Analysis of minimum zone sphericity error using minimum potential energy theory

Theoretical derivation of the minimum zone criteria of sphericity error based on the principle of minimum potential energy is proposed. All the measured data points are enclosed by two concentric spherical surfaces between which a fictitious spring is assumed to be placed. These two concentric spherical surfaces can be mathematically determined by five active data points. When the spring contracts, the potential energy of the simulated mechanical system tends to reduce which yields two new concentric spheres with smaller radial separation and new active data points. Finally, a stable state will be reached to the condition of minimum potential energy. The criteria conforming to such a state can be derived. A direct search scheme to the global minimum solution is also proposed. The clearance between such two concentric spherical surfaces is the minimum zone of spherical form error.     

粉石英制备高纯球形纳米SiO2

摘要:以价格低廉天然优质粉石英矿物为基本原料,采用改进溶胶-凝胶技术,盐酸和硅酸钠溶液共滴加的方式,制备高纯球形纳米SiO2粉体材料。研究了体系中硅酸钠浓度及纯度、pH值、表面活性剂及分散剂等因素对其性能的影响。制备出的高纯纳米SiO2粉体中SiO299.97%、Al3+ 9×10-6、 Fe3+ 1.04 9×10-6、Na+≤3.59×10-6、Cl-≤19×10-6,平均粒径在50～80 nm。研究结果表明:制备的SiO2粉体为高纯、球形、分散度高且粒度均匀,能达到电子封装材料功能填料用高纯球形纳米二氧化硅性能指标要求。本文重点探讨原材料对其纯度的影响,团聚机理及解决团聚的措施。该方法具有成本低及易于工业化的特点。      

3D simulation of the effects of sphericity on char entrainment in fluidised beds

The paper presents a 3-dimensional simulation of the effect of particle shape on char entrainment in a bubbling fluidised bed reactor. Three char particles of 350 μm side length but of different shapes (cube, sphere, and tetrahedron) are injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. Due to the fluidising conditions, reactor design and particle shape the char particles will either be entrained from the reactor or remain inside the bubbling bed. The sphericity of the particles is the factor that differentiates the particle motion inside the reactor and their efficient entrainment out of it. The simulation has been performed with a completely revised momentum transport model for bubble three-phase flow, taking into account the sphericity factors, and has been applied as an extension to the commercial finite volume code FLUENT 6.3.     

巴西赤铁精矿成球性能试验

为确定铁品位为67.45%、SiO₂含量为2.54%、-0.045 mm占95.72%、比表面积为1 647.00 cm²/g的巴西Carajas赤铁精矿造球的合适工艺技术参数,以铁品位为14.38%、SiO₂含量为67.22%、-0.045 mm占87.27%、比表面积为1 698.85 cm²/g的山西某赤铁矿强磁选尾矿为调硅剂,以吸水率为436.01%、蒙脱石含量为62.22%、-0.074 mm占99.4%的某膨润土为黏结剂,以生球落下强度、抗压强度、爆裂温度为评价指标,研究了生球原料的成分和性质、造球工艺参数对生球性能的影响。试验确定的赤铁精矿（含所加铁尾矿）的比表面积为1 768 cm²/g,膨润土的质量分数为0.8%,尾矿与精矿的质量比为2.2%,赤铁精矿水分为8.0%,造球过程中生球的水分为10.0%,造球时间为12 min,造球盘的转速为22 r/min,对应的生球落下强度为6.8次,抗压强度为14.15 N,爆裂温度为427 ℃。     

集料形态特征对集料-沥青黏附及水稳定性的影响

为评价集料形态特征对集料-沥青黏附性及其体系水稳定性的影响,提出了一种定量测试集料-沥青黏附性的新方法.借助集料图像测量系统(AIMS)测试了5种集料的形态特征,并对不同形态集料沥青混合料的水稳定性进行评价,建立了集料形态特征与集料-沥青黏附性及水稳定性的关系,同时基于灰色关联法分析了集料形态特征对集料-沥青黏附性及水稳定性的影响排序.结果 表明:提出的集料-沥青黏附性定量测试方法简单、可靠;沥青混合料水稳定性最佳的棱角性为2500～3000,球度为0.65～0.75;随着集料表面纹理的增大,沥青混合料的水稳定性增强;集料表面纹理对集料-沥青黏附性的影响最大,棱角性对沥青混合料浸水飞散损失指标的影响最大,球度对沥青混合料冻融劈裂强度比、浸水车辙变形拐点指标的影响最大.     

最小外接球法球度误差评价与实现

针对直角坐标系下球体形状的误差评价,介绍一种利用最小外接球法评价球度误差的计算方法。建立基于直角坐标系下的球度误差三维评测模型,并研究外接球体几何曲面关系,得出了利用弦线截交关系快速评价球度误差的理论。利用弦线截交关系构建最小外接球法球度误差评价的“2+1”、“3+1”、“4+1”评价模式统一体,通过两次截交产生的虚拟中心定位,可以准确确定评价点的位置,达到了快速、精确利用最小外接球法评价球度误差的目的。通过分析表明,基于弦线截交关系的最小外接球球度误差评价方法计算效率高、易于实现且具有较高的评定精度,也为球度误差评价提供一种新的方法和思路。     

Morphology and structure characterization of ceramic granules

For the production of brittle materials like technical ceramics it is important to prohibit big defects in the material to achieve high mechanical strength. Due to that already the granule properties are important because they can cause defects in the final product. Characterization and quantification of the granule properties are important steps for improving the production process and properties of the granules for further processing. In this work a novel method for the characterization and quantification of granule morphology, especially sphericity, and internal structure like the ratio of macro pores is provided via digital microscopy. The new quantitative characterization method can be done in an academic and industrial field with appropriate effort. Differences between granules can be characterized, quantified and be used for further development.     

Some Structural Properties of Spray-Dried Chitosan Microgranules

Abstract

The characteristics of concurrent spray dried chitosan microgranules are presented in this article. The investigated parameters were four chemical compositions of solutions subjected to drying to produce chitosan microgranules with different structures and chemical compositions. The analysis of dried product included shape, size, density, porosity, moisture content, and solubility in water. The results show the possibilities of applying spray-drying in the formation of chitosan microgranules with required physicochemical properties.     

Production of Carbopol® 974P and Carbopol® 971P Pellets by Extrusion‐Spheronization: Optimization of the Processing Parameters and Water Content

Pellets obtained by extrusion‐spheronization represent multiparticulate dosage forms whose interest in intestinal drug delivery can be potentiated and targeted through bioadhesive properties. However, adhesion itself makes the process difficult or even impossible. The problem of tackiness encountered with bioadhesive wet masses was previously eliminated by the use of electrolytes such as CaCl₂. This approach is known to reduce the viscosity of polyacrylic acids by disturbing the interactions between carboxylate groups on adjacent polymer molecules, thereby decreasing their bioadhesive properties. The present study aimed at producing pellets containing carbomers without addition of electrolytes in order to maintain their bioadhesive potentiality at its maximum. Carbopol® 974P (10%, 15% and 20%) and Carbopol® 971P (10%) were used in combination with Avicel® PH101. The extrusion speed (30, 45, 60, 90, and 150 rpm), spheronizer speed (350, 700, 960, 1000, and 1300 rpm), spheronization time (5, 10, 15, and 20 minutes) and amount of water (45%, 50%, 54%, and 58%) were optimized in order to obtain the highest yield of spherical pellets ranging 710–1000 µm in diameter. For pellets containing 10%, 15% Carbopol® 974P or 10% Carbopol® 971P and 45% water content, 30 rpm extrusion speed, 960 rpm, and 10 minutes spheronization speed and time led to the highest yields and sphericities, respectively, 72% and 0.91, 67% and 0.78, and 76% and 0.80. Production of pellets with 20% Carbopol® 974P could be achieved through the increase of the water content up to 58% and implementation of 30 rpm extrusion speed, 1300 rpm, and 10 minutes spheronization speed and time. The yield and sphericity were 42% and 0.78 respectively.     

An immune evolutionary algorithm for sphericity error evaluation

An immune evolutionary algorithm (IEA) is proposed by imitating the defense process of the immune system and the ideas of mutation in evolutionary biology. In the IEA, a self-adaptive mutation operator is constructed to decide the mutation step size of every antibody according to its environment, and an affinity calculation process is also embedded to maintain diversity. Application of the proposed algorithm to the evaluation of sphericity error is investigated. The method takes the sphericity error objective function and constraints as antigen. Through genetic evolution, an antibody that most fits the antigen becomes the solution. Finally, the experimental results evaluated by different methods confirm the effectiveness of the proposed IEA. Furthermore, the method has good flexibility and is also suitable for other evaluations of form errors such as circularity, flatness etc.