Optimum structure design of free-fall nozzle in preparation process of superalloy powders by electrode induction gas atomization technology
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摘要: 采用电极感应熔化气雾化制粉法（electrode induction gas atomization，EIGA）制备粉末过程中，非限制式喷嘴的结构设计直接决定气雾化粉末的质量；非限制式喷嘴结构中不合理的喷射角度常常会引起反喷、片状粉、细粉收率低等问题，严重影响粉末的生产效率和质量。采用商业计算流体动力学（computational fluid dynamics，CFD）软件Fluent，以自主设计的第三代EIGA制备高温合金粉末装置中非限制式喷嘴为研究对象进行数值模拟建模，对带有气体回流区的非限制式喷嘴在熔体初次雾化过程中，喷射角度对反喷现象的影响以及反喷产生的机理进行了研究。结果表明，非限制式喷嘴射流角度过大时，熔体液滴会出现明显反喷现象；当非限制式喷嘴射流角度过小时，熔体液流雾化前过热度不足，生产的粉末球形度较差。因此，在优化设计非限制式喷嘴时，要应尽量控制气体回流区位置低于非限制式喷嘴熔体入口位置，保证合金熔体的过热度，同时防止反喷等现象。
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关键词:
- 电极感应熔化气雾化技术 /
- 高温合金粉末 /
- 非限制式喷嘴结构 /
- 喷射角度 /
- 计算流体动力学
Abstract: The structure design of free-fall nozzle directly determines the quality of gas-atomized powders in electrode induction melting gas atomization (EIGA) process, the unreasonable jet angle in free-fall nozzle structure often causes the regurgitation phenomenon, the flake powders, and the low yield of fine powders, which seriously affect the production efficiency and quality of powders. The numerical modeling of free-fall nozzle structure in the self-designed third generation of EIGA superalloy powder preparation device was established using Fluent commercial software for computational fluid dynamics (CFD). The effect of jet angle on the regurgitation phenomenon and the regurgitation mechanism of free-fall nozzle with gas flow recirculation were investigated in the initial atomization of melt. In the results, when the jet angle of free-fall nozzle is too large, there is an obvious regurgitation phenomenon; when the jet angle is too small, the superheat of the melt stream before atomization is insufficient, resulting in the poor sphericity of produced powders. Therefore, to ensure the superheat of melt flow and prevent the regurgitation phenomenon, it is necessary to control the recirculation zone position of gas flow to be lower than the melt inlet position of free-fall nozzle. -
图 2 非限制式喷嘴二维轴对称模型图
Figure 2. Two-dimensional axisymmetric model diagram of the free-fall nozzle
图 3 不同喷射角度非限制式喷嘴气流速度云图：（a）30°；（b）35°；（c）40°；（d）45°
Figure 3. Gas flow velocity field of the free-fall nozzle in different spray angles: (a) 30°; (b) 35°; (c) 40°; (d) 45°
图 4 不同喷射角度下的非限制式喷嘴气体回流区云图：（a）30°；（b）35°；（c）40°；（d）45°
Figure 4. Gas flow recirculation of the free-fall nozzle in different spray angles: (a) 30°; (b) 35°; (c) 40°; (d) 45°
图 5 不同喷射角度下的非限制式喷嘴回流区气体流动轨迹：（a）30°；（b）35°；（c）40°；（d）45°
Figure 5. Gas flow route in recirculation area of the free-fall nozzle in different spray angles: (a) 30°; (b) 35°; (c) 40°; (d) 45°
图 6 不同喷射角度下非限制式喷嘴气流轴向X位置速度分布
Figure 6. Velocity distribution of gas flow in X-axial directionin of the free-fall nozzle in different spray angles
图 7 不同喷射角度下的非限制式喷嘴初次雾化熔体体积分数分布：（a）30°；（b）35°；（c）40°；（d）45°
Figure 7. Volume fraction distribution of the primary atomized melt in different spray angles: (a) 30°; (b) 35°; (c) 40°; (d) 45°
表 1 某牌号镍基高温合金熔体参数表[10]
Table 1. Physical properties of a certain Ni-based superalloy
热容/[J·(kg·K)-1] 热导率/[W·(m·K)-1] 黏度/(mPa·s) 表面张力/(mN·m-1) 密度/(kg·m-3) 720 29.6 0.05 1.84 7705 
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表 2 氩气物理参数
Table 2. Physical properties of Ar gas
密度/(kg·m-3) 黏度/(mPa·s) 热导率/[W·(m·K)-1] 热容/[J·(kg·K)-1] ideal-gas sutherland 0.0158 520.64
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表 3 雾化模拟和实验工艺参数
Table 3. Simulated and experimental parameters in EIGA process
合金类型 合金液流直径/mm 进气口压力/MPa 喷嘴类型 镍基高温合金 4 4 非限制式环缝喷嘴
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表 4 非限制式喷嘴不同气体喷射角度下回流区参数
Table 4. Parameters in the recirculation area of gas flow for the free-fall nozzle in different spray angles
喷射角度/(°) 气体交点位置X轴向坐标/mm 轴向X轴范围/mm 径向Y轴范围/mm 回流区宽/mm 回流区最大速度/(m·s-1) 30 142 146~169 -9~9 18 99 35 146 148.0~175.5 -11~11 22 140 40 143 146~203 -15~15 30 180 45 146 148~180 -16.5~16.5 33 215
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