JPS626898B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for continuously casting aluminum ingots, and more specifically, it is possible to improve the surface of ingots that are continuously cast from molten aluminum or its alloys by a direct chill method, and to improve the surface layer of the ingots. The present invention relates to a long-life mold that can effectively improve tissue structure. Conventionally, casting equipment (including so-called semi-continuous casting equipment) that continuously obtains round or square ingots (billets, slabs) made of aluminum or its alloys using a direct chill method has been used. ), and a typical example has a structure as shown in FIG. That is, a movable mold bottom (bottom plate) 8 is positioned at the bottom of a water-cooled cylindrical mold 1, and molten metal (aluminum or its alloy molten metal) 4 is supplied into the mold 1 through a nozzle 2 and a float 3. By lowering the bottom 8, the inner wall of the mold is cooled by the coolant (usually water) flowing through the channel 5 inside the mold, and the mold is directly cooled by the coolant flowing out from the slit 6 at the lower end of the mold 1. The molten metal column formed in 1 is solidified, and the solidified ingot 7 is continuously taken out from the lower end of the mold. Therefore, since the molten metal 4 supplied to the mold 1 comes into contact with the inner wall of the mold, it forms a thin solidified shell S through primary cooling by the coolant flow passage (water chamber) 5 that cools the inner wall of the mold. However, when this solidified shell S is formed, the metal inside it (aluminum or its alloy) solidifies and shrinks, creating a void between it and the inner wall of the mold, which impedes heat dissipation. At the same time, the solidified shell S is locally remelted, causing a so-called sweating phenomenon in which low-melting point compounds are leached out and molten metal is eluted, and a cold shut (cold welding phenomenon) occurs. etc., which cause surface defects that become a problem in subsequent processing of the ingot. In addition, if this primary cooling is strong, the reverse segregation of alloy components to the surface layer of the formed ingot will increase, producing thick coarse crystalline regions, which will require a lot of surface grinding during plastic working. This also creates the need to remove the reverse segregation layer. Further, when attempting to cast a square ingot using this continuous casting method, it is more difficult than in the case of a round ingot. One of the reasons for this is that the solidification progress is different around the ingot in square molds, resulting in differences in the degree of casting surface, and deterioration is particularly marked at the corners.Also, in square molds, the casting speed is generally is low (because the cross-sectional area is large), and horizontal wrinkles are likely to occur in conventional casting methods.On the other hand, increasing the casting speed improves the cast surface, but increases the shrinkage of the ingot, resulting in poor ingot shape. This may cause problems, etc.
It contains many problems. For this reason, various countermeasures have been proposed in the past with the aim of resolving these problems, but none of these countermeasures can adequately address the structure of the ingot surface or the surface layer of the ingot. In addition, the casting process and mold structure become complicated, and the casting conditions for obtaining a good ingot surface are limited, resulting in a lack of flexibility. It was not completely satisfactory. The present invention has been made against the background of the above, and its gist is to supply molten aluminum or its alloy to a mold and continuously cool and solidify it. In an apparatus that continuously casts a predetermined ingot using a chill method, a means for supplying lubricating oil to the inner wall surface of the mold is provided, and at least a means is provided for supplying lubricating oil to the inner wall surface above the solidified shell that contacts the molten metal of the mold. , a large number of grooves are provided in the casting direction with a groove pitch of 1 to 5 mm and a groove depth of 0.3 to 3 mm, and the lubricating oil supplied from the lubricating oil supply means is distributed through the large number of grooves. The solidified shell is guided to the inner wall surface of the mold in the lower part thereof, and a hardened surface layer is formed on the inner wall surface of the mold where the groove is provided, thereby connecting the mold and the molten metal. The cooling and solidification of the molten metal is progressed while suppressing the heat transfer between the molten metal and the ingot surface formed in the mold part, thereby mitigating the rapid thermal change of the molten metal supplied into the mold. It can reduce the thickness of the sub surface band immediately below and shift it toward the ingot surface layer, and can also effectively reduce the occurrence of surface defects such as sweating and cold shatter, while also reducing the hardened surface layer. Due to the existence of these effects, the durability (persistence) of these effects could be achieved. As described above, according to the present invention, a mold having a large number of grooves on the inner wall surface having a hardened surface layer is used. If a groove is formed on the inner wall surface of the mold that comes into contact with the mold, the surface tension of the molten metal that is being supplied prevents the molten metal from entering the groove, creating a space (air gap) in the groove. , and when this air gap is formed, the heat transfer in that area decreases, so in the present invention, this is utilized to suppress the heat transfer as a whole on the inner wall surface of the mold. By effectively suppressing the cooling of the molten metal by the wall surface (primary cooling), the height and thickness of the solidified shell S that is generated can be minimized, and effective improvement of the ingot surface and the surface layer of the ingot can be achieved. It was. Furthermore, since the grooved inner wall surface that performs this effective action is covered and protected by a hardened surface layer, the groove shape wears out due to semi-molten or solidified metal coming into contact with the sharp groove tips. No deformation occurred, and therefore the mold life could be significantly improved. A specific example of the direct chill mold used in the present invention is shown in FIG.
Shown in b and c. That is, FIG. 2a is a perspective view (portion) showing the inner wall surface of the mold, FIG. 2b is a partially enlarged view thereof, and furthermore, FIG. 2c is an enlarged cross-sectional view. On the inner wall surface of the mold 10 that comes into contact with the molten metal, a large number of grooves 11 are formed along the entire circumference in the casting direction, in other words, in the direction of progress of the ingot (vertical direction in FIG. 1). The grooves 11 are provided at a predetermined pitch on the inner wall surface of the mold 10, as shown in FIG.
As shown, a predetermined hardened surface layer 9 is provided. Further, a lubricating oil groove 12 is provided on the upper surface of the mold 10 so as to connect to the inner wall vertical groove 11 [see Fig. 2b], and the lubricating oil groove 12 is connected to the inner wall vertical groove 11 (recess) from the lubricating oil reservoir 13. It is designed to supply lubricating oil. Therefore, when molten metal is supplied to such a grooved mold 10, the molten metal flows into the peaks 1 of the grooves 11 on the inner wall surface of the mold.
1a, but does not enter the valley (recess) 11b, forming an air gap there, so that heat transfer to the mold as a whole is effectively suppressed, and the supplied lubricating oil is lubricant groove 1
2 to the inner wall vertical groove 11,
In addition to uniform distribution of the supply, air
As the lubricating oil is guided through the gap to the lower part of the solidified shell by forming the gap, the lubricating effect of the lubricating oil can be effectively utilized and further improvement of the ingot surface can be achieved. be. That is,
This brings about the following advantages. (a) Preventing cold shatter on the ingot surface (b) Reducing the thickness of the coarse crystalline region in the ingot surface layer and bringing it closer to the ingot surface layer (c) Reversing the alloy composition in the ingot surface layer Reducing the segregation layer (d) By keeping the cooling rate low in the ingot surface layer, the formation of the so-called fir tree structure (uneven metallurgical structure due to differences in the formation rate of Fe and Al compounds) is controlled. However, the grooved mold 1 having such characteristics
0, due to its structure, when the edge of the sharp groove 11 partially contacts semi-molten metal or solidified metal,
Compared to conventional smooth molds, it is more susceptible to wear and deformation, and when that wear and deformation occurs, the original effect or advantage may be diminished, and furthermore, if it is abnormally deformed, it may even worsen the casting surface. There is also a fear that the so-called twitching phenomenon may occur. Therefore, in the present invention, a predetermined hardened surface layer 9 is formed on the inner wall surface of the grooved mold 10 to suppress the wear deformation as described above. Incidentally, in order to form such a hardened surface layer 9 on the inner wall surface of the mold 10, various known methods are appropriately adopted, but in the present invention, the hard surface layer (plated) is preferably formed by a plating method. A method of forming layers) is adopted. In addition to forming a special hardened layer on the mold surface as in the plating method, it is also possible to employ a method in which the mold surface itself is work-hardened by shot peening or the like to form a hardened surface layer. Incidentally, as is clear from the table below showing an example of the surface hardness of the mold according to the present invention and the mold without a hardened surface layer, the surface hardness of the mold with the hardened surface layer 9 formed according to the present invention is significantly higher. The hardness is improved.

[Table] The average lifespan of the grooved mold with the hardened surface layer (Ni+NiB plating layer) obtained in this way is still being tested, but results have shown that it is more than 5 years. Average of conventional smooth mold 3
This was a significant improvement over the average time of approximately one year (during testing) for grooved molds without a hardened surface layer. In addition, the effect of surface hardening is further increased, especially when considering damage caused by careless scratches during handling. Furthermore, the effect of surface hardening due to the formation of such a hardened surface layer is particularly remarkable in molds manufactured using aluminum or its alloy as a base material, which is prone to deformation and scratches due to wear. It is suitably applied to such molds. Note that since the thickness of the hardened surface layer 9 is very thin, it has no effect on heat transfer in the mold section and does not interfere with the original purpose of the grooved mold. Also,
In particular, by making the hardened surface layer 9 microscopically porous, the lubricating oil can be effectively retained in the porous pores, thereby further improving the casting surface. FIG. 3 also shows a partial perspective view of the inner wall surface of a mold used in another device of the present invention;
Fiber Frax (commercially available under the trade name Fiber Frax, etc.) 15 covers the entire circumference of the upper part of the inner wall surface of the mold where a large number of grooves 11 are provided with a predetermined width.
This heat insulating material 15 covers the inner wall surface of the mold with a predetermined length against the molten metal supplied from above, and the supplied molten metal is rapidly cooled by directly contacting the inner wall surface of the mold. However, according to the present invention, a large number of inner wall vertical grooves 11 are provided on the inner wall surface of the mold 1, so that the heat insulating material 1
5 and the inner wall surface of the mold below it is alleviated by the air gap created in the groove 11 portion, thereby making it possible to obtain a good ingot under a wide range of casting conditions. In particular, the horizontal wrinkles formed at the bottom edge of the insulation material, which were often observed in conventional casting methods using only insulation materials, can be completely eliminated by the present invention, which uses a grooved mold. . Of course, even in such a grooved mold, although not shown, a suitable hardened surface layer is formed on the inner wall surface where the grooves are provided, so as to improve the life of the mold. In addition, in the figure,
13 is a supply reservoir for lubricating oil, and the lubricating oil is supplied from the supply reservoir 13 to each inner wall vertical groove 11 through a supply passage 14.
be uniformly dispersed. Further, 16 is a fixing fitting for attaching the heat insulating material 15 to the upper part of the inner wall surface of the mold, but it may be attached to the mold 10 with other adhesives or the like. It should be noted that the multiple grooves 11 formed on the inner wall surface of the mold that come into contact with the molten metal can be used if the part that comes into contact with the molten metal is a flat or curved surface when a predetermined hardened surface layer is formed. Any shape may be used, but preferably the shape of the protrusion is trapezoidal or S-shaped as shown in FIG. It is also easy and desirable from the viewpoint of Also, the size of the groove depends on the type of molten metal.
Although this will be determined appropriately depending on the size and shape of the mold, it is generally necessary to adopt a groove pitch P of 1 to 5 mm and a groove depth h of 0.3 to 3 mm. However, if the groove pitch P exceeds 5 mm or the groove depth h becomes smaller than 0.3 mm, the effect of cooling relaxation intended by the present invention cannot be fully expected.
If the groove depth is smaller than 3mm, it will be difficult to form a groove with sufficient depth, which will cause cutting problems.Furthermore, if the groove depth exceeds 3mm, the effect of suppressing heat transfer will be too large. This is because it causes problems. In addition, the groove width is appropriately determined in consideration of the desired cooling relaxation effect, the surface tension of the molten aluminum, etc., so that the groove with the groove depth h is formed within the range of the groove pitch P. The Rukoto. If the groove width becomes too wide,
This is because the molten metal enters into the grooves, which not only makes it impossible to achieve a sufficient cooling relaxation effect, but also causes problems such as encroachment into the grooves, making it impossible to cast. Furthermore, although the grooves 11 are provided here over the entire length of the mold inner wall surface in the casting direction (vertical direction), the grooves 11 are not present in the lower part of the mold inner wall surface as they are provided only in the portion that comes into contact with the molten metal. Alternatively, the size of the groove 11 may be made gradually smaller in the casting direction (from top to bottom), or the inner wall surface of the mold may be constructed by fitting a member provided with the groove. too,
It doesn't make any difference. FIGS. 5a and 5b also show further embodiments in which the device according to the invention can be advantageously applied. That is, the purpose is to change the curvature of the long side of the mold and improve the bottom shape of the resulting square ingot (slab), as disclosed in Japanese Patent Publication No. 52-50011, Japanese Patent Application Laid-Open No. 51-67226, etc. The present invention is applied to a mold made of In the figure, 17 is a heat insulating sheet, 18
1 is a grooved mold, 19 is a heat insulating material fixing fitting, and the long sides 18 having vertical grooves 18a in the vertical direction are pulled outward as indicated by arrows by appropriate means at the initial stage of casting. In a mold that requires such an operation, the grooves 18a according to the present invention cause a gentle thermal change in response to the contact of the molten metal column from the heat insulating material 17 to the mold surface with the grooves 18a. In addition to providing a rectangular ingot with a good surface and excellent texture, the life of the mold is also improved by the hardened surface layer (not shown) formed on the inner wall surface. Furthermore, in particular, a rectangular mold for producing such a square ingot is disclosed in Japanese Patent Application No. 1983-1985 filed by the present applicant.
It is recommended to use variable width molds as disclosed in No. 39028 and Utility Model Application No. 54-80787. As shown in FIG. 6, this variable width mold has a long side part 21 and a short side part 22 that are separate bodies, and the long side part 2
1 and/or the short side portion 22, the rectangular shape can be changed. With such a configuration, the long side portion 21 and the short side portion 2
2 can be managed separately, making it possible to reduce costs. In addition to the specific configurations exemplified above, the present invention can be modified and improved in various ways based on the knowledge of those skilled in the art. For example, in the above example, a method of supplying lubricating oil to the inner wall surface of the mold is shown, but supplying lubricating oil is effective in achieving the object of the present invention, and is particularly suitable for the present invention. In some cases, better quality ingots can be obtained by using lubricating oil. This is because the presence of the grooves according to the present invention and the hardened surface layer allows the lubricating oil to exert a more effective lubricating action. In addition, the secondary cooling that is applied following the primary cooling of the molten metal by the mold inner wall surface is the same as in the past.
In addition to the method shown in the figure, in which the coolant flows through the mold and is ejected from the bottom of the mold, there is also a method in which the coolant is ejected from a coolant jet pipe placed around the opening at the bottom of the mold. No problem. Furthermore, the present invention can be applied to other known continuous casting apparatuses such as hot-top casting apparatuses. As described above, the present invention uses a grooved mold having a hardened surface layer formed on the inner wall surface to continuously cast aluminum or its alloy molten metal by a direct chill method. Therefore, an air gap is formed in the groove existing on the inner wall of the mold, thereby suppressing heat transfer on the inner wall of the mold, and at the same time, by preventing wear and deformation of the groove on the inner wall, In addition to reducing the width of the coarse crystalline region just below the lump surface, it also reduces sweating, cold
By reducing the occurrence of surface defects such as shafts, we have achieved a reduction in the amount of surface cutting on the ingot surface, improving yields and extending the life of the mold.
In addition to obtaining a good ingot surface without horizontal wrinkles,
When lubricating oil is used, it is necessary to uniformly distribute the lubricating oil and achieve maximum lubrication effect through penetration, and to improve the shape of the ingot rather than the mold in which the curvature of the long sides of the mold can be changed. Good ingot surface,
This made it possible to obtain ingots (slabs) with excellent texture. The great advantage of the present invention is that all the problems of the structure of the ingot surface and the surface layer of the ingot that have been conventionally recognized in aluminum or its alloys can be solved, and the effects can be made permanent. It has industrial significance.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing a typical example of a continuous casting device, and Fig. 2 a, b, and c are perspective explanatory views of a grooved mold used in the present invention, respectively, and an enlarged plan view of the circled portion thereof. and an enlarged cross-sectional view, FIG. 3 is a perspective explanatory view of a grooved mold used in another example to which the present invention is applied, and FIG. 4 is a cross-sectional view showing two or three examples of grooves formed on the inner wall surface of the mold. Fig. 5a is a plan view of a mold according to still another example to which the present invention is applied, Fig. 5b is a perspective explanatory view of a grooved mold used therein, and Fig. 6 is a plan view of a mold according to another example to which the present invention is applied. FIG. 2 is a plan view showing an example of a variable width rectangular mold. 1: Mold, 4: Molten metal, 5: Coolant channel, 7: Ingot, 10, 18: Grooved mold, 9: Hardened surface layer, 1
1, 18a: Inner wall vertical groove, 12: Lubricating oil groove, 13:
Lubricating oil reservoir, 15, 17: insulation sheet.

Claims (1)

[Scope of Claims] 1. A device that continuously casts a predetermined ingot using a direct chill method by supplying molten aluminum or its alloy to a mold and continuously cooling and solidifying it. A large number of grooves are provided at least on the inner wall surface of the mold above the solidified shell in contact with the molten metal, with a groove pitch of 1 to 5 mm and a groove depth of 0.3 to 3 mm. Provided in the casting direction, the lubricating oil supplied from the lubricating oil supply means is distributed through the plurality of grooves and guided to the inner wall surface of the mold in the lower part of the solidified shell, and the grooves An apparatus for casting an aluminum ingot, characterized in that a hardened surface layer is formed on the inner wall surface of the mold. 2. The device according to claim 1, wherein the hardened surface layer is a hard plating layer. 3. Claim 2, wherein the mold has a base material made of aluminum or an alloy thereof.
Apparatus described in section. 4. The apparatus according to claim 1, wherein the mold is a rectangular mold whose long sides have a variable curvature. 5. Claim 5, wherein the mold is a rectangular mold whose long side and short side are separate bodies, and whose rectangular shape is changed by movement of the long side and/or the short side. The device according to item 1. 6 A device that continuously casts a specified ingot using a direct chill method by supplying molten aluminum or its alloy to a mold, allowing it to cool and solidify continuously, and supplying lubricating oil to the inner wall surface of the mold. A large number of grooves are provided in the casting direction at least on the inner wall surface of the mold above the solidified shell in contact with the molten metal, with a groove pitch of 1 to 5 mm and a groove depth of 0.3 to 3 mm. The lubricating oil supplied from the lubricating oil supply means is distributed through the plurality of grooves and guided to the inner wall surface of the mold in the lower part of the solidified shell, and inside the mold where the grooves are provided. forming a hardened surface layer on the wall surface, and covering the mold inner wall surface provided with the groove with a heat insulating material at a predetermined length portion on the supply side of the molten metal;
An apparatus for casting an aluminum ingot, characterized in that, before the molten metal comes into direct contact with the inner wall surface of the mold, the two come into indirect contact via the heat insulating material. 7. The device according to claim 6, wherein the hardened surface layer is a hard plating layer. 8 Claim 7, wherein the mold has a base material made of aluminum or an alloy thereof.
Apparatus described in section. 9. The apparatus according to claim 6, wherein the mold is a rectangular mold whose long sides have a variable curvature. 10. Claim 1, wherein the mold is a rectangular mold whose long side and short side are separate bodies, and whose rectangular shape is changed by movement of the long side and/or the short side. The device according to item 6.