GB2261268A - Labyrinth seals - Google Patents

Abstract

A seal 2 is sized and shaped so as to fit about a rotatable member 4 and a pressure differential is created across the seal via air port 3 for the purpose of ensuring that small particles do not by-pass the seal; the seal is formed as a composite seal including an outer most bearing layer 2a and an adjacent flexible layer 5 whereby contact between said member and said seal, due to any eccentric movement, results in a corresponding deflection of said seal, due to compression of layer 5, so as to reduce wear of the seal. <IMAGE>

Description

IEAPROVE EKrS RELATING TO SEALS The invention relates to a seal for use in conjunction with a movable member and, particularly, but not exclusively, a rotating member.

Further, the invention also has application in the provision of labyrinth seals.

It is well known to place seals about moving members so as to prevent the ingress or egress of pre-determined substances. A typical example is to be found in the coal industry where coal dust is manufactured as a result of the grinding action of a rotatable member. At least one end of this member is sealed to prevent the escape of coal dust and the sealing achieved by the provision of a seal mounted about an end of the member.

The seal comprises a suitahle fona of bearing material which is fastened so as to fit about an end of the member, but providing sufficient clearance to allow the member to rotate.

In addition, a differential pressure may be provided about the seal so as to prevent ingress of coal dust in the region of clearance between the bearing surface and the member.

Vhere one finds this arrangement - especially on large, vertical, spindle ball mills - problems arise. For example, it is extremely difficult to provide the correct amount of clearance because of dimensional inaccuracies and also because of the fact that the rotating member often runs slightly eccentrically especially on start up of rotation. As a result of this, the rotating member typically contacts the seal bearing face and causes rapid wear. This eventually results in a reduction of sealing, and where a differential pressure is also provided, a loss of seal air pressure.

It is the ohject of the invention to provide a seal for use with a movable member, and ideally a rotatable member which overcomes the above mentioned problems.

According to a first aspect of the invention there is therefore provided a seal for use with a movable member wherein the seal is sized and shaped to fit about at least a part of the member, which seal comprises a composite structure including an outer most bearing layer and adjacent flexible layer whereby contact between said member and said seal results in a corresponding deflection of said seal so reducing wear of the seal.

According to a yet further aspect of the invention there is provided a seal assembly comprising: a) a movable member; b) a seal sized and shaped so as to fit about at least a part of the member; c) a means for creating a pressure differential inboard and outboard of said seal; characterized in that the seal comprises a composite structure including an outer most bearing layer and an adjacent flexible layer whereby contact between said member and said seal results in a corresponding deflection of said seal so as to reduce wear of the seal.

Preferably a region of clearance is created between said bearing layer and said member.

Preferably the flexible layer coniprises a resilient material and ideally a high temperature resistant material such as silicone rubber.

Preferably said moving member is adl,ted to rotate and in a preferred embodiment of the invention the moving member is a grinding tool.

Preferably said seal is sized and shaped to fit about an end of said grinding tool.

Preferably an air port is provided for the introduction of air under pressure so as to create the pressure differential across said seal.

Preferably the bearing layer is made of a wear resistant material.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings wherein: Figure 1 shows a vertical section through a typical vertical spindle labyrinth seal; Figure 2 shows a vertical section through a spindle labyrinth seal modified in accordance with the invention; and Figure 3 shows a simplified section of Figure 2.

Referring to the Figures, and firstly to Figure 1, there is shown a rotating machine element 4 to which may be attached a suitable grinding member (not shown). rviachine element, or spindle, 4 is housed within a housing 6. In this prior art arrangement, a seal 2 having an outer most bearing layer 2a is sized and shaped so as to fit about a lower most end of spindle 4. A region of clearance 7 is provided between bearing face 2a and outer most surface of spindle 4. This region of clearance 7 enables rotation of spindle 4 adjacent seal 2.

Itowever, it also enables small particles to by-pass seal 2 and therefore to this end an auxiliary pressure seal is created behind seal 2. The pressure seal comprises a region of high pressure 1 which is supplied with air under pressure via an air port 3. It follows that air under pressure will pass via clearance 7 and issue from the outer most side of seal 2 thus preventing small particles by-passing seal 2.

As previously mentioned, the disadvantage of this arrangement lies in the fact that it is difficult to obtain the correct amount of clearance 7 and also wearing of bearing face 2a inevitably occurs during rotation of spindle 4.

Illustrated in Figure 2 is an embodiment of the invention which has particular bearing on the afore descried apparatus. In both Figures 2 and 3 like symbols are used to represent those structures previously described.

It can be seen that seal 2 has been modified to provide a composite structure, which structure includes an outer bearing layer 2a, an inner flexible layer 5 and an outer mounting layer 8.

It will be understood that clearance 7 is again provided between layer 2a and the outer most surface of spindle 4.

In the embodiment of the invention the provision of a flexible, and ideally a compressible, layer 5 means that when spindle 4 contacts surface 2a as a result of eccentric movement about its vertical axis, surface 2a exerts a compressive force on layer 5 resulting in a deflection of surface 2a which accommodates movement of spindle 4, thus reducing the effects of frictional wearing. Because of the operating speeds of spindle 4 and the subsequent associated operating temperatures, the material used for layer 5 is a high temperature resistant silicone rubber.

Referring to Figure 3, it can he seen that the composite seal 2 including layers 2a, 5 and 8, extends about the entire lower most surface of spindle 4 so creating a seal which extends about spindle 4.

As mentioned, clearance 7 is provided between surface 2a and the outer most surface of spindle 4 and in order to minimize the risk of small particles by-passing seal 2 a pressure differential is created across the seal by forcing air under pressure through air port 3 and into labyrinth region 1 behind seal 2.

It will be understood that the invention provides an effective means of sealing movable member and what is more extending the life expectancy of a seal in accordance with the invention.

Claims (12)

1, A seal for use with a movable member wherein the seal is sized and shaped to fit about at least a part of the member, which seal comprises a composite structure including an outer most bearing layer and an adjacent flexible layer whereby contact between said member and said seal results in a corresponding deflection of said seal so reducing wear of the seal.

2 A seal according to Claim 1 wherein the flexible layer comprises a high temperature resistant material.

3 A seal according to Claim 2 wherein the material is silicone rubber.

4. A seal according to Claim 1 wherein the bearing material is a wear resistant material.

5. A seal assembly comprising: (a) a movable member; (b) a seal sized and shaped so as to fit about at least a part of the member; (c) a means for creating a pressure differential inboard and outboard of said seal; characterized in that the seal comprises a composite structure including an outer most bearing layer and an adjacent flexible layer whereby contact between said member and said seal results in a corresponding deflection of said seal so as to reduce wear of the seal.

6. An assembly according to Claim 5 wherein a air port is provided for the introduction of air under pressure so as to create the pressure differential across said seal.

7. An assembly according to Claim 5 wherein the flexible layer is a temperature resistant material.

8. An assembly according to Claim 7 wherein the material is silicone rubber.

9. An assembly according to Claim 5 wherein the bearing layer is made of a wear resistant material.

10. A seal or seal assembly according to any preceding Claim wherein a region of clearance is created between said bearing layer and said member.

11. A seal or seal assembly according to any preceding Claim wherein said moving member is adapted to rotate.

12. A seal or seal assembly according to Claim 11 wherein said member is a grinding tool.