Arch formation mechanism and discharge process of cohesive fine powder in a vibrated silo

The arch formation mechanism and discharge process of a very cohesive fine powder(calcium carbonate)in a vibrated silo was investigated by experiments and discrete element method(DEM)simulations.An experimental setup is built to study the flow behaviors with the proposed image-based flow rate measurement method.A cohesive DEM model is used to investigate the dynamic behaviors of the powder bed.Results indicate that the arch formation depends on the vibration acceleration amplitude and is slightly affected by the frequency.The powder discharge flow rate increases with vibration acceleration amplitude and decreases with frequency.When the acceleration amplitude exceeds 15 g,the flow rate tends to stabilize.When the acceleration amplitude exceeds 1 g,there is separation and collision between the powder bed and the silo bottom.This collision leads to a significant increase in the contact force.

废渣粉掺量对混凝土流动性、粘聚性、强度影响试验研究

将工业废渣粉代替部分水泥或骨料制备废渣粉混凝土是一种环保且经济的处理工业废渣粉的方案.研究了不同废渣粉掺量对混凝土流动性、粘聚性、抗压强度影响的作用机理,研究结果表明,废渣粉等体积置换骨料使混凝土的浆膜厚度显著提高,而浆膜厚度是混凝土流动性、粘聚性和抗压强度的关键影响因素之一;随着废渣粉置换量增加,混凝土流动性增强、粘聚性变差、28 d抗压强度先增加后降低;当废渣粉置换骨料量为10%时,混凝土28 d抗压强度达到最大,因此在实际工程中应用废渣粉时,要注意置换骨料量控制在10%左右,这样既能保证混凝土强度,又能实现废渣粉废物利用.

Effect of high stirring speed on the agglomerate behaviors for cohesive SiO_(2) powders in gas fluidization

The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted fluidized bed.The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO2 powders,the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization.The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200μm.Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity.The stirring applied enlarges the operational range of agglomerate particulate fluidization(APF)with a delayed onset of bubbling for cohesive particles.However,the exorbitant speed increases the collision velocity and contact area between small agglomerates,which results in the formation of unstable agglomerates and the whirlpool of powder.

橡胶粉对塑性混凝土抗剪性能影响及在水库加固中的应用

为提高塑性混凝土的抗剪性能,运用直剪试验,研究了不同水胶比和不同橡胶粉掺量对抗剪摩擦系数和粘聚力的影响。结果表明:橡胶粉掺量大,塑性混凝土抗剪摩擦系数增大,但粘聚力下降;减小水胶比,塑性混凝土粘聚力增大。协同调控橡胶粉和水胶比,可提高塑性混凝土的抗剪摩擦系数和粘聚力,增强土石坝坝基和坝体防渗效果,确保大坝安全稳定。

Mathematical approach for understanding deagglomeration behaviour of drug powder in formulations with coarse carrier

Deagglomeration of cohesive particles in combination with coarse carrier is a key requirement for inhaled formulations.The aim of the project was to propose a mathematical approach to understand aerosolization behaviour of micronized particles alone and in formulation with carriers.Salbutamol sulphate and salmeterol xinafoate were blended separately with fine lactose(ratio 1:4)and fine and coarse lactose(1:4:63.5).Laser diffraction was employed to characterize the powder median particle size.The deagglomeration of micronized materials followed an asymptotic monoexponential relationship.When the coarse lactose was added,the relationship fitted a bi-exponential equation showing an easily and a poorly dispersed fraction.Using model hydrophobic and hydrophilic APIs,this study has demonstrated the utility of an analytical approach that can parameterize deagglomeration behaviour of carrier-free and carrier-based inhalation formulations.The analytical approach provides the ability to systematically study the effect of material,formulation and processing factors on deagglomeration behaviour.

Validation of surface coating with nanoparticles to improve the flowability of fine cohesive powders

Fluidization of fine cohesive powders is seriously restricted by the strong interparticle cohesion. The rational combination of nanoparticles with fine cohesive powders is expected to obtain composite par- ticles with improved flowability. In this work, we firstly reviewed the sandwich and three-point contact models regarding the fundamental principles of nano-additives in reducing cohesiveness. Based on these previous models, the effects of the size of nanoparticles, their agglomeration and coverage on the surface of cohesive powders in reducing interparticle forces were theoretically analyzed. To validate the the- ory effectiveness for the irregularly shaped cohesive powders, an extreme case of cubic powders coated with silica nanoparticles was fabricated, and the flowability of the composite particles was determined experimentally. Ultimately, based oN force balance of a single particle, a semi-theoretical criterion for predicting the fluidization behavior of coated powders was developed to guide the practical applications of improving the flowability of cohesive powders through structural design and modulation.

Characterisation of flowability of cohesive powders by testing small quantities of weak compacts

Characterisation of flowability of small quantities of cohesive powders is of great industrial interest, particularly for the pharmaceutical sec- tors, where a limited amount of material is available or the material is not easily accessible. In this paper, ball indentation on a powder bed is evaluated for flow characterisation of small quantities of cohesive powders at low levels of consolidation pressures. In parallel, the bulk powder is subjected to the common test method of unconfined direct compression. Analogous to indentation hardness testing, for which the indentation pressure is related to the flow stress, a constraint factor (C) is defined relating the unconfined yield stress and indentation pres- sure. The constraint factors for the test powders have been evaluated, enabling an easy method to characterize the flow behaviour of cohesive powders.

FLOW PROPERTIES OF COHESIVE NANOPOWDERS

The fundamentals of cohesive powder consolidation and flow behaviour using a reasonable combination of particle and continuum mechanics are explained. By means of the model 搒tiff particles with soft contacts? the influ-ence of elastic-plastic repulsion in particle contacts is demonstrated. With this as the physical basis, the stationary yield locus, instantaneous yield loci and consolidation loci, flow function and compression function are presented. The flow properties of a very cohesive titania nanopowder (dS=200 nm) are shown. These models are used to evaluate shear cell test results as constitutive functions for computer aided apparatus design for reliable powder flow.

基于图像分析-数值拟合的钛白粉体黏聚性表观评估方法及应用

钛白粉是目前综合性能最佳的白色无机颜料,具有优异的颜料性能和稳定的物化性质。钛白粉体的微观黏聚性对钛白粉生产工艺具有重大的影响,例如硫酸法钛白工艺中的雷蒙机粉碎工艺,硫酸法、氯化法通用的钛白粉气力传输过程以及钛白粉成品的“流动性”。粉体微观黏聚性不易精确测量,但可通过粉体堆积休止角进行表观评估。基于钛白粉体黏聚性与自然堆积休止角的相关性,本研究通过图像分析-数值拟合技术,提供了一种判定钛白粉体休止角的方法,从而实现对钛白粉体微观黏聚性的表观评估。该方法在钛白行业中雷蒙机助粉剂选型、汽粉助剂选型、工艺改进、成品质量标准、成品性能异常分析等方面具有潜在应用。

废弃轮胎胶粉改良膨胀土的抗剪强度研究

为了提高资源的循环利用,减少废弃轮胎对环境的潜在影响,对废弃轮胎胶粉改良膨胀土的强度特性进行研究。在不同含水量15%,18%,21%下,以不同比例废弃轮胎胶粉10%,20%,30%与膨胀土混合后进行固结快剪实验。在试验过程中综合考虑法向应力,胶粉含量对膨胀土抗剪强度的影响,以及剪切位移与对应的剪应力的关系,总结出膨胀土改良后的抗剪强度变化特征。结果表明内摩擦角和膨胀土的抗剪强度随废弃轮胎胶粉含量的增加而增大,内摩擦角的变化不大,黏聚力的变化较为显著。同时证实了废弃轮胎胶粉改良膨胀土效果较为显著,为膨胀土改良提供了一个新的改良方法。

粉胶比对沥青胶浆低温黏结强度的影响

选用SBS改性沥青,通过沥青胶浆低温黏结强度定量测试技术,研究了在不同低温条件下不同粉胶比对沥青胶浆低温黏结强度的影响机理,并确定了最佳粉胶比。研究结果表明:低温环境、粉胶比对沥青胶浆的低温黏结强度变化规律有显著影响。合适的粉胶比能够提高沥青胶浆的低温黏结强度。大粉胶比会产生填料附聚现象,截面附加破坏点基数增加,导致沥青胶浆低温黏结强度显著下降。此外,环境温度降低,沥青基体强度有所提高,但当温度低于沥青脆化点后,基体发生脆化,从而导致低温黏结强度显著降低。最佳粉胶比的确定应结合当地的低温条件,综合考虑沥青基体的黏结强度、沥青基体脆化状态及沥青填料界面强度效应。

粘附性颗粒添加组份流态化进展

综述了近年来国内外粘附性颗粒添加组份流态化的进展，并对粘附性颗粒流化床中颗粒受力分析及模型进行了评价．指出了粘附性颗粒添加组份流态化存在的问题及发展方向，提出应开展添加组份的性质、种类、添加比例及其与粘附性颗粒之间相互作用的机理研究．

粘附性颗粒添加组份流态化实验

以不同粒径的ＳｉＣ为物料，考察了表观气速和添加颗粒对其流化性能的影响．实验表明，平均粒径大于１０μｍ的ＳｉＣ物料，可通过增大表观气速使其流化；而小于５μｍ的ＳｉＣ５和ＳｉＣ２物料，不能使用增大表观气速的方法使其流化．添加颗粒能使ＳｉＣ５很好流化，利用流态化聚团准数Ａｅｆ可计算颗粒的最佳添加量ｘｍ．

基于快速原型的金属粉浆无压浇注成型与烧结

通过快速成型技术与硅橡胶软模技术首先制得试样的硅橡胶模具,然后将由铁粉与树脂粘结剂混合而成的粉浆浇注进硅橡胶模具中翻制试样的型坯,再对型坯进行烧结制取内部孔隙均匀的金属骨架状型坯。在试验对比的基础上,探讨了金属粉浆无压浇注成型与烧结工艺中树脂粘结剂的选用、金属粉的选用、粉浆浇注与烧结等问题。结果表明:199聚脂树脂较适合作为该工艺的粘结剂,同时双组分混合铁粉较单一铁粉更有利于形成孔隙均匀的骨架状型坯的烧结成型。

非磁性粘性颗粒在添加磁性大颗粒磁场流化床中的流化性能

通过添加磁性大颗粒,破碎活塞及沟流,显著改善了非磁性粘性颗粒在磁场流化床中的流化性能。为了评价非磁性粘性颗粒在磁场流化床中的流化性能,测量了最小流化速度、床层压力降和床膨胀高度。实验结果表明,非磁性粘性颗粒的最小流化速度,由于添加磁性大颗粒,而显著降低。磁性大颗粒添加量对非磁性粘性颗粒的最小流化速度有较大影响,随磁性大颗粒添加量的增加,最小流化速度降低,但当磁性大颗粒添加量增大到40%后,非磁性粘性颗粒和磁性大颗粒的混合物的最小流化速度就不再降低。

湿陷性黄土侵水前后抗剪强度变化规律研究——以河南巩义地区湿陷性黄土为例

通过侵水前后湿陷性黄土的快剪试验,发现侵水后土样的抗剪强度明显低于天然状态下土样的抗剪强度,且抗剪强度的变化规律与土的类别有关。粉土类湿陷性黄土侵水前后的抗剪强度在各级压力下变幅相当,并且抗剪强度的变化主要表现在黏聚力的降低上,降幅达92%;侵水前后粉质黏土类湿陷性黄土的抗剪强度变化随压力变化分为快速变化和缓慢变化两个阶段,根据土的湿陷程度不同抗剪强度发生快速变化的起始压力也不同,其中内摩擦角的变化随湿陷系数的降低而减小,黏聚力的变幅与土的湿陷程度以及压缩系数有关。

水泥硅微粉固化黄土的冻融试验研究

为了研究水泥硅微粉固化黄土的力学性能,利用宁夏宁东工业园区的黄土,掺入2%的水泥和10%的硅微粉进行固化,分别进行7、28 d龄期的三轴试验和28 d龄期3、9次冻融循环的三轴试验。结果表明:7、28 d龄期的素土与7、28 d龄期固化土相比,水泥和硅微粉的掺入对黄土的黏聚力的影响显著。7 d龄期黏聚力增加了33.99倍,28 d龄期黏聚力增加了57.34倍。素土3次冻融循环黏聚力降低了30.3%,9次冻融循环黏聚力降低了88.8%;固化土9次冻融循环黏聚力降低了8.3%,硅微粉和水泥掺入黄土,使其变形表现为素土呈塑性材料特性向固化土呈脆性材料变化,硅微粉和水泥的掺入有效地提高了黄土的承载力。

包钢自产和巴润精矿粉的成球性对比和连晶性研究

成球性是一个综合指标,它体现了试料的表面特性、粘结力及内摩擦力等的综合影响;判断成球性的主要指标是成球后的抗压强度和在规定时间内的成球直径大小.铁矿粉的连晶性越强,生产出的球团矿抗压强度越大.所以,可以通过比较在同一焙烧条件下,不同配比的铁精矿粉连晶性的强弱,来判断不同配比条件下所生产球团矿的强度.研究结果表明,自产精矿的成球性优于巴润精矿;铁矿粉连晶固结能力由大到小依次为:自产、再磨、巴润、外购.

乳粉喷流性及影响因素的探讨

通过对乳粉颗粒观察及对其喷流性的研究,测定代表流动性的自然坡度角(θr)、压缩率(Cp)、凝集度(Ch)、代表喷流性的崩溃角(θf)、差角(θd)、分散度(Ds),讨论各种性能对乳粉的影响因素。

高速电弧喷涂FeMnCrAl/Ni包覆WC涂层组织与性能

采用无需常规敏化活化的预处理常温超声波化学镀方法制备Ni包覆WC复合粉体,以其作为增强相的粉芯丝材通过高速电弧喷涂技术制备FeMnCrAl/Ni包覆WC涂层。采用光学显微分析(OM)、场发射扫描电镜分析(FE-SEM)、能谱分析(EDS)以及涂层性能测试方法,研究Ni包覆WC复合粉体对涂层组织结构及性能的影响。结果表明:Ni包覆WC复合粉体能改善涂层中各相之间的结合状态,减少涂层中氧化物和孔隙率,提高涂层与基体的结合强度和涂层的内聚强度,改善了涂层抗冲蚀磨损性能。