Electric arc welding was first patented
in France in mid 1800s, by a Russian scientist, Nikolai N. Benardos who was
working in the Cabot laboratory with Auguste De Meritens. Later, Benardos and
his colleague Stanislaus Olszewski patented an electrode-holder in Britain, and
in the USA in late 1800s.
During the middle Ages, the art of blacksmithing was developed and
many items of iron were produced which were welded by hammering.
The production of an arc between two
carbon electrodes using a battery was invented by Sir Humphry Davy in 1800.
Edmund Davy of England is credited with
the discovery of acetylene in 1836.
Edmund Davy was born on 1785 in UK.
He was a professor of Chemistry at the
Royal Cork Institution from 1813 and professor of chemistry at the Royal Dublin
Society from 1826.
In 1836, Edmund Davy discovered a gas
which he recognized as "a new carburet of hydrogen."
It was an accidental discovery while
attempting to isolate potassium metal.
By heating potassium carbonate with
carbon at very high temperatures, he produced a residue of what is now known as
potassium carbide, which reacted with water to release the new gas.
He died on 5th
November, 1857 in Ireland.
He lived for 72 years in this planet and
even today he lives in the form of acetylene.
CASTING
Casting is a 6000-year-old process.
Casting is a manufacturing process in
which a liquid material is usually poured into a mould, which contains a hollow
cavity of the desired shape, and then allowed to solidify.
The solidified part is also known as a
casting, which is ejected or broken out of the mould to complete the process.
METHODS OF JOINING METALS
Soldering, brazing, and welding are
different methods of joining two or more pieces of metal and selected other
materials. They are also methods used to fill gaps in metal parts.
SOLDERING
Soldering is a process in which two or
more metal items are joined together by melting and then flowing a filler metal
into the joint—the filler metal having a relatively low melting point.
Soldering is a group of joining
processes that produces joining of base materials by heating to the soldering
temperature and using a filler metal with a liquidus not exceeding 450°C
(840°F) and below the solidus of the base materials. When soldering, the base
material is not melted.
Metals that can be soldered include
gold, silver, copper and iron. The filler, called solder, melts. When it
solidifies, it is bonded to the metal parts and joins them.
[The liquidus temperature is above which
a material is completely liquid]
BRAZING
Brazing joins two metals by heating and
melting a filler (alloy) that bonds to the two pieces of metal and joins them.
The filler obviously must have a melting
temperature below that of the metal pieces.
Brazing is a group of joining processes
that use a filler metal with a liquidus above 450°C (840°F) and below the
solidus of the base material.
When brazing, the base material is not
melted.
Brazing can join dissimilar metals such
as aluminum, silver, copper, gold, and nickel.
Flux is often used during brazing.
[Solidus is the highest temperature at which an alloy is completely solid]
WELDING
Welding is a process by which two
similar or dissimilar metals may be joined by heating them to a suitable
temperature with or without the application of pressure and with or without the
use of filler metal.
The filler metal has its melting point
either approximately the same as that of the workpiece metal or little lower,
but is normally above 430 degree centigrade.
REVETTING
A rivet is a permanent mechanical
fastener.
A rivet consists of a smooth cylindrical
shaft with a head on one end.
The end opposite to the head is called
the tail.
On installation the rivet is placed in a
drilled hole, and the tail is upset, or deformed, so that it expands to about
1.5 times the original shaft diameter, holding the rivet in place.
To distinguish between the two ends of
the rivet, the original head is called the factory head and the deformed end is
called the shop head.
COMPARISON BETWEEN WELDING TO REVETTING AND CASTING
1. Welding is economical than revetting and casting
2. Welding design
involves less cost.
3. Welding structure is much lighter is
weight.
4. Old and worn out structure can be
easily renovated and reinforced by welding.
5. Welding is more effective in pressure
vessels and tanks.
CLASSIFICATION OF METALS
(a) Ferrous metals and (b) Non Ferrous
metals.
FERROUS METALS -The metals in which iron is the principle element is known as ferrous metal. These are directly attracted by magnets. Iron is extracted from iron ore.
The important ores are, Haematite,
Magnetite, Iron pyrites, Siderite, Limonite etc. E.g: Cast iron, wrought iron, etc.
NON FERROUS METALS - The metals which do not contain iron is called non-ferrous metals. E.g: copper, Aluminium, Tin, Lead
TYPES OF WELDING
1. AUTOGENOUS WELDING
Similar metals are joined with the help
of filler rod of the same metal.
In this method mild steel is joined with
mild steel and cast iron with cast iron only.
2. HOMOGENEOUS WELDING
In homogeneous welding processes, the
filler material used to provide the joint is the same as the parent material.
3. HETEROGENEOUS WELDING
Dissimilar metals are joined. The metals
being joined are brought upto the critical temperature or plastic state and the
filler rod is used. The filler rod is of such metal which
has its melting point less than the parent material.
ADVANTAGES OF WELDING
1. Freedom in choice of design is
possible in welding.
2. Welding can be automatic and
mechanized.
3. Portable welding equipment is
available and can be taken to the site easily.
4. Similar and dissimilar metals can be
welded easily.
5. With modern welding techniques all
alloys can be welded with good finish.
DISADVANTAGES OF
1. The ultra violet rays of welding are very
harmful for the eyes.
2. The fumes and gases are harmful for
the human being.
3. For having good weld the operator
must be a skilled one otherwise the job once it gets spoil it cannot be
rectified.
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