Gas Cutting Wldng Process_06-Rev.4

7/27/2019 Gas Cutting Wldng Process_06-Rev.4

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IIW-ANB refresher course for Transition candidates 1

Indian Institute of Welding-

ANB

Refresher course : Module-06

Gas Welding, Brazing,

soldering and Cutting


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Contents

Part-1 : Introduction Part-2 : Welding & related processes

Part-3 : Brazing and soldering

Part-4 : Cutting & edge preparation

Part-5 : Plasma Cutting

Part-6 : Thermal Cutting Standards

Part-7 : Safety


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Part-1

IntroductionOxy-gas equipment


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Introduction

Oxy gas processes are based oncontrolled combustion of fuel gas andoxygen mixture, and consequentgeneration of heat

Oxy gas processes are popular forwelding, brazing, soldering and cuttingof steel


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Fuel Gases

Acetylene ( C2H2 ) Propane ( C3H8 )

LPG ( Mixture of propane and butane )

Methane (CH4 ) - Natural gas

Hydrogen ( H2 )

Propylene ( C3H6 )

Butane ( C4H10 )


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Combustion Chemistry of Acetylene

Fuel gas + Oxygen = CO2 + H2 OAcetylene C2 H2 + O2 = 2 CO + H2

4CO + 2H2 + 3O2 = 4 CO2 + 2H2 O

C2 H2 + 2.5O2 = 2 CO2 + H2 O overall

However, maximum flame temperature for

Acetylene is reached at 55% oxygen stoichiometryActual oxygen to fuel gas ratios used are :

Acetylene 1.5: 1


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Fuel gases and their characteristics

1226600.5Hydrogen

10425265Propane

5530872.5Acetylene

Heat ofcombustion

MJ/m

Flame

Temperature

Deg C

Oxygen:FG


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Types of flames

Excess of FG

Long white

luminous feather

Reducing

Excess of O2

Blueish, sharpinner cone

Oxidising

Correct mixture

Greenish, rounded

inner cone

Neutral


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Acetylene = 3160 deg C

LPG = 2826 deg CPrimary flame(or inner cone)

Nozzle

Secondary flame (or outer cone)

Hottest point of flame


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Heating Effect of Fuel Gases

HEAT CONCENTRATION

TOTAL 54,772 Kj/m3

Primary 18,890

Secondary 35,882

Flame Temp 3,160 deg C

HEAT CONCENTRATION

TOTAL 95,758 Kj/m3

Primary 10,433

Secondary 85,325

Flame temp 2,820 deg C

OXY-ACETYLENEOXY-LPG


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Gas Equipment

CYLINDER VALVE

FLASHBACK ARRESTOR

FLASHBACK ARRESTOR

ACETYLENE(CYLINDER PAINTED

MAROON)

OXYGEN(CYLINDER PAINTED

BLACK)

ACETYLENE REGULATOROXYGEN REGULATOR

OXYGEN ANDACETYLENE

HOSES

WELDING TORCH

CUTTING TORCH

T-CQ3-2

FLASHBACKARRESTORS


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Cylinders

MaroonLH

Steel body withkisselghur &

acetone inside for

dissolvingacetylene

15DissolvedAcetylene

RH

Connection

Black

Colour

Steel body

Construction

A cylinder normally contains about 6 cu.m of gas

150Oxygen

MaxPressure

(Kg)Service


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Cylinder manifolds


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Part-2

Oxy-gas welding

andrelated processes


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Gas Welding

Oxy-acetylene welding - commonlyreferred to as gas welding - is aprocess which relies on thecombustion of oxygen and acetylene.

Because steel melts at a temperaturegreater than 1500oC, oxy-acetylene isthe only gas combination hot enoughto weld steel.

When mixed in the correct

proportions, an extremely hot flame isproduced with a temperature ofaround 3200oC

Filler

TorchTip

Flame


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Joint design for welding

Bevel of 35-45 deg

Root upto 3 mm depending on platethickness

>6 mm

Double bevel with 3 mm root>19 mm

No special preparation. Butt joint OK< 4 mm

No special preparation.

Slight root opening recommended4-6 mm

Joint recommendationThickness


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Welding techniques

Upto 3mm plate thickness

Pipe welding 6 mm wallthickness

For faster welding

Backhand

SuitabilityTechnique


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Gas welding - Flame types

For most applications, a neutral flame isused, however some materials aredifferent:

Welding brass, and bronze Oxidising flame

Nickel, and alloys

Neutral to slightly carburising (reducing) Copper

Neutral to slightly carburising (reducing)


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Gas welding

Cast IronYesNeutralCast Iron (Gray)

Basemetal

YesNeutralChrome steel

BronzeYesSlightly

OxidisingHigh Carbon Steel

SteelNoNeutralSteel Plate

SteelNoNeutralCast Steel

FILLERFLUXFLAME

SETTINGMETAL


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Special techniques

Large handheld heating blowpipes

are convenient for local heatingStraightening

Large handheld heating blowpipesare used. Custom built burners areused which are configured as perrequirement for heating largeirregular areas.

Preheating

Fishtail burners are normally usedCleaning


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Part-3

Brazing and soldering


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Brazing

Economical for complex assembliesSimple way to join for large joints

Excellent stress and heat distribution

Ability to join dissimilar metals

Ability to join non metals to metals

Ability to join different thickness parts

Joints require no finishing


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Principle of brazing

Parts must be joined withoutmelting

Melting point of filler metal >

450 deg CMolten filler metal must be

able to wet surface of basemetals

Capillary flow is the dominantphysical principle


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Brazing methods

Single/ multiple torch : suitable for lowvolume and maintenance jobs.

Furnace: Suitable for batch productionand automation

Induction: Suitable for continuousautomated production


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Soldering is a joining process which usesa filler material which melts at atemperature lower than the parentmaterial and lower than 450oC.

Brazing is a joining process which uses afiller material which melts at a

temperature lower than the parentmaterial but at a temperature greater than450oC.

In brazing the molten filler metal is drawninto the gap between the pieces of metalto be joined by capillary attraction.

Bonding between the base metal and fillermetal takes place by surface alloyingthrough diffusion

Brazing and Soldering


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Braze welding is a process similar to fusion

welding but a filler wire is used which has amelting point lower than the parent metaland no fusion or capillary attraction takesplace.

The main difference between brazing andbraze welding is in the joint clearance.Brazing, for most commonly used brazingalloys,requires a joint clearance of between0.04-0.20mm. This allows the liquid filleralloy to be drawn between the two closely

fitted surfaces by capillary action.

Braze welding does not require such aclose fitting joint and hence largerquantities of filler alloy are used.

Braze-welding


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Filler metal

Ag,CuAgAg, Au,Cu, Ni

Ag,Au,AlSiSS

Ag,Cu

Ag,Ni

W and

alloys

Ag

Ag

AlSi

Ti and

alloys

Ag, Au,CuZn..

Ag,Au,

CuZn..

Tool

steel

Ag, Au,CuZn..

Ag, Ni,CuZn

Ni

AlSi

carbon

steel

Ag,Au,CuZn..

Ag,Au,CuZn..

Ag,Au,

CuP

Cu and

alloys

Ag, Ni,CuZn

Ag,Au,

CuZn..

Cast

iron

Toolsteel

Castiron

Cu and

alloys

AlSiAl and

alloys

Al and

alloys


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Problems in brazing

High temp.

Time too long

Excess fillerWrong filler

Wrong fillerHigh temp.

Excess filler

Time too longNo stop-off

Wrong fillerLow temp.

Dirty parts

Poor fit-upToo little flux

Bad vacuum

Causes

>>>>>>

Erosion ofparent metal

Excess flow orwetting

No flowNo wetting

Problems>>>>>>


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Parts must be joined without melting

Melting point of solder (filler) < 450 deg C

Molten solder must be able to wet surface of

base metals and flow by capillary actionbetween the surfaces to be joined.

Soldering


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Soldering methodsApplicationMethod

continuous automated productionInduction

in-line continuous process for electronicparts

Vapour phasesoldering

automatic soldering of electronic PCBWavesoldering

batch production and automationFurnace

manual working, electrical &maintenance jobs

Soldering iron

manual working, low volume andmaintenance jobsAir-FG torch


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Selection of flux for soldering

Tin & Tin bronze

Zinc

Cast iron

Steel/SS

Copper

Brass

Al & Al bronze

SpecialInorganicOrganicRosin


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Fluxes

Phosphoric acid

Hydrazine hydrobromideHCl

Acid based or acidforming organicsMetal chloride

Glutamic acidTin chloride

Oleic acidAmmonium chloride

Stearic acidZinc chloride

Organic fluxesInorganic fluxes


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Solders

AluminiumZn-Al

WorkpieceSolder

AluminiumCd-Ag

Glass to glass,

glass to metalIndium-Sn

SS, copper,Sn-Ag, Sn-Cu

AluminiumSn-Zn

Copper, brassSn-Sb-Pb


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Soldering & brazing - comparison

MoreLessVersatile

Higher

Higher

Brazing

LowerWorking temp

LowerMech. strength

Soldering


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Part-4

Oxy-cutting and other

edge preparationprocesses


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Various cutting processes

TITANIUM

SS

LAMINATES

GLASSKEVLAR

RUBBER

CERAMICALUMINIUM

MS

ROUTERWATER

JETLASERPLASMAOXY


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Oxygen cutting process Preheat job to cherry red (around 850C)

Release pure oxygen stream Oxidation of hot metal starts which is

exothermic Helps sustain reaction

Oxide produced should be molten at thattemperature

Kinetic energy of O2 removes molten oxide

producing kerfThese conditions are satisfied by Steel & Titanium.Therefore these metals can be cut by this process


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Oxy-fuel gas cuttingMost widely used cuttingprocess

Can be used for cuttingMS and low alloy steels

Uses a wide range of fuel

gases acetylene, propane,LPG, Methane, Hydrogen

Used in foundries forcutting off runners andrisers

Used for machine cuttingor hand cutting


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Oxy-cutting TorchNozzle mix system

Pre-heat flame

Mixed gas

Cutting oxygen

Cutting oxygenHeating oxygen

Acetylene

Torch head

Cutting NozzleView from the bottom


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CUTTING OXYGEN

FUEL GAS AND

PREHEAT OXYGEN

MIXTUREDIRECTION OF CUT

PRE-HEAT FLAME

CUTTING STREAMDRAG LINES

NOZZLE

Oxygen cutting


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As well as the roughness of the cut face, drag lines across thesurface of the cut can give the operator an indication if the cutting

speed is correct and the right cutting oxygen velocity is beingused.

Drag Lines


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Common defects in Oxy-cutting

Large preheat flameHeavy slag

Large preheat flame

Oxygen pressure lowTop edge melt

Low speedFluted cut

-gouging at the bottom

CAUSESDEFECTS


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If the pre-heat temperature is too high it can have an effect onthe top edge of the cut. Too fierce a flame can cause melting of

the face or upper edge, this defect is called 'top edge melt'



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Example of a good quality cut



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Effects of alloying elements

3Nickel

5Chromium

2Silicon10Manganese

0.3Carbon

MAX LIMIT (%)ALLOYING ELEMENT


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Effects of oxygen purity

O2 CONSUMPTION

O2 PURITY %

50

75

125

150

100 99.5 99 98.5 98

100

175

25CUTTING SPEED

SPEE

D/CONSU

MPTION(%)


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CUTTING

SPE

ED

m/min

60

P L A T E T H I C K N E S S mm > >

10 30 40 500

1.0

0.75

0.25

0.5

20 70

HIGH SPEED

STANDARD

Cutting parametersHigh speed vs standard nozzle


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Plate Edge PreparationFlame Planing Machine

TBA

CONTROLS

WORKPIECE

TorchCarriages


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Triple Burner Assembly


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Profile Cutting & Nesting

OPTIMISE PLATE UTILISATION


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Programming Station

MISMISMISMIS

CUSTOMERS

ORDER

CNC CUTTINGCNC CUTTINGCNC CUTTINGCNC CUTTING

MISMISMISMIS

RAW MATERIALSRAW MATERIALSRAW MATERIALSRAW MATERIALS

BOMBOMBOMBOM

TOOL PATHTOOL PATHTOOL PATHTOOL PATH

GENERATIONGENERATIONGENERATIONGENERATIONNESTINGNESTINGNESTINGNESTINGPART LIBRARYPART LIBRARYPART LIBRARYPART LIBRARY

GRAPHICGRAPHICGRAPHICGRAPHIC

EDITOREDITOREDITOREDITOR

PRODNPRODNPRODNPRODN

PLANNINGPLANNINGPLANNINGPLANNING

DXFDXFDXFDXF

FILESFILESFILESFILES

DESIGN

FINISHEDFINISHEDFINISHEDFINISHED

GOODSGOODSGOODSGOODS

PROGRAMMINGSTATION


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Part-5

Plasma and othercutting processes


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Plasma Cutting

Originally introduced in around 1950s fornon ferrous cutting

Often only method for non-ferrous (SS, Alu)

Suitable for profile or straight cutting

Suitable for Machine/hand cutting

Can also cut MS


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Plasma cutting of MS Produces a taper cut which is often not acceptable

Advantage- high cutting speed at lower thickness Taper not prominent in thin sheets. Therefore, popular for

cutting sheet metal, using low priced air plasma.

May be used low thickness MS (upto 20mm) for speed

advantage, compromising quality WI produces good quality cut at high speed upto 40mm

thickness

Suitable for profile/straight cutting

Suitable for machine cutting or hand cutting

Normally used for square edge cutting

Possible to cut V edge with expensive equipment


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Plasma cutting equipment

RECTIFIER

POWERSOURCE

HIGH

FREQUENCY

SOURCE

PLASMAGAS

SECONDARYGAS

PLASMA

CUTTING

TORCH


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Plasma cuttingCUT QUALITY

T-1

T-2

T3

T-4

T-1>T-2>T-3>T-4

WORKPIECE

TAPER CUTSURFACE


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Air plasma

-

+

Hot ionised gas stream = plasma

(Temp = 30-40 thousand degC)


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Dual flow plasma

+

-


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Water injection plasma

+

-

Steam Layer

Water Injection Plasma


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Water Injection PlasmaUnderwater cutting


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Plasma Cutting parameters


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Commonly used plasma gases

Argon+Hydrogen

(60% + 40%)

WIOpen-arc

Nitrogen(99.999%)

Oxygen

Argon

Nitrogen

AirPlasma gasSecondaryPlasma gas


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Plasma cuttingFurther developments

FASTER CUTTING

OF MS

O2 PLASMA WITH

WATERINJECTION

NARROW KERFFINE PLASMA

REDUCE UV, NOISE

FURTHER

UNDERWATER

CUTTING

REDUCE NOISE FURTHERWATER TABLEREDUCE UV, NOISEWATER MUFFLER


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Oxy vs plasma cutting of MS

GoodGood < 6mmFair > 6mmGoodCut Surface

GoodAcceptable < 6mmBevelled > 6mmGoodCut Squareness

MS, SSMS, SS, Alu, etc.MSSuitable for

--30.9-3Kerf

--0.40.6HAZ (mm)

V. HighHighLowEquipment cost

HighHighLowCutting speed

30-5030-50>200Max Thickness

ContainedV. HighLowUV, IR, Noise

WI-PLASMAOPEN PLASMAOXY FUEL


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Water-jet cutting

High pressure (30-60 K PSI) water is forcedthrough 0.1-0.6 dia orifice

Velocity achieved : 1700-3000 ft/sec

Efficiency increased by adding abrasivepowder with water

Effective upto 3mm thickness

Can cut metals & non metals

Profile cutting possible using CNC machine


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Laser cutting and drilling The heat is provided by laser

Assist gas removes the vaporised/moltenmaterial to form the kerf

O2 used as cutting gas for MS cutting (1max)

CO2 Lasers are most popular

Can be used for profile cutting

Provides high quality clean cut. Low HAZ

Pulsed LASER used for drilling


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Other cutting processes

Severing MS, alloy steel

Oxy-arc

cutting/ gouging

APPLICATIONPROCESS

Gouging of MS, SS, alloy steel,Alu.

Plasma arcgouging

Severing of MS,SS,CI, Bronze,Al/Mg alloys. Gouging.

Carbon arccutting/gouging

Removal of surface defects in MSScarfing

Removal of weld deposit in MSFlame gouging

High alloy steel where normal

oxy-cutting is not possiblePowder cutting


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Part-6

Thermal Cutting

Standards


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Thermal cutting standards

Acceptance testing of

Oxygen cutting machines testing the accuracy andoperational characteristics

DIN EN 28206

Classification of thermal cuts- Geometrical productspecification and quality

tolerances

DIN EN ISO9013

Quality standard for gas cutsurface

WES 2801


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DIN EN ISO 9013

Dimensionalaccuracy

Roughness ofcut surface

along cuttingdirection

Angularity ofcut surface to

plate surface

ISO 9013

Toleranceclass

Mean heightof profile RZ5

Perpendicularity/angularitytolerance, u

Mainnumber ofstandard

4321

Indication of quality of cut

surface & tolerance class

1 2 3 4


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Part-7

S a f e t y


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Safety in oxy-cutting & weldingPERSONAL PROTECTION

Wear apronSpatter, FireApparel

Wear safety shoesSpatter, BurnFeet

Wear leather gloves& apron

IR Radiation,Spatter,

Hot metal, Burn

Skin

Use correct goggles

-shade # 3-6 for cutting

-shade # 4-8 for welding

IR Radiation, SpatterEyes

Recommendation

Protection

from

Protection

of


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Do not draw more than 15% acetylene content perhour from a cylinder

Always use cylinder in upright position

Always use correct hose, regulator & fittings

Do not use oxy-acetylene torch in a closed space

Do not use copper piping/parts in acetylene line

Never use Acetylene at a pressure higher than 1kg.

Safety in oxy-cutting & weldingUSE OFACETYLENE


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Flame burns back inside torch, usually with a

shrill sound, or flame is extinguished with aloud pop. Sustained flashback indicatessomething seriously wrong.

In the event of backfire:

Immediately shut of the oxygen supply, thenshut off FG supply

Set the pressures correctlyClean the nozzle and seat, start again

Safety in oxy-cutting & weldingBACKFIRE

Safety in oxy-cutting & welding


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A flame and its pressure wave (75x gas pressure in bar) travel

back through the torch and into the gas system.

Symptoms

A bang

Cause: Improper purging & pressures of O2 & DA lines.The flame speed is too fast to be blocked by the check valve inthe hose and proceeds right past it through the hose to the FBA

MIXEDMIXEDMIXED

GASGASGAS

PressurePressurePressure

WaveWaveWave

Direction of FlashbackToward Regulator

Flame

Hose

y y g gFlashback


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Safety in brazing

For manual brazing safety requirements areessentially same as in gas welding

Use goggles for eye protection (shade # 3-4

for gas brazing)Additional safety measures must be taken

for protection against flux & toxic metal

vapours by assuring ventilation & respiratoryprotection as required


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Safety in soldering

Precautions for fire hazard, specially whenflame is used,

Use goggles for eye protection (use shade #

1.5 - 3 for soldering with gas torch)

Ventilation to remove toxic metal & chemicalvapours,

Precaution from hot metal and burns.


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Safety in plasma cutting

Use ear plugSoundEar

Wear safety shoesSpatter, BurnFeet

Wear apronSpatter, FireApparel

Follow safetyinstructions

Electric shockBody

Wear leather gloves

& apron

IR, UV Radiation,

Spatter, Hot metal, BurnSkin

Use correct goggles

(shade # 8-14)

IR, UV Radiation,Spatter

Eyes

RecommendationProtection

from

Protectionof


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Eye protection


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Contributors to this presentation:

1) S. Ghoshal

1) Ranajoy Banerjee


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Thank You

Documents

Gas Cutting Wldng Process_06-Rev.4