Introduction

Bridges, boilers, tanks, etc., are made by using riveted joints (Plate 14.1). These are permanent joints and cannot be separated unless and until the rivet is destroyed. Welding is replacing riveted joints slowly, but where welding cannot be done, riveting is still being done.

Rivets

A rivet has a cylindrical part (called shank) and an integral head at one end. Figure 14.1 shows the shape of a rivet. The length of a rivet is about 3 to 4 times the shank diameter and is measured from the bottom of the head. The tail may slightly taper for easy insertion in the hole.

Rivets are available in many diameters. The shank diameter d of the rivet to be used for the joint depends on the thickness t of two plates, which are generally of equal thickness. Small rivets are used for sheet metal and light structural work. These are available from 3 to 10 mm shank diameter sizes. Large size rivets, from 15 to 48 mm shank diameter, are used in heavy steel structures. Type of joint and thickness of the plates decide the length of the rivet needed.

Small rivets are made by cold heading and then heat-treated to remove the work stresses due to cold heading process. Large sized rivets are made by hot forging and then cooled slowly to keep them soft.

For boiler construction or applications, where a leak proof joint is required, the edges are made from 90° to 80° by hammering with a fullering tool and the process is called fullering. Rivet heads can also be caulked [Figure 14.2 (e)] to make leak proof joint.