SU1242295A1 - Method of cooling ingot on curvilinear continuous casting machine - Google Patents

Description

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This invention relates to ferrous metallurgy, namely continuous. casting of steel on curvilinear machines for continuous casting of billets - (caster).

The purpose of the invention is to improve the quality of the surface along the small radius of curvature of the workpiece and increase the service life of the upper rollers of the extension section of the oxJiaaweHHH zone.

Maintenance of specific coolant flow rates applied to the surface of a small radius along the extension section, constant and equal to 0.2-0.3 of the flow rate at the beginning of the cooling zone with simultaneous increase in this area according to a parabolic water discharge along a large radius of 0.85 The -1.10 maximum value at the start of cooling is explained by the need to improve the quality of the surface of the most affected with a small radius and reduce the load on the upper rollers of the straightening section of the ingot. Increase in intensity. The cooling effect of the ingot surface and a small radius at the bending section contributes to the supercooling of the ingot crust, an additional increase in tensile stresses in the shell, often exceeding the allowable values, as well as reducing its plasticity, which generally leads to the formation of surface cracks transverse. Cooling the surface of small radius with a constant intensity of 0.2-0.3 maximum values at the beginning of the cooling zone according to the proposed cooling method allows to have the optimum surface temperature of the workpiece in this area without the formation of surface cracks on it.

The specific consumption of water over a small radius of the extension section at the level of 0.2-0.3 maximum values is determined by the thickness of the cast ingot. Water consumption at a level of 0.2 at all casting speeds is more advisable to install for relatively thick ingots (200-300 mm thick), since the thermal resistance of the billet shell is high enough and a higher coolant flow rate only overcools the surface layers of the metal and degrades the quality surface, and heat extraction does not increase. When the cooling intensity is below 0.2

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The scientific research institute does not ensure the removal of the required amount of heat from the surface of the workpiece, and it is overheated.

The cooling intensity at a level of 0.3 maximum values is more efficient when casting thinner billets (150-200 mm), since the thermal resistance of the shell in this case is sufficient to transfer heat from the liquid core to the surface of the workpiece and there is no local supercooling over the thickness of the crust. An increase in flow rates above 0.3 leads to overcooling of the workpiece surface and increases the number of cracks.

The simultaneous increase in specific water consumption over a large radius to the level of 0585-1.10 maximum cooling start values in order to reduce the load on the upper rollers of the extension section and increase their service life is due to the fact that the ingot casing from the outside in the zone of the bend experiences compression deformation and increase cooling intensity within these limits does not impair the quality of the surface. Creating a cooling intensity over a large radius within the specified limits provides the optimum temperature difference, which contributes to the straightening of the workpiece and allowing a significant reduction in the load on the upper rollers of the extension zone.

The intensity of cooling at the level of 0.85 values of the maximum costs of starting cooling is advisable to maintain relatively thin billets (thickness 200 mm) when casting. Below this level, the cooling of the ingot over a large radius becomes insufficient to create the necessary temperature gradient, which makes it easier to improve the height of the workpiece and reduce the load on the upper rollers. Specific consumption of water at the level of 1.1 maximum values of the beginning of cooling should be established when casting ingots of large thickness (/ 220-300 mm and more). A further increase in the specific consumption of water leads to a noticeable overcooling of the ingot envelope over a large radius and the occurrence of thermal stresses that exceed the allowable values and lead to the occurrence of cracks. Established

that the load on the upper rollers is not reduced.

The increase in the amount of coolant supplied in the cooling section between the extension and horizontal along the surface of a small radius by 10–30% compared with the previous flow rate, and the decrease in the specific flow rate at the start of cooling to 0.3-0.5 is explained by number of shell growth, change in the thermal resistance of the ingot and heat flux. In practice, this leads to a reduction in the knocking of the workpiece between the rollers, as this increases the strength of the ingot shell and reduces the number of cracks in the axial zone. Maintaining such intensity ensures the alignment of the heat sink at the indicated section of cooling to the sides of the large and small radii of the workpiece, and smaller values (an increase of 10% from the small radius and a decrease to 0.3 level of the maximum values of the start of cooling a large radius) also for blanks with a thickness of 220–300 mm, and large ones (30% and 0.5 values) for ingots of lesser thickness (150–200 mm). Maintaining the specific consumption of water both above and below the specified cooling limits does not ensure that the intensity of the heat sink around the perimeter of the workpiece at the last stage of the ingot crystallization, which leads to a deterioration in the surface quality of the workpieces.

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PRI me R. In the process of continuous casting into the mold with a cross section of 150x1200 mm, steel 14G2AF is fed and the billet is pulled at a speed of 0.8 m / min. The secondary cooling zone has a length of 17 m, of which 8 m of a purely radial section, 5 m of a curvilinear extension section, and the remaining m occur in the area of the final straightening of the ingot with a transition to a straight line. At each site, the blanking of the billet is produced by means of a water-air mixture and the specific water consumption in the mixture flow in the radial section is changed exponentially, while the maximum specific values of v3.0 m / m h are set under both of the radii and reduced to 0.9 m / h in

at the radial section of the workpiece, the cooling rate ho a small radius is kept constant at 0.3 maximum values for the start of cooling, i.e. , 9 m / m h, and on the surface of a large radius simultaneously increase to 0.85 values of the onset of cooling, i.e. to 2.4. At the end of the top of the slick and when moving to the horizontal section, the specific costs of delivery will increase by 30% in a small radius, i.e. to values of 1.2. h, and over a large radius is reduced to 0.5 of the initial values of j i. up to 1,5m / m.ch

The use of the proposed cooling mode of slab billets with a cross section of 150x1200 mm makes it possible to reduce the load on the upper rollers over a small radius from 30–32 to 15–18 ts and to obtain them more uniform throughout the entire length of the section of the shaft. As a result of a decrease in the stress state of the upper layers of the small radius billet, the surface quality is improved. The length of transverse cracks decreases Z-2.5 times (from 20-25 to 10 tf), and the depth from 6-8 mm to 3-4 mm. The application of cooling modes below or above the indicated values does not contribute to a noticeable reduction in the load on the upper rollers of small radius and to improve the surface quality, therefore, for the section of the workpiece 1, 150X1200 mm, the indicated values should be considered optimal. I,

When casting an ingot with a cross section of 250 x X 1600 mm and a casting speed of 0.8 m / min, the liquid phase is 15 m. In this case, the specific consumption of water in the secondary cooling zone changes exponentially from the maximum value under the crystallizer (4, 2 m / m2 h) up to 1.2 MVM. h at a distance of 12 m from the metal meniscus. Then, over a small radius of the extension section, the specific consumption of water is kept constant at a level of 0.2 values of the onset of cooling, i.e. in the range of 0.85-0.9, and from the side of the surface of a large radius in the same area costs. The water increases to 1.10 values of the beginning of cooling, i.e. to 4.5. Location on

the termination of the top level and the beginning of the linear motion of the ingot are specific. water consumption over a small radius increases by 1.0%, i.e. to values of 1.0 m3 / m (H, and over a large radius is reduced to 0.3 of the original values, ie, to 1.35.

At the same time, the pressure of the workpiece on the upper rollers is small, the radius decreases and throughout the section is 17-20 ts, and the pressure on the last rollers does not exceed 20-22 ts, i.e. decreases. Lowering the stress state of the surface layers of the slabs, for example, when casting trench-sensitive

Editor E. Papp

Compiled by A. Maslov

Tehred M. Khodanich Proofreader M. Pojo

Order 3648/15 Circulation 757 Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab. „4/5

11production and printing company, Uzhgorod, Projecto st., 4

Art. 09Г2ФБ, helps to reduce the number of transverse cracks on the surface of the ingot from 20-25 pcs. on 1 m to 5-7 pieces. per 1 m using the proposed cooling method. The depth of transverse cracks is reduced from 5-7 mm to 2-3 mm.

The application of the invention will improve the surface quality of the workpiece by reducing the number and degree of development of transverse cracks. In addition, the service life of the upper rollers of the extension section increases on average by 1.5-1.6 times due to a reduction in the load on the upper rollers along a small radius.

Claims (1)

ING COOLING METHOD On a curved billet of continuous billet casting machine, including cooling of the surface of the ingot with a change in the specific flow rate of the cooler along the cooling zone according to the exponential law from the maximum value at the beginning to the minimum to the end of the cooling zone with different flow rates of the coolant with small and large radiuses of curvature of the workpiece, characterized in that, in order to improve the surface quality at a small radius of curvature of the workpiece and increase the service life of the upper rollers of the extension portion of the cooling zone, cool the flow For along the extension section of the cooling zone along the small radius of curvature of the workpiece, they are kept constant and equal to 0.20-0.30 of the maximum value of the specific flow rate at the beginning of the cooling zone, and along the large radius from the beginning to the end of the extension section according to the parabolic law, up to 0.85 -1.10 of the specified value, after which the specific consumption of the cooler. Along the section located between the extension and horizontal along the small radius of curvature of the workpiece, increase from the beginning to the end of this section according to a parabolic law by 10-30% the previous value of the specific flow rate of the cooler, and over a large radius reduce to 0.3-0.5 the values of the specific flow rate at the beginning of the cooling zone. SU. ,,, 1242295 <1242295