Technical Field

The present invention relates to an apparatus for use in a process for casting molten metal. In particular, the invention relates to an apparatus for filtering and distributing a flow of molten metal in a casting process.

Background

Large metal castings can pose some significant challenges in their manufacture. In order to ensure an adequate supply of molten metal to every part of the casting mould, gating systems are used to distribute molten metal via runners to different areas of the casting mould.

Filters are commonly used in metal casting to remove slag or dross from the molten metal and reduce turbulence before the metal reaches the casting mould. This reduces the level of inclusions and defects in the finished casting, leading to reduced scrap levels, reduced rework, improved machinability and overall casting cleanliness and quality. During filtration, inclusions are removed and trapped on the front face of the filter which limits the amount of metal that can pass through the filter. Typically, one cm ² of filter can filter 2.1-2.8 kg of steel or 1.4-2.0 kg of ductile iron, and attempts to put more metal through will result in the filter blocking due to trapped inclusions clogging or plugging the filter.

For medium and large metal castings, multiple filters are required to ensure adequate throughput. Typically, filters are provided in-line within the running system in a pre- formed cavity in the mould for each runner. For heavier castings, filters are often placed in refractory housings such as Foseco’s HOLLOTEX FST ^® which is used in ceramic running systems. These units are typically located in the mould beneath the casting cavity, and connected to in-gates positioned at optimal parts of the casting.

As casting weight increases, the filter requirements mean that it becomes increasingly complex and difficult to design practical runner systems to fit in one mould. For example, a 20 tonne steel casting will require 30 to 40 150 mm square filters. To overcome this, centrifugal filter systems such as those described in DE 4229417 C2 and those sold by Foseco under trade name HOLLOTEX CFU are commonly used for large ferrous castings. These high capacity filtration devices comprise a large refractory unit that houses 6 to 8 filters held together in a circular pattern. One or more units are incorporated into the running system for a casting that is typically bottom filled. Molten metal enters the unit and initially circulates around the filters, the metal then being directed centrifugally though the filters and out through an outlet in the centre of the unit, through one or more in-gates and into the casting cavity. One or more of these units may be used depending on the casting weight and metal volume requirements. These units however are large and heavy, meaning that they are difficult to handle and manoeuvre during moulding, and, together with their associated runner systems, take up a lot of space in the mould.

With these issues in mind, the present invention has been devised to provide a compact filter housing with a high filtration capacity, and which is particularly suitable for the effective filtration of medium and large size ferrous castings.

Summary

According to a first aspect of the invention, there is provided an apparatus for use in a process for casting molten metal, the apparatus comprising:

a base, a roof and a continuous sidewall therebetween, the base, the roof and the sidewall defining a chamber comprising a central inlet cavity;

an inlet opening, which feeds into the inlet cavity;

a plurality of outlet openings; and

a plurality of filters for filtering molten metal, the filters being arranged within flow paths between the inlet opening and the outlet openings,

wherein:

each outlet opening is located within a closed outlet cavity defined by a pair of filters and a portion of the sidewall;

the filters extend inwardly from the sidewall and from the base to the roof; and adjacent outlet cavities are separated from each other by inlet channels extending between the inlet cavity and the sidewall.

It will be understood that the term“closed outlet cavity” is intended to mean that the outlet cavity is closed with respect to the rest of the chamber such that, in use, the molten metal must pass through the filters as it flows from the inlet openings to the outlet openings. However, it will be appreciated that the outlet cavity is not completely sealed, since it comprises an outlet opening through which the molten metal flows out of the apparatus after being filtered, as described below.

In use, the apparatus receives a supply of molten metal, which is filtered within the apparatus and then distributed to different parts of the cast through the plurality of outlet openings, which may be connected to individual runners or in-gates. Molten metal flows into the central inlet cavity of the apparatus, via the inlet opening, and is then directed outwardly along the inlet channels and through the filters, into the outlet cavities. Once filtered, the molten metal flows out of the apparatus through the outlet openings. The velocity of the molten metal is minimised as it passes through the apparatus, thereby preventing turbulence as the molten metal flows into the mould.

The filters extend inwardly from the sidewall. Thus, each filter has an inner end, which is distal to the sidewall and proximal to the inlet cavity, and an outer end, which is distal to the inlet cavity and proximal to the sidewall.

In some embodiments, the filters are arranged radially around the inlet cavity, i.e. the filters are arranged such that they diverge from a common central point. The common central point may correspond to the centre of the inlet cavity. In some embodiments, the respective filters within each pair of filters defining an outlet cavity diverge from each other at an angle of less than 90°. In some embodiments, the respective filters within each pair of filters defining an outlet cavity diverge from each other at an angle of less than 80°, less than 70° or less than 60°. The radial arrangement is advantageous since it enables more filters, and thus more outlet cavities, to fit within the apparatus. The radial design thus allows the apparatus to be relatively compact. The compact design helps to minimise weight to assist handling and improve priming of the unit, and also allows moulding sand to be packed around the apparatus more easily.

The radial design also provides for higher filtration capacity and efficiency, since all filters are engaged simultaneously. It is believed that the flow of molten metal across the filter“washes” the surface of the filter, thereby hindering the build-up of inclusions and delaying the clogging up and blocking of the filter, thus allowing a higher amount of metal to pass through the filter. It will be appreciated that in embodiments wherein the filters are arranged radially, the outlet cavities and the inlet channels separating adjacent outlet cavities will consequently have a radial arrangement. In some embodiments, the volume of the outlet cavities is the same as the volume of the inlet channels, allowing maximum filtration efficiency to be achieved.

In some embodiments, either the roof or the base is removable. This means that the inside of the apparatus can be accessed to allow the filters to be inserted when the apparatus is assembled, or to allow the inside of the unit to be cleaned prior to moulding.

The base and the roof may therefore be connectable to one another. The base and the roof may be connected by any suitable means, such as a friction fit or by adhesive. Additionally or alternatively, the base and the roof may be held together by one or more external fastener such as a strap, typically a metal band.

In some embodiments, the inlet opening is located in the base. In some alternative embodiments, the inlet opening is located in the roof.

In some embodiments, the outlet openings are located in the base. In some alternative embodiments, the outlet openings are located in the sidewall. In some alternative embodiments, the outlet openings are located in the roof. In further embodiments, the outlet openings are located in any combination of the base, sidewall and/or roof (for example, some of the outlet openings may be located in the base and/or roof and some may be located in the sidewall).

Molten metal may flow in through an inlet opening in the base and back out through outlet openings in the base. Alternatively, the metal may flow in through an inlet opening in the base and out through outlet openings in the sidewalls. Alternatively, the metal may flow in through an inlet opening in the roof and out through outlet openings in the sidewall. Alternatively, the metal may flow in through an inlet opening in the roof or the base and out through outlet openings in the roof. The metal may also flow out through outlet openings located in any combination of the base, sidewall and/or roof. The location of the inlet and outlet openings will depend, amongst other things, on the size and shape of the casting, and on the optimal configuration of the runner system for supplying filtered metal to different parts of the casting.

At least one inlet opening may be provided. Where a large supply of molten metal is to be filtered and distributed, the apparatus may comprise additional inlet openings, with each of the inlet openings feeding into the central inlet cavity. In some embodiments, the apparatus comprises from 1 to 4 inlet openings. In some embodiments, the apparatus comprises 1 , 2, 3 or 4 inlet openings.

In some embodiments, the apparatus comprises from 3 to 12 outlet openings. In some embodiments, the apparatus comprises 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 outlet openings. In some embodiments, each outlet cavity comprises one outlet opening, so that the number of outlet cavities is equal to the number of outlet openings. In some alternative embodiments, each outlet cavity comprises from 2 to 4 outlet openings, so that the number of outlet openings is greater than the number of outlet cavities. In an embodiment, each outlet cavity comprises 2, 3 or 4 outlet openings. Since each outlet cavity is partly defined by a pair of filters, the number of filters may be equal to twice the number of outlet cavities.

In some embodiments, the portion of the sidewall which defines each outlet cavity comprises a radially inwardly projecting region (i.e. a projection) configured to direct the flow of molten metal towards the outlet openings. The sidewall within each inlet channel may also, or alternatively, comprise a projection configured to direct the flow of metal from the inlet cavity towards the filters defining the outlet cavities. The projections in the outlet cavities and/or inlet channels are believed to reduce turbulence and enable the metal to flow more efficiently through the apparatus, thus improving the filtration capacity. In an embodiment, the projections extend between the roof and the base.

The projections extend into the outlet cavities and/or inlet channels. The projections may be formed by an inwardly projecting portion of the sidewall (i.e. such that an indent is formed in the outer surface of the apparatus). Alternatively, the projections may be in the form of an insert which is attached to an internal surface of the sidewall or integrally formed with the sidewall, so that the projections effectively form a region of increased thickness of the sidewall. In this case, the projections may provide a convenient location to insert screws, push fit connectors or other means for anchoring the roof and/or base to the sidewall.

The projections may have a cross-section in the shape of a triangle having a base and two sides connected at an apex, the base being connected to the sidewall and the flow of molten metal being bifurcated at the apex and directed along the sides of the triangle. The apex of the triangle may be rounded, so that the projection has a curved shape. Alternatively, the projection may have a cross-section in the shape of a semi- circle having a base and a curved arc, with the base of the semi-circle connected to the sidewall. The skilled person will appreciate that the shape of the projections is not limited to these examples, and that the projections may be of any shape suitable for reducing turbulence and directing the flow of molten metal.

In some embodiments, the apparatus further comprises a plurality of supports arranged in a spaced apart configuration around the periphery of the inlet cavity and extending from the base to the roof, wherein each pair of filters extends between the sidewall and one of the supports.

In some embodiments, each support is in the form of a dividing wall (i.e. divider) which defines a fourth wall of an outlet cavity, in conjunction with the pair of filters and the sidewall. The use of dividers is advantageous over a design in which the filters of each pair are merely joined at their respective ends, since this ensures that molten metal cannot leak between the filters from the inlet cavity and must enter the outlet cavities via the inlet channels, ensuring that the molten metal is filtered before exiting the apparatus. The provision of supports or dividers also allows the filters to be slightly spaced apart, increasing the capacity of the outlet cavities.

The supports or dividers may also serve to hold the filters in place. In some embodiments, the inner end of each filter is located in a respective groove in the support or divider. By locating the inner end of each filter within a groove, the filter is held on both faces, thereby preventing lateral movement or tilting of the filter. It will be appreciated that since one support or divider is provided per filter pair, each support or divider will be provided with a pair of grooves, for receiving the inner ends of the pair of filters. The outer end of each filter may alternatively or additionally be located in a groove in the sidewall.

In some embodiments, a groove for receiving each filter is provided in the base and/or the roof of the apparatus, the filters being held within the grooves. Locating the filters within grooves in the base and/or the roof serves to further secure the filters in position, and helps to prevent lateral movement of the filter even in embodiments in which the filter is not held at either end by a groove in a support and/or in the sidewall. The use of grooves in the base and/or roof also supports the filter against the physical impact of the molten metal flow and minimises the possibility of filter breakages.

The filter may fit within the groove(s) snugly (i.e. a friction fit), preventing lateral movement of the filter. It will be appreciated that the size and shape of the grooves will be configured to correspond to the size and shape of the filters, to ensure a close fit. The filters may be conveniently fitted into the apparatus by simply sliding them into the groove(s), without requiring any additional tools to secure the filters in place.

As used herein, the term“groove” will be understood to mean a channel which has a bottom and two sidewalls. The bottom and the sidewalls of the groove are preferably planar, the sidewalls being perpendicular to the bottom, thereby enabling a close fit with a square edge or end of a filter. The groove therefore provides a contact with both faces of the filter, as well as with an edge or end of the filter that is positioned within the groove.

As well as holding the filter securely in place, the groove(s) in the supports or dividers, the sidewall, the roof and/or the base may provide a seal which prevents metal by- pass, i.e. where some metal does not go through the filter but leaks unfiltered through gaps around the edges of the filter. This is especially important if the filter were to tilt slightly in use, which would result in a significant gap opening up along the edge of the filter.

In some embodiments, each filter is supported between a pair of flanking posts. In some embodiments, the flanking posts extend perpendicularly from the base. In some embodiments, the flanking posts extend from the base to the roof. The flanking posts may be directly opposed on either side of the filter, or offset from each other at different distances along a longitudinal axis of the filter. In an embodiment, the flanking posts are located along the longitudinal axis of the filter at a distance approximately halfway between the sidewall and the inlet cavity, i.e. approximately halfway between the outer and inner ends of the filter, adjacent to a middle region of the filter. The flanking posts serve to hold the filter securely in place and prevent tilting, and, particularly in embodiments where no grooves are provided in the roof, the base, the dividers and/or the sidewall, prevent bowing or potential breakage of the filter when exposed to the stream of molten metal. Preferably, the width of the flanking posts is large enough to provide adequate support to hold the filter in an upright position without tilting, but not so large as to obstruct the flow of molten metal through the filter.

The filters may be of any suitable size and shape, and it will be appreciated that appropriate filter dimensions will be selected by the skilled person in accordance with the size and shape of the apparatus, and the arrangement of the filters therein. In some embodiments, the filters are rectangular or square.

In some situations, it might be desirable to use a filter which is smaller than the space provided in the apparatus for receiving the filter. Therefore, in some embodiments, the filter may be located within an adapter core. An adapter core provides a frame around the filter. The filter may be seated within the adapter core, and the filter and adapter core may then be inserted into the apparatus as a single unit. The adapter core may be made from any suitable material, such as core sand.

In some embodiments, each filter is composed of two filter elements, which are arranged end-to-end. Forming a filter from two filter elements may be particularly useful when relatively large elongated rectangular filters are required, and a single- piece filter may be difficult to manufacture or may not have sufficient strength to withstand the large stream of molten metal. The two filter elements may be joined end- to-end with the join positioned between the pair of flanking posts.

In some embodiments, the roof of the apparatus comprises a recess for receiving metal slag. Any slag present in the molten metal does not pass through the filters and will tend to rise to the top of the metal flow. Providing a recess in the roof of the apparatus for receiving the slag prevents it building up within the course of the flow of metal and obstructing the filters. In an embodiment, the apparatus has a cross-section which is generally circular in shape, with the sidewall defining the circumference of the circle.

The apparatus may be formed of any suitable refractory material which is capable of withstanding the temperature of the molten metal to be cast and the pressure used when compressing sand around the casting mould. Suitable materials include fused silica, precast concrete, fireclay, chemically bonded sand, and chemically bonded refractories and/or fibres. In some embodiments the material is an alumina based cement castable. In some embodiments the material is a slurry formed composition of bonded refractories and fibres.

Any conventional filter suitable for filtering molten metal may be employed in the apparatus. In some embodiments the filters are foam filters. In some embodiments, the filters are extruded or pressed cellular filters. Suitable foam filters include ceramic foam filters, such as silicon carbide-alumina filters such as those described in EP 0412673B1 and references therein, or zirconia filters such as those described by W H Sutton, J C Palmer, J R Morris:“Development of Ceramic Foam Material for Filtering High Temperature Alloys”, AFS Transactions, p339 (1985), and carbon bonded filters such as those described in W002/18075.

In some embodiments, the filters are carbon bonded filters.

It will be understood that the embodiments of the invention described herein may be combined in any way, unless otherwise indicated.

Brief Description of the Drawings

Embodiments of the invention will now be described with reference to the accompanying figures, in which:

Figure 1 a is a cross-sectional view of an apparatus according to an embodiment of the first aspect of the invention.

Figure 1 b is a cross-sectional view of the apparatus of Figure 1 a without filters. Figure 1 c is a perspective view of a part of a casting system comprising the apparatus of Figure 1 a, together with part of a runner system and part of a windmill hub casting;

Figure 2a is a top perspective view of a casting system comprising an apparatus according to an embodiment of the first aspect of the invention, together with part of a runner system and a cone crusher casting; and

Figure 2b is a bottom perspective view of the casting system shown in Figure 2a.

Detailed Description

Figure 1a shows an apparatus 100 for use in a process for casting molten metal according to an embodiment of the first aspect of the invention. The apparatus 100 comprises a base 2, a roof (not shown) and a continuous sidewall 4 therebetween. The base 2, the roof and the sidewall 4 together define an internal chamber which comprises a central inlet cavity 6. The apparatus 100 further comprises an inlet opening 8, which feeds into the inlet cavity 6, and a plurality of outlet openings 10.

A plurality of filters 12 for filtering molten metal are arranged within flow paths between the inlet opening 8 and the outlet openings 10 so that, in use, the molten metal is filtered as it flows from the inlet opening 8 to the outlet openings 10. Each outlet opening 10 is located within an outlet cavity 14 defined between a pair of filters 12 and a portion of the sidewall 4. The filters 12 extend from the sidewall 4 and, in the embodiment shown, are arranged radially around the inlet cavity 6. It can be seen that the angle between the filters within each pair is less than 90°. Adjacent outlet cavities 14 are separated from each other by an inlet channel 16 which extends between the inlet cavity 6 and a portion of the sidewall 4.

The apparatus 100 and the chamber defined within have a cross section which is generally circular in shape, with the sidewall 4 defining the circumference of the circle. The inlet cavity 6 is located in the centre of the circle, and the inlet opening 8 is located in the base 2 within the inlet cavity 6. The inlet cavity 6 itself is also circular in shape, and the filters 12 are arranged radially in an outer ring around the inlet cavity 6. The inlet channels 16 and outlet cavities 14 form segments of the outer ring, which comprises six inlet channels 16 and six outlet cavities 14. The outlet cavities 14 have a smaller volume than the inlet channels 16, because part of the available volume in these segments is taken up by the filters 12. The apparatus may comprise any suitable number of outlet cavities 14 and inlet channels 16, depending on the size and nature of the apparatus 100 and the casting. However, the number of inlet channels 16 should preferably equal the number of outlet cavities 14, so that the inlet channels 16 and the outlet cavities 14 alternate around the outer ring and molten metal enters the outlet cavities 14 from both sides.

In the illustrated embodiment, the apparatus 100 further comprises supports in the form of dividing walls or dividers 18, arranged in a spaced apart configuration around the periphery of the inlet cavity 6. In an alternative embodiment (not shown) the supports may take the form of posts instead of dividing walls. Posts may be useful, for example, in a smaller apparatus where the volume of the internal chamber is more limited. The filters 12 extend between the dividers 18 and the sidewall 4, defining the outlet cavities 14 therebetween.

The sidewall comprises radially inwardly projecting regions (or projections) 20, 21 which are integrally formed with the side wall. The projections 20, 21 are located centrally in the portion of the sidewall within each inlet channel 16 and outlet cavity 14. The projections 20, 21 have a cross-section in the shape of a rounded triangle having a base and two sides connected at a rounded apex. The base of the triangle is connected to the sidewall 4 and the rounded apex extends inwardly from the sidewall into the inlet channel 16 or outlet cavity 14. When molten metal flows into the inlet channels 16, it is bifurcated by the rounded apex of the projections 20 and directed towards the filters 12 on either side. When the metal flows into the outlet cavities 14 through the filters 12 on either side, it is directed up the sides of the projections 21 towards the outlet openings 10. This ensures that the molten metal flows smoothly through the apparatus with minimal turbulence. The projections 21 within the outlet cavities 14 are smaller than the projections 20 within the inlet channels 16 due to the smaller volume of the outlet cavities 14.

The filters 12 are held within grooves 22 in the base 2, which are illustrated in Figure 1 b. The grooves 22 extend between the sidewall 4 and the dividers 18. At a first inner end, the filters are held within grooves 24 in the dividers 18, while at a second outer end, the filters are held within grooves 26 in the sidewall 4, which are also illustrated in Figure 1 b. The filters 12 fit within the grooves 22, 24, 26 snugly (i.e. a friction fit), so that lateral movement of the filters 12 is prevented. A pair of flanking posts 28 on either side of the filter 12 provides further support, to prevent lateral movement and tilting. The flanking posts 28 are directly opposed to each other and positioned adjacent to a middle region of the filter 12, approximately halfway between the sidewall 4 and the divider 18.

In use, molten metal enters the inlet cavity 6 through the inlet opening 8 in the base 2. The metal then flows into the inlet channels 16, where it is directed towards the filters 12 by the projections 20. Slag, dross and other solid impurities are removed from the molten metal as it passes through the filters 12. The removed impurities are trapped on the faces of the filters and smaller inclusions in the body of the filters, whereas larger impurities tend to rise to the surface of the molten metal, where they are received in a recess in the roof (not shown). Some of the smaller inclusions collecting on the filters are removed by the molten metal flowing across the surface of the filters, washing away inclusions building up and delaying filter clogging and blockages. Once the molten metal has filtered through the filters into the outlet cavities 14, it is directed by the projections 21 towards the outlet openings 10 in the base 2, where the molten metal exits the apparatus 100.

The illustrated embodiment is of an apparatus which is suitable for large castings up to 15 tonnes, such as a ductile iron windmill hub housing, and the apparatus 100 may have a diameter of approximately 1 m. In such large pieces of apparatus, long rectangular filters are required. Therefore, each filter 12 is composed of two filter elements which are joined end-to-end between the flanking posts 28.

Figure 1 c shows a part of a casting system 150 comprising the apparatus 100 of Figure 1 a in use in the production of a large ductile iron windmill hub casting 30. The casting 30 weighs approximately 13.3 tonnes and the total poured weight is approximately 17.8 tonnes. Metal enters the mould via a downsprue 32 then flows along the runner 34 and up into the apparatus 100 via an inlet opening 36. After flowing through the inlet channels and filters (not shown), the metal exits the apparatus 100 via outlet openings 38, along runners 40 and enters the mould cavity through in-gates 42 to produce the casting 30. Figures 2a and 2b show a cast system 250 for a steel cone crusher casting 130, produced using an apparatus (not shown) according to an embodiment of the first aspect of the invention. The cast system 250 comprises a steel casting 130, a downsprue 52, two series of runners 58a and 58b, and in-gates 74. The cast system 250 further comprises a disc 200 of residual metal and used filters 68, formed from use of the apparatus (not shown) which is removed after casting together with the mould (also not shown). The casting 130 weighs approximately 3 tonnes and the total poured weight is 4 tonnes. The residual disc of cast metal 200 has the same dimensions of the internal chamber of the apparatus used, and the features of the disc 200 mirror those of the apparatus. Thus, it will be understood that features of the apparatus are described below with reference to the features of the disc 200. These features include the internal shape and profile of a base 51 (shown in Figure 2b), a roof 53 (shown in Figure 2a), and an internal surface of a continuous sidewall 56 therebetween.

At the time of casting, metal entered the apparatus (not shown) via the downsprue 52, and flowed through an inlet opening 50 and into an inlet cavity 66. The metal then flowed into inlet channels 64, and was guided towards a pair of filters 68 by projections on the internal surface of the sidewall 56 within the inlet channels 64, resulting in indents 72 in the disc of solidified metal 200. The metal flowed from the inlet channels 64, through the filters 68 and into the outlet cavities 62. The dimensions of each outlet cavity 62 are defined by the pair of filters 68, a divider 70, and portions of the sidewall 56, roof 53 and base 51. From the outlet cavities 62 the filtered metal flowed through outlet openings 54 into the runners 58a and 58b, through the in-gates 74 (shown in Figure 2b) and into the mould cavity to produce the casting 130. The casting 130 is separated from the running system for inspection and prepared for its end use e.g. cleaned, machined and painted.