US 3045299 A
Description (OCR text may contain errors)
y 1962 K. H. STEIGERWALD 3,045,299
RECIPROCATING MOLD USING A VACUUM AND PRESSURE ASSIST Filed Nov. 1'7, 1959 OSCILLATOR IN VEN TOR. K AR L HE INZ STE IGERWALD ATTORNEYS United States Patent 3,045,299 RECIPROCATING MOLD USING A VACUUM AND PRESSURE ASSIST Karl Heinz Steigerwaid, Sauerbruch-Strasse 10, Heidenheim (Brenz), Germany Filed Nov. 17, 1959, Ser. No. 853,573
3 Claims. (Cl. 2257.2)
This invention relates to the art of continuous casting, and more particularly, to continuous casting reciprocating mold of improved heat transfer characteristics.
Continuous casting of molten metals is known to the art and apparatus for such casting usually comprise a Water-cooled mold positioned vertically, horizontally or at intermediate angles therebetween. Molten metal is poured into the mold to form a continuous casting.
In processes having the greatest acceptance by the art the water-cooled mold is reciprocated or oscillated in a predetermined fashion. The mold moves with the casting at the same speed as the rate of casting withdrawal over a predetermined stroke. The mold is returned to the original position at a higher rate of speed.
During casting by the mold, a shell of material solidifies in the mold. The solidification continues until a solid casting is obtained. It is evident that the transfer of heat .to the mold wall greatly influences the rates of casting since the heat transfer affects the rate of solidification.
However, during solidification of the casting, the shell .shr-inks and thus withdraws from the walls of the mold. Withdrawal of the shell from the mold walls reduces the cooling efiiciency of the mold, thus limiting the rate of casting possible with such process. I
Efforts have been made to overcome this drop in cooling by increasing the pressure on the top (liquid head) of the casting in an attempt to expand the casting in the mold where the shell is still soft and plastic to ensure contact of the casting skin with the mold. Alternatively, the art has attempted to accomplish the same result by application of a vacuum at the exit end of the mold.
However, both processes have been unsatisfactory, particularly when applied to reciprocated molds, which applicationis of greatest interest to the art. The contact pressure between the casting and the mold is constant over the entire mold reciprocating cycle. Therefore, although the pressure increases the contact area between the mold and casting skin which is beneficial during the portion of the mold reciprocation cycle when mold and casting move in the same direction, a concomitant increase in frictional force on the casting during that portion of the mold reciprocation cycle when the mold moves in the direction opposite to casting movement results.
The increase in the frictional force between the mold and the casting greatly increases the possibility of breaking the casting during the mold return stroke, since the end of the casting is being pulled from the mold by withdrawal rolls.
It is, therefore, the primary object of this invention to increase the contact area between the casting skin and the mold walls without destructive increase in frictional force on the casting.
It is a further object of this invention to increase the contact area between the casting skin and themold walls during that portion of the mold reciprocation cycle when the mold and casting move in the same direction and to decrease the frictional force between mold and casting during that portion of the mold reciprocation cycle when the mold and casting move in opposite directions.
In accordance with these objects I have provided in a preferred embodiment of this invention a continuous casting mold of the conventional water-cooled type.
mold'is positioned to receive molten metal flowing from The" 3,i5,2% Patented July 24, 1962 The coupling is related to the mold cycle so that vacuum is applied during the cycle when the mold and casting move together and pressure is applied to the chamber during the period of time when the mold and casting move in opposite directions. Therefore, the rate of heat transfer increased without corresponding increase of frictional force during the mold return stroke.
In another embodiment of this invention the pressure vacuum cycle is combined with a superimposed vibration of the casting to further decrease the frictional force between the casting skin and the mold Walls.
The invention may be more easily understood by reference to the following description, taken in conjunction with the accompanying drawings, of which:
FIGURE 1 is a cross sectional view of one embodiment of this invention;
FIGURE 2 is a cross sectional view of another embodiment of this invention; and
FIGURE 3 is a cross sectional view of still another embodiment of this invention.
In FIGURE 1 there is shown a continuous casting mold Ill. The mold is of conventional construction and in accordance with such conventional construction is watercooled. As illustrated the mold is horizontally mounted, although vertical mounting and mounting at intermediate angles is equally feasible. Molten metal, contained within the pot 12, flows therefrom into the mold through the spout 14. The spout 14 is preferably water-cooled and fits the peripheral aperture of the mold to ensure filling of the mold by the molten metal.
As shown, the mold is a horizontal mold "and is reciprocated in the directions illustrated by arrow 16 at a. rate of reciprocation related to the speed of withdrawal of the casting by the withdrawal rolls conventional fashion. As in many casting devices it has been found desirable to move the mold at the same speed as the withdrawal rate of the casting when the mold is moving in the same direction as the direction of casting withdrawal. The mold is then returned to the original position at a higher speed, such as 3 times the speed of casting withdrawal. The reciprocating drive mechanisms are known to the art and not shown here.
Coupled to the mold in contiguous relationship at the exit end thereof is a chamber 18. The chamberis dimensioned to closely fit the peripheral dimensions of the casting as it is withdrawn from the mold. A vacuum chamber 20 and a pressure chamber "22 are provided. The chamber 18 is selectably coupled .to the vacuum chamber 29 or the pressure chamber 22 through piping 24, 26 and valve 23 or piping 24, 30 and valve 28 respectively. A vacuum pump 25 and pressure pump 27 are provided to maintain the chambers at the desired vacuum and pressure level.
The valve 28 may be mechanically coupled to the oscillating mechanism of the mold to relate the pressure cycle to mold movement. Valve 28 may conveniently be mechanically coupled to the cam regulating the mold reciprocation cycle by a mechanical linkage. Alternatively, the valve may be electrically or pneumatically operated to provide the desired pressure transfer function in synchronism with the mold reciprocation cycle by a drive mechanism 32.
During movement [of the mold and the casting in the same direction the chamber 18 is supplied with vacuum which will force the casting into direct contact with the mold face, increasing the rate of cooling of the casting. Duringreturn of the mold to the original position it is desirable to decrease the frictional force between the mold surface and the casting to eliminate the possibility of breaking of the casting. Therefore, during return of the mold to the original position the chamber is supplied with air under pressure tending to separate the casting skin from the mold thus lowering the frictional force therebetween.
It has been found that a vacuum in the order of to 26-in. Hg and a pressure in the range of 1 to 4 psi. gage is satisfactory. It will be noted, however, that variation in the exact pressure and vacuum may be had in accordance with the dictates of the application.
While the pressure-vacuum cycling in synchronization with the reciprocation cycle of the mold is entirely adequate for most applications, some applications require a further decrease in the frictional force between the casting skin and the mold walls. In these applications, the embod-iment shown in FIGURE 2 may advantageously be employed.
In FIGURE 2 there is shown a reciprocating mold 10 which is fed with molten metal by means of a spout 14 inserted therein. The mold is reciprocated through a conventional reciprocation cycle as explained in connection with FIGURE 1.
Coupled to the mold in contiguous relationship at the exit end thereof is a chamber 18. The chamber is divided into three subchambers 34, 36 and 38 by the separators 40 and 42. The end 44 of the chamber wall and the ends 46, 48 of the internal separators are dimensioned to match the peripheral dimensions of the casting to isolate the chamber from the outside atmospheric pressure and to isolate the subchamber. While it is usually feasible to use a single chamber for the pressurecycling, it has been found advantageous in many applications to divide the chamber into a plurality of pressure chambers as illustrated. The smaller volume of each individual chamber allows more rapid cycling with storage reservoirs 22 of FIGURE 1) of moderate size.
The chambers 34, 36 and 38 are cycled in the same manner as set forth in connection with the explanation of the operation of the embodiment shown in FIGURE 1 by being coupled to suitable reservoir chambers through respective pipes 50, 52 and 54.
In order to decrease the frictional force between the walls of the mold and the skin of the casting, it has been found advantageous to superimpose upon the pressurevacuum cycle a high frequency pressure cycle derived from an acoustical generator 56. The acoustical generator comprises an electromagnetic coil 58 energized at the desired frequency by an oscillator 60. The electromagnetic coil 58 pulsates a diaphragm 62 at the source frequency which pulsations are transmitted to the chamber 38 by means of a pipe 64 coupled thereto. The generator may be tuned to a resonant state for efficient generation of vibrations.
The vibration of the air column particularly during the pressure cycle induces transverse vibrations in the thin walls of the cast strand and the liquid metal contained within the strand walls. The transverse vibrations of the strand skin are transmitted longitudinally through the strand to set up relative transverse vibration between the skin and the mold wall, thus reducing the frictional force between the strand Walls and the walls of the mold.
Although it is entirely possible to induce the vibrations in the strand by superimposed vibration of the pressure within a large chamber 18, it has been found that greater efiiciency in transfer of the vibrational energy can be had with a smaller air volume. For this reason, in addition to the reasons mentioned, it has been advantageous in many applications to divide the chamber into smaller subchambers.
In many applications it has been found advantageous to couple the vibrational energy into the column at both the entrance and exit of the mold. In such applications a chamber 66 is formed at the entrance to the mold by shield 63 extending into a sealing relationship with a bearing block 70 on the periphery of the spout 14. The vibrational energy and the pressure cycle may be then advan- .tageously coupled to the chamber 66 through pipe 72 connected in parallel with pipe 64.
In some applications greater efliciency of the transfer of vibrational energy to the cast strand may be had through a mechanicalcoupling instead of the acoustic coupling shown in FIGURE 2. In those applications the embodiment shown in FIGURE 3 may advantageously be employed.
In FIGURE 3 there is shown a reciprocated mold 10 receiving molten metal through the water-cooled spout 14. The chamber 18 is pressure cycled as explained in connection with the operation of FIGURES l and 2.
Coupled to the spout is a peripherally extending bearin g member '76. Coupled to the bearing member is a source '78 of vibrational energy which may be conveniently in audio range. The generator 78 may be conveniently a vibrator type generator or a mechanical generator operated on the principle of a rapidly rotating eccentric weight to induce the desired vibration in the spout.
Vibration of the spout will be transmitted to the strand due to the resistance of the flow of metal caused by the differencelin diameter of the exit of the spout and the entrance of the mold. Thus, vibration of the spout results in a very eflicient transmission of the mechanical vibrations to the cast strand. The vibrations may be transmitted efiiciently over a very wide range of frequencies to impart the desired effect of decrease of resistance between the cast strand and the walls of the mold.
It will be noted that both acoustical and mechanical vibration may be used conjointly as by coupling an acoustical generator to chamber 18 in addition to the mechanical vibration source 78 or independently to suit the application intended.
This invention may be variously embodied and modified within the scope of the subjoined claims.
What is claimed is:
1. In a continuous casting apparatus having a reciprocated mold, a chamber coupled to the exit end of the mold, said chamber peripherally surrounding the casting, a vacuum chamber, a pressure chamber, and means responsive to the movement of the mold for coupling said first named chamber to said vacuum chamber during the portion of the mold reciprocating cycle in which the mold and the casting move together and for coupling said first named chamber to said pressure chamber during the portion of the mold reciprocating cycle in which the mold and the casting move in opposite directions.
2. A combination in accordance with claim 1 which includes a selectably operable valve to couple said first named chamber to said vacuum chamber when the mold moves in the same direction as said casting and to couple the said first named chamber to said pressure chamber when the mold moves in the direction opposite to said casting.
3. A combination in accordance with claim 1 which includes means for superimposing a pressure pulsation on the pressure in said pressure chamber when it is coupled to said first named chamber during the portion of mold reciprocation cycle in which the mold moves in the direction opposite to said casting.
References Cited in the file of this patent UNITED STATES PATENTS 2,135,183 Junghans Nov. 1, 1938 2,578,213 Welblund Dec. 11, 1951 2,743,700 Toulmin May 1, 1956 2,763,040 KOrb Sept. 18, 1956