Abstract:
A hot chamber die-casting machine has drive assemblies in the form of electrical servomotors instead of hydraulic cylinders for driving and pressing a feed bush to the nozzle. The feed rate of the servomotors is adjustable. In order to avoid the influence of heat from the smelter and the furnace, the rotational axes of the servomotors located above the smelter and the furnace are connected through an angle drive to the spindle drive and aligned approximately vertically. This makes it possible to achieve a time-optimized and precise feed regulation that is independent of temperatures which develop.

Description:
This application claims the priorities of European applications 991 06 242.3, filed Apr. 13, 1999, and 991 11 960.3, filed Jun. 24, 1999, the disclosures of which are expressly incorporated by reference herein. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a hot chamber die-casting machine with a gooseneck located in a metal bath within a smelter, with a vertical channel between the bottom of the sleeve and the seat of nozzle body with a mouthpiece and a nozzle mounted thereon as well as two drive assemblies having axes which are parallel to the nozzle. The assemblies are connected with a crossarm of a machine stand associated with the smelter and with a solid molding plate of a closing unit to which half of a mold is fastened, whose feed bush can be pressed against the nozzle tip during a casting process. 
     Known hot chamber die-casting machines which are on the market, like those manufactured and sold by the applicant, for example (Frech die-casting automatic machine DAW 80S “Druckvermerk” 06.94 KK), have a hydraulic drive in the form of two mutually parallel hydraulic cylinders, each engaging the mold on the solid mold plate, in order to advance the feed bush and press it against a nozzle tip. The cylinders are connected, on a side facing away from the mold plate, with a crossarm of the machine stand that spans the furnace and the crucible. This design is provided in order to permit moving and applying the feed bush to the mold at the nozzle tip with a given feed rate through the hydraulic system. The very high application force required during die casting can also be maintained by such drives. A certain disadvantage of this is that the hydraulic cylinders that usually run horizontally above the furnace grow hot; their regulating ability is also influenced by the variable viscosity of the hydraulic oil used, and this is taken into account. 
     It is also already known (AT-PS 292 222) to provide an electrical drive for a threaded spindle arrangement for closing a mold of an injection molding machine. Since molds of injection molding machines, and also molds of hot chamber injection molding machines, are not located in immediate vicinities of crucibles or furnaces which receive the hot metal melt, there are fewer problems with using electric motors than there are with advancing and retracting drives for feed bushes in hot chamber die-casting machines, in which these drives must necessarily be located directly in the areas of the hot melt. 
     One goal of the invention is to design a drive assembly for advancing a mold to a nozzle in such a fashion that feed regulation that is as time-optimized and precise as possible, and which is independent of temperatures developing in such die-casting machines, can be achieved. 
     To achieve this goal, in a hot chamber die-casting machine of the type mentioned above, the drive assembly is designed as a linear drive driven by electric servomotors with feed rates which can be controlled. This design makes a very delicate adjustment of the feed bush to the nozzle to the mold with varying speeds possible without any influence from the changing viscosities of hydraulic oil. A high adjustment rate combined with a delicate adjustment largely correspond to an optimum process so that a considerable improvement over known hydraulic systems is achieved. 
     Especially advantageously, the influence of heat from the crucible and the furnace is avoided by having the rotational axes of the servomotors located above the crucible and the oven connected to the linear drive through an angle drive and aligned approximately vertically. By this measure, the servomotors are located as far as possible from the furnace and brought into a position in which the heat flow from the oven or crucible is as small as possible. The angle drive located closer to the furnace provides a certain amount of heat insulation and can additionally be provided with a layer of insulation. The linear drive can be designed as a spindle drive and may additionally be surrounded by a continuous cooling jacket as well. It is also possible to equip the servomotors with water cooling. A rack and pinion drive can also form the linear drive, although a spindle drive has proven advantageous. 
     To obtain good travel of the spindle drive, a roll spindle or ball screw arrangement, which itself is known, can also be provided and may have a pitch which is made so that it has a self-locking effect. Consequently, unintentional feed or retraction of the drive is prevented, and the necessary retaining pressure can also be maintained during the die-casting process. Of course, corresponding locking devices can also be provided. In addition, the engine load moments are controlled so that a reliable closure between the feed bush and the nozzle tip is ensured. 
     According to one feature of the invention, the servomotors can be operated at different rates, with the arrangement being made such that the feed rate of the drive shortly before the application of the nozzle tip is reduced considerably relative to the feed rate. In this manner, it is possible to bring the feed neck against the nozzle tip in a precisely regulated fashion. As a result, wear at this point can be largely avoided. It is known to harden the nozzle tip, and the nozzle tip abuts the feed bush over a very small contact area. If the impact is too hard, damage can occur to the nozzle tip; this damage is avoided by the design of the invention. 
     An embodiment of the invention is shown in the drawings and is explained below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic top view of a hot chamber die-casting machine according to the invention; 
     FIG. 2 is an enlarged partially cut away view of the area of the portable furnace with the drive assemblies and the solid die plate; 
     FIG. 3 is a section through the device shown in FIG. 2 along line III—III; and 
     FIG. 4 is a view of the device shown in FIG. 2 as seen in the direction of arrow IV. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a hot chamber die-casting machine on an underframe  1  designed as a machine stand and located above a machine pedestal  2 . On the left side, the closing part  3  of the machine has guide rods  4  for a movable mold clamping plate  5  with an adjusting drive  6 , and a toggle lever closing mechanism  7 , which itself is known, and a fixed solid mold clamping plate  8  are also provided. A furnace  10 , movable on rails  9  (FIG. 4) with a smelter  11 , is located on this fixed mold clamping plate  8 . The smelter is spanned by a crossbar  12 . On the crossbar (see FIGS.  2  and  3 ), the outer cylindrical housing  13  is fastened by two spindle drives  14  located parallel to one another. An angle drive  15  is also permanently connected with the housing  13  and has a spindle  16 , projecting centrally into the housing, designed as a roll spindle or ball screw spindle. This spindle  16  is driven by an electrical servomotor  17  whose rotational axis  18  is aligned approximately perpendicularly to the surface  10   a  of furnace  10  (FIG. 4) and hence approximately vertically to the mounting surface  19  of the hot chamber die-casting machine. The two servomotors  17  are controlled in synchronization with one another so that the mold clamping plate  5  can be moved exactly parallel. Unequal application of force by the two spindle drives is ruled out. 
     A spindle nut  21  with a counterthread  20  adapted to the spindle  16  is in mesh with the spindle  16 . The nut (see FIG.  3 ) penetrates, with a threaded pin  22 , an opening  23  in a lateral flange area  24  of the fixed mold plate  8  and is fastened there by a nut  25 . If spindle  16  is rotated, a relative movement occurs between the furnace equipped with crossbar  12  and its smelter  11  and the fixed mold clamping plate  8 . 
     As can be seen from FIG. 2, a casting container  26  is submerged in known fashion into smelter  11 . The casting container is contacted from above by the crossbar  12  with a piston drive  27  for a piston that dips into the casting container  26  but is not shown in greater detail. This casting container  26 , in the area within the melt located in smelter  11 , has a rise tube which is directed approximately parallel to the casting container  26  upward from the end of the casting container and has a nozzle  29  mounted on its mouth. This nozzle  29 , in the position of the die-casting machine shown in FIGS. 2 and 3, abuts, by way of its tip  29   a , the feed bush  30  of the casting mold  31 , shown only schematically, and is held in this position as long as liquid metal is forced from casting container  26  outward through the vertical channel between the bottom of the sleeve and the seat of nozzle body and through nozzle  29  into the mold. The mold  31  is then moved away to the left from nozzle  29  and returned to the position shown in FIG. 2 only for a new die-casting process. For this purpose, the spindle  16  is rotated by servomotors  17  so that threaded nut  21  moves outward to the left from the housing  13  so that the distance between the cooled feed bush  30  and the heated nozzle tip  29   a  becomes sufficiently large to produce an air insulation bridge between two components. By this measure, the position of the melting zone of the setting metal can be regulated. The travel and the adjustment rate are set so that no cycle time losses occur. 
     The total travel of the outward movement is used for repair and service purposes on nozzle  29 , casting container  26 , and nozzle tip  29   a , and for the assemblies that are necessary for the method technology in this area. 
     As the figures indicate and as was described, the axes  18  of the servomotors  17  are aligned approximately vertically and the servomotors abut the spindle  16  through an angle drive  15 . This design permits the electrical servomotors  17  to be located as far away as possible from the surface  10   a  of furnace  10  and the smelter. The effect of heat from the furnace, therefore, can be largely eliminated so that it is possible to use electrical servomotors that can be regulated very precisely over various speed ranges, even for the rough operation of a hot chamber die-casting machine, as drives for moving the nozzle in and out. By using water-cooled servomotors  17 , additional heat-conducting panels  35 , and an integrated cooling jacket  36 , the heat radiated from the furnace is reduced to such a point that it has no disadvantageous effects on the function of the drives. 
     It is also possible to heat insulate angle drive  15  with, for example, external heat insulation so that having the angle drive  15  lie, in the direction of a heat flow, in front of servomotors  17  serves as protection for the servomotors and their electrical connections  32 . These connections are located at the extreme upper ends of servomotors  17  and hence as far as possible from the heat source. 
     With the selected type of drive it is possible to bring the feed bush  30 , initially, very quickly to the nozzle  29  and then, by appropriate reduction of the feed rate, make the approach to nozzle tip  29   a  very slow and precise in order to avoid any damage to the nozzle tip or the mold. This can be achieved by regulating the two spindle drives which, when they approach (and also when they move away), utilize a so-called “target braking” on the system point. The system point is determined in a search process. The adjustable pressure force is then developed by torque regulation of the motors. This device, therefore, makes it possible to adapt the pressure force required for the melt in the mold and to perform such an adaption or adjustment by way of a mathematical formula. 
     The threads of the spindle  16  and the counterthread  20  of the spindle nut  21  can be designed so that they are self-locking. After the feed bush  31  is applied to nozzle tip  29   a  and the drives are shut off, the nozzle can be held in a stable and permanent fashion in its operating position, so that, naturally, the adjustment must be designed for the drive thread to the high forces expected during die casting. The motor load torques are also balanced so that a more reliable seal between the feed bush and the nozzle tip is ensured. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.