US2870005A

US2870005A - Process for heating the head of an ingot of molten ferrous material

Info

Publication number: US2870005A
Application number: US594201A
Authority: US
Inventors: Kurt O R Gebhard
Original assignee: South African Iron & Steel
Current assignee: South African Iron & Steel; SOUTH AFRICAN IRON AND STEEL INDUSTRIAL Corp Ltd
Priority date: 1955-07-06
Filing date: 1956-06-27
Publication date: 1959-01-20
Anticipated expiration: 1976-01-20

Description

5 1959 I K o. R. GEBHARD 2,870,005

PROCESS FOR HEATING THE HEAD OF AN INGOT OF MOLTEN FERROUS MATERIAL Filed June 27, 1956 PROCESS FOR HEATING THE HEAD OF AN INGOT OF MOLTEN FERROUS MATERIAL Kurt O. R. Gebhard, Brooklyn, Pretoria, Transvaal, Union of South Africa, assignor to South African Iron and Steel Industrial Corporation Limited, Pretoria, Transvaal, Union of South Africa Application June 27, 1956, Serial No. 594,201

Claims priority, application Union of South Africa July 6, 1955 7 Claims. (Cl. 7560) ferrous metallic material being heated by passing through said conduit, oxygen having atleast the concentration of oxygen-enriched air, the mouth of the said conduit being immersed in the molten ferrous metallic material being heated.

Preferably the conduit is in the form of a pipe, and a preferred material for the production ofthe pipe or an essential part thereof is aluminium or an alloy of aluminium with a metal generating large amounts of heat when oxidised, e. g. with magnesium and/ or silicon. Suitable aluminium-silicon alloys can be obtained by the production of clays, e. g. in an electric furnace. This material will be particularly desirable in most applications for economic reasons. 7

Other materials or metalloids yielding slag forming oxidation products may also be employed as conduit materials, e. g. magnesium or silicon or alloys thereof.

The aforesaid conduit materials ma, of course, also contain other constituents, usually in small amounts.

The reactions and heats generated in the oxidation of various elements are as follows:

i (a) Examples of metals undergoing treatment (b) Examples of conduit or lance metal materials In general, the material employed for making the conduit or lance or serving as a substantial constituent thereof should on combustion generate per kilogram at least 3000 Kcals. more than the heat generated by oxidation of a kilogram of the metal undergoing treatment. Materials are very suitable 1 kilogram of which on oxidation generates at least 6000 Kcals.

In order to obtain a sound casting in normal foundry practice, the feeder heads are made so large that they amount to say, 35 percent to about 40 percent of the finished Weight of the finished casting with consequential losses. The feeder heads can be made much smaller, say about 15-20 percent of the finished casting, e. g. about 50 percent smaller, if the iron in the feeder head United States PatenrO into the feeder head by means of a combustible lance or other conduit in accordance with the invention and sound castings are thus produced. In foundry practice approximately only so much oxygen should be introduced as is required for oxidising the lance or conduit material.

The invention is also applicable to the casting of ingots, in particular of killed steel.

' As is known, the cavities formed at the top of freezing ingots of killed steelnormally called pipessubstantially decrease the useful portion of the ingot cast. As a result, a certain percentage of the total steel made and teemed has to be returned for remelting, and so part of the energy, labour, and other cost factors expended in making a certain quantity of steel is wasted.

The effect of pipe formationon the economy of steel making is so great, that many attempts have been made to avoid or decrease the extent of piping in killed steels. In all these attempts, the aim was to keep the top of the ingot molten as long as possible, so that cavities, which have formed in the upper part of the ingotdue to shrinkage in the course of freezing can be filled in again by molten steel from the top.

According to the known art, the ingot topcan be kept molten by either providing a good insulation of the top part of the ingot mould, or by applying heat from a gas burner or electrically. Where applicable, especially in the manufacture of special steels, these methods are well established. In the mass production of commercial steels, the use of pulverulent compositions which when ignited react with a strong exothermic reaction,

. moulds generally consist of two main parts, a lower part is overheated by blowing oxygen or air rich in oxygen for receiving the bulk of the casting and an upper usually tapering part, or feeder h ad, which is well insulated against loss of heat to maintain the ingot top molten as long as possible. The metal in the feeder head or a great part thereof is usually cut away. The portion cut off and discarded for reprocessing is termed the lost head. The so-called lost head usually amounts to about 10 to 20 percent of the total ingot weight. If the feeder head is made too small, not enough metal is available to prevent premature freezing and to fill any cavities 'which may form. As a result a narrow and deep piping may occur.

In accordance with the invention, piping in the casting of ingots from steel, in particular killed steel, can be avoided by passing oxygen or a gas rich in oxygen by means of a conduit, pipe or lance, made of or essentially containing a combustible material as herein specified into the molten metal at the ingot top thus superheating it to prevent premature freezing and avoiding or greatly decreasing the formation of pipes.

This operation may be carried out with advantage in ingot moulds having feeder heads of conventional size, containing e. g. 10 to 20 percent by weight of the total ingot because in accordance with the invention a great part of the said feeder head solidifies to a sound ingot, so that often little more than the slag at the top has to be cut away. I

In accordance with the invention, however, ingot moulds with a smaller feeder head, say containing 6 to 10 percent of the weight of the ingot may be employed. This has the advantage that a great proportion of sound ingot material is obtainable.

According to another modification of the invention the occurrence of piping when casting steels, in particular, in killed steels can be avoided or decreased by superladle by treatment with oxygen or oxygen rich gas introduced by means of a combustible lance as herein specified and using the thus superheated steel for after-teeming.

The feeder head of the ingot mould used can also under these circumstances be kept much smaller, 'say 6 to percent in proportion to the ingot weight than used in normal practice.

According to the invention, in teeming ingots of. killed steel, a suitable amount, e. g. 3 to 8 percent of'th'e steel is poured into a ladle of suitable size and design and treated with a lance in accordance with the invention; Care should be taken by adjustments as regards the content of carbon, manganese, silicon and other elements, and as regards the composition of the lance that the steel used for after-teeming has practically the same chemical composition as the bulk of the ingot.

Any crusts that might already have formed on the surface of the ingot will remelt and the cavities formed be filled in. Any piping which might still occur will not be considerable when using a smaller feeder head, because the shrinkage of only a small volume of steel is involved. Such piping will be confined to the very top of the ingot only. Thus the loss due to piping in further processing is decreased to a small amount.

A sound casting is produced with a smaller lost head and, as a result, great economic advantages are achieved by better exploitation of the smelting capacity and labour involved in cutting the lost heads.

The casting of an ingot of killed steel in accordance with the invention and the advantages obtained will be further described in the following comparative example with reference to the accompanying drawings in which Fig. 1 is a longitudinal section through an ingot top in accordance with the invention and Fig. 2 is a similar section through the top of a conventionally produced ingot.

A heat of a fully killed steel having an, analysis of approximately 0.40% C, 0.10% Si, 0.60% Mn, 0.02% S and 0.03% P was teemed into conventional 4.5 t. hot top ingots. One of the ingots was treated by burning with oxygen an aluminium lance of approximately 6 lbs. weight inserted into the molten steel in the ingot head. This ingot and an untreated reference ingot were split longitudinally.

Referring now to the drawings, 1 indicates the ingot body and 2 the ingot head. 3 (Fig. 2) indicates the boundaries of the piping in the conventional ingot. From free from such pipes. The black areas 4 indicate blow holes and cavities present in the ingots. It will be seen that these occur to a much smaller extent in the ingot in accordance with the invention than in the reference ingot and in the treated ingot, they occur only to a small depth from the surface. It canbe clearly seen that the losses by cropping required for the untreated ingotare much higher than for the treated ingot. It was found that on the untreated ingota loss of approximately 7 percent of the total ingot weight occurred, whilst on the treated ingot 3.5 percent only were lost. Practical experience has shown that on untreated ingots the loss is normally in the range of 10 percent, so that the actual savings are still greater than shown on the experiment.

What I claim is:

1. A process for heating the head of an ingot of molten ferrous material comprising introducing into the head a metal conduit of solid combustible material having an exothermic reaction heat substantially greater than that of the ferrous material, passing an oxidizing gas through the conduit, and oxidizing the conduit in the head of the ingot.

2. A process as claimed in claim 1 wherein the conduit is of a material selected from the group consisting of Al, Si and Mg and combinations thereof.

3. A process as claimed in claim 1 wherein said mentioned material has a reaction heat of at least 6000 Kcal. per kilogram.

4. A process as claimed in claim 1 wherein the gas is oxygen-enriched air.

5. A process as claimed in claim 1 wherein the conduit is progressively fed into the head of the ingot to compensate for the oxidizing of the conduit.

6. A process as claimed in claim 1 wherein the ferrous material constitutes the ingredients of killed steel.

7. A process as claimed in claim 1 wherein the conduit is oxidized to a slag.

References Cited in the file of this patent UNITED STATES PATENTS 937,163 Mesta Oct. 19, 1909 968,350 Harrison Aug. 23, 1910 1,494,003 Malcher May 13, 1924 2,286,191 Aitchison et al June 16, 1942 2,491,440 Boedecker et a1. Dec. 13, 1949 2,502,259 Hulme Mar. 28, 1950 FOREIGN PATENTS 673,605 Great Britain June 11, 1952 696,840 Great Britain Sept. 9, 1953