Abstract:
An apparatus and method for recirculating machine tool coolant in which coolant and entrained debris flowing in a shallow stream trough are raised to a higher level by rotation of a bladed wheel in a housing arranged to receive the liquid flow stream. Coolant and debris is then directed down at a magnetized body in a plunging discharge to bring ferrous debris into contact with an upwardly facing surface of the magnetized body. The coolant and nonferrous remaining entrained debris is collected in a tank and pumped back to the filter apparatus by a chopper pump which has a hardened impeller having cutting edges cutting up the remaining debris as it is pumped by the impeller.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. provisional Ser. No. 60/366,807, filed Mar. 22, 2002 and is a continuation in part of U.S. Ser. No. 09/498,178, filed Feb. 4, 2000 now U.S. Pat. No. 6,705,555. 

   BACKGROUND OF THE INVENTION 
   This invention concerns the return of machine tool coolant to a filter apparatus. It is common practice in machine tool installations to collect the coolant draining from the cutting tools and the chips entrained therein in trenches or troughs extending below the machine tools, the drained coolant flowing down the trough to be collected in a sump from where it is pumped back to a filter apparatus. 
   As described in EP 1122024, industry trends have resulted in quite shallow depth above grade troughs being used to collect the coolant and chips. 
   The lift apparatus described and claimed in that patent was invented by the inventor named in this application to enable coolant in shallow streams to be lifted and collected in a tank so as to be able to be pumped to filter apparatus by a conventional pump. 
   Another problem has been encountered in such installations, in that relatively large steel or other ferrous metal objects occasionally fall into the trough, such as broken cutting tools, large bolts, or other machine parts, etc. These objects can cause damage to pumps, blockage in the piping, etc., particularly where aluminum chips are being generated and the equipment is designed to handle only aluminum turnings and chips. 
   The lift apparatus described in EP1122024 is very effective at removing large objects from the trough along with the chips and coolant, and depositing the same in a collecting tank. 
   It has heretofore been proposed by the present inventor to use a chip shredder conveyor between the lift station and a collector tank to reduce the size of the chips prior to pumping the coolant and chips from the collector tank back to the filtration apparatus. These conveyors have the ability to chop the chips that often form to be of a smaller size to prevent blockages and to achieve improved performance of the filter equipment. However, such conveyors do not operate reliably, particularly when large balls of chip turnings are present, which sometimes occurs. 
   U.S. Pat. No. 6,406,635 describes locating an inducer chopper in the inlet of a pump to chop the chips to a smaller size prior to pumping the same. This arrangement is limited in the size of objects which can be handled. The pump itself has a recessed impeller to avoid the wearing contact of chips with the impeller surfaces. This results in low pumping efficiency since it relies on induced vortices to create pumping action rather than direct pumping action by the impeller. 
   U.S. Pat. No. 3,973,866 describes a chopper pump in which cutting edges on the impeller blades are used to cut particles in the pumped liquid, and also includes a rotary tool ahead of the impeller to slice larger solid particles prior to entering the pump. 
   Large steel objects present a hazard to such conveyors and pumps and the associated piping. 
   It is the object of the present invention to provide a method and apparatus for efficiently and reliably recirculating coolant liquids in which chips and occasionally present items of ferrous metal debris to filtration apparatus from a shallow depth flow of machining coolant with equipment which can operate for long periods without replacement. 
   It is a further object to provide a method for reliably removing ferrous debris contained in shallow streams of machine tool coolant. 
   SUMMARY OF THE INVENTION 
   The above recited objects and other objects which will be understood upon a reading of the following specification and claims are achieved by causing the machine tool coolant with the entrained debris to be collected in an above grade tank to a great level than the depth of the coolant. 
   This is preferably done by the sweeping up the coolant and entrained debris in the shallow flowing stream to be slung over a weir edge by rotation of a wheel having tangential blades moving in the same general direction as the stream flow. An upwardly and reversely extending wall extends over the wheel to guide the movement of the coolant and entrained debris over the weir edge. 
   A discharge chute receives the coolant slung over the weir edge, redirecting the coolant to create a plunging flow of coolant against an upwardly facing magnetized body located below the level of the weir edge, the magnetized body upward facing surface impacted by the plunging coolant flow. The impingement of the coolant flow against the face of the magnetized body brings any ferrous debris items into contact with the surface and redirects the coolant into a collection tank having a sloping bottom extending to a lower well space. Any ferrous metal debris items impacting the magnetized body are captured by magnetic attraction therebetween to attract and hold the same. 
   The coolant and other nonferrous entrained debris is deflected by the magnetic body and cascades down into a collector tank having sloping walls leading to a bottom well space. A chopper pump having an impeller with cutting edges is mounted above the bottom well, and draws coolant and debris into a disintegrator tool which reduces the size of large debris such as turning balls, and subsequently cutting the nonferrous chip debris to smaller size by the cutter blades of the pump impeller. The chopper pump impeller is hardened to allow direct pumping contact with the coolant and chips to be able to efficiently pump the coolant and reduced size debris to a filter apparatus, where the coolant is filtered and returned to the machine tool installation for reuse. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an end view of an apparatus according to the present invention. 
       FIG. 2  is a side elevational diagram of the lift station forming a part of the present invention. 
       FIG. 3  is a side view of the lift station forming a part of the present invention. 
       FIG. 4  is a normal detailed view of the magnetized body and shed plates shown in  FIG. 3 . 
       FIG. 5  is a partially broken away perspective view of the chopper pump shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION 
   In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
   Referring to the drawing figures, the apparatus according to the present invention includes a lift station  10  as described in EP 1122024. 
   The coolant lift station  10  includes a housing  12  and a bladed wheel  14  rotatably mounted therein, driven by a motor  16  ( FIG. 3 ) and right angle drive (not shown). 
   The downstream end of a gravity trough  18  contains a shallow flowing stream of drained coolant collected from a machine tool installation  19 . The gravity trough has a downwardly sloping bottom  20  and is connected to an inlet flange  22  at the right side of the housing  12 . 
   The housing  12  has an inlet opening  24  receiving the coolant and entrained chips and other debris flowing in the shallow depth stream, typically only a few inches deep. 
   The bottom wall  26  of the housing  12  is also inclined downwardly to keep the coolant flowing into the housing interior, where a series of blades  28  are mounted to a hub here comprised of a drum  30  fixed on a rotatable axle shaft  32 . 
   The blades  28  are welded or bolted to angle pieces  27  welded to the drum  30 , optionally having interposed resilient sheets  29  in order to allow deflection when a large object enters the housing  12 . The blades  28  may be constructed of ¼ inch thick sheet steel to be substantially rigid. Alternatively, thinner gauge spring steel or blue steel material can be used which will be deflectable without the interposed resilient sheets  29  to achieve the same result. 
   The blades  28  extends outwardly from the drum  30 , in a direction tangential to the axis of rotation defined by the axle  32 , and in a direction opposite to the direction of rotation, i.e., are backwardly raked to be oriented in a trailing direction. The backward rake of the blades  28  is believed to assist in obtaining improved upward slinging of the coolant and entrained debris from the blades  28  as they accelerate the coolant by the development of centrifugal force to a velocity sufficient to reach a weir edge  40 . 
   Since there is an inherent unequal distribution of coolant being moved by the various blades  28 , it has been found that reasonably smooth rotation is achieved by a set of eight blades as shown, although fewer or more could be used. 
   The blades  28  are shaped in close conformity to the cross sectional shape and size of the housing  12 , i.e., in this embodiment the blades are rectangular about 24 inches wide, with only minimal edge clearances, i.e., on the order of ⅛th of an inch between the sides and ends and the adjacent trough walls. The cross sectional shape of the housing  12  in turn is generally matched to that of the trough  18 . 
   Collection troughs  18  are typically square or rectangular in cross sectional shape due to the lack of available clearance in order to maximize flow area. 
   The housing  12  curves upwardly from the bottom wall  26  to a radiused rear wall  34 , extending above the level of the shaft  32 , which extends into an upwardly and backwardly extending segment  36  (which can also incorporate a removable access panel as shown). The inner surface  35  of the wall  34  follows the path of the outer edges of the blades  28  as the wheel  14  rotates. 
   The panel segment  36  and an opposite segment  38  define an exit chute  42  extending to a weir edge  40  over which coolant and debris are slung by rotation of the blades  28 , weir edge  40  at a height well above the level of the trough bottom  20  and housing bottom  26 . 
   The backward inclination of the outlet chute  42  extending back towards the front of the housing  12  is necessary to be generally aligned with the direction that the coolant is thrown off the blades  28  by rotation of the bladed wheel  14 , as a forward inclination defeats upward flow of the coolant even with increased rotational speed. That is, coolant will be thrown backwardly when coming off the blades  28 . 
   A certain minimum speed is necessary greater than the velocity of the flow stream, depending on the lift height required, an outer edge speed of 12–15 feet per second having been found to be sufficient for the application described. 
   The rotating trailing blades  28  overtake the coolant flowing in from the trough  18  and down the inclined housing bottom  26 , and sweeps the coolant forward. This is accomplished without even any momentary interruption of the coolant flow in the trough  18  which could cause the chips to settle out and pile up, causing a rapid build up which might not be cleared away when flow resumes. 
   Initially, the inertia of the coolant causes it to be moved inward along the blade forward surface, i.e., radially inwardly. To limit the extent of this radially inward flow, a large diameter drum  30  is desirable rather than a small diameter shaft. As the coolant captured by the blade  28  is accelerated, centrifugal force subsequently causes radially outward movement of the coolant at an increasing velocity until achieving sufficient outward momentum so as to be slung from the blade  28  in the approximate direction in which the chute  42  extends, i.e., opposite the direction of inflow of coolant into the housing  12 , passing over the weir edge  40 . The trailing orientation of the blades  28  is believed to assist in slinging of the coolant and chips off the blades  28  in the approximate direction in which the chute  42  extends, i.e., opposite the direction of inflow of coolant into the housing  12 , passing over the weir edge  40 . The trailing orientation of the blades  28  is believed to assist in slinging of the coolant and chips off the blades  28  in an upward direction. 
   A forward housing wall  43  extends downwardly and then curves forwardly at its terminal lip  44 . 
   Any slung coolant which does not reach and pass over the weir edge  40  drains down the forward wall  43  and is redirected towards the direction of the stream inflow, with momentum added in the forward direction of rotation of the blades  28 , such as to be more likely to achieve sufficient upward momentum when again thrown off the blades  28  so as to reach the weir edge  40 . 
   Coolant and entrained debris passing over the weir edge  40  enters a redirection discharge chute  46  extending at right angles to be directed into a collection tank  48  disposed alongside. The collection tank  48  has a series of inclined shed plates  50 A, B, C as shown in  FIG. 4  funneling the discharged coolant, chips and other debris in a plunging flow cascading onto the upper face  52  of a magnetized body  54  disposed at the bottom of the shed plates  50 A, B, C. 
   The magnetized body  54  is preferably constructed of a rare earth material to create a very strong magnetic attraction on any ferrous metal item entrained in the plunging coolant, thereby brought into contact with the face  52  thereof. Face  52  is inclined at a shallow angle (≈10°) to the right as viewed in  FIG. 3 . The coolant and other debris is redirected to the right which is open to allow the coolant to cascade down into the collection tank proper  48 , flowing down the sloping bottom wall to a well space  56  at the right in  FIG. 3 . 
   Any ferrous metal items impacting the face  52  are momentarily arrested at the face  52 , which allows the strong magnetic field of the body  54  to capture and securely retain the same. A trap door  64  may be provided for periodic removal of such items. 
   A washer jet manifold  58  may be mounted at the upper side of the collector tank bottom wall  60  supplied with pressurized clean coolant, spraying down the bottom wall  60  to prevent the accumulation of chips or other debris. 
   Mounted above the well space  56  is a chopper pump  62 , driven by an electric motor  66  mounted above the tank  48  and connected by an oil filled tubular housing  68  to the pump. The chopper pump  62  is of a particular design available from Vaughan Co., Inc. Of Montesano, Wash., USA. This designed features an impeller  70  ( FIG. 5 ) of hardened (60 Rockwell C) alloy steel (A5TM A148) which impeller has cutting edges  72  rotated past a cutter bar  74 . In addition, a disintegrator tool  76  is mounted to rotate with the impeller  70  to agitate and break up chips and/or other debris prior to entering the pump. Vaughan pump model VSM-080 has been successfully employed for this purpose. 
   The aluminum chips are easily chopped up by such pump which also efficiently pumps the coolant to the back to the filtration apparatus  78  via an outlet  80 . 
   Chip balls and tangles are easily handled by the agitator tool, which also captures and forces the same into the pump chamber to be cut up by the impeller cutting edges. 
   The impeller preferably spaced above the bottom of the well space  56  in order to reduce the suction to avoid sucking large objects into the pump  62 . 
   An emergency overflow connection  82  can be provided to return coolant to the trough  18 .