Outershield products are the group of welding consumables developed and produced by Lincoln Electric to be used with the Flux Cored Arc Welding Process (FCAW). This semi-automatic welding process is similar to gas metal arc welding (GMAW) and requires a power source and wire feeder, complete with welding gun and shielding gas supply. FCAW tubular cored wires are mostly used instead of a solid wire and MMA electrodes because of higher productivity and quality of welds.
Depending on the type and composition of the fill or core of the cored wires four main groups can be distinguished each of which are designed for specific applications:
Rutile type (regular or micro-alloyed) for smooth arc characteristics, excellent weldability, easy slag release and smooth bead appearance. CMn type wires are used for all position welding in general constructions and ship building, e.g. Outershield 71M-H for CO2 shielding gas and Outershield 71E-H for argon/CO2 mix gas. With additions of 1-1,5% Ni, Outershield 81Ni-H, 81 K2-H, 550-H and 690-H are recommended for applications where high yield strength and toughness is required.
Basic type for high restraint constructions with excellent mechanical properties for applications in high strength fine-grained steels, e.g. Outershield T55-H.
Metal Cored type for high deposition rates as for example fillets in the down hand welding position in the spray arc. Such type of wire may be also applied for positional welding or root passing in the short arc mode. This wire produces very little spatter and no slag, like the most well-known products on the market Outershield MC 710-H and MC 715-H. The welding process is described as MAG welding with metal cored electrode and is marked as 138 according the ISO standards.
The principle of metal cored wire welding is given in the picture below. Similar to MAG welding torch position and angles can be applied (however rutile flux cored will require different techniques).
Almost the same welding techniques may be applied however metal cored wires will deliver easier to operate and more forgiving arc, more regular bead appearance and lower number of welding defects. There is no need (in EU) to perform additional certification for MAG welders hence their welding qualifications are also valid for welding with metal cored wire (ISO 9606 Part 1, it was published in November 2013 and replaces EN287 Part 1 which will be withdrawn in October).
Range of qualification a - b|
|Wire used on the the test piece||Solid (S)||Metal Cored (M)||Flux-cored (B)||Flux-Cored (R, P, V, W, Y, Z)|
|Metal Cored (M)||x||x||-||-|
|Flux-Cored (R, P, V, W, Y, Z)||-||-||-||x|
|a - Abbreviations : see 4.3.2|||||||
|b - The type of core used in the qualification test of welders for root run welding without backing (ss nb) is the type of core qualified for root run welding a production |
|Key : x indicates those filler materials for which the welder is qualified / - indicates those filler materials for which the welder is not qualified |
Fig. 2 Reprint from 287-1 : Welding qualification for MAG (135) covers also MAG welding with metal cored wire (138)
OUTERSHIELD® METAL CORED WIRES
Metal cored electrodes are produced in such way that very low hydrogen content in the deposited weld metal (HDM < 1,5 ml/100 g) is obtained. It reduces the risk of hydrogen induced cracking to a minimum.
Fig 3. Hydrogen content in the weld metal of Outershield MC710-H and MC715-H as a function of time after unpacking. Storage in workshop conditions.
Typical applications cover all types of welds which can be made with:
Spray arc in dowhand position, short arc mode in all positions including root passing
Pulse modes in all positions
Outershield metal cored wires have gained their popularity because of particular advantages:
- High melt-off and deposition rates resulting from “tubular” nature of electrode (higher current density are obtained than for MAG)
- High resistance against lack of penetration or cold laps, which are especially typical disadvantages of MAG process while welding thicker plates
- Wider and more regular penetration profile
|Fig 4. Macro section of the a4 weld, PB/2F position. Outershield MC 710 – H 1,6 mm.|
|Fig. 5. Fillet weld after mechanical testing: Outershield MC710-H (left); solid wire SG2 (right)|
Wider range of applicable electrode diameters: 1,4 mm is suitable for semiautomatic welding, 1,6mm as the most productive electrode diameter for mechanized or robotic applications
Better than MAG tolerance against porosity caused by contaminations (rust, rests of paints, primers, oils, tec.), the benefit comes from deoxidizers which are added to the flux
Well visible and easy to operate arc provides better tolerance against changing weld preparation and welding gap
Smooth and low spatter welding
Successful applications in robotic welding due to the absence of slag and high travel speeds achievable
Fig. 6. Fillet weld, robotic welding with 1,2 mm Outershield 710-H. Welding mode: Rapid Arc, 24V, 280 A, TS-2,7 m/min, shielding gas Ar/CO2 90/10.
The most popular applications are filling and capping passes in PA/1G and PC/2G positions as well as fillets in PB/2F position. Iron and iron alloys metallic powders are the main flux components, so they are resistant again moisture pick-up. The flux contains small addition of deoxidizers, that’s why metal cored wires gain resistance against porosity while welding contaminated steel.
Fig. 7. Fillet weld on primed steel: Outershield MC710-H 1,2 mm
Argon blends are the most popular shielding gases (Ar/CO2 80/20, Ar/CO2 90/10, three components gas blends), however specific types of wires are designed to work with CO2 as well (Outershield MC 710C-H). The slag forming is minimal so the welds are very similar to that of solid wires with very little number of silicate islands.
The most popular applications of Outershield® metal cored wires are:
- Steel fabrications,
- Heavy machinery,
- Automotive industry and robotic welding,
- Offshore constructions.
Lincoln Electric range of metal cored wires includes
PRODUCTIVITY OF OUTERSHIELD® METAL CORED WIRES
Current density is the main factor determining melt-of rate, deposition rate (kg/h), penetration and resistance against cold laps. Schematic illustration of electrode cross section helps to understand mentioned above unbeatable advantages of metal cored wires. These benefits come from high current density, which is expressed by the ratio of current flow and cross section area of metallic tube. Welding current flows through the tube because of its lower electrical resistance (resistance of steel is lower than of metallic flux).
Fig.8. Cross section: schematic illustration of metal cored and solid wires.
The same current flows through a smaller cross sections comparing to MAG welding with solid wire, that’s why FCW always delivers higher current densities at similar wire feed speed. Because of that lower welding currents can be applied to achieve the same productivity (comparing to MAG welding with solid wires).
Proper electrode diameter is critical to obtain the best process productivity. Metal cored 1,2 mm wires deliver best deposition rate at lower currents; they are also widely applied for thin sheet material welding and work well on smaller power sources. For 1,4 mm and 1,6mm electrodes it is recommended to use power sources and with higher Amps (>280-300A) to obtain maximum process efficiency, however they’ll pose better tolerance against burn through than 1,2mm while welding at lower currents.
Deposition rate curves for 1,2mm, 1.4mm and 1,6 mm metal cored wires are presented at Fig. 5 (blue line represents typical deposition rate of 1,2 mm solid wire).
Fig. 9. Deposition rates of 1,2; 1,4 and 1,6 mm metal cored wires (MC 700, MC 710, MC 715)|
In semiautomatic welding metal cored 1,4mm wires delivers good operability and provide deposition rate which in unbeatable for 1,2 solid wire. 1,6 mm will work the best for mechanized or robotic welding, but this is very popular electrode diameter for heavy plate semiautomatic welding also.
Proper electrode diameter choice is a primary productivity factor. Clear example is given in Appendix 1, where total welding cost for a5 fillet after welding with different electrode diameters is presented. Comparing to solid wires - metal cored wires will always deliver better quality, productivity and will help to reduce the total cost of welding.
Gas metal arc welding with metal cored wires will always deliver easier to operate and more forgiving arc, regular bead appearance, lower number of welding defects, better tolerance against surface contaminations and weld preparation. The benefits come from tubular nature of the electrode and flux components. There is no need to perform additional certification for MAG welders. Metal cored electrodes work well in spray or short arc area on typical CV power sources (Powertec, CV, DC, Flextec, Speedtec) and keep the advantage over solid wires while welding with controlled waveforms (pulse, precision pulse, RapidArc, RapidX on Speedtec SP and Power Wave). Proper electrode diameter choice helps to obtain the best productivity and quality of welds with reduced total welding costs.
Lincoln Electric’s offer of Outershield® metal cored wires covers almost all types of base materials applied in steel fabrications, heavy machinery, shipbuilding, automotive industry and robotic welding, offshore constructions.
Appendix 1. Welding cost calculation for 1,2 1,4 and 1,6 mm metal cored wires
Conditions used for calculation:
- Weld size a5, overwelding - 20%
- Length of the weld: 10 m
- Shielding gas Ar/CO2 80/20
Appendix 2. Recommended starting parameters for 1,2 mm metal cored wires
Quantitative and Qualitative analisys of 10 mm steel plate welding with 135, 136, 138 methods in PB position delivered during the Seminar on Steel Construction, Lincoln Electric Poland, 24-26th of November 2010 by Waldemar Radomski, Academy of Mining and Metallurgy, Cracow, Poland.