RU2009005C1 - Method of producing sheet slab from aluminium and its alloys - Google Patents

Abstract

FIELD: foundry. SUBSTANCE: method of continuous casting of sheet slab of aluminium and its alloys in a roll mould for producing a fine-grained homogeneous structure without shrinkage porosity is characterized in that metallostatic pressure H of melt in crystallization zone is set according to relationship σ/ρ·r≥ H≥ 0,34Q/V≥ 0.56 A, where σ is a surface tension of the melt, r is a specific weight of the melt, r is a radius of the melt meniscus in the crystallization start-up zone, Q is a specific volumetric flow rate of the melt fed into the cavity of rolls, V is a drawing rate of the billet, A is a length of crystallization and deformation zone, 0.34 and 0.56 are empiric coefficients. EFFECT: enhanced efficiency. 1 dwg, 1 tbl

Description

 The invention relates to metallurgy, and in particular to the continuous casting of aluminum and its alloys into a roll mold.

 Known methods for continuous casting of metal into a roll mold, aimed at improving the structure, density, mechanical properties of the obtained strip billets by developing temperature, speed modes of casting and rolling, cooling modes, etc.

A method for continuous casting of strips of steels and alloys based on iron and nickel-based generated in the rolls, molds, wherein the metal is poured into rolls at 1350-1450 ^{° C} and the cooling rate and the outlet temperature of the billet are 500-5000 ^{° C} and 1200 -1350 ^about C.

 The known method does not provide a dense homogeneous structure of the tape due to the presence of shrinkage porosity, looseness associated with insufficient recharge during crystallization of the metal.

 A known method for the continuous casting of a strip into a roll mold, in which the difference between the peripheral speed of rotation of the rolls of the mold and the speed of drawing the strip is set equal to 0.004-1.0 m / min

 The regulation of these parameters also does not provide a fine-grained homogeneous structure of the strip due to the presence of interdendritic shrinkage associated with insufficient recharge during crystallization. A known method for the continuous casting of a workpiece into a roll mold, in which the surface temperature of the rolls is maintained at 0.1-2K higher than the crystallization temperature of the metal, heat is removed through an intensively cooled blank. The specified method is characterized by all of the above disadvantages. The method does not provide a fine-grained homogeneous structure without shrinkage porosity. A known method of producing a thin strip billet of aluminum alloys, including the supply of the melt into the cavity between the rolls-crystallizers, crystallization of the melt, deformation of the hardened strip and stretching the billet. In the method for producing strips with a thickness of 4-5.8 mm, the distance from the nozzle edge to the axis of the rolls is set within 35-60 mm.

 This insufficient distance accurately determines the crystallization zone, the liquid metal hole can be displaced, especially at high speeds, beyond the axis of the rolls, causing porosity, intercrystalline cracks, or the hole can move to the nozzle and crystallize will begin in the nozzle itself, causing its destruction. The method does not take into account the metallostatic pressure of the melt in the crystallization zone, therefore, it does not provide stable production of a fine-grained homogeneous structure, especially when casting billets of larger thickness.

 This method is the closest in technical essence and the achieved result to the proposed and adopted as a prototype.

 The developed method ensures the achievement of a technical result, which consists in improving the quality of the strip and increasing its mechanical properties by obtaining a homogeneous fine-grained structure of the strip.

≥ H ≥

≥ 0,56A, где σ - поверхностное натяжение расплава, Н/м;
ρ - удельный вес расплава, т/м³;
r - радиус мениска расплава в зоне начала кристаллизации, м;
Н - металлостатическое давление расплава в зоне кристаллизации, м;
Q - удельный объемный расход расплава подаваемого в полость валков м³/с. м;
v - скорость вытягивания заготовки, м/с;
A - длина зоны кристаллизации и деформации, м;
0,34 и 0,56 - эмпирические коэффициенты.The specified technical result is achieved by the development of a method for producing a strip billet from aluminum and its alloys, including the supply of the melt into the cavity between the rolls-crystallizers, crystallization of the melt, deformation of the hardened billet and stretching it, in which the metallostatic pressure of the melt in the crystallization zone and the ratio of the specific volumetric flow rate of the melt, fed into the cavity, to the speed of drawing the workpiece is supported by the ratio:

≥ H ≥

≥ 0.56A, where σ is the surface tension of the melt, N / m;
ρ is the specific gravity of the melt, t / m ³ ;
r is the radius of the meniscus of the melt in the zone of crystallization onset, m;
H - metallostatic pressure of the melt in the crystallization zone, m;
Q is the specific volumetric flow rate of the melt supplied to the roll cavity m ³ / s. m;
v is the speed of drawing the workpiece, m / s;
A is the length of the crystallization and deformation zone, m;
0.34 and 0.56 are empirical coefficients.

 In the sources of scientific, technical and patent information, no technical solutions were found containing similar distinctive features of the claimed technical solution. Therefore, it meets the criterion of "Inventive step".

 The method provides for the preparation of a workpiece with a uniform fine-grained structure at optimal casting speeds, which is achieved by supplying a sufficient amount of melt to the interdendritic and intergranular shrinkage voids in combination with an efficient development of the structure.

 The above ratio of process parameters was developed based on the following considerations.

 When forming a workpiece in the roll space, the following processes occur. The incoming melt, in contact with the surface of the rolls, is cooled to a crystallization temperature. Depending on the length of the crystallization and deformation zone (A), dendrites grow at different angles to the crystallization front. It was experimentally established that in the case of short zone A, the apex of the hole moves toward the nozzle, the crystals are pulled toward the melt from the nozzle, which contributes to the formation of a coarse-crystalline fan structure. With an increase in the crystallization and deformation zone A, the top of the hole moves toward the exit of the workpiece from the rolls, the crystallization surface increases, the crystal growth occurs in a direction close to the normal to the surface of the rolls, resulting in a more uniform structure. With such a crystallization scheme, it is required to provide melt access to feed the resulting interdendritic and intercrystalline voids.

 To improve the melt recharge of shrinkage voids, it is necessary to create a metallostatic pressure of the melt with a value sufficient to push the melt into these voids.

 As a result, a homogeneous cast structure is formed, the elaboration of which is achieved by regulating the ratio (Q / V) since it determines the degree of deformation of the hardened metal (the larger this ratio, the greater the deformation of the metal).

является характеристикой используемого металла. При превышении указанного отношения произойдет прорыв металла и остановка процесса. Увеличение металлостатического давления Н выше расчетного нецелесообразно из-за загрязнения расплава окислами, футеровкой и повышения энергозатрат. Уменьшение металлостатического давления Н ниже расчетного ухудшает условия подпитки при кристаллизации, повышает неоднородность структуры вплоть до веерной, вызывает рост зерен. Увеличение отношения удельного объемного расхода расплава, подаваемого в полость валков, к скорости вытягивания заготовки выше расчетного приводит к смещению лунки расплава в сторону насадки, вызывая рост грубых столбчатых кристаллов, ухудшающих качество и механические свойства заготовки. При уменьшении указанного отношения ухудшаются условия проработки структуры, она остается близкой к литой, что снижает механические свойства.Attitude

is a characteristic of the metal used. If the specified ratio is exceeded, the metal will break through and stop the process. An increase in the metallostatic pressure H above the calculated one is impractical due to contamination of the melt with oxides, lining, and an increase in energy consumption. A decrease in the metallostatic pressure H below the calculated one worsens the feeding conditions during crystallization, increases the heterogeneity of the structure right up to the fan structure, and causes grain growth. An increase in the ratio of the specific volumetric flow rate of the melt fed into the cavity of the rolls to the speed of drawing the workpiece above the calculated value leads to a displacement of the melt hole towards the nozzle, causing the growth of coarse columnar crystals that degrade the quality and mechanical properties of the workpiece. With a decrease in this ratio, the conditions for the development of the structure worsen, it remains close to cast, which reduces the mechanical properties.

 The drawing shows a diagram of a unitless rolling and casting (BPL) for implementing the developed method.

 The installation includes a roll mold 1, a nozzle 2, an intermediate tank with a melt 3.

 The melt is fed into the intermediate tank 3 and through the nozzle 2 enters the cavity 4 between the rolls, then the crystallized strip 5 is pulled out of the rolls and wound into a roll.

 When implementing the method at the BPL installation, casting of a strip billet from various alloys was performed at different speeds and the value of the optimum zone of crystallization and deformation A was determined using a probe.

≥ H ≥

≥ 0,56A
определили металлостатическое давление расплава H в полости и отношение Q/V , которые поддерживали в процессе бесслитковой прокатки.By ratio

≥ H ≥

≥ 0.56A
determined the metallostatic pressure of the melt H in the cavity and the Q / V ratio, which were maintained during the process of non-continuous rolling.

 The metallostatic pressure of the melt in the cavity of the rolls, equal to the metallostatic pressure of the melt in the intermediate vessel (according to the principle of communicating vessels), was maintained by controlling the amount of metal supplied to the intermediate vessel from the furnace or ladle.

 The radius of the meniscus of the melt in the zone of onset of crystallization took 0.5 clearance between the nozzle and the rolls. The resulting preforms had a uniform fine-grained structure and high mechanical properties. The method allows to conduct the process in optimal conditions, providing maximum performance.

 If necessary, the developed ratio makes it possible to determine the optimal cross section of the nozzle for supplying metal, which is especially important when changing the cross section of the resulting workpiece.

 The method provides a quick response to changes in external parameters (temperature of the supplied metal, cooling water rolls, and the environment) that cause a decrease or increase in casting speed.

 The test results of the known and proposed method are shown in the table.

 Specific examples of the method.

 PRI me R 1. On the installation of the BPL received a strip billet with a cross section of 8 x 1040 mm and alloy A5 at drawing speeds of 10.0 and 16.7 mm / s. The maximum crystallization and deformation zones A were 30 and 50 mm, respectively.

для сплава А5 равно 50 мм.Attitude

for alloy A5 is 50 mm.

≥ H ≥

≥ 0,56A определили Н и Q/V.In relation

≥ H ≥

≥ 0.56A determined H and Q / V.

 The actual metallostatic pressure was maintained in the intermediate vessel at a level of 20 and 30 mm at the indicated drawing speeds.

 The resulting preforms had a uniform fine-grained structure and high mechanical properties.

 The method allows to conduct the process at maximum speed - in this case, 16.7 mm / s.

 PRI me R 2. Analogously to example 1, a workpiece was obtained with an composition of 8 x 1040 mm from an alloy of AMC at drawing speeds of 14.0 and 18.0 mm / s.

для сплава АМЦ равно 40 мм.The maximum crystallization and deformation zone A was 46 and 55. The ratio

for the alloy AMC is 40 mm.

 The ratio determined H and Q / V.

 The actual metallostatic pressure was maintained at 28 and 35 mm at the indicated drawing speeds. The resulting preforms had a uniform fine-grained structure and high mechanical properties.

 It is advisable to conduct the process at a speed of 13.0 mm / s.

 To implement the method in an industrial environment, the developed ratio of parameters is presented in the form of graphs, which simplifies maintenance.

 As can be seen from the results of the table, the developed method provides a strip blank with a fine-grained structure and increased mechanical properties at a high casting speed. (56) 1. USSR author's certificate N 214754, B 22 D 11/06, 1969.

 2. USSR copyright certificate N 1584240, cl. B 22 D 11/06, 1989.

 3. Copyright certificate of the USSR N 1424950, cl. B 22 D 11/06, 1988.

 4. US patent N 4751958, CL. B 22 D 11/06, 1988.

Claims (1)

METHOD FOR PRODUCING A STRIP BASIS FROM ALUMINUM AND ITS ALLOYS, including the supply of the melt into the cavity between the rolls, the crystallization of the melt, the deformation of the hardened billet and its stretching, characterized in that the metallostatic pressure of the melt in the crystallization zone H and the ratio of the specific volumetric flow rate to the melt, the cavity between the rollers, to the speed of drawing the workpiece V support the ratio

≥ H ≥

≥ 0.56A /
where σ is the melt tension surface, n / m;
ρ is the specific gravity of the melt, t / m ³ ;
r is the radius of the meniscus of the melt in the zone of crystallization onset, m;
Q is the specific volumetric flow rate of the melt fed into the cavity between the rolls, m ³ / s;
A is the length of the crystallization and deformation zone, m; 0.34 and 0.56 are empirical coefficients.

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