GB2159894A - Improvements in rotary shaft seals - Google Patents

Abstract

A rotary shaft seal comprises a moulded sealing ring, of resiliently deformable material, having a bush (1) to fit tight on a shaft, a fluid sealing lip (3) to seal against a surrounding shaft housing, and a set of vanes (6) to operate as an axial flow fluid impeller actively to oppose access of dust-laden air to the seal. The seal may be provided with a plurality of sealing lips and sets of vanes (Figs. 3, 4). <IMAGE>

Description

SPECIFICATION Improvements in rotary shaft seals This invention relates to rotary shaft seals and provides a seal to prevent outward leakage of fluid, usually oil, from between a shaft and its housing, and, in addition, actively to oppose ingress of dust which might spoil the fluid seal or contaminate the shaft mechanism or lubricant.

It is well known to provide shaft sealing rings with both fluid-leakage sealing lips and so-called dust lips to oppose entry of dust between a shaft and its housing. Dust lips make wiping contact with the opposed shaft or housing surface, so that they increase the frictional load of the seals, and also are liable to collect dust which accretes as a layer liable to spoil the sealing action and itself provide a source of contamination.

Labyrinth dust-excluding seals also are known but these usually involve grooves in the shaft and/or a relatively long sealing bush.

The present invention provides a seal which can be used for any shaft and its housing of given diameters.

According to the invention, a rotary shaft seal comprises a ring having an inner periphery for mounting fast and fluid-tight on a rotary shaft and an outer periphery which has both a sealing element, to make a rotary seal against a surrounding cylindrical surface, and an axial-flow fluid impeller, for brush contact, or preferably fine running clearance, with the surrounding cylindrical surface, to oppose access of dust-laden air to the sealing element when the shaft rotates. The ring may be in one-piece or a composite ring of components.

One embodiment of the invention comprises a moulded ring of elastomeric material having a cylindrical bore, to fit on a rotary shaft, and at the outer periphery, towards one face of the ring, a sealing element in the form of a flexible sealing lip and, towards the other face of the ring, a set of axial flow impeller vanes directed to impel fluid away from the sealing lip when the shaft rotates.

Another embodiment of the invention comprises a sealing ring component, with one or more sealing lips at the outer periphery, and an impeller ring component, with one or more sets of axial flow impeller vanes in series at the outer periphery.

The invention is illustrated, by way of example, on the accompanying drawing, in which: Fig. lisa radial section of a rotary shaft seal in accordance with one embodiment of the invention, Fig. 2 is an inverted plan view corresponding to Fig. 1, Fig. 3 is a radial section of a rotary shaft seal in accordance with another embodiment of the invention, and, Fig. 4 is an inverted plan view corresponding to Fig. 3.

A sealing ring as shown by Figs. 1 and 2 is moulded from a resiliently deformable material, such as a nitrile synthetic rubber or other elastomer or other plastics material such as polyethylene or a polyamide.

The ring has an inner bush 1 with a bore designed to fit fast and fluid-tight on a shaft of a given diameter and of which the radius is indicated as d/2.

From the bush 1 there projects an inclined annular cup flange 2, directed towards the eventual inner face of the sealing ring, known as the oil side and indicated as 0.

The flange 2 forms by its outer periphery a sealing lip 3 presenting a circumferential sealing edge 4 which has a diameter greater than a given diameter, indicated by the radius D/2, of a cylindrical surface of a shaft housing, indicated by the line H.

In its as-moulded condition the sealing lip 3 is unstressed and the edge 4 has a diameter greater than D, as shown by Fig. 1. When the sealing ring is assembled on a shaft in a housing, the sealing lip 3 becomes inwardly radially stressed so that the edge 4, under the effect of a resilience of the material of which the ring is made, bears as a seal against the surrounding cylindrical housing surface, represented by H. This provides a fluid seal against outward leakage of oil or other fluid, from the oil side 0, between the shaft and its housing to the air side A.

In shaft lip seals it is known to provide, at the air side, a supplementary lip, indicated in broken lines as 5 in Fig. 1, to contact very lightly or run just clear of the housing surface H and oppose the ingress of dust from the air side.

Such a supplementary lip as 5 also serves to stabilise the attitude of the sealing lip 4 against the housing and may be provided in a sealing ring in accordance with the invention.

The essential feature of the present invention is the provision, at the air side of the sealing ring, of an axial flow fluid impeller, comprising in this embodiment a set of impeller vanes 6, moulded integrally with the sealing ring so as to project radially from the bush 1.

The vanes 6 have a pitch to impel air towards the air side A for a given direction of shaft rotation, as indicated by the arrow R which would in fact be marked on the sealing rings to ensure correct selection and installation of the sealing rings.

The vanes have a fine running clearance with the housing surface H but need not make even brushing contact because they operate positively to repel dust by outward air flow.

For use in specially dirty conditions, provision for static protection against ingress of dust, when the shaft is not running, may include a supplementary dust lip 5, as mentioned above, and/or design of the impellervanes 6 so that they mutually overlap circumferentially and present to the air side a complete radial wall as seen axially. There is then no direct access for dust to pass inwardly between the vanes, when the shaft is not running, but only dodged paths between overlapping vanes. Such paths may be made very narrow and adjacent vanes may even lie one on another at rest, flexing to open for fluid impulsion under the effect of rotation.

More than one set of vanes may be provided in series, as indicated in broken lines for an additional set of vanes 6a.

Alternative features of the invention are illustrated, as incorporated in another embodiment, by Figs. 3 and 4 in which the same references indicate parts corresponding to Figs. 1 and 2.

In Figs. 3 and 4, the sealing ring component 1,2 has multiple sealing lips 7 and a separately-made impeller ring component 8, conveniently a moulded plastics ring, has two sets in series of impeller vanes 9.

Claims (4)

1. A shaft seal comprising a ring having an inner periphery for mounting fast and fluid-tight on a rotary shaft and an outer periphery which has both a sealing element, to make a rotary seal against a surrounding cylindrical surface, and an axial-flow fluid impeller, for brush contact or fine running clearance with the surrounding cylindrical surface, to oppose access of dust-laden air to the sealing element when the shaft rotates

2. A shaft seal according to claim 1 and comprising a moulded ring of elastomeric material having a cylindrical bore, to fit on a rotary shaft, and at the outer periphery, towards one face of the ring, a sealing element in the form of a flexible sealing lip and, towards the other face of the ring, a set or sets of axial flow impeller vanes directed to impel fluid away from the sealing lip when the shaft rotates.

3. A shaft seal according to claim 1 and comprising a sealing ring component, with one or more outer peripheral sealing lips, and an impeller ring component, with one or more sets of outer peripheral axial flow impeller vanes.

4. A shaft seal substantially as described and shown by Figs. 1 and 2 or Figs. 3 and 4 of the accompanying drawings.