Presentation on theme: "ПАРАМЕТРЫ ОБЛАСТИ УДАРНО-СЖАТОГО ГАЗА В СВАРОЧНОМ ЗАЗОРЕ ПРИ СВАРКЕ ВЗРЫВОМ И ЕГО ВОЗДЕЙСТВИЕ НА СВАРИВАЕМЫЕ ПОВЕРХНОСТИ PARAMETERS OF SHOCK-COMPRESSED."— Presentation transcript:
ПАРАМЕТРЫ ОБЛАСТИ УДАРНО-СЖАТОГО ГАЗА В СВАРОЧНОМ ЗАЗОРЕ ПРИ СВАРКЕ ВЗРЫВОМ И ЕГО ВОЗДЕЙСТВИЕ НА СВАРИВАЕМЫЕ ПОВЕРХНОСТИ PARAMETERS OF SHOCK-COMPRESSED GAS IN TECHNOLOGICAL GAP AND ITS INFLUENCE ON THE WELDED SURFACES 2010 S. Yu. Bondarenko, O. L. Pervukhina, L. B. Pervukhin and D. V. Rikhter PARAMETERS OF SHOCK-COMPRESSED GAS IN TECHNOLOGICAL GAP ON THE NATURE OF PROCESSES TAKING PLACE IN TECHNOLOGICAL GAP DURING EXPLOSIVE WELDING
Flow over a body with a flat forward part (Photo from Air Flow Branch, U. S. Army Ballistic Research Laboratory) 1. General view of the pattern of calculation of shock-compressed gas area Flow over the welded plates by shock-compressed gas m ent - The entrained mass of air m out - The outflow mass of air
The equations connecting with gas parameters astride the disintegration of discontinuities any desired relation of parameters can be expressed. Whence taking the expression: р 1 и р 0 –the absolute pressures in the shock- compressed gas area and surrounding atmosphere; V 1 и V 0 – gas volumes before and after compression; ρ 1 и ρ 0 – gas densities behind and before break; γ – adiabatic exponent; М – Mach number. The theoretical mass flow of gas for a time unit and its theoretical outflow velocity 2. Two jointly solved problems f – the area of output cross-section; γ – adiabatic exponent for the flowing out gas; ρ 1 – gas density between plates; ν 1 – specific volume of gas; р 1 и р 0 – the absolute pressures between the plates into the shock-compressed gas area and surrounding atmosphere. ex m out - The expiring mass of air
3. Equations of dependence determining the size of shock-compressed gas area Dependence l = f(t): Dependence l = f( L): Dependence of extent of shock-compressed gas area (l) from the contact point velocity (Vк) and the width of welded sheets (b). Dependence of extent of shock-compressed gas zone ( l ), from the distance passed by a contact point ( L ).
4. The characteristic layers and components of velocity The characteristic layers of hydrodynamic wall area: 1 – a solid body; 2 – an external "atomic" metal layer; 3 – Knudsen sublayer; 4 – a viscous boundary layer; 5 – flow core.. The components of velocity forming the total velocity of shock-compressed gas element: Vк – the velocity of contact point; υ – outflow velocity of gas. Contact line shock-compressed gas area
5. The thermal action of shock-compressed gas area on the surface - heat flow from gas to the plates surface S t – Stanton number ; с р – Thermal capacity of gas ρ – Density of gas ; Т УСГ – temperature of shock-compressed gas ; Т 0 – initial temperature. - Stanton number at the turbulent flow of plates by gas stream λ и а –Heat conductivity and heat diffusivity of plates material - Depth of fusion of metal - The warming up law of metal plates The velocity of a contact point Vк, m/s The maximal heating temperature of the metal surface, Тс, К Depth of fusion of metal, ζ, μm. Heat time, s 25006000 10 10 -5 30009000 8,3 10 -5 350012000 7,2 10 -5 400015000,3 6,3 10 -5 450020001,5 5,5 10 -5 500025006 5 10 -5
6. Calculation of ionization degree of shock-compressed gas area а - degree of gas ionization, i.e. a number of free electrons, falling on an initial atom; I - ionization potential; Т – temperature; ρ – density; V – specific volume; N – atoms quantity in 1g of gas at known temperature Т and density ρ or specific volume V. - Saha equation for unitary ionization Ionization of shock-compressed gas area а~10 -10 Ionization of air in a boundary layer а~10 -1 In view of associative ionization N + О + 2,8 эв = NO+ + e ionization of air in a boundary layer а~1
7. Calculation of the surface ionization degree - ionization degree ; - ionization coefficient n 0 – Stream of atoms on 1 square centimeter in 1 second n + и n – Streams of positive ions and the neutral atoms evaporating from the same surface for 1second For a stationary case ( n 0 = n + n + ): -Saha-Langmuir equation - the relation of statistical weights of ionic and atomic state of the adsorbed atom; φ k – work function ; F k – collection of areas with work function φ k ; ε – ion charge; I - ionization potential ; - reflection coefficient for ions and atoms accordingly
8. Calculation of ionization degree for shock-compressed gas area velocity of contact point Vк, m/s ionization degree of near-surface layer, % ionization degree according to the mechanism N+О+2,8 эв = (NO+) + e, % 250011100 300015100 350022100 400036100 450055100 500070100 (Me'-O)=(Me'- Me")+O Me и Me" – Atoms of metals on interfaced surfaces, O - Oxygen The near-surface layer of solid bodies is essentially nonequilibrium system with high mobility of particles. Its irradiation by ionic or plasma streams is a cause of surface modification. At surface modification a destruction of organic pollutions on the surface and oxides, and also lattice of metal in a near-surface layer is occurred. I.e. there is an activation of welded surface. In real conditions the efficiency of emission depends on surface condition.
Samples The size of "trap" mm calculated layer thickness on trap surface according to, m Experimental data m The sizes of plates, mm Material (Atmosphere) Konon, Explosion welding Deribas, Physics of hardening and explosion welding Baum, Physics of explosion 500х1200 Steel-steel (air) 250х 500 48528192no Steel-titanium (air) 250х 500 4852819220-80 1400х5900 Steel-steel (air) 250х 1400 2362600944no 2700х2800 Steel-titanium (argon) 250х 2700 1121232448no 9. Research of processes ahead of the contact point h Surface – Thickness of metal removed from a surface of a welded sheet, m S plate – The area of sheet, mm 2 ; S trap – The area of trap, mm 2.
The supersonic flow (5–6 Mach numbers) of shock- compressed gas gives rise to thermal ionization of gas ahead of the contact point accompanied by formation of thin layers of low-temperature plasma. Dissociation oxides and pollution occurs at influence of plasma. The positive ions of the metals which have formed as a result dissociation come back to the cleaned surface. Atoms of oxygen, nitrogen, carbon form the elementary gaseous connections СО 2 and Н 2 О which are taken out from technological gap by the shock- compressed gas. Dissociation oxides leads to the sharp increase of activation of welded surfaces before contact point. Hypothesis 10. The mechanism of cleaning and activation of welded surfaces
Metod Density of energy, w/m 2 Time of influence of plasma, second Thickness of deleted layer, m in a zone of durability stabilization on other site Plasma-arc clearing* 10 3 5-10 200-300 Shock Plasma **10 7,6·10 -6 - 1,2 ·10 -5 2,4 ·10 -5 - 1,12 ·10 -4 3-5 *Е.С.Сенокосов, А.Е.Сенокосов ПЛАЗМЕННАЯ ЭЛЕКТРОДУГОВАЯ ОЧИСТКА МЕТАЛЛОПРОКАТА, КАТАНКИ, ПРОВОЛОКИ, ТРУБ И ШТУЧНЫХ МЕТАЛЛИЧЕСКИХ ИЗДЕЛИЙ ОТ ОКАЛИНЫ, РЖАВЧИНЫ И ДРУГИХ ЗАГРЯЗНЕНИЙ **В.К.Ашаев, Г.С. Доронин, Е.И. Ермолович, В.П.Новичков, В.Б. Яшин ИСПОЛЬЗОВАНИЕ МЕТОДОВ СВАРКИ ВЗРЫВОМ И ВЗРЫВНОЙ ТЕРМИЧЕСКОЙ ОБРАБОТКИ МЕТАЛЛОВ ДЛЯ СОЗДАНИЯ МНОГОСЛОЙНЫХ БРОНЕВЫХ КОМПОЗИЦИЙ, ИМЕЮЩИХ ПОВЫШЕННУЮ ПУЛЕСТОЙКОСТЬ И ЖИВУЧЕСТЬ Structure of a surface 11. The mechanism of cleaning and surfaces activation Line of ledges Line of hollows Activation of a surface Stream of activating particles The original Intermediate condition After activation Condition of a surface
Scheme of joint f ormation Initial condition The beginning of process, formation of the shock-compressed gas area Volumetric interaction with formation of connection behind a contact point. Clearing and activation of welded surfaces Formation of physical contact t = 7,6·10 -6 - 1,12 ·10 -4 s. shock-compressed gas area Plasma heats gas 12
At pressure welding Our suggestion 1. Formation of physical contact 2. Surface activation 3. Volumetric interaction 1.Cleaning and surface activation of welded plates occurs due to the interaction of shock-compressed gas and plasma stream formed at high-rate flow and plastic deformation in deformation hillock in the localised zone the limited isobar of high pressures 1.Formation of physical contact and joint in contact point 3. Volume interaction with joint formation and plastic deformation behind a contact point Sequence of joint formation
Conclusions 1. Joint solution of the two problems (1) piston pushing with determination of gas parameters behind the shock wave and (2) determination of gas outflow rate from the gap has allowed to define the sizes of shock-compressed gas area ahead of the contact point. Gas parametres in this area are defined: pressure, temperature and density. It is shown that the size of shock-compressed gas area is limited. The effect of stabilization of the sizes of shock-compressed gas area provides constant parameters of process on almost unlimited surfaces. 2. Thermal ionisation of gas and formation of thin layers low-temperature plasma occur at supersonic flow (5–6 Mach numbers) of shock-compressed gas of welded surfaces on their border of section in a technological gap ahead of a contact point. The irradiation ionic or plasma streams leads to modification of surfaces..