Oxyfuel gas welding and cutting

Use of gas flame Welding Brazing Cutting Gouging Heating Straightening Blasting Spraying

OFW - Principle of operation

OFW fuel gasses Requirements for fuel gasses: high flame temperature high rate of flame propagation adequate heat content minimum chemical reaction of the flame with base and filler metals

acetylene (C2H2) propane (C3H8) methylacetylene-propadiene stabilised (MPS - C3H4) hydrogen Common fuel gasses Flame temp.with O2 3087°c 2526°c 2927°c 2660°c

OFW flame Distance from the tip of the nozzle Temperature (°C) 3100 1000 300 2÷5 mm Inner cone Outer envelope Bright nucleus OFW flame

Combustion reactions In the outer envelope - secondary burning 2CO + O2  2CO2 + Heat 2H2 + O2  2H2O + Heat 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)

Flame types

Flame types Oxy acetylene flame Neutral flame Carburising flame Oxidising flame welding of most materials (including cast iron, Cu, Mg) brazing cutting reducing flame welding of cast iron (slightly reducing!), Al, Ni and high C steels hardfacing with Cr and W carbide excess O2 can combine with many metals to form hard, brittle oxides welding of bronze and brasses

OFW fluxes Why? to remove oxides that fail to flow from the welding zone to protect the weld pool from the atmosphere When ? when the oxides have a higher melting point than the parent metal applied during preheating and welding not required for carbon steels required for Al and brazing operations How? dry powder paste or thick solution preplaced coating on the welding rod

Acetylene cylinder (section) Oxyfuel gas welding equipment Acetylene cylinder (section) Low pressure valve Acetone Porous material Steel container Fusible safety plugs

Electric furnace smelting What is the acetylene pressure? Acetylene generators 2CaC2 Lime Coke Electric furnace smelting + 2H2O  C2H2 + Ca(OH)2 What is the acetylene pressure? 0,07-1,05 bar Low pressure <0,07 bar Medium pressure Stationary type Acetylene generators Portable type Carbide-to-water type Intermittent contact type Water-on-carbide type

OFW torch Mixing tube Injector Oxygen valve Handle Oxygen connection Welding nozzle Union (mixer) nut Fuel gas valve Fuel gas connection Torch inset

OFW torch C2H2 in contact with Cu forms acetylides (explosive!) Injector Mixing nozzle/tube Union (mixer) nut Oxygen valve Fuel gas valve Handle Mixing chamber C2H2 in contact with Cu forms acetylides (explosive!) if the pressure of fuel gas > 14 kPa  a medium pressure type mixer is used if the pressure of fuel gas < 14 kPa  an injector type mixer is used

OFW torch

OFW torch

Regulators Oxygen regulator Fuel gas regulator Single stage used when slight rise in delivery pressure from full to empty cylinder condition can be tolerated Regulator type Two stage used when a constant delivery pressure from full to empty cylinder condition is required

Single stage regulator Second ary spring Cylind er press ure gauge Regula tor body Bon net Adjust ing screw Flexibl e diaphra gm Gas to torc h Worki ng press ure gauge Gas from cylind er Caps ule Prima ry sprin g 13

Single stage regulator Gas from cylinder Gas to torch Adjusting screw Primary spring Regulator body Flexible diaphragm Secondary spring

Cylinder pressure gage Two stage regulator Bonnet Adjusting screw Primary spring Gas from cylinder Cylinder pressure gage Working pressure gage Capsule Regulator body Secondary spring Gas to torch Flexible diaphragm 13

Two stage regulator Adjusting screw Primary spring second stage 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 13

Flashback arrestors Flashback - recession of the flame into or back of the mixing chamber Normal flow Reverse flow Flashback Flame barrier Built-in check valve Built-in check valve stops reverse flow Flashback flame quenched at the flashback barrier

OFW parameters Type of parent/filler Thickness of plates to be welded Tip size (Diameter of hole) Joint preparation Welding technique Flame type Approximate gas pressure Filler rod diameter Approximate gas consumption

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

Oxyfuel gas cutting process A jet of pure oxygen reacts with iron, that has been preheated to its ignition point, to produce the oxide Fe3O4 by exothermic reaction.This oxide is then blown through the material by the velocity of the oxygen stream Different types of fuel gases may be used for the pre-heating flame in oxy fuel gas cutting: i.e. acetylene, hydrogen, propane. etc By adding iron powder to the flame we are able to cut most metals - “Iron Powder Injection” The high intensity of heat and rapid cooling will cause hardening in low alloy and medium/high C steels  they are thus pre-heated to avoid the hardening effect

Oxyfuel gas cutting process

Oxyfuel gas cutting equipment The cutting torch Neutral cutting flame Neutral cutting flame with oxygen cutting stream

Oxyfuel gas cutting equipment 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 Torch-mix cutting torch fuel and oxygen for preheat flame are mixed within the torch can be injector type (for pressure less than 14 kPa) or medium pressure type

Oxyfuel gas cutting equipment Cutting oxygen Three tube design Cutting oxygen lever Preheat oxygen Preheat fuel gas Preheat valves Handle Tip nut Tip mix Tip mix cutting torch fuel and oxygen for preheat flames are mixed in the tip of the torch

Oxyfuel gas cutting related terms

Oxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge Cut too slow - top edge is melted, deep groves in the lower portion, heavy scaling, rough bottom edge Cut too fast - pronounced break in the drag line, irregular cut edge

Oxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge Preheat flame too low - deep groves in the lower part of the cut face Preheat flame too high - top edge is melted, irregular cut, excess of adherent dross

Oxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge Nozzle is too high above the works - excessive melting of the top edge, much oxide Irregular travel speed - uneven space between drag lines, irregular bottom with adherent oxide

Mechanised oxyfuel cutting can use portable carriages or gantry type machines  high productivity accurate cutting for complicate shapes

Mechanised oxyfuel cutting Cutting and bevelling head

OFW/C advantages/disadvantages 1) No need for power supply  portable 1) High skill factor 2) Wide HAZ 2) Versatile: preheat, brazing, surfacing, repair, straightening 3) Safety issues 4) Slow process 3) Low equipment cost 5) Limited range of consumables 4) Can cut carbon and low alloy steels 6) Not suitable for reactive & refractory metals 5) Good on thin materials

Special oxyfuel operations Gouging Rivet cutting

Special oxyfuel operations Thin sheet cutting Rivet washing