Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1998-05-15
2000-06-27
Pyon, Harold
Metal founding
Process
Shaping liquid metal against a forming surface
164 41, 164 61, B22D 2700, B22D 4600
Patent
active
060794763
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing pre-treated molten metal for casting objects.
The Swedish patent application 9304347-9 discloses a method of continuous and/or semi-continous casting of compacted graphite iron (CGI) wherein a structure modifying agent is added to the molten iron before it is supplied to a closed conditioning furnace provided with inlet and outlet channels, e.g a pressurized pouring furnace. In operation, the quantity of molten cast iron is maintained within predetermined limits by replacing, intermittently, the cast iron tapped from the conditioning furnace with a compensation amount of molten cast iron taken from a reaction vessel. Magnesium as structure modifying agent is added to the molten cast iron in the reaction vessel and, optionally, in the conditioning vessel. FIG. 1 discloses a preferred embodiment of this prior art.
The overpressure in the furnace space (16) can be regulated for controlling the melt flow through the tapping hole (13) placed in the spout (9). In case of longer stoppages the overpressure is removed so that the melt (5) in the spout (9) will be drawn back into the furnace (16) such that the melt level will be the same in the inlet and outlet channels as within the furnace chamber as indicated with broken lines in FIG. 1. Therewith, the fading rate of magnesium is reduced. The magnesium loss from the melt within the furnace chamber can be calculated and compensated by feeding Mg-wire (6) through the magnesium infeed valve (19) before restart of the operation.
However, the melt in the outlet channel will be subjected to relatively rapid magnesium losses due to evaporation and oxidation since the outlet is open to the atmosphere. In addition, the melt in the outlet channel cannot be re-charged with magnesium. As a result thereof, the first castings produced after the stop have to be scrapped as they will not have the desired structure.
From SE-328 673 (corresponding to U.S. Pat. No. 3,764,305) there is known a method to protect the melt in the outlet and inlet openings by flushing with inert gas. However, this method only reduces the magnesium losses to a limited extent and is not sufficient to produce good first CGI castings.
SUMMARY OF THE INVENTION
It is an object of this invention to solve the problems related to fading of nucleation and/or structure modifying agents in the outlet channel of a conditioning furnace and, hence, to improve the yield in the casting of structure modified molten metal.
The present invention is a method for producing pre-treated molten metal castings comprising the steps of: channel, with pre-treated molten metal; level lower than the level of the molten metal in the conditioning furnace such that the molten metal in a spout of the furnace and in the outlet channel, is at least partly brought back into the furnace body where it can be recharged with a nucleating and/or structure modifying agent; molten metal when necessary; of structure modifying agent.
According to the present invention, the molten metal in the spout and in the outlet channel can be revitalized after longer stoppages by forcing it back into the conditioning furnace and retreat it with the desired nucleation and/or structure modifying agent.
When practicing the present invention, different types of conditioning furnaces can be used. The furnace may be of the open type when the melt is protected by a slag layer and/or by an inert shielding gas atmosphere. According to one particularly preferred embodiment of the invention, a closed conditioning furnace is used which is also preferably provided with the combined provision of pressurizing and vacuum facilities. The conditioning furnace is also preferably equipped with induction heating and means for measuring or detecting the melt level in the outlet channel.
The inventive method will now be described in more detail with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 discloses a schematic view of a prior art method and a furnace asse
REFERENCES:
patent: 3764305 (1973-10-01), Andersson
patent: 4390362 (1983-06-01), Khusnutdinov et al.
patent: 5161604 (1992-11-01), Chandley et al.
patent: 5758706 (1998-06-01), Backerud et al.
Andersson Conny
Walker Mike J
Lin I.-H.
Pyon Harold
Sinter-Cast AB
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