RU2025208C1 - Method of manufacturing bimetal rolls - Google Patents

Abstract

FIELD: metallurgy, in particular, production of rolls. SUBSTANCE: method involves locating band and electrode-solenoid in casting mold in axially aligned position and in spaced relation with respect to inner surface of band, with electrode-dummy bar being disposed in casting mold; forming slag in intermediate device and feeding liquid slag into casting mold. As electrode-solenoid is consumed, molten metal is maintained at predetermined level in intermediate device by continuous supplying of molten metal from ladle, with above mentioned predetermined level of molten metal being not below 0.85 of required design value. EFFECT: high quality of rolls and increased efficiency of method. 1 dwg

Description

 The invention relates to ferrous metallurgy, in particular to the electroslag process, and can be used for the production of rolling rolls.

A known method of manufacturing bimetallic rolling rolls (ed. St. N 1323226, CL L 22 D 19/46, published. 1987). According to this method, the outer cast iron shell of the roll and the tubular consumable electrode are coaxially mounted in the mold. Liquid slag is fed into the mold, then siphon or from above through the cavity of the tubular electrode, molten steel gradually rises in the mold at a speed of (1-10) ˙10 ^-3 m / s.

The disadvantage of this method is the unstable nature of the electroslag process, especially at high speeds of lifting steel, comprising (7-10) ˙10 ^-3 m / s. This is due to the fact that the self-regulation of the electroslag process at high steel lifting speeds is difficult. The cross section of the melting electrode is very large. Under these conditions, even when using a power source with a sufficiently rigid external characteristic, the process of self-regulation is difficult. Electroslag welding and surfacing (Edited by B.E. Paton. M: Mechanical Engineering, 1980, p. 42, 43).

 The closest in technical essence to the proposed invention is a method implemented using a device for the manufacture of bimetallic castings of rolling rolls [1]. When using this device in a mold with a bandage, which is an integral part of the mold, a consumable electrode in the form of a solenoid is coaxially installed. Steel is poured from the intermediate device along the roll axis through a pouring nozzle with an outlet hole d = 8 mm, and it is necessary to ensure that the melt rises in the cavity of the upper and lower half-molds at a speed of 30 mm / s, and in the cavity of the bandage at a speed of 5 mm / s.

 The electroslag process in the manufacture of bimetallic castings occurs only during the pouring of liquid steel in the cavity of the bandage.

 The disadvantage of this method is that the electroslag process is unstable, since self-regulation of the electroslag process at high steel lifting speeds is difficult.

In order to ensure good weldability of the molten metal with the bandage, electroslag remelting of the consumable solenoid electrode should contribute a sufficient amount of additional thermal energy to the fusion zone. Therefore, power sources are used, for example, powerful transformers for electroslag welding, such as TShS-3000-1, TShS-3000-3 and others with a welding current of up to 6000 A. (Electroslag welding and surfacing / Ed. B.E Patona, Moscow: Mashinostroenie, 1980, p. 190.191). Significant currents flowing through the solenoid-shaped electrode necessitate the use of a large cross-section electrode. Under these conditions, at a high steel lifting speed V _pm ≥1-2 mm / s, even when using a power source with a fairly rigid external characteristic, the self-regulation process is difficult (ibid., P. 42.43). This means that the process of self-alignment, self-stabilization of the interelectronic gap is weak, inefficient. So, with a random decrease in the interelectrode gap, the electrical resistance of the slag bath decreases, the current strength increases, which leads to an increase in the melting rate of the electrode. If the increased melting rate of the electrode is higher than the rate of rise of the level of the cast steel, then the interelectrode gap Nm is restored at the same level. If it is less, then the distance between the end of the electrode and the mirror of the metal bath will be reduced up to a short circuit.

Since the pouring of molten steel from the tundish is performed, in which once filled half of the volume portion of the roll axis, the hydrostatic head H _rH liquid metal column in a spacer during the subsequent casting of the metal portion varies from a maximum to a value close to zero. In accordance with this, the rate of metal entry into the axial part of the roll and the rate of metal rise during casting vary over a wide range (Efimov V.A. Steel casting. M: Metallurgy, 1976, formula (1-29), p. 24). In fact, it is impossible to ensure a stable melt rise rate in the most critical middle part of the roll, equal to 5 mm / s.

 If you set the electroslag process to one speed of rise of the metal bath, then with a significant change in the speed of rise, self-regulation is difficult. Thus, there are no favorable conditions for realizing the possibilities of self-regulation of the electroslag process, with a large cross section of the electrode, very significant levels of disturbances in the rate of rise of the metal bath occur.

The permissible range of variation of the interelectrode gap N _m during electroslag process is small
5-6 mm≅ N _m ≅ N _sh.v. (1) where H _seam is the height of the slag bath.

When N _m <(5-6) mm, a short circuit occurs, the electroslag process goes into an arc process, and it is not possible to restore it. The fusion quality of steel with a bandage is sharply reduced.

When N _m > N _sh.v. the end of the electrode leaves the slag, the process goes into an arc. The stability of the penetration of the bandage, the quality of the alloy steel with the bandage fall.

Therefore, to ensure a high quality of rolls manufacturing, reliable stabilization of N _m is required.

 The objective of the invention is to improve the quality of bimetallic rolls by stabilizing the supply of liquid metal from the intermediate device, in the process of melting the electrode-solenoid.

 The essence of the invention lies in the fact that after a coaxial installation in a mold with an electrode-seed bandage and placed in it at a distance of 5-100 mm from its surface, a consumable electrode in the form of a solenoid, guidance in the intermediate device and feeding liquid slag into the mold, accumulation and supplying liquid metal to the lower half-mold, a stable supply of liquid metal is carried out during the melting of the solenoid electrode by maintaining the established level of liquid metal in the intermediate put device m gravies continuous steel from the ladle and pouring the final upper mold.

The quality of bimetallic rolling rolls is improved by ensuring good alloying of the cast steel with the bandage due to the stabilization of both the electroslag process mode and the supply of liquid metal during the melting of the solenoid electrode from the intermediate device. The electroslag process mode is stabilized by stabilizing the interelectrode gap N _m The regulation problem N _m is solved in two stages. At the first stage, the interference level is limited by the lifting speed of the metal bath, affecting N _m . This creates the conditions for the implementation of self-regulation of the electroslag process, which carries out fine regulation in the second stage.

The level of interference on the metal bath lift speed is limited by the stabilization of the hydrostatic head H _rH metal bath in a spacer shroud during casting. The value of H _{gn is} maintained near a pre-calculated level by continuously pouring steel from a steel-pouring ladle.

Since the level of interference with the rate of rise of the metal bath is limited, and the current underflows and overflows relative to the required level of the metal bath of the intermediate device, due to its large area, lead to a smooth change in the speed of rise of the metal bath in the mold, self-regulation performs well the task of fine stabilization of N _m .

During stabilization of _{Hn, the flow of} molten steel from the intermediate device to the mold is simultaneously stabilized. In this regard, the flow of stored heat is fixed. As a result, the quality of fusion of the liquid melt with the bandage is stabilized, and hence the quality of the bimetallic castings of the rolling rolls.

The continuity of the steel pouring from the steel pouring ladle to the intermediate device eliminates the need for portioned pouring of steel into the intermediate device. This eliminates the significant fluctuations in H _ng between the beginning and end of pouring a portion into the inner part of the bimetallic roll. When pouring steel, they tend to maintain the metal mirror in the intermediate device at a predetermined level. For this, the metal intake from the steel pouring ladle is either reduced or increased by monitoring the metal level in the intermediate device by any known method. Thus, the current stabilization of the GNH and a finer restriction of the level of interference by the rate of rise of the metal bath in the bandage are carried out. On the whole, the continuous stabilization of _Hnn limits the level of interference, creates the conditions for self-regulation of the electroslag process, and stabilizes the thermal state of the slag metal bath. As a result, the quality of fusion of steel with a bandage is stabilized, and therefore the quality of the rolls.

 The drawing shows a device for implementing the proposed method.

 The device consists of a mold 1, an integral part of which is a roll band 2, located inside the band 2 of a consumable solenoid electrode 3. The band 2 and the solenoid electrode 3 are installed coaxially. One terminal of the power source is connected to the solenoid electrode 3, the other to the seed electrode 4 located at the bottom of the lower half-mold 5. To guide and feed slag, heat and supply steel, stabilize the level of NG, an intermediate device 6 with a graphite electrode 7 is used. Melt from the intermediate device 6 is poured through a steel pouring nozzle 8 with an outlet d = 8 mm. In the intermediate device 6, steel is continuously poured from the steel pouring ladle 9 with a stopper.

The slag melt at a temperature of 1700-1800 ^about With poured into a mold. The intermediate device steel poured from a ladle so that metal bath level H _rH reached the desired value. This level is maintained constant throughout the fill time. It can be determined from the expression (Efimov V.A. Casting of steel. M: Metallurgy, 1976, formula 1-27 p. 23).

(2) где V_мас - массовая скорость истечения металла из промежуточного устройства, кг/с;
μ- коэффициент расхода струи, μ= =0,82 - 0,92 в зависимости от отношения площади сталевыпускного отверстия к площади поперечного сечения промежуточного устройства, а также конструкции насадки или отверстия (там же, табл.1-1 с. 21);
ρ- плотность стали, кг/м³;
S_с - площадь сталевыпускного отвер стия, м², S_c=

d_с - диаметр сталевыпускного отверстия промежуточного устройства, м;
g - ускорение силы земного притяжения, g = 9,81 м/с²;
Н - высота уровня металла в промежуточном устройстве, м.v _wt = μρS

(2) where V _wt is the mass flow rate of the metal from the intermediate device, kg / s;
μ is the flow rate coefficient, μ = 0.82 - 0.92 depending on the ratio of the area of the steel outlet to the cross-sectional area of the intermediate device, as well as the design of the nozzle or hole (ibid., Table 1-1 p. 21);
ρ is the density of steel, kg / m ³ ;
S _with - the area of the steel outlet, m ² , S _c =

d _with - the diameter of the steel outlet of the intermediate device, m;
g is the acceleration of gravity, g = 9.81 m / s ² ;
N is the height of the metal level in the intermediate device, m

- площадь поперечного сечения отверстия бандажа, м²;
d_вн - внутренний диаметр отверстия бандажа, м;
S_э - площадь сечения соленоидообразного электрода зеркалом металла, м²;
V_ме - линейная скорость подъема металлической ванны внутри бандажа, м/с.The mass velocity is related to the rate of rise of the metal bath inside the bandage by the ratio
V _mas = V _me ˙ (S _int - S _e ) ˙ρ, kg / s (3) where S _int =

- the cross-sectional area of the hole of the bandage, m ² ;
d _int - inner diameter of the hole of the bandage, m;
S _e - the cross-sectional area of the solenoid-shaped electrode with a metal mirror, m ² ;
V _me - the linear velocity of the metal bath inside the bandage, m / s.

(4) где d_э - диаметр соленоидообразного электрода, м;
α- угол наклона соленоида к горизонтали, град.S _e =

(4) where d _e is the diameter of the solenoid-shaped electrode, m;
α is the angle of inclination of the solenoid to the horizontal, deg.

·

v $\genfrac{}{}{0ex}{}{\text{2}}{\text{м}}$ _e (5)
Для обеспечения устойчивого саморегулирования электрошлакового процесса ограничивают скорость подъема металлической ванны V_ме ≅3 мм/с и колебания ΔН_гн при подаче жидкого металла в бандаж, которые не должны превышать 10-15% Н_гн.Substituting (4) into (3), as obtained in (2) are H _rH
H _mn =

·

v $\genfrac{}{}{0ex}{}{\text{2}}{\text{m}}$ _e (5)
To ensure stable self electroslag process limit speed V metal bath lift _IU ≅3 mm / s and the fluctuations? H _rH when applying the liquid metal in the bandage, which should not exceed 10-15% _rH H.

Since electroslag remelting must contribute a sufficient amount of additional thermal energy to the fusion zone, powerful and expensive power sources are used as power sources. Significant power losses with a significant decrease in the rigidity of the external characteristics of the power source are unproductive and undesirable. Therefore, in the proposed method, the constant most favorable rigid external characteristic of the source is used. Management N _m with exposure to the power source is not carried out.

·

0,002² = 0,45 м
Способ позволяет надежно вести электрошлаковый переплав при изготовлении биметаллических отливок прокатных валков при V_ме≅3 мм/с и колебаниях ΔН_гн до 10-15%, что позволяет обеспечивать высокое качество сплавления жидкой стали с бандажами, а следовательно, и высокое качество биметаллических валков.PRI me R. For V _me = 2 mm / s, a glass with a steel outlet with a diameter d _c = 8 mm with a conical converging nozzle (α = 13 ^о ) μ = 0.94, d _int = 300 mm, d _e = 10 mm, α = 10 ^{o the} height of the metal level in the intermediate device according to the formula (5) is determined as follows:
H _mn =

·

0.002 ² = 0.45 m
The method allows reliable electroslag remelting in the manufacture of bimetallic castings of rolling rolls at V _me ≅ 3 mm / s and fluctuations ΔН _gn up to 10-15%, which ensures high quality alloying of molten steel with bandages, and, therefore, high quality of bimetallic rolls.

 The implementation of the proposed method for producing bimetallic rolling rolls will allow an economic effect by increasing the operational resource, reducing the number of transhipments, increasing the strength characteristics of the fusion zone of the poured metal with a bandage, as well as reducing the cost of restoration.

Claims (1)

 METHOD FOR PRODUCING BIMETALLIC ROLLING ROLLS, including the installation of a seed electrode on the bottom of the mold, and in its cavity-bandage and coaxially from it at a distance of 5-100 mm from its inner surface - the solenoid electrode, guidance in the intermediate device of liquid slag, feeding it into a mold, melting the solenoid electrode, accumulating and supplying a liquid metal through an intermediate device, characterized in that during the melting of the solenoid electrode, a predetermined level of liquid metal is maintained in the industrial a daily device by continuously supplying liquid metal from a ladle, and a predetermined level of liquid metal in the intermediate device is maintained at a level not lower than 0.85 of the required design value.

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