WO1989002999A1

WO1989002999A1 - Mechanical seal

Info

Publication number: WO1989002999A1
Application number: PCT/US1988/003418
Authority: WO
Inventors: Mark James Wayne Petch
Original assignee: Durametallic Corporation
Priority date: 1987-10-02
Filing date: 1988-09-30
Publication date: 1989-04-06
Also published as: AU2551188A

Abstract

A cartridged mechanical seal (10) having a pair of axially opposed primary seal rings (18, 34), each of which is intentionally split, by induced fracture, to form two complementary halves, wherein the first split seal ring (18) is mounted for rotation with a shaft, and the second split seal ring (34) is fixed against rotation in the seal housing (12), with a spring-biased thrust plate (32) pressing the second split seal ring (34) against the first (18) to provide sealing contact between them. A rubber cup element (33) is sandwiched between the thrust plate (32) and the rear of the second split seal ring (34) to provide a frictional coupling between them, and thereby prevent the spring-biased second split seal ring (34) from being rotated by contact with the first split seal ring (18), without interfering with the free floating action of the sethe second split seal ring (34).

Description

MECHANICAL SEAL

FIELD OF THE INVENTION

The present invention relates to mechanical seals, and particularly relates cartridged "split" rotary face mechanical seals.

It is an object of the present invention to provide a novel and improved split form of a cartridged mechanical seal.

In the mechanical seal of this invention, the seal has a rotary sealing interface between two seal elements, a first said seal element being associated with a housing and the second said seal element being associated with a rotatable shaft passing through the housing, said mechanical seal having both non-split annular or cylindrical elements, and split annular or cylindrical elements composed of a plurality of complementary parts.

Further, in the mechanical seal of this invention, the seal has a rotary sealing interface between two seal elements, wherein a first said seal element is held by a retaining member, the retaining member being movable in a direction substantially parallel to the axis of rotation of a said seal element, and provided with biasing means to urge said retaining member axially relative to the second said seal element, to press said first seal element against said second seal element, and wherein an elastomeric lining is provided between said first seal element and said retaining member. BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of one preferred form of the invention, given by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a seal of the present invention in end view.

Figure 2 shows the seal of Figure 1 in side view, sectioned along line A-A.

DETAILED DESCRIPTION

In its preferred form the invention comprises a cartridged form of split mechanical seal for providing a positive seal between a rotatable shaft and a housing through which it passes. With such seals a sealing interface is formed between rotating and non-rotating parts, this comprising a "mechanical seal".

Two extremely flat radially extending surfaces, each formed on a fractured ring element comprised of two complementary half-rings, are brought together, one of which rotates with the shaft and the other of which is fixed with the housing. Variation in the contacting surfaces is reduced to within the order of two helium light bands. Because the surfaces are so flat, a seal is formed by the contact between the two. To maintain the integrity of the seal function however, it is important that the two surfaces do not move axially apart at all, and it is therefore necessary to compen¬ sate for axial movement of the shaft relative to the housing, to prevent such movement from separating the - 3 - two surfaces. It is also necessary to compensate for wear on the contacting surfaces, and also to prevent the two halves of each seal ring element from separating.

The preferred embodiment of the present invention comprises-a cartridged form of mechanical seal assembly 10 as shown in Figures 1 and 2, for use at a point where a rotating shaft 11 passes through a housing 12.

Elements of the seal 10 are associated with the shaft 11, and rotate with it, while other elements of the seal 10 are associated with the housing 12 and do not rotate. The present invention in its preferred form particularly relates to the interface between rotating and non-rotating parts of the seal, and to the join between the two complementary parts of the fractured seal rings. In another aspect the present invention also relates to means for facilitating removal and replacement of worn or damaged parts of the seal.

Rotary Elements of the Preferred Apparatus The principal rotating elements of the seal 10 comprise a sleeve 13, a clamping collar 14, an O-ring 15, a capping ring 16, a boot seal 17 and a rotary split real ring 18.

The sleeve 13 is clamped onto the shaft 11 by the clamping collar 14, and comprises a single unbroken cylindrical element. A number of slots 19 are provided in the sleeve 13 adjacent one end, to form a "collet" clamping mechanism which allows constriction of the sleeve 13 at that end by the collar 14, such that it can be firmly clamped in the correct axial position on the rotatable shaft 11 of the equipment to be sealed. A lip 20 may be provided on the end of the sleeve 13 to retain the clamping collar 14, which preferably comprises a pair of half-rings joined by cap screws 21. By removing the cap screws 21, the clamping collar 14 can also be removed, and this allows the non-split gland end plate 31 to be axially moved away from the rest of the seal, to facilitate easier access to parts of the seal 10 which may from time to time require replacement.

Setting clips 25 are provided at intervals around the clamping collar 14, which bear against the non- rotating gland end plate 31. Preferably they are formed of reinforced plastic, and are fixed to the clamping collar by cap screws. The setting clips 25 act to hold the seal 10 together during assembly, transport and installation, such that it comprises a pre-set "cartridge" unit which is able to be transported and used in a substantially integrated pre-set form. This reduces the need for high precision assembly work at the installation site. The setting clips 25 act not only to keep the parts of the seal assembly 10 in the correct axial positions and spacing, but also to keep the parts in concentric alignment, by lock and correctly locating the rotary components relative to the non-rotating components.

It is important that the non-rotating parts of the apparatus be concentrically aligned with the rotating parts, for proper functioning of the seal to be provided. Proper clearance is required between "non- contacting" rotating and non-rotating parts, and furthermore it is important that hydraulic loads bear evenly on exposed faces of the split seal rings, to avoid separation of the complementary ring sections.

The various rotary elements, such as the sleeve 13 and collar 14, are fixed around the shaft 11 and will in normal use be concentric with it. The non-rotating elements however are not fixed to the shaft, and means must therefore be provided for holding the non-rotating elements in the correct placement while the seal 10 is being installed. The setting clips 25 bridge between the collar 14 (a rotary element) and a recess 38 in the face of the non-rotating gland end plate 31. The inner rim of the recess 38 has the same diameter as the outer circumference of the collar 14, and the setting clips 25, provided at intervals around the collar 14, hold these two surfaces in concentric alignment. All the non-rotating parts of the seal assembly 10 are directly or indirectly connected to the gland end plate 31, and are consequently also held in alignment. At least three setting clips 25 are provided, equidistantly spaced around the collar 14. The setting clips 25 are removed after the glands 30 and 31 are fixed to the housing 12 and the sleeve clamping ring 14 is tightened with screws 21.

At the opposite end of the sleeve 13, a secondary sealing O-ring 15 is provided in a tapered annular recess 22, which in use prevents leakage between the shaft 11 and the sleeve 13. The O-ring 15 is preferably of the split type, such that it can be readily removed and replaced about the shaft 11 if necessary. The capping ring 16 holds the O-ring 15 in the recess 22 in normal use, and comprises a pair of half-ring elements which are clamped together over a flange 23 on the sleeve 13. A tapered recess 24 is provided in the capping ring 16, complementary to the tapered recess 22 in the sleeve 13, and the relative dimensions of the various parts are such that the O-ring 15 is approxi¬ mately two-thirds held within the recess 22 and one- third held within the recess 24. A consequence of this is that when the capping ring 16 is removed, the O-ring 15 partly protrudes from the end of the sleeve 13, and can readily be drawn out of the recess 22 with a suitable tool. If the O-ring 15 was contained com¬ pletely within the recess 22, and the capping ring 16 comprised a simple cover plate, it would be found difficult or impossible in practice to remove the O-ring 15 without first removing the sleeve 13 from the shaft 11. It is preferable that the O-ring 15 be more than half contained within the recess 22, but less than three quarters contained.

The rotary split real ring 18 forms one-half of the sealing interface between rotating and non-rotating parts of the seal 10, the other half being a non- rotating split seal ring 34. The rotary split seal ring 18 and non-rotating split seal ring 34 each comprise a rigid annular member having an extremely flat radially extending sealing face. These faces bear against each other in normal use, to provide intimate sealing contact between them. The rotary split seal ring 18 is preferably formed of silicon carbide ceramic or carbon, and is brittle such that it can be intentionally fracture split under internal pressure to form two substantially perfectly complementary half rings. This allows the split seal ring 18 to be easily removed and replaced around the shaft 11, and the fracture lines along which the two half rings meet do not in normal use allow significant leakage through the split seal ring 18, because the crystalline structure of the split ring join gives a high degree of matching between the fracture faces.

The rotary split seal ring 18 is mounted on the sleeve 13 by an elastomeric rubber boot seal 17, which is in turn held by an extending flange 26 of the capping ring 16. The boot seal 17 comprises an elastomeric split ring sandwiched between the rotary split seal ring 18 and a radially extending flange 27 of the sleeve 13, and provides both frictional engagement between them, and a secondary leak path seal. Of the principle rotating parts of the seal 10, only the sleeve 13 is not split. All rotating parts of the seal 10 other than the sleeve 13 are made pre-split, and can be taken apart and removed for servicing and replacement when necessary. The sleeve 13 is considered to be substantially non-wearing, and should not require replacement in the lifetime of the apparatus.

Non-Rotating Elements of the Preferred Apparatus The principal non-rotating elements of the seal 10 comprise a split gland 30, a non-split gland end plate 31, an annular spring-biased thrust plate 32, a rubber cup element 33, and the split seal ring 34. Means is provided in the non-rotating section of the preferred seal 10 to take into account both axial movement of the shaft 11 and consequently the rotary split seal ring 18, and wear on the sealing faces of the rings 18 and 34, without allowing rotational movement of the split seal ring 34. The split gland 30 in normal use abuts against and is fixed to the housing 12 of the equipment to which the seal 10 is applied. A gasket 35 is provided between the gland 30 and the housing 12. The gland 30 is formed in two halves, to allow removal from the shaft 11, and is provided with a sealing strip 36 between the two halves on either side.

Means are provided for precisely fixing the two halves together, and also for fixing the gland 30 to the housing 12. The non-split gland end plate 31 is fixed to the split gland 30 by securing cap screws 37 and also by bolts or studs which fix the seal 10 to the housing 12. On the outer face of the non-split gland end plate 31 a recess 38 is provided, in which the setting clips 25 are engaged during assembly, transport and installation of - 8 - the seal 10. The non-split gland end plate 31 comprises an annular plate, having an inwardly protruding radial lip 39. In the lip 39 are mounted one or more pins 40, which secure the thrust plate 32 against rotation. A supporter ring 41 and a locator ring 42 are provided to hold parts in place, and a split O-ring 43 is provided to prevent leakage past these elements. The locator ring 42 and the thrust plate 32 are preferably not split, but access to parts in this area of the seal 10 is made available by removing the clamping collar 14 and sliding the non-split gland end plate 31 along the shaft 11, away from the split gland 30.

The thrust plate 32 comprises a metal ring having an outer flange 44, which forms a counterbore in which the rubber cup element 33 is retained. Sockets 45 are regularly spaced around the plate 32, and in these sockets are held springs 46. The springs 46 are seated against the lip 39 of the non-split gland end plate 31, and act to bias the thrust plate away from the lip 39. Clearance is left between the thrust plate 32 and the lip 39, to allow for axial shaft movement.

The rubber cup element 33 fits within the flange 44 of the thrust plate 32, and comprises a lining between the thrust plate 32 and the rear of split seal ring 34. Being formed of rubber, it provides good frictional engagement with both these elements, effectively preventing rotation of one relative to the other in normal use and also pressing and holding the two halves of the split seal ring 34 together. The use of an elastomeric element of this type to prevent rotation of the split seal ring 34 is found preferably to direct action of pins 40 or springs 46 or similar elements on the split seal ring 34, for a number of reasons. The split seal ring 34 is, like the rotary - 9 - split seal ring 18, fractured to provide two complemen¬ tary parts which make up the complete ring, and a pin set in an aperture in one part will not hold the other part.

It is not found possible in practice to machine apertures in both parts accurately enough nor to place anti-rotation pins accurately enough, to hold them both with pins in an exactly matching configuration, as is necessary if opening of the fracture lines and conse- quent leakage is to be avoided. If the seal ring is formed from a soft material such as carbon, it can be prevented from rotating (or made to rotate) by having springs bearing directly on and digging into the soft material. This is not however applicable to hard materials such as hard ceramic materials.

The means employed in the present invention is also considered preferable to bracing the circumference of the seal ring against an enclosing housing, such as for example the split gland 30, by resilient means such as an O-ring. The pressure against the side walls required to hold the seal ring together and hold it against rotation may inhibit or prevent axial movement of the seal ring. This axial movement is necessary if the seal ring is to stay in sealing contact with the rotating split seal ring 18 when the split seal ring 18 moves axially with the shaft 11 or when the sealing faces become worn. Small axial movements of the shaft 11 can not in practice be avoided, and must be compensated for if the seal is to function effectively. It is also important that radio movements - up, down or sideways etc. - of one split seal ring relative to the other, and also "levering" apart of the rings on one side caused by whipping in the shaft 11, be avoided. The springs 46 allow the split seal ring 34 to follow - 10 - such movements in the rotary split seal ring 18, and thereby maintain the integrity of the sealing interface between them.

The apparatus of the present invention allows freedom of movement of the split seal ring 34 in an axial and radial direction, while preventing any rotational movement, by fixing the seal ring with frictional engagement means (cup element 33) into a socket in a metal element (thrust plate 32 with outer flange 44) which moves axially with it and is prevented from rotating by pins. The thrust plate 32 preferably comprises a single piece unit, or could comprise two or more parts screwed or otherwise fixed together, and can therefore be prevented from rotating by contact with a single pin 40.

The split seal ring 34 is preferably formed from a hard ceramic such as silicon carbide or alumina oxide, but could alternatively be formed from a relatively soft material such as carbon. A secondary sealing O-ring 47 is provided around the split seal ring 34, held by the locator ring 42 and supporter ring 41, to prevent leakage past this point. Note that the O-ring 47 only lightly contacts the split seal ring 34, and does not inhibit axial movement of the split seal ring 34. It does perform an additional supportive and retention function on the two split halves of the ring 34, but does not hinder the axial movement of the seal ring, which is able to slide through it.

It will be appreciated that the above description is given by way of example only, and that a variety of changes and modifications might be made within the general spirit and scope of the invention.

The apparatus might be reversed to some extent, with the spring-biased thrust plate and associated mechanism acting on the rotating split seal ring 18, rather than on the seal ring as described above. In such a case the apparatus of the present invention would in normal use ensure that the rotating split seal ring 18 is secured for rotation with the shaft 11 while preventing it from moving axially with the shaft 11 relative to the split seal ring 34. Such an arrangement is however seen as less preferable than the example given above, for a number of reasons.

By having the springs in the non-rotating part of the seal, distortion by centrifugal force is avoided. If the springs were to be rotated with the shaft 11, centrifugal force from the rotation would tend to bow them outwards radially, thereby reducing their pressing force in an axial direction. The springs used in apparatus as described in the above example do not rotate, and consequently are not subjected to centri¬ fugal force.

There is also a question of compensating for slight differences in angle of the split seal rings relative to the shaft. In practice it is often found that due to uneven tightening of bolts or the like, the non-rotating parts of the seal are pitched slightly off square relative to the shaft axis, and consequently the plane of the non-rotating split seal ring is also not quite square to the shaft axis. The springs compensate for this, by pressing the two sealing surfaces into the same plane. If the springs are associated with the rotary split ring 18, they will press the ring 18 out of square with the shaft axis to match the non-rotating ring 34. As the shaft and ring 18 rotate, the springs must constantly readjust and work to keep the sealing surfaces in contact. If the springs are associated with the non-rotating split seal ring 34, as in the above example, they will press the ring 34 square the shaft axis to match the rotary ring 18, and simply hold it there. No readjustment is required as the shaft rotates, and the springs are consequently subjected to less wear.

Aspects of the invention might be used separately or in conjunction with other aspects. For example, the O-ring 15, associated cupping ring 16 and seating recesses might be used on a variety of different seals, whether or not they incorporate the features associated with the seal ring and seat of the present invention.

The feature of a one-piece sleeve 13 and/or gland end plate 31 in association with split elements as described above might also be applied to valves or other types of seals. The use of a cartridge including split and non-split elements is seen as preferable to either completely split or completely non-split seals. Completely split seals, in which all the annular elements of the seal are split to allow easy removal and replacement around a shaft, can not be transported or installed as a cartridge unit, and must consequently be assembled on site. This requires precision work, which is frequently difficult to perform under on site conditions. Dirt or dust on the surfaces of the split seal rings can render them ineffective, but may be difficult to avoid during assembly on site. It is not found possible in practice to provide two half-assem¬ blies which can clamp together around the shaft, because the split seal rings must be matched so precisely that it is only feasible to put each together individually. Completely non-split seals can only be serviced by dismantling the equipment to which it is attached, because it can only be drawn off the end of the shaft. This can involve long stoppages and a difficult operation to replace even a relatively minor part of the seal. A seal assembly as described above can be provided in a cartridge form, because the non-split parts hold the split parts in the correct position and arrangement. The split parts can easily be removed when replacement or servicing is required, and the non-split parts are substantially non-wearing elements of the seal, which should not in normal use require replacement.

The various features of shape, form and arrangement illustrated, while seen as preferable at present are given by way of example and might be altered consi¬ derably in other embodiments of the invention.

A variety of other changes, additions and modifica¬ tions might be made within the general spirit and scope of the invention, which may be exemplified as follows:

In one aspect the invention provides a mechanical seal having a sealing interface between two elements, wherein a first said element is pressed towards the second said element by biasing means, the first said element being associated with said biasing means by means including a retaining member and an elastomeric lining between the first said element and the retaining member.

Preferably the retaining member comprises an annular cup or socket member.

Preferably the retaining member is formed of metal, and the first said element of carbon or a ceramic.

Preferably the first said element comprises a split ring, being fractured into two or more complementary ring sections, and said retaining member further comprises means to assist in holding said complementary ring sections together in sealing contact with each other.

Preferably the retaining member and elastomeric lining are pressed towards the second said element in conjunction with the first said element. Preferably the biasing means includes springs.

Pref rably in normal use the elements are also pressed together by hydraulic pressure.

In another aspect the invention provides a seal having two elements forming a rotary face seal assembly, wherein rotation of one said element relative to the other about an axis is made possible by means including a retaining member held in association with one said element, said retaining member being provided with means for axial movement relative to a substrate but prevented from rotational movement relative to said substrate.

Preferably the retaining member is further provided with biasing means which in normal use bias the associated element towards the other element by biasing the retaining member.

Preferably the retaining member and the associated element are held in association by means including an elastomeric element sandwiched between them.

Preferably the retaining member and the associated element are held against rotation, while the other element is rotatable.

Alternatively the substrate comprises a rotatable shaft, said retaining member and the associated element being mounted for rotation with the shaft.

In a further aspect the invention provides a seal for a rotatable shaft passing through a housing, having split elements and non-split elements.

Preferably the non-split elements comprise substan¬ tially non-wearing parts of the apparatus. In a further aspect the invention provides a seal assembly for a rotatable shaft passing through a housing, including an O-ring seal between a shaft and a surrounding sleeve, said O-ring being retained in a recess at one end of said sleeve and protruding - 15 - therefrom, and a capping element having a complementary recess therein, to in use cover the protruding portion of said O-ring.

Preferably the O-ring is approximately two-thirds contained within the recess in the sleeve, and one-third contained within the recess in the capping elements.

In a further aspect the invention provides a seal assembly for a rotatable shaft passing through a housing, comprising a "cartridge" unit which can be at least partially pre-set and assembled prior to installa¬ tion on said shaft.

Preferably the seal assembly includes split and non-split elements.

Preferably the seal assembly includes setting clips which in normal use act to hold the assembly or parts thereof in place prior to completion of installation.

In a further aspect the invention provides a method for sealing around a rotatable shaft passing through a housing, including the use of a seal as described above.

Claims

What is claimed is:

1. A mechanical seal having a rotary sealing interface between two seal elements, a first said seal element being associated with a housing and the second said seal element being associated with a rotatable shaft passing through said housing, said mechanical seal having both non-split annular or cylindrical elements, and split annular or cylindrical elements composed of a plurality of complementary parts.

2. A mechanical seal as claimed in claim 1, having an annular or cylindrical rotary element in normal use fixed in association with said rotatable shaft, and an annular or cylindrical non-rotary element in normal use fixed in association with said housing, and keying means by which said rotary element and said non-rotary element can be locked into a co-axial configuration and alignment.

3. A mechanical seal as claimed in claim 2, wherein said keying means includes at least three setting clips removably fastened to said rotary element and adapted to engage said non-rotary element.

4. A mechanical seal as claimed in claim 1, including a non-split cylindrical sleeve and means by which said sleeve can be fixed to said rotatable shaft.

5. A mechanical seal as claimed in claim 4, wherein said means for fixing said sleeve to said shaft includes a split annular clamping ring, composed of two or more complementary sections, and wherein said sleeve is provided with a plurality of parallel longitudinal - 17 - slots at one end, such that in normal use said clamping ring can be clamped around said sleeve to constrict the slotted end, and thereby clamp said sleeve to said shaft.

6. A mechanical seal as claimed in claim 4, wherein said sleeve is provided with an O-ring seal to in normal use seal between said sleeve and said rotatable shaft, said O-ring seal being mounted in an annular recess in the inner surface of said sleeve at one end of said sleeve, and protruding from said end of said sleeve and wherein a capping ring is provided, having a complementary recess and being adapted to be fitted onto said end of said sleeve, to in normal use cover protruding portions of said O-ring.

7. A mechanical seal as claimed in claim 4, wherein rotary parts of said seal are removably fastened directly or indirectly to said sleeve, such that said sleeve holds said rotary parts together in a substan¬ tially fixed relationship in normal use.

8. A mechanical seal as claimed in claim 1, including a non-split annular plate, and means by which said plate can be fixed to said housing.

9. A mechanical seal as claimed in claim 8, wherein non-rotary parts of said seal are removably held directly or indirectly by said plate, such that said plate holds said non-rotary parts together in a substantially fixed relationship in normal use.

10. A mechanical seal having a rotary sealing interface between two seal elements, wherein a first said seal element is held by a retaining member, said - 18 - retaining member being movable in a direction substantially parallel to the axis of rotation of a said seal element, and provided with biasing means to urge said retaining member axially relative to the second said seal element, to press said first seal element against said second seal element, wherein an elastomeric lining is provided between said first seal element and said retaining member.

11. A mechanical seal as claimed in claim 10, wherein said retaining member comprises an annular cup or socket.

12. A mechanical seal as claimed in claim 11, wherein said elastomeric lining comprises an annular element having one or more substantially planar areas of contact with said first seal element, and one or more substantially planar areas of contact with said retaining member.

13. A mechanical seal as claimed in claim 12, wherein said elastomeric lining is of a cupped, annular shape, having a radial annular wall and a peripheral cylindrical wall.

14„ A mechanical seal as claimed in claim 10, wherein said elastomeric lining is formed of a rubber produc .

15. A mechanical seal as claimed in claim 10, wherein said biasing means acts between a face of said retaining member and a substrate and wherein at least one engagement element is provided between said - 19 - retaining member and said substrate, to limit rotational movement of said retaining member relative to said substrate.

16. A mechanical seal as claimed in claim 15, wherein said biasing means includes a plurality of springs.

17. A mechanical seal as claimed in claim 10, wherein said first seal element and said retaining member are associated with a stationary housing, and said second seal element is associated with a rotatable shaft passing through said housing.

18. A mechanical seal as claimed in claim 10, wherein said seal elements each include a split carbon or ceramic ring fractured into two or more complementary ring sections, and wherein said retaining member further includes means to assist in holding said complementary ring sections together in sealing contact with each other.