Chains as ornaments are generally made of brass, bronze and the precious metals. Chains used as ships' cables and for hoisting are almost exclusively made of wrought iron, for the ductility and toughness of wrought iron, together with its excellent welding prop erties, make its use desirable despite its com paratively low tensile strength. The iron used is a specially rolled grade, of high tensile strength and great ductility, the object being to secure a chain which, on the application of a sudden stress —as, for instance, is hen a ship is riding at anchor in a heavy seaway— will stretch and so resist the strain gradually, instead of snapping, as would be liable to happen with material of higher tensile strength but small ductility or power of elongation. The small sizes of coil chain are sometimes made of steel but, in general, such chains are inferior to those made of wrought iron. Simple block chains, multiple block chains and silent chains are usually made of mild steel provided, gen erally, with hardened steel bushings and pins. One or two types of silent chains are equipped with rockerJoints which obviate the necessity of using bushings. Roller chains are made of steel and of malleable iron. Roller chains made of steel are similar in construction to block chains. Those made of malleable iron are generally provided with cast iron rollers. Detachable and pintle chains are made, almost exclusively, of malleable iron because of the peculiar form of the links which makes it economical to cast them, although of late many of the smaller sizes of detachable chain have been made from steel on automatic punching presses. The links of pintle chains are some times provided with case hardened renewable bushings. The pins for joining the links of pintle chains are usually steel.
Coil chains of open, studded or twisted link type are usually hand-made. Many of the smaller sizes — up to ;-inch — are made on automatic machines, while chains above two inches are made with the aid of power presses and steam hammers. Whether made by hand, by auto matic machinery or with the aid of power presses and steam hammers, the same opera tions are involved. The bar from which the links are to be made is first cut up into pieces long enough to make single links; the ends of each of these pieces are next scarfed and bent so that when the link is formed the scarfed ends will come together; the scarfed piece is next formed into the shape of the finished link; the formed link is then drawn through the last link of the finished chain and its ends are welded. When making studded or twisted link chain, the additional operation of placing the stud or twisting the link , is necessary. These operations are generally performed after the link has been welded. The weld is usually located at the end of the link.
In the smaller sizes the whole operation of chain-making by hand is done by a single smith without any helper. The length of completed chain is hung upon a hook or some convenient support near the anvil, and the operation of forging the link proceeds as follows: In his fire the smith will have two or three short rods of the required diameter, and as one is heated to, say, a cherry red, he withdraws it, cuts off the desired length for one link, gives it a couple of blows to form the welding scarf, bends it through, say, about 130 degrees, hooks it into the end of the completed chain, and brings the ends together for welding. He then raises the
link to a welding heat in his fire, places the abutting ends over what is known as the bick iron, gives it a few taps to ensure a good weld, brings over a °doll? (which is hinged at the outer end of his anvil and when brought over registers above the hick- iron), and with half a dozen blows on the dolly, accompanied with a dexterous movement of the link, • the weld is completed and the link smoothed up to a neat finish. The rapidity with which the smiths do this work is very remarkable. Thus, in the case of a 7/16-inch chain, with 30 links to the yard, an expert smith will cut off from the iron bar, scarf, bend up into shape, and weld the links, at the rate of 18 yards in a day of nine working hours, which is two yards per hour, or one link per minute.
In forging heavy chain two helpers are used, the iron is cut to about one-foot lengths, and several of these are being heated in the fire at the same time. The operation is as follows, the various steps succeeding each other with great rapidity: First, the helper to the right of the anvil withdraws the heated piece, drops one end into an eye at the end of the anvil, and bearing down upon the tongs, bends the piece over to an angle of about 45 degrees. The smith then takes it in his tongs, and with a few taps of the sledge it is bent around. It is heated again, passed through the end of the chain by the smith, laid flat on the anvil and the welding scarfs are put on with a few blows of the sledge. The link is now raised to a welding heat, welded by a few blows by the helpers, laid over the bick-iron, the hinged dolly is brought over, and a few rapid blows on the dolly, while the smith turns the link to and fro, serve to bring the weld up to a smooth finish. The link is now laid on edge; a single blow from the sledge brings it into shape, and with a final tap or two of the smith's hammer the link is finished. At this forge as many as 35 links will be added to a 1%-inch chain in one hour, or about one every two minutes.
One type of machine making coil chain winds the bar from which the chain is made upon a mandrel in the form of a spiral much similar to a spring. Each loop of the spiral is then cut apart at an angle of 60 degrees so as to form a scarf, and is welded in a set of dies under a drop hammer operated by a workman. Another type of machinery automatically performs all of the operations, including the welding, taking in a plain round bar and turning out a finished, assembly chain. Weldless chains up to one inch have recently been made with some success by passing a red hot cruciform bar through a series of machines. The first operation con sists of impressing the outer form of the links on the bar. The second operation cuts away the webs which join the links, and the third breaks the links apart and finishes the chain. Coil chain larger than 2-inch can be made en - tirely by hand only at a tremendous expense of severe labor and time and it is virtually im practicable to attempt to make such chains without the use of power presses for forming the links and steam hammers for welding them. Chains smaller than 2-inch which are made by hand are generally superior to those made by machinery, while beyond 2-inch machine-made chains, after proper annealing, are by far both stronger and more uniform.