GB2139299A

GB2139299A - Improvements relating to seals

Info

Publication number: GB2139299A
Application number: GB08311321A
Authority: GB
Inventors: Kevin Paul Gayson
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1983-04-26
Filing date: 1983-04-26
Publication date: 1984-11-07
Also published as: GB8311321D0

Abstract

Improvements in the lubrication and cooling of seals for a rotary shaft (1) is effected by offsetting a seal (4) such that it is not in a plane normal to the axis of the rotary shaft. <IMAGE>

Description

SPECIFICATION Improvements relating to seals This invention relates to improvements in seals. In particular this invention relates to improvements in seals around rotatable shafts.

In all fields of applied mechanical engineering the need for sealing rotary shafts projecting through housings is common. Typically sealing will be provided to preclude the ingress of foreign matter e.g. dust, grit or water into the housing and also to preclude the egress of lubricant e.g. oil from within the housing. Seals have been developed to meet this need, commonly known as "oil seals" they consist typically of a rubber ring the outside diameter of which fits tightly in the housing, thus holding the seal fixed, and the inside diameter of which seal forms a sliding fit on the shaft. In some cases the inner section of the seal is biased onto the shaft by a coil extension spring bent to describe a circle and mounted within the outside diameter of the seal and concentric therewith.

The action of the spring is to compress the inside diameter of the seal thus forming a tighter seal on the shaft. The area of the seal lip in contact with the shaft may vary from a narrow line contact around the inside diameter to a wide lip of the same width as the outside diameter of the seal.

When in operation this type of seal sits in a plane normal to the axis of the rotating shaft and thus contacts a circle on the surface of the shaft. This state of affairs leads to two limitations in performance of the seal. The first is that when in rotary operation the small shaft area, in contact with the seal lip, heats up which causes wear problems for both the seal and the shaft. This is in contrast to the situation of a similar seal and shaft when the shaft is reciprocating in that a much larger area of the shaft will sweep the seal lip thus the seal and shaft are better cooled.

The second limitation is that when in rotary operation the seal will, by it's own action, tend to preclude the admission of any lubricant, present within the housing, to that area of the shaft that runs against the seal lip. The resultant lack of lubrication of the lip results in wear of the seal and shaft. Again, this situation is in contrast to that of a similar seal and shaft when the shaft is reciprocating in that in so moving the shaft may pick up lubricant from a reservoir within the housing and carry the lubricant through the seal thus lubricating it.

An object of the present invention is to provide an improved seal for rotary shafts incorporating advantages normally associated with reciprocating shafts.

Accordingly the present invention provides seal means for sealing a round rotatable shaft through a housing wherein the seal means is offset from a plane normal to the axis of the shaft.

Preferably the offset may be large enough to create an axial displacement of one part of the seal diametrically opposite another part of the seal that is greater than the axial thickness of the seal.

Conveniently the seal housing may have incorporated therein a lubricant reservoir.

Preferably the seal may be an elastomer seal such as rubber and may incorporate bias means to bias the seal lip onto the shaft.

Preferably the seal seat within the housing may be offset to the same degree as the seal.

Conveniently the outside of the seal may be cylindrical containing an offset seal lip within.

One embodiment of the seal means according to the present invention will now be described, by of example only, with reference to the single figure of the accompanying drawing which shows an offset seal arrangement in which a round rotary shaft 1 passes through a housing 2 of a gearbox. Within the housing 2, to the right in the figure, is a lubricant reservoir 3. This reservoir may be integral with the machine e.g. the gearbox oil reservoir or may be an integral part of a seal assembly which affixes to the machine. The lubricant will typically be a heavy oil e.g.

S.A.E. 140. A seal 4 sits within a round hole in housing 2 and has a seat 5 that is not in a plane normal to the axis of the shaft 1 but which is offset by an axial distance 6 which is equal to the seal width 7. In this case the seal has a lip 8 in contact with the shaft 1 that is equal in width to the seal 4 itself.

To maintain contact between the shaft 1 and the seal lip 8 in this offset condition the seal must be elliptical in shape when viewed normal to the seal's plane, thus presenting a circle when viewed along the axis of the shaft.

The seat 5, when viewed in section through the centre of shaft 1, at any point around the seat is always normal to the axis of the shaft 1.

It can be seen from the drawing that on rotation of the shaft 1 a greater surface area of the shaft 1 is swept than the surface area of the seal lip 8. This improves cooling of the seal and shaft and hence reduces wear.

It can also be seen that if oil from reservoir 3 contacts the shaft on its bottom face in Fig.

1 as the shaft rotates it will carry oil between the shaft 1 and the seal lip 8 at the top face of the shaft 1 in Fig. 1 thus providing an improved lubrication of the seal which prolongs the life of the seal.

Ideally the axial offset of the seal should be greater than the seal width but in cases where this is impossible any offset will produce an improvement in seal performance.

The body of the seal may be made as a conventional cylinder while within that cylinder the seal lip may be offset. This would allow relatively simpler fitting of the seal in the seal housing.

Claims

1. Seal means for sealing a round rotata ble shaft through a housing, wherein the seal means is offset from a plane normal to the axis of the shaft.

2. Seal means according to claim 1, wherein the offset is large enough to create an axial displacement of one part of the seal diametrically opposite another part of the seal that is greater than the axial thickness of the seal.

3. Seal means according to claim 1 or 2, wherein the housing incorporates a lubricant reservoir.

4. Seal means according to any of the preceding claims, wherein the seal is an elastomer seal.

5. Seal means according to claim 4, wherein the elastomer seal incorporates bias means to bias the seal lip onto the shaft.

6. Seal means according to any of the preceding claims, wherein the seal seat within the housing is offset to the same degree as the seal.

7. Seal means for sealing a round rotatable shaft through a housing, wherein the outside of the seal is cylindrical in form and contains an offset seal lip within.

8. Seal means for sealing a round rotary shaft substantially as hereinbefore described with reference to the accompanying drawing.