Method for producing a porous shaped body

Abstract

A method for producing a porous shaped body may include providing a mixture of a powder including at least one of a metal, a metal alloy, and a ceramic, with a resin/activator mixture. The method may then include introducing the mixture by core shooting into a cavity formed in a forming tool, and solidifying the mixture in the forming tool to give a shaped body. The method may then include heating the shaped body to remove at least one of organic constituents and gases present in the shaped body. The method may further include resolidifying the shaped body by a sintering operation.

Claims

1. A method for producing a porous shaped body, comprising: providing a mixture of a powder including at least one of a metal, a metal alloy, and a ceramic, with a resin and activator mixture; introducing the mixture by core shooting into a cavity formed in a forming tool; initiating a chemical reaction in which the powder enters into a bond with resin from the resin and activator mixture by introducing at least one reactive gas into the forming tool to solidify the mixture in the forming tool to give a shaped body; heating the shaped body to remove at least one of organic constituents and gases present in the shaped body; and sintering the shaped body; wherein the powder includes a layer of metallic powder and one of a layer of ceramic powder or a layer of oxide particles on the layer of metallic powder, and the powder is embedded in an organic matrix.

2. A method according to claim 1, wherein the resin and activator mixture has between 0.5 wt % and 5 wt % of a total weight of the mixture.

3. A method according to claim 1, wherein introducing the mixture takes place fluid-dynamically using a pressurized gas.

4. A method according to claim 3, wherein the pressurized gas includes one of compressed air, nitrogen, and argon.

5. A method according to claim 1, wherein the reactive gas includes amide.

6. A method according to claim 1, wherein the shaped body is heated to a temperature between 25° C. and 700° C. in the heating step.

7. A method according to claim 1, wherein heating the shaped body takes place in one of a neutral, an oxidizing, and a reducing atmosphere.

8. A method according to claim 1, wherein the sintering takes place in one of a reducing, a carbonizing, and a neutral atmosphere.

9. A method according to claim 1, wherein, during or after solidifying the mixture, no mechanical pressure is exerted on the shaped body as it forms.

10. A method according to claim 2, wherein introducing the mixture takes place fluid-dynamically using a pressurized gas.

11. A method according to claim 10, wherein the pressurized gas includes one of compressed air, nitrogen, and argon.

12. A method according to claim 1, wherein the powder includes a metallic powder layer 200 μm thick and a ceramic powder layer 30 μm thick.

13. A method comprising: providing a mixture of a powder including at least one of a metal, a metal alloy, and a ceramic, with a resin and activator mixture; core shooting the mixture into a cavity formed in a forming tool via a pressurized gas; initiating a chemical reaction in which the powder enters into a bond with resin from the resin and activator mixture by introducing at least one reactive gas into the forming tool to solidify the mixture in the forming tool to give a shaped body; heating the shaped body to a temperature between 25° C. and 700° C. to remove at least one of organic constituents and gases present in the shaped body; and sintering the shaped body; wherein the powder includes a layer of metallic powder and one of a layer of ceramic powder or a layer of oxide particles on the layer of metallic powder, and the powder is embedded in an organic matrix.

14. A method according to claim 13, wherein the pressurized gas includes one of compressed air, nitrogen, and argon.

15. A method according to claim 13, wherein the reactive gas includes amide.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The FIGURE illustrates a schematic forming tool having a cavity used to produce a porous shaped body.

DETAILED DESCRIPTION

(2) The method of the invention is discussed below with reference to a first example. In step a) a metallic starting powder is selected which permits in particular the desired functional properties in the end product, such as pore size and mechanical strength, for example.

(3) The two metal powder mixtures SAMPLE A and SAMPLE B as per Table AB1.1 meet these criteria.

(4) TABLE-US-00001 TABLE AB1.1 Composition of the metal mixture [AB1] Iron powder [AB5] Copper powder (150-425 μm) (45-250 μm) Graphite: SAMPLE A balance 3 wt %   0 wt % SAMPLE B balance 3 wt % 0.65 wt %

(5) The two metal powder mixtures of Tab. AB1.1 are then each mixed in step a) with a resin/activator mixture. The mixtures are subsequently shot by core shooting, in each case with different shooting pressures—e.g. 4, 6, 8 and 10 bar—according to step b), into a cavity having external dimensions of 180×24×24 mm.sup.3 and thereafter cured in a step c) under the action of a reactive gas—in the example scenario, the reactive gas “DMPA 706”—for 10 seconds.

(6) The resulting shaped bodies possess a density of 3.5 g/cm.sup.3 and a 3-point flexural strength of 1.4 MPa (SAMPLE A) and 1.9 MPa (SAMPLE B). Higher pressures may lead to moulding defects on the shaped body; low levels of resin/activator diminish the flexural strength and edge resistance. Higher levels of resin and/or activator are detrimental to the demouldability of the shaped body.

(7) In a thermal operation referred to as preliminary sintering, the resin is removed from the shaped body according to step d) by heating of the shaped body at a rate of 2 K/min to 700° C. in an N.sub.2—H.sub.2 atmosphere. Solidification—measured in the form of flexural strength—takes place in step e) by heating from 700° C. at 5 K/min to the sintering temperature T.sub.sinter under the N.sub.2—H.sub.2 atmosphere. For SAMPLE A, there is only a slight increase in flexural strength (see Tab. AB1.3). The graphite-containing powder mixture (SAMPLE B) attains a much higher strength, with a maximum value of around 9 MPa.

(8) TABLE-US-00002 Tab. AB1.3 shows the results of sintering. T.sub.sinter 4.1 (SAMPLE A) 4.2 (SAMPLE B) 1115 4.7 7.4 1120 4.7 6.99 1135 4.6 7.98 1145 4.5 8.6 1175 4.9 9.02

(9) Tab. AB1.3: 3-Point flexural strength in [MPa] of samples sintered at different temperatures

(10) The powder mixtures ready for shooting have a time limit on their workability if compressed air is used as transfer medium. This can be demonstrated by the flexural strength of the “green” components, which decrease with working time. If nitrogen is employed as process gas, the period for working is extended.

(11) In the text below, the method of the invention is discussed with reference to a further, second example. To produce a metallic component which is suitable for filter applications and consists of a self-supporting structure with large pores and a filter medium with small pores, a procedure is adopted in analogy to the first working example, elucidated above. With the second example, in contrast to the first example, a metallic filter fabric—with a thickness of about 0.2 mm and with a pore size/mesh size of 35 μm, for instance—is inserted, in particular in planar fashion, into the cavity of the tool before the core shooting according to step b).

(12) This is followed by a performance of the method steps described in the first working example: in other words, the steps of filling, core shooting, debinding and sintering are carried out. As the result, a planar metallic fine filter component can be reproduced which is carried by a structure with large pores—pore size approximately 200 μm—and which acquires fine filter qualities by virtue of the “sintered-on” membrane. Alternatively it is also possible to use filter fabrics having different mesh sizes.

(13) The method of the invention is discussed below with reference to a third example. In analogy to the second working example, the possibility also exists of using a “green” intermediate for insertion into the cavity. The system in this case is a metal/ceramic powder layer system comprising a coarse metallic powder layer approximately 200 μm thick and a ceramic powder layer approximately 30 μm thick. The powders are embedded in an organic matrix. In contrast to the first and second working examples, the powder mixture to be applied by core shooting is selected such that there is significant contraction during the thermal treatment. This contraction is set so as to be adapted very well to the contraction behaviour of the green intermediate, and produces, after sintering, a predefined, application-oriented porosity. A component of this kind is suitable for filtering particles of around 10 nm to 20 μm. The corresponding pore size is set via the selection of the ceramic powders in the top layer and by the sintering conditions.

(14) In the text below, the method of the invention is discussed with reference to a fourth example. For robust technical applications where a fracture-sensitive ceramic top layer for filtering, as in the above-described third working example, is not an option, it is also possible to replace this layer by readily reducible oxide particles. As a result, after the reducing of these oxide particles and sintering of the overall shaped body, a metallic top layer, which is tolerant to damage and has a fine porosity, is formed on a robust carrier structure, with adjustable porosity.

(15) In the text below, the method of the invention is discussed with reference to a fifth example:

(16) Referring to the first example, it is conceivable, rather than conventionally produced iron powder or copper powder, to use one or more granules (10 to 500 μm) of starting materials which have been formed by known technological processes—examples include processes known to the skilled person such as spray drying, fluidized bed granulation, pelletizing and cogranulation—from fine, commercial, ceramic or metallic starting materials (0.01 to about 25 μm). This procedure produces shaped bodies which on sintering achieve a high density locally, i.e. in the granules, and which in the interstices, in other words in the pore volumes formed by the contact points of the granule grains, permit a high porosity which can be adjusted via the granule size.

(17) A further difference is that shaped bodies of this kind attain a higher strength after sintering at a given sintering temperature. This is because of the use of particularly sinter-active, fine, starting powders for the granules, and ensures that granule grains form more stable contacts with one another, in zones of contact, than conventional starting powders as in the first example, for instance, where the increase in the sintering temperature produces only a small increase in the strength.

(18) Metallic starting powders in the present context include not only powders composed of pure metals but also those formed from different metals, semi-metals (i.e. semiconducting metals) or metalloids, namely alloys, intermetallic compounds, solid solutions or nanocrystalline and/or amorphous states of material.