Oxyfuel gas welding and Oxyfuel gas welding and cuttingcutting

Use of gas flameUse of gas flame

WeldingWelding GougingGougingBrazingBrazing

HeatinHeatingg

StraighteniStraighteningng

CuttingCutting

BlastinBlastingg

SprayinSprayingg

OFW - Principle of OFW - Principle of operationoperation

OFW fuel gassesOFW fuel gassesRequirements for fuel gasses:Requirements for fuel gasses:

high flame temperaturehigh flame temperature high rate of flame propagationhigh rate of flame propagation adequate heat contentadequate heat content minimum chemical reaction of the flame with base and minimum chemical reaction of the flame with base and

filler metalsfiller metals

acetylene (Cacetylene (C22HH22))

propane (Cpropane (C33HH88))

methylacetylene-propadiene methylacetylene-propadiene stabilised (MPS - Cstabilised (MPS - C33HH44))

hydrogenhydrogen

Common fuel gassesCommon fuel gassesFlame temp.with Flame temp.with

OO22

3087°c3087°c

2526°c2526°c

2927°c 2927°c

2660°c2660°c

OFW flameOFW flame

Distance from the tip of the nozzle

Tem

peratu

re (°C)

3100

1000

3002÷5 mm

Inner cone

Outer envelope

Bright nucleus

Combustion reactionsCombustion reactions

In the bright nucleus:

C2H2 2C + H2 + Heat

In the inner cone - first burning stage:

2C + H2 + O2 2CO + H2 + Heat

CO and H2 have reducing effect (no oxides are forming)

In the outer envelope - secondary burning

2CO + O2 2CO2 + Heat

2H2 + O2 2H2O + Heat

Flame typesFlame types

Flame typesFlame types

welding of welding of most most materials materials (including (including cast iron, Cu, cast iron, Cu, Mg)Mg)

brazingbrazing cuttingcutting

Oxy acetylene Oxy acetylene flameflame

CarburisinCarburising flameg flame

Oxidising Oxidising flameflame

Neutral Neutral flameflame

reducing flame reducing flame welding of cast iron welding of cast iron

(slightly reducing!), (slightly reducing!), Al, Ni and high C Al, Ni and high C steels steels hardfacing with Cr hardfacing with Cr and W carbideand W carbide

excess Oexcess O22 can can

combine with combine with many metals to many metals to form hard, form hard, brittle oxides brittle oxides welding of welding of bronze and bronze and brassesbrasses

OFW fluxesOFW fluxesWhy?Why? to remove oxides that fail to flow from the to remove oxides that fail to flow from the

welding zonewelding zone to protect the weld pool from the to protect the weld pool from the

atmosphereatmosphere

WhenWhen??

when the oxides have a higher melting when the oxides have a higher melting point than the parent metalpoint than the parent metal

applied during preheating and weldingapplied during preheating and welding not required for carbon steelsnot required for carbon steels required for Al and brazing operationsrequired for Al and brazing operations

How?How? dry powderdry powder paste or thick solutionpaste or thick solution preplaced coating on the welding rodpreplaced coating on the welding rod

Oxyfuel gas welding equipmentOxyfuel gas welding equipmentAcetylene cylinder

(section)

Low pressure valve

Steel container

Porous material

Acetone

Fusible safety plugs

Acetylene generatorsAcetylene generators

What is What is the the

acetylene acetylene pressure?pressure?

Low Low pressurpressur

ee

<0,07 bar<0,07 bar Medium Medium pressurpressur

ee

0,07-0,07-1,05 bar1,05 bar

Carbide-to-Carbide-to-water typewater type

Water-on-Water-on-carbide typecarbide type

Intermittent Intermittent contact typecontact type

Acetylene Acetylene generatogenerato

rsrs

StationarStationary typey type

Portable Portable typetype

2CaC2CaC

22

LimLimee

CokCokee

Electric Electric furnace furnace smeltinsmeltin

gg

+ 2H+ 2H22O O C C22HH22 + + Ca(OH)Ca(OH)22

OFW torchOFW torch

Welding nozzle

Mixing tube

Injector

Union (mixer) nut

Torch inset

Oxygen valve

Fuel gas valve

Handle Oxygen connection

Fuel gas connection

OFW torchOFW torch

CC22HH22 in contact with Cu forms acetylides (explosive!) in contact with Cu forms acetylides (explosive!) if the pressure of fuel gas > 14 kPa if the pressure of fuel gas > 14 kPa a medium pressure a medium pressure

type mixer is usedtype mixer is used if the pressure of fuel gas < 14 kPa if the pressure of fuel gas < 14 kPa an injector type mixer is an injector type mixer is

usedused

InjectorMixing nozzle/tube

Union (mixer) nut

Oxygen valve

Fuel gas valve

HandleMixing chamber

OFW torchOFW torch

OFW torchOFW torch

Oxygen Oxygen regulatorregulator

Fuel gas Fuel gas regulatorregulator

RegulatorsRegulators

RegulatoRegulator typer type

Single Single stagestage

Two Two stagestage

used when slight rise in delivery used when slight rise in delivery pressure from full to empty pressure from full to empty cylinder condition can be cylinder condition can be toleratedtolerated

used when a constant used when a constant delivery pressure from full to delivery pressure from full to empty cylinder condition is empty cylinder condition is requiredrequired

Single stage regulatorSingle stage regulator

Secondary

springCylinder

pressure

gauge

Regulator

body

Bonnet

Adjusting screw

Flexible

diaphragm

Gas to

torch

Working

pressure

gauge

Gas from

cylinder

Capsule

Primary

spring

Single stage regulatorSingle stage regulator

Gas from cylinder

Gas to torch

Adjusting screw

Primary spring

Regulator body

Flexible diaphragm

Secondary spring

Two stage regulatorTwo stage regulatorBonnet

Adjusting screw

Primary spring

Gas from cylinder

Cylinder pressure

gage

Working pressure

gage

Primary spring

Bonnet

Capsule

Capsule

Regulator body

Secondary spring

Gas to torch

Flexible diaphragm

Gas from cylinder

Regulator body

Pre-set first stage

Flexible diaphragm

Adjusting screw

Primary spring second stage

Gas to torch

Primary spring first stage

Adjustable second stage

Secondary springs

Two stage regulator Two stage regulator

Flashback arrestorsFlashback arrestorsFlashback - recession of the flame into or back of the Flashback - recession of the flame into or back of the

mixing chambermixing chamber

Flashback flame quenched at the flashback barrier

Flame barrier

Built-in check valve

Normal flow Reverse flow Flashback

Built-in check valve stops reverse flow

OFW parametersOFW parameters

ApproximatApproximate gas e gas

pressurepressure

Filler rod Filler rod diameterdiameter

Approximate Approximate gas gas

consumptionconsumption

Type of Type of parent/filleparent/fille

rr

Flame typeFlame type

Thickness of Thickness of plates to be plates to be

weldedwelded

Tip size Tip size (Diamete(Diameter of hole)r of hole)

Welding Welding techniqutechniqu

ee

Joint Joint preparatiopreparatio

nn

Weld qualityWeld quality

OFW quality (left to right) - OK; torch too high; OFW quality (left to right) - OK; torch too high; torch too low; travel speed too slow; travel torch too low; travel speed too slow; travel speed too fastspeed too fast

A jet of pure oxygen reacts with iron, that has A jet of pure oxygen reacts with iron, that has been preheated to its ignition point, to been preheated to its ignition point, to produce the oxide Feproduce the oxide Fe33OO4 4 by exothermic by exothermic reaction.This oxide is then blown through the reaction.This oxide is then blown through the material by the velocity of the oxygen streammaterial by the velocity of the oxygen streamDifferent types of fuel gases may be used Different types of fuel gases may be used for the pre-heating flame in oxy fuel gas for the pre-heating flame in oxy fuel gas cutting: i.e. acetylene, hydrogen, propane. cutting: i.e. acetylene, hydrogen, propane. etcetcBy adding iron powder to the flame we are By adding iron powder to the flame we are able to cut most metals - “Iron Powder able to cut most metals - “Iron Powder Injection”Injection”The high intensity of heat and rapid The high intensity of heat and rapid cooling will cause hardening in low alloy cooling will cause hardening in low alloy and medium/high C steels and medium/high C steels they are thus they are thus pre-heated to avoid the hardening effectpre-heated to avoid the hardening effect

Oxyfuel gas cutting processOxyfuel gas cutting process

Oxyfuel gas cutting processOxyfuel gas cutting process

Oxyfuel gas cutting equipmentOxyfuel gas cutting equipment

The cutting The cutting torchtorch

Neutral cutting flameNeutral cutting flame

Neutral cutting flame Neutral cutting flame with oxygen cutting with oxygen cutting streamstream

Oxyfuel gas cutting equipmentOxyfuel gas cutting equipment

Torch-mix Torch-mix cutting torchcutting torch

•fuel and oxygen for fuel and oxygen for preheat flame are preheat flame are mixed within the mixed within the torchtorch

•can be injector can be injector type (for pressure type (for pressure less than 14 kPa) or less than 14 kPa) or medium pressure medium pressure typetype

Handle

Universal pressure mixer

Mixed preheat gases

Tip nut

Cutting tip

Fuel gas inlet

Preheat fuel gas valve

Oxygen inlet

Preheat oxygen valve

Cutting oxygen lever

Cutting oxygen

Torch head

Oxyfuel gas cutting equipmentOxyfuel gas cutting equipment

Tip mix cutting Tip mix cutting torchtorch

•fuel and fuel and oxygen for oxygen for preheat flames preheat flames are mixed in are mixed in the tip of the the tip of the torchtorch

Cutting oxygen

Three tube design

Cutting oxygen lever

Preheat oxygen

Preheat fuel gas

Preheat valves

Handle

Tip nut

Tip mix

Oxyfuel gas cutting related Oxyfuel gas cutting related termsterms

Oxyfuel gas cutting qualityOxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, Good cut - sharp top edge, fine and even drag lines,

little oxide and a sharp bottom edgelittle oxide and a sharp bottom edge

Cut too fast - Cut too fast - pronounced pronounced break in the drag break in the drag line, irregular cut line, irregular cut edgeedge

Cut too slow - top edge is Cut too slow - top edge is melted, deep groves in the melted, deep groves in the lower portion, heavy lower portion, heavy scaling, rough bottom scaling, rough bottom edgeedge

Oxyfuel gas cutting qualityOxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, Good cut - sharp top edge, fine and even drag lines,

little oxide and a sharp bottom edgelittle oxide and a sharp bottom edge

Preheat flame too high Preheat flame too high - top edge is melted, - top edge is melted, irregular cut, excess of irregular cut, excess of adherent drossadherent dross

Preheat flame too low - Preheat flame too low - deep groves in the deep groves in the lower part of the cut lower part of the cut faceface

Oxyfuel gas cutting qualityOxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, Good cut - sharp top edge, fine and even drag lines,

little oxide and a sharp bottom edgelittle oxide and a sharp bottom edge

Irregular travel speed - Irregular travel speed - uneven space between uneven space between drag lines, irregular bottom drag lines, irregular bottom with adherent oxidewith adherent oxide

Nozzle is too high Nozzle is too high above the works - above the works - excessive melting of excessive melting of the top edge, much the top edge, much oxideoxide

Mechanised oxyfuel cuttingMechanised oxyfuel cutting can use portable carriages or gantry type can use portable carriages or gantry type

machines machines high productivity high productivity accurate cutting for complicate shapesaccurate cutting for complicate shapes

Mechanised oxyfuel cuttingMechanised oxyfuel cuttingCutting and bevelling headCutting and bevelling head

OFW/C advantages/disadvantagesOFW/C advantages/disadvantages

DisadvantagesDisadvantages::

1) High skill factor1) High skill factor

2) Wide HAZ2) Wide HAZ

4) Slow process4) Slow process

5) Limited range of 5) Limited range of consumablesconsumables

3) Safety issues3) Safety issues

Advantages:Advantages:

1) No need for power 1) No need for power supply supply portable portable

3) Low equipment cost3) Low equipment cost

4) Can cut carbon and 4) Can cut carbon and low alloy steelslow alloy steels

5) Good on thin 5) Good on thin materialsmaterials

2) Versatile: preheat, 2) Versatile: preheat, brazing, surfacing, brazing, surfacing, repair, straighteningrepair, straightening

6) Not suitable for 6) Not suitable for reactive & refractory reactive & refractory metalsmetals

Special oxyfuel operationsSpecial oxyfuel operationsGougingGouging Rivet cuttingRivet cutting

Special oxyfuel operationsSpecial oxyfuel operationsThin sheet cuttingThin sheet cutting Rivet washingRivet washing