GB1576231A

GB1576231A - Methods of and apparatus for aerating liquid stored in a machine tool system settling tank

Info

Publication number: GB1576231A
Application number: GB3915/77A
Authority: GB
Original assignee: Cera International Ltd
Current assignee: Cera International Ltd
Priority date: 1977-01-31
Filing date: 1977-01-31
Publication date: 1980-10-01
Also published as: IT7867174A0; FR2378604B1; DE2804091A1; FR2378604A1; CA1116760A; IT1106549B

Description

(54) IMPROVEMENTS IN OR RELATING TO METHODS OF, AND APPARATUS FOR AERATING LIQUID STORED IN A MACHINE TOOL SYSTEM SETTLING TANK (71) We, CERA INTERNATIONAL LIMITED, a British Company of Green wood House, 4/7 Salisbury Court, London, E.C.4., England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following state ment: This invention relates to a method of, and apparatus for aerating liquid stored in a settling tank of a machine tool system in order to inhibit the growth of anaerobic bacteria in that liquid, the settling tank comprising a source from which such liquid is drawn for use as a coolant and/or a lubricant in a machining operation at one or more machining stations of the system when the system is operating and to which liquid so used is returned after such use.

Liquid stored in a machine tool system settling tank can be aerated by injecting compressed air into the liquid within the tank and allowing that compressed air to bubble through the liquid, but the amount of compressed air that is required is such that such a technique for aerating that liquid is costly. An object of this invention is to provide a method of and apparatus for aerating liquid contained within a machine tool system settling tank which does not require such an expensive supply of air.

According to one aspect of this invention we provide a method of aerating liquid stored in a settling tank of a machine tool system comprising drawing off liquid from the tank whilst the machine tool system is shut down, aerating the drawn off liquid outside the mass of liquid stored in the tank and returning the aerated liquid to the mass of liquid stored in the tank.

Liquid may be drawn continuously from the settling tank as a stream, aerated outside the mass of liquid stored in the tank and returned to the mass of liquid stored in the tank continuously whenever the system is shut down. Such a continuous stream of liquid drawn from the settling tank preferably is converted into a spray in a region into which fresh air flows so that the fresh air and spray intermingle in that region to aerate the liquid. Preferably the stream of liquid is converted into a spray by being directed towards the apex of coaxial tapered deflecting means, the stream striking the tapered deflecting means and being deflected thereby to form a substantially circumferentially continuous radially directed flow. Provision of substantially circumferentially continuous outwardly directed flange means on the tapered deflecting means, spaced from the apex, which coact with the deflected liquid, enhances conversion of the liquid stream into a radially directed spray.

Conveniently the spray is allowed to fall onto a sloping surface down which it cascades to a second region into which fresh air flows, the cascading liquid preferably being atomised further as it enters the second region so that the fresh air and liquid droplets intermingle in the second region to further aerate the liquid. The sloping surface may be the first of a series of such sloping surfaces, each of the second and any subsequent sloping surface of the series extending below the region to which the immediately preceding sloping surface of the series slopes downwardly, so that the spray that falls onto said first sloping surface cascades down that surface to the respective region, is atomised further as it enters that region so that the fresh air and liquid droplets intermingle in that region to further aerate the liquid - as it falls through that region onto the second sloping surface of the series down which it cascades to the respective region and so on until the liquid falls onto the lowermost sloping surface of the series from which it is returned to the tank, each such surface being arranged. so that liquid received on it cascades down it to the next region where it is atomised and aerated further. Part of the stream of liquid drawn from the settling tank may be bled from the main stream of liquid that is aerated outside the mass of liquid stored in the tank, the bled liquid being injected back into liquid contained within the settling tank in order to generate movement of the liquid that is contained within the settling tank.

Fresh air flow into the or each region conveniently is induced by the passage of liquid or liquid spray to and through that region.

According to another aspect of this invention there is provided apparatus for use with a machine tool system having a settling tank through which liquid coolant/lubricant is recirculated during normal operation, the apparatus being effective to aerate the liquid stored in said settling tank and comprising control means which are adapted to sense the operational state of the machine tool system, liquid flow inducing means which are adapted to draw liquid from the tank the control means being operatively associated with the liquid flow inducing means such as to actuate the liquid flow inducing means to draw liquid from the tank when they sense that the machine tool system is shut down, aerating means disposed outside the mass of liquid stored in the tank and connected in a liquid recircula tion path with the tank and the liquid flow inducing means, the aerating means being for aerating liquid drawn from the tank by said liquid flow inducing means and thereafter returning aerated liquid to the tank.

Preferably said control means and said liquid flow inducing means are arranged such that the liquid flow inducing means are activiated continuously whilst the machine tool system is shut down so that a stream of liquid is drawn continuously from the tank, aerated outside the mass of liquid stored in the tank and returned to the mass of liquid stored in the tank continuously whilst the system is shut down. The aerating means may include a region into which fresh air flows and means for converting liquid drawn from the tank by said liquid flow inducing means into a spray in that region so that fresh air and the spray intermingle in that region to aerate the liquid and may be arrange such that flow of fresh air into the region is induced by liquid flow through the aerating means.

The aerating means may comprise a hollow casing. an inlet duct. a deflector which has a tapered surface and which is supported within that hollow casing so that its tapered surface tapers towards the inlet duct with which it is substantially coaxial and so that its radially outermost periphery is spaced from the adjacent wall of the casing, and aperture means in the casing wall through which fresh air from outside the casing flow into the region that extends between the tapered surface of the deflector and the adjacent wall of the hollow casing, the arrangement being such that, in use of the apparatus, a stream of liquid that is to be aerated is directed through the inlet duct onto the tapered surface of the deflector by which it is deflected to form a substantially circumferentially continuous radially directed flow which forms a liquid spray within said region and which draws fresh air into the interior of the casing through said aperture means, the fresh air and the spray intermingling within said region to aerate the liquid.

Preferably a radially outwardly directed flange is formed at the radially outermost periphery of the deflector in order to assist in the conversion of the liquid stream into a radially outwardly directed flow of spray.

Conveniently the flange tapers towards the large end of the tapered surface. The deflector may be pyramid shaped and such a flange may be formed along each edge of its base.

Preferably the hollow casing is adapted to be mounted for use with the inlet duct formed in its top surface. One or more members may be supported within the hollow casing below the deflector, the upper surface of each such member sloping downwardly from one end which rests against a respective wall of the hollow casing to another end which is spaced from the opposite wall of the hollow casing. Preferably there are several such members and they extend one below the other, alternate ones of the members resting against alternate ones of the pair of opposed walls of the hollow casing so that the spray that has intermingled with fresh air in the said region falls onto the upper surface of the uppermost one of said members and cascades down that surface to a second region, which is formed between the lower end of that member and the adjacent wall of the casing, to fall through that second region onto the upper surface of the next to uppermost member, cascade down the upper surface of that next to uppermost member to a third region, which is formed between its lower end and the adjacent wall of the casing, and so on until it reaches the bottom of the lowermost downwardly sloping member from whence it flows back into the settling tank. Conveniently further apertures are formed in the casing wall adjacent each of the regions that are formed between the lower end of the downwardly sloping members and the adjacent wall of the casing so that fresh air from outside the casing can flow into the respective region to intermingle within that region with liquid spray which passes through that region en route from one to the other of a juxtaposed pair of the downwardly sloping members. Preferably the hollow casing is adapted to be mounted above liquid contained within the settling tank so that the lower end of the upper surface of the lowermost downwardly sloping member is below the level of liquid within the settling tank during operation of the apparatus to aerate liquid drawn from the settling tank. Conveniently the or each member has an upwardly directed flange at the lower end of its downwardly sloping surface. The upper edge of the or each upwardly directed flange may be notched.

Conveniently further apertures are formed in the casing wall adjacent each of the regions that are formed between the lower end of the downwardly sloping members and the adjacent wall of the casing so that fresh air from outside the casing can flow into the respective region to intermingle within that region with liquid spray which traverses through that region whilst passing from one to the other of a juxtaposed pair of the downwardly sloping members. The further apertures may be arranged such that the flow of fresh air into each region is induced by the passage of spray through that region. Preferably the hollow casing is adapted to be mounted above liquid contained within the settling tank so that the lower end of the upper surface of the lowermost downwardly sloping member is below the level of liquid within the settling tank during operation of the apparatus to aerate liquid drawn from the settling tank, the lowermost downwardly sloping member serving as said means for returning aerated liquid to the tank.

One embodiment of this invention will be described now by way of example, with reference to the accompanying drawings, of which: Figure I is a schematic illustration of a system for aerating liquid contained within a machine tool system settling tank in accordance with this invention; Figure 2 is a side elevation of a practical embodiment of the system illustrated in Figure 1, the settling tank being shown chain dotted and partly broken away for convenience; Figure 3 is a plan view of Figure 2; Figure 4 is an end elevation of Figure 3; Figure 5 is a transverse cross section in a vertical plane of the aerator unit of the system illustrated in Figures 2 to 4, the unit being drawn to a larger scale than in Figures 2 to 4; and Figure 6 is a section on the line VI-VI of Figure 5.

Referring to Figures 1 to 4, a settling tank 10 of a machine tool system stores liquid, conveniently a mixture of oil and water, which is for use as a coolant and/or a lubricant in a machining operation carried out at each machine station of each machine tool of the system. The tank contains rotary drum filter apparatus (not shown) which has its outlet connected to a pump by which liquid within the tank is drawn from the tank through the rotary drum filter apparatus for distribution to each machine station of each machine tool of the system. The pump is located outside the tank. The rotary drum filter apparatus is usually located at the centre of the tank 10.

Liquid used as a coolant or a lubricant in a machining operation carried out at each machine station of each machine tool of the system is collected and returned to the tank 10. The returned liquid, together with soils, dirt, swarf and other foreign matter collected with it, is discharged into the tank at one end 11 which is sloped suitably. Figure 4 shows that the width of the tank 10 at the top is approximately three times that at the bottom, the side walls of the tank tapering inwardly between the top and bottom portions of the tank. A conveyor runs along the length of the bottom section of the tank and up the slope at the end 11 of the tank. A part 12 of the conveyor is shown in Figure 1 at the end 13 of the tank opposite the sloping end 11. Soils, dirt, swarf and other foreign matter discharged into the tank with liquid returned from the machine tools of the machine tool system gravitate to the narrow bottom section of the tank and onto the upper run of the conveyor and are carried by that conveyor out of the tank when the machine tool system is running.

Figure 2 shows that a motor 14 is drivingly coupled to a pump 15, the motor 14 and the pump 15 being mounted outside the tank 10 and below one of the sloping side wall portions of the tank 10. Operation of the motor 14 is controlled by the control system of the machine tool system so that it is energised to drive the pump 15 when the machine tool system is shut down.

The inlet of the pump 15 is connected to one end of an inlet pipe 16 which passes in a fluid tight manner through an aperture in a wall of the tank 10 and which is open at its other end which is located just above the upper run of the part 12 of the conveyor.

Hence the open end of the inlet pipe 16 is located as near to the bottom of the tank 10 as is practicable and also as close as is practicable to the end wall 13 that is opposite the sloping end 11 at which liquid is discharged into the tank along with soils, dirt, swarf and other foreign matter. The liquid adjacent the end wall 13 of the tank 10 tends to be the most stagnant liquid stored within the tank.

The outlet of the pump 15 is connected by a horizontal pipe 17, which runs outside the tank 10 for substantially the total length of the tank 10, to a branch pipe coupling 18 which has two outlets of different diameter.

The larger diameter outlet of the branch coupling 18 is connected by an angled pipe 19 to an inlet duct 21 of an aerator unit 22.

The smaller diameter outlet of the branch coupling 18 is connected by a small bore pipe 23 to an injector 24 which is located substantially at the centre of the tank 10, below the normal level of liquid stored therein and adjacent the sloping end 11 of the tank 10. The small bore pipe 23 passed in a fluid tight manner through an aperture in a wall of the tank 10. A valve 25 in the small bore pipe 23 controls liquid flow through that pipe. The arrangement of the pipes 19 and 23 and the valve 25 in such that the vast majority of liquid drawn from within the tank 10 by the pump 15 is directed to the aerator unit 22 via the angled pipe 19, approximately 8% of the total volume of liquid drawn from the tank 10 by the pump 15 being directed through the small bore pipe 23 and the injector 24 into liquid within the tank.

The aerator unit 22 will be described in detail now with reference to Figures 5 and 6.

It comprises a hollow casing of generally rectangular box construction formed basically of an angle iron framework clad with sheet metal panels which form its vertical side walls 26, 27, 28 and 29 and a top cover 31. The angle iron framework includes four vertical legs, one at each corner of the casing and four horizontal lengths of angle iron at the top. The casing is open at the bottom and is supported from the structure of the tank 10 by suitable support means so that its longitudinal axis is vertical and so that the bottom of each of the four legs of the angle iron framework is immersed in liquid contained within the tank 10. The side wall panels 26 to 29 are shorter than the vertical legs of the angle section framework and their lower edges are above the level of liquid contained within the tank 10. The casing is orientated so that the wider side wall panels 26 and 27 are substantially normal to the longitudinal axis of the tank 10.

The top cover 31 carries the inlet duct 21 which is a vertical tube which passes through a circular hole within which it is spigotted and which is formed at the centre of the top plate 31. A pair of angled strips 32 and 33, which comprise portions of the top panel 31 bent downwardly from the plane of the remainder of the top panel 31, extend parallel to the wider side wall panels 26 and 27 over substantially the total distance between the horizontal lengths of the angle section framework to which the narrower side wall panels 28 and 29 are fastened.

Each angled strip 32, 33 is flat and slopes downwardly in direction outwards from the vertical axis of the aerator unit 221. The wider side wall panels 26 and 27 project above the horizontal lengths of the angle section framework to form flanges 34 and 35 which are bent inwardly towards the axis of the aerator unit 22 so that each of them extends substantially parallel to the adjacent angled strip 32, 33. Each angled strip 32, 33 co-operates with the adjacent angled flange 34, 35 to form an angled inlet slot through which air can be drawn into the interior of the hollow casing from outside, air drawn in through each such angled slot being directed towards the adjacent wider side wall panel 26, 27.

A sheet metal deflector 36 comprises a pyramid-shaped structure with a square base and four outwardly directed angled flanges 37, 38, 39 and 41 which extend one along each edge of the base of the pyramidshaped structure. Each angled flange 37, 38, 39 and 41 and the adjacent triangular face of the pyramid-shaped structure of the deflector 36 converge towards the respective edge of the square base. The deflector 36 is supported by an angle iron support framework 42 so that it is coaxial with the inlet duct 21 and so that its apex is at its end nearer to the inlet duct 21. There is a space between each angled flange 37, 38, 39, 41 and the adjacent wall panel 26, 27, 28 and 29 of the hollow casing.

A pair of angle iron support members 43 and 44 slope downwardly from the wider side wall panel 27 to the wider side panel 26, each support member 43, 44 lining a respective one of the narrower side wall panels 28 and 29. A planar sheet metal member 45 is supported at either edge by the two members 43 and 44 so that it spans the gap between those members 43 and 44 and slopes downwardly. The upper edge of the sheet metal member 45 abuts the vertical legs of the angle section framework to which the wider side wall panel 27 is fastened. The planar sheet metal member 45 has an upwardly directed flange 46 extending over substantially the full distance between the narrower side wall panels 28 and 29 at its lower end. Seven notches are formed in the edge of the flange 46 at equi-spaced intervals. There is a space between the flange 46 and the adjacent wider sheet metal panel 26 which carries an upwardly opening sheet metal shroud 47. The interior of the shroud 47 communicates with the space between the flange 47 and the panel 26 through an aperture which is formed in the panel 26 opposite the flange 46.

A second downwardly sloping planar sheet metal member 45A is supported below the planar sheet metal member 45 in a similar manner by angle iron support members 43A and 44A. The upper edge of the second member 45A abuts the vertical legs of the angle iron framework to which the wider sheet metal side wall panel 26 is attached just below the aperture that is formed in that panel 26 adjacent the lower end of the shroud 47. A notched flange 46A is formed at the lower end of the second member 45A and a space is formed between the notched flange 46A and the adjacent wider sheet metal side wall panel 27. An upwardly opening sheet metal shroud 47A carried by the wider sheet metal side wall panel 27 opens at its lower end into the space formed between the notched panel 46A and that panel 27 through an aperture formed in that panel 27 opposite the notched flange 46A.

A third downwardly sloping planar sheet metal member 45B is supported below the second member 45A in a similar manner by another pair of angle iron support members 43B and 44B, the upper edge of the third member 45B being in abutment with the vertical legs of the angle iron framework to which the wider sheet metal side wall panel 27 is attached just below the aperture that is formed in that panel 27 opposite the notched flange 46A. A notched flange 46B is formed at the lower end of the third member 45B and there is a space between that notched flange 46B and the adjacent wider sheet metal side wall panel 26. The interior of a second upwardly opening sheet metal shroud 47B, which is carried by the panel 26 below the first such shroud 47, communicates with the space formed between the notched flange 46B and that panel 26 through an aperture which is formed in that panel 26 opposite the notched flange 46B.

A fourth sheet metal member 48 is supported by suitable angle iron members below the third downwardly sloping planar sheet metal member 45B. The fourth sheet metal member 48 extends over substantially the full distance between the narrower sheet metal side wall panels 28 and 29, like the other three sheet metal members 45, 45A and 45B, but does not slope downwardly over its whole length. That part, 48A, of the fourth sheet metal member 48 that extends below the space between the edge of the notched flange 46B of the third downwardly sloping planar sheet metal member 45B is substantially horizontal and extends almost to the centre of the hollow casing. The fourth member 48 slopes downwardly from the inner edge of the horizontal portion 48A to a point which is just short of the wider sheet metal side wall panel 27 and which is below the level of liquid stored within the tank 10, even when the pump 15 is being driven to draw liquid from the tank and circulate liquid through the pipes 16, 17, 19 and the aerator unit 22. The lower end of the downwardly sloping portion 48B of the fourth member 48 is connected by a second short horizontal portion 48C to the lower ends of the vertical legs of the angle section framework to which the wider sheet metal side wall panel 27 is attached.

The aerating apparatus described above with reference to and as illustrated in the accompanying drawings is inoperative whenever the machine tool system is in operation. However, as soon as the machine tool system is shut down and the conveyor brought to a halt, the motor 14 is energised and the pump 15 is driven to draw liquid from within the tank 10, adjacent the end 13 of the tank, and to feed the majority of that liquid through the pipes 17 and 19 to the aerator unit 22 through its inlet duct 21. The minor part of the liquid that is directed through the small bore pipe 23 is injected back into the liquid within the tank 10 through the injector 24 adjacent the end 11 of the tank 10 into which the liquid, together with swarf, soils, dirt and other foreign matter is discharged during operation of the machine tool system, such liquid injected into the tank 10 through the injector 24 generating movement of liquid within the tank 10 to reduce stagnation of that liquid.

The main stream of liquid that is directed into the aerator unit 22 through the inlet 21 impinges the surfaces of the pyramid-shaped structure of the deflector 36 and is deflected by that impingement and by the action of the angled deflector flanges 37, 38, 39 and 41 so that it is broken up into a radially outwardly directed spray of liquid droplets which extends substantially continuously around the circumference of the deflector 36. The spray is directed across the space between the deflector 36 and the side wall panels 26, 27, 28 and 29 and some of that spray impinges those side walls panels 26 to 29 and rebounds from those side wall panels 26 to 29 so that it is broken up into an even finer spray. Spray within the space between the deflector 36 and the wider side wall panel 27 as well as spray within the spaces between that deflector 36 and the narrower side wall panels 28 and 29 falls onto the third downwardly sloping planar sheet metal member 45 therebelow. Spray in the space between the deflector 36 and the wider side wall panel 26 falls through the space between the notched flange 46 and that panel 26 onto the downwardly sloping surface of the second planar sheet metal member 45A.

The flow of liquid through the inlet duct 21 onto the deflector 36, radially outwardly from that deflector 36 towards the side wall panels 26, 27, 28 and 29 and then downwardly onto the downwardly sloping members 45 and 45A therebelow, induces air to flow into the hollow casing through the inlets formed by the parallel pairs of angled strips and flanges 32 and 34, 33 and 35 and fresh air so induced to flow into the interior of the hollow casing intermingles with the liquid droplets of the spray within the spaces formed between the deflector 36 and the side wall panels 26, 27, 28 and 29 of the hollow casing and purges that spray of bacteria.

Liquid that falls onto the first downwardly sloping planar sheet metal member 45 tends to bounce on that member 45 and cascades down that member 45 and over the notched edge of the notched flange 46 into the second space formed between that notched flange 46 and the wider sheet metal side wall panel 26. Hence the liquid is further broken up into an atomised spray of liquid droplets which falls through that second space onto the second downwardly sloping planar support member 45A. Air is induced to flow into that second space through the upwardly opening shroud 47 and the aperture formed in the side wall panel 26 at the foot of that shroud opposite the notched flange 46 and that air intermingles with the liquid spray within that second space and further purges that liquid, It will be appreciated that spray that falls onto the second downwardly sloping planar sheet metal member 45A cascades down that slope to the third space where it intermingles with further fresh air drawn into that third space through the upwardly opening shroud 47A and the aperture formed in the wider sheet metal side wall panel 27 opposite the notched flange 46A and that that liquid is further purged in that space. It will be appreciated also that the process is repeated again in the fourth space that is formed between the notched flange 46B and the wider side wall panel 26.

Liquid that falls through the space formed between the notched panel 46B and the wider side wall panel 26 falls onto the lowermost sheet metal member 48A and flows down the sloping portion 48A of that panel 48 into the liquid in the tank 10 within which the lower edge of that panel portion 48A is immersed. A tendency for foam to be formed by the action of pouring liquid into liquid contained in the settling tank 10 is minimised by arranging for the bottom of the downwardly sloping portion 48A to be always immersed in that liquid so that the liquid output from the aerator unit 22 is returned relatively gently into the main body of the liquid in the settling tank 10.

The notches in the edges of the notched flanges 46, 46A and 46B assist in breaking up and atomising liquid that cascades down the respective downwardly sloping planar member and over the notched surfaces into the respective space formed between those notched edges and the adjacent wider side wall panel 26 or 27.

WHAT WE CLAIM IS: 1. A method of aerating liquid stored in a settling tank of a machine tool system comprising drawing off liquid from the tank whilst the machine tool system is shut down, aerating the drawn off liquid outside the mass of liquid stored in the tank and returning the aerated liquid to the mass of liquid stored in the tank.

2. A method according to Claim 1, wherein liquid is drawn continuously from the settling tank as a stream, aerated outside the mass of liquid stored in the tank and returned to the mass of liquid stored in the tank continuously whenever the system is shut down.

3. A method according to Claim 2, wherein such a continuous stream of liquid drawn from the settling tank is converted into a spray in a region into which fresh air flows so that fresh air and spray intermingle in that region to aerate the liquid.

4. A method according to Claim 3, wherein the stream of liquid is converted into a spray by being directed towards the apex of coaxial tapered deflecting means and being deflected thereby to form a substantially continuous radially directed flow.

5. A method according to Claim 4, wherein conversion of the liquid stream into a radially directed spray is enhanced by coacting the deflected liquid with substantially circumferentially continuously outwardly directed flange means which are provided on the tapered deflecting means, spaced from the apex.

6. A method according to any one of Claim 1 to 5, wherein the spray is allowed to fall onto a sloping surface down which it cascades to a second region into w

Claims

**WARNING** start of CLMS field may overlap end of DESC **. strips and flanges 32 and 34, 33 and 35 and fresh air so induced to flow into the interior of the hollow casing intermingles with the liquid droplets of the spray within the spaces formed between the deflector 36 and the side wall panels 26, 27, 28 and 29 of the hollow casing and purges that spray of bacteria. Liquid that falls onto the first downwardly sloping planar sheet metal member 45 tends to bounce on that member 45 and cascades down that member 45 and over the notched edge of the notched flange 46 into the second space formed between that notched flange 46 and the wider sheet metal side wall panel 26. Hence the liquid is further broken up into an atomised spray of liquid droplets which falls through that second space onto the second downwardly sloping planar support member 45A. Air is induced to flow into that second space through the upwardly opening shroud 47 and the aperture formed in the side wall panel 26 at the foot of that shroud opposite the notched flange 46 and that air intermingles with the liquid spray within that second space and further purges that liquid, It will be appreciated that spray that falls onto the second downwardly sloping planar sheet metal member 45A cascades down that slope to the third space where it intermingles with further fresh air drawn into that third space through the upwardly opening shroud 47A and the aperture formed in the wider sheet metal side wall panel 27 opposite the notched flange 46A and that that liquid is further purged in that space. It will be appreciated also that the process is repeated again in the fourth space that is formed between the notched flange 46B and the wider side wall panel 26. Liquid that falls through the space formed between the notched panel 46B and the wider side wall panel 26 falls onto the lowermost sheet metal member 48A and flows down the sloping portion 48A of that panel 48 into the liquid in the tank 10 within which the lower edge of that panel portion 48A is immersed. A tendency for foam to be formed by the action of pouring liquid into liquid contained in the settling tank 10 is minimised by arranging for the bottom of the downwardly sloping portion 48A to be always immersed in that liquid so that the liquid output from the aerator unit 22 is returned relatively gently into the main body of the liquid in the settling tank 10. The notches in the edges of the notched flanges 46, 46A and 46B assist in breaking up and atomising liquid that cascades down the respective downwardly sloping planar member and over the notched surfaces into the respective space formed between those notched edges and the adjacent wider side wall panel 26 or 27. WHAT WE CLAIM IS:

1. A method of aerating liquid stored in a settling tank of a machine tool system comprising drawing off liquid from the tank whilst the machine tool system is shut down, aerating the drawn off liquid outside the mass of liquid stored in the tank and returning the aerated liquid to the mass of liquid stored in the tank.

6. A method according to any one of Claim 1 to 5, wherein the spray is allowed to fall onto a sloping surface down which it cascades to a second region into which fresh air flows.

7. A method according to Claim 6, wherein the cascading liquid is atomised further as it enters the second region so that fresh air and liquid droplets intermingle in the second region to further aerate the liquid.

8. A method according to any one of Claims 1 to 5, wherein the spray is allowed to fall onto a first of a series of sloping surfaces which each slope downwardly to a respective region into which fresh air flows, each of the second and any subsequent sloping surface of the series extending below the region to which the immediately preceding sloping surface of the series slopes downwardly, so that the spray that falls onto said first sloping surface cascades down that surface to the respective region, is atomised further as it enters that region so that the fresh air and liquid droplets intermingle in that region to further aerate the liquid as it falls through that region onto the second sloping surface of the series down which it

cascades to the respective region and so on until the liquid falls onto the lowermost sloping surface of the series from which it is returned to the tank, each such surface being arranged so that liquid received on it cascades down it to the next region where it is atomised and aerated further.

9. A method according to any one of Claims 2 to 5 or any one of Claims 6 to 8 when appended to Claim 2, wherein part of the stream of liquid drawn from the settling tank is bled from the main stream of liquid that is aerated outside the mass of liquid stored in the tank, the bled liquid being injected back into liquid contained within the settling tank in order to generate movement of the liquid that is contained within the settling tank.

10. A method according to any one of Claims 3 to 5 or any one of Claims 6 to 9 when appended to Claim 3, wherein fresh air flow into the or each region is induced by the passage of liquid or liquid spray to and through that region.

11. Apparatus for use with a machine tool system having a settling tank through which liquid coolant/lubricant is recirculated during normal operation, the apparatus being effective to aerate the liquid stored in said settling tank and comprising control means which are adapted to sense the operational state of the machine tool system, liquid flow inducing means which are adapted to draw liquid from the tank, the control means being operatively associated with the liquid flow inducing means such as to activate the liquid flow inducing means to draw liquid from the tank when they sense that the machine tool system is shut down aerating means disposed outside the mass of liquid stored in the tank and connected in a liquid recirculation path with the tank and the liquid flow inducing means, the aerating means being for aerating liquid drawn from the tank by said liquid flow inducing means and thereafter returning aerated liquid to the tank.

12. Apparatus according to Claim 11, wherein said control means and said liquid flow inducing means are arranged such that the liquid flow inducing means are activated continuously whilst the machine tool system is shut down so that a stream of liquid is drawn continuously from the tank aerated outside the mass of liquid stored in the tank and returned to the mass of liquid stored in the tank continuously whilst the system is shut down.

13. Apparatus according to Claim 11 or Claim 12, wherein the aerating means include a region into which fresh air flows and means for converting liquid drawn from the tank by said liquid flow inducing means into a spray in that region so that fresh air and the spray intermingle in that region to aerate the liquid.

14. Apparatus according to Claim 13, wherein the aerating means are arranged such flow of fresh air into the region is induced by liquid flow through the aerating means.

15. Apparatus according to any one of Claims 11 to 14, wherein the aerating means comprise a hollow casing, an inlet duct, a deflector which has a tapered surface and which is supported within that hollow casing so that its tapered surface tapers towards the inlet duct with which it is substantially coaxial and so that its radially outermost periphery is spaced from the adjacent wall of the casing, and aperture means in the casing wall through which fresh air from outside the casing can flow into the region that extends between the tapered surface of the deflector and the adjacent wall of the hollow casing, the arrangement being such that, in use of the apparatus, a stream of liquid that is to be aerated is directed through the inlet duct onto the tapered surface of the deflector by which it is deflected to form a substantially circumferentially continuous radially directed flow which forms a liquid spray within said region and which draws fresh air into the interior of the casing through said aperture means, the fresh air and the spray intermingling within said region to aerate the liquid.

16. Apparatus according to Claim 15, wherein a radially outwardly directed flange is formed at the radially outermost periphery of the deflector in order to assist in the conversion of the liquid stream into a radially outwardly directed flow of spray.

17. Apparatus according to Claim 16, wherein the flange tapers towards the large end of the tapered surface.

18. Apparatus according to any one of Claims 15 to 17, wherein the deflector is pyramid-shaped.

19. Apparatus according to Claim 18 when appended to Claim 16, wherein such a flange is formed along each edge of the base of the pyramid-shaped deflector.

20. Apparatus according to any one of Claims 15 to 19, wherein the hollow casing is adapted to be mounted for use with the inlet duct formed in its top surface.

21. Apparatus according to Claim 20, wherein one or more members are supported within the hollow casing below the deflector, the upper surface of each such member sloping downwardly from one end which rests against a respective wall of the hollow casing to another end which is spaced from the opposite wall of the hollow casing.

22. Apparatus according to Claim 21, wherein there are several such members and they extend one below the other, alternate ones of the members resting against alter nate ones of the pair of opposed walls of the hollow casing so that the spray that has intermingled with fresh air in the said region falls onto the upper surface of the uppermost one of said members and cascades down that surface to a second region, which is formed between the lower end of that member and the adjacent wall of the casing, to fall through that second region onto the upper surface of the next to uppermost member, cascade down the upper surface of that next to uppermost member to a third region, which is formed between its lower end and the adjacent wall of the casing, and so on until it reaches the bottom of the lowermost downwardly sloping member from whence it flows back into the settling tank.

23. Apparatus according to Claim 21 or Claim 22, wherein the or each member has an upwardly directed flange at the lower end of its downwardly sloping surface.

24. Apparatus according to Claim 23, whrein the upper edge of the or each upwardly directed flange is notched.

25. Apparatus according to Claim 22 or either of Claims 23 and 24 when appended to Claim 22, wherein further apertures are formed in the casing wall adjacent each of the regions that are formed between the lower end of the downwardly sloping members and the adjacent wall of the casing so that fresh air from outside the casing can flow into the respective region to intermingle within that region with liquid spray which traverses through that region whilst passing from one to the other of a juxtaposed pair of the downwardly sloping members.

26. Apparatus according to Claim 25, wherein the further apertures are arranged such that the flow of fresh air into each region is induced by the passage of spray through that region.

27. Apparatus according to any one of Claims 21 to 26, wherein the hollow casing is adapted to be mounted above liquid contained within the settling tank so that the lower end of the upper surface of the lowermost downwardly sloping member is below the level of liquid within the settling tank during operation of the apparatus to aerate liquid drawn from the settling tank, the lowermost downwardly sloping member serving as said means for returning aerated liquid to the tank.

28. A method of aerating liquid stored in a settling tank of a machine tool system substantially as described hereinbefore with reference to the accompanying drawings.

29. Apparatus for aerating liquid stored in a settling tank of a machine tool system substantially as described hereinbefore with reference to and as illustrated in the accompanying drawings.