GB1589952A - Continuous or semi-continuous casting of metal - Google Patents

Description

(54) CONTINUOUS OR SEMI-CONTINUOUS CASTING OF METAL (71) I, ZINOVY NAUMOVICH GETSELEV, of kvartira 29, prospect Metallurgov, 73, Kuibyshev, Union of Soviet Socialist Republics, a citizen of the Union of Soviet Socialist Republics, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to methods of continuous or semi-continuous casting of ferrous and non-ferrous metals (elementary metals and alloys) providing for the shaping of metal ingots by electromagnetic field.

In a method of continuous or semi-continuous casting of metal disclosed in British Patent Specification No. 1,157,977, molten metal is fed onto a bottom plate inside an annular inductor, the electromagnetic field thereof shaping the metal into an ingot. As the side surface of the ingot solidifies, the ingot with the bottom plate is lowered and, simultaneously, a cooling medium (water) is sprayed on the peripheral surface of the ingot. In accordance with British Patent Specification No. 1,328,166, the ingot can be cooled by several cooling tiers arranged around and at different levels with respect to the ingot being shaped. The top cooling tier, ensuring the initial solidification of the ingot (appearance of the crust), is level with the bottom of the inductor. In the course of casting, the boundary between the liquid and the solid phases on the peripheral surface of the ingot is close to mid-height of the inductor, where the magnetic field is at its greatest. The liquid zone of the ingot shaped by an electromagnetic field has generally a height of 30 to 50 mm.

The shape of the liquid zone answering the normal ingot shaping conditions approximates in its longitudinal cross section that of the ingot, i.e. the liquid zone has a convex meniscus. This is achieved by partly shielding the magnetic field and also by ensuring that the top of the liquid zone is above the top of the inductor. Because of this, the height of the inductor with due regard to that of the liquid zone is generally 20 to 70 mm. When inductors of this height are used, the known methods are applicable to casting of ingots at withdrawal speeds of 35 to 50 mm/min. As regards high-alloy aluminium alloys, the casting thereof into ingots at low withdrawal speeds (15 to 25 mm/min) becomes altogether impossible, this being due to the causes explained below.

As is generally the case in casting, the boundary between the liquid and the solid phases on the peripheral surface of the ingot is close to mid-height of the inductor, where the magnetic field is at its greatest. The distance between this boundary and the top cooling tier is a function, in the main, of the ingot withdrawal speed, varying inversely with the latter. Thus, when the ingot withdrawal speed drops to 15 to 25 mm Imin, the distance between the solid liquid boundary on the peripheral surface of the ingot and the top cooling tier varies between 80 and 160 mm. As the top cooling tier is located directly underneath the inductor, and the liquid zone is not more than 50 mm high, the solidification front, for an inductor of customary height, emerges on the periphery of the liquid zone, with the effect that the molten metal entering --the shaping zone trickles down and gives -rise to randomly shape accretions on the - peri- pheral surface of the ingot, thus entirely upsetting the ingot shaping process. In con- sequence, a normal ingot being shaped at low casting rates would require a rower arrangement of the top cooling tier with respect to the bottom boundary of the liquid zone on the peripheral surface of the ingot This may be achieved by increasing the height of the inductor to 140 to 300 mm for withdrawal of speeds of 15 to 25 mm/ mm.

However, such an inductor height is objectionable for many reasons. Assuming normal ingot shaping and least consumption of energy, the optimum height of the inductor for a liquid zone 30 to 50; mm high is 30 to 70 mm. A greater inductor height increases the overall dimensions of the ingot casting means, this rendering difficult in their incorporation in continuous casting plants. An ingot casting means with an inductor of increased height cannot be used at relatively high ingot withdrawal speeds (50 mm/min and over), as the boundary between the solid and the liquid phases then moves into the bottom part of the inductor, which is impermissible as regards ingot shaping and consumption of energy.

What is desired is a method of continuously or semi-continuously casting ingots 500 to 1100 mm in diameter from alloys of low solidification rates, using casting means suitable for both low and high ingot withdrawal speeds, so minimizing the number of casting means and the floorspace required.

The surface quality of the ingots could be improved, as a wide range of ingot withdrawal rates would be available to eliminate the pulsation of the liquid phase and thus prevents the flowing of the liquid phase over the outer solidified peripheral face of the ingot.

The present invention provides a method of continuous or semi-continuous casting of metal, comprising feeding molten metal onto a bottom plate inside an annular inductor, shaping the metal into an ingot by the electromagnetic field of the inductor, lowing the bottom plate with a metal while supplying a cooling medium to the peripheral surface of the ingot with the aid of a series of cooling tiers placed along the ingot at different levels, sequentially cutting out one or more cooling tiers, beginning from the topmost tier, as the bottom of the ingot comes level with the next lower cooling tier, and continuing supply of the cooling medium by that cooling tier which maintains the liquid-solid boundary on the peripheral surface of the ingot substantially at the mid-height of the inductor.

The effect of cutting out the cooling tier or tiers nearest the inductor is to decrease the speed of motion of the liquid-solid boundary on the peripheral surface of the ingot. The speed of the boundary should equal the ingot withdrawal speed.

The invention will now be described further, by way of example only, with reference to the accompanying drawing which is a schematic vertical cross section of an apparatus for continuous or semi-continuous casting of an ingdt.

At the beginning of the casting of an ingot 2 on a bottom plate 5, a cooling medium (e.g., water) is supplied from an annular cooler 1 to the peripheral surface of the ingot 2 in- annular streams from cooling tiers 3, 6, 7, 8 arranged at different levels along the ingot 2. The topmost cooling tier 3 is located directly beneath an annular inductor 4 at a distance h from the midheights òf the inductor 4. A normal course of the casting process is - provided by maintaining the boundary between the liquid and the solid phases on the peripheral surface of the ingot 2 at the mid-height of the inductor 4.

The lower cooling tiers 6, 7, and 8 are at distances of respectively h1, h2 and h3 from the mid-height of the inductor 4.

The electromagnetic field of the inductor 4 causes the metal on the bottom plate 5 to take on the shape of a column of a specified height. Acted upon by the cooling medium, the column of molten metal begins to solidify from the bottom upwards and from the peripheral surface towards the longitudinal axis of the ingot 2. The shaping of ingot 2 is accompanied by the lowering of the ingot together with the bottom plate 5.

At the beginning of casting, the cooling medium is supplied from all of the cooling tiers 3, 6, 7, and 8.

In the given example the topmost cooling tier 3 is arranged at a distance of 5 to 15 mm from the bottom edge of the inductor 4. Investigations and experiments have indicated that the topmost cooling tier substantially affects the speed of motion of the liquid-solid boundary on the peripheral surface of the ingot 2. The ratio of the speed at which the ingot 2 is withdrawn from the zone of action of the inductor 4 to the speed of the liquid-solid boundary on the peripheral surface of the ingot 2 should be so adjusted as to give molten metal at the periphery of the ingot 2 enough time to solidify before it leaves the inductor 4 and thus to prevent it from flowing all over the ingot 2. This adjustment is made by sequentially cutting out one or more cooling tiers. In the given example, as the bottom of the ingot 2 comes level with the cooling tier 6 located at a distance h1 from the midheight of the inductor 4, the topmost cooling tier 3 is cut out. The remaining cooling tiers supply the cooling medium to the peripheral surface of the ingot 2 as long as they maintain the liquid-solid bound on the peripheral surface of the ingot 2 substantially at the mid-height of the inductor 4. (As the bottom of the ingot 2 comes level with the next cooling tier 7, at a distance h from the midheight of the inductor 4, the cooling tier 6 is cut out if the liquid-solid boundary comes out on the top face of the solidifying ingot 2.) For lower ingot withdrawal speeds, casting may be stabilized by the third cooling tier 7 located at a distance h2 from the mid-height of the inductor 4 or even by the fourth cooling tier 8 arranged at a distance h3 from the mid-height of the inductor 4, all of the overlying cooling tiers being cut out after the initial stage of casting.

To put the method above-described into practical effect, it suffices to provide four to six cooling tiers which are capable of covering the whole of the required range of ingot withdrawal speeds.

The above-described method has been tested by casting a 485-mm diameter ingot of high-alloy aluminium at withdrawal speeds from 23 to 28 mm/min. The distance between the topmost cooling tier 3 and the second cooling tier 6 was 50 mm, and the value h1 was 70 to 85 mm.

WHAT I CLAIM IS:- 1. A method of continuous or semi-continuous casting of metal, comprising feeding molten metal onto a bottom plate inside an annular inductor, shaping the metal into an ingot by the electromagnetic field of the inductor, lowering the bottom plate with the metal while supplying a cooling medium to the peripheral surface of the ingot with the aid of a series of cooling tiers placed along the ingot at different levels, sequentially cutting out one or more cooling tiers, beginning from the topmost tier, as the bottom of the ingot comes level with the next lower cooling tier, and continuing supply of the cooling medium by that cooling tier which maintains the liquid-solid boundary on the peripheral surface of the ingot substantially at the mid-height of the inductor.

2. A method of continuous or semi-continuous casting of metal, substantially as described herein with reference to, and as shown in, the accompanying drawing.

3. An ingot produced by a method according to claim 1 or 2.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. The above-described method has been tested by casting a 485-mm diameter ingot of high-alloy aluminium at withdrawal speeds from 23 to 28 mm/min. The distance between the topmost cooling tier 3 and the second cooling tier 6 was 50 mm, and the value h1 was 70 to 85 mm. WHAT I CLAIM IS:-

1. A method of continuous or semi-continuous casting of metal, comprising feeding molten metal onto a bottom plate inside an annular inductor, shaping the metal into an ingot by the electromagnetic field of the inductor, lowering the bottom plate with the metal while supplying a cooling medium to the peripheral surface of the ingot with the aid of a series of cooling tiers placed along the ingot at different levels, sequentially cutting out one or more cooling tiers, beginning from the topmost tier, as the bottom of the ingot comes level with the next lower cooling tier, and continuing supply of the cooling medium by that cooling tier which maintains the liquid-solid boundary on the peripheral surface of the ingot substantially at the mid-height of the inductor.

2. A method of continuous or semi-continuous casting of metal, substantially as described herein with reference to, and as shown in, the accompanying drawing.

3. An ingot produced by a method according to claim 1 or 2.