US2937425A

US2937425A - Production of castings and ingots

Info

Publication number: US2937425A
Application number: US821088A
Authority: US
Inventors: Morgan Hugh Myllon
Original assignee: Foundry Services International Ltd
Current assignee: Foundry Services International Ltd
Priority date: 1959-06-18
Filing date: 1959-06-18
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24

Description

r 2,937,425 PRODUCTION OF CASTINGS AND INGOTS Hugh Myllon Morgan, Nechells, Birmingham, England, assignor to Foundry Services International Limited, Birmingham, England, a British company No Drawing. Filed June 18, 1959, Ser. No. 821,088 6 Claims. (Cl. 22215) This invention relates to the production of castings and ingots from killed and semi-killed steels, and has for an object to provide exothermic powders which are used as covers on the surface of the head or riser of the casting or ingot mould to counteract pipe and thus reduce the amount of unsound metal which has to be discarded.

When molten metal cools it contracts and, unless additional molten metal is available to make up for the contraction, voids or contraction cavities are formed in the ingot or casting. As the part of the ingot or casting containing such cavities is unsuitable for general use, it has to be discarded. This scrap metal constitutes a serious wastage of metal and also, owing to high melting costs, it is very expensive scrap.

In the past, the generally practiced method of overcoming or reducing the aforesaid difficulty was to place on top of the ingot or casting, and in contact therewith a reservoir of molten metal of a size such that its latetn heat was sufficient to keep it molten, and thus available for feeding the casting until the casting itself had solidified. This method is extremely uneconomic as quite often the head must contain twice as much metal as the casting it is feeding in order to obtain adequate feeding.

In recent years the above method has been partially superseded by a method in which the riser is poured short, that is to only a third or a half of its normal height, and the surface is then covered by a layer of exothermic material which ignites at the temperature of the metal with the production of carbon-free iron and molten slag at temperatures in excess of 2000 C. In some cases the powders are placed on the riser surface immediately after pouring, but a more efficient reaction is obtained if the powder is not applied until the head metal begins to solidify. The superheated metal produced by the reaction then remelts the head and the latter feeds into the contraction cavities formed in the cooling ingot. By this means all the heat generated by the reaction is usefully used whereas, if the powder is applied directly after pouring, it will only serve to heat already molten metal and will not be 'very effective. As the waiting time before applying the exothermic powder may extend up to a period of some hours, it is common practice to cover the surface of the riser with a layer of insulating or mildly exothermic material to minimise heat losses from the head during this waiting period.

There are a variety of exothermic products available for this purpose and all are based on the aluminothermic reduction of iron oxide, the latter generally present in the form of Fe The reaction which occurs is the well known Thermit reaction:

The amount of superheated iron produced is about 45% by weight of the powder used and this iron remelts the head metal as described above. The slag produced rises to the surface of the head and being at such a high temperature it serves as a very elficient insulating cover and assists in delaying solidification.

, To be really effective there is a critical height for any given diameter of feeding head. If the riser is poured below this height there may not be enough metal in the riser to feed the casting (even with the metal from the Thermit reaction). Also there is the danger of the prod- 2,937,425 Patented May 24, 1960 bridging occurs, feeding of the metal from the head to the casting is prevented and contraction cavities occur in the castings.

. The properties required of exothermic powders for'use as just indicated are that they should give maximum heat generation, minimum silicon contamination of the iron produced-by the reaction and high iron yield.

The degree to which these three properties are achieved depends principally on the iron oxide to aluminium ratio. Thus silicon, and also carbon, pick-up is negligible if excess iron oxide is present, whilst the intensity of the reaction and iron yield are greatest when the aluminium content exceeds the stoichiometric ratio. Silicon contamination is a serious eifect since, when the powders are used on ingots, the molten metal formed during the reaction must remain in the head and any silicon present shows up as hard spots when the ingot metal is eventually machined. Again, when used on castings, although the reactive products do not enter the casting, silicon migration occurs and hard spots are sometimes found in the casting just below the head.

Silicon contamination is probably due either to the presence of silicon impurities in the iron oxide or the aluminothermic reduction of siliceous materials which may be present, i.e. in the sand used to surround the head. Danger of silicon pick-up is therefore always present.

In British Patent No. 673,605 and United States Patent No. 2,791,816 it has been proposed to have iron oxide present in excess of the stoichiometric ratio, for the purpose of reducing carbon pickup, and also presumably siliconpick-up but by this means the reaction is necessarily less intense and a reduced quantity of free iron is produced. It has now been found that the above drawbacks can be minimised or eliminated without lesseningthe efficiency of the reaction, if copper and nickel are included in the mixture. The method by which these metals act in the reaction has not been determined but presumably alloying in some form takes place between the added metals and any silicon present or formed by aluminothermic reducton of any siliceous material, so that silicon migration and consequent hard spots are prevented. It has also been found that proportions of iron oxide well above stoichiometric proportions, e.g. up to 4:1 parts iron oxide to aluminium can be used (whereas the stoichiometric equivalence for Fe O and aluminium is 3.221), without any reduction in the intensity of the reaction or in the iron yield.-

According to the present invention, therefore, an exothermic composition for use in the production of steel ingots and castings comprises an exothermically reacting mixture containing aluminium and iron oxide, said mixture containing 1 to 8% copper and 0 to 4% nickel based on the weight of aluminium present. Preferably a said mixture has a ratio of Fe O to aluminium of 3.3:1 to

Preferably the mixture contains from 3.5 to 6% copper and 0.5 to 2% nickel each based on the weight of the aluminium present, a suitable range of materials being as follows:

Each based on the weight of the aluminium present.

which will tend to flux the slag which is formed during the use of the compositions as aforesaid.

It is a further object of the present invention to pro vide useful compositions for the purpose specified, modified in respect of the relative amounts of the specified ingredients and also containing a slag-fiuxing agent.

According to a further embodiment of the present invention, therefore, an exothermic composition for use in the production of steel ingots and castings consists essentially of a mixture of about 15 to about 30 parts by Weight of aluminium, about 45 to about "84 parts by weight of iron oxide, about 1 to 25 parts by weight of a slag-fiuxing agent, a proportion of copper which is from about 1% to about 8% by weight of the aluminium present and a proportion of nicket which is from to about 4% by weight of the aluminium present, the ratio of iron oxide, calculated as Fe O to aluminium being withinthe range 3311 to 4:1.

Slag-fluxing agents are a known class of materials for use in the foundry industry and specific materials of particular value in the present invention are fluorspar, limestone, calcium carbonate and mixtures of fiuorspar and lime.

The following examples will serve to illustrate the invention:

Example I Parts by weight Aluminium 23 Iron oxide (Fe O 76 Copper 0.7 Nickel 0.3

The resulting ingot is found to be properly formed, free from cavities, and free from carbon or silicon introduced via the exothermic composition.

, Example II The procedure of Example I is followed, but using an equal weight of a composition consisting of:

Parts by weight Aluminium 21 Iron oxide (Fe O 69 Copper 0.7 Nickel 0.3 Fluorspar 9 Results similar to those obtained in Example I are produced but in addition the slag is adequately fluxed so that metal trapped in the slag is enabled to run freely back into the body of molten metal.

Although reference is made above to iron oxide in the form of Fe O it should be understood that the introduction of copper and nickel is also advantageous when using the lower oxide Fe O In this case the nickel is not quite so important and the copper content can be reduced by up to 2% without any deleterious effect, i.e. a content of copper of 1 to 6% and of nickel of 0 to 1% (each based on the weight of the aluminium present) affords adequately satisfactory results.

It will be understood that this invention includes not only the new exothermic compositions above set forth but also includes the production of castings and ingots of steel employing said compositions in the manner indicated.

This application is a continuation in part of application Serial No. 747,853, filed July 11, 1958, now abandoned.

I claim as my invention:

1. An exothermic composition for use in the production of steel ingots and castings consisting essentially of a mixture of to 30% aluminium and 45 to 84% iron oxide, calculated as Fe O the said mixture containing, based on the weight of the aluminium, 1 to 8% of copper and 0 to 4% of nickel, the ratio of iron oxide, calculated as Fe O to aluminium being within the. range of 3.3:1

- 2. An exothermic composition for use in the production of steel ingots and castings consisting essentially of a mixture of 15 to 30% aluminium and 45 to 84% iron oxide, calculated as Fe O the said mixture containing,

' based on the weight of the aluminium, 35w 6% of cop'- consisting essentially of a mixture of 15 to aluminium and 45 to 84% iron oxide, calculated as Fe O the said mixture containing, based on the weight of the aluminium, 1 to 8% of copper and 0 to 4% of nickel, the ratio of iron oxide, calculated as Fe 0 to aluminium being within the range 3.3 :1 to 4:1.

'4. An exothermic composition for use in the production of steel ingots and castings which consists essentially of a mixture of about 15 to about 30 parts by weight of aluminium, about 45 to about 84 parts by weight of iron oxide, about 1 to 25 parts by weight of a slag-fluxing agent, a proportion of copper which is from about 1% to about 8% by weight of the aluminium present and a proportion of nickel which is from 0% to about 4% by weight of the aluminium present, the ratio of iron oxide, calculated as Fe O to aluminium being within the range 3.321 to 4:1.

5. An exothermic composition according to claim 4 wherein the slag fluxing agent comprises fiuorspar.

6. A process for the casting of ingots from killed and semi-killed steels which comprises pouring the steel into the ingot mould so that it does not completely fill the riser of the ingot mould and locating on the surface of the molten metal in said riser an exothermic composition which consists essentially of a mixture of about 15 to about 30 parts by weight of aluminium, about 45 to about 84 parts by weight of iron oxide, about 1 to 25 parts by weight of a slag-fiuxing agent, a proportion of copper which is from about 1% to about 8% by weight of the aluminium present and a proportion of nickel which is from 0% to about 4% by weight of the aluminium present, the ratio of iron oxide, calculated as Fe O to aluminium being within the range 3.3 :1 to 4: 1.

References Cited in the file of this patent UNITED STATES PATENTS Canada Apr. 3, 1956

Claims

1. AN EXOTHERMIC COMPOSITION FOR USE IN THE PRODUCTION OF STEEL INGOTS AND CASTINGS CONSISTING ESSENTIALLY OF A MIXTURE OF 15 TO 30% ALUMINIUM AND 45 TO 84% IRON OXIDE, CALCULATED AS FE3O4, THE SAID MIXTURE CONTAINING BASED ON THE WEIGHT OF THE ALUMINUM, 1 TO 8% OF COPPER AND 0 TO 4% OF NICKEL, THE RATIO OF IRON OXIDE, CALCULATED AS FE3O4, TO ALUMINIUM BEING WITHIN THE RANGE OF 3.3:1 TO 4:1.