Analysis of the Compression Consolidation Characteristics of Powders Under Gas Pressurization
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摘要: 采用气体加压方式和机械加压方式对粉体的压缩固结特性进行了比较研究，并借助力学探针表征了不同固结状态下的粉体床层密度分布规律，分析了气体加压方式对粉体固结特性的影响机制。结果表明，在气体加压方式下，较小的压应力变化就能使得压实密度显著增加，但气体会透入床层，减弱加压气体对床层产生的机械推力，因而气体加压方式下的床层压缩固结特性与机械加压方式下明显不同。气体加压方式下的床层压应力随充压速率的增加近似呈线性增加，且压实密度特征值仅为机械加压方式下该特征值的85%；机械加压相对更易导致粉体床层压实，但气体加压的最终压力对床层压实密度影响不大。力学探针测试结果表明，气体加压方式下床层密度分布比机械加压方式下均匀；量纲为一入侵阻力Fb/Fb,0可有效表征粉体床层的压缩固结程度，该入侵阻力随压应力线性增大、随压实密度的增加呈指数增加。Abstract: In the process of pressurized feeding, powders are compacted under gas pressurization, resulting in cohesive arching and flow blockage. The main reason for these problems is that the mechanism underlying consolidation of powders under gas pressurization remains largely unexplored. In this work, the consolidation characteristics of powders under gas and mechanical pressurization were investigated. The density distribution of powder bed at different consolidation states was characterized by measuring the force on an intruder immersed in the powder bed, and the mechanisms by which gas pressurization determines the consolidation characteristics of powders was analyzed. The results showed that a smaller increase in the compressive stress under gas pressurization increased the compaction density significantly; However, gas was determined to penetrate into the bed, weakening the mechanical force generated by the pressurized gas on the bed. As a consequence, the consolidation characteristics under gas pressurization and mechanical pressurization were markedly different. The compressive stress on the powder bed under gas pressurization increased linearly with the pressurization rate, and the critical value of compaction density under gas pressurization was only 85% of that of mechanical pressurization, making it relatively easier to compact the powder bed under mechanical pressurization. In addition, the final pressure of gas pressurization hardly affected the compaction density of the powder bed. Our study on the mechanical properties of the powder bed suggested that the density distribution under gas pressurization was more uniform than that under mechanical pressurization. The dimensionless resistance force Fb/Fb,0 which determined to characterize the consolidation characteristics of the powder bed was found to increase linearly and exponentially with applied normal stress and compaction density, respectively.
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Key words:
- powder /
- gas pressure /
- compression /
- consolidation /
- compaction density
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图 4 气体加压实验装置流程图
Figure 4. Flow chart of gas pressure experiment device
1—Nitrogen cylinder; 2—Needle valve; 3—Autoclave; 4—Glass cylinder; 5—Expansion valve; 6—Pressure gauge; 7—Computer
图 7 加压前后氧化铝堆积状态
Figure 7. Packing state of alumina before and after pressurization
a,c—Before pressurization; b,d—After pressurization. a,b—Top view; c,d—Front view
图 8 同一充压速率（50 kPa/s）下压实密度与最终压力的关系
Figure 8. Relationship between compaction density and final pressure under the same pressurization rate（50 kPa/s）
图 9 不同充压方式下粉体的压实密度变化
Figure 9. Change of compaction density under different pressurization methods
图 10 充压速率与压应力的关系
Figure 10. Relationship between pressurization rate and compressive stress
图 11 不同加压方式下压实密度与压应力的关系
Figure 11. Relationship between compaction density and compressive stress under different pressurization methods
图 12 自然堆积时床层的入侵阻力变化规律
Figure 12. Resistance forces on the intruder penetrating the statically packed granular bed
图 13 不同加压方式下的入侵阻力的变化规律
Figure 13. Resistance forces on the intruder penetrating the granular bed under different pressurization methods
a—Mechanical pressurization; b—Gas pressurization
图 14 量纲为一入侵阻力与压应力的关系
Figure 14. Relationship between dimensionless resistance force and compressive stress
a—Mechanical pressurization; b—Gas pressurization
图 15 量纲为一入侵阻力与压实密度的关系
Figure 15. Relationship between dimensionless resistance force and compaction density
表 1 实验物料基本物性
Table 1. Properties of experimental materials
Sample ρb/(g·cm−3) ρt/(g·cm−3) w(Moisture)/% HR θ/(°) D[3,2]/μm D[4,3]/μm d10/μm d50/μm d90/μm Span Al2O3 0.5182 0.9504 0.12 1.83 48.70 4.60 9.07 2.05 7.38 17.69 2.12 
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表 2 粉体压缩方程拟合参数及相关性系数
Table 2. Fitting parameters and correlation coefficient of powder compression equation
Material ρb,0/(kg·m−3) σz,0/kPa N R2 Al2O3 518.2 8.79 0.076 0.983
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