陶瓷墙地砖干法造粒制粉效果与立柱长度分析

针对不同立柱长度对陶瓷墙地砖干法造粒制粉效果的影响,以可塑性粉体、瘠性粉体、熔剂性粉体为主要原料,基于不同立柱长度采用陶瓷干法造粒制粉工艺制备坯料颗粒,研究立柱长度对坯料颗粒的有效颗粒质量百分比、级配分布、流动性指数及喷流性指数的影响,并进行数值模拟仿真分析验证实验结果正确性。实验结果表明:当立柱长度分别为14 cm、16 cm、18 cm、20 cm、22 cm时,有效颗粒质量百分比依次为81.8%、86.7%、92.5%、89.2%、87.6%,颗粒流动性指数依次为67.0、71.0、84.0、79.0、67.0,颗粒喷流性指数依次为71.0、69.0、67.0、73.5、76.5。数值仿真结果表明:当立柱长度分别为14 cm、16 cm、18 cm时,造粒过程中坯料颗粒分布体积约占造粒室体积的一半,此时造粒室底部堆积较少颗粒;当立柱长度为20 cm、22 cm时,造粒过程中坯料颗粒分布体积约占造粒室体积的一半,此时造粒室底部堆积较多颗粒。综合分析可知:所造坯料颗粒的有效颗粒最大质量百分比、流动性指数、喷流性指数依次为92.5%、84.0、69.0,均为该操作下的造粒效果最优值,此时造粒过程中坯料颗粒分散度最好,坯料颗粒的有效颗粒质量百分比最大、级配分布最均匀、流动性和喷流性最好,造粒效果最佳。     

陶瓷墙地砖干法制粉坯料颗粒与主轴转速分析

为分析陶瓷墙地砖干法造粒过程坯料颗粒与主轴转速的关系,以黏土、长石、石英等为造粒原料,采用陶瓷墙地砖干法造粒设备制备坯料颗粒,基于主轴转速的改变,分析坯料颗粒流动性及有效颗粒百分比与主轴转速的关系,同时数值仿真验证实验结果正确性。实验结果表明:当主轴转速分别为2500 RPM、2700 RPM、2900 RPM、3100 RPM、3300 RPM时,坯料颗粒的流动性指数依次为58.0、68.0、80.5、74.0、67.0,有效颗粒百分比依次为81.5%、83.1%、88.0%、86.4%、83.9%。数值仿真表明:当主轴转速分别为2500 RPM、2700 RPM、2900 RPM、3100 RPM、3300 RPM时,造粒室底部坯料颗粒最大堆积密度依次为0.40、0.36、0.32、0.36、0.36。综合分析说明:当主轴转速为2900 RPM时,坯料颗粒流动性最好,有效颗粒百分比最优,此时造粒效果最佳。     

陶瓷墙地砖干法造粒机主轴偏心率对造粒效果的研究

针对陶瓷墙地砖干法造粒制粉存在的颗粒级配分布不均匀的现象,搭建试验平台研究主轴偏心率对造粒过程中颗粒级配的影响,同时基于欧拉-欧拉模型模拟造粒过程颗粒的分散性及验证实验结果的可靠性,优化主轴偏心率。实验结果表明:当偏心率为0.15、0.25、0.35时,颗粒的有效质量百分比依次为79.5%、85.5%、79.4%,且当偏心率为0.25时,颗粒级配均匀性最佳。同时数值模拟结果表明:当偏心率为0.15、0.25、0.35时,颗粒在造粒室形成的堆积度依次分别为7%、3%、11%,说明实验结果与数值模拟基本相吻合,验证了实验的可靠性,表明主轴偏心率为0.25时造粒效果颗粒的级配均匀性最佳。     

陶瓷外墙砖干法造粒坯料颗粒与膨润土含量的影响

针对陶瓷外墙砖干法造粒坯料颗粒与膨润土含量的影响,以黏土类、石英类、长石类等超细粉体为主要原料,基于不同膨润土含量采用干法造粒制粉技术制备坯料颗粒,检测坯料颗粒休止角、压缩度、平板角、均齐度、凝聚度以计算分析坯料颗粒流动性指数,筛选坯料颗粒获得颗粒级配以计算坯料颗粒合格率,测量坯料颗粒球形度,基于测定的物性参数,分析膨润土含量对陶瓷外墙砖干法造粒效果的影响,同时数值仿真验证结果的可靠性。实验结果表明:当膨润土含量分别为1%、3%、5%、7%、9%时,坯料颗粒流动性的流动性指数依次为58.0、69.0、91.0、67.5、58.0,坯料颗粒合格率依次为82.1%、82.7%、85.9%、77.6%、20.9%,平均颗粒球形度依次为0.24、0.42、0.71、0.70、0.70。同时数值模拟结果表明:当膨润土含量分别为1%、3%、5%、7%、9%时,在造粒室形成的堆积度依次为0.38、0.36、0.33、0.35、0.39,且当膨润土含量为5%时,坯料颗粒分散性最好,说明实验结果与数值模拟基本吻合,验证了实验的可靠性,表明当膨润土含量为原料的5%时,陶瓷外墙砖干法造粒坯料颗粒流动性指数、坯料颗粒合格率、颗粒球形度最优。     

陶瓷墙地砖干法制粉造粒立柱与颗粒均匀度的影响

针对陶瓷墙地砖干法制粉造粒立柱对颗粒均匀度的影响.基于不同的造粒立柱几何参数,采用干法制粉制备颗粒,分析造粒立柱对颗粒均匀度的影响;同时基于CFD方法构建陶瓷墙地砖干法制粉混料过程欧拉-欧拉双流体模型,数值模拟验证实验的正确性.实验检测表明:当造粒立柱几何参数依次为6 mm、7 mm、8 mm、9 mm、10 mm时,对应制备颗粒最大均匀度为4.81、4.97、5.23、5.17、4.99,颗粒平均均匀度为4.71、4.85、4.98、4.87、4.83.数值模拟表明:当造粒立柱几何参数依次为6 mm、7 mm、8 mm时,粉体的分散性逐渐变好,团聚现象逐渐消失;当造粒立柱几何参数依次为9 mm、10 mm时,粉体的分散性逐渐变差,团聚现象逐渐明显.综合分析说明:造粒立柱几何参数为8 mm时,颗粒均匀度最大,粉体分散性最好,团聚现象不明显,且实验检测与数值模拟基本相吻合.     

陶瓷干法造粒搅拌槽结构对粉体混合效果的影响

为探究圆柱形和双层正八边形陶瓷干法造粒搅拌槽对粉体混合效果的影响.采用欧拉-欧拉方法构建气-固两相流混合过程计算模型,简化搅拌槽模拟区域并通过有限体积法建立空气-粉体混合过程物理模型,利用CFD方法对两种搅拌槽内流场进行数值计算,分析粉体体积分布与速度场,对比搅拌槽结构对粉体混合效果的影响,同时通过实验分析颗粒级配与流动性.结果表明:当搅拌槽为圆柱形时,槽壁区域形成回转抛物面,底部两侧槽底出现搅拌死角,粉体堆积度为12％;当搅拌槽为双层正八边形时,槽壁与两侧槽底湍流强度高,无回转抛物面与搅拌死角,粉体堆积度为4％.实验测得两种结构搅拌槽内有效颗粒百分比分别为71％、84％,流动性指数分别为60.66、75.5,侧面验证了数值模拟的正确性.双层正八边形搅拌槽相对圆柱形搅拌槽可有效提高粉体混合效果.     

挡板结构对陶瓷干法造粒室内粉体混合效果的影响

为研究干法造粒室中挡板结构对粉体混合效果的影响,通过构造欧拉两相流模型模拟粉体与空气的相互作用,采用k-epsilon RNG离散模型模拟湍流情况,采用滑移网格法和多重参考坐标系法分别求解动区域和静区域流场,分析了在造粒室内分别加装三种结构的挡板后对颗粒体积分数和速度场的影响.结果表明:当挡板横截面分别为长方形、三角形和半圆形时,颗粒体积分数径向云图显示体积分数小于0.31的面积占比分别约为26％、18％、2％;体积分数大于0.37的面积占比分别约为1％、15％、27％;颗粒速度大于0.54 m/s的面积占比分别约为45％、20％、40％;颗粒轴向速度大于0.4 m/s的面积占比分别约为80％、40％、35％.该结果显示长方形挡板造粒室更有利于促进粉体混合,提高粉体流动性.     

粘结剂配比对干法制备ZrO2陶瓷轴承造粒粉性能的影响

为探究粘结剂中聚乙烯醇、聚乙二醇、羧甲基纤维素钠的配比对干法制备ZrO2陶瓷轴承造粒粉性能的影响,配制6份不同配比的粘结剂溶液,采用旋转流场式干法造粒机制备ZrO2陶瓷轴承造粒粉。搭建颗粒级配检测平台对造粒粉粒径分布进行分析,借助Carr流动性指数法分析造粒粉流动性。结果表明:聚乙烯醇对造粒粉颗粒级配及流动性影响最大,聚乙二醇次之,羧甲基纤维素钠最小。当粘结剂溶液中聚乙烯醇:聚乙二醇:羧甲基纤维素钠配比为3:6:1时,干法制备ZrO2陶瓷轴承造粒粉的有效颗粒占比为81.6%,流动性指数为81,造粒粉级配均匀、颗粒流动性好。     

挡板对陶瓷干法造粒气-固两相流混合过程的影响

为探究陶瓷干法造粒气-固两相流混合过程挡板对粉体混合效果影响,构建欧拉气-固两相流模型分析空气与粉体相互作用,简化造粒区域并建立粉体混合过程三维物理模型,采用滑移网格法、多重参考系法模拟造粒室旋转运动,修正RNG离散模型分析湍流状态.根据径向及轴向粉体体积分数分布、速度场探究不同挡板对粉体混合影响,并改进挡板位置和结构以提高粉体混合程度.结果表明:当造粒室内分别含矩形壁挡板、矩形底挡板、半圆形壁挡板时,粉体轴向体积分数高于0.27的区域分别占总面积29％、40％、37％;粉体径向体积分数高于0.29的区域分别占总面积24％、15％、33％;粉体轴向平均速度分别为0.4 m/s、0.5 m/s、0.6 m/s;对不同粒径的粉体进行密度测定实验,当造粒室内含矩形壁挡板时,粉体密度基本为1.9 g/cm3,一致性较好.该结果显示矩形壁挡板造粒室内的粉体堆积程度最低,粉体混合性能最优,该模型及结果能够有助于提高对陶瓷干法造粒室气固两相流流场的理解,并对造粒室挡板设计优化提供一定理论指导.     

十字形挡板造粒室内干法制粉混料过程数值模拟

为改善干法制粉造粒室内颗粒混合特性,使其具有良好的造粒效果.采用计算流体力学方法,构建欧拉-欧拉双流体模型,对气固两相流场进行数值模拟,分析了十字形挡板造粒室内的压力场、速度场及颗粒体积分数,并结合实验与数值结果进行对比.结果表明:底部加装十字形挡板后,造粒室底部的压力分布状况更为均匀,提高了造粒室内颗粒整体速度;十字形挡板造粒室内颗粒体积分布达到71％,颗粒能够充满造粒室大部分区域,改善了底部颗粒堆积现象;颗粒合格率提高了6.9％,流动性指数提高了6;实验结果验证了数值模拟的正确性,十字形挡板造粒室有利于促进颗粒混合,提高了颗粒的合格率及流动性,造粒效果更优.     

橡胶硫化促进剂N-环己基-2-苯并噻唑次磺酰胺的团粒法造粒技术

采用团粒(聚)法制备了橡胶硫化促进剂N-环己基-2-苯并噻唑次磺酰胺(CBS)粒状产品,确定了团粒造粒工艺的最佳条件,并在此条件下进行了稳定运行实验.结果表明,用脱水后含水率为20%的CBS湿粉料为造粒原料,采用团粒法制备CBS粒状成品的最佳工艺条件:黏结剂乙烯-乙酸乙烯酯共聚物质量分数为CBS干基料的8%、湿粒含水率为34.77%,造粒盘倾角为35～45°、造粒盘转速为65 r/min,黏结剂乳液喷加时间约为10 min,造粒周期为50～60 min,烘箱干燥温度为(55±2) ℃,烘干时间为210 min;在最佳工艺条件下制得的粒状CBS性能均达到指标要求:初熔点不小于96.0 ℃,粒径为2.0～4.5 mm,粒子的平均强度在2.0～8.0 N,加热减量不大于1.00%,灰分不大于0.40%,成粒率超过60%.该粒状CBS能完全取代粉状产品,对橡胶的硫化性能无不良影响.     

Motion control for uniaxial rotational molding

Motion control parameters of rotational molding can affect process efficiency and product quality. Different motion control schemes will lead to varied powder flow regimes exhibiting different levels of mixing and temperature uniformity. The change in nature of powder flow during a molding cycle suggests that varying the rotational speed could improve the powder mixing and temperature uniformity, therefore potentially reducing processing time and energy consumption. Experiments completed investigating powder flow under uniaxial rotation show that savings of up to 2.5% of the heating cycle time can be achieved. This validates the hypothesis that altering the rotational speed to maintain the ideal powder flow throughout the heating cycle can be utilized to reduce the time taken for all the polymer powder to adhere to the mold wall. The effect of rotational speed on wall thickness uniformity and impact strength were investigated and discussed. Results show a strong influence of rotational speed (and powder flow) on the wall thickness uniformity of the moldings with wall thickness uniformity deviations of up to 50% found (within the 2–35 RPM speed range tested).     

双螺杆湿法制粒关键质量属性调控机理模拟研究

针对我国造粒工艺存在关键质量属性（粒径分布均匀性、颗粒表观质量和制粒收率）难以调控的行业共性问题,基于Edinburgh Elastic?Plastic Adhesion接触模型,构建了连续异向啮合双螺杆高剪切湿法制粒过程的仿真方法,模拟研究了过程参数?粒径分布均匀性和收率的协同耦合演化规律,以此诠释了双螺杆湿法制粒关键质量属性的调控机理。结果表明,连续异向啮合双螺杆高剪切湿法制粒机能制备表面光滑的球化颗粒,粒径与粉体喂料速度呈正关联关系,而与螺杆转速呈负关联关系,制粒收率与粉体喂料速度、螺杆转速均呈现先增后减的演化规律;在粉体喂料速度为360 kg/h或螺杆转速为1 400 r/min时,制粒收率处于最佳状态,其最优制粒收率值分别为87.9 %和83.91 %;制粒粒径主要受控于颗粒平均停留时间和持有颗粒质量,且呈正关联关系,以此提出了通过粉体失重喂料装置螺杆和异向啮合双螺杆高剪切湿法制粒机螺杆的变频转速控制,在线实时调控合格颗粒粒径和收率的技术方法。     

Spray Drying of Elderberry (Sambucus nigra L.) Juice to Maintain Its Phenolic Content

Spray drying was studied with Elderberry (Sambucus nigra L.) juice using a Buchi B-290 spray dryer. Different inlet temperatures ranging from 70°C to 120°C and two feed flow rates of 180 ml/hr and 300 ml/hr were considered for the experiment. The operating parameters were optimized in terms of total phenolic content retention, color, and powder recovery. The inlet temperature of 80°C with feed flow rate of 180 ml/hr gave high phenolic content retention with good color but lower recovery of the dried powder, i.e., less than 50%. To increase the recovery percentage during the drying process, the elderberry juice was spray dried with five different wall materials, i.e., soya milk powder, soya protein powder, isolated soya protein, gum acacia, and maltodextrin. Wall materials were evaluated in terms of total phenolic content retention, color of the powder, and mass recovery percentage. The gum acacia and maltodextrin gave better results and high recovery percentage, i.e., more than 70%. The best three combinations were stored under three different storage conditions in three different packagings to monitor the stability of the phenolic content and color of the powder.     

Stress measurements in high-shear granulators using calibrated “test” particles: application to scale-up

Granulation is a process by which fine powders are agglomerated into larger particles using a liquid binder. In high-shear granulation the powder–binder mix experiences intense agitation inside a mixing vessel as binder is dispersed and granules form and strengthen under the influence of shear and compacting forces in the device.

It is an implicit assumption that in a “high shear” mixer, large forces are transmitted to the powder and this results in a short and efficient granulation process. Owing to these desirable characteristics, high-shear granulation was adopted by several industries including pharmaceuticals and detergents where the process is used almost exclusively. In the work reported here, we attempt to measure shear forces in a moving powder inside a mixer-granulator. The method is based on previous numerical simulations [Powder Technology 110 (2000) 59] and experiments [Journal of Fluid Mechanism 347 (1997) 347] where we showed that at equilibrium between stresses in the mixer and the yield strength of the particles, granules attain a characteristic elongated shape. The measuring method adopted is indirect in the sense that pellets with well-defined mechanical properties were used to interrogate forces inside the granulating vessel at the point where they attain their characteristic elongated shape. We subsequently used the condition of equal shear forces in the device as a scale-up criterion so as to preserve the magnitude of stresses at both scales and thereby to expose forming granules to similar forces in both the small- and large-scale machines.

We found that shear forces in a “High-Shear” mixer-granulator with a vertical axis (Fielder) are actually not always high. The mixer has the potential to produce high shear forces but these forces are transmitted to the powder mass only if the powder is sufficiently cohesive or becomes cohesive due to binder addition. Shear forces in the granulator are strongly wet-mass-dependent and they increase rapidly as soon as a “granulation limit” is achieved, i.e., at the point where granules start to form in the shearing powder mass. We found that granulators with geometrically similar bowls can be scaled to generate comparable shear forces by decreasing the impeller rotational speed of the large machine by the factor (D/d)ⁿ, where D and d are the impeller diameters of the large and small machine, respectively, and n is a scaling index that depends on impeller geometry but not on wet mass properties. For the equipment studied in this work, the coefficient n was obtained as 0.80<n<0.85. We also propose an improved granulation process in which dry powders are pre-wetted before introduction into the main granulating device. This scheme has the potential to produce larger shear forces during wetting and binder introduction and thereby improve homogeneity and consequently final granule properties.     

Foam granulation: Binder dispersion and nucleation in mixer-granulators

Traditional wet granulation method involves spraying of liquid binder onto a moving powder bed to granulate the powder particles in the granulator. A new alternative method of wet granulation has been developed where foam delivery of binder is used to granulate the powder particles.This study investigated binder distribution in wet granulation and focused on the nucleation stage, where nuclei are formed during the initial binder distribution. Nucleation experiments were used to study the formation of nuclei by the foam and spray delivery methods in a high shear mixer-granulator. The distribution of foams on a dynamic powder bed were also investigated by filming small portion of foams as they penetrated into moving powder beds under different powder flow conditions in a high shear mixer-granulator.Nucleation experiments in this study show that foam delivery tends to create a narrower nuclei size distribution during the early stage of wet granulation process compared to spray delivery at the same processing conditions, demonstrating the potential of foam granulation in achieving improved binder distribution. For foam delivery, the nuclei formation is influenced by the foam properties and powder flow conditions in the granulator. The experiments show that the narrowest nuclei size distribution is obtained by granulating with high-quality foam and intensive powder mixing conditions. Coarser nuclei are formed when low-quality foam is dispersed in a less intensively agitated powder. The interactions of foam quality and the powder flow pattern are discussed and two distinct wetting and nucleation mechanisms are proposed: (1) under bumping flow, a low-quality foam tends to induce localised wetting and nucleation. The wetting and nucleation is “foam drainage” controlled. (2) Under roping flow, foam will be dispersed by the motion of the agitated powder. The wetting and nucleation is “mechanical dispersion” controlled.     

Agglomeration of hydrophobic powders via solid spreading nucleation

Wet granulation of a highly hydrophobic fine powder was investigated to elucidate the granule nucleation and growth processes in systems in which distribution of granulating fluid in the granulating mass is complicated by poor wetting. A mixture containing approximately 70 wt.% (90% by volume) of a micronized poorly wetting powder was granulated in a high-shear mixer using water and the microstructure of resultant agglomerates (granules) was studied using optical and electron microscopy as well as X-ray computed tomography (XRCT). The study revealed that granules are typically spherical or elliptical in shape and range in size from 200 to 500 μm. They are strong and consist of a consolidated powder shell and an empty core. Based on the microstructure, a nucleation mechanism for such a hydrophobic system is proposed. Implications for controlling granule growth and granule properties are discussed. This study demonstrates that well-controlled nuclei formation and subsequent granule growth is achievable in a highly hydrophobic system.     

Improving the dispersion kinetics of a cocoa powder by size enlargement

The efficient dispersion of powders in liquids is required in many fields. For this reason, it is useful to understand the mechanisms of dispersion and the physical properties of powders which influence the dispersion rate. Here, we have chosen to work with a low-fat cocoa powder commonly used in the food industry. Firstly, we have determined the physical properties of the powder (densities, cohesion, flowability, size and surface energy) and then measured the dispersion times of cocoa in water using a novel optical method. Further experiments, using the same technique, are performed using larger grains obtained by granulating cocoa powder. It is found that the dispersion times are shorter for the granules and much shorter than the dispersion time for ungranulated powder. The dispersion times for granules increase with the size of granules.