RU2457919C2 - Method of casting aluminium pigs into chill moulds of casting conveyor and casting complex - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to nonferrous metallurgy, particularly, to production of small-size aluminium pigs for continuous casting of metals and alloys. Proposed method comprises filling moulds by teeming appliances and cooling said moulds in their transfer to pig extraction point. Oxide film formed in casting is removed at casting conveyor, at pig crystallisation beginning, on length of 1/5 of conveyor length. Removal of said oxide film is performed from its one edge to another, in direction opposite that conveyor motion. Oxide film removal appliance is made up of plate fixed on guides rigidly secured on horizontal shaft arranged on conveyor frame and cam with one end fitted on said horizontal shaft. Sais cam interacting with conveyor rolls performs angular motion to make lever move upward and downward to adjust plate immersion in liquid metal.

EFFECT: pigs with defect-free surface.

4 cl, 4 dwg, 1 ex

Description

The invention relates to ferrous metallurgy, and in particular to the production of small-sized aluminum ingots during continuous casting of metals and alloys in molds on a casting conveyor, including on automated casting lines.

As written in clause 2.2 of GOST 11070 "Primary aluminum ingots. Technical conditions": "Slag and other foreign inclusions should not be on the surface of ingots. Cracks with a width of more than 1 mm must be blocked. The requirements for other surface defects are established by agreement between the consumer and by the manufacturer. "

In mass conveyor production of products, it is practically impossible to manually crack cracks on all ingots, and on automated casting lines it is fundamentally impossible. In addition to cracks, consumers usually pay attention to deep shrinkage shells ending in voids (dips, cavities) deep in the ingot body. In addition to the worst commercial appearance of the product, the presence of these defects on the ingots affects the safety of processing the product - if the consumer gets moisture in the voids during remelting, metal ejection can occur.

A known and widespread method of casting ingots on a casting conveyor (1. Metallurgy of secondary aluminum: Textbook for universities / GV Galevsky, N. M. Kulagin, M. Ya. Mintsis. - Novosibirsk: Science. Siberian enterprise of the Russian Academy of Sciences, 1998 - 289 p., 2. Casting of aluminum and alloys based on it / Grinberg I.S., Ragozin L.V., Aleksandrov M.F. et al. - St. Petersburg: Maneb Publishing House. - 2004. - 193 p.). Liquid metal from the mixer through the tap hole and stationary trough enters the movable trough. The metal is poured into the conveyor molds using an open method by manually moving the movable trough from the mold to the mold. Removing from the surface of the ingots of slag generated in a turbulent flow is carried out manually using a foundry vane. The removed slag is also manually discharged into the slag. The disadvantages of the method: intense slag formation when filling molds; metal casting and slag removal processes are not mechanized; the presence of an additional person engaged in dangerous monotonous labor; the inability to perform manual operations on automated casting lines; additional loss of aluminum when removing the foam / slag.

The closest analogue of the claimed method of casting metal into molds of a casting conveyor is a similar method, including filling molds with metal to the required level using a metal casting device and cooling the molds during their transportation to the place of extraction of hardened ingots (SU 1148696 A, 08/07/1983).

The disadvantages of the method are: the difficulty of achieving uniformity of the melt and the possibility of marriage of ingots for foreign inclusions and shrinkage defects on the gating surface.

An analog of the device is a complex for pouring liquid metal into molds on a conveyor (RF patent No. 2263557, microliter B22D 35/04, 05/04). The known complex contains a mixer with a groove, a rotary metal receiver in the form of a casting wheel with radially located drain pipes, interconnected by an annular groove placed inside the wheel, and a wheel turning drive made in the form of conveyor molds. Molds have the ability to contact their inner surface with the drain nozzles of the casting wheel. The casting wheel is mounted on rotation bearings set in relation to the molds using gaskets. When the mold moves with its inner longitudinal surface, they press on the drain pipes of the casting wheel, as a result of which it continuously rotates on the supports, ensuring that each mold is filled with metal to the required level. In relation to the molds, the casting wheel is exposed during installation using gaskets. The cooling of the molds is carried out during their transportation to the place of discharge of crystallized ingots.

The disadvantages of the device are: the difficulty of achieving uniformity of the melt and the possibility of marriage of ingots for foreign inclusions and shrinkage defects on the gating surface. The analogue does not exclude the need for manual removal of slag / foam from the surface of the melt in the molds and / or the need for manual driving of shrinkage cracks on the surface of ingots.

The closest analogue of the device is a complex for pouring liquid metal into molds on a conveyor (patent of the Russian Federation No. 2138364, microliter B22D 35/04, 1998). The known complex contains a mixer with a trough, a rotary metal receiver in the form of a casting wheel with radially located drain pipes, interconnected by an annular trough, and a wheel drive from the conveyor with molds. The liquid metal from the mixer through the tap hole, the intermediate tank and the trough, passed through the hollow bearing, the disk and the clutch, enters the casting wheel. The conveyor included in the work by the tides of the molds through the fingers drives the hollow disk, the coupling and the casting wheel in contact with it. From the casting wheel, the metal enters the molds through the drain pipes. Thus, the complex mechanizes the process of pouring metal, but does not extend to the process of cleaning cast metal from slag and preventing the formation of shrinkage defects.

The disadvantages of this design include the following:

- significant oxidation of the metal at the time of its discharge by a turbulent flow through radially located drain pipes from the casting wheel into the molds;

- the need for manual removal of oxide film (slag) to bring ingots in accordance with GOST 11070;

- associated metal loss;

- ingots obtained by this method have a significant heterogeneity of structure and chemical composition.

The objective of the proposed technical solution is to eliminate unacceptable shrinkage defects (cracks and deep sinks - “dips”) on the gating surface of small aluminum ingots in the most simple and effective way, as well as improving the technical and economic parameters of the process by reducing the formation of marriage when filling molds, improving quality products and reduce the complexity of the casting process.

The cracks formed during the hardening of the central part of the ingot, at the time of formation of an open shrink shell with a “dip”, are hot shrink cracks. Therefore, the solution is to change the nature of aluminum shrinkage during the formation of a shrink shell in the central part of the ingot. Studies have shown that the main role in the formation of cracks is played by the presence of an oxide film on the surface of the hardened metal, which has mechanical and physical properties different from those of aluminum. Elimination of captivity allows you to get a defect-free gating surface of ingots. Thus, the task of eliminating shrinkage defects is reduced to the removal / shift of the oxide film.

The technical result consists in the fact that the shift of the formed oxide film leads to the fact that in the central part of the forming ingot instead of shrinkage voids in the form of a shell with a “dip” and accompanying cracks, a smooth, shallow shrinkage cavity without cracks and “dips” is formed.

The technical result is achieved by the fact that in the method of casting ingots into molds of a casting conveyor, comprising filling molds with liquid metal to the required level, using metal casting devices and cooling the molds during their transportation to the place of extraction of hardened ingots, according to the claimed method, when the molds move , in the zone of the beginning of crystallization of ingots, the oxide film formed upon pouring on the open surface of the cast metal in the mold is shifted from one edge to another edge in the direction opposite to the motion of the casting conveyor.

The shift of the oxide film formed during cooling can be carried out in a zone of no more than 1/5 of the length of the casting conveyor from the place of pouring metal, when the plank is immersed to shift to a depth of no more than 1/3 of the ingot cross section.

The technical result is achieved in a complex for casting ingots on a casting conveyor containing a mixer with a trough, a device for filling molds of the casting conveyor with metal and a device for shifting oxide film from the metal surface in the mold, made in the form of a bar fixed on rails rigidly mounted on a horizontal shaft mounted in the conveyor frame parallel to the long side of the mold, a lever rigidly mounted on the shaft, and a copier freely mounted at one end on a horizontal shaft with the possibility of angular movement, when interacting with the other end with the rollers of the casting conveyor, and ensuring the movement of the lever up and down.

The lever may be equipped with a regulator for restricting movement along the depth of the mold mounted on the other end of the lever.

The method and device is illustrated by drawings, where Fig. 1 shows a general view of the complex, Fig. 2 is a top view, Fig. 3a is a cross-sectional view of pigs without using the device, Fig. 3b is a cross-sectional view of pigs using the device, .4 is a photograph of the device.

In the complex for casting metal on a casting conveyor, the device for shifting the foam consists of four main elements: a strap 1, a lever 2, a copier 3, a support 4. A mixer with a trough and a device for filling molds 5 with liquid metal on a casting conveyor 6 are not shown in the figures .

The strap 1 is made of heat-resistant material and is attached on the bushings 7 to the guides 8.

The lever 2 is the drive of the horizontal shaft 9, mounted parallel to the long side of the mold 5 and fixed at both ends on the frame 10 of the conveyor 6 by means of a support 4. Two guides 8 are rigidly attached to the shaft 9.

The copier 3 is mounted at one end on a horizontal shaft 9 with the possibility of angular movement. The other end of the copier is in contact with the rollers of the conveyor 6 and converts the translational motion of the rollers of the conveyor 6 into the movement of the lever 2 up and down.

The complex is equipped with two devices for regulating and limiting the stroke of the lever 2 in the direction along the depth of the mold 5. The travel limiter 11 determines the angle of free movement of the left shoulder of the lever 2 when moving up and, accordingly, the angle of lowering of the guides 8 and the depth of immersion of the bar 1 in molten metal. The limiter 12 determines the angle of free movement of the right shoulder of the lever 2 when it moves up - the amplitude of the movement (the height of the bar).

An example of a specific implementation of the method and device.

The plate 1, mounted on the guides 8, is driven from the rollers of the casting conveyor 6 by means of a copier 3. The plate 1 is lowered into each mold 5 and moves the oxide film to the edge. The copier 3 is freely mounted on the horizontal shaft 9 and drives the lever 2 due to the horizontal movement of the rollers of the casting conveyor 6. The copier slides along the surface of the translating roller of the conveyor 6, thereby raising the lever 2. The lever 2 thus moves up and down. Since there is no rigid connection between the copier 3 and the lever 2, it is possible to control the amplitude of the movements of the lever 2 using the screws of the travel limiters 11 and 12. These adjustments allow the use of heat-resistant plates of various heights, as well as changing the immersion depth in the melt and the height of the bar 1.

Filled molds 5 are transported via a casting conveyor to the cooling zone. The device for shifting the foam is installed in the zone of the beginning of crystallization of ingots, occupying 1/5 of the length of the casting conveyor (the zone for removing overheating with respect to liquidus and the formation of a thin, no more than 5 mm crust of solid metal from the mold side). The immersion depth of the strip for removing the foam should be at least 2 mm, but not more than 1/3 of the cross-section of ingots.

An immersion depth of less than 2 mm from the average level of filling of the molds will not provide a shift of the foam from each ingot while lowering the level of metal in the molds, which happens even on automatic casting lines. Immersion of the plank to a depth of more than 1/3 of the cross section of the ingot will lead to intensive mixing and the possibility of a splash of metal from the mold.

The shift of the captivity leads to a fundamental change in the appearance of the ingot, instead of a sink with a “dip” in the central part and accompanying cracks, a smooth, shallow shrink shell without cracks and “dips” is formed.

The inventive method is implemented using a simple, reliable and efficient device for shifting the foam onto the periphery of the surface of the ingot. The design of the device is universal, measuring the width of the copier, you can install the device on casting conveyors with any mold width, and also has a low dead weight, a minimum of parts that can fail, which makes it cheap to manufacture and reliable in operation. This design has been tested and put into commercial operation on the existing casting conveyor of the BEFESA line in the foundry department No. 3 of OJSC SUAL branch of IrkAZ-SUAL.

Claims (4)

1. A method of casting ingots on a casting conveyor, including filling molds with metal to the required level and cooling molds during their transportation to the place of extraction of hardened and partially cooled ingots, characterized in that in the ingot crystallization start zone, the mold Foams on the open surface of the cast metal in the mold from one edge to another edge in the opposite direction to the motion of the casting conveyor. 2. The method according to claim 1, characterized in that the oxide film formed during cooling is sheared in a zone of not more than 1/5 of the length of the casting conveyor using a device in the form of a bar when it is immersed to a depth of not more than 1/3 of the cross section of the ingot. 3. A complex for casting ingots on a casting conveyor, comprising a mixer with a chute and a device for filling molds of the casting conveyor with metal, characterized in that it is equipped with a device for shifting oxide film from the metal surface in the mold, made in the form of a bar fixed on guides, rigidly fixed on a horizontal shaft mounted in the conveyor frame parallel to the long side of the mold, a lever rigidly mounted on the shaft, and a copier freely mounted at one end on a horizontal shaft with zhnosti angular displacement in the interaction with the other end of the casting rolls of the conveyor and ensures movement of the lever up and down. 4. The complex according to claim 3, characterized in that the lever is equipped with a regulator restricting movement along the depth of the mold installed on the other end of the lever.

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