ПАРАМЕТРЫ ОБЛАСТИ УДАРНО-СЖАТОГО ГАЗА В СВАРОЧНОМ ЗАЗОРЕ ПРИ СВАРКЕ ВЗРЫВОМ И ЕГО ВОЗДЕЙСТВИЕ НА...

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

ment - The entrained mass of air

mout - The outflow mass of air

constdt

dm

dt

dm outent

1 01

0 1 0

6 /

8 / 1

V Vр

р V V

0 1 01

1 0 1 0

/ 6

8 / 1

р рV

V р р

1 1 1

0 0 0

Т р V

Т р V

2 1 0

1 0

/ 17

5 1 /

р рМ

V V

The equations connecting with gas parameters astride the disintegration of discontinuities

any desired relation of parameters can be expressed.

Whence taking the expression:

р1 и р0 –the absolute pressures in the shock-compressed gas area and surrounding atmosphere;V1 и V0 – gas volumes before and after compression;ρ1 и ρ0 – gas densities behind and before break;γ – adiabatic exponent;М – Mach number.

2 1

0 01 1

1 1

2

1мр

p pm f p

p p

1

01 1

1

21

1

pp

p

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;ρ1 – gas density between plates;ν1 – specific volume of gas;р1 и р0 – the absolute pressures between the plates into the shock-compressed gas area and surrounding atmosphere.

ex

mout - The expiring mass of air

3. Equations of dependence determining the size of shock-compressed gas area

0

2

1

1 1 1

2 22

1 1

кt V bl

b t p

0

2

1

1 1 1

2 22

1 1k

L bl

Lb p

V

Dependence l = f(t): Dependence l = f( L):

0,12

0,17

0,22

0,27

0,32

0,37

1500 2000 2500 3000 3500 4000 4500 5000

Vk, (м/с)

L(м

)

b=0,5м

b=1м

b=2м

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)( 0ТTcuStq УСГp St – Stanton number ; ср– Thermal capacity of gas ρ – Density of gas;

ТУСГ – temperature of shock-compressed gas ; Т0 – initial temperature.

2)74,1lg2(8

1

k

aSt

pТ

- 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 plates06

2Tat

qTc

11 r

q

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

2500 600 0 1010-5

3000 900 0 8,310-5

3500 1200 0 7,210-5

4000 1500 0,3 6,310-5

4500 2000 1,5 5,510-5

5000 2500 6 510-5

3I2 2

12 2

0

212

1e kT

m kTuae

a u N h

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

nа

n

0

n

n - ionization degree ; - ionization coefficient

n0 – 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 (n0 = n + n+):1

а

1

а

а

-Saha-Langmuir equation

g

g - the relation of statistical weights of ionic and atomic state of the adsorbed atom;

φk – work function;Fk – collection of areas with work function φk;ε – ion charge;

I - ionization potential ;

- reflection coefficient for ions and atoms accordinglyr 0r

11

0

1( )1

1 exp1

k

kk

Fа

Ir g

r g kT

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, %

2500 11 100

3000 15 100

3500 22 100

4000 36 100

4500 55 100

5000 70 100

(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.

SamplesThe size of

"trap"mm

calculated layer thickness on trap surface according to, m

Experimental data

mThe sizes of plates, mm

Material

(Atmosphere)

Konon, Explosion welding

Deribas, Physics of hardening and

explosion welding

Baum, Physics of explosion

500х1200

Steel-steel (air)

250х500

48 528 192 no

Steel-titanium (air)

250х500

48 528 192 20-80

1400х5900 Steel-steel (air)

250х1400

236 2600 944 no

2700х2800 Steel-titanium (argon)

250х2700

112 1232 448 no

9. Research of processes ahead of the contact point

hSurface – Thickness of metal removed

from a surface of a welded sheet, m

Splate –The area of sheet, mm2;

S trap –The area of trap, mm2.

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 СО2 and Н2О 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/m2

Time of influence of plasma,

second

Thickness of deleted layer,

min a zone of durability

stabilizationon other site

Plasma-arc clearing* 103 5-10 5-10 200-300

Shock Plasma** 1010 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 ИВЗРЫВНОЙ ТЕРМИЧЕСКОЙ ОБРАБОТКИ МЕТАЛЛОВ ДЛЯ СОЗДАНИЯ МНОГОСЛОЙНЫХ БРОНЕВЫХ КОМПОЗИЦИЙ, ИМЕЮЩИХПОВЫШЕННУЮ ПУЛЕСТОЙКОСТЬ И ЖИВУЧЕСТЬ

Structure of a surface

11. The mechanism of cleaning and surfaces activation

Line of ledges

Line of hollows

Activation of a surfaceStream of activating particles

The original

Intermediate condition

After activation

Condition of a surface

Scheme of joint formation

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

kV

lt 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.

.