【作者】 王惠；

【导师】 吴士平；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2012， 硕士

【摘要】 铝合金由于具有密度低、比强度高、耐腐蚀性等特点，在航空航天制造业等得到了广泛的应用。但是由于铝合金熔炼过程中熔体中所含的气体和夹杂物难以很好的去除，使得铝初制品的质量大大降低。现有的净化方法中工业中常用的为旋转喷吹法和熔剂法。旋转喷吹法除气时，喷头的旋转作用将气泡打碎，形成很多的小气泡，除杂效果不错。但是对熔体的搅拌作用非常严重，使得上升到熔体表面的吸收了气体和吸附了夹杂的气泡被重新卷入熔体中，不利于净化过程。熔剂法在熔体中可以产生均匀的小气泡，但是对熔体有很大的污染作用，且不利于于环境保护。现在铝合金净化的发展目标是环保、静态的净化方法。所以研究静态除气过程中气泡的形成以及分布显得尤为重要。本文将旋转喷吹净化和脉冲净化的优点结合起来，自行设计并加工出铝合金净化装置。该装置主要是通过定子与转子的相对运动来实现脉冲进气的目的。气体通过转子杆中心的孔进入装置中，并流向转子上开的六道气槽中。定子上均匀分布一定尺寸和数目的小孔。当气槽转过孔所在的位置时，孔处有气体进入熔体中形成气泡；气槽转离孔口处时，小孔处则没有气体。转子的旋转对孔口处的气体实现切割作用，从而实现脉冲进气，获得小气泡。利用高速摄影技术对水-CO2以及聚乙烯醇-CO2水模拟实验中气泡的运动过程进行捕捉，研究了液体性质、气体流量、转子转速、孔径以及孔间距等参数对气泡脱离以及上升过程的影响。并利用fluent的VOF模型研究气泡脱离以及上升过程，并与水模拟实验相对照，验证数值模拟的正确性。通过改变实验参数，研究单个气泡以及水平双气泡和竖直双气泡在水中上升的形貌变化以及运动轨迹以及氮气泡在铝合金液中的形成过程。对于气泡上升过程，结果表明：单个气泡上升时，大气泡更容易发生变形甚至破碎。随着粘度的增大，气泡上升速度变慢，但是由于气泡横向摆动的影响，使得纵向的质心速度随着粘度的变化而呈现不同的规律。表面张力越大，气泡更难以变形。水平双气泡上升轨迹对称，随着距离的增大，气泡之间的相互影响减弱，可以看成单个气泡独立上升过程。液体物性参数对水平双气泡的影响同单个气泡的运动规律相似。表面张力对竖直气泡接触过程中的融合影响很明显。表面张力比较小时，接触后未形成稳定的大气泡便发生破碎。对于气泡形成过程，结果表明：气泡脱离时大小随孔径和流速的增大而增大。单位时间气泡数目随着孔径的增大而减少，但随着流速的增大而增大。气泡脱离时直径随着粘度以及表面张力的增大而增大，单位时间气泡数目减少。密度增大，气泡脱离时尺寸减小，脱离时间减小，单位时间气泡数目增多。小流速时应用大脉冲，大流速时采用小脉冲，即为保证获得形成一定尺寸气泡的气体流量。气体流速低时，转速对气泡形成有明显的脉冲作用，减小了气泡的聚合的可能性。气体流速较大时，形成的气泡较大，有转速时，将气流切割最终形成小气泡，单位时间小气泡数目明显增多且未发生融合现象。更多还原

【Abstract】 Aluminum alloy has been widely used in aerospace, manufacture and other feldsdue to the properties of low density, high specific strength, corrosion resistance andother perfect properties. However, gases and inclusions in the molten aluminum weredifficulty to remove during refining process. So the quality of the early products ofaluminum was greatly reduced. Purification methods commonly used in industrialwere degass and impeller method and flux method. The bubbles in the moltenaluminum were break by rotor during the purification process when the rotator rotary,so the bubbles were small and less gas and inclusions in the molten aluminum.However, the stirring of the melt was very serious, making the rise bubble withabsorbed gas and the adsorption of a mixture to the melt surface re-involved in themelt, which was not conducive to the purification process. Flux method can produceuniform small bubbles in the melt, but pollute the melt, and not conducive toenvironmental protection. Goals of aluminum alloy refining are environmentalprotection, static purification methods. Study the bubbles’ formation and distributionin static degassing process is particularly important.By combining the advantages of degass and impeller method and pulse gasmethod, self-designed and machined aluminum alloy cleaning device. The device wasmainly to achieve the purpose of the pulse gas into the alloy by the relative motion ofthe stator and rotor. Gases went into the device through the hole in the center of therotor pole and then went through the six air slot opening in the rotor. A certain sizeand a number of small holes were uniformly distribution on the stator. When the gastank turned to the location of the orifices, the gas went through the holes on the statorinto the melt to form bubbles; when the gas tank turned away from the orifices, no gaswould get into the melt. Rotation of the rotor had a cutting action on the gas in orderto achieve a pulse gas intake process and the availability of small bubbles.High-speed photography was used to capture the movement of bubbles in thewater-co2and polyvinyl alcohol-co2water simulation experiment to study the liquidproperties, the gas flow rate, rotor speed, orifice diameter, and distance betweenorifices and other parameters on the bubble departure and rising. Vof model of fluentwas used to the bubble departure and the rise of the process, in contrast to watersimulation to verify the correctness of the numerical simulation. By changing theexperimental parameters, the morphology changes of a single bubble, as well ashorizontal double bubble and vertical pairs of bubbles rising in water and theformation process of the trajectory as well as nitrogen bubbles in the aluminum alloy liquid. To bubble rising in the liquid, the results showed that: to the rising of a singlebubble, big bubbles were more easily deformed or even broken. Bubbles’ risingslowed down with the increase of viscosity, but due to the impact of the bubblehorizontal swing, vertical center of mass velocity presented a different regularity asthe viscosity changed. The greater the surface tension, the bubble is more difficult todeform. The horizontal double bubbles’ rising trajectories were symmetry, as thedistance increases, the interaction between the bubbles was weak. So the doublebubbles could be seen as two single bubbles independent increase in the liquid. Theinfluence of liquid physical parameters on the horizontal double bubbles was similarto the law of motion of a single bubble. Surface tension had large effect on the twobubbles in vertical line, the bubbles got closer with each other to form a unstablebubble then break with smaller surface tension. To the bubble formation anddetachment process, the results showed that: the time for the bubble detaching fromthe orifice and the size of the bubble become larger when the orifice were large. Andso was the large gas velocity. The number of bubbles formed in united time wasincreased with large gas velocity, but decreased with large orifice diameter. Thebubbles size detaching from the orifice increased with the climbing of the liquidviscous and surface tension, the number decreased. The size of bubbles and thenumber of bubbles increased with larger density. Low gas flow rate better to combinewith big pulse time which with corresponding to slower speed and high gas flow ratebetter to combine with small pulse time. Pulse obvious impulsive phenomena of lowflow and high flow remains continuous bubble phenomenon, but the bubble volumedecreases, the aggregate situation improved significantly.更多还原