Welding
Welding
In the welding process, the mechanical effect arising from
the pressing of the parts against each other plays the main role. Its main
types are:
1. Furnace
welding: Parts heated up to the welding temperature are put on top of each
other and beaten. Thus, their unification is achieved.
2. Gas pressure
source: Acetylene, propane, hydrogen or a similar flammable gas is burned with
the help of oxygen, and the desired welding temperature is obtained. Both gases
are taken from the tubes. Necessary adjustments are made on the torch according
to the shape of the weld and the type and thickness of the surfaces to be
welded. The temperature obtained in this way reaches 3000 degrees. The pressure
required for the connection is inversely proportional to the welding
temperature.
3. Electric
resistance welding: In this method, the effect of heating the conductor through
which the electric current passes is utilized. This heating section depends on
the specific resistance and current strength of the material.
There are the following
types according to the source type:
a. Butt
welding: The parts to be welded are taken between two jaws joined by the ends
of the secondary winding of a transformer. As the current passes, the parts
become hot. Connection is provided by applying pressure on the heated parts.
This type of welding is mostly used for welding the ends of steel profiles to
each other.
b. Spot
welding: Used for welding thin sheet metal sheets to each other. It is widely
used in mass production in vehicle, aircraft and light structure constructions.
Between the two copper rod electrodes connected between the ends of the
transformer, the parts are welded to each other in the form of points under
force and with the heat effect provided by the electric current. Electrodes are
pressed mechanically, hydraulically and pneumatically to ensure good contact
between the sheets.
c. Seam
welding: It is used if sealing is required in the welding connection in sheet
constructions. For example, in the construction of tanks and fuel tanks, the
metal parts are passed between the electrodes in the form of round spools that
are cooled with water and continuous welding seam is achieved.
D. Resistance
welding of pipes: It is used in pipe production. After the material passes
through the profile rolls and takes the form of a slit pipe, the joint is
heated by direct current. The pipe passed between the pressure rollers is
welded along the joint under pressure.
4. induction
welding: In this method, which is especially used in modern pipe manufacturing,
the pipe is passed through a coil. With the induction currents generated by the
coil, the pipe heats up and is welded from the joint while it passes between
the pressure rollers.
5. Termite
welding: The welding ends of the parts are embedded in iron oxide aluminum
powder and pressed together. When the mixture is ignited, a very strong
exothermic chemical reaction begins. Once the reaction is initiated, it
continues itself under the protective barium super oxide powder. The
temperature of the resulting melt reaches 3000 degrees. After the welding ends
are sufficiently heated, the welding connection is provided by pressing them
together. It has been used for joining rails since time immemorial.
6. Impulse welding:
It is widely used for the welding of rotationally symmetrical ends of parts
such as profiles, shafts, pipes. One of the pieces is kept fixed. The other is
rotated and pressed to the fixed part in the axial direction. When the welding
temperature arises from the heat arising from friction, the welding connection
is provided by increasing the pressure.
7. Supersonic
welding: In this type of welding, a regional warming is provided in the welding
area by making use of the very high energies of supersonic vibrations. The
surfaces pressed together are obtained with a special device and welded with
the help of the heat generated by the supersonic waves passed between the
electrodes.
8. Blast welding: It is used for the welding of overlapping
sheets. Hair surfaces are slammed against each other due to the explosion
effect of an explosive substance. Welding is made with the help of the
resulting heat and pressure.
9. Cold pressure
welding: It is mostly used in welding plastic materials. Although no heat is
supplied, the required pressure is greater. By pressing the connection surfaces
with force to each other, the material crystals in the pressure zone dissolve
and regenerate the connection. It can be performed as a forehead, point or
stitch.
B. Melting Sources
In these welds, no pressure is applied to the parts to be
welded. The connection surfaces are melted and mixed with the heat effect
applied, or the gap between the parts is filled with a filler material that is
melted in its own way. Its main types are:
1. Gas melting
source: Also called oxy-acetylene source. Acetylene, which is used as a
flammable gas, combines with oxygen in the torch and is burned. With the heat
obtained, the welding surfaces of the pieces brought together and an electrode
made of the same material are melted as a filler metal and a welding connection
is provided. There is no force applied to the parts during welding. The welding
temperature reached with the acetylene flame is 3200 degrees and it is
sufficient for welding all metals except some special cases.
2. Electric arc
welding: By utilizing the heat effect of the generated electric arc, it is
ensured that the welded area of the material is melted. The electric arc is
created between the electrode and the part or between the electrodes when
double electrodes are used. The rod used as a filler in welding can serve as an
electrode, and an independent rod can also be melted for this purpose. Since
the temperature is very high in this type of welding, the welding must be
protected from the atmospheric effect in order to prevent the metal from
burning. It is divided into two groups as open or closed arc sources according
to the form of protection and preventing the contact of the source with the
atmosphere:
a. Open arc
welding:
1) Arc
welding with carbon electrode: In this type of welding, the arc is formed
between the carbon electrode and the part (arc welding with one carbon
electrode) or between two carbon electrodes (arc welding with two carbon electrodes).
Direct current is used for the formation of the arc. In this type of welding,
the welding material is usually melted in the form of a wire to fill the weld
seam. Although the CO and CO2 gases prevent oxidation in the welding area due
to the burning of the carbon electrode, the effect of the atmosphere cannot be
completely prevented, so the welding quality is low.
2) Arc
welding with metal electrode: The arc is formed between the rod-shaped metal
electrode and the part. The electrode melts due to the heat generated by the
arc and fills the weld seam. The electrode is chosen in the properties of the
material being welded. Electrodes are usually covered with a special mantle
material to protect the source from atmospheric effects. During welding, this
mantle melts and forms a layer on the molten source material, preventing the
atmospheric effect. This type of welding is the most widely used welding
method.
b. Closed arc
welding: Even if jacket metal electrodes are used with open arc welding,
quality welding is not performed due to the effects of oxygen and nitrogen in
the air on the weld seam. For this purpose, closed arc welding methods have
been developed to cut off the contact of the weld seam with the atmosphere.
1) Shielding
gas welding: In this method, one of the hydrogen, argon, helium, carbon dioxide
gases is continuously sent to the weld seam and the air is completely removed
from the welding place. Although wire electrodes that melt with carbon dioxide
are used in shielding gas welding, non-melting wolfram electrodes are used in
other methods. Gas is sprayed from inside the electrode housing to the weld
seam. If desired, a welding wire that melts in the welding process can be used
as filler metal.
2) Submerged
arc welding: In this type of welding, welding is performed with a bare
electrode under a special welding dust. Dust laid on the welding seam prevents
contact with the atmosphere. The method can also be applied with automatic
welding equipment. It is widely used in the manufacture of ships, pressure
vessels and pipes in the all steel processing industry.
3) Electron
current source: Electron welding is made by making use of the high energy
density of the electron beam obtained from electrons emitted from a cathode
with a very low potential relative to the anode. Electrons emitted from the
tungsten cathode pass through the circular anode and are focused with the help
of an electromagnetic coil and sent to the part. It is possible to weld any
metal (such as molybdenum, wolfram, titanium, alloy steels, etc.) up to 20 cm
thickness with a very high temperature between 3,000-10,000 ° C at the focal
point adjustable between 2 mm and 20 cm. The method is used in cutting and drilling.
However, the biggest drawback of this kind of welding is that the welding
process has to be done in a vacuum chamber.