GB2444783A - Tapered piston cap in diaphragm actuator - Google Patents

Abstract

A method and apparatus are disclosed for providing an urging force. The apparatus includes a housing member 101 having a closed 103 and open 102 end, a piston member 104 movable in the housing and a diaphragm 109 secured to the piston member and the housing member and arranged to extend the piston member away from the closed end of the housing member when energised. At least a region of the first end 107 of the piston member is tapered inwardly to prevent contact between the piston member and housing member when a side load is applied to the piston member and the piston deviates from a central axis. Used for biasing a ring in ring and ball pulverising mills.

Description

METHOD AND APPARATUS FOR PROVIDING URGING FORCE

The present invention relates to a method and apparatus for providing an urging force at a desired location. In particular, but not exclusively, the present invention provides an apparatus which converts a fluid pressure into a thrust on a piston movable in a piston housing. The apparatus is particularly, though not exclusively, useful for loading a grinding ring of a pulverising mill.

There are many circumstances in day to day life in which it is desired to provide an urging force for urging one element against another. In such circumstances, loading devices are used to provide a mechanical force to load or move equipment.

By way of example, electricity can be generated by a variety of means. A most common manner is to drive an electric alternator device via a steam engine. Steam to be fed to such a turbine can be provided by a number of methods with the most common method :.:::. being through generating heat by burning solid fuel, such as coal, in a boiler. * .

It is known that in order to obtain a high calorific value from the fuel, the fuel, such as *..: coal, us usually pulverised or ground in a mill prior to burning, It is known that such a ** 20 pulverising mill will include relatively rotatable grinding rings and balls disposed between the rings. A fundamental principle of a ring and ball mill for use in generating pulverised * fuel is that the coal or other solid fuel 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. Often the lower track is driven via an electric motor whilst the upper track is forced downwardly onto the balls and lower track by a series of loading devices. These devices provide an urging force in the sense that the loading forces provided by the devices urge the balls onto a grinding surface of the lower track where target material, such as coal, is ground.

It will be appreciated that pulverising mills have many different applications other than for the use of pulverising fuel. For example such mills can be used to pulverise cement to produce a fine powder.

The resilient loading devices are sometimes called loading rams and originally the loading forces of such devices were generated by pressurised nitrogen gas acting on a 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 modern* pulverising mill is of prime importance to ensure economic production of a desired product. A major objective with a ring and ball mill is that all ancillary equipment on the unit will last at least the lifetime of the ring and ball set. However, for many reasons this has provided difficult or not possible in practice. In particular, the sealing arrangement between parts in a loading device is prone to failure.

A number of attempts have been made to overcome such problems. In particular, WO 2005/019657 discloses a resilient loading device which incorporates a sliding bearing arrangement around a piston which is urged outwardly with respect to a housing by virtue of a rolling diaphragm.

Such a mechanism overcomes many disadvantages associated with the prior art and is successful in its own right. However, it is possible under extreme conditions when radial *1* forces are brought to bear on an end of the piston outside the housing that the piston will *:.: be urged off axis with respect to the housing. Under such circumstances a top end, sometimes referred to as a piston cap, can become misaligned and may cause abrasion of the diaphragm which could, in theory, lead to failure. Such non-aligned motion may S.....

also cause a bearing between the housing and piston to wear at a quicker rate than might otherwise be expected.

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

It is an aim of embodiments of the present invention to provide an apparatus which can provide urging forces in a desired direction.

It is an aim of embodiments of the present invention to provide a method for providing an urging force.

It is an aim of embodiments of the present invention to provide a pulverising mill including loading rams having a long service life.

According to a first aspect of the present invention there is provided apparatus for providing an urging force, comprising: a housing member comprising a closed end and an open end; a piston member movable in the housing member; and a diaphragm element secured to said piston member and said housing member and arranged to extend the piston member away from the closed end of the housing member when energised; wherein at least a region of a first end of the piston member is tapered inwardly to prevent contact between the piston member and housing member when a side load is applied to the piston member.

According to a second aspect of the present invention there is provided a method of providing an urging force at a desired location, comprising the steps of: selectively energising a diaphragm element secured to a piston member disposed at least partially in, and movable with respect to, a housing member, at least a portion of said piston member being tapered inwardly at a first end thereof thereby preventing contact between the piston member and housing member when a side load is applied to the piston member.

Embodiments of the present invention provide an apparatus including a piston movable with respect to a piston housing for providing an urging force, such as a loading force, * capable of urging one element against another. Despite the presence of potentially significant radial forces on a piston the apparatus provides a long service life without the risk of failure.

Embodiments of the present invention provide a loading rem in which a cap end of a piston of the ram is tapered so that should radial forces tend to cause an off-axis misalignment of the piston with respect to an associated housing the piston cap will not, in use, contact the housing or diaphragm utilised to provide urging forces.

Embodiments of the present invention will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a view of a loading device; Figure 2 illustrates another view of a loading device; Figures 3A and 3B illustrate a technique for securing a loading ram at a desired location; and Figure 4 illustrates a piston under radial force.

In the drawings like reference numerals refer to like parts.

Figure 1 illustrates a loading apparatus 100 which can be utilised to provide an urging force at a desired location. The illustrated loading apparatus is of a type sometimes referred to as a loading ram. It will be appreciated that embodiments of the present invention may be broadly applied to a range of devices where a central element is forced, with respect to a surrounding housing, against a target object. The loading ram shown has a housing 101 which is formed from a substantially cylindrical body having an open end 102 and a closed end 103. A piston 104 is located within the housing. The ::::. piston 104 includes a substantially cylindrical body 105 carrying at a first end thereof an . urging plate 106 to which an urging element such as a ball or rod can be secured. At a further end of the cylindrical body 105 is a piston cap 107. The cap, cylinder and plate of the ram are integrally formed although parts may be separate and secured together :" 20 according to further embodiments of the present invention.

: A longitudinal central axis of the piston 104 defines a central axis 108 which in normal *. .: use is aligned with a central elongate axis defined by the body of the housing 101. A diaphragm 109 formed of elastomeric material such as rubber or any other suitable material is secured to an end of the housing and the piston cap. By introducing or removing an energising fluid such as nitrogen gas or any other suitable agent into an internal zone 110 of the diaphragm, an urging force can be applied to the piston which tends to force the piston out of the open mouth of the housing along the longitudinal axis 108. The piston is prevented from being urged wholly out of the housing by the fact that the end plate 106 of the piston or an engagement element secured thereto is urged in an opposite direction to the implied piston movement by a target element against which load forces are to be applied. In this way the loading device may be used to provide a mechanical force to load or move equipment. The device includes a piston which is constrained inside an open ended container (which may be referred to as a barrel) to which the flexible elastomeric bellows is attached. A pressurised media, for example nitrogen or other such fluid, is used to energise the piston to actuate motion/load with the bellows containing the energising media.

As illustrated in Figure 1 and Figure 2, the piston housing 101 may be secured to surrounding equipment by a piston linkage 200 which includes a linking plate 201 through which a central circular hole 202 is formed. Bolts 203 secure the linkage 200 to the closed end 103 of the housing. As an alternative the linkage and housing may be integrally formed. As illustrated in Figure 2B the end plate extends upwardly in a longitudinal direction. A bracket 204 may be used to help locate and/or assemble the loading device with respect to surrounding equipment. Figure 3 illustrates the mounting of the loading device in more detail and illustrates that further brackets 300 and associated bolts may be used to secure/locate the loading ram at a desired location by bolting to the surrounding equipment 301.

Referring again to Figure 1, one can see how the linkage plate 200 is aligned within a :.. recess 110 in the equipment 301. A bolt or rivet 111 is then driven through an opening *, in the equipment top passing through the central hole 202 of the linkage, thus securing the loading ram in position. In accordance with prior known loading devices, it is common practice for the housing to have a flexible coupling to adjacent equipment.

*:" 20 Typically this is achieved via a spherical bearing in a clevis or rose bearing arrangement.

This allows flexibility in alignment with the loaded part. However, in accordance with * * embodiments of the present invention the housing is rigidly located with respect to the surrounding equipment. In this sense the housing cannot flex or move beyond an axis of connection. By securing the housing substantially rigidly with respect to the surrounding equipment, collision between the piston, bag and barrel are avoided. Radial forces on the loading ram are accommodated by virtue of the piston tilting. The tilting motion does not cause failure because the piston cap is tapered and because there is no close fitting bearing towards a bottom end of the housing. As a result radial forces can be accommodated by the piston being arranged off centre for part or the whole of a loading cycle.

In general the piston axis will always try to sit central to the barrel due to the symmetrical piston design around the axis. Any force acting on the surface area equally will generate equal forces so the piston is in equilibrium. When the ram 104 is moved off centre by an external load (at the plate 106) the axis will tilt but the piston will try to locate itself in the centre about the point of moment. This is generally at the top centre of the piston, where it meets the central axis. As the piston 107 has a length then there has to be some compensation for this axial movement. This is not a problem in accordance with embodiments of the present invention as the ram is shaped so as to avoid collision/abrasion. Collision means wear of the elastomeric parts due to the high frequency movements. Adding a taper to the piston or part of the piston prevents this and ensures that collision is not possible.

The open mouth 102 of the housing is closed by a flange 112 which is a substantially circular plate having a hole centrally located. The hole has a diameter at least as large as the outer surface of the piston shaft so that the piston can move longitudinally along the axis 106 without hindrance. An elastomeric bellows 112 prevents ingress of dirt or other contaminants into the central region within the housing.

A ball and socket type arrangement may be used to help locate the urging forces of the ram. The plate 106 is secured via bolts, welding or some other such means to a flange *. 112 of an arm 113. A hemispherical ball 114 at the end of the arm is located in a sealed

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cup 115 forming part of or being fastened to equipment where urging forces are to be directed. S. * * . * S.

20 Figure 4 illustrates how embodiments of the present invention provide a tapered end cap for the piston which enables functioning as required despite external mechanical events falling outside normal working parameters for other prior known loading rams. For example, with known loading rams it is known that substantial side loads can occasionally occur which will tend to result in an angular offset on equipment. With prior known loading rams, if such side loads or radial loads are produced then rubbing can occur between the piston, bag and barrel wall. This can cause fatigue and failure of the bag and therefore failure of the unit. In addition, at a lower end of the piston prior art loading rams have utilised bearing mechanisms to support the piston. Where angular offset occurs this has caused in the past excess rubbing and degradation of the bearing.

The present invention helps overcome such problems.

As illustrated in Figure 4 the piston cap 107 includes a tapered side wall 400 providing a substantially frusto conical outer surface tapered outwardly towards the end cap end of the piston. In this way when a radial/side load is present which tends to force the piston off axis with respect to the fixed central elongate axis of the housing, the outer surface 401 of the piston cap can be maintained at at least a predetermined distance from an inner surface 402 from the housing 101. In this way embodiments of the present invention are able to work with side loading and the subsequent misalignment between a barrel and connecting device without causing a collision between the piston, bag and barrel. Advantageously embodiments of the present invention utilise a taper on the piston body having a tapered angle equal to a maximum design angular offset that will ensure collision does not occur.

Due to the design and relationship between the parts of the loading device according to embodiments of the present invention, it is possible to remove any connection device bearing arrangement which is common with existing designs. The piston can be allowed to find its own central position inside the cylinder without fear of collision or damage to the bellows or compromising the functional nature of the loading device. This development significantly extends the time period before or between maintenance or replacement due to the lack of colliding or abrading moving parts.

Throughout the description and claims of this specification, the words "comprise' and *::::* "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to', and is not intended to (and does not) exclude other * * * moieties, additives, components, integers or steps. 20

Throughout the description and claims of this specification, the singular encompasses S.....

* the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims (18)

1. Apparatus for providing an urging force, comprising: a housing member comprising a closed end and an open end; a piston member movable in the housing member; and a diaphragm element secured to said piston member and said housing member and arranged to extend the piston member away from the closed end of the housing member when energised; wherein at least a region of a first end of the piston member is tapered inwardly to prevent contact between the piston member and housing member when a side load is applied to the piston member.

2. The apparatus as claimed in claim 1, wherein the open end of the housing member is bearingless.

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3. The apparatus as claimed in claim I or claim 2, further comprising: sealing bellows closing the open end of said housing member, said bellows being secured to a sealing region of said open mouth and to a region extending circumferentially around said pistorr member.

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4. The apparatus as claimed in any preceding claim, further comprising: said piston member extends through the open end of the housing member.

5. The apparatus as claimed in any preceding claim wherein said housing member comprises a cylindrical barrel element.

6. The apparatus as claimed in any preceding claim, further comprising: said piston member is arranged to exert a thrust when the diaphragm element is energised.

7. The apparatus as claimed in any preceding claim, further comprising: a rigid securing member located proximate to said closed end of the housing member for rigidly locating said housing member at a desired location with respect to adjacent equipment.

8. The apparatus as claimed in any preceding claim, further comprising: diaphragm energising means that energises or disenergises said diaphragm selectively to respectively extend or retract said piston member with respect to said housing member.

9. The apparatus as claimed in claim 8 wherein said diaphragm energising member comprises a pump arranged to pump energising gas into and out of said diaphragm element.

10. A pulverising mill of the ring and ball type in which a loading force on a grinding ring is exerted by at least one apparatus as claimed in any preceding claim.

11. A method of providing an urging force at a desired location, comprising the steps of: selectively energising a diaphragm element secured to a piston member disposed at least partially in, and movable with respect to, a housing member, at least a portion of said piston member being tapered inwardly at a first end thereof thereby preventing contact between the piston member and housing member when a side load is applied to the piston member.

12. The method as claimed in claim 11, further comprising the steps of: rigidly mounting said housing member via a closed end thereof at said desired * location. S. * * . * * *.

13. A method of manufacturing a loading ram, comprising the steps of: securing an inwardly tapered end of a piston member to a closed end of a housing member via a diaphragm element.

14. The method as claimed in claim 13, further comprising the steps of: securing sealing bellows between an open end of said housing member and said piston member.

15. The method as claimed in claim 13 or claim 14, further comprising the steps of: securing said piston member to said housing without providing a bearing element between an open end of said housing and said piston member.

16. Apparatus constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

17. A method substantially as hereinbefore described with reference to the accompanying drawings. * S.

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