KR101620699B1 - Casting roll for twin-roll strip caster - Google Patents

Abstract

The present invention relates to a casting roll of a twin roll type thin plate casting machine, and in a casting roll of a twin roll type thin plate casting machine in which a plurality of fine grooves are formed on a surface thereof, fine grooves are formed in the widthwise edge portion of the casting roll Thus, even if the solidification shell is caught, it is possible to easily fall off, thereby preventing the surface defects of the casting member, and ultimately improving the quality and the product rate of the product.

Description

[0001] Casting rolls for twin-roll strip caster [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting roll of a twin roll thin plate casting machine, and more particularly to a casting roll of a twin roll thin plate casting machine capable of improving the quality of a leading edge in a casting piece and securing casting stability.

In general, a so-called strip casting method using a twin roll thin plate casting machine is a method of casting molten steel between two rotating casting rolls through a nozzle from a tundish molten steel to produce a thin casting piece having a thickness of about 2 to 6 mm It is possible to reduce the production cost by shortening the process time and improve the product quality by rapid solidification, and thus it has been intensively studied in the steel process.

1 is a view schematically showing a twin roll type thin plate casting machine. As shown, the molten steel contained in the ladle 1 is supplied to the sump 4 through the tundish 2 and the immersion nozzle 3. The molten steel supplied to the sump 4 is cast into a thin plate passing between the two casting rolls 5.

When the molten steel in the sump 4 surrounded by the two casting rolls 5 and the edge dam 6 is exposed to the atmosphere, the molten steel is oxidized and the resulting oxide significantly affects the quality of the product. Therefore, The meniscus shield 7 is placed on the upper portion of the sump 4 so as to cover the sump 4 with the atmosphere gas.

Thus, a space defined by the molten steel bath surface, the casting roll 5, and the edge dam 6 is formed in the upper portion of the sump 4. The atmosphere gas is supplied to this space to prevent oxidation of molten steel.

The molten steel fed into the sump 4 is cooled at the surface of the casting roll 5 to form a solidified shell and is assembled at the latest contact points of the casting rolls to produce a cast piece. In this case, since the molten steel is formed as a solidified shell after completion of contact with the casting roll 5 within a short time and forms a cast piece after exiting the casting roll 5, the surface of the cast piece is subjected to rapid thermal stress .

Therefore, when the surface of the casting roll 5 is flat, the surface of the casting roll and the solidifying shell are locally lifted by the atmospheric gas, whereby non-uniform solidification is promoted due to a difference in heat transfer, and cracks may occur in the solidifying shell.

In order to solve such a problem, casting roll surface treatment methods have been proposed in which roughness is formed on the surface of a casting roll or dimples are formed.

For example, Korean Patent No. 1372741, filed and filed by the present applicant for a patent, discloses a method for manufacturing a high nitrogen duplex stainless steel containing 1500 ppm or more of nitrogen using a twin roll thin plate casting machine to prevent surface defects (dent, depression, etc.) A method of surface treatment of cast rolls is proposed.

In this patent, a fine groove is formed on the surface of the casting roll in order to discharge the nitrogen gas generated during solidification. As a method of forming the fine groove, an etching method having advantages in terms of precision and economy is applied.

However, when the fine grooves are processed over the entire width of the casting roll by applying the etching method, when the coagulated shell (hereinafter referred to as skull) locally overcoated during casting is mixed and passes through the roll nip, As a result, it sticks to the fine grooves and sticks to the surface of the casting roll.

As shown in Fig. 2, such a sticking causes a drop at the tip end of the cast piece, and the remaining piece that has fallen off from the cast piece is ridden on the casting roll while being attached to the casting roll, Is gradually getting worse. As a result, the casting has to be stopped due to the incorporation of the residue.

Accordingly, it is a main object of the present invention to provide a casting roll of a twin roll type casting machine capable of improving the quality of a leading end portion of a casting piece and securing casting stability.

The casting roll of the twin roll thin plate casting machine according to the present invention is a casting roll of a twin roll type thin plate casting machine having a plurality of fine grooves formed on the surface thereof, Wherein the second fine grooves are formed by etching the remaining portions of the casting roll except for both edge portions of the casting roll, and the first fine grooves of the edge portion have a depth of 200 to 300 탆 do.

As described above, according to the present invention, when a casting piece is manufactured using a twin roll thin plate casting machine, the fine groove of the casting roll has an inverted triangular cross-sectional shape, It is possible to prevent defects and ultimately improve the quality and the rate of error of the product.

Further, according to the present invention, there is solved the problem that the remaining pieces separated from the casting pieces adhere to the casting rolls and are remarried at the casting rolls and gradually fall off at the front end of the casting pieces, so that the casting stopping rate is greatly reduced, The effect of increasing the temperature is obtained.

1 is a view schematically showing a twin roll type thin plate casting machine.
2 is a photograph showing examples of surface defects caused by dropout at the tip end of a casting piece.
3 is a perspective view showing a casting roll according to the present invention.
4 is a cross-sectional view showing a casting roll according to the first embodiment of the present invention.
5 is a cross-sectional view showing a casting roll according to a second embodiment of the present invention.
6 is a graph showing the relationship between the etching depth at the time of etching the fine grooves and the protrusions formed at the edges of the fine grooves.
7 is a photograph showing the tip of a casting piece manufactured using the casting roll according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 3 is an enlarged perspective view of a casting roll according to the present invention, and FIG. 4 is a sectional view showing a casting roll according to the first embodiment of the present invention.

As shown in these figures, the casting roll 10 of the twin roll type thin plate casting machine according to the first embodiment of the present invention is a casting roll of a twin roll type thin plate casting machine having a plurality of fine grooves formed on its surface, The first fine grooves 14 are formed in the widthwise edge portions 12 of the first and second trenches 10 so as to have an inverted triangular cross-sectional shape. In Fig. 4, reference numeral 11 denotes a cast piece.

In this specification, the edge portion 12 of the casting roll 10 is defined as a portion within approximately 30 mm from the widthwise end of the casting roll, and the portion excluding both edge portions in the casting roll is referred to as the intermediate portion 16 for convenience.

For example, in the case of producing a thin plate made of duplex stainless steel or high manganese steel containing 2000 ppm or more of high nitrogen, there is a problem in that the discharge is not smooth due to a large amount of gas emission, and thus surface defects (dent, depression, Cracks, etc.) may occur.

Accordingly, in the first embodiment of the present invention, the first fine grooves 14 are formed to have an inverted triangular cross-sectional shape so that the gas can be easily discharged to prevent surface defects, . Some of these cross-sectional shapes may be formed to have somewhat rounds depending on the processing method. As a result, sticking of the solidifying shell to the surface of the casting roll is prevented.

At this time, the first fine grooves 14 have an angle? Between approximately 30 and 70 degrees and a depth D of approximately 200 to 300 占 퐉. In the fine grooves having the same angle of inclination, the depth of the fine grooves is advantageous for the gas discharging ability. However, when the depth exceeds 300 탆, the width of the mountains on the roll surface remaining after machining at the same pitch The molten steel penetrates into the fine grooves to narrow the gas discharge passage, resulting in surface defects.

Conversely, if the depth of the fine grooves is less than 200 μm, as described above, when the discharge amount is large, the gas discharge is not smooth and surface defects may occur.

As an example, duplex stainless steel having the composition shown in Table 1 below was prepared and used in thin sheet casting.

Alloy component C Si Mn P S Cr Ni Mo N Content (wt%) 0.02 to 0.1 0.5 to 1.5 1-5 0.03 or less 0.02 or less 19-23 1 to 6.5 0.5 to 3.5 0.1 to 0.3

In order to control the atmosphere during casting, the melt surface of the molten steel was sealed using the meniscus shield (7) shown in FIG. 1, and nitrogen gas was supplied to the upper part of the melt surface as atmosphere gas to have a pressure of about 200 mmAq. Table 2 shows the surface conditions of the edge portion of the casting roll used at this time. Table 2 also shows the occurrence of penetration of molten steel, the occurrence of sticking and the occurrence of depression according to the surface conditions of the edge portion of the casting roll.

Fine groove
Angle between
(°) Fine groove
depth
(탆) Fine groove
pitch
(탆) Fine groove
width
(탆) gas
Emission capacity (G) Penetration of molten steel
Occurrence Depression
Occurrence Cling
Occurrence effect 90 150 700 383 49 radish U radish Poor 200 700 483 80 U U radish Poor 250 700 583 118 U U radish Poor 300 700 683 168 U U radish Poor 70 150 700 314 44 radish U radish Poor 200 700 384 69 radish radish radish good 250 700 454 99 radish radish radish good 60 150 700 289 42 radish U radish Poor 200 700 346 64 radish radish radish good 250 700 404 91 radish radish radish good 300 700 462 122 radish radish radish good 30 150 700 234 38 radish U radish Poor 250 700 287 76 radish radish radish good 300 700 314 97 radish radish radish good

In Table 2, the G value represents the gas discharge capacity, which has the relationship of G = A / P. Here, A is the cross-sectional area (μm ² ) of the fine grooves, and P is the pitch (μm) of the fine grooves.

As can be seen from Table 2, it was confirmed that surface defects do not occur when the G value is 60 or more. In the edge portion 12 of the casting roll 10 according to the first embodiment of the present invention, It can be seen that the size of the groove 14 is preferably determined when the angle? Between the fine grooves is between 30 and 70 degrees.

Fig. 7 is a photograph showing the tip of the casting roll manufactured using the casting roll according to the present invention. In this case, the edges of the casting roll have an angle of 60 deg. Of the first fine grooves in the surface condition of Table 2, , A width of 404 mu m, and a G value of 91. As described above, according to the casting roll of the first embodiment of the present invention, surface defects are eliminated at the tip end of the casting member, thereby improving the quality of the product and the yield of the product.

Particularly, when comparing the before and after application of the casting roll according to the first embodiment of the present invention, the casting abandonment rate caused by the dropping of the residue due to the sticking and the re-marriage of the residue is remarkably reduced from 65% to 5% It can be confirmed that it is improved.

In the casting roll according to the first embodiment of the present invention, the first fine groove of the edge portion can be manufactured by any known method, and is not particularly limited. However, in consideration of excellent precision, it is more preferable that the first fine groove of the edge portion is machined by using a machine tool such as a lathe. Of course, not only the first fine groove of the edge portion but also the fine groove of the entire casting roll may be machined.

On the other hand, a processing method in which a laser having a high energy is irradiated to the surface of a casting roll and then a fine groove is formed by chemical etching may be applied to the casting roll.

FIG. 5 is a cross-sectional view showing a casting roll according to a second embodiment of the present invention, and FIG. 6 is a graph showing the relationship between the etching depth and the protrusions formed at the edges of the fine grooves in the etching process of the fine grooves.

As shown in these figures, the casting roll 10 of the twin roll type thin plate casting machine according to the second embodiment of the present invention is a casting roll of a twin roll type thin plate casting machine having a plurality of fine grooves formed on its surface, The second fine grooves 24 can be processed by etching so that the remaining portions other than the edge portions 12 of the casting roll 10, that is, the intermediate portion 16, The depth D of the second fine grooves 24 is greater than 0 and equal to or less than 175 占 퐉 in the portion in the range of 50mm. In Fig. 5, reference numeral 21 denotes a cast piece.

The casting roll according to the second embodiment of the present invention can be processed by an etching method. In this case, the cross-sectional shape of the second fine grooves is formed roughly in the shape of a jar do.

Furthermore, it has been confirmed that the cause of the coagulation shell being caught in the casting roll is due to the shape of the fine grooves caused by the etching depth. More specifically, as the etching depth increases, the size of the protrusions formed at the corners of the fine grooves increases As a result, the solidification shell is easily caught, and the solidification shell is not pulled out by the projections, so that the dropping phenomenon occurs at the end of the casting.

Accordingly, in the casting roll 10 according to the second embodiment of the present invention, the size of the projections 28 formed at the corners of the second fine grooves 24 is preferably larger than 0 and smaller than 15 탆. Here, the size of the projection is defined as a length protruding in the normal direction from the side wall of the second fine groove. The size of the protrusion 28 formed at the edge of the second fine groove at the time of etching can be controlled by limiting the depth D of the second fine groove 24. Therefore, the depth of the second fine grooves is determined to be greater than 0 and smaller than or equal to 175 μm by the curve shown in FIG.

By thus restricting the depth of the second fine grooves 24 around the edge portion 12 of the casting roll 10 and the size of the projections 28 formed at the corners, Even when the solidification shell is caught in the second fine grooves 24 of the casting roll at the time of manufacture, the solidification shell easily falls off from the casting roll because the force to catch the solidification shell is weak. As a result, it is possible to prevent the surface defects of the cast pieces, especially the tip portions thereof, and to improve the quality and the yield of the product.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention.

For example, instead of a configuration in which the depth of the fine groove described in the second embodiment of the present invention is more than 0 and not more than 175 탆 is formed such that the fine groove has an inverted triangular cross-sectional shape, . In this case, the fine grooves in the intermediate portion of the casting roll may have a depth of about 0 or more and 300 탆 or less.

Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

10: casting roll 11, 21: casting piece
12: edge portion 14, 24: fine groove

Claims (9)

A casting roll of a twin roll type thin plate casting machine having a plurality of fine grooves formed on its surface,
A first fine groove is formed by machining so as to have an inverted triangular cross-sectional shape in a width direction edge portion of the casting roll,
The remaining portions of the casting roll other than the edge portions are etched to form the second fine grooves,
Wherein the first fine groove of the edge portion has a depth of 200 to 300 占 퐉. The method according to claim 1,
Wherein an edge portion of the casting roll is a portion within 30 mm from a widthwise end of the casting roll. delete The method according to claim 1,
Wherein the first fine groove of the edge portion has an angle of 30 to 70 degrees. 5. The method of claim 4,
Wherein the first fine groove has a gas emission capability of 60 or more,
The gas discharge performance has a relationship of G = A / P,
Wherein G is a gas discharge performance, A is a sectional area (μm ² ) of the fine grooves, and P is the pitch (μm) of the fine grooves. delete delete The method according to claim 1,
Wherein a depth of the second fine groove is more than 0 and not more than 175 탆 at a portion in a range of 30 to 50 mm from a widthwise end of the casting roll. The method according to claim 1,
The size of the protrusion formed at the edge of the second fine groove is greater than 0 in the normal direction from the side wall of the second fine groove and not more than 15 mu m in the range of 30 to 50 mm from the widthwise end of the casting roll, Wherein the casting roll of the twin roll type thin plate casting machine is a casting roll.

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