Method and device for removing slag

A method for removing slag comprises: preparing a filter 21 of heat-resistant porous ceramics, which passes a molten metal and catches slag, liquidizing metal material to form a molten metal A on which slag is floating; and traveling filter 21 along a surface of the molten metal A and removing slag. And a device for removing slag comprises: a filter 21 of heat-resistant porous ceramics, which passes a molten metal and catches slag; and a driving device for traveling filter 21 along a surface of the molten metal on which slag is floating and removing slag.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a device for removing slag, which is generated on a surface of molten metal in a metal furnace.

2. Description of the Related Art

When a metal material is liquidized in a liquidizing furnace by heating in a vacuum atmosphere so as to form a molten metal and cast into a mold for precise casing, slag is generated on a surface of the molten metal. Since it is difficult to remove the slag, the molten metal is cast in the mold with the slag, the slag affects the quality of the produced cast products. Particularly in producing precise cast products (for example, parts for air and space industry), any slag is not allowed to be contained. Thus, any contaminant of the slag significantly affects the yield of the cast products particularly in the precise cast products field.

Heretofore, when the molten metal is cast into the mold, slag is conventionally prevented from entering into the mold by the following methods: One method is to remove the slag by tilting the furnace to the other side of the mold for removing the slag before pouring the molten metal into the mold. Another method is to remove the slag by installing a filter at an entrance of the mold for filtering the slag.

However, even though the slag can be removed by tilting the furnace to the other side of the mold before pouring the hot melt into the mold, it is difficult to remove the slag perfectly. By installing a filter at entrance of the mold for filtering the slag, it is easy to remove a larger size of the slag, but it is difficult to remove a smaller size of the slag. If trying to remove the smaller size of the slag by the filter, it is required to make the filter finer, however when making the filter finer, it causes slower of flowing speed of the molten metal into the mold and generates bad products because of lack of the molten metal flowing into the mold. Further, the filter chips easily, and when chip of the filter is entered into the mold with hot melt, it generates bad products because of contaminants of filter chip.

Further, a method of removing slag, which is floating on a surface of the molten metal, in air atmosphere is known as Japanese laid-open patent publication No. H5-240588.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method and a device for removing slag, which is capable of removing slag efficiently in a liquidizing furnace for precise-casting, in which any contaminant of slag is not allowed.

To achieve the above object, there is provided in accordance with the present invention, a method and a device for removing slag comprises traveling a filter of heat-resistant porous ceramics along a surface of the molten metal and removing the slag, which is generated by liquidizing metal material by heating and floating on the surface of the molten metal in the furnace.

According to the present invention, since the filter passes the molten metal and catches slag only, therefore, by traveling the filter along a surface of the molten metal, on which slag is floating, the filter can catch slag and remove slag from the molten metal effectively. Thus, by pouring the molten metal without any contaminants of slag into a mold directly, precise cast products can be produced with high yield.

The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, which illustrate a preferred embodiment of the present invention by way of example.

DETAILS DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will be described with referring to the attached drawings. Like or corresponding parts are denoted by the same reference characters throughout views, and will not repetitively be described.

FIG. 1shows an essential portion of a vacuum liquidizing and casting apparatus. The vacuum liquidizing and casting apparatus11is provided with a furnace14for liquidizing metal such as iron/nickel alloy by heating and mold15for casting precise cast products by pouring molten metal generated by the furnace14. The furnace14is provided with crucible12and coil13for liquidizing metal material loaded in crucible12by induction heating. Inside of vacuum liquidizing and casting apparatus11is evacuated to vacuum atmosphere. Metal material is loaded into crucible12from loading gate (not shown) and heated up to liquidizing temperature by induction heating of applying high frequency current to coil13, and then liquidized to be a molten metal A. Since the molten metal A is formed in vacuum atmosphere, oxidation of the molten metal A is relatively less, and contamination of the molten metal A is quite less, and then pure molten metal A is formed. However, slag is generated in process of liquidizing the metal material by reactions of the molten metal A and crucible12, and so on.

When temperature of the molten metal A reaches to a predetermined temperature, induction heating is stopped and molten metal A becomes settled down to be a quiet state. Then, since the specific gravity of the slag is lower, the slag becomes floating on the surface of the molten metal A. As shown inFIG. 2, by traveling the filter21for filtering slag along the surface of molten metal A, filter21catch slag floating on the surface of molten metal A, and then slag is removed from the molten metal A. Since filter21for filtering slag passes the molten metal and catches the slag only, filter21effectively catches and removes slag floating on the surface of molten metal A.

Molten metal A, from which slag has been removed, is poured directly (without passing through filter) to mold15as shown inFIG. 3and cast product16is produced. Since filter is not provided at entrance of mold15for filtering slag, molten metal A flows fast inside of mold15and fluidity of hot melt A in mold15is excellent. For example, very thin blade for air and space industry parts can be cast with excellent precise-formability. Further, since filter is not provided at entrance of mold15for filtering slag, a problem that the filter at the entrance of the mold easily chips and the fragment of the filter enters into the mold15with the molten metal A never happens. Therefore, since the molten metal A without slag can be poured directly to mold15, excellent fluidity of the molten metal A in mold15can be obtained and precise cast products such as a thin blade for air and space industry parts can be produced at high production yield.

FIGS. 4A and 4Bshow examples of filter structures of the present invention. Material of filter21comprises highly heat-resistant porous ceramics and has been used for the filter, which is installed at entrance of the mold for removing slag as stated in “BACKGROUND OF THE INVENTION”.FIG. 4Ashows an example of disk-shaped filter andFIG. 4Bshows an example of plate-shaped filter having concave portion, which can catch the slag easily. These filters21travel along the surface of the molten metal A such that its lower half portion of filter21is immersed in the molten metal A and its upper half portion of filter21is shown above the surface of the molten metal A. Filter21is provided with an arm22, and arm22is fixed to filter21by fixing element23such as pin. Arm22drives filter21to travel along the surface of molten metal A. Further, the shape and filtering performance of filter21should be determined in correspondence with kinds of the molten metal and so on.

FIG. 5shows an example of a device for traveling filter21and removing slag on the surface of the molten metal A. The device comprises: a rod31disposed above central, portion of crucible12, which accommodates the molten metal A; an outer cylinder32coaxially disposed with rod31, wherein cylinder32is rotatable and vertically movable with rod31, and also rod31is vertically movable relatively against cylinder32; a driving device33for moving rod31vertically relatively against cylinder32; and a driving device34for moving and rotating rod31and cylinder32as one unit. O-ring36seals rod31and cylinder32is sealed by O-ring37, and then vacuum atmosphere can be maintained in vacuum liquidizing and casting apparatus11.

One end of arm22is rotatably fixed to the lower end of cylinder32. Arm22is provided with a long-width hole26, and a pin24disposed at the lower end of rod31is engaged to long-width hole26and then arm22is slidably fixed to rod31. Another end of arm22is fixed to filter21by fixing element23. Therefore, by moving rod31vertically relatively against cylinder32, arm22can be rotated around pin26and radial position of filter21in crucible12is determined. Moving rod31and cylinder32vertically as one unit, vertical position of filter21in crucible12is determined. Rotating rod31and cylinder32around rod31as one unit, filter21travels rotating (in circumference direction) around rod31on the surface of hot melt A in crucible12.

FIGS. 6A and 6Bshow examples of traveling paths of the filters for removing the slag floating on a surface of the molten metal in a crucible.FIG. 6Ashows that filter21travels spirally in crucible12from start position Sa at center of crucible12to stop position Sb at peripheral portion of crucible12. According to this traveling path pattern, filter21catches and removes the slag all over the surface of the molten metal A in crucible12.FIG. 6Bshows that filter21moves in radial direction from start position Sa at center of crucible12to circumference path C1and travels along path C1, next moves in radial direction from path C1to path C2and travels along path C2, and next moves in radial direction from path C2to path C3and travels along path C3to stop position Sb at outer portion of crucible12. Also according to this traveling path pattern, filter21catches and removes slag all over the surface of molten metal A in crucible12.

The device for traveling filter and removing slag can be operated at air atmosphere or at vacuum atmosphere. Also, the device can be operated manually or automatically by pre-inputting total quantity of metal to be liquidized and size of crucible, for example. In vacuum liquidizing and casting process, the process roughly comprises liquidizing metal, measuring temperature of the molten metal, settling down of the molten metal, removal of slag, measuring temperature of the molten metal, and casting the molten metal into a mold to produce cast products. The device can be operated alone or in combination with a temperature measuring equipment (thermo-couple thermometer, radiation thermometer) and switching each process in several seconds while keeping vacuum atmosphere.