METHOD OF EXTRUDING A POWDER METALLURGICAL COMPONENT

Abstract

The invention relates to a method of manufacturing a component (21) from metal-containing powder. A paste is prepared by mixing at least a powder (11) comprising metal, a binder (12) in an amount of 2 to 8 weight % of the paste (10), and liquid (13), such as water, in an amount of 5 to 25 weight % of the paste (10). The paste is transferred to an extruder (31), and the paste is extruded into a green body (20) by using an extrusion pressure (P) of more than 50 bar. Then the green body (20) is dried and sintered or oxidized to obtain the final component.

Claims

1. Method of manufacturing a component from metal-containing powder, the method comprising the following steps: preparing a paste by mixing at least: a powder comprising metal, a binder in an amount of 2 to 8 weight % of the paste, liquid, such as water, in an amount of 5 to 25 weight % of the paste, transferring the paste to an extruder, extruding the paste into a green body by using an extrusion pressure (P) of more than bar, drying the green body, and sintering or oxidizing the dried green body to bond the powder together and thereby form the component.

2. Method according to claim 1, wherein: the binder is in an amount of 2 to 7 weight % of the paste, such as in an amount of 2 to 6 weight % of the paste, such as in an amount of 3 to 5 weight % of the paste, and/or the liquid is in an amount of: 5 to 15 weight % of the paste, such as 5 to 10 weight % of the paste, or 10 to 20 weight % of the paste, such as in an amount of 12 to 18 weight % of the paste.

3. Method according to claim 1, wherein the binder and the liquid are chosen so that the binder is dissolvable in the liquid, and wherein the step of preparing the paste comprises ensuring that the binder is dissolved in the liquid during the mixing.

4. Method according to claim 1, wherein the extrusion pressure (P) is between 50 and 500 bar, such as between 50 and 200 bar, preferably between 60 and 160 bar, most preferably between 60 and 150 bar.

5. Method according to claim 1, wherein the step of preparing the pastes comprises a step of kneading which has a duration until substantially all the binder is dissolved and until the paste has reached a desired state with respect to homogeneity, viscosity, and hardness.

6. Method according to claim 1, wherein the step of preparing the paste comprises the following steps: mixing the powder and the binder, and adding water and kneading in a kneader, such as a Z-blade kneader or sigma blade kneader.

7. Method according to claim 1, wherein the paste further comprises ceramic particles.

8. Method according to claim 1, wherein the green body is formed by forcing the paste through a die which is shaped to form the green body in a geometry having at least one longitudinally extending channel, or wherein the component being manufactured has a plurality of longitudinally extending internal channels, such as having a honeycomb structure.

9. Method according to claim 8, wherein walls forming the longitudinally extending internal channels have a wall thickness of between 0.25 and 2 mm, such as between 0.25 and 1 mm, such as between 0.25 and 0.5 mm.

10. Method according to claim 1, wherein the step of drying comprises guiding a flow of gas through the at least one longitudinally extending channel.

11. Method according to claim 10, wherein the step of drying further comprises covering outer surfaces of the green body so that the drying takes place due to the flow of gas being through the at least one longitudinally extending channel only.

12. Method according to claim 10, wherein the step of drying comprises using a drying tool, the drying tool comprising: a first end comprising or being connectable to a gas flow generating device, and an opposite second end comprising a plurality of nozzles each in fluid communication with the first end so that gas can flow through each of the nozzles under the action of the gas flow generating device during use of the drying tool.

13. Method according to claim 12, wherein the following steps precede the step of drying: arranging the drying tool in relation to the green body so that a nozzle of the drying tool extends into an end region of each of the at least one longitudinally extending channel of the green body, and activating the gas flow generating device so that gas flows into each of the at least one longitudinally extending channel.

14. Method according to claim 1, wherein the step of extruding is performed at room temperature and with the paste having a temperature of at most 50 degrees Celsius, such as at most 40 degrees Celsius, throughout the extrusion step.

15. Method according to claim 14, wherein the step of extruding is performed at room temperature and with the paste having a temperature of at most 30 degrees Celsius, such as at most 25 degrees Celsius, throughout the extrusion step.

16. Method according to claim 1, wherein a step of debinding precedes the step of sintering or oxidizing, the debinding step preferably comprising heating the green body to a temperature at which at least some, such as all, of the binder burns off.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0065] The method of manufacturing a component according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0066] FIG. 1 is a flow-chart of the step of preparing a paste in an embodiment of a method according to the invention.

[0067] FIG. 2 shows schematically how the paste is extruded into a green body.

[0068] FIGS. 3.a and 3.b show schematically examples of different components that can be manufactured by a method according to the present invention. FIG. 3.c shows schematically an example of a die that can be used for manufacturing of a component with an array of longitudinally extending inner channels.

[0069] FIG. 4 shows schematically an embodiment of a drying tool which is used in some embodiments of the present invention. FIG. 4.a is a side view, and FIG. 4.b is three-dimensional partial view of the second end comprising nozzles.

[0070] FIG. 5 shows schematically how the drying tool of FIG. 4 can be arranged with the nozzles being engaged with end sections of channels of a green body during drying.

[0071] FIG. 6 shows schematically a step of drying wherein an auxiliary tool is used to support the green body.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0072] FIG. 1 is a flow-chart of the step of preparing a paste 10 in an embodiment of a method according to the invention. The paste 10 is prepared by first mixing a powder 11 and a binder 12 in an amount of 2 to 8 weight % of the paste 10. As explained above, the combination of the binder and the liquid is preferably chosen so that the binder is dissolvable in the liquid, and the step of preparing the paste comprises dissolving the binder in the liquid during the mixing. The powder 11 comprises metal and may also comprise ceramic. The liquid is in the following described as being water 13, but other liquids may also be used as mentioned above. It is added in an amount of 5 to 25 weight % of the paste 10. In the illustrated embodiment, the adding of water 13 and kneading to obtain a homogenous paste is performed in a kneader 30, such as a Z-blade kneader or sigma blade kneader.

[0073] The prepared paste 10 is then transferred to an extruder 31, where it is extruded into a green body 20 as shown schematically in FIG. 2. This step is performed by using an extrusion pressure P of more than 50 bar. In some embodiments of the invention, the extrusion pressure P is between 50 and 500 bar, such as between 50 and 200 bar, preferably between 60 and 160 bar. The green body 20 is then dried and sintered or oxidized in order to obtain the final component.

[0074] In presently preferred embodiments of the invention, the step of extruding is performed at room temperature and with the paste having a temperature of at most 50 degrees Celsius, such as at most 40 degrees Celsius, preferably at most degrees Celsius. Since the friction between the paste being extruded and the processing equipment may cause an undesired temperature increase in the paste, some cooling of the extrusion die and the extrusion chamber can be necessary in order to be able to control the temperature.

[0075] In some embodiments of the invention, the green body 20 is formed by forcing the paste 10 through a die 32 which is shaped to form the green body 20 in a geometry having at least one longitudinally extending channel. FIG. 3 shows schematically examples of such embodiments. FIG. 3.a shows a component 21 having one longitudinally extending channel 22, and FIG. 3.b shows a having a plurality of longitudinally extending internal channels 22 which are arranged in a regular pattern. These geometries are obtained by using dies 32 having shapes and arrangements corresponding to the cross-sectional shapes of the components. FIG. 3.c shows an example of a possible design of a die 32 that can be used for the manufacturing of a component 21 having an array of longitudinally extending internal channels.

[0076] Experiments performed during the development work leading to the present invention have shown that it is possible to manufacture components 21, wherein walls 23 forming the longitudinally extending internal channels 22 have a wall thickness of between 0.25 and 2 mm, such as between 0.25 and 1 mm, such as between 0.25 and 0.5 mm.

[0077] In a method according to the present invention, the step of drying the green specimen before sintering or oxidizing may comprise guiding a flow of gas through the at least one longitudinally extending channel. This can e.g. be done by use of a drying tool 40 as shown schematically in FIG. 4. FIG. 4.a is a side view illustrating that the drying tool 40 has a first end 41 comprising or being connectable to a gas flow generating device 43, and an opposite second end 42 comprising a plurality of nozzles 44. The nozzles 44 are in fluid communication with the first end 41 so that gas can flow through each of the nozzles 44 under the action of the gas flow generating device 43 during use of the drying tool 40. FIG. 4.b is three-dimensional partial view of the second end 42 comprising nozzles 44. In the illustrated embodiment, the nozzles 44 are arranged in a regular pattern of aligned rows and columns.

[0078] FIG. 5 shows how the drying tool 40 of FIG. 4 can be arranged with the nozzles 44 being engaged with, such as extending into, end sections of the longitudinally extending channels 22 of a green body 20 during drying. It has to be ensured that the nozzles 44 do not damage the green body 20. When the nozzles 44 have been arranged, the gas flow generating device 43 is activated so that gas flows into each of the longitudinally extending channels 22. By using a drying tool 40 as described and letting the nozzles 44 extend into each or a majority of the longitudinally extending channels 22, a uniform drying throughout the volume can be ensured. In addition, the nozzles 44 may be shaped and dimensioned so that they provide structural support to the part of the walls 23 of the at least one longitudinally extending channel 22 that is in contact with the drying tool 40 and thereby prevent deformation thereof. The advantage thereof is both that the green body 20 remains undeformed and that the gas flow is not hindered as it could be by deformed, such as collapsed, longitudinally extending channels 22.

[0079] FIG. 6 shows schematically how an auxiliary tool 47 can be arranged at an opposite end of the green body 20 as the one where the drying tool 40 is arranged. The auxiliary tool 47 is used to support the longitudinally extending channels 22 during drying. In FIG. 6 this is shown schematically as small pins 48 protruding from an end surface of the auxiliary tool 47 so that they can extend into the longitudinally extending channels 22 of the green body 20 being dried.

[0080] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Furthermore, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.