木粉增强木质素／环氧树脂复合材料的制备与力学性能

将玉米秸秆酶解木质素和双酚A环氧树脂共混,利用低相对分子质量聚酰胺作为同化剂,采用热压工艺制备了一种木粉增强的交联型木质素,环氧树脂复合材料,研究了热压温度、热压压力以及木粉的加入对复合材料力学性能的影响。研究结果表明,随着热压温度和热压压力的增加,木粉增强木质素,环氧树脂复合材料的弯曲强度和冲击强度均先升高而后降低,在120℃热压温度、8MPa热压压力下复合材料的力学性能达到最佳。随着木粉含量的增加,复合材料的弯曲强度和冲击强度均升高;木粉的粒径也对复合材料的力学性能有较大影响;综合考虑复合材料的力学性能,优选加入40—80目的木粉,木粉的含量为20％。     

Multi-scale simulation of needle-shaped particle breakage under uniaxial compaction

The breakage of needle-shaped particles within a random packed bed subjected to uni-directional compaction has been simulated using the discrete element method (DEM). Elongated particles with a chosen aspect ratio have been created by linking individual spherical discrete elements by rigid bonds, characterized by a given ultimate bending strength. A randomly packed bed of these elongated particles has been formed and gradually compressed between two infinite parallel solid planes. The particle size distribution as function of the compaction ratio has been studied in dependence on the individual particle strength, the initial particle length, and their distribution. The simulations have shown that the fragmentation generally follows the sequential halving kinetics and that the formation of fines is most profound in systems with a distribution of particle strengths, both within and between individual particles.     

Cold compaction molding and sintering of polystyrene

It is the objective of this paper to demonstrate the applicability of cold compaction molding followed by a sintering treatment to the processing of polystyrene powders. The influence of pressure, compaction speed, and peak pressure dwell time on the green (as compacted) density and the green tensile strength, as well as the effect of sintering on the tensile strength and dimensional change, were evaluated. The resulting data indicate that room temperature compaction alone is insufficient to provide adequate tensile strength for the compacts. Sintering the green compacts at temperatures of 150 to 173°C markedly improves the tensile strength while simultaneously causing a thickness change in the compacts. This thickness change results from gas evolution, pore shrinkage, and viscoelastic recovery of the residual stresses induced by pressure. For compacts of 0.225 in. thickness, an optimum sintering treatment of 173°C for 30 mins is recommended to provide a tensile strength of 4,000 psi and a thickness change of less than + 7 percent. Coining (repressing) the green compacts does not appreciably affect the sintered strength. However, a finer particle size improves the sintered properties. A review of the literature on the flow behavior of polystyrene suggests that a non-Newtonian viscous flow mechanism is followed by a Newtonian one as sintering progresses.     

热压工艺对沥青/中间相炭微球材料致密度及其性能影响的研究

以中间相炭微球为原料，沥青为粘结剂，通过特定热压烧结工艺对其进行烧结，制得各向同性炭块。研究了沥青加入量及烧结过程中加压过程的不同对炭块的密度和弯曲强度的影响。结果表明，当沥青加入量较低时（＜20％），炭块的密度呈现出随着沥青含量的增加而增大的趋势，其密度最大值为1．79g／cm^3,而炭块的弯曲强度却随沥青的含量有一个极大值为59．6MPa；并且在烧结过程中不至于使炭块开裂的前提下，炭块的密度呈现出随着加压时间的增加而增大的趋势，说明要取得性能良好的整体炭块，需要有一个最佳的沥青含量。     

Dependence of Compaction Efficiency in Dry Pressing on the Particle Size Distribution

The compact densification with pressing pressure (compaction efficiency) was determined to be sensitive to the particle size distribution. For the three types of alumina powders used in this research, the compaction efficiency increased with increasing particle size. It has been demonstrated that if the compact density versus log (pressure) has a linear relationship for any two types of powders, so do the blends of the two powders. A model is proposed which can predict the compaction efficiency of a binary particle system based on the Furnas particle packing model and consider the packing efficiency as a function of forming pressure. The composition of the binary mixture at which the highest density is obtained under high pressures is also the composition having the largest compaction efficiency. When coarse particles were added to this composition, the compaction efficiency slowly decreased, and when fine particles were added, the compaction efficiency rapidly decreased. For a continuous particle size distribution, the highest compaction efficiency is related to the average value of -log (porefraction).     

Correlation between powder-packing properties and roll press compact heterogeneity

Experimental work was carried out in order to measure the distribution of the effective applied stress in the roll gap during roll press compaction of lactose monohydrate, alumina and sodium chloride. The purpose of the study was to determine the influence of both powder properties and roll press feeding on the compaction. Therefore, a laboratory roll press was specially instrumented. The stress applied on the compact in the roll gap was measured locally by two piezoelectric transducers. The measured stress fluctuated a lot and was not homogeneous along the roll width. This heterogeneity was characterized by measuring the transmission of light through a sodium chloride compact. In fact, the heterogeneity of the compact properties was caused by the heterogeneity of the feeding pressure. The feeding pressure heterogeneity was principally due to the powder packing that took place in the last flight of the screw feeder. The roll press compaction could be very affected by the powder packing especially when small roll presses (pharmaceutical) were used.     

无粘结剂冷压成型天然鳞片石墨样品力学性能和微观结构的研究

采用天然鳞片石墨粉无粘结剂冷压成型为天然鳞片石墨样品，分别研究了成型压力、保压时间的变化对样品密度、孔隙度和抗折强度的影响，用三点弯曲法测试了样品的室温弯曲力学性能，并利用扫描电镜分析了样品的表面形貌以及断面形貌。结果表明，对样品的成型压力越大，样品的密度和抗折强度越大，而样品的孔隙率越小；保压时间对样品的密度影响不大，在5分钟以上样品的成型性较好；样品的抗折强度与样品成型时的取向有关。定性的分析了天然鳞片石墨样品的微观结构和抗折强度之间的关系。     

Effect of multiple impacts on high velocity pressed iron powder

High velocity compaction (HVC) process is a promising method for preparing high density powder metallurgy (PM) components with cost-effective. In the paper water atomized pure iron powder with 0.5 wt.% zinc stearate added was compacted by HYP35-7 High Velocity Compaction Machine. A computer controlled universal testing machine was used to measure the bending strength of samples. The effect of multiple impacts on the green density, the bending strength and the stress wave was discussed. The results show that at the identical total impact energy the green density and the bending strength of compacts pressed by double impact are the highest, whilst that of compacts prepared by triple impact is the lowest. In addition, the response time of stress wave is shortened gradually with increasing compacting numbers. Furthermore, the duration of stress wave of the second impact of double impact is the longest, but no obvious difference between that of single impact and the third impact of triple impact can be brought out. The comprehensive effect of the pressure and the duration results in the green density and the green strength increasing.     

Strength development in powder processing of poly(tetrafluoroethylene)

Poly(tetrafluoroethylene) (PTFE) is a versatile engineering plastic with excellent chemical and electrical resistance, a wide working temperature range, and a low coefficient of friction. PTFE is processed by the powder processing technique because of its high melt viscosity. The powder processing of polymers involves cold compaction of the polymeric powders, followed by sintering of the preforms at elevated temperatures. Sintering is a critical operation since the mechanical properties of the products are determined by the interparticle coalescence and diffusion of polymer chains across the interface. The results of the studies of the strength development during sintering of PTFE are reported here. The strength was measured in terms of the tensile strength at break, and the dependence of the tensile strength on compaction pressure, particle size, and processing time is discussed. The time dependence of strength development could be described by a diffusion controlled process in which the strength is proportional to the 1/4th power of the processing time.     

Green strength of binder-free ceramics

The Discrete Element Method (DEM) is used to investigate the compaction of ceramic powders by focusing on the role of primary particle and aggregate sizes. Hard aggregates of primary particles are represented as a collection of spherical particles bonded together by solid necks, which may break during compaction. Numerical simulations are performed to investigate the effect aggregate microstructure both on compaction and on the green strength of the ceramic compact. Tensile green strength originates only from van der Waals adhesion, without any action of a binder. It is shown that in such conditions, the green strength is inversely proportional to the size of the primary particles. The size of aggregates also plays a role, with smaller aggregates leading to larger green strength. The results of the simulations are compared to experimental data obtained on dioxide uranium aggregated powders, confirming the particle size effect.     

加压方式对PP／GMT片材孔隙含量和弯曲性能的影响

针对ＰＰ／ＧＭＴ体系,研究了以加压和辊筒加压两种方式下温度和压力对片材孔隙含量和弯曲强度的影响,得了了两种加压方式下的最佳浸渍温度和压力。实验中的各种条件下,辊筒加压所得片材的孔隙含量均低于平板加压所得片材的孔隙含量,而弯曲强度均较高,因而。中压方式明显优于平板加压方式。     

Adhesion properties of soy protein with fiber cardboard

Adhesion properties of soy protein isolate (SPI) on fiber cardboard and effects of press conditions, pre-pressing drying time, and protein concentrations on gluing strength were investigated. Shear strength increased as press time, press pressure, and/or press temperature increased. The effect of temperature on shear strength became more significant at high press pressure. The shear strength of the SPI adhesive on fiber cardboard decreased by 12–25% after water soaking. Shear strength increased as pre-pressing drying time increased and reached its maximal value at about 10 min. An SPI/water ratio of 12∶100 (w/w) gave the highest gluing strength. The specimens showed complete cohesive failure (fiber cardboard failure) except for soaked specimens pressed at low press temperature, low pressure, and short press time. Specimens pressed at 25°C and 2 MPa for 5 min with pre-pressing drying time of 10 min and an SPI/water ratio of 12∶100 (w/w) had T-peel strength and tensile bonding strength of 1.15 N/mm and 0.62 MPa, respectively, without water soaking, and 1.11 N/mm and 0.24 MPa, respectively, with water soaking.     

Uniaxial compaction behaviour and elasticity of cohesive powders

The compression and compaction behaviour of bentonite, limestone and microcrystalline cellulose (MCC) — three cohesive powders widely used in industry were studied. Uniaxial compression was performed in a cylindrical die, 40 mm in diameter and 70 mm high, for three selected cohesive powder samples. The initial density, instantaneous density and tablet density were determined. The influence of maximum pressure and deformation rate was examined. The secant modulus of elasticity E_sec was calculated as a function of deformation rate v, maximum pressure p and powder sample. After compaction experiments in hydraulic press at three pressures - p = 30, 45 and 60 MPa - and two different deformation rates, the strength of the produced tablets was examined in a material strength testing machine.From uniaxial compression tests performed on the universal testing machine for loading and unloading, the modulus of elasticity E was calculated on the basis of the first linear phase of unloading. The total elastic recovery of tablets was also obtained.     

Optimisation of the spark plasma sintering process for high volume fraction SiCp/Al composites by orthogonal experimental design

Based on orthogonal experimental design (OED), the effects of the sintering pressure, sintering temperature and holding time on the mechanical properties of 50 vol% silicon carbide particle (SiCp)/2024Al composites prepared by spark plasma sintering (SPS) were investigated. The sintering pressure had the greatest effect on the density and bending strength of the material among these three factors, followed by sintering temperature and holding time. The optimised process conditions for producing the 50 vol% SiCp/2024Al were sintering at 550 °C for 5 min under 40 MPa, which resulted in a composite material with a density of 99.7% and good interface bonding with a comparatively high bending strength of 766.65 MPa. This work provides a promising method to produce high volume fraction composites that can meet high strength requirements.     

Anisotropic mechanical properties of hot‐pressed PVDF membranes with higher fiber alignments via electrospinning

By the use of a high‐speed collection drum, poly(vinylidene fluoride) (PVDF) was electrospun into aligned ultrafine fibrous membranes from its solutions in a mixture of N,N‐dimethylformamide and acetone (9:1, v/v), and a continuous hot‐press post‐treatment was performed on the membranes to improve their mechanical properties. Anisotropic tensile results and rupture behaviors of the hot‐pressed PVDF membranes with higher fiber alignments in both revolving direction (RD) and cross direction were obtained. It was found that, due to the true fracture of electrospun fibers and improvement of the interfiber compaction by hot‐press, the tensile strength and modulus of the hot‐pressed membranes in RD reached the highest values at 58.12 ± 4.46 MPa and 519.9 ± 34.1 MPa, respectively when the collection speed was 10.42 m/s. The decrease of porosity and liquid absorption also represented the compaction improvement of the electrospun fibrous membranes. The combination of fiber alignments and hot‐press could provide a novel method to fabricate high strength of electrospun membranes which have highly potential applications in filtration or battery separators. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

真空热压烧结制备高性能B4C/Al复合材料

B4C/Al复合材料因其优异的性能,受到了人们广泛关注.以Al粉和B4C粉体为原料,采用真空热压烧结法,在高于Al熔点温度时,制备出了碳化硼含量10wt%的铝基复合材料.研究结果表明:烧结温度为700 ℃,烧结压力为30 MPa,保温时间为45 min时,获得的B4C/Al复合材料力学性能最佳,其相对密度为98.2%,硬度为2.53 GPa,抗弯强度为350 MPa.球磨混料使Al颗粒表面生成少量Al2O3,在烧结过程中,Al2O3与B2O3发生固-液反应形成共融物,改善了B4C/Al之间的界面结合强度,从而获得力学性能优异的B4C/Al复合材料.     

Effect of compaction pressure on the sinterability of submicron powders of tetragonal zirconium dioxide

Conclusions We studied the effect of compaction pressure on the pore structure of the paniculate compacts obtained using two types of agglomerated submicron powders of tetragonal zirconium dioxide, on the structure evolution during the sintering process, and on the strength of the obtained material. It was established that the characteristics of the agglomerates present in the powders have a significant effect on their behavior during compaction and sintering. At a given compaction pressure, the powders having weaker agglomerates densify up to a higher density and give a more uniform distribution of pores in the preform. The low-density compacts obtained using agglomerated powders having a high specific surface area sinter faster and attain high strength levels at a lower temperature; however, the sintered materials obtained from such compacts contain several structural defects in the form of large pores and have a lower strength. The uniformity of the distribution of pore volume with respect to size (or the specific content of the interagglomerate pores) forms the main criterion of the quality of particle packing in the compacts obtained from agglomerated powders. The compacts having a low content of the interagglomerate pores give a defect-free dense and strong material after sintering. The presence of the anion impurities in the original powders leads to a decrease of density during the sintering process after the attainment of a threshold density at which formation of closed porosity occurs. Pressure sintering (HIP) forms an effective method of suppressing the decrease of density.Translated from Ogneupory, No. 2, pp. 5–11, February, 1993.     

Fabrication and characterization of TiC-particle-reinforced MoSi2 composites

TiC particle reinforced molybdenum-disilicide (MoSi₂) matrix composites have been fabricated by two step pH adjustment of aqueous slurry and hot press sintering processing. The effects of TiC on the microstructure and mechanical properties of MoSi₂ matrix were investigated systematically. Due to the well-dispersed containing up to 40 vol.% TiC_p, the composite showed finer structure and improved mechanical properties than unreinforced material; the average 3-point bending strength at room temperature increased from 268 MPa for monolithic MoSi₂ to 445 MPa for 40 vol.% TiC_p–MoSi₂. The fracture toughness at room temperature and load-bearing capability at elevated temperature also obviously was improved by the TiC particle reinforcement. This is in contrast to the result published in literatures in which a decrease in strength with the addition of TiC was reported.     

Physical and mechanical properties of urea formaldehyde-bonded particleboard made from bamboo waste

Development of value-added products from any unutilized woody or non-woody material can play a vital role in economic development and also in forest resources conservation of any country. In this study, the suitabilities of planer waste and chips of Bambusa balcooa and Bambusa vulgaris, two locally grown bamboo species of Bangladesh, were investigated for the production of particleboard. The planer waste is a kind of shavings obtained during planing operation of bamboo splits for making rectangular strips of uniform thickness.Urea formaldehyde glue was used as a binder. Particleboards (12 mm thickness) were made from each type of the material applying 3.5 N/mm² pressure at 140 °C press temperature. The panels were tested to determine bending strength, modulus of elasticity, tensile strength, thickness swelling and water absorption.The variation in particle geometry of the raw materials significantly influenced the physical and mechanical properties of particleboard. The chips showed better strength properties compared to planer waste. B. vulgaris produced better and well glued particleboards compared to B. balcooa because of its superior gluability. The product could be used for indoor application especially as furniture component. Further research on the improvement in dimensional stabilization of product is needed.     

Dry granulation of organic powders—dependence of pressure 2D-distribution on different process parameters

Nowadays dry granulation of powders has become a very important research topic because it is the most economic way of granulation, making the particle handling easier, and avoiding the loss of material during particle processing, or particle transfers. This kind of process has been deeply studied but a better knowledge appears necessary to control the great number of parameters of the process. This is particularly important in cases where the nature of the powder may lead to very complex phenomena during compaction.In order to try and optimise dry granulation process for organic compounds, a roll press has been designed with a series of instruments enabling to control the compaction process. The apparatus consists of three parts: a vertical container with rotating steel blades avoiding arches into which the powder is poured, a feeder transferring the powder towards the rolls; the feeder is equipped with an horizontal helical screw in a cylindrical draft tube (10 mm in internal diameter, 500 mm long) and in the end of the feeder, a junction allows the change from the cylindrical symmetry of the feeder to the prismatic symmetry existing in the roll gap. The roll press (0-500 kN, load per unit length 0-) has been developed to record different major classical parameters: the roll speed, the roll gap, the press strength, the rotation angle, and the feeding rate (between 0 and ). In comparison with different kinds of roll press described in the literature, in this work an original instrumentation system has been developed to catch specific data. The 3D-pressure distribution profiles at the interface between powder and the roll wall and the drive torque applied to the rolls were measured. A large-sized smooth steel-made roll (240 mm diameter, 50 mm width) has been chosen to compare the results to the industrial scale.The results obtained with an organic compound exhibited the dependence—sometimes unexpected—of the rotation angle, the feeding and the rotation speed on the pressure distribution, the roll width, and the drive torque.