1. Gas Welding C k. br-er1-02.cdr ISF 2002

Size: px

Start display at page:

Download "1. Gas Welding C k. br-er1-02.cdr ISF 2002"

Valerie Alexander
6 years ago
Views:

1 1. Gas Welding

2 3propane 1. Gas Welding 7 Although the oxy- process has been introduced long time ago it is still applied for its flexibility and mobility. Equipment for oxy 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/m ] cylinder with pressure reducer 2 cylinder with pressure reducer 3 hose 4 hose 5 welding torch 6 welding rod 7 workpiece 8 welding nozzle 9 welding flame O ignition temperature [ C] air 1.29 air flame temperature with O 2 flame efficiency with O 2 flame velocity with O C k KW / cm cm / s propane propane 0.9 natural gas natural gas 645 natural gas 1.43 br-er1-01.cdr br-er1-02.cdr Equipment Components for Gas Welding Properties of Fuel Gas in Combination with Oxygen Figure 1.1 Figure 1.2 Process energy is obtained from the exothermal chemical reaction between and a combustible gas, Figure 1.2. Suitable combustible gases are C 2 H 2, lighting gas, H 2, C 3 H 8 and natural gas; here C 3 H 8 has the highest calorific value. The highest flame intensity from point of view of calorific value and flame propagation speed is, however, obtained with C 2 H 2.

1. Gas Welding 8 loading funnel material lock C 2 H 2 is produced in gas generators by the exothermal transformation of calcium carbide with water, Figure 1.3.

3 1. Gas Welding 8 loading funnel material lock C 2 H 2 is produced in gas generators by the exothermal transformation of calcium carbide with water, Figure 1.3. Carbide is obtained from the reaction of lime and carbon in the arc furnace. gas exit feed wheel grille sludge C 2 H 2 tends to decompose already at a pressure of 0.2 MPa. Nonetheless, commercial quantities can be stored when C 2 H 2 is dissolved in acetone (1 l of acetone dissolves approx. 24 l of C 2 H 2 at 0.1 MPa), Figure 1.4. to sludge pit br-er1-03.cdr Acetylene Generator Figure 1.3 Acetone disintegrates at a pressure of more than 1.8 MPa, i.e., with a filling pressure of 1.5 MPa the storage of 6m³ of C 2 H 2 is possible in a standard cylinder (40 l). For gas exchange (storage and drawing of quantities up to 700 l/h) a larger surface is necessary, therefore the gas cylinders are filled with a porous mass (diatomite). Gas consumption during welding can be observed from the weight reduction of the gas cylinder. acetone porous mass N cylinder acetone quantity : ~13 l quantity : 6000 l cylinder pressure : 15 bar filling quantity : up to 700 l/h br-er1-04.cdr Storage of Acetylene Figure 1.4

$1. Gas Welding 9 Oxygen is produced by cooling nitrogen gaseous cylinder fractional distillation of liquid air and stored in cyl- air liquid air pipeline liquid bundle inders with a filling pressure$

4 1. Gas Welding 9 Oxygen is produced by cooling nitrogen gaseous cylinder fractional distillation of liquid air and stored in cyl- air liquid air pipeline liquid bundle inders with a filling pressure of up to 20 MPa, Figure 1.5. For higher consumption, storage in a nitrogen vaporized tank car liquid state and cold gasification is more profitable. br-er1-05.cdr cleaning compressor separation supply Principle of Oxygen Extraction Figure 1.5 The standard cylinder (40 l) contains, at a filling pressure of 15 MPa, 6m³ of O 2 (pressureless state), Figure 1.6. Moreover, cylinders with contents of 10 or 20 l (15 MPa) as well as 50 l at 20 MPa are common. Gas consumption can be calculated from the pressure difference by means of the general gas equation. manometer N 50 l cylinder protective cap cylinder valve take-off connection p = cylinder pressure : 200 bar gaseous V = volume of cylinder : 50 l Q = volume of : l foot ring safety valve content control Q = p V liquid vaporizer filling connection still user liquid gaseous br-er1-06.cdr Storage of Oxygen Figure 1.6

5 1. Gas Welding 10 In order 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 old condition DIN EN 1089 br-er1-07.cdr blue Figure 1.7 techn. yellow argon darkgreen nitrogen white blue () brown dark green black darkgreen Gas Cylinder-Identification according to DIN EN 1089 old condition DIN EN 1089 red helium hydrogen argon-carbon-dioxide mixture carbon-dioxide brown red vivid green ISF 2006 The cylinder valves also of are different designs. Oxygen cylinder connections show a right-hand thread union nut. Acetylene cylinder valves are equipped with screw clamp retentions. Cylinder valves for other combustible gases have a left-hand thread-connection with a circumferential groove. cylinder pressure working pressure Pressure regulators reduce the cylinder pressure to the requested working pressure, Figures 1.8 and 1.9. br-er1-08.cdr Figure 1.8 Single Pressure Reducing Valve during Gas Discharge Operation

1. Gas Welding 11 discharge pressure locking pressure At a low cylinder pressure (e.g. cylinder) and low pressure fluctuations, singlestage regulators are applied; at higher cylinder pressures normally two-stage pressure regulators are used.

cdr Single Pressure Reducing Valve, Shut Down increased 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.

6 1. Gas Welding 11 discharge pressure locking pressure At a low cylinder pressure (e.g. cylinder) and low pressure fluctuations, singlestage regulators 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 Single Pressure Reducing Valve, Shut Down increased pressure onto the membrane. Figure 1.9 The injector-type torch consists of a body with valves and welding chamber with welding nozzle, Figure 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 The high outlet speed of the escaping O 2 generates a negative pressure in the gas line, in consequence C 2 H 2 is sucked and drawn-in. C 2 H 2 is therefore available with a very low pressure of 0.02 up to 0.05 MPa -compared with O 2 (0.2 up to 0.3 MPa). br-er1-10.cdr Figure 1.10 welding torch injector or blowpipe coupling nut mixer tube mixer nozzle valve welding nozzle welding torch head injector pressure nozzle suction nozzle fuel gas valve Welding Torch hose connection for A6x1/4" right hose connection for fuel gas A9 x R3/8 left torch body

1. Gas Welding 12 A neutral flame adjustment allows the differentiation of three zones of a chemical reaction, Figure 1.12: 0. dark core: escaping gas mixture 1.

7 1. Gas Welding 12 A neutral 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: decomposition C 2 H 2 -> 2C+H 2 2. welding zone: 1 st stage of combustion 2C + H 2 + O 2 (cylinder) -> 2CO + H 2 3. outer flame: 2 nd stage of combustion 4CO + 2H 2 + 3O 2 (air) -> 4CO 2 + 2H 2 O complete reaction: 2C 2 H 2 + 5O 2 -> 4CO 2 + 2H 2 O welding torch head injector nozzle pressure nozzle coupling nut torch body br-er1-11.cdr Injector-Area of Torch Figure 1.11

1. Gas Welding 13 welding flame combustion welding flame ratio of mixture welding nozzle 2-5 centre cone welding zone outer flame excess of normal (neutral) excess of 3200 C 2500 C 1800 C 1100 C 400

cdr Temperature Distribution in the Welding Flame Effects of the Welding Flame Depending on the Ratio of Mixture Figure 1.12 Figure 1.

middle 3 moderate flame discharging velocity and weld head-input rate: high 4 By changing the mixture ratio of the volumes O 2 :C 2 H 2 the weld pool can greatly be influenced, Figure 1.13.

8 1. Gas Welding 13 welding flame combustion welding flame ratio of mixture welding nozzle 2-5 centre cone welding zone outer flame excess of normal (neutral) excess of 3200 C 2500 C 1800 C 1100 C 400 C sparking consequences: carburizing hardening effects in welding of steel reducing foaming spattering oxidizing br-er1-12.cdr br-er1-13.cdr Temperature Distribution in the Welding Flame Effects of the Welding Flame Depending on the Ratio of Mixture Figure 1.12 Figure 1.13 welding flame balanced (neutral) flame nozzle size: for plate thickness of 2-4 mm discharging velocity and weld heat-input rate: low 2 soft flame discharging velocity and weld heat-input rate: middle 3 moderate flame discharging velocity and weld head-input rate: high 4 By changing the mixture ratio of the volumes O 2 :C 2 H 2 the weld pool can greatly be influenced, Figure At a neutral flame adjustment the mixture ratio is O 2 :C 2 H 2 = 1:1. By reason of the higher flame temperature, an excess flame might allow faster welding of steel, however, there is the risk of oxidizing (flame cutting). Area of application: brass The excess causes the carburising of steel materials. Area of application: cast iron hard flame br-er1-14.cdr Effects of the Welding Flame Depending on the Discharge Velocity Figure 1.14

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

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.

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.

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).

Advantages: easy to handle on thin plates plate thickness range s [mm] from to gap preparations denotation symbol 1,5 ~ s+1 r = s flange weld welding-rod flame welding bead 1,0 Rightward

9 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 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 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. Advantages: easy to handle on thin plates plate thickness range s [mm] from to gap preparations denotation symbol 1,5 ~ s+1 r = s flange weld welding-rod flame welding bead 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 1,0 4,0 3,0 12,0 1,0 8, plain butt weld V - weld corner weld 1,0 8,0 lap seam 1,0 8,0 fillet weld weld-rod flame br-er1-15e.cdr br-er1-16.cdr Flame Welding Gap Shapes for Gas Welding Figure 1.15 Figure 1.16

1. Gas Welding 15 PA butt-welded seams in gravity position gravity fillet welds In rightward welding the flame is directed onto the molten pool; a weld keyhole is formed (s 3 mm).

10 1. Gas Welding 15 PA butt-welded seams in gravity position gravity fillet welds In rightward welding the flame is directed onto the molten pool; a weld keyhole is formed (s 3 mm). Flanged welds and plain butt welds can be PB horizontal fillet welds vertical fillet and butt welds applied to a plate thickness of approx. 1.5 mm without filler material, but this does s f PF PG PC vertical-upwelding position vertical-down position horizontal on vertical wall not apply to any other plate thickness and weld shape, Figure By the specific heat input of the different PE overhead position welding methods all welding positions can be carried out using the oxy welding PD horizontal overhead position method, Figures 1.17 and 1.18 br-er1-17.cdr When working in tanks and confined Welding Positions I spaces, the welder (and all other persons Figure 1.17 present!) have to be protected against the welding heat, the gases produced during welding and lack of ((1.5 % (vol.) O 2 per 2 % (vol.) C 2 H 2 are taken out from the ambient atmosphere)), Figure The addi- PA tion of pure is unsuitable (explosion hazard!). PF PB A special type of autogene method is flame- PC straightening, where specific locally applied flame heating allows for shape correction of workpieces, Figure Much experience is PD PG needed to carry out flame straightening processes. PE The basic principle of flame straightening depends on locally applied heating in connection with prevention of expansion. This proc- br-er1-18.cdr Welding Positions II Figure 1.18

1. Gas Welding 16 ess causes the appearance of a heated zone. During cooling, shrinking forces are generated in the heated zone and lead to the desired shape correction.

11 1. Gas Welding 16 ess causes 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 Hazards through gas, fumes, explosive mixtures, electric current first warm up both lateral plates, then belt protective measures / safety precautions 1. requirement for a permission to enter 2. extraction unit, ventilation 3. second person for safety reasons 4. illumination and electric machines: max 42volt 5. after welding: Removing the equipment from the tank butt weld 3 to 5 heat sources close to the weld-seam double fillet weld 1,3 or 5 heat sources br-er1-19e.cdr br-er1-20.cdr Gas Welding in Tanks and Narrow Rooms Flame Straightening Figure 1.19 Figure 1.20

OXY/ACETYLENE WELDING AND CUTTNG

AN INTRODUCTION TO OXY/ACETYLENE WELDING AND CUTTNG wws group support@weldability.com WARNING: This document contains general information about the topic discussed herein. This document is not an application