Abstract:
A filtration system for metalworking fluids has panel filter elements arranged in cells in which the filter frames and panels are approximately parallel to one another. The filter frames are disposed such that the filter surfaces are oriented at an acute angle with respect to the longitudinal axis of the drag-out tank within which they are installed. The filter elements are constructed by affixing a microscreen filter to a wire mesh support structure. The wire mesh structure provides as much support as the perforated plates of the prior art, while featuring significant gains in effective filter area when compared with perforated plate constructions.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to a filtration system adapted for industrial application, and in particular to a filtration system and automatic settling tank combination designed to remove industrial contaminants, and is more particularly directed toward a filtering system adapted to remove particulates from recirculated fluids used in the metalworking industry for metalworking processes. 
     DISCLOSURE INFORMATION 
     It is often necessary in metalworking operations to provide a lubricating fluid at the junction between workpiece and tool. In addition to a lubricating action, the fluid acts to cool both the workpiece and tool to prevent overheating, aids in protecting the workpiece and machine components from corrosion, and also carries away the metal chips and other byproducts of the process away from the work area. 
     In most large-scale metalworking facilities, it is common practice to consolidate fluid delivery systems into centralized units. This approach consistently provides fluid at specified concentration, temperature, and pressure to each machine tool, yielding an economical means for meeting present day demands for ever tighter tolerances and finishes on machined components. 
     Due to the initial purchase cost of the fluids, the cost of disposal when rendered unusable, and the environmental consequences of disposal, metalworking facilities are inherently motivated to maximize the useful life of these fluids. One of the main prerequisites for fluid longevity is the filtration performance delivered by the design of these central systems. In order to facilitate optimum fluid life, chips and particulate contamination in the fluid must be removed. Metal chips and particles in the fluid will interfere with proper recirculation and promote undesirable biological activity, and these contaminants in the fluid would have an adverse effect on both tools and workpieces if an attempt were made to recirculate this unfiltered fluid. 
     Consequently, a need arises for an effective filtering system for machine tool environments that features high performance filter materials and an optimum arrangement of elements providing ease of servicing and replacement without loss of production time. 
     SUMMARY OF THE INVENTION 
     These needs and others are satisfied by the filtration system of the present invention, in which a plurality of frames of filter elements are arranged in cells in which the filter surfaces of each member frame are approximately parallel to one another. The cell is disposed such that the filter surfaces of each member frame are oriented at an acute angle with respect to the longitudinal axis of the drag-out tank within which they are installed. 
     The filter elements adapted for use in the system of the present invention are constructed by affixing a microscreen filter to a wire mesh support structure. The wire mesh structure provides as much support as the perforated plates of the prior art, while featuring significant gains in effective filter area when compared with the perforated plate embodiment. 
     Further objects, features, and advantages of the present invention will become apparent from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a filtration system suitable for use with metalworking fluids according to the present invention. 
         FIG. 2  is a cutaway side view of a drag-out tank illustrating an arrangement of filter cells in accordance with the present invention. 
         FIG. 3  is a top view of a filter system illustrating the arrangement of the filter frames in an exemplary cell embodiment of the present invention. 
         FIG. 4  is an elevational view of a filter frame according to the present invention. 
         FIG. 5  depicts a stylized cutaway view of a single filter frame. 
         FIG. 6  shows the frame of  FIG. 4  in perspective view. 
         FIG. 7  is an enlarged elevational view of a single filter frame illustrating a preferred mounting method for the filter elements onto the frame. 
         FIG. 8  provides a detail view of a filter support plate. 
         FIG. 9  in a top view of a portion of a drag-out tank more closely illustrating the orientation of the filter frames of a cell with respect to the tank&#39;s longitudinal axis, and the orientation of the pipe network for delivery of a filter aid powder. 
         FIG. 10  is an elevational view in cut-away that illustrates filter frame installation to a receiver. 
         FIGS. 11 through 13  depict progressively larger filter frames that can accommodate an increased filtration area. 
         FIG. 14  is a bottom view of a portion of a filter frame showing the mounting flange and the placement of the internal support plates. 
         FIG. 15  is an enlarged view of area B from  FIG. 14 . 
         FIG. 16  is a further enlarged view of frame portion C from  FIG. 15 , indicating a sealing method that prevents any bypassing of unfiltered fluid. 
         FIG. 17  depicts the components of a filter element of the prior art. 
         FIG. 18  depicts the components of a filter element in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a metalworking fluid filtration system according to the present invention. Contaminated fluid from the machine tools on the shop floor is delivered to the system through inlet pipe  1 . The fluid is dropped into drag-out tank  12  where the shavings, particulates, and heavy contaminants settle, and are eventually removed by drag conveyor  13 . As described below, particulate contaminants that stay suspended due to size and level of turbulence are captured by a microscreen filter and the filter matrix formed on the microscreen. 
     The heart of the filtration process is filter  6 , which will be discussed in more detail subsequently. The microfiltration action is generally enhanced by a filter aid (such as powdered cellulose, perlite, or diatomaceous earth, for example) that is stored in bin  2 , and dropped into slurry tank  3  at the beginning of each filtration cycle through a volumetric feeder. The filter aid is delivered to the filter  6  by a slurry pump  5 , and acts to form a matrix “filter cake” which captures suspended contaminants. When no longer effective, the filter cake is removed from the surface of filter  6  by backflushing, and allowed to drop to the bottom of the drag-out tank  12 . Fragments of filter cake are removed from the drag-out tank  12  by conveyor system  13 , which is interlocked to operate intermittently when the filter element  6  is backflushed, separating the spent filter cake laden with captured particles. System pump  7  provides clean fluid for recirculation to the shop floor through outlet pipe  11 . 
     In order that the periodic backflushing cycles will not interfere with delivery of clean fluid, auxiliary clean tank  9  is provided. Auxiliary clean tank  9  includes an overflow provision  10  to maintain system balance. When filter backflushing is in progress, system valves  8  are configured to draw clean fluid from auxiliary clean tank  9  instead of from filter  6 . 
       FIG. 2  is a cutaway side view of a drag-out tank  12  illustrating filter  6  of  FIG. 1  as an arrangement of filter cells  21  atop suction headers  92  in accordance with the present invention.  FIG. 3  is a top view of a filter system illustrating the arrangement of filter frames  31  in an exemplary cell embodiment. As can be appreciated from an examination of  FIGS. 2 and 3 , a system in accordance with the present invention contemplates disposing a plurality of filter frames  31  to form cells  21  in which each frame  31  of a cell  21  is arranged approximately parallel to the other frames  31  in the cell  21 , and the frames  31  themselves are disposed such that the filter surfaces of the frames  31  are aligned at an angle of approximately 45 degrees with respect to longitudinal axis A of drag-out tank  12 . This orientation of frames  31  produces a two-fold beneficial effect. In the first instance, the parallel relationship between the frames in each cell allow a much greater total filter surface area. Moreover, the movement of conveyor  13  agitates the dirty coolant and causes the coolant to flow along the filter panels, while promoting the settling of contaminants on the floor of the tank, rather than upon the filters. This promotes efficient filtration. The present filter system is much more efficient than that disclosed in U.S. Pat. No. 5,221,469, which uses star-shaped filtration modules which are more prone to uneven exposure and buildup of dirt upon the filter panels, with a corresponding loss of filtration efficiency. 
       FIG. 4  is an elevational view of frame  31 , while  FIG. 6  shows frame  31  in perspective, along with placement of internally disposed support plates  81  which provide structural integrity and internal support for the filter elements themselves, which will be discussed in greater detail below.  FIG. 6  also illustrates the mounting flange  61  designed for attachment to the receiver  51  of  FIG. 5 .  FIG. 5  depicts a stylized cutaway view of a single frame  31 , exposing support plate  81  placement, as well as illustrating the mating flanges  52  disposed along the receiver  51  to support the remaining frames of filtration cell  21 . 
       FIG. 7  is an enlarged elevational view of a single frame  31  illustrating a preferred mounting method for the filter elements onto the frame. Filter elements  161  and  162  are placed in position over support plates  81  and secured in position with bolts  71  that are run through a bezel  72  into threaded mounting holes in frame  31 .  FIG. 8  provides a detail view of support plate  81 , preferably constructed from stainless steel, and including a plurality of openings  82  disposed along it. The openings  82  ensure that the support plate will provide the required support for the filter elements themselves, but will not interfere with fluid flow within the frame. Note that fluid need not flow through openings  82  in order to be filtered. 
       FIG. 9  is a top view of a portion of the drag-out tank  12  more closely illustrating the orientation of the frames  31  with respect to the longitudinal axis of drag-out tank  12 . Also visible in this view are the delivery nozzles  91  for the filter aid.  FIG. 10  is an elevational view in cut-away that illustrates frame installation to the collector (or receiver)  51 , as well as the connection of the receiver  51  to the suction header  92 . Control valves can isolate an individual suction header  92  so that a cell can be removed without affecting system operation. 
     Of course, drag-out tanks are available in a variety of capacities and depths.  FIGS. 11-13  depict progressively larger filter frames that can accommodate increased filtration area. For example, the frame of  FIG. 11  is a single frame with four filter elements (two on each side), with each element being approximately 24 inches square. Because in a preferred embodiment each filter provides 4 square feet of filter surface, this is called a 16 square foot frame.  FIG. 12  shows a four element frame with 32 square feet of filter surface, and  FIG. 13  depicts a four-element frame with 48 square feet of filter surface. 
       FIG. 14  is a bottom view of a portion of a frame  31  showing mounting flange  61  and the placement of the internal support plates  81 . Filter elements  161  and  162  are bolted to opposing faces of the frame  31  to form a panel filter having openings on two sides.  FIG. 15  is an enlarged view of area B from  FIG. 14 . In this view, one can distinguish the individual components of a filter element  74  as a microscreen filter  161  affixed to a support mesh  162 .  FIG. 16  is a further enlarged view of frame portion C of  FIG. 15 . In this view, the bezel  72  that holds filter elements  161  and  162  in place can be seen, as well as mounting bolt  71 . 
     As shown in  FIG. 17 , prior art filter elements used in metalworking coolant filtration systems have generally been fabricated as a laminate of a microscreen filter material  171  fuse bonded to a nominal 0.100 inch thick stainless steel perforated sheet  172 . The perforated sheet  172  has ⅜ inch diameter perforations,  173 , staggered on centers of 7/16 and ½ inch, yielding an open effective area of approximately 51.6%. 
     For a filter panel or element in accordance with the present invention, as depicted in  FIG. 18 , the replacement of the perforated sheet backing  172  ( FIG. 17 ) with wire mesh screen  162  yields a substantial increase in effective area. This provides either increased performance or comparable performance in a smaller structure. For example, a 4×4 mesh stainless steel screen of 0.062 inch diameter wire yields, by contrast, approximately 95% open area. In a preferred embodiment, each of said microscreen elements  161  comprises a metallic sheet having a uniformly distributed plurality of openings, with each of the openings having a diameter ranging from about 0.005 inches to about 0.010 inches, and with the openings being disposed on centers of about 0.010 inches. 
     It should be noted that the prior art utilized primarily the following microscreen selections with their respective open areas. The following table (Table I) provides the resultant effective area of the prior art septum and the resultant effective area of the inventive filter. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Microscreen 
                   
                 % Open Area 
                   
                 % Open Area 
                 Inventive 
               
               
                 .010 Pitch 
                   
                 Prior Art Backing 
                 Prior Art 
                 Improved 
                 Resultant 
               
               
                 Oriented 90° 
                 % Open 
                 Plate ⅜ φ Holes 
                 Resultant 
                 Support 4 × 4 S/S 
                 Effective 
               
               
                 Hole φ 
                 Area 
                 on ½″ Centers 
                 Open Area 
                 Mesh 
                 Area 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 .005 
                 13.2% 
                 52% 
                 6.86% 
                 95% 
                 12.54% 
               
               
                 .006 
                 14.6% 
                   
                 7.59% 
                   
                 13.87% 
               
               
                 .007 
                 19.8% 
                   
                 10.29% 
                   
                 18.81% 
               
               
                   
               
             
          
         
       
     
     Those skilled in the art will appreciate in view of this disclosure that the particular process utilized to affix microscreen  161  onto the mesh screen backing material  162  may vary based upon the material selection of the microscreen and the mesh backing. These processes may include spot welding, laser welding, brazing, fuse bonding, electron beam welding, soldering, or other bonding processes known to those skilled in the art and yield acceptable results and quality. 
     There has been described herein a filtration system that offers distinct advantages when compared with the prior art. It will be apparent to those skilled in the art that modifications may be made without departing from the spirit and scope of the invention.