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。研究表明，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，因而其压缩固结特性与机械加压方式明显不同：气体加压作用下的床层压应力随充压速率的增加呈近似线性增加，且气压方式下压实密度特征值仅为机械加压的85%，机械加压相对更易导致粉体床层压实；而气体加压的最终压力对床层压实密度影响不大。力学探针测试发现，气体加压方式下的床层密度分布比机械加压方式均匀；无量纲阻力系数Fb/Fb,0可有效表征粉体床层的压缩固结程度，其随压应力线性增大、随压实密度的增加而呈指数增加。Abstract: In the process of pressurized feeding, the powders will be compacted under gas pressurization, which will cause the cohesive arching and flow blockage. The main reason for these problems is that the mechanism of consolidation of powders under gas pressurization and the effective regulation method have not been mastered yet. In this work, the consolidation characteristics of powders under gas pressurization and mechanical pressurization were investigated, providing a reference for optimizing pressurized powder feeding. The density distribution of the powder bed under different consolidation states was characterized by using the forces on an intruder immersed in the powder bed, and the influence mechanism of gas pressurization on the consolidation characteristics of powders was analyzed. The results show that a smaller increase in the compressive stress under gas pressurization can make the compaction density increase significantly, but the gas will penetrate into the bed, weakening the mechanical force generated by the pressurized gas on the bed, so the consolidation characteristics under gas pressurization and mechanical pressurization are markedly different: the compressive stress on the powder bed under gas pressurization increases linearly with the pressurization rate, and the critical value of compaction density under gas pressurization is only 85% of that of mechanical pressurization, thus it is relatively easier to compact the powder bed under mechanical pressurization. And the final pressure of gas pressurization hardly affects the compaction density of the powder bed. The research on the mechanical properties of the powder bed shows that the density distribution under gas pressurization is more uniform than that under mechanical pressurization. The dimensionless resistance force Fb/Fb,0 is used to characterize the consolidation characteristics of the powder bed, which increases linearly with applied normal stress and exponentially with the compaction density.
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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. Diagram of experimental equipment
1—Nitrogen cylinder; 2—Needle valve; 3—Autoclave; 4—Glass cylinder; 5—Expansion valve; 6—Pressure gauge; 7—Computer
图 8 同一充压速率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
图 9 不同充压方式下的粉体压实密度变化
Figure 9. Compaction density under different pressurization methods
a—Gas pressurization, b—Mechanical pressurization
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) Mt/% 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. The parameters involved in equation (1) and correlation coefficient
Material ρb,0/(kg·m−3) σz,0/Pa N R2 Al2O3 518.2 8.79 0.076 0.983
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