Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-12-03
2004-07-06
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S496000, C164S497000
Reexamination Certificate
active
06758259
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a method and an arrangement for producing castings.
In energy machine construction there is nowadays a trend to use stationary gas turbines with a high specific output as an alternative to the nuclear power stations which in many cases are rejected for environmental reasons, in which it was possible to manage with steam turbines. The higher working temperatures of gas turbines require the use of high-alloyed iron- and in particular nickel-based alloys which have considerable contents of Ti, Al, B, Nb, Ta, W etc in order to achieve the required properties. Hitherto gas turbines were preferably used as engines for aircraft, for which it was possible to manage with comparatively small turbine shafts. Relatively small ingots of diameters of 500 mm and below were required for the production thereof, which could be produced by means of re-melting methods with self-consumable electrodes, to afford an adequate quality standard. The term adequate quality standard is used in particular to denote a rough ingot which is substantially free from macroscopic textural and structural non-homogeneities such as segregation phenomena and other flaws which are known as ‘freckles’ and ‘white spots’.
White spots are flaw locations which are depleted in respect of alloying elements in comparison with the rest of the material. That flaw phenomenon is only known from the vacuum electric arc method with self-consumable electrodes, and it is assumed that this flaw phenomenon is caused by dendrite branches which drop down from the electrode tip and which are not fused in the molten sump. In the case of the electroslag re-melting method with self-consumable electrodes, that flaw phenomenon has hitherto not been observed.
Freckles are spot-shaped or fleck-shaped segregation phenomena which occur in isolated form and which can occur upon hardening of high-alloyed ingots along the dendrites if the alloy contains elements whose density differs considerably from the density of the basic alloy. Accordingly iron- or nickel-based alloys which contain high contents of specifically light elements such as for example Ti or Al but also specifically heavy elements such as W, Nb, Ta are particularly susceptible to that flaw phenomenon. While in the case of ingots of smaller dimensions of up to about 400 to 500 mm ingot diameters that flaw occurs only in isolation and only under unfavourable re-melting conditions, the production of flaw-free ingots of larger diameter is as good as impossible, even with the best control of the re-melting conditions. This is to be attributed to the fact that the long hardening times and large sump volumes which are inevitable when producing large re-melting ingots on the one hand result in a coarse hardening structure while on the other they promote segregation phenomena.
Now however the construction of stationary gas turbines with a sufficiently high specific output requires large turbine shafts, for the production of which correspondingly large rough ingots of diameters of substantially over 500 mm, preferably up to 1000 mm, are again required. In accordance with the present state of the art in regard to re-melting with self-consumable electrodes sufficiently flaw-free rough ingots cannot be produced from the alloys required for that purpose.
DE-196 14 182 C2 discloses a short, water-cooled, downwardly open chill mold for producing ingots or blocks, in which a casting level is covered by an electrically conductive slag in which the block or ingot is shaped in the lower part and withdrawn therefrom either by lifting the chill mold or by lowering the block or ingot. At least one current-conducting element which is not directly water-cooled is fitted into the wall of the chill mold which is formed from water-cooled elements, in such a way that the current-conducting element on the one hand comes into contact with the slag bath and on the other hand does not reach the level of the liquid metal; contact with a current source is made by way of that element which is disposed completely beneath the surface of the slag bath.
U.S. Pat. No. 5,799,721 discloses a method of re-melting in particular steels and Ni- and Co-base alloys to form an ingot by melting away at least one self-consumable electrode in an electrically conductive slag bath, wherein the ratio of the cross-sectional area of one or more consumable electrodes to the cross-sectional area of the ingot to be produced as the casting cross-section is selected to be greater than 0.5 and a melting rate in kg/h which corresponds to between 1.5 and 30 times the ingot diameter is set; the equivalent ingot diameter which deviates from a round cross-section is calculated from the periphery of the casting cross-section. In a funnel chill mold the melting rate in kg/h corresponds to between 5 and 15 times the equivalent ingot diameter calculated from the periphery of the casting cross-section and the ratio of the cross-sectional area or areas of the consumable electrode or electrodes to the cross-sectional area of the casting cross-section is equal to or greater than 1.0, wherein the ingot is shaped in the lower narrow part of the funnel chill mold and the slag bath extends into the enlarged upper part thereof.
In a method of producing castings of metal in accordance with GB-A-1 568 746 the ESR chill mold is provided with electrically insulated water-cooled current-conducting elements. Solid metal in the form of granules is continuously fed to the slag bath in order to result in the casting of a bloom of any length. Granules of that kind are of a higher density in the solid condition both than the slag bath and also the liquid metal of the molten sump, with the result that granules of that kind fall very quickly through the hot slag and do not or only very partially melt there, by virtue of the short residence time. If unmelted particles pass into the liquid metal sump, they also drop there by virtue of their higher density to the phase limit. There however they no longer melt as there is no longer a sufficient supply of heat in that region. With advancing hardening, particles of that kind are then enclosed in the unmelted condition in the form of foreign metal inclusions of their own specific kind in the hardening structure. As such unmelted particles are of a different structure—and thus involve different properties—from the melted metal, they are unwanted in melted ingots of which a uniform, fine and fault-free hardening structure is required.
It is an object of the present invention to provide a method for producing substantially segregation-free and in particular freckle-free castings of metal, in particular high-alloyed steels and Ni- and Co-based alloys of large dimension in accordance with the electroslag melting or casting method using a per se known short, current-conducting, water-cooled chill mold, in the wall of which current-conducting elements which are not directly water-cooled are fitted in electrically insulated relationship with the part of the chill mold, which forms the casting.
SUMMARY OF THE INVENTION
The foregoing object is attained by the teaching of the independent claim; the appendant claims set forth advantageous developments. The scope of the invention also embraces all combinations of at least two of the features disclosed in the description, the drawing and/or the claims.
In accordance with the invention a substantially segregation-free and freckle-free bloom whose cross-sectional area is at most 90% of the part of the chill mold forming the casting is arranged therein and, using a slag bath which is heated by the flow of current and which is disposed in the region of the current-conducting elements of the chill mold, by continually quantitatively controlledly pouring in liquid metal is connected to the supplied metal; the level of the slag in the chill mold is kept approximately constant by a relative movement between the chill mold and the bloom until the bloom is radially doubled in the desired length—that is to say is surrounded by a cast casing or jacket layer—;
Holzgruber Harald
Holzgruber Wolfgang
Bachman & LaPointe P.C.
Inteco Internationale Technische Beratung Ges.m.b.H.
Lin Kuang Y.
LandOfFree
Method and arangement for producing casting moulds from metal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and arangement for producing casting moulds from metal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and arangement for producing casting moulds from metal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3203465