Abstract:
A casting plant for low-pressure casting of molten metal with operatively and kinematically connected units in the form of linear or revolving conveying devices. The plant includes casting molds constructed and arranged to be filled with molten metal intermittently or continuously, and disposed either in a casting or residual metal receiving station or in a separate casting station, an insulated feeder pressure pot with a recompression unit and a shutoff valve unit having gas charging conduits flanged to the underside of the casting mold, the insulated feeder pressure pot being constructed and arranged to receive excess molten metal from the casting mold after a casting therein has solidified, a casting or residual metal receiving station, disposed beneath the casting molds and including a hermetically sealed, insulated pressurized furnace in which two assembled crucibles are disposed, including an inner crucible forming a pressure chamber and which is adapted to be filled with molten metal, a furnace cover having a movable pressure line and a movable return line for the molten metal passing therethrough, the pressure line extending from the shutoff valve unit to a portion of the crucible which is constructed and arrange to be below the surface of the molten metal therein, and the return line extending from the shutoff valve unit to a portion of the crucible constructed and arranged to be above the surface of the molten metal contained therein.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to casting equipment and a process for producing castings of the type in which the casting molds may comprise either permanent molds, that is, dies, or sand molds. 
     In the known low-pressure die casting process, the casting material is forced directly out of a hermetically sealed heatable pressurized container, with a slight increase in the gas pressure above the melt, through a casting tube into the casting mold located above the pressurized container. The feeding required during the solidification of the casting is assured by the melt that is under pressure and extends from the pressurized container on into the casting mold. The requisite stationary connection of the pressurized container, casting tube and casting mold over the entire process of casting and solidification of the casting leads to the following disadvantages: 
     each casting mold requires at least one separate pressurized container; 
     laborious melt supply due to the pressurized furnace at the casting site and the corresponding melt holding operation; 
     virtually exclusively, each casting mold requires its own mechanizing aid for casting production; 
     labor costs and space requirements are high. 
     The advantages of these methods, such as bottom gating, nonturbulent mold filling, optimally variable solidification geometry, and exclusively non-feeder casting production, are overcome by the highly cost-intensive nature of these methods. 
     Moreover, in German Patent Disclosure DE 1 285 682, a low-pressure casting apparatus and the process for its operation are described in which a heated feeder pressure pot with a shutoff valve and a pressure piston rests between a casting mold and a casting tube connected rigidly to the furnace cover. After the mold has been filled and the melt confined in the feeder pressure pot via the shutoff valve, the pressure on the melt can be increased arbitrarily via a piston or a pressure unit simultaneously embodied as a shutoff slide, by the actuation of this piston or unit. The solidification of the casting occurs independently of the casting furnace. 
     A disadvantage here is that the casting molds are filled via a large-area feeder conduit, that the removal of the casting is dependent on the solidification of the residual metal in the heated feeder pressure pot, that the casting molds have to be placed together with the feeder pressure pot on the pressurized furnace and removed from it, and that for complicated casting geometries, many feeder conduits are required. 
     German Published, Non-Examined Patent Disclosure DE-OS 17 83 046 also describes an injection molding machine in which casting molds are filled with melt in a stationary casting station on an continuous basis. Here the casting molds are connected to the casting station, and separated from it again after the casting has solidified, by being raised and lowered. The overflow of melt takes place directly from the casting furnace into the casting mold via a feeder conduit. The supply of molten metal to the casting furnace is assured by a melt container positioned upstream of the casting station. 
     Since the injection molding machine has no feeder distributor container, castings that have to be made with a plurality of feeder conduits spaced apart from one another cannot be made with it. Another disadvantage is the supply of melt to the casting furnace; the molten melt must be fed from the smelting furnace into the holding container and from there into the casting furnace, which entails major losses of metal and energy. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to create a casting equipment and its method for producing castings in which the disadvantages of the prior art are overcome. 
     The advantages of the casting equipment of the invention and its process for producing castings are that the casting molds are filled with rising, nonturbulent melt; the feeding of castings through the feeder pressure pot is effected independently of the casting furnace; the melt is recompressed in the mold cavity via an arbitrary pressure; the residual melt in the feeder pressure pot is delivered for refilling of the casting mold with only slight heat losses; all the gas charging operations take place with inert gas, with air excluded; optimal thermal insulation of all the units involved in the casting process is assured; and no warming operation with a corresponding supply of melt to the casting stations is necessary. All of this leads to a considerable increase in productivity, major savings of energy, and higher quality, as well as improved mechanical properties of the castings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment will be described in further detail in conjunction with the drawings. Shown are: 
     FIG. 1, a section through a casting plant according to the invention; 
     FIG. 2, a further exemplary embodiment of a casting plant; 
     FIG. 3, an exemplary embodiment of a feeder pressure pot with a recompression unit and a shutoff valve unit, shown in detail; 
     FIG. 4, an exemplary embodiment of a pressure line and return line, in detail; 
     FIG. 5, an exemplary embodiment of a container for molten metal transport. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The casting plant comprises revolving or linear conveying devices, located on which are casting molds  3  whose bottom plate  4  has through openings  5  for the casting material, and a feeder pressure pot  6 , secured below the casting mold bottom plate  4 , with a recompression unit  17  mounted on the side wall of the feeder pressure pot  6  and a shutoff valve unit  32  secured below the feeder pressure pot  6 . A casting or residual metal receiving station  59  is installed under the shutoff valve unit  32  and comprises a heated, hermetically sealed pressurized furnace  60 , whose pressure chamber  74  is filled with melt  73  and on whose furnace cover  70  a movable pressure line  77  and a return line  95  are mounted. In a further version, the casting station  98  and the residual metal receiving station  99  form separate units. As well as a transport container  108  for supplying the molten metal. 
     In detail, as shown in FIG. 3, the feeder pressure pot  6  is formed by a steel housing  7 , a bottom plate  8 , an insulation housing  10 , and a cover plate  11 . The steel pressurized pot is inserted loosely, via a housing  7  by its vertical side walls  7   a , into a corresponding recess of the bottom plate  8  and centered by the shoulder  8 ′. The cover plate  11  is inserted via recesses  10   a  of the vertical side walls of the insulation housing  10 . The shoulders  11   a  of the cover plate  11  fill the openings  14  of the steel housing  7  and, via the recessed face  4   a  of the casting mold bottom plate  4 , seal off the overflow openings  5  and  13  from escaping melt  73 . The insulation housing  10  is received by the bottom plate  8  via a recess  10   b  and an opening  9  and is locked by the inner jacket face of the steel housing. The feeder pressure pot  6  may be embodied in parallelepiped or cylindrical form. Both the insulation housing  10  and the cover plate  11  are made of ceramic fiber materials. 
     The cylindrical steel housing  18  of the recompression unit  17  is inserted and screwed into a groove of the vertical outer wall  7  of the feeder pressure pot  6  via a collar  18   a . In the interior, the steel housing  18  receives the pressure piston  20 , the bush  21 , the coupling  27 , the actuating piston  30 , and the bearing shells  22  and  24 . Via openings  16  and  23  that are centered with respect to the steel housing  18 , the bush  21  is inserted into both the insulation housing  10  and the bearing shell  22 . The bush  21  is locked against displacement by both the collar  21   a , seated in a recess of the bearing shell  24 , and the end face of the bearing shell  22 . The shoulder of the bearing shell  22  that fills the opening  15  in the vertical side wall  7  insulates the bush  21  from the feeder pressure pot  6 . The piston  20 , acting upon the confined melt in the opening  12  with pressure by displacement, is supported and guided in the bush  21 . Via a coupling  27 , the pressure piston  20  is connected to the actuating piston  30  of a displacement device. The peg  20   a  protruding into the interior of the steel coupling housing, and its connection with the steel housing  26 , and the threaded eyelet  26   a  connecting the actuating piston are all enveloped by an insulating lining  28 . With the interposition of a disk  29  made of thermal insulation, the dissipation of heat from the pressure piston  20  to the steel housing  26  of the coupling  27  is reduced. Via openings in the bearing shell  24 , the disk  29 , coupling  27  and actuating piston  30  are supported, and the piston  30  is insulated from the steel housing  18  via a shoulder  24   a  of the bearing shell  24 . Through a bore  31 , the requisite atmospheric pressure equalization in the reciprocation space of the pressure piston  20  is assured. Both the bush  21  and the piston  20  are made from ceramic or ceramic composite materials. The bearing shells  22  and  24 , the disk  29 , and the lining  28  comprise ceramic fiber materials. 
     Whether a plurality of recompression units  17  are provided depends both on the size of the feeder pressure pot and on the casting to be cast. 
     The shutoff valve unit  32  is screwed to the steel plate  8  of the feeder pressure pot  6  through a steel housing  33 , via its vertical side walls  33   a . Via a bottom plate  34 , inserted loosely into the interior of the steel housing  33 , and a cover plate  35  of thermal insulation, the heat loss of the shutoff valve  36  is reduced to a minimum. The valve guide plates  37  and  41 , inserted loosely into the recess  34   a , together with the shutoff slide plate  39  supported between them and connected to the coupling  50 , form the shutoff slide valve  36 . By means of bores disposed centrally to the overflow openings  12   a  in the bottom plate  34  and in the cover plate  35 , spacer bushes  43  and  45  are inserted, which are received by their end faces by correspondingly cylindrical recesses  37   a ,  41   a  of the valve guide plates  37  and  41 . The shoulders  37 ′and  41 ′center and lock the guide plates  37  and  41 , and at the same time the overflow openings  38 ,  42 ,  44  and  46  for the melt  73  are centered both with respect to one another and with respect to the overflow opening  12   a  of the feeder pressure pot  6 . In the melt closing position of the shutoff slide  39  with respect to the feeder pressure pot  6 , the melt confined in the overflow opening  40  is sealed off via the valve guide plates  37  and  41  from leakage. The overflow openings  44  and  12   a  are sealed off from escaping melt by the faces  35   a  and  43   a  towards the bottom face of the insulation housing  10 . The bush  47  of thermal insulation inserted into an opening in the steel housing  33  is received by a cylindrical recess  45   a  of the bush  45 , and its collar  47   a  is centered via a recess in the bottom plate  34  and the spacer bush  45  is locked and heat transfer from the bush  45  to the steel housing  33  is also reduced. Via a coupling  50 , the shutoff slide  39  is connected to the actuating piston  53  of a displacement device. The shutoff slide  39 , protruding into the interior of the steel housing  48 , and its connection with the steel housing  48 , and also the threaded eyelet  48   a  connecting the actuating piston  53 , are enveloped by an insulating lining  51 . In the closed shutoff slide position, the steel housing  48  of the coupling  50  together with the valve guide plates  37  and  41  form an insulation void  52 . Via a bush  54  inserted into the steel housing  33  and the bottom plate  34 , the actuating piston  52  is received and centered. The atmospheric pressure equalization for the gas-tight reciprocation space of the shutoff slide  39  takes place through the opening  55 , and the gas charging of the melt  73 , present under the closed shutoff slide  39  after the casting mold has been filled, takes place through the conduits  49 . The atmospheric pressure equalization of the reciprocation space for the shutoff slide  39 , formed by the valve guide plates  37  and  41 , takes place via the opening  58 . The gas charging through the openings  49  and  55  takes place with inert gas and with air excluded, through a closed system communicating with the casting molds  3 . 
     The components of the shutoff valve  37 ,  39 ,  41  and the bushes  43 ,  45  and  54  are made of ceramic or ceramic composite materials. The bottom plate  34 , cover plate  35 , lining  51  and bush  47  comprise ceramic fiber materials. 
     The feeder pressure pot  6 , together with the recompression unit  17  and the shutoff valve unit  32 , is inserted into a recess  4   a  of the casting mold bottom plate  4  and centered via the shoulder  4 ′ and screwed to the bottom plate  4 . 
     The casting or residual metal receiving station  59  shown in FIG. 1 comprises a pressurized furnace  60 , a pressure line  77 , and a return line  95 . In detail, the pressurized furnace  60  comprises two crucibles  61  and  62 , set one inside the other, whose vertical walls form a void which is filled with insulation material  63 . An insulation plate  64 , supported between the bottom faces  61   a  and  62   a , which receives a heat source  65 , for instance comprising electrical resistors. The heat transfer takes place directly to the bottom wall of the inner crucible  61 . By means of the void filled with insulation material  63 , the heat transfer from the heat source  65  to the outer crucible  62  is reduced to a minimum. By means of conically embodied shoulders  64   a  and  64   b , the inner crucible  61  and the outer crucible  62  are centered with the insulation plate  64 . The outer crucible  62  is supported on the furnace bottom  67   a  via studs  66 . A centrally disposed stud, embodied with a conical shoulder  66   a  and received by a recess of the bottom wall of the outer crucible  62 , the outer crucible  62  is centered with respect to the furnace jacket  67 . To reduce heat dissipation from the outer crucible  62 , the studs  66  are embodied with intermediately supported insulation plates  68 . The voids, formed by the outer crucible  62  toward the furnace bottom  67   a  and the steel jacket  67  of the furnace, are lined with insulation materials  69 . The segments  71 , which are inserted into the furnace cover  70  and may also be annular in shape, are screwed to the threaded eyelets  70   a  of the furnace cover  70  via corresponding recesses. By means of conically embodied shoulders  61   c  and  62   b  of the vertical crucible walls, which are received by corresponding recesses of the segments  71 , both the inner crucible  61  and the outer crucible  62  are centered and locked. The cover interior is lined with an insulation plate  72 , which is positioned via the inclined faces  71   a  and which with the end face  72   a  seals off the pressure chamber  74  toward the end face of the inner crucible  61 . The furnace cover  70 , screwed to the furnace housing  67 , thus forms a hermetically closed unit; the inner crucible  61  is filled with melt  73 , and the gas pressure build up and reduction with insert gas is effected above the melt  73  through the openings  75  and  76 . 
     The materials used for the inner crucible  61  may, depending on the metal melt to be cast, be made of graphite, silicon carbide, cast iron or cast steel. 
     The outer crucible  62  may be made from cast iron or from tamped or cast and sintered refractory compositions. 
     The plate  64 , the insulation plates  68 , and the segments  71  are made of ceramic or ceramic composite materials. 
     The insulation material  63 ,  69  and  72  comprises ceramic fiber materials. 
     The pressure line  77  mounted on the furnace cover  70  is shown in detail in FIG.  4 . 
     Essentially, the pressure line  77  comprises a rigid tube  78 , a movable tube  79 , a coupling  85 , and a motion device  88 . 
     The tube  78  is inserted into an opening of the insulation late  72  of the furnace cover  70  and with the collar  78   a  is nserted into a bearing shell  81 . Via cylindrically offset penings  70   b  and  70   c , the bearing shell  81  is received by the furnace cover  70 . Both the insulation ring  82 , inserted into the furnace cover  70 , and the inserted steel ring  83  are screwed together with the bearing shell  81  to the furnace cover  70  via the shoulder  70   a . By means of the shoulder  78   c  and the end face  78   b , the tube  78  is locked via the bearing shell  81 , the insulation plate  82 , and steel plate  83 , and sealed off against gas leakage to the pressure chamber  74 . With its end face  78   d  in FIG. 1, the tube  78  plunges into the melt  73  at a distance of 100 to 150 mm from the crucible bottom  61   b . The tube  79  is inserted displaceably into the interior of the tube  78  and is positioned via a coupling  85  and the motion device  88 . To minimize heat losses, the tube  79  is sheathed, beginning at the orifice  79   b , with a thermal insulation  84 , which is received by the openings both in the plates  82 ,  83  and in the tube  78 . Via an annular claw  86  and  87 , which clasps the insulated collar  79   a  of the tube  79 , and a ring or annular segment  89  and its plate  90 , the tube  79  is connected to the motion device  88 . 
     The return line  95  shown in FIG. 1 is identical in its embodiment to the pressure line  77 , except for the end face  78   e  that does not plunge into the melt  73 . 
     The tube  78  and  79  is made of ceramic or ceramic composite materials. The bearing shell  81 , insulation ring  82 , and sheathing  84  comprise ceramic fiber materials. 
     A further exemplary embodiment of a casting plant, with a separate casting station  98  and a residual metal receiving station  99  spatially separated from it, is shown in FIG.  2 . ere the casting station  98  is equipped with both a pressurized furnace  60  and a movable pressure line  77  secured to the furnace cover  70 . The residual metal receiving station  99  has a holding furnace  100 , with a movable return line  95  mounted on the furnace cover  105 . The gas supply to the feeder pressure pot  6  is effected through the opening  75  in the furnace cover  105 , at atmospheric pressure with inert gas, over the surface of the molten bath in the crucible space  74 , and via the return line  95  and the opened shutoff valve  36 . Except for the opening  76  made in the pressurized furnace cover  70 , the holding furnace  100  is identical in design to the pressurized furnace  60 . 
     The molten metal transport container  108  shown in FIG. 5 is identical in design to the pressurized furnace  60 , except for the furnace cover  109 . Unlike the furnace cover  70 , the lining  110  of the furnace cover  109  is made with a spherical segment  110   a , which plunges into the melt  73 , reduces the surface area of the melt, and thus prevents sloshing of the melt at the surface during transport. The furnace cover  109  also has no openings. 
     It should also be noted that design details may certainly be different from the exemplary embodiments shown without departing from the scope of the claims. 
     The casting plant and its method for producing castings functions as follows: 
     A casting mold  3 , moved by the conveying device  1  into the casting or residual metal receiving station  59  is locked centrally to the overflow openings  46  and  80  of both the pressure line  77  and the shutoff valve unit  32 . Before the casting mold is filled, the orifice of the pressure line  77 , located spaced slightly below the overflow face of the shutoff valve unit  32 , is pressed against the overflow opening face of the shutoff valve unit  32 , with the interposition of the seal  56 , by actuation of the motion device  88 . By means of a slight gas pressure buildup above the melt  73  in the hermetically sealed pressurized furnace  60 , the melt  73  is forced into the mold void  2  via the openings of the pressure line  77 , the shutoff valve unit  32 , the opening  40  of the shutoff valve, the feeder pressure pot  6 , and the openings  13  and  5  distributing the melt  73  to a plurality. Immediately after the mold has been filled, the melt  73  located above the valve  36  is confined by actuation of the shutoff slide  39 . The immediate actuation of one or more pressure pistons  20  that then ensues leads to an increase in pressure in the confined melt  73  because of the action of the piston on the face end thereon. The magnitude of the pressure can be selected arbitrarily. At the same time, shortly before the terminal closure position of the shutoff slide  39  is reached, the gas pressure above the melt in the pressurized furnace  60  is reduced, and the gas charging conduits  49  embodied below the shutoff slide  39  open; by aspiration of inert gas, the column of melt present below the shutoff slide  39  is lowered into the pressurized furnace  60 . After the melt has been lowered, the pressure line  77  is returned to its outset position by actuation of the motion device  88 , and the casting mold  3  leaves the casting or residual metal receiving station  59 , while at the same time the next casting mold  3  follows it into the casting or residual metal receiving station  59  to be filled with melt  73 . In the ensuing cooling segment, the casting  2  solidifies; the volumetric deficit from the solidification of the casting  2  is compensated for by the piston  20  acting on the melt  73  in the feeder pressure pot  6 . Shortly before the casting solidifies, the casting mold  3  leaves the cooling segment and is locked in the casting or residual metal receiving station  59  centrally to the overflow openings  46  and  80  in both the return line  95  and the shutoff valve unit  32 . By the actuation of the motion device  88 , the orifice face of the return line  95 , which is located spaced slightly below the shutoff valve unit  32 , is pressed with the interposition of a seal  56  against the overflow opening face of the shutoff valve unit  32 . By the actuation of the shutoff slide  39 , the overflow opening  40  to the return line  95  is opened, and the residual melt located both in the feeder pressure pot  6  and above the shutoff slide  39  flows back into the pressurized furnace  60  via the return line  95 , with the aspiration of inert gas that is present at atmospheric pressure above the melt  73  in the pressurized furnace  60 . After the feeder pressure pot has been evacuated, the pressure piston is returned to its outset position by the actuation of the motion device, and the shutoff valve  66  confines the inert gas in the feeder pressure pot  6  by actuation of the motion device. By the actuation of the motion device  88 , the return line  95  is returned to its outset position, and the solidified casting  2  can be removed from the casting mold  3 . Once the casting mold  3  has been made ready for casting, new casting operation takes place in the casting or residual metal receiving station  59 ; in this process, the inert gas confined in the feeder pressure pot  6  forms a protective layer, during casting mold filling, over the melt surface that rises upward in the mold void  2 . Before the gas pressure buildup in the crucible space  74 , the orifice face of the return line  95  is closed in gas-tight fashion, with the interposition of a seal  56  on a plate or the shutoff valve unit  32 , by actuation of the motion device  88 . 
     In conveying devices with a linear course of motion and a contrary direction, the casting molds  3  after being filled in the casting or residual metal receiving station  59  must be returned in opposite directions to their outset position, where, after the casting has solidified, the residual melt in the feeder pressure pot  6  has been evacuated, and the casting has been removed, they can then be refilled with melt  73  in the casting or residual metal receiving station  59 . 
     The course of operation in FIG. 2, in which the casting station  98  is spatially separated from the residual metal receiving station  99 , differs from the casting or residual metal receiving station  59  only in that the residual metal receiving station  99  has a holding furnace  100  and a return line  95  that receives the residual melt, after casting solidification, from the feeder pressure pot  6  via the return line and collects it, and that the travel segment from the residual metal receiving station  99  to the casting station  98 , which has a pressure line  77 , is utilized for removing the castings, cleaning the casting mold  3 , and the placement of cores or loose parts, and the casting mold filling takes place in the casting station  98 . 
     The molten metal furnished by the transport container  108 , as shown in FIG. 5, can be temporarily stored in the transport container  108  by heating via the heat source  65 , or can be poured directly, via a change of furnace cover, into the casting or residual metal receiving station  59  and the casting station  98 .