US3415306A - Method of continuous casting without applying tension to the strand - Google Patents

Description

Dec. 10, 1968 E. A. OLSSON 3,415,306

METHOD OF CONTINUOUS CASTING WITHOUT APPLYING TENSION TO THE STRAND Filed July 25, 1965 I NVEN 70R ATTORNEY} United States Patent 3,415,306 METHOD OF CONTINUOUS CASTING WITHOUT APPLYING TENSION TO THE STRAND Erik Allan Olsson, Oerliltonerstrasse 88, Zurich, Switzerland Filed July 23, 1965, Ser. No. 474,279 Claims priority, application Sweden, July 23, 1964, 8,982/ 64 2 Claims. (Cl. 164---83) ABSTRACT OF THE DISCLOSURE This invention discloses a method for the continuous casting of metal wherein a nozzle for supplying molten metal is telescopically received into one end of an openended water-cooled casting mould. The casting mould is reciprocated in the direction of its length during the process of casting, and as the mould moves forward, i.e., in the direction of the travel of the metal being cast, the partly-solidified casting in the mould travels forwardly with the mould. As the previously-cast metal in the mould recedes from the nozzle, fresh metal enters the mould on this forward stroke. It immediately solidifies around the interior wall of the mould. On the backward stroke of the mould, this solidified ring of fresh metal interposed between the end of the nozzle and the previously-cast metal prevents the metal in the mould from traveling back with the mould, thereby effecting relative movement between the mould and the casting. Rollers may be used on the casting outside the mould to apply a regulated opposing force to the free forward travel of the casting.

A method to manufacture end products and semi-fabricated products directly from a melt by supplying melt to a mould open in both ends and simultaneously withdrawing the casting at least partly solidified within the mould which casting is further cooled in order to wholly solidify, is previously known under the name of continuous casting. Hitherto the casting of the melt has taken place from a pouring box above the mould opening whereby of course the supply of melt and the withdrawing velocity of the strand must be suited to each other so that the metal level in the mould does not fall below or rise above the desired height. Too great an amount of melt in relation to the withdrawing velocity has the effect that the melt flows out over the upper edge of the mould. On the other hand, too rapid withdrawing of the strand in relation to the supplied amount of melt results in a lowering of the melt level in the mould, possibly leading to a too weak cooling and a break out of melt below the mould. It has previously been proposed to supply the melt through a tube connected to the mould but this has not been satisfactory especially where the mould surface must be lubricated to avoid sticking of the mould. Where lubricant must be used, a clearance between the supply tube and the mould which allows for the lubrication of the mould wall, and for the escape of steam and/ or gas occurring at the contact of the melt with the lubricant, with a reciprocating mould, and when such a clearance space is provided, the molten metal enters the clearance space and immediately solidifies by contacting the mould wall and contracts about the end of the nozzle. The solidified metal in the clearance space then resists movement with the mould as the mould moves forward, being firmly attached to the nozzle, thus stressing the already formed skin of the metal, causing it to rupture. By using a supply tube or supply nozzle of the type described in the copending application filed simultaneously herewith Ser. No. 470,280 this disadvantage with the entering of melt into the clearance can be avoided but nevertheless a certain friction and sticking tendency occurs between the supplied melt and the mould wall so that stresses arise in the strand skin on account of the relative movement between the strand and the mould. The friction of the initially solidified metal increases with increased ferrostatic pressure which normally is present when a supply tube or a casting nozzle connected to the pouring box and inserted into the mould opening, is used. Thus the risk of breaking off the strand skin increases where a closed supply tube carries the melt from the pouring box into the mould openmg.

The present invention relates to a method to reduce the drawing otf risk of pulling off the initially formed skin where a reciprocating mould is used wherein the partly solidified strand within the reciprocating mould moves together when the mould moves forward, but it prevented from moving back with the mould in the opposite or backward direction in the travel cycle. This is accomplished by so operating the mould that the hot metal entering the mould on its forward stroke is solidified forming a solidring against the mould wall between the nozzle and the earlier partly solidified strand portion, which prevents the strand from moving with the mould as the mould moves backwards. Thereby a length of formed strand is pushed out of the mould on each back stroke corresponding substantially to the length of stroke of the mould minus any possible upsetting of the solidified ring of material in front of the nozzle that may occur when the ring of metal is resisting the pressure against it On the back stroke of the mould and the tendency of the strand to be moved back with the mould.

The invention will be further described in connection with the embodiment shown on the attached drawing which shows a continuous casting machine for carrying out the method according to the present invention and wherein the figure is a somewhat schematic view in longitudinal section.

In the drawing, 1 designates a pouring box on which a casting nozzle 2 is mounted so that it extends into the inlet end 4 of the mould 3. The mould 3 is reciprocated axially from the position shown in the drawing at the forward limit of its travel rearwardly to the dot-and-dash line position, so that the end of the nozzle 2 telescopes or extends at all times into the mould during the casting operation. Reciprocation of the mould is a common expedient in continuous casting, and known mechanism (not shown) may be used for this purpose. The molten metal in the pouring box 1 fills the cavity in the mould and solidifies against the wall of the mould 3. If the rollers 5 which are positioned to engage the casting at a point sufficiently removed from the mold to prevent distortion of the casting are used to withdraw the casting from the mold, as is usual in the art, tension is applied to the newlyforming portion of the casting, tending to elongate it and reduce its diameter so that the casting contracts away from the mold walls and does not have adequate heat transfer contact therewith. Heretofore such rollers were used to pull the casting from the mold, and when the mold was moving toward the rollers, the mold travel was adjusted to the same speed as the linear speed at which the rollers advanced the casting, so there was then no relative movement between the solidifying metal in the mold and the mold walls. This provided a short period of time for the shell of the solidified metal to thicken, but on the reverse travel of the mold, that is, in a direction away from the rollers, the differential speed between the mold and the product being formed resulted in the metal being pulled out by the rollers while the mold was travelingin the opposite direction, further creating a tension on the casting likely to result in a rupture of the casting. Because of this, the strand skin can be re-heated by transfer of heat from the molten interior of the casting and weakened thereby increasing the risk of the strand being pulled off. Previously it was known to reduce the risk of producing fissures by reciprocating the mould in the direction of the length of the strand whereby the uncovered mould wall above the surface of the melt can be effectively lubricated and further the strand skin has time to increase in thickness and strength during the movement of the mould in the casting direction without being subjeeted to tension stresses. Normally the mould movement is coordinated to the speed of the rollers so that the mould is given substantially the same velocity as that of the strand produced by the withdrawing effect of the rollers.

In the present invention the rollers 5 are not used as withdrawing means, but the strand is fed forward a distance corresponding to the feeding movement or forward stroke of the mould because of the friction between the strand skin and the mould wall. As the mould moves forward, that is in the direction of travel of the strand, a volume of fresh melt enters and fills the mould at the opposite end to a corresponding height or volume. The freshly introduced melt solidifies rapidly along the mould wall so that on the back stroke of the mould the strand is prevented from accompanying the mould because the freshly formed skin at the inlet end of the mould acts as a spacer or thrust ring between the earlier solidified metal and the nozzle. Thus the strand is pressed out from the mould as the mould retracts and tension stresses are thus completely avoided. In the described case the advancing of the strand is obtained by means of the friction of the metal against the forwardly-traveling mould wall and the strand. Of course, it is of interest that the resistance against the forward movement does not become too high and thus it may be advantageous that the strand slopes somewhat relatively to the horizontal plane as shown. Furthermore the forward movement can be secured by using a tapering mould. In this case the inlet end of the mould has a smaller area than that of the outlet end in that the mould walls at the inlet end are slightly inwardly curved but at the outlet end 7 the walls are straight or have the shape which corresponds to the desired finished product. Under all circumstances the mould will move the strand forwardly a distance corresponding to the length of stroke of the mould.

In the present invention the rollers 5 provide a support for the casting but they do not serve in any manner to draw the casting out of the mold. They are idler rollers to support the casting, except that they may resist turning too freely in the direction of forward travel of the casting so that they may prevent over-travel of the casting when it is being pushed from the mold. This pushing, in the nature of an extruding force in the present invention, is generated by the fact that when the mold is moving in a direction toward the rolls, a space is being opened between the metal in the mold and the end of the nozzle into which fresh melted metal instantly flows from the nozzle. This fresh metal almost instantly solidifies around the interior of the mold forming a ring between the nozzle and the previously-solidified metal in the mold. Then when the mold reverses its direction of travel, crowding the metal so freshly introduced between the previouslysolidified metal in the mold and the nozzle, this ring transmits a thrust, forcing the outer end of the solidified casting from the discharge end of the mold. As a result, the casting is always pushed from the mold and never pulled under tension. Since the backward movement of the mold may tend to force the casting forward too fast, so that its ineritia would stress the newly-formed skin of the casting, the rollers 5 may exert a friction to retard the forward movement of the casting under its own inertia.

If there is a slope to the emerging strand so that its forward movement is accelerated by gravity, the rollers can be adjusted to resist the gravitational pullto a point where the maximum travel of the strand is no greater than the forward stroke of the mold. Also other means can be used for providing resistance against the free forward travel of the strand, but in no case should the arrangement be such as to exert a tension on the emerging strand. The method according to the present invention may, under certain circumstances, with advantage be combined with a vibration of the mould and/ or the strand in order to reduce the sticking tendency of the melt to the mould wall, to reduce the friction and to obtain a finer grain structure in the cast product.

Especially when casting difficult molten metals, such as iron and steel, economy of operation requires a casting rate so high that only a relatively thin solidified skin is formed within the mould. Thus, as in other methods, the only partly solidified strand must solidify completely after leaving the mould which can take place in a manner known per se, e.g., by water spraying, the strand being sprayed through nozzles 8 and supported and led through the spraying zone in any suitable way, e.g., between rollers 9 or by having the strand passing between cooling jaws resting against the strand. Under certain circumstances it can be advantageous to move the strand through a bed of a granular material, e.g., foundry sand as with other casting processes.

Of course, the strand manufactured in the above stated way can be processed as continuously cast metal formed in other processes is processed, that is, bent and straightened in desired directions in a manner known per se, e.g., by using a progressive bending, by winding of the strand onto a reel or in a spiral. The strand can also be cut off in desired lengths, e.g., by gas cutting or shearing.

I claim: 1. The method of continuously casting molten metal to produce a formed strand of solidified metal which comprises:

continuously maintaining a supply of molten metal at one end of a cooled open-ended mould through a nozzle which at all times during operation is telescopically entered into the end of the mould,

reciprocating the mould with respect to the nozzle in the direction of the axis of the mould with the forward stroke being in a direction away from the nozzle, its backward stroke being toward the nozzle,

carrying the solidified metal in the mould along with the mould on its forward stroke while fresh metal from the nozzle enters the mould as it moves in a direction away from the end of the nozzle and at a rate such that the freshly-introduced metal forms a solid ring against the mould wall between the nozzle and previously solidified metal in the mould.

maintaining the solidified metal in longitudinal compression during the forward stroke of the mould by applying a regulated opposing pressure to the forward movement of the casting, and

then reversing the travel of the mould and utilizing the solidified ring of metal last formed to establish compression within the already cast strand, and as the sole means of preventing the already cast strand projecting beyond the mould from moving backward with the mould during the rearward stroke of the mould, whereby the strand is expelled from the mould entirely by pressure without applying tension to the strand during either the forward or backward stroke of the mould.

2. The method of continuous casting wherein molten metal poured into one end of a mould is discharged from the other end as a shaped product, the exterior wall of which is solidified, which comprises:

introducing molten metal into the mould through a stationary nozzle having a discharge end projecting at all times into one end of the mould, reciprocating the mould axially relative to the stationary discharge nozzle at a rate to effect the forming of a solidified ring of molten metal between previ- References Cited ously-solidified metal in the mould more remote from UNITED STATES PATENTS the nozzle and the end of the nozzle as the mould travels in a direction away from the nozzle, 2,740,177 4/1956 Smart 22 200'1 utilizing the said ring of metal so for-med to transmit 5 2,891,294 6/1959 1 at 22-4001 thrust to the partially solidified metal previously in- 3045299 7/1962 Stelgerwald 22 200-1 troduced into the mould when the mould moves back- 3,290,734 12/1966 Wen-'1 22 57-2 ward toward the discharge end of the nozzle, 1,088,171 2/1914 Pehl'son 164-260 and utilizing the back-and-forth travel of the mould FOREIGN PATENTS with the newly-solidified ring of metal so formed in 10 252 512 6/1964 Australia each cycle as the principal means of expelling the exteriorly-solidified formed metal product from the 908902 10/1962 Great Bntam' mould and in the absence of any applied tension to W AM STEPHENSON, mary Examiner. the formed product to assist its forward movement R. BALDWIN Assistant Examiner.

when the mould moves forward and to restrain its 15 backward travel when the mould moves backwards. 164 283

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