Generally speaking,, all chains over one inch in size are made by hand, but the great bulk of the chains of smaller sizes are made by machinery. Alachine-made iron chains are of two kinds, known as welded chains and weldless chains. In making welded chains by machine the rod of iron is first run through a machine called a winder, which winds it around a mandrel and turns it out in the form of a long spiral spring. This rod is then cut by a machine so that each twist or spiral is severed from the next and the stock is in the form of rings whose open ends only need to be welded together to form comph.te closed links. The welding is done by heating the ring and placing it in dies, under the blows of a tripdminmer operated by the work man's foot, form it into shape and weld together the open ends. The welding is done link by link as in the case of hand-made chains.
These small sizes of machine-welded chains are often made with twisted links, but are never made in the form of stud chains. WcIdless machine-made chains are manufactured by auto matic machinery which takes the rolled iron, cuts it into lengths, forms these lengths into links, and connects or couples the links into com pleted chains. in weldless chains the links arc formed by twisting or locking the unconnected ends of the short lengths of rod. There are numerous forms of such connections and certain advantages are claimed fur each form. Chains of this construction are made only in the small sizes which are used for horse-halters, cow-ties, dog-chain:, fence-chains, sash-eha curtain chains. picture-chains, harness-chains, and simi lar purposes. For many of these purposes brass, bronze, and composition metals are used instead of iron, but the process of manufacturing the chain is otherwise unchanged. With the single exception of the stud chain. the chains so far de scribed have each link composed of a single piece of metal bent to form and welded, twisted into a closed ring.
Chains for transmitting power arc of an en tirely different construction. In these each link made of several pieces of metal connected by rivets, bolts. or stud screws, and is so formed as to engage with the teeth of a sprocket wheel. The bicycle chain is an excellent example of this variety of chains, but there are several forms in use which are even more perfect. Chains of this kind are made by assembling by hand the several parts composing each link and connecting them together; the separate parts are themselves cut, stamped. turned, threaded or otherwise formed by machinery designed especially for the pur pose.
Wateh-ehains, neck-chains, and other chains made of precious metal for ornament form a class by themselves. Some of the larger and heavier chains of this class which are made in the simple forms common to the chains of brass and iron which have been described. are made by methods closely corresponding to those used in making iron and brass chains. The smaller sizes of wire chains are made by machinery with twisted and locked links, others are formed by methods analogous to that adopted in producing maehine-made welded chains of iron, the links being closed by brazing instead of by welding. In still other forms the links are stamped and cut from metal plate and are assembled and brazed together by hand.
The strength of chains is a very important matter in certain uses to which chains are put. For example. the safety of an anchored ship and the lives of its crew may often depend upon the strength of its chain cable. For this reason the British Admiralty and the organizations corre sponding to this body which exist in other coun tries require all chain cable to undergo severe tests before it is used on shipboard. Similar tests are required by railways, builders of cranes and dredges, and other large users of chain. The size of chains is defined by the diameter of the bar of which the links are made; thus. a one-inch chain is one whose links are made by bars one inch in diameter. According to tests made by the United states Testing Board, "with proper material and construction the ultimate resistance of chains may be expected to vary from 155 per cent. to 170 per cent. of that of the bar used in making the links and to show an average of about 103 per cent." Thi: conclusion refers only to hand-welded chain cable. The Peimsylvania Railroad requires its crane chain to stand without giving way a pull of 70,000 pounds. and not to break under a load of 110.000 pounds. The British Admiralty re quires a 2-inch stud chain cable to withstand a proof load of 72 tons before it. is used. These figures are selected at random for the purpose of illustration. For a statement, of the test re quirements of the Pennsylvania Railroad, the British Admiralty, and the United States Test ing Board, see Kent, Mechanical Engineer's Pocket Book (New York, 1901 ). Special litera ture on the manufacture of chains is very scarce, and such as there is will be found scattered through the engineering papers and the proceed ings of the various engineering societies.