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FUSION WELDING PROCESSES – HEAT SOURCES
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2014.02.17.
1
Prof. Dr. Bla Palots
COLLEGE OF DUNAJVROS
INSTITUTE OF TECHNOLOGY
FUSION WELDING PROCESSES HEAT SOURCES
WELDING
Welding lectures dr. Bla Palots
Identification of welding procedures
For example the numerical sign for manual arc welding is 111, TIG (GTAW) procedure is 141 and shielded metal active gas arc welding received the identification number of 135, shielded metal natural gas welding is 131 and submerged arc welding has the number 12.
Standard naming of the processes usually differ from the terminology used in practice, but it is useful to be aware of the official terms (MSZ ISO 4063-2000).
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Heating sources 1.
Gas heating
Gas Welding (Oxyfuel Gas Welding)
Pressure Gas Welding
Thermal Spraying Methods
Powder Spraying
High Speed Spraying
Explosion Spraying
Flame Wire Spraying.
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Welding lectures dr. Bla Palots
Heating sources 2.
Arc Heating Arc Welding Procedures
Stud Arc Welding Procedures
Magnetically Impelled Arc Welding
Resistance heating Electroslag Welding
Resistance Welding
Diffusion Welding
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Welding lectures dr. Bla Palots
Heating sources 3.
Friction Heating Friction Welding Friction Stir Welding
Electron Beam Heating Electron Beam Welding
Laser Beam Heating Laser Welding and Laser Cutting
Plasma Beam Heating Plasma Welding and Cutting
Light Beam Heating
Light Beam Welding
Thermit Reaction Heating
Thermit Welding
Dielectric Heating
Dielectric Welding
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Welding lectures dr. Bla Palots
Gas Welding Gas Sign * Volume/
mass,
m3/kg
O2/gas Flame
temp. C**
Combustion heat, MJ/m3
I. II.
Acetylene C2H2 0,906 0,91 2,5 3087 19 36 55
Propane C3H8 1,52 0,54 5,0 2526 10 94 104
Metyl acetylene propadin
C3H4 1,48 0,55 4,0 2927 21 70 91
Propilene C3H6 1,48 0,55 4,5 2900 16 73 89
Metan CH4 0,62 1,44 2,0 2538 0,4 37 37
Hydrogen H2 0,07 11,77 0,5 2660 - - 12 * Relative to air **For natural flame
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Welding lectures dr. Bla Palots
The most commonly used gas
Acetylene (C2H2), because its combustion heat is relatively high.
Used for welding, cutting and also for preheating.
It often provides excessive heat, particularly in cases of cutting and preheating.
Gases providing less combustion heat are rather used in cutting (hydrogen) and preheating (propane-butane).
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Welding lectures dr. Bla Palots
The burning of Acetylene
Primary reaction:
(oxygen from a battle)
Secondary reaction (now oxygen is coming from the air):
QHCOOHC 2222 2
QOHCOOHCO 2222 22
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Welding lectures dr. Bla Palots
Acetylene is suitable for
Unalloyed and low alloyed steel welding and cutting
Cast iron welding
Non-ferrous and light metals welding
High alloyed steels
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Welding lectures dr. Bla Palots
Oxyfuel-Gas Welding Equipment
Dissoous gas: Acetylene is dissolved in acetone, to enable acetylene pressure to increase to 30 bars (15 bar). The pressure bottle is filled with porous material (cement asbestos - carbon), so the gas cannot get concentrated in a few cm3-s. The porous material soaks up the gas-fluid mixture. In a few cm3 volume (approx. 15x15x25 mm) acetylene is dissociating explosively.
Dissous gas pressure bottle Oxygen pressure bottle
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Welding lectures dr. Bla Palots
Welding Torch and Reductor
Burning gas and oxygen mixes based on the injector-effect.
Gas blowing through the little diameter hole arrives into a bigger chamber, this way its pressure decreases.
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Welding lectures dr. Bla Palots
Welding Technique
Backward welding is applied to thin metal sheets (s 3 mm), forward welding is used for thicker metal sheets and tubes. In case of forward welding the weld bead is heated, so bigger penetration is archived.
Hegeszts irnya Hegeszts irnya
Balra hegeszts Jobbra hegeszts
Welding direction Welding direction
Backward welding Forward welding
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Welding lectures dr. Bla Palots
Applied flame types
Natural flame (for welding steels and copper)
Oxidizing flame
(for welding brass)
Carburizing flame
(aluminum and its alloys)
Natural Oxidizing Carburizing
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Welding lectures dr. Bla Palots
Application of oxyfuel-gas welding
Welding parameters: df = 1....10 mm (filler material diameter)
pC2H2 = 0,1....0,6 bar pO2 = 2....5 bar vweld = 10....100 mm/min
VC2H2 = 1.....50 l/min VO2 = 1.....55 l/min.
On-site Welding, applying to gas and water pipe welding.
Repairs (for example car chassis).
For building assemblies central heating, water, gas piping other procedures are very difficult apply.
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Welding lectures dr. Bla Palots
Thermal Spraying Processes
Powder Spraying
Flame Wire Spraying
High Speed Spraying
Explosion Spraying
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Welding lectures dr. Bla Palots
Oxyfuel-Gas Cutting
The process:
Preheating for flashing-point temperature
Burning with oxygen
Blowing out combustion products from the gap
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Welding lectures dr. Bla Palots
Oxyfuel-Gas Cutting conditions
The material must be capable to burn in oxygen
The Flash Point Temperature must be lower than the Melting Point Temperature.
The Melting Point of the oxide must be lower than the Melting Point of the metal itself.
The combustion result must be fluid, so it can be flown out from the gap.
Well cuttable materials: Weldable unalloyed and low alloyed steels. Alloying materials usually decrease sweldability.
C, %
A knny lngvghatsg hatra
T, C
2,1
4,3 0,8
Limit of well cuttability
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Welding lectures dr. Bla Palots
Oxyfuel Gas Cutting application
Oxyfuel gas cutting is a very economical thermic manufacturing process, primarily for cutting and preparing raw materials of welded constructions.
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Welding lectures dr. Bla Palots
Characteristics of the Arc
The electric arc is a long lasting electric discharge between solid or liquid state electrodes.
It is followed by strong light and thermal effects. The electric arc is practically capable to melt any kinds of materials (of course other conditions must exist).
DC/AC L
Arc needs particles to carry electric charge. Electrons are the result of thermal emission. Ions are originating from thermal ionization, collision ionization and electromagnetic vibrations.
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Welding lectures dr. Bla Palots
Arc Static Characteristics
Increase in arc length brings an increase in voltage. If the arc length increases, the current must decrease. This is the condition of arc stability.
I
U0
U
U
I 2 1
2
1
I
U
L
L
1
2
M 1
M2
Lapos vagy vzszintes
Es
II 2 1
U1
U2
I Rz
Flat or horizontal
Dropping
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Welding lectures dr. Bla Palots
The condition of stable working point
0
fv I
U
I
U
Gradient of the arc characteristic curve must be higher then the gradient of machine characteristic curve.
As the length of the arc increases, the current of the arc also decreases, this causes less electrode material to melt, so the length of the arc consequently decreases.
arc machine
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Welding lectures dr. Bla Palots
Possibilities of arc ignition
Short circuit
High frequency spark ignition
IG DC/AC
Spark ignition:
Short circuit:
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The dynamic characteristics
Dynamical requirement:
50 V must be available in 0.05 sec, so the speed of voltage increase is:
1000 V/s.
Dinamikusan "rossz" gp Dinamikusan "j" gp
U
I
t
t
U0
U0
resjratRvidzrlat
resjrat
I
I
max
Rz
U
I
t
t
U0
U0
resjratRvidzrlat
resjrat
IRz
U
I
U0
Imax
IRz
IRz
U0
Dynamically bad machine Dynamically good machine
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Welding lectures dr. Bla Palots
The Alternating Current Arc
Less stable, it ignites and goes out 100 times a second.
Inductive circle voltage has advance compared to current. A break time can be sensable between ignitions.
AC is not good dynamically the current can be a max. of 1.8 times more compared to nominal value.
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Welding lectures dr. Bla Palots
The Internal Control
When the legth of the arc increases, the current decreases. When the current decreases, the speed of electrode melting also decreases. The original balance loosens, the wire forwarding speed exceeds the melting speed, this way the length of the arc decreases (flat characteristics needed).
Lv
Lv
1
Lv
2
A fmfrd lengsnek kvetkezmnye az vhossz vltozsa
Lv
2L
vL
v1
Eltolmotor
v eltols
= const.
Lv
=
+
-
Lv
Lv
2
Lv
1
Invl.
U
I
I2
I1
Egyensly: v = vel. leolv.
vhossz n: I 1
Invl.
vleolv.
vel.
vhossz cskken: Invl.
vleolv.
vel.
I2
v leolv.
= f ( I )
ve = constant
Changing arc length is a consequence of weld bad swing.
Larc2 < L arc < L arc1
vwire
Forwarding motor
Balance: vwire = vmelt
vmelt = f (I) Arc length increases:
I1 < Inominal
vmelt < vwire
Arc length decreases:
I2> Inominal
vmelt > vwire
In.
arc
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Welding lectures dr. Bla Palots
The External Control
M
=/
Gerjeszt tekercs
U
vel.
const.
f ( U )
U
U
1
2
U
I
L1
L2
U
Az vhosszsg vltozstl fggen: U ha pozitv ( vhossz n ) n vel.
n ( vhossz cskken )
U ha negatv ( vhossz cskken ) vel.
( vhossz n )cskken cskken
In case of external control we can regulate the wires forwarding speed above the self control of the arc. Increase in arc length results in an increase of voltage. By amplifying voltage increase the motor rpm can be increased, this way the length of arc can be decreased (dropping characteristic needed). 26
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Welding lectures dr. Bla Palots
The Magnetic Blowing Effect
As the Lorentz force law says, in a magnetic field force is directed to a moving charge. (Magnetic Blowing Effect)
Starting from the side of the work-piece, the arc is bending forward, at the end of the part, the arc is bending backwards.
Can be decreasd by: - simm. Current drive in - decrease of arc length - decrease of current - no effect when using AC.
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