Biuletyn Instytutu Spawalnictwa No. 01/2012

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1. linear radiation emitted during the transition of atoms or ions from one discrete energy level to another (transition between bound states); 2. recombination radiation accompanying a capture of a free electron by one of the discrete atom or ion levels (transition between a free state and bound states); 3. radiation of free electron retardation in an ion field (transitions between free states). The total radiation of welding arc plasma is the sum of the continuous radiation and linear radiation of spectral lines [10, 15]. This sum can be written as [15]: λ = ε λ, c λ, L + ∑ε ε (1) where: ε λ,c - intensity of continuous spectrum radiation, ε λ,L - intensity of spectral line; the summation on the right side of the equation is carried out including all lines lying in a given area. For optically thin plasma, the intensity of continuous spectrum radiation can be written in the following form [15] : ⎛ ⎛ hc ⎞⎞ ε λ, c = kλ, c ( T ) ⋅ Bλ ( T ) ⋅ ⎜1 − exp⎜ − ⎟⎟ ⎝ ⎝ λ kT ⎠ ⎠ (2) where: B λ (T) is the Planck function for a black body, and k λ,c (T) is a total absorption coefficient, T – arc temperature [K], h - the Planck constant (6.6262×10 -34 [Js]), c - speed of light in vacuum (2.9979×10 8 [ms -1 ]), λ - wavelength [nm], k - the Boltzmann constant 1.38×10 -23 [JK -1 ]. The formula for continuous radiation intensity applies irrespective of whether plasma is in a state of thermal equilibrium or not. The intensity of a spectral line ε λ,L is expressed by the following formula [15] : 3 hcgq AqpN eN i ⎛ h ⎞ ⎛ Ei, q − ∆Ei ⎞ ε λ , L = ⎜ ⎟ ⋅ exp⎜ ⎟ ⋅ P qp ( λ) 8πλUi ( T ) ⎝ 2πmkT ⎠ ⎝ kT ⎠ (3) 42 BIULETYN INSTYTUTU SPAWALNICTWA where: g q – statistical weight factor of the upper level; A qp – transition probability; E i,q – upper level ionisation energy; ∆E i – ionisation potential reduction; P qp – line profile, N e - density of electrons, N i - density of ions, U i - statistical weight factor of ion, m - particle mass. The spectral distribution and intensity of thermal radiation depend on the temperature of a radiating body. Black bodies of a temperature of up to 500 K emit mainly infrared radiation of wavelength of > 2 μm. Bodies of a temperature exceeding 1000 K emit, in addition to long-wave infrared radiation, also near infrared radiation in the wavelength range of 0.78 μm ÷1.4 μm and very little, below 1%, visible radiation. Bodies of a temperature exceeding 3000 K emit, in addition to infrared radiation and visible radiation, also some (0.1%) long -wave ultraviolet radiation. Only bodies of a temperature exceeding 4000 K emit ultraviolet radiation shorter than 315 nm [11]. Welding arc radiation intensity is the highest in the wavelength range between 200 nm and 1300 nm [16]. The fraction of infrared, visible and ultraviolet radiation in the spectrum of welding arc radiation depends on a welding technology and, in each technology, on welding parameters [11, 16]. The greatest intensity of visible radiation among arc welding processes can be observed in MIG/MAG, MMA, TIG and plasma welding. It was ascertained that the intensity of ultraviolet radiation increases with a square of welding current intensity and that visible radiation intensity does not rise so intensively [11, 16]. The intensity of ultraviolet and visible radiation emitted during metal arc welding and welding with cored electrodes (MIG/MAG methods or self-shielded arc welding) in the presence of welding fumes is lower than in the NR <strong>01</strong>/2<strong>01</strong>2
case of TIG welding (for similar welding current intensity). In the same welding conditions the intensity of infrared radiation does not change significantly. During submerged arc welding visible radiation and ultraviolet radiation is absorbed by a flux layer [11]. The characteristic radiation of ions and atoms in an arc is discrete; argon, iron, oxygen and nitrogen atoms and ions being the main source of radiation. The radiation intensity of other elements is significantly lower. The wavelength range of visible radiation contains mainly spectra of iron, oxygen, nitrogen and, only partially, argon (whose ionisation potential is significantly higher) [17]. The latter also means that the emission of light by argon atoms and ions occurs at higher arc temperatures than temperatures obtained during welding in e.g. Ar+CO 2 mixes. Examinations of a discrete spectrum provide information about a temperature emitting particle radiation; this being due to the fact that the excitation of a particle requires a supply of specific energy, a measure of which can be temperature. The source of this type of radiation in a welding arc is mainly arc column plasma as well as metal transported by an arc, slag and the surface of elements being welded [18]. The energy of areas in the vicinity of the anode and cathode of a welding arc is used mainly for heating and melting of an electrode and base metal. It is known that the potential and kinetic energy of electrons is transformed into thermal energy on the surface of an anode and causes its intensive heating [17]. The radiation of a welding arc is a complex phenomenon depending on many welding parameters. In order to be able to apply the radiation of an arc in the accurate and reliable monitoring of a welding process, one should create a model binding the intensity of welding arc visible radiation with welding parameters [19]. A welding arc can be treated as a point source of radiation. Such an approach, however, appears inadequate in many applications. It seems more proper to treat an arc as a cylindrical source of radiation (Fig. 3) as such a model better reproduces the actual shape of a welding arc and facilitates accurate examination of arc radiation. For this reason, the aforesaid model will be discussed in more detail. A cylindrical model can also be simplified and a welding arc can be presented as a hemisphere. Such an approach is used in designing of systems for monitoring of automated welding processes, based on visual systems [20, 21]. A welding arc column Fig. 3. Model of welding arc in TIG method [6] is composed of three types of particles: electrons, ions and neutral atoms. It is assumed that an arc column is in a state of local thermodynamic equilibrium, at which electron collisions play an important role in excitation and ionisation. Equation 2 illustrates the emission of welding arc radiation of a continuous spectrum. After taking into consideration the dependence between a wavelength and frequency c/λ=ν and the Planck function for a black body, the Rayleigh-Jeans law is satisfied when hν/kT
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Page 3 and 4: Summaries of the articles J. Dworak
Page 5 and 6: Jerzy Dworak Research Impact of las
Page 7 and 8: cess being carried out at a specifi
Page 9 and 10: pulses up to several dozen millisec
Page 11 and 12: ectangular pulse, P i max =702 W, p
Page 13 and 14: ectangular pulse, P i max =1752 W s
Page 15 and 16: Antoni Sawicki Modified Habedank an
Page 17 and 18: 1 dr r dt - in the resistance form
Page 19 and 20: The conditions of the selection of
Page 21 and 22: Similarly as previously (37), one c
Page 23 and 24: Eugeniusz Turyk, Agnieszka Żydzik-
Page 25 and 26: gical weldability, confirmed by the
Page 27 and 28: Damage was also caused to the welde
Page 29 and 30: Initial selection of method for wel
Page 31 and 32: Fig. 19. Assembly table with fixed
Page 33 and 34: Agnieszka Kiszka, Tomasz Pfeifer Va
Page 35 and 36: Fig. 4. Course of changes in curren
Page 37 and 38: extreme, the process was less stabl
Page 39 and 40: Fig. 13. Macrostructure of T-shaped
Page 41: L=1 mm, I=25 A L=1 mm, I=50 A L=1 m
Page 45 and 46: Other, equally important research i
Page 47 and 48: tion of a function connected with t
Page 49 and 50: The intensity of arc radiation was
Page 51 and 52: On the basis of calculations (Table
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Page 55: INSTYTUT SPAWALNICTWA The Polish We

Biuletyn Instytutu Spawalnictwa No. 01/2012

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