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Heat Flow in Welding
Heat Flow in Welding
Lesson ObjectivesWhen you finish this lesson you will understand:• Heat transfer through the welding arc & factors affecting it• Heat flow in welded parts & conservatio of energy• Thermal profiles around moving heat sources & cooling rates & stresses around welds
Learning Activities1. Read Handbook pp
66-842. Look up Keywords3. View Slides; 4. Read Notes, 5. Listen to lecture6. Do on-line
workbook7. Do homework
Keywords:Conduction, Convection, Radiation, Arc Heat Flow, Thermal Conductivity-Gas, Heat Flux, Fourier’s Law, Conservation of Energy, Moving Heat Source, Thermal Cycles
CONDUCTION - Transfer of Thermal Energy between one part of a body and an Adjacent part of the same body or between one body and another which is in physical contact with it.
CONVECTION - Transfer of Thermal Energy through mass movement.
RADIATION - Transfer of Thermal Energy by the emission and absorption of Electromagnetic Radiation.
Heat Flow in the Arc
Plasma
Electron
Ion
Neutral Gas Atom
Ionization Free
Recombination T>10,000K
Thermal
Cathode
Anode
Electrons Emitted
Electrons Absorbed
ConvectionRadiation
ThermionicRadiation
Conduction in the Arc
Plasma
Electron
Ion
Neutral Gas Atom
Ionization Free
Recombination T>10,000K
Thermal
Cathode
Anode
Electrons Emitted
Electrons Absorbed
Argon
Argon
Helium
Helium
Turn to the person sitting next to you and discuss (1 min.):• The thermal conductivity of Argon and Helium increases continuously with increasing temperature, but that of nitrogen and hydrogen show a drop in conductivity where the diatomic gas atom dissociates. What do you think would happen if a significant amount of these gases were in the arc plasma?
Y t < 0
t = 0
Small t
Large t
T (y,t)
(Initial Transient)
Steady State
Y t < 0
t = 0
Small t
Large t
T (y,t)
(Initial Transient)
Steady State
sec
sec
sec2
calflowheatAqq
Kcmcaltyconductivithermal
cmcalfluxheatq
dydq
y
o
y
y
dy
Thot
Tcooler
yq
......
dyyq
qq yydyy
dyyq
Heat In - Internal Energy + Heat Generated = Heat Out
capacityheatCdensity
QGeneratedHeat
AdytTCEnergyInternal
AqInHeat
p
gen
p
y
.
dd
Start
Finish
Thermocouples
Arc
TEMP
Slow Travel Speed
Fast Travel Speed
1 2 34 5
Turn to the person sitting next to you and discuss (1 min.):• This curve was generated when a fast moving arc passed
by the thermocouples. What curves would a slow moving arc produce?
Do the Homework Assignment 5 “Heat Flow in Welding” from the Assignment Page of the
WE300 Website