GB2285101A

GB2285101A - Seal for use with liquids

Info

Publication number: GB2285101A
Application number: GB9326265A
Authority: GB
Inventors: Grant Gerald Kenworthy
Original assignee: John Crane UK Ltd
Current assignee: John Crane UK Ltd
Priority date: 1993-12-23
Filing date: 1993-12-23
Publication date: 1995-06-28
Also published as: GB9326265D0

Abstract

A seal has a first sealing ring (21) mounted non-rotatably and fixed axially relative to a housing (11) and a second sealing ring (37) mounted non-rotatably and movable axially of a shaft (10), a spring (34) being provided to urge the second sealing ring (37) into sealing engagement with the first sealing ring (21), the first sealing ring (21) defining an annular knife edge (22) which sealing engages a planar radial face (38) of the second sealing ring (37) the first sealing ring (22) being mounted eccentrically of the second sealing ring (37), so that as the shaft (10) rotates relative to the housing (11) the knife edge (22) will wipe over the planar surface (38) to maintain a seal therebetween. <IMAGE>

Description

SEALS The present invention relates to seals and in particular to mechanical seals for use with liquids such as latex which coagulate or with high viscosity liquids.

In accordance with US 4,335,888, it has been proposed to use a sealing ring defining a sharp edge-like sealing face running against a sealing ring defining a planar face, for sealing liquids such as latex, in order to prevent 'gumming up' of the seal due to coagulation of the latex between the sealing faces. This form of seal has the disadvantage that due to the very small contact area between the two faces of the seal, the faces will be subject to high wear rates. As a result, US 4,335,888 is restricted to the use of hard ceramic materials for both sealing rings.

According to one aspect of the present invention a seal comprises of a first sealing ring mounted non-rotatably and fixed axially relative to one of a pair of relatively rotatable components and a second sealing ring mounted non-rotatably and movable axially of the other of the relatively rotatable components, means being provided to urge the second sealing ring into sealing engagement with the first sealing ring, one of the sealing rings defining an annular knife edge which sealingly engages a planar radial face of the other sealing ring, one of the sealing rings being mounted eccentrically of the other sealing ring, so that as the components rotate relative to one another, the knife edge of one of the sealing rings will wipe over the planar radial face of the other sealing ring to maintain a seal therebetween.

With the invention disclosed above, the contact area with the planar radial face is significantly increased thus decreasing the wear rate of this face so that softer materials may be used for the sealing ring defining the radial sealing face. Also the wiping action of the knife edge over the planar radial face will remove the sealed liquid from the face.

The width of the knife edge face is preferably from 0.1 mm to 1.5 mm and more preferably from 0.3 mm to 1.0 mm.

The axis of the eccentrically mounted sealing ring is preferably offset from the axis of the other sealing ring by 0.5 mm to 3.0 mm.

An embodiment of the invention is now disclosed, by way of example only, with reference to the accompanying drawing which illustrates, in cross-sectional elevation, a seal in accordance with the present invention.

The seal illustrated in the accompanying drawing provides a seal between the drive shaft 10 and housing 11 of a pump for liquid latex.

A gland plate 15 is bolted to the end of the housing 11 externally thereof, the gland plate 15 being mounted coaxially of the shaft 10 and is sealed to the housing 11 by means of an 0-ring 16.

An annular seat carrier 17 is located coaxially of the shaft 10 at the inner periphery of the gland plate 15, by means of a series of angularly spaced pins 18. The seat carrier 17 is sealed with respect to the gland plate 15 by 0-ring 19. The seat carrier 17 defines an annular recess 20 coaxial of the shaft 10 for location of an annular seat 21 made of cemented tungsten carbide. The end of the seat 21 which extends out of the seat carrier 17 away from the housing 11, defines an annular knife edge 22 typically 0.5 mm wide, which is coaxial with the shaft 10.

A sleeve 25 is mounted on the shaft 10 and is sealed with respect thereto by means of 0-ring 26. A drive ring 27 is located on the sleeve 25 and is clamped thereto by means of a plurality of angularly spaced grub screws 28.

The drive ring 27 is sealed with respect to the sleeve 25 by means of 0-ring 29. A carrier ring 30 is slidably located on the drive ring 27 and is sealed with respect thereto by 0-ring 31. The carrier ring 30 has a series of angularly spaced axially extending slots 33 which correspond in position to the grub screws 28. The grub screws 28 extend outwardly from the drive ring 27 when the screws 28 are tightened down onto the sleeve 25, so that the outer portions of the screws 28 engage the slots 33 to rotationally locate the carrier ring 30 with respect to the drive ring 27 and sleeve 25, while allowing axial movement of the carrier ring 30 relative to the drive ring 27. A wavy spring washer 34 acts between a flange 35 on the drive ring 27 and the outer end of carrier ring 30, to urge the carrier ring 30 towards the seat 21.

The inner end of the carrier ring 30 defines a recess 36 which is eccentric of the axis of the shaft 10. A sealing ring 37 made of cemented tungsten carbide is located in the recess 36, so that under the action of spring 34 a planar radial face 38 of sealing ring 37 is urged into sealing engagement with the annular knife edge 22 of seat 21.

Because of the eccentricity of sealing ring 37, as the shaft 10, sleeve 25, drive ring 27, carrier ring 30 and sealing ring 37 rotate relative to the housing 11 and seat 21, the knife edge 17 will wipe across the radial face 38 of the sealing ring 37, thereby defining a relatively wide wear track. With a typical eccentricity of 1.0 mm, a wear track 2.0 mm wide will result, thus reducing the wear of the radial face by 75% as compared with the conventional, concentrically mounted seal.

Wiping action will also remove latex from the radial face 38 of sealing ring 37, thereby reducing the risk of coagulation of the latex on the face 38 which may otherwise 'gum up' the seal.

An annular quench plate 40 is located coaxially of the shaft 10 outward of the drive ring 27 and is secured to the gland plate 15 by means of three angularly spaced bolts 41 and spacers 42. A drive collar 43 made of stainless steel is mounted on sleeve 25 externally of the quench plate 40 and is located axially and rotationally with respect thereto by means of a plurality of angularly spaced grub screws 44. The grub screws 44 extend through bores 45 in the sleeve 25 into engagement with the shaft 10, to locate the sleeve 25 axially and rotationally with respect to the shaft 10. The drive collar 43 is sealed with respect to the sleeve 25 by means of 0-ring 46.

The inner end of drive collar 43 forms a seat 47 which extends into the bore 48 of quench plate 40. The end of the bore 48 adjacent the drive collar 43 is counterboard to provide a shoulder 49. A centralising ring 50 made of PTFE is located in a recess 51 at the outer end of bore 48, the internal diameter of ring 50 engaging the drive collar 43.

A carbon sealing ring 52 is slidably located in the smaller diameter portion of bore 48. The outer end face 53 of the sealing ring 52 has an outwardly directed flange formation 54 which extends towards the surface of the larger diameter portion of the bore 48, so that it radially overlaps the shoulder 49. The seat 47 is arranged such that when the outer end 53 of sealing ring 52 engages the opposed face of seat 47, an annular cavity 55 is formed between the shoulder 49 and the flange formation 54. An elastomeric band 56 is located in the cavity 55, the band 56 being under compression when the face 53 engages the seat 47, so that the face 53 is urged into sealing engagement with the seat 47 to form a fluid tight seal.A plurality of angularly spaced pins 60 are located at the inner end of quench plate 40 and extend inwardly into engagement with correspondingly positioned axially extending slots 61 in the sealing ring 52, to rotationally locate the sealing ring 52 with respect to the quench plate 40 while allowing axial movement of the sealing ring 52 relative thereto.

A cylindrical cover 65 extends between the gland plate 15 and quench plate 40 and is sealed with respect thereto by 0-rings 66 and 67 respectively, in order to form a fluid chamber 68 between the inner seal formed by seat 17 and seal ring 37 and outer seal formed by seat 47 and sealing ring 52. An inlet 69 is provided to the chamber 68 and an outlet 70 from the chamber 68, by which water may be passed through the chamber 68 to cool and lubricate the seals.

When sealing liquid latex, latex leaking across the seal formed by seat 17 and sealing ring 37 may form a streamer which will wrap itself around the seal and cause a malfunction. In order to avoid this, a cutting ring 75 is mounted over the carrier ring 30 and is located rotationally with respect thereto by one or more pins 76.

The cutting ring 75 has an axially extending portion 77 with a plurality of slots 78. A fixed cutter 79 is mounted with respect to the gland plate 15, so that it overlaps axially with the cutting ring 75. In operation, the cutting ring 75 and cutter 79 will chop streamers of latex into -hips which may be washed away by water flowing through the chamber 68.

For assembly purposes a circumferential groove 80 is provided in the sleeve 25, externally of the drive collar 43. A setting disc 81 is located in the groove 80, the setting disc 81 being bolted te the quench plate 40 with spacer tubes 82 located between the setting disc 81 and quench plate 40 in order to accurately locate the sleeve 25 on the shaft 10, prior to clamping the sleeve 25 to the shaft 10 by means of the grub screws 44. This ensures that the sleeve 25 is accurately set with respect to the seat carrier 17 and quench plate 40 and appropriate axial loading of the sealing rings 37 and 52 is achieved.

Various modifications may be made without departing from the invention. For example, while in the above embodiment both seat 17 and sealing ring 37 are formed from cemented tungsten carbide any other hard materials, for example ceramics or refractor materials such as silicon carbide, cemented carbides or allumina may be used. Furthermore, because of the relatively wide wear track on the sealing ring defining the planar face, softer materials, for example carbon or bronze may be used for this sealing ring.

According to further embodiments of the invention, the annular knife edge sealing formation may be provided on either of the sealing rings and either of the sealing rings may be eccentrically mounted.

Preferably, the knife edge formation of the present invention may have a width of from 0.1 mm to 0.3 mm.

The invention covered by the present application is directed to the inner seal assembly and the provision of a quench chamber and the form of the outer seal assembly is incidental to the present invention. Seals in accordance with the present invention may be used, where appropriate, on their own and where a quench chamber is desirable, any suitable form of outer seal may be used.

While the present invention is particularly suitable for sealing materials such as latex, it may also be used for sealing high viscosity liquids such as paints and inks.

Claims

1. A seal comprising of a first sealing ring mounted non-rotatably and fixed axially relative to one of a pair of relatively rotatable components and a second sealing ring mounted non-rotatably and movable axially of the other of the relatively rotatable components, means being provided to urge the second sealing ring into sealing engagement with the first sealing ring, one of the sealing rings defining an annular knife edge which sealingly engages a planar radial face of the other sealing ring, one of the sealing rings being mounted eccentrically of the other sealing ring, so that as the components rotate relative to one another, the knife edge of one of the sealing rings will wipe over the planar radial face of the other sealing ring to maintain a seal therebetween.

2. A seal according to Claim 1 in which the knife edge is from 0.1 mm to 1.5 mm wide.

3. A seal according to Claim 2 in which the knife edge is from 0.3 mm to 1.0 mm wide.

4. A seal according to any one of Claims 1 to 3 in which the axis of the eccentrically mounted sealing ring is offset radially of the axis of the other sealing ring by 0.5 mm to 3.0 mm.

5. A seal according to any one of the preceding claims in which the sealing ring defining the annular knife edge is made from a hard material.

6. A seal according to Claim 5 in which the sealing ring defining the knife edge is made of a ceramic or refractory material.

7. A seal according to any one of the preceding claims in which the sealing ring defining the plana sealing surface is made of a hard material.

8. A seal according to Claim 7 in which the sealing ring defining the planar sealing surface is made of a ceramic or refractory material.

9. A seal according to any one of Claims 1 to 6 in which the sealing ring defining the planar sealing surface is made of a relatively soft material.

10. A seal according to Claim 9 in which the sealing face defining the planar sealing surface is made of carbon or bronze.

11. A seal according to any one of the preceding claims in which the sealing ring defining the knife edge is mounted coaxially of the shaft, the sealing ring defining the planar sealing face being mounted eccentrically of the shaft.

12. A seal according to any one of Claims 1 to 10 in which the sealing ring defining the knife edge is mounted eccentrically of the shaft, the sealing ring defining the planar sealing surface being mounted coaxially of the shaft.

13. A seal according to any one of the preceding claims in which the sealing ring defining the knife edge is mounted in fixed axial and rotational relationship with respect to its associated component, the sealing ring defining the radial sealing face being urged axially into sealing engagement with the knife edge.

14. A seal according to any one of the preceding claims in which cutting means is provided to cut up streamers of coagulated liquid escaping from the seal.

15. A seal according to Claim 14 in which the cutting means comprises a rotating cutter mounted for rotation with one of the sealing rings, and a fixed cutter

16. A seal according to any one of the preceding claims in which a second seal assembly is located outboard of the seal assembly including the first and second sealing rings, to define a close chamber through which a liquid may be circulated to cool and lubricate the seal assembly.

17. A seal substantially as described herein, with reference to and as shown in the accompanying drawing.