A METHOD AND A PLANT OF MANUFACTURING CORES

Abstract: A method for manufacturing cores for casting purposes in special core boxes provided with closed cavities apart from a limited filling opening through which a mixture of a sand material and a water-glass is introduced by means of a core forming machine, said filling opening having limited dimensions normally not permitting water to escape freely from an uncured core mixture in the core box. According to the invention the core boxes (20), which are constructed entirely of materials which are transparent to microwaves, are moved in a continuous and repetitious process between various treating stations comprising a core forming station (22) with a core forming machine for filling the core boxes (20) with said mixture, at least one heating station (23) having at least one microwave oven to cure the core mixture, and a removal station (28) for opening the core boxes and removing the cured core and for re-assembling the core boxes for repeated use. The core mixture in the core box is subjected during at least a final period of time of its stay in the heating station (23) to a combined and simultaneous treatment with microwaves and negative pressure so that the water present in the core mixture is caused by the raised curing temperature induced by the microwave energy supplied, to leave the core mixture through one or more evacuation openings (31, 32) in communication with a means (38, 39, 40, 41, 47) generating a negative pressure. During the combined treatment the heated water is drawn by suction action to the evacuation openings at an increased diffusion rate through the core mixture, thus enabling curing and correspondingly shortening the curing time for the core mixture.

Description: A method and a plant of manufacturing cores The present invention relates to a method of manufacturing cores for casting purposes in core boxes provided with cavities, said cavities being closed apart from a filling opening through which a mixture of a sand material and an aqueous binder in the form of water-glass is introduced by means of a core forming machine, said filling open¬ ing having limited dimensions normally not permitting water to escape freely from an uncured core mixture in the core box. The invention also relates to a plant for performing this method. The manufacture of cores for casting purposes using water-glass (in- organic) as binder is associated with many problems and a plurality of methods have therefore been suggested and used to solve these prob¬ lems, with more or less satisfactory results. Although the methods using thermal curing have a number of advantages, they have not hith¬ erto proved competitive due either to long curing times for the cores or other negative effects when CC is used to reduce the curing time. Due to the fact that the forming machines have large capacity and require e short time for filling (i-1 minute for each core depend¬ ing on the core size) the requirements of short curing times to suit the forming machines have therefore become necessary. Short curing times are obtained with organic binders by adding hardeners. The cur¬ ing is then performed either purely chemically (as in the cold-box method, for instance) or in combination with heat (as in the hot-box and shell sand methods, for instance). The 'use of organic binders, however, involves environmental problems, among others. it has not been possible to cure cores containing water-glass with the aid of microwave energy to the general extent desired since it has not been possible to provide core boxes which will resist the considerable internal and external stresses to which they are sub¬ jected in a core forming machine. SU 700272 describes the curing of casting moulds and casting cores in accordance with the hot-box method while using negative pressure in order to lower the boiling point of the binder. As mentioned, the hot-box method is characterized in that organic binders are used, which are then cured chemically while supplying heat. According to the present invention water-glass is used as binder, which is cured thermally while water is removed, whereby it is important that the centre of the core is also heated as this will otherwise be incom¬ pletely cured. JP 58-107 250 describes a method for curing moulding sand containing water-glass by means of microwaves. This method requires a completely open sand surface against which the microwaves are directed from above to be absorbed therein. A channel is provided in the centre of the sand core to enable evacuation of vaporized water. Extremely few cores have a geometry permitting the use of this method. The method accord¬ ing to the present invention solves the problem generally for the manufacture of cores where the whole core must be quickly cured in a core box which lacks any open surface for liquid evacuation but where instead the core is enclosed in a cavity which is closed. DE 2 940404 is directed to solving the very great problem encoun¬ tered in the vacuum-forming techinique, of drying the "blacking layer" with the aid of microwaves, the blacking being applied on a plastic film. A stationary device is used, having two mould frames which are filled with binder-free sand to surround a core placed therein, the core having been manufactured earlier in another place. The sand is compacted to form a coherent body by placing the mould frames under negative pressure, while the intention is that the water from the blacking shall at the same time be drawn away through the increasingly hard sand body, with the risk of this sand body becoming moist, at least in the inner sections close to the core with resulting strength problem. This patent specification does not therefore relate to the manufacture of cores, neither does it have anything in common other¬ wise with the method and the technical field to which the invention pertains as described in the preamble. A method used in. practice for manufacturing cores in the manner de¬ scribed in the preamble is directed to effect surface-curing by heating the core box itself, which is usually of metal. Extremely long cur¬ ing times are required for this technique, lasting one hour or sever¬ al hours depending on the type of core. In order, therefore, to reduc¬ ing the curing time for such cores containing water-glass as binder, a method is used in which C0 2 gas is introduced into the core mixture in the core box. This known method requires greater quantities of water-glass in comparison with the method according to the present invention, viz. up to twice the amount, which results in problem in that the sand cannot be re-used due to the high content of slag prod- ucts and that the casting moulds casted from these cores are difficult to clean from sand since the core has poor disintegrating properties. Merely to perform microwave heating in the method described in the preamble from which the invention starts does not give any results within a reasonable time in practice, since the water remains in the core mixture and no curing will therefore be effected. Neither does treatment with only negative pressure give any results since the prac¬ tical curing must be performed at elevated temperature. The object of the present invention is to eliminate the problems mentioned above and provide an improved method of manufacturing cores of the type described in the preamble, (a) which can be used for all types of cores irrespective of their geometry, (b) which can make use of conventional core forming machines to form the cores prior to curing, (c) which can make use of microwaves for heating and cur¬ ing the cores, (d) which thereby utilizes core boxes which are not only sufficiently transparent for microwaves, but also have the same mechanical properties as a conventional core box made of steel, but still are free of metal support which prevents the supply of microwaves in one or more directions into the core, (e) which can be carried out in a continuous and repetitious process, suiting the curing time to the forming time for the cores, thus achieving optimal production without increasing production costs, (f) which results in cores which can be treated with blacking while retaining their strength or can be prepared in accordance with other methods to ensure good casting quality, and (g) which results in cores with sand pouring properties and conditions for sand recovery at least comparable to cores manu¬ factured conventionally. This complicated object is achieved according to the present invention substantially in that said core boxes, which are constructed entirely of materials which are transparent to microwaves, are moved in a continuous and repetitious process between various treating stations comprising a core forming station with a core forming machine for filling the core boxes with said mixture, at least one heating station having at least one microwave oven to cure the core mixture, and a removal station for opening the core boxes and removing the cured cores and for re-assembling the core boxes for repeated use; and in that the core mixture in the core box is subjected throughout or during a later period of time of its stay in the heating station, said period of time ending with the core mixture having been cured, to a combined and simultaneous treatment with microwaves and negative pressure so that the water present in the core mixture is caused by the raised curing temperature induced by the microwave energy supplied, to leave the core mixture through one or more evacuation openings in the core box, said evacuation openings having been brought in com- munication with a means generating a negative pressure, during which combined treatment the water is drawn by suction action to the evacua¬ tion openings at an increased diffusion rate through the core mixture, thus enabling curing and correspondingly shortening the curing time for the core mixture. By increasing the negative pressure it is thus possible to decrease the curing time to an optimal level. According to a preferred embodiment of the invention the negative pressure is connected first after at least a part of a predetermined quantity of energy to raise the temperature has been supplied to the core mixture in the core box by means of microwaves during an initial period of time of the period spent by the core box in the heating sta¬ tion. Said combined treatment is preferably performed during the last half of the period spent in the heating station while a second core box is introduced into the heating staiton for its core mixture to be supplied with said predetermined quantity of temperature-raising energy, the number of cured cores per time unit thus being suited to the production rate of the core forming machine for filling the core boxes. A plant for carrying out the method according to the invention is characterized in that it substantially comprises a plurality of treating stations between which said core boxes, which are con¬ structed entirely of material which is transparent to microwaves, are moved in a continuous and repetitious process, said stations comprising a core forming station with a core forming machine for filling the core boxes with said core mixture, at least one heating station having at least one microwave oven to cure the core mixture, and a removal station for opening the core boxes and removing the cured cores and for re-assembling the core boxes for repeated use; and in that the heating station comprises means for generating a negative pressure at the evacuation openings in the core box of such a value that the water present in said mixture, having a raised temperature by the microwave energy supplied, is brought to said evacuation openings at an increased diffusion rate through the core mixture. The present invention eliminates the problems associated with the known methods mentioned and enables an improved method for manufac¬ turing cores containing water-glass as binder in specific core boxes with closed cavities while using microwaves as heat medium, thus enabling a favourable reduction of up to 50% of the content of water- -glass. It should be particularly emphasized that for practical use the curing can only be achieved by said combined and simultaneous treatment with microwaves and negative pressure. By applying a suit¬ able negative pressure the heated water (liquid or vapour) is removed ery rapid, and the combined treatment with negative pressure and microwave heating results in shortening the curing time from several minutes down to two minutes, while the microwave heating itself en¬ ables said reduction of the amount of water-glass. The production capacity of a plant is thus correspondingly increased and the method of manufacture will be competitive and its many advantages, including microwave heating and the use of water-glass bonded cores can be uti- lized completely. The invention will be described further in the following with refer¬ ence to the accompanying drawings. Figure 1 shows schematically from above a plant for continuous, automatic manufacturing of cores according to the invention. Figure 2 shows schematically a microwave oven with a special arrange¬ ment for achieving negative pressure in a core box. Figures 3 and 4 show schematically from above two further plants for continuous, automatic manufacture of cores according to the invention. Figures 5 and 6 show schematically from above and from the side, respectively, one part of a core box which advantageously can be used in carrying out the method according to the invention. Figure 1 shows schematically a plant for continuous and automatic manufacture of cores according to a preferred embodiment of the in¬ vention. A desired number of core boxes 20 are moved continuously, stepwise, in a repeated curcuit along a suitable conveyor path 21, such as a roller conveyor, or some other transport means conveying the core boxes between the various stations. These stations comprise a core forming station 22 with a core shooting machine which injects a mixture of a sand material and an aqueous binder in the form of a water-glass into a core box 20 positioned in the station. The core box usually consists of two or more parts which are held together by hydraulic cylinders (not shown) in order to withstand the high pressure when the mixture is injected by the core shooting machine. Following the core filling machine is a station 23 with a microwave oven, preferably built together with the core shooting machine 22 and comprising two microwave units 24, 25 on each side of the conveyor path 21. The microwave oven is thus divided into a first treating department 26 and a second treating department 27. The time spent by a core box is approximately equal in each of the two treating de- partments. When a core has been cured, the core box is conveyed to a removal station 28 where its parts are separated and the finished core is conveyed to a storage place. The parts are then re-assembled to a core box which is again conveyed to the first station 22 having the core shooting machine. Each core box thus constitutes a free, movable unit. The microwave oven is provided with a device for generating negative pressure at at least one evacuation opening in the core box, in direct communication with the core in the process of being cured. Figure 2 shows schematically a suitable embodiment of such a device. Each part 29, 30 of the core box is provided with an evacuation opening 31, 32 communicating with channels 33, 34 to the cavity 35 inside the core box, the space also communicating with an upper filling opening 36 for connection to the core shooting machine for injecting said mixture of sand material and water-glass as binder. The device includes a sealing member 37 which is vertically movable to be brought to a sealing position over the filling opening 36. If desired this can be replaced by suction means connected to a source of vacuum, whereby the opening 36 will also act as evacuation opening. In the embodiment shown the suction means 38, 39 are arranged in the microwave oven 23 to be moved horizontally to the opposite evacuation openings 31 and 32, respectively, of the core box and thus placed in communication with the space inside the core box. The suction means may be displacea- ble horizontally to and fro with the aid of hydraulic cylinders (not shown) and are connected by pipes 40, 41 to a common negative pressure source such as a vacuum pump 47 which, when the suction means are connected to the core box, generates a suitable negative pressure in the evacuation openings 31, 32 and the channels connected to them. After being heated by means of microwaves for a suitable period and at a suitable power, the water in the core will be drawn by suction action towards the evacuation openings via the channels. The provision of a suitable negative pressure in the evacuation openings 31, 32 greatly accelerates the transport of water out from the core. Since the curing of the water-glass is a direct result of the removal of water, the application of a negative pressure in accordance with the present invention results in a reduction in curing time at the same rate as the diffusion rate of water increases due to the action of the negative pressure. Depending on temperature and pressure, the water will be in either liquid or vapour phase. The water thus removed is then withdrawn from the microwave oven by suction action. According to a suitable embodiment of the invention the suction means is arranged in the second treating department 27 in the microwave oven, and microwave energy is supplied during substantially the whole time the core box remains there. Initial heating of the water content in the core occurs in the first treating department 26. The water having the raised temperature in turn heats the sand particles which will thus serve as a heat source for the water should its temparature drop at a later stage. A conventional water-glass is preferably used as curable binder, having suitable proportions of its constituents, including water. By utilizing the technique with the combination of microwave heating and negative pressure in a plant according to Figure 1 it is possible to produce one cured core per minute, each core thus having a transit time of two minutes through the microwave oven, during which time microwave irradiation occurs, apart from the time spent when passing a core box through doors between closable openings at each end of the microwave oven and between the two treating departments. In the example shown here, therefore, the forming machine has a capacity of one core per minute. If the forming machine has a higher capacity, e.g. half a minute per core, the number of core boxes in the microwave oven is increased to four so that two cured cores are produced per minute (for a curing time of two minutes). The production capacity mentioned above can also be achieved using the plants illustrated schematically in Figures 3 and 4 wherein two stations are provided with two microwave ovens, each oven having two microwave units 24, 25 and suction means of the type shown in Figure 2, for instance. The core boxes are then moved along longitudinal paths and side-paths in accordance with Figure 3, and along two par¬ allel paths in accordance with Figure 4. In both cases the core filling machine is common and designed to deliver one filled core box every minute, for curing. To enable optimal utilization of the plant and method according to the invention with a high production rate giving cores of satis- factory quality and a low rejection it is important for the core boxes to fulfil the specific strict requirements placed on them, particularl with respect to mechanical strength, manufacturing costs, dimension tolerances, part sealing and transparency to microwaves. The hollow space or cavity 35 of such core boxes is closed except for the limited filling opening 36 through which a core mixture of sand and water-glas is inserted by a core forming machine. The dimensions of this filling opening are so limited, i.e. the opening is so small, that it does not normally permit water to escape freely from an uncured core mixtur not even during heating. Furthermore, the core boxes are provided with a prefabricated body of one or more plastic materials and an inner layer of a mouldable plastic or rubber material with an exposed surface forming the contour of the cavity, said layer being by means of moulding in situ directly or indirectly joined to a unit with the body, said plastic material and rubber material being sufficiently transparent to microwaves. The body has a tensile strength of at least 55 MPa, preferably at least 70 MPa, and a bending module of at least 2.5 GPa, the body thus having a mechanical strength which is sufficien ly high so that the core box as to its form resists high internal and external pressures in the subsequent core production. The plastic or rubber material used for the inner layer gives this a tear resist¬ ance of at least 10 N/mm, preferably at least 15 N/mm, and most prefer ably at least 20 N/mm, so that the layer has sufficiently high tear resistance to enable the surface to resist extensive repeated core production. The body also has a coefficient of heat expansion of at most 6.5x10 " mm/mm°C, preferably at most 6.0x10 mm/mm°C, which coef¬ ficient of heat expansion is sufficiently low to ensure that the core box achieves narrow tolerances at the varying curing temperatures occurring during thermal curing of said cores. Due to said high mechan ical strength of the body, the core box is self-supporting and thus free from external support, such as metal, which would otherwise imped supply of microwaves in a desired direction or directions towards the core. The inner layer preferably consists of a silicone rubber material of a quality giving the inner layer said properties, and an inter¬ mediate layer of a second mouldable silicone rubber material is suitably arranged between the body and the inner layer, which silicone rubber material is of a quality having a lower coefficient of heat expansion than the silicone rubber material used for the inner layer. The inner layer has suitably a thickness of less than about 1 mm, whereas the intermediate layer has a thickness of less than about 5 mm. Figures 5 and 6 show schematically a part 42 of a core box, said part having a part surface 43 provided with four semi-spherical recesses 44 arranged at the corners of the part surface and communicating with a nonreturn valve 45 via an inner channel system 46. The twin part (not shown) has the same semi-spherical recesses in its part surface at the corresponding places but preferably lacks said channel system and nonreturn valve. When the parts are assembled to form a core box, four spherical spaces are formed which are placed under negative pressure by drawing out the air by suction action through nonreturn valve 45 which thus prevents air from returning to the spaces. An extremely strong joint is thus obtained between the parts, which is not broken until the core box arrives at the removal station 28 when the cured core is to be removed, after which the negative pressure joint can be obtained again when the parts have been reassembled. Conventional clamping means around the core box can thus be entirely or for the most cases omitted, thus making the core box lighter and easier to handle. Each part has a hollow space or cavity and comprises a body 49 and an inner layer 47 having the properties and construction described above. The inner layer forms a seal 48 at the part surface 43, which efficiently seals the cavity at the part division. Similar seals can be formed around each recess 44, which in that case are provided with similar layers having over-dimensions. Figure 2 shows an evacuation opening 31, 32 in each part half which comprises two channel connections to the inner cavity 35 of the core box. If desired, each evacuation opening may be provided with several such channel connections, four for instance, distributed over the most suitable places for removing water from the core. Heating the cores containing water-glass binder by means of micro¬ wave energy gives considerably more efficient utilization of the energy supplied, in comparison with other heating methods, since heat is only generated inside the mixture of sand material and water- glass injected into the core box, and the heating process occurs considerably more quickly, usually up to 100°C/min which in turn results in higher production in comparison with using other heating methods. The application of negative pressure is beneficial to this heating process due to the fact that the heated water from the water- -glass leaves the core more quickly. As opposed to other heating methods, microwave heating ensures that even the centre portion of the core will be heated, also extremely quickly. In order to achieve the desired negative pressure in one or more evacuation openings in the core box, the device according to the invention may be designed in many different ways and still achieve the desired effect. Instead of suction means being connected directly to the evacuation openings of the core box, the core box may be located in a negative pressure chamber which may consist of the treating chamber itself in the microwave oven, or of a separate chamber into which the core box is placed. In both cases the negative pressure chamber is connected to a source of negative pressure such as a vacuum pump, in which case the microwave oven or said separate chamber is sealed in a suitable manner to ensure sufficient negative pressure at the evacuation openings of the core box to produce the desired or accelerated evacuation of water from the core mixture. According to an alternative embodiment, the means generating nega¬ tive pressure may comprise a chamber or a channel system formed in the body of the core box, which communicates by means of one or more evacuation openings of the type described, to the inside of the core box. Said chamber or channel system may then be closable to the out¬ side, by means of a nonreturn valve, for instance, so that the evacua¬ tion of air serves as a built-in vacuum accumulator coming into operation in accordance with the principle of the invention as soon as the mixture in the core box and more specifically its water content acquires an elevated temperature in the heating phase.

Claims: 13 C L A I M S 1. A method of manufacturing cores for casting purposes in core boxes provided with cavities, said cavities being closed apart from a filling opening through which a mixture of a sand material and an aqueous binder in the form of water-glass is introduced by means of a core forming machine, said filling opening having limited dimensions normally not permitting water to escape freely from an uncured core mixture in the core box, characterized in that said core boxes (20), which are constructed entirely of materials which are transparent to microwaves, are moved in a continuous and repetitious process between various treating stations comprising a core forming station (22) with a core forming machine for filling the core boxes (20) with said mixture, at least one heating station (23) having at least one microwave oven to cure the core mixture, and a removal station (28) for opening the core boxes and removing the cured cores and for re- -assembling the core boxes for repeated use; and in that the core mixture in the core box is subjected throughout or during a later period of time of its stay in the heating station (23), said period of time ending with the core mixture having been cured, to a combined and simultaneous treatment with microwaves and negative pressure so that the water present in the core mixture is caused by the raised curing temperature induced by the microwave energy supplied, to leave the core mixture through one or more evacuation openings (31, 32) in the core box, said evacuation openings having been brought in communication with a means (38, 39, 40, 41, 47) generating a negative pressure, during which combined treatment the heated water is drawn by suction action to the evacuation openings at an increased diffusion rate through the core mixture, thus enabling curing and corresponding¬ ly shortening the curing time for the core mixture. 2. A method according to claim 1, characterized in that the negative pressure is connected first after at least a part of a predetermined quantity of energy to raise the temperature has been supplied to the core mixture in the core box by means of microwaves during an initial period of time of the period spent by the core box in the heating station. 14 3. A method according to claim 2, characterized in that said combined treatment is performed during the last half of the period spent in the heating station while a second core box is introduced into the heating station for its core mixture to be supplied with 5 said predetermined quantity of temperature-raising energy, the number of cured cores per time unit thus being suited to the production rate of the core forming machine for fill ng the core boxes. 4. A method according to any of the preceding claims, character¬ ized in that the cores are manufactured from a core mixture contain- 10 ing 1.5-2.0 per cent by weight water-glass. 5. A method according to any of the preceding claims, character¬ ized in that the negative pressure is provided by means of a negative pressure source (47) and one or more suction means (38, 39) connected thereto and to one or more evacuation openings (31, 32) in the core 15 box (20). 6. A method according to any of claims 1-4, characterized in that the negative pressure is provided by means of a negative pressure chamber connected to the negative pressure source, the core box being placed in said negative pressure chamber, and the chamber communicating 20 with the cavity (35) of the core box via its evacuation opening or openings (31, 32). 7. A method according to any of the preceding claims, character¬ ized in that each evacuation opening in the core box includes a channel system with channel connections (33, 34) to two or more places of 25 the cavity (35) of the core box. 8. A method according to one or more of the preceding claims, characterized in that the core boxes (20), each consisting of two or more parts (42), are being moved between the various stations (22, 23, 28) while the parts of the core box are held together by means 30 of negative pressure maintained in inner spaces formed by recesses (44) in at least one of two opposing part surfaces (43). 9. A method according to any of the preceding claims, character¬ ized in that core boxes are used which comprise a body of one or more plastic materials and an inner layer of a mouldable plastic or rubber material with an exposed surface forming the contour of the cavity, said layer being by means of moulding in situ directly or indirectly joined to a unit with the body, said plastic material and rubber mate¬ rial being sufficiently transparent to microwaves; that said body (7) has a tensile strength of at least 55 MPa, preferably at least 70 MPa, and a bending module of at least 2.5 GPa, whereby the body has a mechanical strength which is sufficiently high so that the core box as to its form resists high internal and external pressures in the subsequent core production; that the rubber material used for the inner layer gives this a tear resistance of at least 10 N/mm, prefer¬ ably at least 15 N/mm, and most preferably at least 20 N/mm, whereby the layer has a tear resistance which is sufficiently high to enable the surface to resist extensive repeated core production; that the -5 o body has a coefficient of heat expansion of at most 6.5x10 mm/mm C, -5 o preferably at most 6.0x10 mm/mm C, said coefficient of heat expansion is sufficiently low to ensure that the core box achieves narrow toler- ances at the varying curing temperatures occurring during thermal curing of said cores; and that due to said high mechanical strength of the body, the core box is self-supporting and^thereby free from external support which would otherwise impede supply of microwaves in a desired direction or directions towards the core. 10. A method according to claim 9, characterized in that the inner layer consists of a silicone rubber of a quality giving the inner layer said properties and that an intermediate layer of a second mould¬ able silicone rubber material is arranged between the body and the inner layer, said silicone rubber material being of a quality having a lower coefficient of heat expansion than the silicone rubber material used for the inner layer. 11. A plant for the manufacture of cores for casting purposes in core boxes provided with cavities, for carrying out the method accord¬ ing to any of claims 1-10, said cavities being closed apart from a 16 filling opening through which a mixture of a sand material and an aqueous binder in the form of water-glass is introduced by means of a core forming machine, said filling opening having limited dimen¬ sions normally not permitting water to escape freely from an uncured core mixture in the core box, characterized in that it comprises a plurality of treating stations between which said core boxes (20), which are constructed entirely of materials which are transparent to microwaves, are moved in a continuous and repetitious process treating, said stations comprising a core forming station (22) with a core forming machine for filling the core boxes (20) with said core mixture, at least one heating station (23) having at least one micro¬ wave oven to cure the core mixture, and a removal station (28) for opening the core boxes and removing the cured cores and for re-assem¬ bling the core boxes for repeated use; and in that the heating station comprises means (38, 39, 40, 41, 47) for generating a negative pressure at the evacuation openings (31, 32) of the core box of such a value that the water.present in said mixture, having a raised temperature by the microwave energy supplied, is drawn by suction action to said evacuation openings at an increased diffusion rate through the core mixture. 12. A plant according to claim 11, characterized in that the heating station comprises a first treating department (26) arranged by means of microwaves to effect initial heating of the water content in the core mixture, and a second treating department arranged by means of microwaves to complete the heating process and by means of negative pressure from the means generating negative pressure connected first in this department, to draw by suction action the water out of the core mixture. 13. A plant according to claim 11 or 12, characterized in that the means generating negative pressure comprises a negative pressure source (47) and one or more suction means (38, 39) connected thereto and to one or more evacuation openings (31, 32) of the core box. 14. A plant according to claim 11 or 12, characterized in that the means generating negative pressure consists of a negative pressure chamber, in which the core box is placed and which is connected to a negative pressure source, the negative pressure chamber communi¬ cating with the inner cavity (35) of the core box via its evacuation opening or openings (31, 32). 15. A plant according to any of claims 11-14, characterized in that each evacution opening (31, 32) of the core box includes a channel system with channel connections (33, 34) to two or more places of the cavity (35) of the core box. 16. A plant according to any of claims 11-15, wherein each core box used repeatedly in the plant consists of at least two parts having part surfaces facing each other, characterized in that at least one of the part surfaces (43) is provided with recesses (44) which, with the opposite part surface or with corresponding recesses in this part surface of the twin part, form closed hollow spaces, that said spaces communicate with a channel (46) in at least one part (43), said channel having an external connection and a nonreturn valve (45), the parts being arranged to be held sealingly together after evacuation of air from said spaces via said channel and nonreturn valve.

Inventors: IVERLUND BERTIL, UDDBORN HANS, IVERLUND, BERTIL, UDDBORN, HANS
Applicants: MIKROVAOGSAPPLIKATION AB
Application year: 1985
Main classification: B22C9
IPC codes: B22C7, B22C9