CHAINS AND CHAIN MAKING. A chain consists of a series of similar links which either interlock or are joined to each other so that they form a continuous flexible metal line. The chain is one of the most familiar as well as one of the most useful of mechanical devices. Its origin is undoubtedly very ancient; remnants of excellent Roman chains may be found in the museums of the world. The uses of chain are many. The three principal uses are for the hoisting of materials, for the transmission of power and for the conveying of materials. Chains are also used as surveyors' measures, as ornaments, as restraints, as elevator counterweights, for preventing the slipping of motor car wheel and in many other ways too numerous to mention.
All chains may be divided into two gen eral classes which receive their names from the fundamental forms of the links. Coil chains consist of series of links, generally oval in shape, which interlock by passing through one another. Block chains consist, fundamentally, of flat bars which are joined together by cylin drical pins so that the bars are free to articulate about the pins. Coil chains are sometimes loosely called crane chains from the fact that they are generally used in connection with cranes. Block chains are sometimes called link chains, pitch chains and sprocket chains. Coil chains may be subdivided into open link chains, studded link chains, twisted link chains, safety chains, ladder chains and jack chains, while block chains may be subdivided into simple block chains, multiple block (leaf) chains, silent chains, detachable chains and pintle chains. Open link chains are composed of series of interlocking oval links. The links of such chains are generally made from round bars, the size of the chain being taken as the diameter of the bar from which the links are made. The most common example of an open link chain is the ordinary crane hoisting chain. The links of studded link chains are similar to those of open link chain, being provided, in ad dition, with studs or braces across the centres of the links. These studs strengthen the links,
enabling such chains to safely carry loads 20 to 25 per cent in excess of those which may be safely carried by open link chains of the same dimensions. Twisted link chains are made up of links similar to those of open link chains but which have been twisted through an angle of 90 degrees. Safety, ladder and jack chains are of minor importance. The first is made up of small flat links which are stamped from sheet metal; the latter two consist of twisted interlocking wire links. Simple block chains consist of single series of flat bars, each hav ing round holes near its ends, which are joined togethei by means of pins, rivets or bolts which pass through these holes. The ordinary bicycle chain is, perhaps, the most common example of such a chain. Multiple block chains, or leaf chains, consist of series of flat bars, similar to those which compose simple block chains, which are placed side by side upon the same pins. A chain of this type has the gen eral appearance of a number of bicycle chains joined side by side. Silent chains are of the multiple block type, being made up of series of flat bars which have profiles on one side much like gear teeth in appearance. Chains of this type operate over sprocket wheels which look very much like spur gears. Roller chains are essentially block chains in which the flat bars have been separated to allow of the introduc tion of a roller between them. Detachable chains are composed of rectangular links which interlock by sliding over one another. This interlocking of the links by sliding over one another eliminates the necessity of using pins for joining the links. Pintle chains are made up of U-shaped links which have barrels at one end and which are joined by means of pins in the form of either rivets or bolts. Chains are generally made of wrought iron, steel or malleable iron. When iron or steel may be subject to excessive corrosion, brass, bronze or some other corrosion-resisting material is used.