Auxiliary filter and process for removing residual particles from filtered cutting fluid

Abstract: An auxiliary filter for removing residual particles from already filtered cutting fluids used in metal cutting machines, the auxiliary filter including a hollow wheel member (20) rotated in a sealed tank (16) into which the filtered liquid flows. Pressurized liquid passes through a fine screen (38) on the perimeter of the rotating wheel to capture any residual particles. A high pressure backwash jets are directed at the screen as it rotates past an array of nozzles (78), and a collection trough (76) draws any dislodged material away and out of the tank.

Description: Background of the Invention This invention concerns filters and more particularly filters used to remove contaminating particles from cutting fluids used in metal working machining. Large volumes of contaminated cutting liquids are generated in the machining of metal in large scale metal cutting operations such as in the manufacture of engine components in the automotive industry. These liquids are filtered to remove solid particles such as grit, metal chips, etc. in a recirculating system, which returns the filtered liquid for reuse with the machine. Such volumes of liquids are required for large machining installations, that indexing belt filters indexed through large tanks are required. See U.S. patent no. 5,601,729 for an example of such filtering apparatus. These filters allow great volumes of liquid to be filtered, but do not totally eliminate the presence of stray particles which can get around the edges of the belts pass through tears in the belt, or otherwise get into the filtered liquid. Even one metal chip can cause plugging of a nozzle to a machine tool creating rapid tool failure and possible shut down of the entire installation. There is thus a need for a failsafe auxiliary filter for removing residual particles from the filtered liquid. A particular problem associated with cutting fluids in particular is the build up of gelatinous material which has a great tendency to rapidly plug up fine filter openings, such that simply passing the filtered liquid through fine screen cannot eliminate these stray particles. Also, such apparatus is often operated continuously with automatic controls, such that the auxiliary filters should not require constant maintenance. Document US-A-5,423,977 describes a filter according to the preamble of claim 4. This device is useful for filtration of marine fuel oils or lubricants. Document US-A-5,992,642 describes a process of filtering according to the preamble of claim 1. It is the object of the present invention to provide a filter and process for filtering out residual particles from filtered cutting fluids recirculated from a machining operation. Summary of the Invention The above object and others which will be understood upon a reading of the following specification is achieved by a process of filtering and a filter according to claim 1 and 4 respectively. The filter comprises a hollow wheel member carrying a filter screen on its perimeter, the wheel continuously rotated in a sealed tank receiving under pressure the filtered liquid. The hollow wheel member has an outer cylindrical perimeter covered with a fine screen supported by wedge wire windings and a circumferential array of bars welded to the outer portion of oppositely dished hub pieces. The hub pieces are axially spaced apart to define a flow path for liquid received under pressure from the main filter apparatus and flowing through the fine screen, which is thereafter directed back to the machining center. The screen is backwashed by a series of high pressure jets directed at the screen as it rotates past the jets. An open side of a collection trough faces the screen at the location of the spray jets, to collect dislodged material and draw the same out of the tank. The combination of the rotation of the wheel and the cleaning effect of the backwash jets keeps the fine screen clear of both gelatinous material and any captured residual particles so as to allow continuous operation of the auxiliary filter. Description of the Drawing Figures Figure 1 is a sectional view of the filter according to the present invention with diagrammatic representations of the associated components. Figure 2 is a partially sectional end view of the hollow wheel member included in the filter of Figure 1. Figure 3 is an enlarged fragmentary view of a portion of the hollow wheel in partial section showing details of the support for a fine screen extending about the perimeter of the hollow wheel. Figure 4 is an end view of the collection trough and spray nozzle away shown in Figure 1. Figure 5 is an enlarged fragmentary view of a portion of the filter shown in Figure 1, showing an optional modification. 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 drawings and particularly Figure 1, the auxiliary filter apparatus 10 according to the present invention is designed for use with a main filter system 12 which is associated with a machine tool coolant system 14. The filtered cutting fluid from the main filter system 12 is directed under pressure into a sealed tank 16, which is constructed of two separable halves 18A, 18B secured together by swing bolts 20 and flanges 22, 24. A perimeter gasket 26 insures a pressure tight sealing of the tank 16. A hollow wheel member 28 is rotatably supported within the tank 16 on a drive shaft 30 passing through the wheel 28 and welded to a pair of oppositely dished disk pieces 32, 34. The disk pieces 32, 34 are spaced apart axially to define a radial flow space 36 to receive inflow through a fine microscreen 38 extending around the outer perimeter of the hollow wheel 28. The outer region 40, 42 of each of the disk pieces 32, 34 are flared away from each other to create a widened axial spacing to accommodate an increased width of the fine microscreen 38 to increase the filtering area available. The microscreen 38 is a commercially available material having very fine openings (25-300 microns), and is constructed of thin metal only a few thousandth's thickness to be incapable of being scraped and must be supported at closely spaced interrupts. For this application typically a 50-70 micron size would be used. The details of this support structure is shown in Figure 3. The flared portions 40, 42 extend to radial rim portions 44, 46, and a circumferentially spaced array of thin bars 48 are welded at each end to a respective rim portion 44, 46. Turns of a commercially available triangular in-section wire (called wedgewire) are wound onto the outer faces of the bars 48 and welded thereto, with the peaked side of the facing out to increase the open area beneath the screen 38, the pressurized liquid passing through the mesh 38, between the wedgewire turns and then between the thin bars 48 and into the interior space 36. The left disk piece 32 has a series of holes 52 at an inner region allowing outflow from space 36. A sealing ring 54 is welded to the outer surface of the disk piece 32 and carries a rotary seal 56 engaging the inside of an axially extending central tube 58 welded to tank half 18A. The central tube 58 is supported on a series of radial webs 60 to allow liquid flow into the interior of tube 58 and thence to an outlet 62. A spacer tube 64 holds a pair of bearing sleeves 66, 68 journalled on the shaft 30, with rotary seals 70 insuring that no leakage out of the tank 16 occurs. A drive motor 72 and gear reducer 74 power the shaft 30 to provide rotation of the hollow wheel 28 at a speed sufficient to keep the screen 38 clear (4,57 - 6,1 m/s (15-20 surface feet per second)) when combined with the effects of a backwashing spray. A collection trough 76 is fixed to the inside of the tank 16, with its open side facing the outer perimeter of the hollow wheel 28, and a series of spray nozzles 78 project from a backwash header pipe 80 (Figure 4) supplied with over tank pressure liquid from a source 82 (such as a reservoir of filtered liquid) pressurized to a level substantially over the pressure in the tank 16, i.e., 6,89·10 5 - 20,7·10 5 Pa (100-300 psi) higher than tank pressure. An outlet 84 connects the trough to a low pressure side of a backwash return pump 84 to direct collected liquid into the main filter system 12. The trough 76 and outflow collects material dislodged from the screen 38. The combination of rotating movement of the screen 38 and the spray nozzle jets keeps the screen 38 clear of solid particles and gelatinous material to allow continuous operation of the auxiliary filter 10, insuring that no residual particles of any size are recirculated into the machine tool coolant system 14. The backwashing may be operated continuously (where considerable gelatinous material is present), or may be operated intermittently to allow solids to accumulate for better filtration. The wheel 28 may in this case also be merely indexed rather than the more usual continuous rotation. Figure 5 shows that an axial flow propeller 90 can be driven by shaft 30 so as to boost the pressure of the exiting liquid, offsetting the losses experienced in passing through the auxiliary filter 10.

Claims: A process of filtering cutting fluids used in a metal cutting machine comprising the steps of collecting cutting fluids contaminated with solid particles in said metal cutting machine and passing said fluid through a main filter apparatus to remove said particles therefrom; directing filtered liquid from said main filter apparatus (12) through an auxiliary filter (10) to remove residual particles, said auxiliary filter including a hollow member (28) having a filter screen (38) mounted about the outer perimeter thereof; rotating said hollow member (28) while said member is disposed in a tank (16) with said filtered liquid; directing liquid in said tank (16) through said screen (38) and into a liquid receiving hollow space in said hollow member (28) and, returning liquid directed through said screen (38) to said metal cutting machine. characterized by the steps of directing a series of spray jets at the outside perimeter of said screen (38) as said screen is rotated past a series of spray nozzles (78) at a surface speed of 4,57 to 6,1 m/s to thereby clean said screen as it is rotated past said spray nozzles by the combined effects of said rotation of the hollow member (28) and said spray jets; providing a pressure tight sealing of the tank (16) and directing pressurized liquid in said tank (16) through said screen (38) into the interior space (36) of the hollow member (28). The process according to claim 1 further including the step of continuously rotating said hollow member (28) and directing said spray jets at said screen (38) to continuously clean said screen. The process according to claim 1 or 2 further including the step of disposing an open face of a trough (76) across the perimeter of said rotating screen (38) at the location of said spray nozzles (78), and drawing liquid out of said trough and said tank (16) to collect material dislodged from said screen (38) by said spray jets. A filter comprising: a sealed tank (16) adapted to receive a pressurized liquid to be filtered; a hollow wheel (28) mounted for rotation in said tank (16); said hollow wheel (28) having an outer perimeter covered with a fine screen (38), pressurized liquid directed through said screen (38) and into an interior space (36) in said wheel (28); means for directing liquid out of said interior space (36) and said tank (16); drive means (72) for rotating said wheel (28) in said tank (16); and an array of spray nozzles (78) extending across said screen (38) and means for supplying high pressure liquid to said nozzles (78) for directing backwash jets at said screen (38) as said screen rotates past said spray nozzles (78), characterized by said wheel member (28) comprising a pair of oppositely dished disk members (32, 34) spaced apart to define said interior space (36), a circumferential array of bars (48) fixed extending across the space between said disk members (32, 34) adjacent said perimeter thereof and a series of wedgewire windings over said bars (48), said screen (38) overlying said wedgewire windings. The filter according to claim 4 further including an Open sided collection trough (76) disposed across said screen (38) with said open side facing said screen adjacent said spray nozzles (78) and means (84) for drawing liquid out of said trough (76) and said tank (16) to carry away dislodged material. The filter according to claim 4 or 5 further including a drive shaft (30) having said disk members fixed thereon, and a motor (72) drivingly connected to said shaft (30) for rotating said wheel (28). The filter according to claim 6 further including a center tube (58) extending through a side of said tank (16) and over said drive shaft (30), said center tube (58) fixed to said side of said tank (16), and means mounting said drive shaft (30) for rotation within said fixed center tube (58), said center tube communicating with said interior space (36) in said wheel member (28) and scaled thereto; an outlet (62) connected to said center tube (58). The filter according to any one of claims 4 to 7 wherein said screen (38) comprises a very thin micro screen with openings on the order of 50-70 microns. The filter according to any one of claims 4 to 8 with means for continuously rotating said wheel member (28) to produce a surface speed of said screen (38) on the order of 4,57 - 6,1 m/sec. The filter according to any one of claims 4 to 9 wherein said spray jets are produced by high pressure liquid on the order of 20,68 bar. The filter according to any one of claims 4 to 10 further including a propeller (90) driven by said drive means (72) to increase the pressure of liquid flowing out of said tank (16).

Inventors: BRATTEN JACK R, BRATTEN, JACK R.
Applicants: FILTRA SYSTEMS COMPANY, FILTRA-SYSTEMS COMPANY
Application year: 2000
Main classification: B23Q11
IPC codes: B23Q11, B01D35, B01D29, B01D33