Patent Description:
Molten metal, particularly molten aluminum, often contains entrained solids which are deleterious to a final cast metal product. These entrained solids appear as inclusions in the final cast product after the molten metal is solidified and cause the final product to be less ductile or to have poor bright finishing and anodizing characteristics. The inclusions may originate from several sources. For example, the inclusions may originate from surface oxide films. In addition, the inclusions may originate as insoluble impurities, such as carbides, borides and others derived from eroded furnace and trough refractories.

Rigorous melt treatment processes, such as fluxing, minimize the occurrence of such defects; however, these are not always successful in reducing them to a satisfactory level for critical applications. Conventionally, melt filtration is utilized in order to further decrease the extent of such defects. One type of filter in common use is porous ceramic foam. Exemplary porous ceramic foam filters are known in the art, for example, representative examples are described in <CIT> and <CIT>. These porous ceramic foam materials are known to be particularly useful in filtering molten metal, as described in <CIT>, and also as described in copending <CIT>.

Porous ceramic foam materials are particularly useful for filtering molten metal for a variety of reasons included among which are their excellent filtration efficiency, low cost, ease of use and ability to use same on a disposable, throwaway basis. The fact that these ceramic foam filters are convenient and inexpensive to prepare and may be used on a throwaway basis requires the development of means for easily and conveniently assembling and removing the filters from a filtration unit.

In the conventional filtering devices, molten metal flows downwardly to the filter medium. When the inflow of the molten metal from smelting furnaces to the filtering device is stopped during switching from one smelting furnace to another or after the end of the filtering operation, the molten metal left in the filtering device flows away from the device through the filter medium. After the molten metal is finished passing through the filter medium, the filter must be replaced. Similarly, the filter medium may become clogged because the oxide film, such as aluminum oxide film, which is formed on the surface of the molten metal contacted with the ambient air in the filtering device, flows into the filter medium with the remaining molten metal and sticks on the medium. Traditionally, when a filter must be replaced, a hole is punched into the filter while the metal is still in liquid form and it is then allowed to cool in the filtration box to below <NUM>° C at which point it is grasped with a hook. This process requires time for cooling down and heating up, wears down the refractory material of the filtration box, and contaminates the filtration box with pieces of broken filter medium as a result of the punching step.

This disclosure relates to a device for use in association with filtering of a molten metal such as molten aluminum, and more particularly to a molten metal filter handling device so constructed that the filter medium can be changed with reduced difficulty.

Thus, the development of a device which permits easy and safe changing of the filter medium has long been in demand. Moreover, in order to fully utilize the advantageous properties of the filter medium made of porous ceramic material, i.e. large capacity for filtration and effective treatment of successive lots of molten metal, there is a need for the development of a device capable of improving the process of changing such filter media. <CIT> relates to a filter assembly for filtering solids from molten aluminum metal comprising at least one open-ended rigid refractory filter tube having an interior passageway, a bottom plate acting to close one end of such tube, a top plate having an aperture communicating with the interior passageway of such filter tube, and means, such as a tie rod to maintain the top and bottom plate and the interposed filter tube or tubes in sealed relationship so that the molten metal will flow through the walls of the rigid refractory filter tube without leakage at the ends or joints, to remove solid contaminants from the metall. <CIT> describes an interchangeable ceramic filter assembly and a molten metal processing apparatus including the same. The ceramic filter assembly includes a ceramic housing tube having at least one inlet, an outlet and a sidewall defining a central chamber, in which a ceramic filter is positioned providing a barrier between the inlet and the outlet of the ceramic housing tube.

According to a first embodiment of the invention, a method for mounting and removing a filter from a filtration box is provided. The method comprises the steps of (a) providing a tool that comprises a shank <NUM>, a head end <NUM> secured to a first end of the shank, a lifting eye <NUM> secured to a second end of the shank, and a handle <NUM> configured to be removably received by the lifting eye <NUM>; (b) detaching the handle <NUM> from the tool shank <NUM>; (c) inserting the tool shank <NUM> through a hole formed in a filter medium <NUM> made of porous ceramic material in the shape of a flat plate; (d) re-attaching the handle <NUM> to the tool shank <NUM>; and (e) positioning the filter medium <NUM> in a desired location within a filter box <NUM> using said tool.

According to a further embodiment of the invention, a molten metal filter box is provided which comprises a filter housing <NUM> provided in a flow path <NUM> for molten metal, said filter housing including an induction coil providing an electromagnetic current; a horizontal partition <NUM> disposed within said filter housing and having at least one filter receiving passage; a filter medium <NUM> made of porous ceramic material in the shape of a flat plate positioned within said filter receiving passage and below an inflow path of said molten metal, said filter medium including a hole <NUM>; a filter handling tool disposed within said hole <NUM>, said filter handling tool <NUM> including a handle <NUM> and a head portion <NUM> interconnected by a shank <NUM>, at least one of the handle <NUM> and the head portion <NUM> being removable from the shank <NUM>; wherein the filter handling tool improves channeling of the electromagnetic current within the filter; and wherein said filter medium can be removed by grasping the filter handling tool by the handle <NUM> and removing said filter medium. Advantageously, the filter medium can be removed by grasping the filter handling tool and removing the filter medium without completely emptying molten metal from the filter housing. The filter box includes an induction coil.

Referring now to <FIG>, a molten metal filtering device <NUM> made of refractory material and providing a flow path for molten metal, with the inner surfaces thereof defining the lateral sides of an inversed, truncated quadrangular pyramid is depicted. A filter housing <NUM> is formed within filtering device <NUM>. Inside the filter housing <NUM>, a horizontal partition <NUM> is extended from lateral wall <NUM>. In one edge portion of the horizontal partition <NUM>, a vertical partition wall <NUM> is integrally raised upwardly as separated from the opposite lateral wall <NUM>. The horizontal partition <NUM> and the vertical partition wall <NUM> divide the filter housing <NUM> into two halves.

Horizontal partition <NUM> has a generally quadrangular filter-setting hole <NUM> whose inner walls are converged downwardly. In filter-setting hole <NUM>, an optional filter frame <NUM> is formed of a refractory material such as refractory bricks in a pattern enclosing an empty space of the shape of an inverted, truncated quadrangular pyramid. Frame <NUM> can be detachably yet liquid-tightly fitted so that the upper part of the frame <NUM> will protrude from the horizontal partition <NUM>. A filter medium <NUM> made of porous ceramic material in the shape of a flat plate whose lateral walls define the sides of an inverted, truncated quadrangular pyramid liquid-tightly set in position in the opening of filter frame <NUM>. The filter medium <NUM> can be a porous ceramic material such as a ceramic foam which can be prepared by coating a flexible polyurethane foam having a substantially skeletal reticulated structure with a ceramic slurry and subsequently drying and sintering the coated foam, thereby removing the polyurethane foam through carbonization to leave ceramic strands.

Flow path <NUM> is provided for the delivery of molten metal at a position higher than the upper surface of the filter medium <NUM> in enclosure 12A of the two enclosures produced by the interposition of the horizontal partition <NUM> and the vertical partition wall <NUM>.

The bottom wall of the enclosure 12B is slanted downwardly from the lateral wall to the other lateral wall. A molten metal outlet <NUM> is formed at the substantially lowest position of the bottom wall which is normally kept closed with a lid <NUM> and opened when necessary. Above enclosure 12B, a molten metal overflow path <NUM> is formed in the shape of a groove at a level higher than the filter medium <NUM>.

The molten metal, such as molten aluminum from a smelting furnace (not shown) flows through the molten metal inflow path <NUM> into the filter housing <NUM> and into the enclosure 12A, passes downwardly through the filter medium <NUM>, and enters the enclosure 12B. In this case, solid impurities entrained by the molten metal are retained on the filter medium <NUM>. The molten metal which has been freed from the solid impurities and passed into enclosure 12B ascends the flow path <NUM> formed between the other lateral wall <NUM> and the vertical partition wall <NUM> and overflows into the overflow path <NUM>.

A filter handling tool <NUM> is provided to allow insertion and removal of the filter medium <NUM>. Accordingly, the change of the old filter medium to a new one is easily carried out by utilizing the filter handling tool. Thus, the filtering device can be expected to provide safe and easy exchange of the filter medium as compared with the conventional filtering devices which can involve the dangerous, time-consuming work of thoroughly removing the hot molten metal from the filter box, subsequently breaking the exhausted filter medium and removing the fragments of the broken filter medium. This process with a conventional device entails the possibility that such fragments of the broken filter medium will remain in the filter housing and mingle into the molten metal to be treated in the subsequent cycle of filtration. While the tool is described primarily in association with the removal of ceramic foam filters, the tool can easily be used in other filter applications.

Referring now to <FIG>, the filter handling tool <NUM> is described in greater detail. The tool <NUM> includes a shank portion <NUM> having a lifting eye <NUM> at a first end. A head portion <NUM> is disposed at a second end of the shank portion <NUM>. A handle <NUM> is removably received through the lifting eye <NUM>.

The lifting eye <NUM> can also be detachable from the shank portion <NUM>. For example, the lifting eye can be threadedly secured to the shank at <NUM>. As illustrated, a threaded male lifting eye and female shank connection can be used. Of course, alternative mechanisms are contemplated including pinned or slot/groove arrangements. Alternatively, the lifting eye can have an outer dimension which is less than the greatest width dimension of the shank. Similarly, although lifting eye <NUM> is depicted as a closed circle, any shape configured to receive the handle would be acceptable. Furthermore, a closed shape is not required. Rather, a hook shape is also contemplated.

Although depicted herein as an "X" shaped head portion <NUM>, the head portion can be of many various shapes provided the filter plate <NUM> (note multiple stacked filter plates are shown, A-B-C) is sufficiently engaged. Moreover, the head is not required to be formed of spokes. For example, the head portion could be a contiguous plate. In this regard, the plate or spokes could form any shape that adequately engages the filter plate(s). The head portion can be permanently attached to the shank by a weld, for example.

In many environments, the filter handling tool will be comprised of metal. Desirable metals include steel, such as mild steel. To improve the resistance of the steel filter handling tool, it may be beneficial to provide the surface of the filter lifting tool with a coating of a refractory material. For example, the hanger can be coated with boron nitride to prevent metal adhesion during the filtration process. Another exemplary coating material is RFM, a composite refractory made of fiberglass fabric embedded in either a calcium silicate slurry, a fused silica slurry, or a combination thereof (available from Pyrotek Inc. of Spokane Washington). It is possible that only those portions of the filter handling tool that enter molten metal will receive the coating.

Generally speaking, the shank <NUM> can have a cylindrical shape to correspond with a hole <NUM> formed in filter plate <NUM>. However, it is noted that certain advantages may be achieved by forming the hole and shank of mated shapes that could prohibit rotation of the filter plate about the longitudinal axis of the shank. For example, corresponding cross-sectional rectangle or star shapes could be employed on each of the shank and hole. In many situations, it may be beneficial to have a close tolerance between the shank and the filter hole to prevent molten metal from traveling through any space created therein and not passing through the filter body. One mechanism for addressing this is to provide a gasket material or insert <NUM> between the shank and the filter plate. Ceramic fiber is a suitable material for forming the insert/gasket. Alternatively, an expandable material such as available from Shureseal may be used to form the gasket.

In certain installations, although unlikely, there is a "theoretical argument" that molten metal could by-pass the ceramic foam filter (CFF) by passing between the shank portion of the tool and the hole in the filter. Accordingly, a gasket may be included to prevent the metal bypassing the filter. In certain embodiments, the gasket can be placed at the top of the filter. For example the top filter plate could have a bigger hole than the lower second and/or third filter plates and this hole could be lined with a ceramic fibre tube. Similarly, in the case of a single plate filter, the hole can have different dimensions. For example, the hole can be larger at a top portion for receiving the gasket material and narrower at a lower portion to provide a closer tolerance with the shank portion of the tool. By placing the gasket seal at the top it reduces the possibility of bottom seal washing" into the melt. The installer can slide the bar through the hole to provide an improved seal. Ceramic fibre tube is desirable because it is inexpensive, molten metal resistant and compressible. The gasket may further prove advantageous because the bar may become worn and damaged over time and the chance of bye-pass increases.

The assembly can be constructed by first removing the lifting eye <NUM> and handle <NUM> from the shank <NUM> and inserting the shank through the filter(s) <NUM>. Lifting eye <NUM> can be reattached to the shank <NUM> and handle <NUM> inserted through lifting eye <NUM>. In this manner, the filter(s) are suspended on the hanger and can be lowered into the filter box <NUM>. The handling tool and associated filter(s) are prevented from dropping because the handle <NUM> is received in the locating grooves <NUM> in the filter box <NUM>.

In certain embodiments, the handle might be omitted such that the head portion of the tool rests on a floor of the filtration box during filtering. It is also noted that the filter may be slightly lifted using the tool during the tap out phase. By creating a small gap between the filter and the filtration box while the metal is still molten, freezing of the filter to the box can be prevented.

At the end of the filtration process the handle <NUM> is removed and a suitable lifting device is used in conjunction with the lifting eye <NUM> to remove the filter(s) from the filter box <NUM>. Advantageously, the filter including the present handling tool can be removed from an emptied filtration box much sooner than a filter removed using traditional techniques. Moreover, the filter can be removed using the present handling tool when the filter has cooled to a temperature below metal solidification. For example, a filter used for pure aluminum could be removed at about <NUM> or less. Traditional techniques cannot engage the filter until it has cooled to about <NUM>. The lifting eye is removed from the hanger tool and the hanger can be removed from the filter(s). If a reduced outer dimension eye configuration is used, the eye removal and reattachment steps can be omitted.

The present invention can provide a safer mechanism by which to insert and remove a filter to/from a hot filter box. The present invention can be adapted to any size or shape filter (for this disclosure a <NUM>" square filter is shown). The present invention can be used on single or multiple filters. The present invention can be used on ceramic foam filters, bonded particle filters, or other types.

When used with an electromagnetic filter box a steel hanger can help to channel and concentrate the electromagnetic fields. Accordingly, in one embodiment, a low frequency induction coil can be placed around and in very close proximity to a ceramic filter media. The presence of a magnetic field may allow priming of thicker filters. The orientation the coil and filter elements can be either vertical or horizontal, provided a path is made available for gas to escape during priming. The electrical conductors of the induction coil can have many different shapes. For example, flat round, tubular, rectangular, or square. Unlike traditional induction furnace coils, the coils of the present invention need not be constructed for low electrical resistance, as they are not being used as part of a device primarily intended for electrically efficient melting. Thus, a higher current density can be advantageously used (e.g. <NUM> A/mm<NUM> vs. typical values from <NUM>-<NUM> A/mm<NUM>) resulting in proportionately smaller diameter conductors that can provide more turns in a given height of coil, with a corresponding increase in the magnetic field strength. Single, double or more layers of coils can also be used advantageously to achieve even higher magnetic field strengths over the height of the filter media. Induction coils with more than <NUM> layers can also be used, but with diminishing benefits of additional magnetic field strength.

With continuing reference to <FIG>, in certain embodiments it may be desirable for the shank <NUM> to have a length greater than a depth of the filtration box from a top surface <NUM> of the filter(s) <NUM> to a floor <NUM> of the filter box <NUM>. In this manner, when inserted into the filter box, the shank <NUM> of handle <NUM> slides through hole <NUM> until head portion <NUM> engages floor <NUM>. This spaces head portion from the filters <NUM> to prevent head portion <NUM> from interrupting filtering surface area. By employing expandable gasket material in the filter hole <NUM>, the filter headling tool <NUM> can slide into engagement with the filter box floor yet the hole <NUM> becomes impervious to molten metal flow once the gasket material is heated and expands.

<FIG> shows a filter assembly <NUM> including an induction coil <NUM>. A two layer induction coil <NUM> is shown in <FIG>. A ceramic foam filter <NUM> is shown installed within the induction coil <NUM>. The induction coil <NUM> is preferably placed as close as possible to the edge of filter <NUM> to achieve the most advantageous results of the magnetic field. Suitable space must be allowed for gasket material <NUM> to prevent leakage of the liquid metal around the filter <NUM> and for thermal insulation and refractory material <NUM>. An exemplary gasket material would be a high temperature insulation wool such as alkaline earth silicate wool, alumina silicate wool and/or polycrystalline wool. The high temperature insulation wool can have minimal expansion at elevated temperature. In certain embodiments wherein multiple filter plates are used, it may also be desirable to place a layer of high temperature insulation wool between adjacent filter plates. Sufficient thermal insulation and refractory material must be present to avoid the contact of the hot metal in the upper portion of the bowl <NUM> or discharge portion of the bowl <NUM>, with coil <NUM> or with the coil leads <NUM>. In order to function as a filtration device, the bowl must be equipped with a suitable liquid metal feed <NUM> and discharge means <NUM>. The sides <NUM> and bottom <NUM> of the bowl must be designed with adequate refractory to maintain the heat balance of the metal to be filtered. Advantageously, the presence of the steel filter handling tool <NUM> can improve the performance by channeling the current within the filter <NUM>.

A current can be impressed on the induction coil of sufficient magnitude to generate an average magnetic flux density of <NUM>-<NUM> T, across the width of the unprimed filter. The frequency of the coil excitation current is preferably between <NUM> and <NUM>. The frequency of the coil excitation current is preferably in a range where the ratio between the electromagnetic penetration depth (. ) in the liquid metal in the upper portion of the bowl <NUM> and the average radius or width of the filter <NUM> is between preferably <NUM> and <NUM>, and more preferably between <NUM> and <NUM>, in order to achieve both a sufficiently high magnetic penetration and avoid excessive heating.

In one embodiment, liquid metal is added to the upper part of the bowl <NUM> via inlet <NUM> with current applied to coil <NUM>. Alternatively, liquid metal is added first, and then current is applied to coil <NUM>. In another embodiment, liquid metal fills the upper portion of bowl <NUM> to a sufficient height over the last turn of coil <NUM>, such that an electromagnetic meniscus is prevented from forming. This embodiment also avoids excessive oxidation of the metal during priming.

With reference to <FIG>, an alternative configuration of the head part of the lifting tool is depicted. Particularly, head portion <NUM> constitutes a cross provided with perimeter elements <NUM> to achieve an increased surface area for mating with a filter. This increased surface area is advantageous when the filter is being removed from the filtration box at elevated temperatures. Moreover, at the time of removal, the filter can contain entrained solidified and liquid portions of metal resulting in high weight and brittleness. An increased surface area head portion improves the ability of the tool to remove the filter at elevated temperatures, before solidification of the metal, without breakage. Of course, the shape of the head portion is not limited to rectangular.

Claim 1:
A method for mounting and removing a filter from a filtration box, said method comprising:
(a) providing a tool that comprises a shank (<NUM>), a head end (<NUM>) secured to a first end of the shank, a lifting eye (<NUM>) secured to a second end of the shank, and a handle (<NUM>) configured to be removably received by the lifting eye (<NUM>);
(b) detaching the handle (<NUM>) from the tool shank (<NUM>);
(c) inserting the tool shank (<NUM>) through a hole formed in a filter medium (<NUM>) made of porous ceramic material in the shape of a flat plate;
(d) re-attaching the handle (<NUM>) to the tool shank (<NUM>); and
(e) positioning the filter medium (<NUM>) in a desired location within a filter box (<NUM>) using said tool.