CORRUGATED IRON (Lat. ruga, a wrinkle). Common sheet-iron, and what is improperly called "galvanized iron" (i.e., sheet-iron coated with zinc by immersion in a bath of the fused metal), have of late been made available for ninny useful pur poses, by virtue of the great additional strength imparted to the sheets by corruga tion, which is merely an application to metallic substances of the old contrivance of "goffering or crimping," by means of which the frills of the olden time were made to keep their shape.
The sheets of metal are passed between rollers, the surfaces of which are formed into rounded grooves and ridges, the ridges of one roller filling the grooves of the other. The metal in passing between these is compressed into a waving form, or corrugated. It will be easily understood that a piece of shect-metal, of given size and thickness, if rolled up to form a tube, will resist a much greater bending strain than when fiat. Now the curves of the corrugation may be regarded as a series of half-tubes, and the additional strength is due tothe application of the same principle.
See STRENGTII OF MATERIALS. Walls and roofs of temporary buildings are now exten sively made of this material. Railway sheds, emigrants' houses, temporary churches, store-rooms, and sheds for dock-yards, etc., are among the common applications. Mr. Francis, of New York, has applied the principle to the construction of light boats, the strength of which, and their power of resisting violent blows, such as boats are subject to on landing through a surge, is said to be remarkably great. Ou this account, they are proposed to be used for life-boats, Ships' boats, etc. They are made by stamping the metal in enormous dies, of the shape and size of the boat, and grooved for the required corrugations. Small boats thus constructed require no internal bracings, the requisite rigidity and strength being given entirely by the corrugations.