工學院: 應用力學研究所指導教授: 陳發林蘇昱光Su, Yu-GuangYu-GuangSu2017-03-062018-06-292017-03-062018-06-292016http://ntur.lib.ntu.edu.tw//handle/246246/277046非晶結構可改善金屬物理的特性與增進材料的性能，而平面流鑄法(planar flow casting process, PFC)是能連續鑄造非晶質金屬薄帶的快速固化方法，其過程為熔融金屬經噴嘴直接流入快速旋轉的輥輪上，此時熔融金屬被快速冷卻而固化，且固化所形成的薄帶被連續地製造出來。本研究首先經由整理歸納平面流鑄相關的實驗文獻，並透過因次分析製作各種金屬合金操作條件的參數地圖，基於這些參數地圖的應用，提出方便工程人員於現場調整製造參數的方法，其可對想要製作的薄帶厚度，在固定的噴嘴狹縫開口寬下，預測所需噴嘴與輥輪之間的間隙、熔潭內外的壓降及輥輪切線速率。此預測之製造參數值是可成功製作出金屬薄帶，同時也可作為製程設計或改良時的參考。 接著使用商用計算流體力學來模擬平面流鑄熔潭的發展與熱傳的行為，使用一二維模型包含慣性力、黏滯力、表面張力、濕潤效應與相變化熱傳，並以流體體積法(volume of fluid method, VOF)來描述熔融合金與空氣之二相流行為，分析不同的噴嘴形貌和熔潭與噴嘴及輥輪間不同的濕潤效應對熔潭形狀和薄帶厚度的影響，及其對穩態流場與溫度場的分布情形。結果顯示，下游間距較大的噴嘴，其熔潭會較慢達到穩定狀態，且具有較長的熔潭長度和較厚的薄帶厚度。此外，熔潭形貌受到與噴嘴間濕潤的影響比與輥輪間濕潤的影響更大，且為了使熔潭較快達到穩定狀態，熔潭與噴嘴間須為非濕潤接觸，而熔潭與輥輪間須為濕潤接觸，此可減少空氣的捲入與降低氣潭出現的頻率。 在實驗方面，先研究平面流鑄之過程參數對Fe78B13Si9合金之薄帶形成與熔潭穩定的影響，探討在不同的過程參數下所製造之薄帶的樣貌、薄帶表面的品質與熔潭穩態的高速影像，同時也對熔融金屬流出噴嘴到形成熔潭的整個暫態變化過程作詳盡的觀察。建立Fe78B13Si9合金薄帶製作成功的操作視窗，其分布區域是不同於鋁合金的分布。此外，也發現薄帶厚度與壓降間成近似0.45次方的變化，而與輥輪切線速率成近似-0.9次方的變化。藉由增加壓降、增加輥輪切線速率、降低間隙與較低的澆鑄溫度都有助於小氣潭的形成。接著研究不同的輥輪表面粗糙度對薄帶樣貌與表面品質的影響，並對薄帶製作過程中的平均冷卻速率作探討。結果發現，越光滑的輥輪表面，在薄帶與輥輪接觸面的表面上越容易出現人型花紋(herringbone pattern)，且熔潭上游彎月形外的空氣也越容易被誘捕進來而形成較大的氣潭。相反地，越粗糙的輥輪表面，則越不容易將熔潭上游彎月形外的空氣誘捕進來，反而是在輥輪表面上的凹坑處形成氣潭。此外，薄帶與輥輪接觸的表面會隨著輥輪表面粗糙度的增加而變粗糙，但與空氣接觸的表面反而是隨著輥輪表面粗糙度的增加先變光滑後再變粗糙。當輥輪表面越粗糙，會造成薄帶與輥輪間具有較高的熱阻抗，而使得平均冷卻速率減小，且越容易導致結晶顆粒的形成。 最後由於鐵合金熔融所發出的強光，使得高速攝影機只能拍攝到熔潭的外貌變化，為了要能觀測流體在熔潭內的流動狀態，規畫設計流場模擬儀的實驗裝置。依據所完成平面流鑄的實驗數據，在相同的流力動力相似分析下，計算出所需之操作參數值，並選用適當的流體與可觀測的示蹤粒子(seeding particles)，且對輥輪的尺寸及轉動馬達的規格等進行設計。而整個實驗架構為矽油加入示蹤粒子並透過定量與微壓幫浦的推送，經噴嘴流到向右旋轉的輥輪上，再由回收桶回收使用過的矽油。觀察發現，在熔潭上游區域可明顯看到順時針旋轉的渦流，至於熔潭的後視影像會隨著輥輪速率的不同而有明顯的差異，從外凸現象到逐漸消失，最後產生波浪的狀態，同時也與Taylor-Dean流的理論結果作比較，藉此來預測系統的穩定性。 未來可再延續的研究項目有熔潭流場的穩定特性及動態接觸角與氣潭形成的關係。前者可藉由平板流與圓柱流的線性穩定分析結果，進一步來探討平面流鑄熔潭流場的穩定性；後者可搭配流場模擬儀的使用，並對接觸線進行線性穩定性分析，以達到減少氣體被吸入的目標。An amorphous structure improves the physical properties of metal and enhances material performance. Planar flow casting process (PFC) is a rapid solidification method for continuously producing microcrystalline and amorphous ribbons. In the PFC process, molten metal flows through a nozzle onto the chill wheel where the melt is frozen and a continuous ribbon is spun. First, this study reorganizes the related experimental studies and performs the operability diagrams for all kinds of metal ribbons using dimensional analysis. Based on these diagrams, a rapid method that can assist on-site operators to adjust parameters is proposed. The method is able to determine the wheel-nozzle gap, applied pressure difference and wheel speed for the designated the ribbon thickness with a preset nozzle slot breadth. The determined operating variables enable the successful production of continuous ribbon and can serve as a reference for designing and modifying the processes. Then, the puddle development and heat transfer behavior in the PFC process are simulated using the computational fluid dynamics (CFD). A two-dimensional model is developed for the puddle in which the inertial force, viscosity, surface tension, wettability, and heat transfer with phase transformation are incorporated and the volume of fluid (VOF) method is employed to characterize the behaviors of the two-phase flow including the melt and air. The effects of the nozzle shapes and wetting conditions between the puddle/nozzle and puddle/wheel on the puddle shape and ribbon thickness are evaluated and their velocity and temperature fields are examined. The result shows that the nozzle with larger gap in the downstream tends to produce a longer puddle length and a thicker ribbon and it takes more time to reach a steady state for the casting process. In addition, the puddle shape was affected significantly by the wetting condition on the nozzle surface rather than that on the wheel surface. The contact condition between the puddle and nozzle must be non-wetting in order to make the puddle reach a steady state rapidly. However, the wetting contact condition is preferable between the puddle and wheel surface to reduce the amount of air entrainment and the air-pocket frequency on the ribbon surface. At the experimental section, the effects of manufacturing parameters in the PFC process on the ribbon formation and the puddle stability of Fe78B13Si9 alloy are investigated. The ribbon morphology, surface quality, and puddle geometry are examined at different conditions and the transient evolution processes of puddle for molten metal passing through a rectangular nozzle are observed. The successful operability window for the production of Fe78B13Si9 ribbon is established and it is found the scope is different from that of Al-based alloy. The ribbon thickness is found to vary with the applied pressure across the crucible and the wheel speed to the power of 0.45 and , respectively. The formation of small air pockets could be enhanced by increasing the applied pressure difference and wheel speed, or by decreasing the nozzle-wheel gap and the jetting temperature. Next, the influences of surface roughness of chill wheel on ribbon topography and surface quality are examined and the average cooling rate during the PFC process is evaluated. The result reveals that a lower roughness tends to induce the appearance of herringbone pattern on the wheel-side ribbon surface and capture more air at the wheel-melt interface to form larger elongated air pockets on the ribbon surface. On the contrary, less air is trapped at higher roughness and the distribution of air pockets on the ribbon surface is mainly corresponding to the concave spots on the wheel surface. The roughness on the wheel-side ribbon surface increases monotonically with the wheel roughness, while a minimum roughness is observed on the opposite air-side surface exhibiting the smoothest air-side ribbon surface. A higher wheel roughness enhances the thermal contact resistance at the interface between the ribbon and the chill wheel, which reduces the average cooling rate during the casting process and results in the occurrence of crystalline structure in the ribbon formation. Finally, a high-speed imaging system only records the evolution of puddle geometry due to the glare of the melt. The layout for the simulated apparatus of flow field is carried out in order to view the fluid flow in the puddle. According to the experimental data of the PFC process, the required operating variables are calculated, the suitable fluid and seeding particles are selected and the wheel size and the motor specification are designed under the same dimensionless parameters. The whole process is that the silicon oil with seeding particles conveyed by the metering and pressurizing pump is fed through a nozzle onto the rotating wheel and is collected in the recycling tank. The result discovers that a strong clockwise vortex is formed clearly in the upstream region of the puddle. The back views of the puddle are found to vary from convex to waves distinctly with the wheel speed. Simultaneously, the system is predicted the stability by comparing with the theoretical results of the Taylor-Dean flow. The research issues in the future include the puddle stability of the PFC process and the relationship between dynamic contact angles and air pockets. The former is investigated progressively by the results of linear stability analysis for the plate flow and cylinder flow. The latter is studied by the use of the simulated apparatus of flow field and applies the linear stability analysis for the contact line to attain the aim of avoiding the air entrainment.4696631 bytesapplication/pdf論文公開時間: 2019/8/24論文使用權限: 同意有償授權(權利金給回饋學校)非晶薄帶平面流鑄法熔潭發展氣潭形成Fe-B-Si合金amorphous ribbonplanar flow casting processpuddle developmentair-pocket formationFe-B-Si alloy[SDGs]SDG11thesis10.6342/NTU201601664http://ntur.lib.ntu.edu.tw/bitstream/246246/277046/1/ntu-105-D99543007-1.pdf