Oxyfuel%20gas%20welding%20and%20cutting

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Oxyfuel gas welding and cutting
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Use of gas flame
Welding
Gouging
Brazing
Cutting
Heating
Straightening
Blasting
Spraying
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OFW - Principle of operation
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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

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OFW flame
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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)
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Flame types
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Flame types
Oxy acetylene flame
Oxidising flame
Carburising flame
Neutral flame

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

• excess O2 can combine with many metals to form
  hard, brittle oxides welding of bronze and brasses

• reducing flame
• welding of cast iron (slightly reducing!), Al, Ni
  and high C steels hardfacing with Cr and W
  carbide

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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

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Oxyfuel gas welding equipment
Low pressure valve
Acetone
Porous material
Steel container
Fusible safety plugs
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Acetylene generators
Low pressure
Medium pressure
Acetylene generators
Stationary type
Portable type
Carbide-to-water type
Water-on-carbide type
Intermittent contact type
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OFW torch
Mixing tube
Injector
Oxygen valve
Handle
Oxygen connection
Welding nozzle
Union (mixer) nut
Fuel gas valve
Fuel gas connection
Torch inset
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OFW torch

• C2H2 in contact with Cu forms acetylides
  (explosive!)
• if the pressure of fuel gas gt 14 kPa ? a medium
  pressure type mixer is used
• if the pressure of fuel gas lt 14 kPa ? an
  injector type mixer is used

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OFW torch
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OFW torch
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Regulators
Fuel gas regulator
Oxygen 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

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Single stage regulator
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Single stage regulator
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Two stage regulator
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Two stage regulator
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Flashback arrestors

• Flashback - recession of the flame into or back
  of the mixing chamber

Normal flow
Reverse flow
Flashback
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OFW parameters
Type of parent/filler
Thickness of plates to be welded
Tip size (Diameter of hole)
Welding technique
Joint preparation
Flame type
Approximate gas pressure
Filler rod diameter
Approximate gas consumption
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Weld quality
OFW quality (left to right) - OK torch too high
torch too low travel speed too slow travel
speed too fast
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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
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Oxyfuel gas cutting process
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Oxyfuel gas cutting equipment
The cutting torch
Neutral cutting flame
Neutral cutting flame with oxygen cutting stream
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Oxyfuel gas cutting equipment
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

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Oxyfuel gas cutting equipment
Tip mix cutting torch

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

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Oxyfuel gas cutting related terms
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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

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Oxyfuel gas cutting quality

• Good cut - sharp top edge, fine and even drag
  lines, little oxide and a sharp bottom edge

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

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

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Oxyfuel gas cutting quality

• Good cut - sharp top edge, fine and even drag
  lines, little oxide and a sharp bottom edge

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

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

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Mechanised oxyfuel cutting

• can use portable carriages or gantry type
  machines ? high productivity
• accurate cutting for complicate shapes

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Mechanised oxyfuel cutting

• Cutting and bevelling head

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OFW/C advantages/disadvantages
Disadvantages
Advantages
1) High skill factor
1) No need for power supply ? portable
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
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Special oxyfuel operations

• Rivet cutting

• Gouging

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Special oxyfuel operations

• Rivet washing

• Thin sheet cutting