Abstract:
A coolant purification system for purifying and removing particles from the coolant used in machining operations. The system uses a rare earth magnetic separator in combination with bag-type filters and deep level filters that are arranged in sequences so that the filters that tend to clog more frequently due to the removal of small particles will not be clogged by particles that are easily removed by coarser filters of this system.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a coolant purification system and more particularly to an improved apparatus for removing foreign particles from the cooling and lubricating fluid used in machining operations. 
     In many types of machine operations, a coolant is supplied to the area being machined for a number of purposes. One of these purposes is to cool and lubricate the machining operation. The other and equally important purpose is to remove the machined particles as well as other foreign matter from the area where machining is occurring so as to improve surface finish. 
     Although in principle this appears to be simple and obvious, accomplishing these results and being able to operate the equipment over long periods without servicing presents substantial considerations. Environmental concerns also require the reclaiming of the coolant and lubricant and recirculation of it, and this adds greatly to the aforenoted problems. 
     In some ways, this invention relates to an improvement or an alternative arrangement for providing coolant purification to that shown in my copending United States Letters Patent of the same title, Ser. No. 09/063,017 filed Apr. 20, 1998, now U.S. Pat. No. 6,015,487, and assigned to the assignee hereof. 
     A prior art type of apparatus is illustrated in FIG.  1  and the effectiveness of various types of prior filtering materials utilized for coolant purification is shown in FIGS. 2 and 3. The apparatus shown in FIG. 1 includes a machining station  21  having a cutting tool  22  that operates to machine the surfaces of a work piece  23 . In the illustrated embodiment, by way of example, the cutting tool  22  is a grinding wheel and the work piece  23  is a gear blank onto which gear teeth are formed by the grinding operation. 
     This grinding operation takes place over a catch tank  24  with a coolant supply nozzle  25  being provided so as to spray the cooling liquid to the machined area. This liquid is then collected in the catch tank  24  and is returned to a purification apparatus, indicated generally by the reference numeral  26 , where the cutting liquid is collected in a storage tank  27 . A pump  28  draws the coolant from the storage tank  27  and delivers it via the nozzle  28  to the machine area. 
     In the specific prior art example shown, the purification apparatus  26  comprises a centrifugal separator including an impeller element  29  that is driven by an electric motor  31  and which separates foreign particles from the coolant in a manner known. The purified coolant is returned to the storage tank  27  through a purification return line  32 . 
     FIG. 2 shows the typical efficiency of this type of centrifugal apparatus by indicating the NAS value. This NAS value is a standard by which the number and size of entrain particles captured by the filter are measured. On the absissa, the size of particles is shown, while on the ordinate, the NAS number is indicated. 
     It will be seen that the centrifugal type separator is fairly consistent in the NAS number of the particles of varying sizes, but nevertheless does not exclude as many particles as desired, particularly those in the larger sizes, such as 50-100 μm. Thus its efficiency is not great. 
     Another type of filter which may be employed for purifying coolant and which has a higher filtration efficiency is the diatomaceous earth type. FIG. 3 shows the efficiency of this type of filter. 
     As may be seen in this figure, the efficiency is higher, particularly with larger size particles. However, this type of filter requires frequent servicing and hence is expensive to operate and does not afford long operational cycles between servicing. Also, the smaller size particles are more difficult to capture with this type of filter if reasonable flow velocities and small size of the filter are obtained. 
     Therefore, it is a principle object of this invention to provide an improved coolant purification system usable with machining operations that will remove with high efficiencies particles of a variety of sizes and which can be operated for long time intervals without necessitating servicing. 
     It is a principle object, therefore, to provide an improved coolant purification system for a machining apparatus that has high efficiency and long service life while permitting operation at lower cost. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, there is provided a coolant purification system for machining operation that includes a system for supplying coolant to the machined area and collecting the utilized coolant and purifying it. The purification apparatus includes at least a rare earth magnetic separator, bag filters, and a deep level filter that are disposed in a flow path along a coolant circulation arrangement and for returning the coolant to a storage tank for recirculation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a prior art type of coolant purification system employing primarily a centrifugal separator. 
     FIG. 2 is a graphical view showing the efficiency of the centrifugal separator. 
     FIG. 3 is a graphical view showing the efficiency of a diatomaceous earth type purifier. 
     FIG. 4 is a schematic view in part similar to FIG. 1, but showing an embodiment of the invention. 
     FIG. 5 is a partial cross-sectional view showing one embodiment of return arrangement to the main coolant storage tank. 
     FIG. 6 is a cross-sectional view, in part similar to FIG. 5, and shows another arrangement for returning coolant to the main storage tank. 
     FIG. 7 is a cross-sectional view showing how the Q-pot works. 
     FIG. 8 is a top plan view showing the relationship of the fluid return and its cooperation with the Q-pot to improve efficiency. 
     FIG. 9 is a cross-sectional view, in part similar to FIG. 8 showing another embodiment of fluid return to the Q-pot for improving efficiency. 
     FIG. 10 is a cross-sectional view, in part similar to FIGS. 8 and 9, and shows yet another arrangement for returning fluid and improving the efficiency. 
     FIG. 11 is a perspective view showing an arrangement for a secondary storage tank for achieving centrifugal separation. 
     FIG. 12 is a schematic view showing the construction of the mechanical type filter arrangement including the bag and deep level filter arrangement of the construction shown only generally in FIG.  4 . 
     FIG. 13 is a cross-sectional view showing another arrangement for returning fluid and removed particles to the main storage tank. 
     FIG. 14 is an efficiency curve showing the efficiency of the rare earth magnetic separator of this embodiment. 
     FIG. 15 is a graphical view showing how the relationship between the roller gap and the magnetic particle capture rate at varying flow quantities is effective in improving the service life of the magnetic type separator. 
     FIG. 16 is a graphical view showing the efficiency of the coolant purification degree through the bag filters. 
     FIG. 17 is a graphical view showing the filtration efficiency or coolant purification degree of the deep level type filter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail initially to FIG. 4, this figure shows a coolant purification system embodying the invention in conjunction with a machining apparatus which basically has the same general layout as a prior art type of apparatus and which, therefore, has been indicated by the same reference numerals applied in the description of prior art FIG.  1 . Thus, this apparatus includes the machining section  21  wherein the grinding wheel  22  grinds the finished form on the gear blank  23 . The coolant is supplied to the machining area by a spray nozzle  25  from the purification system. 
     This purification system includes a main coolant storage and collection tank  51 . Coolant is delivered from the drain or collection tray  24  to this storage tank  51  by means of a rare earth type magnetic separator, indicated generally by the reference numeral  52 . This separator includes a rotating magnetic drum  53  that operates to rotate through the collected fluid in a trough and remove the extracted particles through a discharge chute  54  before return of the purified coolant to the storage tank  51  through a return  55 . 
     The return  55  may have configurations as will be described later by reference to FIGS. 5 and 6 for controlling the flow amount and cooperates with a supply line  56  in which a pump  57  is provided. The pump  57  pumps fluid through a check valve  58  and past a control valve  59  to a mechanical filter assembly, indicated generally by the reference numeral  61 , and which has a construction that will be described later in more detail by reference to FIG. 13. A pressure gauge  60  is placed in this line  56  between the check valve  58  and the flow control valve  59 . 
     Air may be bleed from the mechanical filter assembly  61 , through an air bleed path  62  in which a flow control valve  63  is provided and which communicates back with the rare earth magnetic filter  52  above the coolant level therein. 
     Fluid flows primarily from the filter element  61  through a main supply line  64  to a coolant (heat exchanger) cooler and purifier, indicated generally by the reference numeral  65 . This type of device  65  includes a second storage tank  66  in which the fluid is contained and a suitable cooling arrangement for removing heat from the circulated coolant. This includes a circulating or agitating propeller  67  that circulates the coolant in the tank and also a sensor  68  which senses if the coolant falls to a low level to give a warning signal. An overflow line  69  permits excess coolant to flow directly back to the main storage tank  51 . 
     The purified and cooled coolant from the coolant device  65  is delivered to the spray nozzle  25  through a conduit  71  in which an on/off valve  72  is provided upstream of a secondary pump  73 . The pump  73  discharges into the line  71  through a check valve  74  and flow control valve  75 . 
     Pressure gages  76  and  77  are disposed between the check valve  74  and the flow control valve  75  and downstream of the control valve  75 , respectively. The conduit  71  then discharges directly to the spray nozzle  25  for delivering the coolant to the machining area. 
     Coolant from the filter  61  also may be returned to the main storage tank for cleaning purposes past the cooling device  65  through a drain return line  78 . This will be described in more detail later. The drain return line  78  communicates with the lower level of the main storage tank  51  through an on/off valve  79  or in another manner to be described by reference to FIG.  13 . 
     Coolant for flushing the catch tray  24  is also drawn from the tank  51  through a conduit  81  and delivered to a pair of spray nozzles  82  and  83 . A main shut off valve  84  connects the main storage tank  51  to a high pressure pump  85  that discharges into the conduit  81 . A check valve  86  and flow control valve  87  are provided in the line  81  with a pressure gauge  88  being disposed therebetween. The line  81  branches into two lines, each connected to a respective one of the spray nozzles  82  and  83 . On/off valves  89  and  91  control the communication with the spray nozzles  82  and  83 . These nozzles may be employed for flushing additional coolant into the catch tray  24  and returning it back to the rare earth magnetic filter  52  to remove accumulated particles even when no machining operation is being performed. 
     Finally, the main system also includes a Q-pot device, indicated generally by the reference numeral  92 , which has a construction as will be described later by reference to FIG. 7 that serves the purpose of removing floating particles from the coolant and separating them. This Q-pot  92  has a pick up device that communicates with a further conduit  93  in which a pump  94  is provided. The pump  94  has the capability of supplying fluid to a further spray nozzle  95  through a line in which an on/off valve  96  is provided. A priming funnel  97  and on/off valve  98  is provided in the line  99  that extends to the spray nozzle  95  so as to start up this system if desired. This system can be used fir flushing the catch tray  24  as well as preventing these particles from entering the machining area. 
     Thus, on the basic principle of operation, the coolant is filtered first by the rare metal magnetic filter  52 , floating impurities are removed by the Q-pot  92  and the fluid is filtered by the deep filter and bag filters in the filter unit  61 . Then, the fluid may be passed through the cooler  65  for recirculation. 
     Embodiments of desirable ways in which the fluid is returned at controlled rates from the rare earth magnetic separator  52  to the main storage tank  51  will be described by reference to FIGS. 5 and 6. In the first of these embodiments, the main storage tank discharge  55  functions as a funnel formed at the bottom of a body assembly  101  of the separator  52 . 
     This funnel  55  discharges to a further funnel  102  that is fixed to the lower wall of the main storage tank  51  and which is connected to the line  56  in which a main shut off valve  103  is provided. The opening of this funnel arrangement and the cooperation with the pump  57  is such that the pump  52  pumps a flow quantity Q   2   which is larger than the flow quantity of fluid that enters the magnetic separator  52  (Q   1   ). That is, Q   2   is greater than Q   1   (Q   2   &gt;Q   1   ). 
     A modified configuration for accomplishing this result is also shown in FIG. 6 wherein the discharge section  51  is provided with a converging nozzle portion  104  that cooperates with a further conical shaped portion  105  of the discharge portion  102  and which communicates with the line  56 . Again, the arrangement is such that the flow quantity Q   2   is greater than Q   1   (Q   2   &gt;Q   1   ). 
     The structure of the Q-pot  92  will now be described by reference to FIG.  7  and later figures will describe how the fluid is returned to the main storage tank  51  so as to assist in the operation of the Q-pot by reference to FIGS. 8-11. 
     The Q-pot  92  is comprised of a central tube  111  that has a fitting  112  at its lower end above which is placed four, equally spaced flow openings  113 . An elastic bellows  114 , which is impervious in nature, is affixed to the end fitting  104  at its, lower end. The upper end of the bellows  114  is fixed to a ring  115  which surrounds the tube  111  but is spaced radially outwardly therefrom so as to permit a flow into this area, indicated as  117 , as shown by the arrows in FIG.  7 . Thus, any floating particles will be drawn into the bellows  114  and picked up through the openings  113  and drawn from the pick up  111  into the return lines  93  and  99  for continuous recirculation and redelivery to the rare earth magnetic separator  52 . This will assist in ensuring that these floating particles do not find their way back into the cooling fluid that is delivered by the spray nozzle  25 . 
     As seen in FIG. 8, the magnetic separator  52  may be provided with a discharge port  116  that flows across the upper surface of the storage tank  51  so as to provide a swirling action toward the Q-pot  92  and specifically the inlet opening  117  formed at the upper end thereof by the member  15 . This will assist in ensuring that these floating particles are skimmed off and prevented from being mixed with the coolant that is delivered by the spray nozzle  25 . 
     FIG. 9 shows another way in which this can be done. In this figure, there is depicted a mist acquisition device  121  that functions to collect vapors from above the collection tray  24  and deliver them through a conduit  122  across the upper surface of the main storage tank  51 . This will cause the foreign particles entrained into these vapors to flow directly toward the opening  117  of the Q-pot  92 . 
     Also, as shown in FIG. 10, the overflow pipe  69  from the cooler  65  may also be so directed toward the upper surface of the liquid in the main storage tank  51  so as to direct the floating particles toward the opening  117  of the Q-pot  92 . 
     FIG. 11 shows another arrangement for assisting in the centrifugal separation of solid particles from the coolant that is delivered to the cooler  65 . In fact, this shows more detail of the structure shown in FIG. 4 wherein the return conduit  64  mates with a manifold  123  which, in turn, has four depending pipe sections  124  at the four corners of the rectangular container and which have discharge nozzles so as to give a circumferential swirl to the fluid so as to provide centrifugal separation to a conical shape lower area for separation and draining periodically. The heavier particles will be thrown outwardly by the centrifugal action and then collected by gravity to the lower part of the conical section for periodic removal. This will reduce the frequency at which the tank  66  of the cooler need be cleaned. 
     The construction of the main mechanical filter assembly  61  will now be described in initial detail by primary reference to FIG.  12 . As seen in this figure, and as previously described, the line  56  enters the filter assembly  61 . This communicates with a main distribution line  131  which discharges to bag-type filters  132   a ,  132   b  and  132   c  that are disposed in parallel flow fashion, each having a respective inlet  133  from the line  131 . 
     Each bag filter  132  is formed with a bag-like configuration having a woven or non-woven cloth made of a synthetic fiber and which may have meshes that are either the same size or in different sizes. However, the preference is to use a smaller number of bag filters with course meshes, particularly where the machining operation is such so as to not provide long length chips. In a preferred embodiment, the three bag filters  132   a, b  and  c , have a mesh of approximately 40 μm. 
     The bag filters  132  all have respective discharges  134   a, b  and  c  that communicate with respective manifold lines  135   a ,  135   b  and  135   c , respectively. These manifold lines extend at one end thereof to a main filter conduit  136  which, in turn, communicates with a deep filter element  137  through a line in which a main shut off valve  138  is provided. 
     The deep level filter  137  is formed from a lamination with woven or non-woven cloth of synthetic fibers with course cylindrical outer layers and progressively finer cylindrical inner layers. Thus, the larger particles will be accumulated in the external portion of this filter, and the smaller particles will be in the inner portion. However, by using a large number of small diameter cylinders, each having respective meshes, it is possible to contain the filter in a small volume and permit replacement of the cylinders, either as a group or individually. It is has been found that by utilizing filter meshes of 15 μm, it is possible to obtain a level of purification similar to that of a diamatatious earth filter. 
     A pressure gauge  139  and pressure sensors  141  are associated with the inlet to the deep level filter  137  and in a like manner, pressure gauges  142  are associated with each of the bag-type filters  132  with a pressure sensor  143  being connected to one of them. 
     A shut off valve  144  is provided at the outlet from the deep level filter  138  to the line  78  connecting the filter back to the cooler  65 . 
     In addition, a clean out line  145  is associated with the deep level filter  137  for its cleaning purposes and this line has in it a main shut off valve  146 , pressure gauge  147  and pressure sensor  148 . This line can either be connected back to the return  64  or can be opened for drain purposes through a drain valve  149 . The bag-type filters  132   a ,  132   b  and  132   c  may also be cleaned by opening a clean out line valve  151  which dumps the fluid through a diffuser  152  from a line  153  that parallels the line  136 . 
     The diffusion  152  is shown in more detail in FIG.  13  and communicates with the main storage tank  51 . This diffusion  152  is coupled by a coupling  155  to the line  153  and has an elbow fitting  156  with discharge openings  157  spaced therearound. These are formed in a plug-like member  158  so that the discharge can be returned to the tank  51  through an upper surface thereof so that any floating materials cleaned can be removed by the Q-pot  92 . 
     If it is desired to run the system without utilizing the filter  61 , it can be bypassed by means of a bypass line, indicated by the reference numeral  159  in FIG. 12 in which a shut off valve  161  is provided. If the filters are to be bypassed the shut off valve  161  is opened and the valves  161  and a further valve  162  in a bypass line  163  between the manifold branch  136  and the return line  145  is closed. At this time, the valve  146  should also be closed. 
     By utilizing the filters in the arrangement described, it is possible to obtain very high degrees of filtration and, at the same time, minimize the necessity for servicing the individual elements of the filtration system. This may be understood best by reference to FIGS. 14-17. 
     FIG. 14 shows the efficiency NAS of the rare earth magnetic separator  52 . As may be seen, this picks out the larger particles and thus removes them before passing through the finer filters. Of course, the purification range is in the range of 12 to 16 NAS and hence very small particles are not removed in this portion of the system. 
     FIG. 15 shows the efficiency of the rare earth magnetic filter and how its capture rate raises in inverse proportion to the flow velocity. Also, the magnetic force by the magnet raises in inverse proportion to the square of the distance between the magnet and the particles. 
     The family of curves shown in this figure indicate the efficiencies with respect to these two characteristics. The spacing is indicated on the absessa, while the efficiency is indicated on the ordinant. Thus by using a high flow velocity of 240 liters per minute and a gap of five millimeters, it is possible to remove 90% of the larger particles, as well as particles which may be large but have low density. By utilizing this arrangement, the lives of the bag filters  132  and the deep level filter  137  can be prolonged considerably, for example, to two to six months in each case. Thus, this system provides very good filtration as well as long life. 
     FIG. 16 shows the purification ability of the bag filters  132 . As may be seen, they are particularly efficient in removing particles of the size of 50 μm or larger and even have a good efficiency on smaller size particles. Also, because of the high efficiency of the bag filters even with very small particles, this means that the deep filter  137  can be operated for long periods without servicing, even though it is removing extremely small particles. 
     The efficiency of this deep level filter is shown in FIG.  17  and it will be seen that it is extremely efficient and thus coupled with the efficiencies of the other filters provides not only good filtration capability but very long life without servicing. 
     There is also provided an arrangement that facilitates cleaning of the bag filters  132 . Because of their nature, the grinding chips and cuttings will collect on the inner surface of the bag filters and form a cake which may get to 10 mm thick or even thicker. This makes it very difficult to drain the filters and also to clean them. Thus, in order to provide cleaning and breaking up of these congealed deposits, a cleaning system is incorporated that will be described by reference to FIG.  12 . 
     In order to provide this cleaning, the on/off valve  138  on the discharge side of the system is closed and the valve  151  is opened. In addition, there is provided a high pressure air source such as a factory air line, indicated at  164  in FIGS. 2 and 12 that communicates with the inlet sides of these bag filters through a conduit  165 . Shut off valves  166  and  167  are provided in the line  166  as well as an oil separator  167  that separates any oil from the high pressure air line. 
     When the pressure is exerted and the residue is broken up, it will then be forced out of the discharge lines  134   a ,  134   b  and  134   c  and into the discharge line  153 . By opening the valve  151 , the diffuser nozzle  152  can deliver the sediment particles back to the storage tank  51  where they can be easily removed. The diffuser  152  will provide a collecting function to avoid disbursement of these particles and facilitate their collection. 
     Thus, from the foregoing description, it should be readily apparent that the described construction provides a very effective filtration system that will filter coolant for machining operations and which will operate for long time periods with minimum servicing and with minimum diminution of efficiency. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.