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Oxyfuel gas welding and cutting. Use of gas flame WeldingGougingBrazing Heating Straightening Cutting BlastingSpraying.

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Presentation on theme: "Oxyfuel gas welding and cutting. Use of gas flame WeldingGougingBrazing Heating Straightening Cutting BlastingSpraying."— Presentation transcript:

1 Oxyfuel gas welding and cutting

2 Use of gas flame WeldingGougingBrazing Heating Straightening Cutting BlastingSpraying

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 (C 2 H 2 ) propane (C 3 H 8 ) methylacetylene-propadiene stabilised (MPS - C 3 H 4 ) hydrogen Common fuel gasses Flame temp.with O 2 3087°c2526°c2927°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

7 Combustion reactions In the bright nucleus: C 2 H 2 2C + H 2 + Heat In the inner cone - first burning stage: 2C + H 2 + O 2 2CO + H 2 + Heat CO and H 2 have reducing effect (no oxides are forming) In the outer envelope - secondary burning 2CO + O 2 2CO 2 + Heat 2H 2 + O 2 2H 2 O + Heat

8 Flame types

9 welding of most materials (including cast iron, Cu, Mg) welding of most materials (including cast iron, Cu, Mg) brazing brazing cutting cutting Oxy acetylene flame Carburising flame Oxidising flame Neutral flame reducing flame reducing flame welding of cast iron (slightly reducing!), Al, Ni and high C steels hardfacing with Cr and W carbide welding of cast iron (slightly reducing!), Al, Ni and high C steels hardfacing with Cr and W carbide excess O 2 can combine with many metals to form hard, brittle oxides welding of bronze and brasses excess O 2 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 when the oxides have a higher melting point than the parent metal applied during preheating and welding applied during preheating and welding not required for carbon steels not required for carbon steels required for Al and brazing operations required for Al and brazing operations How? dry powder dry powder paste or thick solution paste or thick solution preplaced coating on the welding rod preplaced coating on the welding rod

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

12 Acetylene generators What is the acetylene pressure? Low pressure <0,07 bar Medium pressure 0,07-1,05 bar Carbide-to-water type Water-on-carbide type Intermittent contact type Acetylene generators Stationary type Portable type 2CaC 2 LimeCoke Electric furnace smelting + 2H 2 O C 2 H 2 + Ca(OH) 2 + 2H 2 O C 2 H 2 + Ca(OH) 2

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

14 OFW torch C 2 H 2 in contact with Cu forms acetylides (explosive!) C 2 H 2 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 a medium pressure type mixer is used if the pressure of fuel gas < 14 kPa an injector type mixer is used if the pressure of fuel gas < 14 kPa an injector type mixer is used InjectorMixing nozzle/tube Union (mixer) nut Oxygen valve Fuel gas valve HandleMixing chamber

15 OFW torch

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

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

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

21 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

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

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

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

25 A jet of pure oxygen reacts with iron, that has been preheated to its ignition point, to produce the oxide Fe 3 O 4 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

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

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

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

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

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

33 Oxyfuel gas cutting quality Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge 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 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 Nozzle is too high above the works - excessive melting of the top edge, much oxide

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

35 Mechanised oxyfuel cutting Cutting and bevelling head

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

37 Special oxyfuel operations Gouging Gouging Rivet cutting Rivet cutting

38 Special oxyfuel operations Thin sheet cutting Thin sheet cutting Rivet washing Rivet washing


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