US2793410A

US2793410A - Method and apparatus for continuously casting

Info

Publication number: US2793410A
Application number: US345554A
Authority: US
Inventors: Junghans Siegfried; Muller Erich
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-03-29
Filing date: 1953-03-30
Publication date: 1957-05-28
Anticipated expiration: 1974-05-28
Also published as: FR1079898A; GB786334A

Description

y 23, 1957 s. JUNGHANS ET AL 2,793,410

METHOD AND APPARATUS FOR CONTINUOUSLY CASTING Filed March so, 1953 2 Sheets-Sheet l lwvsw-r rze 5|E6 Fr-znao J UN GHANS.

HANs KLEIN 5i ERICH MULLEQ May 28, 1957 s. JUNGHANS ET AL 2,793,410

METHOD AND APPARATUS FOR CONTINUOUSLY CASTING Filed March 50, 1953 2 Sheets-Sheet 2 \NVENTOR5 a m H 8 m wNL JQ U L H :2 @AQ aHE ATTORNEW 2,793,410 6 Patented May as, 1957 United States, Patent 650 2,793,410 METHOD AND APPARATUS FOR CONTINUOUSLY CASTING a Siegfried Junghans, Hans Klein, and 'Erich Miil'ler, Schorndorf, WurttembergfGermany Application'March 30, 1953,.Serial'N0. 345,554

Claims priority, application Germany March 29, 1952 3 Claims. (Cl. 22-572) nalzone of'tne casting head with the supply of the-casting material have not been sufficiently taken into account. If the method in accordance with the invention is followed, it is'possible to produce castmernbers of thin wall thickness, for example, tubes with a diameter of 800 mm. and-a wall thickness of mm. or even less, which are excellent as regards their surface and internal nature. The,

process according to the invention consists in that the casting jet is aligned above the surface of the casting and itsflow is adjusted in such manner that it enters the .surface of the casting at such a distancefrom and in sucha direction relatively to the mould wall and at such a speed that it is no longer able to unsettle that portion ofthe meniscus which is disposed directly in front ofthe solidification shell and is no longer able to damage the solidification shell itself. This requirement is based on the knowledge that the shape of the meniscus must not be destroyed by the fiow movement of the casting jetentering the surface of the casting, but that it must be applied in-a completely constant manner to the Wall of the mould in order to avoid formation of irregularities, channels and overlaps on the surface. The casting material must therefore be so introduced into the surface of the casting that it isno longer able to disturb the meniscus. Ithas further been recognised 'by -the inventor that when casting thin cross-sections, the casting jet after entering "the surface of the casting can cause damage due to the fact that it penetrates to the depth of the liquid cavity or piping into the solidification shell already formed, sothat liquid metal can penetrate into the shrinkage gap between the continuous casting and the wallet the mould. From this knowledge, there is derived the requirement thatthe flow of the casting jet is to be so adjusted and the jet so aligned that it can only reach predetermined parts of the liquid cavity or piping and cannot cause damage at other places either by mechanical or thermal action.

In the preferred embodiment of the invention, the cast- :ing jet is shaped on the guide surface to correspond to the cross-section to be cast, that is to say, is spread out into a thin layer when casting thin cross-sections. In such a case, the guide surface expedientlyextends parallel to or as a continuation of the next adjacent wall'of the mould. It istpossib'le to arrange a plurality of guide surfaces in series, preferably in such manner that the casting jet is reflected at the first guidesurface, falls from the Zlatter'on'to the second surface on which it then'runs down smoothly without being reflected.

When not working with a casting jet of substantially the same longitudinal extent as that of-the cross-section to be cast, it is recommended to operate with at least one travelling casting jet, provision being'made in orderto be able to adjust the travelling speed in accordance withthe casting conditions. I v

The arrangement of a-guide surface for the casting-jet offers the possibility of supplying heat to-the latter or, on

the contrary, withdrawing heat therefrom, andalso of influencing the casting 'jet chemically-and/or metallurgi callyby suitable choice of the materialof the guide surface. 1 v

In order to carry the process of the invention into -effect, it is recommended to use an arrangement in which atleast one guide surface is arranged above the level of the casting as a continuation of or parallel to one wall of 'the mould, which surface is so shaped and is capable of being so aligned relatively to the mould that the metal jet flowing down thereon enters the surface of the casting at a distance from and in a direction towards the wall of the mould, and at a speed at which the casting jet is no longer able to unsettle the meniscus or todamage the solidification shell.

.The guide surface expediently extends parallel to the wall 'of the mould, it being possible for its effective part to 'be shaped the same as or similar to the cross-section to be cast in 'order suitably to change the shape of the casting jet, which usually will have a round or in any case composite cross-section.

The guide surfaces can be arranged in sections or continuously around the entire inlet opening of themould the continuous arrangement being used'when the casting jet covers the entire cross-section, for example in the casting of tubes.

The guide means may also serve for chemically and/or metallurgically influencing the casting material if they are made of a suitable substance.

The supply means for the casting jet and the guide surface can be arranged movable relatively to one another. However, it is also possible to conceive cases where it is expedient to connect the supply means for the casting jet and the guide surface rigidly with one another and to move them over the casting cross-section.

A number of devices for carrying out the process according to the invention are hereinafter explainediby way of example and with reference to the drawings, wherein:

Figures 1 and 2 show diagrammatically a section through the marginal solidification zone'of a'cooled continuous mould, Figure 2 indicating the method for the approximate determination of the dangerous zone 'of the casting head,

Figure 3 is a fragmentary section through a mould for casting thin-walled iron tubes with an associated rotating casting vessel,

Figures 4 and 5 are respectivelya vertical section and a plan view of the upper portion of a continuous mould for casting iron tubes with the rotating casting vessel arranged above the same, the casting jetbeing directed towards the core,

Figure 6 is a diagrammatic view showing the series arrangement of two guide surfaces, the first being :a reflecting surface and the second a non-reflecting surface.

In Figures 1. and 2, 1 is the cooled wall of a continuous mould, 2 is the casting surface which is'curved at the margin under the surface tension and which is referred to hereinafter as the meniscus, 3 is the liquid portion of the casting head, 4 is the solidification shell and 5 is the casting jet. I

The endangered Zone of the marginal zoneis indicated as regards its extent by a circular line 6; this endangered zone comprises essentially the curved portion 2a of the angles.

3 meniscus and the initial portion 4a shell.

The exact shape of the meniscus is capable of being observed during casting. In addition, however, it is also possible to calculate the meniscus shape by means of of the solidification 'measured physical properties of castingmetal and the wall of the mould or lubricants. For this purpose,'it is necessary The basic data for this calculation, the formation of the differential equation of the surface and the solution thereof under the different limiting conditions are found, for

example in Ioos, Lehrbuch der Theoretischen Physik, 1st edition, Leipzig 1932, pages 187-191, and in volume 70f the Handbuch der Physik by H. Geiger and K.

Scheel, Mechanik der gasformigen und flussigen Korper,"

chapter 6, Capillarity, by A. Gyemant Springer, Berlin,

cus (see Figure 3).

The endangered region of the meniscus surface can then be considered as the portion of the metal surface which is disposed above the major horizontal axis of the ellipse. It is also possible to refer to the entire ellipse surface as the endangered portion of the casting bed.

On the basis of this definition, assuming the usual casting conditions and the usual casting metals, it is finally also possible to establish the endangered region as being the portion of the casting head which is within a certain distance from the wall of the mould, this distance s being a certain multiple C of the height h of the meniscus and the value of C being substantially between 2 and 4, according to the casting conditions; therefore,

s=Ch and C=2 to 4 In prolonged tests, it was ascertained that the

endangered zone

2a, 4a must not be disturbed by the incident casting stream or jet in such manner that the curved portion 2a of the meniscus 2 becomes unsettled by flow forces. The portion 2a must rather be constantly renewed v with absolute smoothness, that is to say, be able to prosolidify at a different time and form a solidification shell with strong transverse grooves, fissures and overlaps.

In order to avoid such harmful effects, it is necessary that the casting material is supplied outside the endangered zone 6 and is brought into the endangered zone in a steady flow in the direction of the arrow 7.

In the course of prolonged experiments in the continu- Jous casting of thin tubes of iron and steel, it has been found that it is necessary to fulfil a second condition, which is that it is necessary to avoid the casting jet (see Figure 2) melting and penetrating the depth of the solidification shell 4 after it has entered the casting head. It is obviously on this account that it has not hitherto been possible to cast thin-walled cast products from highmelting metals in continuous form, because the liquid casting head is enclosed by two extremely thin solidification shells which are adjacent one another with a small spacing, but the extent of which in the depth of the casting head is, however ten or more times its spacing. Under the peculiar flow conditions which obtain when operating with a liquid metal jet, it is not possible in practice, as becomes apparent from the known supply means, to introduce this jet into the casting head in such manner that it always enters the casting head at the same to know the surface tensionsor the marginal spacing from the inner and outer solidification shells and loses its energy of movement in the depth of the liquid cavity or piping and only penetrates forwardly with its heating effect to such an extent that a stable edge solidification can be formed. As shown from experience, the casting jet Will vary its direction according to the composition of the casting material, its temperature and the condition of the supply means, with the danger of melting and breaking through the solidification shell.

The arrangements which are hereinafter described render it possible for the conditions explained with reference to Figures 1 and 2 to be met and for tubes with comparatively small wall thicknesses to be produced, which tubes are at least comparable with the tubes hitherto produced in accordance with other processes as regards their sur face quality and their internal nature.

The arrangement shown in Figure 3, which for sake of simplicity is only partly illustrated, serves for the casting of tubes, and 10 represents the outside wall of a cooled continuous casting mould, 11 the core thereof, which is also cooled, and R the cast member. Fitted on the upper edge of the mould wall 10 is a graphite ring 12, said ring being secured by means of screws 13 to a supporting ring 14. The graphite ring 12 engages for some distance by means of its flange 12a serving as a guide surface over the wall 10 of the mould and terminates just above the casting surface R1; the flange is bevelled outwardly at 12b.

An annular casting vessel 15 is rotatable above the mould about an axis which is not shown and which coincides with the axis of the mould. The metal to be cast is supplied to the said vessel by way of a channel or directly from a heat retaining ladle. At its bottom, the casting vessel is formed with a discharge nozzle directed at an inclination towards the graphite ring 12,

the angle of incidence of the nozzle in relation to the inner peripheral surface of the graphite ring and the spacing between the nozzle 16 and the ring 12 being so adjusted that the jet of metal issuing from the vessel 15 is braked and deformed on the surface of the ring 12 in such manner that the casting metal runs down in a thin strip on the annular flange 12a and steadily enters the casting head R2 without spraying or moving out laterally. It has been found that the bevel 1211 on the bottom edge of the annular flange 12a contributes to enabling the thin liquid metal strip to be detached smoothly from the flange 12a.

In contrast to the arrangement which has just been described, the casting jet in the constructional example shown in Figures 4 and 5 is directed towards the core of the mould; in these figures, 21 is the outer wall of the mould, 22 the core, 23 a pipe for supplying cooling medium, 24 a pipe for discharging the cooling medium and 25 is a metal plate closing the core of the mould. The graphite ring 26 is placed around the upper edge of the core 22/25 of the mould to serve as a guide surface. The surface of the casting has to be imagined as being approximately at the level 27.

The casting Vessel 29 is rotatably arranged about the axis 28 of the mould and above the latter, said vessel being supported by means of arms 2911 on an annular mounting (not shown). The channel-shaped crosssection 29b of the vessel 29 comprises three bulged portions 290 which are directed towards the axis and which open at the bottom into discharge nozzles 30. The nozzles 30 are directed at an inclination towards the graphite ring 26 and are arranged close in front of the latter so that the jet of metal which issues from the nozzle is braked on the graphite ring 26, steadied and spread out to form a thin strip which enters the liquid casting head in a steady manner and exactly parallel to the

walls

21 and 22 of the mould. The arrangement of the nozzles 30 in bulges 290 of the rotating casting vessel 29 has the advantage that it is possible to have a substantiall free view of the surface of the casting.

Means (not shown in the drawing) are provided for varying the speed of rotation of the vessel 29. In order to prevent the action of air oxygen, more especially on the thin metal layer, which runs down on the guide surfaces of the devices in accordance with the invention, it is recommended that the entire metal supply or parts thereof be in certain cases arranged in gas-tight manner.

Whereas hitherto supply devices with a single guide surface have been described, there is hereinafter referred to (see Figure 6) an arrangement with two guide surfaces arranged in series. The casting metal falls in a free jet 40 on to the first guide surface 41 at an angle cc which is such that the jet is reflected at an angle a and now reaches the second guide surface 42, but this time at an angle 'y, at which surface there is no further reflection, but the jet 40 runs down substantially tangentially into the mould cavity 43a of the mould 43.

We claim:

1. A process for the continuous casting of thin wall metal tubes in an open top continuous casting mold comprising pouring molten metal in the mold at a rate to form a head of metal adjacent the top edge of the mold, solidifying a metal shell in said mold with the upper edge of said shell starting at substantially the lower edge of the meniscus of the molten metal head, and further pouring said molten metal in a jet entering the head of molten metal immediately adjacent to but outside of the portion of the meniscus contacting the upper edge of the solidified shell at a distance s from the wall of the mold wherein s=Ch, C being from 2 to 4, and It being the height of the meniscus.

2. An apparatus for the continuous casting of thin wall metal tubes comprising a continuous casting mold adapted to hold molten metal having a meniscus near the upper edge of the mold and a solidified shell immediately below the meniscus, guide surface means mounted in said mold above the meniscus level at a distance s=Ch from the wall of the mold, wherein C=2 to 4, and h is the height of the meniscus, for guiding molten metal into said mold as close as possible to the wall of the mold but outside of the portion of the meniscus disposed directly in front of said solidified shell, a ladle mounted above said mold, and nozzle means in said ladle for directing a stream of molten metal at an angle onto said guide surface means.

3. An apparatus as in claim 2, further comprising a means rotatably mounting said ladle above said mold, sidewall bulged portion in said ladle, and said nozzle means being mounted in said bulged portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,516,049 Luetscher Nov. 18, 1924 1,755,411 Peirce Apr. 22, 1930 1,944,611 Reinartz et al Jan. 23, 1934 2,590,311 Hatter et a1 Mar. 25, 1952 2,631,343 Hunter Mar. 17, 1953 2,659,121 Easton et a1 Nov. 17, 1953 FOREIGN PATENTS 502,347 Belgium Apr. 30, 1951