US3129474A

US3129474A - Apparatus in continuous casting machines having a reciprocating mold

Info

Publication number: US3129474A
Application number: US154284A
Authority: US
Inventors: Olsson Erik Allan
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-01-03
Filing date: 1961-11-22
Publication date: 1964-04-21
Anticipated expiration: 1981-04-21
Also published as: DE1433044B2; DE1433044A1

Description

Apr1l21, 1964 E. A. oLssoN 3,129,474

APPARATUS IN CONTINUOUS CASTING MACHINES HAVING A RECIPROCATING MOLD Filed Nov. 22. 1961 FgJ ERIK ALLAN 0LS`SON ATTORNEYS nited States Patent 3,129,474 APPARATUS IN CONTINUUS CASTING MA- CHlNES HAVEN@ A RECIPRQCATING MOLD Erik Allan Olsson, Zurichstrasse 66, Kusnacht, Zurich, Switzerland Filed Nov. 22, 1961, Ser. No. 154,284 Claims priority, application Sweden Jan. 3, 1961 2 Claims. (Ci. 22-57.2)

In continuous casting of metals, comprising non-ferrous metals and alloys as well as more particularly iron and ferrous alloys, the fluid metal is supplied to one end of an open-ended mold which is made from a material having good thermal conductivity, e.g. copper. Due to the cooling action achieved by the mostly water-cooled mold, the metal solidies in the marginal zone of the crosssection of the casting, whereupon the at least partly solidiled casting is withdrawn at the opposite end of the mold.

Within the mold there is formed a solid outer layer or shell on the casting passing through the mold on account of its contact with the cooled mold wall. However, this contacts lasts only as long as the pressure of the fluid metal is able to force the solidified outer layer or shell into contact with the mold wall. When the solidified layer has reached a certain thickness, the continued shrinkage of, eg., a polygonal section will cause initially the corner portions of the casting to be disengaged from the mold wall, while the intermediate flat surfaces are still for a certain period forced against the mold wall by the action of the pressure of the iluid metal before they, too, lose contact with the wall. As soon as the contact of the casting with the wall ceases, the gas layer formed in the resulting clearance will restrict the dissipation of heat and thereby the growth of the solidified layer. In order that the partly solidified casting shall be capable of being withdrawn from the mold, however, the solid surface layer must have a certain strength so that it can withstand the sum of all mechanical forces involved, including the head of the lluid metal in the interior of the casting. The higher the rate of supply of fluid metal to the mold, i.e. the higher the casting velocity chosen relatively to a given section of the casting, the greater the amount of heat removed per unit time must be in order that a solidified surface layer having the requisite strength shall be formed. The efficiency of a continuous casting mold or the casting velocity which can be achieved depends to a large extent on the heat transfer properties of the mold. The casting efhciency of a continuous casting mold can be improved by imparting to the mold a definite rhythmical reciproeating movement in such a manner that the mold for a certain period of time accompanies the movement of the casting with at least approximately the same speed as the casting, so that during this period a relative movement between the mold and casting is prevented. Thereupon the mold is moved in a direction opposite to that of the casting back to the starting point. During the synchronous movement of the mold and the casting the effect of the friction forces is eliminated, wherefore the solidifying outer layer at the weakest point immediately below the fluid metal surface is not subjected to mechanical stresses.

It has been suggested to make the mold so short that the casting leaves the mold immediately after it has been disengaged from the mold wall. In practice, however, this is not possible, because the length of the mold must not be below the minimum necessary to make sure that if the casting speed is increased briefly the zone of disengagement will not be below the mold which would inevitably result in a rupture in the solidified outer layer. On the other hand, it is also disadvantageous to extend the mold far beyond the zone of disengagement, since practi- 3,129,474 Patented Apr. 21, 1964 ICC cally no cooling action is achieved between the disengagement zone and the lower end of the mold.

It will be seen from the above that the greatest danger of rupture on the solidified outer layer is present at the exit of the casting from the mold. In normal conditions, the solidified outer layer of the casting is suillciently strong at this point to withstand the mechanical stresses referred to above, in particular the inner pressure caused by the fluid metal. There is no absolute certainty, however, that rupture will not occur since even the smallest fissure in the outer layer can reduce the strength to an impermissible degree. Several means of reducing the danger of rupture have been proposed, one such proposal involving the provision of water-cooled elements at the outlet end of the mold, said cooling elements being kept pressed with a slight pressure toward the casting and serving to increase the strength in the outer layers of the casting through further indirect cooling and to prevent rupture by supporting the solidified outer layer externally. Immediately below the cooling elements direct cooling takes place by means of water under pressure as is usual in most continuous casting processes. In this subsequent cooling system there are usually provided a plurality of small guide rollers which also serve to prevent bulging of the solidified outer layer by the action of the internal pressure of the unsolidifled metal. Considering the process in connection with a reciprocating movement of the mold, it will be seen, however, that the cooling elements, which accompany the mold in such movement, in each stroke expose a length of the casting corresponding at least to the length of the stroke, which length of casting at that point is unsupported from the outside and the outer layer of which under some circumstances has not yet obtained a suicient strength to withstand the internal pressure of the fluid metal.

The object of this invention is to remove that disadvantage, the invention being characterized substantially by one or more cooling elements provided at the exit end of the mold and movable independently of the mold, said cooling elements surrounding the casting withdrawn from the mold and cooling it to increase the thickness and consequently the strength of the outer layer solidified in the mold.

The invention will be explained more in detail below with reference to the accompanying drawing, which diagrammatically illustrates an embodiment thereof, FIG- URES 1-5 illustrating the cooling process in live stages during a complete stroke of the mold.

FIGURE l shows the first stage in which the mold 6 and the cooling elements 7 are in their starting position, i.e. the upper reversing position, indicated at 8, of the stroke which is altogether designated 9. The cooling water nozzles y10 and 11 which are provided around the casting section and the cooling elements 7 and mold 6, are stationary as is also the subsequent cooling means 12 which also includes guiding rollers 13. The casting 14 is withdrawn at a continuous speed the magnitude of which is indicated by the arrow 15. In this starting position the cooling members are immediately below the lower end of the mold.

FIGURE 2 shows the second stage in which the mold 6 moves in the direction of withdrawal of the casting 14 at a speed, which is substantially equal to the velocity of withdrawal of the casting. In this stage, too, the cooling elements 7 move in the same direction but at a speed which is greater, e.g. twice the speed of the mold 6. Between the mold and the cooling members there will be formed a gap 18 which is equal to the distance 19 traveled by the mold if the speed of the cooling members as indicated by the arrow 17 is twice the speed of the mold (indicated by the arrow 16). lThe casting portion thus exposed is sprayed with water from the nozzles 10.

In the third stage, illustrated in FIGURE 3, the cooling elements 7 have traversed the entire distance 9 while the mold has moved only half that distance which means that the exposed portion 18 is doubled and is subjected to cooling water from the nozzles 11. In the fourth stage illustrated in FIGURE 4 the cooling elements 7 remain in the lower position 20, while the mold 6 is still moving down at a constant speed, whereby the exposed portion 18 is reduced while it is still subjected to cooling water from the nozzles 11.

At the end of the fth stage shown in FIGURE 5, the mold has caught up with the cooling elements 7, whereby the casting is Iagain wholly enclosed. Thereupon, the mold and cooling elements return at a constant speed to their starting positions (FIGURE l) and the process is repeated.

Considering a casting section 21 during the stages described it will be seen that this best cooled section after the simultaneous return of the mold and cooling elements to the upper end position 8 will be immediately below the lower ends 22 of the cooling elements in case the cooling elements have a length which is at least as great as the stroke 9 of the reciprocating movement. The solidified outer layer of the casting section 23 which is exposed during the return movement and wherein the danger of damage is the greatest, due to the cooling by the cooling elements 7 and the direct cooling by the cooling water nozzles 10 and 11, has increased in thickness to such an extent that a rupture at this place is no longer to be feared in normal circumstances.

The invention is not limited to the embodiment shown and described which can be varied in many Ways without departing from the spirit and scope of the invention.

I claim:

1. The combination with a continuous casting machine having a reciprocating mold, of at least one cooling element `at the outlet end of the mold and movable independently of the mold, said cooling elements wholly enclosing a casting leaving the mold, means for moving said cooling elements faster than the mold in the direction of casting to form a gap between the mold and the cooling elements, means for stopping said cooling elements to close said gap, means for moving said mold and cooling elements together as a unit in the direction opposite said casting direction, and at least one cooling water nozzle positioned to project cooling water onto a portion of a casting exposed by said gap during said movement of the mold and the cooling elements in the casting direction.

2. The method of casting comprising pouring a molten metal into one end of a reciprocating mold and continuously withdrawing partially solidied metal from the other end of the mold while wholly surrounding and engaging the entire peripheral surface of the cast metal at said other end with at least one cooling element, moving said cooling element in the casting direction at a speed greater than that of the mold to open a gap between the mold and the cooling element, projecting a cooling fluid onto the cast metal in said gap, stopping said cooling element to close said gap, and returning said mold and cooling element together at the same speed in the direction opposite the casting direction.

References Cited in the le of this patent UNITED STATES PATENTS 2,726,430 Rossi Dec. 13, 1955 2,871,534 Wieland Feb. 3, 1959 2,895,190 Bungeroth July 2l, 1959 FOREIGN PATENTS 44/1961 Sweden Jan. 3, 1961

Claims

1. THE COMBINATION WITH A CONTINUOUS CASTING MACHINE HAVING A RECIPROCATING MOLD, OF AT LEAST ONE COOLING ELEMENT AT THE OUTLET END OF THE MOLD AND MOVABLE INDEPENDENTLY OF THE MOLD, SAID COOLING ELEMENTS WHOLLY ENCLOSING A CASTING LEAVING THE MOLD, MEANS FOR MOVING SAID COOLING ELEMENTS FASTER THAN THE MOLD IN THE DIRECTION OF CASTING TO FORM A GAP BETWEEN THE MOLD AND THE COOLING ELEMENTS, MEANS FOR STOPPING SAID COOLING ELEMENTS TO CLOSE SAID GAP, MEANS FOR MOVING SAID MOLD AND COOLING ELEMENTS TOGETHER AS A UNIT IN THE DIRECTION OPPOSITE SAID CASTING DIRECTION, AND AT LEAST ONE COOLING WATER NOZZLE POSITIONED TO PROJECT COOLING WATER ONTO A PORTION OF A CASTING EXPOSED BY SAID GAP DURING SAID MOVEMENT OF THE MOLD AND THE COOLING ELEMENTS IN THE CASTING DIRECTION.