US2503819A - Continuous casting - Google Patents

Description

April 1950 s. F. GUNN ETAL 2,503,319

com'nwous CASTING Filed Dec. 8, 1945 IN V EN TORS George F. Gunn BY Clarence E. Logan ATTORNEYS Patented Apr. 11, 1950 CONTINUOUS CASTING George F. Gunn and Clarence E. Logan. Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application December 8, 1945, Serial No. 633,614

1 Claim. 1

The invention relates to an improved apparatus for the continuous casting of metal and is particularly advantageous in forming ingots of magnesium-base alloy.

One of the well-known p-ocesses for the continuous casting of ingots involves introducing molen metal continuousy into one end of a permanent mold to form a liquid metal pool in the upper end, cooling the metal to cause it to soli ify in the mold, and withdrawing the solid metal soformed continuously from the other end of. the mold. The process, however, has the disadvantage that the surface of the ingot is not generally smooth. Instead, it is usually indented by folds or creases formed apparently as a result of irregularities in the manner in which the liquid metal at the edge of the upper surface of the pool moves toward and solidifies against the mold wall. The movement of metal in the upper surface toward the mold wall and the way in which the metal lies against the mold is affected by the oxidic film normally covering the exposed metal surface and by the reduction in temperature and resulting decrease in fluidity of the meal as it approaches the mold wall. Particles of solidifying metal may also form in the liquid metal near the surface of the pool adjacent to the meld and interfere with the metal lying smoothly against the mod wall. However the folds and creases may be f -rm'd. such blemished surface of the ingot must be removed as by machining to make the ingot useful for many purposes, as for example, extrusion. Not only does this considerably increase the cost of the ingot but it also wastes a significant .percentage of the metal as the entire surface of the ingot generally must be machined off to the depth of the deepest indentation.

gravated by the creases, laps, and folds produced in the surface of the ingot because the points of the beginning of the segregation are deepened to the depth of the creases, laps, and folds.

It is an object of the invention to provide an apparatus for the continuous casting of metals and pa;ticularly of magnesium-base alloys in a mold, as briefly described above, which prevents surface indentations due to creasing, lapping, or folding of oxidic skins adjacent to the mold wall and reduces the depth of stratification of the metal adjacent to the mold.

Other objects and advantages will appear as the description of the invention proceeds.

These objects are obtained in a. continuous casting process and apparatus of the invention in which excessive indentation of the cast metal sur- The continuous casing in this manner of magnesium-base alloy, which is quite readil reacted upon by the ambient atmosphere when the rretal is molten forming a trough oxidic skin, ives rise to creasing and folding of the metal adjacent to the mo'd wall to a very severe exten In addition, segregation or stratification of alloying constituent usually occurs, being greatest at the external cast metal surface and ex ending to a depth of one-half of an inch or more into the ingot. Such segregation gives rise to hot short cracks when such ingots are used for making extrusions. This problem is furt er ma' nified in the case of magnesium-ba e alloys containing from 3 to 10 per cent of aluminum as the major alloying element, since the scmewhat unusual manner of solidification of these alloys renders sub-surface segregation or stratification to be almost inevitable. Such segregration is further agface due to creasing, folding or lapping of the metal is obviated and depth of segregation rdjacent to the mold wall is reduced by subjecting the molten porticn of the metal within the mold to an undulatory motion of relaively low amplitude and frequency, so as to create undulations in the upper surface of molten metal while the mold remains in a substantially fixed position. The actual frequency and amplitude of undulations do not appear to be critical as eflecive resultsare obtained over a relativelywide range of magnitude of these factors. The area of exposed molten metal surface appears to be a'factor and determines to some extent the amplitude and frequency required. In order to impart the undulator motion to the molten metal so as to create the desired undulations. we oscillate a submerged, preferably horizontal paddle therein, the oscillations being largely in the vertical direction. Any sulabe re atively thin object. whose dimensions as t length and width are maintained in a more or less horizontal plane, preferably under the pturing spout, and large enough to extend to near the mold wall, may be used as a paddle. One of t e most advantageous forms of the s bme-ged paddle, for cylindrical molds. is a circular hori zontal disc or dish having a diameter s mewhat less than that of the interior diameter of the mold and centrally disposed therein, just below the pourin": spout, so that the flow of liquid metal into the mold is bafllecl and deflected laterally at the same time as the o"cillatory motion 11 impared to the molten body of metal to create a current su-ge in the liq-id in the region of the junction of the mold wall and the metal surface and to create undulations therein. For rectan ular cr other shapes of molds, the baflle or paddle is giv-"n a peripheral shape preferablyfcorresponding to that of the horizontal cross section of the mold, allowing a clearance of about 1% inch or more between the edge of the bald: and the.

, a modification thereof.

Fig. 4 is a perspective view of an alternate form ofbafiie for producing undulations in the liquid metal surface.

In the several views like numerals designate like parts.

As shown in Figs. 1 and 2, a magnesium ingot is continuously formed in a hollow cylindrical thin wall mold I open at the bottom 2 and top 3 and attached to a flange 4 resting upon a suitable substantially rigid supporting means 5. Surrounding the mold near the upper end is a cooling fluid distributor 6 with openings I directed toward the exterior of the mold wall 8. Molten metal is introduced into the mold continuously through a pipe 9 from a source of molten metal (not shown). Below the lower open end In of the pipe 8 is a submerged baille H, which also functions as a deflector and is secured to the pipe by brackets l2. A pneumatic vibrator i3 is secured to the pipe 9 by a clamp H and serves to impart vibrations to the baflle II by motion imparted to the pipe 9. The solidified ingot I is guided by pinch rolls It as the ingot forms and descends below the mold, the rate of descent being controlled by regulating the speed of rotation of the pinch rolls to maintain an appropriate balance with the rate of introduction of molten metal to the mold.

In the modification of Fig. 3, the paddle or baffle in the form of a fiat disc is held in the molten metal beneath the pipe 9 by a bracket 2| secured to a support 22. Vibratory motion, mostly in the vertical plane, is imparted to the baille by the vibrator 23 secured to the bracket 2| by the clamp 2|.

The alternate form of baflle, shown in Fig. 4, may be secured to either the bracket 2| which is mounted independently of the pipe or the brackets I2 which are supported by the pipe. The opening 25 may be positioned so as to be directly below the pipe if desired. The diameter of the annular ring 26 is made preferably from about to 1 inch less than the internal dimeter of the mold, and these dimensions may be followed with the other baille shown in Figs. 1 and 3.

Inoperation of the apparatus and method, a cooling fluid is directed from pipe 6 against the mold so as to abstract heat from it and to cool the ingot below the mold wall, the boundary between the solidified metal at the top of the ingot and the molten metal being generally dish-shape, as shown at IT.

While the metal is thus continuously cast, the baliie or paddle is continuously vibrated, preferably in the vertical plane, so as to impart an undulatory motion to the unsoidifled or liquid metal in the mold creating a cont'nuous series of undulations, like waves, in the liquid surface. With the modification of Fig. 1, this is accomplished by operating the pneumatic vibrator 13 so as to oscillate the pipe 9 and its attached baffle or paddle ll, preferably in the vertical direction. We have found that oscillating the baflie up and down with an amplitude of from about 0.05 to 0.2 of an inch or more and with a frequency of 5-50 cycles per second produced satisfactory results, although other frequencies and amplitudes may be employed. In the modification of Fig. 3, the baflle 20 is similarly oscillated by the vibrator 23, the oscillations being imparted to the baflle by the support 2| independently of the pipe. Other forms of bailles or paddles, such as shown in Fig. 4, may be used with either the modification of Fig. 1 or 3. If desired, the baiile may be perforated with a series of holes.

v The undulations thus produced in the molten metal have the effect of continuously breaking the oxidic film which normally forms on the surface IB of the molten metal. As a result, the film moves toward the inner surface IQ of the mold in more or less discontinuous pieces and does not form tenacious skins or folds to indent the surface of the ingot. Instead, the oxidic film, being broken into substantially discrete particles, causes the convexity of the meniscus to be greatly reduced so that the oxidic particles and metal lie smoothly against the mold wall as the casting proceeds without producing laps or folds, and

'there is a corresponding reduction in depth of segregation or stratification otherwise produced at the interface between the mold and the solidifying metal.

In the use of this method with magnesiumbase alloys, that is, alloys in which the magnesium content amounts to per cent or more of the weight of the alloy, ingots having rectangular and circular cross sections of various diameters of from about 6 to 16 inches have been cast continuously in unbroken lengths of several hundred feet with no significant indentation of the surface of the ingot due to creases, laps or folds in the wall of the casting, and the depth of segregation or stratification of the alloying constituents adjacent to the surface hasbeen greatly reduced. In addition by means of the invention, these desirable results are achieved without adversely afiecting the grain structure of the cast metal.

We claim:

In a metal casting apparatus, in combination with a mold adapted to contain a pool of molten metal, a delivery means positioned in said mold to feed metal to said pool and a baffle positioned in said mold to contact the pool therein, means for supporting said baiile in said mold, said means comprising an arm fixed to said baflle and mounted at a point removed from said battle and means for periodically and momentarily applying a force to said arm at a point beyond said point of support to cause momentary displacement of said arm from its normal'position.

GEORGE F. GUNN. I CLARENCE E. LOGAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Nur ber Name Date 550,089 Armand et al. Nov. 19, 1895 2,225,414 Junghans Dec. 1'7, 1940 2,290,083 Webster July 14, 1942 FOREIGN PATENTS Nore Country Date 824,785 France Nov. 18, 1937

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