GB2125492A

GB2125492A - Fluid seals for marine propulsion shafting

Info

Publication number: GB2125492A
Application number: GB08223549A
Authority: GB
Inventors: Alfred Hill
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1982-08-16
Filing date: 1982-08-16
Publication date: 1984-03-07
Also published as: ES8400572A1; ES516276A0; GB2125492B

Abstract

A fluid seal for a rotating shaft 2 comprises a stationary annular surface 1, a resilient annular seal 4, and a ring 3 which is rotationally stationary relative to the surface 1. The seal 4 is constrained between the shaft 2 and the ring 3. The ring 3 is axially slidable and has an angled face which is urged against the seal 4 by means of a spring 5 thereby transmitting the force to annular surface 1 and the shaft 2. The seal may be urged against a stationary surface and the side face of a rotatable collar by a spring loaded member, the stationary surface and side face being at right angles to each other. The surface of the ring which engages the seal may comprise the arc of a circle or section. The ring may be biassed by a garter spring or an annular sheet metal spring. The seal may be other than circular in section. <IMAGE>

Description

SPECIFICATION Fluid seals for marine propulsion shafting There are in existence a large number of sealing devices for rotating shafts most of which are either unsuitable or are not ideal for marine propulsion shafting. In this context the term marine shafting applies to the shaft between the engines and the propeller for the sole or main propulsion of the vessel and also to the shafts of any auxiliary propulsion or positioning units such as for example "Bow Thrustors".

Most existing seals are of one piece ring construction requiring access to the end of the shaft for assembly or replacement when worn or damaged and, if split to permit assembly without such access they are less effective as seals.

In the case of marine shafting, particularly the main propulsion shafts of large vessles, access to the end of the shaft is extremely expensive so there is a need for a split seal.

The most popular of the existing types of seal use elastomeric sealing elements which have to be produced by moulding techniques and therefore, for economic reasons the number of sizes must be limited. To provide an adequate service for replacements it becomes necessary to carry stocks and here again -eco- nomic factors dictate a minimum number of sizes. In practice the seals are produced in a range of standard sizes, commonly to suit shaft diameters increasing in steps of 50mm or thereabouts, but when it is realised that the total range of diameters extends from about 50mm to 1 500mm it is clear that a large number of sizes is still involved.Even steps of 50mm place restraints upon the design of shafting and adjacent components since at the smaller end of each range the seal can be too bulky to fit into the space available, necessitating an uneconomic increase in the size of other components. Moreover the elastomeric sealing elements commonly used are sensitive to damage if not stored and handled in a proper and careful manner and in practice are often damaged when attempting to fit them.

Sometimes such damage is not apparent until the vessel is at sea again and another expensive lay up becomes necessary.

In attempts to solve these various problems most of the existing seals have grown more complex and costly to manufacture.

It is an object of the present invention to provide a simple seal which can be easily replaced without disturbing the shaft of adjacent components and in which the wearing component is not tied to particular sizes of shaft.

According to the invention-there is provided a fluid seal for a rotating member comprising a resilient sealing element of annular form which is constrained and compressed between two annular surfaces and the rotating member, the first annular surface being rotatable relative to the rotating member and the second annular surface being rotationally fixed relative to one of the first surfaces and the rotating member and being arranged to apply a compressive force to the sealing element.

Thus the invention may provide much greater flexibility in the design and may also obviate the need to carry large stocks of spare elements for servicing.

The sealing element may be of any material which has elastic properties. It will conveniently be a solid material and most commonly will be a natural or synthetic elastomer compatible with the fluids being sealed; for example rubber, meoprene, urethane and the like. Alternatively it may be coated on the contact surfaces with another material, such as for example polytetrafluoroethylene (PTFE).

By using a sealing element produced as a continuous filament which can be cut to the required length, wrapped around the shaft and joined in situ there is practially no design restraint on the diameter of the shaft and seal and the only stock required for servicing replacements is a coil of the chosen crosssection from which lengths can be cut as needed.

The invention may be carried into practice in various ways and some embodiments will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a part section of a shaft seal in accordance with the invention; Figure 2 shows a half cross section of a face seal; Figures 3, 4, and 4a shows alternative constructions of 4 shaft seals; Figures 5a to 5e show alternative crosssections of the sealing element; and Figures 6a and 6b show the seal applied to spherical surfaces.

Fig. 1 is a half section through the seal in a plane containing the axis of the annular components and the shaft.

The sealing element 4 is constrained between the surface 1, the second surface 2 which rotates about the axis 7 and slides rotativbely against the sealing element 4, and the third surface 3 which is prevented from rotating relative to 1 but which can slide axially to transmit a closing force to the element 4 from the springs 5. The effect is to press the sealing element 4 against both surfaces 1 and 2 simultaneously. The forces operating are indicated by the arrows within the seal 4.

As shown in Fig. 1 the spring force is divided between surfaces 1 and 2 according to the angle a. If angle a is 45D the forces acting against surfaces 1 and 2 are equal. As angle a decreases so the force against surface 2 increases and vice versa.

Surfaces 1 and 2 are conveniently at 90 to each other but this is not essential to the invention and for some applications the angle may be greater or less than 90 .

The sealing element 4 can be produced as a continuous filament of appropriate crosssection, for example by an extrusion process, stored in coil form, and cut to length as required. The ends are joined by a suitable method after placing the cut element around the shaft. For example, if the element is an elastomer, the joint may be made using an adhesive, and possibly vulcanised in place.

These are established techniques and need no further description here.

The axially slidable surface 3 is formed on a component 6 of annular form, usually but not necessarily of metal which transmits the forces from the springs 5. It is prevented from rotating relatively to surface 1 by keys, pins or other suitable mechanical means all of which are weil-known devices and need not be detailed here.

Fig. 2 shows a face seal operating against the surface 22 of a collar fixed to or integral with the rotating shaft. The sealing element 24 is of circular cross-section when in the free state and contacts the stationary surface 21 and the sliding surface 23 at point 27 where the surfaces of 24 and 23 are tangential to each other. The cross-section of surface 23 is circular of radius 28 formed in component 26 which transmits the forces from the springs 25. An end cap 29 retains the seal assembly.

Rotation of ring 26 is prevented by the pins 30.

As drawn, radium 28 is equal to 0.75 d where d is the diameter of the cross-section of element 24, but it may be anything between 0.51d and infinity, i.e. the cross-section of surface 23 would then be a straight line.

The ring 26 may be in halves but since it is not a wearing part it can often be in one piece. It is free to float in equilibrium under the action of the forces acting upon it, the radial component of force due to angle a being taken as a compressive hoop stress within the ring. Thus any angular misalignment between surfaces 22 and 21 can easily be accommodated as can radial or axial movement of the shaft within the mechanical confines of the components. Radial displacement or vibration of the shaft will not affect the sealing properties (as may occur with some existing types of elastomeric seals).

Fig. 3 illustrates an alternative design where the rotating surface (32) is cylindrical, i.e. a shaft, and the stationary surface 31 is planar.

The sealing element 34 is constrained in a similar manner to that of Fig. 2, by surface 33 of ring 36 transmitting the forces from springs 35. A difference lies in ring 36 where the halves, in the case of a split ring, must be held together by bolts or similar suitable mechanical means, to transmit the hoop stress resulting from angle a which in this case is tensile.

The cylindrical surface 32 may move axially without affecting the sealing properties and may move radially within the mechanical confines by the sealing element sliding on surface 31.

An alternative design is shown in Fig. 4 where the rotating surface 42 is cylindrical and the stationary surface 41 is planar, as in Fig. 3. The third surface 43 is formed on ring 46 which, in this case, transmits a radial force from the circumferential or "garter" spring 45, the reaction of the resolved component.

of force from angle a being taken by a second stationary face on the end plate 49.

In this particular design the ring 46 must be flexible in a circumferential direction since radial compression entails a reduction in circumferential length. This may be conveniently achieved by making it of an elastomer, preferably of harder grade than the sealing element 44, or it may be made of metal or other rigid material divided into a number of sectors. An alternative construction is to form the ring 46 from spring temper sheet metal as shown in Fig. 4a so that it combines the functions of 46 and 45, producing it in the form of a continuous strip to be wrapped around the shaft and joined by a hook.

It is a matter of preferred convenience that the sealing element 4, 24, 34 etc. is formed from a continuous filament of circular crosssection but the invention can equally be applied to rings of other cross-sections as indicated by the examples, shown in Figs. 5a to 5d. In these examples the stationary surface is 1, the rotating surface is 2, the non-rotating closing surface is 3 and the seal element is numbered 4. In Fig. 5Fthe seal 4 is coated with PTFE.

The invention may equally be applied to seal spherical surfaces in various modes, two examples, being illustrated in Figs. 6a and 6b.

Fig. 6a shows a seal across the diameter of a spherical surface. Fig. 6b illustrates a seal across the chord of a spherical surface.

Claims

1. A fluid seal for a rotating member comprising a resilient sealing element of annular form which is constrained and compressed between two annular surfaces and the rotating member, the first annular surface being rotatable relative to the rotation member and the second annular surface being rotationally fixed relative to one of the first surfaces and the rotating member and being arranged to apply a compressive force to the sealing element.

2. A seal. as in Claim 1 in which the sealing element is produced as a continuous filament which can be cut to the length required, bent into ring form and the ends joined.

3. A seal as in Claim 2 in which the sealing element is an elastomer produced in a continuous length by extrusion.

4. A seal as in any of Claims 1 to 3 in which the sealing element is of circular crosssection.

5. A seal as in any of Claims 1 to 3 in which the sealing element is of non-circular cross-section.

6. A seal as in Claim 4 or Claim 5 in which the rotating member is a shaft rotating about its axis and surrounded by the first stationary surface of annular form whose axis is substantially coincident with that of the shaft, the sealing element being held in contact with both of these surfaces by the second annular surface which is non-rotating and mutually inclined to the other two surfaces and arranged to apply a compressive force to the sealing element.

7. A seal as in Claim 4 or Claim 5 in which the rotating member is an annular collar face fixed normally to the axis of a rotating shaft, the first annular surface is a cylindrical bore substantially co-axial with the shaft, and the second annular surface is inclined to the first surface and the collar face and is arranged to be non-rotative relative to the first surface and to apply a compressive force to the sealing element holding it in contact with the collar and the first surface.