ES2423825T3 - Nonferrous Metal Casting - Google Patents

Abstract

A method of continuously casting a molten metal to obtain a metallic product comprising the steps of: providing a non-ferrous molten metal on a pair of separate, forward-moving casting surfaces; solidifying the molten metal on the casting surfaces while advancing the metal between the casting surfaces to produce solid metal outer layers adjacent to the casting surfaces and a semi-solid inner layer containing globular metal dendrites between the solid metal outer layers; solidifying the semi-solid inner layer to produce a solid metal product composed of the inner layer and the outer layers; and removing the solid metal product from between the casting surfaces, the casting surfaces being the surfaces of rotating cylinders with a defined narrowing point between them or the casting surfaces being the surfaces of belts that run on the rotating cylinders, defining the cylinders a point of narrowing between them, characterized by the fact that the metal is an alloy of magnesium, titanium, copper, nickel, zinc or tin and because the product is made to leave the point of constriction at a speed of 7, 6 to 122 meters per minute (25 to 400 feet per minute); the force applied by the cylinders to the metal advancing between them is not more than 525 N per cm of product thickness (300 pounds per inch of product thickness), and the product comprises a metal band having a thickness of 0.15 to 0 , 64 cm (0.06 to 0.25 inches), the method being carried out in such a way that the completion of said solidification step occurs at the point of narrowing, and according to the method the dendrites are broken in the semi-solid inner layer before the completion of said solidification step and where said dendrites have not been worked.

Description

Nonferrous Metal Casting

Field of the Invention

[0001] The present invention relates to the casting of non-ferrous metal alloys, more specifically, to the casting of non-ferrous metal alloys to create a rapidly solidified crust or crust and a central area without segregation containing broken dendrites.

Background of the invention

[0002] Continuous casting of metals, such as aluminum alloys, is conventionally carried out in twin cylinder casting machines, block casting machines and tape casting machines. The casting of aluminum alloys between twin cylinders has given good results and has enjoyed a good commercial application success despite the low production speeds obtained to date. Casting between twin cylinders traditionally consists of a combined solidification and deformation technique that consists in feeding the molten metal into the bite between a pair of cooled counter-rotating cylinders where solidification begins when the molten metal comes into contact with the cylinders. The solidified metal is formed as a "freezing front" of the molten metal within the bite between the cylinders and the solid metal advances towards the point of narrowing, the minimum separation point between the cylinders. The solid metal passes through the point of narrowing like a solid sheet. The solid sheet is deformed by the cylinders (hot rolled) and leaves the cylinders.

[0003] Aluminum alloys have been slipping between cylinders successfully obtaining sheets of 0.63 cm (1/4 inch) thick at about 1.22-1.83 m / min (4-6 feet per minute) ) or about 0.89-1.25 kg per hour per cm of laundry thickness (50-70 pounds per hour per inch of laundry thickness (lbs / hr / in)). Attempts to increase the speed of laundry between cylinders have normally failed due to segregation in the center line. Although it is generally accepted that a reduced gauge sheet (for example, with a thickness less than 0.63 cm (1/4 inch)) could be produced more quickly than a sheet with a larger gauge in a cylinder casting machine , the ability to cast aluminum between cylinders at speeds significantly greater than 1.25 kg / hr / cm (70 lbs / hr / inch) has proved difficult to achieve.

[0004] The normal operation of a fine gauge twin cylinder casting machine is described in US Patent No. 5,518,064 and can be seen in Figs. 1 and 2. A molten metal retention chamber H is connected to a feed tip T that distributes the molten metal M between twin water-cooled cylinders R1 and R2 that rotate in the direction of arrows A1 and A2, respectively. The cylinders R1 and R2 have smooth surfaces U1 and U2; and any roughness thereon is the result of the grinding technique of the cylinders used during its manufacture. The center lines of the cylinders R1 and R2 are in a vertical or more or less vertical plane L (for example, up to about 15 ° from the vertical) so that the casting band S is formed in a more or less horizontal path. With other versions of this method a band is formed in a vertically upward direction. The thickness of the cast band S is determined by the thickness of the tip T. The plane L passes through a region of minimum separation between the cylinders R1 and R2 called the point of narrowing between the cylinders N. Between the solid cast band S and the molten metal M is a solidification region between which it includes a mixed phase region of liquid and solid X. Between the region X and the casting band S a freezing front F is defined as a complete solidification line.

[0005] In conventional aluminum alloy casting, the heat of molten metal M is transferred to cylinders R1 and R2 so that the location of the freezing front F is maintained upstream of the narrowing point N. From this Thus, molten metal M solidifies to a thickness greater than the dimension of the narrowing point N. The cast solid band S is deformed by the cylinders R1 and R2 to reach the final thickness of the band. With the hot rolling of the solidified web between the R1 and R2 cylinders in accordance with conventional inter-cylinder casting, unique properties are obtained in the characteristic band of the aluminum alloy band cast between cylinders. In particular, a central zone through the thickness of the band is enriched in eutectic forming elements (eutectic forming) in the alloy such as Fe, Si, Ni, Zn and the like and impoverishes in peritectic forming elements (Ti , Cr, V and Zr). This enrichment of eutectic formers (namely, alloy elements other than Ti, Cr, V and Zr) in the central zone occurs because that portion of the band S corresponds to a region of the freezing front F in which solidification occurs in the last place and is known as "segregation of the central line". Extensive segregation of the center line in the raw band is a factor that restricts the speed of conventional cylinder casting machines. The raw band also shows work signals from the cylinders. The grains that are formed during solidification of the metal upstream of the point of narrowing are flattened by the cylinders. Therefore, cast aluminum between cylinders includes elongated grains at an angle to the rolling direction.

[0006] The separation between the cylinders at the point of narrowing N can be reduced to produce a band with a finer gauge S. However, by reducing the separation between the cylinders, the separation force of the cylinders generated by the metal increases solid between cylinders R1 and R2. The amount of separation force of the cylinders is affected by the location of the freezing front F with respect to the point of narrowing of the cylinders N. By reducing the separation between the cylinders, the

reduction percentage of the metal sheet as well as the force of separation of the cylinders. At some point, the relative positions of the cylinders R1 and R2 to achieve the desired separation between the cylinders cannot withstand the force of separation of the cylinders and the minimum gauge thickness is reached for that position of the freezing front F.

[0007] The force of separation of the cylinders can be reduced by increasing the speed of the cylinders to move the freezing front F downstream towards the narrowing point N. By moving the freezing front downstream (towards the narrowing point N) , the separation between the cylinders can be reduced. This movement of the freezing front F reduces the ratio between the thickness of the band at the initial solidification point and the separation between the cylinders at the point of narrowing N, thus reducing the separation force of the cylinders since, proportionally, compress and hot rolled less solidified metal. Thus, as the position of the freezing front F moves towards the narrowing point N, a proportionally larger amount of metal solidifies and then hot rolled to finer calibres. According to conventional practice, the inter-cylinder casting of a thin gauge band is achieved by first casting between the cylinders a band with a relatively high caliber, reducing the caliber until reaching a maximum force of separation of the cylinders, advancing the freezing front to reduce the force of separation of the cylinders (based on increasing the speed of the cylinders) and continue reducing the caliber until again reaching the maximum force of separation of the cylinders, and repeat the process of advancing the freezing front and reduce the caliber iteratively until the desired caliber is reached. For example, a band of 10 millimeters S can be laminated and the thickness reduced until the separation force of the cylinders becomes excessive (for example, at 6 millimeters), for which it is necessary to increase the speed of the cylinders.

[0008] This process of increasing the speed of the cylinders can only be carried out when the freezing front F reaches a predetermined position downstream. Conventional practice dictates that the freezing front F does not advance towards the point of narrowing between the cylinders N to ensure that the solid band is laminated at the point of narrowing N. It is generally recognized that it is necessary to laminate a solid band at the point of narrowing N to avoid failures in the cast metal strip S that is hot rolling and provide a tensile strength to the existing band S sufficient to withstand the tensile force of a winder, drag rollers or the like arranged downstream. Consequently, the separation force of the cylinders of a twin-cylinder casting machine used in the conventional manner where a solid band of an aluminum alloy is hot rolled at the point of narrowing N is of the order of several tons per inch thick. Although the caliber can be reduced somewhat, the use of such high separation forces of the cylinders so high to ensure the deformation of the band at the point of narrowing N makes it even more difficult to reduce the band gauge. The speed of a cylinder casting machine is restricted by the need to keep the freezing front F upstream of the narrowing point N and avoid segregation in the center line. Therefore, the casting speed of the aluminum alloys between the cylinders has been relatively low.

[0009] In US Patent No. 6,193,818 some reduction of the force of separation of the cylinders to obtain an acceptable microstructure in aluminum alloys having a high alloy element content is described. Alloys that are 0.5 to 13% by weight of Si slip between the cylinders, obtaining a band between 0.15 and 0.05 cm (0.05 to 0.02 inches) thick at forces of separation of the cylinders of about 8757 to 70053 N / cm (5000 to 40,000 pounds / inch) at speeds of about 1.7 m / sec at 6.3 m / min (5 to 9 feet per minute). Although this represents a breakthrough in the reduction of cylinder separation forces, these forces continue to pose significant challenges to the process. In addition, productivity is still compromised and the band produced according to patent 6,193,818 apparently has some segregation in the central line and an elongation of the grain as shown in Fig. 3 thereof.

[0010] A major impediment to high-speed casting between cylinders is the difficulty of achieving uniform heat transfer from molten metal to smooth surfaces U1 and U2, namely cooling of molten metal. In reality, surfaces U1 and U2 include several imperfections that alter the heat transfer properties of the cylinders. At high rolling speeds, said lack of uniformity in heat transfer is problematic. For example, some areas of surfaces U1 and U2 with a correct heat transfer will cool the molten metal M at the desired location upstream of the narrowing point N while some areas with insufficient heat transfer properties will allow a portion of the molten metal advances beyond the desired location and creates a lack of uniformity in the cast strip.

[0011] In vertical casting machines, fine gauge steel bands have been cast between cylinders successfully at high speeds (up to about 122 m / min (400 feet per minute)) and low cylinder separation forces. The cylinders of a vertical cylinder casting machine are placed side by side so that the band is formed in a downstream direction. According to this vertical orientation, the molten steel is fed to the bite between the cylinders to form a bath of molten steel. The upper surface of the molten steel bath is normally protected from the atmosphere by an inert gas.

[0012] Although vertical casting between twin cylinders of a molten metal bath is suitable for steel, vertical casting of oxidation-sensitive alloys (eg aluminum) requires additional control. A proposal to solve this problem of oxidized aluminum in vertical casting between laboratory-scale cylinders is described in Haga et al., "High Speed Roll Caster for Aluminum Alloy Strip," Proceedings of ICAA-6, Aluminum Alloys, Vol. 1 , P. 327-332 (1998). According to that method, a stream of molten aluminum alloy is directly ejected with a pressurized gas nozzle onto one or both twin cylinders of a vertical cylinder casting machine. Although high-speed aluminum alloy band casting is achieved, one of the major drawbacks of this technique is that the feed rate of the molten aluminum alloy has to be carefully controlled to ensure uniformity in the casting band. When only one is ejected

single current on a cylinder, the current solidifies forming the band. If a current is ejected on each of the cylinders, each current becomes half the thickness of the cast strip. In both cases, any variation in the gas pressure or the feed rate of the molten aluminum alloy results in the lack of uniformity in the cast strip. The control parameters for this type of casting of an aluminum alloy between cylinders are not practical on a commercial scale.

[0013] Tape casting machines have achieved continuous casting speeds of aluminum alloys of about 6.1 to 7.6 m / min (20-25 feet per minute) at a 19 mm caliber (¾ of inch) at a productivity level of about 250 kg per hour per casting thickness (400 pounds per hour per inch of thickness). In a conventional strip casting as described in US Patent No. 4,002,197, the molten metal is fed into a casting region between opposite portions of a pair of rotating flexible metal bands. Each of the two flexible casting belts rotates in a path defined by upstream laminators located at one end of the casting region and downstream laminators located at the other end of the casting region. In this way, the casting belts converge directly opposite each other around the upstream laminators to form an inlet in the casting region at the point of narrowing between the upstream laminators. The molten metal is fed directly at the point of narrowing. The molten metal is confined between the moving belts and solidifies as it is transported. The heat released by the metal that is solidifying is removed through the portions of the two tapes adjacent to the metal being cast. This heat is removed by cooling the inverse surfaces of the tapes by rapidly moving substantially continuous films of water flowing in and coming into contact with these inverse surfaces.

[0014] The operating parameters for belt casting are significantly different from those for cylinder casting. Specifically, there is no intentional hot rolling of the web. The solidification of the metal is completed at a distance of about 30-38 mm (12-15 inches) downstream of the narrowing point for a thickness of 1.89 cm (¾ inch). The tapes are exposed to high temperatures upon contact with molten metal on a surface and cooled with water on the inner surface. This can lead to a distortion of the tapes. The tension in the tape must be adjusted to account for the expansion or contraction of the tape as a result of temperature changes to achieve a constant quality of the surface of the band. The casting of aluminum alloys in a belt casting machine has been used to date mainly for products with minimum surface quality requirements or for products that are to be painted later.

[0015] The problem of thermal instability of the belts is avoided with block casting machines. Block casting machines include a plurality of cooling blocks mounted side by side on a pair of opposite tracks. Each set of cooling blocks rotates in the opposite direction to form a casting region between them in which the molten metal is fed. The cooling blocks act as heat sinks as the heat of the molten metal is transferred to them. The solidification of the metal is completed about 30-38mm (12-15 inches) downstream from the entrance of the casting region to a thickness of 1.875 cm (¾ inch). The heat transferred to the cooling blocks is eliminated during the return loop. Unlike the belts, the cooling blocks are not functionally distorted by heat transfer. However, block casting machines need dimensional control to avoid spaces between the blocks that cause a lack of uniformity and defects in the casting band.

[0016] This concept of transferring heat from molten metal to a casting surface has been used in certain modified tape casting machines such as those described in US Patent Nos. 5,515,908 and 5,564,491. In a heat dissipation tape casting machine, molten metal is fed to the belts (the casting surface) upstream of the narrowing point where solidification begins before the narrowing point and the continuous heat transfer of the metal to the tapes downstream of the narrowing point. In this system, the molten metal is supplied to the belts along the curve of the upstream mills so that the metal solidifies substantially by the time it reaches the point of narrowing between the upstream mills. The heat of the molten metal and the cast strip is transferred to the tapes that are within the casting region (including that found downstream of the narrowing point). This heat is then removed from the tapes when the tapes cease to be in contact either with the molten metal or with the cast strip. In this way, the portions of the belts that are within the casting region (in contact with the molten metal and the casting band) are not subjected to large temperature variations as is the case with conventional tape casting machines. The thickness of the band can be limited by the thermal capacity of the belts between which the casting takes place. Production speeds of 429 kg / hr / cm (2400 lbs / hr / inch) have been reached in the case of a 2-2.5mm (0.08-0.1 inch) band.

[0017] However, there are still problems associated with the belts used in a conventional laundry. In particular, the uniformity of the cast strip depends on the stability of (ie, the tension in) the tapes. In any tape casting machine, of conventional or thermal dissipation type, the contact of the hot molten metal with the tapes and the heat transfer of the metal that is solidifying to the tapes creates instability in the tapes. In addition, the tapes have to be changed at regular intervals which interrupts production.

[0018] The non-ferrous alloy band material is suitable for use as an iron in the automobile and aerospace industries and in the production of can bodies and cans and can rings. Conventional manufacturing of can bodies follows a series of batch processes that include a wide sequence of independent steps. If an ingot is needed to continue with the process, the surface layer is first removed, heat treated to homogenize the

The alloy is cooled and laminated while still hot in a series of passes, hot rolled for finishing and finally rolled up, cooled with air and stored. The coil can be annealed in one batch step. The rolled sheet is then further reduced to a final gauge by cold rolling with single, / or tandem unwinders, winders and rolling mills. These batch processes, normally used in the aluminum industry, require many different material handling operations to move the ingots and coils between what are normally independent processing steps.

[0019] US Pat. Nos. 4,260,419 and 4,282,044 describe efforts to expedite the production of can bodies by direct casting in a shell and continuous casting of bands in a mini-mill, respectively. In both processes many material handling operations are necessary to move the ingots and coils. These operations are laborious, consume energy and often produce damage to the product.

In US Pat. Nos. 5,772,802 and 5,772,799, casting methods are presented with ribbons for obtaining cans or lids and a method for their manufacture according to which an aluminum alloy band with a low content of Alloy to form a hot-band cast material, the hot feed material is quickly rewound to avoid substantial precipitation, quickly coated and reverted to avoid substantial precipitation of the alloy elements, and then laminated cold This process has been satisfactory despite the relatively low production speeds obtained to date.

A process for the manufacture of sheets from a molten metal is presented in US Patent 2,693,012. The molten metal is fed continuously to the bite of a pair of cooled cylinders operated at high rotation speed to produce a sheet with a thickness of 1.65 mm. As the metal cools on the surface of the cylinder, a retention coating is formed with the metal adjacent to the cylinder and a plastic condition is created in the central portion of the rest of the metal. The plastic metal is mechanically worked and finally freezes completely immediately before the moment when the metal sheet passes through the bite of the cylinders.

In addition, on an industrial scale, alloys other than aluminum, such as magnesium alloys, have not been continuously cast. Magnesium metal has a hexagonal crystalline structure that greatly restricts the amount of deformation that can be applied, especially at low temperatures. Therefore, the production of forged magnesium alloy products is usually carried out by hot work in the range of 300 to 500 ° C and even, under these circumstances, several rolling passes and intermediate annealing are necessary. In the conventional method with ingots, a total of up to 25 rolling passes with intermediate anneals are used to obtain a finished product with a 0.5 mm caliber. As a result, forged magnesium products tend to be expensive.

Consequently, there remains a need for an economical method for casting non-ferrous alloys with which uniformity is achieved on the casting surface.

Summary of the Invention

According to the present invention, there is provided a method for continuous casting of molten metal to obtain a metallic product consisting of the steps of:

feed a non-ferrous molten metal onto a pair of separate casting surfaces that move forward;

solidify the molten metal on the casting surfaces while advancing the metal between the casting surfaces to produce outer layers of solid metal adjacent to the casting surfaces and a semi-solid inner layer containing globular metal dendrites between the outer layers of solid metal;

solidify the semi-solid inner layer to produce a solid metal product composed of the inner layer and the outer layers; Y

remove the solid metal product from between the casting surfaces, the casting surfaces being the surfaces of rotating cylinders with a defined narrowing point between them or

the casting surfaces being the surfaces of some belts that move on the rotating cylinders, the cylinders defining a narrowing point between them, which is characterized in that the metal is an alloy of magnesium, titanium, copper, nickel, zinc or tin and because the product is expelled from the point of narrowing at a speed of 7.6 to 122 meters per minute (25 to 400 feet per minute); The force applied by the cylinders to the metal that advances between them is not more than 525 N per cm of product thickness (300 pounds per inch of product thickness), and the product comprises a metal band having a thickness of 0.15 at 0.64 cm (0.06 to 0.25

inches), the method being carried out as the completion of said solidification step occurs at the point of narrowing, and according to the method the dendrites are broken in the semi-solid inner layer before the completion of said solidification step and where said dendrites have not been worked.

Preferably, the metal is a magnesium or titanium alloy.

Advantageously, the product leaves the narrowing point at least 30.5 meters per minute (100 feet per minute).

Conveniently, the thickness of the solidified inner layer comprises between 20% and 30% of the product thickness.

Preferably, the casting surfaces are textured to form irregularities in the surfaces that come into contact with the molten metal.

Advantageously, said surface irregularities are in the form of grooves, dimples or grooves.

Conveniently, said surface irregularities are separated according to a regular pattern of 8 to 48 irregularities per centimeter (20 to 120 irregularities per inch).

Preferably, said surface irregularities are separated according to a regular pattern of 24 irregularities per centimeter (60 irregularities per inch).

Conveniently, said irregular surfaces have a height of 5 to 50 micrometers.

Advantageously, said irregular surfaces have a height of 30 micrometers.

Preferably, the casting surfaces are brushed continuously in the remote regions of the product to eliminate debris that could accumulate.

Brief description of the drawings

The invention will be fully understood from the following description and in relation to the figures of the accompanying drawings, where, in all of them, the same reference characters identify the same pieces.

[0027] Fig. 1 is a schematic diagram of a portion of a casting machine with a molten metal feed tip and a pair of cylinders;

[0028] Fig. 2 is an enlarged cross-sectional schematic diagram of the die nozzle of the molten metal and the cylinders shown in Fig. 1 operating according to prior art;

[0029] Fig. 3 is a flow chart of the steps of the casting method of the present invention;

[0030] Fig. 4 is a schematic diagram of molten metal casting performed in accordance with the present invention;

[0031] Fig. 5 is a schematic diagram of a casting machine manufactured in accordance with the present invention with an optional band clamping mechanism and cooling elements; Y

[0032] Fig. 6 is a schematic diagram of a casting machine manufactured in accordance with the present invention with another band fastening mechanism and optional cooling elements.

Detailed description of the invention

[0033] For the purposes of the description that follows, it should be understood that the invention may assume different modifications and sequences of alternative steps, except where expressly stated otherwise. It should also be understood that the specific devices and processes illustrated in the accompanying drawings, and described in the following specification, are simply embodiments of the invention offered by way of example. Therefore, the specific dimensions and the rest of the physical characteristics related to the embodiments presented here should not be considered limiting. In relation to any numerical margin of values, said margins should be interpreted as including each and every one of the numbers and / or fractions between the specified maximum and minimum margins.

[0034] The present invention includes a casting method of a non-ferrous alloy consisting of feeding a molten non-ferrous alloy into a casting apparatus. Non-ferrous alloy should be understood as an alloy of an element such as magnesium, titanium, copper, nickel, zinc or titanium. Non-ferrous alloys especially suitable for use in the present invention are magnesium alloys and titanium alloys.

[0035] With the phrases "magnesium alloys" and "titanium alloys" it is intended to indicate alloys containing at least 50% by weight of the indicated element and at least one modifying element. It is considered that magnesium and titanium alloys can be interesting options for structural use in the aerospace and automobile industry given their light weight, high strength in relation to weight and high specific stiffness both at room temperature and at elevated temperatures. Examples of magnesium-based alloy systems are the Mg-Al system; the Mg-Al-Zn system; the Mg-Al-Si system; the Mg-Al-Rare Earths (TR) system; the Mg-Th-Zr system; the Mg-Th-Zn-Zr system; the Mg-Zn-Zr system; and the Mg-Zn-Zr-TR system.

[0036] The most basic form of the invention has been schematically represented in the flow chart of Fig. 3. In step 100, the molten nonferrous metal is fed into a casting apparatus. The casting apparatus includes a pair of separate casting surfaces that move forward as described in detail below. In step 102, the casting apparatus rapidly cools at least a portion of the non-ferrous alloy to solidify an outer layer of the non-ferrous alloy while maintaining a semi-solid inner layer. The inner layer includes a molten metal component and a solid metal dendrite component. The thickness of the solidified outer layer increases as the alloy is cast. The dendrites of the inner layer are altered in step 104, for example, breaking the dendrites to obtain smaller structures. In step 106, the inner layer is solidified. The product exiting the casting apparatus includes the solid inner layer formed in step 106 containing the broken dendrites interposed within the solid outer layer of the alloy. The product can have various forms such as, but not exclusively, sheets, plates, plates and sheets. In the case of extrusion casting, the product can be in the form of wire, rod, bar or any other extrusion. In either case, the product can be further processed and / or treated in step 108. The order of steps 100-108 is not fixed in the method of the present invention and may occur sequentially or some steps may occur simultaneously.

[0037] The present invention balances the rate of solidification of the molten metal, the formation of dendrites in the metal being solidified and the alteration of the dendrites to obtain the desired properties in the final product. The cooling rate is selected so that rapid solidification of the outer layers of the metal is achieved. In the case of non-ferrous alloys, cooling of the outer layers of the metal can occur at a rate of at least 100 ° C per minute. Suitable casting apparatuses include cooled casting surfaces such as in a twin cylinder casting machine, a belt casting machine, a plate casting machine or a block casting machine. Vertical cylinder casting machines can also be used in the present invention. In a continuous casting machine, the casting surfaces are normally separated and have a region in which the distance between them is minimal. In a cylinder casting machine, the region where the distance between the casting surfaces is minimal is the point of narrowing. In a belt casting machine, the region in which the distance between the belt casting surfaces is minimal may be the point of narrowing between the pulleys of the casting machine. As described in more detail below, the operation of a casting apparatus according to the regime of the present invention includes the solidification of the metal in the place where the distance between the casting surfaces is minimal. Although the method of the present invention is described below as being carried out using a twin cylinder casting machine, it does not mean that it is exclusive. Other continuous casting surfaces can be used to practice the invention.

[0038] By way of example, a cylinder casting machine (Fig. 1) can be used to practice the present invention as shown in detail in Fig. 4. Referring to Fig. 1 (in the that horizontal continuous casting is represented in accordance with the prior art and in accordance with the present invention), the present invention is implemented using a pair of cooled counter-rotating cylinders R1 and R2 rotating in the directions of arrows A1 and A2, respectively. With the term horizontal it is meant that the cast band is produced in a horizontal orientation or at an angle of about 30 ° to the horizontal. As shown in more detail in Fig. 3, a feed tip T, which can be made of a refractory material or any other ceramic material, directly distributes the molten metal M in the direction of the arrow B on the cylinders R1 and R2 rotating in the direction of arrows A1 and A2, respectively. The separations G1 and G2 between the feed tip T and the corresponding cylinders R1 and R2 are kept as small as possible to prevent the leakage of molten metal and minimize the exposure of molten metal to the atmosphere along the cylinders R1 or R2 to avoid contact between the tip T and the cylinders R1 and R2. A suitable dimension of the G1 and G2 separations is about 0.25 mm (0.01 inches). A plane L through the center line of cylinders R1 and R2 passes through a region of minimum separation between cylinders R1 and R2 called the point of narrowing of cylinders N.

[0039] The molten metal M is fed to the casting surfaces of the cylinder casting machine, the cooled cylinders R1 and R2. The molten metal M comes directly into contact with the cylinders R1 and R2 in regions 2 and 4, respectively. Upon contact with the R1 and R2 cylinders, the metal M begins to cool and solidify. The metal that is cooling solidifies as

upper crust 6 of solidified metal adjacent to cylinder R1 and lower crust of solidified metal adjacent to cylinder R2. The thickness of the crusts 6 and 8 increases as the metal M advances towards the narrowing point N. In the interfaces between each of the upper and lower crusts 6 and 8 and the molten metal M large dendrites 10 of solidified metal (not shown to scale). The large dendrites 10 break and drag into a central portion 12 of the flow of molten metal M that moves more slowly and are dragged in the direction of the arrows C1 and C2. The flow drag action can cause large dendrites 10 to continue breaking into smaller dendrites 14 (not shown to scale). In the central portion 12 upstream of the narrowing point N referred to as region 16, the metal M is semi-solid and includes a solid component (small solidified dendrites 14) and a molten metal component. The metal M of the region 16 has a pasty consistency due, in part, to the dispersion of the small dendrites 14 inside. In the place of the narrowing point N, part of the molten metal is pressed back in the opposite direction to the arrows C1 and C2. The forward rotation of the cylinders R1 and R2 at the point of narrowing N only substantially advances the solid portion of the metal (the upper and lower crusts 6 and 8 and the small dendrites 14 of the central portion 12) while forcing the molten metal of the central portion 12 upstream from the narrowing point N so that the metal passes to a completely solid state when it leaves the point of the narrowing point N. Downstream of the narrowing point N, the central portion 12 is a solid central layer 18 containing the small dendrites 14 interposed between the upper crust 6 and the lower crust 8. In the central layer 18, the small dendrites 14 can have a size of about 20 to about 50 microns and have a generally globular shape. In a web-shaped product, the solid inner portion may constitute approximately 20 to 30 percent of the total thickness of the web. Although the casting machine of Fig. 4 is shown to produce an S band in a generally horizontal orientation, this should not be considered as limiting since the S band can exit the casting machine at an angle or in a vertical direction.

[0040] The casting process described in relation to Fig. 4 follows the steps of the method mentioned above. The molten metal fed in step 100 in the cylinder casting machine begins to cool and solidify in step 102. In the metal being cooled, outer layers of solidified metal 6 and 8 are formed near or next to the surfaces cooled laundry (R1 and R2). The thickness of the solidified layers 6 and 8 increases as the metal advances through the casting apparatus. In relation to step 102, metal dendrites 10 are formed in an inner layer 12 that is surrounded, at least partially, by solidified outer layers 6 and 8. In Fig. 4, outer layers 6 and 8 substantially surround the inner layer 12 so that the inner layer 12 is interposed between the two outer layers 6 and 8. In other casting devices, the outer layer may completely surround the inner layer. In step 104, the dendrites 10 are altered, for example, they break to form smaller structures

14. Before the complete solidification of the metal, in the inner layer 12 the metal is semi-solid and includes a solid component (the small solidified dendrites 14) and a molten metal component. At this stage, the metal has a pasty consistency due, in part, to the dispersion of the small dendrites 14 inside. In step 106, in the place of complete solidification of the metal of the casting apparatus, the solidified product includes an inner portion 18 containing the small dendrites 14 surrounded, at least partially, by an outer portion. The thickness of the inner portion may constitute approximately 20 to 30 percent of the thickness of the product. In the inner portion, the small dendrites can have a size of about 20 to 50 microns and the casting apparatus has not worked them substantially so they have a generally globular shape.

[0041] According to the present invention, the molten metal of the inner layer 12 is pressed in a direction opposite to its flow through the casting apparatus (as described in reference to the casting between cylinders) and / or can be forced to enter the outer layers 6 and 8 and reach the outer surfaces of the outer layers 6 and 8. This feature of pressing and / or forcing the molten metal into the inner layer occurs in any of the described casting devices in this document.

[0042] The breakage of the dendrites of the inner layer of step 104 occurs during the casting between the cylinders by the shear forces resulting from the speed differences between the molten metal inner layer and the outer layer. Cylinder machines that operate at conventional speeds of less than 3.3 m / min (10 feet per minute) do not generate the shear forces necessary to break any of these dendrites. Although high speed operation (at least 8.2 m / min (25 feet per minute)) of a conventional cylinder casting machine with solidification control as described above allows casting according to the regime of the present invention, Other conventional casting devices can also be adapted to function in a way that results in the process of the invention. An important aspect of the present invention is the breakage of the dendrites of the inner layer. The breakage of the dendrites minimizes or prevents segregation in the central line, obtaining improved conformation and elongation properties in the finished product due to the reduction or absence of thick constituents such as those that would be present in a cast product with a machine of cylinders or one of belts that would present a segregation in the central line. Other suitable mechanisms for breaking the dendrites of the inner layer include application to the mechanical stirring liquid (e.g., propeller), electromagnetic stirring including stirring with a rotational stator and stirring with a linear stator, as well as ultrasonic vibration of high frequency.

[0043] The casting surfaces act as heat sinks of molten metal. In the present invention, heat is transferred uniformly from the molten metal to the cooled casting surface to ensure uniformity on the surface of the cast product. The cooled casting surfaces can be made of steel or copper and can be textured and include irregularities in the surfaces that come into contact with the molten metal. The irregularities of the surfaces can serve to increase the heat transfer of the surfaces of the cooled casting surfaces. The imposition of a controlled degree of lack of uniformity on the surfaces of the cooled casting surfaces can result in a uniform heat transfer across the surfaces thereof. Surface irregularities may be in the form of grooves, dimples, stretch marks or other structures and may be separated according to a regular pattern of about 8 to 47 surface irregularities per cm (about 20 to about 120 surface irregularities per inch) or about 24 irregularities per cm (60

irregularities per inch). The irregularities of the surfaces can have a height of about 5 to about 50 microns or about 30 microns. The cooled casting surfaces can be coated with a material such as chromium or nickel to facilitate separation of the cast product therefrom.

[0044] Casting surfaces generally heat up during casting and are prone to oxidize at elevated temperatures. Non-uniform oxidation of the casting surfaces during casting can change the heat transfer properties thereof. Therefore, casting surfaces can be oxidized before use to minimize changes during casting. Periodic or continuous brushing of casting surfaces is beneficial for removing debris that accumulates during the casting of non-ferrous alloys. Small fragments of the cast product can peel off the product and adhere to the casting surfaces. These small fragments of the non-ferrous alloy product are prone to oxidizing which results in a lack of uniformity of the heat transfer properties of the casting surfaces. The brushing of the casting surfaces avoids the problems of lack of uniformity as a consequence of the residues that can accumulate on the casting surfaces.

[0045] In a cylinder casting machine operated according to the regime of the present invention, the control, maintenance and selection of the appropriate speed of the R1 and R2 cylinders may influence the operability of the present invention. The speed of the cylinders determines the speed at which the molten metal M advances towards the point of narrowing N. If the speed is too low, the large dendrites 10 will not receive sufficient forces to be drawn into the central portion 12 and breaking into small dendrites 14. According to this, the present invention is suitable for operation at high speeds such as about 7.62 to about 1.22 m / min (about 25 to about 400 feet per minute) or about 30.5 a about 122 m / min (about 100 to about 400 feet per minute) or about 46 to about 91 m / min (about 150 to about 300 feet per minute). The linear speed per unit area at which molten aluminum is fed to cylinders R1 and R2 may be less than the speed of cylinders R1 and R2 or about a quarter of the speed of cylinders. According to the present invention, continuous high speed casting can be achieved, in part, because the textured surfaces D1 and D2 ensure uniform heat transfer from the molten metal

M.

[0046] The force of separation of the cylinders can be an important parameter when practicing the present invention. A significant advantage of the present invention is that the solid band is not produced until the metal reaches the narrowing point N. The thickness is determined by the dimension of the narrowing point N between the cylinders R1 and R2. The force of separation of the cylinders can be high enough to press the molten metal upstream and away from the point of narrowing N. If an excessive amount of molten metal passes through the narrowing point N, the layers of the upper crusts e bottom 6 and 8 and the solid central portion 18 can move away from each other and misalign. If an insufficient amount of molten metal arrives at the point of narrowing N, the band will be formed prematurely as occurs in casting processes with conventional cylinders. A prematurely formed band 20 can be deformed by cylinders R1 and R2 and undergo segregation in the center line. Suitable separation forces of the cylinders are about 44 to 525 N / cm (about 25 to about 300 pounds per inch) of casting thickness or about 175 N per cm (100 pounds per inch) of casting thickness. In general, lower casting speeds can be set by casting a thicker nonferrous alloy to remove heat from the thick alloy. In contrast to conventional cylinder castings, with the present invention said lower casting speeds do not generate excessive cylinder separation forces since the completely solid nonferrous web does not occur upstream of the narrowing point.

[0047] The non-ferrous alloy band can be produced with a thickness of about 0.254 cm (0.1 inch) or less (for example, 0.152 cm (0.06 inch)) at casting speeds of about 7.62 to about 1.22 m / min (about 25 to about 400 feet per minute). By means of the method of the present invention a nonferrous alloy band of a thicker gauge can also be produced, for example, with a thickness of about 0.63cm (0.25 inches). With the laundry at the linear speeds contemplated in the present invention (i.e., about 7.62 to about 1.22 m / min (about 25 to about 400 feet per minute)), the non-ferrous alloy product solidifies about 1000 times faster than in non-ferrous alloy casting as ingot and improves the properties of the product with respect to the casting of non-ferrous alloys such as ingot.

[0048] The non-ferrous alloy product produced according to the method of the invention includes an inner portion substantially surrounded by an outer portion. The concentration of alloy elements may differ between the inner portion and the outer portion. The molten alloy may have an initial concentration of alloy elements that includes peritectic forming alloy elements and eutectic forming alloy elements. The concentration of alloy elements may differ between the outer portion and the inner portion. The inner portion of the product may be depleted in certain elements (such as eutectic trainers) and enriched in other elements (such as peritectic trainers) compared to the concentration of eutectic trainers and peritectic trainers in each of the metals and the outer portion. The grains of the non-ferrous alloy product of the present invention have not been substantially worked, that is, they have an equiaxial structure, such as globular. In the absence of hard particles in the inner portion of the product, segregation and cracking in the central line characteristic of many non-ferrous alloys is minimized or eliminated.

[0049] By practicing the present invention, it may be beneficial to support the product leaving the apparatus until the product cools sufficiently to self-support. A support mechanism shown in Fig. 5 includes continuous conveyor belt B placed under a belt S leaving the cylinders R1 and R2. The belt B travels around the pulleys P and supports the band S a distance that can be about 3.05 m (10 feet). The length of the belt B between the pulleys P can be determined from the casting process, the outlet temperature of the S band and the alloy of the S band. Suitable materials for the B belt include fiberglass and metal (by for example, steel) in solid state or mesh mode. Alternatively, as shown in Fig. 6, the support mechanism may include a fixed support surface J such as a chock on which the band S travels while cooling. The chock J can be made of a material to which the hot band S cannot easily adhere. In some cases in which the band S is subjected to a break when leaving the cylinders R1 and R2, the band may cool in the E points with a fluid such as air or water. Normally, in the case of aluminum alloys, the S band leaves the R1 and R2 cylinders at about 593 ° C (1100 ° F), and it may be convenient to lower the temperature of the aluminum alloy band to about 538 ° C (2000 ° F) from 20.3 to 25.4 cm (8 to 10 inches) approximately of narrowing point N. In US Patent No. 4,823,860 a suitable mechanism for cooling the band at points E is described. to reach said cooling point.

Examples (comparative)

[0050] An aluminum alloy containing a weight% of 0.75 of Si, 0.20 of Fe, 0.80 of Cu, 0.25 of Mn and 2.0 of Mg was cast in accordance with the present invention and then hot rolled and cooled in line to a 0.038 cm (0.015 inch) caliber. The resulting properties of the two products are listed in Table 1. Example 1 shows the properties obtained in the raw state of lamination after cooling the coil. The combination of high strength and good formability (elongation) is remarkable. The combination of the high elastic limit and the elongation achieved in Examples 1 and 2 had not been achieved so far in the aluminum-magnesium alloys of the 5xxx series. By way of comparison, aluminum alloy 5182, has at most an elastic limit of 372 MPa (54 ksi) and an elongation of 7%. The properties obtained after having heat treated the sheet with a solution and having aged it at 135 ° C (275 ° F) in the laboratory are shown in Example 2. A good elastic limit and superior flexural properties were obtained.

Table 1

Property

Example 1 Example 2

Elastic limit (ksi)

60 43

Breaking Tension (ksi)

65 55

Elongation (%)

10 16

Radius of curvature (r / t)

1.7 0.3 *

Lüders lines

any any

Olsen height (inches) - lubricated

0.195 -

Corrosion

- -

Orange peel

any any

Finish

semi bright sparkly

Temple type O

yes yes

* Flat hem - 1 ksi = 6.9 Mpa

[0051] By implementing the method of the present invention, cast products of non-ferrous alloys with an improved elastic limit and elongation can be produced compared to conventional cast products. Such improved properties allow the production of a finer product, convenient in the market.

[0052] The product leaving the casting apparatus can be shaped, by subsequent lamination, for example, by giving it a different shape or by treating it in any other way for the manufacture of can bands, ring bands, car plates and other end products including lithographic plates and shiny plates. Subsequent processing of the product exiting the casting apparatus can be performed by in-line lamination to take advantage of the heat of the raw sheet (in accordance with the following US Patents No. 5,772,799; 5,772,802; 5,356,495; 5,496 .423; 5,514,228; 5,470,405; 6,344,096 and 6,280,543). Alternatively, the raw sheet can be cooled and subsequently laminated off-line. Other sheet processing can be performed in accordance with one or more of the aforementioned patents.

[0053] Although the preferred embodiments of the present invention have already been described above in terms of being especially valuable for the production of non-ferrous alloy parts for the automobile and aerospace industries and beverage can industries, those versed in the They will understand that the present invention will also be valuable for the production of parts such as boats, canoes, skis, pianos, harps, truck bodies, truck cabins, buses, garbage collector containers, racing boat hulls, aircraft parts private, fire truck hose containers, material handling equipment, loading and unloading docks, portable ramps, aerospace equipment parts, including rockets and satellites, radar tracking systems, electronic equipment cabinets, vibrating screens , pallet boxes, racks and sides for luggage, stairs, anodes d e water heaters, typewriters, rocket launchers and mortar holders, textile machine parts, concrete pails and manual finishing tools, templates and accessories and vibration testing machines.

[0054] Although preferred embodiments of the present invention have already been described above in terms of being

5 especially valuable for horizontal casting of non-ferrous base alloys, those skilled in the art will understand that the present invention will also be valuable in a vertical casting in addition to any angle between vertical and horizontal casting. [0055] Although the preferred embodiments of the present invention have already been described above in terms of an aluminum metal strip product leaving the casting apparatus that includes a solid inner layer containing structures

10 altered dendritic substantially surrounded by the solid outer layer of the alloy, the product may be in the form of a sheet, plate, plate, sheet, wire, rod, bar or extrusion.

[0056] Although the preferred embodiments of the present invention have already been described above in terms of which the narrowing point of the twin cylinders is used to break the dendrites that are formed as the metal solidifies, that is, the metal of Aluminum, those skilled in the art will understand that the present invention will also be valuable with other non-ferrous metals including titanium, magnesium, nickel, zinc, tin and copper.

Claims (11)

1. A method of continuous casting of a molten metal to obtain a metallic product comprising the steps of: provide a non-ferrous molten metal on a pair of separate casting surfaces that move forward; solidify the molten metal on the casting surfaces while advancing the metal between the casting surfaces to produce outer layers of solid metal adjacent to the casting surfaces and a semi-solid inner layer containing globular metal dendrites between the outer layers of solid metal; solidify the semi-solid inner layer to produce a solid metal product composed of the inner layer and the outer layers; Y removing the solid metal product from between the casting surfaces, the casting surfaces being the surfaces of rotating cylinders with a defined point of narrowing between them or the casting surfaces being the surfaces of some ribbons moving on the rotating cylinders , the cylinders defining a point of narrowing between them, which is characterized by the fact that the metal is an alloy of magnesium, titanium, copper, nickel, zinc or tin and that the product is removed from the point of narrowing at a speed of 7.6 to 122 meters per minute (25 to 400 feet per minute); The force applied by the cylinders to the metal that advances between them is not more than 525 N per cm of product thickness (300 pounds per inch of product thickness), and the product comprises a metal band having a thickness of 0.15 at 0.64 cm (0.06 to 0.25 inches), the method being carried out so that the completion of said solidification step occurs at the point of narrowing, and according to the method the dendrites are broken in the inner layer semi-solid before the completion of said solidification step and where said dendrites have not been worked.

2.

The method of Claim 1, wherein the metal is a magnesium or titanium alloy.

3.

 A method according to Claim 1, wherein the product leaves the point of narrowing at least 30.5 meters per minute (100 feet per minute).

Four.

A method according to any of the preceding claims, wherein the thickness of the solidified inner layer comprises between 20% and 30% of the product thickness.

5.

A method according to any of the preceding claims, wherein the casting surfaces are textured to form irregularities in the surfaces that come into contact with the molten metal.

6.

A method according to Claim 5, wherein said surface irregularities are in the form of grooves, dimples or grooves.

7.

 A method according to Claim 5 or Claim 6, wherein said surface irregularities are separated according to a regular pattern of 8 to 48 irregularities per centimeter (20 to 120 irregularities per inch).

8.

 A method according to Claim 5 or Claim 6, wherein said surface irregularities are separated according to a regular pattern of 24 irregularities per centimeter (60 irregularities per inch).

9.

A method according to any one of Claims 5 to 8, wherein said surface irregularities have a height of 5 to 50 micrometers.

10.

 A method according to any one of Claims 5 to 8, wherein said surface irregularities have a height of 30 micrometers.

eleven.

 A method according to any of the preceding claims, wherein the casting surfaces are continuously brushed in the remote regions of the product to eliminate residues that could accumulate.