Fig. 128.—The Scroll Former.
Fig. 128.—The Scroll Former.
143. Scroll Former.—Fig. 128. This is a very handy tool for producing scrolls in a rapid and uniform manner. It should be a perfectly designed variable spiral. If several are provided, they should be exactly alike, otherwise the scrolls produced with them will be unequal and irregular and will present an inartistic appearance. The former illustrated is made of 1 ×1⁄2-inch soft steel. Draw the end and form the central portion, gradually tapering to about3⁄16of an inch thick, but leave it of a uniform width. Thisend should be slightly beveled from one side to form a protruding edge, over which the small curled end of the material is securely held while the scroll is being bent. A view of the former as it is used to start a scroll is given inFig. 129showing the metal in proper position for forming. The end indicated ata,Fig. 128, may be bent downward and edgewise to a right angle, as shown, or, if desired, it may be forged square to fit the hardy hole of the anvil, but as this tool is most conveniently used when held in the vise, the method shown atais better.
Fig. 129.—Starting a Scroll on the Former.
Fig. 129.—Starting a Scroll on the Former.
144. Bending or Twisting Fork.—Fig. 130. This fork is shown with dimensions suitable for bending material1⁄8or3⁄16inch in thickness. For thicker material all dimensions should be proportionately increased.
Fig. 130.—Bending or Twisting Fork.
Fig. 130.—Bending or Twisting Fork.
This tool is very serviceable and quite easily made of round tool steel; if such stock is not at hand, octagonaltool steel can be swaged to the desired dimension. If it is made of soft steel, it will meet requirements for a considerable length of time.
145. Bending or Twisting Wrench.—Fig. 131. This should be made from the same quality of steel of the same dimensions as the preceding tool.
Fig. 131.—Bending or Twisting Wrench.
Fig. 131.—Bending or Twisting Wrench.
Fig. 132.—Scroll Bending.
Fig. 132.—Scroll Bending.
The bending wrench is used in connection with the bending fork for shaping a scroll, as shown inFig. 132. When the wrench is placed over the material so that its jaws will grip the sides and the handle of the wrench is pulled in the direction indicated by the arrow, bending will take place ate. If the straight end of the scroll were pulled in the same direction, bending would occur atf. Sometimes when scrolls are being connected with the band, they are sprung out of place. By the use of this wrench they can be brought again into position by bending them close to where the band was put on.
These tools may be used together for twisting light material, when the vise and monkey wrench could not readily be utilized.
Fig. 133.—Clip Former.
Fig. 133.—Clip Former.
146. Clip Former.—Fig. 133. This and the two following tools should be made of 0.80 to 0.90 per cent carbon tool steel. A convenient size of material for the one shown is 1 ×1⁄2inch. The portion forming the connecting loop must be flattened and forged to about1⁄4inch thick to provide a spring for retaining its shape. The ends should be forged to two different thicknesses. The1⁄4-inch side is used in bending clips for banding two pieces of1⁄8-inch material, and the3⁄8-inch side for three pieces. When a different thickness of material is to be used, these ends should be made to correspond with it. The inner and outer edges of these ends should be made slightly rounding to prevent cutting the material from which the clips are made. Most of this light scroll work is made from stock with round edges, therefore it is not necessary to have the clips bent sharp and square.
Fig. 134.—Use of the Clip Former.
Fig. 134.—Use of the Clip Former.
The former should be so proportioned that it can be placed between the jaws of the vise, as shown inFig. 134. Here the loop is resting on the box of the vise, which supports it and prevents it from falling out of positionwhen the pressure of the vise is released. The ends of the clip former should extend above the jaws of the vise about 2 inches, so that the clips can be bent without striking the vise with the hammer. A view of these ends, with a piece of half-oval iron in position for bending, is shown atA,Fig. 137. One end of the clip material should be placed between the ends of the former, one half the width of the scroll stock,3⁄16of an inch if the stock is3⁄8inch wide. By tightening the jaws of the vise upon the sides of the former, the half-oval iron will be securely held, while it is being bent over with the hand hammer to the form indicated by the broken lines. The clip will then be ready for fastening the scrolls together.
Fig. 135.—Clip Holder.
Fig. 135.—Clip Holder.
Fig. 136.—Use of the Clip Holder.
Fig. 136.—Use of the Clip Holder.
147. Clip Holder.—Fig. 135. Stock3⁄4inch square is best suited for making this tool. The central portion forming the loop should be drawn and forged to about1⁄4inch thick, gradually increased to1⁄2inch where the shoulders are formed. The distance from these shoulders to the outside end of the loop should be less than the distance from the top of the vise jaws to the vise box. Then the tool will be supported entirely on these shoulders, as shown inFig. 136, and the tool may be placed near the ends of the vise jaws, which sometimes will prove to be quite an advantage.The length from the shoulders to the ends may be about 2 inches. These ends should be drawn tapering from the outer sides to about1⁄2inch square. On the inside a depression3⁄16inch deep should be formed so that the holder will fit over the bent end of a clip, as shown atB,Fig. 137.
Fig. 137.—Forming a Clip.
Fig. 137.—Forming a Clip.
The clip and a sectional view of the two pieces of material that are to be connected are shown atBas they are placed in this tool. By tightening the vise upon the holder, the lower portion of the clip will be clamped securely on the pieces and held while the upright end of the clip is bent over and around the upper half of the material with the hand hammer. Then the following tool will be brought into use.
148. Clip Tightener or Clincher.—Fig. 138. The most convenient stock from which to make this tool is3⁄4-inch octagon tool steel. It is made by upsetting and forging the end to about 11⁄4×1⁄2inches, then filing a depression not more than3⁄16inch deep and wide enough to fit tightly over the outer portion of the bent end of a clip. The corners indicated ateshould be made slightly round to prevent them from marring the outside of the clips. This tool should be about 61⁄2inches long, with the head end drawn as for a cold chisel.
Fig. 138.—Clip Tightener or Clincher.
Fig. 138.—Clip Tightener or Clincher.
By holding this tool on top of the bent-over clip, as shown atC,Fig. 137, and delivering a few heavy blows upon it, the clip will be tightened and clinched securely over and around the pieces.
Fig. 139.—Jardinière Stand or Taboret.
Fig. 139.—Jardinière Stand or Taboret.
149. Jardinière Stand or Taboret.—Fig. 139. The height from the floor line to the top of the circular board is 26 inches; the height from the floor line to the upper ringEis 191⁄2inches; the height from the floor line to the lower ringFis 7 inches; the extreme width is 181⁄2inches.
The process of making this stand will be given here. By following a similar course, any of the other designs given in this chapter may be made. The material usually employed for making this is1⁄2×1⁄8-inch, and there should be four sections or legs, as shown at the left, also two bands or rings, like the one shown in the upper right, and one top board7⁄8inch thick and 8 inches in diameter, which isshown under the ring. The following list gives the number and lengths of the various pieces required:—
4 pieces 451⁄2inches long.4 pieces 221⁄2inches long.4 pieces 151⁄2inches long.4 pieces 15 inches long.2 pieces 141⁄2inches long.4 pieces 13 inches long.
All pieces should be straightened immediately after being cut to length. The main branch, 451⁄2inches long, should be marked with a center punch at all places where bending or twisting is to be done. From the end of the stock toAis 6 inches; fromAtoB, 9 inches;BtoC, 41⁄2inches; the length of the twisted portion is 21⁄2inches.
All ends that are to be scrolled, should be drawn, curled, and fitted to the central portion of the former, as previously indicated. Whenbothends of the same piece are to be scrolled, observe carefully whether they revolve in thesameor inoppositedirections. These ends should not be cooled after drawing and fitting, because cooling will have a tendency to harden them slightly and prevent uniform bending. All ends that are to be connected to another piece by clips should now be drawn out to a thin edge, but of a uniform width.
Now proceed to form the main branch by making the twisted portion betweenBandC; straighten if necessary. Form the upper angular bend of 90 degrees atAwhile it is held in the vise; this can be done cold, by carefully avoiding breaking or cutting the material with the sharp edge of the vise. Now form a scroll at the top on the former. Next bend atBin the same manner and direction as before, and make the two quarter circles betweenAandB, with the bending fork alone or by combining the use of it with the bending wrench. Exercise carein doing this, in order to have the correct space for scroll 2 and ringE, which should be 5 inches outside diameter. The lower angular bend atCshould now be made, followed by forming as much of the scrollDas possible on the former. Then bend the irregular curve betweenDandC.
The next member to be scrolled and fitted into position is the 151⁄2-inch piece, 4. This must be carefully made in order to have the extreme height of the scroll at the proper distance from the bottom line, also at the proper distance from the center line, to provide an exact dimension where the lower ringFis to be connected. The outside diameter of ringFshould be 5 inches. Then scroll and fit the 15-inch piece, 3, followed by the 13-inch piece, 5, and finish this leg by arranging the 221⁄2-inch piece, 2, last, so that it will not extend above the bottom line of the circular board and will leave at least a1⁄4-inch space between the center line and the sides of the curves.
All parts should be assembled on the drawing after they are fitted, and marked with crayon wherever the clips are to be placed to secure them. The material for the clips, which should be3⁄8-inch half-oval Norway iron, should be cut up in lengths equal to the four outside dimensions of the combined materials plus1⁄8of an inch for bending, or 15⁄8inches in this case. After these pieces are bent on the clip former, fasten the scrolls together with the clip holder and the clincher.
After the four legs or parts have been assembled, lay each separately on the drawing, to make sure that the places, where they are to be connected with the rings and the circular board, are properly located. If they arecorrect, mark these places with a center punch, and drill9⁄64-inch holes where the rings are to be connected and3⁄16-inch holes where the top is to be secured.
The two 141⁄2-inch pieces are for the rings. Drill a9⁄64-inch hole3⁄8of an inch from each end in both pieces, countersink one side of one end of each piece, and grind a beveled edge on this end, but on the opposite side from the countersink. Form them into rings having the countersink inside. Connect the ends of each ring with a1⁄8×3⁄8-inch round-head rivet, inserting it from the outside of the ring and riveting the ends together, filling the countersink. Place the rings separately on the mandrel and make them perfectly round on the inside by forming a slight offset on the outside end where it begins to lap over the beveled inside end.
Draw a 5-inch circle on a piece of board and divide it into quarters. Place the rings on this outline with the outside end about1⁄4inch from one of the quarter lines. Mark where each quarter line crosses the ring, center-punch these places, drill9⁄64-inch holes, and countersink them on the inside. Then assemble the legs by riveting the upper ring to the standard with1⁄8×1⁄2-inch rivets, the lower one with1⁄8×3⁄8-inch rivets, their heads toward the exterior so that riveting will be done on the inside of the rings filling the countersink. Place the circular top board in position and secure it with 1-inch #10 round-head wood screws. This will complete the construction, with the exception of a coat of black japanning, if a glossy finish is desired, or a coat of dead black lacquer if a rich dull black is desired.
Fig. 140.—Umbrella Stand.
Fig. 140.—Umbrella Stand.
150. Umbrella Stand.—Fig. 140. Extreme height, 271⁄2inches; extreme width, 181⁄2inches; upper rings, 91⁄4inches inside diameter; lower ring, 51⁄4inches inside diameter. Provide a small deep pan to rest on top of this ring.
Fig. 141.—Reading Lamp.
Fig. 141.—Reading Lamp.
151. Reading Lamp.—Fig. 141. Extreme height, 23 inches; height of the stand, 14 inches; base, 81⁄4inches wide; shade, 14 × 14 inches wide, 61⁄4inches high, top opening, 4 × 4 inches.
Fig. 142.—Andirons and Bar.
Fig. 142.—Andirons and Bar.
152. Andirons and Bar.—Fig. 142. Extreme height, 24 inches; extreme width of base, 18 inches; height from the floor line to the top of the upper scroll, 111⁄2inches; length of bar, 40 inches.
Fig. 143.—Fire Set.
Fig. 143.—Fire Set.
153. Fire Set.—Fig. 143. Extreme height, 30 inches; heightto the holders, 24 inches; height to the top of the upper scroll, 111⁄2inches; extreme width of the base, 14 inches.
Fig. 144.—Fire Set Separated.
Fig. 144.—Fire Set Separated.
154. Fire Set Separated.—Fig. 144. Extreme length of implements, 22 inches.
Questions for Review
Explain three methods of obtaining the length of a scroll. Should scrolls be bent hot or cold? Why are the ends of the clip former made to different thicknesses? Why is the clip former made thinner at the loop? How is that tool placed in the vise? Why is the clip holder made with shoulders on its outer sides? Give the rule for cutting off clip stock. After the scroll material has been cut to length, what should be done? When ready to draw and bend the curl for a scroll what should be observed? Why shouldn’t it be cooled after drawing and curling? What is done with the ends of a scroll if they are to be fastened with clips? Explain how the rings are made for the jardinière stand. Describe the process of making the umbrella stand inFig. 140.
Explain three methods of obtaining the length of a scroll. Should scrolls be bent hot or cold? Why are the ends of the clip former made to different thicknesses? Why is the clip former made thinner at the loop? How is that tool placed in the vise? Why is the clip holder made with shoulders on its outer sides? Give the rule for cutting off clip stock. After the scroll material has been cut to length, what should be done? When ready to draw and bend the curl for a scroll what should be observed? Why shouldn’t it be cooled after drawing and curling? What is done with the ends of a scroll if they are to be fastened with clips? Explain how the rings are made for the jardinière stand. Describe the process of making the umbrella stand inFig. 140.
155. Iron Ore.—An ore is a portion of the earth’s substance containing metal for which it is mined and worked; the class to which it belongs depends upon the amount and variety of the metal it contains. Any ore that is to be used for the extraction of a certain metal must contain the metal in sufficient amounts to make the operation profitable.
Iron, ordinarily, does not occur in a native state or in a condition suitable for use in the arts and manufactures. The iron in meteors, frequently called native iron, is the nearest possible approach to it. Meteorites, commonly known as falling stones or shooting stars, are solid masses that have fallen from high regions of the atmosphere and are only occasionally found in different parts of the world. They are considered more valuable as a curiosity than as material for manufacturing purposes. The metallurgist, chemist, or geologist can readily distinguish them from other masses, because they invariably contain considerable nickel, which seldom appears in any of the ordinary iron ores. They are usually found in a mass containing crystals and are nearly always covered with a thin coating of oxide, which protects the metal from further oxidation. Several large meteors have been found, one in Germany weighing 3300 pounds and a larger one in Greenland weighing 49,000 pounds. The largest one known wasdiscovered by Lieutenant Peary in the Arctic regions. It weighs 75,000 pounds. He brought it to New York City, where it can now be seen at the American Museum of Natural History.
Pure iron is obtainable only as a chemical, and as such it is used in the preparation of medicines. As a commercial product, such as is used in the arts and manufactures and by the smith, it is always combined with other substances, such as carbon, silicon, and phosphorus.
Iron is distributed through the earth very widely, but not always in sufficient quantities to make its extraction from the ore profitable; consequently the ores used for the extraction of iron are somewhat limited. There are four general grades of iron ore, which are known by the following names: magnetite, red hematite, limonite, and ferrous carbonate. These are subdivided and classified according to the particular composition of each.
156. Magnetitewhen pure contains about 72 per cent of iron, and so is the richest ore used in the manufactures. It is black, brittle, and generally magnetic, and leaves a black streak when drawn across a piece of unglazed porcelain. It sometimes occurs in crystals or in a granular condition like sand, but generally in a massive form. It is found principally in a belt running along the eastern coast of the United States, from Lake Champlain to South Carolina. There are considerable quantities of it in New Jersey and eastern Pennsylvania, but the greatest deposits are found in Missouri and northern Michigan; some is mined also in eastern Canada. It is a valuable ore in Sweden.
A mineral known as franklinite, which is closely allied to magnetite, is a mixture of magnetite and oxides ofmanganese and zinc. In appearance it resembles magnetite, but is less magnetic. In New Jersey, where it is found quite abundantly, it is treated for the extraction of the zinc, and the residue thus obtained is used for the manufacture of spiegeleisen, which is an iron containing a large amount of manganese, usually from 8 to 25 per cent.
157. Red hematiteis found in earthy and compact forms. It varies in color from a deep red to a steel gray, but all varieties leave a red streak on unglazed porcelain. It is found also in a number of shapes or varieties, such as crystalline, columnar, fibrous, and masses of irregular form. Special names have been given to these. The brilliant crystalline variety is known as specular ore, the scaly foliated kind as micaceous ore, and the earthy one as red ocher. Each one of this class contains about 70 per cent of iron, and on account of the abundance, the comparative freedom from injurious ingredients, and the quality of iron it produces, it is considered the most important of all the ores in the United States.
Until the discovery of large deposits of this ore in the Lake Superior district it was chiefly obtained from a belt extending along the eastern coast of the United States just west of the magnetite deposits and ending in Alabama. Some of this ore is found in New York, but there is not a great amount of it north of Danville, Pennsylvania. At present the greatest quantities that are used come from the Lake Superior district. There, ore of almost any desired composition may be obtained, and the enormous quantities, the purity, the small cost of mining, and the excellent shipping facilities have made it the greatest ore-producing section of the United States.
158. Limonite or brown hematitecontains about 60 percent of iron and is found in both compact and earthy varieties. Pipe or stalactitic and bog ore belong to this grade. The color varies from brownish black to yellowish brown, but they all leave a yellowish brown streak on unglazed porcelain. It is found in a belt lying between the red hematite and magnetite ores in the eastern United States. Formerly there was considerable of this mined in central Pennsylvania, Alabama, and the Lake Superior district.
159. Ferrous carbonatecontains about 50 per cent of iron. It also is found in several varieties, called spathic ore, clay ironstone, and blackband. Spathic ore when quite pure has a pearly luster and varies in color from yellow to brown. The crystallized variety is known as siderite; this ore frequently contains considerable manganese and in some places is used for the production of spiegeleisen. When siderite is exposed to the action of the air and water, brown hematite is formed.
Clay ironstone is a variety that is found in rounded masses or irregular shapes and sometimes in layers or lumps, usually in the coal measures. It varies in color from light yellow to brown, but the light-colored ore rapidly becomes brown when exposed to the atmosphere. Like the former it also contains considerable manganese.
Blackband is also a clay ironstone, but it is so dark in color that it frequently resembles coal; hence the name. The ore is not very abundant in this country nor extensively used; it is generally found with bituminous coal or in the coal measures, therefore it is mined to some extent in western Pennsylvania and Ohio. It is an important ore in England.
160. The Value of Ores.—Ores are valued according tothe amount of iron they contain, the physical properties, the cost of mining, the cost of transportation to the furnace, and their behavior during reduction. The ores of the Mesaba range in the Lake Superior district are very rich, and free from many impurities; they are soft and easily reduced, and as they are found near the surface, they can be mined with steam shovels. These are great advantages, but the greatest disadvantage is the fact that the ore is fine and some of it blows out of the furnace with the escaping gases; this also fouls the heating stoves and clogs the boiler flues.
161. Preparation of Ores.—Most of the ores are used just as they come from the mines, but in some cases they are put through a preliminary treatment. This is sometimes done as an advantage and at other times as a necessity. This treatment is very simple and consists of weathering, washing, crushing, and roasting.
162. Weatheringis a common process. Sometimes ores that have been obtained from the coal measures and others that may contain pyrites or similar substances are left exposed to the oxidizing influence of the weather. This separates the shale and the pyrites. The former can easily be removed, and the latter is partly oxidized and washed away by the water or rain falling upon it. The ore piles shown inFig. 149are exposed to the atmosphere and partly weathered before being used.
163. Washingis also done for the purpose of removing substances that would retard the smelting process. For instance, the limonite ores, which are generally mixed with considerable clay or earthy compositions, are put through an ore washer to remove those substances before they are charged into the smelting furnace.
164. Crushingis done with machinery to reduce to a uniform size such refractory ores as are mined in rather large lumps. If the ore were charged into the furnace as mined, the coarseness would allow the gases to pass through the ore too readily without sufficient action upon it. Smaller pieces will pack more closely together, thus offering greater resistance to the blast, and hastening the reduction.
165. Roasting or calcinationis done to desulphurize ore which contains an excess of sulphur. It is done also to expel water, carbon dioxide, or other volatile matter which it may contain. Ore, made more porous by roasting, exposes a larger surface to the reducing gases. In the case of magnetic ores, roasting converts the ferrous oxide into ferric oxide, which lessens the possibility of the iron becoming mixed with the slag, thereby preventing considerable loss of metal.
Ore is frequently calcined in open heaps, but in more modern practice stalls or kilns are employed. Where fuel is cheap and space is abundant, the first process may be used. A layer of coal a few inches thick is laid on the ground, and a layer of ore is spread upon it; then coal and ore are laid in alternate layers until the pile is from 4 to 9 feet high. The coal at the bottom is then ignited, and the combustion extended through the entire mass. If at any time during the operation the combustion proceeds too rapidly, the pile is dampened with fine ore and the burning allowed to proceed until all the coal is consumed. Blackband ore frequently contains enough carbonaceous matter to accomplish roasting without the addition of any fuel except the first layer for starting the operation.
When the ore is calcined in stalls, it is placed in a rectangularinclosure with walls on three sides; these are from 6 to 12 feet high and are perforated to allow a thorough circulation of air. This method is very much like that of roasting in open heaps, but less fuel is necessary, for the draft is under better control and a more perfect calcination is accomplished.
When the same operation is performed in kilns, it is more economical in regard to fuel and labor than either of the two methods explained above. The process is under better control, and a more uniform product is obtained. The kilns are built in a circular form of iron plates, somewhat like a smelting furnace and lined with about 14 inches of fire brick. The most common size of the kilns is about 14 feet in diameter at the bottom, 20 feet at the widest part, and 18 feet at the top; the entire height is about 30 feet. They are capable of receiving about 6000 cubic feet of ore.
166. Fuels.—A variety of fuels may be used in the blast furnace reduction process, but the furnace should be modified to suit the particular quality of fuel. In this country the fuels most used are coke, charcoal, and anthracite coal. Coke is the most satisfactory and is more generally used than either of the others. Charcoal is used to a certain extent on account of its freedom from impurities and because it is generally considered that iron produced with charcoal is better for some purposes than that made by using other fuels. Anthracite coal is used principally in eastern Pennsylvania because the coal mines are near at hand, and it is therefore the cheapest fuel available. In some instances a mixture of anthracite and coke is used.
167. Fluxes.—The materials that are charged into thefurnace with the ore, to assist in removing injurious elements that it may contain, are called fluxes. They collect the impurities and form a slag which floats on top of the molten iron and which is tapped off before the metal is allowed to run out. The fluxes also assist in protecting the lining of the furnace by thus absorbing the impurities which would otherwise attack the lining and destroy it.
Limestone is almost universally employed as a flux, although dolomite is used also to some extent. The value of limestone as a flux depends upon its freedom from impurities, such as silicon and sulphur.
Sulphur and phosphorus are two elements which must be kept out of the product. When there is too much sulphur, the iron is exceedingly brittle at a dull red heat, although it can be worked at a higher or lower temperature. It is called red-short iron and makes welding difficult. With steel, sulphur diminishes the tensile strength and ductility. If there is too much phosphorus combined with iron, the metal will crack when hammered cold. Iron of this kind is called cold-short iron. This metal can be worked, however, at a higher temperature than can the red-short iron just described.
168. The Blast.—The air blown into the furnace to increase and hasten combustion is called the blast. Formerly when a cold blast was used, considerable extra fuel was required to heat the air after it entered the furnace, but a hot blast is used now almost exclusively. The air is heated by passing through large stoves built for that purpose. The stoves are heated by burning the waste gases which are generated in the furnace and which are conducted from the top of the furnace through a pipeleading into the stoves. Four of these stoves are shown inFig. 149at the left of the picture.
Fig. 145.—Running Metal from the Blast Furnace to Ladles for Transporting to either the Open Hearth Furnace or the Pig Molder.
Fig. 145.—Running Metal from the Blast Furnace to Ladles for Transporting to either the Open Hearth Furnace or the Pig Molder.
169. The Reduction or Blast Furnace.—Fig. 145. The reduction or blast furnace is almost universally used for the reduction of iron ore. It is a large barrel-shaped structure, the exterior of which is formed of iron plates about1⁄2inch thick, bent and riveted together like the outer shell of a boiler. This is lined with brickwork or masonry, the inner portion being made of fire brick to protect the furnace from the intense heat. Figure146shows a sectional view of a furnace of this kind.
Fig. 146.—Sectional View of a Blast Furnace.
Fig. 146.—Sectional View of a Blast Furnace.
The stackDis supported on a cast-iron ring, which rests on iron pillars. The hearthKand the boshesEare beneath the stack and are built independent of it, usually after the stack has been erected. This is done so that the hearth can be repaired or relined whenever it becomes injured. The hearth is also perforated for the introduction of the tuyèrest, through which the blast enters the furnace from the blast mainB. The openingto the downcomer or pipe leading to the stoves is shown atA.
Figure147shows the mechanical arrangement at the top of the furnace, called the bell and hopper, for receiving and admitting the ore flux and fuel. By lowering the bellCthe material is allowed to drop into the furnace.
Fig. 147.—Sectional View of the Bell and Hopper.
Fig. 147.—Sectional View of the Bell and Hopper.
The fuel, ore, and flux are charged into the furnace at the top in alternate layers, as previously explained; the iron settles down through the boshes, is melted, and drops to the bottom or hearth. The slag is drawn off at the cinder notchc,Fig. 146, after which the iron is tapped off at the iron notchg. Hollow platespfor water circulation are inserted in the boshes to protect the lining from burning out too rapidly.
The melted iron runs from the tapping notch into a large groove made in sand. This groove is called the “sow.” It is connected with smaller grooves called the “pigs.” Into these the metal runs and forms pig iron. Considerable sand adheres to pigs thus formed, and as the sand is objectionable for foundry, Bessemer, and open-hearth purposes, and as an enormous amount of hand labor is required in breaking up and removing it, pig moldingmachines are used. Figure148shows one of these machines with a ladle pouring the metal into it.
The only objection to this method is that the metal is chilled rather suddenly by the water through which the molds are led. This sudden chilling causes a structure different from that found in the same quality of metal molded in the sand and allowed to cool off gradually, and most foundrymen as well as other users of iron judge the quality by the appearance of a fracture. On this account machine-molded pigs are objectionable. It is claimed, however, that some machines in use at present have overcome this difficulty.
The approximate dimensions of a modern coke-burning furnace are as follows (seeFig. 146): The hearthKis about 13 feet in diameter and about 9 feet high. The diameter of the portion above the hearth increases for about 15 feet to approximately 21 feet in diameter at the boshesE. From the top of the boshes the diameter gradually decreases until it is about 14 feet in diameter at the stock line. The throat, or top, where the fuel and ore are charged in through the bell and hopper, is about 70 feet above the hearth. On the brackets which are connected to the pillars, the blast main rests, completely surrounding the furnace, and at numerous places terminal pipes convey the blast to the tuyères. After the furnace has been charged, or “blown in,” as it is commonly called, it is kept going continually night and day, or until it becomes necessary to shut down for repairs.
A general view of a smelting plant is shown inFig. 149. The four circular structures to the left with a tall stack between them are the stoves for heating the blast. Next to these in the center of the picture is the blast furnace,somewhat obstructed by the conveyor which carries the ore and fuel to the top for charging. The structural work to the right is the unloader, which takes the ore from the vessels and conveys it to the stock pile in the foreground, where the ore is allowed to drop.
Fig. 148.—Pig Molding Machine.
Fig. 148.—Pig Molding Machine.
170. Classification of Pig Iron.—The pig iron produced by the blast furnace is graded as to quality, and is known by the following names: Bessemer, basic, mill, malleable, charcoal, and foundry iron. This classification indicates the purpose for which each kind is best suited.
171. Bessemer ironis that used for making Bessemer steel. In this grade the amounts of sulphur and phosphorusshould be as low as possible. Bessemer iron is generally understood to contain less than 0.1 per cent of phosphorus and less than .05 per cent of sulphur.
172. Basic ironis that which is generally used in the basic process of steel manufacture. It should contain as little silicon as possible, because the silicon will attack the basic lining of the furnace; therefore the surface of the pig iron used for this purpose should, if possible, be free from sand. By the basic process of making steel, most of the phosphorus in the pig iron is removed, consequently basic iron may contain considerably more phosphorus than if it were to be used in the Bessemer process.
173. Mill ironis that which is used mostly in the puddling mill for the manufacture of wrought iron. It should contain a low percentage of silicon. Therefore pig iron that has been made when the furnace was working badly for foundry iron is sometimes used for this purpose.
174. Malleable ironis that used for making malleable castings. It usually contains more phosphorus than Bessemer iron and less than foundry iron. The percentage of silicon and graphitic carbon is also very low in this class.
175. Charcoal ironis simply that which has been made in a furnace where charcoal has been used as the fuel. It is generally used as a foundry iron for special purposes.
176. Foundry ironis used for making castings by being melted and then poured into molds. For this purpose an iron that will readily fill the mold without much shrinkage in cooling is desired. Other properties of foundry iron will depend upon the character of the castings desired.
177. Grading Iron.—Iron is graded and classified according to its different properties and qualities by two methods; namely, chemical analysis and examination of fracture.
Grading by analysis, although not universally used at present, is no doubt the more perfect method, because the foreign substances contained in the metal can be accurately determined. Grading by fracture is more generally used, although it cannot be considered absolutely perfect, but when done by one who has had years of experience and has trained his eye to discover the different granular constructions and luster of the fractured parts, it is very nearly correct; unless the properties are to be known to an absolute certainty, grading by fracture is sufficiently accurate for all practical purposes.