1. Oxyfuel gas welding and cutting

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

3. OFW - Principle of operation

4. 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

5. 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

6. 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

7. 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)

8. Flame types

9. 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

10. 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

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

12. 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

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

14. 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

15. OFW torch

16. OFW torch

17. 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

18. 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

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

20. 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

21. 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

22. 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

23. 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

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

25. 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

26. Oxyfuel gas cutting process

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

28. 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

29. 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

30. Oxyfuel gas cutting related terms

31. 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

32. 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

33. 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

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

35. Mechanised oxyfuel cutting
Cutting and bevelling head

36. 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

37. Special oxyfuel operations
Gouging
Rivet cutting

38. Special oxyfuel operations
Thin sheet cutting
Rivet washing