GB2260581A

GB2260581A - De-aeration of water-based hydraulic fluid

Info

Publication number: GB2260581A
Application number: GB9210733A
Authority: GB
Inventors: Roger Artindale Heron
Original assignee: Litton UK Ltd
Current assignee: Intermec Europe Ltd
Priority date: 1991-10-19
Filing date: 1992-05-20
Publication date: 1993-04-21
Anticipated expiration: 2012-05-20
Also published as: WO1993007947A1; AU2697992A; GB9210733D0; GB2260581B

Abstract

In apparatus for de-aerating water-based hydraulic fluid flowing in an hydraulic circuit to service a unit such as a high speed hydrostatic bearing in a grinding tool, the fluid flows without interruption through a de-aerating tank having at the bottom an immersed array of ultrasonic transducers (22). Foam may be removed from the tank by a cased fan adjustable in height. The tank may be incorporated in a reservoir. <IMAGE>

Description

Title De-aeration of Water-based Hydraulic Fluids Field of the invention This invention relates to the removal of air bubbles from a water-based hydraulic fluid, such as employed for the lubrication of hydrostatic bearings incorporated in high speed machine tools, especially grinding machines.

Background to the invention When a water-based hydraulic fluid is in use, for example for servicing a high speed hydrostatic bearing, it is frequently found that the returning fluid is aerated.

Typically the entrained air is in the form of fine bubbles, which are slow to rise to the surface and disperse. As a result, aerated fluid can enter into the pressure pump of the system, whereupon the resultant apparent lack of fluid bulk modulus (the specific gravity of the fluid is reduced by about 10 per cent) can at least reduce the stiffness of the bearing and possibly give rise to failure of the bearing.

It would, therefore, be highly advantageous if the returning hydraulic fluid could be positively de-aerated.

The invention According to one aspect of the invention, a flow of waterbased hydraulic fluid containing air bubbles in suspension is de-aerated by transmitting ultrasonic waves therethrough, substantially without interrupting the fluid flow.

According to another aspect of the invention, there is provided apparatus for de-aerating a flow of water-based hydraulic fluid containing air bubbles in suspension, comprising a tank through which the fluid continuously flows with an air space above, said tank containing an immersed array of ultrasonic transducers in use operative to transmit ultrasonic waves through the flowing fluid.

Preferably, the transducer array extends lengthwise of the fluid flow substantially at the bottom of the tank.

Flow control baffles are preferably provided above the transducer array to ensure a slow and even progress of the flowing fluid and to prevent recirculation within the tank.

Means are preferably provided to ensure a minimum depth of fluid above the transducer array. This means may be constituted by a level-limiting outlet.

The tank is preferably mounted on a support frame of adjustable height for the purpose of controlling the fluid level in the tank above the minimum permitted level.

The tank is preferably fitted with a sight gauge.

Additionally, a fluid density monitor capable of producing an alarm or shut-down signal is preferably provided in the region of the tank outlet. Such monitor may be constituted by a ballasted float switch.

It is sometimes found that at least in part, owing to a de-aeration of the water-based hydraulic fluid by the use of ultrasound, an amount of foam is produced on the surface of the fluid in the de-aeration tank. It is important, however, to ensure that foam does not build up and/or give rise to re-aeration of the hydraulic fluid.

To some extent, the formation of foam can be controlled by optimising the level of dissolved solids in the water used to make up the water-based hydraulic fluid, and/or by adding an anti-foam agent to the fluid. However, it has been found that, even if these measures are adopted, foam can often still be produced on the surface of the hydraulic fluid in the tank.

According to a further feature of the invention, therefore, the de-aeration tank incorporates means for removing any foam which is produced on the surface of the hydraulic fluid in the tank.

The foam removal means preferably a cased fan for sucking foam from the surface of the fluid in the tank through one or more apertures in the fan casing . In the casing, the foam tends to be spattered against the internal wall of the casing and is broken down with liquid and air. The liquid drips back into the tank and the air is suitably vented.

Means are preferably provided for adjusting the height of the cased fan above the surface of the fluid in the tank, in order to ensure that only foam and not liquid is sucked into the fan casing. Means may also be provided for adjusting the speed of the fan and/or for adjusting the size of the apertures through which foam is sucked into the fan casing.

Tyically, in an hydraulic circuit, using water-based hydraulic fluid, the apparatus will be incorporated between the unit being serviced, e.g. a high speed hydrostatic bearing, and the main reservoir to which fluid is returned from said unit.

According to another aspect of the invention, therefore, there is provided a high speed bearing serviced by waterbased hydraulic fluid flowing in an hydraulic circuit which includes a fluid reservoir and a pump, wherein the hydraulic circuit also includes a de-aeration tank through which the hydraulic fluid flows in its return path from the bearing to the reservoir, said de-aeration tank containing an immersed array of ultrasonic transducers operative in use to transmit ultrasonic waves through the flowing fluid.

Further features of the de-aeration tank, as previously mentioned, can readily be incorporated.

The fluid preferably enters the de-aeration tank at one end through a submerged level inlet having an associated diffuser and exits the tank through an outlet adjacent the other end of the tank, which is dimensioned to give maximum time of exposure of the fluid to the ultrasonic waves whilst minimising the height through which the entrained air bubbles must travel to reach the surface of the flowing fluid.

In order to save space, the de-aeration tank may be incorporated within the confines of the reservoir. In this case, at the outlet end of the de-aeration tank, the hydraulic fluid may, owing to its forced flow, overflow a weir into the body of water-based hydraulic fluid which forms the reservoir.

According to still another aspect of the invention there is provided a tool spindle bearing in a machine tool wherein the bearing is serviced by water-based hydraulic fluid and, in a path of flow of said fluid between exit from and entry into the bearing, the flowing fluid is deaerated by an immersed array of ultrasonic transducers in use operative to transmit ultrasonic waves through said flowing fluid.

According to yet another aspect of the invention, there is provided a machine tool, especially a high speed machine tool such as a grinding machine, in which the tool spindle is supported by a bearing serviced by water-based hydraulic fluid, wherein fluid de-aerating means is immersed in the flow of fluid between its exit from and re-entry to the bearing, said de-aerating means comprising an array of ultrasonic transducers in use operative to transmit ultrasonic waves through the flowing fluid.

In the bearing and machine tool in accordance with these further aspects of the invention, further features of the de-aerating means, as previously mentioned, can readily be incorporated.

Description of embodiment Two practical examples of apparatus in accordance with the invention are shown in the accompanying drawings in which: Figure 1 primarily shows a de-aeration tank in side elevational view; Figure 2 shows in diagrammatic manner a grinding machine having a bearing serviced by high water-based hydraulic fluid flowing in a circuit in which de-aerating means is incorporated; and Figure 3 and 3A show a means for foam removal means which may be incorporated in the de-aeration tank Referring to Figure 1, the apparatus of the invention comprises a de-aeration tank 10 inserted in an hydraulic circuit using a high water-based hydraulic fluid, for example in the return path from a high-speed hydrostatic bearing (not shown) to a main reservoir 12. The inlet to the tank 10 of fluid returning from the bearing is referenced 14. At the reservoir can be seen a reservoir level monitor 16.

The tank 10 may conveniently be made of stainless steel with fully welded seams and may have a part-perspex top to allow the de-aeration process to be observed. An air vent 18 incorporates a filter to prevent ingress of dirt.

Aerated fluid enters through inlet 14, below the fluid level in the tank, via a diffuser 20, which aids settling of the fluid. The fluid then flows slowly and evenly across the tank, which is dimensioned to give maximum time of exposure to treatment to the fluid whilst minimising the height of fluid through which bubbles must pass to reach the air space above the fluid.

Extending along the bottom of the tank 10 is an array of ultrasonic transducers 22 powered from an electronic driver generator 24.

Above the transducer array 22 are mounted flow control baffles 26 which ensure the slow and even progress of the fluid along the tank in the de-aeration zone above the emitting surface of the transducer array 22. The baffles 26 also prevent recirculation and remixing of de-aerated fluid from the outlet zone of the tank with the inlet fluid.

The treated fluid is fed into the main reservoir 12 via a submerged outlet pipe 28 from the tank and an outlet diffuser 30. The height of the infeed end 32 of the outlet pipe 28 is such as to ensure at all times a minimum depth of fluid above the transducer array 22, thereby to avoid damage, even if the fluid level in the reservoir falls.

Both inlet and outlet connections to the tank may, for example, be made with clear reinforced flexible tube secured by worm drive clips fitted to machined stub pipes and bulkhead fittings.

The fluid level in the tank 10 is suitably controlled. In the illustrated embodiment, which is only exemplary, the tank is mounted on a height adjustable support frame 34 to control the fluid level in the tank 10. Level control is assisted by an external sight gauge 36 having level markings.

A ballasted float switch 38 is fitted in the outlet region of the tank to give an audible and/or visual warning at an indicator 40 in the event of system failure, which will be detected by a drop in fluid density. In one arrangement, the operator can then immediately shut the system down to prevent aerated fluid reaching the hydraulic circuit pump.

The switch 38 can be replaced by any other convenient means of electrical, optical or other nature for detecting the presence of air. In an alternative arrangement in which this air detection means emits a suitable signal, this signal is employed to organise an orderly shut-down of the drive to the machine incorporating the serviced bearing, so as to prevent air entrapped in the high waterbased hydraulic fluid from entering the bearing. One or more pressurised cannisters can be employed to maintain hydrostatic pressure during braking.

In use, a degree of foaming can occur within the tank as the rising air bubbles escape. This can sometimes be controlled to some extent by optimising the level of dissolved solids in the water used to make up the high water-based hydraulic fluid, which may conveniently comprise water incorporating up to 5 per cent by volume of Quintolubric E.6 F (Trade Mark) produced by Quaker Chemicals. Additionally an anti-foam agent may be added to the high water-based fluid if desired. However, the effect of the ultrasound, which tends to soften the waterbased hydraulic fluid in the de-aeration tank, can still give rise to foam production in many instances and it is important to prevent this foam from building up to an extent where the water-based hydraulic fluid tends to reaerate.

Figure 3 and 3A show the incorporation in the de-aeration tank 10 of a cased fan 42, driven by an electric mutor 44 external to the tank, for removing foam which may be produced on the surface of the water-based hydraulic fluid. The fan casing has apertures 46, which may be adjustable in size, through which foam is sucked into the casing by the operating fan. The height of the cased fan is preferably adjustable to ensure that only foam and not liquid is sucked into the casing.

Within the casing, the foam tends to be destroyed by the revolving fan blades and by spattering on the internal casing wall, breaking down into air and liquid. The liquid drips back into the main body of liquid in the tank and air is vented.

Figure 2 shows a grinding machine 50, which could in practice be any other kind of high speed machine tool, having a tool spindle 52 supported by hydrostatic bearings 54 serviced with high water-based hydraulic fluid which continuously flows in an hydraulic circuit which includes a reservoir 56 and a pump 58. Hydraulic fluid enters the bearing at 60 from the pump and exits at 62 toward the reservoir. A de-aeration tank 64, substantially as hitherto described with reference to Figure 1, and possibly also incorporating the foam removal meands of Figures 3 and 3A, is incorporated in the hydraulic circuit in the path of fluid flow from the bearing to the reservoir.

However, Figure 2 also serves to show a further advantageous feature of the invention, according to which, in order to save space, the de-aeration tank 64 is incorporated within the reservoir 56.

Features of the de-aeration tank similar to those described with reference to Figure 1 are similarly referenced in Figure 2, and description thereof is not repeated. However, it will be noted that the de-aerated fluid now exits from the tank 64 over a weir 66, and that the de-aeration tank itself is open topped, the expelled air entering the air space within the reservoir, which is closed by a top wall in which the filtered vent 18 is provided. In Figure 2, reference 68 denotes a power pack for the ultrasonic transducer array 22.

As the weir 66 extends the full width of the de-aeration tank, the fluid flow over said weir under the drive of the pump is relatively gentle, and a counterpart to the outlet diffuser 30 of Figure 1 is not required.

Claims

1. A method wherein a flow of water-based hydraulic fluid containing air bubbles is de-aerated by transmitting ultrasonic waves therethrough, substantially without interrupting the fluid flow.

2. Apparatus for de-aerating a flow of water-based hydraulic fluid containing air bubbles in suspension, comprising a tank through which the fluid continuously flows with an air space above, said tank containing an immersed array of ultrasonic transducers in use operative to transmit ultrasonic waves through the flowing fluid.

3. Apparatus according to claim 2, in which the transducer array extends lenghtwise of the fluid flow substantially at the bottom of the tank.

4. Apparatus according to claim 2 or claim 3, in which flow control baffles are provided above the transducer array to ensure a slow and even progress of the flowing fluid and to prevent recirculation within the tank.

5. Apparatus according to any of claims 2 to 4, in which means are provided in the tank to ensure a minimum depth of fluid above the transducer array.

6. Apparatus according to claim 5, in which said means is constituted by a level-limiting outlet.

7. Apparatus according to any of claims 2 to 5, in which the tank is mounted on a support frame of adjustable height for the purpose of controlling the fluid level in the tank above a minimum permitted level.

8. Apparatus according to any of claims 2 to 7, in which the tank is fitted with a sight gauge.

9. Apparatus according to any of claims 2 to 8, in which a fluid density monitor capable of producing an alarm or shut-down signal is provided in the region of the tank outlet.

10. Apparatus according to claim 9, in which the monitor is constituted by a ballasted float switch.

11. Apparatus according to any of claims 2 to 10, incorporating a means for foam removal in the tank.

12. Apparatus according to claim 11, in which the foam removal means is a cased fan.

13. Apparatus according to claim 12, in which the height of the cased fan is adjustable relative to the level of the water-based hydraulic fluid in the tank.

14. Apparatus according to claim 12 or claim 13, in which the fan casing has one or more foam inlet operations of adjustable size.

15. Apparatus according to claim 14, in which the fan casing has one or more air vents.

16. In an hydraulic circuit using water-based hydraulic fluid, apparatus according to any of claims 2 to 15 incorporated between a unit being serviced by the fluid and a main reservoir to which fluid is returned from said unit.

17. Apparatus in the form of a high speed bearing serviced by water-based hydraulic fluid flowing in an hydraulic circuit which includes a fluid reservoir and a pump, wherein the hydraulic circuit also includes a deaeration tank through which the hydraulic fluid flows in its return path from the bearing to the reservoir, said de-aeration tank containing an immersed array of ultrasonic transducers operative in use to transmit ultrasonic waves through the flowing fluid.

18. Apparatus according to claim 17, in which the deaeration tank incorporates the further features of any of claims 2 to 15.

19. Apparatus according to any of claims 2 to 18, in which the fluid enters the de-aeration tank at one end through a submerged level inlet having an associated diffuser and exits the tank through an outlet adjacent the other end of the tank, which is dimensioned to give maximum time of exposure of the fluid to the ultrasonic waves whilst minimising the height through which the entrained air bubbles must travel to reach the surface of the flowing fluid.

20. Apparatus according to any of claims 2 to 19, in which the de-aeration tank is incorporated within the confines of the reservoir.

21. Apparatus according to claim 20, in which, at the outlet end of the de-aeration tank, the hydraulic fluid is, owing to its forced flow, caused to overflow a weir into the body of water-based hydraulic fluid which forms the reservoir.

22. Apparatus in the form of a tool spindle bearing in a machine tool wherein the bearing is serviced by waterbased hydraulic fluid and, in a path of flow of said fluid between exit from and entry into the bearing, the flowing fluid is de-aerated by an immersed array of untrasonic transducers in use operative to transmit untrasonic waves through said flowing fluid.

23. Apparatus in the form of a machine tool, in which the tool spindle is supported by a bearing serviced by waterbased hydraulic fluid, wherein fluid de-aerating means is immersed in the flow of fluid between its exit from and re-entry to the bearing, said de-aerating means comprising an array of ultrasonic transducers in use operative to transmit ultrasonic waves through the flowing fluid.

24. Apparatus according to claim 18, in which the machine tool is a grinding tool.

25. Apparatus according to any of claims 22 to 24, having de-aerating means incorporating the features of any of claims 2 to 21.

26. Apparatus for de-aerating a water-based hydraulic fluid substantially as hereinbefore described with reference to the accompanying drawings.

26. A method of de-aerating a water based hydraulic fluid substantially as hereinbefore described.

27. Apparatus having meant for de-aerating a water-based hydraulic fluid substantially as hereinbefore described with reference to the accompanying drawings. Amendments to the claims have been filed as follows.

Claims 1. Apparatus for de-aerating a flow of water-based hydraulic fluid containing air bubbles in suspension, comprising a tank through which the fluid continuously flows with an air space above, said tank containing an immersed array of ultrasonic transducers in use operative to transmit ultrasonic waves through the flowing fluid.

2. Apparatus according to claim 1, in which the transducer array extends lenghtwise of the fluid flow substantially at the bottom of the tank.

3. Apparatus according to claim 1 or claim 2, in which flow control baffles are provided above the transducer array to ensure a slow and even progress of the flowing fluid and to prevent recirculation within the tank.

4. Apparatus according to any of claims 1 to 3, in which means are provided in the tank to ensure a minimum depth of fluid above the transducer array.

5. Apparatus according to claim 4, in which said means is constituted by a level-limiting outlet.

6. Apparatus according to any of claims 1 to 4, in which the tank is mounted on a support frame of adjustable height for the purpose of controlling the fluid level in the tank above a minimum permitted level.

7. Apparatus according to any of claims 1 to 6, in which the tank is fitted with a sight gauge.

8. Apparatus according to any of claims 1 to 7, in which a fluid density monitor capable of producing an alarm or shut-down signal is provided in the region of the tank outlet.

9. Apparatus according to claim 8, in which the monitor is constituted by a ballasted float switch.

10. Apparatus according to any of claims 1 to 9, incorporating a means for foam removal in the tank.

11. Apparatus according to claim 10, in which the foam removal means is a cased fan.

12. Apparatus according to claim 11, in which the height of the cased fan is adjustable relative to the level of the water-based hydraulic fluid in the tank.

13. Apparatus according to claim 11 or claim 12, in which the fan casing has one or more foam inlet operations of adjustable size.

14. Apparatus according to claim 13, in which the fan casing has one or more air vents.

15. In an hydraulic circuit using water-based hydraulic fluid, apparatus according to any of claims 1 to 14 incorporated between a unit being serviced by the fluid and a main reservoir to which fluid is returned from said unit.

16. Apparatus in the form of a high speed bearing serviced by water-based hydraulic fluid flowing in an hydraulic circuit which includes a fluid reservoir and a pump, wherein the hydraulic circuit also includes a deaeration tank through which the hydraulic fluid flows in its return path from the bearing to the reservoir, said de-aeration tank containing an immersed array of ultrasonic transducers operative in use to transmit ultrasonic waves through the flowing fluid.

17. Apparatus according to claim 16, in which the deaeration tank incorporates the further features of any of claims 2 to 15.

18. Apparatus according to any of claims 1 to 17, in which the fluid enters the de-aeration tank at one end through a submerged level inlet having an associated diffuser and exits the tank through an outlet adjacent the other end of the tank, which is dimensioned to give maximum time of exposure of the fluid to the ultrasonic waves whilst minimising the height through which the entrained air bubbles must travel to reach the surface of the flowing fluid.

19. Apparatus according to any of claims 1 to 18, in which the de-aeration tank is incorporated within the confines of the reservoir.

20. Apparatus according to claim 19, in which, at the outlet end of the de-aeration tank, the hydraulic fluid is, owing to its forced flow, caused to overflow a weir into the body of water-based hydraulic fluid which forms the reservoir.

21. Apparatus in the form of a tool spindle bearing in a machine tool wherein the bearing is serviced by waterbased hydraulic fluid and, in a path of flow of said fluid between exit from and entry into the bearing, the flowing fluid is de-aerated by an immersed array of untrasonic transducers in use operative to transmit untrasonic waves through said flowing fluid.

22. Apparatus in the form of a machine tool, in which the tool spindle is supported by a bearing serviced by waterbased hydraulic fluid, wherein fluid de-aerating means is immersed in the flow of fluid between its exit from and re-entry to the bearing, said de-aerating means comprising an array of ultrasonic transducers in use operative to transmit ultrasonic waves through the flowing fluid.

23. Apparatus according to claim 22, in which the machine tool is a grinding tool.

24. Apparatus according to any of claims 21 to 23, having de-aerating means incorporating the features of any of claims 1 to 20.

25. A method of de-aerating a water based hydraulic fluid substantially as hereinbefore described.