Abrasion test of flexible protective materials on hydraulic structures

In this study, several kinds of flexible protective materials sprayed with polyurea elastomers （hereinafter referred to as polyurea elastomer protective material） were adopted to meet the abrasion resistance requirement of hydraulic structures, and their abrasion resistances against the water flow with suspended load or bed load were studied systematically through tests. Natural basalt stones were adopted as the abrasive for simulation of the abrasion effect of the water flow with bed load, and test results indicate that the basalt stone is suitable for use in the abrasion resistance test of the flexible protective material. The wear process of the polyurea elastomer protective material is stable, and the wear loss is linear with the time of abrasion. If the wear thickness is regarded as the abrasion resistance evaluation factor, the abrasion resistance of the 351 pure polyurea is about twice those of pure polyurea with a high level of hardness and aliphatic polyurea, and over five times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with suspended load. It is also about 50 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load. Overall, the abrasion resistance of pure polyurea presented a decreasing trend with increasing hardness. Pure polyurea with a Shore hardness of D30 has the best abrasion resistance, which is 60 to 70 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load, and has been recommended, among the five kinds of pure polyurea materials with different hardness, in anti-abrasion protection of hydraulic structures.

Abrasion Resistant Refractory Materials

1 Scope This standard specifies the definition, classification, technical requirements, test methods, quality appraisal procedure, packing, marking, transportation, storage, and quality certificate of abrasion resistant refractory materials.

High Speed Lapping of SiC Ceramic Material with Solid (Fixed) Abrasives

An experimental investigation is carried out to machine SiC ceramic material through the method of high speed plane lapping with solid(fixed) abrasives after the critical condition of brittle-ductile transition is theoretically analyzed. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasives for brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic in the ductile mode using W3.5 grit and a high efficiency, low cost and smooth surface with a surface roughness of R_a 2.4?nm can be achieved.

Optimization of Abrasive Water Jet Cutting of Ductile Materials

Full factorial design of experiments was developed in order to investigate the effects of jet pressure, abrasive mixing rate, cutting feed, and plate thickness upon three response variables, surface finish of cutting wear zone, percentage proportion of striation free area, and maximum width of cut. The set of sixteen experiments was performed on each of the following two ductile materials： AISI 4340 （high strength low alloy steel, hardened to 49HRc） and Aluminum 2219. Analysis of Variance （ANOVA） was performed on experimental data in order to determine the significance of effects of different parameters on the performance measures. It was found that cutting feed and thickness were highly influential parameters, while abrasive mixing rate is influential upon surface roughness only. Strong interaction was found between jet pressure and workpiece material. Multi-criteria numerical optimization was performed in order to simultaneously maximize/minimize different combinations of performance measures.

A review on the erosion mechanisms in abrasive waterjet micromachining of brittle materials

The fabrication of miniature structures on components with high-integrity surface quality represents one of the cutting edge technologies in the 21st century.The materials used to construct such small structures are often difficult-to-machine.Many other readily available technologies either cannot realise necessary precision or are costly.Abrasive waterjet(AWJ)is a favourable technology for the machining of difficult-to-machine materials.However,this technology is generally aimed at large stock removal.A reduction in the scale of this technology is an attractive avenue for meeting the pressing need of industry in the production of damage-free micro features.This paper reviews some of the work that has been undertaken at UNSW Sydney about the development of such an AWJ technology,focusing on the system design currently employed to generate a micro abrasive jet,the erosion mechanisms associated with processing some typical brittle materials of both single-and two-phased.Processing models based on the findings are also presented.The review concludes on the viability of the technology and the prevailing trend in its development.

Experiments and computer simulation analysis of impact behaviors of micro-sized abrasive in waterjet cutting of thin multiple layered materials

The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of AWJ.However,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated problem.In this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally investigated.In addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.

Feasibility Study on V Fe Alloy Slag as Abrasive Material

The possibility of using V-Fe alloy slag as abrasive material was investigated. The chemical constitution and microstructure of the V-Fe alloy slag were examined. It is found that the slag contains about 90% Al2O3 existing as corundum with high hardness (> 30 GPa) and high bulk density (> 3.6 g/cm(3)). The V-Fe alloy slag can be applied to abrasive material instead of brown alumina (or black alumina).

A Structural Study of High Cr Cast Iron as a Grinding Ball Material

In present paper, the 3-body abrasion and impact fatigue resistance of a 12％Cr-2.65％C-1.4％Si high Cr cast iron are comprehensively evaluated. The results indicated that the lower the C content of the martensitic matrix, the better the impact fatigue resistance of the iron. The retained austenite is always harmful to both 3-body abrasion and impact fatigue resistances. The low C content martensitic matrix free from retained austenite is suitable for making grinding balls.

A New Test Method for Hot Abrasion Resistance on Refractories

Test methods for hot abrasion resistance of refractories in China and overseas were briefly introduced. A new test method for hot abrasion resistance was researched. The new method inherits test principle of cold abrasion resistance in Chinese standard totally, adopts compressed air pre-heating and electricity heating sam- ples, and is featured with complete structure, good con- trollability, simple operation, and small size. The characteristics and operating procedure of HAT-14A tester were introduced. The hot abrasion resistance of various refractories at different temperatures was tested.

FORMING AND PRECISION MACHINING TO NANOMATERIALS LUMP

The technology of forming and machining lump nano-materials has beeninvestigated. Grinding, abrasive machining test has been conducted to Fe, Co, Ni and Al lumpnano-materials. Experiments have been done to measure grinding force, grinding thermal, machiningroughness and micro-hardness. Image analysis is carried out by metallographic and scanning tunnelmicroscopic microscope. Researches provide the basis data for forming and machining lumpnano-materials.

交流高压静电防护服装标准的解读

为推动标准的有效推广和实施,以及交流高压静电防护服装的科学制备和合理适用,对GB/T18136—2008《交流高压静电防护服装及试验方法》和DL/T 1238—2013《1000 kV交流系统用静电防护服装》中的关键技术指标进行了探讨。对比分析了两个标准的异同点,并提出了合理化建议,为标准的修订提供参考。认为:应进一步增加衣料撕破强力、透湿量、色牢度、甲醛含量、pH值、接缝强力等考核指标,并明确相关考核指标的测试参数。

微磨料气射流加工技术研究现状与展望

微磨料射流加工技术是一种基于高能流体的磨粒冲蚀磨损加工技术,已广泛应用于难加工材料、复杂三维型面、光滑表面的加工。为进一步提高磨料射流加工过程中的精准控形控性能力,国内外学者开展了诸多基础加工理论与工艺探索等方面的研究工作。本文在概述磨料射流加工技术发展的基础上,全面总结了国内外学者在微磨料气射流加工(MAJM)技术中的微磨料气射流束发散效应及其抑制策略、材料力学性能对材料冲蚀去除模式的影响、材料冲蚀加工过程磨料嵌入抑制策略、微结构冲蚀加工几何特征等方面的主要研究成果,并对微磨料射流加工技术的难点与发展趋势进行了展望。

面向钢轨修复的不同槽型接触轮砂带打磨接触行为及材料去除特性

为掌握不同槽型接触轮砂带对钢轨打磨接触行为及材料去除特性的影响规律,基于橡胶接触特性,建立X齿型、锯齿型和人字型3种典型接触轮砂带打磨仿真模型,模拟分析不同槽型特征对接触轮-钢轨静态接触行为和动态冲击应力的影响机制;通过钢轨砂带打磨试验,对比研究3种槽型接触轮的材料去除特性。结果表明:3种槽型接触轮与钢轨的接触区域整体均呈椭圆形态,符合赫兹接触理论,内部接触形态则随槽型特征呈现为块状分布;接触区域应力分布总体符合弹性半空间接触理论,但在接触块边缘会出现应力集中;X齿型接触轮和人字型接触轮因齿尖和齿槽结构的存在而具有较高的材料去除能力,同等打磨条件下X齿型接触轮较平型接触轮的材料去除能力提高了79%;顺磨条件下的材料去除能力高于逆磨,以X齿型接触轮为例,顺磨比逆磨的材料去除能力提高了22.7%;X齿型和人字型接触轮砂带打磨的噪声、振动、粗糙度、平均电流均较高,锯齿型接触轮具有较低的振动、粗糙度及平均电流,平型轮则具有较低的噪声和电流。

小孔内表面磁力研磨加工技术研究进展

磁力研磨加工是提高小孔内表面质量的一种重要光整技术,利用该技术能高效提升小孔类零部件在极端环境下的使役性能。针对小孔内表面的磁力研磨光整加工,按其发展历程对磁力研磨加工技术进行总结,归纳了磁性磨粒研磨、磁针磁力研磨、液体磁性磨具研磨、超声辅助磁力研磨和电解磁力复合研磨等加工方法的技术特点,并分析评述了其局限性。对磁力研磨加工过程中材料去除机理进行了研究,材料主要以微量切削与挤压、塑性变形磨损、腐蚀磨损、电化学磨损等方式去除,材料种类不同,去除机理也不同。其中,硬脆性材料主要以脆性断裂、塑性变形和粉末化的形式去除;塑性材料在经历滑擦阶段、耕犁阶段和材料去除阶段后主要以切屑的形式去除。此外,还对磁力研磨加工过程中的材料去除模型进行了研究,对单颗磁性磨粒材料去除模型和“磁力刷”材料去除模型进行了分析讨论。最后,对磁力研磨加工技术今后的研究发展给出了建议并进行了展望。

基于磨粒三维轨迹的钽酸锂双面研磨均匀性

为了改善钽酸锂(LiTaO_(3),LT)晶片的材料去除均匀性,提出一种考虑磨粒三维微切削的材料去除均匀性模型。根据钽酸锂晶体脆/塑性去除机理,结合研磨垫表面磨粒的分布特征,运用力平衡方程计算了研磨垫上各磨粒的切入深度与切屑截面积。通过运动学分析推导了双面研磨中磨粒运动轨迹方程,建立了考虑磨粒三维微切削的材料去除均匀性模型,并研究了齿圈与太阳轮转速比m、下研磨盘与太阳轮转速比n对材料去除均匀性的影响。最后,开展了钽酸锂晶片固结磨料双面研磨实验,测量了不同转速比m,n下晶片的总厚度变化,验证了模型。实验结果表明:材料去除均匀性受转速比m,n的影响较大,当转速比m,n分别为0.85,1.3时材料去除均匀性最佳,此时晶片的总厚度变化为0.83μm,实验结果与仿真一致。所建模型对改善钽酸锂晶片双面研磨材料的去除均匀性有一定的指导意义。

管件内壁磁粒研磨时的磨粒动力学行为仿真及分析

为探究磁性磨粒在管件研磨过程中的动力学行为,对其研磨过程进行离散元仿真,并分析其运动轨迹和磨削力随管件转速和加工间隙的变化;通过单磨粒球运动及磁粒研磨试验,验证磁场力模型的准确性与粒子运动学行为可视化的可行性。结果表明:随管件转速提高,磁性磨粒在离心力作用下向加工区域外运动,且加工间隙越大越容易被“甩飞”;在达到临界转速之前,随管件转速提高,磨削力减小,材料去除效率提升。当管件转速由400 r/min提高至临界转速,加工间隙为2 mm和4 mm时,磨削力分别下降5.4μN和2.3μN,材料去除效率明显提升;当加工间隙为6 mm时,磨削力变化较小,且当转速大于临界转速650 r/min时,材料去除效率下降。同时,材料去除量在达到临界转速之前随管件转速提高而增大,但加工间隙的增大会使临界转速降低;且材料去除量的变化趋势与仿真结果一致,验证了仿真分析的可靠性。

纳米SiO_(2)/桐油基环氧树脂复合材料的制备及性能

通过制备环氧化桐油酸甲酯,并将其与E51环氧树脂共混,得到桐油基环氧树脂。再用硅烷偶联剂KH-570改性纳米SiO_(2),并以不同的质量比添加到桐油基环氧树脂中,探究不同纳米SiO_(2)含量在力学性能、接触角以及耐磨损性能上对桐油基环氧树脂复合材料的影响。结果表明:质量比为6%的纳米SiO_(2)的桐油基环氧树脂复合材料的拉伸和冲击强度都得到了提高,冲击强度较未加入纳米SiO_(2)提高了53.3%,水接触角也从93.3°提高到104.76°,并且添加纳米SiO_(2)之后复合材料的耐磨损性能也随之增强。

弹性基体软固结磨料磨具的材料去除机理

基于弹性磨具的磨抛工艺为硬脆材料超精密加工效率与加工质量的兼顾平衡提供了新的解决思路,但其磨抛过程的材料去除机理尚未明确。为研究弹性磨抛过程中的材料去除行为,以硅橡胶作为磨具基体材料,混合微米级金刚石磨料制备弹性基体软固结磨料磨具,利用有限元仿真分析方法研究弹性基体软固结磨粒的受力状态,结合接触力学与运动学分析建立考虑单颗磨粒磨损行为与有效磨粒数量的材料去除模型,通过石英玻璃试件的弹性磨抛加工试验验证预测模型的准确性。结果表明:石英玻璃试件的材料去除率随着磨抛压力、主轴转速、磨具偏角的增大而显著增加,而磨料粒径对其影响程度较小;当工艺参数组合为磨料粒径100μm、磨抛压力7 N、主轴转速1500 r/min、磨具偏角20°时,经60 min磨抛后,工件已加工表面粗糙度由1.069μm降至0.089μm,材料去除率为8.893×10^(8)μm^(3)/min;该试验条件下,建立的材料去除模型预测准确度相比Preston经典模型提高36.7%。研究成果可为实现硬脆材料的确定性材料去除提供技术支持和理论依据。

泥沙浓度对水力机械材料磨损及磨蚀特性的影响

多泥沙河流上运行的水力机械受到泥沙磨蚀而导致过流部件变形、破坏,严重威胁机组安全运行。本研究对水力机械常用材料开展了旋转喷射磨蚀试验,采用失重法和微观形貌分析法研究了泥沙浓度对材料磨损及磨蚀特性的影响。结果表明:材料受到冲击磨损和磨蚀的累积失重量均随泥沙浓度变化呈近线性增长;当泥沙浓度小于60 kg/m^(3)时,3种材料累积失重量随泥沙浓度增长较缓;当泥沙浓度大于60 kg/m^(3)时,材料失重量增长较快。随着泥沙浓度的增大,冲击磨蚀对材料造成更严重的破坏,但空蚀损伤呈减弱趋势,材料表面硬度越高,抗空蚀性能越好,磨损和磨蚀失重量相等的临界泥沙浓度越低。空蚀作用会影响沙粒撞击材料表面的角度,导致颗粒水平冲击载荷更大,磨痕呈现切削唇边和堆积,在更高泥沙浓度下沙粒切削破坏占据主导作用。

磨粒间距和材料特性对磨削温度影响的有限元仿真研究

针对磨削过程中,磨粒间距和工件材料特性对工件表面温度的影响规律进行了有限元仿真研究,结果表明,随着磨削过程的进行,工件表面温度逐渐升高;磨削过程中,相比多磨粒磨削,单颗磨粒磨削的工件表面温度更低,且随时间增加上升速度更小;磨粒间距越大,工件表面温度越低且随磨削过程的进行变化速度越小;工件材料导热率越大,工件表面温度越低,当导热率大于1 W/(m·K)时,温度随导热率增大而下降的趋势不再明显;工件的比热容和密度对磨削温度的影响规律相似,随着比热容、密度增大,工件表面温度降低,且当比热容大于200 J/(kg·℃)、密度大于4000 kg/m3时,工件表面温度随比热容、密度持续增大而降低的趋势不再明显,且温度随时间推移而上升的速度下降。