Riveting is the means by which " first-class "wrought-iron and steel framings are connected together, and especially girders built up of several members, the common class of work being connected by bolts in lieu of rivets. It can be done by hand or by machinery, and consists of circular tapered wrought-iron pins, as it were, similar to fig. 420, with heads of various patterns, which are driven when hot into holes concentrically made in the two pieces of wrought-iron or steel to be connected together. The rivets should be made of the very best (B B B) wrought-iron, the Staffordshire and Yorkshire qualities being the most suitable, as they are capable of withstanding an ultimate shearing strain (to which rivets are subjected) of about 25 tons per square inch, with a contraction of area of from 40 to 50 per cent., and elongation of 20 per cent, before a permanent set takes place.
Good rivet-iron should admit of being doubled up, when cold, without showing any signs of fracture; and the heads, when hot, should be capable of withstanding hammering down to almost a flattened thin surface before cracking at the edges, and they should allow of a hole being punched through them of nearly their own diameter without cracking round the hole.
Inasmuch as the entire strength, and consequently the successful adaptation to its work, of the structure or girder often depends wholly at certain points on these rivets - which have to transmit unaided a complete series of great and heavy strains from one plate or member to another, which they are connecting together - it is absolutely necessary that the best rivet-iron should always be used, and fully up to the specification on which the calculations for the girder or framing have been based; and it is also necessary that the operation of riveting should be performed in the best, soundest, and most workmanlike manner.
The method of proceeding in " hand riveting " is as follows: A gang, of two boys and three men, is set on to each job, the boys having to heat the rivets in a portable smith's forge adjoining the work, and to hand them up in buckets, when hot, to one of the men who stands under the plates to be connected up. This single-handed man - having previously knocked out of the rivet-holes a punch with which he has tested them for position, so as to see that the holes in the plates coincide properly and are concentric - pushes up the red-hot rivet through the holes, and places his hammer on its head underneath. On the pin of the rivet coming through the hole, and when the man underneath has secured his iron to its head, one of the two men who are at the top of the plates then hammers the tail of the rivet down, so that it fills the holes completely. It is to be noted, that it cannot be driven downwards again through the plates, because of the man's iron below; and, as the plates should previously have been hammered close together, the metal shank cannot be squeezed between the plates, and so keep them apart afterwards.
This being done, the second man at the top then places an iron die over the red-hot iron, which has now been compressed within the holes, and the other hammers it down, so that the die forms the upper end or other head of the rivet The rivet-heads may be of various patterns, as hereinafter explained. The whole of this process only lasts a few seconds, and on the iron cooling it contracts and pulls the plates together by means of the ends of the pin of the rivet, as the sketches will explain.