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![1. Gas Welding
7
Although the oxy-acetylene process has been introduced long time ago it is still applied for its
flexibility and mobility. Equipment for oxyacetylene welding consists of just a few elements, the energy necessary for welding can be transported in cylinders, Figure 1.1.
density in normal state [kg/m3]
7
br-er1-01.cdr
© ISF 2002
0
0
°C
10.3
370
8.5
330
KW
k
/cm2
natural gas
natural gas
2850
2770
propane
flame temperature with O2
flame efficiency with O2
flame velocity with O2
43 1350
acetylene
3200
510
propane
air
300
490
335
acetylene
200
oxygen
400
oxygen cylinder with pressure reducer
acetylene cylinder with pressure reducer
oxygen hose
acetylene hose
welding torch
welding rod
workpiece
welding nozzle
welding flame
cm
/s
br-er1-02.cdr
© ISF 2002
Properties of Fuel Gas in
Combination with Oxygen
Equipment Components
for Gas Welding
Figure 1.1
oxygen
645
645
600
2
1
2
3
4
5
6
7
8
9
1.43
0.9
ignition temperature [OC]
9
1
1.17
natural gas
8
1.29
propane
6
5
2.0
acetylene
4
2.5
2.0
1.5
1.0
0.5
0
air
3
Figure 1.2
Process energy is obtained from the exothermal chemical reaction between oxygen and a
combustible gas, Figure 1.2. Suitable combustible gases are C2H2, lighting gas, H2, C3H8 and
natural gas; here C3H8 has the highest calorific value. The highest flame intensity from point
of view of calorific value and flame propagation speed is, however, obtained with C2H2.
www.SeminarsTopics.com
2005](https://image.slidesharecdn.com/05122013072956-gas-welding-done-140223094033-phpapp02/85/gas-welding-report-2-320.jpg)
![1. Gas Welding
14
By changing the gas mixture outlet speed the flame can be adjusted to the heat requirements
of the welding job, for example when welding plates (thickness: 2 to 4 mm) with the welding
chamber size 3: “2 to 4 mm”, Figure 1.14. The gas mixture outlet speed is 100 to 130 m/s
when using a medium or normal flame, applied to at, for example, a 3 mm plate. Using a
soft flame, the gas outlet speed is lower (80 to 100 m/s) for the 2 mm plate, with a hard
flame it is higher (130 to 160 m/s) for the 4 mm plate.
Depending on the plate thickness are the working methods “leftward welding” and “rightward
welding” applied, Figure 1.15. A decisive factor for the designation of the working method is
the sequence of flame and welding rod as well as the manipulation of flame and welding rod.
The welding direction itself is of no importance. In leftward welding the flame is pointed at
the open gap and “wets” the molten pool; the heat input to the molten pool can be well controlled by a slight movement of the torch (s ≤ 3 mm).
Leftward welding is applied to a plate thickness of up to 3 mm.
The weld-rod dips into the molten pool from time to time,
but remains calm otherwise. The torch swings a little.
1,5
welding-rod
flame
welding bead
denotation
flange weld
1,0
Rightward welding ist applied to a plate thickness of 3mm
upwards. The wire circles, the torch remains calm.
Advantages:
- the molten pool and the weld keyhole are easy to observe
- good root fusion
- the bath and the melting weld-rod are permanently protected
from the air
- narrow welding seam
- low gas consumption
plain butt
weld
4,0
3,0
12,0
1,0
8,0
8,0
lap seam
1,0
8,0
fillet weld
V - weld
1-2
1-2
corner weld
flame
br-er1-15e.cdr
© ISF 2002
Flame Welding
Figure 1.15
1,0
1,0
weld-rod
symbol
s
gap
preparations
~ s+1
~
plate thickness
range s [mm]
from to
r=
Advantages:
easy to handle on thin plates
br-er1-16.cdr
© ISF 2002
Gap Shapes for Gas Welding
Figure 1.16
2005](https://image.slidesharecdn.com/05122013072956-gas-welding-done-140223094033-phpapp02/85/gas-welding-report-9-320.jpg)
Uploaded byPankaj Yaduvanshi
gas welding report
1. The document describes gas welding, which uses an oxy-acetylene flame produced by combusting acetylene and oxygen. 2. Equipment for gas welding consists of oxygen and acetylene cylinders equipped with pressure regulators, hoses, and a welding torch that mixes the gases. 3. Various parameters of the welding flame such as composition, velocity, and nozzle size can be adjusted to suit different materials and thicknesses being welded.
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gas welding report
- 1.
- 2. 1. Gas Welding 7 Althoughthe oxy-acetylene process has been introduced long time ago it is still applied for its flexibility and mobility. Equipment for oxyacetylene welding consists of just a few elements, the energy necessary for welding can be transported in cylinders, Figure 1.1. density in normal state [kg/m3] 7 br-er1-01.cdr © ISF 2002 0 0 °C 10.3 370 8.5 330 KW k /cm2 natural gas natural gas 2850 2770 propane flame temperature with O2 flame efficiency with O2 flame velocity with O2 43 1350 acetylene 3200 510 propane air 300 490 335 acetylene 200 oxygen 400 oxygen cylinder with pressure reducer acetylene cylinder with pressure reducer oxygen hose acetylene hose welding torch welding rod workpiece welding nozzle welding flame cm /s br-er1-02.cdr © ISF 2002 Properties of Fuel Gas in Combination with Oxygen Equipment Components for Gas Welding Figure 1.1 oxygen 645 645 600 2 1 2 3 4 5 6 7 8 9 1.43 0.9 ignition temperature [OC] 9 1 1.17 natural gas 8 1.29 propane 6 5 2.0 acetylene 4 2.5 2.0 1.5 1.0 0.5 0 air 3 Figure 1.2 Process energy is obtained from the exothermal chemical reaction between oxygen and a combustible gas, Figure 1.2. Suitable combustible gases are C2H2, lighting gas, H2, C3H8 and natural gas; here C3H8 has the highest calorific value. The highest flame intensity from point of view of calorific value and flame propagation speed is, however, obtained with C2H2. www.SeminarsTopics.com 2005
- 3. 1. Gas Welding 8 C2H2is produced in acetylene gas genera- loading funnel tors by the exothermal transformation of calcium carbide with water, Figure 1.3. Carbide material lock is obtained from the reaction of lime and carbon in the arc furnace. gas exit C2H2 tends to decompose already at a pres- feed wheel sure of 0.2 MPa. Nonetheless, commercial quantities can be stored when C2H2 is disgrille solved in acetone (1 l of acetone dissolves sludge approx. 24 l of C2H2 at 0.1 MPa), Figure 1.4. to sludge pit br-er1-03.cdr © ISF 2002 Acetylene Generator Figure 1.3 Acetone disintegrates at a pressure of more acetone acetylene than 1.8 MPa, i.e., with a filling pressure of 1.5 MPa the storage of 6m³ of C2H2 is possible in a standard cylinder (40 l). For gas ex- porous mass change (storage and drawing of quantities up to 700 l/h) a larger surface is necessary, N acetylene cylinder therefore the gas cylinders are filled with a acetone quantity : porous mass (diatomite). Gas consumption acetylene quantity : 6000 l during welding can be observed from the cylinder pressure : 15 bar ~13 l weight reduction of the gas cylinder. filling quantity : up to 700 l/h br-er1-04.cdr © ISF 2002 Storage of Acetylene Figure 1.4 2005
- 4. 1. Gas Welding 9 Oxygenis produced by fractional distillation of gaseous cooling liquid air and stored in cyl- cylinder nitrogen air inders with a filling presbundle sure of up to 20 MPa, Fig- oxygen liquid air oxygen ure 1.5. For higher oxygen pipeline liquid consumption, storage in a liquid state and cold gasifi- tank car nitrogen vaporized cleaning compressor separation cation is more profitable. supply br-er1-05.cdr © ISF 2002 Principle of Oxygen Extraction Figure 1.5 The standard cylinder (40 l) contains, at a 50 l oxygen cylinder filling pressure of 15 MPa, 6m³ of O2 (pres- protective cap cylinder valve sureless state), Figure 1.6. Moreover, cylin- gaseous take-off connection N ders with contents of 10 or 20 l (15 MPa) as p = cylinder pressure : 200 bar V = volume of cylinder : 50 l Q = volume of oxygen : 10 000 l well as 50 l at 20 MPa are common. Gas consumption can be calculated from the pres- content control Q=pV sure difference by means of the general gas foot ring equation. manometer liquid safety valve vaporizer filling connection user still liquid gaseous br-er1-06.cdr Storage of Oxygen Figure 1.6 2005
- 5. 1. Gas Welding 10 Inorder to prevent mistakes, the gas cylinders are colour-coded. Figure 1.7 shows a survey of the present colour code and the future colour code which is in accordance with DIN EN 1089. old condition DIN EN 1089 blue white old condition DIN EN 1089 grey brown grey blue (grey) also of are different designs. Oxygen cylinder connec- helium oxygen techn. yellow The cylinder valves brown red red tions show a right-hand thread union nut. Acetylene acetylene grey hydrogen dark green grey vivid green grey grey argon-carbon-dioxide mixture argon darkgreen black grey grey carbon-dioxide br-er1-07.cdr © ISF 2006 valves are equipped with screw clamp retentions. Cylinder valves for darkgreen nitrogen cylinder other combustible gases have a left-hand thread-connection with a Gas Cylinder-Identification according to DIN EN 1089 circumferential groove. Figure 1.7 cylinder pressure working pressure Pressure regulators re- duce the cylinder pressure to the requested working pressure, Figures 1.8 and 1.9. br-er1-08.cdr © ISF 2002 Single Pressure Reducing Valve during Gas Discharge Operation Figure 1.8 2005
- 6. 1. Gas Welding 11 Ata low cylinder pressure (e.g. acetylene cylinder) and low pressure fluctuations, singlestage regulators discharge pressure locking pressure are applied; at higher cylinder pressures normally two-stage pressure regulators are used. The requested pressure is set by the adjusting screw. If the pressure increases on the low pressure side, the throttle valve closes the br-er1-09.cdr © ISF 2002 increased Single Pressure Reducing Valve, Shut Down pressure onto the membrane. Figure 1.9 The injector-type torch consists of a body with valves and welding chamber with welding nozzle, Figure 1.10. By the selection of suitable welding chambers, the flame intensity can be adjusted for welding different plate thicknesses. The special form of the mixing chamber guarantees highest possible safety against flashback, Figure 1.11. welding torch injector or blowpipe The high outlet speed of the escaping O2 generates a negative pressure mixer tube coupling nut mixer nozzle oxygen valve hose connection for oxygen A6x1/4" right in the acetylene gas line, in consequence C2H2 is sucked and injector pressure nozzle suction nozzle drawn-in. C2H2 is therefore avail- fuel gas valve welding nozzle hose connection for fuel gas A9 x R3/8” left able with a very low pressure of 0.02 up to 0.05 MPa with O2 0.3 MPa). welding torch head br-er1-10.cdr -compared (0.2 up torch body © ISF 2002 Welding Torch to Figure 1.10 2005
- 7. 1. Gas Welding 12 Aneutral flame adjustment allows the differentiation of three zones of a chemical reaction, Figure 1.12: 0. dark core: escaping gas mixture 1. brightly shining centre cone: acetylene decomposition C2H2 -> 2C+H2 1st stage of combustion 2. welding zone: 2C + H2 + O2 (cylinder) -> 2CO + H2 2nd stage of combustion 3. outer flame: 4CO + 2H2 + 3O2 (air) -> 4CO2 + 2H2O complete reaction: 2C2H2 + 5O2 -> 4CO2 + 2H2O acetylene oxygen acetylene welding torch head injector nozzle coupling nut pressure nozzle torch body br-er1-11.cdr © ISF 2002 Injector-Area of Torch Figure 1.11 2005
- 8. 1. Gas Welding 13 weldingflame ratio of mixture welding flame combustion welding nozzle centre cone welding zone 2-5 excess of oxygen normal (neutral) excess of acetylene outer flame 3200°C 2500°C 1800°C 1100°C effects in welding of steel foaming spattering sparking 400°C consequences: carburizing hardening br-er1-12.cdr © ISF 2002 Temperature Distribution in the Welding Flame reducing br-er1-13.cdr oxidizing © ISF 2002 Effects of the Welding Flame Depending on the Ratio of Mixture Figure 1.12 Figure 1.13 welding flame By changing the mixture ratio of the volumes balanced (neutral) flame nozzle size: for plate thickness of 2-4 mm O2:C2H2 the weld pool can greatly be influ- discharging velocity and weld heat-input rate: low 2 enced, Figure 1.13. At a neutral flame adjustment the mixture ratio is O2:C2H2 = 1:1. By reason of the higher flame temperature, an soft flame excess oxygen flame might allow faster discharging velocity and weld heat-input rate: middle 3 welding of steel, however, there is the risk of oxidizing (flame cutting). Area of application: brass moderate flame discharging velocity and weld head-input rate: high 4 The excess acetylene causes the carburising of steel materials. Area of application: cast iron hard flame br-er1-14.cdr © ISF 2002 Effects of the Welding Flame Depending on the Discharge Velocity Figure 1.14 2005
- 9. 1. Gas Welding 14 Bychanging the gas mixture outlet speed the flame can be adjusted to the heat requirements of the welding job, for example when welding plates (thickness: 2 to 4 mm) with the welding chamber size 3: “2 to 4 mm”, Figure 1.14. The gas mixture outlet speed is 100 to 130 m/s when using a medium or normal flame, applied to at, for example, a 3 mm plate. Using a soft flame, the gas outlet speed is lower (80 to 100 m/s) for the 2 mm plate, with a hard flame it is higher (130 to 160 m/s) for the 4 mm plate. Depending on the plate thickness are the working methods “leftward welding” and “rightward welding” applied, Figure 1.15. A decisive factor for the designation of the working method is the sequence of flame and welding rod as well as the manipulation of flame and welding rod. The welding direction itself is of no importance. In leftward welding the flame is pointed at the open gap and “wets” the molten pool; the heat input to the molten pool can be well controlled by a slight movement of the torch (s ≤ 3 mm). Leftward welding is applied to a plate thickness of up to 3 mm. The weld-rod dips into the molten pool from time to time, but remains calm otherwise. The torch swings a little. 1,5 welding-rod flame welding bead denotation flange weld 1,0 Rightward welding ist applied to a plate thickness of 3mm upwards. The wire circles, the torch remains calm. Advantages: - the molten pool and the weld keyhole are easy to observe - good root fusion - the bath and the melting weld-rod are permanently protected from the air - narrow welding seam - low gas consumption plain butt weld 4,0 3,0 12,0 1,0 8,0 8,0 lap seam 1,0 8,0 fillet weld V - weld 1-2 1-2 corner weld flame br-er1-15e.cdr © ISF 2002 Flame Welding Figure 1.15 1,0 1,0 weld-rod symbol s gap preparations ~ s+1 ~ plate thickness range s [mm] from to r= Advantages: easy to handle on thin plates br-er1-16.cdr © ISF 2002 Gap Shapes for Gas Welding Figure 1.16 2005
- 10. 1. Gas Welding 15 Inrightward welding the flame is directed onto the molten pool; a weld keyhole is gravity fillet welds PA butt-welded seams in gravity position formed (s ≥ 3 mm). Flanged welds and plain butt welds can be horizontal fillet welds applied to a plate thickness of approx. vertical fillet and butt welds PB 1.5 mm without filler material, but this does f PF PG vertical-upwelding position vertical-down position PC s not apply to any other plate thickness and horizontal on vertical wall weld shape, Figure 1.16. By the specific heat input of the different PE welding methods all welding positions can be overhead position carried out using the oxyacetylene welding PD method, Figures 1.17 and 1.18 horizontal overhead position © ISF 2002 br-er1-17.cdr Welding Positions I Figure 1.17 When working in tanks and confined spaces, the welder (and all other persons present!) have to be protected against the welding heat, the gases produced during welding and lack of oxygen ((1.5 % (vol.) O2 per 2 % (vol.) C2H2 are taken out from the PA ambient atmosphere)), Figure 1.19. The addition of pure oxygen is unsuitable (explosion hazard!). PB PF A special type of autogene method is flame- PC straightening, where specific locally applied flame heating allows for shape correction of PG workpieces, Figure 1.20. Much experience is PD needed to carry out flame straightening proc- PE esses. The basic principle of flame straightening de© ISF 2002 br-er1-18.cdr pends on locally applied heating in connecWelding Positions II tion with prevention of expansion. This procFigure 1.18 2005
- 11. 1. Gas Welding 16 esscauses the appearance of a heated zone. During cooling, shrinking forces are generated in the heated zone and lead to the desired shape correction. Safety in welding and cutting inside of tanks and narrow rooms Flame straightening welded parts first warm up both lateral plates, then belt Hazards through gas, fumes, explosive mixtures, electric current protective measures / safety precautions 1. requirement for a permission to enter 2. extraction unit, ventilation butt weld 3 to 5 heat sources close to the weld-seam 3. second person for safety reasons 4. illumination and electric machines: max 42volt double fillet weld 1,3 or 5 heat sources 5. after welding: Removing the equipment from the tank br-er1-19e.cdr © ISF 2002 br-er1-20.cdr Gas Welding in Tanks and Narrow Rooms Figure 1.19 © ISF 2002 Flame Straightening Figure 1.20 2005