WO2005019657A2

WO2005019657A2 - Resilient loading device

Info

Publication number: WO2005019657A2
Application number: PCT/GB2004/003449
Authority: WO
Inventors: Mark S. Mccormack
Original assignee: Ftl Seals Technology Limited
Priority date: 2003-08-19
Filing date: 2004-08-11
Publication date: 2005-03-03
Also published as: GB0319403D0; GB0417796D0; GB2405362B; GB2405362A; WO2005019657A3

Abstract

A method and apparatus is disclosed which includes a piston and sleeve arrangement. One end of the piston is provided with at least one bearing element and a bearing housing. The bearing element is provided with a bearing sleeve.

Description

RESILIENT LOADING DEVICE

This invention relates to a resilient loading device. In particular, but not exclusively, the present invention relates to a loading device for use in pulverised fuel grinding mills.

Electricity can be generated by a variety of means. The most common is to drive the electric alternator device via a 3 stage steam turbine. Steam to feed the turbine can be raised by a number of methods, the most common being through heat generated by solid fuel, e.g. coal, fired boilers.

To obtain maximum calorific value from the fuel, coal is usually pulverised or ground in a mill, specifically a ring and ball mill, to form a fine powder. This pulverised fuel is then transported pneumatically directly into the steam raising boilers where combustion takes place.

Babcock type "E" slow speed ring and ball mills (types 7E9; 7E10, 8.5E9, 8.5E10, 10E10, 10.9E8, 10.9E10, 10.9E11, 12E10 and 12.9E10) have been widely used for many years by the world wide power generation. They are also used, for example, in the manufacture of cement.

The fundamental principle of a ring and ball mill is that the coal is fed by gravity onto two rotating horizontally mounted circular tracks, an upper track and a lower track. Sandwiched between the upper and lower tracks are a ^"number of cast, spherical balls. Usually, the lower track is driven via an electric motor and reduction gearbox, whilst the upper track is forced down onto the balls and lower track by a series of resilient loading devices. The loading forces provided by these devices urge the balls onto a grinding surface of the lower track where target material, such as coal, is ground. The resilient loading devices, called loading rams, were originally generally similar in principle to a single acting hydraulic/pneumatic actuator. The loading force however, was generated by pressurised nitrogen gas acting on the ram surface. Radial loads were accommodated by a sleeve bearing which was lubricated with mineral oil at a pressure greater than the nitrogen gas. The sleeve was sealed at both ends and thus provided the assembly with both a lubricated bearing and a barrier to prevent loss of nitrogen gas.

Availability of plant in a modem power station is of prime importance to ensure economic production of electricity. A major objective with a ring and ball mill is that all ancillary equipment on the unit will last at least the life of the ring and ball set.

However, for many reasons, this had proven not to be possible. In particular, in practice, the original sealing arrangement for the oil lubricated sleeve had to be modified many times.

Attempts have been made to overcome this problem. Thus, South African Patent No.

9707146 describes a resilient loading device for use with a ring and ball mill wherein the oil lubricated sleeve arrangement is replaced with a plain unlubricated sleeve wherein there is fitted a modified plastic material bearing liner. The non atmospheric side of the device is totally sealed from the atmospheric side by the use of a rolling element diaphragm seal, sometimes referred to as a "bladder" or "bag".

However, it has been found that, although the service life of the device is generally extended to equal, and some times exceed, the requirements of the industry there remains the disadvantage that the ram can wear through the modified plastic bearing liner and contact the metal (normally mild steel) housing causing damage to the surface of the ram.

Another problem is that whilst loading rams are required around the world and for different uses, the connection of such rams to machinery such as a mill is dictated by the particular machine itself. Many different kinds of connection are known and it is inconvenient to have to adapt rams to fit a connection at a particular site.

It is an aim of embodiments of the present invention to at least partly mitigate the above-mentioned problems.

Thus, according to the invention we provide a loading device comprising a piston/sleeve arrangement wherein one end of the piston is provided with at least one bearing element and a bearing housing characterised in that the bearing element is provided with a bearing sleeve.

Thus the loading device is, preferentially, a resilient loading device. The bearing element may comprise a single, e.g. annular, bearing. However, preferably, the device is provided with a plurality of bearings, e.g. two bearings. The bearings may surround the whole of the end of the shaft. However, it is prefeπ-ed that when the device comprises a plurality of bearings that the bearings are slidably mounted about the shaft of the device, e.g. axially slidable.

In an especially preferred embodiment the bearing sleeve is positioned such that it completely surrounds the bearing(s). Preferentially the bearing sleeve is positioned between the bearing elements and the bearing housing.

In one aspect of the invention the device is provided with a retaining collar and a second seal assembly. Thus, the bearing sleeve may be positioned between the retaining collar and the second seal assembly. Alternatively, the bearing sleeve may be positioned such that the sleeve is held in position by the retaining collar, e.g. the retaining collar overlies the bearing sleeve.

The second seal assembly may comprise a variety of seals known per se. Preferably the second seal assembly is designed to prevent the ingress of particulate matter, e.g. dust, such as ground coal dust. Thus, the second seal assembly may comprise a single seal or a plurality of seals. Preferably, the second seal assembly may comprise a dirt wiping seal or a gaiter seal. In an especially preferred embodiment the second seal assembly comprises both a dirt wiping seal and a gaiter seal.

The bearing sleeve is novel per se. Thus, according to a further aspect of the invention we provide a bearing sleeve suitable for use in connection with a loading device as hereinbefore described.

The bearing sleeve bearing elements may be made from a suitable bearing material, however, a preferred material is a composite low friction thermoset plastic. An example of a suitable thermoset plastic is a PTFE compound, such as, PTFE bronze, PTFE graphite, PTFE carbon, etc..

According to a further aspect of the invention we also provide a ring and ball mill comprising a loading device as hereinbefore described.

We especially provide a ring and ball mill comprising a plurality of such loading devices.

We further provide the use of a loading device as hereinbefore described in the manufacture of a ring and ball mill.

In an alternative aspect of the invention we provide the use of a bearing sleeve in the manufacture of a loading device as Tiereinbefore described.

We do also provide a method of pulverising a material, e.g. coal, which comprises the use of a ring and ball mill of the invention.

We have now therefore improved the design of known bearing arrangements and incorporated a replaceable bearing sleeve together with replaceable bearing bands such that should they wear through the ram will come into contact with a phosphor bronze bearing grade material. Furthermore, the whole bearing sleeve assembly is now replaceable and can be renewed without the need to causing major damage to the entire unit.

Another particular advantage of the use of the bearing sleeve according to embodiments of the invention is that it may, inter alia, act as, for example, a type of sacrificial device. The bearings, e.g. annular bearing rings or bands, which are located within the sleeve, support the radial loads imparted by the ram and are in intimate contact with the ram. In normal use, the bearing sleeve inner diameter does not actually "bear" onto the ram, and is toleranced to be clear of the ram. However should one or more of the bearings fail or wear, the ram may then run against the sleeve. Thus, the sleeve, or a portion of the sleeve, can act as an emergency bearing.

The invention will now be described hereinafter, by way of example only, and with reference to the accompanying drawing, in which:

Figure 1 is a cross-sectional representation of a loading device;

Figure 2 illustrates a further embodiment of a biasing apparatus;

Figure 3 illustrates a still further embodiment of a biasing apparatus; and

Figure 4 illustrates a bearing.

The loading device (10) consists of cylindrical steel housing which has one end closed (11). The housing is generally C-shaped. A rod or other shaft-like member (12) is supported at one end by an elastomeric rolling diaphragm device (13), attached to a piston like arrangement (14) at the end of the rod.

The other end of the rod or shaft is supported by a sliding bearing arrangement (15). The whole assembly is mounted on spherical self aligning bearings (16) at the closed end and by a flanged coupling (17) at the moving end., The coupling methods used are dependent upon application, to ensure that the assembly, when in service, is positively located.

To provide the loading force the inner void (18) created by the rolling diaphragm is charged with a suitable medium, for example nitrogen gas, at a pressure greater than atmospheric pressure which will create rod extension. However it is more likely to be in the region of 12 times atmospheric pressure minimum and 25 times atmospheric pressure maximum. This causes the rod to move out from the body of the loading device creating a compressive load between the fixed points of the ring and ball mill.

A dirt wiping seal (19) and bellows or gaiter seal (20) are included in the design to exclude the ingress of ground coal dust into the bearing area of the loading device as this would have a negative effect on the integrity of the bearing arrangement.

The design of the bearing assembly as described in ZA9709146 shows a one piece steel bearing housing welded to the cylinder , the bearing housing utilises bearing elements of a composite low friction thermoset plastic . The disadvantage of this was that should the plastic bearing elements fail in service, resulting in the rod contacting the steel bearing housing extreme wear would occur.

However, we have found that by utilising a sliding bearing arrangement (15) which includes a bearing sleeve (21) manufactured from a suitable bearing material, for example phosphor bronze, should the bearing elements (22) wear such that the rod (12) comes into contact with the bearing sleeve (21) the rod will not be damaged.

Moreover, we have also designed the bearing sleeve (21) in such a manner so that it may be positively located in a bearing housing (23) by a retaining ring or collar (24). The retaining ring is of split construction to facilitate ease of fitting to the end cap (25). This design has the advantage over the prior art in that should the bearing sleeve (21) need replacing, following metal to metal contact, the sliding bearing housing (23) does not have to be destroyed to remove the bearing. Figure 2 illustrates a loading device according to a further embodiment of the present invention.

Figure 2a illustrates a cut-away image whilst Figure 2b illustrates an outer view of the device which is rotated through 90° with respect to the device shown in Figure 2a. As described above, the loading device (10) provides apparatus which can produce urging forces such as the loading forces needed in grinding mills. A generally C or U-shaped outer housing has a closed end (11) which houses within it a rolling diaphragm (13). The open mouth of the housing is closed with an end cap (25) on which a sliding bearing arrangement (15) is secured. The rod (12) extends longitudinally within the housing and is supported by the bearing arrangement at one end of the housing. This provides a sliding support. At the other end of the piston rod is a piston-like arrangement (14) which is secured to the rolling diaphragm (13). As fluid, such as nitrogen gas, is introduced into the diaphragm, the piston rod is urged away from the closed end of the housing (in a direction to the right of Figure 2). A free end of the rod may be secured to other elements by the flanged coupling (17). By continually maintaining a high pressure within the diaphragm the free end of the piston is continually urged away from the closed end of the housing.

-According to the embodiment of the present -invention illustrated in Figure 2, an end cap (30) is provided to close the closed end (11) of the housing. The end cap includes a first portion (31) to which an open mouth of the diaphragm (13) is sealed and a connecting portion (32) secured to the cap (31). The connecting portion (32) provides a coupling which is arranged to receive a broad range of bearings. This enables different types of bearing to be connected to the loading device according to the particular bearing required at a particular work site. As illustrated in Figure 2, a radial rod end bearing (33), which looks like a tongue element, may be connected to the end cap (30) via securing pins (34). Figure 2b illustrates a side view of the radial rod end bearing (33) in more detail. A central hole (35) is provided in the tongue member (33) and this can receive a securing pin, which may be a clevis pin, to secure the radial rod end bearing to a clevis joint or other such member.

Figure 2c illustrates an end-on view of the loading device and illustrates an arrangement of securing holes (36) which may receive securing screws (34) to fix the radial rod end bearing to the closed end of the loading device. By selectively arranging the holes on the end cap (30) during manufacture the angle at which the radial rod end bearing may be secured to the loading device may be selected.

Figure 3 illustrates apparatus for providing loading forces according to a further embodiment of the present invention.

Figure 3a illustrates a cut-away view of the apparatus whilst Figure 3b illustrates a view of the outer surface of the device of Figure 3a rotated by 90°. The apparatus illustrated in Figure 3 is similar to that described with respect to Figure 2, except that the end cap (30) formed by a first portion (31) to which the diaphragm is connectively sealed, and connecting portion (32) is secured to a housing (40) having a screw-threaded receiving region (41) which is arranged to receive a similarly screw-threaded lug region (42) as illustrated in Figure 4. As shown in Figure 4, the loading device may be secured to a body (43) of a mill via a connecting bearing. The bearing in Figure 4 is of the type known as an axial thrust bearing (44) which includes two sliding members (45) and (46) which have a substantially hemispherical lower and upper surface respectively. These surfaces are slidably engaged with matching sliding surfaces to enable the axial thrust bearing to rock and twist with respect to the body. In this way the loading device may be axially constrained with respect to the mill body but rotational compliance is permitted. As illustrated in Figure 3c, which shows an end-on view of the urging apparatus, the connector (40) may be connected to the connecting portion (32) of the end cap (30) of the loading device. The device may then be attached by screwing the lug (42) into the orifice (40) at a work site or other target location.

Embodiments of the present invention thus provide an apparatus which can provide urging forces in a desired direction. The apparatus may be secured in any direction at a target location by means of a bearing. By providing a universal connection formed by an end cap, the device provides a modular unit which enables a multitude of ways of fitting the device to a desired bearing and thus to a mill or other such device.

Embodiments of the present invention have been described hereinabove by way of example only. It will be understood that the present invention is not limited to the specific detail set out in the description. Rather, it will be understood that modifications to the present invention may be made without departing from the scope of the present invention.

Claims

1. A loading device comprising a piston/sleeve arrangement wherein one end of the piston is supported with at least one bearing element and a bearing housing characterised in that the bearing element is provided with a bearing sleeve.

2. A loading device according to claim 1 wherein the bearing sleeve is a replaceable bearing sleeve.

3. A loading device according to claim 1 wherein the loading device is a resilient loading device.

4. A loading device according to claim 1 wherein the bearing element comprises a single annular bearing.

5. A loading device according to claim 1 wherein the bearing element comprises a plurality of bearings.

6. A loading device according to claim 5 wherein the bearing element comprises two bearings.

7. A loading device according to claim 1 wherein each bearing element surrounds the whole of the end of the piston shaft.

8. A loading device according to claim 5 wherein the device comprises a plurality of bearings slidably mounted about the piston shaft.

9. A loading device according to claim 8 wherein the bearings are axially slidable about the piston shaft.

10. A loading device according to claim 1 wherein the bearing sleeve is located within a bearing housing.

11. A loading device according to claim 1 wherein the bearing sleeve is positioned such that it completely surrounds each bearing element.

12. A loading device according to claim 11 wherein the sleeve is positioned between the at least one bearing element and the bearing housing.

13. A loading device according to claim 1 wherein the device is provided with a retaining collar and a second seal assembly.

14. A loading device according to claim 13 wherein the bearing sleeve is longitudinally positioned between the retaining collar and the second seal assembly.

15. A loading device according to claim 13 wherein the bearing sleeve is positioned such that the sleeve is held in position by the retaining collar.

16. A loading device according to claim 13 wherein the retaining collar overlies the bearing sleeve.

17. A loading device according to claim 13 wherein the second seal assembly is arranged to prevent the ingress of particulate matter.

18. A loading device according to claim 13 wherein the second seal assembly comprises a plurality of seals.

19. A loading device according to claim 18 wherein the second seal assembly comprises a dirt wiping seal or a gaiter seal.

20. A loading device according to claim 18 wherein the second seal assembly comprises both a dirt wiping seal and a gaiter seal.

21. A loading device according to claim 10 wherein the bearing housing comprises a phosphor bronze material.

22. A loading device according to any preceding claim, further comprising an end cap arranged to receive a plurality of bearing types.

23. The loading device according to claim 22 wherein the end cap includes two or more securing elements arranged to enable a bearing to be secured to the loading device at more than one possible angle.

24. A bearing sleeve suitable for use in connection with a loading device according to any preceding claim.

25. A bearing sleeve according to claim 24 wherein the bearing sleeve is made from a suitable material.

26. A bearing sleeve according to claim 25 wherein the bearing sleeve is made from composite low friction thermoset plastic.

27. A bearing sleeve according to claim 26 wherein thermoset plastic is a PTFE compound.

28. A bearing sleeve according to claim 27 wherein the PTFE compound is selected from the group, including PTFE bronze, PTFE graphite and PTFE carbon.

29. A ring and ball mill comprising at least one loading device according to claim 1.

30. A ring and ball mill according to claim 29 wherein the ring and ball mill comprises a plurality of loading devices according to claim 1.

31. The use of a loading device according to claim 1 in the manufacture of a ring and ball mill.

32. The use of a bearing sleeve in the manufacture of a loading device according to claim 1.

33. A method of pulverising a material which comprises the use of a ring and ball mill device according to claim 29.

34. A method according to claim 33 characterised in that the material is coal.

35. A loading device or ring and ball mill substantially as hereinbefore described with reference to the accompanying drawings.