NL2013406B1

NL2013406B1 - Shaft seal.

Info

Publication number: NL2013406B1
Application number: NL2013406A
Authority: NL
Inventors: Swarte Pepijn
Original assignee: Lagersmit Sealing Solutions B V
Priority date: 2014-09-03
Filing date: 2014-09-03
Publication date: 2016-09-27

Abstract

A sealing structure for a rotatable shaft comprises a housing with an annular cavity on an inside of the housing; and a cartridge which sits within the annular cavity and is able to move radially within the annular cavity. The cartridge comprises a plurality of annular sealing elements to seal against the rotatable shaft.

Description

SHAFT SEAL

BACKGROUND

Seals around rotating shafts, for example, around a shaft connecting a propeller to an engine of a vessel, work to keep lubricating or flushing fluid in place around bearings for properly lubricating and/or flushing the bearings. Seals also work to ensure that the lubricating or flushing fluid does not leak into other parts. Typically, a propeller is mounted with a forward bearing and an aft bearing, each having a seal associated with the bearing to seal in the lubricant for the bearing. The lubricant is typically oil-based lubricant.

Recent vessels have begun using outboard water for lubricating or flushing bearings, and this outboard water is introduced into the system by removing the aft seal to allow water in. Thus, outboard water systems typically only have a seal associated with the forward bearing. When using outboard water, the bearings can be more prone to wear as the outboard water often contains abrasive particles. Additionally, when the shaft is not rotating, growth of biological content on the bearings can increase causing wearing down of the bearings rapidly when shafts start running again. The wear of the bearings can result in fairly large shaft movement in the radial direction.

SUMMARY

According to a first aspect of the invention, a sealing structure for a rotatable shaft comprises a housing with an annular cavity on an inside of the housing; and a cartridge which sits within the annular cavity and is able to move radially within the annular cavity. The cartridge comprises a plurality of annular sealing elements to seal against the rotatable shaft.

Such a sealing structure allows for sealing on a shaft that is subject to movements in the radial direction.

According to an embodiment, the cartridge further comprises one or more bearing surfaces positioned to contact the rotatable shaft.

According to an embodiment, the plurality of sealing elements comprise a plurality of coaxial lip seals held by the cartridge to seal against the rotatable shaft. Optionally, each of the plurality of lip seals extend in a sealing plane transverse with respect to the rotatable shaft.

According to an embodiment, the cartridge comprises a plurality of annular rings. Optionally, a sealing element is secured between each of the plurality of annular rings. Further optionally, the plurality of annular rings forming the cartridge are secured together by a plurality of bolts.

According to an embodiment, the sealing structure further comprises antirotation means to keep the cartridge from rotating within the housing. Optionally, the anti-rotation means comprises a projecting element extending from a cavity in the housing to a bore in the cartridge.

According to an embodiment, the sealing structure further comprises one or more o-rings for sealing the cartridge axially within the annular cavity of the housing.

According to an embodiment, the sealing structure further comprises a seal condition monitoring system connected to an interior chamber formed between a first and a second sealing element, and able to indicate when the first sealing element has failed.

According to an embodiment, the seal condition monitoring system comprises a tank fluidly connected to the interior chamber between the first and second sealing element; and a fluid inside the tank, wherein the fluid inside the tank will rise when the first sealing element has failed.

According to an embodiment, the cartridge comprises two sealing elements and three bearing surfaces.

According to an aspect, a propeller shaft can include the sealing structure.

According to a second aspect of the invention, a method of sealing around a rotatable shaft comprises positioning an annular cartridge with a sealing element into a cavity in a housing so that the cavity is sealed with respect to the cartridge axially and so that the cartridge can move radially within the cavity; and connecting the rotatable shaft through the cartridge so that a sealing element contacts the rotatable shaft and the cartridge moves with the radial movement of the rotatable shaft.

According to an embodiment, the method further comprises inserting a projecting element to extend between a bore in the cartridge and a cavity in the housing so that the cartridge cannot rotate with the rotatable shaft.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective view of a rotatable shaft with a sealing structure. FIG. 2a shows a cross-sectional view of the sealing structure of Fig. la. FIG. 2b shows a close up view of portion lib of Fig. 2a FIG. 3 shows a cross-sectional view of a sealing structure with a seal condition monitoring system.

DETAILED DESCRIPTION FIG. 1 shows a perspective view of a rotatable shaft 10 with a sealing structure 12, and includes liner 14 and housing 16 with end ring 18. Liner 14 secures to rotatable shaft 10 and rotates with rotatable shaft 10. Rotatable shaft 10 can be connected between, for example, an engine and a propeller of a vessel.

Sealing structure 12 works to ensure that lubricating and/or flushing fluid for an adjacent bearing stays in place and does not leak out into other spaces. As mentioned, some vessels have begun using outboard water to lubricate and/or flush bearings holding rotatable shaft 10. This outboard water typically includes abrasive particles which cause wear on bearings. Thus, when bearings wear sufficiently, shaft 10 will lower. Shaft 10 is particularly prone to lowering in systems that use outboard water because in such systems typically only have a forward seal (not an aft seal) to allow the outboard water in. This movement of shaft 10 can interfere with proper sealing around bearing(s).

Sealing structure 12 allows for a sealing connection despite movement of shaft 10 through the use of a structure that can move sealing elements with rotatable shaft 10. FIG. 2a shows a cross-sectional view of the sealing structure 12 and liner 14 which rotates around axis of rotation RA (in combination with shaft 10, not shown in Figs. 2a-2b). FIG. 2b shows a close up view of portion lib of Fig. 2a Sealing structure 12 includes housing 16 (with end ring 18, axial cavity 19 and annular cavity 20), cartridge 22, projecting element 26, o-rings 28 and inflatable seal 30. Cartridge 22 includes rings 32, 34, 36 with bearing surfaces 33, 35 and 37 and lip seals 38a, 38b.

Housing 16 includes annular cavity 20 which extends radially from an inside of the housing 16 and axial cavity 19 which extends axially on an inside wall of end ring 18. Cavity 20 is sized in relation to the diameter of the rotatable shaft 10 and/or expected shaft movement during system use. Axial cavity 19 is sized to receive projecting element 26, and allows for radial movement of projecting element 26 but not rotational movement around axis of rotation RA.

Cartridge 22 is formed of rings 32, 34 and 36, though could be a different number of rings or one piece in other embodiments. Rings 32, 34 and 36 can be joined by, for example, bolts. Cartridge 22 includes bearing surfaces 33, 35 and 37 which contact to rotating liner 14. Cartridge 22 holds sealing elements, in this case lip seals 38a, 38b, against liner 14. Lip seals 38a, 38b sit coaxially around liner 14 and extend in a sealing plane transverse with respect to liner 14. O-rings 28 form a seal between cartridge 22 and housing 16 in an axial direction on each side of cartridge 22. Cartridge 22 is sized to be able to move radially within cavity 20, with a set amount of clearance between the outer side of cartridge 22 and the side of cavity 20. This amount of clearance depends on shaft size, the acceptable tolerance for shaft 10 movement within system, expected bearing wear, and other system factors.

Inflatable seal 30 sits within housing 12 and is axially displaced from cartridge 22. Inflatable seal 30 can be inflated or deflated through an air inlet and an air outlet (not shown). When inflated, inflatable seal contacts shaft 10 to form a seal against shaft 10.

In operation sealing structure 12 works to form a seal between housing 16 and a rotating surface, in this case, liner 14. Cartridge 22 fits into annular cavity 20, sealed axially by o-rings 28. Annular cavity 20 is sized to allow for movement of cartridge 22 radially within cavity 20. Projecting element 26 extends between cartridge 22 and housing 16 to ensure that cartridge 22 does not rotate around axis of rotation RA with liner 14 (and shaft 10).

The seal is formed by the connection between cartridge 22 and liner 14, with bearing surfaces 33, 35 and 37 and lip seals 38a, 38b contacting liner 14. Lip seal 38a forms the seal, with lip seal 38b acting as a backup seal in the case of a failure of lip seal 38a. The tight fit between cartridge 22 and cavity 20, and o-ring 28 form a seal to ensure that fluid does not enter cavity 20 radially outward from cartridge 22.

As mentioned above, particularly when outboard water is used to lubricate or flush bearings, the bearings for rotating shaft 10 wear away, and shaft 10 descends. This can happen from abrasive particles in the lubricating or flushing water. Sealing structure 12 with moveable cartridge 22 allows lip seals 38a, 38b to move with any movement of shaft 10, keeping seals 38a, 38b in contact with liner 14 to ensure proper sealing despite radial movement of shaft 10 and/or liner 14. Bearing surfaces 33, 35 and 37 of cartridge 22 ensure that cartridge 22 stays in contact with shaft 10. Bearing surfaces 33, 35, 37 also work to protect lip seals 38a, 38b, reducing wear on lip seals 38a, 38b by being the weight bearing component of cartridge 22 of sealing structure 12.

Sealing structure 12 provides a simple way of sealing against rotating shaft 10 and/or liner 14 by forming a seal using cartridge 22 that is moveable within cavity 20 of housing 16. Floating cartridge 22 allows for sealing with lip seals 38a, 38b despite large movements of shaft 10, which could not be accommodated by lip seals 38a, 38b alone. Thus, sealing structure 12 can have a longer lifespan by allowing for sealing despite wear on bearings and subsequent large movement of shaft 10 (and liner 14). FIG. 3 shows a cross-sectional view of a sealing structure 12 around liner 14 with a seal condition monitoring system 40. Similar parts are labeled similarly to Figs. la-2b. Sealing structure 12 includes housing 16 with cavity 20, cartridge 22, o-rings 28 and inflatable seal 30. In this embodiment, cartridge 22 is formed as one integral part which includes bearing surfaces 33, 35 and 37 and holds lip seals 38a, 38b.

Seal condition monitoring system 40 includes tank 42 with fluid 44, connected to chamber 46. Chamber 46 is the area between lip seal 38a and 38b. In normal operation, chamber 46 is dry (with the exception of grease to ensure lubrication of seals 38a, 38b), as lip seal 38a seals against liner 14 to prevent fluid from entering chamber 46. If lip seal 38a were to fail, chamber 46 would fill with liquid, causing liquid 44 level in tank 42 to rise. Thus, a rise in liquid 44 within tank 42 indicates that seal 38a has failed, and needs replacing. In the meantime, seal 38b can form the sealing connection between cartridge 22 and liner 14 until seal 38a is replaced. Replacement can take place, for example, using inflatable seal 30 to seal off system, and then take out and replace seal 38a in cartridge 22. Seal condition monitoring system 40 is a simple system which can be used to indicate the failure and/or need for replacement of seal 38a within sealing structure 12.

While Figs. 1-3 show sealing of sealing structure against liner 14, sealing structure 12 could seal directly against rotating shaft 10. This may be, for example, in an embodiment that uses a different sealing element than lip seals 38a, 38b shown. Additionally, other configurations and/or types of sealing elements could be used in combination with cartridge 22 for sealing against a rotating element.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

A sealing structure for a rotatable shaft, the sealing structure comprising: a housing with an annular recess on an inner side of the housing; and a cartridge located in the recess, the cartridge comprising a plurality of annular sealing elements to seal against the rotatable shaft, the cartridge being able to move radially within the annular cavity.

A sealing structure according to claim 1, wherein the cartridge further comprises: one or more bearing surfaces placed in contact with the rotatable shaft.

A sealing structure according to any one of the preceding claims, wherein the plurality of sealing elements comprise: a plurality of coaxial lip seals held by the cartridge to seal against the rotatable shaft.

A sealing structure according to claim 3, wherein each of the plurality of lip seals extend transversely of the rotatable shaft in a sealing surface.

A sealing structure according to any one of the preceding claims, wherein the cartridge comprises a plurality of ring shapes.

A sealing structure according to claim 5, wherein a sealing element is attached between each of the plurality of ring shapes.

A sealing structure according to any of claims 5-6, wherein the plurality of ring shapes are attached to each other by means of a plurality of bolts.

A sealing structure according to any one of the preceding claims, and further comprising: anti-rotation means to prevent rotation of the cartridge in the housing.

A sealing structure according to claim 8, wherein the anti-rotation means comprise a protruding element which extends from a cavity in the housing to a cavity in the cartridge.

A sealing structure according to any one of the preceding claims, and further comprising: one or more O-rings for axially sealing the cartridge within the annular cavity of the housing.

A sealing structure according to any one of the preceding claims, and further comprising: a sealing condition sensing system connected to an internal chamber formed between a first and a second sealing element and capable of indicating when the first sealing element has collapsed.

The seal structure of claim 11, wherein the seal condition sensing system comprises: a reservoir smoothly connected to the internal chamber between the first and second seal element; and a fluid in the reservoir, wherein the fluid will rise in the reservoir when the first sealing element has collapsed.

A sealing structure according to any one of claims 2-12, wherein the cartridge comprises two sealing elements and three bearing surfaces.

14. Propulsion shaft with the sealing construction according to one of the preceding claims.

A method of sealing around a rotatable axis, the method comprising: positioning an annular cartridge with a sealing element in a cavity in a housing so that the cavity is axially sealed with respect to the cartridge and so that the cartridge can move radially in the cavity; and connecting the rotatable shaft through the cartridge so that a sealing element contacts the rotatable shaft and moves the cartridge with the radial movement of the rotatable shaft.

The method of claim 15, and further comprising: inserting a protruding element to protrude between a bore in the cartridge and a cavity in the housing so that the cartridge cannot rotate with the rotatable shaft.