Casting tool and casting machine comprising a casting tool

TECHNICAL FIELD AND PRIOR ART

The invention relates to a casting tool for use in a casting machine for the purpose of producing castings, which casting tool comprises a bottom mold element having a top-open mold recess defining at least part of the shape of the casting to be produced, and an ejector assembly which can be moved relatively to the first mold element in the direction of a vertical Z-axis and comprises at least one ejector rod, which can be inserted into the mold recess of the bottom mold element by displacing the ejector assembly relatively to the bottom mold element. In a generic casting tool, a base member of the ejector assembly to which the at least one ejector rod is attached, is disposed in an ejector region or ejector zone below the bottom mold element. Furthermore, at least two force transferring members extending in the direction of the Z-axis are provided, which are designed to transfer downward forces applied to the mold element to a bed of the casting machine disposed below the casting tool, at least one outer force transferring member being provided which is disposed next to the base member such that said force transferring member is offset in the horizontal direction, while at least one inner force transferring member is provided, which extends through a through bore in the base member.

Generic casting tools are used in the production of sand castings, for example. Sand is shot into a cavity formed by a top and a bottom mold element and is then converted to a dimensionally-stable sand body by subjection to gas treatment.

In this and other casting processes, it is necessary for the two mold elements to be pressed together with the application of very large forces so that the cavity formed by the mold elements retains its dimensional stability even when subjected to high pressure during the sand shooting process and so that the sand and/or gas cannot escape through gaps between the mold elements.

The forces required for this purpose are coupled into the casting tool by the casting machine. The force flow in the region of the bottom tool half from the bottom mold element down to the machine bed disposed below the casting tool poses a problem in this context, since the base of the ejector assembly is provided below the bottom mold element. This base member has to be vertically displaceable relatively to the bottom mold element in order that the ejector rod attached to said base member can be moved into the mold recess following solidification of the sand body and thus cause the casting to leave the wall of the mold recess. This base member of the ejector assembly prevents the downwardly directed forces acting on the bottom mold element from being transferred through the entire base area of the mold element to the machine bed. Instead, the forces in generic casting tools are mostly transferred, to a significant extent or exclusively, by way of a peripheral frame as the outer force transferring member, this completely surrounding the base member of the ejector assembly. The transference of forces to the machine bed exclusively by way of such a frame or other outer force transferring members is detrimental, since the large forces can result in deflection or warping of the bottom mold element if the latter is supported only in border regions. It is therefore known from the prior art to attach the additional inner force transferring members mentioned above to the underside of the mold element, which inner force transferring members extend downwardly from the bottom mold element and, like the outer force transferring members, transfer the downwardly applied forces directly to the machine bed.

This described construction of generic casting tools suffers from a significant drawback. The bed of those casting machines in which a generic casting tool can be used, usually has only defined load bearing regions that are suitable for absorbing the forces transferred through the inner force transferring members. Thus the inner force transferring members cannot be arranged in an arbitrary manner but must be adapted to comply with the casting machine used such that the inner force transferring members are aligned with said load bearing regions in the direction of the Z-axis. This circumstance is particularly detrimental, since no ejector rods of any kind can be provided in that region of the casting tool in which the inner force transferring members are located, because the base member of the ejector assembly must have through bores in said regions for the inner force transferring members. Therefore, unsatisfactory compromises have had to be accepted as regards the arrangement of the ejector rods.

OBJECT OF THE INVENTION AND ITS ACHIEVEMENT

It is therefore an object of the invention to improve a generic casting tool to the effect that the forces acting downwardly on the bottom mold element can be transferred by inner and outer force transferring members to the machine bed without restricting the flexibility in terms of the arrangement of the ejector rods of the ejector assembly.

This object is achieved, according to the invention, by providing the casting tool with a tool bed beneath the base member of the ejector assembly, which tool bed is permanently connected to at least one of the force transferring members, this tool bed being designed in such a way that when the bottom mold element is subjected to a downwardly acting force, both the downwardly transferred forces acting on the outer force transferring member and the downwardly transferred forces acting on the inner force transferring member are coupled into the tool bed.

According to the construction of the invention, a device in the form of the tool bed closing the bottom end of the casting tool is provided as part of the casting tool, which device absorbs forces transferred via the different force transferring members and couples said forces into the machine bed. To this end, the tool bed is of a substantially rigid design. Due to this tool bed, it is irrelevant as to what parts of the machine bed, on which the tool bed rests, can be subjected to load, since all downwardly transferred forces acting on the bottom mold element are transferred through the inner and outer force transferring members to the common tool bed, which can then in turn be adjusted such that it imparts load to those parts of the machine bed that are specific to the casting machine. Due to the presence of the tool bed, the arrangement of the inner force transferring members no longer has to comply with the specific load bearing regions of the machine bed but can make allowance for other parameters such as the locations at which no ejector rods are required.

For the purposes of this invention, all relevant designations relating to position such as, “beneath”, “above”, “near” and all indications of direction and orientation such as, “downward”, “upward”, “horizontal”, and “vertical” refer to a standard and preferred orientation of the casting tool in which the machine bed is oriented horizontally and represents the bottom supporting surface for the casting tool. Nevertheless, the invention naturally also relates to casting tools and casting machines used in different orientation, in which case the appropriately modified designations referring to position and direction shall apply.

For the purposes of this invention, the bottom mold element includes all components which are provided above the base member of the ejector assembly and are in a fixed position relative to the mold recess of the bottom mold element with the exception of the force transferring members themselves. The bottom mold element thus also includes, in particular, a supporting plate to which both the force transferring members and a molding block can be attached, the mold recess of the bottom mold element being provided in the top surface of said molding block.

The mold recess in the bottom mold element itself forms part of the contour of the casting to be produced. Usually, a top mold element is additionally provided, which comprises a bottom-open mold recess, which together with the top-open mold recess defines the overall shape of the casting to be produced. This top mold element can be displaced relatively to the bottom mold element for opening and closing the casting tool.

The base member of the ejector assembly is preferably in the form of a base plate to which the preferably more than one ejector rods are fixed, at least in relation to the Z-axis, with the aid of screw connections.

The tool bed itself is preferably of a flat design. It extends horizontally at least in such a way that all inner and outer force transferring members can couple the downwardly acting forces further downwardly into the tool bed. The tool bed is preferably in the form of a separate unit attached to the inner and/or outer force transferring members, preferably by screw connections.

In the simplest case, the tool bed can be in the form of a one-piece plate. The invention also includes multi-piece designs of the tool bed.

The tool bed preferably extends in a horizontal plane at least to such an extent that it projects beyond all sides of the base member of the ejector assembly in the horizontal direction. The tool bed can thus support inner force transferring members guided at arbitrary locations through through bores of the base member.

The at least one inner force transferring member is preferably in the form of an at least substantially cylindrical column extending in the direction of the Z-axis. The outer force transferring member is preferably in the form of a peripheral frame which surrounds all sides of the base member in the horizontal direction. Such a peripheral frame, which may be composed of several parts, is well-suited for the transference of forces. Furthermore, such a frame is suitable for producing a gastight seal around the ejector region. This is advantageous when using a casting tool of the invention for producing sand castings since the sand is gas-treated after being shot in during the sand casting process in order to solidify the sand core. The peripheral frame effectively prevents the gas escaping through the ejector bores from the mold recess into the ejector region from being released at the sides of the ejector region into the environment.

The peripheral frame preferably has four sides disposed in the form of a rectangle, the tool bed extending to below all four sides of the frame. This construction firstly makes possible a particularly advantageous transference of forces to the tool bed, since the latter can be subjected to forces on all four sides of the frame forming an outer force transferring member. Secondly, such a construction is advantageous in that it makes it possible to connect the periphery of the tool bed to the frame in a gastight manner. Such a peripheral gastight connection makes it possible to provide, with the aid of the underside of the bottom mold element, the frame, and the tool bed, a buffer region, which is closed in an at least substantially gastight manner, and from which the gas can escape only from those parts of said buffer region which are intended for this purpose. Optionally necessary access openings in the ejector region that are used for subjecting the base, member of the ejector assembly to a force in order to raise the ejector assembly can be sealed with little effort, for example by means of O-rings and sealing lips.

As regards the displacement of the ejector assembly relative to the bottom mold element, it is advantageous when actuating extensions are attached to the underside of the base member of the ejector assembly. These actuating extensions project into through bores that are disposed in the tool bed and that extend in the direction of the Z-axis, sealants being provided that seal the through bores at least in an end position of the ejector assembly. These actuating extensions allow actuators disposed on the machine side to control, from below, the position of the ejector assembly relative to the bottom mold element. The provision of actuating extensions on the tool side, which extensions project into the through bores in the tool bed that are provided for this purpose, can help produce a particularly advantageous seal with the aid of sealants since the latter only have to act between components provided on the tool side and not between the casting machine or, in particularly, the machine bed on the one hand and the casting tool on the other. The sealants are formed in such a way that they seal the through bores in the tool bed in a gastight manner at least in the bottom end position of the ejector assembly, which end position is ensured when the ejectors assume their predetermined positions for the sand-shooting and gas-treatment processes. The ejector region can be completely encapsulated in a gastight manner during operation, as a result of this measure and due to the horizontal extension of the tool bed described above, and the design of the outer force transferring member in the form of a peripheral frame.

In the simplest case, a tool bed of the invention can comprise contact regions for contact with the underlying machine bed only in the outer peripheral region. In such a case, the forces transferred by way of the inner force transferring members to the tool bed are further passed on toward the outer regions and coupled into the machine bed in the outer peripheral contact region described above. However, it is particularly advantageous when planar contact regions are provided on the underside of the tool bed for direct contact with the casting machine bed, at least one inner contact region being disposed directly beneath the base member and at least one outer contact region being offset in the horizontal direction relative to the base member. The inner contact region makes it possible to reduce the occurrence of bending moments inside the tool bed so that the latter can be designed to absorb only small bending moments. The at least one inner contact region is disposed directly below the base member of the ejector assembly, that is to say, without being offset in relation to the base member of the ejector assembly. By contrast, the at least one outer contact region is disposed outside the base member and thus offset in relation thereto. The contact regions can be part of a uniform, flat plane. They can also be formed as separate convex regions so that this design ensures that the forces are coupled into the machine bed only at locations provided for this purpose on the machine side.

The inner force transferring members must be provided in a manner that enables the forces that are transferred downwardly to the bottom mold element to be transferred to the machine bed in such a way that the bottom mold element does not experience severe torsion or deflection. For this purpose, preferably at least three inner force transferring members are provided which are disposed in a non-linear manner in relation to a horizontal plane.

In a particularly preferred design of the tool bed, at least two superimposed, permanently interconnected plates are provided, the uppermost plate being in tangible contact with the at least two force transferring members when the casting tool is subjected to force, and the bottom plate being in tangible contact with the machine bed, thus forming the bottom closure of the tool bed and thus also the bottom closure of the casting tool. Such a design of the tool bed comprising at least two plates makes it possible to adapt the topmost plate to specific tool parameters, such as the arrangement of the inner or outer force transferring members, and to adapt the bottommost plate to the casting machine, particularly to those load regions of the casting machine bed that may be subjected to forces. The result is a modular concept, which with the aid of predetermined connecting dimensions of the plates in relation to each other makes it possible for only the specific plate of the tool bed to be replaced or adapted during replacement of the casting tool or the casting machine.

It is particularly advantageous when the tool bed comprises at least three plates stacked as a layered construction, at least one intermediate plate being made of aluminum or an aluminum alloy and preferably one bottom closure plate made of a steel material being disposed beneath said intermediate plate. There are many advantages gained by such a construction comprising an intermediate plate of aluminum. The intermediate plate of aluminum can be used in order to achieve a predefined overall height of the tool in spite of the varying height of the mold elements. Aluminum is particularly suitable for this purpose due to its comparatively low density. As a result of the use of a bottom closure plate of a steel material beneath the intermediate plate of aluminum, the assembly or disassembly of the casting tool does not subject the intermediate plate to any heavy mechanical loads. The intermediate plate does not come into direct contact with the bed of the casting machine.

It is particularly preferred that the intermediate plate have a thickness of at least 30 mm in the direction of the Z-axis in order to provide the tool bed with a high degree of stability. It is further advantageous when the intermediate plate is made of a high-strength aluminum alloy since this makes it possible to achieve a particularly distortion-free construction of the tool bed.

In order to keep down the weight of the intermediate plate, bores aligned preferably in the direction of the Z-axis are provided in the intermediate plate, the internal volume of the bores being preferably at least 25% and more preferably at least 50% of the material volume of the remaining intermediate plate. It is considered to be particularly advantageous when the arrangement of these bores resembles a matrix construction or a hexagonal honeycombed construction. The bores give rise to considerable weight reduction without significantly impairing the stability of the intermediate plate.

In a development of the invention, at least one of the force transferring members is attached only to one side of the bottom mold element or the tool bed, while at least one other force transferring member is attached to both the bottom mold element and the tool bed. The force transferring member that is attached to the bottom mold element and the tool bed provides permanent attachment of the tool bed to the casting tool. However, it is not necessary for all of the force transferring members to be attached on both sides. Installation can be facilitated considerably when the force transferring members are attached, at least in part, on one side only. Since the force transferring members are continually subjected to pressure and not to tensile forces, the merely one-sided attachment of the force transferring members does not pose any problems. Preferably, the at least one outer force transferring member is attached on both sides while the at least one inner force transferring member is attached on only one side, preferably to the bottom mold element.

Furthermore, the invention also relates to a casting machine equipped with a casting tool proposed by the invention and of the type described above, the casting machine being designed to subject the casting tool to a closing force from two opposing sides in the direction of a vertical Z-axis.

The casting machine preferably comprises a machine bed comprising at least one central load bearing region disposed in the direction of the Z-axis beneath the base member of the ejector assembly, this load bearing region being offset in relation to the Z-axis and the at least one inner force transferring member of the casting tool. The possibility of this offset provided by the tool bed allows the inner force transferring members to be positioned ideally within the casting tool irrespective of the casting machine and the load bearing regions thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional aspects and advantages of the invention will become apparent from the claims and the following description of a preferred exemplary embodiment of the invention explained below with reference to the figures, in which:

FIG. 1 is a sectional view of a casting tool of the invention resting on the bed of a casting machine, and

FIG. 2 is an exploded view of the casting tool shown in FIG. 1.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 show a casting tool of the invention. This casting tool comprises a series of components which can be moved relatively to each other during the intended operation of the tool.

These different components are briefly described below and the operating mode of the casting tool is explained with reference to these components. These components are explained with reference to FIG. 1, in particular. FIG. 2 serves for the purpose of clarification. Some components of the casting tool such as the ejector rods 34 and the corresponding bores 22a and the molding blocks 16, 26 are not shown in FIG. 2 for the sake of clarity.

Referring to FIG. 1, the topmost of the components illustrated is the top mold element 10. The top mold element 10 comprises a horizontal top supporting plate 12, on which a downwardly oriented peripheral frame 14 is mounted. In the open space delimited by the supporting plate 12 and the frame 14, a top molding block 16 is disposed, on the underside of which a mold recess 18 is provided which defines the shape of the top surface of a casting 8 to be produced. The top supporting plate 12, the peripheral frame 14 and the top molding block 16 are in a fixed position relative to each other during operation.

The bottom mold element 20 is disposed below the top mold element 10. The former comprises a bottom supporting plate 22, on the top surface of which a bottom molding block 26 is mounted, on the top surface of which a bottom mold recess 28 is provided.

The top molding block 16 and the bottom molding block 26 are formed in such a way for the purpose of interaction that in the closed state shown in FIG. 1, the mold recesses 18, 28 form a substantially closed, joint cavity. The shape of this cavity corresponds to that of the casting 8 to be produced.

An ejector assembly 30 is provided below the bottom mold element 20. This ejector assembly has a horizontally extending base plate 32, to which individual ejector rods 34 extending upwardly in the direction of the bottom mold element 20 are attached with the aid of screw connections. These ejector rods 34 protrude through ejector bores 22a, 26a in the bottom supporting plate 22 of the bottom mold element 20 and the bottom molding block 26 toward the mold recess 28. This ejector assembly 30 makes it possible to lift the casting 8, following solidification thereof by gas treatment, from the bottom mold recess 28 by raising the base plate 30 together with the ejector rods 34 in the direction of the bottom mold element 20. The function of the ejector assembly 30 will be explained below in more detail. The ejector assembly 30 is guided in a manner, not illustrated in detail, with the aid of guide bolts 36 and guide bores 22b in the bottom supporting plate 22.

The operating mode of the components of the casting tool explained so far is as follows: the casting tool is used to produce sand cores 8 which define cavities inside the workpiece in subsequent metal-casting processes. For producing such a sand core 8, the top mold element 10 and the bottom mold element 20 are moved toward each other until the molding blocks 16, 26 bear against each other. The height of the molding blocks 16, 26 is such that only a sealing cord 14a provided in the direction of the periphery of the underside of the top frame 14 comes into contact with the bottom supporting plate 22 in the closed state of the casting tool 16, 26. As a result of closing the casting tool 16, 26, the ejector rods 34 are simultaneously pushed through from the bottom mold recess 28 until they assume the position illustrated in FIG. 1 since, when closing the casting tool, the distal end 36a of the guide bolt 36 of the ejector assembly 30 comes into contact with the top supporting plate 12 of the top mold element 10 and is pressed down by the same. In the closed state of the casting tool 16, 26, sand is shot into the cavity formed by the mold recesses 18, 28 via injection channels 16a and nozzles provided for this purpose. The sand in the mold recesses 18, 28 is then solidified by feeding in a gas, as intended for this purpose, through the injection channels 16a to produce a dimensionally stable sand body 8, which can be removed from the bottom mold recess 28, after opening the casting tool 16, 26, by raising the ejector assembly 30 and thus causing the ejector rods 34 to move into the bottom mold recess 28.

During the process of shooting the sand into the mold recesses 18, 28 and the gas treatment, it is necessary for the molding blocks 16, 26 to be tightly pressed against each other so that neither sand nor significant amounts of gas can escape from the cavity formed by the mold recesses 18, 28 in the region of the mold parting line. In order to achieve this end, the casting machine illustrated only partially subjects the casting tool to large forces—in this case, upwardly and downwardly directed forces of about 60 kN. For the purpose of guiding these considerable forces from the bottom mold element 20 to a machine bed 6 disposed beneath the casting tool, several force transferring members 40, 44 are provided at the level of the base plate 32 of the ejector assembly 30. A frame 40, acting as an outer force transferring member surrounding the base plate 32, is attached to the bottom supporting plate 22. Since the frame 40, acting as an outer force transferring member, is clearly offset outwardly in the horizontal direction in relation to the bottom molding block 26, additional inner force transferring members are provided in the form of columns 44 that are likewise attached to the bottom supporting plate 22. In order to enable these columns 44 to cause the transferred force to by-pass the base plate 32 of the ejector assembly 30, through bores 32a, through which the columns 44 can protrude, are provided in the base plate 32.

The force transferring members in the form of the frame 40 and the columns 44 do not act directly on the machine bed 6. Instead, a tool bed 50, which is part of the casting tool described, is provided between the force transferring members 40, 44 and the machine bed 6. This tool bed 50 comprises a top closure plate 52, a bottom closure plate 54 and an intermediate plate 56 located therebetween. The plates 52, 54, 56 are permanently interconnected by means of screws. The plates 52 and 54 are made of a steel material while the intermediate plate 56 located therebetween is made of a high-strength aluminum alloy. For the purpose of weight reduction, both the bottom closure plate 54 and the intermediate plate 56 are provided with vertical bores 54a, 56a, which, in the case of the intermediate plate 56, consequently reduce the weight of the same by almost 50%. It has been found that these bores 54a, 56a do not reduce the stability of the tool bed 50 to a significant extent.

The tool bed 50 is permanently connected to the frame 40 in the region of the top end plate 52 with the aid of screw connections so that the tool bed is always stationary in relation to the bottom mold element 20. By contrast, as inner force transferring members, the columns 44 are merely fixed to the bottom supporting plate 22 for the purpose of facilitating assembly. However, they extend downwardly to such an extent that they are in contact with the top closure plate 52 either constantly or at least when the casting tool is subjected to force by the casting machine.

The inner force transferring members in the form of the columns 44 and the outer force transferring member in the form of the frame 40 together serve to guide forces that downwardly act on the casting tool into the machine bed 6. The arrows 90a, 90b indicate the manner in which the forces acting on the top mold element 10 are transferred via contact regions of the molding blocks 16, 26 and the sand in the mold recesses 18, 28 to the bottom molding block 26, whence they are transferred to the bottom supporting plate 22, as indicated by the arrows 91. The forces transferred to the bottom supporting plate 22 are transferred, in part, to the frame 40 in the manner indicated by the arrow 92a. However, a considerable force component, in particular a component of at least 50% of the force, is transferred in the direction of the arrows 92b to the columns 44. Both the forces transferred to the frame 40 and those transferred to the columns 44 are directed further to the tool bed 50, the forces being first coupled in the direction of the arrows 93 into the top closure plate 52 and thence to the intermediate plate 56 and then to the bottom closure plate 54. This bottom closure plate 54 can be provided with a planar underside. Here, the underside of the bottom closure plate 54 comprises a convex boundary region 54b and central regions 54c that are also slightly convex. These convex regions correspond in position to the load bearing regions 6b, 6c of the machine bed 6 so that the forces coupled into the tool bed 50 are coupled in the direction of the arrows 94a, 94b exclusively into these regions of the machine bed 6.

The primary purpose of the tool bed 50 is to enable the downward forces acting on the tool bed to be absorbed at arbitrary points and to be coupled into regions of the tool bed that are provided for this purpose. It is therefore not necessary for the inner force transferring members in the form of columns 44 to be aligned with the coupling regions 6c of the machine bed 6. Instead, the columns 44 can be provided at those points on the bottom supporting plate 22 that require no ejector rods 34. If the resultant arrangement of the columns 44 on the bottom supporting plate 22 is offset in relation to the contact regions 6c, this offset is compensated by the tool bed 50.

An additional advantage of the tool bed 50 is that the region 70, which is surrounded by the bottom supporting plate 22 and the frame 40 and in which a major part of the ejector assembly is disposed, is substantially sealed on its underside by the top end plate 52 of the tool bed 50. The region 70 is thus sealed in a gastight manner in relation to the environment except for purposes of access that will be explained below, so that the gas escaping through the ejector bores 26a, 22a in the direction of the arrows 80 during gas-treatment of the sand core 8 can only be released into this region 70 but not into the environment. The gas can be extracted from the region 70 with the aid of suction devices in a manner not illustrated. It is important to prevent this gas from escaping, since harmful gases are used for solidifying the sand core 8. In devices known in the prior art and in which the frame and/or the columns come directly into contact with the machine bed 6, it is difficult to produce a perfect seal, because this seal must be produced between the casting tool on the one hand and the casting machine on the other.

To make it possible to raise the ejector assembly 30 in relation to the bottom mold element 20, downwardly extending extensions 38 are attached to the base plate 32 of the ejector assembly 30, which extensions 38 extend through corresponding access bores in the plates 52, 54, 56 and can be raised by force applied by actuators 7 provided in the machine bed so that the entire ejector assembly 30 can be raised in relatively to the bottom mold element 20. In order that a gastight seal of the region 70 against the environment can still be produced, sealing rings 39 are provided on the extensions 38 on the underside of annular flanges 38a. These sealing rings 39 rest against the top closure plate 52 of the tool bed 50 in the state shown in FIG. 1 and thus prevent gas from escaping through the bores in the tool bed 50.

As mentioned above, the top and the bottom closure plates 52, 54 are made of a steel material, while the intermediate plate 56 is made of a much lighter, high-strength aluminum. The top closure plate is adapted to suit the casting tool. Depending on whether larger or smaller frames 40 are used, different types of top closure plates 52 can be reserved for this purpose. However, the bottom closure plate 54 is adapted in a manner that is predominantly specific to the casting machine since the convex regions 54b, 54c are positioned to agree with the load bearing regions 6b, 6c of the machine bed 6. In addition to its force-distributing function, the intermediate plate 56 also serves the purpose of height compensation, in particular. This makes it possible to use casting machines that are designed for taller casting tools by using an appropriately thicker intermediate plate 56.

This modular construction of the tool bed 50 allows for the production of a casting tool of this type from a variety of reserved versions of the top and bottom closure plates 52, 54 and the intermediate plate 56 in a short period of time. It is not necessary to additionally adapt the bottom mold element 20 or the force transferring members 40, 44 and the ejector assembly 30 to suit the casting machine being used.