Nippon Steel Technical Report

NIPPON STEEL TECHNICAL REPORT No. 95 January 2007
UDC 621 . 791 : 8 . 661 . 97

CO2-gas-shielded One-side Welding Process Two-electrode “NS-Oneside MAG® ”
Isamu KIMOTO*1 Ryuichi MOTOMATSU*2

Abstract The one-side submerged arc welding (SAW) process has been a principal method for butt welding of large steel plates in the field of shipbuilding for many years. A simple automatic, one-sidewelding process using backing materials and flux-cored wires was newly developed to substitute the SAW process. The developed process enables one-side welding of heavy plates by a single pass, not adversely affected by tack-weld beads in the groove. Because of its lower heat input, the process causes significantly reduced rotational distortion, and hence, is capable of preventing cracking caused bythe distortion.

1. Introduction
One-side, submerged arc welding has been a common practice for butt welding of large steel plates in the shipbuilding and other industries as a labor-saving and highly efficient method. At work fields, one-side, semi-automatic CO2 welding using flux-cored wire and a backing material has also been widely employed for the pur-

pose. However, as shown in Table 1,the efficiency of the conventional CO2 welding method is low, because the method requires restricting fittings on the back side of the plates to secure a gap between the beveled edges and the joining work requires two or more weld passes. Nippon Steel Welding Products & Engineering Co. Ltd. studied automation of the one-side, semi-automatic CO2 welding to signifi-

Table 1 Comparison betweenconventional MAG process and welding NS-Oneside MAG process Conventional NS-Oneside MAG

Preparation for welding

Welding process

CO2 gas shielded welding process

CO2 gas shielded one-side welding process two electrodes

Example of pass sequence

*1

Nippon Steel Welding Products and Engineering Co., Ltd.

*2

Steel Research Laboratories

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NIPPON STEEL TECHNICALREPORT No. 95 January 2007
cantly enhance its work efficiency, and as a result, has established a high-efficiency, automatic CO2 welding process (trade name: NSOneside MAG) capable of forming a good penetration bead in a single pass with two electrodes; the developed process does not require a root gap, and allows there to be tack-weld beads inside the groove.

2. Outline of NS-Oneside MAG ProcessFig. 1 schematically illustrates the welding process by NSOneside MAG, Photo 1 shows the equipment for the process, and Fig. 2 the configuration of the equipment. As seen in Fig. 1, the NSOneside MAG process follows the following procedures: plates are set with beveled edges contacting each other; tack weld is applied at several points in the groove; a backing material for common CO2 welding isattached on the back side; cut wires are put in the groove; and the plates are welded in a single pass using two electrodes. During the welding pass, two large-current CO2 electrodes arranged in tandem in the welding direction, approximately 300 mm apart from each other, form two molten pools, while being oscillated laterally: a solid wire is used for the leading electrode (L electrode), and aflux-cored wire for the trailing electrode (T electrode); a solid wire can also be used for the T electrode. The L electrode using a solid wire, getting a deep-penetration.

Fig. 2 Schematic illustration of equipment components of NS-Oneside MAG

melts the tack-weld beads completely and forms a back side bead. It also serves for making the width of the back side bead sufficiently large, uniformmixing the molten pool and applying optimum welding conditions coping with the fluctuation of the gap between the plate edges. The T electrode, on the other hand, forms a face-side bead of an adequate width; the use of a flux-cored wire makes the slag easily removable and forms a bead of good appearance. The shielding gas is CO2 gas for welding use under JIS K 1106-1990.

3. Characteristics of...