WO2003033206A1

WO2003033206A1 - Grinding method and apparatus

Info

Publication number: WO2003033206A1
Application number: PCT/AU2002/001372
Authority: WO
Inventors: Rodolfo Duran
Original assignee: Lewis Australia Pty Ltd; Queensland Alumina Limited
Priority date: 2001-10-17
Filing date: 2002-10-10
Publication date: 2003-04-24

Abstract

A method for grinding scale from a valve seat and a valve disc each having a covering of a layer of scale comprising the steps of, (i) bringing the valve seat (9) and valve disc (11) together whereby the scale layers covering each of the valve seat and valve disc are brought into frictional abutment, (ii) rotating the valve disc (11) with respect to the valve seat (9) to grind off some of the scale layers by rubbing them against each other, (iii) generating an electrical signal characteristic of a grinding stage by sensing a physical characteristic of the method which characterises the grinding stage, (iv) detecting when the electrical signal characteristic changes sufficiently to denote the scale layers have been ground away sufficiently that the grinding has substantially ceased, (v) incrementally advancing the valve disc towards the valve seat to repeat steps (i) to (iv) until substantially all of the scale layers between the valve disc and valve seat are ground away.

Description

GRINDING METHOD AND APPARATUS

Field of the Invention

This invention relates to a method and control system for grinding scale from valves and to a clutch assembly which may be used in the operation of the method. In a preferred aspect it particularly relates to an automatic control system and apparatus which may be used to grind valves common in a number of industries such as alumina processing, sewage, water treatment, petrochemical and mining industries.

Background of the Invention

The alumina industry, in processing alumina ore, needs to pipe large quantities of caustic slurry fluid throughout an alumina refinement plant. In order to satisfactorily control flow of these very large amounts of caustic slurry fluid, large size valves commonly known as angle valves, are typically used throughout the plant. These may number as much as a thousand valves in a large alumina processing complex.

Over time, the caustic slurry fluids deposit scale on the internal pipe surfaces and the sealing surfaces of the valves. Ultimately the build up of scale on the valves is so great that the valves cease to function properly. Typically, these valves include a valve seat and a valve disc for sealing against the seat. A build up of scale occurs on both the valve seat and the valve disc. In order to remove this scale from the sealing surfaces it has been a general practice in the industry to bring the valve disc into frictional abutment with the valve seat. The valve disc is then rotated clockwise and counterclockwise to grind off a small amount of the scale. When the grinding has proceeded to a stage where the valve disc rotates relatively freely with regard to the valve seat, the rotation is stopped and the valve disc is advanced a further small distance. The grinding process is repeated and the valve disc is advanced forward so many times in association with grinding until the sealing surfaces of the disc and valve seat can make contact when substantially all the scale has been ground away. Generally the operator relies upon his subjective experience to assess when the grinding process is complete at each step.

Given that the build up of scale can be as much as 75mm and each incremental grinding procedure may only remove about 0.4mm to 0.6mm, a very large number of steps (eg. as much as 150 or more) may be needed to completely grind off scale obstructing the sealing of the valve.

As the valves used in the alumina industry are relatively complex and require a considerable amount of effort to both advance the valve disc and reset it so that it can be driven to rotate, the amount of time and effort required to grind off the scale can be quite large. There is therefore a need to provide a method for automatically determining when the various grinding steps are complete. There is also need for a control system and apparatus which facilitates more rapid transition between the valve disc advancement mode and valve disc grinding mode. Preferably this control system and apparatus should be capable of being automated.

Disclosure of the Invention

In one aspect the invention provides a method for grinding scale from a valve seat and a valve disc each having a covering of layers of scale comprising the steps of,

(i) bringing the valve seat and valve disc together whereby the scale layers covering each of the valve seat and valve disc are brought into frictional abutment,

(ii) rotating the valve disc with respect to the valve seat to grind off some of the scale layers by rubbing them against each other, (iii) generating an electrical signal characteristic of a grinding stage by sensing a physical characteristic which characterises the grinding stage, (iv) detecting when the electrical signal characteristic changes sufficiently to denote the scale layers have been ground away sufficiently that the grinding has substantially ceased,

(v) incrementally advancing the valve disc towards the valve seat to repeat steps (i) to (iv) until substantially all of the scale layers between the valve disc and valve seat are ground away.

The physical characteristic sensed may comprise vibration characteristic of grinding. It may comprise the level of torque required to rotate the valve disc, hi this regard, where the torque is supplied via a hydraulic motor the torque may be sensed via a variation of hydraulic pressure. It may comprise a change in the speed of rotation of the valve disc.

The method can also measure the relative position of the disc in terms of advance from the last grinding cycle. If it cannot advance without increasing the torque to excess, it means that the valve must be on the seat ie. metal to metal contact.

The method may include the extra step of sensing a change in the electrical signal characteristic of the grinding which denotes that all of the scale layers between the valve disc and valve seat have been ground away thereby denoting a final vibration and/or torque stage and ceasing further repetition of steps (i) to (iv) when this condition has been reached. A signal or alarm may be provided to inform the operator that such a condition has been reached.

In another aspect the invention provides a control system for carrying out the method as hereinbefore described comprising, motor means for rotating the valve disc and advancing the valve disc towards the valve seat based upon a drive configuration set by clutch means, a sensor for sensing a change in a physical characteristic associated with a stage of grinding, such as vibration and/or torque and/or valve disc rotational speed and/or position, and generating an electrical signal characteristic of the stage of grinding, and a micro processor for determining the stage of grinding based upon the electrical signal characteristic and generating control signals to control operation of the motor means and clutch means to perform the method.

The method and control system may be used to operate a combination valve and clutch assembly as hereinafter described.

The combination valve and clutch assembly may include a valve which comprises, a valve body, a valve stem having a screw thread, the valve stem extending into the valve body, a valve disc mounted on the valve stem, a valve seat arranged in the valve body so that the valve stem may move the valve disc into and out of engagement with the valve seat, and internally threaded drive means mounted on the screw thread of the valve stem, and includes a clutch assembly which comprises, an internally threaded member mounted on the screw thread of the valve stem, a piston cavity, and a piston arranged for axial movement in response to application of fluid pressure to the piston cavity, wherein the arrangement is such that application of fluid pressure to the piston cavity causes the piston to push against the drive means with sufficient pressure to lock the drive means with respect to rotation relative to the valve stem whereby rotation of the drive means causes rotation of the valve stem and valve disc.

The cavity may form a housing for the piston. Alternatively the piston may itself be formed with the piston cavity. It may be an annular cavity.

The valve may be a typical large scale valve as used in the alumina industry. It may be an angle valve. The clutch assembly may include rotation control means for allowing and stopping rotation of the valve stem and valve seat with respect to the valve body. The purpose of the rotation control means is to control advancement of the valve stem and valve disc in relation to the valve seat so that any scale formed on the valve disc may be brought into frictional engagement with scale formed on the valve seat so that the disc may be rotated with respect to the valve seat to grind off a proportion of the scale. Thus, in one mode, the rotation control means when it operates to stop rotation of the valve stem allows advancement of the valve stem towards the valve seat when the drive means is rotated on the screw thread of the valve stem. However when the rotation control means is disengaged to allow relative rotation between the valve disc and valve seat, the clutch assembly may operate to lock the drive means with respect to rotation of the valve stem whereby rotation of the drive means causes rotation of the valve disc to grind off scale layers sandwiched between the valve disc and valve seat.

The rotation control means may comprise locking means to prevent relative rotation between the clutch assembly and valve stem as well as brake means to prevent rotation of the clutch assembly.

hi another aspect the invention provides a clutch assembly which may be used in association with a control system as hereinbefore described.

The locking means of the clutch assembly may comprise a lock ring fitted to the valve stem particularly the screw thread of the valve stem. The lock ring may be secured to the clutch assembly by a fixing member such as a screw. The screw may also act to tighten the lock ring to the screw thread of the valve stem to prevent relative rotation therebetween and hence relative rotation between the clutch assembly and the valve stem.

The braking means may comprise means for gripping the clutch assembly. The means for gripping the clutch assembly may include a pair of arms pivotally connected to each other. The pair of arms may pivot to engage a brake support forming part of the clutch assembly whereby to prevent rotation of the brake support and hence clutch assembly. The arms may be pivoted away from each other to allow free rotation of the clutch assembly. Alternatively the pair of arms may comprise a continuous bendable band such as a steel band.

The braking means may include hydraulic or pneumatic means to cause engagement and disengagement of the braking means.

Preferred aspects of the invention will be described with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows a longitudinal cross section of an angle valve typically used in the alumina industry;

Figure 2 shows an isometric view of a grinding control assembly;

Figure 3 shows a cross sectional view of a clutch and brake assembly;

Figure 4 shows an isometric cut away view of the clutch and brake assembly of

Figure 3; Figure 5 shows an elevational view of braking means for operation in association with the clutch assembly;

Figure 6 shows a block diagram of a control system according to the invention;

Figure 7 shows a graph of acceleration in G's vs frequency in H_z for metal to metal contact in the wet condition; Figure 8 shows a graph of acceleration in G's vs frequency in H_z (Horizontal axis) for metal to metal contact in the dry condition;

Figure 9 shows a graph of acceleration in G's vs frequency in H₂ for grinding scale;

Figure 10 shows a graph of acceleration in G's vs frequency in H_z when the valve disc is free spinning; and

Figure 11 shows a cross sectional view of an alternative form of clutch and brake assembly. Detailed Description of the Preferred Embodiments

Referring to Figure 1, the angle valve generally designated 1 shown therein comprises a valve body 3 provided with an inlet 5 having a throat liner 6. The inlet leads to the outlet 7 via the valve seat 9 formed at one end of the throat liner 6.

A disc 11 mounted on the valve stem 13 extending through the valve body, is mounted for relative rotation with respect to the valve body via the bearings 17 and 19 and the gland packing 15.

A bush yoke 21 associated with bearings 23 is also provided to assist with locating and mounting the valve stem for rotation with respect to the valve body.

A stem lock 25 is provided within the valve body intermediate the ends of the valve stem. The stem lock is a device which may be used to prevent relative rotation between the valve stem and valve body by insertion of locking means, such as a pin, whilst still allowing axial movement of the valve stem with respect to the valve body. Thus, in its normal operating mode, the stem lock will be applied to prevent rotation of the valve stem so that rotation of the main gear 27 which is mounted on the bush yoke 21, operates to move the valve stem axially with respect to the valve body. This occurs by virtue of the operation of the screw thread formed on the outer surface of the section of the valve stem surrounded by the bush yoke and the complementary action of the screw threads formed on the internal surface of the bush yoke itself.

The main gear 27 by virtue of the fact that it is connected via the intermediate gear 29 pinion 31 and drive nut 33 can be driven through the drive nut 33. Thus a portable motor acting through a coupler can open and close the valve by rotating the drive nut in either direction.

The bush yoke 21 end may be compressed by the jam nut 37 ie. when the jam nut 37 is screwed along the valve stem so that it abuts the end of the bush yoke 21 the pressure of the jam nut pushing against the drive means comprising the bush yoke and main gear locks, the drive means in frictional engagement with the valve stem so that rotation of the main gear causes rotation of the valve stem. A locknut 35 may be provided around the bush yoke.

In the alumina industry, the jam nut is usually brought into engagement with the end of the bush yoke using a sledge hammer to apply sufficient torque to the jam nut to force the necessary level of frictional engagement required between the bush yoke and valve stem. Clearly, sledge hammer blows applied by an operator are not a precise method of applying torque. As well use of a sledge hammer represents a level of danger to the operator and causes damage to the components particularly the jam nut. Depending upon the strength, and number of blows applied by the sledge hammer the amount of frictional engagement can be quite variable.

This crude method of fiictionally engaging the drive means using a jam nut is replaced by a more controllable clutch assembly 41 shown in Figures 2 to 5 applied to the angle valve shown in Figure 1. The clutch assembly described with reference to Figures 2 to 5 can also do away with the need for the stem lock 25, as the clutch assembly may be associated with a brake 49 which can be used to prevent relative rotation between the drive means and valve stem.

Referring specifically to Figure 2 there is shown a grinding control assembly generally designated 39 which may be used to move and mount the clutch assembly generally designated 41 of the invention.

The grinding control assembly which is provided with wheels for portability, includes a drive motor 43 driving through a coupler 44. The coupler is engageable with the drive nut 33 of the angle valve. The drive motor may include torque sensing and a position sensing device 44a (rotary encoder) means for reasons to be described hereinafter. A hydraulic pump 45 is provided for providing hydraulic pressure. This provides hydraulic pressure through the hydraulic pressure line 47 to the brake lock valve 51 which in turn controls the brake 49.

The bottom of the clamp arm 77 forming part of the brake is connected to a torque reaction arm (not shown) for holding the clamp arm against rotation. The torque reaction arm may be connected to a point on the cart forming part of the grinding control assembly.

A hydraulic cylinder 55 is arranged to raise or lower the suspension arm 57 so that the clutch assembly 41 may be lifted to the correct level to bring it into engagement with the valve stem.

The suspension arm connects to the support extension 80 attached to the upper part of the brake.

Referring to Figures 3 and 4 of the drawings the clutch assembly generally designated 41 comprises a body 59 forming an annular piston cavity 61. The inner part of the annular piston cavity is provided with a screw thread for allowing the body to be screwed onto the valve stem 13.

A piston 63 is mounted within the annular piston cavity and is provided with O rings 65 for sealing the sides of the piston against the walls of the piston cavity.

The arrangement is such that the piston will move to engage the end of the yoke 21 abutting the main gear 27 when pressure is applied to the piston cavity.

A lock ring 67 forms part of the clutch assembly. It is provided with a screw thread so that it may be screwed onto the valve stem in the manner illustrated. A lock screw 69 extending through the body 59 serves to compress the lock ring 67 against the valve stem so as to lock the lock ring against relative rotation between the two. The lock screw also, by virtue of the fact that it extends through the body 59, locks the body against movement with respect to the lock ring and hence the valve stem.

A rotary union 71 provided on the end of the brake support 73 serves to connect the hydraulic pressure line 47 to the clutch assembly and to direct the hydraulic pressure via the tubing 75 into the annular piston cavity.

The brake 49 provided around the brake support 73 comprises two clamp arms 77 and 79 joined together for relative pivotal movement therebetween via the pin 81.

Bearings 85 are provided to ensure smooth rotation between the brake and the brake support when the brake is in the off position.

Each of the clamp arms are provided with brake pads 87 for frictional engagement with the brake support when the brake is applied.

The brake includes a spring assembly 90 having two springs 92 arranged to pivot the ends of the clamp arms towards each other to apply the brake. (In the alternative arrangement described later with reference to Figure 11, there are no springs 90 and the cylinder 89 does the clamping not the release.)

A hydraulic piston assembly 89 is arranged to push the ends of the brake arms apart to release the brake as and when required.

h a typical operation for grinding scale from the valve seat and disc, pressure to annular piston cavity 61 is released so that the clutch assembly disengages from the main gear. At the same time, the brake 49 is applied so as to prevent rotation of the valve stem.

The main gear is rotated to move the disc 11 into frictional engagement with the valve seat. As soon as this frictional engagement is obtained, the brake 49 is disengaged and the piston 63 is moved by hydraulic pressure to exert substantial pressure against the end of yoke 21 and hence lock the main gear against rotation with respect to the valve stem by virtue of the strong frictional engagement caused by the piston pressure. Thus rotation of the main gear results in rotation of the valve stem and hence rotation of the disc 11.

Rotation of the disc is carried out in clockwise and counterclockwise directions until sufficient scale is rubbed off the disc and valve seat to allow relatively unrestricted rotation. When this point has been reached, the pressure from the piston 63 is released, the brake is reapplied and the disc is advanced slightly (say 0.4mm to 0.6mm) and the process repeated for as many times as are required until the scale is completely ground off both the disc and the valve seat in the areas where the two seal.

The grinding control assembly can then easily be removed from engagement with the angle valve and moved to another angle valve for the whole operation to be repeated.

Referring to Figure 6, the control system shown in block diagram form comprises a sensor means 100. One part of the sensor may be mounted onto the body of the valve described with reference to Figure 1. This part of the sensor means senses acceleration produced by vibration caused by the rotation of the valve stem under various conditions and produces an electrical signal which is fed to the microprocessor 102. Different components of the sensor means may measure speed of the motor, torque of the motor, hydraulic pressure, and position of the valve disc/valve stem.

As can be seen from Figures 7 to 10, the vibration signal provides a spectrum signature characteristic of the mode in which the valve stem is spinning. Signals characteristic of motor speed, torque and position are also fed from different components of the sensor means to the microprocessor. Thus the microprocessor includes circuitry and programming which allows it to recognise the particular signal characteristics associated with grinding, free spinning, metal to metal contact and position. Based upon the particular stage recognised, it sends control signals to control means operating the clutch assembly 41, brake 49 and motor 43 to operate them in the sequences required and previously described to grind away scale.

Thus after the grinding control assembly has been wheeled into position, the clutch assembly 41 is secured to the valve stem and the valve disc 11 and is brought into engagement with the valve seat 9 by rotating the main gear 27 to advance the valve stem. The following control steps are carried out in a typical grinding operation:-

(i) The microprocessor 102 activates application of hydraulic pressure to the piston 63 to lock the main gear with respect to rotation relative to the valve stem.

(ii) The microprocessor activates the motor 43 so that the main gear is rotated to rotate the valve disc and hence grind scale between the valve disc and valve seat. If the microprocessor receives signals that torque is too high it may back off (say 6°) to reduce torque and may then proceed to grind.

(iii) The sensor 100 senses the signal characteristic of the grinding to indicate grinding has been completed, if the torque required is low and the speed is close to the free wheeling speed, that denotes that the grinding operation is too easy and it is time to advance the stem/disc closer to the seat. The microprocessor 102 sends signals to release hydraulic pressure to the piston

63, applies the brake 49 and rotates the main gear (say 12°) to advance the valve stem a predetermined distance, (iv) The microprocessor releases the brake, activates the hydraulic pressure to the piston and activates the motor to rotate the valve disc to repeat the grinding. (v) Steps (ii) to (iv) are repeated until the change in signal characteristic indicates that all scale has been ground off. The change in signal characteristic may be based on the inability of the disc to advance in three consecutive attempts, (vi) The microprocessor generates a signal indicating grinding is complete, releases piston pressure and releases the brake so that the control assembly may be removed. Referring to Figure 11, the clutch and brake assembly 141 shown therein operates in a manner similar to that described with reference to Figures 3 to 5. Hence components of Figure 11 which operate in a similar fashion to those described with reference to Figures 3 to 5 are marked with the same reference numerals. The main difference in the construction for Figure 11 relates to the piston 63 which has its own internal annular piston cavity 61 which fills with fluid to push the piston forward. By comparison the piston of Figures 3 to 5 is housed within a piston cavity formed in the clutch body. The net overall effect of the two constructions is however quite similar.

It is to be understood that the word comprising as used throughout the specification is to be interpreted in its inclusive form ie. use of the word comprising does not exclude the addition of other elements.

It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

Claims

1. A method for grinding scale from a valve seat and a valve disc each having a covering of layers of scale comprising the steps of,

(i) bringing the valve seat and valve disc together whereby the scale layers covering each of the valve seat and valve disc are brought into frictional abutment, (ii) rotating the valve disc with respect to the valve seat to grind off some of the scale layers by rubbing them against each other,

(iii) generating an electrical signal characteristic of a grinding stage by sensing a physical characteristic which characterises the grinding stage, (iv) detecting when the electrical signal characteristic changes sufficiently to denote the scale layers have been ground away sufficiently that the grinding has substantially ceased, (v) incrementally advancing the valve disc towards the valve seat to repeat steps (i) to (iv) until substantially all of the scale layers between the valve disc and valve seat are ground away.

2. A method according to claim 1 wherein the electrical signal characteristic of a grinding stage is generated from sensing at least one of, vibration, speed of rotation of the valve disc, torque required to rotate the valve disc and hydraulic pressure for driving a hydraulic motor which is arranged to rotate the valve disc.

3. A method according to claim 2 comprising sensing when substantially all of the scale layers between the valve disc and valve seat are ground away and generating a signal to indicate grinding is complete and/or to prevent further grinding.

4. A control system for carrying out the method of claim 1 comprising, motor means for rotating the valve disc and advancing the valve disc towards the valve seat based upon a drive configuration set by clutch means, a sensor for sensing a change in a physical characteristic associated with a stage of grinding and generating an electrical signal characteristic of the stage of grinding, and a micro processor for determining the stage of grinding based upon the electrical signal characteristic and for generating control signals to control operation of the motor means and clutch means to perform the method.

5. A control system according to claim 4 wherein the clutch is an assembly of components comprising, an internally threaded member for mounting on the screw thread of a valve stem on which the valve disc is mounted, a piston cavity, and a piston arranged for axial movement in response to application of fluid pressure to the piston cavity, wherein the arrangement is such that application of fluid pressure to the piston cavity causes the piston to push against drive means driven by the motor means with sufficient pressure to lock the drive means with respect to rotation relative to the valve stem whereby rotation of the drive means causes rotation of the valve stem and valve disc.

6. A control system according to claim 5 wherein the cavity comprises one of a housing within which the piston slides and an open ended annular cavity formed within the piston body which is co-operable with a ring shaped element slidable within the annular cavity.

7. A control system according to claim 5 wherein the clutch means comprise, locking means for preventing relative rotation between the clutch assembly and valve stem; and brake means for preventing rotation of the clutch assembly.

8. A control system according to claim 7 wherein the locking means comprise a lock ring fitted to the valve stem.

9. A control system according to claim 7 wherein the braking means comprise, a pair of pivotally connected arms arranged to engage a brake support forming part of the clutch assembly, and means for pivoting the pair of arms together or away from each other to engage and disengage the arms in relation to braking contact with the brake support.

10. A control system according to claim 4 comprising, a mobile trolley for mounting of components of the control system, and a hydraulic lifter mounted on the trolley arranged to raise and lower the motor means.

11. A combination valve and clutch assembly wherein the valve comprises, a valve body, a valve stem having a screw thread, the valve stem extending into a valve body, a valve disc mounted on the valve stem, a valve seat arranged in the valve body so that the valve stem may move the valve disc into and out of engagement with the valve seat, and internally threaded drive means mounted on the screw thread of the valve stem, and wherein the clutch assembly comprises, an internally threaded member mounted on the screw thread of the valve stem, a piston cavity, and a piston arranged for axial movement in response to application of fluid pressure to the piston cavity, - wherein the arrangement is such that application of fluid pressure to the piston cavity causes the piston to push against the drive means with sufficient pressure to lock the drive means with respect to rotation relative to the valve stem whereby rotation of the drive means causes rotation of the valve stem and valve disc.

12. A combination valve and clutch assembly according to claim 11 comprising, motor means for rotating the valve disc and advancing the valve disc towards the valve seat based upon a drive configuration set by the clutch assembly, a sensor for sensing a change in a physical characteristic associated with a stage of grinding, and generating an electrical signal characteristic of the stage of grinding, and a micro processor for determining the stage of grinding based upon the electrical signal characteristic and for generating control signals to control operation of the motor means and clutch assembly to perform the method.

13. A control system according to claim 12 wherein the clutch is an assembly of components comprising, an internally threaded member for mounting on the screw thread of a valve stem on which the valve disc is mounted, a piston cavity, and a piston arranged for axial movement in response to application of fluid pressure to the piston cavity, wherein the arrangement is such that application of fluid pressure to the piston cavity causes the piston to push against the drive means driven by the motor means with sufficient pressure to lock the drive means with respect to rotation relative to the valve stem whereby rotation of the drive means causes rotation of the valve stem and valve disc.

14. A control system according to claim 13 wherein the cavity comprises one of, a housing within which the piston slides and an open ended annular cavity formed within the piston body which is co-operable with a ring shaped element slidable within the annular cavity.