GB2143911A

GB2143911A - Face seals

Info

Publication number: GB2143911A
Application number: GB08417037A
Authority: GB
Inventors: Alan Cecil Lane
Original assignee: Crane Packing Ltd
Current assignee: Crane Packing Ltd
Priority date: 1983-07-23
Filing date: 1984-07-04
Publication date: 1985-02-20
Also published as: GB2143911B; GB8417037D0

Abstract

A mechanical face seal comprising a seat 13 fixed axially and sealed with respect to a first component 10 and an axially movable annular seal face member 15 associated with a second component 12 includes one or more elastomeric rings 16 located in opposed offset grooves 20, 21 in circumferential surfaces of the seal face member 15 and a casing 18 secured to the second component 12, said ring or rings 16 acting in shear to urge the seal face member 15 associated with a second component 12, includes one or more elastomeric rings 16 located in opposed offset grooves 20, 21 in casing. The seal face member may be supported between two concentric elastomeric biassing rings (Fig. 3) compressed fluid in a chamber sealed by the two rings augmenting the biassing force thereof. Two rings may be provided in a single pair of grooves (Fig. 4). <IMAGE>

Description

SPECIFICATION Mechanical face seals This invention relates to mechanical face seals.

According to one aspect of the present invention, a mechanical face seal for forming a fluid tight seal between a pair of relatively rotatable components comprises; a seat fixed axially and sealed with respect to a first of said components and an axially movable annular seal face member associated with the second component; the second component having a wall portion coaxial with and overlapping axially said seal face member, the opposed surfaces of the seal face member and wall portion being provided with circumferential grooves, said grooves overlapping one another but, within the wear limits of the sealing faces of the seat and seal face member, the groove in the wall portion being offset towards the seat relative to the groove in the seal face member; and a ring of elastomeric material interposed between the seal face member and wall portion so as to engage in the opposed grooves and impose, under shear, an axial load which forces the seal face member into sealing engagement with the seat, said ring of elastomeric material also providing a secondary seal between the seal face member and second component.

In order to facilitate assembly and servicing of the seal face member, the circumferential groove in the second component may be provided by a circumferential recess in the end of that component and a clamping ring which may be bolted to the end of the component.

Also, in order to facilitate replacement, the elastomeric ring may be split so that it can be mounted around the coaxial components without disassembling them.

The spring rate and amount of axial movement permitted by the ring of elastomeric material of the present invention, will of course, depend on the properties of the elastomer, the dimensions of the ring and the separation of the coaxial components. However, for a given ring, the spring rate of an assembly may be a multiple of the spring rate of a single ring by using a plurality of individual elements. Alternatively, using the same elastomeric rings, the spring rate may be reduced and the permitted axial movement increased, by incorporating a plurality of said rings side by side in a single pair of opposed grooves.

Various embodiments of the invention are now described by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a mechanical face seal for the propeller shaft of a ship, formed in accordance with the present invention; Figure 2 illustrates a modification of the seal illustrated in Figure 1; Figure 3 illustrates an alternative form of mechanical face seal formed in accordance with the present invention; and Figure 4 illustrates a further example of a mechanical face seal formed in accordance with the present invention.

The seal illustrated in Figure 1 is located between the propeller boss 10 which is attached to the propeller shaft 11 and the stern tube 1 2 through which the propeller shaft 11 passes. A seat 1 3 is secured to the propeller boss 10 by a series of angularly spaced bolts 14, for rotation with the propeller.

Seal face member 1 5 comprising a sealing element 1 spa mounted on a carrier ring 17, is urged axially into sealing engagement with the seat 1 3 by means of a rubber "0' 'ring 1 6. The "O"-ring 16 engages between the carrier ring 1 7 and a coaxial outer casing 18, which is secured to the stern tube 1 2 by a series of angularly spaced bolts 1 9. Circumferential grooves 20, 21 are provided in the opposed surfaces of the carrier ring 1 7 and outer casing 18, for location of the "O''-ring 16.

The grooves 20, 21 are positioned in the carrier ring 1 7 and outer casing 1 8 respectively, so that within acceptable wear limits of the seal face member 15, the grooves 20, 21 will overlap, but groove 20 will be offset towards the stern tube 1 2 relative to the groove 21. In this way, the "O"-ring 16 which is located between the carrier ring 1 7 and outer casing 18 in the groove 20, 21 will be distorted, so that the shear stress will impose an axial load between the carier ring 1 7 and outer casing 1 8 which will force the carrier ring axially towards the seat 1 3 and thus maintain sealing engagement between the seat 1 3 and seal face member 1 5.

The groove 21, in the outer casing 18 is formed by a recess in the end of the outer casing 1 8 and a clamping ring 22 which is bolted to the end of the outer casing 1 8 by means of a series of angularly spaced bolts 23. By this means, the "O"-ring 16 may be securely clamped in the groove 21 and also axially compressed to a degree, so that it extends radially into the opposed groove 20 in the carrier ring 1 7. In this way, the "0"ring 1 6 is securely located between and is also held in sealing engagement with the carrier ring 1 7 and outer casing 18, thus providing a secondary seal therebetween.

Furthermore, the "0' 'ring 1 6 may be replaced by removing clamping ring 22. To permit replacement of the "O"-ring 1 6 without having to remove the propeller, a split "O"-ring may be used and the clamping ring 22 may also be split. In this case, however, care must be taken to ensure that the secondary seal between the carrier ring 1 7 and outer casing 1 8 is maintained. In addition to applying an axial load to the seal face member 15, the "O"-ring 1 6 described above also provides radial constraint thereon, thus providing an extremely stable arrangement. The spring rate of the "O''-ring 1 6 described above depends on the composition of the rubber.It may consequently be increased or reduced by varying the rubber composition.

Alternatively, using the same composition "O"-ring 16, the spring rate of the assembly may be increased by using two or more individual "O"-rings 16, as illustrated in Figure 2.

In this embodiment, two grooves 20 are provided on the carrier ring 1 7 at axially spaced locations. A spacing ring 30 is inserted between the clamping ring 22 and the end of the outer casing 18 to define two grooves 21 corresponding to the grooves 20, in the outer casing 1 8. As with the embodiment with reference to Figure 1, each pair of grooves 20, 21 are arranged such that they overlap, but groove 20 in the carrier ring 1 7 is offset towards the stern tube 1 2 relative to the groove 21 in the outer casing 18.With this arrangement, the spring rate will be doubled and also the secondary seal between the carrier ring 1 7 and outer casing 1 8 and the radial constraint on the seal face member 1 5 will be enhanced.

In the seal illustrated in Figure 3, the seal face member 40, is urged axially into sealing engagement with the seat 42 by means of a pair of "0"-rings 43. The "O"-rings 43 are positioned radially of one another, one between the outer circumferential surface of the carrier ring 41 of seal face member 40 and a coaxial outer casing 44 and the other between the inner circumferential surface of the carrier ring 41 and an inner coaxial casing 45. The inner and outer casings 44, 45 are formed from coaxial cylindrical flanges on an annular component which may be secured to a fixed housing 46 by means of a series of angularly space bolts (not shown).

Opposed pairs of circumferential grooves 47, 48 are provided in the outer circumference of carrier ring 41 and outer casing 44 and the inner circumference of carrier ring 41 and inner casing 45 respectively, for location of the "O"-rings 43, in the manner described with reference to Figure 1 and 2. The "O"- rings 43 which urge the seal face member 40 into sealing engagement with the seat 42 and provide radial constraint, will thereby also provide a fluid tight chamber 49 between the carrier ring 41 and component defining the inner and outer casings 44, 45. An inlet may be provided to this chamber 49, so that air or fluid under pressure may be introduced to increase the axial loading on the seal face member 41.

In the embodiment described above, only limited axial movement is provided by the individually mounted "O"-rings 16, 43. This movement is restricted by the degree to which the "O"-rings will distort without being dislocated from the grooves in the surface of the opposed components. This depends on the characteristics of the elastomer from which the "O"-ring is made and the dimensions of the "0' '-ring, grooves and separation between the components. Nevertheless, using standard "0' '-rings, the amount of axial movement may be increased and at the same time the spring rate decreased, by providing a plurality of "O"-rings side by side in one pair of opposing grooves, as illustrated in Figure 4.

The seal illustrated in Figure 4 is of similar construction of that illustrated in Figure 1.

However, the grooves 60 and 61 are elongated so that two "O"-rings 62, 63 may be positioned side by side, between the carrier ring 1 7 and the outer casing 1 8. The axial load produced by the "O''-rings 62, 63 acts between the trailing edge of groove 61 in the outer casing 1 8 and the leading edge of groove 60 in the carrier ring 1 7. The upper portion of the leading "O"-ring 62 is, however, resiliently cushioned by the trailing "0"ring 63 while the lower portion of the trailing "O"-ring 63 is resiliently cushioned by the leading "O"-ring 62. As a consequence, for given misalignment of the grooves 60, 61 the distortion of the "O"-rings 62, 63 will be less than if individual "O"-rings were to be used as illustrated in Figure 1 to 3.This arrangement will consequently permit greater axial movement and will exert a reduced spring rate.

In fact, the spring rate is inversely proportional to the number of "0' '-rings located within the pair of the opposed grooves. Consequently, lower spring rates and increased axial movement may be achieved by increasing the number of "O"-rings even further.

Various modifications may be made without departing from the invention. For example, although in the above embodiments, rubber "0' '-rings have been used, elastomeric elements of any cross-section can be used.

While in the above embodiments the seal face member is formed by a sealing element and separate carrier ring, which is normally necessary when the sealing element is made of a relatively fragile material such as carbon, with more robust materials, such as sintered refractory materials, the seal face member may be of monolithic construction.

Claims

1. A mechanical face seal for forming a fluid tight seal between a pair of relatively rotatable components comprising; a seat fixed axially and sealed with respect to a first of said components and a axially movable annular seal face member associated with the second component; the second component having a wall portion coaxial with and overlapping axially said seal face member, the op posed surfaces of the seal face member and wall portion being provided with circumferential grooves, said grooves overlapping one another but, within the wear limits of the sealing faces of the seat and seal face member, the groove in the wall portion being offset towards the seat relative to the groove in the seal face member; and a ring of elastomeric material interposed between the seal face member and wall portion so as to engage in the opposed grooves and impose, under shear, an axial load which forces the seal face member into sealing engagement with the seat, said ring of elastomeric material also providing a secondary seal between the seal face member and second component.

2. A mechanical face seal according to Claim 1 in which the grooves on the opposed surfaces of the wall portion and seal face member are arranged to accommodate a plurality of rings of elastomeric material in axially abutting relationship to one another.

3. A mechanical face seal according to Claim 1 or 2 in which a plurality of pairs of opposed grooves are provided in the opposed surfaces of the wall portion and seal face member, at least one ring of elastomeric material being provided in each pair of opposed grooves.

4. A mechanical face seal according to any one of the preceding claims in which the second component is provided with coaxial wall portions which overlap the seal face member adjacent its inner and outer surfaces respectively, pairs of opposed grooves being provided between each adjacent pair of surfaces and rings of elastomeric material being provided in these pairs of grooves, thereby providing a fluid tight chamber between the seal face member and its associate component which may be pressurised to increase the axial loading on the seal face member.

5. A mechanical face seal according to any one of the preceding claims in which the circumferential groove on the wall portion of the second component is defined by a circumferential recess and a detachable clamping ring.

6. A mechanical face seal according to any one of the preceding claims in which the ring of elastomeric material is split.

7. A mechanical face seal for forming a fluid tight seal between a pair of relatively rotatable components substantially as described herein, with reference to, and as shown in Figures 1, 2, 3 or 4 of the accompanying drawings.