GB2181796A

GB2181796A - Improvements in or relating to rotary shaft seals

Info

Publication number: GB2181796A
Application number: GB08623950A
Authority: GB
Inventors: Samuel Dolman
Original assignee: TILCON Ltd
Current assignee: TILCON Ltd
Priority date: 1985-10-18
Filing date: 1986-10-06
Publication date: 1987-04-29
Also published as: GB2181796B; GB8525763D0; GB8623950D0

Abstract

A shaft seal arrangement is provided for a mixing device in which paddles (10, Fig. 10) or the like are mounted upon a shaft 6 driven externally of the device and thus passes through a wall 8 thereof. The seal comprises a first and a second member 22, 24 of a face seal arrangement which members are spring-biased together. The second face seal member 24 is secured to a first labyrinth seal member 30 which interleaves with a second labyrinth seal member 36. Lubricant grease is charged to the labyrinth seal members under pressure and normally does not enter the face seal stage. If, however, ingress of material being mixed forces the two face seal members apart, grease from the labyrinth stage enters the space between the face seals and is driven outwardly of the confronting faces along a spiral groove (42, Fig. 3) in one of the face seal members, so that the grease and material is ejected from the face seal. <IMAGE>

Description

SPECIFICATION Improvements in or relating to rotary shaft seals The invention is concerned with improvements in or relating to rotary shaft seals for use to prevent passage of flowable material therepast. Such seals find use particularly but not exclusively in situations where finely-divided particles are to be mixed in a container by an externally driven mixing device, a rotary shaft passing through a container wall.

The invention provides a shaft seal including a first stage face seal arrangement comprising a first member annular rotatable with said shaft and a second, stationary, annular member having a surface confronting a surface of the first member, and a second stage labyrinth seal arrangement comprising a first, stationary, multiple ring labyrinth member interleaving with a second, rotatable, multiple ring labyrinth member, wherein a supply of lubricant is provided under pressure to the interleaved multiple rings of the labyrinth seal and to any clearance occurring between the confronting surfaces of the first and second face seal members and caused by the ingress of flowable material in use, the confronting surfaces of said first member being provided with a spiral groove leading from an inner region adjacent the shaft to an outer peripheral exit, so that the flowable material and the lubricant in the groove is ejected through said exit.

Advantageously, the second member of the face seal arrangement is secured to the first member of the labyrinth arrangement. Conveniently the second face seal member may be constructed of a selflubricating or so-called dry bearing material and include a channel or groove arranged to permit migration of lubricant from the labyrinth seal arrangement to the face seal as required.

In an example to be described below, the flowable material comprises finely divided particles of cementitious material in a mixing drum in which mixing paddles or like members are mounted on an externally driven horizontal shaft. Such an arrangement is particularly suitable for use on a mobile platform for example a lorry or truck, which may be adapted to carry a plurality of drums.

An example of a shaft seal according to the invention will now be described with reference to the drawings. It will be understood that the description is given by way of example only and not by way of limitation.

In the drawings: Figure 1 is a part-sectional view through a shaft seal according to the invention; Figures 2 and 3 are plan and sectional views respectively of a first face seal member; Figures 4 and 5 are fragmentary plan and sectional views respectively of a second face seal member; Figures 6 and 7 are fragmentary plan and sectional views respectively of a first labyrinth seal member; Figures 8 and 9 are fragmentary plan and sectional views respectively of a second labyrinth seal member; Figure 10 is a part-sectional view of a shaft seal in use in a mixing drum; and Figure 11 is a side view of a mobile arrangment including a plurality of drums of Figure 10.

A hydraulic motor 2, operating through speed reduction gearing 4, drives a shaft 6, which passes through a container wall 8. The container is used for the transport of finely-divided particulate material, for example sand or cement and the shaft 6 is provided with mixing blades 10 (see Figure 10).

Where the shaft 6 enters the container a shaft seal is provided as indicated by the reference numeral 12. The shaft 6 is supported externally of the container by a frame 14 including two support bearings 16 in which the shaft freely rotates. An arrangement of disc springs 18 acts against a collar 20 to extert a predetermined and adjustable amount of pressure between confronting surfaces of a first and second member 22,24, of the face seal stage of the shaft seal 12.

The first face seal member 22 is secured to the shaft 6 by a wear ring 26, and runs against the second member 24 which in the present example comprises a nylon-filled synthetic plastics bearing plate secured to the container wall 8 by bolts 28 which also secure in place a first labyrinth seal member 30. The member 30 is thus arranged to support the plate member 24. The multiple rings 32 of the member 30 interleave with the co-operating rings 34 of a second labyrinth member 36.

The long leakage path so formed by the interleaved rings is charged with lubricant in the form of grease forced therein under pressure. The grease is introduced in metered amounts into the seal assembly through an inlet 38 formed in the first labyrinth seal member 30 and a radially inwardly extending passageway formed buy a grease groove 40 provided in the second face seal member 24. The grease is then forced into the labyrinth stage of the seal.

There is normally no passage of grease to the face seal stage as the first member 22 and the second member 24 thereof are in sealing contact with each other. However, there will be occasions when fine material penetrates between the members 22 and 24 and in doing so causes a gap to occurthere- between. The grease provided under pressure to the seal assembly is therefore able to enter this gap and entrain the leaked material. It will be observed that the member 22 is provided with a spiral groove 42 in the face thereof which confronts the member. This groove acts as a clearing groove and together with the grease pressure causes the grease and the entrained material to be urged spirally outwards of the face seal and to be flushed back into the container.

The container itself is charged with material for transport to a site location and the mixing blades 10 are arranged to rotate on the shaft 6 not only to ensure proper mixing of the materials but to scrape material from the inner walls to avoid accretion.

The mixed material is dispensed from the container through a screw conveyor 44. A similar seal assembly 12' is also provided for the screw shaft of the conveyor. In Figure 11, three such containers are illustrated side-by-side on a mobile platform 46. Each container may carry a different constituent if desired.

Various modifications may be made within the scope of the invention as defined in the following

Claims

claims. CLAIMS

1. A shaft seal including a first stage face seal arrangement comprising a first member annular rotatable with said shaft and a second, stationary, annular member having a surface confronting a surface of the first member, and a second stage labyrinth seal arrangement comprising a first, stationary, multiple ring labyrinth member interleaving with a second, rotatable, multiple ring labyrinth member, wherein a supply of lubricant is provided under pressure to the interleaved multiple rings of the labyrinth seal and to any clearance occurring between the confronting surfaces of the first and second face seal members and caused by the ingress of flowable material in use, the confronting surfaces of said first member being provided with a spiral groove leading from an inner region adjacent the shaft to an outer peripheral exit, so that the flowable material and the lubricant in the groove is ejected through said exit.

2. A shaft seal as claimed in claim 1 wherein the second member of the face seal arrangement is secured to the first member of the labyrinth arrangement.

3. A shaft seal as claimed in either one of claims 1 and 2, wherein the second face seal member is of self-lubricating or dry bearing material.

4. A shaft seal as claimed in either one of claims 2 and 3 wherein the second face seal member includes a channel or groove arranged to permit migration of lubricant from the labyrinth seal arrangement to the face seal.

5. A shaft seal as claimed in claim 4 wherein the lubricant is introduced in metered amounts through an inlet formed in the first labyrinth seal member and a radially inwardly extending passageway in the second face seal member.

6. In a mixing drum in which mixing apparatus are mounted on an externally driven shaft, a shaft seal as claimed in any one of the preceding claims, wherein the flowable material is of a cementitious character.

7. A shaft seal as claimed in claim 6, arranged upon a shaft rotatable about a horizontal axis, there being provided a plurality of said shafts each mounting mixing apparatus and housed in one of a plurality of mixing drums supported on a mobile platform.

8. A shaft seal constructed and arranged substantially as hereinbefore described with reference to and as shown in the drawings.