The disclosures in Italian Patent Application No. PD97A000264 from which this application claims priority are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a low-pressure die-casting apparatus. 
     Conventional low-pressure die-casting apparatuses are usually constituted by a flowing furnace into which a tube is immersed in order to dispense, by feeding pressure into the furnace, the liquid metal into a die which is connected in an upward region to the metal draw tube. 
     In order to form hollow bodies, such as for example faucets and the like, a molding-sand core is arranged inside the die; the core must be destroyed, for example by simple shaking, once casting is completed. 
     At the furnace there is usually a handling unit which allows to perform the various handlings of the die and to load the cores, unload the cast part and perform all the operations for the graphitization and cooling of the dies. 
     The die is loaded so that the molten metal must enter it from below, because if the molten metal were to enter from above it would prevent the escape of the air and bubbles would therefore form which would reduce the quality of the finished product. 
     As mentioned above, the furnace has a tube which enters its crucible to draw in the vicinity of the bottom and in any case with a head which is sufficient to perform a certain number of die filling operations before having to open the furnace and introduce further material to be melted. 
     In conventional methods, the die is carried by a handling unit exactly above the furnace, as occurs for example in the Italian patent application no. MI96A001138 in the name of the same applicant, is made to descend vertically above it until its lower part, in which there is a hole through which the molten material must enter, makes contact with the tube that draws from the furnace. 
     Casting occurs by pressurizing the furnace by means of compressed air or another inert gas, so that the liquid metal rises along the tube, filling the entire die. 
     This method, however, required a very complicated handling unit. 
     Said handling unit, when it moves from the position above the furnace toward the discharge region, must in fact open in order to allow the exit of the finished product but must also rotate the die halves that constitute the die in order to place them in front of the operator. 
     In addition to this, the handling unit must be able to overturn the two die halves to allow graphitization and washing and cleaning of all the slag. 
     Accordingly, the handling unit must have the ability to perform a translatory motion and also to move downwards. 
     In the system described by the above-mentioned patent application no. MI96A001138 there are two furnaces and the handling unit must operate by moving to one region and then to the other and is accordingly very complicated. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to provide an improved low-pressure die-casting apparatus the constructive structure whereof is simplified with respect to conventional apparatuses. 
     A consequent primary object of the present invention is to provide a die-casting apparatus which has a better coupling centering between the furnace and the die. 
     Another important object of the present invention is to provide an improved casting apparatus which allows to work even with very large dies without any particular difficulty. 
     Another object of the invention is to provide an improved die-casting apparatus which ensures practical, durable and effective operation. 
     This aim, these objects and others which will become apparent hereinafter are achieved by an improved low-pressure die-casting apparatus comprising at least one flowing furnace with which at least one handling unit cooperates, said at least one handling unit being selectively connectable to a respective die, characterized in that said at least one handling unit is associated with a guide for horizontal translatory motion between a casting position, which lies above said at least one furnace, and a discharge position, said at least one furnace being movable vertically in order to couple and uncouple with respect to said die connected to said at least one handling unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the present invention will become apparent from the description of a preferred embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a furnace of an improved low-pressure die-casting apparatus according to the invention; 
     FIG. 2 is a sectional view, taken along a transverse plane, of the flowing furnace shown in FIG. 1; 
     FIG. 3 is a side view of a part of the improved casting apparatus, according to the invention; 
     FIG. 4 is a side view of the part of the apparatus shown in FIG. 3 during casting, with the furnace coupled to a die; 
     FIG. 5 is a perspective view of a detail of the flowing furnace of FIG. 1; 
     FIG. 6 is a sectional view, taken along a longitudinal plane, of the detail of FIG. 5; 
     FIG. 7 is a sectional view, taken along a longitudinal plane, of the detail of FIG. 5 during casting. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the above figures, an improved low-pressure die-casting apparatus comprises a flowing furnace  10  of the electric type, or of an equivalent type, controlled by a computerized central unit schematically designated by the reference numeral  11 . 
     The apparatus comprises, in this case, a handling unit  12  which can move horizontally along guides  13  and is adapted to move a die  14  into the casting position. 
     The handling unit  12  can be arranged above the furnace  10  for casting into d then move horizontally and be arranged at a station for loading/unloading said die  14 . 
     The furnace  10  is supported by a frame  15  provided with means, generally designated by the reference numeral  16 , for lifting/lowering with respect to the ground. 
     The means  16  comprise threaded legs  17   a ,  17   b ,  17   c ,  17   d  which are provided with a foot  18 ; each leg is coupled to a female thread  19  accommodated inside a box  20 . 
     Each one of the female threads  19  is externally provided with teeth and is coupled, in this case, to a worm screw  21  which is also accommodated inside the box  20 . 
     The lifting/lowering means  16  comprise a motor drive  22  with an output shaft  23  on which a driving pulley  24  is keyed and which engages the worm screw  21  of a first leg  17   a.    
     In particular, said driving pulley  24  (see FIGS.  3 - 4 ) is coupled, by means of a toothed belt  25  (see FIG. 2) (or another equivalent flexible element), to a driven pulley  26  which is arranged at a second leg  17   b  and is in turn keyed to a second shaft  27  which engages the worm screw  21  of the second leg  17   b.    
     The output shaft  23  and the second shaft  27  are each connected, by means of a first coupling  28 , to a third shaft  29 . The third shafts  29  are connected, by means of a second coupling  28 , to a driven shaft  30  on which said worm screw  21  of said third and fourth legs  17   c  and  17   d  engages. 
     In this case, each one of the third shafts  29  is constituted by a first shaft portion and by a second shaft portion  31  which are mutually fixed by means of a flanged coupling  32 . 
     The engagement of each one of the shafts  23 ,  27  and  30  with the worm screws  21  of each one of the legs  17   a ,  17   b ,  17   c  and  17   d  is performed by means of holes  33  formed on each one of said boxes  20  and by means of keys  34  which ensure the transmission of the torque from the shaft  23 ,  27  or  30  to the worm screw  21 , which by meshing with the female thread  19  transmits the rotary motion imparted thereto, causing a consequent lifting or lowering with respect to the corresponding legs  17   a ,  17   b ,  17   c  or  17   d.    
     The means  16  in fact ensure the simultaneous lifting or lowering of all the female threads  19  to avoid even the slightest imbalance of the furnace  10 , which contains molten metal to be cast into the dies  14 . 
     In this manner, in fact, the handling unit  12  acts only as a device for the horizontal translatory motion of the dies  14 , and once it has reached the end of its stroke it is assuredly centered above the furnace  10 , so that it is sufficient for the central unit  11  to activate the lifting of the furnace  10  to produce, by pressurizing the furnace  10 , the casting of the molten metal into the die  14 . 
     In addition to this, the frame  15  that supports the furnace  10  is mounted on load cells  35  of a per se known type which are also connected to the computerized central unit  11 . 
     The load cells  35  are capable of detecting the load condition of the furnace  10 , indicating any need to introduce new material to be melted and the amount introduced. 
     In particular, however, the load cells  35  detect the moment when the furnace  10 , lifted by the female threads  19  actuated by the motor drive  22 , makes contact with the handling unit  12  that lies above it and is thus ready to perform casting. 
     Each load cell  35  in fact detects the activation of the motor drive  22 , which synchronously transmits motion to the female threads  19 , lifting the furnace  10  while each cell  35  detects the weight of the furnace  10  and the weight of the molten metal contained therein. 
     Apart from entirely negligible small oscillations, this weight remains constant until said furnace  10  makes contact with the handling unit  12 . 
     At this point the furnace  10  eventually pushes against the die  14  and accordingly each load cell  35  detects a load increase peak due to this slight thrust. 
     In addition, the load cells  35  allow to automatically vary the pressure in order to always reach the set threshold in the pressurization process for casting the metal into the die, regardless of the variation of the level of the metal in the furnace  10 . 
     The improved apparatus of the invention also allows to work with very large dies, since all the translatory motion problems are considerably simplified and the handling unit merely provides the simple horizontal translatory motion. 
     Another advantage is achieved with the present invention in that a die-casting apparatus has been provided which has a very simple structure and at the same time ensures truly effective operation. 
     In practice it has been observed that the present invention fully achieves the intended aim and all the objects. 
     The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the same inventive concept. 
     All the details may furthermore be replaced with other technically equivalent elements. 
     The materials used, so long as they are compatible with the contingent use, as well as the dimensions, may be any according to the requirements.
The apparatus comprises at least one flowing furnace with which at least one handling unit cooperates, the handling unit being selectively connectable to a respective die. The at least one handling unit is associated with a guide for horizontal translatory motion between a casting position, which lies above the at least one furnace, and a discharge position. The at least one furnace can move vertically in order to couple and uncouple with respect to the corresponding die connected to the at least one handling unit.