fusion welding proc heating

2014.02.17.

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Prof. Dr. Bla Palots

[email protected]

COLLEGE OF DUNAJVROS

INSTITUTE OF TECHNOLOGY

FUSION WELDING PROCESSES HEAT SOURCES

WELDING

Welding lectures dr. Bla Palots

Identification of welding procedures

For example the numerical sign for manual arc welding is 111, TIG (GTAW) procedure is 141 and shielded metal active gas arc welding received the identification number of 135, shielded metal natural gas welding is 131 and submerged arc welding has the number 12.

Standard naming of the processes usually differ from the terminology used in practice, but it is useful to be aware of the official terms (MSZ ISO 4063-2000).

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Heating sources 1.

Gas heating

Gas Welding (Oxyfuel Gas Welding)

Pressure Gas Welding

Thermal Spraying Methods

Powder Spraying

High Speed Spraying

Explosion Spraying

Flame Wire Spraying.

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Heating sources 2.

Arc Heating Arc Welding Procedures

Stud Arc Welding Procedures

Magnetically Impelled Arc Welding

Resistance heating Electroslag Welding

Resistance Welding

Diffusion Welding

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Heating sources 3.

Friction Heating Friction Welding Friction Stir Welding

Electron Beam Heating Electron Beam Welding

Laser Beam Heating Laser Welding and Laser Cutting

Plasma Beam Heating Plasma Welding and Cutting

Light Beam Heating

Light Beam Welding

Thermit Reaction Heating

Thermit Welding

Dielectric Heating

Dielectric Welding

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Gas Welding Gas Sign * Volume/

mass,

m3/kg

O2/gas Flame

temp. C**

Combustion heat, MJ/m3

I. II.

Acetylene C2H2 0,906 0,91 2,5 3087 19 36 55

Propane C3H8 1,52 0,54 5,0 2526 10 94 104

Metyl acetylene propadin

C3H4 1,48 0,55 4,0 2927 21 70 91

Propilene C3H6 1,48 0,55 4,5 2900 16 73 89

Metan CH4 0,62 1,44 2,0 2538 0,4 37 37

Hydrogen H2 0,07 11,77 0,5 2660 - - 12 * Relative to air **For natural flame

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The most commonly used gas

Acetylene (C2H2), because its combustion heat is relatively high.

Used for welding, cutting and also for preheating.

It often provides excessive heat, particularly in cases of cutting and preheating.

Gases providing less combustion heat are rather used in cutting (hydrogen) and preheating (propane-butane).

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The burning of Acetylene

Primary reaction:

(oxygen from a battle)

Secondary reaction (now oxygen is coming from the air):

QHCOOHC 2222 2

QOHCOOHCO 2222 22

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Acetylene is suitable for

Unalloyed and low alloyed steel welding and cutting

Cast iron welding

Non-ferrous and light metals welding

High alloyed steels

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Oxyfuel-Gas Welding Equipment

Dissoous gas: Acetylene is dissolved in acetone, to enable acetylene pressure to increase to 30 bars (15 bar). The pressure bottle is filled with porous material (cement asbestos - carbon), so the gas cannot get concentrated in a few cm3-s. The porous material soaks up the gas-fluid mixture. In a few cm3 volume (approx. 15x15x25 mm) acetylene is dissociating explosively.

Dissous gas pressure bottle Oxygen pressure bottle

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Welding Torch and Reductor

Burning gas and oxygen mixes based on the injector-effect.

Gas blowing through the little diameter hole arrives into a bigger chamber, this way its pressure decreases.

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Welding Technique

Backward welding is applied to thin metal sheets (s 3 mm), forward welding is used for thicker metal sheets and tubes. In case of forward welding the weld bead is heated, so bigger penetration is archived.

Hegeszts irnya Hegeszts irnya

Balra hegeszts Jobbra hegeszts

Welding direction Welding direction

Backward welding Forward welding

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Applied flame types

Natural flame (for welding steels and copper)

Oxidizing flame

(for welding brass)

Carburizing flame

(aluminum and its alloys)

Natural Oxidizing Carburizing

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Application of oxyfuel-gas welding

Welding parameters: df = 1....10 mm (filler material diameter)

pC2H2 = 0,1....0,6 bar pO2 = 2....5 bar vweld = 10....100 mm/min

VC2H2 = 1.....50 l/min VO2 = 1.....55 l/min.

On-site Welding, applying to gas and water pipe welding.

Repairs (for example car chassis).

For building assemblies central heating, water, gas piping other procedures are very difficult apply.

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Thermal Spraying Processes

Powder Spraying

Flame Wire Spraying

High Speed Spraying

Explosion Spraying

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Oxyfuel-Gas Cutting

The process:

Preheating for flashing-point temperature

Burning with oxygen

Blowing out combustion products from the gap

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Oxyfuel-Gas Cutting conditions

The material must be capable to burn in oxygen

The Flash Point Temperature must be lower than the Melting Point Temperature.

The Melting Point of the oxide must be lower than the Melting Point of the metal itself.

The combustion result must be fluid, so it can be flown out from the gap.

Well cuttable materials: Weldable unalloyed and low alloyed steels. Alloying materials usually decrease sweldability.

C, %

A knny lngvghatsg hatra

T, C

2,1

4,3 0,8

Limit of well cuttability

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Oxyfuel Gas Cutting application

Oxyfuel gas cutting is a very economical thermic manufacturing process, primarily for cutting and preparing raw materials of welded constructions.

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Characteristics of the Arc

The electric arc is a long lasting electric discharge between solid or liquid state electrodes.

It is followed by strong light and thermal effects. The electric arc is practically capable to melt any kinds of materials (of course other conditions must exist).

DC/AC L

Arc needs particles to carry electric charge. Electrons are the result of thermal emission. Ions are originating from thermal ionization, collision ionization and electromagnetic vibrations.

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Arc Static Characteristics

Increase in arc length brings an increase in voltage. If the arc length increases, the current must decrease. This is the condition of arc stability.

I

U0

U

U

I 2 1

2

1

I

U

L

L

1

2

M 1

M2

Lapos vagy vzszintes

Es

II 2 1

U1

U2

I Rz

Flat or horizontal

Dropping

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The condition of stable working point

0

fv I

U

I

U

Gradient of the arc characteristic curve must be higher then the gradient of machine characteristic curve.

As the length of the arc increases, the current of the arc also decreases, this causes less electrode material to melt, so the length of the arc consequently decreases.

arc machine

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Possibilities of arc ignition

Short circuit

High frequency spark ignition

IG DC/AC

Spark ignition:

Short circuit:

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The dynamic characteristics

Dynamical requirement:

50 V must be available in 0.05 sec, so the speed of voltage increase is:

1000 V/s.

Dinamikusan "rossz" gp Dinamikusan "j" gp

U

I

t

t

U0

U0

resjratRvidzrlat

resjrat

I

I

max

Rz

U

I

t

t

U0

U0

resjratRvidzrlat

resjrat

IRz

U

I

U0

Imax

IRz

IRz

U0

Dynamically bad machine Dynamically good machine

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The Alternating Current Arc

Less stable, it ignites and goes out 100 times a second.

Inductive circle voltage has advance compared to current. A break time can be sensable between ignitions.

AC is not good dynamically the current can be a max. of 1.8 times more compared to nominal value.

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The Internal Control

When the legth of the arc increases, the current decreases. When the current decreases, the speed of electrode melting also decreases. The original balance loosens, the wire forwarding speed exceeds the melting speed, this way the length of the arc decreases (flat characteristics needed).

Lv

Lv

1

Lv

2

A fmfrd lengsnek kvetkezmnye az vhossz vltozsa

Lv

2L

vL

v1

Eltolmotor

v eltols

= const.

Lv

=

+

-

Lv

Lv

2

Lv

1

Invl.

U

I

I2

I1

Egyensly: v = vel. leolv.

vhossz n: I 1

Invl.

vleolv.

vel.

vhossz cskken: Invl.

vleolv.

vel.

I2

v leolv.

= f ( I )

ve = constant

Changing arc length is a consequence of weld bad swing.

Larc2 < L arc < L arc1

vwire

Forwarding motor

Balance: vwire = vmelt

vmelt = f (I) Arc length increases:

I1 < Inominal

vmelt < vwire

Arc length decreases:

I2> Inominal

vmelt > vwire

In.

arc

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The External Control

M

=/

Gerjeszt tekercs

U

vel.

const.

f ( U )

U

U

1

2

U

I

L1

L2

U

Az vhosszsg vltozstl fggen: U ha pozitv ( vhossz n ) n vel.

n ( vhossz cskken )

U ha negatv ( vhossz cskken ) vel.

( vhossz n )cskken cskken

In case of external control we can regulate the wires forwarding speed above the self control of the arc. Increase in arc length results in an increase of voltage. By amplifying voltage increase the motor rpm can be increased, this way the length of arc can be decreased (dropping characteristic needed). 26

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The Magnetic Blowing Effect

As the Lorentz force law says, in a magnetic field force is directed to a moving charge. (Magnetic Blowing Effect)

Starting from the side of the work-piece, the arc is bending forward, at the end of the part, the arc is bending backwards.

Can be decreasd by: - simm. Current drive in - decrease of arc length - decrease of current - no effect when using AC.

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fusion welding proc heating

Documents

manual arc welding

submerged arc welding

metal natural gas welding

cast iron welding

low alloyed steel welding

bla palots acetylene

bla palots heating sources

bla palots wel