KR100470662B1 - Method For Manufacturing Strip By Twin Roll Strip Caster - Google Patents

Abstract

The present invention relates to a method of manufacturing a thin plate by using a twin-roll thin plate casting apparatus for producing a thin plate by injecting molten metal between two cooling rolls and rapidly solidifying through contact with the roll, the nitrogen or oxygen of the roll edge portion Reduces the thickness of the gas layer and cuts off edge dam wear and oxidized scale from the side of the roll to increase the cooling capacity of both ends of the roll, thereby eliminating bulging or hot bands, which are abnormal solidification phenomena due to the solidification delay occurring at the edge of the roll. The purpose of the present invention is to provide a thin plate manufacturing method using a twin-roll thin plate casting machine that can improve the shape quality and error rate of the cast steel.

The present invention, in the method for producing a thin plate using a twin roll type sheet casting machine,

Roll surface edge portion of 0.023-0.08 W (W: roll width direction length) in the roll width center portion of the roll surface from the roll end and 0.032-0.12 R (R: roll radius) in the roll radius center direction of the roll surface. Double roll type to reduce the thickness of gas layer of roll edge part by giving vacuum degree of 1 torr or more on the roll side, and to absorb the edge dam abrasion and oxidized scale which flow into the edge part from the roll side part to increase the cooling ability of the roll edge part. Sheet metal manufacturing method using sheet casting machine is main point.

Description

Sheet manufacturing method using twin roll sheet casting machine {Method For Manufacturing Strip By Twin Roll Strip Caster}

The present invention relates to a method of manufacturing a thin plate by using a twin-roll thin plate casting apparatus for manufacturing a thin plate by injecting molten metal between two cooling rolls and rapidly solidifying through contact with the roll, and more specifically, the slab edge The present invention relates to a thin plate manufacturing method using a twin-roll thin plate casting apparatus that can improve the shape quality and the error rate of the cast through the prevention of hot band due to the coagulation delay generated in the part.

In general, the twin roll type sheet casting apparatus is formed of two rolls 1 and an edge dam 2 attached to the side of the roll through the nozzle 4 as the molten steel received in the tundish 3 as shown in FIG. 1. After the molten steel pool 5 is formed by supplying the space to be formed, the molten steel is rapidly solidified by heat flux into the inside of the roll through contact between the roll and the molten steel while rotating the rolls 1 in opposite directions. In the thickness direction of the cast slab produced by the apparatus, the profile is closely related to the shape of the outer surface of the roll in the casting space.

In FIG. 1, reference numeral 7 denotes a brush roll, 8 denotes a gas knife, and 9 denotes a meniscus shield.

The cast steel produced by the above process is ideally rolled in the cold rolling step, which is a post-treatment process, so that the flatness of the final product is good, the cross section of which is rectangular or slightly convex in the center.

In order to have such a cross-sectional shape of the cast steel, it is preferable that the bus bar of each roll is a straight line or a slightly concave shape in the roll 하는 which the two rolls 1 are closest to each other in the casting space.

However, in practice, since the roll is heated to a high temperature during casting, even when the roll has a completely straight busbar during cooling, the outer surface of the roll becomes convex due to thermal expansion, so that the plate thickness profile of the solidified slab is Since the cross-sectional shape of the casting space of the gap portion of the roll is accurately reproduced, a slab having a cross-sectional shape is made to be slightly thicker from the center to the edge.

The cast iron, which is a shape defect of the plate thickness profile, causes a rolling failure during cold rolling, which greatly reduces the quality and the real ratio of the final material.

In order to compensate for the thermal expansion of the casting roll as described above, it is common to provide a roll crown in a shape in which the roll width center portion 12 is flat or concave and the roll ends 13 are convex, as shown in FIG. In spite of being shown in FIG. 3, the central portion 11 of the cast steel is flat but ended by the bulging or hot band of unsolidified molten steel in the plate thickness center at both ends 10 of the cast steel. (10) has a rather thick shape, in which the temperature of the cast steel is relatively high compared to the center portion, so that both ends of the hot band generated as shown in FIG. 10) is distinguished from the central portion 11 and observed in bright colors.

As such, once a bulging or hot band phenomenon occurs at both ends 10 of the cast steel, it causes a serious problem that results in deterioration of the quality of the sheet and a decrease in error rate.

Therefore, not only in terms of stable operation but also in terms of improving the quality of the cast and improving the error rate, a technique of preventing bulging or hot band generation, which are unsolidified phenomena of both ends 10, is essential for the commercialization of sheet metal casting (S / C) processes. to be.

Until now, the methods for preventing the non-coagulation phenomenon of the above-described both ends 10 of the cast steel have been examined by various inventors from various angles.

In the early stage of the development of sheet casting process, it is judged that the bulging or hot band phenomenon of both ends 10 is caused by the relative deterioration of the coagulation ability of the roll itself at both ends of the roll. We tried to solve this problem by providing cooling differential in the width direction of.

Japanese Patent Laid-Open No. 6-297108 and Japanese Patent Laid-Open No. 6-328205 disclose a method of adjusting the cooling capacity by dividing a cooling channel into several in the width direction. The method of imparting a roll crown amount to a predetermined solid phase ratio at the center of thickness of both ends of the cast iron in rolls is proposed. As another method, Japanese Patent Application Laid-Open No. 9-327753 et al. Through the technique of adjusting the cooling capacity in the roll width direction has been proposed.

These methods can prevent the non-solidification of both ends of the cast steel under the same casting conditions as the cast rolls of the sheet casting machine or the same steel grade or cast steel thickness, but the target steel grade, cast steel thickness, casting size, heat size, etc. If there is a change, there is a problem of changing it to a proper condition.

Furthermore, even in the same casting conditions where the hot band pattern at both ends of the cast steel is very different depending on the edge dam material, the application method, or the type or composition of the atmosphere gas, the hot band at both ends of the cast steel becomes more severe as the casting time elapses. You cannot solve the problem of time dependency.

On the other hand, the present inventors have developed a method for adjusting the roll edge cooling ability by supplying nitrogen gas to Korean Patent Application No. 98-57611, and through on-line control of the thickness and composition of the gas film on the roll surface. The patent application of Korean Patent Application No. 99-42986 was developed to prevent the hot band phenomenon caused by the coagulation delay occurring in the edge of the cast.

MEANS TO SOLVE THE PROBLEM The present inventors made the research in order to solve the above-mentioned all the said prior art, and based on the result, this invention proposes this invention, and this invention reduces the thickness of the nitrogen or oxygen gas layer of a roll edge part, and roll side part part. Absorption of edge dam wear and oxidized scale that flows into the edge part in vacuum increases the cooling ability of both ends of the roll to prevent bulging and hot bands, which are abnormal solidification phenomena due to the solidification delay occurring at the edge of the cast steel. Not only can the error rate be improved, but it can effectively cope with the diversification of the steel grades.

It is to provide a thin plate manufacturing method using a twin-roll type sheet casting machine, the purpose is.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

According to the present invention, a pair of rolls rotating in opposite directions, an edge dam installed to form molten steel pools on both sides thereof, a meniscus shield 9 for supplying inert nitrogen gas to the molten steel upper surface, and the width of the rolls are provided. In the method of manufacturing a thin plate using a twin roll thin plate casting machine having a pair of gas knife (8) in the direction to cast a thin plate,

Roll surface edge portion of 0.023 -0.08W (W: roll width direction length) in the roll width center portion of the roll surface at the roll end and 0.032-0.12R (R: roll radius) in the roll radius center direction at the roll surface By providing a vacuum degree of 1 torr or more, preferably 1-0.1 Torr, on the side of the roll to reduce the thickness of the gas layer at the edge of the roll, and vacuum suction the edge dam wear and oxidized scale from the side of the roll to the edge. The present invention relates to a thin plate manufacturing method using a twin roll thin plate casting machine for increasing the cooling ability of the roll edge portion.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

FIG. 5 shows the behavior of the fluid present around the rotating roll.

The fluid behavior in FIG. 5 is a general phenomenon applicable to all fluids in which the target fluid is capable of mass transfer even by a small driving force.

FIG. 5 shows the nitrogen, which is an atmospheric gas, which is a factor directly affecting the hot band phenomenon at both ends of the slab during actual sheet casting, and the oxygen introduced from the outside, and the edge dam 2 and the roll side end face 14 The edge dam wear of ceramic material produced by abrasion and) and fine oxide scale powder dropped from roll surface or cast steel are shown.

6 shows the change in build-up of the edge dam wear and oxides attached to the casting roll surface and the center part after the actual casting is completed.

In general, as shown in FIG. 5, which shows a simulation result of fluid behaviour around a roll when the roll is rotated, when the roll is rotated, the roll surface, the side surface, and the roll shaft ( 25) Three different types of forces F1, F2, and F3 act on the surrounding fluid, and the driving force of these three forces is determined by the rotational speed of the rotor, physical properties of the fluid, and roll surface characteristics. The concentration of the fluid at the barrel edge is seen as a general phenomenon of the rotating roll, the amount or width 15 of the fluid concentrated at the edge is determined by the interaction of the driving forces F1, F2 and F3 in different directions.

That is, when there is no fluid supplied from the roll side, even if the driving force F2 does not exist, the driving force F3 exists, so that the fluid on the roll surface gradually moves to the edge of the roll side, whereby the fluid builds up. do.

When the fluid is continuously supplied from the roll side, a relatively large force F2 is generated, and the fluid concentration position or width at the edge portion is determined by the force balance of the F2 and F3 forces.

The influence of the fluid on the hot band phenomenon occurring at both ends of the slab in the sheet casting process is as follows.

Firstly, the gas film thickness of nitrogen gas on the surface of a rotating body such as a casting roll is not equal in thickness in the roll width direction, but is relatively thick at both ends of the roll, thereby greatly reducing the cooling ability of the roll. Hot bands are generated due to uncoagulation at.

Secondly, the casting roll side portion and the roll shaft are in direct contact with the atmosphere. The oxygen gas in this portion is moved to the roll edge surface through the path as shown in FIG.

Since the oxygen gas is an expandable gas having low solubility in molten steel, the adhesion between the coagulation shell and the roll is not only greatly reduced, but also the coagulation performance is greatly reduced, which promotes oxidation of the coagulation shell. do.

Third, a large amount of roll surface oxidation scale formed by side ceramic rolls installed to remove fine ceramic wear powder and roll surface contaminants caused by abrasion between the side portion of the rotating roll and the edge dam, or an oxidation scale dropped from the slab, etc. Fluid with a large heat transfer resistance is continuously supplied, and this fluid builds up at the side edge of the roll, thereby greatly reducing the solidification performance between the solidification shell and the roll.

In general, it is known that the boundary layer thickness δ of the fluid formed on the flowing flat plate is proportional to the square root of the Reynolds number of the gas as shown in the following equation (1).

Where υ is the kinematic viscosity of the gas, x is the distance from the tip of the plate, and Vp is the moving speed of the plate.

In addition, the type and film thickness of the fluid present between the roll and the molten steel have a great influence on the solidification shell formation.

Factors that dominate the heat flux between molten steel and roll during sheet casting are heat resistance, which includes the roll body, gas film between roll and molten steel, oxide film or ceramic powder, and overall heat transfer between molten steel and roll at the top. Coefficient h is represented as following formula (2).

  h = 1 / dr / kr + dg / kg + ds / ks + dc / kc

Here, d is thickness, k is heat transfer rate, subscript r is roll, g is gas, s is oxide film on molten steel surface, c is ceramic powder with very high heat resistance such as oxide scale powder or edge dam wear powder.

Formula (1). From (2), it can be seen that the total heat transfer coefficient varies greatly depending on the type and composition of the gas present between the roll and the molten steel, the type and thickness of these gas layers, the type and thickness of the oxide film, and the type and thickness of the ceramic wear powder. Even with the same gas composition, the overall heat transfer coefficient decreases rapidly as the gas film thickness δ increases, and as the cumulative degree of oxide layer or ceramic wear powder increases. That is, the heat accumulation resistance 16 (FIG. 6) at both ends of the roll side is very large in heat transfer resistance between the roll and the solidification shell compared with the center portion of the roll width, and thus, it is determined that bulging or hot band, which is an unsolidification phenomenon, is generated.

In addition, the simulation results of the fluid behavior showed a good agreement with the hot band generation at both ends of sheet casting during thin plate casting.

As mentioned above, both edges of the roll are caused by the above three causes, that is, by increasing the thickness of the nitrogen gas layer at the roll edge, by introducing oxygen from the roll side and the wear build-up between the roll side and the edge dam. Compared to this, the decrease in cooling capacity is remarkable, and non-coagulation phenomenon such as bulging or hot band occurs, and as the casting time elapses, the hot band gradually increases due to edge build-up of a material having high heat resistance.

The present invention intends to prevent the non-coagulation phenomenon such as the bulging or hot band described above, the present invention will be described in detail with reference to FIGS.

An example of an apparatus for preventing slab edge portion hot band for implementing the present invention is shown in FIGS. 7 and 8.

As shown in Figs. 7 and 8, the slab edge portion hot band prevention device 24 for implementing the present invention is provided at both ends of a pair of rolls to pass the molten steel to produce the slab 6 while rotating in the opposite direction Each of them is configured to reduce the thickness of the nitrogen or oxygen gas layer of the roll edge portion, and vacuum suction the edge dam wear and oxide scale flows from the roll side portion into the edge portion to increase the cooling ability of both ends of the roll.

The slab edge part hot band prevention device 24 is provided in the both ends of each said roll in the same structure, the same code | symbol is attached | subjected about the same member, and only one side is demonstrated.

As shown in FIG. 7, the slab edge portion hot band prevention device 24 includes a vacuum suction chamber 17 having an empty internal space, and one end of the vacuum suction chamber 17 has a vacuum pump 20. Connected to the vacuum suction tube 19 is connected.

The portion of the vacuum suction tube 19 connected to the vacuum suction chamber is preferably configured to have a plurality of branch pipes as shown in FIG.

The vacuum suction chamber 17 is preferably shaped like a 'c'.

In addition, the vacuum suction chamber 17 is installed in a 'c' shape so as to maintain a gap between the roll surface edge portion and the roll end face 14 at a predetermined interval, preferably about 1-3 mm.

In addition, the end of the vacuum suction chamber 17 in the longitudinal direction (the circumferential direction of the roll) is close to the meniscus shield 9, the opposite side is installed so as not to block the roll end face 14 and It is preferable to be configured to effectively suck in oxygen, edge dam wear, and oxide scale layer attached to the roll shaft to move to the roll side barrel.

The vacuum suction chamber 17 has a roll surface edge of 0.023 -0.08 W (W: roll width direction length) in the roll width center direction of the roll surface at the roll end and 0.032-0.12 R in the roll radius center direction at the roll surface. It is preferable to be comprised so that the said roll surface edge part and roll side part corresponding to 0.075D (D: circumferential length) or more at least in the circumferential direction of a roll among the roll side parts to (R: roll radius).

More preferably, the vacuum suction chamber 17 has a roll surface edge portion of 0.023-0.039W in the roll width center portion of the roll surface at the roll end and a roll side portion of 0.035-0.04R in the roll radius center direction at the roll surface. It is configured to surround the roll surface portion and the roll side portion corresponding to at least 0.075-0.085D in the circumferential direction of the roll.

In addition, the frame of the vacuum suction chamber 17 is made of a material having high heat resistance and high strength (for example, STS304 steel), and the contact portion between the 'c' shaped opening, the roll surface, and the roll end face is a roll surface. Wool O-ring (Wool 0) made of cotton that does not burn and crack very quickly even if it comes into direct contact with the roll surface due to malfunction without causing scratches on the roll surface due to abrasion. -ring) 26 is preferably inserted into the frame by digging into the groove.

The wool O-ring is made of 100% cotton, the diameter is preferably about 5-7mm.

In the vacuum suction tube 19 between the vacuum suction chamber 17 and the vacuum pump 20, it is preferable to include a vacuum capacity control valve 19.

In addition, it is preferable to provide the controllers 21 and 22 which can individually control the operation and the vacuum capability of the vacuum suction units installed in the four side portions of each of these rolls, and the central controller 23 which can adjust them in conjunction.

A method of preventing the occurrence of the slab edge portion hot band by providing the slab edge portion hot band prevention device configured as described above will be described.

Before casting operation, caster edge hot band prevention device is properly installed so that the open two parts of the vacuum suction chamber are maintained at the surface of the roll and the side surface of the roll 1-3mm.

At this time. During casting, the steel sheet is properly adjusted so as not to be in contact with the outer surface of the roll which is thermally expanded due to the high temperature of molten steel and the volume is expanded.

Simultaneously with the start of casting, the vacuum pump 20 is operated, while observing whether hot bands are generated in the edge portion of the cast steel and interlocking the vacuum capacity control valve 19 installed at the four sides of the roll side by the vacuum controller central controller 23.

At this time, if one edge part of the slab is observed hot spot generation compared to the other edge part, the vacuum capacity of the part is increased, and if excessive vacuum suction is caused by black band (over-solidification phenomenon) at the edge part. ) When this black band is observed, the black band is released by reducing the vacuum capacity.

The degree of vacuum in the vacuum suction chamber 17 is preferably 1 Torr or more, more preferably 1 to 0.1 Torr.

In general, as described above, as the casting time elapses, wear and oxide scale accumulated between the roll side portion 14 and the edge dam 2 accumulate. The control valve 19 is used to increase the vacuum capability of the vacuum pump 20 to operate to prevent hot band generation in advance of the slab edge portion.

As described above, the present invention is to control the thickness of the nitrogen gas layer of the atmospheric gas at the fluid accumulation concentration of the both edges of the roll at the same time as the casting operation, to block the oxygen gas introduced from the outside and to continue to be generated on the roll side surface to contaminate the roll surface Vacuum suction of edge dam wear and oxidized scale prevents abnormal solidification such as bulging or hot band due to solidification delay occurring in the edge of cast steel during casting, so that the product of good shape at both ends of cast steel can be obtained. In addition to improving the error rate, it is also possible to effectively cope with changes in the cast steel grade.

1 is a schematic diagram of a general twin roll type sheet casting apparatus

Figure 2 is a schematic view of the roll shape with the crown of a typical twin roll sheet caster

Figure 3 is a schematic view of the cast slab shape produced on both ends hot band cast in a general twin-roll sheet caster

FIG. 4 is a photograph of a hot strip in which hot bands, which are unsolidified phenomena of the slab edges, are observed. FIG.

FIG. 5 is a schematic view showing fluid behavior of roll surface, side and surroundings in a typical twin roll sheet casting machine

6 is a change in the concentration of contaminants attached and formed on both sides of the roll side and the central surface after completion of casting in general sheet casting

7 is a side schematic view of a twin roll sheet caster equipped with a slab edge portion hot band prevention device according to the present invention;

Figure 8 is a detailed view of the vacuum suction chamber of the slab edge hot band prevention device according to the present invention

Explanation of symbols on the main parts of the drawings

One . . . Roll 2. . . Edge dam 9. . . Meniscus shield 10. . . Cast edge hot band generator 14. . . End face of the roll 15. . . Fluid band with roll surface 16. . . Fluid accumulation concentration at both ends of roll surface 17. . . Vacuum suction chamber 18. . . Hoses for vacuum inhalers 19. . . Vacuum Control Valve 20. . . Vacuum pump 24. . . Hot band prevention device for cast edge 25. . . Roll shaft 26: wool 0-ring

Claims (2)

A pair of rolls rotating in opposite directions, an edge dam installed to form molten steel on both sides thereof, a meniscus shield 9 for supplying inert nitrogen gas to the upper surface of the molten steel, and a pair in the width direction of the roll. In the method of manufacturing a thin plate by using a twin roll thin plate casting machine for casting a thin plate with a gas knife (8) of Roll surface edge portion of 0.023-0.08 W (W: roll width direction length) in the roll width center portion of the roll surface from the roll end and 0.032-0.12 R (R: roll radius) in the roll radius center direction of the roll surface. Provides a degree of vacuum of at least 1 torr on the side of the roll to reduce the thickness of the gas layer at the edge of the roll, and vacuums the edge dam wear and oxide scale from the side of the roll to the edge to increase cooling capacity of the roll edge. Sheet manufacturing method using double roll type sheet casting machine The method of manufacturing a thin plate using a twin roll plate casting machine according to claim 1, wherein the vacuum degree is 1 to 0.1 Torr.