EWAC flux core arc welding for construction equipment industry

There is a new wave of demand for more cost-effective application in welding through increased deposition rate and automationThe immediate concern of the industrial user is production cost and productivity. New technologies, material and other changes are following one another in an ever faster rhythm to address competitiveness. As a result, there is a demand for more cost-effective application in welding through increased deposition rate and automation.A continuing race is ongoing among different welding processes and their modifications or adaptations in search for increasing weld deposition rate and productivity. Traditionally due to its simplicity & easy of operation Shielded Metal Arc Welding (SMAW) has been in use for several years though it has its own dis advantages like low productivity & recoveries, need for re backing, dependency on operator skill & automation not possible etc. It would be nice, it was thought, to feed a long wire trough the torch like it is done with Gas Metal Arc Welding (GMAW) but without the additional complexity of shielding gas supply. Along these lines probably the concept flux core arc welding (FCAW) was evolved.As adequate protection of the weld bead in outdoor applications, where wind interferes with shielding gases, is more achievable using either Shielded Metal Arc Welding (SMAW), or Flux Cored Arc Welding (FCAW). The Self-shielded processes cut down on the amount of equipment needed, i.e. no need to haul in a gas cylinder, hose and regulator.These two are most common processes for construction welding. FCAW-S, where S stands for self-shielded (without additional gas), produces more productive joints, using automatic process — an advantage when performing welding on joints with poor fit-up, i.e. outdoor construction joints.Needs of FCAW process in construction industriesOn-site construction of boiler, pressure vessels, offshore platforms for oil prospecting and extracting, and process piping are some of the hot areas requiring skilled welding labour which weighs much in the overall production costs. Any small increase of productivity in these areas can have significant impact on the economy of fabrication.Recognising the superior productivity achievable by flux cored wires as opposed to shielded metal arc electrodes, special attention was devoted to all positions welding, fast freeze slag, controlled amount of diffusible hydrogen levels to reduce crack susceptibility.This welding method is applicable to manual, semi-automatic and automatic welding procedures, in all positions, especially with thin diameter wire. Minimum thickness of sheet material weldable with this process is 1.6 mm.Considering the mentioned features, FCAW process is one of the most cost-effective methods for a large segment of fabrication applications. The high productivity is one of the key features which make this process suitable not only for welding of joints but also for weld surfacing. Low dilution with the parent metal can be achieved by the selection of suitable welding parameters and flux core wire.Its high deposition rate, application flexibility and good surface quality make it attractive to manufacture and are developed high-quality corrosion-resistant, temperature-resistant and wear-resistant components.FCAW processFlux-Cored Arc Welding (FCAW) uses a continuously fed tubular electrode, electrical power to melt the electrode, and may or may not use shielding gas from an externally supplied source when depositing material in the weld joint. The resulting weld bead is covered by a residual slag (melted and solidified flux) which helps protect and shape the finished weld and is easily removed upon completion of the weld. Flux Cored Welding combines the high productivity of MIG welding, using a solid electrode with the ability to weld on more contaminated base material. When compared with MIG welding, higher deposition rates are possible, especially when welding out of position.The FCAW uses semiautomatic, mechanised and fully automatic welding systems. The basic equipment includes a power supply, wire feed system and welding gun. The required auxiliary equipment, such as shielding gas, depends on the process variant used and the degree of automation. Fume-removal equipment must also be considered in most applications of the FCAW process.Power source and wire feed systemThe recommended power supply for the semi-automatic FCAW process is a constant-voltage direct current (DC) machine. Most power supplies used for semiautomatic FCAW have output ratings of 600 A or less. A power supply rated at 60 per cent or more duty cycle is the best choice for most industrial applications, whereas a duty-cycle rating as low as 20 per cent may be sufficient for maintenance and repair applications. Constant current power supplies are used in certain situations, such as field welding applications, where portable constant current SMAW power supplies are readily available. The addition of a contactor and a voltage-sensing wire feeder makes this an adequate welding system. However, such a system is only recommended when the use of a constant voltage system is not feasible, because constant current systems produce an inherently less stable welding arc than constant voltage systems.Wire feeders for constant voltage FCAW systems are generally simple and provide a constant wire feed speed. The power supply provides sufficient current to maintain an arc at the voltage that is preset at the power supply. A change in wire feed speed results in a change in the welding current.In a constant current system, the wire feeder is more complex. The welding current is preset at the power supply. The wire feeder has a voltage-sensing feedback loop that allows it to adjust the wire feed speed to maintain the desired welding voltage. The wire feeder generally contains systems to close the contactor and open the shielding gas solenoid valve (gas-shielded FCAW process only) when welding is started. Because flux-cored wires are easily deformed by excessive feed roll pressure, knurled feed rolls are generally used in the FCAW process. Some wire feeders use a single-drive roll paired with an un driven pressure roll. Others have one or two pairs of drive rolls. It is generally believed that systems having two pairs of drive rolls require the least drive roll pressure to provide dependable feeding.Manufacturing of continuous electrode for FCAWIn general flux-cored electrodes are manufactured using the process shown in Fig 1. A flat sheath material is first formed into a “U” shape. The core ingredients are poured into this “U” at the desired rate. The sheath is then closed around the core materials to form a round tube. The diameter of this tube is then reduced, generally by drawing or rolling operations, to compress the core materials and bring the electrodes to a size that is usable for welding. The finished wire is then wound on spools, coils, or other packages.Application areaFlux-cored arc welding enjoys widespread use in many construction industries. Both process variants are used for shop fabrication, but the self-shielded FCAW process is preferred for field use. Hard facing by flux core arc welding is a surfacing operation to extend the service life of industrial components, pre-emptively on new components, or as part of a maintenance program. The result of significant savings in machine down time and production costs has meant that this process has been adopted across many industries such as steel, cement, mining, petro chemical, power, construction etc. This category of flux core wire include alloy systems like work-hardening manganese alloys, low and medium alloyed steel, anti-abrasion which contains very hard metal carbides, martensitic steel alloys, nickel-base and cobalt-base alloy systems etc.Advantages of FCAW processHigh-quality weld deposit with excellent appearanceCan be used to join many types of metals over a wide thickness range  Relatively high electrode efficiency and process duty cycleExcellent weld penetration simplifies joint designThe arc is visible and easy to useBecause of its g
reater tolerance for base plate contamination, flux cored welding requires less pre-cleaning than MIGDeposition rate is up to four times greater than stick weldingThe use of self-shielded electrodes eliminates the need for flux handling or gas apparatus and is more tolerant of windy conditions present in outdoor construction than gas-shielded processes.Limitations of FCAW processPresently limited to welding ferrous metals and nickel-based alloysProcess produces a slag covering that must be removedFlux-cored welding electrode wire is more expensive on a weight basis than solid electrode wires, except for some high alloy steelsEquipment is more expensive and complex than required for stick welding; however, increased productivity usually compensates for thisIn general, more fume is generated than with MIG welding.Acceptance of FCAW in construction industriesAdvancements in technology have played an important role in evolving FCAW into a viable, relevant process option for structural steel fabricators. At one time lugging around a power source with a wire feeder was not portable or practical. But today they are more portable and easier to use than ever.Using the right equipment for FCAW is critical to ensure that the process is successful. Years ago when FCAW started taking a foothold in structural applications, contractors did not have equipment designed for that process, so they would simply hook up a wire feeder to the power source they had—mainly constant current (CC) machines set up for SMAW. That was OK and it did the job, but if you want high strength joint with more emphasis on the toughness of the weld, using the right equipment is a major factor. There’s a big difference if you use a true wire feed power source like a CV (constant voltage) machine. Even with a voltage-sensing wire feeder, a CC power source does not yield consistent results.Technology advancements have gone beyond power sources. Lightweight guns for self-shielded FCAW help prevent user fatigue. Some guns also are designed specifically to extract smoke and fume, while others come equipped with a trigger-hold capability so welders don’t have to continuously press down the trigger while making a weld pass. Volt-sense wire feeders employ a single weld cable to connect to the power source and can accommodate a variety of cored-wire diameters.On average, only 10 per cent of a welder’s time is spent actually welding when using SMAW. FCAW, on the other hand, boasts a 60 per cent welder arc on time.Flux-cored wire is being developed and manufactured to achieve mechanical and weld properties required by a particular industry, such as structural steel. Both gas-shielded and self-shielded wires are engineered to provide weld stability, which helps the welder meet requirements.If a weld has to meet a seismic code or a critical weld code, manufacturers are developing wire specifically for that industry. Honestly, that’s not happening as much with SMAW electrodes. The development of flux-cored wires — both gas-shielded and self-shielded — has been driven by industry wanting to use those wires. That’s been pulling ahead of SMAW for a while now.Hard facing by flux core arc welding is a surfacing operation to extend the service life of industrial components, preventively on new components or as a part of maintenance program. Productivity, performance and quality criteria are becoming more and more stringent and require newly developed complex materials to meet service requirement during maintenance program as part of surfacing of construction machineries. Shortages of raw materials, economy of man, machine and material etc. are leading causes for  development of sophisticated alloy system using non-conventional advance material technology like composite materials, nano crystal materials etc. in hard facing welding. These alloys are processed as filler metal in form of flux core wire consumables and welded with FCAW process to meet extra ordinary service requirements in field.Trends in hard facingHard facing is applied in cases where the surface of part is being subject to wear (abrasion, erosion, gouging), corrosion or heat. For example crushing, conveying, mixing and separating in mining, steel and iron industry, cement industry, power plants, chemical industry, over ground and underground working etc. The objective of hard facing is to surface a layer on to the base body which is most beneficially resisting to the wear causing mineral. Layers of 2 mm to 200 mm thickness can be produced using different welding processes to develop surfacing layer over base body.For this purpose, SMAW using stick electrode or tubular electrode is quite popular for small job for repair or if welding position is difficult to access. Low productivity is the major disadvantage of this process. FCAW with self-shielded wire type is popular choice for surfacing on the job or to produce pre-fabricated hard faced plate called as wear plate. These plates are made of brittle metal carbides surrounded by ductile matrix on mild steel base plate using controlled automatic FCAW process followed by plasma cutting and forming to required shape and size. These plates can be used in construction parts such as hoppers, chutes, screens, tubes, fans, separators etc.EWAC contributionsEWAC Alloys Ltd. is a wholly owned subsidiary of Larsen & Toubro Ltd. For more than 50 years, EWAC Alloys is in field of preventive maintenance and repair of machinery, using own developed welding consumables which are used in construction industries, i.e. flux-cored continuous wires and wire feeders, gas brazing rods etc.EWAC productsEWAC alloys manufactures widest range of electrodes, flux core wire and wear plates in terms of coating alloys, wear factor, hardness etc. From simple chromium carbide rich overlay to sophisticated refractory complex carbides the products are manufactured to meet application demands with reference to temperatures and other service conditions. Unique features of these products include cutting-edge manufacturing technology, precise control on raw material, ensuring consistent quality, uniform microstructure with optimised matrix to carbides ratio, special alloys to meet cost to performance requirements etc.EWAC manufactures wear plates with several types of weld-bead patterns like straight bead, E-wave beads etc. (Refer Fig 2) depending on application requirements. The wave type of weld-bead patterns offer several benefits with reference to wear properties and service life. For example, conventional straight bead wear plates when exposed to extra fine erodent can suffer from major linear wear that cause pre mature failure. In case of E-wave plates, overlay weld beads are in a weld pattern with specified directional changes. This ensures superior wear resistance. EWAC product and services to construction industriesConstruction industry employs different types of earth-moving equipment for faster execution of projects. Due to their continuous usage, there is heavy wear and tear taking place on several parts which will end up with frequent breakdowns and repairs if not attended at regular intervals. Based on service requirements, special applications engineering welding consumable are introduce to combat such a sever wear and tear of components due to abrasion, erosion, temperature, corrosion etc. These consumables are available in form of stick electrodes or FCAW wires were the deposition requirements are high. Following table highlights some of the components used in this equipment and type of wear taking place.These are some of the examples where in the service life of these components is increased by specially developed surfacing alloys. The consumables are in form of stick electrodes or continue wires or value-added “ready to use” products like wear plate and wear parts. EWAC R&D centre keeps track of customer requirements and introduces innovative value-engineered products.New technologiesEWAC’s endure has been to introduce new technologies so as to offer cost-economic solutions. Some of the technology-based products and services which are under considerations are. Nano
technology-based productsNano-based technology is rapidly emerging almost in all fields of science and technology. Application of Nano technology in welding has its own challenges. New types of alloy system are being designed and develop to form Nano size structure as especially for hard facing services which demonstrate extra ordinary properties.  Other developments include an advance surface engineering technique, using laser cladding, high performance W-C coated plates, components with tungsten carbide tipping.Conclusions Though the SMAW using conventional flux-coated electrode enjoy its own benefits of convenience of operation and capital cost effectiveness. In the recent past, both flux core and metal cored wires are gaining more popularity in view of large increase in productivity, good weldability and high-weld quality. The recent study shows that labour study is biggest cost in welding. Due to the possibility of automation, high deposition rate and efficiency, use of flux core wires greatly eliminate much of the direct labour cost associated with SMAW.  The ever-increasing demand for high-performance, cost-effective solutions has led to introduction of new consumables based on Nano technology, advanced surfacing technique like LASER, HVOF etc. These emerging technologies not only provide improved service life but can give overall cost-effective solutions in reducing down time increase productivity etc.

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