GB2414282A

GB2414282A - Mechanical seal

Info

Publication number: GB2414282A
Application number: GB0509460A
Authority: GB
Inventors: Easa Taheri Oskouei
Original assignee: AES Engineering Ltd
Current assignee: AES Engineering Ltd
Priority date: 2004-05-10
Filing date: 2005-05-10
Publication date: 2005-11-23
Also published as: GB0509460D0; GB0410329D0

Abstract

A mechanical seal assembly wherein at least one of the rotary 10 and stationary 11 seal faces comprises means 6a for minimising the leaking of fluid beyond the seal faces by impeding the flow of fluid when in use. The means may be a groove 6a that produces turbulence/eddy-currents 55. Various forms of grooves are disclosed.

Description

P106747GB1 10-5-05 24 1 4282

A MECHANICAL SEAL

FIELD OF INVENTION

This invention relates to mechanical seals for sealing fluids between rotating parts (e.g. a rotating shaft) and stationary parts (e.g. a housing). The invention particularly relates to a mechanical seal having means for minimising the leak of fluid between the seal faces of the said seal.

BACKGROUND INFORMATION

Mechanical seals comprise a "rotary" component that rotates with the shaft and a "stationary" component that is secured to the housing. A seal is formed by urging the rotary and stationary components together using one or more springs, or similar elastic means, such that the respective seal faces of the rotary and stationary components mate forming a sealing relationship with a sliding seal interface.

The seal faces of the rotary and stationary components are typically referred to as the "rotary seal face" and the "stationary seal face". The seal faces are typically annular or radial. Preferably, the seal face is a flat and smooth surface.

A mechanical seal having a spring-loaded rotary component is called a "rotary seal", meanwhile a mechanical seal having a spring-loaded stationary component is called a "stationary seal".

. . . . . . . :. . :e. . . .. :. :e P106747GB1 10-5-05 Mechanical seals with pre-assembled and pre-set rotary and stationary components are known as "cartridge seals", whereas mechanical seals that are built in-situ with components despatched individually by the manufacturer are known as a "component seal".

It is well known that if the seal faces are arranged in direct contact then unwanted heat is generated at the seal interface, the overall power consumption increases, the seal faces wear more quickly and ultimately the life-time of the mechanical seal is reduced.

Therefore a thin layer of fluid is commonly provided between the seal faces during the operation of the mechanical seal. The film of fluid has a lubricating and cooling effect.

The fluid film is usually provided by sufficiently separating the seal faces and such that a small amount of fluid is able to flow from one circumferential edge of the sealing faces to the other. The thickness of the film is determined by the size of the gap between the seal faces, hence the distance of separation is known as the Fluid Film Thickness It.

Obviously, the mechanical seal is at risk of failing if the Fluid Film Thickness is too small because there will not be enough fluid between the seal faces to prevent the above- mentioned undesirable operating conditions. Furthermore, the mechanical seal is also at risk if failing if the Fluid Film Thickness is too wide because the rate of leaking fluid will be too high.

The fluid film may be a film of gas or liquid. The fluid film may be a film of process or product fluid or a secondary fluid such as a buffer or barrier fluid.

US Patent No 4,212,475 (Sedy), US Patent No. 5,454,572 (Pospisil) and US Patent No. 5,529,315 (Borrino et al) describe a commonly used method of forming a fluid film using grooves formed on the mating seal faces. The grooves are arranged so that they extend . . . . . . : . . . : .

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P106747GB1 10-5-05 inwardly from a circumferential edge of the seal faces such that when the mechanical seal is in operation the grooves act as a pump drawing fluid in between the seals faces and forcing the seal faces apart. US Patent 6,046,430 (Etsion) and US Patent 6,341,782 (Etsion) also describe a method of lubricating the separated seal faces of a mechanical seal using a plurality of micropores.

As explained above, a mechanical seal is used to seal fluids. However, the sealing effect of the mechanical seal is compromised when the seal faces are separated to provide a fluid film. Unfortunately, when the seal faces are separated the fluid is able to flow freely and leak. It is essential that the leaking of the mechanical seal is controlled. In certain applications it may be acceptable for the leaking of fluid to be controlled so that it never exceeds more than a few millimetres per hour. If the fluid is hazardous, it is critical that the leakage is eliminated.

STATEMENTS OF INVENTION

The present invention seeks to counteract the sealing problems incurred by providing a fluid film between the sealing faces of a mechanical seal. The present invention seeks to control the leaking of fluid from between the sealing faces. The present invention seeks to overcome the compromised sealing effect by reducing or stopping the leaking of fluid.

The present invention particularly seeks to provide a means and method for minimising the leaking of fluid by impeding the flow of fluid between the seal faces.

A first aspect of the invention relates to a mechanical seal assembly comprising: a rotary seal face of a rotary component arranged in sealing engagement with a stationary seal face of a stationary component; : ': . . e.: :: : . .e:e:e P106747GB1 10-5-05 a fluid forming a film of fluid between the rotary and stationary seal faces as it flows in a first direction from a first diameter side of the seal faces towards a second diameter side when the assembly is in use; and at least one of the rotary and stationary seal faces including means for minimising the leaking of the fluid beyond the second diameter side of the seal faces by impeding the flow of the fluid between the rotary and stationary seal faces when the assembly is in use.

Preferably the means for minimising the leaking of the fluid comprises one or more grooves for changing the direction of fluid flow.

Preferably, the rotary seal face comprises at least one groove when the fluid flows in the first direction from an outer diameter side towards an inner diameter side of the seal faces. Alternatively, the stationary seal face comprises at least one groove when the fluid flows in the first direction from an inner diameter side towards the outer diameter side of the seal faces Preferably the one or more grooves comprises an entry portion for drawing fluid into the groove and an exit portion for directing the fluid out of the groove such that it flows between the rotary and stationary seals in a second direction.

Preferably the one or more grooves are arranged along a balance point of the one or more seal faces.

Preferably a plurality of grooves are arranged bi-directionally on the one or more seal faces to accommodate the bi-directional rotation of the rotary component.

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P106747GB1 10-5-05 A second aspect of the invention relates to a method of minimising the leaking of fluid beyond a rotary seal face and stationary seal face using a mechanical seal assembly according to the first aspect of the invention comprising the steps; of changing the direction of the flow of fluid between the seal faces using the at least one groove; and creating eddy currents to impede the flow of fluid between the seal faces.

Preferably the method further comprises the steps of; drawing fluid into the groove; and directing fluid from the groove such that it flows between the rotary and stationary seal faces in a second direction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings in which: Figure 1 depicts a single seal mechanical seal assembly according to a first embodiment of the invention; Figure 2a depicts a magnified view of the seal interface of the mechanical seal of Figure 1; Figure 2b depicts a cross-sectional view of the rotary seal face of the mechanical seal of Figure 1; ::- .e::e.: ë .. :.e:.

P106747GB1 10-5-05 Figure 2c depicts a magnified cross-sectional view of the rotary seal face of the mechanical seal of Figure 1; Figure 3a depicts a separated rotary seal face and stationary seal face; Figure 3b depicts the restricted flow of fluid between the rotary seal face and stationary seal face of the mechanical seal of Figure 1; Figures 4a, 4b, 4c, 4d and 4e depict different shapes and arrangements of grooves on the rotary seal face of the mechanical seal of Figure 1; Figures 5a, 5b and 5c depict different shaped grooves on the rotary seal face of the mechanical of Figure 1; Figure 6 depicts a single seal mechanical seal assembly according to a second embodiment of the invention; Figure 7a depicts a magnified view of the seal interface of the mechanical seal of Figure Figure 7b depicts a cross-sectional view of the stationary seal face of the mechanical seal of Figure 6; Figure 7c depicts a magnified cross-sectional view of the stationary seal face of the mechanical seal of Figure 6; Figure 8a depicts a separated rotary seal face and stationary seal face; :-:: :..:. . . ::: : be. :-. :e P106747GB1 10-5-05 Figure 8b depicts the restricted flow of fluid between the rotary seal face and stationary seal face of the mechanical seal of Figure 6; Figure 8c depicts the further restricted flow of fluid between the rotary seal face and stationary seal face of the mechanical seal of Figure 6; Figures 9a, 9b and 9c depict different shapes and arrangements of grooves on the stationary seal face of the mechanical seal of Figure 6; and Figures 10a, 10b and 10c depict different shaped grooves on the stationary seal face of the mechanical seal of Figure 6.

DETAILED DESCRIPTION OF INVENTION

The single seal mechanical seal assembly depicted in Figure 1 seals process fluid (4) between a rotatable shaft (1) and a pump housing (2). A rotary component (10) is mounted such that it rotates with the shaft (1). The rotary component (10) comprises a radial rotary seal face (100) arranged in sealing relationship with a stationary seal face (101) of a radial stationary component (11), which is connected to the pump housing (2) via a gland (3). The rotary seal face (100) and stationary seal face (101) are preferably flat and smooth surfaces. In this particular embodiment of the invention a process or product fluid (4) extends across the outer circumferential edges or outer diameters (OD) of the seal faces. However, there is no process fluid in a region (5) bounded by the inner circumferential edges or inner diameters (ID) of the seal faces and a sleeve (102) extending along the shaft (1). The process fluid (4) may be a liquid or gas.

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P106747GB1 10-5-05 Figure 2a depicts a magnified view of the rotary component (10) and the stationary component (11) of the embodiment of the invention shown in Figure 1. The rotary seal face (100) of the rotary component (10) has an inner circumferential edge or inner diameter B and an outer circumferential edge or outer diameter E. The stationary seal face (101) of the stationary component (11) has an inner diameter A and an outer diameter F. The rotary seal face comprises a groove (6a) having an inner diameter C and outer diameter D. Figures 2b and 2c depict a cross-sectional view of the rotary seal face (100) across axis M marked in Figure 2a.

As explained above, a mechanical seal must include a film of fluid between the seal faces for it to function appropriately. Figure 3a shows the rotary sealing face and stationary sealing face separated by a distance to and process fluid flowing from the outer diameter (OD) towards the inner diameter (ID) forming a beneficial lubricating and cooling film (7a). It can be clearly seen that the process fluid will ultimately leak from the inner diameter edges (ID) of the seal faces into region (5) if its flow is unrestricted.

The groove (6a) located on the seal face of the rotary component in Figure 3b is shaped and positioned to impede the flow of fluid such that the leakage of fluid is reduced or eliminated. A film of fluid is formed between the separated seal faces when fluid flows in a first direction from one diameter side of the seal faces towards the other. Upon rotation, the groove acts like a pump forcing a change in the direction of fluid flow. The groove comprises an entry portion and an exit portion. The entry portion is shaped for drawing the fluid into the groove. The exit portion is shaped for directing fluid from the groove into the gap space between the separated seal faces such that it flows in a second direction. The exit portion preferably redirects the fluid in the opposite direction e. . .e ' . . .. : :.

P106747GB1 10-5-05 to that of first direction of flow. This has the effect of producing a swirling effect in the fluid and setting-up eddy currents. The eddy-currents create a barrier-effect, which minimises or even prevents process fluid from leaking from beyond the rotary and stationary seal faces. In the embodiment depicted in Figures 2 and 3, process fluid flows from the outer diameter OD towards the inner diameter ID of the seal faces and forms a film of fluid. The groove (6a) formed on the rotary seal face (100) pumps fluid away from the ID and towards the OD of the seal faces such that eddy- currents are set- up and the leakage of process fluid from ID of the seal faces is reduced.

Figure 6 depicts a second embodiment of the invention where the process or product fluid (4) is stored in the region (5) of the mechanical seal which is bounded by the inner circumferential edges or inner diameters ID of the seal faces. Thus, when the rotary seal face (100) and stationary seal face (101) are separated, a film of fluid (7b) forms as the process fluid flows from the inner diameter side ID of the seal faces towards the outer diameter side (OD).

Figures 7a depicts a magnified view of the rotary component (10) and stationary component (11) of the second embodiment of the invention. As with the first embodiment, the rotary seal face (100) of the rotary component (10) has an inner circumferential edge or inner diameter B and an outer circumferential edge or outer diameter E. The stationary seal face (101) of the stationary component (1 1) has an inner diameter A and an outer diameter F. The stationary seal face comprises a groove (6b) having an inner diameter C and outer diameter D. Figures 7b and 7c depict a cross-sectional view of the stationary seal face (101) across the axis BE, marked in Figure 7a.

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P106747GB1 10-5-05 Figure 8a shows the rotary seal face (100) and stationary seal face (101) separated by a distance t1 and process fluid flowing from the inner diameter edges ID forming a beneficial film of fluid (7b). If the flow is unrestricted then the process fluid will ultimately leak from the outer diameter edges OD of the seal faces.

As with the groove (6a) formed on the rotary seal face in the first embodiment of the invention, the groove (6b) formed on the stationary seal face in the second embodiment of the invention is shaped and positioned to impede the flow of fluid such that leakage from the outer diameter OD of the seal faces is reduced or eliminated.

As the shaft rotates, the groove (fib) redirects the flow of fluid from a first direction (from ID towards OD) to a second direction (from OD towards ID), eddy currents are created and thus the leakage of process fluid from the OD of the seal faces is restricted. See Figure 8b.

Depending on the application and the pumping action required to minimise the leakage of fluid from between the rotary and stationary seals, it may be beneficial to include a one or more further grooves (6c) on the rotary seal face (100) as depicted in Figure 8c.

The further grooves (6c) may be used to aid the creation of eddy currents and barrier effect.

The pumping action is determined by the grooves (e.g. number, shape, arrangement and position on seal faces etc.), the process fluid (e.g. speed of flow, pressure, viscosity etc.) and seal face (e.g. material, speed of rotation, direction of rotation etc.).

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P106747GB1 10-5-05 The pumping action of the grooves formed on the rotary or stationary seal faces is controlled to ensure a lubricating and cooling film of fluid is maintained between the sealing faces of the mechanical seal.

The pumping action of the grooves may generate a pressure which pushes the seal faces further apart (e.g. distance of separation t2, to). Hence, the pumping action is controlled so as to ensure any increase in the distance of separation is minimised such that the mechanical seal does not fail.

One or more grooves may be arranged on a seal face in accordance with the pumping action required. Figures 4a, 4b, 4d and 4e depict a rotary seal face having a plurality of grooves (6a). Figures 9a and 9b depict a stationary seal face having a plurality of grooves (fib) The one or more grooves are preferably arranged along the "balance point" of a seal face. The "balance point" is a region of a seal face surface where the sealing pressure of the seal interface is balanced. The location of the balance point is dependent on the geometry of the seal faces and pressure acting on the seal faces. If the seal face is radial then the balance point extends circumferentially around the seal face surface. The grooves are arranged such that the inner diameter C and outer diameter D extend within the balance point region of the seal face.

The grooves are aligned on the seal face in accordance with the direction of the rotation of the shaft and subsequently the rotation of the rotary seal face. The grooves of a seal face may be bi-directionally aligned, as shown in Figure 4a, 4d, 4e and 9a so that they provide a pumping effect when the shaft rotates in either the clockwise or anti-clockwise direction.

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P106747GB1 10-5-05 The grooves are essentially shaped to change the flow of fluid. As indicated above, the grooves comprise an entry portion for drawing fluid, having a first direction of flow, into to the groove and an exit portion for directing fluid from the groove with a second direction of flow. The grooves may have a V-shaped cross-sectional profile as depicted in Figures 5a and 10a, a triangular cross-sectional profile as depicted in Figures 5b and 10b or alternatively the grooves may have a tear-drop profile as depicted in 5c and 10c. The grooves may also be conical, cylindrical, elliptical or A-shaped. The cross-sectional profile, length, diameter and depth (h) of the grooves is chosen in accordance with the pumping action required to minimise the leakage of process fluid.

A seal face may also comprise a plurality of uniformly shaped or nonuniformly shaped grooves, depending on the effect required.

A plurality of grooves may be arranged to extend along the balance point of a seal face in one or more rows.

The seal faces of the present invention may be formed from a generally soft material or hard material. However, it is preferable for the rotary and stationary seal faces to be formed from hard materials such as silicon or tungsten carbide.

The grooves may be formed on the seal faces using conventional cutting/drilling means and methods. For example the grooves may be cut into the seal faces using a laser.

The grooves help to maintain a film of fluid even when the shaft is not rotating. Process fluid collects in the grooves such that a lubricating effect between the seal faces is always provided. As a consequence, the start-up torque is reduced and hence damage to seal faces and power consumption is reduced when rotation recommences.

i.. . : s: .c P106747GB1 10-5-05 The mechanical seal of the present invention may be a single or multiple seal having two or more sets of sealing faces. The seal faces at the in-board side and/or out-board side of the mechanical seal may comprise one or more grooves.

The mechanical seal of the present invention may be a rotary or stationary seal. The mechanical seal may be a cartridge seal or component seal.

If a mechanical seal includes fluid on both the outer diameter side OD and inner diameter side ID of the seal faces then the pressures and viscosity of the respective fluids determines the location of the grooves. If the fluid on the OD side of the seal faces has a higher pressure and/or viscosity with respect to the fluid on the ID side then one or more grooves must be formed on the rotary seal face. However, if the fluid on the ID side has a higher pressure and/or viscosity with respect to the fluid on the OD side then the one or more grooves must be formed on the stationary seal face. Alternatively, it may be more appropriate to locate one or grooves on both the rotary seal face and the stationary seal face.

The grooves may be used in conjunction with other mechanisms for improving the performance of a mechanical seal.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article i A. ' .. .

P106747GB1 10-5-05 is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

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Claims

P106747GB1 10-5-05 CLAIMS

1. A mechanical seal assembly comprising: a rotary seal face of a rotary component arranged in sealing engagement with a stationary seal face of a stationary component; a fluid forming a film of fluid between the rotary and stationary seal faces as it flows in a first direction from a first diameter side of the seal faces towards a second diameter side of the seal faces when the assembly is in use; and at least one of the rotary and stationary seal faces including means for minimising the leaking of the fluid beyond the second diameter side of the seal faces by impeding the flow of the fluid between the rotary and stationary seal faces when the assembly is in use.

2. A mechanical seal assembly according to claim 1 wherein the means for minimising the leaking of fluid comprises at least one groove for changing the direction of fluid flow.

3. A mechanical seal assembly according to claim 2 wherein the rotary seal face comprises at least one groove when the fluid flows in the first direction from an outer diameter side towards an inner diameter side of the seal faces.

4. A mechanical seal assembly according to claim 2 wherein the stationary seal face comprises at least one groove when the fluid flows in a first direction from an inner diameter side towards an outer diameter side of the seal faces.

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5. A mechanical seal assembly according to any of claims 2 to 4 wherein the at least one groove comprises: an entry portion for drawing fluid into the groove; and an exit portion for directing the fluid out of the groove such that it flows between the rotary and stationary seal faces in a second direction.

6. A mechanical seal assembly according to any of claims claim 2 to 5 wherein the at least one groove is arranged along a balance point of the at least one seal face.

7. A mechanical seal assembly according to any of claims 2 to 6 wherein a plurality of grooves are arranged bi-directionally on the at least one seal face.

8. A method of minimising the leaking of fluid beyond a rotary seal face and a stationary seal face using a mechanical seal assembly according to any of claims 1 to 7 comprising the steps of: changing the direction of the flow of fluid between the seal faces using the at least one groove; and creating eddy-currents to impede the flow of fluid between the seal faces.

9. A method according to claim 8 further comprising the steps of: drawing fluid into the groove; and directing fluid from the groove such that it flows between the rotary and stationary seal faces in a second direction.

10. A mechanical seal assembly as herein described with reference to any of the drawings.

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11. A method of minimising the leaking of fluid beyond a rotary seal face and a stationary seal face as herein described with reference to any of the drawings. ...

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