Method for reducing outer arc angle transverse cracks of casting blank of Darnell casting machine

Abstract

The invention belongs to the technical field of steel smelting, and particularly relates to a method for reducing outer arc angle transverse cracks of a casting blank of a Darnell casting machine. Comprising the following steps that (1) a bolt fixing mode of a lower trunnion of a bent section is changed into half tightening from complete tightening, a gap exists between a bolt and the trunnion, and a gasket is additionally arranged in the gap; (2) during offline reconditioning, abraded burrs and the like of the trunnion are polished, the elevation of a reconditioning table is adjusted according to the size of the polished trunnion, and the offline reconditioning precision is guaranteed; (3) in a cold state, the whole bent section is translated towards the outer arc side by 0.5 mm; (4) the gap between the lower trunnion of the bent section and the baffle is adjusted to be within 0.2 mm; and (5) adjusting a secondary cooling process after the casting blank is taken out of a crystallizer according to whether the transverse crack defect of the outer arc angle of the casting blank penetrates. The structure and the process are improved aiming at the design defects of the Dalnell casting machine, so that the defects such as transverse cracks of the outer arc angle of a casting blank are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for reducing transverse cracks at outer arc angles of Danieli casting machine billets. Background Art

[0002] Due to design reasons, the continuous casting machine has a small arc radius and the bending section is fixed in a way that causes the bending section to be displaced during production. The outer arc of the billet is prone to corner cracks and other defects.

[0003] The transverse cracks at the outer arc angle of the ingot caused peak cracks in the steel plate, which seriously affected the cost and quality. Later, it frequently caused steelmaking to be re-produced, seriously affecting order delivery and the company's reputation. Summary of the invention

[0004] The object of the present invention is to provide a method for reducing transverse cracks at the outer arc angle of a Danieli casting machine billet, so as to solve the problems existing in the prior art.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] A method for reducing transverse cracking of the outer arc angle of a Danieli casting machine billet comprises the following steps:

[0007] (1) Change the bolt fixing method of the lower trunnion of the bending section from fully tightened to half-tightened, so that there is a gap between the bolt and the trunnion, and install a gasket in the gap;

[0008] (2) During offline maintenance, the burrs and other burrs of the trunnions should be polished away, and the elevation of the maintenance table should be adjusted according to the size of the polished trunnions to ensure the accuracy of offline maintenance;

[0009] (3) In the cold state, the entire bending section is translated toward the outer arc side by 0.5 mm;

[0010] (4) Adjust the gap between the lower trunnion of the bending section and the baffle to within 0.2 mm;

[0011] (5) According to whether the transverse crack defect at the outer arc corner of the ingot penetrates the corner, adjust the secondary cooling process after leaving the crystallizer.

[0012] Furthermore, the adjustment method of the secondary cooling process in step (5) is as follows: if non-corner-penetrating defects occur, the secondary cooling water volume is increased by 10%-15%.

[0013] The present invention has the following beneficial effects:

[0014] 1. The present invention improves the structure and process of the Danieli casting machine in view of the design defects, thereby reducing defects such as transverse cracks at the outer arc angle of the casting.

[0015] 2. When the casting machine is running at high temperature, the bending section will expand due to heat and shift to the inner arc side. The cold pre-outward displacement of 0.5mm can offset about 80% of the thermal displacement, making the actual position of the bending section in the hot state close to the theoretical design center line.

[0016] 3. The 0.2mm gap between the lower ear shaft and the baffle constrains the macro displacement, and the gasket absorbs the micro stress, forming a graded control to improve the cooling uniformity of the corners of the casting.

[0017] 4. If non-corner-penetrating defects occur, the amount of secondary cooling water should be increased by 10%-15% to allow the cooling temperature of the ingot to quickly exceed the first brittle transition temperature and reduce transverse crack defects at the outer arc corners of the ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the bolt fixing method of the lower ear shaft of the bending section of the present invention.

[0019] Among them: 1. Lower ear shaft; 2. Gasket; 3. U-shaped seat; 4. Bolt. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] A method for reducing transverse cracking of the outer arc angle of a Danieli casting machine billet comprises the following steps:

[0022] (1) Change the bolt 4 fixing method of the lower ear shaft 1 of the bending section from fully tightened to half-tightened, so that there is a gap between the bolt 4 and the lower ear shaft 1, giving the bending section a certain amount of stress release space. And install a gasket 2 in the gap. Generally, a gasket 2 of 0.05-0.1mm is installed. The specific size should be determined according to the actual working conditions. When the gap between the bolt 4 and the lower ear shaft 1 is abnormally stressed, the lower ear shaft 1 of the bending section can move in the U-shaped seat 3. Install a gasket 2 to adjust the gap size. Figure 1 As shown, the lower ear shaft 1 of the bending section is arranged in the U-shaped seat 3. The existing design adopts a fully tightened connection method, which is changed to a semi-tightened method, and a gasket 2 is added. It should be noted that the drawings are only for explanation of the principle, and the shape and structure are not completely consistent with the actual one.

[0023] (2) During offline maintenance, the burrs and other burrs of the trunnions should be polished away, and the elevation of the maintenance table should be adjusted according to the size of the polished trunnions to ensure the accuracy of offline maintenance;

[0024] (3) In the cold state, the bending section is pre-adjusted by 0.5mm to the outer arc side to reduce the force on the billet in the hot state during the production process. When the casting machine is running at high temperature, the bending section will expand due to heat and shift to the inner arc side. The cold pre-shift of 0.5mm can offset about 80% of the thermal displacement, making the actual position of the bending section in the hot state close to the theoretical design center line.

[0025] (4) Adjust the gap between the lower ear shaft 1 and the baffle of the bending section to within 0.2 mm to prevent the corner transverse crack defect caused by large displacement of the bending section. The original 10 mm gap allows the lower ear shaft 1 to swing radially in the hot state, causing the casting strand to deviate from the theoretical center line. When the gap is reduced to 0.2 mm, the swing amplitude of the ear shaft can be greatly reduced. As a result, the symmetry of the thermal deformation of the bending section is improved and the temperature difference between the outer arc side and the inner arc side is reduced.

[0026] (5) According to whether the transverse crack defect at the outer arc corner of the ingot penetrates the corner, adjust the secondary cooling process after leaving the crystallizer. If non-corner-penetrating defects occur, increase the secondary cooling water volume by 10%-15% to quickly allow the cooling temperature of the ingot to pass the first brittle transition temperature and reduce the transverse crack defect at the outer arc corner of the ingot.

[0027] The root cause of the non-corner defect problem: the billet is cooled too slowly at 700-900℃ (the first brittle zone), and brittle phases such as AlN precipitate at the austenite grain boundary, resulting in intergranular cracks. Increase the amount of secondary cooling water by 10%-15% (such as 1.0→1.13L / kg) to rapidly cool the billet surface at a rate of ≥50℃ / s, shortening the residence time in the brittle temperature range.

[0028] The above embodiments are only for describing the preferred implementation of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made by ordinary persons in the art to the technical solution of the present invention should fall within the protection scope of the present invention.

[0029] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A method for reducing transverse cracking of the outer arc angle of Danieli casting machine, characterized in that: The following steps are involved: (1) Change the bolt fixing method of the lower trunnion of the bending section from fully tightened to half-tightened, so that there is a gap between the bolt and the trunnion, and install a gasket in the gap; (2) During offline maintenance, the burrs and other burrs of the trunnions should be polished away, and the elevation of the maintenance table should be adjusted according to the size of the polished trunnions to ensure the accuracy of offline maintenance; (3) In the cold state, the entire bending section is translated toward the outer arc side by 0.5 mm; (4) Adjust the gap between the lower trunnion of the bending section and the baffle to within 0.2 mm; (5) According to whether the transverse crack defect at the outer arc corner of the ingot penetrates the corner, adjust the secondary cooling process after leaving the crystallizer.

2. The method for reducing transverse cracking of the outer arc angle of the Danieli casting machine according to claim 1 is characterized in that: The adjustment method of the secondary cooling process in step (5) is as follows: if non-corner-penetrating defects occur, the secondary cooling water volume is increased by 10%-15%.

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