GB2155377A - Forming boxless foundry moulds by vacuum packing - Google Patents

Abstract

A plastics film 10 is sucked by vacuum against the whole of the interior of an open-topped moulding box 1, pattern plate 3, and pattern 4, and the box 1 is filled with unbonded, dry sand 23 which is vibrated and a cover 24 is sealed to the plastics film 10 to form a compact mould which is largely or completely enclosed by plastics film and is then evacuated. After release of the plastics film 10 the compact mould is removed for use in a boxless moulding assembly for vacuum metal casting, in which venting may be effected along the parting plane between the halves of the moulding assembly. The cover 24 may be a plastics film with a mould evacuation piece employed within the sand to evacuate the mould, or it may be a lid vacuum sealed to the film 10 and through which the mould is evacuated. The lid may also be used as a vacuum-operated mould handling device. The boxless mould halves (76,77, Figure 4) are held together for casting by vacuum, the plastics films at the parting plane having been perforated, prior to assembly of the halves, by pricking (78), there being peripheral seals (79,80) at the edge of the parting plane. <IMAGE>

Description

SPECIFICATION Foundry moulds The invention relates to foundry moulds for the socalled vacuum process, in which unbonded, dry aggregate material is retained in the moulding box by vacuum, with the face of the mould covered by a plastics film.

In the existing process for forming vacuum moulds, the pattern is first covered by a film of plastics which has been heated and is in a ductile condition. The film is then sucked into close contact with the pattern, a vacuum being applied by means of many small holes drilled through the pattern in communication with a vacuum plenum below the pattern plate. The empty moulding box is then placed over and around the pattern in the usual way, resting on the plastics film which covers the pattern, and is filled with dry, unbonded aggregate material, such as silica sand, level with the top of the box. A cover which may be in the form of a further plastics film is then placed over the box.Vacuum is then applied to the box to consolidate the sand, and the vacuum holding the plastics film over the pattern is released and the box lifted off the pattern ready for use in casting as half of the moulding box assembly. The vacuum is maintained on all parts of the moulding box assembly until after the castings have been poured; during pouring the film adjacent the hot metal melts and sinks into the surface of the mould, and the metal flows quietly whilst gases emitted from the moulds are sucked away into the vacuum system.

In this known process, when the castings are ready for stripping the moulds are placed on a grid and the vacuum is released. The castings remain on the grid and the sand falls through to be reused, any remaining plastics film being removed at this stage.

The process described above has certain inherent disadvantages. Firstly, the moulding boxes need to be rigidly constructed, and their complex construction makes them both heavy and expensive. Secondly, in common with all other moulding processes using boxed moulds, the box is occupied by sand from the moment the mould is made until the time when the casting is removed from the box.

This means that a large number of boxes is required, representing a high capital investment and a considerable need for maintenance and storage.

It is an aim of the invention at least partially to overcome these difficulties.

According to a first aspect of the invention, we provide a method of forming a foundry mould comprising at least the following steps: (i) applying a plastics film by a vacuum to a pattern plate and to the whole of the interior surface of an opentopped moulding box; (ii) filling the box with unbonded, dry aggregate material, and applying vibration to compact the aggregate material; (iii) applying a cover to the open top of the box and sealing the cover to the film to form a sealed compact mould; (iv) evacuating the compact mould; (v) releasing the film from the pattern plate and the moulding box; and (vi) removing the compact mould from the box.

After the sealed compact mould has been removed from the moulding box it may be transported to a casting location where it is brought together with a similar complementary sealed compact mould to form a moulding assembly; the moulds each forming a half of the moulding assembly and having a mould cavity between them.

It will be appreciated that the moulding box is absent from the moulding assembly when the castings are poured.

In this way, a single box is employed merely as a supporting frame whilst making the compact mould and it does not require the complex construction of conventional moulding boxes. The capital tied up in boxes and the problem of maintaining and storing a large number of boxes are both reduced.

The complete moulding assembly may assume any desired orientation during casting, that is to say the parting plane between the halves of the moulding assembly may be horizontal, vertical or even inclined.

It is often necessary, during casting, to provide means for venting the mould cavity to atmosphere so as to maintain the shape of the mould cavity while it is being filled with molten metal. Since there is no restriction of a moulding box surrounding the sealed compact moulds of the moulding assembly, such venting means can easily be provided along the parting plane between the halves of the moulding assembly.

Another advantage of the present invention is that it is particularly suitable for the formation of a moulding assembly which has a substantially vertical parting plane between the halves of the assembly. This normally requires the clamping together of the two halves of the assembly which may be achieved in a conventional manner by using support plates and clamps. However, according to a further feature of the invention a vacuum connection is provided between the mating surfaces of the halves of the moulding assembly and the moulding assembly is sealed around its edge and around the perimeter of the mould cavity at the parting plane between the halves so that the two halves are clamped together by the vacuum applied to the moulds.

In the formation of a sealed compact mould, the sides of the box are preferably slightly tapered to assist in removal of the mould. Additionally or alternatively the sides of the box may be formed integrally with the pattern plate, or secured to it, or the pattern plate may be movable with respect to the box to assist in removal of the mould.

The periphery of the film is preferably clamped to the upper edges of the moulding box using a vacuum which may be derived from the same pump and applied at the same time as the vacuum drawing the film to the pattern plate. In a preferred embodiment, the upper ends of the walls of the moulding box are provided with an open-topped channel containing porous material to which vacuum may be applied to draw the film down onto the porous material and thereby clamp the film.

The porous material may, for example, be bonded aggregate material or a perforated gauze.

The cover applied to the open top of the box may comprise a second plastics film. The seal between the first and second films may be made by welding the films together, for example by means of gas burners. The first and second films preferably are brought into engagement before sealing by means of a clamping frame.

Alternatively, instead of a second plastics film the cover applied to the open top of the box may comprise a lid having a peripheral sealing rim. The lid may be sealed to the film applied to the interior of the box by any convenient means, but preferably the sealing rim of the lid is vacuum sealed to the periphery of the film.

The mould may be evacuated by means of a mould evacuation piece connected to a vacuum pump and positioned within the moulding box before the moulding box is filled with aggregate material.

When the cover comprises a lid having a sealing rim which is vacuum sealed to the periphery of the film, the mould may be evacuated through the lid instead of by means of a mould evacuation piece.

Preferably, the lid then comprises a body of porous material partially enclosed by a backing plate having a peripheral sealing rim or skirt, one face of the body being engageable with the upper surface of the aggregate material in the box and the porous body being connectable to a vacuum pump. The porous body may comprise a body of bonded aggregate material such as silica sand or sintered metal.

The mould may be removed from the moulding box by means of a vacuum-operated mould handling device, which may also be used for transporting the mould to a casting location and for supporting the mould during casting, particularly when the mould forms half of a moulding assembly which has a substantially vertical parting plane.

The vacuum-operated mould handling device may comprise the lid which is vacuum sealed to the film and through which the mould is evacuated. When the cover of the mould comprises a second plastics film the vacuum-operated mould handling device may be of similar form to the lid as described above.

According to a second aspect of the invention we provide a mould evacuation piece for evacuation of a sealed foundry mould comprising a body disposed in use within the mould, the interior of which is connectable with a vacuum pump, prefer ably by means of a releasable connector which in use is disposed substantially externally of the mould and a non-return valve. Preferably, the mould evacuation piece is arranged sealingly to engage the internal wall of the mould.

The mould evacuation piece may comprise a po rous body within which is located a perforated duct connectable with the vacuum pump. The porous body preferably comprises a body of bonded aggregate material such as silica sand or sintered metal.

Alternatively, the mould evacuation piece may comprise a rigid body having at least one opening or perforate section covered with a perforate material, such as gauze. In this case the body may comprise an arrangement of tubes connectable with the vacuum pump, or a box having an opening or perforate section in at least one face covered with a perforate material.

According to a third aspect of the invention we provide a vacuum-operated mould handling device comprising a partially sealingly enclosed body of porous material one face of the porous body being engageable with the body to be handled surrounded by a peripheral sealing rim or skirt and the porous body further having disposed within it a perforated duct connectable to a vacuum pump.

The porous body may comprise a body of bonded aggregate material such as silica sand, or sintered metal.

Either or both of the above mould evacuation piece or vacuum-operated mould handling device may be employed in the above method of forming a foundry mould, with a common vacuum system being used in connection with either or both the former devices together with the vacuum used to apply the film to the interior of the moulding box.

According to a further aspect of the present invention we provide a method of clamping together two complementary sealed, compact moulds to form a moulding assembly having a mould cavity comprising the steps of applying a vacuum to each compact mould, bringing the mating surfaces of the moulds together to form the moulding assembly, providing a vacuum connection between the mating surfaces of the moulds, sealing the moulding assembly around its edge at the parting plane between the mating surfaces, and sealing around the perimeter of the mould cavity so that the moulds are clamped together by the vacuum applied to the moulds.

Some embodiments of the above aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic cross section through a moulding box and a pattern plate for use in a method in accordance with the first aspect of the invention; Figure 2 is a section corresponding to Figure 1 of an alternative moulding box and pattern plate; Figure 3 is a section corresponding to Figure I of another alternative moulding box and pattern plate; Figure 4 is a diagrammatic cross-section through a moulding box and pattern.plate showing the formation of a mould in accordance with the first aspect of the invention; Figure 5 is a diagrammatic cross-section through a mould evacuation piece in accordance with the second aspect of the invention in place against part of a wall of a moulding box;; Figure 6 is a diagrammatic perspective view of the mould evacuation piece of Figure 5; Figure 7 is a plan view of an alternative mould evacuation piece in accordance with the second aspect of the invention; Figure 8 is a perspective view of another alternative mould evacuation piece in accordance with the second aspect of the invention; Figure 9 is a diagrammatic cross-section through part of a moulding box and showing a further alternative mould evacuation piece in accordance with the second aspect of the invention; Figure 10 is a perspective view of the upper part of a wall of a moulding box showing a port and a removable section of the wall; Figure 11 is a perspective view of the upper part of a wall of a moulding box and a mould evacuation piece;; Figure 12 is a diagrammatic cross-section through a moulding box with a cover in the form of a second plastics film and a clamping frame in place; Figure 13 is a sectional view of an alternative cover in the form of a porous body partially enclosed by a backing plate; Figure 14 is a sectional view of the cover of Figure 13 vacuum sealed to a mould; Figure 15 is a perspective view of the cover of Figure 13 vacuum sealed to a mould; Figure 16 is a sectional view of a vacuum-operated mould handling device in accordance with the third aspect of the invention; Figure 17 is a diagrammatic cross-section through an alternative vacuum-operated mould handling device; Figure 18 is a cross-section on the line 18-18 of Figure 17; Figure 19 is a cross-section through part of a moulding assembly which has a horizontal parting plane and a side vent;; Figure 20 is a cross-section similar to Figure 19 and showing an alternative side vent; and Figure 21 is a diagrammatic cross-section through a moulding assembly in which the mould halves are clamped together by a method in accordance with the fourth aspect of the invention.

A foundry mould is formed in a moulding box 1.

Figure 1 shows a moulding box I having tapered walls 2 and in engagement with, or alternatively formed integrally with, a pattern plate 3 carrying a pattern 4. The pattern plate 3 incorporates standard core box vents and in addition small holes of approximately 0.5mm diameter leading to a vacuum plenum chamber 6 beneath the pattern plate 3. In an alternative construction shown in Figure 2, a clearance of approximately 0.5mm is provided between a movable pattern plate 3 and the moulding box walls 2 in the lowest position of the pattern plate. In this construction, the pattern plate 3 is upwardly movable with respect to the walls 2. In another alternative construction, shown in Figure 3, a clearance of approximately 0.5mm is provided between the upper surface of the pattern plate 3 and the lower ends of the walls 2 in the highest position of the pattern plate.In this construction, the pattern plate 3 is downwardly movable with respect to the walls 2.

The tapered walls 2 are in addition provided at their upper ends with an open-topped channel 7 filled with porous bonded aggregate 8 or a perforated gauze and connectable to a vacuum pump (not shown) by means not shown. As shown in Figures 1, 2 and 3 the channel 7 is formed in an outwardly directed flange 9.

In the formation of a mould, a plastics film 10 is draped over the top of the box and over the flanges 9, as shown in Figure 4. The channel 7 in the upper ends of the walls 2 is.then evacuated and the film is clamped to the flange 9 by the vacuum. The plastics film is heated and the plenum chamber 6 is evacuated. The plastics film 10 is drawn by the vacuum into close conformity with the walls of the box and with the pattern and pattern plate.

The box 1 is then filled with dry, loose aggregate material such as sand 23 and vibrated to compact the sand in a known manner. A strickling device (not shown) is then used to level the sand at the top of the box 1. A very. effective vacuum strickling device may be used, consisting of a straight edge containing a slot connected to the vacuum system, which removes any excess sand as it is passed across the top of the box.

With the vacuum plenum chamber 6 and channel 7 still evacuated, a cover 24 is applied to the top of the box 1 and sealed to the periphery of the plastic film 10 which overlies the channel 7. The cover 24 may comprise a second plastics film which can be sealed to the film 10 by a method illustrated in Figure 12. Alternatively, the cover 24 may be of the form described with reference to Figures 13, 14 and 15. The compacted sand 23, the plastics film 10 and the cover 24 form a sealed compact mould which is then evacuated by one of various means to be described. When the compact mould has been evacuated it consists of a hard body of aggregate material largely or wholly enclosed by plastics film which can then be removed from the box 1 prior to casting.

One way of evacuating the compact mould when it is in the moulding box 1 is by means of a mould evacuation piece 12 or pieces positioned within the moulding box before the moulding box is filled with aggregate material. Various forms of mould evacuation pieces are shown in Figures 5 to 9.

Figures and 6 show a mould evacuation piece 12 which comprises a porous body 16 of bonded aggregate material such as sand or sintered metal, disposed within which is a perforated duct which may be in the form of a tube 17. The porous body 16 is mounted on a rigid steel support plate 18 which may be backed with a resilient sealing layer 19 of rubber. The tube 17 is connectable by means of a stem 20 including a nog-return valve 21 and a quick-release connector 22 to a vacuum pump (not shown).

Figure 7 shows an alternative mould evacuation piece which comprises a body 16 in the form of a tubular ring 25 having perforate sections 26 covered with a fine gauze 27. The ring 25 is connecta ble to a vacuum pump (not shown) by means of a rigid stem 20 which may also includes a non-return valve and a quick-release connector (not shown).

The stem 20 extends through a steel support plate 28 backed with a resilient sealing layer of rubber 29. The rigid stem 20 may also provide a means of handling a mould.

Figure 8 shows a further alternative mould evacuation piece 12 which comprises a body 16 in the form of a box-like structure 30 having a perforate panel 32 in a side face 31 covered with a fine gauze. The interior of the box structure 30 is connectable with a vacuum pump by a stem 20 similar to those of Figures 5, 6 and 7. A resilient sealing layer 33 of rubber may be provided on the face of the body opposite face 31.

When a mould evacuation piece having a stem 20 (as shown in Figures 5 to 8) is used to evacuate the sealed compact mould, the moulding box 1 is preferably so constructed as to allow the compact mould complete wth the mould evacuation piece to be removed from the moulding box without the mould evacuation piece having to be disconnected from its vacuum pump. Figures 10 and 11 show alternative ways of achieving this.

in Figure 10 a port 11 is provided in a wall 2 of the moulding box by means of which a mould evacuation piece 12 is fitted to the mould. A hole 13 (Figure 5) is made in the film 10 in the region of an aperture 14 in the wall 2, above which a portion 15 of the wall 2 is arranged to be partially or completely removable so that the mould can be removed from the box 1 at a later stage. The portion 15 of the wall may be hinged to the rest of the wall 2 for this purpose. When the mould evacuation piece 12 is positioned in the moulding box the stem 20 is passed through the hole 13 in the film 10 and the aperture 14 in the wall, with the sealing layer 19, 29 or 33 in engagement with the film 10.

When a cover is sealed to the film 10 the compact mould is then evacuated by means of the mould evacuation piece 12, by making the connection between the valve 21 and the vacuum pump. Evacuation is rapid and complete and the compact mould then consists of a hard body of compact sand largely or wholly enclosed by plastics film, which can be removed from the box 1 prior to casting.

The portion 15 of the wall is removed and with the mould still under vacuum, atmospheric pressure is restored to the plenum chamber 6 and the channel 7 of the flange 9, so releasing the film 10 from the box 1 and the pattern plate 3. The mould can then be lifted out of the moulding box 1 and taken to a casting location with its interior still under vacuum.

In the arrangement shown in Figure 11 the moulding box 1 is provided with a recess 35 in the upper edge of one of the walls 2. The stem 20 of the evacuation piece 12 includes a portion 36 which fits neatly into the recess 35. This arrangement enables the mould evacuation piece 12 to be lowered into the moulding box 1, eliminating the need for a hole to be formed in the plastics film 10 to accommodate the stem 20. This is a much simpler arrangement than that shown in Figure 10.

Figure 9 shows a further alternative mould evacuation piece 12 positioned inside a moulding box 1. This evacuation piece 12 comprises a porous body 16 of bonded aggregate material having a female vacuum line connection 37 connectable to a complementary plug-in male connection 38 from a vacuum pump. This stemless mould evacuation piece aids removal of the spent plastics film 10 after casting and may be disposable.

Figure 12 shows the application of a cover 24 in the form of a second plastics film to the top of the moulding box 1. A clamping frame 39 brought into engagement with the edges of the films in the region of the flange 7, clamps the films 10, 24 together. The mould may then be evacuated by means of a previously inserted mould evacuation piece 12 such as one of those shown in Figures 5 to 9. A gas burner (not shown) with a ring of appropriately placed burner nozzles may then be used to flame weld the films together at their edges, thereby to enclose the sand 23 in between the two films to form a compact mould, and the clamping frame 39 is removed.

Figures 13, 14 and 15 show an alternative cover 24 which may be applied to the top of the moulding box 1. The cover 24 comprises a lid in the form of a porous body 40 of bonded aggregate material partially enclosed by a backing plate 41 having a peripheral sealing skirt 42. The porous body is connectable with a vacuum pump (not shown) by means of a stem connection 43 which extends through the backing plate 41 and vacuum distribution channels 45. Reinforcing bars 44 are provided around the perimeter of the backing plate 41.

When the lid 24 is placed over the moulding box 1 filled with compact aggregate material, the stem connection 43 is connected with a vacuum pump so that the periphery of the plastics film overlying the upper edges of the box is sealed by vacuum to the skirt 42 of the lid as shown in Figure 14. The film 10 and the lid 24 forming a complete enclosure for the compact mould in the box. The compact mould may then be evacuated by means of the vacuum applied to the porous body 40 of the lid through the stem connection 43. The cover 24 shown in Figures 13 to 15 may also be used as a vacuum-operated mould handling device for lifting the mould from the box 1 and for transporting it to a casting location. For this purpose the cover 24 is provided with lifting handles 46 on the end reinforcing bars 44 and support trunnions 47 on the sides of the skirt 42 which enable the mould to be rolled-over into the desired orientation for casting in the complete moulding assembly.

When the cover 24 comprises a second plastics film as already described with reference to Figure 12, the mould may also be lifted out of the box 1 and transported to a casting location by a vacuumoperated mould handling device of a similar form to the device shown in Figures 13 to 15. Alternative vacuum-operated mould handling devices are shown in Figure 16 and Figures 17 and 18.

The vacuum-operated lifting device 50 of Figure 16 comprises a porous body 51 of bonded sand or sintered metal partially enclosed by a body portion 52, the porous body having a flat face 53 for engagement with the mould to be lifted. The flat face 53 is surrounded by an annular rubber seal 54 carried by the body portion 52. Embedded in the porous body 51 is a perforated duct in the form of a tube 55 similar to that of the mould evacuation piece 12 of Figures 5 and 6. A stem 56 attached to the tube 55 passes through the body portion 52 for connection with a vacuum pump (not shown) and a lifting ring 57 is attached to the upper face of the body portion 52.In use, the device 50 is lowered onto the top of the compact mould to be lifted and the porous body 51 evacuated to vacuum seal the device 50 to the compact mould, and the device lifted by means of ring 57 to lift the compact mould from the box 1.

An alternative vacuum-operated mould lifting and handling device 60 is shown in Figures'17 and 18. The device 60 also comprises a porous body 61 partially enclosed by a body portion 62 and having a flat face 63 surrounded by a rubber seal 64. The porous body 61 is evacuated by means of a duct 65 extending along the body and which forms one side of the body portion 62. The side of the duct 65 adjacent to the body 61 has openings 66 along its length covered with a gauze 67. The duct 65 is connectable with a vacuum pump (not shown) through a hollow support arm 68 rotatably mounted in a bearing 69. The whole device 60 is able to rotate through at least 180= and enables a half mould to be rotated into the correct orientation in the complete mould assembly.

A single vacuum system or separate vacuum systems may be used to evacuate the mould, the plenum chamber, the channel of the box flange and the porous body of the vacuum-operated mould handling device 50 or 60.

Two compact moulds prepared as described above can be placed together to form a moulding assembly having a mould cavity into which the casting is poured whilst the vacuum in the moulds is maintained. In a moulding assembly which has a horizontal parting plane the top half of the moulding assembly will contain a sprue through which the metal is poured to enter the mould cavity, and may also contain vents and feeders. The sprues can be formed by methods conventionally used in vacuum process moulding, but alternatively sprues and runners may be provided by the use of foamed polystyrene inserts, which vapourise on contact with molten metal. Vents are necessary to maintain the shape of the mould cavity while it is being filled with molten metal. The formation of vents by methods conventionally used in vacuum process moulding is a tedious and time consuming task.Usually such vents are made from pre-prepared inserts or they may be formed by pulling the heated plastics film over vertical pegs on the pattern. In both instances it is necessary to open the vents to atmosphere, for example, by using a hot wire. Because the physical restriction of the moulding boxes is removed in the boxless method of mould making, vents can be easily directed towards the mould edge, usually along the parting plane, where they open directly to atmosphere, considerably increasing mould production rate.

One or more vents per casting may be provided.

Two alternative methods of side venting are shown in Figures 19 and 20.

In Figure 19 the vent from the mould cavity 73 to atmosphere comprises a gap 70 of approximately 0.5mm between the upper half 71 and the lower half 72 of the moulding assembly. In Figure 20 the vent from the mould cavity 73 to atmosphere comprises a porous insert 74, such as of bonded aggregate material, moulded into the upper half 71 of the moulding assembly and a gap 75 of approximately 3mm between the outer edges of the halves 71 and 72 of the moulding assembly.

Accurate location of the top and bottom mould halves of the moulding assembly can be achieved by incorporation of complementary male and female tapered lugs on the two halves, which are features of the pattern plate and formed on the mould surface.

As with conventional vacuum process moulds, pouring basins may be formed into the surface of the mould by removable inserts. When this method is used, the surface of the inserts must be covered by a plastics film which is transferred to the mould when the insert is removed. Alternatively, such basins may be moulded separately in a refractory material and placed on top of the sprue prior to pouring.

The above method can also be applied to moulding assemblies subsequently assembled with a vertical parting plane. Vertically poured moulds have the advantage that time is saved in forming and cutting sprue and vent holes because these are formed directly from the pattern, but are difficult to achieve in conventional vacuum process moulds because of the presence of the moulding boxes.

When a second plastics film is used as a cover, so that the mould is completely encased in sealed plastics film, support plates are usually required in a moulding assembly having a vertical parting plane to enable the halves of the assembly to be clamped together. When the cover comprises a lid through which the mould is evacuated and which is used as a vacuum-operated mould handling device, the lid may provide a built-in support for the mould in the moulding assembly.

Figure 21 shows a moulding assembly having a vertical parting plane and in which the two halves 76 and 77 are clamped together by the vacuum applied to each half. Vacuum communication between the two halves 76 and 77 is established through fine holes 78 in the plastics films 10 on the mating surfaces of the halves; the holes 78 having been formed by pricking of the plastics films before the halves were brought together. In the complete moulding assembly seals 79 and 80 are respectively provided around the perimeter of the moulding cavity 81 and at the edge of the parting plane between the mould halves. Vacuum clamping of the halves of the moulding assembly eliminates the need for support plates and conventional clamps.A thin clay paste may be used to provide the seals 79 and 80 but sealing may alternatively be achieved by moulding a small ridge around the perimeter of the moulding cavity and around the edge of the mating surface of one or both of the moulds.

Using the method of mould making described, with boxless moulds completely or largely encased in sealed plastics sheeting, it is possible to maintain the vacuum within a mould for a limited period of time with the vacuum shut off. This provides greater latitude for handling than is normally the case with vacuum formed moulds in moulding boxes where it is very difficult to maintain good vacuum seals between the plastics sheet and moulding box. However, the vacuum must be maintained during pouring, at which stage the seal may be broken by molten metal splashes and some gases which are formed have to be sucked away through the vacuum system.

After casting, when solidification has been completed, the moulds are transported, still under vacuum, to a shake-out station at which the vacuum is released and the contents of the mould disintegrate. If this is carried out over a suitable grid the castings remain on the grid. The remaining plastic film is removed from the sand and the sand is reused. When a mould evacuation piece 12 is used it may be reclaimed at this point for re-use in the production of another mould.

Claims (40)

1. A method of forming a foundry mould comprising the steps of applying a plastics film by a vacuum to a pattern plate and to the whole of the interior surface of an open-topped moulding box; filling the box with unbonded, dry aggregate material and applying vibration to compact the aggregate material; applying a cover to the open top of the box and sealing the cover to the film to form a sealed compact mould; evacuating the compact mould; releasing the film from the pattern plate and the moulding box; and removing the compact mould from the box.

2. A method of forming a foundry mould as claimed in claim 1 in which the sides of the box are slightly tapered to assist in removal of the mould.

3. A method of forming a foundry mould as claimed in claim 1 or claim 2 in which the pattern plate is movable with respect to the box to assist in removal of the mould.

4. A method of forming a foundry mould as claimed in any of the preceding claims in which the periphery of the plastics film is clamped to the upper edges of the moulding box by a vacuum.

5. A method of forming a foundry mould as claimed in claim 4 in which the upper ends of the walls of the moulding box are provided with an open-topped channel containing porous material to which vacuum is applied to draw the film onto the porous material and thereby clamp the film.

6. A method of forming a foundry mould as claimed in any of the preceding claims in which the cover comprises a second plastics film which is sealed to the first plastics film so that the sealed compact mould is completely enclosed by plastics film.

7. A method of forming a foundry mould as claimed in claim 6 in which the first and second films are brought into engagement and welded together.

8. A method of forming a foundry mould as claimed in any of claim 1 to 5 in which the cover comprises a lid having a peripheral sealing rim which is sealed to the film applied to the interior of the moulding box so as to form a sealed compact mould that is largely enclosed by plastics film.

9. A method of forming a foundry mould as claimed in any of the preceding claims in which the mould is evacuated by means of a mould evacuation piece connectable with a vacuum pump and positioned within the moulding box before the box is filled with aggregate material.

10. A method of forming a foundry mould as claimed in claim 9 in which the interior of the body of the mould evacuation piece is connectable with a vacuum pump by means of a releasable connector which in use is disposed substantially externally of the mould, and a non return valve.

11. A method of forming a foundry mould as claimed in claim 9 or claim 10 in which the mould evacuation piece is arranged sealingly to engage the internal wall of the mould.

12. A method of forming a foundry mould as claimed in any of claims 9 to 11 in which the body of the mould evacuation piece comprises a porous body of bonded aggregate material.

13. A method of forming a foundry mould as claimed in any of claims 9 to 11 in which the body of the mould evacuation piece comprises a rigid body having at least one opening or perforate section that is covered with a perforate material.

14. A method of forming a foundry mould as claimed in any of claims 9 to 13 in which the mould evacuation piece has a hollow stem which extends from the interior of the body and which is connectable with a vacuum pump.

15. A method of forming a foundry mould as claimed in claim 12 in which the porous body incorporates a female vacuum line connection.

16. A method of forming a foundry mould as claimed in any of claims 9 to 15 in which the moulding box is so constructed and arranged as to allow the compact mould complete with the mould evacuation piece to be removed from the moulding box without the mould evacuation piece having to be disconnected from its vacuum pump.

17. A method of forming a foundry mould as claimed in claim 16 in which a wall of the moulding box has a removable upper section provided above a port through which the connection from the mould evacuation piece to the vacuum pump extends when the mould evacuation piece is in place within the moulding box, the upper section being removable to allow the compact mould to be lifted out of the moulding box while still being connected to the vacuum pump.

18. A method of forming a foundry mould as claimed in claim 16 in which the moulding box is provided with a recess in the upper edge of one of its walls for receiving the connection from the mould evacuation piece to the vacuum pump allowing the compact mould to be lifted out of the moulding box while still being connected to the vacuum pump.

19. A method of forming a foundry mould as claimed in claim 8 in which the peripheral sealing rim of the lid is vacuum sealed to the film.

20. A method of forming a foundry mould as claimed in claim 19 in which the mould is evacuated through the lid which is applied to cover the open top of the moulding box.

21. A method of forming a foundry mould as claimed in claim 20 in which the lid comprises a body of porous material partially enclosed by a backing plate having a peripheral sealing skirt, one face of the body being engageable with the upper surface of the aggregate material in the box and the porous body being connectable with a vacuum pump.

22. A method of forming a foundry mould as claimed in any of the preceding claims in which the mould is removed from the moulding box by means of a vacuum-operated mould handling device.

23. A method of forming a foundry mould as claimed in claim 22 in which the mould is transported to a casting location by the vacuum-operated mould handling device.

24. A method of forming a foundry mould as claimed in claim 23 in which the mould handling device helps to support the mould during casting when the mould forms half of a moulding assembly which has a substantially vertical parting plane.

25. A method of forming a foundry mould as claimed in any of claims 22 to 24 in which the mould handling device comprises a body of porous material partially enclosed by a backing plate having a peripheral sealing skirt, one face of the body being engageable with the upper surface of the mould and the interior of the body being connectable with a vacuum pump.

26. A method of forming a foundry mould as claimed in any of claims 22 to 24 as appended to claim 20 or 21 in which the lid which is applied to cover the open top of the box also constitutes the vacuum-operated mould handling device.

27. A method of forming a foundry mould as claimed in any of the preceding claims comprising the further steps of transporting the sealed compact mould to a casting location, bringing the mould together with a similar sealed compact mould to form a moulding assembly which has a mould cavity between the two halves of the assembly, and providing venting means along the parting plane between the two halves of the moulding assembly.

28. A method of forming a foundry mould as claimed in any of claims 1 to 26 comprising the further steps of transporting the sealed compact mould to a casting location, transporting a similar complementary sealed compact mould to the casting location, applying a vacuum to each compact mould, bringing the mating surfaces of the moulds together to form a moulding assembly, providing a vacuum communication between the mating surfaces of the moulds, and sealing the moulding assembly around its edge and around the perimeter of the mould cavity at the parting plane between the moulds so that the moulds are clamped together in the complete moulding assembly by the vacuum applied to the moulds.

29. A method of forming a foundry mould as claimed in claim 28 in which vacuum communication between the complementary moulds is established through holes pricked into the plastics films on the mating surfaces of the moulds.

30. A method of forming a foundry mould substantially as described herein with reference to Figures 1 to 4 of the accompanying drawings.

31. A method of forming a foundry mould as claimed in claim 30 and using a mould evacuation piece substantially as described herein with reference to any of Figures 5 and 6, Figure 7, Figure 8 or Figure 9 of the accompanying drawings.

32. A method of forming a foundry mould as claimed in claim 31 and using a moulding box substantially as described herein with reference to Figure 10 of the accompanying drawings.

33. A method of forming a foundry mould as claimed in claim 31 and using a moulding box substantially as described herein with reference to Figure 11 of the accompanying drawings.

34. A method of forming a foundry mould substantially as described herein with reference to Figure 12 of the accompanying drawings.

35. A method of forming a foundry mould as claimed in claim 30 and using a cover substantially as described herein with reference to Figures 13 to 15 of the accompanying drawings.

36. A method of forming a foundry mould as claimed in claim 31 and using a vacuum-operated mould handling device substantially as described herein with reference to Figure 16 of the accompanying drawings.

37. A method of forming a foundry mould as claimed in claim 31 and using a vacuum-operated mould handling device substantially as described herein with reference to Figures 17 and 18 of the accompanying drawings.

38. A moulding assembly formed from two complementary foundry moulds made by the method of claim 30 and provided with venting means substantially as described herein with reference to Figure 19 of the accompanying drawings.

39. A moulding assembly formed from two complementary foundry moulds made by the method of claim and provided with venting means substantially as described herein with reference to Figure 20 of the accompanying drawings.

40. A method of clamping together two complementary foundry moulds formed by the method of claim 30 substantially as described herein with reference to Figure 21 of the accompanying drawings.