THE IRONFOUNDER.
FOUNDRY.
FOUNDRY.
Having already described the various operations of the trades employed in building and fitting a house, we willsay something of the manufacture of those cast iron columns, girders, gratings, balconies, pipes, gutters, air traps, coal plates, stoves, and other articles which are so necessary to the Builder before his work can be completed. All these, as well as a great variety of other goods made in black or bronze iron, such as gates, bridges, pieces of furniture (like umbrella stands), iron taps, and even pots and frying pans, are made at theIron Foundry.
Iron is a metal of a bluish gray colour; but in its pure state it looks almost white when polished, and has a brilliant lustre, while when it is broken the broken portion looks dull and fibrous. It is the hardest of all the malleable and ductile metals, and the most tenacious of all metals, an iron wire of ⅟₃₆th of an inch in diameter bearing a weight of 60 pounds.
In the pure state it requires the strongest heat of what is called a wind furnace to melt it.
Iron may be called the most precious of all metals; it is certainly the most beneficial to man, and its uses are innumerable; indeed, there is not a branch of human industry that could well afford to dispense with its aid and services; nearly all the tools, implements, instruments, and engines used by man are wholly or partly made of it, and we could better afford to give up all the other metals than to part with this, which is the most useful.
Iron is used in two different states, ascast ironandwrought iron, the differences between them depending on the proportion of carbon combined with the metal, cast iron containing the most and wrought iron the least.
For the production of wrought iron in the ordinary way, two distinct sets of processes are required; first the extraction of the metal from the “ore” that is brought upfrom the mine, which metal is cast iron; and secondly the conversion of this cast iron into malleable or bar iron, by remelting,puddling, andforging. Bar iron is turned into steel by placing it in contact with charcoal in a peculiar kind of furnace.
When the ore is taken from the mine it is first burnt or calcined, and then removed to a blast furnace to be smelted. These blast furnaces are generally built of brick, and look like small towers. The ore is mixed with limestone, which causes it to melt more easily, and the fire is lighted with pit coal or coke. The melted metal sinks to the bottom of the furnace in consequence of its weight, while the limestone and dross float on the top, and are allowed to run off when they cool into a mass of what is called “slag.”
The melted metal is run off from the bottom of the furnace, either into moulds for some sort of castings, or into a large furrow made in a bed of sand. This large furrow has several smaller furrows on each side of it, and has received the name of the “sow;” the smaller furrows being called “pigs;”—and the iron when it is formed in this shape to be afterwards made malleable is called “pig iron.”
The pig iron is taken to other and smaller furnaces called puddling furnaces, the bottoms of which are lined with clay mixed with the slag just mentioned, and forming a substance which the puddlers call “bull-dog,” though it would be difficult to discover why it received that name.
About four hundred weight of the pigs is placed in the furnace, and as it melts the puddler stands at the furnace mouth with a longiron rodbent at the end, and stirs it about, until it comes to resemble several great balls of iron paste. These balls are removed, and fall into iron truckspushed along a small railway by boys, who wheel them at once to the “shingling hammer,” an immensely powerful hammer worked by steam, and this beats the iron into small square bars called “blooms.”
The blooms are next carried to the rolling mill, which is a pair of great rollers cut into grooves of various sizes, and between these grooves the bars are squeezed, as the rollers turn round, until they become much longer and narrower, when they are known as “forged bars.”
Some of the rolling mills, however, are plain cylinders without grooves, and when a slab of white-hot iron is placed between these it comes out from the pressure in a great broad sheet of metal.
These operations require great bodily strength as well as considerable skill on the part of the workmen, who are obliged to seize the heated metal with long tongs, and to catch it in the same way as it comes out from the mill.
Casting Ladle.
Casting Ladle.
The iron which is intended for castings is melted in a “cupola furnace,” so called on account of the dome-like shape in which it is built, which has something to do with the more perfect heating of the metal. When the iron is completely melted so that it will run freely, the lower portion of the furnace is opened, and the white-hot streamis received in thecasting ladle, or, where it has to be carried for some distance, and the casting is large, in great iron pails carried in a sort of frame by two men. From the casting ladle it is at once poured into themould.
Mould. Small Casting Ladle.
Mould. Small Casting Ladle.
The mould is a sort of iron box filled with a peculiar sort of sand, into which a wooden pattern of the intended casting is pressed, and the sand firmly rammed down and made solid. There are, in fact, two boxes of sand, each of which is impressed with one half of the thickness of the required casting, so that when they are brought together, and firmly fastened with the pins, as shown in the picture, the patterns which have been taken out have left a half of the impression in each box, each corresponding exactly to the other. A hole in the box receives the melted metal, for which a channel has been left in the sand, that it may freely run into the hollows left by the pattern, and completely fill them; then, when it has sufficiently cooled, the casting is removed, and when the rough edges have been removed, and the irregularities trimmed off, it is ready for use, and may be fitted to its other parts, which have perhaps been separately cast, as in the case of garden seats, fenders, chandeliers, umbrella stands, or ornamental girders and columns.
Furnace Iron. Brush. Trowel. Bellows. Foot Rule. Level. Shovel. Spatera. Hammer. Mould Weight. Rammer.
Furnace Iron. Brush. Trowel. Bellows. Foot Rule. Level. Shovel. Spatera. Hammer. Mould Weight. Rammer.
We have only described solid castings, but as ornamental iron work is generally made hollow, this has to be cast in rather a different way, though the only difference is thatwhat are called “cores” are used. These cores are in fact solid metal patterns made a little smaller than the hollow left by the real pattern, and allowed to remain in the mould. The melted iron then flows between the surface of the core and the surface of the mould, and the casting is hollow, so that when the core is removed the metal is only the thickness of the space left between the two surfaces. You will see what is meant by placing a small teacup inside a larger one, and then pouring water between them.
The tools used by the Ironfounder are not very numerous: the casting ladles and mould have already been mentioned; the uses of theshoveland themould weight, therammer, and thefurnace ironneed no description.
The designers, and pattern makers, and the mould maker have the most important duties, and the latter will have to use a smalltroweland aspaterafor arranging his sand and loam, alevelthat it may be perfectly true, and abrushand apair of bellowsfor removing any particles of grit from the surface of the channels where the pattern has been impressed.
Almost all irons are improved by admixture with others, and, therefore, when superior castings are required they should not be run direct from the smelting furnace, but the metal should be remelted in a cupola furnace, which gives the opportunity of suiting the quality of the iron to its intended use. Thus, for delicate ornamental work, a soft and very fluid iron will be required, whilst for girders and castings exposed to cross strain the metal will require to be harder and more tenacious. For bed-plates and castings which have merely to sustain a compressing force, the chief point to be attended to is the hardness of the metal.
Castings should be allowed to remain in the sand untilcool, as the quality of the metal is greatly injured by the rapid and irregular cooling which takes place from exposure to air if removed from the moulds in a red hot state, which is sometimes done in small foundries to economise room.