RU2073585C1 - Method and apparatus for continuous casting of small-section bimetallic billets - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: method involves continuous pouring of two different metals 8 and 9 into crystallizer with movable belts by joining conjugated faces of ingots in semiphase state along pouring boundary. Apparatus has intermediate ladle 1 with separating wall 2. Ladle bottom has opening with forming head 3 and shield 4 connected with dividing wall 5 inserted into working cavity of crystallizer, which is defined by two endless belts 6. Upper part of shield 4 is connected with movable stem 7 providing displacement of shield 4 and dividing wall 5 in vertical plane. Thermocouple 10 is calked in lower end of dividing wall 5. EFFECT: increased efficiency, simplified construction and improved quality of bimetallic billet. 4 cl, 1 dwg

Description

 The invention relates to metallurgy, and more particularly to continuous casting of bimetallic ingots.

 A known method of continuous casting of bimetallic ingots, including the supply of various metals and steel tape to prevent their mixing in the mold, and a device for its implementation (Japanese Application N 55-68156, CL 11 B 091, 1980).

 The disadvantage of this method and device is the need for complex and lengthy preparation of a steel strip in the form of stripping, degreasing, washing, etc. which complicates the casting process and does not guarantee the quality of the metals being welded.

 Closest to the proposed method is a continuous casting of bimetallic billets of small cross section, including the supply of melts with the regulation of their flow into a mold with moving walls, the formation of two-phase states of both ingots in it, measuring the temperature of the melts and bringing the welded faces of the ingots into contact, and a device containing a mold with movable walls, a partition and a temperature sensor (ed. St. USSR N 539668, class B 22 D 11/00, 1977).

 The disadvantage of this method is the possibility of complete mixing of hardened metals, the formation of oxide films on the open surfaces of the meniscus of metals.

It is known that the quality of welding and adhesion of various metals in the casting of bimetallic billets depends on the degree of development and characteristics of the two-phase zone of the welded ingots. If the ingots are connected in a liquid or two-phase state, when the fraction of the solid phase f _s over the entire cross section of the connected ingots is less than 20 40% (f _s = f $\genfrac{}{}{0ex}{}{\text{*}}{\text{s}}$ ≅ 0.2-0.4), then there is intense mixing of the melts, as a result of which the zone of mixed composition will have a large extent up to the peripheral layers, which affects the mechanical properties of the bimetallic product. For high-quality metal joining, it is first necessary to ensure the independent formation of two-phase states of both ingots, and then bring the faces to be contacted, for example, from the pour out boundary of an alloy having a higher liquidus temperature.

 The aim of the invention is to improve the quality of bimetallic billets of small cross section.

где Т_A температура плавления чистого компонента растворителя; Т_l температура ликвидуса; k коэффициент распределения. Из (1) после несложных преобразований получим выражение для температуры границы выливаемости
T_выл=T_A-β(T_A-T_l), (2)
где β=(1-f $\genfrac{}{}{0ex}{}{\text{*}}{\text{s}}$ )^k-1..The goal is achieved by the fact that according to the method of continuous casting of bimetallic billets, including supplying molten metals with a controlled flow rate to a mold with moving walls, the formation of two-phase states of both ingots in it, bringing the conjugate faces of the ingots into contact, which is carried out along the pour out boundary of a high-temperature alloy, determined by measurement temperature, the value of which for metal alloys corresponds to the cross section (fraction) of the solid phase f $\genfrac{}{}{0ex}{}{\text{*}}{\text{s}}$ = 0.2-0.4.
According to the rule of non-equilibrium lever (Borisov VT Theory of a two-phase zone of a metal ingot. M. Metallurgy, 1986), the temperature in the two-phase zone of an ingot T is related to the cross section of the solid phase f _{s by the} ratio

where T _A is the melting point of the pure solvent component; T _l liquidus temperature; k distribution coefficient. From (1), after simple transformations, we obtain the expression for the temperature of the pour out boundary
T _sc = T _A -β (T _A -T _l ), (2)
where β = (1-f $\genfrac{}{}{0ex}{}{\text{*}}{\text{s}}$ ) ^k-1 ..

 Thus, comparing the readings of a thermocouple hammered into the lower edge of the partition with the temperature value following from (2), they control the immersion of the partition to the required depth.

In a device for continuous casting of bimetallic billets of small cross section, containing a mold with movable walls and a septum installed in it, the septum is immersed in a liquid well to a depth of H _howl = nd, where n = (4.0 10.0); d, H _howling respectively the thickness of the ingot and the distance from the "mirror" metal to vylivaemosti alloy boundaries having a higher liquidus temperature, the outer surface of the partition walls is formed tapered downwardly at an angle May 10 ^o to the vertical, and the inner surface walls of the top portion of the mold constituting one a third of its length, has a slope to the vertical at an angle of 5 15 ^o .

The implementation of the outer surfaces of the partition and the inner surfaces of the upper part of the mold at an angle α ~ 5 ÷ 15 ^° provides free movement downward of the crystallized metal volume, optimal joining and feeding of the welded faces of the ingots, allows you to adjust the volume of the liquid metal bath. An increase in the angle of the solution of the inner surfaces of the mold can cause the formation of a developed crust of hardened metal, which will lead to large tensile stresses and defect of the surfaces of the ingot.

 Improving the quality of bimetallic billets occurs due to the absence of excessive movement of the alloys and the sufficient development of the two-phase state of the ingots. Moreover, the zone of metal joining has a sufficient width, as a result of which there is no stratification of bimetallic alloys during further redistribution and the rejection of finished metal products is reduced.

 The drawing shows a device for implementing the method of continuous casting of bimetallic billets (longitudinal section).

 The device comprises an intermediate bucket 1 with a dividing wall 2, in the bottom of which there is an opening with a forming nozzle 3 and a fairing 4 connected to the partition 5 included in the working cavity of the mold, formed by two endless belts 6 moving in opposite directions; in the upper part of the fairing is connected to a movable rod 7, providing movement of the fairing and partitions in a vertical plane; liquid metals 8 and 9, thermocouple 10, the zone of the connection of metals (alloys) 11.

 The operation of the device is as follows. During continuous casting, metal 8 (for example, Fe + 0.11% C alloy) is poured into one half of the intermediate ladle 1 with the partition 2, and liquid steel 12 x 13 (metal 9) is fed into the other half. From the ladle 1, metals 8 and 9 enter through the nozzle exit openings formed by the nozzle 3 and the cowl 4 into a movable mold formed by two endless belts 6 with a refractory partition immersed into it 5. The endless belts 6 move in opposite directions at the same speeds.

 The formed ingots of metals (alloys) 8 and 9 are conjugated in a two-phase state by their internal faces at the level of the lower edge of the septum and below. Next, both ingots are welded by mixing metals up to the solidification boundary. In this case, the bimetallic billet is continuously pulled down from the mold with a constant speed.

Example. As an example, consider the formation of a bimetallic billet from iron-based alloys. Alloy 8: Fe + 0.5% C, and alloy 9 steel grade 12 x 13. The liquidus temperature T _{l of} alloy 8 is 1525.42 ^o C, alloy 9 1504 ^o C. The melting temperature of the pure solvent component (Fe) T _A = 1538 ^o C, the distribution coefficient of the hydrocarbon C in the α-iron k = 0,163. Therefore, according to formula (2), the pour out isotherm for the higher temperature alloy 8 at f $\genfrac{}{}{0ex}{}{\text{*}}{\text{s}}$ = 0.3 is determined by the temperature T _v = 1538 1.35 (1535 1525.42) = 1503.85 ^o C.

где Т_l температура ликвидуса сплава 8; ΔT_пер значение перегрева этого сплава; Н_пер высота зоны отвода теплоты перегрева. Для оценки величины Н_пер воспользуемся формулой (А. Н.Степанов, Ю.В.Зилберг, А.А. Неустроев. Производство листа из расплава. М. Металлургия, 1978).From the condition of the balance of axial heat fluxes, neglecting the heat transfer of the metal to the partition, we find the approximate value of the distance from the melt mirror 8 to its pour out boundary

where T _l the liquidus temperature of the alloy 8; ΔT _lane the superheat value of this alloy; N _{lane the} height of the heat removal zone of overheating. To estimate the value of H _{per we} use the formula (A. N. Stepanov, Yu.V. Zilberg, A. A. Neustroev. Production of a sheet from a melt. M. Metallurgy, 1978).

где c, ρ теплоемкость и плотность металла соответственно; k - коэффициент теплопередачи от металла к охлаждающей среде, имеющей температуру Т_c; v₁= 2v_od/(d+b) средняя скорость движения металла в кристаллизаторе между поверхностями ленты и перегородки; d толщина слитка из сплава 8; v_o скорость вытягивания заготовки; b ширина зеркала ванны сплава 8. При этом b=d+H_ltgα, где α угол наклона ленты кристаллизатора в его верхней части к вертикали; d $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ приведенный размер объема металла между наклонной поверхностью ленты кристаллизатора, а поверхность перегородки и свариваемыми гранями слитков (приведенная толщина объема металла в верхней области кристаллизатора), определяемый выражением

Из соотношений (3) (5) следует
Н_выл=nd, (6)
где

Примем для технологических и кристаллизационных параметров следующие характерные для рассматриваемого процесса значения: d=3•10^-3 м; Т_пер=30^oС; v= 0,2 м/с; k=1,2 •10³ Вт/(м²•^oС); κ_o=2,72•10⁵ Дж/кг; ρ=7,02•10³ кг/м³ с=838 Дж/(кг•^oС); Т_c= 313^oС; α5^o. Подставив эти величины в (4) (6) и выполнив соответствующие вычисления, найдем
Н_l=59,2 мм, Н_выл=101,76 мм.

where c, ρ are the specific heat and density of the metal, respectively; k is the heat transfer coefficient from the metal to the cooling medium having a temperature T _c ; v ₁ = 2v _o d / (d + b) the average speed of the metal in the mold between the surfaces of the tape and the partition; d thickness of the alloy ingot 8; v _{o the} speed of drawing the workpiece; b the width of the mirror of the alloy bath 8. Moreover, b = d + H _l tgα, where α is the angle of inclination of the mold ribbon in its upper part to the vertical; d $\genfrac{}{}{0ex}{}{\text{*}}{\text{one}}$ the reduced size of the metal volume between the inclined surface of the mold ribbon, and the surface of the partition and the welded faces of the ingots (the reduced thickness of the metal volume in the upper region of the mold), defined by the expression

From relations (3) (5) it follows
H _yout = nd
Where

Let us take the following characteristic values for the process under consideration for the process and crystallization parameters: d = 3 • 10 ^-3 m; T _lane = 30 ^o C; v = 0.2 m / s; k = 1.2 • 10 ³ W / (m ² • ^o С); κ _o = 2.72 • 10 ⁵ J / kg; ρ = 7.02 • 10 ³ kg / m ³ s = 838 J / (kg • ^o С); T _c = 313 ^o C; α5 ^o . Substituting these quantities in (4) (6) and performing the corresponding calculations, we find
H _l = 59,2 mm H _howling = 101.76 mm.

Thus, the septum depth of immersion into the liquid well to vylivaemosti border, characterized _howling isotherm T = 1503,85 ^o C is ≈ 102 mm. This value is adjusted in accordance with the temperature sensor by moving the mold in a vertical plane. Assessing the width of the filtration mixing zone of the metals in question gives L _c = 0.2 mm.

 For more precise control of the metal flow instead of a moving fairing, electromagnetic valves or a gas-dynamic method of compensating the hydrostatic pressure of the melt using moving bubble channels and a hermetic intermediate mixer can be used.

 The application of the proposed method and device allows you to adjust the value of the mixed state of metals in the process of casting, depending on their composition and product drawing speed, thereby determining the high quality of the connection of the constituent layers of the bimetallic billet, which excludes separation during further processing.

Claims (4)

 1. The method of continuous casting of bimetallic billets of small cross section, including the supply of melts with the regulation of their flow into a mold with moving walls, the formation of two-phase states of both ingots in it, measuring the temperature of the melts and bringing the welded faces of the ingots into contact, characterized in that, in order to improve product quality, bringing the welded faces of the ingots into contact is carried out along the pour out boundary of a melt having a higher crystallization temperature.  2. A device for continuous casting of bimetallic billets of small cross section, containing a mold with movable walls, temperature sensors and a partition, characterized in that, in order to improve the quality of products, the partition is made with the possibility of vertical movement, and temperature sensors are installed on its lower end.  3. The device according to p. 2, characterized in that the partition is made in the form of a fairing connected to the rod. 4. The device according to p. 2, characterized in that the surface of the walls of the partition is made conical downward at an angle of 5 10 ^o to the vertical, and the inner surface of the upper part of the walls of the mold 1/3 of its length is inclined to the vertical at an angle of 5 15 ^o .