architecture of the shaped composite material is consolidated by reducing the water content, so that a green compact is obtained. After drying, the wound fiber architecture can be removed from the core. This is followed by sintering at 1200? C. Reworking can be performed by turning, milling or grinding.