FR2546429A1 - METHOD FOR SLOWING A BAR, ESPECIALLY A BAR OF ALUMINUM OR ALUMINUM ALLOY - Google Patents

Abstract

THIS CASTING PROCESS THROUGH LINGOTIER USES WATER CONTAINING CARBON ANHYDRIDE TO COOL THE BAR. ACCORDING TO THE INVENTION, DURING THE PROCESS OF STARTING THE FLOWING, THE FLOW OF CARBON ANHYDRIDE ADDED TO THE WATER IS MAINTAINED AT A CONSTANT VALUE, BUT ITS CONCENTRATION IN THE COOLING FLUID BY INCREASING THE FLOW OF WATER, IS DECREASED, WHICH AT THE SAME TIME INCREASES THE THERMAL CONTACT BETWEEN THE SURFACE OF THE BAR AND THE COOLING WATER.

Description

The invention relates to a method for casting a bar, in particular a

  aluminum bar or aluminum alloy, through a casting mold with cooling of the bar

  formed by water containing carbon dioxide.

  In direct cooling continuous casting,

  heat is extracted from the casting bar

  By cooling the surface of the bar with a cooling fluid directly under the mold During the casting start process, the coolant first comes into contact only with the starting bottom or bottom block. of indirect heat thus produced leads to a smooth solidification of the liquid metal and to the formation of a flat bar foot. As the bottom block descends, the cooling fluid comes into direct contact with the

  surface of the bar, which is linked to a sudden rise in the

  The thermal stresses generated by this thermal shock are greater than the resistance to the extension of the bar and cause a permanent deformation in the form of a convex bulge of the foot of the bar.

  cracks in the bar if the resistance is exceeded

  To obtain a bar with a flat or straight foot, do not cool the bar too much during

the startup process.

  For this purpose, patent US Pat. No. 3,441,079 proposes to spray the cooling fluid intermittently on

  the bar during the start-up phase This however has the incon-

  claim that different thermal solidification patterns are formed in the casting bar due to intermittent jet

of cooling fluid.

  German patent application DE-AS 12 93 956 relates to a method for cooling strips, plates or similar thin products continuously cast, o a mixture of water and air is produced in the mold by an effect ejector

  and used-before the output and the direct cooling,

  that is, cooling by direct application of the coolant to the thin strip or like product itself for indirect cooling, i.e., cooling through the ribs of the mold. The depth of the crater of liquid metal and / or the temperature of the thin cast strip is or are adjusted by variation of the air flow rate and / or the water flow rate As the mixture of water and air is sprayed in the form of a fog, especially during direct cooling, it is not possible to modulate the cooling This is even more true for the proposal of the German patent application DE-AS 12 93 956, according to which the flow of water is increased for indirect cooling of the cast bar inside the mold, that is during indirect cooling, and the air flow is increased for direct cooling It is not possible to apply this way a cooling fluid nt

  to a bar modulated and even less continuously.

  Another embodiment of the mentioned method

  above is described in the German patent application DE-Cg 2 (08 285.

  In this case, a mixture of water and air is also used to cool the cast bar leaving the ingot mold. The cooling water first enters under pressure into water chambers or channels of the mold and cools surfaces

  of the cavity of the mold, defining the shape-

  The water then flows out of the mold and cools the cast strip directly. As a result of the provision of different sections in the coolant outlet ports and the provision of additional air slots, air is

  sucked from these slots, according to the principle of a water jet pump.

  The air thus added to the cooling water, however, has little influence on the cooling power. Moreover, it is probable that the modulation of the cooling is also very problematic in this case, for example because the rise in the flow rate of water also causes the suction of much more air,

  which does not necessarily produce a better cooling effect

  but only a stronger transformation into fog

mixture of water and air.

  German patent application DE-OS 29099 M discloses a method for the continuous casting of metal blocks where the rate at which the liquid coolant discharges heat from the casting bar is slowed down at least during the process. For this purpose, a gas, preferably carbon dioxide, is added under pressure in a mixture with the cooling fluid. The gas thus dissolved forms, at the impact of the cooling fluid on the surface of the bar, a film insulation that reduces heat dissipation and thus reduces

the cooling intensity.

  The start-up phase completed, the speed of

  cuation of heat is increased by reducing the flow of gas

  added as a mixture to the cooling fluid.

  The essential disadvantage of this process lies in its complexity, in particular as regards the mixing and adjustment devices necessary for dissolving the gas in

  the cooling fluid Similarly, the modulation of the cooling

  the cooling remains dependent on the solubility of the gas in the liquid cooling fluid, solubility which is determined by various parameters which are also a function also of the conditions

  changing during the entire casting process.

  The object of the invention is to create a process of the type mentioned above, which avoids these drawbacks and by means of which it is possible in particular to modulate the cooling process in a precise manner, both as regards the indirect cooling phase as far as cooling is concerned

direct.

  The invention solves this problem by a method which is characterized in that, during the start-up process of the casting, the flow rate of carbon dioxide added to the water is maintained at a constant value, but its concentration in the cooling fluid by increasing the flow of water, which at the same time increases the thermal contact between the surface of the

  the bar and the cooling water.

  This means that the action of carbon dioxide

  no longer depends on its solubility in the water of the cooling fluid.

  This is because a predetermined and valid concentration of a mixture of water and carbon dioxide is used, for which a saturation limit or other limiting values that are difficult to define are of no importance. The thermal insulation property of carbon dioxide is influenced, during the cooling of the cast bar, by reducing its concentration and by raising the energy or the speed of the cooling water, which is achievable in a simple manner by increasing the flow of water Thus , more cooling water comes into contact with the surface of the bar, since the "insulating film" of

  the carbon dioxide becomes increasingly thin and permeable.

  Finally, the "film" is completely torn and the known cooling action of the water alone can develop. It is naturally within the scope of the invention to completely interrupt the supply of carbon dioxide, either prefixed

  concentration of carbon dioxide in the cooling fluid

  at the latest, at the end of the start-up process.

  It is essential to ensure that the mixture of water and carbon dioxide is initially

  solubilization such as the thermal shock between cooling

  indirectly by the ingot mold and the direct cooling which starts at the lowering of the bottom block or similar element is as low as possible This solubilization ratio is in

  same time the maximum value needed to obtain for the concentration

  tion of carbon dioxide in water, the reduction of which by the addition of water does not cause difficulties, while the reduction of the flow of carbon dioxide with the maintenance of the flow of water at the same value is accompanied by the imponderability of the quantity of carbon dioxide actually dissolved It is therefore within the scope of the invention to prepare before

  starting a mixture of carbon dioxide and water of a concentration

  in a tank, for example, and add additional water to this mixture during the casting start process. It is also possible to prepare continuously

  carbon dioxide and water as a cooling fluid

  in a mixing device and continuously increase

the fraction of water.

  It has been found, in each case, that the modulation according to the invention of cooling makes it possible to produce bars

  castings with minimal cross-sectional variations, in particular

  in the region of the helm.

Claims (2)

R E V E N D I C A T I 0 N S   Process for casting a bar, in particular an aluminum or aluminum alloy rod, through a casting mold with cooling of the bar formed by water containing carbon dioxide, characterized in that during the casting start process, the flow of carbon dioxide added to the water is maintained at a constant value, but its concentration in the cooling fluid is lowered by raising the water flow rate, which increases in same time the contact   between the surface of the bar and the cooling water.   Process according to Claim 1, characterized in that the supply of carbon dioxide is interrupted after the start-up process of the casting or after the concentration of the carbon dioxide has fallen below a certain value. determined.