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Development Of Basic Agglomerated Flux For Submerged arc welding - harry_krish2004 - 10-06-2017 Development Of Basic Agglomerated Flux For Submerged Arc Welding
Deviprakash K J & Anand Krishnan O K Department of Mechanical Engineering Mohandas College of Engineering and Technology [attachment=10243] Abstract A significant percentage of the flux used in submerged are welding gets converted into very fine particles particles termed as flux dust due to transportation and handling. If these very fine particles are not removed fromt he flux before welding, it may results into defect like surface pitting and porosity. At the same time dumping of this flux dust will create pollution. Therefore to reduce the cost of welding and pollution, in the present study, attempts have been made to investigate the feasibility of using developed basic agglomerated flux by urilizing wasted flux dust in place of parent commercial basic flux. The chemical composition, tensile strength, toughness and radiographic examination of the all weld metal prepared by using the developed basic flux as well as same parent commercially available basic flux were compared. These properties for the all weld metal prepared by using the developed basic flux were found to be in the same range as that being prepared from the parent basic flux. Keywords : Submerged arc welding. Tensile properties, Toughness Introduction Submerged arc welding (SAW) produces coalescence of the metals by heating them with an arc between a basic metal electrode and the work. The arc and molten metal are submerged in blanket of granular fusible flux on the work. Submerged arc welding contributes to approximately 10% of the total welding. It is one of the most widely used processes for fabrication of thick plates, pipes, pressure vessels, rail tanks, ships, heat exchangers etc. Submerged arc welding process is characterized by higher metal deposition rate, deep weld penetration, high speed welding of plates at over 2.5 m/min and minimum emission of welding fume or arc light [I). Deposition rates approaching 45kglh have been reported[2]. This process is commercially suitable for welding of low carbon steel, high strength low alloy steel, nickel base alloys and stainless steel [3]. Shielding is obtained from a blanket of granular flux, which is laid directly over the weld area. Flux plays an important role in deciding the weld metal quality [4]. It may cost 50% of the total welding cost in submerged arc welding. It influences the weld metal physically, chemically and metallurgically. Physically, it influences the bead geometry and shape relationships, which in turn affects the load carrying capacity of the weld metal [5]. Chemically it affects the chemistry of weld metal, which in turn influences the mechanical properties of the weld metal [6]. Metallurgically, it influences the microstructure and hence again affects the mechanical properties of the weld metal [7]. It has been reported that agglomerated fluxes produce weld deposits of better ductility and impact strength as compared with fused fluxes [8]. Alloy transfer efficiency is also better in case of agglomerated fluxes. These f1uxes are hygroscopic in nature, therefore baking is essential for good weld metal integrity [9]. Prashad and Dwivedi [10] investigated the influence of submerged arc welding process parameters on microstructure, hardness and toughness of HSLA steel weld joints. Datta and Band)'opadhyay [11] has recycled slag generated during conventional submerged arc: welding (SAW) by mixing varying percentages of crushed slag with fresh flux to use in subsequent runs. In the work of Datta [12] application of the Taguchi method in combination with grey relational analysis has been applied for solving multiple criteria (objective) optimization problem in submerged arc welding (SA W). No work so far has been performed to develop the flux by using waste flux dust. Approximately i 015% of the flux used in submerged arc welding gets converted into very fine particles termed as flux dust due to transportation and handling. At the same time dumping of this flux dust will create pollution. In the present study an attempt has been made to investigate the influence of the developed basic flux prepared by utilizing wasted flux dust on the tensile properties and toughness of the welded joints. The chemical composition and properties viz. tensile strength and toughness of the all weld metal using basic developed flux as well as commercially available flux of the same type were compared. The radiographic examinations of all the welded joints were conducted to check weld metal integrity. Therefore the developed flux prepared from the waste flux dust can be used without any compromise in mechanical properties and quality of the welded joint. It will reduce the cost of welding and pollution. Experimental Work In the present study one agglomerated cost effective basic flux was developed by using the flux dust of parent flux with addition of potassium silicate as binder and aluminum powder as deoxidizer. The solution of potassium silicate binder (90 ml in 550 grams of flux dust) was added to the dry mixed powder of he flux dust and aluminum powder (4%of the weight of the flux dust) and it was wet mixed for 10 minutes and then passed through a 10 mesh screen to form small pellets. Potassium silicate was added as binder because of better are stability . The pallets of the flux were dried in air for 24 hours and then baked in the muffle furnace between 650-750 C for nearly 3 hours. After cooling these pallets were crushed and subsequently sieved. After sieving, fluxes were kept in air tight bags and baked again at 300 C before welding. A constant voltage D.C submerged arc 'welding power source was used for preparing the joints of mild steel plates of the dimensions 300 x 125 x 25 nm using 4 mm diameter wire electrode of grade C (AWS-5.17-S0 EH-14). DCEP polarity was used throughout the experimentation. The plates were cleaned mechanically and chemically to remove the rust, oil and grease from the fusion faces before welding. The surfaces bf the backing plates were also made free from rust and scale. The backing plates of 12 mm thick were tack welded to the base plates.The plates were preset so that they remain approximately flat after the welding operation has been complete, The inter-pass temperature was maintained in the range 200-225 C. Four layer high weld pads were made for the basic developed agglomerated flux and parent flux as per AWS AS.23 90 standard with the same welding conditions. The chemical compositions of all weld metal were evaluated by using spectrometer. The. two. butt weld joints were made with mild steel as base. plate and backing strip. The welded assembly was, subjected to radiographic examination to ascertain weld integrity prior to mechanical testing. The backing' plate was removed by machining before conducting radiographic examination. Three all weld metal tensile test pieces were cut from each welded plate and machined. The tensile tests were carried out on a universal testing machine (Make FIE-India). Scanning electron microscopy of the fractured surfaces of tensile test specimens were carried out at 20kV and 1500 X on microscope (Make J0EL Japan, JSM- 6100). Charpy V notch impact test was carried (lut to evaluate the toughness 'of the welded joints at 0 C. Charpy impact tests were performed on standard notched specimens obtained from the welded joint. The notch was positioned in the centre of the weId and was cut in the face of the test specimen perpendicular to the surface of the plates. Five all weld metal impact test samples were cut from welded joint of plates. These samples were then fine polished by the surface grinder . Among the five values Of the impact strength the lowest and highest values were discarded and average of the 3 values was taken for the evaluation of impact strength of the groove welds.The charpy impact tests results obtained from the weld metal showed rather good repeatability.The same procedure was applied to the developed flux and commercially available parent flux to investigate the compatibility of the Results and Discussions The flux behavior of the basic developed fluxes was found to be satisfactory. The bead service appearance was observed to be excellent and free from any visual defects and is comparable with the parent As shown in Table 3. the compositions of all weld metal of the developed and parent flux are found to be in the same range. However manganese content of the weld metal laid by using the developed flux is slightly lower than the weld metal laid by using the parent flux. The silicon content of the weld metal laid by using the Reference 1. Kalpakjian, Serope, and Steven Schmid. Manufacturing Engineering and Technology. '5th ed'. Upper Saddle river, NJ: Pearson Prentice Hall, 2006. 2. Jeffus, Larry. Welding: Principles and Applications. Florence, KY: Thomson Delmar Learning, 2002 |