Background Art Hot and cold metal rolling processes often require the addition to and subsequent removal of coolant fluids from metal strip which is being advanced in a continuous line.

The presence of such coolant fluids is often essential for maintaining the temperature of strip materials when undergoing compression between the work rolls in a roll stand. However the coolant can cause problems in downstream processes. Water coolant may impair the performance of rolling lubricants at the roll stands and, if the strip is water-stainable, excessive residual water in the rewound coil may cause unacceptable surface staining. The surface of the strip itself may also retain unwanted adherent particulates introduced from upstream

processing or from unclean coolant fluids or lubricants.

Present techniques of using physical wiping' apparatus which contact the moving strip itself necessitate a reduction in the speed of the strip in order to provide an effective removal of pooled liquid material or particulates. While leading to production inefficiencies, such techniques also do not provide an even wiping control across the width of the strip surface nor yield an adequately thin amount of surface fluid overall.

US Patent No. 5,701, 775 describes an apparatus including two consecutive liquid knife nozzles directed across the width of a moving strip surface to remove all of the residual cooling water from an advancing strip. As shown in US 5,701, 775, a first liquid knife supplies a jet of water which intercepts forwardly directed coolant retained on the strip with sufficient momentum to arrest its advance. A subsequent, second liquid knife nozzle can supply a jet of a liquid immiscible with water to displace any residual water, where the immiscible liquid does not stain the strip surface (such as a lubricant oil). In one example given in US 5,701, 775, the second knife is an air knife directed to entirely blow residual amounts of water off the strip. However, the second fluid jet is directed at the strip at a location around a roller bend in the strip and away from the location of the first fluid jet.

Consequently the second fluid flow jet has a less significant and less direct influence on the first fluid flow jet. The second fluid flow jet that is directed at the moving strip is also diffused at the roller bend in the strip. In fact, US 5,701, 775 concludes that air knives are required to be operated unacceptably close to the surface of a strip and present significant noise and water spraying problems, and in actual fact teaches away from the use of an air knife.

In strip surface coating processes, attaining of a very even and thin coating is desirable from an economic

and quality control standpoint, although difficult to achieve in practice. Coatings can pool unevenly on a strip surface and the known physical wiping'apparatus which contact the moving strip itself are inadequate. Jet spraying techniques do not generally yield an adequately thin overall surface coating.

Summary of the Invention In a first aspect the present invention provides a method of controlling an amount of a residual material on a surface, the method including the steps of: (a) applying a material to the surface; (b) directing a flow of a first fluid from a fluid flow source at an acute angle to the surface for impingement upon and the deflection removal of part only of the material located on the surface; (c) directing a second fluid flow from another fluid flow source at either the surface or the first fluid flow to reduce the acuity of impingement of the first fluid flow; wherein steps (b) and (c) occur whilst effecting relative movement between the fluid flow sources and the surface.

Preferably the material is a liquid and application of the liquid involves retaining the liquid on the surface.

Preferably the first and second fluid flows are disposed at an acute angle relative to one another and to the surface. Most preferably the direction or angle of either or both of the first and second fluid flows is adjustable with respect to the surface and to each other.

Preferably the velocity of at least one of the first or second fluid flows is controlled. Preferably, control of the velocity of one or both fluid flows is effected by adjusting the pressure at which the fluid is expelled from a respective source thereof.

Preferably there is an adjustable distance between the source of the first fluid flow and the source of the second

fluid flow.

Preferably there is an adjustable width outlet at the respective sources of one or both of the fluid flows.

Preferably the first and second fluids are of substantially different densities. Most preferably the first fluid is a liquid and the second fluid is a gas.

The method for controlling the residual liquid or other material on a surface represents a significant improvement over other known removal methods because of the interaction of the individual fluid flow streams. This can result in both improvements to the material removal rate and in the control of the quantity of residual material to a pre-determined depth.

By directing the second fluid flow either directly toward the first fluid flow or against the surface where it subsequently intersects the first flow, the impingement of the second flow can deflect the first flow and reduce its surface impingement angle to very small values so that the flow of the first fluid becomes substantially parallel to the surface. This maximises the upstream first fluid flow momentum in one direction to most efficiently retard and deflect at least some of the surface liquid or other material.

When the material is a liquid, the application of the liquid involves coating of the surface with the liquid. In such cases coating of the liquid is effected preferably by part of the flow of the first fluid. The present method, when used for controlling a residual coating thickness, allows for a very thin coating to be applied evenly over the surface. The prior art US 5,701, 755 is directed toward complete removal of the liquid coating.

In a second aspect the present invention provides an apparatus arranged to control an amount of a residual material on a surface, the apparatus including: - a device for applying a material to the surface; and

first and second fluid directing devices for respectively directing a flow of a first and second fluid, the directing devices arranged so that, in use: the first fluid flow impinges upon and deflectingly removes part only of the material located on the surface; and the second fluid flow is directed at the surface or the first fluid flow to reduce the acuity of impingement of the first fluid flow, wherein the apparatus and surface are arranged to move with respect to one another during the direction of flow from the first and second fluid directing devices.

Preferably the first and second fluid directing devices are fluid knives.

Preferably the first and second fluid flows are pressurised jet streams. Most preferably the pressurised jet streams each flow from a pressurisable plenum.

Preferably the direction angle of either or both of the first and second fluid flows is adjustable with respect to the surface and to each other.

Preferably there is an adjustable distance between the source of the first fluid flow and the source of the second fluid flow.

Preferably there is an adjustable width outlet at the respective sources of one or both of the fluid flows.

Preferably in use the apparatus is static and the surface is arranged to move therebelow. Most preferably the surface is a strip. Even more preferably the strip is substantially horizontal in use.

In a third aspect the present invention provides a method of cleaning a material from a surface, the method including the steps of: (a) directing a flow of a first fluid from a fluid flow source at an acute angle to the surface for

impingement upon and the deflection removal of at least some of the material located on the surface ; and (b) directing a second fluid flow from another fluid flow source at the first fluid flow to reduce the acuity of impingement of the first fluid flow; and wherein steps (a) and (b) occur whilst effecting relative movement between the fluid flow sources and the surface.

Preferably the second fluid flow directly contacts and coincides with the first fluid flow at or adjacent the surface.

Preferably the method of the third aspect is as otherwise defined in the first aspect.

The method for cleaning a material from a surface represents a significant improvement over other known cleaning methods because of the interaction of the individual fluid flow streams. Where the material to be cleaned is particulate, the method can result in both improvements to particulate removal rate and in the control of the quantity of a particulate material on the surface.

By directing the second fluid flow directly toward the first fluid flow, the impingement of the second flow can deflect the first flow and reduce its surface impingement angle to very small values so that the flow of the first fluid becomes substantially parallel to the surface. This maximises the upstream first fluid flow momentum in one direction to most efficiently dislodge or deflect at least some of the particulates located on the surface.

In a fourth aspect the present invention provides an apparatus arranged to clean a material from a surface, the apparatus including: - first and second fluid directing devices for respectively directing a flow of a first and second fluid at the surface, the directing devices

arranged so that, in use the first fluid flow impinges upon and deflectingly removes at least some of the residual material located on the surface; and the second fluid flow is directed at the first fluid flow to reduce the acuity of impingement of the first fluid flow; wherein the apparatus and surface are arranged to move with respect to one another during the direction of flow from the first and second fluid directing devices.

Preferably the second fluid flow directly contacts and coincides with the first fluid flow at or adjacent the surface.

Preferably the apparatus of the fourth aspect is otherwise as defined in the second aspect.

In a fifth aspect the present invention provides a method of cleaning a material from a planar surface, the method including the steps of: (a) directing a flow of a first fluid from a fluid flow source at an acute angle to the surface for impingement upon and the deflection removal of at least some of the material located on the surface; and (b) directing a second fluid flow from another fluid flow source at either the surface or the first fluid flow to reduce the acuity of impingement of the first fluid flow; wherein steps (a) and (b) occur whilst effecting relative movement between the fluid flow sources and the surface.

In the prior art methods for controlling residual liquid or other material on a surface, the surfaces shown are not planar and as a result the same degree of interaction between the first and second fluid flow sources is not achievable to maximise the upstream first fluid flow momentum in one direction.

Preferably the method of the fifth aspect is otherwise

as defined in the first aspect.

In a sixth aspect the present invention provides an apparatus arranged to clean material from a planar surface, the apparatus including: - first and second fluid directing devices for respectively directing a flow of a first and second fluid at the surface, the directing devices arranged so that, in use - the first fluid flow impinges upon and deflectingly removes of some of the residual material located on the surface ; and - the second fluid flow is directed at either the surface or the first fluid flow to reduce the acuity of impingement of the first fluid flow, wherein the apparatus and surface are arranged to move with respect to one another during the direction of flow from the first and second fluid directing devices.

Preferably the method of the sixth aspect is otherwise as defined in the second aspect.

Preferably the first fluid flow includes water or a hydrocarbon liquid. Most preferably the hydrocarbon is kerosene.

Preferably the first fluid flow has a temperature in the range from about 20 to 90 degrees celcius.

Preferably the first fluid flow has a pressure in the range from about 30 to 175 pounds per square inch gauge.

Preferably the first fluid flow has a fluid flow source with a nozzle aperture width in the range from about 0.005 to 0.1 inch.

Preferably the first fluid flow has a fluid flow source is directed at an angle to the surface in the range from about 10 to 55 degrees.

Preferably the first fluid flow has a fluid flow source which is spaced from the surface by a distance in the range from about 0.5 to 2 inches.

Preferably the second fluid flow includes a nitrogen- containing gas. Most preferably the nitrogen-containing gas is air.

Preferably the second fluid flow has a temperature in the range from about 20 to 90 degrees celcius.

Preferably the second fluid flow has a pressure in the range from about 4 to 12 pounds per square inch gauge.

Preferably the second fluid flow has a fluid flow source with a nozzle aperture width in the range from about 0.010 to 0.2 inch.

Preferably the second fluid flow is directed at an angle to the surface in the range from about 15 to 55 degrees.

Preferably the second fluid flow has a fluid flow source which is spaced from the surface by a distance in the range from about 0.5 to 2 inches.

Preferably the distance between the source of the first fluid flow and the source of the second fluid flow is in the range from about 0.5 to 4 inches.

Preferably the surface moves with a speed up to about 6000 feet per minute.

Brief Description of the Drawings Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a plan view of one embodiment of a surface undergoing a method of controlling an amount of a residual material thereon, in accordance with the invention.

Figure 2 shows a side view of one embodiment of an apparatus to control an amount of a residual material on a surface, in accordance with the invention.

Figure 2A shows a side view of one embodiment of an apparatus to control an amount of a residual material on a

surface, in accordance with the invention.

Figure 3 shows a side view of a further embodiment of a device used as an apparatus to control an amount of a residual material on a surface, in accordance with the invention.

Figure 3A shows a side view of a further embodiment of a device used as an apparatus to control an amount of a residual material on a surface, in accordance with the invention.

Figure 4 shows a detailed side view of the interaction of a fluid jet onto the surface shown in Figure 2, in accordance with the invention.

Figure 4A shows a detailed side view of the interaction of a second fluid jet with the fluid jet shown in Figure 4, in accordance with the invention.

Figure 4B shows a detailed side view of the interaction of a second fluid jet with the fluid jet shown in Figure 4, in accordance with the invention.

Modes for Carrying out the Invention Referring to the drawings, an apparatus 5, 5A is shown which is arranged to control the depth of an amount of a residual liquid 50 on a surface. Typically the surface is the upper exterior face of a substantially horizontal metal strip 12 which moves with some velocity with respect to the apparatus 5,5A which is static. Liquid 8 is applied by a device such as a sprayer or pourer onto the upper exterior face of the strip 12 at a location upstream of the apparatus 5,5A so that the liquid 8 is retained on the strip surface 12 before the strip surface 12 is moved under the apparatus 5,5A.

As shown in Figures 1,2, 2A, the apparatus 5,5A includes first and second fluid directing devices in the form of respective fluid knives 14,20 (slot-type orifices). As shown in Figure 2,2A, the fluid knife 14 is arranged to direct a flow of a first fluid at the strip

surface 12. Typically the first fluid is a pressurised jet stream 16 of liquid flowing from a pressurised plenum in the form of a reservoir 18, the jet stream 16 at an acute angle A to the surface of the strip 12. The jet stream 16 impinges upon and deflectingly removes part only of the excess surface liquid 8 which initially located on the strip surface 12. The advance of the excess liquid 8 past the jet stream 16 is thus at least partially arrested, as shown in greater detail in Figure 4.

A second fluid directing device in the form of a fluid knife 20 is arranged to direct a flow of a second fluid either at the strip surface (Figure 2,2A) or the first fluid flow (Figure 3,3A) to reduce the acuity of impingement of the first fluid flow with respect to the strip surface (ie to reduce the acute angle A between the jet stream 16 and the strip surface 12). Typically the second fluid is a pressurised jet stream 22 of a gas flowing at an acute angle B to the strip 12 from a fluid knife 20. The gas jet stream 22 is sourced from a pressurised plenum in the form of a reservoir 26. In one preferred embodiment shown in Figures 2,2A, the jet stream 22 of gas is directed at the strip surface 12 (typically at an angle B of 45°) the gas stream then being deflected to move along that strip surface 12 to encounter jet stream 16 so as to reduce the acuity of impingement (angle A) of that jet stream 16, as shown in more detail in Figure 4A. In another preferred embodiment shown in Figures 3,3A (where like parts are numbered as for previous embodiments to avoid repetition) the jet stream 22 of gas is directed from apparatus 5A via knife 34 to directly coincide with the jet stream 16 at a location M adjacent the strip surface 12 to reduce the acuity of impingement (angle A) of the jet stream 16 (which is directed from reservoir 18 via knife 32) without first being directed at the strip surface 12.

In the preferred embodiments, the reservoirs 18,26 are located in a housing 11 of rectangular cross-section

which is spaced vertically above the plane of the moving strip surface 12 and extending across the width of that strip surface 12 as shown in Figure 1. In other embodiments the fluid delivery apparatus can be moveable and the surface adjacent to it static, which may be useful in some coating applications. In still further embodiments the strip need not be horizontal and can be angled or even vertical.

In use the apparatus 5,5A can remove excess liquid 8 from a surface and in other applications can be used for the thinning of an applied surface coating to the strip.

Typically the strip surface is flat, elongate and of finite width, and moving with a surface velocity Vs in the direction of the arrow X as shown in the drawings. The region of the surface which is moved toward the apparatus 5,5A is referred to as the"upstream"region 4 and the region of the surface which has moved past the apparatus 5, 5A is referred to as the"downstream"region 6. Liquid or other surface coatings are in part moved off the strip surface in a direction transverse to the direction of movement of the strip in the direction of the arrows Y.

In cooling or washing operations, for example, excess liquid 8 can pool on the strip surface 12 across its width upstream of the apparatus 5,5A and, because of viscous forces, this excess liquid 8 generally attains the velocity Vs of the strip 12. Because excess liquids are generally undesirable in downstream processes, the apparatus 5,5A forcibly applies fluids such as a jet stream 16 of water and the jet stream 22 of gas in order to in part remove and thus control the quantity of residual liquid 50 remaining on the surface 12 in the downstream region 6 to a pre- determined depth, as shown in Figures 2 and 3 and in detail in Figure 4A. In still further embodiments shown in Figures 2A, 3A, and in detail in Figure 4B, the apparatus 5,5A can be used to forcibly applies fluids such as a jet stream 16 of water and the jet stream 22 of gas in order to

remove some or all of the residual liquid remaining on the surface 12 in the downstream region 6.

The pressurised jet stream 16 is typically a substance that is compatible with any further processing of the excess surface liquid 8, and most frequently is water or water based, although oils or other surface lubricating materials, organic chemicals, kerosene, paints and the like can be used in various applications. The pressurised jet stream 22 is typically a gas such as air, although other gases such as pure oxygen, nitrogen or inert gases such as helium etc or gas mixtures thereof are suitable. In the most preferred embodiment the jet stream 16 is of water and the jet stream 22 is of compressed air. As indicated in the Figures, the jet stream 16 is located at least some way upstream of the jet stream 22, and both fluid knives 14,20 span the transverse width of the strip surface 12. In a preferred embodiment shown in Figure 1, both fluid knives 14,20 are configured in the symmetrical chevron pattern shown in Figure 1. In further embodiments either or both fluid knives 14,20 may be configured in a variety of other patterns having various degrees of symmetry, or asymmetry, with respect to the longitudinal edges 28,30 of the strip surface 12.

The pressure in the respective reservoirs 18,26 is determinant of the velocity of the jet streams 16,22. The product of the respective outlet width aperture 14A, 20A, 32A, 34A of the fluid knives 14,20, 32,34 and the respective fluid velocity of each jet 16,22 determines the flow intensity of each jet stream 16,22. The momentum flux intensity of either jet stream 16,22 is proportional to the product of its velocity, density and flow intensity.

In order to control the depth of the residual liquid 50 in the downstream region 6 of the strip surface 12, the velocity of the liquid jet stream 16 can be controlled from the reservoir 18. The gas jet stream 22 is simultaneously controllably released at a specified velocity (directed

upstream) from the reservoir 26 and directed either at the strip surface 12 (as shown in the apparatus 5 in Figures 2, 2A) or at the liquid jet stream 16 (as shown in the apparatus 5A in Figures 3,3A) in either case to reduce the acuity of the angle A of impingement of the liquid jet stream 16 with respect to the strip surface 12.

In some embodiments of the invention the direction angle of either or both of the jet streams 16,22 is adjustable with respect to the strip surface 12 and to each other by adjusting the orientation of the lips of the outlet mouths of the fluid knives 14,20, 32,34 for example. This can allow adjustment of the direction angle B of the flow of the jet stream 22 to directly impinge on the jet stream 16 or to another angle of impingement with respect to the strip surface 12, as well as being able to adjust the angle A. In still further embodiments there can be an adjustable distance between the fluid knife pairs 14 and 20 and/or 32 and 34 to allow even more adjustment of the positioning and interaction (if any) between the fluid jets. In some embodiments there can also be an adjustable width outlet aperture 14A, 20A, 32A, 34A from either or both reservoirs 18,26 at the respective fluid knife mouths 14,20, 32,34.

In order to control of the velocity of both the liquid and gas jet streams 16,22, control of the pressure at which these fluids are expelled from their respective reservoir sources 18,26 is required. In preferred embodiments, appropriate liquid and gas pressurisation apparatus is used in conjunction with control of the outlet width aperture 14A, 20A, 32A, 34A of the respective fluid knives 14,20, 32,34. In further embodiments the reservoirs 18,26 need not be located in a single housing 11 as illustrated, but in separate housings, possibly spaced at different distances from the strip surface 12.

In still further embodiments of the apparatus, means can also be provided for control of the various fluid

properties such as viscosity, temperature, where necessary, for example by installation of a heater.

Referring now to the embodiment shown in Figure 1, upon impingement onto the strip surface, the liquid jet stream 16 resolves into an upstream and a downstream velocity component, respectively VLU, VLD, the upstream flow having a transverse velocity component VLT, and the downstream flow having a transverse velocity component VLTD.

Similarly the gas jet stream 22 resolves into an upstream and a downstream velocity component, respectively VGU, VETO, the upstream flow having a transverse velocity component VGT, and the downstream flow having a transverse velocity component VGTD- The liquid jet stream 16 generally has a large momentum flux intensity and is used to retard the majority of upstream excess surface liquid 8 and to effect its transverse removal. After impingement on the strip surface 12, the upstream momentum component of the liquid jet stream 16 of fluid velocity VLu opposes the downstream momentum of the surface excess liquid 8, and contributes to the generation of turbulence and the development of a static head in the upstream liquid. A portion of the momentum of the transverse liquid jet fluid velocity VLT is lost to viscous interaction with the surface and to turbulence generation, but the majority of this fluid momentum acts in conjunction with the static head to cause the upstream liquid 8 to flow transversely across the longitudinal edges 28,30 of the strip surface 12 in direction Y.

The residual surface liquid which remains on the strip downstream of the liquid jet stream 16 between the liquid and gas jet streams 16,22 will be referred to as"emergent residual liquid"40. The gas jet stream 22 can further reduce the quantity of emergent residual liquid 40 to the desired depth of downstream residual liquid 50 in three ways, due to:

1) an upstream momentum component of the gas jet stream, of gas velocity VGU, which opposes the downstream momentum of the emergent residual liquid 40; 2) some evaporation of the emergent residual liquid 40 because of the inherent dryness of the gas; and 3) formation of a pressure distribution with a generally upstream gradient capable of retarding movement of downstream emergent residual liquid 40.

Generally the first liquid removal mechanism ascribed to the action of the gas jet stream 22 alone is the predominant mechanism and is dependent on the acuity of the gas jet stream at angle B to the strip surface.

Referring now to either the embodiment shown in Figures 2,2A or Figures 3,3A by directing the gas jet stream 22 upstream and toward the liquid jet stream 16, the impingement of the flow of gas can deflect the liquid jet and reduce its surface impingement angle A to very small values so that the flow of the liquid jet stream 16 becomes substantially parallel to the strip surface 12. Typically the angle A is reduced to 15-20° (shown in Figures 4A, 4B).

This maximises the upstream liquid momentum in order to most efficiently retard the bulk of the upstream excess liquid 8 and provide enhanced finesse of control of the excess liquid 8.

The length of the gas jet stream 22 can be arranged so that the housing 11 can be spaced at a sufficient distance from the strip surface 12 to reduce altogether the possibility of any damaging contact between the apparatus 5,5A and the surface during relative motion therebetween, due to any slight height undulations or raised surface imperfections which may occur on the strip surface 12. In the present embodiment is has been found that a typical spacing between the housing 11 and the strip surface 12 of 25-30mm can be achieved in practice. In US5701775 the usefulness of air knives was rejected because they were said to be required to be operated unacceptably close to

the surface of a strip, at a stand-off spacing from the strip of only 1. 5mm.

While control of the remaining quantity of residual liquid 50 can be effected solely by the controlled variation of the gas jet stream 22 velocity, adjusting any or all the aforementioned parameters (such as liquid jet pressure, knife outlet width, shape and angle to the surface, gas or liquid temperature, etc) can also be used jointly or separately to effect control of the residual liquid 50 quantity.

In one preferred embodiment the liquid jet stream has a temperature in the range from about 20°C to about 90°C, most preferably around 40°C. The pressure in the respective plenum is in the range from about 30 to about 175 psi gauge, most preferably 50psig. The nozzle outlet width aperture is in the range from about 0.005 to about 0.1 inch, most preferably 0.020 inch. The angle the liquid jet stream makes with the strip surface 12 is in the range from about 10 to about 55 degrees, most preferably 20 degrees. The fluid plenum is spaced from the strip surface by a distance in the range from about 0.5 to about 2 inches, most preferably 1 inch (around 25mm).

In the same preferred embodiment the gas jet stream has a temperature in the range from about 20°C to about 90°C, most preferably around 40°C. The pressure in the respective plenum is in the range from about 4 to about 12 psi gauge, most preferably 7.5 psig. The nozzle outlet width aperture is in the range from about 0.010 to about 0.2 inch, most preferably 0.035 inch. The angle the gaseous jet stream makes with the strip surface 12 is in the range from about 15 to about 55 degrees, most preferably 35 degrees. The gas plenum is spaced from the strip surface by a distance in the range from about 0.5 to about 2 inches, most preferably 1 inch (around 25mm).

In a preferred embodiment the distance between the source of the liquid jet and the source of the gas jet is

in the range from about 0.5 to about 4 inches. The strip surface moves with a speed in the range up to about 5500- 6000 feet per minute relative to a fixed plenum.

The apparatus for controlling the residual liquid 50 to a pre-determined depth represents a significant improvement over other known fluid jet surface liquid removal devices because of the interaction of the individual jet fluid streams. This can result in both improvements to the removal rates of excess surface liquid 8 and in the control of the quantity of residual liquid 50.

In another application the apparatus and method described previously and shown in Figure 2 or Figure 3 can be used to control an amount of an applied coating material on a surface by the thinning and deflection removal of some of the freshly applied coating. For example where an evenly thin coating 50 is required, the coating can either be applied to the strip surface upstream of the apparatus 5,5A or even effected by part of the flow of the pressurised jet stream 16.

The apparatus and method described and shown in Figures 2,2A, 3,3A can also be used to clean some adherent contaminants or other residual material such as particulates from a surface by deflection from that surface.

The metal strip is typically aluminium or steel etc being rolled in a strip mill. In an experimental trial the new apparatus and method have been able to achieve very low or zero downstream residual surface liquid depths at a strip throughput rate of 5500-6000 ft/min, whereas in the past to achieve a comparable (but not as thin) residual surface liquid depth by using known physical strip wiping apparatus, a strip throughput rate of 1500-2000 ft/min only has been typical.

It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms a part

of the common general knowledge in the art, in Australia or any other country.

Whilst the invention has been described with reference to preferred embodiments it should be appreciated that the invention can be embodied in many other forms.