Study on typical hole defects in AZ91D magnesium alloy prepared by low pressure lost foam casting

The hole defects can easily occur in magnesium alloy castings that are prepared by low pressure lost foam casting(LP-LFC)process when the process parameters such as vacuum,pouring temperature and f illing velocity are not properly selected.In this study,the forming mechanism of the hole defects in AZ91D magnesium castings by LP-LFC process was investigated.The shape,location and surface appearance of the hole defects were observed using optical microscopy and scanning electron microscopy,and the chemical composition on the surface of the holes was analyzed using energy spectrometer.The result indicates that there are two types of hole defects,i.e.,the pyrolysis products related hole defects,including concentrative hole and blow hole defects,and slag related hole defects.The concentrative hole and the blow-hole defects were formed either by the liquidEPS degradation products entrapped in the molten metal under the condition that the pouring temperature is equal to or lower than 730℃,or by the hindered transport of EPS pyrolysis products.Some irregular shape hole defects were caused by slag or by coating slough entrapment when the pouring temperature is equal to 750℃and the f illing velocity is equal to or greater than 100 mm·s-1.To reduce or eliminate the hole defects,the vacuum and f illing velocity must be properly chosen to ensure that the metal front prof ile exhibits convex shape and in laminar current state,and the pouring temperature should be just high enough to ensure that the molten melt has adequate heat energy to complete the foam pyrolysis and to fully occupy the mould.For AZ91D magnesium castings in this study,the parameters should be 730℃pouring temperature,0.02-0.03 MPa vacuum and 80mm·s-1f illing velocity.

Single-mode low threshold current multi-hole vertical-cavity surface-emitting lasers

A multi-hole vertical-cavity surface-emitting laser （VCSEL） operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-refleetor of an oxidation- confined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10% are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes.

Numerical simulation and experiment analysis of improving permeability by deep-hole presplitting explosion in high gassy and low permeability coal seam

Created a new damage model for explosive for LS-DYNA3D,taking advantageof the Taylor method aimed at the high gassy and low permeability coal seam,and numericallysimulated and analyzed the deep-hole presplitting explosion.The entire processof explosion was represented,including cracks caused by dynamic pressure,transmissionand vibration superposition of stress waves,as well as cracks growth driven by gas generatedby explosion.The influence of the cracks generated in the process of explosion andthe performance of improving permeability caused by the difference of interval between.explosive holes were analyzed.A reasonable interval between explosive holes of deepholepresplitting explosions in high gassy and low permeability coal seams was proposed,and the resolution of gas drainage in high gassy and low permeability coal seam was putforward.

基于不同加工工艺的微孔节流空气静压轴承的特性研究

随着超精密加工技术和地面微低重力仿真的发展,相关产业对空气静压轴承的性能要求越来越高。由于传统的孔式节流器其结构特点不能完全满足实际使用的需要,节流孔直径与气膜间隙同一数量级的微孔节流空气静压轴承因其良好的刚度和承载特性,越来越受到关注。但在微孔节流器的发展过程中,微孔的加工工艺却限制了其推广应用。针对目前常用的三类微孔加工工艺,进行了理论仿真研究,通过建立不同加工工艺轴承仿真模型,运用双向流固耦合仿真方法,对比分析了基于不同加工工艺的微孔节流空气静压轴承的动静态特性。研究结果表明:锥孔类轴承承载性能优于其他两类,但耗气量大且在小间隙时刚度较差;薄壁直孔类轴承承载性能稍逊,但在大间隙下轴承刚度较佳;嵌套类轴承承载性能较差,但在小间隙下轴承刚度较大且耗气量较低。

Analysis on Micro Complex Shape Via Hole Punching on Low Temperature Co-Fired Ceramics

The quality of a via hole on a multilayer stack of Low Temperature Co-fired Ceramic (LTCC) tape is of utmost importance to its functionality. This paper investigates a substitute for the commonly used circular shape hole to a more complex one and its implications when different parameters such as sheet thickness, punch speed, travel distance and tool clearance are?changed. Fabrication of the punch tools and the punching process is carried out at the same machine, ensuring alignment. Two types of non-circular shape are chosen to carry out the experiment. Pre-sintered complex shape hole measurements show that while punch conditions such as speed and tool gap have?little effect on the size, sheet thickness and travel depth play a vital role in the overall dimension. Albeit having only a slight effect on the size, those parameters are significant in other aspects of hole quality. Post-sintering investigation is also observed and discussed.

渠式切割水泥土连续墙的应用和发展

作为超深、等厚、连续、可靠的截水挡土帷幕,渠式切割水泥土连续墙在国内有广泛应用。本文概括了渠式切割水泥土连续墙在国内的引进、应用和发展历程。结合对国内200多个既有应用案例的统计分析,研究了渠式切割水泥土连续墙的施工设备保有情况、成墙深度范围、常用墙体厚度和主要应用场景;罗列了渠式切割水泥土连续墙在复杂地层施工的辅助措施以及典型案例;指出了渠式切割水泥土连续墙在敏感环境微扰动施工的控制要点;介绍了渠式切割预制装配式混凝土连续墙的设计要求和用途,尤其是内插预制板材的截面设计和制造工艺;最后用工程实例表明渠式切割预制装配式混凝土连续墙同时继承了渠式切割微扰动和地下连续墙支护刚度好的特点,无论是切割成墙期间还是土方开挖期间,施工对周边环境的影响都较小。

孔洞对疲劳裂纹扩展路径的影响

为了研究孔洞位置和尺寸对疲劳裂纹扩展路径的影响,利用ABAQUS有限元仿真软件建立改进CT试样的裂纹扩展仿真模型,采用扩展有限元法研究了在低周疲劳加载条件下Q235钢圆孔与裂纹尖端的角度、距离以及圆孔半径对裂纹扩展路径的影响,并通过引入裂纹偏转系数来定量描述不同参数对裂纹扩展路径偏转程度的影响。结果表明:当圆孔与裂纹尖端的夹角为45°时,裂纹偏转系数取得最大值;裂纹偏转系数随着孔洞半径的增加逐渐增大,随着圆孔与裂纹尖端距离的增大逐渐减小。

石门揭煤局部防突措施研究进展及展望

随着矿井开采深度的增加,瓦斯突出问题日益凸显,如何快速安全地进行石门揭煤,是保障煤矿安全生产的重要目标。选取中国知网数据库中近30年相关文献为样本,基于图谱分析法,分析了石门揭煤局部防突领域中的研究热点;对防突措施的研究进展和不足之处进行了系统探析,分析发现低温冷冻技术从降低煤层储能及提高煤体强度2个角度实现防突。煤与瓦斯突出事故的发生是煤层储能失稳后突破了煤体抵抗能力导致的,基于目前局部防突领域存在的技术难题以及人工冻结存在的不足,结合智能化技术,提出智能“钻-抽-注”一体化措施,通过信号基站及局域网络进行实时监控及预警,实现精准防突;通过建立多物理场耦合模型、理论分析及工程实践验证3方面相结合,掌握冷冻条件下煤岩体瓦斯赋存状态及运移规律,为低温冷冻技术在石门揭煤局部防突中的应用提供理论依据;借助智能液氮冻结系统,实现“一孔多功能”,为石门揭煤局部防突工作提供新的选择和支持,从而快速、安全揭开突出危险性煤层。

黑菊芋加工工艺设备优化与验证

为解决传统黑菊芋加工设备工序繁杂、加工周期长、加工成本高的问题,设计结构合理、可监测温湿度及气压的小型试验箱。采用控制变量法,改变试验箱开孔密度,对菊芋进行分组加工试验,结合感官评价和营养成分分析确定最佳生产条件。再以此条件对传统小型黑菊芋加工设备进行改进,对传统加工程序进行优化。改造后的黑菊芋加工设备工序减少50%,加工时间减少45%,各项生产费用节省了83%。改造后的的黑菊芋加工设备生产效率明显提升,生产成本大幅下降;同时降低了塑料制品的使用,节能减排、低碳环保。

基于低相干干涉的孔类零件内表面测量系统研究

对孔类零件的内表面进行测量是判断其加工质量和使用寿命的重要手段。针对精密孔类零件内表面测量的需求,提出一种基于低相干干涉的内表面测量及信号处理方法,并搭建了完整的检测系统。对低相干干涉的测量原理进行了分析;搭建了以迈克尔逊干涉仪为主体,主要包含光源、探测器、数据采集仪、参考臂、样品臂等部分的检测系统;研究了干涉信号滤波以及包络峰值提取算法;最后,通过实验验证了此系统可以表征孔类零件的内部特征,并且其测量精度可达10μm以内。

基于CEEMD的露天深孔爆破振动信号降噪光滑模型

由于爆破区域地形地质条件的复杂、监测仪器的误差、振动传播介质的反射以及磁场的干扰等原因,采集的原始爆破振动信号常常会掺杂大量的噪声,针对此问题提出了基于互补集合经验模态分解(CEEMD)的信号降噪光滑模型。此模型将爆破振动信号进行CEEMD,基于分解所得到的IMF分量建立低通滤波算法。根据滤波算法的相似度与光滑度,构造目标函数并计算最优解,其对应的滤波算法模型即为爆破振动信号的最优降噪光滑模型。通过构造仿真信号验证了降噪光滑模型算法的可行性,并将模型应用了实际露天深孔爆破振动信号的研究。采用信噪比和均方根误差两种指标对比经验模态分解(EMD)方法、小波阈值法、CEEMD-小波阈值法与滤波算法模型BP3的降噪效果,验证了降噪光滑模型在对露天矿山爆破振动信号降噪方面的有效性,并通过频谱分析进一步验证了降噪光滑模型较CEEMD-小波阈值法的优越性。结果表明:基于CEEMD的露天深孔爆破振动信号降噪光滑模型具有良好的降噪能力,能够在保留原始爆破振动信号真实特征信息的前提下对信号进行降噪,且降噪效果优于EMD方法、小波阈值法和CEEMD-小波阈值法。

一种局域共振型声学超材料的半解析建模与带隙机制研究

基于声学黑洞(acoustic black hole, ABH)弧形梁体积小且模态频率丰富的特点,将声学黑洞弧形梁作为附加结构周期分布在直梁上,达到促进局域共振效应和拓宽低频带隙的作用,由此构建一种新的局域共振型声学超材料。针对局域共振型超材料,采用高斯展开法,建立其半解析理论分析模型,基于零空间法处理其内部连接以及周期边界条件,并通过有限元法验证半解析理论分析模型的准确性。分析和计算其能带结构,研究结构参数以及ABH效应对布拉格带隙以及局域共振带隙的影响机理。研究结果表明,该半解析理论模型能够对结构的带隙进行有效计算,附加弧形ABH的陷波机制能够促进结构的局域共振效应并对主梁进行有效减振,为声学黑洞声学超材料的应用提供了新的思路。

低合金高强钢螺纹孔摩擦塞补焊修复接头的组织与性能研究

针对轨道车辆零件螺纹孔摩擦塞补焊修复工艺及性能进行了研究。在优化的塞孔/塞棒几何参数和焊接工艺参数下制备了无缺陷的焊接接头,并分析焊接接头的微观组织、拉伸性能、冲击韧性和疲劳性能。结果显示,当轴向压力过大,接头界面处会形成未焊合缺陷。在转速为7 000 r/min、轴向压力35 kN、顶锻压力40 kN、塞棒进给量18 mm的参数下,可以获得成形良好的无缺陷接头。靠近结合界面的微观组织主要为珠光体、铁素体和部分板条状贝氏体。焊缝中的微观组织为针状铁素体和大量晶界铁素体,以及少量的板条状贝氏体。焊接接头具有优良的力学性能,其拉伸性能与母材相当,室温拉伸试验中,接头断裂位置均位于母材;疲劳实验中,螺栓外螺纹总是先于修复螺纹孔内螺纹发生疲劳断裂,修补螺纹的500万次疲劳强度达到142 MPa。

低水压掏穴扩孔技术在卸压增透钻孔中的应用

为解决煤矿井下卸压增透钻孔掏穴施工过程中需要配套高压泥浆泵的问题,提出了低水压掏穴扩孔技术。该技术配套开发了双通道掏穴装置、双通道钻杆及双通道送水器等成套技术装备。该技术在朱仙庄煤矿进行现场应用,结果表明,该技术能够在水压2~3 MPa条件下实现卸压增透钻孔“钻进-掏穴”一体化施工,为煤矿煤层卸压增透提供了新的技术方案。

下向低浓钻孔“抽-注”排水排渣抽采一体化技术研究

为了防止永夏矿区陈四楼煤矿煤与瓦斯突出事故的发生,在采用水力排渣钻孔进行抽采瓦斯时,发现在钻孔内存在着大量的水和煤渣,堵塞了煤体内部的孔隙通道,对煤层瓦斯运移和钻孔孔壁的稳定性产生不利影响,从而严重影响了瓦斯抽采的效果。针对煤矿急需解决的俯孔排水排渣问题,提出采用压风吹孔技术,将孔内水和煤渣带出孔外,疏通钻孔堵塞通道。该技术在陈四楼煤矿井下现场应用效果良好,吹孔后钻孔平均在抽浓度由11.86%提升到了18.73%~56.38%,低浓钻孔提升效果明显;代替了以往水力排渣钻进技术,达到高效抽采瓦斯、保证煤矿安全生产的目的,对钻孔抽采瓦斯过程中能够及时排出水和煤渣有一定指导意义。在此基础上,形成的一套下向低浓钻孔“抽—注”排水排渣一体化技术及工艺,为下向低浓钻孔排水排渣工作提供参考借鉴。

A case study of gas drainage to low permeability coal seam

Gas drainage at low gas permeability coal seam is a main barrier affecting safety and efficient production in coal mines. Therefore, the research and application of drainage technology at low permeability coal seam is a key factor for gas control of coal mine. In order to improve the drainage effect, this paper establishes a three-dimensional solid-gas-liquid coupling numerical model, and the gas drainage amounts of different schemes are examined inside the overburden material around the goaf. The Yangquan mine area is selected for the case study, and the gas movement regularity and emission characteristics are analyzed in detail, as well as the stress and fissure variation regularity. Also examinations are the released gas movement, enrichment range and movement regularity during coal extraction. Moreover, the gas drainage technology and drainage parameters for the current coal seam are studied. After measuring the gas drainage flow in-situ, it is concluded that the technology can achieve notable drainage results, with gas drainage rate increase by 30%–40% in a low permeability coal seam.

Effect of impeller reflux balance holes on pressure and axial force of centrifugal pump

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5 m3/h, H=60 m, n=2950 r/min was selected to be designed with eight axial reflux balance holes with 4.5 mm in diameter. The simulated Q-H curve and net positive suction head(NPSH) were in good agreement with experimental results, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic; however, it showed to little superiority in head and efficiency. The pressure in rear pump chamber at 0.6 times rate flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rate flow and 28.33% at 1.4 times rate flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreases as flow rate increases. Radical reflux balance holes chosen to be 5.2 mm and 5.9 mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics was conducted based on momentum equations and standard turbulence model(κ-ε). It is found that axial force of pump with radical reflux balance holes of5.2 mm and 5.9 mm in diameter is significantly less than that with radical reflux balance holes of 4.5 mm in diameter. Better axial force balance is obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.

水敏性复杂地层深孔绳索取心钻进工艺研究与应用

宝山矿区地质构造较复杂,存在多个断裂破碎带,地层软硬互层交替,炭质页岩厚度大,遇水膨胀,钻孔缩径严重,钻进过程中易发生粘附卡钻、坍塌及埋钻等事故,属于典型的水敏性地层。针对该类地层在钻进过程中出现的这些问题,通过优化钻孔结构、合理钻具级配,采用金刚石绳索取心钻进工艺和低固相钻井液护壁技术,适当控制回次进尺长度和回次进尺时间等措施,保证了钻孔孔壁的稳定性及工程安全,有效地解决了水敏性地层钻进中出现的问题,加快了施工进度,取得了较好的钻进效果,使项目得以顺利完成。本次钻探施工完成了钻探进尺9500余米,达到了地质找矿目的,取得了较好的经济和社会效益。此外,希望适用于该矿区的钻进工艺方法对其他相似水敏性复杂地层的钻探施工具有一定的参考意义。

低压低产气井井底净化处理剂研制及现场应用

低压低产气井井底污染原因复杂,井底净化效果不明显,本文通过井底污染类型的梳理,明确低压低产气井污染是水锁伤害、乳状液污染和结垢堵塞等多种污染共同作用的结果。针对性研制一种具有降低表面张力和改变储层润湿性的解除水锁处理剂,通过优选破乳剂和垢处理剂,研究形成能有效降低表面张力、改善储层润湿性、破乳及溶垢阻垢为一体的井底净化处理剂,处理剂表面张力25.66 mN·m^(-1),pH值6,能够使岩心接触角增加12.63°,针对ZJ122沙溪庙组岩心,返排24 h渗透率恢复率明显提高,溶垢阻垢能力强,破乳速度快,有利于提高井底净化效果。

GFRP低频轴向振动制孔的钻削力特性和套料钻磨损分析

GFRP的套孔钻削过程中极易产生分层、撕裂等加工损伤,其与轴向钻削力直接相关。为提高GFRP的制孔质量,采用新型金刚石薄壁套料钻,结合低频轴向振动加工技术,建立单颗磨粒的运动学模型和动力学模型,试验研究GFRP制孔中的轴向力变化规律,并对套料钻的烧焦概率、自动落料率进行分析。结果表明:对比常规钻削,低频振动钻削时的瞬时进给量和轴向力比常规钻削时的大,且随着振幅的增加,轴向力也随之增大;低频振动钻削和常规钻削时的轴向力皆随进给速度的增加而增大,随主轴转速的升高而降低。同时,低频振动钻削时磨粒间断性地参与钻削,大大降低了套料钻的烧焦概率,提高了其自动落料率,自动落料率高达88.24%,可实现GFRP的连续批量制孔。