EWAC flux core arc welding for construction equipment industry

April 11, 2014 11:09 am

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

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