Riveted Joint

Riveted Joint is formed when plate, bar, angle, or T- irons, & c, are united by rivets usually made out of a tough and ductile iron, either scrap or a quality specially manufactured for them and known as rivet-iron, the tenacity of which ought not to be less than 22 tons per square inch of section. This joint is almost universal in wrought iron structures. Girders are formed of plates, bars, angles, etc, riveted together either directly or with joint and gusset plates, and with bent, cranked, and joggled stiffeners. Simple iron roof trusses are made by riveting the heads of the principals to a third piece or joint plate and bolting thereto the jaws of the suspending rod, and where the span is small, riveting the tie-rod also to the other members. In larger spans the members are built up with bars, angle, or T- irons, etc, riveted back to back and to one another, bolts being only used by rights for tensile strains, though they are not unfrequently put in positions where they are exposed to shearing. Angle iron cleats are much used for supporting purlins, and these should be riveted on before raising. A rivet consists of head and shank, or spindle, or tail, sufficiently long to pass through the parts to be joined and to be hammered down to a protuberance as large as the head. Good rivets when cold should stand doubling without showing a flaw, and the rivet holes ought to be spaced out with templets and be accurately bored so that they may exactly coincide when the pieces are put together. In hand riveting, a drift having been forced in and out again through opposite holes, the rivet, whose diameter when cold is about eleven-twelfths of the aperture's, is inserted red-hot from the inside and a hammer immediately pressed against it, unless it can be laid upon an anvil or something handy and suitable. The plates are brought together by hammering round the rivet, which is clinched with a blow and finished off to a convex end, if so desired, with a riveting set having the proper concavity, whilst at the same time the shank is thickened out so as to leave no part of the hole empty. Twenty minutes is the longest time 1 in. or ⅞ in. rivets should be in the fire, and all showing signs of burning must be rejected. Loose rivets are detected by tapping, but the detection is not so certain when the holes are punched. The operation of riveting is now frequently carried out by a steam or hrydraulic machine where it can be easily applied, but not in awkward situations. Sometimes cold rivets are used instead of hot where it would be impracticable to manipulate the latter. Rivets have different names according to the shape imparted to their terminations. Fig. 89 represents a button or cup-shaped snap rivet, or one to which a round and symmetrical shape has been communicated before cooling by means of a tool called a snap, having a hollow face of the proper concavity. Fig. 90 shows a hammered or staff rivet; and Fig. 91 a countersunk one, useful in obtaining close bearing surfaces. The heads also vary both in name and shape, but mostly in name, being styled either flat, pan, cheese, button, cup, or rose shaped. As a rule, their diameter equals about two thicknesses of plate when less than in. thick, but when that or more it equals only 1 its thickness. The height of head should not be more than half the diameter of shank, and the diameter of head should about equal two diameters of shank, and the length of the shank exclusive of head before clinching equals the sum of the thickness of the plates to be joined, plus a length equal to about 1 the diameter of the rivet for the tail or point. The contraction of the rivets in cooling produces a grip which adds considerable frictional force to the strength of the joint, which, however, in double and single riveting, owing to the abstraction of metal for the holes, is usually from 20 to more than 30 per cent, less than the strength of the plate, which itself is sometimes reduced nearly 20 per cent. through clumsy punching and rough usage during the operation of riveting. Since it is impossible to paint rivets and rivet-holes and joints where the metal is in contact, oxidation is assisted in exposed structures at these parts by the incessant vibration occasioned by wind and moving loads, and any protective film, such, for instance, as that of black oxide produced by Barff's process, would be lost in forcing rivets into their holes. In practice, a riveted joint fails either by the crushing of the plates between the rivets and edge, which rarely ever occurs, or by the tearing of the plate along the line of rivets between the holes, or by the shearing of the rivets; and these three modes of fracture respectively depend on the thicknesses of plate and rivet, the pitch, of the rivets and thickness of plate, and the rivet's thickness. The quality of the iron used, even if occasionally too hard, is scarcely ever the cause of disaster, but the same cannot be averred as regards the quality of workmanship. Various kinds of riveted joint are noticed under their specific names.

Riveted Joint 89

Fig. 88.

Riveted Joint 90

Fig. 89.

Riveted Joint 91

Fig. 90.

Riveted Joint 92

Fig. 91.