US3315323A - Method of continuous casting - Google Patents

Description

P 1967 K. G. SPEITH ETAL 3,

METHOD OF CONTINUOUS CASTING Filed Oct. 2, 1963 Ad -vex United States Patent 3,315,323 METHOD OF CONTINUOUS CASTING Karl Georg Speith and Adolf Bungeroth, Duisburg, and

Klaus Frenken, Essen-Verden, Germany, assignors to Mannesmann Aktiengesellschaft, Dusseldorf, Germany, a corporation of Germany Filed Oct. 2, 1963, Ser. No. 313,249 Claims priority, application Germany, Oct. 4, 1962,

M 54,396; June 18, 1963, M 57,209

1 Claim. (Cl. 22-200.1)

The invention relates to a method for continuous casting.

The manufacture of continuous billets from metals with high-melting points by continuous casting plants giving satisfactory surfaces still involves many difliculties. The causes of the surface defects are the marginal crusts and oxidation films which arise at the edge of the bath surface and are drawn along by the billet, forming scabs or scarfs.

In this specification metals with high melting points are understood to be steel, iron and so-called base nonferrous metals and their alloys.

The object of the invention is toobtain satisfactory billets, with perfect surfaces in particular, when casting any grade of metal by continuous casting, the amount of slag on the bath surface being as small as possible.

According to the invention it is proposed that after pouring on, as soon as the fluid metal, such as steel, in r the mould has reached a certain predetermined level required for casting, a powdery covering material is applied to the bath surface in an amount sufficient to cover this surface completely, and that at least part of this material should remain powdery while the rest may melt so that after a few minutes of the temperatures prevailing in the top of the billet a fluid slag layer is formed whose surface tension is such that the mould wall is not wetted.

The quantity of covering powder may be such that only part of it melts while the rest stays on top of it in a solid, powdery state, reducing the heat radiation of the slag and preventing the slag from forming a coating. The quantity applied may then be 3 to 10 grams per :square centimeter of the billet surface area, and preferably 3 to 6 grams per square centimeter, the larger quan- I tities being associated with the longer casting times. Results so far obtained indicate that in steel casting a maximum of .7 kg. and an average of .4 to .6 kg. of covering powder is needed per tonne of steel. If because of a very unstable pouring jet the slag surface is covered with steel spatters or if because of unexpectedly long casting times the covering material melts the slag may be skimmed off and the covering material applied again.

The casting surface in continuous casting moulds can be covered with loosely poured, that is, drippable, powdery materials which, partly melting and forming slag, make a slag layer which is thin compared with the powdery layer above it and is tough enough not to touch the mould wall. These covering powders for use in extrusion have a relatively high melting point, preferably above 1400 C., in case of partial melting a high viscosity, preferably above 100 poises, and a relatively high surface tension. They are used in layers of moderate thickness, with the mould lubrication turned ofl, up to about 50 mm. on the casting surface in a moved sliding mould. If the covering powder melts where it touches the casting surface, it is essential that the tough slag layer in permanent contact with the powder above and gradually forming from this should be only moderately thick (up to about 25 mm.).

total Good results were obtained with covering materials of the following composition:

Percent Si0 35-50 A1 0 20-40 CaO 2-10 MgO 0-5 Na O+K O 3-12 Fe-l-Mn (total content of the oxides) 5-15 C (total content) 3-13 P, S .5

A change in composition within the limits given if possible if, for example, when greatly varying grades are being cast, the casting temperature fluctuates over a wide range. Other compositions of the covering material are possible if they only form a suitable viscous slag at the casting temperatures concerned, part of the quantity applied remaining in a powdery state.

Another covering powder has the following composition:

Percent SiO 41.0 Al O +TiO 23.5 CaO 3.0 MgO 2.0 Na O+K O 3.7 Fe-i-Mlltdt l3 P,S .3 Heat loss 7 It is possible to use fine-ground powder of substances which do not melt at steel casting temperatures. These substances may for examples consist of CaO or A1 0 or other high-melting oxides of the alkaline-earth metals or of the group of rare earths, alone or in a mixture, preferably with an admixture of up to 30% of pulverized graphite, coal or coke.

The use of such covering powders has the result that the heat losses from the casting surface and with them the risk of cold run formation are greatly reduced, and that oxidation of the casting surface is prevented and that the slag skimmings usually appearing on the casting surfaces are taken up by the covering and prevented from passing radially over the casting surface edge and prevented from. forming inclusions on or in the surface and method of using them described can the invention be satisfactorily used. Because the thickness of the tough slag layer arising in the case of partial melting of the covering powder is kept down as stated earlier, and because of its relatively large surface tension, the mould wall, which is favorably cold and dry, is not touched by the tough slag. To make sure that when tough slag is formed there is, even over long periods, no wetting of the mould wall which might greatly endanger the casting process, it is essential that the mould movement continually bring traces of the easily flowing, not lumpy covering powder into the space between the mould'wall and the edge of the tough slag. The liberation, resulting from heating, of repellent gases which, as is well known, adhere to the large surfaces of fine powders in considerable amounts also helps to prevent the tough slag from approaching and sticking to the mould wall and to cause then, friction-reducing layers of gas to form between the billet skin and the mould wall.

The method according to the invention is particularly suitable for casting steels containing aluminum. Contrary to all expectations, it was found that these steels, despite the high A1 content of the slag, had a much lower content of aluunina inclusions than steels cast in the usual way. The surface of the billet, moreover, was always in very good condition, although steels containing aluminum are notorious for involving special casting problems as regards the surface condition.

It was also found that in spite of the high carbon content of the covering coating there is no carbonization of the steel. Moreover, surprisingly, the good results obtained are not adversely affected by the omission of the mould lubrication otherwise needed, regardless of the grade of steel.

The powdery covering material is preferably fed to the bath surface by means of a neutral gas through a ring conduit with nozzles on the upper edge of the mould. The number of nozzles depends on the size of the billet. Other known mechanical feeding means may, of course, be used instead.

To prevent the slag from being washed into the billet by the pouring jet and the slag from being enriched with granulated material, a ceramic pipe, for example of zircon silicate, with a suitable diameter may be fixed to the mould or the feed pipe for the covering powder so as to project into the top of the billet.

The invention will now be described, by way of example only, with reference to the accompanying drawings. In these:

FIG. 1 shows a continuous casting mould; and

FIG. 2 shows another embodiment of a continuous casting mould, with the feed device for the covering material omitted.

A continuous casting mould 1 (FIG. 1) contains a continuous billet 2 which has solidified at the edges. Above this there is a conventional distributing vessel 3, from which the fluid steel drops in a free fall to the bath surface through a spout 4. Above the mould 1 there is a ring conduit 6 with nozzles 5 through which the covering mixture which is to be applied to the bath surface is sent by means of a neutral gas. The crosssection of the ring conduit 6 and the number of nozzles 5 depend on the quantity to be supplied and the crosssection of the billet. Part of the powdery covering material applied to the bath surfare there forms a tough slag 7, while the rest stays above this in a powdery state 8.

The embodiment shown in 'FIG. 2 also has the fluid part 7 and powdery part 8 of the covering material on the bath surface. To prevent the covering material from being carried away by the pouring jet, a ceramic pipe 9 is suspended in the mould 1. The lower end of this reaches into the top of the billet, and its diameter is such that it does not interfere with the free fall of the pouring jet.

The method as a whole has a number of quite considerable advantages over the state of the art. By adding the slag mixture in a solid state no special melting devices are needed for the slag. Feeding is completely safe and much easier to carry out. The smallness of the amount that has to be added is a considerable saving. As the method can be used without any mould lubrication there are advantages over conventional lubrication on the grounds of this saving alone, and with slag lubrication the cost of subsequent removal of the slag layer from the casting surface is saved. Above all, however, there is the certainty of good surfaces at all times, for no change in the consistency of the slag is caused by non-metallic inclusions coming up out of the steel.

We wish it to be understood that we do not desire.

to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

Having thus described the invention, what we claim as new and desire to be secured by Letters Patent is as follows.

We claim:

In a method of continuously casting, in an open ended casting mould, metals of high-melting points and their alloys, respectively, the steps comprising applying a powdery covering material to the upper metal bath surface after the upper metal bath surface has reached a substantially predetermined height in the casting mould, at least some of said material being operative to melt, thereby forming a covering slag on a portion of said surface, where the covering slag layer is not more than 25 mm. thick and has a viscosity of over 100 poises, so that the covering slag layer does .not touch the mould wall, the gap between the covering slag layer and the mould wall is being filled with the powdery material, and the powdery layer remaining on top of the covering slag layer is at least as thick as the covering slag layer.

References Cited by the Examiner UNITED STATES PATENTS 2,304,258 12/1942 Junghans 22.2-00.1 2,568,525 9/1951 Waddington et al. 22-57.2 X 2,737,696 3/ 1956 Shields 22-215 2,760,859 8/1956 Graf 94 2,797,990 7/1957 Froats 75-94 2,825,947 3/1958 Goss 22-200 1 3,034,186 5 1962 Holhouser 22-200.l 3,089,209 5/1963 Phillips et a1. 22-2001 3,153,820 10/1964 Criner 22-57.2 3,167,829 2/1965 Hess et al 22-.57.2

FOREIGN PATENTS 835,084 5/1960 Great Britain.

J. SP-ENCCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, Assistant Examiner.

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