JPS5976646A - Rotary wheel type continuous casting method - Google Patents

Abstract

PURPOSE:To prevent the internal cracking in the solidified shell of a billet in synchronized rotary wheel type continuous casting by drawing the billet from a moving casting mold then cooling forcibly the part near the corners at the opposite angles of the billet having the interior angle increased by sectional deformation to the angle larger than the interior angle of a normal billet from the outside. CONSTITUTION:Rotary wheel type continuous casting which draws a billet 12 having a solidified surface from the space of the moving casting mold formed of a rotary wheel 8 having a casting groove on the outside circumference and a metallic belt 10 is performed by the following method. The direction of the sectional deformation of the billet 12 which is approved to have the sectional deformation is detected in the section of the above-described casting mold and in the outlet of the casting mold. The two corner parts (for example, the positions 3, 4 shown in the figure) at the opposite angles where the interior angle in each corner part has a tendency toward an increase from the normal angle at the beginning of the casting are forcibly cooled from the outside in the specified section from the outlet of the casting mold. The cooling in the two corner parts is thus accelerated and the formation of the solidified shell in said part is accelerated, whereby the progression of the sectional deformation owing to shrinkage on solidification is ceased. The corner parts are further restored to the normal interior angle to correct the sectional deformation. The internal cracking of the solidified shell is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a rotating mold formed by a rotating ring having a casting groove on its outer periphery and a metal belt. The present invention relates to a rotary wheel continuous casting method in which solidified slabs are continuously pulled out from a moving mold.

[Prior art]

BACKGROUND ART The cross-sectional shape of slabs produced in synchronous rotary continuous casting equipment, in which a rotary ring and a metal belt are rotated synchronously for casting, has a trapezoidal cross-sectional shape. In the overcasting method, if there is uneven cooling in the mold or in the secondary cooling zone or improper equipment, cross-sectional deformation will occur during the growth process of the solidified shell of the slab. As a result, internal cracks occur in the solidified shell, resulting in deterioration of the slab member.

As the internal cracks progress, breakouts occur due to rupture of the solidified shell.

The form of cross-sectional deformation of the slab will be explained.

Figure 1 shows a typical shape of slab cross-sectional deformation.

When the slab 12 is pulled out from the mold, only the outside is solidified and the inside is still molten. 1 indicates a solidified shell, and 2 indicates an unsolidified portion. The slab with cross-sectional deformation is particularly severely deformed on the side located at the bottom of the casting groove of the rotating wheel. FIG. 1 shows a state in which the side of the slab located at the bottom of the casting groove (the top side in the figure) has moved to the right. The dotted line shows the cross section of a normal slab. Due to cross-sectional deformation, the internal angle of each corner of the slab becomes αl>α2. βl is β2.

When the slab undergoes cross-sectional deformation, the inner surface α1 of one diagonal corner.
β2 is larger than the internal angle at the initial stage of casting, that is, the internal angle when a normal slab is obtained. The thickness of the solidified shell in this part is smaller than the thickness of the solidified shell in the other corner part.

The internal angles of the corners at the time of casting are α1-α2゜β1-β2, respectively.
It is. As the solidification progresses, the cross section deforms and α1. ＞
α2. β1 becomes β2. As a result of this cross-sectional deformation, tensile stress is generated on the inner surface of the solidified shell on the α1 side, and when the stress exceeds an allowable limit, internal cracks 3 occur from the inner surface of the solidified shell. Similarly, on the lower surface side of the slab, tensile stress is generated on the inner surface of the solidified shell on the β2 side, and when the stress exceeds the allowable limit, internal cracks 4 occur on the inner surface of the solidified shell 1. Particularly on the β2 side, the corner shape is acute and there is no roundness, so the cast structure develops regularly during solidification, making it easy for cracks to propagate and cause breakouts when they reach the surface, resulting in a shutdown of the operation. I will invite you.

Cross-sectional deformation of the solidified shell in the early stage of solidification is caused by uneven cooling of the slab, irregularities in the equipment, such as misalignment of the section bending straightening mechanism, insufficient adjustment of the pinch rollers, etc., and inappropriate molten metal injection conditions. arise.

After the slab is pulled out from the movable mold, it is usually cooled by spraying cooling water onto the surface, but even if cooling water is sprayed over the entire surface of the slab, internal cracks in the solidified shell cannot be prevented. .

[Purpose of the invention]

An object of the present invention is to provide a rotary wheel continuous casting method that prevents internal cracks from occurring in the solidified shell in synchronous rotary continuous casting. After being pulled out from the movable mold, the vicinity of the diagonal corners, where the internal angle is larger than when a normal slab is obtained due to cross-sectional deformation, is forcibly cooled from the outside.

The inventors of the present invention have discovered the following from an analysis of the generation mechanism of slab cross-sectional deformation, a relationship between cross-sectional deformation and internal cracking, and an investigation of the formation of solidified shells in various parts of the slab cross section. In other words, the direction of cross-sectional deformation of the section is detected for a section in which cross-sectional deformation has been observed in the mold section and the mold exit, and the interior angle of the corner section is found to be two diagonal corners where the interior angle tends to increase from the normal interior angle at the beginning of casting.
The two corner parts are forcedly cooled in a certain section from the mold outlet to promote cooling of the two corner parts.
It was discovered that by promoting the formation of a solidified shell in the inner corner, preventing solidification shrinkage, stopping the progress of cross-sectional deformation, and returning it to a normal internal angle, cross-sectional deformation can be corrected and the occurrence of internal cracks can be prevented. . The solidified shell thickness at the corner portion, where the internal angle of the corner portion is larger than the normal internal angle at the time of casting, is smaller than the solidified shell thickness at the corner portion when a normal slab is obtained. Therefore, the corner portion where the solidified shell thickness is small is strongly cooled to increase the solidified shell thickness and correct the cross-sectional deformation.

The cross section of the slab is trapezoidal and usually deforms into a diamond shape.

Therefore, two diagonal corners among the four corners form a pair, and the interior angle increases or decreases. The diagonal two-corner portion with increased internal angles is separated from the mold and does not come into sufficient contact with the mold, resulting in a reduced cooling effect and a reduced solidified shell thickness.

Therefore, the forced cooling of the corner portions must be performed on the two diagonal corners where solidification is delayed in order to obtain a sufficient effect.

By quantitatively detecting the direction and amount of cross-sectional deformation, υ
By adjusting the degree of forced cooling of the corner portion, it is possible to automatically correct the cross-sectional deformation of the slab during continuous casting and prevent the occurrence of internal cracks.

In particular, localized cooling at the bottom corners not only has the effect of correcting cross-sectional deformation, but since breakouts of slabs are common at the bottom corners, localized rapid cooling of these areas is extremely effective in preventing breakouts. Thick.

Incidentally, the local cooling method usually uses corner spray water, but for even stronger cooling, direct water jet is used.

Local cooling should be direct cooling in which cooling water is injected directly onto the light surface of the slab. Injecting cooling water directly onto the slab not only has a great cooling effect, but also makes it difficult to form an oxide film. Furthermore, even if an oxide film exists on the slab, it can be removed by cooling water, so the surface of the slab is always cooled by fresh cooling water.

While the side of the slab with the larger internal corner angle is being forcedly cooled, it is desirable that the other diagonal corner is not cooled.

When cooling, the amount of cooling water should be significantly smaller than that for forced cooling.

It is highly desirable to perform forced cooling of the corners with large internal angles as well as cooling each side of the slab. This method is most effective for growing solidified shells.

Even if a method other than the present invention is used, for example, forced cooling of the left and right corner portions on the upper surface side in FIG. 1, internal cracking of the solidified shell cannot be prevented. Even if the left and right corners of the lower surface of FIG. 1 are forcibly cooled, internal cracking of the solidified shell cannot be prevented.

[Embodiments of the invention]

Examples of the present invention will be described below. Figures 2 and 3
In the figure, molten metal 5 is injected through a tandate/yu 6 and a nozzle 7 into a moving mold space formed by a rotating ring 8 and a metal belt 10 tensioned by a guide roller 9, solidified, and cast. Piece 12 is formed. The mold section of the circumference of the rotary ring 8 forms a mold space, and the molten metal 5 poured into the mold is primarily cooled in the mold section and its outer surface solidifies.

The slab 12 whose outer surface has solidified is straightened horizontally by the guide O-ra group 13 and the knife 14, and is then moved by the pinch roller 15.
is continuously pulled out. In the section after the guide roller group 13, secondary cooling is performed on the four sides of the slab 12 by surface spray nozzles.

A forced cooling device to correct the cross-sectional deformation of the slab is installed immediately after the mold section. In FIG. 2, such a forced cooling system consists of a slab upper corner local cooling system 16 and a slab lower corner local cooling system 17.

It is better to install the forced cooling device as close to the mold as possible. Although the installation section depends on the degree of cross-sectional deformation, it is usually sufficient to extend from the mold outlet to the pinch roller 15. Amount of cross-sectional deformation (
When the difference between ■ and ■ in FIG. 4 exceeds about 10 mm or when the manufacturing speed increases, it is desirable to locally cool the corners after the pinch roller 15 as well.

FIG. 4 shows a cross section of the slab 12 that has passed through the mold section. Since the upper surface of this slab is deformed to the right in the figure, the upper corner spray 18 and top corner spray 19
The amount of cooling water used in the corner spray to forcefully cool, promote the growth of the solidified shell in the forcedly cooled area, and correct cross-sectional deformation is determined mainly by measured values such as the amount of cross-sectional deformation, the surface temperature of the four corners of the slab, and the casting speed. , is injected to the diagonal two-coin portion. Furthermore, the - clause is applied in response to variations in these factors. At this time as well, it is desirable to continue cooling by the surface spray nozzles 7 and 11. If the direction of deformation of the slab is opposite to that shown in FIG. 4, forced cooling is performed by corner sprays 18', 19'.

FIG. 5 shows the progression of cross-sectional deformation in the solidification process of the slab 12 and its correction process.

The cross-sectional deformation rate on the vertical axis is the difference in diagonal length shown in Figure 4, 1-
It was calculated by dividing II by the diagonal length of a normal slab and multiplying by 100. The dotted line indicates the one-corner cooling method for the top surface of the slab. - An example is shown, and the solid line shows an example of the cross-sectional deformation correction effect when using the diagonal two-coin slab local cooling method according to the present invention. In one-corner spray cooling, the cross-sectional deformation rate gradually decreases, but the limit is around 5 inches. Even if forced corner cooling is continued, the cross-sectional deformation correction will stagnate because the rigidity of the solidified shell thickness will increase as solidification progresses. When the cross-sectional deformation rate is around 5-5, internal cracking of the solidified shell cannot be prevented. Breakout on the bottom side of the slab cannot be prevented by this method because it occurs immediately after the mold section is completed.

On the other hand, when the diagonal two-corner spray cooling of the present invention is carried out immediately after the casting section, the cross-sectional deformation rate is approximately 6.
%, but it can be seen that the cross-sectional deformation has been corrected by V. (Solid line I), ) 1 Just like the corner spray cooling method, after passing the slab forced cooling section, the diagonal 2:! ff-
It can be seen that even if the local cooling method is applied, the cross-sectional deformation is rapidly reduced and y can be completely corrected, which is very effective. (Solid line ++) Internal cracks in the solidified shell can be prevented by suppressing the cross-sectional deformation rate to about 2 inches or less. According to the present invention, it was possible to correct the cross-sectional shape without internal cracks.

The deformation of the slab cross section can be detected by not only visual inspection but also by known means such as direct measurement using a differential transformer, non-contact measurement of displacement such as a television camera or laser beam, etc., to detect the amount and direction of deformation. You can do it by doing this. The amount of local cooling water at the corner of the slab is determined by taking into account the surface temperature of the slab and the casting speed, and the forced cooling section is also determined. The amount of cooling water in the corner spray is preferably about 5 to 100 times the amount of water in the surface spray, although it depends on the amount of cross-sectional deformation.

〔Effect of the invention〕

As described above, according to the present invention, the cross-sectional deformation of the slab once generated in the mold section can be corrected and the slab can have a normal shape. Therefore, internal cracks occurring in the solidified slab shell can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a typical shape of a slab with cross-sectional deformation, Fig. 2 is a cross-sectional view of a synchronous rotary continuous casting apparatus according to an embodiment of the present invention, and Fig. 3 is a cross-sectional view of Fig. 2. (2) Cross-sectional view, FIG. 4 is a cross-sectional view showing the cross-sectional deformation correction device according to the present invention, and FIG. 5 is a graph showing the process of correcting the cross-sectional deformation rate of the slab. 1... Solidified shell, 2... Unsolidified part, 8... Rotating ring,
DESCRIPTION OF SYMBOLS 10... Metal belt, 12... Slab, 16... Slab upper corner local cooling device, 17... Slab lower corner local cooling device, 18... Upper corner spray, 19... Lower Corner play No. II￥1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 243-

Claims (1)

[Claims] 1. Injecting molten metal into a moving mold space formed by a rotating ring having a casting groove on its outer periphery and a metal belt that covers the opening of the casting groove over a predetermined length; In a rotary ring continuous casting method in which a slab with a solidified surface is continuously pulled out from the moving mold, the casting groove bottom corner of the slab pulled out from the moving mold has a larger internal angle and the corner diagonal thereto. A rotating wheel type continuous casting method characterized by forced cooling of the area around the part from the outside. 2. A rotary wheel continuous casting method according to claim 1, characterized in that cooling water is directly injected into the vicinity of the corner of the slab for forced cooling. 3. The rotation according to claim 2, wherein the amount of cooling water is adjusted based on the relationship between the amount of cross-sectional deformation of the slab and the amount of cooling water injected to the vicinity of the corner portion. Ring continuous casting method. 4. Molten metal is poured into a moving mold space formed by a rotating wheel having a fishing groove on the outer periphery and a metal belt that covers a predetermined length of the opening of the casting groove, and the surface solidifies. In a rotary wheel continuous casting method, in which a slab is continuously pulled out from the movable mold, and a portion of the pulled slab that has a larger internal angle at the bottom corner of the casting groove and the vicinity of a diagonal corner thereof are forcibly cooled from the outside. . A rotary wheel continuous casting method, characterized in that the surface of the slab other than the corner portion is cooled weakly even in the vicinity of the corner portion. 5. The rotary wheel continuous casting method according to claim 4, characterized in that cooling water is directly injected onto the surface of the slab other than the corners. , Mo., 76. Claim 4, A rotary wheel continuous casting method characterized in that each surface of the slab except for the corners is uniformly cooled.7, Claim 7. 5. The rotary wheel continuous casting method according to item 4, wherein cooling of the vicinity of the corner portion is started immediately after the slab is pulled out from the movable mold.