Method and apparatus for casting a metal article in a mold at least as long as the article, utilizing a cooled mold of elongated form having top and bottom portions. The method includes the steps of introducing molten metal from a source through the bottom portion of the mold, flowing molten metal into the mold so as to form a solidifying casting shell which a during casting occupies at least 40% of the cross-sectional mold area and a has a molten core, and flowing molten metal from the source through the core towards the mold top at a filling rate, dependent on the mold cross sectional area, such that the product produced will have a relatively fine grained structure throughout the cross-section thereof.
|
1. A method of casting a metal article in an elongated mold having a cross-sectional area substantially between 25.8 cm2 and 967.74 cm2, a thermal conductivity of at least 0.20 cal/cm2 /cm°C./sec., and a length at least as long as the article to be cast, said mold having top and bottom portions comprising:
inclining said mold to the vertical; introducing molten metal from a source through said bottom portion of said mold at a filling rate substantially between 0.239 kg/cm2 /min. and 23.9 kg/cm2 /min., the combination of filling rate and cross-sectional area of the mold being defined by the hatched area of the graph as shown in FIG. 3; flowing molten metal along said mold by applying a differential pressure across said source and said top portion of said mold; cooling the mold while regulating the flow of said molten metal therealong to form a solidified casting shell which, during casting, occupies at least 40% of the cross-sectional mold area and has a molten core; flowing molten metal from said source to extend said casting shell and said molten core toward said top portion of said mold; and subsequently solidifying said molten core to produce a product having a relatively fine-grained structure throughout the cross-section thereof.
9. Apparatus for casting an elongated article comprising:
a source of molten metal; a mold inclined towards the vertical and being at least as long as said article to be cast, said mold associated with said source of molten metal having a bottom including an opening and a top portion, said mold further having a cross-sectional area between 25.8 cm2 and 967.74 cm2 and a thermal conductivity of at least 0.20 cal/cm2 /cm/°C./sec.; means for introducing molten metal into said mold opening at a filling rate substantially between 0.239 kg/cm2 /min. and 23.9 kg/cm2 /min., the combination of filling rate and cross-sectional area of the mold being defined by the hatched area of the graph as shown in FIG. 3, said introducing means associated with said source of molten metal including means for applying a differential pressure between said source and said top portion of said mold to regulate the flow of molten metal along said mold; means cooling said mold to form a solidifying casting shell which, during casting, occupies at least 40% of the cross-sectional mold area and has a molten core, said introducing and means associated with said mold for flowing molten metal from said source along said core to extend said casting shell and said molten core toward said top of said mold and after casting is completed for solidifying said molten core to produce a product having a relatively fine-grained structure throughout the cross-section thereof.
2. A method as defined in
3. A method as defined in
4. A method as defined in
5. A method as defined in
6. A method as defined in
7. A method as defined in
10. A mold as defined in
11. Apparatus as defined in
12. Apparatus as defined in
|
|||||||||||||||||||
This invention relates to casting elongated metal articles such as billets in a mold at least as long as the cast article. It provides for control of the rate of solidification of the article during casting for improved physical and morphological characteristics of the cast metal including, but not limited to, significantly improved surface characteristics such as smoothness and subsurface inclusion distribution, for example. It also provides an improved internal microstructure of the casting.
Heretofore, both in casting metal articles of greater or lesser length than their molds, i.e., continuous and non-continuous casting, attempts have been made to control the rate of solidifying metal along a solid/liquid interface during casting, i.e., within the casting at the interface of the solidifying casting shell and the molten metal. These attempts have been characterized by the use of costly and space-consuming apparatus added to the basic casting apparatus to adjust flow of molten metal about the solid/liquid interface subsequent to and independently of the introduction of molten metal into a mold. Such apparatus has taken the form of molten metal stirrers and induction coils, either about the mold or the casting as in Tzavaras U.S. Pat. No. 3,693,697. These coils generate moving magnetic fields in the molten metal which induce flow along such interface for the purpose of removing or inhibiting columnar dendrites, effecting improved dispersion of chemical solutes and inhibiting stratification of inclusions within the major portion of the casting, while inhibiting central porosity.
In my U.S. Pat. No. 3,517,725 issued June 30, 1970, there is disclosed a technique of continuous casting of metal wherein billets of steel and other metals are cast from a closed-end, cooled mold which is relatively separated from a source of molten metal. The closed-end mold forms a shell of the billet being cast through which molten metal flows to the relatively retreating mold, the mold forming the outer shell of the billet at its end remote from the source of molten metal.
In casting metals in a cooled or uncooled mold at least as long as the casting, as opposed to the continuous casting technique of the aforesaid U.S. Pat. No. 3,517,725, it has been a practice to pour molten metal into the mold through the bottom thereof to a height within the mold. During such pouring, a casting shell solidifies against the mold, and the molten metal flows through the shell from the bottom to the top. However, the shell forms significantly less than 40% of the mold cross-sectional area during such casting during mold filling. While the volumetric flow into such mold may be relatively large, there is little or no washing effect of the relatively large liquid core on the solid/liquid interface. Hence, unless otherwise controlled, the rate of solidification cannot be effectively governed, and solidification will take place with the undesirable growth of columnar dendrites resulting in localized solute concentrations, segregated inclusions and centerline porosity, all undesirable in a casting microstructure.
The present invention overcomes many of these difficulties with the prior art.
It is an object of the present invention to achieve the effect of such solidification control apparatus at least largely as a function of molten metal introduction into a mold, to dispense with such costly and cumbersome apparatus of addition, and to generally improve the technique of casting elongated metal articles, particularly those having a melting point in the range of approximately 1,088° to 1,643°C This invention provides a method and apparatus for casting a metal article in a mold at least as long as the article, utilizing a cooled mold of elongated form having top and bottom portions. The method includes the steps of introducing molten metal from a source through the bottom portion of the mold, flowing molten metal into the mold so as to form a solidifying casting shell which in the examples described occupies at least 40% of the cross-sectional area of the mold and has running therethrough a molten core 48. The introduction of the molten metal into the mold is such that the liquid core 48 sweeps the solid/liquid interface formed in part by the shell 46 in such manner as to inhibit columnar dendritic growth during filling of the mold. It is believed that such sweeping action of the molten core results in at least partially equiaxed dendritic growth but other microstructures are possible. Such sweeping action of the liquid core inhibits the formation of a so-called mushy zone between the truly liquid core and the solidifying shell 46 to thereby enhance the desired thermal gradient for proper solidification of the casting. Such a thermal gradient exists both in longitudinal and transverse directions with reference to the axis of the casting. The axial gradient is highest at the nozzle end of the casting. Solute elements tend to be dispersed uniformly throughout the casting and a portion of inclusions tend to be captured by the casting powder 44 as the liquid metal washes across such casting powder 44 on the filling of the mold. Such chemical and physical action during the casting operation is detailed in Tzavaras U.S. Pat. No. 3,693,697. The aforementioned inclusions, formed prior to solidification, are mainly oxides which are stable at high temperatures. Inclusions formed during solidification are mostly sulfides, tellurides, arsenides, nitrides and some oxides. The usual inclusions in steel are compounds of various solutes or deoxidizers used in steel combined with oxygen, sulphur, and less frequently with nitrogen. The aforementioned solutes, e.g., in steel, are elements other than iron, such as alloying elements. Such pressure pouring of the casting is completed on filling the mold 26 to the top. On completion of the mold filling, the gate valve 23 is closed and the remaining cooling jets are turned off. When all the coolant jets are turned off, the remaining portion of the mold rises in temperature and is melted off leaving the casting supported in the manner in which the mold was previously supported from the columns 34. However, the portion of the mold 26 in which the cap 28 is inserted may not melt off. Such a cast metal product exhibits superior surface characteristics, among others. If desired, several such molds may be filled simultaneously from a single molten metal source as will be obvious. While pressure pouring of the molten metal has been described with reference to the casting technique, it will be evident to those skilled in the art that the mold 26, may be filled by vacuum pouring, and indeed the mold may be filled from the bottom by other pouring techniques.
The metal to be cast is AISI-304 stainless steel having a composition of 0.08% carbon max., 2.0% Mn max., 1.0% Si max., 18-20% Cr, 8.0-11% Ni, 0.040% P max., 0.030% S max., (balance Fe) and solidus at 1,427°C and liquidus at 1,510°C, wherein the thermal conductivity is 0.039 cal/cm2 /cm/°C./se at 100°C The mold composition is aluminum 2024 alloy having a composition of 4.5% Cu, 1.5% Mg, 6% Mn (Balance Al) and solidus at 502°C and liquidus at 638°C, wherein the thermal conductivity is 0.45 cal/cm2 /cm/°C./sec. at 25°C The mold is 30.48 meters long, has a wall thickness of 4.75 mm and has an internal cross-section of 100 mm×100 mm. The mold filling rate by pressure pouring is 4.834 kg/cm2 /min (483.4 kg/min). The liquid core diameter is approximately 50.8 mm while the liquid core velocity is 31.39 meters/min approximately.
There is shown in FIG. 3 a graph illustrating different metal introduction rates with reference to molds of different cross-sectional areas. As shown there, a mold having a cross-sectional area of 25.81 cm2 has molten metal introduced thereinto for filling at a rate between approximately 2.39-23.9 kg/cm2 /min. There is also shown that for a mold having a cross-sectional area of 967.74 cm2 the molten metal introduction rate is between approximately 0.239-4.78 kg/cm2 /min. in this non-linear relationship. This relationship requires the use of a mold whose thermal conductivity is at least 0.20 cal/cm2 /cm/°C./sec. Molds having intermediate cross-sectional areas have intermediate molten metal introduction rates as indicated by the graph.
While several forms of the method and apparatus for casting a metal article have been described, it will be apparent, especially to those versed in the art, that the invention may take other forms and is susceptible to various changes in details without departing from the principles of the invention.
| Patent | Priority | Assignee | Title |
| 4580616, | Dec 06 1982 | Techmet Corporation | Method and apparatus for controlled solidification of metals |
| 4586557, | Apr 14 1983 | Egon, Evertz | One-piece, open-ended, water-cooled continuous casting mould and method of making the same |
| 5309976, | Mar 16 1993 | Howmet Research Corporation | Continuous pour directional solidification method |
| Patent | Priority | Assignee | Title |
| 2891294, | |||
| 2978764, | |||
| 3191292, | |||
| 3417810, | |||
| 3517725, | |||
| 3680624, | |||
| 3814166, | |||
| 3868988, | |||
| FR1070042, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| May 05 1980 | Technicon Instruments Corporation | (assignment on the face of the patent) | / |
| Date | Maintenance Fee Events |
| Date | Maintenance Schedule |
| Jun 22 1985 | 4 years fee payment window open |
| Dec 22 1985 | 6 months grace period start (w surcharge) |
| Jun 22 1986 | patent expiry (for year 4) |
| Jun 22 1988 | 2 years to revive unintentionally abandoned end. (for year 4) |
| Jun 22 1989 | 8 years fee payment window open |
| Dec 22 1989 | 6 months grace period start (w surcharge) |
| Jun 22 1990 | patent expiry (for year 8) |
| Jun 22 1992 | 2 years to revive unintentionally abandoned end. (for year 8) |
| Jun 22 1993 | 12 years fee payment window open |
| Dec 22 1993 | 6 months grace period start (w surcharge) |
| Jun 22 1994 | patent expiry (for year 12) |
| Jun 22 1996 | 2 years to revive unintentionally abandoned end. (for year 12) |