船舶焊接生产基础 (7).pdf
Welding arc foundation Content Establishment of welding arc 1 Construction and stability of welding arc 2 Droplet transition in arc welding 3 Establishment of welding arc Arc is the welding heat source of arc welding.It is a conductive process in which charged particles pass through the gas space between two electrodes.In general,gases do not conduct electricity and are made up of neutral gas molecules or atoms.Neutral gas molecules or atoms must be dissociated into charged electrons and positive ions in order to conduct electricity.one Establishment of welding arc TWO low voltage heavy current Up to 6000 8000.high temperature The arc light is strong and can hurt the eyes.high luminance Characteristics of arc Establishment of welding arc Three In arc welding,gas ionization and cathode electron emission are two basic physical processes to produce charged particles.Establishment of welding arc Gas ionization：The separation of neutral gas molecules or atoms into electrons and positive ions under the action of applied energy.Ionization voltage：When other conditions are constant,the ionization voltage of a gas reflects how easy it is to produce charged particles in a certain atmosphere.Ionization can be expressed by voltage,low ionization voltage means that the ionization of gas is easier and the arc is more stable.Ionization Establishment of welding arc The temperature of arc column is generally in the range of 5000 30000K,which is the main way of generating charged particles in arc column area Ionization Thermal ionization Field-induced ionization The electric field intensity in the cathode and anode regions is very high,up to about in the range of105107 V/cm，gas ionization is mainly caused by electric field Photo ionization minor path Establishment of welding arc Cathode electron emission When oxides are visible,the escape work is relatively low,so electrons are easy to escape from the oxide film and form cathode spots The escape work of commonly used metals（eV）Establishment of welding arc Classification of electron emission mechanisms thermal emission field emission light emission Particle collision emission In practical welding,electron emission is usually accomplished by a variety of electron emission mechanisms.Cathode electron emission Establishment of welding arc arc pole area Welding arc construction Construction and stability of welding arc positive clutch negative polarity zone arc zone Stability of welding arc Stability of welding arc:whether the arc voltage and welding current can remain relatively stable,but also to maintain a certain arc length,no deviation,no sway,no extinguish.The stability of arc combustion has a great influence on the welding quality,which also affects the quality of products.Construction and stability of welding arc Magnetic deflecting of electric arc welding source The welding is not clean air current Coating Factors affecting arc stability Welding source Factors affecting arc stability Coating Factors affecting arc stability Air current Factors affecting arc stability The welding is not clean Factors affecting arc stability Magnetic deflecting of electric arc Magnetic deflection caused by wire connection position Factors affecting arc stability Droplet transition in arc welding Gravity Surface tension Electromagnetism Droplet bursting force The force on the droplet The gas blowing force of the arc Spot pressure Granular transition Short circuiting transfer Explosive transfer Spray transfer Attached to the wall of the transition Droplet transition in arc welding Droplet transition form Short circuiting transfer：Arc length(small voltage),small current,filament;Such as CO2 welding,electrode arc welding.Attached to the wall of the transition：Such as submerged arc welding,electrode arc welding.Spray transfer：Small droplet,fast frequency,stable transition,small splash,deep melting,beautiful shape.Explosive transfer：The last thing you want.Granular transition：Coarse granular transition is not smooth;Fine granular transition is more stable.Droplet transition form Droplet transition in arc welding Thanks for watching
