Types Of Riveted Joints and their Applications-Machine Design
Often small machine components are joined together to form a larger machine part. Design of joints is as important as that of machine components because a weak joint may spoil the utility of a carefully designed machine part. Mechanical joints are broadly classified into two classes viz., non-permanent joints and permanent joints. Non-permanent joints can be assembled and dissembled without damaging the components. Examples of such joints are threaded fasteners (like screw-joints), keys and couplings etc.
Permanent joints cannot be dissembled without damaging the components. These joints can be of two kinds depending upon the nature of force that holds the two parts. The force can be of mechanical origin, for example, riveted joints, joints formed by press or interference fit etc, where two components are joined by applying mechanical force. The components can also be joined by molecular force, for example, welded joints, brazed joints, joints with adhesives etc. Not until long ago riveted joints were very often used to join structural members permanently. However, significant improvement in welding and bolted joints has curtained the use of these joints. Even then, rivets are used in structures, ship body, bridge, tanks and shells, where high joint strength is required.
Rivets and riveting
A Rivet is a short cylindrical rod having a head and a tapered tail. The main body of the rivet is called shank.
|Rivets and its Parts|
According to Indian standard specifications rivet heads are of various types. Rivets heads for general purposes are specified by Indian standards IS: 2155-1982 (below 12 mm diameter) and IS: 1929-1982 (from 12 mm to 48 mm diameter). Rivet heads used for boiler works are specified by IS: 1928-1978. To get dimensions of the heads see any machine design handbook.
Types of rivet joints
Riveted joints are mainly of two types
1. Lap joints
2. Butt joints
The plates that are to be joined are brought face to face such that an overlap exists, as shown in figure Rivets are inserted on the overlapping portion. Single or multiple rows of rivets are used to give strength to the joint. Depending upon the number of rows the riveted joints may be classified as single riveted lap joint, double or triple riveted lap joint etc. When multiple joints are used, the arrangement of rivets between two neighbouring rows may be of two kinds. In chain riveting the adjacent rows have rivets in the same transverse line. In zig-zag riveting, on the other hand, the adjacent rows of rivets are staggered.
In this type of joint, the plates are brought to each other without forming any overlap. Riveted joints are formed between each of the plates and one or two cover plates. Depending upon the number of cover plates the butt joints may be single strap or double strap butt joints. A single strap butt joint is shown in figure Like lap joints, the arrangement of the rivets may be of various kinds, namely, single row, double or triple chain or zigzag.
The classification of riveted joints is based on following :
(a) According to purpose,
(b) According to position of plates connected, and
(c) According to arrangement of rivets.
According to purpose the riveted joints are classified as :
In these joints strength is the only criterion. Joints in engineering structure such as beams, trusses and machine frames are strong joints.
These joints provide strength as well as are leak proof against low pressures. Joints in reservoirs, containers and tanks fall under this group.
Strong Tight Joints
These are joints applied in boilers and pressure vessels and ensure both strength and leak proofness.
|Types Of Riveted Joints and their Applications-Machine Design|
- The riveted joints are classified as (i) lap joint and (ii) butt joint according to position of plates. In a lap joint the edges of plates are simply laid over each other and riveted.
- Figures (a) and (d) show lap joints. If we pull the plates by application of tensile forces, they do not fall in the same line and hence cause the rivets and plates to bend. Plates placed end-to-end and jointed through cover plates form single cover butt joint.
- Such joints are shown in Figures (b) and (e). You can see that pulling plates apart by colinear tensile forces may still cause bending of rivets.
- Figures (c) and (f) show the butting plates covered by two straps and then riveted. Such joints are called double cover butt joint. Plate bending and rivet bending are eliminated.
- According to arrangement of rivets, the joints are called single riveted, (Figures (a), (b) and (c)) It may be noted that in a single riveted lap joint there is only one row of rivets passing through both plates while in a single riveted butt joint either of single cover or double cover type one row of rivets will pass through each of the plates. Similarly as shown in Figures (d) and (e) when two rows of rivets pass through both plates of lap joint it is called double riveted lap joint and two rows of rivets pass through each of butting plates the joint is a double riveted single cover butt joint. A double riveted double cover butt joint is shown in Figure (f).
- The arrangement of rivets in Figure (d) can be described that in both the rows the rivets are opposite to each other while in Figure (e) the rivets in the adjacent rows are staggered. The joint in Figure (d) is said to be chain riveted while that in
- Figure (e) is zig-zag riveted joint. In zig-zag riveting the rivet in one row is placed at the middle level of the two rivets in the adjacent row.