Abstract:
A method and apparatus for coolant recovery system is shown. A holding tank is positioned above a cleaning tank. The holding tank receives contaminated coolant from a pre-existing machine coolant tank, and the cleaning tank holds a quantity of relatively clean coolant. Contaminated coolant is pumped into the holding tank and allowed to settle, creating a thin layer of contaminants on top of the coolant. Clean coolant is pumped from the cleaning tank into the holding tank, causing the thin layer of contaminants to drain out of the holding tank via a skim line into a processing zone in the cleaning tank. The processing zone is designed to allow only the coolant portion of the skimmed liquid to pass to the remainder of the cleaning tank. The processed coolant remaining in the holding tank is then pumped back to the machine coolant tank.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to coolant treating, and in particular to both a method and an apparatus for separating and removing lubricating oil and other contaminants from manufacturing machinery coolant.  
         BACKGROUND ART  
         [0002]    Manufacturing machines that cut, drill, turn, and otherwise fashion metal pieces use a mineral oil or similar aqueous-based coolant to prevent overheating of cutting edges and the workpiece. The coolant inevitably becomes contaminated with metal particles, lubricating oil and other contaminants. If they are not removed, these contaminants will clog the coolant delivery system and cause the coolant to decompose and lose effectiveness. The oil, known as tramp oil, and the coolant also tend to emulsify quite readily, so that simple settling methods fail to provide substantial separation of the oil/coolant mixture.  
           [0003]    Several methods have been devised for cleaning oily liquids, but they fail to satisfy the concurrent needs for inexpensive, simple operation and low coolant loss. Filtering methods are not fully effective because the oil and coolant are mechanically emulsified. Centrifugal methods can overcome the emulsification problem, but are relatively expensive to purchase and maintain.  
           [0004]    U.S. Pat. No. 5,795,478 issued to Hirs, discloses an oil extraction system for industrial machining fluid that makes use of an assembly of nested horizontal polymer tubes, through which the machining fluid passes. The tubes are oleophilic, so that tramp oil in the fluid is attracted to the polymer and coalesces into droplets which are then separated from the coolant in a settling tank.  
           [0005]    A commercially available apparatus, using a method similar to the Hirs patent, has multiple separation chambers packed with oleophilic spherical media. The emulsified oil is intended to adhere to the spherical media and coalesce into droplets that rise to the surface to form an oil layer. The unit is intended to run with a continuous, steady input of oily water, and required compressed air to operate, which is not present in every location. Also, the oily water fed to the unit must be pre-filtered before being sent to the separation chambers, to prevent harming the spherical media.  
           [0006]    U.S. Pat. No. 4,422,931 issued to Wolde-Michael, discloses a device for cleaning tramp oil and contaminants from machine coolant. The oily coolant is fed to a first compartment and aerated to cause foaming of the oil, which is well known to hasten separation. The coolant and foamy oil are then fed into a larger main compartment via an inclined quietener baffle that is intended to minimize disturbance of the fluid. Oil is extracted through an outlet placed roughly at the level of the inclined baffle. Coolant exits through a vertical hairpin path having an agglomeration baffle that is intended to remove remaining tramp oil. If flow to the first compartment is interrupted, or when draining the main compartment, the level in the main compartment falls below the oil outlet, so that any remaining oil is sent out the coolant outlet. Rapid emulsification of the oil and coolant while passing through the hairpin path will likely make the agglomeration baffle largely ineffective.  
           [0007]    U.S. Pat. No. 5,458,770 issued to Fentz, discloses another device for cleaning tramp oil and contaminants from machine coolant. This device uses several adjacent chambers separated by vertical rectangular baffles. Each baffle has a single aperture located at or near a corner, and diagonally opposite from the aperture-containing corner on the immediately adjacent baffles. The device is intended to trap the oil in the first chambers, while only coolant is intended to travel completely through the device. The device is continually full of coolant, whether filtering is being performed or not.  
           [0008]    Some of the methods, such as the oleophilic coalescer devices described above, inadvertently promote the growth of anaerobic microbes that remain in the coolant, which can decompose the coolant and produce undesirable odors when the coolant is not used for long periods. Finally, most of the existing methods produce a disposal product that is predominantly made up of coolant, some as much as ninety percent coolant. This means that coolant must be replaced more frequently, raising operating costs. A waste product made up mostly of coolant also means that much more liquid must be disposed of, which creates environmental problems along with higher disposal costs.  
           [0009]    A need exists for a method and apparatus that avoid or overcome the drawbacks of the existing methods and apparatus. A method and apparatus that are simple to understand, and relatively inexpensive both to purchase and to operate are also desirable.  
         DISCLOSURE OF THE INVENTION  
         [0010]    A structure having the desired features and advantages has an upper holding tank positioned above a lower, cleaning tank. Throughout the following discussion and in the claims, the term “line” includes any means used in the art for transporting fluid, which can be flexible where appropriate. Some non-limiting examples are pipes, tubing, and hoses.  
           [0011]    A pump in a pre-existing machine coolant tank is connected to a fill line located in the holding tank, and provides the means for filling the holding tank from the machine coolant tank. A cleaning pump on the bottom of the cleaning tank connects to a clean coolant line that extends into the holding tank with the clean coolant line&#39;s outlet at a predetermined distance from the bottom of the holding tank. A skim line is also located in the holding tank, with its inlet located below both the fill line outlet and the clean coolant line outlet. The skim line empties into a processing zone within the cleaning tank, where solid contaminants are removed and emulsified oil is coalesced before the skimmed liquid enters the rest of the cleaning tank. The oil then settles out on top of the coolant. A return pump sends the processed coolant from the holding tank back to the pre-existing machinery coolant tank.  
           [0012]    In a method for using the apparatus, contaminated coolant from the pre-existing machine coolant tank is pumped into the upper coolant tank. Preferably, air is allowed to mix with the oily coolant during pumping to promote the generation of an oil-based foam for more rapid oil/coolant separation. The contaminated coolant is allowed to settle, and contaminants that settle on top of the coolant are skimmed off into the processing zone. The remaining processed coolant in the holding tank is then pumped back to the pre-existing machine coolant tank for further use. Filtering can be optionally employed on the coolant returned to the machine coolant tank. Collected contaminants are periodically removed from the cleaning tank for disposal. When aeration is employed, an additional optional step can be performed, wherein clean coolant is pumped into the holding tank while the holding tank is being filled with the contaminated coolant so that liquid and foam are skimmed off to the processing zone. 
       
    
    
       [0013]    Additional features and advantages of the invention will become apparent in the following detailed description and in the drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective view of a coolant recovery apparatus of the invention when in use, with pre-existing manufacturing machinery shown in dotted lining.  
         [0015]    [0015]FIG. 2 is a cross-sectional front elevation thereof, taken along the sight lines indicated in FIG. 1, without liquid in the system, and with the front walls in the holding tank filtering zone and the cleaning tank processing zone removed to show additional internal elements.  
         [0016]    [0016]FIG. 3 is a top plan view of the holding (upper) tank during use.  
         [0017]    [0017]FIG. 4 is a top plan view of the cleaning (lower) tank during use. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    As shown in FIG. 1, the coolant recovery system  11  includes a holding tank  13  mounted above a cleaning tank  15 . The holding tank  13  is designed to stack on top of the cleaning tank  15 , and can be removed to allow cleaning and access to the inside of the cleaning tank  15 . The cleaning tank  15  is filled with clean coolant prior to the first use of the system  11 .  
         [0019]    A low pressure pickup pump  19  is located within the pre-existing machine coolant tank  17 . The pickup pump  19  has an inlet tube  21  that can be rotatably adjusted to allow the tube&#39;s inlet to be set over a range of heights. This rotatable feature serves two purposes: it prevents sending more liquid to the holding tank  13  than the tank can hold, and by proper adjustment of the inlet  21  air can be drawn into the pump  19  along with the liquid to aerate the oily contaminant, causing it to foam. Some machines will have more than one machine coolant tank. In this case, each tank would preferably have its own  
         [0020]    As shown in FIGS. 1 and 2, a line  23  connects the pickup pump  19  to a fill line  25  located in the holding tank. The fill line  25  terminates in a U-bend  27  with the outlet  28  at a predetermined height. In the case of multiple machine coolant tanks, each pump would connect to a separate fill line. Identical fill lines  25 B and  25 C with identical U-bends  27 B and  27 C can be provided for connection to additional machine coolant tanks. Any further description will reference only the first fill line  25  and its associated elements, but the description applies to the duplicate lines as well.  
         [0021]    A cleaning pump  29  is located in the cleaning tank  15 , and provides means for transferring coolant to the holding tank  13  via a clean coolant line  31  having an outlet  33  at a predetermined height above the fill line outlet  28 . The coolant flow rate is controlled by a valve  35  or other well-known flow control means, such as a restriction orifice. A baffle  37  spanning the width of the cleaning tank helps prevent contaminants floating on the coolant from entering the cleaning pump  29 , while an aperture  38  allows coolant to enter the cleaning pump  29  from the cleaning tank  15 .  
         [0022]    A skim line  39  is also located within the holding tank  13 , with its inlet  41  at a predetermined height below the height of the fill line outlet  28 . The skim line empties into a processing zone  43  located in the cleaning tank  15 . The processing zone  43  is physically separated from the remainder of the cleaning tank  15  except for an aperture  45  located at the bottom of the processing zone  43 . A filter  47  fills the bottom of the processing zone  43  to a height above the top of the aperture  45 . The filter  47  is made of a material such as steel wool suitable for catching particulates that collect in the processing zone. The filter  47  also reduces flow turbulence and attracts the re-emulsified oil and causes it to coalesce. Both of these affects promote more rapid separation of the oil and coolant in the cleaning tank  15 .  
         [0023]    A filtering zone  49  is located within the holding tank  13 , but is physically separated from the rest of the tank  13  except for an aperture  51 . A return pump  53  is located in the filtering zone  49 , and pumps processed coolant through a filter  55  and a return line  57  back to the machine coolant tank  17 . The return pump  53  can be omitted and the coolant returned to the machine coolant tank  17  by natural flow (i.e. occurring strictly by gravitational force), but the filter  55  would need to be omitted or designed for very low pressure drop.  
         [0024]    Entrained oil and other lighter-than-coolant contaminants will form a separate layer floating on top of the coolant in the cleaning tank  15 . A valve  59  is provided for disposal of the collected contaminants. The liquid removed from the cleaning tank  15  will be almost completely made up of lighter-than-coolant contaminants, with relatively little entrained coolant. A waste product containing only ten percent coolant is typical. This permits significantly less frequent disposal, thereby reducing disposal costs.  
         [0025]    An overfill line  61  is installed on the cleaning tank  15  to drain off any excess coolant to the machine coolant tank  17 . The overfill line  61  connects near the bottom of the cleaning tank  15  to prevent sending lighter-than-coolant contaminants present in the cleaning tank  15  to the machine coolant tank  17 .  
         [0026]    As previously discussed, the holding tank  13  can be removed from its location above the cleaning tank  15  to allow both tanks to be accessed and cleaned. A drain valve  63  is provided on the bottom of the holding tank  13  to allow the tank to be emptied for easier removal, and to allow a quick flush-out of the holding tank  13 . The drain valve  63  can also be used to return coolant to the machine coolant tank  17  by gravity flow. Preferably, the drain valve  63  should connect to the interior of the holding tank  13  through a vertical line having an inverted inlet (not shown), to prevent both solid particulates at the bottom of the liquid and lighter-than-coolant contaminants at the top of the liquid from being drained off.  
         [0027]    Operation of the coolant recovery system is simple and straightforward. The process begins with the holding tank  13  substantially empty and with the cleaning tank  15  filled with clean coolant. The pickup pump  19  is turned on and run for a predetermined time to fill the holding tank  13  with contaminated coolant to a level just below the skim line inlet  41 . As previously discussed, the pump inlet  21  is preferably adjusted to allow air to be drawn in with the contaminated coolant, so that the oil will form a foam that will separate more quickly from the coolant. During this step, oil will settle out from the coolant and form a layer on top of the coolant. This is especially true when the oil is aerated into a foam.  
         [0028]    The second step is optional, but it is preferred that this step be performed, especially when a shorter overall operation time is desired. The step begins when most of the holding tank  13  has been filled, for example when the tank is filled to roughly seven-eighths of the height of the skim line inlet  41 , measured from the bottom of the holding tank  13 . At this point, the cleaning pump  29  is turned on, and a clean coolant flow is added via the clean coolant line  31  to the contaminated coolant. The holding tank is filled to the height of the skim line  39 , so that liquid flows into the skim line at the skim line inlet  41  and flows into the processing zone  43 . The flow is continued until the separated oil has been drawn off by the skim line  39 . Both the machine coolant pump  19  and the cleaning pump  29  are then shut off. The point at which the pumps are shut off can be determined manually, or automatically.  
         [0029]    In the next step, the contaminated coolant is left standing in the holding tank  13  for a predetermined time, during which the coolant and the immiscible contaminants settle out into separate layers. Particulates and other heavier-than-coolant contaminants will settle at the bottom of the tank, while lighter-than-coolant contaminants such as entrained oil will collect on top of the coolant. When the predetermined time (typically about 30 minutes) has elapsed, the next step is performed.  
         [0030]    In the fourth step, the cleaning pump  29  is turned on and run for a predetermined time. As the holding tank  13  fills with coolant from the cleaning tank  15 , the level of the coolant in the holding tank  13  will rise above the skim line inlet  41 , and liquid will flow down the skim line  39  into the processing zone  43  in the cleaning tank  15 . At first, this liquid will consist mostly of the lighter-than-coolant contaminants, but preferably the cleaning pump  29  continues to run until only clean coolant flows into the processing zone. As in the second step, he point at which the pumps are shut off can be determined manually, or automatically.  
         [0031]    An alternative arrangement is envisioned for the apparatus, wherein the clean coolant line  31  can be omitted, and the clean coolant pumped into an opening at the bottom of the holding tank  13 . This has the advantage that disturbance of the top surface of the liquid in the holding tank  13  is kept to a minimum, while a certain amount of disturbance is unavoidable from pouring the coolant down into the holding tank  13  from the clean coolant line outlet  33 . However, this arrangement would make additional equipment necessary, such as a check valve or filter downstream of the flow control valve  35 , to prevent particulates from backflowing through the valve and into the pump. This arrangement would also result require more frequent cleaning of the equipment. Therefore, the simpler arrangement shown in the figures is preferred.  
         [0032]    In the final step, the return pump  53  is turned on and pumps the cleaned coolant in the holding tank  13  back to the machine coolant tank  17  via the tubing  57 . The individual steps can be performed manually, or can be automatically performed by any known control scheme. A bank of timers  65  is preferred for simplicity and low cost.  
         [0033]    Both the apparatus and the method have several advantages over the existing art. First, the apparatus is simple to construct, inexpensive, and easy to understand and operate. The two tanks can be easily separated, and all filter elements easily accessed and removed, so that the apparatus can be cleaned. The combination of the skim line  39  and the overfill line  61  make the system automatically self-draining back to the machine coolant tank  17 , preventing the system from being accidently overfilled and spilling coolant. Since the control functions can be performed by turning pumps on and off for predetermined times, automatic control equipment can be very simple and inexpensive. The coolant in the tanks is exposed to air, preventing the growth of anaerobic microbes. Finally, the method and apparatus produces a waste that contains significantly less entrained coolant than existing methods and apparatus, thereby reducing the cost of coolant replacement and waste disposal.  
         [0034]    The invention has been shown in only one embodiment, although other embodiments are described. It should be apparent to those skilled in the art that the invention is not limited to these embodiments, but is capable of being varied and modified without departing from the scope of the invention as set out in the attached claims.