GB2106196A

GB2106196A - Seals

Info

Publication number: GB2106196A
Application number: GB08225776A
Authority: GB
Inventors: Ian Bernard Robert Elliott
Original assignee: ASHLOW Ltd
Current assignee: ASHLOW Ltd
Priority date: 1981-09-16
Filing date: 1982-09-09
Publication date: 1983-04-07
Also published as: SE8205261L; DE3233760A1; IT1153727B; FR2512914B1; FR2512914A1; SE8205261D0; GB2106196B; IN156605B; IT8223302A1; IT8223302A0; JPS58121358A

Abstract

A seal arrangement enabling a shaft (3) to run at peripheral speeds in excess of 15 M/sec. comprises a pair a lip seals (10) disposed back to back in a chamber (11) and with a space (15) between them and means for introducing both air under pressure and lubricant into that space. The means for introducing the air/oil mixture is preferably adapted to inject small quantities of oil intermittently into a continuous air stream. Application to a rolling mill is particularly described, a labyrinth seal (25) being provided on the cooling water side of the assembly. <IMAGE>

Description

SPECIFICATION Seals This invention relates to a seal arrangement for a shaft rotatable in a bearing.

It is known to lubricate a lip seal, which is generally spring loaded, with a suitable lubricant such as oil. This lubricant is normally directed to the sealing lip of the seal, either by placing the lip adjacent to the supply of lubricant, or by introducing the lubricant to the side of the lip away from a medium to be excluded from the bearing, e.g., cooling water in a rolling mill.

Because a lip seal is essentially uni-directional in its sealing capability, then two such seals are arranged 'back to back' when contamination between two mediums is to be avoided, and if either or both of these media are not in themselves acceptable lip lubricants then a suitable lubricant is introduced between the seals, but even with these known seal lubricating arrangements, friction and ultimately wear at the sealing point cannot be satisfactorily reduced thus impairing the efficiency and life of the seals.

It has been found that a lip seal cannot generally operate satisfactorily at shaft peripheral speeds in excess of 1 SM/sec. Any axial movement between the shaft and the bearing will increase the friction and wear on the seal.

The object of the invention is to minimise the friction between sealing lip and shaft, generated heat, and ultimately wear, thus producing longer seal life and sealing efficiency at peripheral speeds greatly in excess of 1 SM/sec.

According to the present invention a seal arrangement for a shaft rotatable in a bearing comprises a pair of lip seals disposed back-toback within a chamber and with a space between the lip seals and means for introducing both air under pressure and lubricant into that space.

In use, the air under pressure causes the force between each sealing lip and the shaft to tend to zero, and may even lift the lip very slightly from the surface of the shaft. Sealing efficiency is maintained, however, by the closeness of each lip to the shaft and, where a gap is generated, by the passage of air and lubricant through that gap.

Since the friction creating force between each sealing lip and the shaft is substantially zero, wear of the seals is greatly reduced and, therefore, their life and efficiency are greater increased, thus affording considerable cost savings in maintenance of machinery.

Theoretically if a perfectly uniform air gap could exist between each sealing lip and the shaft, no friction or wear would occur and therefore no lubricant would ba required. However, it is necessary to introduce a trace of lubricant into the air in the space between the seals. Each sealing lip is efficiently lubricated and is also cooled by the passage of air/oil mixture or air/oil mist through any slight gap. Appreciable shaft deflections and eccentricities often encountered in mechanical machinery can be efficiently accommodated by the invention, since the aforementioned passage of air/oil mixture or air/oil mist seals any small gaps produced at the sealing lip/shaft interfaces.

This invention is of particular advantage in a rolling mill, where it is known that it is difficult to seal against both the ingress of cooling water into the work roll bearing housings and leakage of lubricating oil from these housings, because of a combination of high peripheral speeds and shaft deflections. In this application it is desirable to utilise a labyrinth seal, in addition to the seal arrangement of the invention, situated on the cooling water side of the assembly thus preventing the ingress of scale carried by the cooling water. A further advantage of the invention in a rolling mill is that the rotating shaft can be moved very appreciable distances axially within the sealing assembly without impairing sealing efficiency.

The means for introducing both air under pressure and lubricant into the space between the lip seals may be any known air/oil injector device, but is preferably one which injects small quantities of oil intermittently into a continuous air stream, or, in the case of a rolling mill, into two continuous air streams, one to each space between each pair of back-to-back lip seals for the respective roll bearings.

An embodiment of the invention in a rolling mill will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a fragmentary vertical section through a rolling mill taken along the axis of one of a pair of work rolls the other of which is omitted; Figure 2 is a section through an air/oil injector device in a block shown in section on the line X-X of Figure 3; Figure 3 is an elevation of the air/oil injector block indicating the incorporation of two air/oil injector devices to serve the seal arrangements of the pair of work roll bearings; and Figure 4 is an enlargement of part of Figure 1 in more detail.

In Figure 1 a work roll 1 has a profiled rim 2 and is secured on a shaft 3 rotatable in a bearing:4 by drive means (not shown), and the bearing is provided in a housing 5 mounted in a roll stand 6, which has a face plate 7 with an aperture 8 for the shaft 3 and accommodating a seal arrangement 9 in accordance with the invention.

The seal arrangement 9 comprises a pair of lip seals 10 disposed back-to-back within a chamber 11 formed between rings 12, 1 3 secured to the housing 5 and a bush 14 secured on the shaft 3, and a space 1 5 is provided between the lip seals into which is introduced both air under pressure and lubricant supplied by a device 1 6 shown in Figure 2.

The device 16 consists of an air/oil injector feeding oil from a feed bore 1 7 in a block 18 intermittently in small quantities into a tapping 1 9 from a pressure air supply bore 20 in the block, the air/oil mixture or air/oil mist being supplied through a pressure hose 21 to a banjo union 22 (Figure 1) leading to passages 23 in the housing 5 and thence to passages 24 in the ring 12 communicating with the space 1 5 between the back-to-back lip seals 10 in the chamber 1 The block 1 8 also contains a second air/oil injector device 1 6A (Figure 3) with common oil and air feeds 1 7, 20 and a tapping 1 9A for connection (in similar manner to that described above) to the seal arrangement in accordance with the invention provided for the other work roll bearing (not shown).

The work roll 1 and the ring 1 3 are provided with annular tongues and grooves together forming a labyrinth seal 25.

In use, the air under pressure in the space 1 5 in the chamber 11 causes the force between each sealing lip 26 (Figure 4) and the bush 14 on the shaft 3 to tend to zero, and may even lift the lip very slightly from the surface of the bush. Sealing efficiency is maintained, however, by the closeness of each lip 26 to the bush 14 and, where a gap is generated, by the passage of air and lubricant through that gap.

Since the friction creating force between each sealing lip 26 and the bush 14 on the shaft 3 is substantially zero, wear of the seals 10 is greatly reduced and, therefore, their life and efficiency are greatly increased, thus affording considerable cost savings in maintenance of machinery. Each sealing lip 26 is efficiently lubricated and is also cooled by the passage of air/oil mixture or air/oil mist through any slight gap, and air (with some oil) passing through to between the ring 1 3 and the work roll 1 passes outwards to the labyrinth seal 25 where it assists in preventing the ingress of scale carried by cooling water for the work rolls.

Appreciable shaft deflections and eccentricities and axial movement can be efficiently accommodated by the invention and allow the rolling mill to operate satisfactorily at shaft peripheral speeds well in excess of 1 SM/sec.

Claims

1. A seal arrangement for a shaft rotatable in a bearing comprising a pair of lip seals disposed back-to-back within a chamber and with a space between the lip seals and means for introducing both air under pressure and lubricant into that space.

2. A seal arrangement as in Claim 1, incorporating in a rolling mill.

3. A seal arrangement as in Claim 2 wherein a labyrinth seal, is situated on the cooling water side of the assembly.

4. A seal arrangement as in any one of the preceding Claims, wherein the means for introducing both air under pressure and lubricant into the space between the lip seals is adapted to inject small quantities of oil intermittently into a continuous air stream.

5. A seal arrangement substantially as hereinbefore described with reference to the accompanying drawings.

6. A rolling mill provided with a seal arrangement substantially as hereinbefore described with reference to the accompanying drawings.