KR100360176B1 - High Speed Roll Casting Process and Product - Google Patents

Abstract

The present invention relates to a metal casting method by supplying molten metal (16) between two casting surfaces (8, 10), such as a roll casting machine. A fine, uniform carbonaceous layer 32 is applied to the upper strip of casting surface 28 of the casting zone 2. Thereafter, the molten metal solidifies while passing through the casting zone (Z), and the gauge of solidified metal is reduced to at least 10%. The cast sheet 12 of the present invention exhibits a uniform surface appearance.

Description

Technical Field [0001] The present invention relates to a high-speed roll casting process,

Metal sheets, flat plates, and foil products have been manufactured in a number of ways. One method of manufacturing aluminum and aluminum alloy products is roll casting. The present invention relates in particular to roll casting using paired rolls. In a preferred example, molten metal which is generally filtered, alloyed and refined is fed into the casting rolls. Such rolls have different widths and diameters, typically roll diameters of 600-1000 mm, and widths of strip products of 1-2 m. The rolls are cooled, for example by internal liquid cooling, to maintain the outer surface of the roll shell at a temperature sufficient to solidify the metal as it passes through the roll, resulting in a gauge due to high applied load The weight loss and extrusion are carried out and generally run out at a gauge of 2 to 8 mm. The metal sheet drained from the casting machine is wound and sent to subsequent hot rolling, cold rolling, homogenization and quenching processes.

In roll casting, there are several factors that affect productivity and product quality. These factors include solidification, such as metal production, metal transition, gauge control, centerline separation, component distribution and thermal management, surface uniformity, flatness and appearance, and adhesion of the sheet and roll during casting.

Solidification is, of course, a limiting factor in achieving increased productivity in casting, especially roll casting. The casting speed should be adjusted at a rate that ensures that the outer wall of the sheet is properly and progressively solidified. The casting speed should also ensure that the sheet is fully solidified prior to hot rolling the sheet. Solidification should be uniform so that no internal voids appear. As the casting speed increases, the surface temperature of the casting roll rises. Likewise, the external surface temperature of the cast article also increases. As the temperature of the aluminum sheet to be cast and the outer shell of the iron casting roll rises, the sheet experiences a surface weld that tends to compress and compress the roll. When such adhesion occurs, the casting speed must be reduced.

One way to alleviate stickiness is to provide the formulation on the roll surface. Such formulations include a release agent to prevent adhesion of the sheet and the outer shell of the casting roll. Typical formulations used in roll casting are graphite and magnesium oxide.

However, since the heat insulating material acts as an insulating layer between the sheet and the roll shell, application of the heat insulating material can also impart cooling efficiency to the casting process. Therefore, when using a mold release agent capable of maintaining the casting speed to avoid sticking, there is a need to reduce the thermal efficiency and thereby reduce the casting speed to avoid melting or flow conditions.

It is also difficult to uniformly coat the release agent on the surface of the roll shell. In regions where the mold release agent is not applied, there is a tendency to cause micro-welding between the cast strip and the roll shell.

There is a known technique for casting surface treatment of various purposes. For example, U.S. Patent Nos. 4, 487, 157, 4, 487, 790, 4, 588, 021, 4, 749, 027 and 5, 086, ≪ / RTI > describes the importance of the permanent insulation coating provided on the casting surface of the belt used in the belt. Such a permanent surface coating is a welded permanent matrix coating covered with a dry, clear belt dressing. In operation, a gas layer such as helium is also provided. Examples of dry belt dressings for insulation purposes include graphite, acetylene soot or other carbonaceous materials. Coating of the binder or bicomponent silica may also be provided continuously or intermittently to the coated belt of this horizontal belt casting machine. U.S. Patent No. 3,322,184 discloses applying a soot-like thermal barrier to the groove of a copper casting wheel to delay heat transfer from the cast product to a casting wheel.

Other casting processes have described the use of insulation. For example, U.S. Patent No. 4,842,042 discloses the use of a roll skimmer to control the gauge in a melt-blocking process, and can be used in roll skimmers to prevent adhesion of skimmers and metals A carbonaceous graphite powder or a separator such as soot. U.S. Patent No. 4,027,716 discloses a coating or surface treatment for applying an insulating layer to a continuous casting belt. Examples are dispersions of refractory materials to which carbon or graphite has been added.

Apparatuses are known for obtaining the insulation necessary for the bar casting machine to avoid deformation or abrasion of the casting surface. U.S. Patent No. 3, 557, 866 describes a device for applying liquid insulation and release agent to the bottom and side walls of the peripheral grooves of the casting surface where the bars are cast. The U.S. patent also discloses a device for applying a carbonaceous insulating layer to the grooves of the rotating mold surface to act as a lubricant capable of removing the bars from the grooved copper mold and acting as an insulating material between the copper casting surface and the metal being cast .

Despite efforts to apply surface agents to various casting surfaces, there has been a need for an aluminum roll casting method that has a casting speed that is faster than a common roll casting speed.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a metal sheet by a casting process, and more particularly to a method of manufacturing a roll-casting aluminum sheet product at a speed higher than a known casting speed in a pair of roll casting machines.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a typical apparatus for horizontal roll casting operations that produces a final product from a melting furnace through a roll casting machine into a coiler.

Figure 2 is a cross-sectional view taken along the centerline of a pair of horizontally aligned casting rolls illustrating the thickness and conditions of the metal as it passes through the roll bite and solidifies as the gauge is reduced.

3 shows an example of a device which can be used to deposit a carbonaceous layer on the outer surface of a rotating casting roll;

Figures 4, 5, 6, and 7 show another example of an apparatus that can be used to deposit a carbonaceous layer onto the outer surface of a rotating casting roll.

FIG. 8 is a micrograph showing a 2000 times magnification of a fine soot layer applied to the surface by once passing acetylenesorbate along the surface. FIG.

Figure 9 is another micrograph of the 2000 times magnification of the fine soot layer applied to the surface by passing the acetylenic soil through the surface four times.

10 is a micrograph of a 2000-fold magnification of the colloidal graphite layer of the prior art applied to the surface.

FIG. 11 is a micrograph of the fine soot layer of FIG. 8 magnified 10,000 times. FIG.

The present invention relates to a high-speed casting method of a metal sheet. The casting process includes equalizing two oriented casting surfaces, such as paired rolls arranged in parallel with each other. The casting surface is maintained at a temperature sufficient to gradually solidify the molten metal between the casting surfaces. A very fine layer of carbonaceous material is applied to the casting surface to a thickness of less than 1.5 microns, preferably less than 0.4 microns. The molten metal solidifies as the metal passes through the casting zone of the casting machine. After solidification is complete, the solidified product is compressed between the casting surfaces to reduce the gauge of the product that is solidified by more than 10%.

In a preferred embodiment, the present invention relates to the uniform application of fine carbonaceous material to the outer surface of a roll casting machine. The aluminum strip is solidified and wound on a roll bite with an appropriate roll pressure to achieve a gage reduction of at least 10%.

It is an object of the present invention to provide an improved roll casting which uniformly applies fine carbonaceous material to the outer surface of a roll casting machine which avoids the disadvantages of the insulation while maintaining the advantages of the release agent preventing the adhesion between the roll surface and the surface of the casting product Method. Another object of the present invention is to provide a roll casting method in which the speed of a roll casting machine is remarkably improved.

An advantage of the present invention is that the casting product is hot rolled when the sheet passes through the centerline of the roll after solidification under the unique compression conditions for roll casting to prevent a thin and uniform layer of carbonaceous material from adversely affecting the insulation, To maintain the properties of the release agent.

Another advantage of the present invention is that water or other liquid formulation is not required to transfer the carbonaceous material to the casting surface. As a result, the life of the roll shell is prolonged because the roll shell does not undergo rapid thermal fatigue.

Another advantage of the present invention is that the sheet to be cast is relatively fast, resulting in a more uniform surface texture and appearance.

These and other objects of the present invention can be understood more clearly and completely by the following detailed description and drawings.

Figure 1 is a schematic view of a typical apparatus for horizontal roll casting operations. The metal is melted in furnace 2, as shown in Fig. The molten metal is alloyed, refined and filtered through a general melt processing apparatus (3). The molten metal is conveyed along a trough 4 heated to maintain its temperature and sometimes covered with a roll between a pair of rolls 8, 10 rotating relative to each other as indicated by arrows on the roll in Figure 2 And is supplied to the byte 6. The metal gradually solidifies on the roll bite and the cast strip 12, which has flowed out of the casting machine, is generally wound on the coiler 14 and made into a finished product. As shown, the strip guide and shearing device 15 can be used to guide the strip and cut the product when the coil changes. The controller 9 adjusts various roll casting factors.

Although the present invention is particularly suitable for horizontal roll casting, it is also suitable for vertical roll casting and other casting where progressive solidification and subsequent gassing of hot, solidified metals occurs.

Fig. 2 shows the casting zone Z of the roll casting machine. As shown, molten metal 16 is supplied in roll bite. It is important that the temperature of the molten metal is uniform along the nozzle width for supplying the molten metal. It is also important to minimize the turbulence of the molten metal so that steady-state conditions can be maintained. As shown, the molten metal begins to solidify at the initial contact point 20 with the top roll 10 and simultaneously with the initial contact point 18 with the bottom roll 8. The solidification of the molten metal proceeds continuously from the opposing outer surface of the sheet being cast towards the center of the product.

The casting zone Z shown in Fig. 2 is generally 100 mm or less in total length. Depending on the diameter of the casting rolls, the casting zone is generally from 50 to 80 mm and is determined according to the alloy being cast, the roll temperature, the product gauge and the like. The casting zone Z is specified in three regions. The first zone (A1) is the zone where solidification begins but most of the metal is molten. The thermal efficiency of this zone is high. The second zone A2 is the zone where the molten metal has not yet solidified but is not in a molten state. This area is known as the thickened area 21. The thermal conductivity of this zone is generally low, as the metal begins to solidify and shrinks from contact with the surface. In addition, in the known art using water or other agents to apply a surface agent such as graphite to a roll, liquid is present in this zone. The evaporation of the liquid forms a gas barrier between the metal and the roll to further isolate them and reduce the thermal efficiency of the cooling process. The third zone (A3) is where the solidification of the metal begins to end at the roll centerline. The thermal efficiency in this third zone is also high.

During the progressive solidification of the metal through these three zones, various phenomena occur. As the solidification of the metal progresses, the metal tends to shrink in the zone A2. A small gap is created between the solidified metal and the cooled roll surface. This gap drastically reduces heat cooling efficiency. And, as the metal proceeds in the boundary zone (A3), the metal is compressed between the rolls. Such compression forms a significant separation pressure in the roll bite and brings the metal into direct contact with the cooled roll surface. Hot rolling at the centerline reduces the gauge of the solidified metal sheet by 10% or more, and generally by 10 to 20%. The reduction of the gauge is possible at about 50% in the roll casting machine.

As mentioned above, the productivity of roll casting machines is an important issue. It can be seen that as the speed of the roll casting machine increases, the temperature of the roll surface and the casting product both increase. This temperature rise is combined with a relatively high separation pressure of 7.5 to 1.25 ton / m < 2 > to weld the casting product to the outer surface of the roll. At high speeds, the solidification progresses further by moving to the roll bytes and the hotter metal is placed at higher pressure. This condition causes adhesion. The formation of an aluminum-ferrous metal bond indicating that a chemical reaction has taken place is observed at the interface.

To avoid sticking, the casting speed can be reduced, but this has a negative effect on productivity. Another method is to apply a surface agent which inhibits adhesion. Common agents that perform this are graphite and magnesium oxide. However, coatings applied in such a manner act as a barrier to chemical reactions between aluminum and iron. Such a coating may also be an insulating coating between the cooled roll surface and the product surface being cast. Such an effect lowers the cooling efficiency of the roll casting machine and limits the casting speed. Thus, in the past, operators of roll casting machines have struggled to make fine adjustments between avoiding sticking and maximizing thermal efficiency to maximize productivity.

The present invention eliminates the need to consider coordination between these. In the present invention, a very fine carbonaceous layer is uniformly applied to the surface of a roll casting machine. In a preferred embodiment, a very thin layer of very fine soot is applied to the outer surface of the casting roll at the roll-over-top stream location. The soot particles of the present invention are generally 0.1 microns or less in size. FIG. 10 is a soot particle having such a particle size magnified by a factor of 10,000. Soot is a very thin layer, typically less than 1.5 microns, applied by burning acetylene gas and directing the flame to the roll surface. A soot deposit layer of 0.4 microns thick was formed by passing acetylenesorbate once through the roll surface. In addition, a soot deposit layer having a thickness of 1.5 microns is formed by passing acetylene tallow through the roll surface four times. Such a thickness, of course, depends on the soil factor, for example the flow, the distance from the roll surface, and so on.

In the present invention, the fine carbonaceous material covers the entire surface of the roll. As can be seen in Figures 8 and 9, the soot layer is thinner than 0.4 microns in Figure 8 and thinner than 1.3 microns in Figure 9, but covers the entire surface.

Also, the thickness of the soot layer is uniform. The thickness of the soot layer is the same along the roll on which the metal is cast. Such uniformity can also be seen in Figs. 8 and 9 in which the soot layer is enlarged to 2000 times, and is extremely uniform. For comparison, the prior art colloidal graphite without the fine particle size of Fig. 10 is not applied as a thin layer, does not cover the entire surface, and is not uniformly applied along the surface. 10 shows spots where molten aluminum is in direct contact with the iron on the roll surface and shows aluminum-iron welds or adhesion. The soot coating of the present invention eliminates the opportunity for such adhesion.

Propane and natural gas can also burn close to the roll and form a uniform, thin soot layer. The soot can also be produced as fine powder and the powder can be applied to the surface of the roll by means of an injector or atomizer.

As shown in Fig. 3, the tip 24 of the acetylene soil 26 rotates in the direction indicated by the arrow toward the roll surface 28. As shown in Fig. It is preferable to slightly collide the acetylene flame 30 with the surface on which the soot is deposited. It is also important that the flame should not be concentrated in the same area over time, and this concentration can deposit too much soot. The soot layer 32 should be thin enough, such as less than 1.5 microns, to avoid adiabatic heat and uniformly applied at the same thickness along the roll casting surface. For this reason, it is important to move the soot applicator in a uniform shape with respect to the casting surface.

Figure 4 shows a plurality of acetylenesorbates erected in parallel along the width of the casting roll. Care should be taken to deposit the carbonaceous material along the entire surface of the moving drum. Therefore, the spacing of the soil is important. The soil as shown in Fig. 4 can be rotated for a complete and uniform coating of the roll surface.

Figures 5 and 6 illustrate an example in which a single acetylenic soil is driven along the face of a rotating drum to provide a uniform and thin coating on the casting roll surface. Figure 6 shows the drive sprocket and chain mechanism 34 in which the soil moves along the track 36 but other mechanical, electrical or instrumental devices or combinations thereof may be used to move the soil or multiple soil . The rate of movement of the soot suitable for providing a thin and uniform soot layer in the casting roll is 1.5-2 m / min along the casting roll surface. At fast casting speeds, the speed of movement of the soil can be increased or soil can be added to ensure a uniform coating on the roll surface.

Figure 7 shows another example of burning gas to deposit a thin, uniform layer of carbonaceous material close to the rotating drum. In this example, a burner tube 38 having a plurality of holes 40 is provided. The holes are formed with size, spacing and location for optimum results. The burner is suspended or rotated alone or in combination with another burner to perform the carbonaceous layer formation or deposition of the present invention.

Example

The following comparisons have been made to illustrate the present invention. Casting alloy 1145 was cast into a 5 mm casting gauge by manipulating a roll casting machine with thick, non-uniform colloidal graphite and casting the same alloy to the same gauge using a thin, uniform soot layer. The following operating parameters and measurement results were obtained.

The roll casting surface of the metal strip according to the invention exhibits a more uniform appearance compared to metal strip casting using conventional colloidal graphite. Such improvement in uniform appearance is due to the direct application of fine soot on the roll casting surface. Such uniform application eliminates small welding areas due to coating non-uniformity of graphite.

The life of the roll shell was also extended by 56% by the present invention. This is the result of reducing or eliminating intermetallic welds or sticking which leads to cracks in the roll shell. Also, the increased life of the roll shell is due to less temperature change on the roll shell surface because it is not cooled by a formulation such as water used to transport the surface agent by sprays or the like.

The insulating effect of soot, which is caused by applying a uniform, thin soot layer to the outer surface of the casting roll of the roll caster, is negligible. Soot can be applied at various densities.

It has been found that the soot of the present invention, which is applied as an acetylene soil, does not contain unburned hydrocarbons through thermogravimetric analysis. Therefore, in a preferred example of the present invention, there is no hydrocarbon residue in the carbonaceous layer of soot.

The present invention increases the roll casting speed. The insulating effect of a uniform, thin carbonaceous soot layer, if any, is negligible. The speed improvement can be up to 25% and up to 60%. Thus, the present invention is particularly useful for advancing roll casting technology faster than conventional speeds.

As noted above, the roll casting machine of the present invention hot-rolls the solidified strip as it passes through the roll bite. Such hot rolling is performed at 10% to 50%. Heat generated in such a hot rolling operation has a complete combustion effect of the carbonaceous material from the roll surface. Complete combustion ensures that the carbonaceous material does not leave invisible contaminants on the strip surface. Most users of the strip material prefer to have no such residue.

The above embodiment is the best example of the present invention. It will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the present invention.

Claims (21)

A metal consisting of cooling the outer surface of the roll internally so as to maintain a temperature sufficient to cause gradual solidification of the molten metal fed to the roll bite between the rolls while rotating a pair of rolls horizontally aligned with one another of the roll casting machine, In a casting method of a sheet, After applying a uniform coating of fine carbonaceous material along the outer surface of the roll in which the metal is cast in the upper stream of roll bite; Feeding molten metal into the roll bite; Gradually solidify the molten metal supplied by the roll bite to complete the solidification before the metal passes the centerline of the roll; Characterized in that the solid metal is hot-rolled as it passes the centerline of the roll at a separation pressure suitable for reducing the gauge of the solid metal by at least 10%. The method of claim 1, wherein the metal is aluminum or an aluminum alloy. The method of claim 1 wherein the outer surface of the roll is iron. The method of claim 1 wherein the casting roll is internally cooled with water. 5. A process according to claim 4, characterized in that the external surface temperature of the casting roll at the inlet of the casting zone is between 60 and 250 ° C. 5. A process according to claim 4, characterized in that the external surface temperature of the casting roll at the outlet of the casting zone is between 400 and 600 < 0 > C. The method of claim 1, wherein the carbonaceous material is soot. 8. The method of claim 7, wherein the soot has a particle size of less than 0.1 microns. 8. The method of claim 7, wherein the soot particles are amorphous particles. 8. The method of claim 7, wherein the soot covers the entire surface of the casting roll where the metal is cast. 8. The method of claim 7, wherein the soot is applied at a uniform thickness of less than or equal to 1.5 microns. 8. The method of claim 7, wherein the soot is applied at a uniform thickness of less than or equal to 0.5 microns. 8. The method of claim 7, wherein the soot is applied by directing the flame to the outer surface of the roll by burning a carbonaceous gas selected from the group consisting of acetylene, natural gas and propane. 8. The method of claim 7, wherein the soot is fine grains of 0.1 micron or less in diameter and is applied to a uniform thickness of 0.5 microns or less. The method of claim 1, wherein the rolling pressure is suitable to reduce the gauge of solidified metal to 30 to 80%. 8. The process of claim 7, wherein the soot does not comprise hydrocarbon residues. The method of claim 1, wherein the carbonaceous layer is completely burned at the temperature and pressure of the roll bite of the roll casting machine to prevent carbonaceous residues from being present on the casting product. An outer surface of the roll being arranged horizontally to each other and cooling the outer surface of the roll internally so as to maintain the outlet temperature of the casting zone at 120 to 200 DEG C while rotating a pair of rolls having an outer diameter of 400 mm or more, In a casting method of a sheet, A uniform coating of soot was applied to the outer surface of the roll pair in the upper stream of the roll bite so as to sufficiently cover all the surfaces of the roll opposite to the aluminum sheet cast to a thickness of 0.5 microns or less by burning acetylene against the outer surface of the moving roll In addition, Continuously feeding the molten metal into the roll bite of a pair of soot coated rolls and progressively solidifying the molten aluminum as it passes through the casting zone and passing it through the thick zone of the solidified overhead stream of the roll centerline, Characterized in that the gauge of solid aluminum metal is reduced by 10% to 80% at the rolling center line to the rolling pressure and temperature which completely burns the soot so that there is no soot residue in the cast product and eliminates the insulating effect of the soot layer. 19. The method of claim 18, wherein the casting zone has a length of no more than 100 mm from the zone where the molten metal initially contacts the casting surface of the roll centerline. A metal consisting of cooling the outer surface of the roll internally so as to maintain a temperature sufficient to cause gradual solidification of the molten metal fed to the roll bite between the rolls while rotating a pair of rolls horizontally aligned with one another of the roll casting machine, In a casting method of a sheet, After applying a soot having a particle size of 0.1 micron or less along the outer surface of the roll on which the metal is cast in a top stream of roll bytes with a uniform coating of 1.4 microns or less; Feeding molten metal into the roll bite; Gradually solidify the molten metal supplied by the roll bite to complete the solidification before the metal passes the centerline of the roll; Characterized in that the solid metal is hot-rolled as it passes the centerline of the roll at a separation pressure suitable to reduce the gauge of the solid metal by at least 10%. 21. The roll casting sheet product of claim 20, wherein the sheet is aluminum or an aluminum alloy.