Mechanical seal arrangement having sliding surfaces of different hardness

Abstract

The invention relates to a mechanical seal arrangement comprising: a rotating slide ring (2) having a first slide surface and a stationary slide ring (3) with a second slide surface which between them define a sealing gap 4, wherein the first and second slide surfaces have different hardnesses, wherein the harder slide surface has a diamond coating (20) and the softer slide surface is produced from carbon composite material, and wherein an average initial roughness R.sub.a1 (of the diamond coating 20) is less than an average initial roughness R.sub.a2 of the slide surface made from carbon composite material.

Claims

1. Mechanical seal arrangement comprising: a rotating slide ring having a first slide surface and a stationary slide ring having a second slide surface which define a sealing gap between them; wherein the first and second slide surfaces have different hardnesses; wherein the harder slide surface has a diamond coating and the softer slide surface is produced from carbon composite material, wherein the carbon composite material is a silicon carbide graphite composite material comprising silicon carbide, graphite and free silicon; and wherein an average initial roughness (Ra1) of the first slide surface of the diamond coating is smaller than an average initial roughness (Ra2) of the second slide surface made from carbon composite material, wherein the diamond coating of the slide ring is additionally provided on a non-sliding surface on an outer peripheral region of the slide ring.

2. Mechanical seal arrangement as claimed in claim 1, wherein the average initial roughness (Ra1) of the slide ring with the diamond coating is 50% less than the average initial roughness (Ra2) of the slide ring made from carbon composite material.

3. Mechanical seal arrangement as claimed in claim 2, wherein the average initial roughness (Ra1) of the diamond coating is in a range of 0.01 μm to 0.06 μm and/or that the average initial roughness (Ra2) of the slide surface made from carbon composite material is in a range of 0.1 μm to 0.2 μm.

4. Mechanical seal arrangement as claimed in claim 1, wherein the diamond coating has doping such that the diamond coating is electrically conductive.

5. Mechanical seal arrangement as claimed in claim 4, wherein the doping is boron doping.

6. Mechanical seal arrangement as claimed in claim 1, wherein the diamond coating is provided only partially on the outer peripheral region of the slide ring and in particular the diamond coating on the outer peripheral region has a tapering region.

7. Mechanical seal arrangement as claimed in claim 1, wherein a support ring at least partially covers the diamond coating provided on the outer peripheral region of the slide ring.

8. Mechanical seal arrangement as claimed in claim 1, wherein the diamond coating of the slide ring is additionally provided on an inner peripheral region of the slide ring.

9. Mechanical seal arrangement as claimed in claim 1, wherein the first slide surface of the diamond coating is polished.

10. Mechanical seal arrangement as claimed in claim 1, wherein the rotating slide ring comprises the diamond coating.

11. Mechanical seal arrangement as claimed in claim 1, wherein the first slide surface of the diamond coating has a support portion of ≧50%.

12. Mechanical seal arrangement as claimed in claim 1, wherein the carbon composite material comprises 60 to 75% by weight silicon carbide, 15 to 40% by weight carbon and 0.5 to 10% by weight free silicon.

13. Mechanical seal arrangement as claimed in claim 1, wherein on the second slide surface made from carbon composite material are formed graphite-containing regions, in particular with a Rockwell hardness of 50 to 100 HR15T, which are arranged to receive free particles.

14. Power station feed pump comprising a mechanical seal arrangement as claimed in claim 1.

15. Mechanical seal arrangement comprising: a rotating slide ring having a first slide surface and a stationary slide ring having a second slide surface which define a sealing gap between them; wherein the first and second slide surfaces have different hardnesses; wherein the harder slide surface has a diamond coating and the softer slide surface is produced from carbon composite material, wherein the carbon composite material is a silicon carbide graphite composite material comprising silicon carbide, graphite and free silicon; and wherein an average initial roughness (Ra1) of the first slide surface of the diamond coating is smaller than an average initial roughness (Ra2) of the second slide surface made from carbon composite material.

16. Mechanical seal arrangement as claimed in claim 15, wherein the average initial roughness (Ra1) of the slide ring with the diamond coating is 50% less than the average initial roughness (Ra2) of the slide ring made from carbon composite material.

17. Mechanical seal arrangement as claimed in claim 15, wherein the diamond coating has doping such that the diamond coating is electrically conductive.

18. Mechanical seal arrangement as claimed in claim 15, wherein the rotating slide ring comprises the diamond coating.

19. Mechanical seal arrangement as claimed in claim 15, wherein the first slide surface of the diamond coating has a support portion of ≧50%.

20. Mechanical seal arrangement comprising: a rotating slide ring having a first slide surface and a stationary slide ring having a second slide surface which define a sealing gap between them; wherein the first and second slide surfaces have different hardnesses; wherein the harder slide surface has a diamond coating and the softer slide surface is produced from carbon composite material, wherein the carbon composite material is a silicon carbide graphite composite material comprising silicon carbide, graphite and free silicon; and wherein an average initial roughness (Ra1) of the first slide surface of the diamond coating is smaller than an average initial roughness (Ra2) of the second slide surface made from carbon composite material, wherein the diamond coating of the slide ring is additionally provided on an outer peripheral region of the slide ring.

Description

(1) A preferred exemplified embodiment of the invention is described in detail hereinunder with reference to the accompanying drawing.

(2) In the drawing:

(3) FIG. 1 is a schematic cross-sectional view of a mechanical seal arrangement for a power station feed pump in accordance with one exemplified embodiment of the invention,

(4) FIG. 2 is an enlarged cross-sectional view of the slide rings of FIG. 1 and

(5) FIG. 3 is a further enlarged schematic cross-sectional view of the slide rings of FIG. 1 and FIG. 2.

(6) A mechanical seal arrangement 1 according to one preferred exemplified embodiment of the invention is described in detail hereinunder with reference to FIGS. 1 to 3.

(7) FIG. 1 schematically shows the mechanical seal arrangement 1 for a power station feed pump comprising a rotating slide ring 2 and a stationary slide ring 3. A sealing gap 4 is formed in a known manner between the two slide rings 2, 3. The rotating slide ring 2 is connected to a shaft bushing 8 via a rotating support ring 7. First and second pins 10, 11 are provided for rotation and for transfer of torque. The shaft bushing 8 is arranged on a rotating shaft 5.

(8) The stationary slide ring 3 has a binding 9 which is fixed to a housing 6 via a stationary support ring 12.

(9) The mechanical seal arrangement 1 thus seals off a medium 13, to be conveyed by the power station feed pump with respect to the surroundings 14. The medium 13 in this exemplified embodiment is pure water. The poor electrical conductivity of the pure water and the high sliding speed of the rotating slide ring 2 result in high electric potentials of a number of volts between the slide rings. The sliding speeds are conventionally between 40 m/s to 60 m/s.

(10) The rotating slide ring 2 is further provided with a diamond coating 20. In so doing, the whole slide surface 40 of the rotating slide ring 2 is coated with diamond. This is shown in detail in FIGS. 2 and 3.

(11) The diamond coating 20 is thus formed both on a slide surface 40 of the rotating slide ring 2 and also on an outer peripheral region 2a and an inner peripheral region 2b. Thus a region 20a tapering in the direction away from the slide surface 40 is formed on the outer peripheral region 2a. In the same manner, a region 20b tapering in the direction away from the slide surface 40 is formed on the inner peripheral region 2b of the slide ring. In other words, the diamond coating 20 is also partially provided on the inner and outer periphery of the slide ring.

(12) Furthermore, the rotating support ring 7 partially covers the outer, tapering region 20a of the diamond coating. It is thereby ensured that the medium 13 located on the outer periphery does not come into contact with the base material of the slide ring 2. In this way, the diamond-coated rotating slide ring can also be used in highly aggressive media. The diamond coating protects the basic material of the slide ring. By virtue of the tapering region 20a on the outer peripheral region of the slide ring, in particular a very good seal can be obtained between the support ring 7 and the tapering region 20 of the diamond coating.

(13) As also shown in FIG. 3, the diamond coating 20 is subjected to a polishing step after the coating process and so in addition to the depressions 22 still present, a multiplicity of flattened regions 21 are formed. In order for the diamond layer to be electrically conductive, it also comprises boron doping 23.

(14) The stationary slide ring 3 is produced from a carbon composite material which includes approx. 62% by weight silicon carbide, approx. 35% by weight graphite and a small proportion of ca. 3% by weight free silicon. A slide surface 41 of the stationary slide ring 3 has a multiplicity of raised areas 31 and depressions 32 on the surface of the stationary slide ring.

(15) FIG. 3 shows the average roughness R.sub.a. The average roughness R.sub.a is an arithmetical average value of all deviations of the roughness profile from a centre line. In the diamond coating 20 the centre line is designated by M1 and on the roughness profile of the stationary slide ring 3 by M2. The average roughness in the case of the diamond coating 20 is designated by R.sub.a1 and the average roughness R.sub.a in the case of the stationary slide ring 3 is designated by R.sub.a2.

(16) It is thus clear that the average roughness R.sub.a1 of the diamond coating 20 is clearly smaller than the average roughness R.sub.a2 of the stationary slide ring 3 made from carbon composite material. The reason for this is that the surface of the diamond coating 20 has been subjected to a further polishing step to form the flattened regions 21. Between the flattened regions 21, depressions 22 are present in each case. The stationary slide ring 3 made from carbon composite material has not been polished or has been polished less than the diamond-coated rotating slide ring 2.

(17) The selection of the different materials for the rotating and stationary slide rings means that, by reason of the diamond coating 20 on its slide surface 40, the rotating slide ring 2 also has greater hardness on the slide surface than the stationary slide ring 3 produced from the carbon material. In accordance with the invention, the reduced roughness profile on the diamond coating 20 means that a harder rotating slide ring 2 can now run against a softer stationary slide ring 3 without this causing damage or abrasion or wear or the like on the softer stationary slide ring 3. By virtue of the lower average roughness R.sub.a1 of the harder diamond coating 20 it is therefore possible to prevent the increased wear usually expected with such a slide ring pairing.

(18) This discovery which is also surprising to a person skilled in the art now makes it possible for mechanical seal arrangements to be able to be used in which only one of the slide rings, particularly the rotating slide ring 2, has been provided with a diamond layer 20. The other, softer slide ring has no such hard layer but rather has a slide surface of carbon composite material. Nevertheless, a long service life for the mechanical seal arrangement 1 corresponding to a service life of a mechanical seal arrangement in which both slide rings have a diamond coating can be obtained.

(19) Furthermore, the doping 23 in the diamond coating 20 ensures that between the two slide rings no high electric potential occurs between the two slide rings and so the slide surfaces 40, 41 cannot be destroyed by electric discharges.

(20) Therefore, the mechanical seal arrangement 1 in accordance with the invention is suitable particularly for use in feed water pumps of power stations, which are frequently started up and stopped and in which constantly changing thermal conditions are present. Nevertheless, the mechanical seal arrangement in accordance with the invention is highly robust and has a long service life.

(21) The support portion of the slide surface 40 of the diamond coating 20 is about 60%. The support portion is defined as the quotient of the sum of all flattened regions 21 with respect to the total surface of the slide surface 40 on the diamond coating 20 (annular surface).

(22) In this exemplified embodiment an average roughness R.sub.a1 of the diamond coating 20 is about 0.03 μm and an average roughness R.sub.a2 of the slide surface 41 of the stationary slide ring 3 made from carbon composite material is about 0.15 μm. In other words, the average roughness R.sub.a2 of the carbon composite material on the stationary slide ring 3 is about five times as high as the average roughness R.sub.a1 of the diamond coating 20.

LIST OF REFERENCE NUMERALS

(23) 1 mechanical seal arrangement

(24) 2 rotating slide ring

(25) 2a outer peripheral region

(26) 2b inner peripheral region

(27) 3 stationary slide ring

(28) 4 sealing gap

(29) 5 shaft

(30) 6 housing

(31) 7 rotating support ring

(32) 8 shaft bushing

(33) 9 binding

(34) 10 first pin

(35) 11 second pin

(36) 12 stationary support ring

(37) 13 medium

(38) 14 surroundings

(39) 20 diamond coating

(40) 20a tapering region on the outer periphery

(41) 20b tapering region on the inner periphery

(42) 21 flattened regions

(43) 22 depressions

(44) 23 boron doping

(45) 31 raised areas

(46) 32 depressions

(47) 40 slide surface diamond coating

(48) 41 slide surface carbon composite material

(49) R.sub.a1 average initial roughness of the diamond coating

(50) R.sub.a2 average initial roughness of the carbon composite material

(51) M1, M2 reference line