JP3095679B2 - Cooling drum for continuous casting of thin cast slab and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling drum of an apparatus for continuously casting thin cast slabs from molten metal and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a device for continuously casting a thin cast piece having a thickness of about 1 mm to 10 mm, a twin-drum continuous casting device having a pair of cooling drums or a single-drum continuous casting device having one cooling drum. 2. Description of the Related Art A casting apparatus, a drum-belt type continuous casting apparatus including a cooling drum and a belt, and the like are known.

FIG. 2 shows an example of the cooling drum. The body of the cooling drum 1 is composed of a sleeve 3 and a base 4, and a rotating shaft 2 is connected to both sides of the body. A large number of cooling water passages 5 are provided in the sleeve 3 over the entire peripheral surface 8 of the cooling drum, and the cooling water C is discharged from the inlet 6 through the cooling water passage 5 through the outlet 7. Pumped. The amount of heat of the molten metal in contact with the peripheral surface 8 of the cooling drum is absorbed by the cooling water C via the sleeve 3 and discharged out of the system.

In order to quickly release heat from the molten metal, a material having good heat conductivity, such as copper or a copper alloy, is often selected as the material of the sleeve 3. As shown in FIG. 4, the outer peripheral surface of the sleeve 3 is formed of a plating layer 10 made of nickel, cobalt, or the like, which has poorer heat conduction and higher mechanical durability than the sleeve 3 in order to adjust the cooling rate of the thin cast slab. Is often formed as an outer protective layer.

One of the problems in the continuous casting using the cooling drum as described above is that the cooling drum 1 is heated by the molten metal and thermally expanded and bulges into a barrel shape, so that the shape of the thin cast slab becomes inferior. The cooling rate of the thin slab over the width direction becomes uneven, and defects such as cracks and wrinkles occur on the surface of the thin slab.

[0006] In order to solve the above-mentioned problem relating to the shape of the thin cast slab, a method of offsetting the thermal expansion by providing a drum-shaped drum crown having a concave center in the cooling drum 1 has been proposed.
It is disclosed in JP-A-61-37354. According to this method, the crown amount of the thin cast slab can be adjusted by adjusting the drum crown amount, and when the crown amount is adjusted by other than this method, the rolling process after casting becomes extremely complicated, and the cost increases. Become. Therefore, in a continuous casting apparatus using a cooling drum, the cooling drum 1
It is necessary to apply a drum-shaped drum crown to the drum.

However, even when a thin cast piece is cast using a cooling drum provided with a drum-shaped crown on the peripheral surface, it has been impossible to make the cooling rate in the width direction of the thin cast piece quite uniform. In some cases, cracks and wrinkles occurred on the surface of the thin cast slab. Since surface cracks and wrinkles on thin cast slabs significantly impair product quality, a large amount of trimming and surface grinding are required to avoid them, resulting in problems such as complicated processes and reduced yield. .

Therefore, it is necessary to make the cooling rate in the width direction of the thin slab more uniform, but as a related method, a cooling water passage is divided into a plurality of sections in the direction of the rotation axis of the cooling drum. In addition, there is known a method of making the cooling capacity different for each section. For example, JP-A-6-29710
No. 8 discloses a method in which the distance of the cooling water passage from the peripheral surface of the cooling drum differs for each section. Also, Japanese Patent Application Laid-Open No. 6-328205 discloses a method in which the density of the cooling water pipe differs in each section. As another method, Japanese Patent Application Laid-Open No. 4-344852 discloses a method in which a plurality of spray nozzles are provided inside a cooling drum and the amount of cooling water jetted from the spray nozzles varies in the width direction of the cooling drum. .

However, the method of adjusting the amount of cooling water inside the cooling drum complicates the apparatus and increases the cost. In addition, the cooling water passage and the amount of cooling water are finely adjusted for a slight temperature change of the molten metal or the cooling water. This is complicated and extremely difficult to implement.

Japanese Patent Application Laid-Open No. 55-86660 discloses a method in which the inner surface of a sleeve is formed so that the inner surface of the sleeve is thicker at the center and gradually thinner from the center toward both sides. Japanese Patent Application Laid-Open No. 4-253551 discloses a method for processing the inner surface near the sleeve corner to reduce the thickness near the sleeve corner, and a method for forming the protection on the outer peripheral surface of the sleeve. A method of reducing the thickness of the layer near the sleeve corner is disclosed.

However, the method of processing the inner surface of the sleeve requires a complicated processing method and has a problem in processing accuracy, and the method of adjusting the thickness of the protective layer in the vicinity of the sleeve corner causes cooling of the thin cast slab in the width direction. The speed cannot be made sufficiently uniform.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a method for continuously casting thin slabs using a cooling drum provided with a drum-shaped crown on the peripheral surface thereof. The aim is to homogenize over

[0013]

As described above, a drum-shaped drum crown is provided on the peripheral surface of the cooling drum 8 as shown in FIG. 3, but is shown in a portion 9 surrounded by a dotted line in FIG. As described above, the drum crown amount of the cooling drum 1 is provided so as to increase as approaching both ends of the cooling drum 1. Hereinafter, this portion is referred to as an arc-shaped portion 9 of the drum crown.

The present inventor has investigated the growth of the solidified shell 12 on the peripheral surface 8 of the cooling drum over the width W direction of the cooling drum 1. As a result, the solidification of the thin cast slab was delayed in the arcuate portion 9 of the drum crown. found. The reason is described below.

The solidified shell 12 is formed and grown on the peripheral surface 8 of the cooling drum. At this time, the solidified shell 12 contracts in the direction of the arrow S as the temperature decreases. Due to this contraction force, both ends of the solidified shell 12 are lifted from the peripheral surface 8 of the cooling drum. When casting a thin cast slab, the solidified shell 12
Is thin and has high strength because of high temperature, and easily deforms. Further, since the molten metal directly touches the cooling drum 1, the solidified shell 12 is rapidly cooled, so that the contraction force is extremely large.
For this reason, when casting a thin cast slab, the solidified shell 12
The rise of appears remarkably. This lifting increases with an increase in the width W of the cooling drum 1, that is, with the width of the thin cast slab, and increases with an increase in the drum crown amount.

As described above, the solidified shell 12 serves as the cooling drum 1
, A gas gap G is generated between the cooling drum 1 and the solidified shell 12. Although the size of the gas gap G is as small as at most several tens of μm, the increase in heat transfer resistance due to this is not negligible. As a result, the cooling rate at both ends of the cooling drum 1 is lower than at the center in the width.

Further, since the generation of the gas gap G appears remarkably in the arcuate portion 9 of the drum crown, the growth of the solidified shell 12 is particularly delayed in the arcuate portion 9 of the drum crown,
Defects such as surface cracks and wrinkles of the thin cast slab occur.

In the conventional cooling drum shown in FIG. 3, as shown in FIG. 4, a plating layer 10 is formed on the outer peripheral surface of a sleeve 3 having a cylindrical shape (in FIG. 4, it is flat because of a cross section in the rotation axis direction of the cooling drum). After the formation, the plating layer 10 is ground to give a drum-shaped crown, so that the thickness of the plating layer 10 having poor heat conduction is thicker at both ends of the cooling drum 1 than at the center, and the cooling drum 10 Had a small cooling capacity at both ends.

As a result of the above investigation by the present inventor, in order to make the growth of the solidified shell 12 uniform in the width direction, the heat transfer resistance is increased by the gas gap G generated between the cooling drum 1 and the solidified shell 12. It is important to adjust the cooling capacity in the width direction of the cooling drum 1 so as to compensate for the above, and it is also important to smoothly adjust the cooling capacity in the width direction of the cooling drum 1 following the change in the drum crown. It turned out to be.

The cooling capacity of the cooling drum 1 is governed by the thermal conductivity of the material constituting the sleeve 3 and the plating layer 10 and the thickness of the material. Of course, the smaller the thermal conductivity and the greater the thickness of the material, the greater the heat transfer resistance. However, it is extremely difficult to smoothly change the thermal conductivity of the material forming the sleeve 3 and the plating layer 10 across the width of the cooling drum 1. Therefore, the present invention is configured such that the thickness of the plating layer 10 having a smaller heat conductivity and a larger heat transfer resistance than the sleeve 3 becomes thinner from the center of the cooling drum 1 toward both ends.

[0021]

FIG. 1 shows an embodiment of a cooling drum according to the present invention. In FIG. 1, a drum-shaped drum crown is provided on the outer peripheral surface of a sleeve 3 made of copper or a copper alloy, and a plating layer 10 of nickel, cobalt, or the like having a lower thermal conductivity than the sleeve 3 is formed. I have. A drum-shaped crown is also provided on the surface of the plating layer 10.

At this time, it should be noted that since the solidification is delayed at the end of the cooling drum 1 as compared with the center of the width as described above, the cooling capacity at the end of the cooling drum 1 is made larger than that at the center. It is necessary. For this reason, it is important that the crown amount of the joint interface 11 between the sleeve 3 and the plating layer 10, that is, the crown amount of the sleeve 3, is larger than the crown amount of the outer peripheral surface of the cooling drum 1, that is, the surface of the plating layer 10. When the crown amount is adjusted in this manner, the thickness of the plating layer 10 is smaller at both ends than at the center of the cooling drum 1, so that the cooling capacity of both ends of the cooling drum can be increased, and the air gap G can be increased. Can compensate for an increase in heat transfer resistance.

In the manufacture of the cooling drum, the peripheral surface of the sleeve 3 is processed by a method such as grinding to give a drum-shaped crown to the peripheral surface of the sleeve 3 according to the required cooling capacity. The plating layer 10 is formed by plating the peripheral surface of No. 3 and then the surface of the plating layer 10 is processed by a method such as grinding to give a drum-shaped crown.

Assuming that the crown amount at the outer peripheral surface 8 of the cooling drum is A and the crown amount at the joint interface 11 between the sleeve 3 and the plating layer 10 is B, B / A is adjusted to a range of 1.1 to 4.0. It is desirable to do. This is because the thickness of a thin cast slab cast by a continuous casting device using a cooling drum is generally in the range of 1 mm to 10 mm. In this case, if B / A is less than 1.1, the air gap compensation becomes insufficient. sell. On the other hand, if it exceeds 4.0, thermal strain in the shear direction is accumulated at the joint interface between the sleeve and the plating layer, and peeling of the joint interface may occur.

As described above, according to the cooling drum of the present invention, the cooling capacity in the width direction of the cooling drum can be made uniform without requiring a complicated cooling mechanism and adjustment of the amount of cooling water. A slab can be easily obtained.

[0026]

EXAMPLES The effects of the present invention will be described below based on examples. The thin cast slab was cast using a twin-drum continuous casting apparatus. Thin cast slab is made mainly of 18Cr-8Ni SU
S304 steel, 3mm thick at a casting speed of 65m / min
Was cast. The diameter of the cooling drum used was 12
00 mm and width is 1000 mm. The sleeve of the cooling drum is made of copper, and its surface is plated with nickel having a purity of 99% and the remainder being inevitable impurities. The thickness of the sleeve and the plating layer and the crown amount at the peripheral surface of the cooling drum and at the interface between the sleeve and the plating layer were adjusted to the values shown in Table 1. The processing of the crown was performed with an NC lathe, and the crown amount was measured by scanning in the width direction of the cooling drum using a non-contact type distance meter.

[0027]

[Table 1]

Next, the casting results and the properties of the obtained thin cast slabs will be described with reference to Table 1. First, when casting was performed using a cooling drum as shown in FIG. 4 (Experiment Nos. 1 and 2), surface cracks occurred at both ends of the thin cast piece corresponding to the arc-shaped portion of the drum crown. When the thickness of the plating layer was large (Experiment No. 2), a breakout occurred at a position corresponding to the arc-shaped portion of the drum crown, and the casting was stopped. Next, when casting was performed by a cooling drum as shown in FIG. 1 (Experiment Nos. 3 and 4), the casting was stably performed, and cracks and wrinkles did not occur in the thin slab.

[0029]

As described above, according to the present invention, the cooling capacity over the width direction of the cooling drum is made uniform by the simple means of processing the surface of the sleeve and the plating during the production of the cooling drum. It is possible to stably obtain a thin cast piece having good properties. As a result, the casting is stabilized, and care such as surface grinding of the thin cast slab is not required, so that the steps can be omitted and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a partial sectional front view of a cooling drum of the present invention.

FIG. 2 is a partial cross-sectional front view of a conventional cooling drum.

FIG. 3 is a partial cross-sectional front view showing a state in which a solidified shell is pressed against a cooling drum of a conventional example in casting of a thin cast slab.

FIG. 4 is a partial cross-sectional front view of a conventional cooling drum.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling drum 2 ... Cooling drum rotating shaft 3 ... Sleeve 4 ... Base 5 ... Cooling water channel 6 ... Cooling water introduction port 7 ... Cooling water discharge port 8 ... Cooling drum peripheral surface 9 ... Drum crown arc shape Part 10: Plating layer 11: Bonding interface between plating layer and sleeve 12: Solidified shell C: Cooling water S: Shrinkage direction of solidified shell G: Gas gap between cooling drum and solidified shell W: Width of cooling drum

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-70648 (JP, A) JP-A-7-323353 (JP, A) JP-A-7-51805 (JP, A) JP-A-5-705 220547 (JP, A) JP-A-1-218743 (JP, A) JP-A-4-253551 (JP, A) JP-A-64-83340 (JP, A) JP-A-7-256401 (JP, A) Hikaru 1-165149 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/06 330

Claims (2)

(57) [Claims] 1. A drum-shaped crown is formed on an outer peripheral surface of a sleeve formed on an outer peripheral portion of a cooling drum, a plating layer is formed on an outer peripheral surface of the sleeve, and a plating layer is formed on a surface of the plating layer. A cooling drum for continuous casting of a thin cast slab, wherein a drum-shaped crown having a crown amount smaller than the crown amount is formed. 2. A continuous thin cast slab characterized in that a drum-shaped crown is formed on an outer peripheral surface of a sleeve and then plating is performed, and a crown having a smaller amount than a crown amount of the sleeve is formed on a surface of a plating layer. Manufacturing method of cooling drum for casting.