Method of making the compact metal semiproduct and device for executing the same

The invention relates to a method of manufacturing a solid metal blank from at least one solidified continuous metal strip formed on a cooled surface of a carrier moving in a molten metal bath.

When casting the molten metal into the mold, the solidification of the metal proceeds from the setting layer, which is formed almost immediately on the metal-to-mold contact surface, towards the center of the metal in the mold. Solidification rate · depends on the coefficient of heat transfer through the mold walls, the excess heat in the molten metal above the amount of heat required to melt, which must be dissipated to cool the metal to the freezing point, and the heat transfer coefficient through the solidified metal layer in the mold .

To determine the solidification rate of molten metal, a simplified formula is commonly used in the foundry technology, having the form s = k (Tj). ^1/2where denotes s the thickness of the solidified layer in mm, T is the time elapsed since. the start of solidification in minutes and k is the coefficient related to the cooling metal. The coefficient k for steel varies from 22 to 33 mm per minute and can be calculated from various data taken from practical tests. The effect of excess heat, i.e., the heat contained in the molten metal as an excess of the heat required to melt the metal, is not included in the formula but need not be considered for the purposes of the invention.

From this equation, it is apparent that the rate of cortex growth, i.e. the outward-to-inward solidification, rapidly decreases from the beginning of cortex formation and with its increasing thickness. For example, at the beginning of cooling or solidification, the formation of a 5 mm bark takes only about 0.028 minutes, provided that k is 30. After four minutes, the bark has a thickness of 60 mm and then takes another 4.7 minutes to increase the bark thickness. 5 mm.

The setting rate has a considerable influence on the structure and composition of the metal. The metal layer which solidifies rapidly near the mold wall has fine randomly oriented crystals and forms a supercooled zone whose thickness varies from about 5 mm to about 10 mm and sometimes 12 mm, depending on the steel or other metal.

The calm steel forms a supercooled zone with a thickness of about 10 mm. The chemical composition of the casting in the supercooled zone corresponds to the composition of the molten metal and its mechanical properties are. for most steels better than the properties of the metal that later solidified. As the cooling rate decreases towards the inside of the ingot, large crystals - dendrites and the formed structure - are formed. is brittle at the rolling temperature and may cause internal cracks if:. does not roll with little removal at the beginning of forming. Towards the center of the cast, the crystal structure changes more and more and randomly oriented dendritic crystals of relatively large size are formed.

In addition to increasing the size of the dendritic crystals and changing their arrangement in the casting, the composition of the metal also changes. In the supercooled zone, the composition of the solidified metal is practically the same as that of the molten metal, while the co-constituents segregated from the crystals formed first are constantly. concentrate more in the middle of the casting.

Material that solidifies. Last, it has the highest concentration of these elements that were gradually. secreted during crystallization. The tendency to segregation increases with increasing setting time, so that larger castings show higher segregation than smaller castings. In mold castings, the chemical composition of the metal is rarely the same in cross-section along its entire length. Continuous casting can substantially eliminate this variability in chemical composition in different regions along the length of the casting, but differences in chemical composition and texture from surface to surface. it does not remove the inside of the casting, especially for larger castings.

In order to eliminate the adverse effects of the resulting changes and to produce the desired mechanical properties, it is necessary to reduce the cross-section. . casting by rolling or forging. The original structure of large-crystal castings must be crushed by rolling or forging to reduce the casting size in a ratio of about 1: 5 to 1:30, depending on the size of the castings and the metal composition. Heat treatment to homogenize the metal composition by diffusion is also necessary or desirable.

The conversion of molten metal into an adequate annual production of rolled or semi-finished products requires high investment costs. for casting fields, rolling mills and heating. furnaces, high labor costs and, in many operations, high fuel costs. '. Continuous casting greatly reduces overall costs by reducing wage costs. cost. and increases productivity and allows economical production of castings with a smaller cross-section, so that rolling large ingots to smaller dimensions and lengths is eliminated. On . However, capital and labor costs are considerably high per ton of final product.

It is known that molten metal can be directly made into a strip on the surface of a water-cooled roller that is partially immersed in a bath of molten metal. In this way, however, it is not possible to produce a strong casting comparable in size to the ingot mold or to the casting produced by continuous casting.

It is an object of the present invention to provide a solid metal blank from at least one solidified continuous metal strip formed on a cooled surface of a carrier moving in a molten metal bath. The essence of the invention is that at least. one continuous metal strip, solidified on the cooled surface of the carrier in an enclosed space with an inert atmosphere, the composition of which corresponds to the composition of the molten metal in the bath and the crystalline structure consists of a random

66 6'6 oriented fine crystals, fold over at least one fold line or coil on a roll or at least two continuous metal strips are stacked and the contact surfaces are pressed together at solid temperature above the hot rolling temperature and reducing the original thickness by 0.2 to 3%.

According to the invention, the continuous metal strip is withdrawn from the cooled surface of the carrier in a tangential horizontal plane over the support surface and its underside is pressed from above onto at least one other parallel-guided continuous metal strip and discharged therefrom. Alternatively, longitudinal fold lines parallel to the direction of movement of the metal strip are formed on the continuous metal strip during solidification, the longitudinal strips of the continuous metal strip between the fold lines are pressed together and set by pressing.

The invention also relates to an apparatus for producing a solid metal blank, wherein the cooled rotary cylinder is partially submerged in molten metal in a ladle and coupled to a drive, the entire apparatus being housed in a closed chamber provided with a cover and outlet for the metal blank. According to the invention, there is at least one further cooled rotary cylinder parallel to the cooled rotary cylinder, and between each pair of adjacent cooled rotary cylinders there is a support plate with a flattened front end lying in a tangent plane of the cooled rotary cylinder. An adjustable pressure roller is positioned on a vertical plane interspersed by its axis of rotation and above another cooled rotary cylinder. According to a further embodiment of the invention, the cooled rotating cylinder has an outer surface of the housing perpendicular to its axis of rotation, a series of side-by-side ribs and grooves with oblique walls and a pair of vertical forming cylinders with peripheral grooves lying in the plane of travel belt.

The metal blank produced according to the invention corresponds in its chemical composition to the molten metal in the bath and has the same crystalline structure with fine crystals as the supercooled surface layer of the ingot cast into the mold, and the associated excellent processing properties. The blank can be rolled to the required thickness with much lighter stools and fewer passes. The conventional casting of a large cross-section, its cooling to a solid state and subsequent rolling to the final dimension in heavy rolling mills with several stands are dispensed with.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-sectional view of a device for manufacturing a blank of several metal strips; FIG. 2 is a perspective schematic view of a second embodiment of a device for making a blank of a longitudinally folded metal strip; 6 is a schematic example of another method of folding a metal strip into a blank, and FIG. 7 axonometric view of a device with two grooved rollers for compacting a metal strip, coiled into a pipe in several layers, into an integral blank.

Referring to FIG. 1, a vessel 3 with a controlled spout 4 for dispensing molten metal into the refractory lining is disposed above the refractory lining. the ladle 2 in such a way that a constant level of molten metal 8 is maintained in the ladle 2; rotatable, water-cooled cylinders 5 are mounted across the pans 2.

Each cooled rotary cylinder 5 is positioned such that its shaft 6 and the bearings 7 are marked with rings. they are above the level of the molten metal 8 in the ladle 2, while the bottom of the perimeter is immersed in the molten metal 8.

The rotary cooled cylinders 5 are driven at the same speed by a drive (not shown). The cover 9, located above the pan 2, allows^Jholding the non-oxidizing atmosphere by means of inert gas or vacuum above the ladle 2. As a result of the rotation of each cooled rotary cylinder 5, a metal strip 10 having a thickness of about 5 mm to 10 mm to 12 mm or more is continuously formed. the composition essentially corresponds to the composition of the molten metal in the bath. The thickness of the metal strip 10 formed in this manner on each rotatable chilled cylinder 5 depends on the peripheral length of that portion of the surface of the cooled rotatable cylinder 5 that is immersed in the molten metal 8, the thickness of the metal forming the rotatable chilled rolls 5, their rotational speeds and ratios. in the molten metal 8 with respect to the amount of excess heat and the type of metal and its quality.

When the first rotatable cooled cylinder 5, shown on the left side of the device in FIG. 1, is rotated, a metal strip 10 is formed thereon, which is carried upwardly from the molten metal 8 and contracted by the support strip 11, cooled rotary cylinder 5. There it hits a metal strip 12, which is similarly formed on the central cooled rotating cylinder 5, the colder and stronger lower side of the first metal strip 10 abutting on the warmer upper side of the second metal strip 12.

The two metal strips 10, 12 are pressed together by an adjustable pressure roller 13 positioned vertically above the second cooled rotating roller 5, and are mutually positioned in a thicker strip on the contact surfaces. This thicker strip moves over another support strip 14 and hits the top of the third rotatable cooled cylinder 5 on a metal strip 15 formed on its surface. The colder underside of the mutually interposed metal strips 10, 12 abuts the top of the last hottest metal strip 15 and is positioned under the pressure exerted by the pressure roller 16.

The pressure rollers 13, 16 can either be driven, or can only rotate by contact with the upper side of the metal strip 10. The blank 17 now consists of three interlocking metal strips 10, 12, 15, passes over the support strip 18 and exits the device a conduit 19 formed by a cover extension 9. The conduit 19 serves to reduce the ingress of air into the space under the cover 9 or the leakage of inert gas. The housing 9 is provided with a duct 20 for evacuating air from below the housing 9 or for refilling inert gas. Each pressure roller 13, 16 has a schematically indicated pressure adjusting means 13, 16 '.

Each water-cooled rotating roller 5 may have a coating device 21 for applying a coating to facilitate peeling off the metal strip 10, 12, 15 from its jacket. The applicator 21, in the form of an applicator roller, is located next to the descending side. The fresh, molten metal rises in the pan 2 through the openings 22 in the bottom 23 below the rotatable cooled cylinders 5, where the refractory bulkheads 24 keep slag and surface debris away from where the rotatable cylinders 5 are immersed in the molten metal 8 .

When. the metal blank 17 exits the conduit 19 at a sufficient distance to cool the metal to a normal rolling temperature, it can either cool or continue to roll on a duct rolling mill. 25, after which it can either be cooled or further rolled to the final product. Although the rolling mill 25 is shown directly behind the outlet of the guide 19 in FIG. 1, it is understood that it can be located a considerable distance from the guide 19.

Although three rotatable cooled cylinders 5 are shown in FIG. 1, the apparatus may also include a plurality of rotatable cylinders. cooled cylinders. In addition, several separate narrow strips can be formed side by side on the cooled rotary rollers 5 and joined by fitting and pressing them into rods or rods. Although the described apparatus includes as rotatable chilled rollers 5 as carriers of the resulting metal strips 10, 12, 15, which represent the simplest embodiment of a cooled, continuously moving surface, chilled endless belts or a continuous sequence of chilled bead-like elements may also be used. In all cases, metal strips are formed. separately from the molten metal in the ladle and then join together above the level of the molten metal in the ladle by pressure and their internal heat.

Although it has been stated that the thickness of the fine crystalline structure layer can vary between 5 mm and 12 mm for different steel grades, it may be desirable to form and join metal strips less than 5 mm thick or to produce metal strips thicker than 12 mm . If the upper limit of 12 mm is exceeded, partial deterioration of the product must be expected; however, since it is not customary to produce strips of less than 100 mm & apos; according to the invention, to produce a better product and to save the cost of rolling a much thicker casting, for example a continuously cast strip, up to the final shape. That is, making a solid blank of metal strips, which may have a greater thickness than the fine crystalline structure layer, may be more economical and give the opportunity to produce a better product than the conventional method of casting a heavy piece and then processing into a thin product.

FIG. 2 shows another apparatus for producing a metal blank. A single, water-cooled hollow rotary cylinder 30 is mounted rotatably in a refractory lining pan 31 in which a constant level of molten metal is maintained by a storage source (not shown), for example, of the container 3 of Figure 1. The circumference of the rotary cylinder 30 is immersed in the molten metal. As in FIG. 1, the rotary cylinder 30 is driven by a drive (not shown). For simplicity it is not shown in Fig. 2. a closed cover is drawn that maintains an inert atmosphere over the molten metal. or vacuum.

On the surface of the cooled rotary cylinder 30 is formed a system of ribs and grooves with inclined walls 'perpendicular to' its axis. Behind the pan 31 is a pair of vertical forming rolls 34 provided with horizontal circumferential grooves 36. As the cooled rotary cylinder 30 is rotated, a metal strip 32 with longitudinal fold lines is formed on its jacket, between which there are planar strips 33. Instead of individual discrete strips 10, 12, 15 of FIG. thus, according to FIG. 2 a single longitudinally folded metal strip 32, which upon withdrawal from the rotating roller 30, comes between the rotating forming rolls 34. In the circumferential grooves 36 of the forming rolls 34, the longitudinal planar strips 33 of the hot metal strip 32 are pressed together and compacted into a solid rod-shaped blank. which can be further weakened down to the final product or discharged as a blank. The support plate (not shown) may be analogous to FIG. 1 support the metal strip 32 as it is pulled off the rotating cylinder 30, to which a metal strip 32 can also be applied.

1 and 2, the blank 17, 35 is continuously formed.

3 to 6. there is shown another procedure in which the joined sections. one metal strip. 2. The metal strip 40, FIG. 3, is formed on a water-cooled rotating roller or similar moving carrier and then retracted therefrom. Medium. the portion 41 of the metal strip 40, FIG. 4, remains straight, while the two edge portions 42 are the same length as. the middle portion 41 is avoided upwards. One edge portion 42 is then folded over the central portion 41, FIG. 5 and thereafter the second edge portion 42, FIG. 6, is folded thereafter and the whole is uniformly compressed to position the mating surfaces together. This process can be performed on unlimited lengths of the metal strip 40 or individual sections can be cut from the continuous metal strip 48. When the blank 43 has cooled to a normal cylindrical temperature, it can be rolled in a reduction mill as in Fig. 1.

In Fig. 7, the flat metal strip is cut either lengthwise or widthwise to the desired dimension and then tightly rolled into a coil 50 which is still hot guided between the grooved rollers 51 to join the individual layers to form a tubular or rod blank. which can be rolled or machined after cooling .

The dimensions, temperatures and pressures of the process of the invention may vary and cannot be accurately determined. It is advisable to determine specific parameters on a case-by-case basis. In certain cases, it may be necessary to supply additional thermal energy when folding or coiling in order to achieve build-up of the blank layers. In all cases, the blank shown in the drawings indicates lines where the individual layers meet, but in practice this composite structure is not visible.

When solidified from liquid to solid state, some metals have plastic properties at relatively few degrees below the solidus temperature, while for other metals the range between the solidus temperature and the suitable plasticity temperature may be 100 ° C to 200 ° C or more. The alignment of the blank layers may occur around the solidus temperature at which it appears as a solid phase, although due to the low plasticity there are indications that partially molten metal is present between the dendrites. That is, the banding of the strips is performed above the temperature at which the metal has suitable plasticity for conventional rolling.

As a basic rule, the pressure of the rollers which first compress the layers together should cause a reduction in the original thickness of the two or more joined layers in the range of 0.2 to 3%. For low carbon steel with a carbon content of 0.01%, good plastic properties quickly develop below the thermal solid, and the steel can in many cases be subjected to a pressure such that the original thickness is reduced by 20 ° / o for compression into a single body. On the other hand, steels with a high content of impurities such as S, P, Cu, Sn etc. have low plasticity up to 150 ° C below the solidus temperature and do not allow a reduction of more than 0.3%. In general, the pressure for joining the metal layers should be such that the thickness reduction is not greater than that required for good joining, i.e. about + 2% depending on the metal. If the pressure exceeds the critical limits, the solid blank will have different degree of weakness or internal defects. Once the normal rolling temperature has been reached, the thickness of the reinforced blank can be reduced by 20% or more per roll.

It is clear that when, for example, three metal layers of about 10 mm thickness having a fine crystalline structure according to the invention are combined into a 30 mm thick unit and reduced by 20 ° / o to a blank, much less work is required to produce sheets of 10 or 20 mm thickness than to roll out sheets of the same thickness from a casting having a thickness of several tens of centimeters; there is no need for intense heating because the metal has a thickness corresponding entirely or predominantly to the ingot surface layer and hence a crystalline structure of randomly oriented fine crystals and a composition corresponding to the molten metal in the bath.