Metal joining Processes( Riveting, Soldering, Welding)

Unit No 5
Joining of Metals
By:- Prof. P.B. Borakhede
MGI-COET, Shegaon
Manufacturing Process I

Contents
• Riveting
• Soldering
• Brazing
• Welding
a) Arc Welding
b) Gas Welding
• Types of flames

Metal Joining Processes
• Metal joining processes
a) Soldering
b) Brazing
c) Fastening
d) Welding
e) Riveting
Prof. P.B. Borakhede MGI-COET, Shegaon

a) Riveting
• Riveting is a permanent fastening method.
• A riveted joint is easily conceived between two plates overlapping at
edges, making holes through thickness of both, passing the stem of
rivet through holes and creating the head at the end of the stem on the
other side.
• A number of rivets may pass through the row of holes, which are
uniformly distributed along the edges of the plate.
• With such a joint having been created between two plates, they cannot
be pulled apart.

• If force at each of the free edges is applied for pulling the plate apart
the tensile stress in the plate along the row of rivet hole and shearing
stress in rivets will create resisting force.
• Now it is largely used in the manufacture of boilers, pressure vessels,
rail wagons and coaches, furnace bodies, steel bridges, different types
of steel structures.

Types of Rivets
Classification of rivets is done according to shape of its head.

Riveted Joints
 There are two main kinds of riveted joints used in engineering work.
a) Lap Joint b) Butt Joint
I) Lap Joint
In this type of joint, the end of the plates to be joined are made to overlap each
other and then joined by means of the rivets.

Lap joint is sub divided into two types
i) Single Riveted Lap joint ii) Double Riveted Lap joint
i) Single Riveted Lap Joint
When the joint is made with only one row of rivets, it is called a single-
riveted lap joint.

ii) Double Riveted Lap Joint
 When there are two rows of riveted joints then it is double riveted joint.
When multiple joints are used, the arrangement of rivets between two
neighboring rows may be of two kinds.
 In chain riveting the adjacent rows have rivets in the same transverse
line.
 In zigzag riveting, on the other hand, the adjacent rows of rivets are
staggered.

II) Butt Joint
 In this type of riveted joint, the end of the plates are brought near to
each other and then the plates are connected by means of rivets after
providing one or two cover plates of cover straps.
 Depending upon the number of cover plates the butt joints may be
single riveted or double riveted butt joints.

a) Single Riveted Butt Joint
i) Single Riveted single strap
ii) Single riveted double strap

b) Double Riveted Butt joint
i) Double Riveted single strap chain joint
ii) Double riveted double strap chain joint

iii) Double riveted single strap zigzag joint
iv) Double riveted double strap zigzag joint

Failures of Riveted Joints
A riveted joint may fail in the following ways :
1. Tearing of the plate at an edge.
A joint may fail due to tearing of the plate at an edge as shown in Fig.
This can be avoided by keeping the margin, m = 1.5d, where d is the
diameter of the rivet hole.

2. Tearing of the plate across a row of rivets.
 Due to the tensile stresses in the main plates, the main plate or cover plates
may tear off across a row of rivets as shown in Fig.
 In such cases, we consider only one pitch length of the plate, since every rivet
is responsible for that much length of the plate only.
 Resistance offered by plate against tearing is known as
tearing resistance.

3. Shearing of rivets
 The plates which are connected by the rivets exert tensile stress on the
rivets, and if the rivets are unable to resist the stress, they are sheared off
as shown in Fig. 9.15.
 It may be noted that the rivets are in single
shear in a lap joint and in a single cover butt joint.
 But the rivets are in double shear in a double
cover butt joint as shown in Fig.9.16.
 The resistance offered by a rivet to be sheared off is known as shearing
resistance or shearing strength or shearing value of the rivet.
 Let d = Diameter of the rivet hole,
τ = Safe permissible shear stress for the rivet material, and
n = Number of rivets per pitch length.

• Shearing resistance or pull required to shear off the rivet per pitch length,
4. Crushing of the plate or rivets
 Sometimes, the rivets do not actually shear off under the tensile stress, but
are crushed as shown in Fig.
 Due to this, the rivet hole becomes of an oval shape and hence the joint
becomes loose.
 The failure of rivets in such a manner is also known as bearing failure.

 The area which resists this action is the projected area of the hole or rivet on
diametral plane.
 The resistance offered by a rivet to be crushed is known as crushing
resistance or crushing strength or bearing value of the rivet.
• Let d = Diameter of the rivet hole,
t = Thickness of the plate,
σc = Safe permissible crushing stress for the rivet or plate material, and

• n = Number of rivets per pitch length under crushing.
We know that crushing area per rivet (i.e. projected area per rivet),
Ac = d.t
∴ Total crushing area = n.d.t
and crushing resistance or pull required to crush the rivet per pitch
length,
Pc = n.d.t.σc

b) Soldering
 Soldering is a joining process used to join different types of metals
together by melting solder.
 This is a process in which two or more items are joined together by
melting and putting a filler metal (solder) into the joint, the filler metal
having a lower melting point than the adjoining metal.
 A soft solder is primarily an alloy of lead and tin to which some other
metals are sometimes added to lower its melting point.
 Composition of solder are as follows:
1. Tin 67%; Lead 33%
2. Tin 50%; Lead 50%
3. Tin 33%; Lead 67%

 Similarly hard Solder is an alloy of copper
and zinc to which silver is also added.
 German silver, used as a hard solder for
steel, is an alloy of copper, zinc and nickel.
 Soft solder melts at a temperature below
350⁰C and hard solder below 600 ⁰C.
 Before starting the operation the metal pieces should be properly cleaned.
 Soldering bits are used for operation.
 After joining and cleaning metal parts to be soldered, the flux is employed.
 Flux prevents the formation of oxide on joint.

 The soldering iron may either heated electrically or by some external
source of heat.
 After soldering iron heated to the desired heat its surface is cleaned by
means of filling and then dipped in a mixture of flux and solder.
 The solder melts and forms a joint on the metal parts.
Applications:
Jointing automobile radiator cores, plumbing, electronic industry including
radio, TV and computers, electrical industry for joining wires and cables to
lugs and many more.

c) Brazing
 Brazing is a joining process traditionally applied
to metals in which molten filler metal
(the braze alloy) flows into the joint.
 The brazing solder used is the mixture of
Copper, zinc, and tin.
 This method provides much stronger joint as compared to soldering
process.
 But here the metal pieces to be joined should be heated instead of the bit.
 For this muffle or smith furnace is used.

 The ends of metal pieces, are cleaned well by means of fillings.
 Brass fillings or spelter (filler metal) is then spread over the surface
together with flux.
 The filler metal melts with flux and flows along the contacting surfaces,
unites with them and solidifies on cooling to form the joint.
Advantages:
• used to bond a variety of metals, dissimilar metals and even non-metals.
• They produced a clean joint; the completed joint requires little or no
finishing. It is profitable because it does not require an expensive secondary
operation.
• Brazing preserves metallurgical characteristics of material because low
temperatures.
• Thin sheets and pipes that cannot be joined by welding can be joined by
brazing.

Difference between Soldering, Brazing and Welding
Prof. P.B.Borakhede MGI-COET, Shegaon

d) Welding Process
 Welding is a fabrication process where two or more parts are fused
together by means of heat, pressure or both forming a join as the parts
when cool.
Classification:
• Arc Welding
• Gas Welding
• Submerged arc welding
• Resistance Welding
• Friction Welding
• Plasma Arc
• Thermit Welding

1. Arc Welding Method
 Arc welding is a welding process that is used to join metal to metal by
using electricity to create enough heat to melt metal, and the melted
metals when cool result in a binding of the metals.
 The principle of shielded metal arc welding
consist of establishing electric arc between a
metal electrode and the workpiece is to be
welded.
 The arc can be described as incandescent
vapor which acts as conducting medium for
electric current from one terminal to the other
to complete the circuit.

 The metal of the work piece to be joined is called base metal or parent
metal, and that provided by the electrode as filler metal.
 The metal electrode is coated with flux which performs following
functions:
a) It produces a gas which provides a shield around the arc to protect it
from atmosphere.
b) It forms slag by mixing with impurities of the molten metal and thus
refines metal.
c) Slag is lighter and floats over surface of molten metal and forms a
layer when solidifies which helps in gradual cooling of weld and
prevents its oxidation during cooling.
 The electrode is wire made of mild steel which is coated by flux.

 Ingredients of flux for slag formation are mica, silica, fluorospar,
stealite, titanium dioxide, iron oxide, magnesium carbonate, calcium
carbonate, borax powder etc.
 Ingredients used for producing reducing atmosphere are calcium
carbonate, dolomite dextrin etc.
 Electrode size are of standard lengths of 250 mm, 300 mm, 350 mm and
450 mm etc.

Flux Coating
 Weld flux is a welding agent that prevents the weld from interacting
with the surrounding medium (like air).
 The reason why it is so important is that the base and filler material
can interact with the atmosphere and cause the formation of oxides or
other unwanted compounds.
Importance of flux
• During a welding process, the base metal and the filler undergo
significant temperature changes in a very short amount of time.
• The heated metal may interact with the surrounding air and cause
oxidation, which creates an oxide layer on the weld, reducing the weld
strength.
• And, it is not just oxygen that can create infective welds, the formation
of sulfides and nitrides can also hurt the weld's strength.

Composition of Flux coating
• A bonded welding composition or flux for welding or surfacing of
metals which is free-peeling, essentially non-hygroscopic.
• The composition contains calcium carbonate as its major ingredient
together with a sodium or potassium silicate binder.
• The flux is rendered non-hygroscopic by heating the ingredients to a
temperature in the range of 1,450° F. to about 1,800° F.

PURPOSE OF FLUX COATING –
Gas shielding of arc.
Stabilizer of the arc (potassium silicate).
 Provides slag blanket.
Alloying elements will improve mechanical properties (Iron oxide,
Ferro manganese).
Gives good penetration.
Welding in all positions becomes easy.
Compensate oxidation loss.

2. Gas Welding
• It is a fusion or non – pressure welding method in which a strong gas
flame is used to raise the temperature of the ends of the pieces to be
joined to a heat sufficient to melt them.
• The metal thus melted starts flowing along a definite path to form a
strong weld.
• Filler metal may be added to fill the cavity made during preparation.
• So many combinations of gases can be used to obtain a heating flame,
but most common of these gases are oxygen and acetylene, oxygen
and hydrogen, oxygen and coal gas etc.

Oxy-acetylene welding
 The process of Oxy-acetylene welding can be used for welding almost
all metals and alloys used in engineering practices.
 Advantage is Oxygen produces higher temperature and also inert gas
envelope, consisting of carbon dioxide and water vapors, which
prevents molten prevent from oxidation.
 Highest temperature that can be produced by a flame of oxygen and
acetylene is nearly 3200 c.
 Great for joining dissimilar metals together.
Chemical Reactions
CaC2 + 2H2O = Ca (OH) 2 + C2H2
C2H2+2.5O2= 2CO2+H2O(vapour)+ 306.800 cal /mol

• A number of welding processes use a flame produced by burning a
mixture of fuel gas and oxygen. The gas usually used is Acetylene but
other gases are also used.

 It consist of two large steel cylinders; one containing oxygen at high
pressure and other contains dissolved acetylene, also at high pressure.
 Separate cylinders and a hose pipe from each cylinder transports the
gases to a torch. Gas and fuel mix in the torch.
 Both these cylinders are painted in different colours Oxygen cylinder
in Black and Acetylene cylinder in Maroon.
 Oxygen is placed at pressure of 125 to 140 kg/sq cm.
 Acetylene cylinder carry a porous mass inside, soaked in acetone,
which has a capacity to dissolve 25 times its own volume of acetylene
for every atmosphere of pressure applied.
 Acetylene is compressed into these cylinders so as to dissolve in
acetone and that is why it is usually termed as dissolved acetylene.

• It should be handled with care and should not be exposed to such
conditions which may result in an appreciable rise in temperature.
• Blow pipes (welding torch) are used both in welding and cutting are made
in different designs and sizes to suit the work.
• It consist of different passages which mix in
chamber.
• One passage is for oxygen and other is
for acetylene.
• Both gases mixed in chamber and driven out
through the orifice of the nozzle with desired velocity.

• Pressure regulators are fixed just on the top of the gas cylinders and
carry reducing valve each.
• The gases from high pressure cylinders are just passed through these
regulators and then fed to blowpipe after their pressure has been
reduced.
• Fluxes are added to the welded metal to remove oxides
•Common fluxes used are made of sodium, potassium. Lithium and
borax.
•Flux can be applied as paste, powder, liquid, solid coating or gas.

Types of flames
 The properties and nature of gas flame have the maximum effect on
oxy-acetylene welding.
 Proper adjustment of the flame leads to successful and efficient
welding.
 This adjustment can be made both in regard to characteristics and
power of the flame by regulating pressures of oxygen and acetylene.
 Flame in which only acetylene burns is yellow in colour .
 Three kinds of oxyacetylene flames which are used in engineering
works, are as follows:
1. Oxidizing Flame
2. Neutral Flame
3. Carburizing Flame

1. Oxidizing Flame
 The formation of inner cone is the result of
increasing oxygen pressure.
 Oxidizing flame can be attained by increasing
the supply of oxygen ( having excess of oxygen than acetylene).
Ratio (1.5:1).
 Such case of flame is required for only brass material.

2. Neutral Flame
 If equal quantities of oxygen and acetylene are
Mixed they produce neutral flame having well
defined white cone.
 The neutral flame has a clear, well-defined,
or luminous cone indicating that combustion is
complete.
• There are two clearly defined zones in the neutral flame.
1)The inner zone consists of a luminous cone that is bluish-white.
2)Surrounding this is a light blue flame envelope or sheath.

3. Carburizing Flame
 The carburizing flame has excess acetylene,
the inner cone has a feathery edge extending
beyond it.
 This flame is obtained by first adjusting to
neutral and then slowly opening the acetylene
valve until an acetylene streamer or “feather” is at the end of the inner
cone.
 This type of flare burns with a coarse rushing sound. It has a
temperature of approximately 5700ºF (3149ºC) at the inner cone tips.

Metal joining Processes( Riveting, Soldering, Welding)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Metal joining Processes( Riveting, Soldering, Welding)

Similar to Metal joining Processes( Riveting, Soldering, Welding) (20)

More from prashantborakhede1

More from prashantborakhede1 (10)

Recently uploaded

Recently uploaded (20)

Metal joining Processes( Riveting, Soldering, Welding)