Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-01-22
2001-11-20
Nguyen, Nam (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S312000, C164S119000, C164S306000
Reexamination Certificate
active
06318444
ABSTRACT:
The invention relates to a device and a method for charging horizontal and vertical cold chamber pressure die-casting machines with metal.
The generally known cold chamber die casting method is not sufficiently suitable for producing pressure die castings of high ductility because of the entrained air as well as the impurities in the molten mass and the gas absorption as a result of the turbulent molten mass feeding into the pressure chamber, as well as the size of the pressure chamber, which can only be filled to approximately 50%. Also, heat treatments or coatings above 400° C. are not possible without the danger of bubble formation. In order to prevent these disadvantages and to do justice to the increasingly rising demand for ductile, heat-treated castings, the so-called “Vacural—Die-Casting Method” is increasingly employed. Here, the pressure chamber charge takes place by means of a vacuum generated over the casting mold, wherein a riser pipe inserted into the molten mass of a stationary holding furnace fills the pressure chamber. Here, too, chemical reactions as well as gas absorption of the molten mass occur during,the withdrawal of the metal from the pressure chamber transfer opening to the holding furnace because of the aspiration of air. For example, the adhesion of oxides in the pressure chamber cannot be prevented, which considerably reduces the service life of the pressure chamber and the pressure piston. In addition, the leakages being created from this during the filling of the pressure chamber lead to additional swirling of the casting material because of the aspiration of air.
Moreover, making the casting material available by operating holding furnaces, as well as the charging of the holding furnaces, which are arranged stationary on the pressure die-casting machines, with liquid metal, represents an avoidable waste of resources. For example, DE 196 13 668 C1 shows a system for providing and supplying metal, wherein a furnace provides the functions of a casting and holding furnace as well as of a transport container by changing its cover.
SUMMARY OF THE INVENTION
It is the object of the invention to disclose a device and its method, wherein the entire casting process takes place under the exclusion of air. This is attained: by a vertical, or respectively lateral, arrangement of the casting furnaces in respect to the pressure chamber, having a pressure, or respectively aspirating line, which is fastened by means of a housing on the furnace cover and whose riser pipe is inserted into the casting furnace pressure container filled with the molten mass, wherein a movable connecting line and its actuating device assures the hermetic as well as intermittent connection with the pressure chamber. Moreover, there is a gas injection piston between the pressure piston and its drive rods which, together with the guide bush of the latter, forms a hermetic gas injection ring conduit. The pressure chamber is filled with casting material by means of an appropriate gas pressure buildup over the surface of the molten mass in the casting furnace pressure vessel, or by the buildup of a vacuum over the casting mold. After closing the metal transfer opening by means of the pressure piston entering the pressure chamber for the purpose of filling the casting mold, in the course of filling the pressure chamber with casting material by means of gas pressure, the gas pressure over the surface of the molten mass in the casting furnace pressure chamber is reduced, and the remaining molten mass on the surface of the pressure piston casing is withdrawn into the casting furnace by means of aspiration or of an appropriate gas pressure when the gas injection ring conduit is opened. In the process, gas injection of the remaining molten mass with inert gas is performed. The gas pressure buildup and reduction, as well as the atmospheric gas pressure equalization during the filling of the pressure chamber by means of a vacuum over the surface of the molten mass in the casting furnace pressure chamber, takes place by means of a closed inert gas cycle. Following the removal of the casting, return of the pressure piston and closing the casting mold, during the next filling of the pressure chamber the air is pushed out of the pressure chamber and the casting mold by the inert gas present in the pressure, or respectively aspirating line, as well as in the riser pipe.
The supply with molten mass, as well as the return of the remaining molten mass which could not be cast, takes place directly from and to the foundry. The conversion of the casting furnace into a liquid metal transport container, which is also used as a liquid metal buffer by heating, is performed by means of a change of the furnace cover. A free-floating plate is placed into the surface of the molten mass for minimizing the movement of the molten mass bath. After conversion of the transport container filled with molten mass into a casting furnace by changing the cover, the air in the pressure, or respectively aspirating line, as well as that above the surface of the molten mass in the casting furnace pressure container, is displaced by the application of inert gas.
This object is attained by means of an installation and a method according to the invention.
The duration of the pressure chamber temperature is a positive or negative variable, because of its rise from approximately 20° C. to approximately 200° C. at the start of the casting process, as well as of its drop after the casting process has been interrupted or terminated. Because of these problems, in accordance with the prior art the riser pipes are made of a pipe which is immersed into the molten mass with its lower end and is connected in a gas-tight manner with the pressure chamber. The changes of the position of the pressure chamber here present no problems because of an opening in the casting furnace. Filling of the pressure chamber and withdrawing of the remaining molten mass leads to a continuous movement of the molten mass bath under the influence of air, which leads to chemical reactions as well as to an absorption of gas in the molten mass. This, as well as the withdrawal of the remaining molten mass by the aspiration of air, has the result that the riser pipes are again and again clogged by oxides as well as by components of the molten mass. The problem can also not be solved by ceramic filters inserted into the riser pipe, since the oxides formed during the withdrawal of the remaining molten mass are present in the casting furnace at the bath level of the molten mass. Also, abrasive wear, along with corresponding formations of hollow spaces and oxide adhesions, in particular in the area of the molten mass transition of the pressure chamber, cannot be prevented by this. In addition, because of the heat loss, the riser pipes must be heated. By means of the advantageous design of the pressure, or respectively aspirating line via a steel housing which is screwed to the furnace cover and is designed to be spatially variable, the movable connecting line with inclined embodiment of the separation surface with the connection flange of the pressure chamber, t he withdrawal of the remaining molten mass without contact with the air by means of the gas injection piston and inert gas, the displacement of the air out of the pressure chamber by the inert gas located in the pressure, or respectively aspirating line and the riser pipe, and the closed casting mold during the filling of the pressure chamber by means of gas pressure, as well as the interruption of direct heat removal by ceramic or fiber-ceramic materials for all heat-conducting components, it is possible to achieve a filling of the pressure chamber, during which the described disadvantages are avoided.
To assure the hermetic connection between the pressure chamber flange and the movable connecting line, the inclined separating surface of the latter is embodied in such a way that at the start of the casting process the longitudinal expansion of the pressure chamber is compensated by a seal located in the separating surfac
Bandt Gerold
Ohnsmann Gustav
Brezina & Ehrlich
Lin I,-H.
Nguyen Nam
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