y •^.^'* V rr,'* ^0^ v*'^'*.-!,*- 'q, **tT;-* iO '• V.%* *' . 47 ^. • •^ ..V,. '^^ •*y^ *\*'^-*\o'^ 'V***^\-?,'*'^ '°^**«M**\o'^ %''*« HOW TO MAKE CONVERTER STEEL CASTINGS By Arthur Simonson A comprehensive discussion of the methods involved in the manufacture of steel castings by the converter process. This work is compiled from a series of articles by the author, written for and published by The Foundry. Cleveland., Ohio, U . S. A. The Penton Publishing Co., Publishers 1914 SECOND EDITION .56 Copyright, 1914 THE PENTON PUBLISHING CO CLEVELAND, OHIO FEB 13 1914 CONTENTS Page Chapter I 1 Construction of the Converter Arrangement of the Converter and Cupohi Converter Operating Station Special Cupola for Melting the Iron Heating the Ladles Sand Grinding and Mixing for Steel Foundry Work Chapter II 12 Lining the Converter Kind of Brick Used Life of the Lining Construction of Wood Forms L'sed for Lining the Converter Chapter III 18 Analysis of the Iron to be Converted into Steel Calculation of the Cupola Charge Graphic Method of Figuring the Cupola Charge Chapter IV 22 Operation of the Converter Blowing the Steel How to Overcome Difficulties During the Blow Analysis of Converter Castings Chapter V 29 Hot Cracks in Steel Castings and How They May be Overcome Chapter VI 32 The Steel Foundry Laboratory Equipment and Necessary Determinations Index 38 111 CHAPTER I. Construction of the Converter — Arrangement of the Converter AND Cupola — Converter Operating Station — Special Cupola FOR Melting the Iron — Heating the Ladles — Sand Grinding and Mixing for Steel Foltndry Work. XT will Ije the author's ohject. in this and succeeding chapters, to give a general idea of the science and art of making steel castings in a foundry equipped with the Tropenas system of steel-making. It is a mistake to think that the company operating a small converter plant can successfully compete in all lines of the casting business. There are, undoubtedly, branches where it cannot compete with the open-hearth and the malleable iron foundry. There are few things so light that they cannot be cast from the excessively hot steel made in the small converter, but for these tiny pieces, gray iron, malleable iron or brass are generally strong enough. On the other hand, for the very large pieces, say over 8 tons in weight, the open-hearth is probably cheaper, in America at any rate, though in England a plant operating five converters is successful in com- petition with the open-hearth and produces over 600 tons per month of mis- cellaneous castings of all analyses, and varying from less than a pound up to 10 tons. The field of the small converter is ideally in the small and medium castings, and those calling for a specially high-grade material. It is an undisputed fact, that a well-handled converter of the Tropenas type pro- duces a superior quality of steel, sounder, closer-grained and stronger than can be otherwise obtained. In automobile work, motor boats for gears, valves and levers, turbine work, gas engines and general machine work, converter castings are particularly desirable. The realization of what can be done in the way of making light and intricate castings has led to the elaboration of engine and machine details in a remarkable way. A designer has no longer to take into consideration the possibility of not being able to get the castings he requires in steel. The small converter has made it possible to develop tremendous power engines occupying small space, and as proposition after proposition is put before Hoiv to Make Conz'erter Steel Castings the founder and solved, he is beginning now to reaHze the possibilities of the process. The increasing number of plants being erected and the success with which they are meeting, testifies to the realization of the claims made for the side blow converter since its inception. It is worthy of note that the open-hearth steel founders are now be- ginning to realize the usefulness of a small converter as an annex to their large furnaces, in this way being able to take care of absolutely any busi- ness that comes along, and thereby relieve the large furnaces of the tedi- ous, costly necessity of making the small castings. There is today also at least one case of a malleable iron foundry installing a Tropenas converter. It seems probable that the time is near at hand when every open-hearth furnace operating on castings will have as an adjunct one or more con- verters, the idea would then, be to make all the small castings with the con- verter and just enough of the larger ones to fill-in up to capacity. In dull times the entire output might be economically made with the converter. We will now describe in detail a plant consisting of one two-ton con- verter and having a capacity of about 40 tons of castings per week. It con- sists of converter, converter blower and motor, pulpit or operating station, cupola, cupola platform and elevator, cupola blower and motor, ladles and ladle heating plant, sand grinder and mixer. An analytical laboratory is also indispensable, and this has been made the subject of a special chapter. As for the foundry equipment, including cranes, flasks and miscellaneous rigging, it is the same for all foundries, no matter what process is used, but it may be well to make a few remarks on this subject in passing. Electric traveling cranes are now almost exclusively used with wall or jib cranes as accessories. All foundry buildings are, or should be of steel construction with ample lighting facilities. Up-to-date plants are pro- vided with heating and ventilating systems so that in summer, air from out- side can be distributed through the building, and in winter it is passed through steam coils. The heating of foundries is a very important mat- ter. If the sand is allowed to freeze it will cause endless trouble, particu- larly if green sand castings are made. The artificial lighting of a foundry for night work is a problem requiring considerable attention. The atmos- phere in a foundry is often smoky and always very dusty, and it requires a very good distribution of powerful lights to enable the men to work when necessary, at night as well as in the day time. The ovens for drying molds should be as large as possible, and their trucks designed of such type that the heating of axles and bearings will not affect their operation. Flasks, chains and general tackle should be as heavy as is convenient to handle. The less risk taken the better — and the foundry business has enough of them under the most favorable conditions. The writer is of the opinion that any amount of money judiciously ex- pended on the special tackle and rigging in the foundry pays a good dividend in safety, speed and economy. Hoiv to Make Con-c'crter Steel Castings The Converter. The converter is of 2 tons capacity, that is to say, it is capable of turn- ing out at each operation approximately 2 tons of steel. In this chapter it will be considered as a machine only ; its metallurgical side will be dealt with in a succeeding chapter. The illustrations, Figs. 1, 2, 3 and 4, will give a good idea of the general appearance of the converter. Fig. 1 shows the arrangement of the steel converter and the cupola ; Fig. 2 shows the Fig. 1 — Arrangement of Steel Converter and Cupcjla. The Metal From the Cupola is Conveyed to the Converter by a Jib Crane converter tilted while the metal is being poured into the vessel for the blow ; Fig. 3 shows the converter in operation and Fig. 4 shows the converter tilted to empty the slag after the metal has all been poured out. Hotv to Make Converter Steel Castings The shell of the converter is 5 feet in diameter and is made of ^ inch steel plates, perforated with .)/:^-inch holes spaced 8 inches center to center to allow the steam to escape when drying the lining. The amount of floor space occupied by the converter is about 16 feet square and the head room Fro. 2 — Pouring the Metal Into the Converter. required is al)out 18 to 20 feet to enable the whole of the flame, which comes out of the mouth, and which constitutes the means for judging the condition of the steel, to be seen at all times. How to Make Converter Steel Castings The converter is supported on steel trunnions, one of which is hollow and forms a duct for the air, connecting with the blast box at the back of the converter. This enables the air to be kept on continuously while the position of the converter is being changed. The blast box is double, and air can be admitted to either side separately, or in varying proportions. This is partly shown in Fig. 6, which is a section of the converter, both vertical Fig. 3 — The Converter in Operation and horizontal, showing the arrangement of the tuyeres, the level of the bath and the approximate position of the vessel while the blow is being made. The other trunnion is extended and carries a worm wheel which, through suitable gearing, is connected to a 4 horsepower motor. A hand wheel is also provided for making small movements of the vessel as required Hozv to Make Converter Steel Castings from time to time. The electric motor has been generally adopted for tilt- ing the converter, although any means may be employed, and plants are in operation in various places using compressed air, steam and hydraulic power. This is a mere detail and de])ends on circumstances. The converter is firmly bolted to pedestals, which are sufficiently high to allow the converter to make a complete revolution if necessary. This is advisable for facility in emptying the converter, and also to enable the whole of the metal to be poured out before the vessel is too low for the men to hold the ladles. The covers of the blast boxes are fastened on by means of keys, for quick removal to clean out a tuyere or to set the converter at the commence- ment of a blow. The upper box is fitted with a pipe having an independ- ent valve so that it may be shut off entirely if desired, or any required amount of blast admitted according to the conditions that arise as the blow proceeds. The lining of the converter will be dealt with in the next chapter. Converter Blower and Motor. The blower is of the positive pressure type, and must be capable of maintaining a constant pressure up to 4 pounds per square inch through the area of both sets of tuyeres, which consist of seven in the lower row, \}i inches in diameter, and seven in the upper row about l>4x->^ inches. A water-jacketed blower running at about 400 revolutions per minute, is commonly used and is satisfactory. Blast may be supplied by a blowing engine, but is not so satisfactory, as the pulsations of the engine, unless absorbed by a very large receiver, are manifest in the flame and interfere with the observation of the reactions. A rotary blower is best on this ac- count as it gives a practically constant stream of air, and makes the flame perfectly steady, at least as far as outside influences are concerned. The blower should be direct-connected to a motor of about 73 horsepower ; no less is advisable, as it is better to have a little power in reserve and not run the risk of the circuit breaker flying out all the time, for when this happens, it always seems to occur at a critical time in the blow and may lead to clogging of the tuyeres, loss of time and possibly disaster to the blow. The blower should be placed close to the converter, but not too close, as a fair length of the 12-inch air main serves as a reservoir and gives elasticity to the blast. Elbows in the pipe should always be avoided. Operating Station. This is the place where the operator stands to watch the progress of the blow and to tilt the converter according to the different requirements of charging, pouring, etc. It is better to place this at one side of the vessel,. Ho-iV to Make Converter Steel Castings about 20 feet away, if possible, so that the heat will not inconvenience the operator and that he may see the whole of the flame. It is not advisable to place the pulpit across the building as in this case the flame is fore- shortened, and it is not possible to see the smoke, sparks, etc.. so clearly. The pulpit contains the controller for tilting the motor, the lever of the by- pass valve to regulate the pressure of air going into the converter, a signal whistle to the blower room to signal the engineer when to start and stop the blower, and a mercury pressure gage. The engineer, on receiving the signal of two short blasts, starts the blower at full speed and maintains it at this speed all through the blow. Variations of pressure are then obtained by the operator opening or closing the by-pass and allowing more or less air to escape through a pi])e leading to the outside. The blast gage, read- FiG. 4 — Converter Tilted to Empty THE Slag After the Metal Has Been Poured Out Fig. 5 — The Converter Operat- ing Station ing in pounds, is attached to the blast main between the blower and the by-pass. Fig. 5 gives a view of the pulpit ; A is the lever of the by-pass valve ; B is the controller of the tilting motor ; C is the whistle, and D is the mercury gage. Cupola. There has been a great deal of discussion as to the best type of cupola for the Tropenas converter. It is largely a matter of opinion. The fact Hoiv to Make Comrrter Steel Castin Qs is, that it is required to melt about 5 tons per hour of a charge consisting oftentimes of as much as 50 per cent of steel scrap, to melt it hot, and to be capable of running very long heats, sometimes as long as eight or nine hours. Any cupola that will meet these conditions is suitable. It must Fig. 6 — Vertical and Horizontal Fig. 7 — Special Cupola for Melt- Sections OF vSteel Converter. ing Iron for the Converter be remembered that in melting low phosphorus stock such as is used in steel-making, a hot melting cupola is necessary, and facilities must be pro- vided for taking care of a large quantity of slag, as considerable flux is used to keep the sulphur as low as possible. There has also been considerable Hozv to Make Converter Steel Castings Fig. 8 — Heating a Large Ladle With an Oil Burner discussion as to the desirability of having a cupola large enough to melt the total charge for one blow at one tap, or getting it at two taps. After long experience, the author has come to the conclusion that a somewhat special cupola is the best, and this after using almost every kind that could be mentioned. The writer's idea of a suitable cupola is one built on the lines of a blast furnace, with a bustle pipe and pendant tuyeres, such as is illustrated in Fig. 7. The bustle pipe or blast box must be ample in size in order to maintain equal pressure at all of the six tuyeres. The advantage of this type of cupola is that the tuyeres are always clean, and if any slag or iron runs into them it runs out again without going into the blast box. The cupola should be about 54 inches in diameter, lined with two rows of 4j^-inch bricks, giving an in- side diameter of 36 inches. The tuy- eres should then be placed so that the slag hole, which is 6 inches lower than this, will be sufficiently high to allow of the required amount of iron being tapped out when it has melted up to this height. In this way the cupola will be kept entirely free from slag, the tapping spout will be kept clear through a long heat, and there will be little risk of scaffolding. A blast pressure of from 10 to 14 inches of water should be maintained. Cupola Platform and Elevator The cupola platform should be higher than is usual in iron foundries, as it should be arranged to take care of a height of not less than 13 feet of cupola from bottom plate to charging door. The platform should be strong enough to carry a day's run of melting stock, and should be figured to carry not less than 500 pounds per square foot. It should be roomy, and pro- FiG. 9 — Method of Heating Hand Ladles vided with facilities for good ventilation as a good deal of smoke from the Hoiv to Make Comrrtcr Steel Castings converter finds its way up there and at times it is a Aery undesirable place to work. The elevator, preferably electric, should have a large platform and should be capable of lifting about 3 tons at a time at a speed of about 60 feet per minute. Cupola Blower and Motor. Any of the accepted types of cupola blowers are satisfactory, whether fan or pressure blower, but they should be designed to give ample volume, on account of the high tuyeres and the large percentage of steel scrap used in the charges. The motor is of about 25 horsepower. Ladles. The Tropenas converter makes such exceedingly hot steel that it can all be poured over the lip of the ladle, bottom-pour ladles not being necessary. For pouring small work such as is made in snap molds, hand or bull ladles holding about 150 pounds, are commonly used. They are about 13 inches in diame- ter at the top and are lined to a thickness of ly^ inches. The shanks are about 7 feet long, and have one double end for the man Fig. 10 — Oil Burner for Heating Ladles Fig. 11 — Roller T^pe Grinder for Grinding and Mixing the Molding Sand Fig. 12. — Type of Grinder ferred by the Author Pre- who is to do the pouring and a single end for the helper. The crane ladles are the same as iron foundry ladles, except that they are generally a little smaller in diameter in proportion to their height, to reduce the loss of heat by radiation. They are preferably geared with pin spur gearing instead of 10 Hoiv to Make Converter Steel Castings worm and wheel, as this gives a greater control, steadier liow and less possibility of a drop of the ladle when the gearing is worn. Ladle Heating Furnace. Ladles are generally heated to redness before filling with steel. In the case of the large ladles, this is done either by inverting them over an oil- burning furnace, or introducing an oil burner through a portable cover placed over the top of the ladle. The latter is illu.strated in Fig. 8. A device for heating small ladles, arranged by the author, is shown in Fig. 9. It consists of a series of small oil burners placed side by side, spaced about 18 inches apart from center to center, and a vertical plate with a two-inch hole opposite each burner, through which the flame passes and fills the bull ladle, which is reared against the plate. In this way any number of ladles can be heated, according to the length of the plate, or, if required, one ladle can be heated white hot in 10 minutes. It takes up very little floor space, is clean and easy to operate. Fig. 10 is a detail of the burner. Sand Grinder and Mixer. A grinder of the roller type is generally used. The usual type of mixer is illustrated in Fig. 11, but the author prefers the type shown in Fig. 12. In this mixer, while a perfect mixture of the sand is obtained, there is not so much crushing of the grains, and the resulting sand is more open, as is desirable in steel molding. This mixer is also very speedy in mixing sand, making it "strong" in much less time than the heavy roller grinder. 11 CHAPTER II Lining the Converter- — Kind of Brick Used — Life of the Lining — Construction of Wood Forms Used for Lining the Converter XN attempting to give a detailed description of the operation of a Tropenas plant, it is realized that no amount of written instruction will enable one not thoroughly acquainted with steel-making in general, to produce any kind of castings, to say nothing of the high grade of work that is called for today. The only way to learn how to operate a converter plant is to spend a long time in company with one who has had considerable experience and is perfectly familiar with the reactions that take place. It is true that when the converter was first introduced the pioneers had no one to instruct them, but it would be much too costly for all to learn by the same method. It is true, indeed, that after being under personal instruction and seeing a great many blows made, conditions may arise, after the operator is left to himself, which may puzzle him, and cause him to forget some of the principles that have been drilled into him. It is only by the strictest attention to details that success is achieved, but this is true of all trades, not only steel-making. An unsuccessful foundry business resembles a Kansas cyclone in its certainty of disaster — quick and complete. A foundry that is not watched at every point can absorb money as fast as Rockefeller can pour it in, as many a poor man has discovered. The essentials to success are shrewdness, watchfulnes and science. Lining of the Converter. There are two or three ways to line the converter, and they are all equally good, the factors determining the use of any one being convenience and local conditions. It may be lined with special blocks, which, while expensive, make the time occupied in repairs much less, this being often a very serious matter when the converter needs repairing and orders are waiting fulfillment. The chief drawback to the use of special blocks is that in making repairs, a large amount of good brick has often to be cut away to make room for the new ones. A sand lining, rammed in to shape, may be used and is probably as good and cheap as any, provided the proper 12 Hoiv to Make Converter Steel Castings grade of material is available. The third way is to use the ordinary shapes of furnace brick. This is probably the most common way and will be de- scribed in full detail, as it probably calls for more explanation than the others. Whatever material is used, it is necessary that it should be as refractory as possible, and nothing should be used in the way of brick that has been burnt at a lower temperature than is necessary to turn over a 3,500-degree Seger cone. This means about 95 per cent silica and almost absolutely free of lime and magnesia. In the case of the ganister mixture. Fig. 13 — Wood Form Used for Lining the Converter the very best quality of silica clay must be used and in order to cause it to set very hard, it may be mixed with weak lime water. Lining the Converter With Silica Brick. The bricks used are the square, 9 x 4>4 x 2^^ inches, with the arch 9 X 4^ X 2>4 x 1>4 inches, the wedge, 9 x 4i/^ x 2^^ x 1^ inches, and a special wedge used in the mouth. 9 x 414 x 2^/2 x 1 inches. A small quantity of split brick is also required. This is a rectangular brick one-half the thickness of the ordinary square. 13 Hoiv to Make Converter Steel Castings Two or three rough wooden forms should be prepared, having dimen- sions as shown in Fig. 13. They are made by sawing out boards for top and bottom, 2 inches less in dimensions each way, and then nailing 1-inch strips on the edges. The forms are 18 inches high. Set the converter in a vertical position by means of a plumb line, and then commence the lining operations by laying ordinary firebrick in the circular bottom until a level of about 26 inches below the center of the lower tuyere slot in the bottom wind box is reached. Break all joints and set alternate courses at right angles. Use ordinary firebrick of good quality for this part of the oper- FiG. 14 — One of the Wood Forms Set IN THE Converter ation, as they are less friable than the silica brick, and do not come into direct contact with the heat. The cement used may be made of one-half each, high-grade silica clay and crushed silica rock. For grouting in the courses after laying, this cement may be thinned with water. The next step is to set one of the forms. The illustration. Fig. 14, shows the location of this. It will be seen that the circular part of the form is eccentric with the circular shell of the converter, and the part of larger radius, which gives the conformation of the face of the tuyeres, is set so that a line joining the ends of the arc is parallel to the center line 14 Hoiv to Make Converter Steel Castings of the trunnions. A course of arch hrick on end is laid around the form, and outside of this, a row of ordinary firebrick backing, and the remaining space between brick and shell is rammed-in with ganister. This procedure is continued until a level, 2^ inches below the center of the slot in the shell referred to is reached. This brings us to the most important point in the lining, namely the setting of the tuyeres. Upon this depends a great deal of the assurance of success in the subsequent manufacture of the steel, "the tuyeres, both individually and as a whole, must be set absolutely level, both m a direc- tion parallel to their length and also in a direction at right angles to this. In other words, the tuyeres must all be in exactly the same plane. Fig. 15 shows the tuyeres grouped together and it will be noted that for con- venience, they are numbered No. in the center. No. 1 for the first tuyere on each side, then No. 2 and No. 3, respectively. The higher numbers diverge more from the center than the lower numbers, and the whole sys- 2 . -^ 1 Fig. 15 — Tuyere Block. tem is symmetrical. These tuyeres are made of the very highest grade of silica material available, and they are burnt at a very high temperature as they are subjected to the greatest amount of wear and tear and the greatest amount of chemical action. In setting the tuyeres, it must be borne in mind that the holes must be leveled and not the outside of the bricks, as the outside may be warped to some extent. Round iron bars, of smaller diameter than the tuyeres, should be in- serted in the holes and the leveling done on the protruding ends of these, this being the only w^ay that accuracy can be insured. Together with this leveling, care should be exercised that the tuyeres come opposite the slot in the shell communicating with the lower wind box to allow of an 15 How to Make Converter Steel Castings unrestricted passage of the air into the converter and the possibiHty of cleaning out any slag or iron that may inadvertently get into the tuyeres. After being satisfied that the lower tuyeres are correctly set in every par- ticular, the upper tuyeres are set directly on top of them. The upper wind box has a slot corresponding wnth the lower one, and the rectangular open- ings in these tuyeres should be in line with it. It is not necessary to use the same care in setting these tuyeres, as they are merely combustion tuyeres and do not at any time approach the surface of the iron. They are numbered similarly and have the . same conformation as the lower tuyeres. The body of the converter is then lined up to a point about 2 feet below the top of the cylindrical part of the shell, at which point the wooden forms may be dispensed with. Be sure to leave no open spaces between the bricks, and grout all the joints well with thin grout. From this point a certain amount of mechanical skill is required in setting the brick, as it is largely a matter of hand and eye. It is not an easy matter to describe, nor is it an easy matter to accomplish, but the principle is to overlap each course from this point up the cone until the lining terminates at the mouth of the converter in a circular opening, 15 inches in diameter. The last two rows in the mouth may be made with the special wedge brick mentioned. After the lining is completed, the wooden forms may be burnt out. The bottom is then built-up with pure silica brick until a depth of from 16 to 17 inches below the bottom edge of the tuyeres is reached. This corresponds very closely to a capacity of 2 tons. The lining being now complete, a wood fire is started, the blast valve being shut-off and all covers have been removed from the wind boxes. If the blast valve from the blower is left open, it may happen that gas will accumulate in the pipe and cause an explosion, which may be more or less serious. In describing the lining of the converter, nothing has been said of the manhole door in front of the converter, which some operators use all the time an i 1 / ; 1 1 1 1 1 i "^^ -- [ - ; ^ 1 1 1 i / _[ ' 1 / / / / / / - J / r' w .. OJ -' ^«, e- / Xi 1 u„. ^ei y 1 / N S 1 \X 1 / L - y 1 \ / > /^ / s / y' / \ J y 7 A /• "' i ' / / X / 1 1 l/l > f N V y ^\^ll^ / y\ s 1 j / y k / ^ s / /, y \ \ / IJT s u/ J s 1 / y f s ! / ^ J s 1/ , / f \ ^ \/ 1 X , ' ■c >u et it- »/- B s 1 1 / 1 / 1 / ' i- } ' ' / / 1 1 f 1 / ■ 1 !/ Endtif Bof,l ^ i 1/ / J/ ; / y / f y i / / j / y ( / y / I/' 1 /' y y j / y I / / Ciitnuieiii-Knieht of Liist F^Ui nie / 1 ! / ^ y /] , ■>^ \ «.« ^~. ]vv. "-^ >^ After Recf^vb u'rat idn o u o n < (Ki O rt o p^ (/) z o '^ « « < :SO o kJ cq w 'A J 1— " < s 1— < n >< U H Q < « z a "^ < K ?-, fe < W O hJ 2: W < =- fe i< o ^ ;? U o H < "A (— 1 ►4 W ^ O rn W > « t3 u 24 Hozv to Make Converter Steel Castings and fastened in position. Blast is then turned on by giving the customary signal of two short blasts on the whistle or bell communicating with the blower room, and the motor should be speeded to give 3 pounds on the mercury gage when the by-pass valve is entirely closed. A record of the exact time of starting the blow should be made. Blowing the Steel. At the beginning, sparks and smoke should come out of the mouth of the converter but very little flame. The sparks should be copious, large and scintillating, and light yellow in color, the smoke noticeable but not too voluminous, and not too dark brown in color. An experienced operator, by noting the appearance of the sparks and smoke, can tell during the first minute of the blow whether the silicon content is right, and if he is going to have a hot blow or if it will be necessary to doctor it up as it goes along. The sparks should all go up the chimney in parallel lines, not crossing or shooting out at different angles. In from three to five minutes the char- acter of the sparks should change and become non-scintillating, and at the same time a flame should appear at the mouth of the converter. This is the time to open the upper tuyeres slightly, as the carbon is commencing to burn and extra oxygen is needed to complete its combustion and reap the full benefit from the heat generated. At the same time, the position of the converter should be advanced from 2 to 3 degrees, to compensate for the shrinkage in bulk due to the elimination of the impurities. During the next four or five minutes the flame increases in bright- ness and volume until what is known as the "boil" occurs. The flame should be carefully watched and if there is a tendency to throw out any metal, the blast pressure should be reduced. In extreme cases it may be reduced to 1^ pounds, but this is as low as it is advisable to go. There will always be a certain amount of projection of slag, and this is imma- terial unless it interferes with the observation of the flame. Sloppy blows are indicative of incorrect composition of metal, bad position of converter or too much blast. After maintaining its top position for one or two minutes, the flame dies down somewhat, and remains in a quiet condition for some minutes. The upper tuyeres may now be fully opened. The flame then rises again, becomes particularly bright and clear, and finally dies down for the last time with the evolution of copious brown smoke. The blow should be turned down a few seconds before the brown smoke appears, as this smoke represents burning iron, which means waste of metal and ruination to the remainder. The operator throws over his controller, turning down the vessel into the horizontal position, and a second after signals one whistle to the engineer to stop the blower. At this stage there is in the converter a bath of practically pure iron at a temperature 25 Hoiv to Make Converter Steel Castings well over 3,000 degrees Fahr. Fig. 18 gives the approximate curves of elimination of the elements in a typical blow. In order to recarburize it to the desired point, a weighed final addition of ferro-manganese, ferro- silicon, silicon-spiegel, or what not, is introduced. This may be added melted, in which case a small cupola or crucible furnace may be used, or it may be thrown in cold in lumps at the mouth of the converter immedi- ately after turning down the blow, before the slag gets too hard. In this case the lumps must first be dipped in water so that the explosion of the vapor as they strike the hot slag will part it and allow the alloy to go en- tirely into the bath of metal. This latter method has been found by the author to be far the most useful and regular way of adding final addi- tions. A special shaped core for skimming back the slag is fixed in the mouth of the converter and the metal is then ready to be tapped into the ladle. How TO Overcome Difficulties in Blowing Steel. This is a description of a perfectly normal blow, which should take place in from 15 to 20 minutes. Unfortunately all blows are not normal, a great many conditions having to be harmonized to produce this result, some of which occasionally go wrong. Some of the difficulties that arise, with their cause and cure will be briefly touched upon. The flame should make its appearance at the mouth of the converter in from 3 to 5 minutes. If it comes in less time, it is a sign that the silicon content of the metal is too low and the probabilities are that the blow will not l)e as hot as desired, for the silicon is the fuel, and the chief source from which heat is derived. To olTset this, when the flame makes its appearance, the con- verter should be advanced not more than two degrees and about 100 pounds of ferro-silicon in pig form thrown into the mouth of the converter. This has an astonishing eft'ect and as it melts and gives up its silicon the blow becomes noticeably hotter. If the blow goes on for more than five minutes, at the same time the blast pressure remaining the same on the blast gage, it is a sign that the iron is either too high in silicon or it is too cold. If caused by too high silicon, there may not be very serious results except that the blow will certainly be very sloppy, the loss will be abnormally great, the blow will be longer and the resulting steel may be high in silicon on account of tlie fact that the carbon burns out before the silicon is en- tirely eliminated. If the latter is the case there is nothing to do but coax it along and dose it with silicon after the flame makes its appearance. A frequent trouble due to various causes is the corking of the tuyeres. Its signs are an increase of pressure in the blast gage without any increase in the speed of the motor ; a change in the directions of the sparks, some of which shoot out at right angles instead of all being parallel, and delay in the progress of the reactions. Stoppage of the tuyeres may cause serious troubles, such as cold blows, and violent reactions. The tuyeres are corked 26 Hozv to Make Converter. Steel Castings by the formation of nozzles of slag on their extremities which tend to lengthen the tuyeres and may have openings in many directions, dispersing the blast and possibly permitting only a small amount of it to react on the metal. They are caused by cold metal, not setting the position of the vessel correctly, and not skimming it clean from slag at the commencement. When this corking is noticed it generally occurs before the flame makes its ap- pearance, and the converter should be turned down, the blast shut off and the projections or nozzles knocked off with an iron bar. The blast is then started and the converter returned to its original position, when it will usually proceed all right. It may be necessary to repeat this procedure two or even three times. The result of corked tuyeres is almost invariably a sloppy blow if nothing worse. Analyses of Converter Castings. In regard to the amount of final addition to be used a good deal could of course be written, also as to the materials to be used. In the first place, let us take the ordinary grades of simple or carbon steel. The analysis to be aimed at varies principally with the use to which the castings are to be put, and secondly to a less extent with the shape and weight of the piece. Speaking from the first standpoint it may be said that the analysis for ordi- nary machine or engine castings on which a good deal of machining has to be done should be carbon 0.25 to 0.30 per cent, silicon 0.25 to 0.30 per cent, manganese 0.60 to 0.75 per cent, and sulphur and phosphorus as low as possible, under 0.05 per cent. For castings which will be subject to a greater amount of wear than ordinary, and for those which require a greater tensile strength such as levers, connecting rods and gears the carbon may be raised to from 0.35 to 0.40 per cent, and in cases where the castings are liable to "pull" on ac- count of differences in section, great length, etc., the carbon may be raised to 0.50 per cent, silicon 0.30 per cent, and manganese up to 1.10 per cent. The castings last referred to will have to be annealed in all cases. For the purpose of recarburizing to these points the common materials used are ferro-silicon containing about 12 per cent of silicon, silicon-spiegel containing about 10 per cent silicon and 20 per cent manganese, and ferro- manganese containing 80 per cent manganese. The amount to be used can easily be figured by an ec^uation such as was used for calculating cupola charges, but it must be borne in mind that an excess of from 20 to 30 per cent of ferro-manganese must be used to compensate for that which goes to deoxidize the metal, and an excess of about 5 per cent of the calculated amount of ferro-silicon. The action of the steel in the ladles is somewhat of an indication of its carbon content to the close observer. The softer and purer the steel the higher is the melting point and therefore in order to have it to remain 27 Hozv to Make Converter Steel Castings fluid in the ladle and allow it to free itself from gases, it needs to be super- heated to a higher degree than the harder grades. It is more difficult to "dead melt" soft steel than hard steel, and soft castings are more difficult to run and are more liable to blow-holes. This is borne out by the fact that gray iron remains fluid in the ladle at a temperature where steel would set. For making the special or alloy steels such as tungsten steel, chrome steel, manganese steel or nickel steel, either the ferro-alloys of these ele- ments or the pure products of the electric furnace or alumino-thermic proc- ess are used, and the amounts vary widely according to the purpose for which the castings are to be used. The materials produced by the alumino- thermic process are very useful on account of their concentration, rendering it necessary to use only the minimum amount to produce the maximum effect, and by the freedom from carbon, etc.. making control of the ultimate analysis more simple and certain. 28 CHAPTER V Hot Cracks in Steel Castings and How They May Be Overcome N attempt will be made in this chapter to outline the principal causes of one of the greatest difficulties that a steel founder has to contend with, and to suggest some means by which it may be overcome, at least partially. Cracks in steel castings are of two kinds, which differ in their appearance and cause very materially. Hot cracks , take place at the time of solidification of the metal or very soon after; cold cracks are formed while the metal is below red heat. The former take the appearance of a tear, are very ragged and there is a sinking of the metal at the edges ; they are generally quite wide and have a film of blue or black oxide on their fractured surfaces. Cold cracks, while they may be open occasionally, are generally very fine, clean cut as with a knife, and unless the castings are carefully inspected may sometimes escape observa- tion. Ringing the castings with a hammer will often reveal the presence of cold cracks which are almost invisible. It is with the former, or hot cracks, that this chapter is intended to deal. The two principal causes of hot cracks are obstructions to the free contraction of the metal, and unsuitable composition of the metal itself. First then look into the causes which may prevent the unrestricted contrac- tion of the metal. They are chiefly the rigidity of the mold and the varying thicknesses of section of the casting. The mold has to be made sufficiently strong to stand the weight of the steel and the fluid pressure of the head of metal while it is being poured. Molds for steel castings are generally made in dry sand, which consists of silica sand mixed with a certain pro- portion of clay to bind it together. And though it is very weak in its green or damp condition, it becomes quite hard and firm after baking. The molds are faced with a wash made of silica flour and molasses water, which gives a very hard, refractory skin. It is therefore important that while the mold should be strong' enough to stand all the pressure it is to receive, it should not be any stronger than is necessary for the above purpose. Means may be provided for making the mold stronger in some parts than others, for instance near the gate, where the cutting action is greatest. At these places the mold may be made of a stronger grade of sand, or if its shape allows, hard cores, or fire brick cvit to shape, may be fitted in, to take the wear of the stream of metal. All scpiare corners, both inside and outside, 29 How to Make Converter Steel Castings should be amply filleted, and wherever a rib or a projectiiii^ arm of the pattern protrudes, the sand in its immediate vicinity should be loosened up by rammin_^ in cinders, sharp sand or saw dust ; or the mold can be cut away to within 2 or 3 inches of the pattern, after it has been dried, and the space filled in with burnt sand. Another point to be attended to with the idea of reducing^ the danger of hot cracks is the drying of the molds. To produce the best results, a mold should be rather over-dried than under-dried, that is to say it should be almost but not quite burned. A mold that is only just dry is in the most rigid possible condition ; it can be baked a good deal more and yet preserve sufficient strength to stand the wear and tear of pouring, and it will then ofifer much less resistance to the shrinkage of the metal. The ideal mold, as has been said before, consists of a hard refractory skin and a collapsible backing, which will give way as soon as the cooling skin of the casting has become sufticiently rigid to support itself, and begins to shrink. It is to the production of these conditions, as nearly as may be possible in practice, that foundrymen have to bend their efforts. Cores for Steel Castings. Defective construction of cores is another fruitful source of cracked castings. Coremaking is a branch of the steel foundry trade that does not receive the attention it merits. It is equally as important as the mold itself, calls for as much skill, and contributes equally to the success or failure. And yet we often find the coremaking relegated to a sec- ondary place. Core sand mixtures should be as carefully studied as mold- ing sand mixtures, and a great saving may be effected, not only in the mat- ter of cracking, but in the cost of cleaning and the soundness of the castings by careful attention to this point. The same description applies to a core as to a mold — it should have a hard, smooth face, which will resist the cutting and fusing action of the metal, but it should crumble and fall out in the form of powder when burnt. Careful handling will permit the use of cores which seemingly are exceedingly delicate. As the author has previously stated, cores can be made of almost anything, provided the wash is satisfactory. When the core is rammed up it should have a good coat of a wash made of silica flour, Ceylon graphite and molasses water, and then put in the oven and baked until after scratching the skin the inside is thoroughly "rotten". Then another coat of wash or two if necessary may be given, and the core is redried. It is surprising how strong this skin becomes, and it is no more than 1/32 inch thick. In a great many cases a core has to stand much greater pressure than the mold itself, as for instance in a pipe or cylinder, where the metal is shrinking on the core from every direction. If the core is not collapsible 30 How to Make Converter Steel Castiii