Powder-metallurgical body and method for the production thereof

Abstract

A powder-metallurgical body and a method for producing such a body. The powder-metallurgical body is formed with a seating base for seating a sealing element to produce a seal with respect to fluids, such as liquids and/or gases. The body is redensified in a low-lying depth region of the seating base.

Claims

1. A method of producing a powder-metallurgical body to be sealed by way of a sealing element, the method which comprises: providing a seating base of the body for receiving and seating the sealing element, wherein the seating base has a material elevation; machining the material elevation to cause the body to be redensified, after the machining, in a depth region of the seating base and to cause the depth region to have a lower mean porosity than a porosity of the body as a whole; and seating the sealing element on the seating base after the material elevation has been machined.

2. The method according to claim 1, wherein the machining step comprises flattening the material elevation.

3. The method according to claim 1, wherein the machining step comprises machining the material elevation by calibration pressing.

4. The method according to claim 1, which comprises providing the body together with the seating base and the material elevation as a powder-metallurgical blank.

5. The method according to claim 4, which comprises sintering the powder-metallurgical blank and subsequently machining the material elevation.

6. The method according to claim 1, which comprises sealing pores on the surfaces of the body at least partially after the material elevation has been machined.

7. The method according to claim 6, which comprises sealing the pores by impregnation with a plastic.

8. The method according to claim 1, which comprises forming the body with a closed porosity in the depth region.

9. The method according to claim 8, which comprises forming the closed porosity exclusively in the depth region.

10. The method according to claim 1, which comprises, given a material depth proceeding from the seating base of up to 0.05 mm, forming the depth region with a mean porosity of at most 4%.

11. The method according to claim 10, which comprises forming the depth region with a mean porosity of no more than 2%.

12. The method according to claim 1, which comprises, given a material depth proceeding from the seating base of up to 0.5 mm, forming the depth region with a mean porosity of at most 5%.

13. The method according to claim 12, which comprises forming the depth region with a mean porosity of no more than 2.5%.

14. The method according to claim 1, which comprises, given a material depth proceeding from the seating base of up to 1.0 mm, forming the depth region with a mean porosity of at most 6%.

15. The method according to claim 14, which comprises forming the depth region with a mean porosity of no more than 3%.

16. The method according to claim 1, which comprises, given a material depth proceeding from the seating base of up to 1.5 mm, forming the depth region with a mean porosity of at most 7%.

17. The method according to claim 16, which comprises forming the depth region with a mean porosity of no more than 3.5%.

18. The method according to claim 1, which comprises forming the seating base to extend continuously in a circumferential direction of the body.

19. The method according to claim 1, which comprises forming the seating base as a constituent part of a sealing groove for receiving the sealing element.

20. The method according to claim 19, which comprises forming the seating base as a constituent part of a groove base of the sealing groove.

21. The method according to claim 19, which comprises forming the sealing groove in a region of a front end of the body.

22. The method according to claim 1, which comprises seating the sealing element on the machined material elevation of the seating base.

23. A method of producing a powder-metallurgical body to be sealed by way of a sealing element, the method which comprises: providing a seating base of the body for receiving and seating the sealing element with a material elevation; machining the material elevation to cause the body to be redensified, after the machining, in a depth region of the seating base and to cause the depth region to have a lower mean porosity than a porosity of the body as a whole; sealing pores on the surfaces of the body at least partially after the material elevation has been machined; and seating the sealing element on the seating base.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a schematic, sectioned side view of a powder-metallurgical body with attachment parts and sealing elements,

(2) FIG. 2 is an enlarged illustration of detail II shown in FIG. 1,

(3) FIG. 3 is a schematic, sectioned side view of a sealing groove with a material elevation,

(4) FIG. 4 shows an optical micrograph of a solid body section of a ready-to-press mixed powder (iron, copper, carbon, pressing aid) after sintering, without a material elevation and without redensification in the region of the groove base,

(5) FIG. 5 shows an enlarged micrograph of detail V shown in FIG. 4,

(6) FIG. 6 shows an optical micrograph of a solid body section of the powder mixture according to FIG. 4 after sintering, but with redensification in the region of the groove base,

(7) FIG. 7 shows an enlarged micrograph of detail VII shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

(8) The sealing of an apparatus 1 against the escape of liquid 2 (e.g. oil) will be explained on the basis of FIG. 1 and FIG. 2. The apparatus 1 comprises a body 3 which has been produced by powder metallurgy and has a continuous side wall 4 in the circumferential direction of the body 3. The side wall 4 delimits an inner space 5. The liquid 2 is located in the inner space 5. An attachment plate 8 is arranged on each of the end sides 7 of the body 3 which lie opposite one another in the axial direction 6. The attachment plates 8 are mounted (e.g. screwed) on the body 3 using suitable fastening means (not illustrated here) and close off the inner space 5 in the axial direction 6. Sealing elements in the form of two elastically deformed sealing rings 9 which are each continuous are intended to prevent the liquid 2 from passing from the inner space 5 into the outer environment 10 in the transition regions between the attachment plates 8 and the body 3.

(9) In order to prevent liquid 2 from penetrating through the side wall 4, the body 3 is sealed. For this purpose, it is preferably impregnated with a plastic. The impregnation is effected by immersing the porous body 3 in the liquid impregnation medium at negative pressure, in which case the impregnation medium penetrates into the pores of the body 3. After the body 3 has been removed from the impregnation medium, excess impregnation material is rinsed off and the impregnation medium in the pores cures to form a solid mass, as a result of which the imperviousness to fluid is obtained. Method conditions mean that impregnation medium can undesirably be washed out during the rinsing-off process. Particularly in edge regions and/or in regions of the body 3 where the wall thickness is small, there is the risk in this respect that the body 3 is not sufficiently sealed or remains pervious, and therefore a pervious channel is formed. Such a channel is indicated in FIG. 2 by means of the arrows 11. It is located in the region of contact surfaces 12 of the porous body 3, against which the sealing element 9 rests in an elastically deformed manner.

(10) In order to avoid such a pervious channel, a local reduction in porosity is provided in a depth region 13 of a contact surface 12 for the sealing element 9.

(11) FIG. 3, again in enlarged form, shows a sealing groove 15 of the porous body 3 for receiving a sealing element (not illustrated here). Provision is made of a seating base 16 (it corresponds to a contact surface 12 in FIG. 2), which is a constituent part of a groove base 17 of the sealing groove 15. In the assembled state, the sealing element is seated on the groove base 17 or on the seating base 16. The sealing element may also be seated on the lateral groove flanks 18. The groove flanks 18 can therefore likewise each form a seating base or contact surface.

(12) The seating base 16 is provided with a material elevation 19. In a manner which is still to be explained, the material elevation 19 is machined by means of a redensification tool W which is moved in a direction of transport P parallel to a body axis A (and is only illustrated schematically here), in such a manner that, following the machining on the seating base 16, the adjoining depth region 13 has a locally much lower porosity than a region remote therefrom (e.g. region 14). The mean porosity of the depth region 13 is then also much lower than the mean porosity of the body 3 as a whole. The material depth T, extending in the depth direction TR, of the region 13 with the locally relatively low porosity can vary here depending on the technical application and profile of requirements of the body 3.

(13) In FIG. 3, the body 3 is illustrated only in part. It is formed continuously in the circumferential direction, the circumferential plane being arranged at right angles to the body axis A. The plane of the machined seating base 16 or the surface thereof likewise extends substantially transversely or at right angles to the body axis A (see FIG. 6). The sealing groove 15 is located in the region of a front end 7 of the body 3. The sealing groove 15 is likewise continuous for receiving apreferably elasticannular seal as the sealing element. Accordingly, the seating base is also formed continuously, e.g. as an annular surface, in the circumferential direction of the body 3. It is also possible for a plurality of sealing grooves 15be they continuous in the circumferential direction of the body 3 or notto be provided on the body 3. In particular, the body 3 has a second sealing groove 15 arranged so as to lie opposite the sealing groove 15 shown in the depth direction TR (see also FIG. 1).

(14) The text which follows describes the production of a porous body 3 with a locally relatively low porosity or locally relatively high density in the depth region 13 on the basis of an example.

(15) A metal powder mixture of copper (1 to 1.5% by weight), graphite (0.45 to 0.65% by weight), manganese sulfide (0.3 to 0.4% by weight), microwax (0.75 to 0.85% by weight), remainder iron was pressed to form a green compact at an applied pressure of 380 MPa. The pressing tool was designed in such a manner that the material elevation 19 on the sealing groove 15 was also shaped and pressed. This green compact provided was then sintered in a through-type belt kiln at 1120 C. under endothermic gas for 20 minutes. After sintering, the material elevation 19 of the sintered body 3 was machined by means of calibration pressing with an applied pressure of 700 MPa and flattened and thereby locally redensified (see the optical micrographs shown in FIG. 6 and FIG. 7). The redensification tool used for calibration pressing (which corresponds in principle to the tool W shown schematically) was transported here in the direction of transport P, i.e. parallel to the body axis A, in the direction of the seating base 16 or the material elevation 19, and flattened the material elevation 19. On account of this redensification, the depth region 13 had a much lower porosity than regions 14 of the porous body 3 which were remote therefrom and were not redensified. Similarly, the depth region 13 shown in FIG. 6 and FIG. 7 had a much lower porosity than the corresponding regions of a body of identical construction without this local remachining or redensification in the region of the seating base 16 (see the depth region 13 in FIG. 4 and FIG. 5).

(16) The porosity profile along the material depth T was determined by means of quantitative image analysis (sum of the pore surfaces in relation to the overall surface considered). Pores having a pore size <6 m were not taken into account in the measurements. The measurements were carried out on polished surfaces of a transverse microsection with 200-fold magnification (fully automatic optical microscope LEICA DM 4000-M with image analysis program from Clemex Vision). The cross section for the microsection was effected by means of a conventional cutting apparatus and SiC cut-off wheels. The cross section was ground in a plurality of steps with a differing grain size (80 to 1200). This transverse microsection was also subjected to final polishing by means of a polishing pad. Here, the polishing pad was sprayed with an alcohol suspension containing diamond grains (grain diameter 1 to 3 m).

(17) For the measurements, the region of the porous body 3 to be investigated was divided into a grid. Proceeding from the seating base 16, five successive portions each having a material depth of 0.5 mm were defined along the material depth T. Each portion comprised two subfields F1 and F2, which were arranged on both sides of a defined groove center line 20. Each subfield F1, F2 had a field width or material width B oriented in the width direction BR of 0.6 mm. The width direction BR is arranged at right angles to the material depth T and, in FIG. 6, extends parallel to the groove width of the sealing groove 15. The grid consequently comprised two columns each with five subfields, each subfield having a cross-sectional area of 0.6 mm by 0.5 mm.

(18) The porosity values determined in the case of a first porous body 3 with local redensification can be gathered from table 1. For material depths >0.5 mm, the porosity values for field 1 are given in each case as a mean value, which results from the porosity values in the corresponding subfields F1. Example: Porosity field 1 (where T=00.5 mm)=0.76% by volume, identical to porosity subfield F1 (where T=00.5 mm). Porosity subfield F1 (where T=0.51.0 mm)=1.56% by volume. This results in porosity field 1 (where T=01.0 mm)=(0.76+1.56% by volume)/2=1.16% by volume. The porosity values for field 2 were determined analogously proceeding from the porosity values in subfields F2.

(19) Since the pores of the body 3 had no preferred orientation, the area-related porosity determined substantially also corresponds to the volume-related porosity.

(20) TABLE-US-00001 TABLE 1 Material depth T in mm 0-0.5 0-1.0 0-1.5 0-2.0 0-2.5 Field 1, porosity in % by 0.76 1.16 1.81 2.36 2.85 volume Field 2, porosity in % by 1.00 1.54 1.80 2.49 3.36 volume Mean value of the 0.88 1.35 1.81 2.43 3.11 porosity from field 1 and field 2 in % by volume

(21) The porosity values determined in the case of a second porous body 3 with local redensification can be gathered from table 2. The values were determined analogously to the procedure in table 1.

(22) TABLE-US-00002 TABLE 2 Material depth T in mm 0-0.5 0-1.0 0-1.5 0-2.0 0-2.5 Field 1, porosity in % by 1.52 1.68 2.07 2.5 3.21 volume Field 2, porosity in % by 1.72 2.16 2.31 2.72 3.29 volume Mean value of the 1.62 1.92 2.19 2.61 3.25 porosity from field 1 and field 2 in % by volume

(23) On the basis of the measurements, it is apparent that the porosity in the depth region 13 increases proceeding from very low values at the seating base 16 as the material depth T increases.

(24) It should be pointed out that details shown in the drawings are not necessarily true to scale. For example, the limits of details V and VII shown in FIG. 4 and FIG. 6 and also the lengths of the arrows shown in relation to the material depth T, the material width B and the subfields F1, F2 are not necessarily true to scale, despite the information relating to the scale which can be seen in FIG. 4 to FIG. 7.