A specific energy-based size reduction model for batch grinding ball mill

A particle size reduction model has been developed as the first component of an upgraded ball mill model. The model is based on a specific energy-size reduction function, which calculates the particle breakage index, t₁₀, according to the size-specific energy, and then calculates the full product size distribution using the t₁₀–t_n relationships and the mass-size balance approach. The model employs an ore-specific and size-dependent breakage function, whose parameters are independently measured with a fine particle breakage characterisation device, the JKFBC. This has effectively overcome the limitation of using a default breakage appearance function for all ores in the perfect mixing ball mill model. Since the ore-specific characteristics and the machine-related specific energy parameters are mechanistically incorporated in the size reduction model, it has the capability to predict size reduction in response to changes in the ball mill feed breakage characteristics and the operation-related specific energy.     

Twin screw granulation – review of current progress

Twin screw granulation (TSG) is a new process of interest to the pharmaceutical community that can continuously wet granulate powders, doing so at lower liquid concentrations and with better product consistency than found by a high shear batch mixer. A considerable body of research has evolved over the short time since this process was introduced but generally with little comparison of results. A certain degree of confidence has been developed through these studies related to how process variables and many attributes of machinery configuration will affect granulation but some major challenges still lay ahead related to scalability, variations in the processing regimes related to degree of channel fill and the impact of wetting and granulation of complex powder formulations. This review examines the current literature for wet granulation processes studied in twin screw extrusion machinery, summarizing the influences of operational and system parameters affecting granule properties as well as strives to provide some practical observations to newly interested users of the technique.     

Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B₄C-TiB₂-SiC composites were fabricated via hot pressing using ball milled B₄C, TiB₂, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84?GPa, 858?MPa and 8.21?MPa?m^1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B₄C-TiB₂-SiC composite.     

场协同对PP/PS复合体系传热传质性能的影响

从动量和能量守恒方程出发,提出速度场与温度场的协同耦合作用对聚合物流动与换热具有重要影响,并以此为依据设计了新型扭转螺杆结构和场协同螺杆。以聚丙烯(PP)和聚苯乙烯(PS)为原料制备PP/PS复合材料体系,通过挤出试验对比研究了常规螺杆与场协同螺杆的传热传质性能。结果表明,相对于常规螺杆,设置有扭转螺杆结构的场协同螺杆的数均粒径更小、粒径分布密度和平均停留时间更大,提高了挤出机的混合能力;场协同螺杆的对流换热系数更大、径向温差更小,提高了挤出机的换热能力。     

Effect of additive distribution in H2 absorption and desorption kinetics in MgH2 milled with NbH0.9 or NbF5

This paper presents a comparative study of H₂ absorption and desorption in MgH₂ milled with NbF₅ or NbH_0.9. The addition of NbF₅ or NbH_0.9 greatly improves hydriding and dehydriding kinetics. After 80 h of milling the mixture of MgH₂ with 7 mol.% of NbF₅ absorbs 60% of its hydrogen capacity at 250 °C in 30 s, whereas the mixture with 7 mol.% of NbH_0.9 takes up 48%, and MgH₂ milled without additive only absorbs 2%. At the same temperature, hydrogen desorption in the mixture with NbF₅ finishes in 10 min, whereas the mixture with NbH_0.9 only desorbs 50% of its hydrogen content, and MgH₂ without additive practically does not releases hydrogen. The kinetic improvement is attributed to NbH_0.9, a phase observed in the hydrogen cycled MgH₂ + NbF₅ and MgH₂ + NbH_0.9 materials, either hydrided or dehydrided. The better kinetic performance of the NbF₅-added material is attributed to the combination of smaller size and enhanced distribution of NbH_0.9 with more favorable microstructural characteristics. The addition of NbF₅ also produces the formation of Mg(H_xF_1-x)₂ solid solutions that limit the practically achievable hydrogen storage capacity of the material. These undesired effects are discussed.     

滚珠丝杠螺母副热态特性建模方法

以某外循环滚珠丝杠螺母副为研究对象，对其热态特性及其建模方法进行研究。在分析滚珠丝杠进给系统的热源和边界条件的基础上，建立了丝杠稳态温度分布的数学模型，并通过软件编程求解得到丝杠温度场和滚道的存在对丝杠稳态温度的影响；建立了考虑滚道影响的滚珠丝杠进给系统有限元分析模型，获得了滚珠丝杠进给系统稳态和瞬态热特性分析结果；最后通过滚珠丝杠螺母副热特性试验，获得了滚珠丝杠进给系统关键点的温度及其变化情况。研究结果表明：所建立的滚珠丝杠螺母副热特性分析数学模型可以较准确地获得滚珠丝杠的温度场，忽略滚道会使滚珠丝杠螺母副的温度场仿真结果产生15%～20%的误差。     

Preparation of presintered zirconia blocks for dental restorations through colloidal dispersion and cold isostatic pressing

This work proposes an effective method for dispersion of zirconia suspension for dental block preparation and optimizes the cold isostatic pressing (CIP) pressure to improve the densification of slip-casted zirconia blocks. Two batches of 44 wt% zirconia suspension were prepared using distilled water in a pH 2 medium containing 0.5 wt% polyethyleneimine as dispersant. The first batch was sonicated for different durations (from 5 min to 30 min), and the second batch was dispersed through ball milling at rotational speeds of 200, 300, and 400 rpm for 60, 90, and 120 min. All suspensions were subjected to sedimentation test and particle size measurement. Results revealed that the optimum ultrasonication duration was 10 min, which yielded the smallest particle size of 133 nm. Ball milling at 300 rpm for 120 min achieved the maximum dispersion of particles, with an average size of 75 nm. Under the optimum conditions of ultrasonication duration, ball milling duration, and ball milling speed, the particle size decreased to 48 nm, which is close to the primary particle size. These dispersion techniques and parameters were selected for preparing a suspension to be consolidated into blocks through slip casting and were enhanced through CIP at pressure ranging from 100 MPa to 300 MPa. CIP compaction at 250 MPa significantly increased the shrinkage percentage of green zirconia blocks, with pore radius decreased to 18 nm. The density of zirconia pressed at 250 MPa and presintered at a low temperature of 950 °C was 59% of the theoretical density and was higher than that of commercial presintered blocks. Thus, CIP should be conducted under a compaction pressure of 250 MPa to produce dense and homogeneous zirconia blocks.     

Homogeneous dispersion of boron nitride nanoplatelets in powder feedstocks for plasma spraying

Hexagonal Boron nitride nanoplatelet (BNNP) with the combination of excellent mechanical properties, high-temperature thermal stability, and self-lubrication is a promising strengthening agent in plasma-sprayed composite coatings. However, it is a significant challenge to produce plasma sprayable feedstocks with homogeneously dispersed BNNPs owing to the intrinsic agglomeration of BNNPs. In this research, three powder preparation processes (electrostatic interaction, ball milling, and shear mixing) were employed to disperse BNNPs in Ni-Cr-Cr₂O₃ (NCCO) powders. The shear mixing process presents a competitive advantage in powder preparation, providing stable shear force and achieving exfoliated BNNPs homogeneous distribution in the composite powders. The spray drying technique was finally utilized to obtain spherical agglomerated BNNP-NCCO feedstocks with characteristics of relatively smooth surface and uniform size distribution. Hence, shear mixing and spray drying processes are expected to produce large-scale spherical composite powders with a homogeneous distribution of 2D layered nanomaterials for industrial application.     

旋挖钻进中硬岩及卵砾层钻头结构及施工工艺研究

旋挖钻进技术作为一种高效优质的钻进方法近年来广泛地被用于公路、铁路及大型水电站基础工程施工建设中，取得了良好的社会效益和经济效益。探讨了在卵砾石、漂石等复杂地层以及坚硬基岩中进行旋挖钻进所用钻头的结构及其施工工艺。     

吊环螺钉系列零件三维模型的制作

介绍了用Solidworks软件制作吊环螺钉GB82 5 - 88(A)系列零件三维模型的方法和步骤。步骤是首先建立吊环螺钉默认标准件三维模型 ,然后建立吊环螺钉系列零件三维模型。使吊环螺钉GB82 5 - 88(A)形成正确配置的方法是 :增加尺寸约束、增加特征及分割系列零件设计表。这些方法在制作其他比较复杂系列零件时同样具有借鉴意义