การออกแบบและพัฒนาระบบควบคุมบรรยากาศและคัดขนาดผงโลหะสำหรับเครื่องอะตอมไมเซอร์แบบใช้หลักการหมุนเหวี่ยงเพื่อใช้ในการผลิตผงโลหะบัดกรีไร้สารตะกั่วที่มีลักษณะเป็นเม็ดกลมขนาดละเอียดและมีออกซิเจนเจือปนในปริมาณต่ำ

Abstract

This research work consisted of two main parts, namely part 1, and part 2. The part 1 research was the design and fabrication of an atmospheric control system for using with the centrifugal atomizer for production of SAC305 lead-free solder powder containing fine particles, spherical shape and low oxygen content in the powder. The part 2 research was the design and fabrication of a powder classification system used for particle size separation of the atomized SAC305 powder produced from part 1. In the part 1 research, a vacuum and nitrogen gas purging system was designed and built for reducing the oxygen containing in the atomizer chamber to the levels of 2, 0.2, 0.05, and 0.01 vol.% before the atomization was started. The SAC305 alloy was melted and atomized in the atomizer chamber under the controlled oxygen atmosphere. After atomization, the SAC305 powder was sampled for analysis, including median particle size, particle size distribution, powder shape, circular shape factor, oxygen content in the powder, and production yield. In the part 2 research, a turbo air classifier was designed and manufactured for particle size separation of the SAC305 powder produced from part 1 in order to obtain the powder having average size range of 25-45 μm (the so called type 3 powder) and to meet the standard of solder powder used in the electronics packaging industry. In the part 2 research, the effects of operating parameters of turbo air classifier, namely rotor speed, feed rate, and air inlet velocity on the cut size (dso) and the sharpness of classification (K) were studied. The 2* factorial design was used in the study. The experimental results were statistically analyzed by using the MINITAB 16 software to identify the significant operating parameters affecting the dso and K. Additionally, some experiments extended from the factorial design were performed to verify the results.The results from part 1 showed that with decreasing oxygen content in the atomizer chamber, it had significant impact on the median particle size, particle size distribution, powder shape, circular shape factor, oxygen content in the powder, and production yield. With decreasing the oxygen content in the atomizer chamber the median particle size decreased, the particle size distribution narrowed, the powder shape become rounder, the circular shape factor reached to about one (1), the oxygen content in the powder decreased and the production yield increased. The optimal operating condition for producing SAC305 powder used for the electronics industry was achieved, when the oxygen content in the atomizer chamber was reduced to 0.01 vol.%. The SAC305 powder with oxygen content less than 100 ppm, nearly spherical shape particles and about 53% production yield was obtained. The results from part 2, the statistical analysis of the cut size (ds) revealed that the rotor speed and air inlet velocity had strongly significant effects on the cut size, but the feed rate had weaker effect with respect to the rotor speed and air inlet velocity. The cut size decreased with increasing rotor speed and it increased with increasing air inlet velocity. However, with increasing the feed rate, the cut size slightly decreased. Moreover, the interaction effects between rotor speed and air inlet velocity also significantly affected the cut size. The statistical analysis results of the sharpness of classification (K) showed that only the feed rate had significant effect on it. With increasing feed rate, the sharpness of classification was decreased. In addition, the interaction effects between feed rate and air inlet velocity, and rotor speed and feed rate significantly affected on K as well. The optimal operating condition for classification of SAC305 powder with size range 25-40 μm was obtained, when the turbo air classifier was operated at the rotor speed 406 r/min, the feed rate 4 kg/h and the air inlet velocity 5 m/s. The cut size and the sharpness of classification were about 27.8 μm and 0.66, respectively. The results from the additional experiments showed that the trend of cut size was in good agreement with those from the statistical analysis. However, the trend of sharpness of classification K was not consistent with the statistical results.