Abstract:
A preferred embodiment of a workpiece finishing system impinges a grit and fluid slurry onto a workpiece and then recycles the slurry for subsequent reuse. In another aspect of the present invention, a recovery tank is used for generally settling and concentrating the grit in the slurry, and for separating out a portion of the fluid from the grit. A further aspect of the present invention provides a venturi-type nozzle for expelling the grit and fluid onto a workpiece, wherein the nozzle has a selectively movable inlet thereby varying the slurry concentration properties of the nozzle.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to a workpiece finishing system, and more particularly to a system for impinging and recycling a grit and fluid slurry used to finish a workpiece. 
     Traditionally, metal workpieces must be belted, polished and then buffed prior to plating. The conventional wisdom has been that any “item to be plated, if the plating is to be a bright plate, must be highly polished. The plating can be no brighter than the surface to which it is applied.” C. W. Ammen,  Electroplater&#39;s Handbook , 1986, page 69, published by Tab Books Inc. The belting employs a course grit belt, or wheel, which must be replaced approximately every five or six pieces. The polishing and buffing wheels also require extensive manual preparation, set up and replacement. The belting, polishing and buffing steps are typically performed by hand and must be very meticulously and uniformly done to ensure a bright base surface. However, the workplace is often extremely contaminated with oil and the like, and the operations are often tedious and time-consuming. Accordingly, part-to-part inconsistencies are prevalent, and labor and scrap costs are significant. Furthermore, an animal tallow, fatty acid and wax grease-stick compound is used on the polishing wheels to retain grit. A subsequent high temperature or acidic washing step is often employed in an attempt to remove the polishing compound, but with limited success. Any polishing compound remaining on the workpiece during plating leads to unacceptable plating adhesion to the base material, thus causing a very high scrap rate during plating. 
     It is also know to use a sand and water slurry to clean, but not finish, metal workpieces. An exemplary water and sand abrasive system is disclosed in U.S. Pat. No. 4,817,342 entitled “Water/Abrasive Propulsion Chamber” which issued to Martin et al. on Apr. 4, 1989. It is common for such systems to simply discard the water and inexpensive sand after each use. Moreover, the sand is not of a fine enough grit and sufficient hardness to adequately finish a workpiece for subsequent plating or for grit reuse. 
     Moreover, various slurry recycling systems have been attempted. For example, reference should be made to the following U.S. Patent Nos.: U.S. Pat. No. 5,791,970 entitled “Slurry Recycling System for Chemical-Mechanical Polishing Apparatus” which issued to Yueh on Aug. 11, 1998; U.S. Pat. No. 5,664,990 entitled “Slurry Recycling in CMP Apparatus” which issued to Adams et al. on Sep. 9, 1997; and U.S. Pat. No. 5,477,844 entitled “Slurry Recovery System for a Wet Cutting Saw” which issued to Meister on Dec. 26, 1995; all of which are incorporated by reference herewithin. However, none of these traditional systems exhibit the quick, efficient, cost effective and high performance characteristics of the present invention which is suitable for use on a variety of workpieces. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a preferred embodiment of a workpiece finishing system impinges a grit and fluid slurry onto a workpiece and then recycles the slurry for subsequent reuse. In another aspect of the present invention, a recovery tank is used for generally settling and concentrating the grit in the slurry, and for separating out a portion of the fluid from the grit. A further aspect of the present invention provides a venturi-type nozzle for expelling the grit and fluid onto a workpiece, wherein the nozzle has a selectively movable inlet thereby varying the slurry concentration properties of the nozzle. Still another aspect of the present invention provides a liquid overflow shelf above a set of baffles in the recovery tank for assisting in the separation of the grit and a portion of the liquid, whereby the liquid can be recycled without grit damaging the high pressure pumping device. A method of operating a workpiece finishing system suitable for recycling a grit and fluid slurry is also provided. 
     The present invention workpiece finishing system is advantageous over conventional devices in that the present invention does not require the expensive, labor intensive and scrap inducing polishing and buffing steps prior to plating. It is also envisioned that the belting operation may be minimized or even potentially deleted with the present invention. The very fine size and significant strength of the preferred carbide and water slurry, in combination with the impinging angles and high pressures, provide a dull matte-type workpiece finish which is not bright. Notwithstanding, it has been found that this matte finish of the present invention provides a superior bright mirrored appearance to the final plated workpiece as compared to conventional belted, polished and buffed workpieces. The part-to-part consistency and repeatability is also tremendously improved. Furthermore, a polishing compound is not necessary by use of the present invention, thereby eliminating the conventional washing operation and significantly reducing over all cycle time and/or plating scrap rates. The slurry separation and recycling devices and function of the present invention allows the use of the carbide and water slurry to be cost effective in a production environment, considering the high cost of the carbide grit. Moreover, the present invention recovery tank and nozzle constructions minimize maintenance while encouraging flexible usage for different workpiece designs. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view showing the preferred embodiment of a workpiece finishing system of the present invention; 
     FIG. 2 is a side elevational view showing a recovery tank employed in the preferred embodiment workpiece finishing system; 
     FIG. 3 is a perspective view showing the recovery tank employed in the preferred embodiment workpiece finishing system; 
     FIG. 4 is an exaggerated diagrammatic view showing a workpiece and nozzle employed in the preferred embodiment workpiece finishing system; 
     FIG. 5 is a schematic view showing the fluid control system employed in the preferred embodiment workpiece finishing system; 
     FIG. 6 is a longitudinally sectioned view showing the preferred embodiment nozzle employed in the workpiece finishing system; 
     FIG. 7 is a top elevational view showing an outlet of the preferred embodiment nozzle employed in the workpiece finishing system; 
     FIG. 8 is an exploded, longitudinally sectioned view showing the preferred embodiment nozzle employed in the workpiece finishing system; 
     FIG. 9 is a sectional view showing a portion of the fluid control system employed in the preferred embodiment workpiece finishing system; and 
     FIG. 10 is a perspective view showing an alternate embodiment nozzle and an alternate embodiment workpiece employed in the workpiece finishing system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of a workpiece finishing system of the present invention is used to impinge a grit and fluid slurry upon a workpiece and to recycle the slurry for subsequent reuse. Referring to FIG. 1, workpiece finishing system  21  employs a nozzle  23 , a recovery tank  25 , a gravity separator  27 , a media filter  29 , a high pressure fluid pump  31  and a spray booth  33 . A workpiece  35  is either stationarily clamped in place inside booth  33  or is located on a moving conveyor (not shown) inside booth  33 . Workpiece  35  is preferably a metal part which can be of a flat sheet, rounded or contoured configuration. Nozzle  23  is preferably a hand-held spray gun nozzle which operably sprays the slurry onto workpiece  35  inside booth  33 . Alternately, nozzle  23  may be part of a robotically controlled reciprocating unit. 
     Spray booth  33  has a receptacle  41  located below workpiece  35  for receiving the slurry after the slurry is applied to workpiece  35  from nozzle  23 . The slurry is preferably in the form of water and a very fine silicon carbide grit. Carbide of a 400-1200 grit is believed to be suitable and is maintained as an emulsion in the slurry. Furthermore, water is a superior fluid, as compared to air, for the present use due to the high slurry pressures needed to properly finish workpiece  35 . Spray booth  33  additionally has a fan and a zigzag ceiling exhaust which deters airborne moisture from leaving booth  33 . A diaphragm pump  43  is located in a first transmission line for flowing the used slurry  37  from receptacle  41  to an inlet  45  of recovery tank  25 . A check valve  47  and a T-connector  49  are also disposed in the first transmission line. The transmission lines can be of any standard tube or pipe construction and length. 
     As can best be observed in FIGS. 2 and 3, recovery tank  25  has an outer casing consisting of four generally triangularly shaped walls  61  made of flat, stainless steel sheet metal and welded together at their edges. Furthermore, at outlet  63  is disposed in a bottom apex of walls  61 . Side walls  61  have an approximately 20 degree angle off of a vertical plane. Additionally, a flat and horizontal shelf  65  is welded within the casing. Shelf  65  is spaced away from the wall  61  opposite inlet  45  such that a vertically open passageway  67  is thereby created. Shelf  65  is also located above inlet  45  but below the top edge of the casing. 
     Four baffles  67 ,  69 ,  71  and  73  are welded to a pair of opposite walls  61  and are all oriented in a somewhat vertically angled manner. The upper edges of baffles  67  and  71  are welded to an underside of shelf  65  while an upper edge of baffle  73  is welded to one side wall  61 . It is also noteworthy that there is a very slight separation between baffles  69  and  73 . An air vent  75  allows trapped air to escape from below shelf  65  while a water collector  77  is juxtaposed adjacent to an opening in one side wall  61  above shelf  65 . Accordingly, the used slurry enters recovery tank  25  through inlet  45  and travels through the baffles in a serpentine-type flow pattern. This causes the grit to settle out of the slurry toward the bottom of the tank to create a highly concentrated grit and slurry composition while a predominantly water based portion of the slurry is allowed to gradually flow through passageway  67 , above shelf  65  and out of collector  77  when the slurry is being expelled out of nozzle  23 . The amount of water flowing above shelf  65  is directly proportional to the water flowing to the nozzle from the high pressure pump; in other words, when the nozzle is not actively spraying in a high pressure manner, no water will be flowing above shelf  65 . Furthermore, the slurry flows slowly through the approximately four foot square wide by ten foot high recovery tank at about 30-40 pounds per square inch of pressure. The tank pressure depends on the driving pressure of diaphragm pump  81 . The vertical construction of recovery tank  25  maximizes packaging in the manufacturing plant. 
     The highly concentrated slurry is then allowed to flow through a second transmission line from outlet  63  to another diaphragm pump  81  as is shown in FIG.  1 . The slurry, again having a highly concentrated grit mixture, is then allowed to either flow to a grit inlet  83  (see FIG. 6) of nozzle  23  when slurry spaying is occurring, or to a three-way valve  85  which operably causes the concentrated grit mixture to flow through a bypass transmission line  87 . Diaphragm pump  81  pumps at about twenty-five to thirty pounds per square inch, given a ninety pounds per square inch air source, whereby the grit is supplied to inlet  83  even when no high pressure water venturi action is occurring. During short non-spraying durations, such as for workpiece handling, the nozzle is placed in booth  33  so the grit concentrated slurry will flow at a low pressure back into receptacle  41  for reuse. 
     Bypass line  87  joins the first transmission line at T-connector  49  for recirculation back into recovery tank  25 . Bypass line  87  is employed when nozzle  23  is not spraying the slurry. Agitation of the grit in the bottom of recovery tank  25  is necessary to avoid packing or immovable densification of the very fine grit in the bottom of recovery tank  25 . This causes constant agitation and suspension of the grit in a portion of the water to allow free flowing, albeit in a concentrated form, of the settled slurry for eventual application through nozzle  23 . Alternately, an agitation screw or propeller can be installed in the bottom of recovery tank  25  in place of bypass line  87 . A nozzle clean out valve  121  and fresh water  123  are used to clean out the grit from nozzle  23  after a predetermined period of use, such as between shifts. 
     During active use, the separated water flows from collector  77  and through a third transmission line to an inlet of gravity separator  27 . A set of alternating and generally vertical baffles  101  are positioned inside of gravity separator  27  for causing a second serpentine flow pattern of the water. This allows further settling out of any grit therein. A set of bar magnets  103  are also located in gravity separator  27  for removing metal offal sheared from workpiece  35  in the finishing process of the present invention. Periodically, the magnets will need to be cleaned and a bottom tray will need to be removed and cleaned. It is also envisioned that an anti-rust compound may need to be dripped into gravity separator  27 . 
     A fourth transmission line subsequently carries the water exiting gravity separator  27  through a centrifugal pump  111 , through media filter  29  and into high pressure fluid pump  31 . This media filter  29  can removed grit as small as between one and five microns in size. A pair of pressure gauges  113  are positioned on the inflow and outflow sides of media filter  29  for detecting when the filter requires cleaning. A second media filter is in parallel to the first so water can temporarily flow through the second while the first is cleaned. A satisfactory high pressure fluid pump  31  is Model No. 32010SS which can be purchased from Tritan Corp. of Houston, Tex. High pressure pump  31  is of a triple piston type which can supply between 7,000 and 20,0000 pounds per square inch of water pressure. 
     A receiver tank  120  for holding the water is located between media filter  29  and pump  31 . Receiver tank  120  has a capacity of around sixty gallons or more and ensures a sufficient water supply to pump  31 . Pump  31  is allowed to constantly run regardless of nozzle activation. Another transmission line connects high pressure fluid pump  31  to a water inlet  115  (see FIG. 6) of nozzle  23 . A ball valve  117  is connected to a T coupling  119  and disposed in this fluid transmission line to dump the water directly from high pressure fluid pump  31  to receiver tank  120 , when nozzle  23  is not actively spraying. 
     Referring to FIG. 4, nozzle  23  expels the mixed high pressure water and grit slurry upon the surface of workpiece  35  that is desired to be finished. The slurry impinges upon the work surface at an acute angle a relative to the plane of the part. If the workpiece is hardened steel, for example, an a angle of about 10-15 degrees is used with the nozzle placed within about one inch of the work surface while employing between about 8,000-9,000 pounds per square inch of water pressure measured at the high pressure fluid pump. In another example, a softer workpiece material such as one made of aluminum, brass or copper may require an a angle of about 3-4 degrees, about 4,000 pounds per square inch of water pressure, and it may be desirable to place the nozzle about 1-2 inches from the work surface. Generally, α angles between 2 and 30 degrees are preferred. The impingement of slurry at the preferred acute angles and high pressures serves to shear off extreme portions of discontinuities  131 , such as machining marks, common manufacturing voids or the like, thereby leaving a more uniform and finished surface. The present invention can provide a one micro inch width of depression on the finished workpiece surface as compared to the traditional two-four micro inch width. However, the finished surface of workpiece  35  has a dull matte-like appearance rather than a bright and shiny one. Thus, conventional polishing, buffing or use of a grease compound is not needed for this finishing operation. While a minor amount of belting (in cross directions) may be required prior to the slurry impingement finishing operation, this may not always be necessary depending on the quality of finish desired and slurry performance. 
     FIGS. 5 and 9 illustrate the preferred pneumatic control system  151  for allowing water to flow from the high pressure fluid pump  31  (see FIG.  1 ), which is continuously running. A trigger jet  153  is mounted to a handle of the nozzle. Trigger jet  153  operates at about 1.5 pounds per square inch of air pressure, and has an atmospherically accessible aperture connected to a downstream side of a venturi block  453  by a hose. The nozzle operator places his thumb over the open aperture  155  to create a positive pressure in a cavity  455  of venturi block  453 , thereby upwardly moving a diaphragm  457  and a spring biased spool  459  of a connected amplifier relay  154 . A sleeve is inserted into a smaller diameter, upstream bore of block  453 , although it may not be necessary. An air pressure supply, filter, regulator and pressure gauge are connected to venturi block  435 . Similarly, an air pressure supply, filter, regular and air pressure gauge are connected to amplifier relay  154 . Activation of amplifier relay  154  then causes a valve  156  to change orientation against a biasing spring  157 . Valve  156  is connected to an air pressure supply and to a pair of atmospheric outlets. Valve  156  is of a four-way, two-position, air pilot and spring return-type which applies piston advancing pressure to one side and dumps the other to the atmosphere, and vice versa. Amplifier relay  154  is preferably of a Clippert 2010 type controlling flow of a regulated air pressure supply of about 90 pounds per square inch. 
     A pair of valve operated, piston cylinders  159  are connected to valve  156  by way of flow control restrictors and check valves. The restrictors control the return air flow and, thus, the speed of the cylinder movement. A ball valve  161  is connected to a piston of the corresponding cylinder  159  for allowing water from high pressure fluid pump  31  (see FIG. 1) to the nozzle. The other cylinder  159  controls ball valve  117  which dumps the high pressure water to receiver tank  120  (see FIG. 1) before shutting off valve  161 ; this prevents system damage due to deadheading. Thus, pneumatic control circuit  151  provides remote control activation for the high pressure fluid. Alternately, a mechanical lever, electric switch or foot pedal can be employed with the nozzle or in another location for controlling the on/off spraying of the slurry out of the nozzle. An accumulator can also be used in combination with the high pressure fluid pump to enhance the pressure curve. 
     The preferred embodiment nozzle construction is shown in FIGS. 6-8. Nozzle  23  has a steel body  201  with an internal slurry receiving chamber  203 . A fan-shaped outlet  205 , made of carbide is threadably fastened to a first end of body  201 . Outlet  205  has a laterally elongated, slotted opening  207  for expelling the mixed slurry. Outlet  205  is burned from two separate pieces by an EDM process and then subsequently joined together by brazing or welding. It is alternately envisioned that the carbide outlet can be compression molded from powdered carbide metal. The portion of outlet  205  that engages body  201  is generally cylindrically shaped and hollow. 
     High pressure water inlet  115  is a rigid and hollow, hardened metal tube which is inserted into a second end of body  205  opposite outlet  205 . An externally threaded metal fitting  209  threadably engages body  201  and has a frusto conical internal taper  211 . Inlet  115  is movably disposed within an internal bore  213  of fitting  209 . A metal bushing  215  is securely fastened around an external surface of inlet  115 . A longitudinally elongated and open slot  217  allows bushing  215  to be circumferentially compressed when an internally threaded nut  219  enmeshes with threads of fitting  209 . Bushing  215  has an external frusto conical shape  221  which generally matches surface  211  of fitting  209 . Thus, inlet  115  can be longitudinally moved relative to body and grit inlet  83  to an infinite variety of position between the longitudinal end positions by tightening or loosening nut  219  relative to fitting  209 ; the engagement of nut  219  relative to fitting  209  varies the degree of interference and insertion of bushing  215  within fitting  209 . Furthermore, a carbide tip  223  is pressfit inside a pocket in the distal end of inlet  115 . An internally threaded outer cap is attached to inlet  115  and sandwiches a circular brim of tip  223  therebetween. Nozzle  23  acts in a venturi manner wherein the high pressure expulsion of water through inlet  115  causes a vacuum-like pressure which aids in drawing the concentrated grit/slurry mixture from grit inlet  83 . Thus, when inlet  115  is retracted away from outlet  205 , a greater venturi force is created for assisting in drawing more grit, thereby providing a grit-rich slurry solution. Conversely, further advancement of inlet  115  toward outlet  205  causes less of a venturi action and a greater restriction of area between inlet  115  and the adjacent portion of outlet  205 , wherein there is less grit in the final sprayed slurry relative to the water content. This allows for an easy change in the slurry concentration for different types of workpieces without requiring separate fixed nozzles. 
     FIG. 10 illustrates an alternate embodiment nozzle  23  and workpiece  35 . This exemplary nozzle is similar to the preferred one except that the outlet  205  has a vertically elongated, small width and fanned opening. The handle and trigger jet shown for this nozzle are also employed in the preferred embodiment nozzle. 
     Workpiece  35 ′ is constructed from a cylindrical steel rod  251  having a pair of right angle bends, and a flat steel baseplate  253 . Rod  251  and baseplate  253  are welded together at weld  255 . The present invention finishing system is ideally suited for this type of curved workpiece  35 ′ whereby the entire curved shape and the weld can be thoroughly finished with a minimum of effort. In contrast, traditional systems had great difficulty, if it could be done at all, in reaching tight curves and welds by use of large manually operated belted sanders, polishing wheels and buffing wheels. Workpiece  35 ′ is subsequently chrome or nickel plated such as is disclosed in the following U.S. Patent Nos.: U.S. Pat. No. 3,992,211 entitled “Electroless Plating Composition” which issued to Skoll on Nov. 16, 1976; U.S. Pat. No. 3,963,527 entitled “Chromatizing Process and Composition” which issued to Lindemann on Jun. 15, 1976; and U.S. Pat. No. 3,791,801 entitled “Electroplated Steel Sheet” which issued to Ariga et al. on Feb. 12, 1974; all of which are incorporated by reference herewithin. 
     While the preferred embodiment workpiece finishing system and method have been described, it should be appreciated that other embodiments may be employed with the present invention. For example, a ferrite metal grit may be used if it can be obtained in a very fine form. Furthermore, the slurry spraying and recycling system can be used with a nozzle having an elongated wand for use in finishing an interior gun barrel bore for subsequent rifling. The present invention can also be used for finishing silicon wafers, but by using the high pressure impingement, acute angles and recovery system disclosed. Molds and dies can also be finished with the present invention system. Moreover, other baffle and filtering devices and arrangements can be employed for the recovery tank and system. Additionally, multiple, angled nozzles can be fixed in the spray booth and aimed at a moving workpiece, such as on a hanging or underlying conveyor system. It is intended by the following claims to cover these and any other departures from the disclosed embodiments which fall within the true spirit of this invention.