Mechanical Seal with Enhanced Face Stability

Abstract

A seal assembly for use with a rotating shaft. The seal assembly comprises a seal ring, a seal ring shell and bellows. The seal ring defines an axially extending annular surface and a radially extending seal face. The seal ring shell has a front piece and a back piece secured together. The front piece includes a foot portion defining an axially extending engagement surface for interference-fit engagement with the annular surface of the seal ring. The front piece further includes a radially extending shin portion connected to the foot portion and located radially outward of the foot portion. The foot portion includes an inner foot portion extending axially from connection of the foot portion with the shin portion. The foot portion at its engagement surface has an axial length. The inner foot portion at its engagement surface has an axial length. The shin portion has an axial length. The bellows defines an effective diameter at zero pressure applied on the seal ring. The interface of the foot portion with the seal ring defines an interference diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional (prior art) primary ring assembly of a bellows mechanical seal.

FIG. 2 is a cross-sectional free-body diagram of the conventional (prior art) primary ring assembly of FIG. 1, showing contact pressure distribution under room temperature and no differential pressure applied on the primary ring by process/barrier liquid.

FIG. 3 is a cross-sectional free-body diagram of the conventional (prior art) primary ring assembly of FIG. 1, showing forces and contact pressure distribution under full operating temperature and external pressure applied on the primary ring by process/barrier liquid.

FIG. 4 is a cross-sectional free-body diagram of the conventional (prior art) primary ring assembly of FIG. 1, showing forces and contact pressure distribution under full operating temperature and internal pressure applied on the primary ring by process/barrier liquid.

FIG. 5 is a cross-sectional view of a primary ring assembly of a bellows mechanical seal embodying the features of the present invention.

FIG. 5A is a cross-sectional view of an alternative primary ring and an alternative primary ring shell embodying the features of the present invention.

FIG. 6 is an enlarged cross-sectional view of the primary ring and primary ring shell of the primary ring assembly of FIG. 5.

FIG. 7 is a cross-sectional free-body diagram of the primary ring assembly of FIG. 5, showing contact pressure distribution under room temperature and no differential pressure on the primary ring by process/barrier liquid.

FIG. 8 is a cross-sectional free-body diagram of the primary ring assembly of FIG. 5, showing contact forces and contract pressure distribution under full operating temperature and external pressure applied by process/barrier liquid.

FIG. 9 is a cross-sectional free-body diagram of the primary ring assembly of FIG. 5, showing contact forces and contract pressure distribution under full operating temperature and internal pressure applied by process/barrier liquid.

FIG. 10 is a cross-sectional view of the primary ring assembly of FIG. 5 used in conjunction with a conventional mating ring assembly.

FIG. 11 is a cross-sectional view of the primary ring assembly of FIG. 5 used in conjunction with a mating ring assembly embodying the features of the present invention.

FIG. 12 is a cross-sectional view of an alternative primary ring assembly embodying the features of the present invention, with a symmetrical, unbalanced primary ring.

FIG. 13 is a cross-sectional view of an alternative primary ring assembly embodying the features of the present invention, with a symmetrical, balanced primary ring.

Claims

1. A seal assembly for use with a rotating shaft, the seal assembly comprising: a seal ring defining an axially extending annular surface and a radially extending seal face; anda seal ring shell having a foot portion defining an axially extending engagement surface for interference-fit engagement with said annular surface of said seal ring, said seal ring shell further includes a radially extending shin portion connected to said foot portion and located radially outward of said foot portion, said foot portion at its engagement surface has an axial length greater than the axial length of said shin portion.

2. The seal assembly as claimed in claim 1 wherein said foot portion further includes an inner foot portion extending axially from the connection of said foot portion with said shin portion.

3. The seal assembly as claimed in claim 2 wherein said inner foot portion at its engagement surface has an axial length, the ratio of the length of the inner foot portion at its engagement surface to the length of the foot portion at its engagement surface is greater than 0.5.

4. The seal assembly as claimed in claim 3 wherein said inner foot portion extends axially from the connection of said foot portion with said portion in a direction away from said seal face of said seal ring.

5. The seal assembly as claimed in claim 2 wherein said foot portion further includes an outer foot portion extending axially from the connection of said foot portion with said shin portion in a direction away from said inner foot portion.

6. The seal assembly as claimed in claim 1 wherein said seal ring shell further includes an axially extending thigh portion connected to said shin portion and located radially outward of said shin portion.

7. The seal assembly as claimed in claim 6 wherein said seal ring shell further includes a hub extending radially outward from connection of said shin portion with said thigh portion.

8. The seal assembly as claimed in claim 1 wherein said seal ring shell has a front piece and a back piece secured together.

9. The seal assembly as claimed in claim 8 wherein said seal ring shell further includes a welded joint securing said front piece to said back piece.

10. The seal assembly as claimed in claim 9 further comprising bellows secured to said back piece of said shell.

11. The seal assembly as claimed in claim 5 further comprising a bellows and wherein said seal ring shell further includes a back piece secured to said thigh portion, said bellows secured to said back piece.

12. The seal assembly as claimed in claim 1 wherein said seal ring shell is formed of Alloy 718.

13. The seal assembly as claimed in claim 1 wherein said seal ring is a primary ring axially movable with a shaft, said seal further comprising a mating ring fixed against axial movement and a mating ring shell, said mating defines a seal face for engagement with said seal face of said primary ring, said mating ring shell having a foot portion defining an engagement surface for interference-fit engagement with said mating ring, said mating ring shell further includes a shin portion connected to said foot portion and located radially outward of said foot portion, said foot portion of said mating ring shell includes an inner foot portion extending axially from the connection of said foot portion with said shin portion.

14. The seal assembly as claimed in claim 13 wherein said foot portion of said mating ring shell further includes an outer foot portion extending axially from the correction of said foot portion with said shin portion in a direction away from said inner foot portion of said mating ring shell.

15. A seal assembly for use with a rotating shaft, the seal assembly comprising: a seal ring defining an axially extending annular surface and a radial extending seal face;a bellows defining an effective diameter at zero differential pressure applied on said seal ring; anda seal ring shell having a front piece and a back piece secured together, said front piece includes a foot portion defining an axially extending engagement surface for interference-fit engagement with said annular surface of said seal ring, the interface of said foot portion with said seal ring defines an interference diameter, the interference diameter is within +10% and −10% of said effective diameter of said bellows at zero differe-ntial pressure.

16. The seal assembly as claimed in claim 15 wherein the interference diameter is within +6% and −6% of said effective diameter of said bellows at zero differential pressure.

17. The seal assembly as claimed in claim 15 wherein said seal ring shell further includes a welded joint securing said front piece to said back piece

18. The seal assembly as claimed in claim 15 wherein said seal ring shell is formed of Alloy 718.

19. A seal assembly for use with a rotating shaft, the seal assembly comprising: a seal ring defining an axially extending annular surface and a radially extending seal face; anda seal ring shell includes a foot portion defining an axially extending engagement surface for interference-fit engagement with said annular surface of said seal ring, said seal ring shell further includes a radially extending shin portion connected to said foot portion and located radially outward from said foot portion, said foot portion includes an inner foot portion extending axially from connection of said foot portion with said shin portion, said foot portion at its engagement surface has an axial length, said inner foot portion at its engagement surface has an axial length, the ratio of the length of the inner foot portion at its engagement surface to the length of the foot portion at its engagement surface is greater than 0.5.

20. The seal assembly as claimed in claim 19 wherein the ratio of the length of the inner foot portion at its engagement surface to the length of the foot portion at its engagement surface is between 0.556 and 0.625.

21. The seal assembly as claimed in claim 19 wherein said foot portion further includes an outer foot portion extending axially from the connection of said foot portion with said shin portion in a direction away from said inner foot portion.

22. The seal assembly as claimed in claim 19 wherein said seal ring shell has a front piece and a back piece secured together.

23. The seal assembly as claimed in claim 19 wherein said seal ring shell is formed of Alloy 718.