Title of Invention

A CENTRIFUGAL CASTING APPARATUS.

Abstract

This invention relates to a centrifugal casting apparatus has a hollow mold (13) suitable for the centrifugal casting. For the manufacture of cast workpieces by the centrifugal casting method a plurality of mold cavities (14) formed by at least one hollow mold (13) are arranged and driven such that the mold cavities (14) rotate about a common axis of rotations (18). At least three mold cavities (14) which rotate in a single plane are provided.

Full Text

The invention relates to a centrifugal casting method, a centrifugal casting apparatus and a hollow mould according to the preambles of the independent main claims. The invention further relates to a runner bush moulder for the manufacture of a hollow mould and the application of the method or apparatus according to the invention for the manufacture of specific workpieces from specific materials. In generic centrifugal casting methods the mould filling of the mould cavity in a hollow mould is based on the hollow mould being displaced around an axis of rotation in a rotational movement. As a result of this rotational movement, a corresponding centrifugal force acts on the liquid molten casting material during pouring in, pressing the casting material into the mould cavity and ensuring complete filling. Depending on the density and heat capacity of the casting material, different rotation speeds are required for complete filling of the mould cavity. On the one hand, this is based on the fact that only a corresponding relatively weak centrifugal force acts on materials having a relatively low density, for example titanium, so that a correspondingly higher rotational speed must be selected to apply a sufficiently high filling force. In addition, materials having a low heat capacity such as titanium solidify relatively quickly so that complete filling of the mould cavity which requires sufficient flowability of the casting material must be accomplished in a very short time. A high rotational speed is again required for such short filling times. In commercially available centrifugal casting apparatus for high-quality casting, such as those used for example in dental technology and jewellery manufacture, there is only one hollow mould which rotates at a 2 certain distance about an axis of rotation located outside the hollow mould. From this it follows that considerable centrifugal forces act on the hollow mould itself. Thus, in order to keep the hollow mould on its rotational path in known centrifugal casting apparatus, solid mechanical superstructures are required to absorb the centrifugal forces and compensate for the imbalance produced by the rotating mass of the hollow mould and the mass of the casting material. The solid mechanical structure of known centrifugal casting apparatus results in a high weight with correspondingly high moments of inertia from which follow long acceleration or braking phases. DE 195 05 689 Al discloses a centrifugal casting apparatus with a reusable hollow mould in which mould cavities each of the same type are arranged in pairs such that they rotate about a common axis of rotation and can be filled through a common downgate. If more than two workpieces are to be cast at the same time using this known apparatus, the mould cavities each arranged in pairs are arranged one above the other in several layers so that they come to lie in several planes. A disadvantage of this apparatus is that only an even number of workpieces of the same type can be produced in one centrifugal casting process. In addition, the overall height of the hollow mould varies as a function of the number of mould cavities provided together in the hollow mould so that, depending on the number of workpieces to be manufactured together in each casting process, different components are required for the superstructure of the centrifugal casting apparatus. Starting from this prior art, it is an object of the present invention to propose a new centrifugal casting method, a new centrifugal casting apparatus, a new hollow mould suitable for centrifugal casting, a suitable runner bush moulder for manufacturing such hollow moulds and new types of applications of these apparatus and methods. 3 The invention is based on the fundamental idea that during the implementation of the centrifugal casting method, in order to increase the workpieces which can be manufactured in one casting process, three or more mould Cavities rotate about one axis and are arranged such that they are intersected by a common plane. The arrangement of the various mould cavities according to the invention is thus to be understood as that formation in which the different mould cavities are arranged such that they extend at least partly in a common plane of rotation. Parts of the mould cavities in the sense of this invention are also the sprue runners which connect the cavity to delimit the actual casting workpiece to be manufactured with a runner bush into which the liquid casting material is poured. As a result, it is thus obviously not necessary for all mould cavities to be arranged exclusive in the common plane of intersection. Rather, the various mould cavities generally extend in sections over the common plane depending on shape and size in each case. Ultimately, in order to satisfy the principle according to the invention, it is for example sufficient if the discharge gates with which the sprue runners of the individual mould cavities open into the runner bush are intersected by the common plane of intersection. As a result of the arrangement of the mould cavities in a common plane, a simple balancing of masses can be achieved between the mould cavities or the hollow moulds since imbalances caused by the mould cavities or hollow moulds are substantially mutually compensated and thus the centrifugal forces to be absorbed by the centrifugal casting apparatus can be minimized. Both re-usable hollow moulds and dead hollow moulds can be used to 4 form the mould cavities when implementing the centrifugal casting method according to the invention. In order to achieve as uniform as possible balancing of masses between the individual mould cavities, it is particularly advantageous if in an arrangement of n mould cavities, these are arranged offset as uniformly as possible by an angle of rotation of approximately 360°/n. That is, the various mould cavities lie on circular orbits offset with respect to one another with an intermediate angle of 360°/n so that only a small imbalance is obtained overall. There are basically two design solutions for the development of the centrifugal casting apparatus for implementing the method according to the invention. According to a first embodiment of a centrifugal casting apparatus according to the invention, this is provided with at least three holding devices in each of which at least one hollow mould can be secured. Each of the hollow moulds contains at least one mould cavity. According to the invention, the hollow moulds are arranged in the holding device such that the mould cavities rotate in a single plane when the centrifugal casting apparatus is driven. If three hollow moulds are used, for example, these can be arranged in a star shape, for example, on the centrifugal casting apparatus so that the imbalance caused by the mass of the individual hollow moulds is compensated overall. Since the weight of the individual hollow moulds in such an embodiment can differ completely one from the other, for example, as a result of differently sized mould cavities in the individual hollow moulds, it is especially advantageous if the various hollow moulds are individually adjustable. For example, it is feasible that the distance between the individual hollow moulds and the axis of rotation can be adjusted independently of one another so that the different moment of inertia of the various hollow moulds can be compensated by changes in the 5 rotational distance. According to a second embodiment of a centrifugal casting apparatus according to the invention, this is provided with one holding device for attachment of a hollow mould. In this hollow mould however, there is not only one mould cavity but at least three mould cavities are incorporated. The holding device of the centrifugal casting apparatus must thus be designed such that the hollow mould is attachable in a fashion so that the mould cavities rotate about a common axis of rotation in a single plane when the centrifugal casting apparatus is driven. In other words, this means that in this centrifugal casting apparatus the hollow mould can rotate about an axis of rotation which, for example, extends through the centre of gravity of the hollow mould. As a result of this arrangement, an extensive balancing of masses can be achieved overall during the rotational movement of the hollow mould since each mass point of the hollow mould substantially has a corresponding counterweight on the opposite side. Imbalances can then only be caused by the irregular shape and arrangement of the different mould cavities. However, the imbalance can be reduced to a tolerable level with a sufficiently uniform distribution of mould cavities which are as far as possible the same size. The individual mould cavities in the hollow mould are then preferably arranged substantially rotationally symmetrically about the principal axis of inertia of the hollow mould. As already put forward, different casting materials require different centrifugal forces or casting times. According to a preferred embodiment, the rotational speed can be set at the centrifugal casting apparatus according to the invention depending on the hollow mould used and/or the material to be cast. By this means, for example, materials having a high heat capacity or high density, especially gold, can be cast at a relatively low rotational speed and materials having a low density and low heat capacity can be cast at relatively high 6 rotational speeds. In order to implement the centrifugal casting method according to the invention in a centrifugal casting apparatus according to the second embodiment, there is proposed a hollow mould in which at least three mould cavities are substantially arranged in a single plane. In this case it is especially advantageous if on the hollow mould there is provided a runner bush into which open the discharge gates of the sprue runners provided on the individual moulds. By this means it can be achieved that during pouring of the liquid casting material into the runner bush, the various mould cavities are filled substantially at the same time and thereby relatively uniformly. The sprue runners can preferably extend from the discharge gates lying in the plane of intersection alternately obliquely upwards and radially downwards towards the outside. By this means the cavities which later form the actual cast workpiece can be packed more closely in the hollow mould since these cavities then come to lie in at least two planes lying one above the other and are connected to the discharge gates lying in the plane of intersection by the obliquely running sprue runners. The runner bush itself should be constructed as rotationally symmetrically as possible in order to consequently have no influence itself on the resulting imbalance of the hollow mould. In order to substantially eliminate any escape of liquid casting material poured into the runner bush, it is advantageous if the runner bush tapers upwards. Any escape of liquid casting material is reliably avoided by the overhanging upper edge of the runner bush thereby formed. This can be achieved constructively by the runner bush being constructed as conical at least in sections. 7 Circular ring-shaped muffle rings can be used to form hollow moulds according to the invention. During the manufacture of the hollow mould, a model made of wax, for example, which has the positive shape of the desired mould cavities, is first manufactured. This model is arranged together with a runner bush moulder at the centre of the muffle ring and embedded in a moulding material. After hardening the moulding material, the model material is then expelled thermally, chemically or in an otherwise suitable fashion so that the hollow mould is formed as a result from the circular ring-shaped muffle ring and the mould material hardened therein. Alternatively to using a muffle ring, the hollow moulds according to the invention can also be manufactured without a ring, for example, using suitably shaped casting apparatus. If a circular ring-shaped muffle ring is used to manufacture the hollow mould according to the invention, the volume present in the muffle ring must be substantially completely filled to achieve the desired balancing of masses when the hollow mould is rotationally driven. If, however, only a relatively small embedding volume is required as a result of the small volume of the individual mould cavities or the small number of mould cavities overall, the wastage of an unnecessarily large embedding volume can be avoided by arranging insertion elements in the muffle ring. The available volume in the muffle ring is reduced by these insertion elements so that as a result, less embedding material is required to fill the remaining volume. When arranging the insertion elements in the muffle ring, care must naturally be paid to ensure that the insertion elements are placed such that a sufficient balancing of masses is again obtained overall and imbalances caused by the insertion elements are substantially avoided. The centrifugal casting method according to the invention or the centrifugal casting apparatus or hollow mould suitable therefor can 8 basically be used for any cast workpieces. However, their application for the manufacture of workpieces in high-quality casting, especially in the manufacture of pieces of jewellery, dentures or tool parts, offers particular advantages. The centrifugal casting method according to the invention or the centrifugal casting apparatus or hollow mould suitable therefor can basically be used for any casting materials, for example, gold or steel. The application of the method according to the invention or the centrifugal casting apparatus or hollow mould suitable therefor offers particular advantages for casting materials having low density, for example titanium, since these materials can only be cast with unsatisfactory quality or with very expensive apparatus using conventional methods or apparatus because of the high rotational speeds required in this case. Embodiments of the invention are explained in detail hereinafter with reference to the accompanying drawings wherein: Fig. 1 is a schematic top view of a first embodiment of a centrifugal casting apparatus; Fig. 2 is a schematic top view of a first embodiment of a hollow mould; Fig. 3 is a cross-section along the line I-I of the hollow mould from Fig. 2; Fig. 4 is a schematic top view of a second embodiment of a hollow mould; Fig. 5 is a cross-section along the line II-II of the hollow mould 9 from Fig. 4; Fig. 6 is a centrifugal casting apparatus for use with hollow moulds from Fig. 2 to Fig. 5. The centrifugal casting apparatus 01 shown in a schematic view in Fig. 1 has three holding devices 02, 03 and 04 arranged in a star shape which rotate jointly in a single plane about an axis of rotation 06 by driving a drive shaft 05. A hollow mould 07, 08 or 09 can be attached to each holding device 02, 03 or 04. A mould cavity 10, 11 or 12 is incorporated in each of the hollow moulds 07, 08 and 09 by embedding and melting a suitably modelled wax model. Each mould cavity 10, 11 or 12 has three sprue runners which each connect a tooth-shaped cavity with a runner bush not shown in Fig. 1. The radial distance of the individual hollow moulds 07, 08 or 09 with respect to the axis of rotation 06 can be adjusted individually independently of one another in order to thereby compensate for mass imbalances. During implementation of the centrifugal casting method according to the invention the three hollow moulds 07, 08 and 09 rotate jointly in a single plane about the axis of rotation 06. When a sufficiently high rotational speed is reached, the liquid casting material is poured into the runner bush not shown in Fig. 1 and is pressed into the mould cavities 10, 11 or 12 as a result of the centrifugal forces thereby acting. As a result of the very highly adjustable rotational speeds according to the invention, substantially complete filling of the mould can be achieved in very short times so that materials with a low heat capacity or low density can be cast with sufficiently high quality. 10 Fig. 2 shows a top view of a hollow mould 13 wherein, to obtain a better understanding, the mould cavities 14 which are inherently unrecognisable from outside are shown with their respective adjoining sprue runners 36. The hollow mould 13 has a circular ring-shaped muffle ring 15, made of steel for example, at its external circumference. A model, made of wax for example, whose shape corresponds to the positive shape of the desired mould cavities 14 with sprue runners and a sectionally conical runner bush 16, is used in the manufacture of the hollow mould 13. To produce this model, the cast objects to be manufactured, e.g. dentures, are modelled in wax and then fused onto a standardised sprue runner moulder using a standardised runner bush moulder. The substantially rotationally symmetrically formed model thus produced is then arranged at the centre of the muffle ring 15 and is subsequently embedded in a hardenable moulding material 17. After the moulding material 17 has hardened, the model material is removed by melting so that the desired negative shape of the mould cavities is formed in the moulding material 17. As can be seen especially from Fig. 3, the individual mould cavities 14 and the runner bush 16 are arranged rotationally symmetrically with respect to the axis of rotation 18 of the hollow mould 13. In addition, all mould cavities 14 lie in a common plane around the principal axis of inertia 18. Each mould cavity has a sprue runner 36 with a discharge gate 37 so that the liquid casting material can flow from the runner bush 16 into the mould cavities 14. As a result, the hollow mould 13 can be arranged in a centrifugal casting apparatus so that the principal axis of inertia 18 runs along the axis of rotation of the centrifugal casting apparatus so that the imbalances occurring when the hollow mould is driven rotationally are substantially compensated and reduced to a permissible extent. During the actual casting process the liquid casting material is poured into the runner bush 16 while the hollow mould 13 11 rotates about the principal axis of inertia 18 at a sufficiently high rotational speed. As a result of the centrifugal forces acting on the casting material, the mould cavities 14 are cast quickly and substantially free of shrink holes. The embodiment 19 of a hollow mould shown in Fig. 4 corresponds to the hollow mould 13 in terms of its essential structure. The circular ring-shaped muffle ring 15 is again used and a runner bush 16 with adjoining sprue runners and mould cavities 14 is again provided in the hardenable moulding material 17. In order to make it possible to manufacture a relatively small number of workpieces, i.e. in the present case of dentures, in the hollow mould 19, two circular-segment-shaped insertion elements 20 or 21 can be arranged axially symmetrically with respect to one another in the muffle ring 15. By means of the insertion elements 20 and 21, the volume to be filled by the moulding material 17 inside the muffle ring 15 is reduced wherein the inertia masses of the insertion elements 20 and 21 compensate for each other during a rotational movement of the hollow mould 19 around the principal axis of inertia 18. The insertion elements 20 and 21 can be constructed as solid components or as hollow members, e.g., in the fashion of bent-sheet components, wherein a corresponding reduction in the inertial mass as a whole is obtained when bent-sheet components are used. Fig. 6 shows a schematic cross-section of a second embodiment 22 of a centrifugal casting apparatus. This is suitable for use with hollow moulds 13 and 19 as shown in Fig. 2 to Fig. 5. The centrifugal casting apparatus 22 has a drive device 24, for example an electric motor, in a housing 23, which drive device is controlled or regulated using a control and regulating device 25 in accordance with settings preset by the 12 operator. The drive shaft 26 can be driven rotationally by means of the drive unit 24 such that it rotates about a central axis 27. At the upper end of the drive axis 26 there is provided a base plate 28 on whose upper side a circular-disk-shaped holding device 30 can be attached with a spacer 29 arranged in between. The upper side of the holding device 30 has a circular-disk-shaped recess whose diameter is the same as the outside diameter of the hollow mould 13. The hollow mould 13 is attached to the holding device 30 by means of clamping devices 31 and 32, shown only schematically, which can be constructed in the fashion of clamping screws for example. After attaching the hollow mould 13 to the base plate 30, a lid 33 is attached to the housing 23 from above so that the hollow mould 13 is enclosed towards the outside. Above the runner bush 16 the lid 33 has a recess 34 through which the molten casting material can be poured into the runner bush 16 from above. A rotatable lid 35 serves to cover the recess 34 after pouring in the liquid casting material. As a result of the size and shape of the runner bush 16, special casting techniques such as bar casting or lost heads are no longer required as a reservoir to take care of solidification shrinkage. This function is fulfilled by the melt remaining in the runner bush since the casting material in this region is the last to solidify and can thereby be conveyed into the mould cavities 14. 13 WE CLAIM 1. A centrifugal casting apparatus (22) for the manufacture of cast..; workpieces, in particular pieces of jewellery denture workpieces of semi- finished denture products, with at least one holding device to attach a dead hollow mould (13) containing at least three mould cavities (14), wherein the hollow mould (13) can be arranged in the holding device such that the mould cavities (14) rotate about an axis (27) when the centrifugal casting apparatus (22) is driven characterized in that the mould cavities (14) each have at least one sprue runner (36) each with a discharge gate (37) to runner bush (16) wherein the liquid casting material can be poured into the runner bush (16) so that the mould cavities (14) can be filled with casting material through the sprue runners (36), the discharge gates (37) of the mould cavities (14) lying in a single plane, and wherein the runner bush (16) is constructed rotationally symmetrical, tapering upwards from below, and especially is constructed conically at least in sections, and wherein the central axis of the runner hush (16) extends substantially along the axis of rotation (18) of the hollow mould. 2. The centrifugal casting apparatus as claimed in claim 1, wherein the rotational speed can be adjusted depending on the hollow mould (07,08,09,13,19) used and/or on eth material to be cast. 14 3. The centrifugal casting apparatus as claimed in claim 2, wherein the rotational speed is automatically adjustable. 4. The centrifugal casting apparatus as claimed in one of claims 1 to 3, wherein the number of n mould cavities (14) used is arranged offset substantially uniformly by an angle of rotation of approximately 360°/n. 5. The centrifugal casting apparatus as claimed in one of claims 1 to 4, wherein the sprue runners (36) extend from the discharge gates (37) lying in a single plane alternately obliquely upwards and radially downwards towards the outside. 6. The centrifugal casting apparatus as claimed in one of claims 1 to 5, wherein the external diameter of the hollow mould (13,19) is formed by a circular ring-shaped muffle ring (15). 7. The centrifugal casting apparatus as claimed in claim 6, wherein insertion elements (20,21) which abut positively on the inner circumference of the muffle ring (15) can be arranged in the muffle ring (15) in order to reduce the volume available for the production of the hollow mould (19) in the muffle ring (15). 15 8. The centrifugal casting apparatus as claimed in one of claims 1 to 7, wherein for the production of the runner bush (16) a runner bush moulder is used which is constructed circularly symmetrically and/or at least contcally in sections. 9. The centrifugal casting apparatus as claimed in claim 8, wherein the runner bush moulder is made of a material which can be expelled. This invention relates to a centrifugal casting apparatus has a hollow mold (13) suitable for the centrifugal casting. For the manufacture of cast workpieces by the centrifugal casting method a plurality of mold cavities (14) formed by at least one hollow mold (13) are arranged and driven such that the mold cavities (14) rotate about a common axis of rotations (18). At least three mold cavities (14) which rotate in a single plane are provided.

Documents:

00053-kolnp-2003 abstract.pdf

00053-kolnp-2003 claims.pdf

00053-kolnp-2003 correspondence.pdf

00053-kolnp-2003 description(complete).pdf

00053-kolnp-2003 drawings.pdf

00053-kolnp-2003 form-1.pdf

00053-kolnp-2003 form-18.pdf

00053-kolnp-2003 form-2.pdf

00053-kolnp-2003 form-26.pdf

00053-kolnp-2003 form-3.pdf

00053-kolnp-2003 form-5.pdf

00053-kolnp-2003 letters patent.pdf

00053-kolnp-2003 priority document.pdf

53-KOLNP-2003-FORM-27-1.pdf

53-KOLNP-2003-FORM-27.pdf

53-kolnp-2003-granted-abstract.pdf

53-kolnp-2003-granted-claims.pdf

53-kolnp-2003-granted-correspondence.pdf

53-kolnp-2003-granted-description (complete).pdf

53-kolnp-2003-granted-drawings.pdf

53-kolnp-2003-granted-examination report.pdf

53-kolnp-2003-granted-form 1.pdf

53-kolnp-2003-granted-form 18.pdf

53-kolnp-2003-granted-form 2.pdf

53-kolnp-2003-granted-form 26.pdf

53-kolnp-2003-granted-form 3.pdf

53-kolnp-2003-granted-form 5.pdf

53-kolnp-2003-granted-letter patent.pdf

53-kolnp-2003-granted-priority document.pdf

53-kolnp-2003-granted-reply to examination report.pdf

53-kolnp-2003-granted-specification.pdf

53-kolnp-2003-granted-translated copy of priority document.pdf