Ladder, jack and similar type weldless chains are made by machines which automatic ally cut off the wire, form the links, interlock them and twist or bend the ends of the links together. Chains of this type can only be made in small sizes and can be used for only unimportant work such as for horse halters, fences, dog chains and the transmission of hand power. Chains made of precious metal are generally made by machinery in a manner analogous to that used in making iron coil chains, with the exception that the links are either left open or are closed by brazing instead of welding. Very often the links of such chains are stamped and brazed by hand. The operations involved in the manufacture of block chains are few and simple. The bars from which simple and multiple block chains, silent chains and steel roller chains are made are stamped from metal bars of the required width and thickness, the holes for the pins being gen erally punched while the links are being stamped. In the case of extremely accurate chains, the holes are drilled and the links are finished and polished. The pins of chains of this type are either drop forged, cold rolled or machine turned. The rollers of roller chains intended for light duty are made of pipe or tubing cut to proper length. For severe duty it is necessary to use rollers which are made by boring out solid shafting. Chains of these types are assembled by hand, usually with the assistance of a small power hammer for form inAthe rivet heads. The links of malleable iron detachable and pintle chains are cast and annealed in the usual manner. After annealing, the links are thoroughly cleaned by tumbling and are then assembled to form the finished chain. Some of the smaller sizes of detachable chain are assembled by machines, all of the larger sizes being assembled by hand. All pintle chains are hand assembled with the aid, when the chain pins are riveted, of small power hammers for upsetting the heads of the rivets. All chains which are to be used for important work are tested after manufacture in order to eliminate the defective links. This is done by subjecting them to test loads well above those under which they are to work and cutting out all links which exhibit defects. Chains which operate over sprocket wheels are also tested for accuracy of pitch and are well oiled and well limbered up before being shipped.
Chains used to hoist materials are generally of the coil type — open link chains being most commonly used. In unusual cases and under peculiar conditions block chains have been used for this work, one notable though disastrous instance being the attempted hoisting, in 1916, of the centre span of the Quebec bridge.
Chains used for ship's cables are of either the open link or the studded link type. Chains for this duty have been made from bars as large as four inches in diameter. Chains for the transmission of power are generally of the simple block, multiple block, roller, silent or pintle types. For low speeds, simple and multi ple block and pintle chains are most satis factory; for medium speeds, roller chains are used; for high speeds, silent chains are usually employed. Small sized coil chains are fre quently used for the transmission of hand power. Chains for the conveying of materials are generally of the simple block, roller, de tachable or pintle type, although long pitch, open link coil chains were formerly quite exten sively and are now sometimes used for this work.. Chains which convey materials are gen erally equipped with attachments which serve to carry buckets, flights, aprons, etc., which actually do the conveying. Block chains for the conveying of materials are made with pins up to three inches diameter and in pitches up to three feet.
Surveyor's chains are open link chains of peculiar construction. The links are relatively long and the ends, instead of being welded, are joined by means of small circular links. A consists of 100 links, which aggregate 100 feet in the United States and 66 feet in England.
Although each coil chain link consists of two thicknesses of bar, it must not • be presumed that a chain possesses double the strength of a single bar; actually there is a reduction of three-tenths in the strength, due to the forma tion into links, so that the chain has but about seven-tenths of the united strength of two bars of the same diameter of iron. Moreover, as the strength per square inch of a heavy bar is not so great as that of a smaller diameter iron, there is further reduction to be made on this account.
The chain industry is not confined to any one particular country or any one locality. The complete absence of statistics makes it impos sible to even approximate its extent.
Technical data on chains may be found in various standard works on machine design and in the following works :