US2772459A - Continuous casting of metals - Google Patents

Description

1956 H. WIELAND 2,772,459

CONTINUOUS CASTING "0F METALS Filed July 10, 1951 IN VENTOR' Y HAM/5" W/EL 4M9 A TTOEN Y5 United States Patent CUNTINUOU CASTING OF METALS Hans Wieland, Ulm (Danube), Germany, assignor to Wieland Werke A. G., Ulm (Danube), Germany, a corporation of Germany Application July 10,1951, Serial No. 235,987

Claims priority, application Switzerland July 21, 1950 1 Claim. (Cl. 22-2001) This invention relates to the continuous casting of metals. In particular, the invention is directed to the continuous casting of metals in an unlubricated mold.

In the ordinary casting of metals in a chilled mold, it is necessary to use a lubricant, usually containing carbon, on the casting surface of the mold in order to prevent sticking of the metal being cast. Otherwise, the mold becomes unserviceable, and the ingot is cast with surface roughness, overlaps, and the like. However, the use of a lubricant is but the lesser of two evils, for the lubricant may react unfavorably with some metals and cause defects extending into the ingot, and incomplete combustion of the lubricant during casting will produce surface defects regardless of the metal being cast. Consequently, metals such as tough pitch copper, which are particularly sensitive to carbon containing lubricants at fusion temperature a cannot be cast by a continuous casting process, although, by contrast, a copper deoxidised with phosphorous can so be cast.

Non-metallic molds have been tried for continuous casting, including the use of a non-metallic lining in a metal mold. Ordinary graphite has been tried as a lining, but as far as is known, has not heretofore been successful due to rapid erosion and burning out. To avoid these difficulties, a special material has been used both as a mold by itself, and as a lining for a metallic mold. This material comprises chemically precipitated graphite with colloidal carbon as a binding agent under very high pressure, the porosity being at least and the grain size not greater than microns. In the first case only small molds can be used and although satisfactory ingots are cast, the output is only about a twentieth of that obtainable with metal chill molds. The small output of the nonmetallic mold, together with certain apparatus difliculties, makes this mold unsatisfactory for production in quantity, even though a good ingot surface structure is obtained. In particular, neither a non-metallic mold nor a lined mold has been able to successfully cast the large quantities daily needed of tough pitch copper, even though no supplernentary lubricant was needed.

The object of this invention is to produce a process for the lubricant-free continuous casting of metals, including the non-ferrous metals and alloys, precious metals and alloys, iron, steel, and other ferrous metals and their alloys.

In general, these objects are achieved by constructing a metal mold with an ordinary graphite lining and a water cooling jacket of sufiicient capacity to make the process possible. The molten metal poured into the mold is solidified by contact with the chilled graphite lining at a rate to form a surface crust which will not be broken by the liquid molten metal core of the ingot as the ingot leaves the mold, and then indirectly cooling the ingot to elfect the major heat extraction to solidify the ingot interior.

The means by which the objects of the invention are obtained are described morefully in the accompanying drawings, in which:

Figure l is a cross-sectional view through the lubricant free continuous casting mold; and

2,772,459 Patented Dec. 4, 1956 Figure 2 is a plan view of the mold.

The mold is formed of an inner cylindrical member 1 telescoped within an outer member 2. inwardly turned flanges 2a and 212 at the ends of member 2 serve to close the ends to form a water jacket between the inner and outer members. The lower end of inner member 1 is beveled and spaced from the beveled inner edge of flange 2b by means of set screws 3, which are also used to adjust the height of the inner member 1 and fix the size of the annular cooling fluid discharge opening 4. This opening has less cross-sectional area than the inlet pipe 5 to insure the cooling jacket being kept full of fluid.

An ordinary graphite liner 7 is inserted in member 1, the liner resting on a collar 8 adjacent the lower edge of member 1.

According to the process of this invention, cooling fluid entering the cooling jacket produces a strong cooling action through liner 7 on the metal poured. into the mold, and the cooling medium discharged through opening 4, causes an intensive cooling of the partially solidified ingot leaving the mold. Because of the strong cooling of liner 7, an ordinary graphite liner can be used and kept at a temperature at which it is not attacked by the molten metal in the short period of time before the metal solidifies. Graphite exposed to air at a temperature of above 600 C. will burn. By the process of this invention the graphite temperature is kept below 600 C., and no oxidation is observed where the top surface of the molten metal touches liner 7. However, if higher casting temperatures are encountered, a reducing atmosphere can be created by well known means over thesurface of the molten metal.

As the molten metal fills the mold it is solidified against liner 7 into a crust thick enough to keep the liquid interior from breaking through as the ingot leaves the lower edge of member 1. The partially solidified ingot is Withdrawn from the mold at a speed which permits solidification of this crust. The thickness of this crust will vary within limits in dependence upon the metal cast, the cross-sectional area of the ingot, the intensity of the cooling both within and outside the mold, etc. The crust begins to form slightly below the upper surface of the molten metal in the mold and increases in thickness as the distance from the upper surface increases. It has been discovered that this crust is formed substantially as fast as a crust would be formed in an unlined mold, and a comparable speed of casting achieved. As the graphite lining 7 is self lubricating, the ingot being formed can slide downwardly and emerge from the mold without surface damage.

A practical operation of the process is given in the following example:

The slotted chill mold had a structural height of 200 mm. The graphite lining of the inner mold wall was 3 mm. thick. By the term graphite within the scope of the invention is to be understood all graphites or materials containing graphite which, like graphite-coated carbon, are not moistened by molten materials and have been well tested in ironworks and metalworks for similar purposes. The internal diameter of the chill mold and the lining was 172 mm. The molten material for casting was supplied to the mold from the forehearth of a furnace by means of a nozzle pipe with an outlet diameter of 5.5 mm., said pipe being resistance heated in known manner. The casting output was 2 tons per hour, both with tough pitch copper and with copper deoxidised with phosphorous. The surface of the casting was completely smooth and,.in particular, free from annular folds and overlaps. The depth of the sump in the centre of the ingot was 200 mm. The sump thus extended below the bottom edge of the mold, since the surface of the moldten metal in the mold was about 50 mm. below the upper edge of the mold.. However, the sump may extend only up to the metal col lar 8, or the block, solidified over the entire cross-section,

, ,anvnnso may even extend into the non-metallic lining, when the casting material undergoes a sudden direct cooling without heat stresses occurring of such a height in the continuously cast block that they have to be liberated in heat fissures. The solidification at the margin commenced about 1 cm. below the surface of the metal in a very thin marginal layer becoming thicker in a downward direction. In the present case, a water trap was placed below the mold around the ingot, and no water flowed through said trap ecausc the casting was so smooth that a complete sealing against the outlet of water was produced. This advantage was achieved with rubber rings.

By means of the process of the invention, primarily there is achieved'an essentially higher crude output of continuously cast products from metal chill molds with non-metallic linings, as compared with the formerly known outputs, the yield, surprisingly, corresponding to that which it is normally possible to obtain with undivided cooled metal chill molds, depending upon the nature of the material actually used, the composition of the alloy, the cross section of the casting, the intensity of the direct and indirect cooling, the length of the chill mold, etc. In addition, it is found that in accordance with the invention, continuously cast articles having a smooth surface are obtained which are free from annular folds and overlaps, so that the solid or hollow castings which are obtained can be supplied, without sWarf-removing treatment, for further swarfless working, when they are not to be directly employed in the condition in which they are cast. As a result of this particular condition which arises from the use of the invention, it is further found that the comparable pure output is even greater than that obtained by using the known undivided metal chill molds, because with the latter, the castings generally have to be subjccted to a swarf-removing treatment before undergoing the further swarfiess treatment in order to eliminate surface defects on the cast products, such as rough surfaces, overlaps, etc. Only in special cases is the swarf-removing not necessary.

I The use of the lining 7 also increases the life and durability of the casting mold, particularly in rough casting work.

It has hitherto been believed that in the continuous casting of metallic materials with the use of non-metallic casting molds, it was at least necessary to dissipate the whole of the fusion heat of the casting through the nonmetallic wall of the mold in order to achieve an appropri' ate angular position of the crystals in the solidified casting,- such being "favourable for a subsequent swarfless finishing treatment, and it was also attempted to employ this method of working in connection with metal molds having a non-metallic inside wall in the upper part of the mold, but this did not work out in practice. With the latter constructions, moreover, in another known process, not only was the aim to obtain no solidification at all in the region of the non-metallic lining, but provision was even made by a heating action that in any case no marginal or surface crust solidification occurred within the meaning of the present invention, the result of which was that the marginal solidification which was subsequently established could only commence in the metallic part of the combination mold. Because of the lack of a lubricant between the metal inside wall of the mold and the solidified marginal crust of the casting, however, the casting in the process remained adhering to the metal wall of the mold, so that it was not possible hitherto, with this proposal for metallic materials, to be continuously cast successfully. -However, if this previously known process was employed in accordance with another proposal in such manner that also no marginal solidification took place in the metallic bottom portion of the combination mold, then such a process again could not be exploited in practice, because the molten casting core could not be caused to solidify so rapidly throughout the whole cross-section that a softening of the already solidified marginal crust 4. was excluded, which is however absolutely necessary for a safe process from the point of view of accidents.

Since with cooled metal chill molds, only a fraction of heat extraction from the molten casting material takes place indirectly through the metal inside wall of the mold, and the main heat extraction is usually carried out in known manner and with known means by the directly following abrupt cooling of the casting, which is at least solidified in its marginal crust, the heat extraction from the casting material in molds having non-metallic internal walls must be even smaller with the arrangements already known. In these processes, the direct cooling of the casting has been abandoned in many cases, and it has frequently been preferred to employ the indirect cooling method. The consequence of this, however, is that the casting speed must be adapted to the essentially slower solidification speed at the expense of the former, especially when the casting mold is combined with the furnace, whereby there is produced a lower output of continuously cast products as compared with a process using cooled metal chill molds. metal chill molds with a nonmetallic lining, so long as in this case the solidification of the casting throughout the entire cross-section within the region of the non-metallic lining is sought after.

The process of the instant invention canbe employed for the continuous casting of all metallic materials, whether they be light metals, non-ferrous heavy metals and their alloys, iron, steel, ferrous metals and their alloys, and the like. However, it is particularly advantageous that it is now possible for tough pitch copper to be continuously cast by the process of the invention. As is known, with this material, upon the solidification at the grain limits, the known copper-copper oxide eutectic alloy is separated out. and this can easily be reduced just beneath the melting point of the copper by substances having a reducing action, such as, for example, hydrogen, carbon, carbon monoxide, etc. This reaction results in the damage to the copper known under the name of hydrogen defect, because due to the removal of the oxygen by these reducing agents, the cohesion between the crystal grains is loosened, so that with the swarfiess shaping in the cold or hot state, fissures are unavoidably produced which make unserviceable the semi-finished articles produced from the cast block.

The process according to the invention can also be used with advantage with alloys which tend to reverse ingot liquation. With the known cooled metal molds, the reverse ingot liquation with alloys which readily liquate is promoted by various conditions. In contrast hereto, the reverse liquation in the process according to the invention is checked on the one hand due to the lower heat conductivity of the graphite and 011 the other hand due to the increased resistance to passage of heat between the graphite and copper wall.

The resistance capacity of the combination mold employed according to the invention as regards mechanical stresses is in no way inferior to that of a comparable cooled metal chil'l mold.

It is also important that with the process of the invention, the direction of solidification is guided into the direction of the axis of the casting.

Having now described the means by Which the objects of the invention are obtained, I claim:

The process for the continuous casting of oxygen hearing metals in a metal mold having an open top and open bottom, formed by an outer metal jacket of substantial structural strength supporting and reinforcing a relatively thin graphite liner having a thickness such that the inner surface thereof is coolable below a liner reactive temperature of about 600 C. during casting, said mold being unconnected with the container holding the source of metal so that the molten metal in themold can have its own free surface, said method comprising pour- The same would apply for knowning molten metal into the open top, cooling said jacket and withdrawing the congealed metal from the open bottom, the fit of the liner in the jacket and the thickness of the liner being such that the mold extracts heat from the congealing metal through the liner substantially as intensively as an all-metal lubricated mold would extract heat, said 1 tiring. cooling and withdrawing being at such rate that a free surface of molten metal is maintained in said mold, and the upper edge of the congealing crater shell is maintained in close proximity to said free surface, and the crater shell is of considerable depth, but of such thickness as not to break through at the lower edge of the mold.

References Cited in the file of this patent UNITED STATES PATENTS 253,176 Billings Feb, 7, 1882 2,136,394 2, i-i5,4 l 6 2,225,373 2,242,350 2,264,288 2,284,703 2,301,027 2,363,695 2,376,518 2,517,931 2,530,854 2,590,311

Poland et al. Nov. 15, Crainpton Jan. 31, Goss Dec. 17, Eldred 2 May 20, Betterton et al. Dec. 2, Welblund et at June 2, Ennor Nov. 3, iuppik -2 Nov. 28, Spence May 22, Rossi Aug. 8, Brennan Nov. 21, Harter et a]. lviar. 25,

FOREIGN PATENTS Great Britain Apr. 26, France May 10,

i938 1939 1940 194i 194i 1942 194-2 i944 i945 1950 1950 i952

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