FI69972C - METAL CONTAINER CONTAINER - Google Patents

Description

69972

Continuous metal casting

The present invention relates to a continuous casting process for a metal ingot having a smooth and beautiful surface.

A metal casting made as a continuous casting generally does not have a completely smooth surface, but is uneven and often cracked at some points. This is because all conventional continuous casting methods use a cold mold in which a solid surface layer (shell) delimiting the surface of the ingot is formed. Friction is created between the inner surface of the mold and the surface layer by the ingot through the mold. If an ingot with a defective surface has to be immediately shaped, e.g. forged or rolled, a lot of defects remain in the final product. Therefore, the surface of the ingot must first be cleaned, i.e. the casting shell must be removed from it, and if the ingot has a deep crack, it cannot be used but must be remelted.

In a conventional continuous casting process using a cold casting mold, the ingot usually comes out through the bottom of the mold. If the solid surface layer formed by the metal to be cast adheres to the inner surface of the mold, the ingot 25 will not be able to move into the outlet of the mold, but a crack will appear in the ingot. If such a crack occurs at the mold outlet, the molten metal surrounded by the solid surface layer will exit through the bottom of the mold. This phenomenon is called "breakout" 30 (breakout). It prevents further casting and also poses a serious risk to occupational safety. A breakthrough occurs precisely in a metal or alloy that has a wide solidification temperature range.

Therefore, in the production of ingots as a continuous casting of such a metal, e.g. cast iron or phosphor bronze, an intermediate process has to be used, ___ —ι 2 69972 in which the molten metal is allowed to solidify completely in the mold. However, this is a very cumbersome method and takes a lot of time.

The present invention thus relates to a new casting method 5 which does not involve the above-mentioned drawbacks and which is capable of producing a casting with a smooth and beautiful surface as a continuous casting, while at the same time keeping the production capacity high and eliminating the risk of breakthrough completely. More specifically, in accordance with the invention, a continuous metal casting method has been developed which comprises feeding molten metal into a casting mold having a molten metal feed port and an ingot outlet. The temperature of the surface of the inner wall of the mold exceeds the solidification temperature of the metal to be cast, so that the surface of the molten metal at the mold outlet may have approximately zero pressure on the dummy bar 2o, in which case a solidified metal body is formed at the end of the model bar in continuous operation.

The method according to the invention can be used for continuous casting downwards, upwards and in a horizontal or other direction, so as to obtain an ingot which is a conventional metal or alloy and which has a cross-section of a plate, rod, tube or other profile. The surface of the ingot is smooth and beautiful and there are no factors endangering occupational safety during casting.

It is an object of the invention to provide a new method by which a metal casting with a smooth and beautiful surface is produced as a continuous casting very easily and efficiently without the above-mentioned risk of breakthrough.

In addition, the invention seeks to produce metal castings which have bars, plates, tubes and the like in cross section and whose surface practically does not need to be peeled.

3,69972

It is a further object of the invention to economically manufacture metal ingots having so-called unidirectional columnar structure. These objects and advantages of the invention will become apparent from the following detailed description of the principal principle and various structures of the invention.

Figures 1 (a) and 1 (b) are diagrams illustrating the main principle of the invention, Figure 2 is a vertical section of an apparatus used to apply the method of the invention in upward continuous casting, Figure 3 is a vertical section of another apparatus structure used to apply the method of the invention. in the upward continuous casting, Figure 4 is a vertical section of the apparatus used to apply the method of the invention in horizontal continuous casting, and Figure 5 is a vertical section of the apparatus used to apply the method of the invention in the downward continuous casting.

Figure 1 (a) shows the situation just before the start of the continuous casting according to the invention, and Figure 1 (b) illustrates the situation after the start of the casting. Figures 1 (a) and 1 (b) show a mold 1 for downward casting with a heater. In addition, these figures show molten metal 2, model casting 1. bar 3, which moves vertically by means of the drive in question (not shown). Further, Figs. 1 (a) and 1 (b) 30 show a casting 4 and 5 to be made in a continuous casting, with which the model rod or the casting j is continuously cast.

The inner wall of the mold 1 is heated by a heater above the solidification temperature of the molten metal and the molten metal 2 is fed to the mold 1. The pressure of the molten metal 2 is zero or approximately zero at the lower end of the mold 1 4 69972 X delimiting the outlet. The molten metal can be fed into the mold, e.g. with the system shown in Figure 5. This includes a paddle tube with one end immersed in molten metal in a melting furnace. The other end of the tube is connected to the mold. The mold outlet is flush with the surface of the molten metal in the furnace.

The model bar 3 is placed at the lower end of the mold 1 (Fig. 1 (a)) before feeding the molten metal 2 into the mold 1. Since the temperature of the upper end 10 of the model bar 3 contacting the molten metal 2 is lower than the solidification temperature of the molten metal 2, the molten metal 2 , but not at the hot inner wall of the mold 1. When the model rod 3 is moved downwards from the lower end of the mold 1 while the cooling device 5 is in operation, the solidified metal body 1. the ingot 4 increases gradually and comes out of the mold 1 as a continuous operation as shown in Fig. 1 (b). Because the temperature of the inner wall of the mold is higher than the solidification temperature of the metal, the mold does not form a solid surface layer (shell) delimiting its circumferential surface, but this is formed immediately below the mold outlet, so that the ingot has a very smooth surface.

According to an important aspect of the invention, the pressure of the molten metal in the mold bottom outlet is kept close to zero because the molten metal protrudes if a solid surface layer does not form in the ingot approximately 1 mm below the mold outlet.

According to the invention, it is also important to control the temperature of the molten metal and the cooling and outlet rate of the ingot in a suitable manner. It is very important that there is a sufficient balance between the cooling and outlet velocities of the ingot. If the ingot is cooled too fast compared to its outlet velocity, the molten metal solidifies in the mold and the solid surface-35 layer of the ingot adheres to the mold. The ingot then has a poor surface, which damages the inner wall of the mold and also makes it impossible to easily remove the ingot from the mold. To eliminate these drawbacks, a heater is provided in the mold, which keeps the inner wall of the mold at a suitable temperature.

5 Ko. in addition, in order to eliminate the drawbacks, it is advisable to make the inner wall of the mold somewhat inclined in the direction of the out-opening. The ingot is then removed from the mold without damaging its inner wall, even when the model rod has cooled too quickly. In this case, the molten me-10 stable cannot be solidified on the surface of the mold either.

The inventor has found in his experiments that when the pressure of the molten metal at the mold outlet is less than 196 Pa, continuous casting can be performed without the above-mentioned breakthrough as an upward or downward operation for almost all metals and alloys. In addition, it has been found that a pressure of up to 490 Pa can be applied to molten metal in horizontal casting if the solidified core 20 of the metal is allowed to form mainly in the mold.

The mold may be made of graphite or a refractory material consisting essentially of an oxide, e.g. silica, alumina, beryllium, magnesium or thorium oxide, or of a refractory material whose main part is a nitride, e.g. boron or silicon nitride, and also silicon carbide and a suitable refractory metal, e.g. platinum, tungsten, tantalum or an alloy of such a metal. A glass mold can also be used to cast a low melting point metal, e.g. tin.

A metal having a melting point of about 500 ° C (zinc-lead, cadmium, tin, or a mixture thereof) and a metal having a melting point of about 1,000 ° C (e.g., copper, aluminum, magnesium, or a mixture thereof) may be cast in 35 open spaces in a mold made of graphite, 6 69972 silicon carbide, boron nitride, alumina, silica, magnesium oxide, or oxides or nitrides from almost all countries.

The mold heater may be an ordinary resistance heating element made of e.g. chromium iron, chromium nickel, tungsten or rhodium rhodium alloy, molybdenum, platinum, tantalum or silicon carbide. However, when casting iron or steel or another metal or alloy with a high melting point, the mold and heater must be protected from oxidation or breakage in hot air by a suitable inert gas, e.g. nitrogen, argon or helium.

The model rod and the continuously cast ingot from the mold are sufficiently cooled in free air if the ingot is a low melting point metal or a mixture of such a metal. However, it is a good idea to use pressure circulating cooling with water or some gaseous refrigerant if the ingot is a metal with a medium melting point. Such metals include aluminum, magnesium and copper or a mixture thereof. Pressure circulating cooling should also be used when the ingot is made of a metal with a high melting point, e.g. iron, steel or a mixture thereof.

25 For the water cooling of the upstream casting, it is possible to use a cooling device with an upturned nozzle. This is directed at the circumferential surface of the ingot and blows an upward jet of pressurized water so that water cannot fall on the molten metal surface.

Figure 2 shows, by way of example, a water-cooled and upwardly directed continuous casting device with an inert gas-protected mold. The upper end of the mold 22 has an outer circumferential edge which prevents the molten metal from flowing out of the mold. The electric resistance heater 23 is embedded in the inner wall of the mold 22. The mold 22 is immersed almost 7,69972 in completely molten metal 25 in a molten metal furnace 24.

The surface of the molten metal 25 is maintained in the furnace at a constant height by feeding the molten metal as a controlled operation along a feed pipe 26. The water cooling device 28 is lined with insulating refractory material 27 and placed on top of the furnace 24 and divided into two vertically separated parts (Figure 2). Cooling water is fed through the bottom and removed through the top. The lower part has a water inlet 29 through which pressurized water is fed to the cooling device and an outlet 35 through which an upwardly directed water jet is directed to the circumferential surface of the model rod 32 or the continuously cast ingot 34. Water moves up along the surface of the rod 32 or ingot 34 and falls into a tank 36 at the top of the cooling device 28. The tank is emptied through the opening 37.

Furnace 24 has an inlet 30 for an inert gas, e.g. nitrogen, argon or helium. The gas is fed to the furnace 24 from the orifice 30 so that the pressure of the gas remains higher than the atmospheric pressure in the furnace-20 and a layer of inert gas is applied to the enclosure of the mold 22. The friction roller pair 33 controls the vertical movement of the model bar 32 and the upward removal of the ingot 34 from the casting device. The oven 24 has a support portion 38 which holds the mold 22 in place.

In the apparatus of Figure 2, the mold is embedded in molten metal so that the temperature of the inner wall of the mold remains higher than the solidification temperature of the metal. However, the mold does not always have to be immersed during upward continuous casting. As an example, a furnace having a separate molten metal zone and a casting zone can be used, and an externally heated casting mold can be connected to the casting zone / so that the molten metal can be fed under pressure from the storage zone to the mold. This type of device is shown as 35 examples in Figure 3.

69972

Figure 3 shows a furnace 41 for molten metal with a molten metal zone 42 and a casting zone 43 of the closed type. A mold 50 with an external heater 45 is placed on the casting zone 43 in the middle po 5. zone. The mold 50 is open at both vertically spaced ends. An opening 51 at the lower end of the mold is connected to a molten metal outlet 52 located on the casting zone 43. The model rod 53 moves in the vertical direction 10 by means of a pair of friction rollers 49 connected to ao.

to the drive (not shown). The model rod 53 is in contact with the molten metal in the mold and gradually raises the continuously cast ingot 46.

The device according to Figure 3 is characterized in that it has a molten metal zone 42 in which the surface of the molten metal can be kept at a suitable height so that the metal can be fed into the mold at a certain pressure. This greatly facilitates the production of a cast product having a relatively small cross-sectional area 20. An example is a plate or wire ingot with a very small diameter. Po. a further advantage of the device is that the mold 50 is easy to remove for repair because it is outside the oven.

25 The mold 50 can be tilted somewhat so that the model bar can raise the ingot upwards along an inclined path. Thanks to this arrangement, when using the model rod and the Valante water cooling device, there is no need to worry about the cooling water flowing down on the molten metal in the mold.

Figure 4 shows an example of a device for continuous casting in the horizontal direction. The apparatus has a mold 61 and an associated electric resistance heater 62. The upper end of the mold recess 61 is at the same height as the surface of the molten metal 64 in the cast metal furnace 63. The furnace 63 has a molten metal supply pipe 65 and 969972 an overflow opening 66 for excess metal, so that the surface of the molten metal in the furnace is always maintained at a constant height. In this case, the pressure of the molten metal is at most 490 Pa at the lower end of the mold outlet. The cooling device 5 67 sprays water which cools the model rod 68 or the continuously cast ingot 69. Between the mold 61 and the cooling device 67 there is a wall 70 which prevents water from splashing into the mold 61 and cooling the mold. A pair of friction rollers 71 controls the horizontal movement of the model rod 68 and the die 10 from the mold 61. Although the mold shown in Figure 4 is in a horizontal position, it can also be placed in a downwardly inclined position to prevent cooling water from entering the mold. To monitor the solidification of the molten metal, the mold 61 can be formed without an upper half. This design alternative-15a has no effect on the arrangement between the heating elements 62 and the mold 61 or on the final solidification result.

The application of the invention to downward continuous casting is described below. The molten metal is fed along the flap tube to the mold so that the pressure of the molten metal at the outlet of the mold 20 is approximately zero. Such a device is prevented as an example in Figure 5.

Figure 5 shows a mold 81 having a heater and a lap tube having one end connected to the mold 81 and the other end immersed in a furnace 83 containing molten metal 84. The moon 25 is an electric resistance heater that holds the bottom of the inner wall of the mold 81 above the solidification temperature of the molten metal. The model rod 86 is attached to the lower end of the mold 81 and is moved downward by a pair of friction rollers 88. Cooling takes place by a jet of water from the cooling device 87, whereby an ingot comprising a smooth 30 and a beautiful surface is formed as a continuous casting on the model rod 86.

The flap tube 82 is provided with a vent valve 90 and the furnace 83 has an overflow port 91. The valve 90 is opened and the overflow port 91 is closed as it begins to feed molten metal 35 into the mold 81 along the flap tube 82. As the surface of the molten metal rises in the furnace 83, the molten metal fills the tube 82 and enters the mold 81. The valve 90 then closes and the overflow port 10 69972 91 opens so that the surface of the molten metal 84 is lower and maintained at the same height as the lower end of the mold 81. As the model bar 86 gradually descends, the ingot can be cast as a continuous casting without the above.

5 risk of breakthrough. The flap tube 82 is covered with insulation, which can be heated if necessary.

In the process according to the invention, the molten metal is approximately zero pressure at the mold outlet, with the exception of small castings, such as small diameter wire rod or very thin sheet. In making these, the molten metal is preferably somewhat pressurized at the mold outlet. In this case, there is no need to fear the breakthrough of molten metal. Since the temperature of the inner wall of the mold is higher than the solidification temperature of the molten metal, the metal does not form a solid surface layer in the mold, but regardless of the metal or alloy used, a smooth and beautiful ingot is obtained. Since the solid surface layer (shell) does not adhere to the inner wall of the mold, the invention can be advantageously applied to the production of relatively simple ingots which can be made in all conventional continuous casting processes, and also to castings with relatively complex cross-sectional shapes and can be supplied directly from the casting process. sale.

The casting method according to the invention makes it possible to produce an ingot with a unidirectional, columnar structure, i.e. the "causes" of the ingot are unidirectionally colomnar fiber structure. This method is therefore very advantageous for the production of magnetic ingots, silicon steel sheets and eutectic composite or similar products which require such a unidirectionally solidified structure. This method can also be used to make 11,69972 plates, tubes, profiles or similar products from stainless steel (other metals or alloys are also possible) which are difficult to shape. When the metal bar is rotated about its own axis as it moves out of the mold, it is possible to cast a wire or 5 or a bar twisted longitudinally, e.g. a bar material used in concrete reinforcement.

According to the invention, it is also possible to cast as a continuous function a so-called high melting point. a superalloy ingot with a unidirectional grain structure, 10 e.g. a gas turbine blade, and to use po. process as a substantially preferred alternative to a conventional method having a cooling block and a hot top end for a refractory mold in which po. the products are cast individually. The following examples illustrate a preferred method for continuous casting of metal ingots in accordance with the invention.

Example I

A cylindrical graphite mold having an inner diameter of 12 mm, an outer diameter of 20 mm and a height of 30 mm and 20 open at its upper and lower ends was attached to an upward continuous casting apparatus (structure according to Figure 2) so that its upper end was at the same point in the molten metal furnace with the surface of the molten metal. The metal was 5% phosphorus-25 bronze containing 94.75% by weight copper, 5% by weight tin and 0.25% by weight phosphorus. The temperature of the metal was 1,100 ° C. The metal was fed to the furnace as a continuous operation in proportion to the amount of continuously cast metal leaving the mold, so that the pressure of the metal at the mold outlet remained approximately zero. There was a layer of nitrogen around the mold and the mold was heated with a platinum wire heater embedded therein so that its inner wall temperature was 1,100 ° C. A stainless steel model rod 35 in diameter approximately equal to the inside diameter of the mold came into contact with the molten metal surface 12,69972 in the mold. The model rod was then raised upwards at 15 mm per minute and water was sprayed at 100 cm -1 per minute 100 mm above the surface of the molten metal, forming a continuous phosphor bronze rod at the lower end of the model rod with a very smooth and beautiful surface.

Example 2

A cylindrical zirconia mold with an inner diameter of 5 mm, an outer diameter of 12 mm and a height of 30 mm 10, open at its upper and lower ends, was attached to an upward continuous casting apparatus (structure according to Figure 3) so that its upper end was slightly lower than the surface of the molten metal in the molten metal furnace, wherein the metal pressure at the outlet of the mold 15 was 196 Pa. The iron melt containing 3.8% by weight of carbon and 1.8% by weight of silicon was kept at 1200 ° C and fed to the furnace as a continuous operation so that the feed rate corresponded to the amount of metal leaving the mold in continuous casting.

The mold was heated with an embedded platinum wire heater so that its inner wall temperature was 1200 ° C. A steel model rod with a diameter approximately equal to the inside diameter of the mold came into contact with the surface of the molten metal in the mold. The model bar was then raised 10 mm per minute and water was sprayed at 50 cm per minute 120 mm above the surface of the molten metal, forming at the lower end of the model bar a 5 mm diameter cast iron wire with a very smooth surface and a beautiful surface.

Example 3

A boron nitride mold with a rectangular recess (height 3 mm, width 20 mm and wall thickness 3 mm) was attached to a device for continuous casting 3 5 (structure according to Fig. 4).

is 69972

The temperature of the mold was maintained at 680 ° C by a built-in heater. Molten aluminum (99.9% Al) at 700 ° C was fed as a continuous operation from the tank furnace to the mold so that the feed rate corresponded to the amount of metal leaving the mold in continuous casting, with the aluminum pressure at the mold outlet being approximately zero. The casting product moved out of the mold horizontally at a speed of 60 mm / min. Cooling took place with water at a feed rate of 600 3 10 cm / min, 50 mm from the mold outlet. The finished product was an aluminum strip with a thickness of 3 mm and a width of 20 mm. The surface of the tape was smooth and beautiful.

Example 4

A columnar, 12 mm diameter core made of stainless steel was placed in a hollow cylindrical mold (stainless steel). The wall thickness of the mold was 1.5 mm and the inner diameter 16 mm. As the casting device, a downward continuous casting device according to Fig. 5 was used. A chromium-20 heater immersed in a mold maintained its temperature at 240 ° C. The melt (99.9% Sn) having a temperature of 270 ° C was fed into the mold as a continuous operation, the feed rate corresponding to the amount of metal leaving the mold in continuous casting, the tin pressure at the mold outlet being approximately zero. The casting product exited the mold downwards at a speed of 40 mm / min. Cooling air was blown into the casting product at 50 rpm 20 mm from the mold outlet. The surface of the tin tube thus cast was really good.

Claims (13)

1. Continuous metal casting process, characterized in that a molten metal is measured into a mold which is provided with an inlet and an outlet opening in such a way that the pressure of the molten metal can be poured at substantially zero. at said outlet opening, wherein said mold has an inner wall which is poured at a temperature which exceeds the solidification temperature of the melon; that the starting string having a temperature lower than said solidification temperature is contacted with the molten metal at the outlet opening; and that the starting string is moved away from the outlet opening, whereby a solidified body of said metal is formed as continuous casting at the end of the starting string. 2. A method according to claim 1, characterized in that the starting string is stirred upwards and that said pressure is in the range 0 - 196 Pa. 3. A method according to claim 1, characterized in that the starting string is moved down and that said pressure is in the range 0 - 196 Pa. 4. A method according to claim 1, characterized in that the starting string is moved horizontally and said pressure is in the range 0 -490 Pa. 25 5. A method according to claim 1, characterized in that at least the said inner wall is heated at the outlet opening by means of a heating device embedded therein, such that a temperature higher than the solidification temperature is achieved at said location. 30 6. A method according to claim 1, characterized in that the molten metal is measured into the mold by means of a siphon tube, which has one end immersed in the molten metal in a molten metal furnace. 7. A process according to claim 1, characterized in that a liquid or gaseous