GROUP MEMBERS: 1. FAHMIDA BINTE SHAFIQUE, ROLL: 145003 2. MD. NAZMUL AHSAN, ROLL: 145012 3. ISHTIAQ AHMED BHUIYAN, ROLL: 145022 4. MD. ASIF KHAN SHARON, ROLL: 145031 5. MIR ABDUR RAHIM SHOHUG, ROLL: 145041 6. MAHABUB HOSSAIN, ROLL: 145050 7. MD. RAHBAR KHAN, ROLL: 145058 COURSE TITLE: Production Process - I COURSE NO: IPE 2211 DEPARTMENT: IPE CLASS: 2nd year – Even Semester SUBMITTED TO: Md. Ariful Islam, Assistant Professor, Department of IPE, RUET. SUBMISSION DATE: 22.01.2017 SESSION: 2015-16 1 Electro Slag Welding 1. Introduction: Electroslag Welding is a process that produces coalescence of metals with molten slag that melts the filler metal and the surface of the workpieces. It is virtually arc less, except for the first few minutes. It is studied in order to apply special welding joint with thick plate where cannot be applied by conventional auto-welding processes. In this paper, electroslag welding, its features, welding process, its advantages, drawbacks, applications etc. are explained briefly. 2. Definition: Electroslag welding is a process in which the electrical resistance of a molten slag held in the joint area furnishes the heat necessary for welding. The heat generated melts both the filler metal and the adjacent joint walls.1 3. Features: Electro-slag welding is primarily a method for welding heavy thicknesses in the vertical or near vertical position. 2 The mechanical properties of electro-slag welds may be inferior to multi-pass submerged arc welds. 3 High deposit rate (upto 20 kg of weld metal per hour).4 By this process, a plate of thickness 200 mm, can easily be welded in a single pass. 5 The process shows a distinct economic advantage over manual metal arc-welding of long vertical seams of above ¼ in. thickness. 6 1 D. H. Stones and G.G. Knupp, Rail Steels – Developments, Processing and Use (Philadelphia: American Society For Testing and Materials, 1976), p.135. 2 P. T. Houldcroft, Welding Processes (London: Cambridge University Press, 1967), p.59. 3 Ibid. 4 Er. R. K. Rajput, Utilisation of Electrical Power (New Delhi: Laxmi Publication, 2006), p.117. 5 P. N. Rao, Manufacturing Technology – Foundry, Forming and Welding, 2nd ed. (New Delhi: Tata McGraw-Hill, 2007), p.432. 6 Houldcroft, Welding Processes, p.59. 2 4. Power Supplies and Controls: Figure 1: Power Supply of Electroslag Welding7 The power source for electro-slag welding usually has a flat or near-flat output characteristic. This is partly a result of the low open-circuit voltage requirement, but it means in practice that a self-adjusting control system can be used in which pre-set constant-speed wire-feed motors are employed. Operating voltages of about 50 V are usual with thick plate and are determined by the open-circuit voltage. When welding plate of less than 25 mm thickness, the voltage may be reduced by about 15V. For an average size wire of 4 mm diameter, welding currents would be given between 300 and 600 A. 8 7 Jane Blunt and N. C. Balchin, Health and Safety in Welding and Allied Processes. 5th ed. (Cambridge: Woodhead, 2002), p.139. 8 P.T. Houldcroft, Welding Process Technology. 1977. Reprint (Cambridge: Cambridge University Press, 1988), p.74-75. 3 5. Working Procedure: Electroslag welding is primarily used for producing butt welds in a vertical plane. The plates to be joined are set with a gap between them and water-cooled copper shoes or dams are placed on the sides of the joint. At start of the joint, flux is placed at the bottom of the preparation and an arc is struck between the electrode wire or wires and a plate at the bottom. This melts the flux and the filler wire(s) are then dipped into the molten slag. The molten slag conducts electricity and heats and melts the sides of the joint and the end of the wire. As the joint fills up with metal, the dams are moved up at a rate that matches the rate of formation of the weld. Some slag is lost in the process when it forms a skin between the weld metal and the dams. This is replaced by feeding in more flux powder.9 Electroslag welding is therefore virtually arcless, except for the first few minutes. Even at this time the arc is largely submerged under the flux and is also shielded by the copper shoes. Thus there is no visual hazard for personnel working in the vicinity. 10 Figure 2: Working Process11 9 Blunt, Health and Safety, p.138. Ibid. 11 Rajput, Utilisation of Electrical Power, p.117. 10 4 6. Fume: The fluxes in common use may be of the fused, bonded or mechanically mixed type, the last being mixtures of several fused or bonded fluxes. The fused fluxes are the products of fused oxides and halide salts; the bonded fluxes consist of a mixture of finely divided oxides of manganese, aluminium, silicon, silicon, zirconium and titanium, bonded together with a suitable binder and agglomerated.12 Much less fume is evolved than with most other processes, because only very small amounts of flux are actually consumed. Consequently it is safe for the process to be operated in a large, well-ventilated workshop without additional precautions, but exhaust ventilation should be provided in a small inadequately-ventilated location.13 7. Wire Electrode Electroslag: The equipment comprises a carriage which is elevated by a rack mechanism on a column placed alongside the joint. On the carriage there are usually between one and three guide and contact tubes through which the electrode wires are fed changing direction from the horizontal to the vertical-down direction. One motor may feed all the wires or there may be a separate motor for each wire. The reels of electrode filler wire are also generally mounted on the carriage.14 12 Blunt, Health and Safety, p.140. Ibid. 14 Peter Houldcroft and Robert John, Welding and Cutting: A Guide to Fusion Welding and Associated Cutting Processes. 1988. Reprint (Cambridge: Woodhead, 2004), p.131. 13 5 Figure 3: Wire Electrode ESW 15 8. Consumable Guide Electro-slag Welding: The equipment for welding is considerably simpler than that for the wire electrode type of electro-slag welding chiefly because the welding head and wire feed mechanism do not need to be moved up the joint as the welding is made. After the joint has been assembled for welding with a gap slightly narrower than for wire electrode electro-slag welding a grooved steel guide plate is fitted into the joint. The essential feature of this plate is that it should contain passageways down which wire can be fed, a requirement that can be met in many ways from very thick-walled tube to a plate assembled from steel bars and sheet metal. 16 15 16 Houldcroft, Welding Processes Technology, p.72. Ibid. p.78. 6 Figure 4: Consumable Guide ESW17 9. Plate Electrode Electro-slag Welding: Another type of electro-slag welding in which plate or bar electrodes are suspended in the joint gap and lowered slowly as they are melted away by the slag bath. A three-phase system may be used with three plate electrodes connected in star fashion. The process is controlled by setting the feed motor to lower the plates at approximately the correct rate, final control being through.18 17 18 Ibid. Houldcroft, Welding Processes, p.58. 7 10. Advantages: Lower flux consumption. High deposit rate. Owing to uniform heating of the weld are, distribution and residual stresses are reduced to the minimal amounts. No special joint preparation is required. Welding is accomplished in a single pass rather than in costly multiple. Theoretically, there is no maximum thickness of the plate it can wide. There is also no theoretical electrical power per kg. Requires less electrical power per kg of deposited metal than either the submerged arc welding process or the shield arc process.19 11. Drawbacks: One of the problems which has arisen in Electroslag welding is control of the slag composition. The toughness of the weld made by this process is very low. Submerged arc welding is more economical than electroslag welding for joints below 60 mm. In ESW, there is some tendency toward hot cracking and notch sensitivity in the heat affected zone. Only flat or vertical position welding is possible in this process. Setup is very complicated.20 12. Applications: Electro-slag welding is primarily a method for welding heavy thicknesses in the vertical or near vertical position. For metal over 50 mm thick, where it competes mainly with submerged-arc welding, it has the advantage of speed and reduced distortion. because the joint is completed at one attempt, and not in a series of passes, rotational distortion is absent. The mechanical properties of electro-slag welds may be inferior to multi-pass submerged-arc welds, however. 21 19 Rajput, Utilisation of Electrical Power, p.117. William L. Galvery Jr. & Frank M.Marlow, Welding Essentials. Second Edition (Industrial Press), p.231-32. 21 Houldcroft, Welding Process Technology, p.80. 20 8 Some typical applications of this welding process are – In the fabrication of high pressure vessels. Frames of heavy mechanical and hydraulic presses. Rolling mill frames. Ship hulls. Locomotive frames. 22 Heavy structural engineering. Water turbine fabrication. Storage tank welding.23 The wire-electrode type is most common and equipment comprises a vertical boom up which the electrode feed and oscillation mechanisms and the water-cooled shoe supports are moved by rack and pinion or chain drive. Consumable guide electro-slag welding is particularly useful for the shorter lengths of weld where a variable cross-section is required. The plate-type electrode is used for short welds of exceptional thickness, where the joint cross-section approaches a square.24 In various forms, the electro-slag process is used for such widely different purposes as surfacing, ingot refining, ingot hot-topping and the butt joining of bar.25 13. Conclusion: Electro slag welding provides one of the highest rates of weld metal deposition. Unfortunately, the high heat input and the long thermal cycle inherent in the process produce a large heat affected zone which is subject to grain coarsening and a loss of fracture toughness. It is possible to improve the properties of an electro slag weld join by normalization or quenching or tempering; however, this generally impractical due to the large size of the structures fabricated by electro slag welding. 22 Rao, Manufacturing Technology, p.432. Houldcroft, Welding Process Technology, p.80. 24 Ibid. 25 Ibid. p.81 23 9 Bibliography Blunt, Jane and N. C. Balchin, Health and Safety in Welding and Allied Processes. 5th ed. (Cambridge: Woodhead, 2002), p.138-40. Galvery Jr, William L. and Frank M. Marlow, Welding Essentials. 2nd ed. (Industrial Press), p.231-32. Houldcroft, P. T. Welding Processes (London: Cambridge University Press, 1967), p.58-59. Houldcroft, P.T., Welding Process Technology. 1977. Reprint (Cambridge: Cambridge University Press, 1988), p.72-74, 77-81. Houldcroft, Peter and Robert John, Welding and Cutting: A Guide to Fusion Welding and Associated Cutting Processes. 1988. Reprint (Cambridge: Woodhead, 2004), p.131-34. Rajput, R. K., Utilisation of Electrical Power (New Delhi: Laxmi Publication, 2006), p.116-17. Rao, P. N., Manufacturing Technology – Foundry, Forming and Welding, 2nd ed. (New Delhi: Tata McGraw-Hill, 2007), p.432. Stones, D. H. and G.G. Knupp, Rail Steels – Developments, Processing and Use (Philadelphia: American Society For Testing and Materials, 1976), p.135.