Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-09-20
2001-09-04
Dunn, Tom (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S497000
Reexamination Certificate
active
06283198
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of metallurgy, and more specifically to the method of an electroslag cladding of elongated round-section parts mainly and can be used, in particular, in production and repair of all kinds of mill rolls, rollers of machines for a continuous casting of billets, roller tables, rollers of heating furnaces, etc.
PRIOR ART
The application of different methods of cladding for these purposes, including electroslag cladding, is widely known, allowing deposition on the above-mentioned products of a working layer made from metal or intermetallics of the chemical composition similar or different to that of the basic product.
This application will not deal with the known methods of cladding using solid electrodes in the form of wire, strip, tube, etc. as a material for cladding.
The most up-to-date method of cladding of the above-mentioned products is a cladding with a liquid metal which can drastically reduce the cost of the process and products and use the cladding materials of almost any chemical compositions, the production of which in the form of solid electrodes is very expensive or impossible in separate cases.
For example, patent of UK No. 1469113 of Mar. 30, 1977 describes the method of electroslag cladding using the liquid metal. However, the use of a conventional, non-current carrying mould could not realize this process on an industrial scale, as the device for its realization was too complicated and expensive.
In publication “Development of High-Performance Roll by Continuous Pouring Process for Cladding” (ISIJ International, Vol. 32 (1992), No. 11, pp. 1202-1210) a method of cladding with a liquid metal is described which is similar in principle to the process of a vertical continuous casting of steel. This method is implemented in industry, however, it does not realize the fusion of the metal to be clad and billet to be clad, but it brazes them. This limits the feasibility of combination of different metals: for example, this method can be used for coating steel rolls from low-alloyed steels with a high-speed steel. However, his method cannot be applied for cast iron rolls. In addition, the above-mentioned method is performed within very limited ranges of technological parameters, thus often leading to the violation of continuity of the brazed joint of the roll and metal being clad.
The U.S. Pat. No. 4,305,451 of Feb. 15, 1981 describes the method of electroslag cladding in a sectional current-carrying mould, which has no majority of the above-mentioned drawbacks, however, it describes mainly the solid lumpy filler materials (shot, powder, chip, etc.) as a material for cladding, thus limiting the application of this process only for the cast iron rolls, which are clad also with the same cast iron.
Method, described in French patent No. 93-03925 of Apr. 02, 1993, MPK B22D 19/16,11/00, is most close by combination of features and, therefore, it was taken, as a closest prior art. In this method the cladding of elongated billets (mainly of round section) is performed using a sectional mould with a current-carrying part and a non-current carrying forming part and includes a mounting of billet to be clad into a said mould, a pouring a liquid metal and a molten slag to the gap between the billet to be clad and a mould wall for cladding, a passing of the electric current and proceeding of cladding process with a simultaneous withdrawal of the clad billet.
However, this method does not allow the process of cladding to be realized with a formation of a reliable joining of the material being clad and a billet due to the following reasons The method is performed with vertical oscillations of the a current-carrying mould, similar to the continuous casting. However, all the known electroconductive slags for the electroslag process possess, as to their physical and mechanical properties, a low viscosity within the range of temperatures, close to the temperature of their solidification and being an operation range of temperatures for the electroslag process with a withdrawal of billets. The above-said circumstance leads inevitably to destroying a thin slag crust in the process of withdrawal of the billet, which consequently leads inevitably to a spillage of the metal being clad. The method is performed with a pouring of a cladding metal into a current-carrying (heated) part of the mould and subsequent pouring of an electroconductive slag. At such sequence of pouring operations, i.e. first metal, then slag, there exists a risk of a short-circuiting between the current-carrying upper part of the mould and the billet during cladding.
The above-mentioned circumstances are the essential drawbacks of the present method which complicate it unjustifiably and almost reject its realization.
SUMMARY OF THE INVENTION
The invention proceeds from the task of improvement of the known method of electroslag cladding by changing the sequence of operations of pouring the molten slag and liquid metal, fulfilment of operations of pouring of the molten slag, at least, in two stages, conductance of operation of pouring liquid metal after the operation of setting-up the mould for an electrical condition of starting the process of electroslag cladding, and an automatic control of the liquid metal level in the mould to realize the simple and reliable method of cladding at almost unlimited combination of chemical compositions of the billet to be clad and metal to be clad.
The above task is solved by a proposing a method of electroslag cladding of elongated round-section billets mainly using a sectional mould with a current-carrying part and a non-current carrying forming part, including a mounting of billet to be clad into the above-said mould, the pouring of a molten slag, being electroconductive in a molten state and non-electroconductive in a solid state, and a liquid metal for cladding into the gap between the billet to be clad and the mould wall, a passing of electrical current through a melt and conductance of the process of the electroslag cladding with a simultaneous with-drawal of the clad billet. In accordance with the invention the molten slag is poured into a gap between the billet to be clad and the mould wall in, at least, two stages, prior to pouring the liquid metal for cladding, with the first portion of the slag being poured in the amount sufficient for filling all the air gaps between the sections of the mould with a subsequent holding up to a complete solidification in the above-said gaps, and then the electrical voltage is supplied to a current-carrying part of the mould and billet to be clad, and the second and next portions of the molten slag are poured, the mould is set for electrical conditions of starting the process of the electroslag cladding and a force magnetic field is created in the mould, after which the liquid metal is poured for cladding and the electroslag cladding process is realized at a stable rotation of the molten slag and liquid metal, being created in the mould by an action of a force magnetic field.
In the of the present invention method, first in the routine of the electroslag cladding, a reliable electrical isolation of elements of the sectional mould is made as if automatically with a non-electroconductive solid-state slag. When pouring the first portion of the molten slag it fills all existing air gaps in the mould, between sections in particular, solidifies in these gaps and guarantees the complete isolation. Only after making such an isolation the electroslag process is proceeding,the stable conditions for the start of the cladding process are created and the accident-free operation of the mould is guaranteed. The stable rotation of the molten flux and liquid metal which is set in the mould under the action of a force electromagnetic field, provides an effective averaging of the pool temperature, intensifies the processes of refining, contributes to averaging the chemical composition and refining the structure of the layer being clad and provides the intensive cleaning of surface being clad with a slag melt.
I
Dunn Tom
Tran Len
Young & Thompson
Zakrytoe Aktsionernoe Obschestvo “Elmet-Rol-Guppa Medovara”
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