Tham khảo tài liệu 'advanced welding processes episode 1 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Gases for Advanced Welding Processes 85 limited by the sporadic appearance of fine inter-run porosity. This has been ascribed to argon entrapment and nitrogen absorption 55 and is known to be reduced by increasing the operating current or raising the CƠ2 level of the gas. Intermediate levels of CO2 argon plus 8-15 carbon dioxide give a decreased risk of porosity improved fusion and still maintain good operating characteristics in the spray and pulse transfer operating modes. Mixtures of argon with 15 25 carbon dioxide are characterized by increased fusion with bowl-shape penetration profiles but arc stability tends to decrease as the CO2 level approaches 25 . These mixtures are ideally suited to the welding of thicker sections and for multirun butt welds. When the CO2 content exceeds 25-35 the characteristics of the gas are similar to those of pure co2. Pure CO2 gives good fusion characteristics but higher weld bead reinforcement than the argon-rich mixtures. The heat input of the arc is increased and this may provide slightly better performance --- Argon 20 CO2 ---CO2 Spatter ---Argon 20 CO2 --- CO2 Drop Frequency Figure Comparison of spatter losses for CƠ2 and argon 20 CO2 mixtures GMAW mm wire after Scheibner 56 . 86 Advanced Welding Processes on oxidized or primed plate. Although satisfactory dip transfer can be obtained in CO2 the setting tolerances are narrower than those for argon-based mixtures and transfer under spray and pulsed conditions tends to be globular with much higher levels of spatter 56 . An indication of the difference in spatter levels associated with the use of CO2 compared with an argon CO2 is shown in figure . Ternary argon carbon dioxide oxygen mixtures have similar performance characteristics to argon CO2 but slightly improved arc stability has been observed. The results of arc stability measurements for dip transfer in these three-part mixtures is illustrated in figure and it can be seen that mixtures containing 12-15 CO2
