DK142156B - Underpressure casting furnace. - Google Patents

Description

14215 G

The present invention relates to a negative pressure casting furnace which is tightly encapsulated and heat-insulated and which is provided with electric heating elements as well as with a filling opening and a downwardly directed drain pipe, each of which is provided with 5 seals, which negative pressure casting furnace is arranged for melting metal and casting the molten metal under pressure while maintaining a negative pressure in the furnace space above the molten metal.

In casting furnaces of the type mentioned, where solid metal is introduced through the filling opening and melted in the casting furnace by means of electric heating elements, and where the molten metal is cast under pressure in a mold connected to the tapping pipe, it has not previously been possible to introduce solid metal into the furnace simultaneously with the draining of molten metal through the drain pipe due to said negative pressure which is desired to be maintained in the furnace above the molten metal to remove from the metal undesirable gases or any air introduced into the melt via the introduced solid metal to be melted.

Generally, the said negative pressure has hitherto been generated by means of large vacuum pumps, and the negative pressure has had to be rebuilt each time the filling opening is opened for the introduction of a new supply of solid metal, the scan must be melted. The use of said large vacuum pump as well as still restoration of said negative pressure in the casting furnace is economical and irrational in connection with melting and casting of a number of metals, such as e.g. low melting point metals, and in cases where the molten metal is to be cast under pressure in molds connected directly to the drain pipe for the manufacture of e.g. bearing liners and other articles for industrial use or 30 jewelery. The metal or metal alloy to be used for the casting is, of course, selected depending on the objects to be manufactured.

It is of course possible to build locks in connection with the filling opening in order to be able to maintain the negative pressure in the casting furnace during the introduction of solid metal therein, but one will introduce unwanted air which is in the sluice chamber together with the solid metal, which air then must be removed by means of the said vacuum pump. In addition, such a sluice device in the filling opening to the furnace is relatively complicated and expensive.

The object of the present invention is to remedy the above-mentioned disadvantages and to provide a casting furnace in which the prevailing negative pressure remains constant during volume variations, and from which any undesired gases are removed in an energy-saving manner while maintaining a controlled atmosphere over the molten bath.

This is achieved according to the invention by what is stated in the characterizing part of claim 1. During the evaporation and densification of the liquid, a constant gas state is maintained above the metal melt 15 to protect it against unwanted gas contaminants.

Densification removes unwanted gases in an energy-saving way. The constant gas state maintains the negative pressure over the melt by volume variations in it during the filling and / or draining of the furnace, which can thereby also take place simultaneously.

As stated in claim 2, it is ensured that the liquid lock at the inlet pipe contains liquid metal during operation of the furnace, so that solid metal melting and outflow of the molten takes place continuously from the liquid lock without sudden pressure variations in the furnace atmosphere.

The invention is explained in more detail below with reference to an embodiment of a casting furnace according to the invention schematically shown in the drawing.

The drawing shows an encapsulated casting furnace 1, where the introduction 30 of the material into the kiln space takes place through an insertion pipe 2 provided with a sealing arrangement in the form of cooperating pipes, which form a liquid lock 3, where the liquid column is made of U21B6 3 liquid metal 4. arranged a drain pipe 5 with an operable shut-off valve 6 at the lower bent and upwardly directed end of the drain pipe. Draining of liquid metal can take place by the pressure of gravity, the liquid metal being pressed into a closed mold 7 at the end of the draining tube 5. The mold is provided with small air holes at its upper edge 8 and an inlet opening for liquid metal under pressure is arranged at lower edge of the mold 9.

The free space 10 above the molten bath 11 'in the furnace space 11 10 is connected via a pipe from the upper part of the chamber to a container 12 with liquid 13, which at a certain negative pressure evaporates, so that gas or steam 14, which fills said connecting pipe and the space above the molten bath 11, protects the metal in the molten bath and keeps the negative pressure in the space 15 constant constant independent of volume variations of the molten bath in the furnace chamber 11 during filling and draining from the furnace, respectively.

In order to prevent the ambient air from penetrating the furnace chamber 11 through the insertion pipe 2, the height of a liquid column column 3 'of the liquid lock 3 and thus the liquid metal column 4 is adjusted so that the pressure of this metal column is at least equal to or greater than the negative pressure in the space 10 above the metal melt 11 '.

At said negative pressure, ie. upon dilution of the gas atmosphere 10 10, the liquid 13 in the container 12, which is connected to the upper part of the furnace chamber 11, must begin to form steam, which fills the space 10 above the molten bath 11 '. This occurs by draining liquid metal through the drain pipe 5 into the mold 7.

When the pressure rises in the steam atmosphere in the room 10 at e.g. supply of solid metal materials through the filling tube 2, in which the materials melt due to an electric heating element 16 arranged around the filling tube 2, will

14 21 5 G

4, the steam 14 flows back to the container 12 and condenses to liquid 13 therein, because the container 12 is arranged so as to be kept at a lower temperature in the chamber 11 of the furnace.

The height of the melting pipe 5 of the melting furnace is adjusted so that the metal column in the pipe and in the melting bath 11 'has a total height which, in addition to compensating for the negative pressure in the space 10 above the metal melt 11', gives the desired casting pressure in the mold 7.

Any amount of gas encapsulated which the filler metal constituted by the metal column 4 can carry with it into the furnace and which is not continued is led to the liquid tank 12 and can be pumped out of the system by means of a small vacuum pump 15 which is connected to the furnace system. .

15 the casting furnace 1 and the liquid lock 3 are heated by means of electric heating elements arranged around the filling pipe 2, and the tapping pipe 5 is heated by means of electric heating elements 161 the melting furnace 1 itself and the tapping pipe 5 are provided with thermal insulation 17.

A casting furnace of the above type can be built for different metals by taking into account during construction the specific gravity of the metal used, the desired negative pressure in the furnace chamber, the casting pressure and the boiling point as well as chemical properties of the container 12 liquid 13 whose steam is intended to protect the molten bath. 11 '.

By making the liquid lock outlet pipe 3 'telescopically extendable, this can be adjusted in relation to the specific gravity of the various metals to form the desired column height and thus the desired negative pressure in the space 10. With a corresponding telescopic extendability that the end part of the drain pipe 5 can be also the casting pressure is regulated.

5

14215G

The foundry has been tested with a 50/50% metal alloy consisting of Sn and Pb, using as hydrocarbon 13 in the shielding vessel 12 for the shielding gas the hydrocarbon C The ambient temperature of the container 12 was 18 ° C 5 and the negative pressure in the space 10 was 52% (53.3 kPa). The casting oven worked exactly as described.