Shielding Gases Innovation. Consultation. Application

Shielding Gases Innovation. Consultation. Application

Industrial gases from Linde: practical development for better quality and productivity Good ideas are often just in the air. One example is the invention of air liquefaction in 1895 and of air separation in 1902 by Carl von Linde. That was the birth of industrial gases and right from the beginning their range of applications was so varied that the inventor himself took on the marketing of these innovations. Back in 1903 the first air separation plant started operation in Höllriegelskreuth near Munich. That was the foundation for a company that is still expanding successfully today. Linde Gas now has a worldwide network of production sites and sales offices and is market leader in Europe and a leading gas supplier worldwide. Linde Gas cares for 1.5 million customers. However, size is indeed not everything. Therefore, Think global -act local is our motto, which means that we are flexible at every location and take care of the individual requirements of our customers. Continuous development following the inventor s spirit Carl von Linde s innovative spirit is still present everywhere in the company. For example, it can be seen in the successful sales strategy and, in particular, in the constant further development of our products and the development of new applications. And behind this there is the one clear aim of making applica- tions with gas even more efficient and more economical. Besides high motivation and self-initiative, this demand for quality requires extensive specialist knowledge. This special know-how is continually kept updated in our company through training courses, seminars and qualification programmes. And this bears fruit for our engineers apply for around 100 patents every year. This range of services is supplemented by joint research projects with institutes and by co-operation with innovative manufacturers of equipment and materials. Our technical facilities are an important building block for further development. The modern Linde Technology Centre in Unterschleissheim near Munich Welding laboratory in Linde s Technology Centre Cover photo: CORGON He 30 improves process stability and results during MAG tandem welding 2

That is why our shielding gases and welding solutions are always tailored specifically for the customer s requirements and tested with regard to quality and performance in our Technology Centre, the aim always being to produce excellent results while increasing the travel speed and/or the deposition rate. The advantages for our customers are reduced manufacturing time and consequently lower wage costs per component with manual welding and especially with robot welding, a field with dynamic growth. Metallurgical impact of shielding gases: control of the ferrite/austenite ratio in the weld metal of a duplex steel offers our specialists ideal conditions for them to evaluate results from all over the world and to try out and optimise new technologies and manufacturing processes. They always work with practical applications in mind, i.e. using specific problems which we regularly receive for example from our customers. In this way customised solutions are developed that fulfil all the customer s requirements. The right connections for good results Industrial gases from Linde are used as invisible helpers in virtually all fields of industry and trade and in science, research, medicine and aerospace technology. For example, they fulfil important tasks in metal processing, e.g. in welding and cutting, which are tasks that require not only first-class quality but also increasingly need to be solved very efficiently. Nowadays, the value of a certain product or technique is not however measured entirely using values that can be counted and calculated exactly. With the increasing significance of environmental regulations and the elevated demands for compatibility of process and human the selection of the gas should also take into account the criterion of pollution at the workplace. And even on these issues you can always depend on us for expert advice and support. Shielding gas from Linde: more than a commodity The developments in our technical and financial environment require new ways of thinking in the classification of our product and your relationship to us as a gas partner. The potential of a welding process can only be fully utilised if the shielding gas succeeds in changing from a commodity to become an optimising tool. Our knowledge about how this tool works is what we offer to you as our active contribution to the value adding in your production chain. 3

The right shielding gas for every welding process EN 439 Process ISO 857 Shielding gases Materials ISO 14175 MAG GMAW with active gas CORGON 1 and 2 CORGON 10 and 18 MISON 8 and 18 CORGON 6 to 40 CORGON S5 and S8 CORGON He series Carbon dioxide Structural steel, steel for shipbuilding, boilers and pipes, fine-grain steels, casehardened and heat-treated steels, galvanised and aluminised coated steel sheets CRONIGON 2 MISON 2 CRONIGON He 20 CRONIGON He 50 CRONIGON S1 and S3 CRONIGON He 30S CRONIGON He 50S CRONIGON HT Stainless steels, Nickel alloys, duplex steel MIG GMAW with inert gas Argon VARIGON He MISON Ar VARIGON S MISON He VARIGON He S Aluminium, copper, nickel and their alloys TIG Tungsten inert gas Argon VARIGON He All weldable metals such as MISON Ar MISON He unalloyed and alloy steels Helium VARIGON S series aluminium, copper VARIGON H VARIGON N Argon 4.8 and 5.0 Stainless steel and Ni alloys Ni alloys, duplex, austenitic steels Reactive materials such as titanium, tantalum, zirconium PAW Plasma Arc Welding Plasmagas: Argon VARIGON H VARIGON He Shielding gas: Argon VARIGON H VARIGON He All weldable metals See TIG without gas backing With gas backing Root protection Argon For all materials where oxidation Nitrogen at the root must be avoided. Forming gas with 5 20 % H 2 Technical literature recommends and balance N 2 burning off excess gas if H 2 percentage VARIGON H is above 10%. VARIGON N Laser beam LASGON Helium Argon Gas mixtures All weldable metals Arc stud welding CORGON 18 VARIGON He 30 Structural steel, high-alloy steels Aluminium and aluminium alloys 4 CORGON, CRONIGON, MISON, VARIGON, LASGON are all registered trademarks of the Linde Group

Composition of Linde shielding gases Linde gas Name according Carbon Oxygen Nitrogen Nitrogen Helium Hydrogen Argon to EN 439 dioxide monoxide % by vol. % by vol. % by vol. % by vol. % by vol. % by vol. % by vol. Argon (Ar) I 1 100 Helium (He) I 2 100 Kohlendioxid (CO 2 ) C 1 100 CORGON 1 M 23 5 4 Balance CORGON 2 M 24 13 4 Balance CORGON 6 25 M 21 6 25 Balance MISON 8 S M21+0,03 NO* 8 0,03 Balance MISON 18 S M21+0,03 NO* 18 0,03 Balance CORGON S 5 M 22 5 Balance CORGON S 8 M 22 8 Balance CORGON He 30 M 21 (1) 10 30 Balance CORGON He 25 S M 22 (1) 3,1 25 Balance CORGON He 25 C M 21 (1) 25 25 Balance T.I.M.E. M 24 (1) 8 0,5 26,5 Balance CRONIGON 2 M 12 2,5 Balance MISON 2 S M12+0,03 NO* 2 0,03 Balance CRONIGON S 1 M 13 1 Balance CRONIGON S 3 M 13 3 Balance CRONIGON He 20 M 12 (1) 2 20 Balance CRONIGON He 50 M 12 (2) 2 50 Balance CRONIGON He 30 S M 11 (1) 0,05 30 2 Balance CRONIGON He 50 S M 12 (2) 0,05 50 Balance CRONIGON HT S M12(1) + 5 N 2 0,05 5 5 10 Balance VARIGON N 2 S I 1+2 N 2 2 Balance VARIGON N H S R 1+2 N 2 2 1 Balance VARIGON N He S I 3+2 N 2 2 20 Balance VARIGON He 30 I 3 30 Balance VARIGON He 50 I 3 50 Balance VARIGON He 70 I 3 70 Balance VARIGON He 90 I 3 90 Balance MISON Ar S I 1+0,03 NO 0,03 Balance VARIGON S M 13 0,03 Balance MISON He 30 S I 3+0,03 NO 0,03 30 Balance VARIGON He 30 S M 13 (1) 0,03 30 Balance VARIGON H 2 15 R 1 2 15 Balance Forming gas 95/5 70/30 F 2 Balance 5 30 Nitrogen (N 2 ) F 1 100 * These mixtures have the same welding properties as Ar/CO 2 mixtures with corresponding carbon dioxide content. Note: In addition to the shielding gases listed above other gas mixtures are available for special applications. Subject to change in the course of technical progress and upon customer request. 5

Properties of shielding gas components Aimed choosing of the shielding gas with the right properties The welding process can be influenced in numerous ways with the aid of shielding gases and can thus be optimised for specific applications. This means that the gas or gas mixture must be selected according to the required effects on the welding process. The opportunities for optimisation cover virtually every factor that is relevant for the welding process: Physical gas properties affect metal transfer, wetting behaviour, depth of penetration, shape of penetration, travel speed and arc starting. Compared with gases with high ionisation energy (e.g. helium), gases with low ionisation energy (e.g. argon) facilitate arc starting and arc stabilization. Proper doping of inert gases with vpm amounts of active components such as CO 2, NO or O 2 results in arc stabilisation which can improve the weld result. The dissociation energy of polyatomic components in gas mixtures enhances the heat input to the base material due to the energy released by recombination. Plasma welding of pipes Gas Dissociation Ionization energy energy [ev/molecule] [ev/molecule] (first ionization stage) H 2 4.5 13.6 O 2 5.1 13.6 CO 2 4.3 14.4 N 2 9.8 14.5 He 24.6 Ar 15.8 Kr 14.0 Physical properties of gases CORGON gas mixtures for safety relevant components in automotive industry 6

Thermal conductivity of gas components Thermal conductivity [ W/cm C ] 0.16 H 2 0.12 0.08 He 0.04 CO 2 O 2 Ar 0 2,000 4,000 6,000 8,000 10,000 Temperature [ C ] The thermal conductivity of the shielding gas influences weld geometry, weld-pool temperature and degassing and travel speed. For example, travel speed and penetration can be markedly increased by the addition of helium in MIG and TIG welding of aluminium materials or by the addition of hydrogen in TIG welding of stainless steels. Chemical properties influence both the metallurgical behaviour and the weld surface quality. Oxygen and carbon dioxide, for example, cause alloying elements to be burnt off and more fluid weld pools to be formed. Both gases act as oxidising agents. Hydrogen is a reducing gas. Argon and Helium do not react with metals: they are inert. The nitrogen contained in the VARIGON N shielding gases is dissolved by unstabilised high-alloy weld metal and thus enables the control of austenite/ferrite formation. Argon + 6 % CO 2 CORGON 18 Slag formation with different amounts of CO 2 in the shielding gas MIG welding of aluminium heat exchangers using VARIGON He Linde provides optimized shielding gases for all welding applications. Special gases can be developed to suit individual requirements. 7

Arc types in GMA welding their impact and range of applications A variety of different arcs are employed in gas-shielded metal arc welding (GMAW) with consumable wire electrodes. The type of arc is selected taking into consideration the material and its thickness, the welding position and the weld requirements. A crucial factor for good work with a certain arc is the shielding gas. In the tandem process (MIGT/MAGT) using two electrodes a combination of two arc types is possible, mainly pulse-pulse or spray-pulse. Short arc for thin sheets, out-of-position welding, and root-pass welding at Iow performance levels. The metal transfer takes place with short-circuiting and little spatter. Transition arc for medium-performance MAG welding of moderate plate thicknesses under argon gas mixtures. Metal transfer is globular with partial short-circuiting, but spatter formation is higher than with short arc welding. Long arc for higher-performance MAGC welding of thicker sections under carbon dioxide. Metal transfer is globular and there is considerable spatter. GMAW arc ranges with Ar/CO 2 mixtures (schematic) Arc voltage [ V ] Short arc Pulsed arc Transition arc Spray arc HP-short arc Arc instability Wire feed rate [ m/min ] HP = High-performance HP-spray arc Rotating arc Short arc Transition arc/long arc 8

Pulsed arc generally for all performance levels. Preferably used in MIG and MAG welding with argon-rich mixtures (instead of transition arc). Metal transfer without short-circuiting with welldefined droplet formation and transfer per pulse. Less spatter than with other arc types. The pulsed arc cannot be used with shielding gases containing more than 20-25 % CO 2. Pulsed arc Spray arc for high deposition rates and travel speeds on thicker sections under argon gas mixtures. Metal transfer in fine droplets, without short-circuiting, and virtually spatterless. Spray arc High-performance arcs for high deposition rates and travel speeds, preferably under special argon gas mixtures containing helium. The composition of the shielding gas influences metal transfer and arc stability. This enables defects caused by certain types of arc and instability to be avoided. Rotating arc 9

Shielding gases for MAG welding of structural steel The shielding gases for MAG welding of structural steels are: CORGON 1 CORGON 2 CORGON 10 CORGON 18 CORGON other mixtures with 6 40 % CO 2 MISON 8 MISON 18 CORGON S 5 CORGON S 8 Carbon dioxide/co 2 Besides quality criteria such as penetration or spatter, the composition also affects the mechanical and technological properties of the deposited weld metal. Recommendations on permissible wire/gas combinations should also be taken into account for demanding applications. Filler metals in the form of solid wire are standardised in EN 440 and in the form of cored wire in EN 758. Leaflet DVS-0916 gives filler metal recommendations for high-strength fine-grain structural steels. These shielding gases are also suitable for pipe steels, fine-grain structural steels, case-hardened steels and heattreatable steels. The composition of the shielding gas affects the welding process and the results. Using CORGON for MAG robot welding Effect of shielding gas on mechanical and technological properties * R m : Tensile strenght R e : Yield strength A 5 : Elongation at break Shielding gas Weld metal analysis Impact energyj O 2 content R m R e A 5 * % mean of 4 specimens in weld metal N/mm 2 N/mm 2 % C Mn Si + 20 C ± 0 C 20 C 30 C 40 C 50 C % by weight CORGON 1 91 % Ar, 5 % CO 2 610 472 28.1 0.08 1.32 0.67 138 124 87 83 58 48 0.031 4 % O 2 CORGON 10 90 % Ar, 10 % CO 2 CORGON 18 82 % Ar, 18 % CO 2 CORGON 25 75 % Ar, 25 % CO 2 CORGON S 12 88 % Ar, 12 % O 2 640 544 25.7 0.09 1.43 0.72 130 88 64 55 60 41 0.029 620 522 26.8 0.09 1.37 0.70 144 120 86 62 50 40 0.0305 601 505 29.3 0.09 1.30 0.65 124 97 76 61 51 41 0.034 591 510 27.5 0.06 1.20 0.60 138 126 87 67 46 40 0.0355 100 % CO 2 594 437 27.8 0.10 1.21 0.62 84 54 48 35 28 22 0.062 Wire electrode to EN 440 G3Si1 0.115 1.53 0.98 47 J boundary 10

Effects of shielding gases on MAG process and the weld results Criteria Ar/CO 2 Ar/O 2 CO 2 Penetration Flat position Out-of-position Good More reliable with increasing CO 2 content Good Can become critical if fluid weld pool leads arc (risk of incomplete fusion) Good Very reliable Thermal load on torch Lower with higher quantities of CO 2 High. Excessive torch temperature can limit performance Lower Degree of oxidation Increases with higher quantities of CO 2 High, e.g. at 8% O 2 High Porosity Decreases with higher quantities of CO 2 Most sensitive Very low Gap bridging Improves with lower quantities of CO 2 Good Worse than with gas mixtures Spatter formation Increases with higher quantities of CO 2 Low Highest spatter, increases with higher performance Heat input Increases with higher quantities of CO 2 Lowest High Slower cooling rate. Smaller risk of cracking as a result of hardening Fast cooling rate. Greater risk of cracking as a result of hardening Slow cooling rate. Little danger of cracking as a result of hardening Arc type Short arc Transition arc Spray arc Pulsed arc (max. 20-25% CO 2 ) High-performance short arc High-performance spray arc Short arc Transition arc Spray arc Pulsed arc High-performance short arc Rotating arc Short arc Long arc Knowledge of the properties listed above is necessary for successful welding. Cost-effectiveness is improved by the selection of the right gas. Thanks to their diversity and universality, CORGON shielding gases are the predominant gases used. The addition of helium extends the range of performance. 11

High-performance MAG welding with the LINFAST concept The preferred shielding gases for high-performance MAG welding are: CORGON He 30 CORGON He 25 S CORGON He 25 C T.l.M.E. Gas High-performance MAG welding is defined in DVS leaflet No. 0909-1. The term high-performance MAG welding is valid for processes with deposition rates above 8 kg/h, which is equivalent to wire feed rates above 15 m/min for a 1.2 mm solid wire. The LlNFAST concept offers specific solutions for applications in this highly productive field. The right process, arc type, shielding gas and supply method are selected taking the individual requirements into account. High-performance MAG welding with single wire Travel speeds of 150 cm/min with MAG tandem welding under CORGON He 30 in shipbuilding The spray arc (MAGs) or pulsed arc (MAGp), e.g. under CORGON He 30, is used for wire feed rates up to approx. 18 m/min. For faster rates CORGON He 25 C stabilizes the spray arc (MAGs). Above approx. 20 m/min CORGON He 25 S stabilizes the rotating arc (MAGr). The composition of the shielding gas is thus decisive for the type of arc* and for the prevention of weld defects. High-performance MAG welding with two wires Fully mechanised welding with two electrodes allows a further increase in travel speeds and/or deposition rates. Separate control of each arc in the Tandem method (MAGT) offers the advantage of flexible application. The balanced proportions of CO 2 and He in the CORGON He 30 improves the process and the welding results. *Linde patents: EP-0857533/ 0857534 CORGON He gas mixtures used for manual high-performance MAG welding on machinery Robot welding of machine beds with deposition rates of up to 13 kg/h with a rotating arc under CORGON He 25 S 12

Processes Penetration profiles Performance In the single wire process seam preparation, weld requirements and the equipment available determine the choice of the arc type. The selection of the shielding gas depends on the arc and individual quality criteria: CORGON He 30 for pulsed and spray arcs Advantages: Good wetting behaviour over the entire sheet thickness, minimum formation of spatter and oxidation CORGON He 25 S for spray, pulsed and rotating arcs Advantages: Good seam surface particularly on thin sheets, highest possible deposition rate for the single-wire process with a rotating arc on thick sheets CORGON He 25 C for spray arc - and to a limited extent for pulsed arc Advantages: Low-porosity weld for demanding tasks, reliable penetration Of course, every gas can also be used for conventional MAG welding. Here too, the helium content offers advantages: Improved wetting behaviour Increased travel speed Avoidance of lack of side wall fusion Examples of performance possible with MAG single wire: Shielding gas: CORGON He 30 CORGON He 25 C CORGON He 25 S Process: MAGs / MAGp MAGs MAGr Wire feed rate: 17 m/min 22 m/min 24 m/min Welding speed: 80 cm/min 100 cm/min 80 cm/min Whereas single-wire welding can be used for semi-mechanised (manual) applications, welding with two wire electrodes (two electrode welding) is only used for fully mechanised applications. With the MAG Tandem process seam preparation, seam requirements and the equipment available determine the choice of the arc combination and the different control of the separate wires. The advantage compared with singlewire welding is the possible increase in the travel speed. CORGON He 30 enables optimum results for a wide range of sheet thicknesses. Other mixtures can be used for special requirements. Examples of performance possible with MAG Tandem: Shielding gas: CORGON He 30 CORGON He 30 Task: Overlap joint PB on 2.5 mm sheet Fillet weld PB on 10 mm steel Welding speed: 2.8 m/min 2 m/min 13

Shielding gases for MAG welding of high-alloyed materials Shielding gases for the MAG welding of high-alloyed materials are: Carbon pick-up and burn-off for different shielding gases CRONIGON 2 MISON 2 CRONIGON S 1 CRONIGON S 3 CRONIGON He 20 CRONIGON He 50 CRONIGON He 30 S CRONIGON He 50 S CRONIGON HT These shielding gases are suitable for: stainless steels according to EN 100088 high-temperature rolled and forged steels according to SEW 4670 special stainless steels nickel-based alloys The filler metals for the shielding gas welding of stainless and high-temperature steels are standardized in EN 12072. % C Wire electrode 0.07 0.06 0.05 0.04 0.03 0.02 0.016 0.01 Type of alloy (ELC) 0.002 CORGON S8 ELC limit 0 0.006 CRONIGON S1 CRONIGON 2 0.01 CORGON 1 0.023 CORGON 18 0.049 CO 2 The carbon content is decisive for maintaining the intercrystalline corrosion resistance. For low-carbon CrNi steels (ELC steels) the amount of carbon in the weld metal should not exceed 0.03 %. The diagram with carbon pick-up and burn-off clearly shows that corrosion problems cannot occur when CRONIGON shielding gases are used. Although the carbon content measured in the weld metal lies below the ELC limit with CORGON 1, this gas should not be used for parts made of the above-mentioned alloys if they are to be used in corrosive environments. Stainless steel cladded beam using CRONIGON 2 14

Important application notes Austenitic and ferritic Cr(Ni) steels can be welded excellently in short and spray arcs. Compared with unalloyed steels the spray arc begins at approx. 20 % lower wire speeds. Pulsed arcs have advantages for the welding of high-alloy steels. They ensure stable metal transfer with little spatter over the full range of melting rates. It is also possible to use thicker wires, which are easier to feed. Nickel steels and most special stainless steels should preferably be welded with a pulsed arc. Because of their improved wetting characteristics, gas mixtures containing helium are especially advantageous for use with relatively viscous Mo-alloy steels. The CRONIGON He S series shielding gases have been developed for the MAG welding of nickel alloys*. Their low CO 2 content of only 0.055% ensures a very stable arc, retaining the corrosion properties of the material at the same time. Helium and hydrogen are added to ensure excellent wetting properties and suitability for out-of-position welding. CRONIGON HT is a new shielding gas for the MAG welding of certain hightemperature and heat-resistant nickel alloys. The nitrogen content minimizes the risk of hot cracking, which is characteristic for these materials. With CRONIGON HT the economic advantages of MAG welding can also be made available for these demanding materials. Selecting the shielding gas Material Properties Ferritic Cr steels Corrosion-resistant austenitic stainless steels Heat-resistant austenitic stainless steels Duplex and Superduplex Ni and Ni alloys CRONIGON S1 CRONIGON S3 Oxidation + o + + + + ++ ++ ++ Wetting properties o + + + ++ ++ ++ ++ ++ Travel speed o o + + ++ ++ ++ ++ ++ Interpass fusion + o + + ++ ++ ++ ++ ++ Spatter + ++ + + + + ++ ++ ++ Arc stability + ++ + + + + ++ ++ ++ Out-of-position suitability o o + + + + + o o o conditional + good ++ very good CRONIGON 2 MISON 2 CRONIGON He20 CRONIGON He50 CRONIGON He30S CRONIGON He50S CRONIGON HT *Linde patents: *EP-05 44 187, EP-06 39 423, *EP-06 39 427 MAG welding of an exhaust gas diffuser made of a nickel alloy. CRONIGON He 50 S is the shielding gas. 15

Shielding gases for MIG welding of aluminium and other non-ferrous metals The shielding gases for MIG welding of non-ferrous metals are: Argon VARIGON He MISON Ar MISON He VARIGON S VARIGON He S Short-, spray- and pulsed arcs can be used. Besides less spatter, pulsed arcs have the advantage of allowing the use of the next largest diameter of wire electrode. The thicker the wire is, the more constant the feed rate is. The filler metals for non-ferrous materials can be found in the following standards: aluminium in EN ISO 18273 copper in DIN 1733 The comparatively hotter arc produced by helium gas mixtures has proven to be especially suitable for materials with good thermal conductivity such as aluminium and copper. Magnesium and its alloys can be welded better using shielding gases without helium. Doping of inert gases (275 vpm NO in MISON Ar or MISON He and 300 vpm O 2 in the VARIGON S series) results in improved arc stabilization for gas-shielded welding of aluminium. Advantages: Considerably less spatter in MIG welding Improved weld appearance due to finer bead ripples Argon: 20 l/min VARIGON He 30: 20 l/min VARIGON He 50: 28 l/min 280 A / 25 V 282 A / 27 V 285 A / 30 V VARIGON He 70: 38 l/min 285 A / 34 V Helium in the shielding gas alters the weld geometry and affects welding voltage 16

Information on MIG welding using shielding gases containing helium Arc voltage For a given arc length, a higher arc voltage is required as the helium content increases. Weld geometry A higher level of helium produces a wider and flatter weld. Penetration is no longer finger-shaped as when argon is used but is rounder and deeper. Shielding gas quantity Helium is lighter than air. This property must be taken into account both in measuring the flow rate and in setting the minimum quantity of shielding gas. See Linde brochure No. 158 for correction factors. Advantages of added helium: 1. Better penetration Avoidance of lacks of fusion Higher travel speed 2. Hotter arc Reduced porosity Savings in filler metal 3. Wider, flatter seam Lower notch effect More favourable lines of force Using Linde Argon in MIG welding of safety relevant chassis components in the automotive industry These positive properties make helium mixtures more cost-effective than argon for many applications. Portchester Microtools (U.K.) Specialist Aluminium Container Manufacture & Design MIG welding of aluminium containers with VARIGON He 50: considerable savings in costs due to doubling of the travel speed and reduction of the arc time by 50 % compared with argon. 17

Shielding gases for TIG welding In contrast to MIG/MAG welding, the arc in TIG welding is generated between a non-consumable tungsten electrode and the base material. Inert gases such as argon or helium or gas mixtures with non-oxidizing components are necessary to protect the tungsten electrode and the weld pool. TIG welding can be used with all fusion-weldable metals. The choice of current, polarity and shielding gas depends on the parent material. Application notes Argon-helium mixtures promote the development of heat in the arc. Increased amounts of helium allow higher travel speeds. Hydrogen can also be used to improve the energy balance of the TIG arc although it should only be used with high-alloy CrNi or Ni and Ni alloys. Up to 10 % hydrogen in the argon improves penetration and travel speed. Gases containing hydrogen should never be used to weld aluminium alloys (increased porosity) and steels that react with hydrogen. Shielding gas Material Comments Argon All weldable metals Most common application Root protection necessary for reactive materials, purity 4.8 MISON Ar Al and Al alloys Increased arc stability VARIGON S and arc starting reliability MISON He 30 in AC welding VARIGON He 30 S VARIGON He 30 VARIGON He 50 VARIGON He 70 VARIGON He 90 Helium Al and Al alloys Cu and Cu alloys Additional helium for hotter arc better penetration increased travel speed Arc starting difficulties may occur with old power sources arc starting under argon VARIGON H 2 Additional Hydrogen for hotter arc VARIGON H 5 High-alloy CrNi steels better penetration VARIGON H 6 increased travel speed VARIGON H 10 Ni and Ni alloy To avoid porosity VARIGON N2/N3 Fully austenitic steels Control of the austenite/ferrite ratio VARIGON NH Duplex Higher performance through VARIGON NHe Superduplex steels additions of H 2 or He Shielding gases and materials Materials Current type Polarity Small additions of active components such as NO or O 2 to the inert gases provides additional arc stabilisation. The results obtained especially in welding aluminium with alternating current can be improved through the use of these gases. Very pure argon or argon-helium mixtures are recommended as shielding gases for the welding of metals such as titanium, tantalum or zirconium that react with gases. Therefore, gases with a minimum purity of 4.8 (equivalent to 99.998 %) are used for these materials whereas other materials can be welded using 4.6 (equivalent to 99.996 %). TIG welded container connections Unalloyed and alloy steels Copper and Cu alloys Nickel and Ni alloys = ( ) Titanium and Ti alloys Zirconium, tantalum, tungsten Aluminium ~ and Al alloys and Magnesium = ( ) and Mg alloys VARIGON He 90 or helium is used for direct current TIG welding of Al and Mg alloys. 18

TIG Argon arc TIG VARIGON H5 arc TIG Helium arc Three shielding gases used in TIG welding and their effects on the arc. Current I = 240 A. Base material = 1.4301 Argon VARIGON He 50 10 l/min 15 l/min Travel speed: 10 cm/min 20 cm/min Effects of shielding gases on the travel speed. A higher level of helium results in a higher travel speed. The photographs show welds in a 3 mm thick AlZn 4.5 Mg 1 alloy. Argon VARIGON H 6 Travel speed: 7 cm/min 11 cm/min TIG arcs with and without addition of H 2. Penetration and travel speed can be considerably increased by adding H 2 to the shielding gas. 19

Root protection and forming gases for improved corrosion resistance In many cases protection of the weld root is needed in order to ensure optimal corrosion resistance of the part. Oxidation and tarnish are prevented by displacing atmospheric oxygen. Relative densities of shielding gases for root protection 1.4 Two methods can be used: Displacement of air by inert gases such as argon or by virtually inert gases such as nitrogen Displacement of air plus utilization of the reducing action of hydrogen Reducing root shielding gases consist of: Nitrogen with hydrogen additions These mixtures are generally called forming gases. Argon with hydrogen additions VARIGON H series Heavier than air 1.3 1.2 1.1 1.0 Air Ar mixtures Pure argon is only used rarely, for example for steels that react with hydrogen or nitrogen or for highly reactive materials such as titanium. Gases in the MISON series are unsuitable for root protection because they contain NO as an active component. Proper use of forming gases requires that their relative densities are taken into account, e.g. in the purging of containers from below (high-density gases) or above (Iow-density gases). Lighter than air 0.9 0.8 0.7 N 2 mixtures 0.6 4 8 12 16 20 24 % by vol. H 2 Safety information: For safety reasons DVS leaflet No. 0937 recommends the burning off of hydrogen in the case of mixtures containing 10 % by vol. hydrogen and more. Shielding gases for root protection with more than 4 % by vol. hydrogen can form explosive mixtures with air or oxygen. The user must take precautions to prevent the formation of such gas mixtures, e.g. prevention of air pockets, prevention of uncontrolled air penetration, etc. During forming processes involving large closed parts, it should be ensured that there is no risk of suffocation before any worker enters the part. The possible lack of oxygen must also be taken into account during work in confined spaces. 20

Application notes Gases for root protection are standardized in EN 439 as follows: Group R (Ar/H 2 mixtures) Group I (Ar + Ar/He mixtures) and Group F (N 2 + N 2 /H 2 mixtures). To prevent the formation of any tarnish, forming gas must be continually supplied until the part has cooled to approx. 220 C. To prevent any oxidation during welding, certain pre-purging times must be observed to displace air. The times required depend on the relevant purge gas flow rate and the geometry of the part. As a guideline, the required volume of shielding gas is 2.5-3.0 times the geometric volume of the pipe measured from the injection point to the weld. The flow rate should be approx. 5 to 12 l/min. depending on the diameter of the workpiece. In titanium-stabilized CrNi steels. forming gases containing N 2 cause a yellow discoloration of the weld root. For base materials containing N 2. e.g. super duplex steels, forming gases containing high percentages of N 2 (up to 100 %) are beneficial, e.g. to improve corrosion resistance. Forming gas Argon Ar/H 2 mixtures N 2 /H 2 mixtures N 2 Ar/N 2 mixtures Base material All materials Austenitic steels. Ni and Ni alloys Steels, excepted high-strength fine-grain structural steel, austenitic steel (not Ti-stabilized) Austenitic CrNi steels, duplex- and super duplex teels Welding under forming gas Root protection gases for various materials Typical yellow discoloration: titanium-stabilized CrNi steel with nitrogen forming No discoloration: titanium-stabilized CrNi steel with argon/hydrogen forming 21

Shielding gases for plasma-arc welding As in TIG welding, the arc in plasma welding is generated between a nonconsumable tungsten electrode and the base material. However, in contrast to TIG welding, the plasma-arc is concentrated by the torch design (water-cooled copper tip), resulting in a significantly higher power density. There are three variants of the plasma-arc welding process: Microplasma welding for thin and very thin sheets at least approx. 0.1 mm with minimum currents of approx. 0.3 A Melt-in welding for sheet thicknesses of 1-3 mm Keyhole plasma-arc welding for thick sections up to approx. 8 mm in one run, or thicker sections in multiple runs Plasma-arc welding always requires two gases: Plasma-arc welding of spiral aluminium pipes Plasma gas (centre gas), chiefly argon, sometimes with hydrogen or helium additions Shielding gas (outside gas), which may have other constituents added to argon, e.g. hydrogen for stainless steel and Ni alloys, or helium for welding aluminium, AI alloys, titanium and copper alloys. Other plasma techniques include: Plasma powder arc welding for joining and cladding Plasma hot-wire cladding Plasma-MIG welding for high-performance joining. Plasma-arc welding of galvanized structural steel 22

Shielding gases for arc stud welding Recent investigations have shown that the quality of drawn arc stud welding using the methods BH 10 and BH 100 can be improved significantly through the use of proper shielding gases. Tried and tested combinations of shielding gases and materials are shown in the table on the right. Combinations of shielding gases and materials Base material Stud material Shielding gas Structural steel Structural steel CORGON 18 High-alloy steel High-alloy steel CORGON 18 AlMg 3 Al 99,5 or AlMg 3 VARIGON He 30 Through the avoidance of ceramic rings, shielding gases are particularly advantageous for fully mechanised welding, including robot welding. Steel and aluminium studs welded using shielding gas 23

Shielding gases for laser welding In comparison with conventional welding processes (MAG, TIG, etc.) laser beam welding allows heat to be applied more accurately with less distortion and higher travel speeds. The majority of laser welds can be made without filler metal. However, filler metal may be necessary for gap bridging or metallurgical reasons. Laser welding is suitable for example on steel, light metal and thermoplastics. Two different types of laser are commonly used for laser welding: the CO 2 laser and the Nd:YAG laser. Both types of laser require shielding gases to make high-quality welds. As with metal inert gas techniques, more and more uses are being found for gas mixtures for laser welding. As the process becomes more widespread, further advances are being made in the development of shielding gases. One example is LASGON C1 that is used for the laser welding of unalloyed, alloyed and galvanised steels. CO 2 lasers CO 2 lasers are the most commonly used lasers for welding in the automotive and related industries. The choice of the right shielding gas is of major importance in order to produce high-quality welding seams. High-quality shielding gases such as LASGON C1, diverse gas mixtures, helium or argon assist the user. But it is not simply the type of gas that is of importance for the quality of the resulting weld: the way the shielding gas is supplied also plays a significant role. A large nozzle allowing a slow, laminar flow as near as possible to the welding site prevents turbulences of the shielding gas and the surrounding air, the result being an optimum weld. Welding a gear with a CO 2 laser Source: Trumpf Cam welded with a CO 2 laser 24

Argon Helium Plasma development and penetration behaviour using a CO 2 laser with different shielding gases Nd:YAG lasers The main welding applications for Nd:YAG lasers are in precision engineering and in electrical and electronic engineering. However, more and more applications are also arising in metal machining. Laser powers of up to 4 kw are commonly used. Since the wavelength of a Nd:YAG laser exhibits little or no interaction with shielding gases, their choice only needs to take account of metallurgical factors. Accordingly, Argon in LASPUR quality is mainly used, although Helium, Nitrogen or gas mixtures are also suitable. Heart pacemaker casing welded with a Nd:YAG laser Source: Lumonics 25

Linde Publications and Applications Notes for Practical Use Special Releases 92 Effect of Welding Conditions on Airborne Contaminants Generated in Gas-Shielded Arc Welding and Effect of the Workplace Conditions 146 MAGM Welding (GMAW) of Corrosion Resistant Duplex Steel - 22 Cr 5 (9) Ni 3 Mo - Effect of Shielding Gases and Process Variations 156 Application Technology Criteria for Orbital TIG (GTA) Welding of Electropolished High-Alloy Steel Tubes 158 Shielding gas for Welding and Backup Purging - Factors to be taken into account 03/90 Control of the Arc Welding Process in Manufacturing 22/93 Gas-Shielded Arc Welding of Aluminium 34/97 Pulsed MAGM Welding of Nickel Alloy 36/97 High-performance MAG Welding with the LINFAST Concept 38/97 TIG Welding of Aluminium Alloys 04/99 A Choice of Shielding Gases for Welding the Variety of Steel Grades 11/99 Hydrogen in the Shielding gas 42/01 Shielding gases for Welding and Root shielding of Chrome Nickel Steels Data Sheets (on request) Safety Data Sheets (on request) Safety Instructions (on request) Brochures Centralised Gas Supply Systems LASPUR Gases for Laser Technology LASPUR Guide for Laser Users: Gases and Gas Supply Systems Tank Installations for the Supply of Liquefied Gases Technology Centre - Research, Development, Consulting Tips for practitioners (on request) 26

Economical gas supply Modern production plants, regular quality control and a international supply network lead to our extremely reliable supply service. Not only are our supply methods very diverse, they are also economical. Linde offers tailored and economical supply methods for every customer: from 10 litre cylinders to 75,000 litre tanks. Our dense network of supply sites, the many production sites and a complete product range are a guarantee for high product availability, excellent supply reliability and short distances for personal callers. In addition, Linde offers safe and reliable, economic and functional gas supply systems. We design and manufacture these systems to suit your special requirements. Steel cylinders Capacity Contents* Litres m 3 10 2.1 2.4 20 4.0 4.7 52 9.1 11.8 * Gaseous contents. The amount in the cylinder depends on the type of gas. Cylinder bundles Contents* m 3 106.8 141.6 Caution: New colour markings To comply with the new EN 1089 Part 3, the colour markings must now be on the cylinder shoulder. As the standard foresees a transition period up to 2006, there may still be cylinders with the old colour markings in circulation up to this date. * Gaseous contents. The amount in the bundle depends on the type of gas. Storage tanks Contents 600 75,000 l Further information on the transition to the new colour markings is available from every Linde sales centre. 27

Linde Gas Making the difference 00043487670 0998. 0902-3.4 un Subject to alteration. Printed on chlorine-free bleached paper. Linde Gas is in the business of making a difference in everything we do. For the benefit of our customers. Through innovative solutions within manufacturing industry, metallurgy, chemistry, food processing, medicine, specialty gases, alternative fuel technologies and the environment. This difference is reflected in our position as a leading company in Europe and as a major driving force world-wide. Gas technology that works for you Created through forward thinking, a close customer relationship and a sound business sense, the Linde Gas combination of gas products and support services, innovative hardware, customized solutions and on-site supply systems generates new and profitable opportunities. Linde Gas technology daily drives entrepreneurship the world over with our employees all working concertedly to keep making that difference. Linde AG Linde Gas Division Phone: +49 89 7446-0 Fax: +49 89 7446-1230 www.linde-gas.com