US3231371A - Cast iron resistant to heat growth and method for producing the same - Google Patents

Description

1956 J. G. SCHAEFFER ETAL 3,231,371

CAST IRON RESISTANT T0 HEAT GROWTH AND METHOD FOR PRODUCING THE SAME Filed April 16, 1962 3 Sheets-Sheet 1 lg soo STRUCTURAL STEEL /8 200* com-z /7 1500* FIG IRON /6-2o0 COKE /5'1o00 STUCTURAL STEEL /4 400* com: (NORMAL CHARGE) 500* STRUCTURAL STEEL 200* COKE 1000* STRUCTURAL STEEL 400* COKE (NORMAL CHARGE) no 0F 0.05 FERRO SILICON JOHN G. SCHAEFFER ARDEN L. IMM

JAMES W. BEAVIS LOUIS S. GHAMBLESS ALBERT H. ANGERMAN IZ g- QK INVENTORS TEAPOT LADLE K FIG. I

FIGZ) ATTOR EY 1966 J. G. SCHAEFFER ETAL 3,

CAST IRON RESISTANT T0 HEAT GROWTH AND METHOD FOR PRODUCING THE SAME Flled April 16, 1962 3 Sheets-Sheet 2 QM i5: 550: 00:

36x5 $238 3 Rm 3.

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mama- 0 23-0440 Oh 22323: .No it m 1. wFEfi mm $8 925 2233 JOHN G. SCHAEFFER ARDEN L. IMM

JAMES W. BEAVIS LOUIS S. CHAMBLESS ALBERT H. ANGERMAN INVENTORS BY Q 35 3 ATTORNEY Jan, 1966 J. G. SCHAEFFER ETAL 3,231,371

CAST IRON RESISTANT T0 HEAT GROWTH AND METHOD FOR PRODUCING THE SAME Filed April 16, 1962 a Sheets-Sheet s 6400* women METAL TEAPOT LADLE FIG. 7

FINAL CASTING FIG. 6

wwwmw JOHN G.SCHAEFFER ARDEN L. IMM JAMES W. BEAVIS LOUIS S. CHAMBLESS ALBERT H. ANGERMAN INVENTORS:

ATTORNEY United States Patent 3 231 371 CAST IRON RnsisrArJr :io HEAT Gnowrn AND METHOD FOR PRODUCMG THE SAME lohn G. Schaefier, Monongahela, Arden L. 1mm, Charleroi, and James W. Beavis, Monongahela, Pa., Louis S.

Chambless, Simsbury, Conn, and Albert H. Angernian,

Monongahela, Pa., assignors to Combustion Engineering, Inc, Windsor, Conn, a corporation of Delaware Filed Apr. 16, 1962, Ser. No. 187,562 4 Claims. (Cl. 75-130) This application is a continuation-in-part of application Serial No. 75,213, filed Dec. 12, 1960, now abandoned.

This invention relates to ferrous alloys of the cast iron type, and has particular reference to a novel and advantageous method for producing a ferrous alloy composition.

Broadly stated, the object of our invention is to provide a novel ferrous alloy composition which has the advantages of ordinary cast iron and which combines added practical advantages therewith.

Other broad objects are to provide a novel method for producing a ferrous composition which is capable of resisting volumetric growth when subjected to repeated cycles of heating and cooling throughout a wide temperature range, and which also can be cast in molds without requiring allowance for shrinkage of casting dimensions.

A more specific object is to provide for producing this ferrous composition by the aid of metal melting and molding equipment such as is available in a conventional foundry where ordinar gray cast iron is produced.

Another object is to accomplish production of the terrous composition by the aid of conventional metal melting and molding equipment and by the further utilization of certain supplemental apparatus which we uniquely coordinate with the conventional equipment in providing a cast-metal production cycle of new and advantageous character.

A further object is to organize and control such production cycle in a way which assures consistent and reliable production of the ferrous composition and which minimizes scrappage losses.

A still further object is to produce this cast iron composition at a cost not substantially greater than that of ordinary cast iron.

An additional object is to produce castings from the metal on a reliable basis with a minimum of special training on the part of the operating personnel.

Other objects and advantages will become apparent as the disclosure and description hereof proceeds.

One illustrative form of apparatus provided by us for carrying out the invention is shown by the accompanying drawings wherein:

FIG. 1 is a sectional representation of a cupola melting furnace which is shown as containing the special charge needed for producing the metal and the spout of which is equipped with means for metering a first silicon alloying element into the charge as it leaves the cupola in melted condition;

FIG. 2 is a sectional showing of a teapot-type ladle placed below the cupola spout for receiving therefrom the melted metal containing the first added silicon alloying element, after another silicon alloying element has been initially placed in the ladle;

FIG. 3 is a top plan representation of the teapot ladle as viewed from line 3--3 of FIG. 2;

FIG. 4 shows the teapot ladle of FIGS. 2-3 after it has received the charge of molten metal and has been moved away from the cupola furnace of FIG. 1 into the new location of FIG. 4 where an inoculation apparatus, also there illustrated, is lowered into the molten metal for the purpose of injecting calcium carbide and other ingreclients thereinto;

3,231,371 Patented Jan. 25, 1966 Illustrative composition of the metal The present invention provides a ferrous product containing approximately percent iron plus the other ingredients listed below:

Percent Total carbon, minimum 3.25 Combined carbon, maximum 0.50 Silicon 3.80-4.20 Sulphur, maximum 0.01 Magnesium, maximum 0.014 Phosphorous, maximum 0.25 Manganese, minimum 0.50

The product of the invention has the general appearance of chilled cast iron, but is still machineable in the as-cast form. It is somewhat harder than ordinary cast iron, exhibiting Brinell hardness values of 220 to 250; and has a tensile strength considerably greater, of the order of over 60,000 lbs. per sq. in. When dropped or struck it emits a bell-like ring similar to steel. This shows a general absence of carbon in the flake form and indicates at least some of the carbon is in nodular form. The metal is somewhat brittle as compared to steel, and is comparable in this respect to ordinary cast iron.

The metal has a solidification rate closely similar to that of steel; but castings made therefrom are found to have the same dimensions as do the mold cavities in which they are cast. Stated in another way, the patterns used in forming mold cavities for this metal need make no allowance for loss of dimension on the part of the finished casting. This no-shrinkage characteristic has been accurately verified for castings of small dimensions (up to 1 foot), and it is believed that it also will hold true for castings of larger dimensions. 7

Likewise of significance from a practical point of view is the fact that this new cast iron composition combines with the advantages of ordinary cast iron the further capability of resisting volumetric growth when subjected to repeated cycles of heating and cooling throughout a wide temperature range. More specifically, a casting made from this metal having the Stoker-key configuration of PEG. 7 is found upon tests to be capable of withstanding up to 25 cycles of repeated heating and cooling from room temperature to 1600 F. with accompanying volumetric growth limited to 6.50 percent maximum. For applications such as fuel-firing stokers and other heatexchange apparatus including steam generating boilers and the like, this low-growth characteristic at elevated operating temperatures is extremely valuable and makes the new metal highly desirable from a commercial point of view. Thus, grate keys Z made of such metal will normally give several times the service of gray iron under equal conditions, and they likewise are superior to the low chrome materials previously used in grate surfaces.

Our novel foundry technique for producing the new metal FIGS. 1 through 7 of the drawings illustrate foundry apparatus by which the metal referred to above can be successfully produced in an economical and reliable manner and with extremely low scrap losses. Such apparatus includes a conventional cupola furnace C supplemented at its spout with a metering device 24 in the manner shown by FIG. 1; a teapot ladle K shown by FIGS. 2-5 as also being of conventional construction, and chosen for purposes of the present disclosure to have a capacity of 7,000 pounds; special inoculation apparatus generally represented at I in FIG. 4 as being lowerable into the ladle K when at a second location in the production cycle; and hand ladies of the conventional design shown at H in FIGS. 5-6 by which molten metal received from the main teapot ladle K at a third location in the production cycle is poured into molds M for production of the cycle castings Q.

Referring to FIG. 1, the production cycle is started by charging the cupola furnace C with the successive layers of conventional ingredients there designated. The cupola itself has the usual discharge spout 10, and heat for melting the metal charge is produced by the usual burning of coke 11 by the aid of combustion air blown thereinto from wind box 12 through tuyere openings 13. The heat thus liberated melts the metal above the lower coke bed, and drops of such metal flow downwardly between the coke pieces 11 and out of the cupola by way of spout 10.

Still referring to FIG. 1, the ingredients for a 6400 pound charge of metal to be received by the teapot ladle K when melted are placed upon the top of the coke split 14 here shown as comprising 400 pounds of coke. Upon this there is placed a layer 15 consisting of 1000 pounds of structural steel in the various and assorted forms usually available to foundries, but predominantly free of rust or oxidation. Superimposed upon this is another layer 16 consisting of 200 pounds of coke, the purpose of which is to increase the carbon content of the special charge. Above 16 is a 1500 pound layer 17 of pig iron, having relatively low sulphur and phosphorus contents (typical of the Pittsburgh area). Upon 17 is a 200 pound coke layer 18, which may be the same as or similar to the coke layer -16 earlier described, and upon 18 is a further 500 pound layer 19 of structural steel. Superimposed upon these layers of charge is a series of layers identical to the above mentioned layers and indicated as 14' through 19.

In place of the layers 19 and 19 of structural steel, similar amounts of metal obtained from scrapped melts of the present process may be employed to obtain a metal having the desired composition.

These charge layers 14 through 19' are melted down by the cupola C operating in customary fashion. Other cupola charges below and above 14-19 add some metal to the special charge, so that approximately 6400 pounds of melted charge will be discharged through spout 10 into the main teapot ladle K.

The withdrawal of the melt from the cupola is preceded by the placement in the bottom of ladle K, which is in the position shown at 20, of 110 pounds of ferro-silicon material. This is a granular substance and may be carried to the FIG. 2 location of the main ladle K in suitable containers such as the buckets 22 'of FIG. 2. The range of grain size of this material maybe from in. to 12 mesh screen size. Chemical ingredients of the ferrosilicon material used by 'us include:

The melted charge 14-19 is withdrawn from cupola furnace C at a temperature which for best results should be kept within the range of from 2680 F. to 2800 F. In dropping from the spout 10 int-o the ladle K the molten charge impinges upon the ferro-silicon material 20 just described. Such impingement melts the material 20 causing the silicon to go into solution with the molten iron, while the other ingredients predominantly formed into a slag which rises to the surface of the molten metal. Before receiving the melted charge 14-19 from cupola C and the material 20 from buckets 22, it is important that the interior of ladle K be clean and free from unwanted substances that might contaminate the charge to the detriment of the final product.

Above the cupola spout 10 we mount a metering device 24 shown in FIG. 1 as being in the form of a hopper.

Into it is placed 156 pounds of exothermic silicon 25..

This also is in granular form with particle sizesranging from 8 mesh screen on down. This eXo-thermic material 20 consists of:

Percent Silicon 61 Aluminum 1.25

Calcium 0.50

Magnesium 2.75 Sodium Nitrate 13.50

iron Balance stream in spout 10 is accompanied by a chemical reaction which produces violent flames and flashing, that result from the liberated exo-thermic heat.

Whereas the 'ferro-silicon 20 in combining with the melted iron in the ladle K absorbs heat and thus tends to cool the metal, the eXo-thermic silicon 25 dropped into the molten metal flowing through cupola spout 10 liberates heat, as already observed. Both sources ZG-and 25 of silicon addition are in practice found desirable. This is because if all of the extra silicon needed were added at 20 in the ladle K the total cooling effect would be excessive; and if all were dropped into the spout 10 in eXo-thermic form, the exothermic reaction would become too violent. Moreover, attempts to add too much silicon at location 20 have been accompanied by failure of all of the addition to go into solution.

Inoculation at the FIG. 4 location As finally received into the main ladle K, the 6400 pound charge of melted iron has a temperature within the earlier mentioned range of from 2680 F. to 2800 F. At this .point the ladle is moved from its first position of FIGS. 1 and 2 into the second position of FIG. 4 for inoculation treatment. The layer of slag shown at 29 in FIG. 4 as having collected on top of the ladle metal is removed to permit escape of oxides and other gases in the melt. Removal of the slag is also desirable in order to allow the ladle to accommodate the slag which is produced upon inoculationof the melt. We find, it extremely important for best inoculation and other results'that the molten material 28 and ladle K at FIG. 4 have a temperature within the narrower range of from 2680 -F. to 2700 F. when the inoculationis begun. If the metal temperature rises within this range when the ladle K is delivered to the FIG. 4 location, the inoculation can be started immediately. However, if the metal temperature is about 2700 F. the ladle K is held uncovered long enough to effect cooling to within the range of 2680 F. to 2700 F. Experience shows that each minute of holding time is accompanied by a cooling of approximately 5 F. and by the aid of this established rate the holding time is, in each instance, chosen so as to bring the metal temperature down to within the desired range.

Once such proper temperature has been reached, the teapot ladle K of FIG. 4 has a cover 27 placed over its top. In the construction used by us this cover utilizes a 2 inch lower layer of refractory plus a 2 inch upper layer of insulation thereupon. The purpose of this 4 inch cover 27 is to prevent undesirable escape of heat from the molten metal 28 during the inoculation treatment which now follows.

The ladle-contained metal 28 of FIG. 4 now is ready for our inoculation treatment, during which calcium carbide and associated ingredients are introduced thereinto.

As shown in FIG. 4, our inoculation apparatus utilizes an injection tube 39 which extends downwardly through an opening in the ladle cover 27 with the tube end being about inches above the ladle bottom. The tube itself is of a carbon material capable of withstanding the intense heat of the molten metal. In the form shown it has an inside border of /2 in. and an outside diameter of 2 inches.

Extending upwarding from the top of tube 30 is a h xible or other tubular connection 31 that leads into a Y- connection 32 the main branch of which communicates with a valve 33 attached to the lower end or" an outer vessel or tank 34. Inside of this outer vessel 34 is an inner tank 35 having a tapered bottom opening concentric with and slightly above the outer tank 34.

In preparation for the inoculation cycle, the inner tank 35 is charged with 70 pounds of calcium carbide 37. The material 37 is granular in character with particle sizes ranging from 20 mesh to 0 mesh screen size. It is made up of the following chemical ingredients:

Into the bottom of the outside tank 34, we also place 22 pounds of this same calcium carbide material, as indicated at 37' in FIG. 4. Further placed in the outside tank 34, above the lower material 37, are 46.5 pounds of calcium carbide (93%) and rare earth (7%) mixed with an additional 1 lb. and 14 oz. of magnesium. This mixture is designated as 33 in FIG. 4.

All three of these ingredients have a granular form. The calcium carbide ingredient of mixture 38 has the same composition as each of the mixtures shown at 37 and 37' in FIG. 4. The rare earth portion of themixture 38 has the following composition:

Percent Cerium Oxide 52.3 Lanthanum Oxide 27.3

Praseodymium Oxide 5.0

Neodymium Oxide 14 Inert Material (made up of: Barium Sulphate, Magnesium Oxide, Silica, Iron Oxide, Iron) 0-5 The inoculation tank structure 34-35 just described is held in the position of FIG. 4 by a chain 40 for other suspension support. Communicating with the top of the outer tank 34 is a pressure connection or conduit 41 through which a compressed inert gas from a supply cylinder 42 is admitted at proper times. Because of the post-inoculation step described hereinafter we find it expeditious to employ nitrogen as the inert gas. A branch 43 from the main gas conduit 41 by-passes some of the compressed gas through a needle valve 44 directly into the inoculation feed connection 31 and thence into the injection feed tube 30. Such by-pass flow keeps the tube a e 30 open at all times and in readiness to carry the calcium carbide material to tanks 34-35 into the molten metal 28 in the main ladle K.

With the inert gas in supply conduit 41 being maintained at a pressure of approximately 30 lbs. per sq. in., the pin valve 44 is adjusted so that the pressure in the upper portion of tank 34 is maintained at approximately 810 lbs. per sq. in. This is conveniently measured by a meter 39. Such pressure Within the top of outer tank 34 also is communicated to the upper interior of inner tank 35.

To start the injection treatment, we open the normally closed valve 33 that is between tanks 3435 and the conduit 31. Such opening causes an initial flow of the calcium carbide 37 downwardly out of the inner tank 35 and thence into the molten metal 28 via injection tube 30, with the compressed gas acting as a carrier. During this portion of the inoculation cycle a flow control valve 45 at the supply cylinder 42 is adjusted so that the gas from that cylinder at 30 lbs. per sq. in. pressure flows through the conduit 41 to the inoculation apparatus I at a rate of cubic feet per hour. A flow meter 45' at cylinder 42 serves to measure such rate.

Approximately six minutes are required for the inner tank 35 to empty its calcium carbide 37 into the molten metal 28 within ladle K. At this point flow control valve 45 is adjusted to produce a rate of flow of approximately 230 cubic feet per hour. During this portion of the inoculation cycle the contents of the outer tank 34, comprising the 22 pounds of calcium carbide 37' and 46.5 lbs. of a mixture of calcium car-bide, rare earth oxides and magnesium 38, are injected into the melt. Another five minutes or so are required to ar'iect transfer of the contents of the outer tank into the molten metal. Injection of the contents of the inoculation tank has a duration of approximately twelve minutes.

Upon completion of the inoculation of the melt with the aforementioned materials but prior to removing the inoculating apparatus from the melt pure nitrogen is injected into the melt through the injection tube 30 for a period and at a rate suiiicient to inject approximately from three to five cubic feet of gas into the melt. By means of the present apparatus it is merely necessary to continue the flow of the inoculant carrier for a period of time after the flow of inoculants has ceased. Such nitrogen flow is maintained from one to five minutes in order to obtain the desired results.

The eifect of the inoculation treatment is to reduce the sulphur content of the molten metal 28, to homogenize or refine the grain structure size of the metal, and to change at least some of the graphitic form of carbon into nodular form. Without such inoculation the molten metal 28 and ladle K at the FIG. 4 location would not differ a great deal from ordinary gray cast iron with a high silicon content. The resistance to growth from cyclic heating and cooling just described would not be present,

and the major objectives of our inventive improvement thus would not be achieved. Moreover, our disclosed use of the double tank 3435 apparatus itself permits the total inoculation time to be kept within the desired 12 minute period stated. This is preferable to using two separate tanks or recharging a single tank twice during each cycle. An important benefit of the short 12 minute period is minimizing the loss of heat during inoculation, which eifects a drop in temperature of approximately F. during the 12 minute inoculation time. Were this period to be lengthened the loss of heat and the decrease in temperature would be correspondingly greater. With 160 F. drop, the contents of ladle K are at a temperature within the preferred range of 25 10 F. to 2530 F. when inoculation has been finished.

This post-inoculation of nitrogen creates a high degree of turbulence in the melt serving to enhance the effect of the inoculants upon the base metal. Additionally, it has been found that the nitrogen favorably affects the transformation of some of the perlitic matrix into ferrite rings about the graphite nodules and compacted flakes which are interspersed throughout the matrix. The added nitrogen also enables the molten metal to maintain its nodular or compacted flake structure for a longer period of time, it now being possible to obtain the desired metal structure even when the cooling period is extended over several minutes.

Without a post-inoculation addition of nitrogen it was necessary to pour the molten metal into molds within ten or twelve minutes so as to prevent the nodularized structure from fading out or being transformed back into the flake graphite structure common to gray cast iron. A melt subjected to the post-inoculation addition of nitrogen will maintain its microstructure for periods of time longer than thirty minutes which is highly desirable in that it greatly reduces the amount of scrap loss due to a melt not measuring up to specifications.

While the main ladle K is still at the inoculation location of FIG. 4, and after the post-inoculation addition of nitrogen there is added upon the top of the slag layer 29 a further insulating material layer which is shown at 48 in FIG. and which has a thickness of approximately one inch. Any material suitable for reducing escape of heat from the ladle contents may be used for this purpose.

Metal pouring at the FIGS. 56 location Thus prepared the teapot ladle K together with the molten. metal 28 therein now is transferred from the FIG. 4 location to the third or pouring location of FIG. 5. Here the ladle is supported by a crane (not shown) which permits tilting and pouring of metal from the spout thereof. A. metal shield 49 with asbestos backing is at this point placed over the ladle top to protect the iron pourers from radiation and also further to prevent heat escape.

At this FIG. 5 location a number of molds corresponding to M of PEG. 6 have been prepared for the formation of castings corresponding to Q of FIG. 7 when molten metal from the main ladle K is poured into sprue openings 50 thereof.

Such transfer of metal to the molds M is accomplished in conventional fashion by the aid of hand ladles H. Each of these is filled with molten metal as indicated in FIG. 5 and then manually carried to the molds M that are to be filled therefrom.

The pouring operations depicted in FIGS. 5-67 are for the most part conventional. The slag and insulation layers 29 and 48 on top of the molten metal 28 in the main ladle K never flow out into the hand ladles H, since they are restrained in K as FIG. 5 indicates.

Preferably the setup is such that the entire contents of the main ladle K can be transferred into the waiting molds M in a period of from to 30 minutes. Upon arrival at the FIG. 5 pouring location it is preferable that the molten metal 28 have a temperature within the aforementioned range of from 2510 F. to 2530 F. We find that this temperature maintains itself without substantial loss during the entire pouring operation. In fact, the metal 28 taken from ladle K when only partially emptied is found to be slightly hotter than that taken from the ladle when completely filled or when nearly emptied.

Final castings Q are highly superior As earlier mentioned, the casting Q taken from the molds M of FIG. 6 following the pouring and solidification are found to have essentially the same dimensions as did the mold cavities into which they were poured. Just why such original dimensions maintain themselves is something which we find diflicult to explain. Such result is however realized and constitutes a desirable characteristic of our new cast iron material.

This coupled with the earlier-described resistance to volumetric growth from repeated temperature cycling throughout wide ranges makes the new cast iron material extremely attractive for uses such as in the grate keys of fuel-firing stokers, in the tubes of steam generation boilers and other heat exchange apparatus, and elsewhere. The comparatively high silicon content of the new material imparts corrosion resistance characteristics thereto which are comparably desirable. The materials high tensile strength (60,000 pounds per square inch and higher) further enhances its attractiveness for practical utilization.

Scrappage loss drastically reduced Our new cast iron composition when produced in the novel Way herein disclosed has the important advantage of being relatively free from scrappage loss on the part of the final castings Q. Such loss can easily be kept less than 5 percent, and can even be reduced to 2 percent when the various controls already explained for the production procedure are adhered to more rigidly.

In addition to the addition of nitrogen gas to the melt earlier referred to, a major contribution to scrappage loss reduction centers around our introduction at the FIG. 1 cupola furnace location of the silicon additives into teapot ladle K of FIG. 2. We have found that adding the silicon in this way ahead of the calcium carbide inoculation treatment performed at FIG. 4 is far superior to adding any portion of the silicon after such inoculation has been accomplished. Such post-inoculation addition of even a few grains of silicon tends to create a gaseous metal the bubbling action of which in the mold M produces castings Q which have pinholes and otherwise are unsound.

This one cause of gaseous metal has been corrected in accordance with our invention by restricting all silicon additions to the charge of molten metal before that metal is given the calcium carbide inoculation of FIG. 4. This beneficial result from our pre-inoculation addition of silicon is both surprising and unexpected, since it is directly contraray to accepted foundry practices and teachings of the past. Our discovery of it thus constitutes a practical advance of high order.

Even when the silicon is so uniquely added by us ahead of the FIG. 4 inoculation treatment, we further find that the metal poured into the molds M of FIG. 6 again will have gaseous characteristics it the melted charge 14-19 of FIG. 1 is drawn from the cupola furnace C at a temperature above 2800 F. Under that condition the cast ings Q of FIG. 6-7 will again have pinholes and otherwise be unsound due to the bubbling of the molten metal 28 poured into the mold M from the ladles K and H of FIGS. 5-6.

In producing the cast iron composition it is therefore important that the melted charge 14-19 of FIG. 1 be withdrawn from cupola C at a temperature not greater than 2800 F. Our findings are that this withdrawal temperature can be brought down as low as 2680" F. with satisfactory conduct of the production cycle which FIGS. 1 to 7 depict; andthe earlier stated range of 2680 F. to 2800 F. accordingly is the one which we adhere to. Withdrawal below 2680 F. may be accompanied by too much cooling of the melted metal 28 before it is poured into the molds M of FIG. 6, and it is this factor which sets the lower limit.

Another point in the production cycle to which prescribed temperature conditions must be carefully maintained is the inoculation location of FIG. 4. Here we find that the comparatively narrow range of 2680 F. to 2700 P. which the molten metal 28 in ladle K has at the inoculation start must be rigidly adhered to. The lower limit is set by the necessity of having the molten metal 28 sutiiciently hot at the FIGS. 5-6 location as to be properly pourable into the molds M and satisfactorily castable therein into the final castings Q of FIG. 7.

The upper limit of this 2680 F. to 2700 F. range for the metal 28 at FIG. 4 is set by two factors. The first is delivery of the metal in ladle K to the FIG. 5 pouring 9 location at a temperature which is not so excessively high that immediate pouring into the molds M of FIG. 6 will be accompanied by excessive shrinkage therein and accompanying imperfections in the castings Q. The size of the riser ring and gating provision in molds M control this in part; but, for molds of conventional dimensions and designs, we find that pouring of the cast iron composition can best be done at a temperature not exceeding 2530" F. It is because of the Various critical factors outlined above that our earlier described controls, both as to temperature and as to time, have been incorporated into and made an essential part of the complete production cycle which FIGS. 1-7 depict.

Subject matter of parent application Serial No. 75,213

The present application is a continuation in part of, and replaces application Serial No. 75,213. The parent application disclosed a material that exhibited substantially the same properties and possessed substantially the same constituents as that presented here.

The present application recites, in essence, an improved method for producing the metal whereby, while in its molten state, the metal possesses an increased amount of stability, being able to maintain its niicrostructure over a wider range of temperatures. This feature permits the manufacture of the metal in greater amounts, melts made according to the original process being limited to approximately half the size of the melts manufactured by the present process.

According to the original method, the eupola charge, represented in FIG. 1 hereof, was restricted to layers 14-19, or approximately half the present charge. These layers were melted in a cupola similar to that shown at C in FIG. 1 and discharged therefrom by means of the spout 10 into the teapot ladle K which held 53 pounds of ferrosilicon. During discharge of the cupola, 55 pounds of exo-thermic silicon in granular form was slowly added to the melt by means of the metering device 24. Following this, the ladle K, filled with the molten metal, was transported to an inoculation site where it was injected, through the use of inoculation apparatus similar to that shown in FIG. 4, with calcium carbide and other associated ingredients. The inoculation apparatus consisted of a double tank arrangement wherein the outer tank held 23% pounds of a mixture of calcium carbide (93%) and rare earths (7%) and 1 pound 2 oz. of magnesium along with an initial charge of 11 pounds of calcium carbide while the inner tank held 35 pounds of calcium carbide. Injection was effected by means of an inert gas compressed to 30 pounds per square inch which carried the inoculants into the melt. This gas was caused to flow at a rate of 130 cubic feet per hour.

According to this method, there was no post-inoculation addition of pure nitrogen into the melt, the stability thereof being solely dependent upon the rigid temperature controls which were adhered to throughout the entire process. After the inoculation was completed, the ladle was transferred to the pouring site where the metal was poured from the teapot ladle K into the molds "VI.

As was earlier mentioned, the post-inoculation step, which comprises the essence of the improved method of making our novel metal, enhances the effect of the inoculants upon the base metal and affects the transformation of the pearlitic matrix into ferrite rings about the graphite nodules and compacted flakes thus enabling the molten metal to maintain its graphitized structure for a longer period of time.

Summary as to production-cycle controls To summarize, the production-cycle controls employed in the improved process disclosed herein, the melted charge 14-19 should be withdrawn from the cupola furnace C of FIG. 1 at a temperature within the range of 2680 F. to 2800 F. At the beginning of the FIG. 4 inoculation treatment the melted metal 28 in ladle K 10 should have a temperature within the range of 2680 F. to 2700" F.; and, if the metal received by ladle K at FIG. 2 is initially too hot, it should be permitted to cool at least to 2700 F. before the FIG. 4 inoculation is started.

The inoculation treatment itself at FIG. 4 then should be accomplished within about 12 minutes, so that the accompanying temperature drop of metal 28 is restricted to about F. A greater drop will cause the metal 28 as delivered by ladle K to the FIG. 5 pouring location to be too cool. A lesser drop will occasion a waiting or a cool ing off time which detracts from the metal quality. If the metal is poured while too hot, the shrinkage tendencies in molds M will be objectionably higher.

And finally, the metal pouring at FIGS. 5, 6 and 7 can most advantageously be done when the metal 28 in the main ladle K has a temperature within the range of 25 10 F. to 2530 F. If the inoculation treatment at FIG. 4 and earlier steps of the production cycle have been carried out as per our novel controls earlier described, the metal 28 arriving in ladle K at FIG. 5 following inoculation at FIG. 4 will be at a temperature which is within this preferred range.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departure from the spirit and scope of the invention as those skilled in the art will readily understand. Such variations and modifications apparent to those skilled in the art are considered to be within the purview and scope of the invention and the appended claims.

What is claimed is:

l. The method for producing a cast iron wherein free carbon is in the form of compacted graphite in the ascast condition and containing at least 3.25 percent total carbon, including not more than 0.50 percent combined carbon, from about 3.80% to 4.20% silicon, about 0.010% to 0.014% magnesium, up to 0.010% sulphur, and the balance being ingredients that are common to gray cast iron comprising the steps of establishing a molten iron bath of such carbon and silicon content that when cast is a gray cast iron, withdrawing said molten iron from its heat source while introducing an amount of exothermic silicon, pouring said so treated metal into a container bearing an amount of ferro-silicon thereafter inoculating said molten metal with a mixture of calcium carbide, magnesium and rare earths by forcing said mixture into the metal by means of a tube emersed in said metal below the surface thereof through which is passed an inert gas bearing said mixture and casting the treated bath into molds to obtain a casting containing free carbon in compacted form.

2. The method for producing a cast iron wherein free carbon is in the form of compacted graphite in the as-cast condition and containing at least 3.25% total carbon including not more than 0.50% combined carbon, from about 3.80% to 4.20% silicon, about 0.010% to 0.014% magnesium, up to 0.010% sulphur, and the balance being in ingredients that are common to gray cast iron comprising the steps of establishing a molten iron bath of such carbon and silicon content that when cast is a gray cast iron, withdrawing said molten iron from its heat source while introducing an amount of exothermic silicon, pouring said so treated metal into a container hearing an amount of ferro-silicon thereafter inoculating said molten metal with a mixture of calcium carbide, magnesium and rare earths by forcing said mixture into the metal by means of a tube emersed in said metal through which is passed an inert gas bearing said mixture, flowing nitrogen gas into the melt after introduction of the mixture has ceased, and casting the treated bath into molds to obtain a casting containing free carbon in compacted form.

3. A method for producing a cast iron wherein free carbon is in the form of compacted graphite in the as cast condition and containing at least 3.25% total carbon including not more than 0.50% combined carbon, from about 3.80% to 4.20% silicon, about 0.010% to 0.014% magnesium, up to 0.010% sulphur, and the balance being ingredients that are common to gray cast iron comprising the steps of establishing a molten iron bath of such carbon and silicon content that when cast is a gray cast iron, withdrawing said molten iron from its heat source at a temperature of from 2680 F. to 2800 F. while introducing an amount of exothermic silicon, pouring said so treated metal into a container bearing an amount of ferro-silicon material thereafter inoculating said molten metal with a mixture of calcium carbide, magnesium and rare earths wherein said metal is at a temperature of between 2680 F. and 2700 F. by forcing said mixture into the metal by means of a tube emersed in said metal through which is passed an inert gas bearing said mixture, while permitting the temperature of the bath to drop to between about .2510 F. and 2530 F. and casting the treated bath into molds to obtain a casting containing free carbon in compacted form.

4. The method for producing a cast iron wherein free carbon is in the form of compacted graphite in the ascast condition and containing at least 3.25 total carbon including not more than 0.50% combined carbon, from about 3.80% to 4.20% silicon, about 0.010% to 0.014% magnesium, up to 0.010% sulphur, and the balance being ingredients that are common to gray cast iron comprising the steps of establishing a molten iron bath of such carbon and silicon content that when cast is a gray cast iron, withdrawing said molten iron from its heat source at a temperature of from 2680 F. to 2800 F. while introducing an amount of exothermic silicon, pouring said so treated metal into a container bearing an amount of ferro-silicon material thereafter inoculating said molten metal with a mixture of calcium carbide, magnesium and rare earths wherein said metal is at a temperature of between 2680" F. and 2700 F. by forcing said mixture into the metal by means of a tube emersed in said metal through which is passed an inert gas bearing said mixture, flowing nitrogen gas into the melt after inoculation of the mixture has ceased, while permitting the temperature of the bath to drop to between 2510 F. and 2530 F. and casting the treated bath into molds to obtain a casting containing free carbon in compacted form.

References Cited by the Examiner UNITED STATES PATENTS 2,716,604 8/1955 Bogart et al. 75-130 2,963,364 12/1960 Crockett et al. 75130 FOREIGN PATENTS 528,600 7/1956 Canada.

DAVID L. RECK, Primary Examiner.

Claims (1)

1. 2. THE METHOD FOR PRODUCING A CAST IRON WHEREIN FREE CARBON IS IN THE FORM OF COMPACTED GRAPHITE IN THE AS-CAST CONDITION AND CONTAINING AT LEAST 3.25% TOTAL CARBON INCLUDING NOT MORE THAN 0.50% COMBINED CARBON, FROM ABOUT 3.80% TO 4.20% SILICON, ABOUT 0.010% TO 0.014% MAGNESIUM, UP TO 0.010% SULPHUR, AND THE BALANCE BEING IN INGREDIENTS THAT ARE COMMON TO GRAY CAST IRON COMPRISING THE STEPS OF ESTABLISHING A MOLTEN IRON BATH OF SUCH CARBON AND SILICON CONTENT THAT WHEN CAST IS A GRAY CAST IRON, WITHDRAWING SAID MOLTEN IRON FROM ITS HEAT SOURCE WHILE INTRODUCING AN AMOUNT OF EXOTHERMIC SILICON, POURING SAID SO TREATED METAL INTO A CONTAINER BEARING AN AMOUNT OF FERRO-SILICON THEREAFTER INOCULATING SAID MOLTEN METAL WITH A MIXTURE OF CALCIUM CARBIDE, MAGNESIUM AND RARE EARTHS BY FORCING SAID MIXTURE INTO THE METAL BY MEANS OF A TUBE EMERSED IN SAID METAL THROUGH WHICH IS PASSED AN INERT GAS BEARING SAID MIXTURE, FLOWING NITROGEN GAS INTO THE MELT AFTER INTRODUCTION OF THE MIXTURE HAS CEASED, AND CASTING THE TREATED BATH INTO MOLDS TO OBTAIN A CASTING CONTAINING FREE CARBON IN COMPACTED FORM.

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