US2294170A - Metal casting - Google Patents

Description

Aug. 25, 1942.

C. B. FRANCIS ET AL METAL CASTING Filed April 9, 1941 3 Sheets-Sheet l 12209211072? (#49455 5. fa /v05,

E0) H NOOEEEE and g- 1942- c.. FRANCIS Ei- AL METAL QASTING Filed April 9, 1941 3 Sheets-Sheet 2 v ,M 5 mm m ONEK WZ M i 5w N na If a 4V4 m Q Patented Aug. 25, 1942 METAL casrmc Charles B. Francis, Pittsburglnand Roy H. Noderer and Ralph B. Porter, Johnstown, Pa.

Application April 9, 1941, Serial No. 387,742

17 Claims.

This invention relates to an improved method and apparatus for the casting of metal articles f 1arge cross section, and particularly to the casting of such articles made of either iron or steel, which are the materials most widely used for such purposes and are also the most diflicult to cast properly. Therefore, while the process of our invention may be applied in the casting of any metal used in the production of articles of large size, we confine the description of this disclosure to casting of iron and steel, and to further simplify the description of the practice and the explanation of the principles of our invention, we restrict thefollowing specification to one example of its application; namely, a large steel roll such as is used in mills for the rolling of steel. Any roll of this type has a varying cross section, and such rolls frequently. require 20,000

to 100,000 pounds of molten metal, both of whichfactors make the casting operations difilcult and contribute to the many defects found in such castings. Frequently these defects are a cause for the rejection of the casting and are revealed only after much work has been done upon it.

Besides the defects attributable to improper melting and molding practices, large castings of the type in question are subject toothers con-- sidered unavoidable byrthe practices of the prior art. These unavoidable defects result from segregation and changes in volume during solidification of the metal and are known as center zone porosity, pipe, cokey texture, dendritie and columnar structures, shrinkage cavities, shrinkage draws and internal-hot tears. -All weaken the casting, and many are accepted as sufiicient reason for rejection of the casting by the purchaser.

A principal object of our invention is to eliminate these defects-entirely,- while secondary objects are to improve the finished casting "and to cheapen the process of manufacture as comtices of the prior art, by decreasing the amount of molten metal required to make a given cast-' Figure 2 is similar to Figure 1 but shows apparatus embodying the present invention;

Figure 3 is a detail of the apparatus;

Figures 4 and 5 are modifications of Figure 2;

Figure 6 shows the progress of the solidification of the molten casting;

Figure 7 is a vertical sectional view of a sinkhead and associated apparatus used in carrying out certain, phases of the invention;

Figure 8 is a cross section taken from the line V11IVIII in Figure 7; and

Figure 9 is a modification of Figures 2, 4 and 5.

In these drawings are found the numeral I representing the mold, 2 the casting and 3 the gate through which the molten metal was introduced into the mold. By this practice the upper neck 4 of the roll must be cast much larger than required by the finished casting, so-that the metal in it will be the last to solidify and will fiow down ward from the sinkhad 5 until the metal in the roll proper has-solidified. In such a mold, solidification of the molten metal progresses very slowly in directions at right angles to the inner surfaces of the mold, and the progress of solidification may be represented by isothermal lines 6, Following these isothermal lines to the center line ofthe casting, it is observed that large cavities appear in the sinkhead 5, which represents metal that has fioweddownward to compensate for the iiquid-to-solid contraction of the metal below. Usually, the capacity of this sinkhead is approximately $4, of the volume of the mold below it, because the metal freezes from the top of the sinkhead as well as from the sides.

These statements refer w the practices of the prior art. In the complete application of our process we employ a mold with a sinkhead hav- '40 pared with the cost of manufacture by the pracing a smaller diameter than the sinkheads of the molds that are used in the practices of the prior art, the sinkheads of our molds having a facing of refractory brick as illustratedin the drawings, Figures 2, 4, 5 and 6; and wepreheat the interior of this sinkhead to a high temperature Just ments to refine the structure and the amount 4 of machining ne cessary to be done after the casting has beenv formed. The following examples suflice to show how and to what exterrt'; we have succeeded in the accomplishment of these objects Referring to the drawings, Figurel represents a vertical sectional drawingof a large grooved roll as it stands in the mold after casting and solidifying slowly in accordance with the'practices of the prior art;

prior tb casting, by a method and apparatus described, in a copending application bearing Serial No. 385,172 and filed March 25, 1941.

Below this pipe cavity other cavities of small size are formed about the periphery of thecasting, starting 1% to 2 inches under the outer sur-' face and extending downward. These small cavities are formed as a result of selective freezing and segregation, giving rise to pockets of low melting constituents that flow downward as the metal below solidifies, and are liable to be exposed in machining this portion of the casting to size, and are sure to be encountered if the rim'of metal removed bymachining is more v than/ 2 inches thick. 7

To prevent the formation vof these defects is an immediate object of our invention, an object we accomplish by controlling both the direction and the rate or solidification, causing the metal to commence solidifying at thevbottom of the casting and to continuerapidly upward.

Figure 2 represents the design of mold in vertical cross section we employ to produce the same roll-as that shown'in Figure 1, in which the part designated bythenumeral is the gate to the mold and the part designatedby the numeral 8 is the casting itself. It will be noted, especially, that we have greatly reduced the diameter of the neck 9, and the size of the sinkhead 10, as compared with the corresponding parts 4 and of Figure 1 representing a mold for the same casting made by the practices of the prior art.

By drawing in isothermal lines I3, marking the advance of solidification as it occurs naturally,

it can'be' shown that the neck 9 would completely be solid long. before'the metal in the large body below has-solidified, a'condition that would rethe upper portion of the .body and across the "suit in the formation of a large pipe located in Another typeofQ feeding e vice w have-Faust- "especially for adding balls-fof. small size; is t e tub is provided with steel strapsfi Ia which-sup; v

even more satisfactory gthan" that {of Figure '3, open tube of Figure 2.1 The lower er'id-g iithis t port a water soaked woodblock 111 such 'a distance below the end of. the'tube'fthatthe,spacef between the upper surface of the block and the; tube is slightly greater than e-diameter; the balls to be introduced into. the; swirling metal. By properly supporting thistube atfan-q angle, as shown in the drawings, ballsfed inat; I the upper end first strike the block of wood then 5 tumble gently into the molten metal at'va'rious points, thus preventing the balls'from' descend ing in clusters as are likely to be formed whenf f the balls'are introduced by any othe'rj imethod Both of these operations are-carried out in' a" few seconds of time, so that the balls drop-into the molten metal while itis .stillswirling. The effect of thus introducing av suitable num ber of balls of propersize is explainedfasfollows: j};

If the balls should be' introduced after the swirl ceases, they would descend ina continuous- 1 before they are'melted,.and these may not melt' pidly upward," by adding at proper inte lfl a correct quantity of specially treated 'iron or-steel-v balls to theliquid steel after it has been poured into the moldi-i'or-by, inserting a bar of iron or @5- steel before 'oriafter. casting to" initiate solid'iflca-; tion' at the bottom of the casting, and subse -li-,j 9 quently adding-steel-in the form of'small bodies; such as balls 'orrcub'es. Instead of balls, we may 4 use small bodies of iron or steel in various forms such as cubes, short cylinde'rs or pieces of plates" of irregular shape. Both the size or weight of each body and its shape are important because they affect the rate offall and also the rate of For example, spheroidal bodies heat transfer. will fall faster through the liquid and heat up more slowly-than flat bodies of the same weight.

In order that we maythus control the rate and direction of solidification in tallcastings the same-"composition as: that zj offithe casting," in? of the" catti'ng; .I-When the cballsjarerad o 1 our inventi n;the?mi itia: he' m 1 rated and thrownjpfl center y so that they. descend in e; :spiral';pathfiasjr sented by the {line- II in the drawing'iof Figure 2 completely because of-insufflcient heat as, a reel suit of thecombined-heatabsorptionof the balls'l "and themoldt wedesire particularly thatj all of the ba lls in this first; addition should melt ;en- 'tirely, "unless; the] balls *are made of steel having.

whichfi case. it A is"fiinniateri'alf whether the balls melt' orniot, as'theybecome bonded with Thus separatedfrom others inlthe column, eac

yball is at-ffirst drawn downward through the 1 f,

having a height of -10 t) inches or more, we proceed as followsz."

First, we introduce the liquid metal-through thegate 'luntil-its top surface rises. into the l lower part of the sinkli'ead ll), which is preferably p t i g,

Next by means 'i afile apparatus such as that shown-in'cross section in Figures 2 and, 3, we initiate the first stage of solidification by introducinga predetermined; Weight of specially byan alloyhaving a low meltingpoint, such as -trea'ted-bodies of steelor iron, preferably in the form of balls. with the apparatus of. Figure 3. the" container, filled'with the required numberof balls, 'is'lowered until its tip ll, which is capped aluminum; just touches the center of the liquid metal surface, the heat froni which melts the cap almost instantly; so that the bottomtip gives way. permitting the balls to 'descend' into the molten metal. -Generally. the surface of the metalis-covered by foreign material gathered as the swirling metal rose in the mold, and to the center with a small bar of iron or apole of charred wood iust before the tip of the container 'part in the-process of our-invention; and are mem nto ban force of-grayity.

liquid steelby the force of g'rjavity, -'the liquid steel having'a density ofabout 7.25--g. per 0.; c. and the'cold solid balls a density of about 7.78" g, perc.c. I t ,g The ratesor speeds of descent of the balls, as welliias the direction of descent, play; a--vital"' described as follows;

I repr sents the I cubic centimeters and'g the As soon-as the'ball .entersthe liquid steelfthis' "force is partly counteracted by.

.- the buoyant force ofthe liquid, which is equal to 7.25 -'Vg times, so; that the Ieflective. downward A force in only 0.53 Va. dynes,-or 0.53 g.', and

acceleration caused by gravity is reduced. fron about 32 feetpersecondltq slightly lessthan 2.18 i t .7.25),

, feet persecond, per second; mak e maximum i space through which the bail could move in'the flrst second'iabout ,1,09 feet. 'In the liquid steel the acceleration isfiniuch 'less' and the distance the ball travels the 'flrst second is also much prevent this dirt from being carried downward by the rushing of balls, it isbrushed aside from less than 11.09 feet per second, because the viscosity'of the liquidmetal creates a force of dissurfaces lying" horizontally and the resistance of their fall is proportional to the horizontal cross square of the speed or velocity of the ball, the fall of the latter becomes constant, that is, the speed of the ball attains a certain constant or terminal velocity within 2 seconds, the exact terminal velocity depending upon the temperature and viscosity of the liquid steel andthe size of the ball, as well as the speed with which it enters the liquid.

By experiment we have found that a ball V to inch in diameter, starting from'rest at the surface of the liquid steel, reaches a terminal velocity of about 6 inches per second within a period of about 1.2 seconds and a space of to 8 inches. The distances are increased slightly if the balls are propelled by afforce at a low velocity as the balls enter the surface of the liquid steel, but if they enter at high velocity, as when dropped through the air for a distanceiof 20 or 30 inches,

the opposing force of displacement is-such that they are forced along a path forming a loop at a depth of 10 to inches, which may propel them against the mold wall of the neck of the roll where they may adhere permanently. This eventuality is avoided by introducing the balls from a tube-like container, as shown in Figures 2 and 3. By this means we are assured that all the balls will pass below the level of the upper roll neck during the first 2 or 3 seconds of their descent throug'h.the liquid, a result that'is important for another reason also. Other means may be employed to obtain a like result.

After a ball has traveled at terminal .velocity for about 2 seconds, or a total distance of to inches in a total time of 3 seconds, its descent becomes constantly retarded so that the velocity of a l-inch ball becomes almost zero 8 to 12 seconds later, because, as soon as the cold ball contacts liquid steel, it solidifies up to 2% times its weight or volume of the liquid ,upon its surface, thus increasing its size and its temperature, so that the effective downward force of gravity is decreased to about 0.23 Vg and the opposing force of displacement is increased, not only because of I the increased size of the ball, but also because the metal at the bottom of the mold is losing heat and becoming more viscous. This shell of newly solidified metal ordinarily begins to form 'as soon as contact is made with the liquid steel, but, to permit the ball to drop to a greater depth the first second, we delay the formation of the shell by special treatment of the balls as described later. Thus we assure that the balls drop rapidly. through the neck, then more and more slowly unsectional area.

The time of holding after pouring before adding the balls is also a factor affecting the maximum size of ball. that maybe used. For example, if

the casting after pouring can be permitted to stand 15 to 20 minutes to permit the formation of a solid shell 1 to 2 inches thick before any balls are added, larger balls may be used for the first additions than when they are added in the swirl.

Concerning the weight, or number of balls of agiven size, to be added to any casting or any part thereof, this quantity may be calculated from the following equation:

:c(ut 0.1451) (0.27 st) su+ (0.145 X at) 1w:

specific heat of the sand in the mold; st, the average temperature ,rise of the'sand; su, the

weight of the sand; 0.145, the specific heat of the flask; at, the average rise in temperature of the flask; fro, the weight of the flask; dt, the temperature drop of the liquid steel in cooling to the liquidus; 0.15, the specific heat of the liquid steel; 65, theheat of solidification of the liquid til they come to rest at points near the bottom of ball we have found may reach the bottom of any i mold and cause solidification of so much metal about it that it will'not melt. We, therefore,

have selected 2 inches as a medium or standard size of the bah that may beused for any casting, and vary the size from to 3 inches according .to the size c1 casting, the smaller sizes being used in the smaller castings and the smallest size for first additions in all castings. For short or low molds, say less than 72 inches tall, balls smaller than 1 inch in diameter are desirable for the first addition, and small, flat thin bodies may be more desirable than tballs for shorter castings, as such bodies heat faster and fall more slowly than balls since they-fall with their flat 75 steel; andw, the weight of the steel in the lower part of the mold it .is desired to solidify.

In practice we have found it desirable to coolthe liquid steel only to .within 5 or 10 of the liquidus point, as this cooling'permits the balls to melt and also brings about rapid solidification of the liquid steel through the heat absorbing capacity of the mold, which may vary greatly according to the construction of the mold. Now, good casting practice requires that the steel be poured at as low a temperature as possible to avoid fusion of the sand to the casting, the highest permissible being approximately 120 F. above its liquidus,-and we allow 40 F]. drop in this temperature for cooling eflect in pouring, making the temperature drop to be effected by the balls F. or about 50 C. As the specific heat of the liquid steel is 0.15 cal. per gram, the heat to be absorbed is 70 0.15=10.5 ca'ls, per gram. Now the heat absorbed by 1 g. of the balls may be calculated from the formula,

in which 1171. is the heat absorbing capacity in calories of 1 g. of the balls; 0.145 the average specific heat of'steel; tl the temperature rise in degrees centigrade to bring the temperature of the balls to the solidus; 65 the heat of fusion of the balls; 10 the temperature in degrees centigrade above the liquidus; and 015 the specific heat of liquid steel.

For steels containing about 1.5% carbon, the heat absorbing capacity of the balls is found to be about 241 cals. per gram, or 23 times the heat to be absorbed from the liquid steel. With this factor established, we find the maximum weight of balls to be added from the weight of metal in the portion of the mold to-be cooled, 1 inch being subtracted from the height and the diameter, that is, V inch from the radii,.-to allow forv fing upon the composition of the steel, the pourgber of lesser-factors. Incidentally, the volume is approximately the same as the liquid-to-solid 1 contraction of the metal in'this part of the mold, .zwhich weg find by multiplying the volume, less 1 1 the volume of ashell'l inch thick, by'the factor 4.4,; Both methods give the maximum number; of balls to.be added, and'we'generally use 75% of this numbenincreasing the number, if the pouring temperature is high. Other methods 01'; quickly finding theproper number of balls to a add may also be used. For example, we have J found that 1 ball linch in diameter will lower the temperature sufficiently of 20 cubic inches of liquid metal in large castings or 40 cubic inches of metal in small castings, theexact number depending. upon the heat absorbing capacity of kthe mold'and the flask. l Qneapparatus we have found suitable for introducing the balls into plain rolls at thisstage of*tlie process'is-shown filled with calls in' Figure' It may be made of wood or steel, and

consists essentially of a tube H, provided with a suitable handle i5, and a special tip I4, which of the balls added in accordance with this method temperatures, the rate of pouring and a numameter in proportion to the size of casting up to a maximum insert diameter of 3inches. For

. illustration, an 18-inch casting will require an is made of a low melting alloy in the form of v used, because thefballsi jam? qr, ss the opening of a'hopper or funnel- For this, reason we prefer a straight ower it by machine, or with a small v ,v 7 he balls by the simple method dei-scribedbelow.

In the casting of certain rolls, for example,

'thos'efwith small, necks and deep grooves, we. have found'it advantageous to insert a bar of irietalv f the. same composition as'thecasting. either-T efore or immediately after casting and i Ee QM -ZfiMt, F 11; 1 r atop por n e clo in 'iasnira In general, however, we prefer to covering to'initiate the solidification'asthe botthisipurpose we have found-it feasible to use he-g'at'es which are of the same length as the castings withfajmuch smaller bar attached by- -tcm, insteadflof adding balls in the swirl- For 'weldingjto one end of the gate. In carrying out the process, the gate, thoroughly cleaned, is suspended or lowered coincident with the long axis of the roll, an'd supported so that its upper endjust protrudes from the liquid steel. After 5 to 20 minutes, according to the diameter of the insert 4 bar, the lower end of, the insert bar has melted. Then we lower the upper portion until the attached bar istotally immersed, by which opera tion we are assured that the-crystallized column formed by and about the insert bar is lowered through the sinkhead and neck into the 'lower part ofthe body of the roll, where it acc rates the cooling of the metal by abstractingmeat and forces the hotter metal upward into the neck and sinkhead, which we desire to keep fluid until-all the metal in the body has solidified, Subsequently, we make additions of balls as when no insert insert of 1 inch diameter. Three inches is the maximum diameter of bar which will melt in the cast molten metal within the 20-minute pemediately following the first addition of balls.

Consequently, as soon as the first lot of ballshave been introduced into the swirling metal, the ladle is moved over the sinkhead, which is then filled to,the top with liquid steel. Any dirt on the surface of the steel is rakedofi, and the metal is covered by an exothermic insulating mixture of nonmetallic substances such as that sold under the trade name of Lunkerite to prevent a crust .forming onthe surface. This mixture consists of powdered aluminum, alumina, fiuorspar, and calcium carbide, and reacts with both iron oxide and the oxygen of the air to produce heat and form at first a fluid slag which later becomes very viscous or a brittle solid. In casting rolls shorter than 100 inches we may not attempt to add balls until the mold is full, when we may add the first lot of balls just before the top covering is applied except about the edges of the sinkheads which should be covered as soon as possible to prevent the formation of a thick crust of metal. Y

. Withthis mixture the method we have found most satisfactory for application in the addition of the steel balls to both large and small cast- ;ings is illustrated by Figure 4. By this method :we-proceed as follows: v

As soon as the sinkhe'ad has been filled with molten steel and the dirt skimmed off and the first lot of balls added, if these have not been previously added in the swirl; we add the exothermic covering mixture to a depth of about inch,'and place upon this covering a charred wood block, which is in turn immediately covered with finely crushed bituminous coal to prevent the block from burning.

This block is 2 to 3 inches thick, and is l to 2 inches smaller in other dimensions than the section of the sinkhead. It contains a hole at its center slightly larger than the largest ball to be added to the liquid steel, and as soon as,

or before, the block is placed upon the covering, this hole is filled with the exothermic covering mixture and covered with a piece of boardg so that the coal poured upon 'the block cannot get into ,the hole or become mixed with the exethermic covering mixture. By brushing aside the coal, removing the piece of board, entry to the molten steel beneath the exothermic covering may be had at any time by pushing a rod through the mixture'filling theho'le in the block.

- After a period of 5 to 10 minutes has elapsed,

weproceed with the second step of our process,

which is represented by Figure 4. By this time solidification of the metal at the bottom of the mold has progressed inward and upward, as indicated by the isothermal lines 20, and the casting is in a condition to receive more balls. Be-

iore these balls are added, a circular metalshield bar is usedinitially. The insert will vary in (11- to use a, shield. To addthe balls, a hole is punched through the insulating cover at the center of the wood block, which is over the center of the sinkhead, and the additional balls required to initiate solidification to the level desired are fed slowly through a tube or trough 24, to drop through the center hole in the wood block. Since these balls descend in a straight line coincident with the center line of the casting, they are added slowly, the 1-inch balls at the latent 1 per second and the 2-inch balls at the rate of 1 every 2 seconds. To assure that all, or the greater portion, of these balls will be melted, a number sufiicient to initiate solidification only in the lower half 'of the body are added at this stage,'and thenumber required to obtain this result is calculated as expla n d above for those added while the metal is swirling. Usually the weight of balls added in this second step is 2 or 3 times the weight of those added in the first step, but seldom more than /4 of the total to be added.

As soon as these balls have been added, the shield is set aside, the hole in the center of the wood block is filled with the exothermic covering mixture, the piece of board is placed over the hole and the block is covered with coal as before.

After another interval of to 20 minutes, the hole in the wood block is opened, and the level to whichsolidification has progressed is detercovering as described above for the second step of the process. If the metal has sunk to a. depth in the sinkhead, we have found it convenient to brush the coal covering the wood block aside, which soon permits it to burn through at the center, and then to introduce the balls with the apparatus of Figure 3, as described for the first step of the process. After this final addition of balls, the metal remaining molten in the sinkhead is again covered by adding more of the exothermic or thermite mixture and another charred block of wood, as previously described herein.

By proceeding in this manner, we bring about rapid solidification of the casting from the bottom upward, leaving, after the final addition of balls, only the metal in the neck to solidify. The

withdrawing it quickly and measuring the length upon which metal has solidified upon its surface,

The final addition of balls to initiate solidification of the metal in the upper half of the body is made in one or more lots 1 to 3 hours after pouring, the exact time of adding each lot, as well as the number of lots, being determined y the size of the casting and the diameter of the neck, for it is evident the addition or additions must be made before solidification in the neck 26 of Figure 5 has progressed to within about- To find the maximum- 6 inches of the center. time interval after casting, we assume that solidification has advanced inward from the wall of the neck a distance of 1 inch in a time of 1 minute after pouring and that thereafter solidification advances at a rate measured in inches whch varies inversely as the square of the time measured in minutes. At this rate, it requires about 1 hour for a shell 1% inches thick to solidify about the walls of the mold, but solidification in the neck may be faster and the metal in this part of the mold may become so viscous that any balls added will not pass through it. The exact time when the addition of balls should cease can be judged by the speed with. which the gage rod descends and the amount of metal that solidifies upon itduring the 3 seconds of its exposure to the liquid steel. Thus, the insertion of a gage rod into the liquid steelin the mold becomes a means by which we control the solidification and also a means of ascertaining when the addition of balls should cease.

The number of balls to add at this stage may be found by calculation from the volume of metal enclosed by the third isotherm (see 25 of Figure 5), and are to of the number added in the second step. To introduce these bails, one of twoprocedures may be used. If the metal in the surface of the sinkhead has not sunk per- .ceptibly, the balls may be introduced through the hole in the Wood block and the insulating the drawings of Figure '7, showing the shield in progress of the solidification is illustrated by the isotherms 3| of Figure 6, in which 30 represents the grating to the mold; 32 the portion solidified by. the first addition of balls; 32 the portion solidified by" the second addition of balls; 32 the portion solidified by the third addition; and 32 the portion solidified by the fourth addition, leaving only the metal 34 in the neck 33 in the liquid state to be fed by the liquid steel inthe preheated sinkhead 35, which metal is protected by the covering oi the thermite mixture and charred wood. The sunken top portion 36 we fill with the hot charcoal and coke formed up to the final operation, and cover this with a heavy layer of crushed bituminous coal to prevent rapid heat loss through the top of the sinkhead.

The construction of the shield used for adding the balls in the second step, after the mold has been filled with liquid steel, is indicated by vertical cross section, and of Figure 8. showing a cross section of the bottom part of the shield and of the chute'thr'ough which the balls are This shield is preferably provided with a top portion ll, provided with a peep hole 40.

The composition and preparation of the balls require explanation. With respect to composition, the balls may be made from any grade of steel desired without markedly aifecting' the results obtained with regard to solidification and the elimination of columnar and dendritic structures and other causes of center zone weakness. To accomplish these objects, we prefer the balls to be made of steel having the same composition as the rest of the casting, because there is no danger that these balls will produce hard or soft spots in the roll if they fail to melt entirely. However, the balls may be of any composition desired, and it is thus possible to alter the composition of the steel in the interior portion of a casting to improve its toughness, or strength and ductility. Thus, it is possible to produce a kind I castor oil and parts crude turpentine. I

turpentine is. added to the castor oil to thin it; This mixture is added to the soy bean or linseed tings from the lathes, or other discarded parts of castings, a procedure that simplifies the problem of providing balls having the same composition as the castings.

The preparation of the balls is important. To avoid starting gas forming reactions within the steel of a casting and assure perfect bonding between the cast metal and any balls that may fail to be completely melted, the balls must be free from scale, rust or iron oxide in any form as well as from any other foreign matter, such'a's dust, sand, clay, or other dirt. To obtain these qualities in the balls and also provide a method whereby the balls maybe prepared at any time convenient and used at any subsequent date, we treat them as follows:

To avoid absorption of hydrogen and supply heat to the solution, we first heat the balls to a dull red color, then transfer them to a basket made of acidproof metal and immerse them in a 6% to 10% solution of sulphuric acid until all scale and oxide are removed. We then rinse them in a 1% solution of hydrochloric acid to remove the ferrous sulphate, dip them in a 5% oil, and the slushing oil is then added to the mixture. 5 E

Figure 9 illustrates a special modification of the process of our invention, adapting it to the production of rolls and similar articles having an extremely wide body section. In this drawing,

which is a vertical section through the center of the casting as it stands in the mold, 46 represents the gate through which the liquid metal is introduced into the mold and 41 the-casting itself. In such a'casting the extremely wide body makes it difiicult to build a mold that will cause upward solidification of the liquid metal to progress uniformly across the section by the simpler procedure described above. Failure to accomplish this object leaves'a zone of unsoundness in the casting that occurs as an annular ring a few inches inward from the outer surface of the body. We' overcome this difiiculty and produce a sound casting by modifying the construction of the mold and the method of introducing the bodies of solid metal as follows:

In constructing the mold we build into it one or more steel tubes, 48 and 49, at a point or points suitably located between the outer circumference 50 of the body of the roll and of the neck 5|.

Each of these tubes has a straight wall except at the bottom near the outlet tothe mold, where the wall of the tube is indented at point 52 to hold a neatly 'fitting ball 53, which descends with the The small particles of solid of copper wire. The tubes are inserted when the mold is prepared. and filled with the small particles of steel after the mold has been set up for machine or under a steam hammer.

casting.

With the mold thus prepared and mounted, the procedure in casting is as follows:

First, we will fill the tubes 48 and 49 with the cold steel to be added to the liquid steel to initiate the solidificationof the molten steel in the body of the roll. This steel is in the form of small bodies, which have been pickled to free them of scale and treated with sodium cyanide and oil to prevent them from rusting, as described for the treatment of the cold steel in the form of balls. However, the cold steel we introduce into the liquid steel, in the present instance, must be in the form of bodies smaller than 1 inch, and may consist of coarse chips obtained in the rough machining of the castings or of pieces broken in any manner to pass a /2 inch round hole screen. As the steels used for castings are generally high in carbon and alloys that give a very hard metal by quenching, we may obtain them by forging the gate runners into flats less than inch thick, heating the flattened plates to about 1500 F., hardening them by cooling rapidly or slowly as required and quenching them in water and breaking them in a crushing ing the tubes 48 and 49 with these small bodies steel ball, 53 and 53, that neatly fits the inside of each of the tubes 48 and 49, which may vary from 2 inches to 3 /2 inches in diameter, according to the quantity of steel we desire to add at this point. The total weight of steel to be added is determined by the size of the roll body, and the extent to which it is desired to initiate the solidification, and iscalculated as already described for the addition of the balls. With the tubes thus filled with the pieces of cold steel to be added, the introduction of liquid metal through the gate may be started at any time convenient.

The molten metal is introduced through the gate 46 in the usual manner'until the liquid rises through the neck to a level 51, 6 to 10 inches above the top edge of the neck. During this operation the tubes 48, 49 are automatically emptied of the charges of small particles of steel they contain, as follows:

When the top surface of the liquid metal in the mold rises to the level 58, it contacts the bottom of the net 55 and immediately melts the aluminum wire, which ruptures and permits the load of small bodies of steelit supports to flow into the liquid steel. Since this metal is swirling at a fast rate, the particles of steel are scat- Then as the liquid continues to rise to level 59, y

it contacts the aluminum net of the second tube, which melts and permits the contents 54 of the. tube 49 to descend into the liquid steel 2 or 3 inches below the top surface of this portion smaller particles of steel 54,. and performs the 'of the mold. The large ball 53 descends with the contents of the tube and is stopped by the indentation 52, as in the case of tube 48.

As the metal fills the mold and starts to rise in tubes 48 and 49, it contacts these large balls and is immediately chilled, or solidified, so that further upward fiow through these openings is S oppedv at these points.

The metal thus introduced through these tubes is kept near the circumference by the centrifugal force of the swirl, and by properly proportioning the cold metal added in this manner to thesize of the bocLv, we cause such a chilling effect that this metal is quickly solidified against the mold wall by the heat it abstracts, and adJa-i Thus,

idly progressing inward towards the isothermal lines I. To make sure that solidification has progressed inward to the loci'of points indicated by this line, we cover the surface of the metal in the sinkhead with the exothermic covering mixture previously described and stop pouring through the gate It. After 5 to 10 minutes, we

then introduce a quantityof cold steel in the form of bodies, such asb'alls, through themface 51, sufllcient to cause solidification to progress upward to the isothermal line 62, then fill the sinkhead with molten metal introduced through its top. The top surface of the metal is then covered as described above for the treatment of rolls with bodies of smaller diameter in proportion to the neck, and the solidification is sequently adding at intervals portions of the treated solid bodies to cause solidification of the liquid metal to advance upward at a rate so that the body of the roll is practically solid before the metal in the upper neck of smaller diameter has completely solidified.

3. The process of casting rolls of iron and steel, and of causing the liquid metal of which they are made to solidify upwards at a rate faster than the solidification in directions normal to the inner surfaces of the mold, by the addition at intervals of portions of solid metal in the formof small bodies, which process involves the steps of freeing the surfaces of the solid bodies from oxide and coating them to prevent them from rusting, forming a mold of the desired shape and dimensions with a suitable sinkhead,

- admitting the molten metal through a gate at the bottom of the mold, adding portions of. the solid metal to the liquid metal as itrises in the mold, filling the sinkhead with the molten metal, covering the surface of the top of ,the liquid metal with an insulating mixture of compounds that made to progress upward in'steps indicated by the isothermal lines 3 and 64, by the addition atintervals of cold steel in the form of balls, as described previously for the control of the solid:- ification of the steel in rolls having bodies of :smaller diameters.

react exothermally with iron oxides and oxygen, placing upon the exothermic mixture a dry charred wooden block with a hole in the center, and subsequently adding at intervals portions of the treated solid bodies to cause solidification of the liquid metal to advance upwar at a rate so that the body of the roll is practic lly-solid before the metal in the upper neck of'smaller diameter has completely solidified, said solid metal Having thus made a complete disclosure of our invention by exposition and example, we desire to have it understood that various modifications may be-made in itsapplication to different metals and castings of iron or steel without exceed-' ing the scope of our invention as defined following claims.

We claim: a

1. The process of producing castings of iron and steel which involves the steps of preparing a by 'the I being of a different chemical composition from .that of the liquid metal that is cast.

mold of the desired form and dimensions, introducing the molten metal in this mold through a gate at the bottom until the mold is filled with the liquid metal, covering the surface of the liquid metal with a mixture of compounds that react exothermally with iron oxide and oxygen,

and thereafter adding at intervals portions of I metal, in the form of small scale-free bodies and of a composition similar to that of the casting,

to cause solidification of the liquid metal of the casting to progress upward at a faster rate than solidification advances'in directions normal to the inner surfaces of the mold.

2."!he process of casting rolls of iron and,

steel, and of causing the liquid metal of which they are made to soiidifyupwards at a rate faster than the solidification in directions normal to the inner surfaces of themold, by the addition at intervals of portions of solid metal in the form of small bodies, which process involves the steps of freeing the surfaces of the solid bodies of oxide and coating them to prevent them from rusting, forming a mold of the desired shape and dimensions with a suitable sinkhead, admitting the molten metal through a gate at the bottom of the mold, adding portions of the solid metal to the liquid metal as it rises in the mold, filling the fsinkhead with the molten metal, covering the surface of the top of the liquid metal with an inthat of the liquid metal that is ing a solid bar of metal approximately the same composition as the liquid metal and by the addition at intervals of portions of solid metal in the form of small bodies,- which process involves the'steps of freeing the surfaces of the solid bodies from oxide and coating them to prevent them from rusting, forming a mold of the desired shape and dimensions with a suitable sinkhead, mounting therein a bar of steel having the same composition as the liquid steel and being coincident with the long axis of the casting, admitting the molten metal through a gate at the bottom of the. mold, adding portions of the solid metal to the liquid metal as it rises in the mold; filling the sinkhead with the molten metal, covering the surface of the top of the liquid metal with an insulating mixture of compounds that react exothermally with iron oxides and oxygen, placing upon the exothermic; mixture a dry charred wooden block with a hole in the center, and subsequently adding at intervals portions of the treated solid bodies to cause solidification of the liquid metal to advance upward at'a rate so that the body of-the roll is practically solid before the metal in the upper neck of smaller.diameter has completely solidified, said solid metal being of a difierengchemical composition from cast.

5. The process of casting rolls of iron and steel, and of causing the liquid metal of which they are made to solidify upwards at a rate faste than the solidification in directions normal the inner surfaces of the mold, the insertion of solid metal in the form of a bar and by the addition at intervals of portions of solid metal in the form 0% small bodies, which process involves the 8 a '1 V j a,294,i7o- L V I steps of, freeing the surfaces of the solid bodies 1 metalimthe mold freely molten free from covering the surface of the top of the liquid metal metal in the moldl'and proportioning."additions from rusting, forming a mold of the desired shape 'maining metal'in the mold hasfloccurred; and dimensions with a suitable,sinkhead,.sus- 'i "9'.' Theprocessfof castingferrousmetalfor pending a cleaned solid barwithin the mold hibitin'gf formation of internal vdefectsand -u along the central axis of the casting, admitting "soundness-iii the finished -casting". during solidi the molten metal through a gate at the bottom ficationfof the metal being-ca whichjcomprises; of the mold, covering the top surface of the introducing' molten-metal intoa'stationary-open molten metal with an exothermic mixture, then (top, mold addin'g pieces oflmetal in solid fbr'mf lowering the remainder of the suspended bar 10' into the molten-metal throu'gh'the open top of downward through the sinkhead and the upper I l the mold so that-{the pieces'are' caused to neck into the body of the roll, and subsequently I Q into the me'talthrough-the surface of 'the molten from oxide and'coating them to prevent them solidf crust until after. solidification ofthe re with an insulating mixture of compounds that and amounts'bf'the said piece'sil to the molten react exothermally with iron oxides and oxygen, metal for effecting acontliqlled accelerated .up g placing. upon the exothermic mixture a dry wardcooling and upwa'rd 'sol idificatidn ratev or v charred wooden block with a hole in the center, molten metal"substantially morezrapid-ftha'ri lat-5* and subsequently adding at intervals portions of eral cooling thereof, wherebytth e "molten metal the treated solid bodies to cause solidification of solidifies progressively upwardly from the bottom the liquid metal to advance upward at a rate so of "the-mold substantially rfast'erxithan from the that the bod of the roll is practically solid before sides thereof, while causing the solid pieces'being the metal in the upper neck of smaller diameter added tomeltjprior to theircontactin'g' the solidi has completely solidified, said solid metal being I 5 of a different chemical composition from thatjof, the liquid metal that iscast. a

6. The process of "producing castings ofiron and steel which consists of the steps'of preparing" a mold of, the desired form and dimensions, said mold having a sinkhead with a refractory facing, Y o v I I heating the interior of the .sinkhead to a high restricted neck 'and a. bottom restrictedneckwit temperature, introducing the molten metal into a body intermediate the necksgreatly ,large the mold through a gate at the bottom until the than .the said'necks, which'comp'rises' making a mold is filled with the liquid metal, covering the mold having approximately the configuration of surface of the liquid metal with amixture, of thecastingso that when the mold is filled, the compounds that react exothermally withiron metal will be cast into the aforesaid necks and oxide and oxygen, and thereafter adding at in- :b0dy,'-'fi1,1ing'the said mold with moltenzfmetal. tervals portions of solid metal, in the form of, iywhile maintaining the top restricted"neck open, small scale-free bodies, to cause solidification of ,a'dding into the molten body of metal in the i, the liquid metal of the casting to progress upmold through the open top neck, pieces o'fmetal ward atafaster rate than solidification advances 40 in ol 1111. allowing the Said pie to Sink in directions normal to the inner surfaces of the through the body of metal in'the-mold, proper-- mold. tioning additions and amounts of the said pieces 7. The process "of making steel castings inhibto the molten metal for effecting a controlled iting formation of internal defects in the casting Jacceler'ated upward cooling and upward solidifiduringsolidification 1 of the metal being'cast, '45 cation rate of molten metal substantially more which comprises introducing molten metal into a rapid than lateral cooling thereof, whereby the H l and adding solid piecesv of steel proporigmolten metal solidifies progressively upwardly tioned as to time of additions and'amount for from the bottom of the casting substantially controlling the rate of cooling of the-metal in faster than from the sides thereof, and maintainthe mold by accelerating normal progressive upin t t p restricted n k of th stin fr ly ward solidification of the metal in the mold until molten and freely open from solid crust until a the upward solidification of the metal substan- .after',the entire remaining casting is solidified. tially exceeds in rate the normal rate of lateral 11.".t'he process of producing ferrous metal solidification, while maintaining'the top portion castings, such as rolls or the like, which as cast of the metal in the mold freely fluiduntil after and prior to removal from the mold having a top solidification of the remainder of the metal has restrictedneck and a bottornrestricted neck with "been completed. a bodyintermediate to the said necks greatly 8. The process of casting ferrous rolls for inlarger than the said necks, which comprises hibiting formation of internal defects and unmaking a mold having approximately the configsoundness in the finished casting during solidiuration of the casting so that when the mold is fication of the metal being cast, which comprises filled, the metal will be cast into the aforesaidintroducing molten metal into a mold until the necks and body, filling the said mold with molten mold is filled, adding pieces of metal in solid metal while maintaining the top restricted-neck form into the molten metal through the top of open, introducing, in requisite installments into, the mold so that the pieces are caused to sink the molten body of metal inthe mold, solid pieces into the metal through the top surface of the Qof metal, allowing the pieces to sink into the molten metal in the mold, proportioning the adbody of metal in the mold to locations well below ditions and amounts of the said pieces to the the top restricted neck, proportioning additions molten metal for effecting a controlled accelerand amounts of the said pieces to the molten ated upward cooling and upward solidification metal for effecting a controlled accelerated up- 'rate of molten metal substantially more rapid ward cooling and upward solidification rate of than lateral cooling thereof, whereby the molten molten metal substantially more rapid than latmetal solidifies progressively upwardly from the oral cooling thereof, whereby the molten metal bottom of the mold substantially faster than from solidifiesprogressively upwardly from the bottom the sides thereof, and maintainihgthe top of the of the mold substantially faster than from the 4 sides thereof, while causing the solid pieces of metal being added to melt prior to contact with the solidified metal of the casting but always below zones of pipe and cavity formation in the casting, and maintaining the metal in the top restricted neck continuously freely molten and free from crust until after solidification of the entire remainder of the casting.

12. The process of producing ferrous metal castings, such as rolls or the like, which as cast and prior to removal from the mold having an open top restricted neck and a bottom restricted neck with a body intermediate to the said necks greatly larger than the said necks, which comprises forming a mold conforming approximately in size and shape to the size and shape of the resulting rough finished casting, with a sinkhead having a capacity not substantially more than the minimum required to compensate for total contraction of the casting, which comprises filling the mold with molten metal, preventing solidification of metal at its exposed surface by applying thereto, in order, coverings consisting of an exothermic mixture, a charredwood block, and powdered coking coal, permitting the metal to stand in'the mold until a solid shell of metal is formed around the metal and mold wall, and subsequently to formation of such shell but while the remaining metal is still liquid, adding chemically clean solid metal in the form of small pieces and at controlled intervals and in controlled amounts for causing a controlled solidification of metal upwardly at a rate substantially greater than from directions normal to the wall of the, mold.

13. The process of producing ferrous metal castings, such as rolls or the like, which as cast and prior to removal from the mold having an open top restricted neck and a bottom restricted neck with a body intermediate to the said necks greatly larger than the said necks, which comprises forming a mold conforming approximately in size and shape to the size and shape of the resulting rough finished casting, with a sinkhead having a capacity not substantially more than the minimum required to compensate for total contraction of the casting on solidification, the open top restricted neck being between the mold and sinkhead, filling the said mold with molten metal, and thereafter adding portions of clean solid metal, each portion being added at predetermined intervals of time while controlling the size ofthe pieces and intervals of time so that the added pieces of metal fuse in the metal as solidification thereof proceeds, and solidification of the metal advances progressively upwardly at a rate substantially faster than soldification proceeds horizontally, thereby maintaining the metal in the top restricted neck of the casting freely liquid until after solidification of the remainder of the casting.

14. The process of casting ferrous metal rolls having restricted neck portions and a relatively adding to the molten metal portions of solid metal I in small pieces at varying intervals of time, controlling the weights and intervals of time of the additions of solid pieces so as to effect solidification of the metal below the said upper neck be fore a column of metal coincident with the central axis of the neck has solidified, and measuring the progress of thesolidification by quickly inserting-and withdrawing a, gauge rod just prior to adding solid metal at later intervals for ascertaining the requisite amount of solid metal to bethe molten metal to points beneath zones of formation of internal cavities of the casting, proportioning the additions and amounts of the said pieces for efiecting a controlled accelerated up- 10 minutes, the total metal thus added being from between about 0.5% and about 2.0% of the weight of the casting, the weight of each portion added being less than about 0.2% of the weight of the casting, and the size of the pieces added being varied according to the time of addition and the size of the casting so that they will fuse with the cast metal preferably before solidification there-v the pieces during predetermined time intervals for effecting a controlled accelerated upward cooling and upward solidification rate of molten metal substantially more rapid than lateral cooling thereof by abstracting heat by the solid pieces from the molten metal from the bottom thereof upwardly, whereby the molten metal solidifies progressively upwardly from the bottom of the mold substantially faster than from the sides thereof, and maintaining the top of the metal in the mold freely molten and at least substantially free from solid crust until after solidification of the remaining metal in the mold has occurred.

17. The process of casting ferrous metal for inhibiting formation of internaLdefects and unsoundness in the finished casting during solidification of the metal being cast, which comprises introducing molten metal into a mold until the mold is filled, adding small pieces of metal in solid form into the molten metal so that the pieces contact the bottom portion of the molten metalin the mold, and making predetermined additions of pieces the predetermined time intervals -for eflecting a controlled accelerated upward cooling and upward solidification tate of 1 nolten metal substantially more rapid than lateral cooling thereof by abstracting heat by the solid pieces mm the molten metal from the bottom upwardly, whereby the molten metal solidithe mold 'su thereof.

bstantially iaster than trom the sldea SJ .crs; I ROY HtNQDERERQ

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