tailieunhanh - Submerged Arc Welding Episode 3

Tham khảo tài liệu 'submerged arc welding episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Travel Speed Travel speed is one of the most important variables affecting penetration and bead size. High speeds decrease penetration and increase tendencies for undercut arc blow porosity and non-uniform bead shape. Proper speeds give gases time to escape from the molten metal before it solidifies which reduces porosity. Very slow speeds will produce bead shapes that are subject to cracking excessive open arc exposure for the welding operator and a large uncontrollable molten pool that results in a rough bead and possible slag inclusions. For single pass welds the current and travel speed should be as high as possible and still obtain proper weld bead size and proper penetration without burning through. In multiple pass welding the travel speed can be varied to obtain the desired fill for the joint. Travel Speed Varied Weld Electrode Size The electrode diameter choice can affect weld bead shape and penetration depth for a fixed current setting. See picture. Wire Sizes Small electrodes are used in semi-automatic applications because of the flexibility and ease of handling. They are also used with dual wire and tandem wire systems. Large wire diameters are generally used for poor fitup because of their ability to bridge large root openings. The electrode diameter will affect deposition rates. At a given current setting a small wire will give a higher current density and thus a higher deposition rate than a larger diameter wire. However a larger wire can carry more current so larger wires give a higher deposition rate at higher currents. For a given diameter size a high current gives a high current density with deep penetration of the base plate. Low current on the same size wire gives a less penetrating arc. Wire size also affects arc starting. Small diameter wire arc starts are more consistent. Automatic submerged arc will begin most often with 1 16 diameter wire with a common maximum of 3 16 or 1 4 diameter wire. Occasional situations will show a need for 5 16 1