GB1574084A

GB1574084A - Process for forming an article from a ferrous metal powder

Info

Publication number: GB1574084A
Application number: GB2257577A
Authority: GB
Original assignee: SKF Industrial Trading and Development Co BV
Current assignee: SKF Industrial Trading and Development Co BV
Priority date: 1976-05-28
Filing date: 1977-05-27
Publication date: 1980-09-03
Also published as: FR2352617A1; FR2352617B1; CH628548A5; SE7706155L; DE2724053A1; NL7605725A; JPS52151609A; DK237177A; IT1114787B

Abstract

First of all, an element determining the shape of the cavity is embedded in the powdered metal, the material of the element (37) having the property of being absorbable by the metal powder. The material of the element (3) is, furthermore, chosen in such a way that the element (3) maintains its shape during isostatic compaction at a pressure between 2000 and 8000 kg/cm<2>. Subsequent sintering is carried out in such a way that the wall of the cavity is saturated evenly and completely with the material of the element (3). The method can be used to manufacture a sintered product having cavities of any shape required, the walls of said cavities being leakproof. <IMAGE>

Description

(54) PROCESS FOR FORMING AN ARTICLE FROM A FERROUS METAL POWDER (71) We, SKF INDUSIRIAL TRADING AND DEVELOPMENT COMPANY BV, a Company organised and existing under the laws of the Kingdom of the Netherlands, of P.O.

Box 50, Nieuwegein, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process of forming an article having a recess or an internal cavity and to an article so formed from a ferrous metal powder.

According to the invention a process of forming an article having a recess or an internal cavity comprises isostatically compressing in a mould a ferrous metal powder and a solid element at a pressure in the range of from 2000 to 8000 kgf/cm2, the solid element defining the intended recess or cavity and retaining its form under compression, and then sintering the compressed metal powder at a temperature at which the solid element melts and is absorbed into the article so forming the intended recess or cavity.

The weight ratio of the element to the powder may be at least 1 to 10.

The element may be located by a support during the isostatic compression and the support may be a shaft.

The element may be hollow and may be filled with liquid during the isostatic compression, which liquid is removed after compression.

The invention includes an article formed by a process according to the invention from a ferrous metal powder having a uniform density of substantially 90% and a recess or internal cavity, the walls of which recess or cavity may be impregnated with copper or an alloy of copper.

The article may be tubular and have a plurality of recesses along the bore of the tube. In such a construction each recess may be part of a closed path, the rest of which path may be a channel extending inside the wall of the tube.

The article may be tubular and have a helically extending recess along the bore of the tube. In such a construction a channel may extend inside the wall of the tube and connect each end of the helically extending recess.

The article may be a sleeve for a hydrodynamic or hydrostatic bearing and have at least one pocket in the bore of the sleeve connected to a duct extending through the wall of the sleeve.

The article may be a flow control device and have ducts extending from a common chamber inside the article and a ball arranged for movement in the chamber and having a larger diameter than any one of the ducts.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings of which: - Figure 1 is a schematic view of an article before compression; Figure 2 is a perspective view of a tubular article with part cut away; Figure 3 is an axial section of another tubular article; Figure 4 is a perspective view of a sleeve for a hydrostatic or hydrodynamic bearing with part cut away; Figure 4A is a cross-section of the sleeve of Figure 4 in the process of being formed; Figure 5 is a cross-section of a flow control device; and Figure 6 is a cross-section of an article in which the element is hollow and filled with a liquid.

Referring to Figure 1 an article 1 is shown comprising a ferrous metal powder 2 in which is embedded a solid sinusoidal element 3 of the copper. The article 1 will be isostatically compressed, i.e. subiected to equal pressure in every direction, during which the element 3 retains its form or original shape. The compressed article is then sintered during which the element 3 melts and is absorbed into the article.

Thus a sinusoidal cavity is formed in the article 1, which cavity has walls which are impregnated with the copper, and are impermeable to liquids and gases.

The isostatic compression is carried out at a pressure in the range of from 2000 to 8000 kgf/cm2 to give a density of about 80% of the solid metal. Sintering is preperably carried out at a temperature in the range of from 1100 to 12000C for a period in the range of from 30 to 60 minutes in an atmosphere of dissociated ammonia or of hydrogen after which the article has a relative density of substantially 90%. The weight ratio of element to powder is at least 1 to 10.

Figure 2 is a view of a tubular article 4 which in the embodiment shown is the sleeve of a recirculating ball mechanism.

The sleeve 4 is formed from a ferrous metal powder having copper or copper alloy elements embedded in the wall 6.

After sintering each element is absorbed into the sintered ferrous metal leaving a recess 11 along the bore 12 of the sleeve forming part of a closed path 5, the rest of the path being a channel 13 extending inside the wall of the sleeve. Each element also leaves two extensions 7 and 8 of the recess along the bore. The balls for the bearing are inserted through the apertures 9 and 10 formed by the extensions 7 and 8 and then the extensions 7 and 8 are plugged.

Figure 3 is a section of another tubular element 14, which is the sleeve of another recirculating ball mechanism. In this embodiment there is one helically extending recess 15, the ends of which are connected by a channel extending inside the wall.

The element used to form the recess and channel is also used to form an aperture 16, for filling the balls 17, which aperture is subsequently plugged.

Figure 4 is a cut away view of a sleeve 18 for a hydrostatic or hydrodynamic bearing having pockets 19 and 20 in the bore of the sleeve. Each pocket 19, 20 is connected to a duct 22A, 22 and 23A, 23 resnectivelv extendin throu the wall 21 of the sleeve. Each end 22B, 23B is formed to have a screw thread 24, so that far end or side 25 can be connected to oil supply pipes.

Figure 4a shows a sleeve similar to sleeve 18 being formed from ferrous metal powder 18A w;th solid elements 19g, 20B, 22B and 23B embedded in the powder. The powder is contained in a resilient, e.g.

rubber mould ready for compression. To ensure accuracy in the relative positioning of the Dockets 19, 20. the elements are located hv a support, which in this case is a shaft S. The elements are also spaced apart by a ring or annulus R which is Dreferably compressed ferrous metal powder.

After the isostatic compression the shaft S is removed and the compressed article is then sintered.

Figure 5 is a schematic representation in section of a flow control device 26 comprising a block 27 in which ducts 28, 29 and 30 extend from a common internal cavity or chamber 31. A ball 32 is arranged for movement in chamber 31 and has a larger diameter than any one of the ducts 28, 29 and 30. To form this article a T-shaped copper or copper alloy element is formed with ball 32 embedded in it, so that after sintering the cavity is formed with a ball in it.

Figure 6 is a cross-section of an article 33 which has been isostatically compressed but not sintered. A relatively large duct 34 is formed by a solid element 36 which is hollow and filled with a liquid 35 such as oil. Liquids are relatively incompressible and will therefore support or maintain the shape of the element 36 during compression. This allows the minimum amount of material, e.g. copper to be used in forming element 36 that is consistent with forming a cavity wall in article 33 that is impermeable to fluids. Normally the liquid will be removed after compression via channel 37, but it may be left and removed after sintering, and by carefully measuring the amount of liquid before and after sintering, any leaks in the cavity wall can be spotted.

The isostatic compression allows the formation of an article of uniform density to be achieved, which article has a recess or internal cavity with walls that are impermeable to fluid. The amount of element used is kept to a minimum and the weight ratio of element to powder is at least 1 to 10.

WHAT WE CLAIM IS: 1. A process of forming an article having a recess or an internal cavity comprising isostatically compressing in a mould a ferrous metal powder and a solid element at a pressure in the range of from 2000 to 8000 kgf/cm2, the solid element defining the intended recess or cavity and retaining its form under compression, and then sintering the compressed metal powder at a temperature at which the solid element melts and is absorbed into the article so forming the intended recess or cavity.

2. A process as claimed in claim 1 wherein the weight ratio of the element to the powder is at least 1 to 10.

3. A process as claimed in claim 1 or 2 wherein during the iso static compression the element is located by a support.

4. A process as claimed in claim 3 wherein the support is a shaft.

5. A process as claimed in any one of claims 1 to 4 wherein the element is hol

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. impregnated with the copper, and are impermeable to liquids and gases. The isostatic compression is carried out at a pressure in the range of from 2000 to 8000 kgf/cm2 to give a density of about 80% of the solid metal. Sintering is preperably carried out at a temperature in the range of from 1100 to 12000C for a period in the range of from 30 to 60 minutes in an atmosphere of dissociated ammonia or of hydrogen after which the article has a relative density of substantially 90%. The weight ratio of element to powder is at least 1 to 10. Figure 2 is a view of a tubular article 4 which in the embodiment shown is the sleeve of a recirculating ball mechanism. The sleeve 4 is formed from a ferrous metal powder having copper or copper alloy elements embedded in the wall 6. After sintering each element is absorbed into the sintered ferrous metal leaving a recess 11 along the bore 12 of the sleeve forming part of a closed path 5, the rest of the path being a channel 13 extending inside the wall of the sleeve. Each element also leaves two extensions 7 and 8 of the recess along the bore. The balls for the bearing are inserted through the apertures 9 and 10 formed by the extensions 7 and 8 and then the extensions 7 and 8 are plugged. Figure 3 is a section of another tubular element 14, which is the sleeve of another recirculating ball mechanism. In this embodiment there is one helically extending recess 15, the ends of which are connected by a channel extending inside the wall. The element used to form the recess and channel is also used to form an aperture 16, for filling the balls 17, which aperture is subsequently plugged. Figure 4 is a cut away view of a sleeve 18 for a hydrostatic or hydrodynamic bearing having pockets 19 and 20 in the bore of the sleeve. Each pocket 19, 20 is connected to a duct 22A, 22 and 23A, 23 resnectivelv extendin throu the wall 21 of the sleeve. Each end 22B, 23B is formed to have a screw thread 24, so that far end or side 25 can be connected to oil supply pipes. Figure 4a shows a sleeve similar to sleeve 18 being formed from ferrous metal powder 18A w;th solid elements 19g, 20B, 22B and 23B embedded in the powder. The powder is contained in a resilient, e.g. rubber mould ready for compression. To ensure accuracy in the relative positioning of the Dockets 19, 20. the elements are located hv a support, which in this case is a shaft S. The elements are also spaced apart by a ring or annulus R which is Dreferably compressed ferrous metal powder. After the isostatic compression the shaft S is removed and the compressed article is then sintered. Figure 5 is a schematic representation in section of a flow control device 26 comprising a block 27 in which ducts 28, 29 and 30 extend from a common internal cavity or chamber 31. A ball 32 is arranged for movement in chamber 31 and has a larger diameter than any one of the ducts 28, 29 and 30. To form this article a T-shaped copper or copper alloy element is formed with ball 32 embedded in it, so that after sintering the cavity is formed with a ball in it. Figure 6 is a cross-section of an article 33 which has been isostatically compressed but not sintered. A relatively large duct 34 is formed by a solid element 36 which is hollow and filled with a liquid 35 such as oil. Liquids are relatively incompressible and will therefore support or maintain the shape of the element 36 during compression. This allows the minimum amount of material, e.g. copper to be used in forming element 36 that is consistent with forming a cavity wall in article 33 that is impermeable to fluids. Normally the liquid will be removed after compression via channel 37, but it may be left and removed after sintering, and by carefully measuring the amount of liquid before and after sintering, any leaks in the cavity wall can be spotted. The isostatic compression allows the formation of an article of uniform density to be achieved, which article has a recess or internal cavity with walls that are impermeable to fluid. The amount of element used is kept to a minimum and the weight ratio of element to powder is at least 1 to 10. WHAT WE CLAIM IS:

1. A process of forming an article having a recess or an internal cavity comprising isostatically compressing in a mould a ferrous metal powder and a solid element at a pressure in the range of from 2000 to 8000 kgf/cm2, the solid element defining the intended recess or cavity and retaining its form under compression, and then sintering the compressed metal powder at a temperature at which the solid element melts and is absorbed into the article so forming the intended recess or cavity.

4. A process as claimed in claim 3 wherein the support is a shaft.

5. A process as claimed in any one of claims 1 to 4 wherein the element is hol

low and is filled with liquid during the isostatic compression, which liquid is removed after compression.

6. A process for forming an article having a recess or an internal cavity substantially as herein described with reference to Figure 1 or with reference to Figure 2, or with reference to Figure 3, or with reference to Figures 4 and 4a, or with reference to Figure 5, or with reference to Figure 6 of the accompanying drawings.

7. An article formed by a process as claimed in any one of claims 1 to 6.

8. An article as claimed in claim 7 formed from a ferrous metal powder, having a uniform density of substantially 90% and having a recess or internal cavity, the walls of which recess or cavity are impregnated with copper or a copper alloy.

9. An article as claimed in claim 8 wherein the article is tubular and has a plurality of recesses along the bore of the tube.

10. An article as claimed in claim 9 wherein each recess is part of a closed path, the rest of which path is a channel extending inside the wall of the tube.

11. An article as claimed in claim 8 wherein the article is tubular and has a helically extending recess along the bore of the tube.

12. An article as claimed in claim 11 wherein a channel extending inside the wall of the tube connects each end of the helically extending recess.

13. An article as claimed in claim 8 wherein the article is a sleeve for a hydrodynamic or hydrostatic bearing and has at least one pocket in the bore of the sleeve connected to a duct extending through the wall of the sleeve.

14. An article as claimed in claim 8 wherein the article is a flow control device having ducts extending from a common chamber inside the article and a ball arranged for movement in the chamber and having a larger diameter than any one of ducts.

15. An article as claimed in claim 7 formed from a ferrous metal powder substantially as herein described with reference to and as shown in Figure 1 or with reference to and as shown in Figure 2 or with reference to and as shown in Figure 3 or with reference to and as shown in Figure 4 and Figure 4a or with reference to and as shown in Figure 5 or with reference to and as shown in Figure 6 of the accompanying drawings.