RU2113935C1 - Method for continuous casting of strip - Google Patents

Abstract

FIELD: metallurgy, more specifically, methods for continuous casting of strip. SUBSTANCE: method includes supply of melt to under level by separate streams, to gap between two rotating cylindrical rolls-molds with end face refractory side walls; solidification of melt on surface of rolls-molds and formation of strip. To enhance reliability of casting process and strip quality, melt is supplied through distributor to under level at depth of 0.1-0.35 length of liquid phase of formed strip. In so doing, 0.3-0.9 volume of supplied melt is directed in horizontal streams, while the remaining part, in vertical streams. A layer of liquid slag is brought onto melt surface. Melt volume supplied in horizontal streams is determined in direct proportion to width of cast strip, and slag is brought-on in the form of inert one to material of side walls, or use is made of side walls with slag-protecting belts. EFFECT: higher efficiency. 4 cl

Description

 The invention relates to the field of metallurgy, and more particularly to methods for continuous casting of a strip.

 There is a method of continuous casting of a strip in which the surface of the melt is coated with a flux layer before being fed to the mold roll [1].

 The disadvantage of this method is the narrow branded (quick-hardening metals and alloys) and dimensional (strip thickness up to 0.4 mm) range of products due to the use of the extraction method in the method.

 The closest in technical essence and the achieved result is a method of continuous casting of a strip, comprising supplying the melt under the level with separate jets into the gap between two rotating cylindrical rolls-crystallizers with end refractory side walls, solidification of the melt on the surface of the rolls-crystallizers and forming a strip in which the jets the melt is directed parallel to the generatrix of the rolls-crystallizers along the opposing misaligned trajectories [2].

 The disadvantage of the prototype is the low reliability of the casting process due to the freezing on the end of the melt distributor and its fusion with the melt hardening on the surface of the rolls in crust and the quality of the strip due to the formation of captures and related cracks. The first is due to the fact that the distributor is bulky, and heat losses are large from the open surface of the melt, and the second is due to the fact that the melt jets directed along misaligned paths are characterized by high intensity at its surface.

 The technical result of the invention is to increase the reliability of the casting process and the quality of the strip by eliminating freezing of the melt on the distributor and reducing the intensity of the melt flows on its surface and near the mold rolls.

 The result is achieved in that in the known method of continuous casting of a strip, comprising supplying the melt below the level by separate jets into the gap between two rotating cylindrical rolls-crystallizers with end refractory side walls, solidification of the melt on the surface of the rolls-crystallizers and forming a strip, according to the invention, the melt is fed under level at a depth of 0.1 - 0.35 of the length of the liquid phase of the formed strip, 0.3 - 0.9 of the volume of the supplied melt is directed horizontally, and the rest is vertical bubbled jets, thus impose on the melt surface layer of molten slag. The volume of the melt supplied by horizontal jets is set in direct proportion to the width of the cast strip and induce slag inert to the material of the side walls, or use side walls with slag protective belts.

 The proposed set of features — the regulated melt supply depth to the level and volume ratio of the melt directed by horizontal and vertical jets, the dependence of the ratio on the strip width and guidance of the liquid slag layer on the melt surface — provides high stability of the casting process and strip quality by eliminating freezing of the melt at the end part distributor and prevent perturbations of the melt surface, since heat losses from the melt surface and nsivnost flows of the melt not only on its surface, but also on the surfaces of the rolls-crystallizers. Bringing the slag walls inert to the material or using walls with slag protective belts improves the stability of the casting process and the quality of the strip by preventing melt from seeping through the gaps between the walls and the ends of the mold rolls.

 Example 1. Get a strip with a cross section of 5x800 mm from electrical steel grade 2111 for subsequent redistribution on a cold rolling mill. To this end, metal from a 50-ton ladle is fed through an intermediate ladle with a deep-sea submersible nozzle under the level of separate jets into the gap between two rotating cylindrical rolls-molds with a diameter of 1200 mm with end refractory side walls and form a strip of solidified metal rolls on the surface of the molds with compression of the solid phase. The metal level in the stream is maintained equal to 450 mm from the alignment of the rolls (the length of the liquid phase of the strip is also equal to 450 mm).

According to the invention, the metal is fed under a level at a depth of 0.25 of the length of the liquid phase of the strip and 0.5 volumes of the supplied metal are directed in horizontal and vertical streams. For this, a quartz submersible bucket with a casting channel diameter of 70 mm is equipped with two lateral outlet holes with a diameter of 30 mm and one hole with a diameter of 45 mm in the bottom (holes are in the same vertical plane) and immersed to a depth of 110 mm (along the axes of the side holes). The glass is mounted on the axis of the stream, while the axis of the side holes are parallel to the forming rolls. A slag melt of the CaO-SiO ₂ -Al ₂ O _{3 system} with alkali and fluorine additives is added to the stream inert to the side wall refractory (quartz) on the metal surface of the stream, the slag liquidus temperature is 1250 ^o C. During the casting, the slag layer thickness is maintained equal to 5 - 10 mm.

 The casting of the strip is stable, without clumping of slag, drilling of metal on the surface and violation of the density of the junction of the partitions with the rolls. The resulting strip has a high-quality, defect-free surface with smooth edges.

 Example 2. Get a strip with a cross section of 4x1250 mm from steel X18H10T. To this end, metal is fed from a 25-ton ladle through an intermediate ladle with a deep-sea submersible nozzle under the level of separate jets into the gap between two rotating cylindrical rolls-molds with a diameter of 1200 mm with end refractory side walls and form a strip of solidified metal rolls on the surface of the molds with compression of the solid phase by rolls. The metal level in the stream is maintained equal to 520 mm above the roll roll (the length of the liquid phase is also 520 mm).

According to the invention, the metal is fed under a level at a depth of 0.20 of the height of the liquid phase of the formed strip, and 0.75 of the volume of metal supplied is directed horizontally, and the remainder (0.25 of the volume) is directed by vertical jets. For this, an immersion cup made of corundum graphite with a channel diameter of 70 mm is equipped with two lateral outlet holes with a diameter of 45 mm and one hole in the bottom with a diameter of 35 mm (holes are made in the same plane) and immersed to a depth of 100 mm (along the axes of the side holes). The glass is mounted on the axis of the stream, the axis of its side openings are parallel to the forming rolls of the molds. A slag melt of the SiO ₂ -CaO-Al ₂ O _{3 system} with the addition of alkalis, fluorine and boron is induced on the surface of the metal in the creek, which is inert to the side wall refractory (corundum graphite). The liquidus temperature of the slag is 1050 ^° C. The thickness of the slag layer during casting is maintained at 10-15 mm.

 The strip casting went steadily, without clumping of slag, metal drilling on the surface and violation of the density of the junction of the partitions with the rolls. The resulting strip had a high-quality, without defects, surface with smooth edges.

 The proposed method provides a high-quality strip without defects on the surface and edge due to the protection of the metal surface by slag, low intensity of metal flows and reliable sealing of the gaps between the rolls and side walls. Compared with the prototype, eliminating the cleaning of surface and edge defects, the yield of the strip increases by 15-20%. Sustainable metal casting on a stream can be 4-5 hours, which is 2-5 times higher than that of the prototype.

Claims (4)

 1. A method of continuous casting of a strip, comprising supplying the melt under a level with separate jets into the gap between two rotating cylindrical rolls-crystallizers with end refractory side walls, solidifying the melt on the surface of the rolls-crystallizers and forming a strip, characterized in that the melt is fed under the level at a depth 0.1 - 0.35 of the length of the liquid phase of the formed strip, 0.3 - 0.9 of the volume of the supplied melt is directed horizontally, and the rest - by vertical jets, while on the surface of the spread Ava induce a layer of liquid slag.  2. The method according to p. 1, characterized in that the volume of the melt supplied by horizontal jets is set in direct proportion to the width of the cast strip.  3. The method according to p. 1, characterized in that induce slag inert to the material of the side walls.  4. The method according to p. 1, characterized in that use the side walls with slag protective belts.