UNIT-2

Riveted Joints, Welded Joints and Shaft

Dr. Nitin Kumar Waghmare

Associate Professor
RIVETED JOINTS:
The joints used in mechanical assemblies are
classified into two groups—permanent and
separable.
Permanent joints are those joints which cannot be
disassembled without damaging the assembled
parts. Riveted and welded joints are permanent
joints. Separable joints are those joints which permit
disassembly and reassembly without damaging the
assembled parts.
Bolted joints, cotter joints and splined connections
are the examples of separable joints.
A rivet is specified by the shank diameter of the rivet, e.g., a 20
mm rivet means a rivet having 20 mm as the shank diameter. The
standard sizes of rivets are 12, 14, 16, 18, 20, 22, 24, 27, 30,
33,36, 39, 42 and 48 mm.
Riveting methods are also classified on the basis of temperature
of the shank, viz., hot riveting and cold riveting. The difference
between hot and cold riveting is as follows:

(i)In hot riveting, the end of the rivet shank is heated to about
1000° to 1100°C till it becomes bright red and then the blows are
applied by a hammer. In cold riveting, there is no such heating.
(ii) In hot riveting, when the rivet cools, the reduction in the
length of the shank is prevented by the heads resting against
the connected members. Therefore, the shank portion of the rivet
is subjected to tensile stress while the connected parts are
compressed. This is illustrated in Fig.
There are two methods of riveting—hand riveting and machine
riveting. In hand riveting, a die is placed on the protruding end of
the shank as shown in Fig. 8.44(c) and blows are applied by a
hammer. In machine riveting, the die is a part of the hammer,
which is operated by pneumatic, hydraulic or steam pressure.

Riveting methods are also classified on the basis of temperature

of the shank, viz., hot riveting and cold riveting. The difference
between hot and cold riveting is as follows:
(i)In hot riveting, the shank of the rivet is subjected to tensile
stress. In cold riveting, the shank is mainly subjected to shear
stress
.(ii) Cold riveting is applicable for steel rivets up to 8 to 10 mm
diameter and rivets made of non-ferrous metals like brass, copper
and aluminium alloys.
TYPES OF RIVET HEADS
There are number of shapes for the head of the rivet. The most
popular type of rivet head is snap head as shown in Fig. 8.46(a).
It is also called button head. Riveted joint with a snap head has
strength and fluid tightness. It is used in boilers, pressure vessels
and general engineering applications.
Pan head rivet, illustrated in Fig. 8.46(b), consists of frustum of
cone attached to the shank. It is also called cone head rivet. Pan
head rivets are mainly used in boilers and ship hulls and are
ideally suited for corrosive atmosphere.
Countersunk head rivets are used in structural work and ship
hulls below the waterline.
The flat head rivet is shown in Fig. 8.46(d). The height of the
protruding head is less than that of snap head rivet or pan head
rivet.
A combination of countersunk head and snap head
is shown in Fig. 8.46(e). It is also called half countersunk head.
Depending upon the application, there is slight variation in
proportions of rivet heads. There are various standards which
give dimensions of various types of rivets.
The desirable properties of rivets are as follows:
(i) The rivet should be sound, free from cracks, flaws, burrs,
seams, pits and other defects.
(ii) The head of rivet should be concentric with the axis of the
shank.
(iii) The end of rivet should be square with respect to the axis.
TYPES OF RIVETED JOINTS:
Riveted joints used for joining the plates are classified into two groups—lap
joint and butt joint. Lap joint consists of two overlapping plates,
which are held together by one or more rows of rivets.
Depending upon the number of rows, the lap joints are further classified
into single-riveted lap joint, double-riveted lap joint or triple riveted lap joint.
TYPES OF RIVETED JOINTS:
The construction of a butt joint is shown in Fig. 8.51. It consists of two plates,
which are kept in alignment against each other in the same plane and
a strap or cover plate is placed over these plates and riveted to each plate.
Depending upon the number of rows of rivets in each plate, the butt joints are
classified as single-row butt joint and double-row butt joint.
Depending upon the number of straps, the butt joints are also classified into
single-strap butt joint and double-strap butt joint
RIVET MATERIALS :
Rivets used in most of the applications are made of mild steel. There are two
varieties of steel rivet bars—hot rolled steel rivet bar and high-tensile steel
rivet bar. Their chemical composition is as follows:
carbon = 0.23% (max), sulphur = 0.05% (max),phosphorus = 0.05% (max)
TYPES OF FAILURE :
The types of failure in riveted joints are illustrated in Fig. 8.54.
According to conventional theory, the failure of the riveted joint
may occur in any one or more of the following ways:
(i) shear failure of the rivet;
(ii) tensile failure of the plate between two consecutive rivets;
(iii) crushing failure of the plate;
(iv) shear failure of the plate in the margin area; and
(v) tearing of the plate in the margin area.
Based upon the above-mentioned criteria of failure, strength
equations are written for riveted joints.
EFFICIENCY OF JOINT :
The efficiency of the riveted joint is defined as the ratio of the
strength of riveted joint to the strength of unriveted solid plate.
The strength of the riveted joint is the lowest value of Ps, Pt and
Pc determined from Eqs (8.35) to (8.38). The strength of solid
plate of width, equal to the pitch p and thickness t,
subjected to tensile stress σt is given by,
CAULKING AND FULLERING :
 In applications like pressure vessels and boilers, the riveted joint
should be leak proof and fluid tight.
 Caulking and fullering processes are used to obtain such leak
proof riveted joints.
 The caulking process is applied to the edges of plates in a lap
joint and the edges of strap plate in a butt joint. These edges are
first beveled to approximately 70° to 75° and the caulking tool
is hammered on the edge as shown in Fig. 8.58(a).
 The caulking is done either by hand hammer or by the use of
pneumatic or hydraulic hammer. The head of the rivet is also
hammered down with the caulking tool.
 Caulking cannot be applied to plates with less than 6 mm
thickness.
Example 1 A brake band attached to the hinge by means of a riveted
joint is shown in Fig. 8.59. Determine the size of the rivets needed
for the load of 10 kN. Also, determine the width of the band. The
permissible stresses for the band and rivets in tension, shear and
compression are 80, 60 and 120 N/mm2 respectively. Assume,
margin (m) = 1.5d
transverse pitch (pt) = p
Find the pitch of the rivets.

Solution
Given P = 10 kN t = 3 mm
σt = 80 N/mm2
t = 60 N/mm2
σc = 120 N/mm2
Example 2 Two flat plates subjected to a tensile force P are connected together by
means of double-strap butt joint as shown in Fig. 8.60. The force P is 250 kN and the
width of the plate w is 200 mm. The rivets and plates are made of the same steel and
the permissible stresses in tension, compression and shear are 70, 100 and 60 N/mm2
respectively. Calculate:
(i) the diameter of the rivets;
(ii) the thickness of the plates;
(iii) the dimensions of the seam, viz., p, pt and m; and
(iv) the efficiency of the joint.
LONGITUDINAL BUTT JOINT FOR BOILER SHELL

• There are two types of riveted joints in a cylindrical boiler shell. They are
called longitudinal butt joint and circumferential lap joint.
• The plate of the boiler shell is bent to form the ring and the two edges of
the plate are joined by a longitudinal butt joint.
• This longitudinal joint is usually a double-strap triple riveted butt joint. The
longitudinal joint makes a ring from the steel plate.
• The circumferential joint is used to get the required length of the boiler shell
by connecting one ring to another.
• For this purpose, one ring is kept overlapping over the adjacent ring and the
two rings are joined by a circumferential lap joint.
• Boiler joints are subjected to steam pressure. They should withstand the steam
pressure and also prevent leakage.
• Indian Boiler Regulations are highly exacting and mandatory.
LONGITUDINAL BUTT JOINT FOR BOILER SHELL

• The following procedure is adopted for the design of a longitudinal butt joint
for the boiler shell as illustrated in Fig..
LONGITUDINAL BUTT JOINT FOR BOILER SHELL
LONGITUDINAL BUTT JOINT FOR BOILER SHELL
LONGITUDINAL BUTT JOINT FOR BOILER SHELL
LONGITUDINAL BUTT JOINT FOR BOILER SHELL

Example 8.21 A cylindrical pressure vessel with a 1.5 m inside diameter is

subjected to internal steam pressure of 1.5 MPa. It is made from steel
plate by triple-riveted double-strap longitudinal butt joint with equal
straps. The pitch of the rivets in the outer row is twice of the pitch of the
rivets in
the inner rows. The rivets are arranged in a zigzag pattern. The efficiency
of the riveted joint should be at least 80%. The permissible stresses for the
plate and rivets in tension, shear and compression are 80, 60 and 120
N/mm2 respectively. Assume that the rivet in double shear is 1.875 times
stronger than in single shear. Design the joint and calculate:
(i) thickness of the plate; (ii) diameter of rivets;
(iii) pitch of rivets; (iv) distance between the rows of rivets;
(v) margin; (vi) thickness of the straps; and
(vii) efficiency of the joint.
Draw a neat sketch of the riveted joint showing calculated values of
dimensions.
LONGITUDINAL BUTT JOINT FOR BOILER SHELL
LONGITUDINAL BUTT JOINT FOR BOILER SHELL

Solution
Given For vessel, Di = 1.5 m Pi = 1.5 Mpa h = 80% st = 80 N/mm2 t = 60 N/mm2
sc = 120 N/mm2
The triple-riveted, double-strap butt joint with equal straps, is shown in Fig. 8.63.
LONGITUDINAL BUTT JOINT FOR BOILER SHELL