Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D43/00—Mechanical cleaning, e.g. skimming of molten metals
  • B22D43/001—Retaining slag during pouring molten metal
  • B22D43/004—Retaining slag during pouring molten metal by using filtering means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D35/00—Filtering devices having features not specifically covered by groups B01D24/00 - B01D33/00, or for applications not specifically covered by groups B01D24/00 - B01D33/00; Auxiliary devices for filtration; Filter housing constructions
  • B01D35/02—Filters adapted for location in special places, e.g. pipe-lines, pumps, stop-cocks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
  • B22D11/11—Treating the molten metal
  • B22D11/116—Refining the metal
  • B22D11/119—Refining the metal by filtering
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
  • B22D21/04—Casting aluminium or magnesium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D43/00—Mechanical cleaning, e.g. skimming of molten metals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• TECHNICAL FIELD This invention relates to the filtration of molten metal, e.g. molten aluminum.
• JP 06-49551 there is disclosed a continuous in-line filter device, based on a porous tube filter where a fan was used to force the metal that is passed through the filter element from the tube outlet.
• the fan operates only to blow and does not provide any suction.
• a furnace stirring device is described in WO 88/07165 in which a molten metal in a closed side chamber was raised and lowered repeatedly to cause the metal to flow through shaped orifices and thereby cause mixing in the main furnace.
• the metal was raised and lowered by the alternate application of pressure and suction by a fan operating on the gas above the metal in the closed side chamber. There was no suggestion of the use of such a fan with a filter.
• the present inventors were faced with the problem of trying to prime a relatively large commercial filter typically having a relatively large cross sectional area compared to its thickness.
• a filter has a relatively large exit well and it was found that a system such as that described in the JP 60-5829 document was not suitable. For instance, it was found that for the level of vacuum required in the JP 60-5829 system, a vacuum pump was needed and a typical vacuum pump is not able to remove air from a commercial exit well sufficiently fast. For a commercial operation with the larger filter, the need was not so much for a high level of vacuum but for being able to remove the air from the exit well at a sufficiently high rate.
• the present invention relates to a method of priming an in-line molten metal filtration unit having a porous ceramic or refractory filter mounted substantially horizontally in a filter box.
• This filter box has an inlet for molten metal and an outlet for molten metal, the outlet being a closeable outlet in an exit well connecting to the downstream side of the filter.
• the method of the invention comprises the steps of adding a molten metal to the filter box sufficient to entirely cover the upstream side of the filter with a depth of molten metal and temporarily closing the outlet in the exit well with a sealable cover.
• a steadily increasing vacuum is then applied to the closed exit well at a rate between 0.1 and 10 kPa per second by withdrawing a stream of air from the exit well by means of a fan until molten metal begins to flow through the filter. At that point the vacuum is quickly released and the sealable cover is removed from the molten metal outlet.
• a fan in the above manner has been found to have several important advantages. Firstly, a vacuum tank is not required and the fan is capable of removing air from the exit well very rapidly so that the level of vacuum required for priming of the filter is reached very quickly.
• the invention also relates to a novel apparatus for filtering molten metal.
• This apparatus includes a filter box, a feed trough for feeding molten metal into the filter box and a porous ceramic or refractory filter mounted substantially horizontally within the filter box to receive molten metal from the feed trough.
• An exit well is located beneath the filter for receiving filtered molten metal. This exit well also extends laterally beyond the filter box and beneath a bottom portion of discharge trough.
• An opening in the discharge trough bottom portion connects to the exit well so that filtered molten metal can flow from the exit well into the discharge trough.
• a vertically movable closure unit is adapted to sit over and seal the opening between the discharge trough and the exit well.
• An air conduit is connected at a first end to the closure unit and at a second end to a fan or air venturi for withdrawing air from the exit well.
• the apparatus also includes means for raising and lowering the closure unit and a valve for releasing vacuum formed within the exit well.
• Fig. 1 is a schematic illustration in partial section of the filtration unit of the invention
• Fig. 2 is a modification of the view of Fig. 1
• Fig. 3 is a perspective view of the filtration unit of the invention
• Fig. 4 is a further perspective view of the filtration unit of Fig. 3 from a different direction
• Fig. 5 is a micrograph showing how pore diameters are measured.
• Fig. 6 is a plot showing increase in vacuum with time.
• the fan requirements will depend on the size of filter used but typically should be capable of evacuating to a vacuum of between 2 and 20 kPa, and to evacuate the filter outlet volume to the desired vacuum within about 1 to 120 seconds, preferably 2 to 30 seconds.
• a vacuum of 2 to 20 kPa means 2 to 20 kPa below the standard atmospheric pressure (101 kPa) .
• the type of fan that meets these requirements is a duct fan or regenerative blower. However any fan meeting these requirements may be used. An air venturi sized to these requirements may also be used.
• a fan suitable for typical commercial filter installations and meeting the above requirements has an exhaust rate of 320 standard litres per minute at 6 kPa of vacuum.
• a closure member which closes the exit well, including the molten metal outlet.
• This closure member is adapted so that when the vacuum is released, the closure member may be lifted from the top of the exit well and from the trough so that the exit well is immediately returned to atmospheric pressure and the trough is open to receive filtered molten metal.
• the fan may be equipped with a variable speed control to permit ramping the evacuation rate smoothly, but in a preferred embodiment, the conduit may also include a three- way valve which permits the fan to draw air solely from the outside, or to apply vacuum solely to the filter, or any intermediate combination, by varying the valve position between two extremes.
• the valve In a typical operation the valve is placed in a position where the fan draws air solely from the exterior (and the filter is isolated) , at which point the fan is started and run up to full speed. The valve is then moved gradually (e.g. by a motor control) toward the other extreme position so that the fan progressively draws a higher proportion of air flow from the filter box.
• FIG. 1 A particular embodiment of a filtration unit according to the invention is shown Figures 1 and 2.
• the filtration unit includes a filtration box 10 having side walls and a bottom wall 14. These walls are formed of a heat resistant insulating material. At one side of the unit is a feed trough 16 for feeding molten metal 18 into the box. Within the box is a horizontal filter element 20 supported between side walls and an inner divider wall 22. An exit well 23 is provided beneath the filter 20 and a closeable outlet drain 32 is provided for emptying the filter box when necessary.
• the exit well 23 includes an outlet opening 25 through which molten metal discharges to trough 28.
• closure unit 24 For priming the filter 20, the opening 25 and exit well 23 are closed by means of a closure unit 24 which, as shown in Figure 1, sits over and seals the outlet opening 25.
• An opening in closure member 24 connects to a conduit 34 by way of a connector 30 and conduit 34 connects to a fan intake duct 36 containing a valve 38.
• This valve 38 can be moved between a position allowing flow through conduit 34 to the pump intake duct 36 or it can be switched to draw air in from the atmosphere by means of a motor drive.
• the valve 38 is such that at any position between these two extremes, the fan can draw a portion of air from the atmosphere and the remainder from the conduit 34.
• the connector 30 has a fast acting solenoid valve 31 connected to the atmosphere.
• the filter unit is initially filled with molten metal 18 as shown and the fan 40 is started with the valve 38 fully open to the atmosphere and the conduit 34 shut off from the fan.
• the valve 38 is moved by a motor drive toward its other extreme in order to gradually increase the proportion of air flow coming from the exit well 23 thereby creating a vacuum within the space beneath the filter.
• This vacuum quickly and smoothly increases by the action of fan 40 and valve 38 until the point is reached at which metal flow commences through the filter 20 and priming has been achieved. At this point it is important to quickly release the vacuum and this is done by opening valve 31 to the atmosphere.
• valve 31 is preferably a solenoid valve that is released upon detection of molten metal in the bottom of the well 23, for example, by means of a conductive probe which detects the metal by completion of an electric circuit.
• the closure 24 is lifted away from the filter box as shown in Figure 2 so that the entire open end of exit well 23 is exposed to the atmosphere, and, of course, this also opens the discharge trough 28 to metal flow.
• a more detailed version of the present invention is shown in perspective views in Figures 3 and 4.
• a refractory lined filter box 10 typical of the size and type used for commercial ceramic foam filtration units is provided.
• a porous filter element 20 is mounted substantially horizontally within the box.
• the filter element is mounted within about 10 degrees of the horizontal. This provides, for example, for release of trapped gases.
• An inlet 16 and outlet 28 comprising refractory lined troughs are provided that are in turn connected to a conventional metal delivery system.
• a removable cover 41 is provided for the filter box.
• the cover contains a burner 42 for preheating the filter element prior to use.
• the cover is mounted on a vertical post 43 and can be raised and swung out of the way when not required.
• a closure 24 in the form of a hollow box with an open bottom is provided mounted on a post 44 so that it can be moved into position and lowered into the exit trough 28 so as to cover and seal the hole 25 and thereby seal off the exit well 23 under the filter element.
• the closure box 24 is connected by pipe 34 to a fan 40.
• Mounted on the connection pipe 34 and close to the closure is a quick opening solenoid valve 45 to release vacuum when the metal is detected in the exit well.
• the closure can be raised automatically (when metal is detected) by pneumatic means controlled by a controller 46 on the post.
• Metal is detected by electrical contacts 47 fed through the closure. These are in the form of steel or graphite tipped steel rods.
• the priming is conducted within a time of about of 1 to 120 seconds, preferably in a time of about 2 to 30 seconds.
• a filter having a filtration cross sectional area of about 25.8 to 10130 square centimeters (4 to 1570 square inches) .
• the filtration area preferably is at least 645 square centimeters (100 square inches) .
• This filter also typically has a thickness of about 1.25 to 10.2 centimeters (0.5 to 4.0 inches), preferably about 2.5 to 7.6 centimeters (1 to 3 inches).
• the filter used can be selected from a variety of commercial filters and typically has a filter pore size ranging from an average of about 150 to 500 microns.
• This average pore size is defined as the average "window” or size of interconnecting necks or passages between the cells of the porous refractory media.
• the average pore size is measured as follows. A sample is cut from the filter media in the centre of the media thickness and perpendicular to the flow direction. From a scanning electron micrograph of the sample, the size of the "windows" visible between the ceramic necks is measured and the average value over the sample is determined. Figure 5 shows a typical result for such measurements. Pores that have a diameter below 50% of the average of all pores measured are not taken into account in the final average pore size calculation because they will not be primed by molten metal.
• Filters having an average pore size greater than 500 microns typically can be started without the need of priming, while filters having an average pore size below 150 microns may be capable of being primed by applying a vacuum to the exit well, but will require an excessive head of metal above the filter to continue the filtration without the vacuum. Filters of this type are conventionally defined in terms of pore per inch (ppi) , but this parameter is not a unique definition of average pore size since it depends on the manufacturing methods used. For comparison, certain commercial filter media are listed in Table 1 below: Table 1
• the first four items in the above table are filter materials that are typically used in low depth CFF boxes for filtering metal in commercial casting plants.
• the last five materials are not used in conventional systems unless very high metal heads can be provided for priming. They are typical of the filter media that may be conveniently used with the present invention.
• the depth of metal over the filter is defined as the sum of the vertical distance from the trough bottom to filter top (VDTF) plus the height of the metal in the trough.
• the height of metal in the trough would generally range from about 20 to 30 cm (8 to 12 inches) .
• the VDTF typically ranges from about 0 to 10 cm (0 to 4 inches) and, therefore, the depth of metal over the filter will typically be about 20 to 40 cm (8 to 16 inches) .
• the VDTF ranges from 0 to 50 cm (0 to 20 inches) and therefore the depth of metal over the filter will be from 20 to 80 cm (8 to 32 inches) .
• the filter box size i.e. the filter cross section and depth required to accommodate the metal head over the filter
• the filter box size can be less in the present invention than in conventional ceramic filtration equipment or can be installed in substantially the same space as an existing conventional ceramic filter.
• the filtration efficiency is higher than in conventional ceramic filters and is closer to the efficiency of deep bed filters which occupy substantially larger volumes.
• the smaller volume of the present invention compared to both conventional ceramic filter units and bed filters means that less metal must be drained at filter change.
• the invention has been shown with a single filter element mounted in the filter box.
• the single filter element may be replaced by two or more, mounted beside each other to permit larger cross-sectional areas than may be possible with a single element.
• use of two filter elements mounted one above the other in the filter box is possible with this invention.
• Example 1 A test was conducted on a pilot filtration unit of a design as shown in Fig. 1.
• the filter used was a commercially available filter having a pore density of 70 pores per inch (PPI) . It had a thickness of 5.1 cm (2 inches) and a cross-sectional area of 929 square centimeters (144 square inches) .
• the exit well was connected by way of a conduit to the intake of a duct fan (Spencer VB-055 manufactured by The Spencer Turbine Company, Windsor, CT USA) , the conduit including a venting valve and a three-way valve for bleeding atmospheric air into the air being drawn into the fan.
• Molten aluminum alloy was added to the filtration unit to a depth of about 20 cm (8 inches) above the filter.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
• Filtering Materials (AREA)
• Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)
• Treatment Of Steel In Its Molten State (AREA)

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• 2005
  • 2005-02-23 US US10/590,472 patent/US7666248B2/en not_active Expired - Lifetime
  • 2005-02-23 JP JP2007500020A patent/JP4785828B2/ja not_active Expired - Lifetime
  • 2005-02-23 AT AT05714490T patent/ATE463313T1/de not_active IP Right Cessation
  • 2005-02-23 DE DE602005020435T patent/DE602005020435D1/de not_active Expired - Lifetime
  • 2005-02-23 EP EP05714490A patent/EP1735120B1/en not_active Expired - Lifetime
  • 2005-02-23 WO PCT/CA2005/000248 patent/WO2005080028A1/en not_active Ceased
  • 2005-02-23 CA CA002556860A patent/CA2556860C/en not_active Expired - Lifetime
  • 2005-02-23 AU AU2005215071A patent/AU2005215071B2/en not_active Expired
  • 2005-02-23 ES ES05714490T patent/ES2343733T3/es not_active Expired - Lifetime
  • 2005-02-23 CN CNB200580011073XA patent/CN100409977C/zh not_active Expired - Lifetime
• 2006
  • 2006-09-25 NO NO20064316A patent/NO340534B1/no unknown

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