Research on cracking mechanism of the thin shell mould in expendable pattern shell casting during pattern removal process

Aiming at the cracking phenomenon of the thin shell mould in the expendable pattern shell casting during the pattern removing process, some systemic researches are presented.The influence of the pattern removing method and temperature on the pattern removing were investigated.The shell mould cracking mechanism was analyzed by using thermo-gravimetric analysis (TGA), and combining the temperature field and the volume change of the expanded polystyrene (EPS) foam pattern being tested.The results indicated that the shell mould was not easily cracked when the pattern removing process was carried out with the furnace being heated little by little because of the shell slowly shrinking with dehydration and shell strength gradually increasing.The shell mould was soon destroyed when it was set directly into the furnace at above 400 oC because of the thin shell mould rapidly shrinking and the foam pattern hindering.However, the shell mould had no cracking when it had been preheated for a long time even if the furnace temperature was above 400 oC and the shell was put into the furnace directly.Moreover, when the shell mould was directly set into the furnace at lower temperatures, 250 to 300 ℃, the shell would shrink slowly and the foam pattern would stay at the maximum expansion stage temperature of 100 to 110 ℃ for a long time; and the shell mould would experience an expansion force from the foam pattern for a long time.The expansion force is related to the pattern removing temperature, holding time, foam pattern thickness and density.Therefore, the foam pattern with higher density could make the shell crack.

Principles and practice of low pressure-expendable pattern casting process for magnesium alloys

A newly developed low-pressure expendable pattern casting (LP-EPC) process was introduced and its basic principles or effect factors were further analyzed. According to theoretical calculation and experimental results, the major casting parameters that are of great and critical importance on the process include pressure and flux of filling gas, decomposition characteristic and density of foam pattern, thickness and permeability of coating, pouring temperature, vacuum degree and their combination. Most of casting defects can be effectively avoided by choosing the suitable parameters. The success achieved in pouring motor housing and exhaust manifold castings demonstrates the advantages of LP-EPC process in the production of high-complicated castings with high dimension accuracy.

Research on key techniques of expendable conductivity temperature depth measuring system

This paper analysis the developing of expendable conductivity temperature depth measuring system(XCTD)and introduce its principle of measuring about temperature,salinity and depth of ocean.Some key techniques are put forward.According to the real needs of XCTD,conductivity sensor with high sensitivity is designed by principle of electromagnetic induce,the ocean conductivity from induced electromotive force has been calculated.Adding temperature correction circuit would help to reduce error of conductivity measurement because of sharply changing temperature.Advanced temperature measuring circuit of high precision and the constant current source is used to weaken effect of self-heating of resistance and fluctuation of the source.On respect of remote data transmission,LVDS is a good choice for the purpose of guarantee the quality of data transmitted and the transmission distance is reaching to thousand meters in the seawater.Modular programming method is also brought into this research aimed at improve the stability,reliability and maintainability of the whole measuring system.In February,2015,the trials in South China Sea demonstrate that the developed XCTD realize effective measurement at a speed of 6 knots and detection depth at 800 m.The consistency coefficient of the acquired data is greater than 0.99 and the success rate of probe launching is above 90%.

Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.

Effect of process parameters on density of magnesium alloy parts by low-pressure expendable pattern casting

The combination of magnesium alloys with the low-pressure expendable pattern casting(LP-EPC) process would bright future for application of magnesium alloys. The researches are focused on the effect of process parameters on the internal casting quality of magnesium alloy parts. AZ91D magnesium alloy castings were produced for different combinations of the LP-EPC process parameters. Specifically,pouring temperature,vacuum,filling velocity and coupling action of these factors were manipulated to observe their effect on the casting porosity and density distribution. The results indicate that the pouring temperature with LP-EPC process is lower than it in gravity casting. The selected process parameters,such as vacuum,filling velocity and coupled modes of them,must ensure melt metal flowing front profile exhibiting smooth and convex shape. The optimal process parameters for the castings are pouring temperature 983-1 023 K,vacuum 0.02-0.03 MPa,filling velocity 60-95 mm/s,and simultaneous filling with sucking.

不同灌水处理对春玉米土壤水分、耗水特征及产量的影响

【目的】探究不同灌水定额对春玉米全生育期耗水特征及产量的影响,优化克拉玛依地区春玉米节水灌溉制度,以提高当地水分利用效率。【方法】于2021年5—9月在克拉玛依农业综合开发区开展春玉米田间试验,设置6个灌水处理W1(225 m^(3)/hm^(2))、W2(300 m^(3)/hm^(2))、W3(375 m^(3)/hm^(2))、W4(450 m^(3)/hm^(2))、W5(525 m^(3)/hm^(2))、W6(600 m^(3)/hm^(2)),探究不同灌水定额对春玉米耗水特征及产量的影响。【结果】①各生育期不同灌水处理0~100 cm土层土壤含水率随土层深度增加呈“增-减-增”的变化趋势。W5处理在喇叭口期、抽雄散粉期、乳熟期、完熟期较W1、W2、W3、W4、W6处理0~100 cm土层土壤贮水量平均增加了2.35%~9.11%、0.21%~4.37%、0.39%~1.79%、0.60%~4.48%。②完熟期W5处理百粒质量显著高于W1处理和W2处理,但与W3、W4、W6处理无显著性差异。W5处理穗粒数较其他处理显著提高10.49%~36.01%,穗长较其他处理显著提高8.31%~27.12%。③综合评判模型计算得出W5处理(525 m3/hm^(2))综合评价指数最高。【结论】因此,全生育期灌水10次,灌水定额为525 m3/hm^(2)是克拉玛依地区最优灌水处理。

机载自卫对抗消耗型射频诱饵分析

当前,随着各种防空武器装备和技术的迅速发展,其对作战飞机的威胁与日俱增。消耗型射频诱饵是近年来国外空军列装的一种新型自卫对抗手段,能够有效提升作战飞机生存力。重点分析了机载消耗型射频诱饵的主要装备情况和关键技术。

低成本可消耗无人机极限不可用燃油量确定方法研究

对于低成本可消耗无人机,为了发挥其燃油的最大效能,需要在预定的飞行作战轨迹下测算出其极限的不可用燃油量。本文针对某型低成本可消耗无人机提出了一种极限不可用燃油量的确定方法。通过切割油面角建立该无人机特定姿态下的不可用燃油数据库,在此数据库的基础上拟合出该无人机所有姿态下不可用燃油量与俯仰角、滚转角之间的数学关系;将该无人机根据六自由度数学模型仿真出的随时间变化的理论剩余油量与相应时刻下对应姿态的不可用燃油量进行比较,确定特定飞行任务下该无人机的极限不可用燃油量。通过这种方法计算得到的极限不可用燃油量和该无人机实际飞行剩余油量误差仅有0.27L,误差小于传统民航飞机不可用油量计算方法的3.68L,误差减小了3.41L,燃油利用率提高了3.9%,表明此方法的准确性与可行性。

海洋投弃式温深剖面仪应用发展概述

海洋温度的变化会显著影响水下声传播、生物活动、气象和洋流等现象,温深是反映海洋变化运动规律的基本参数。投弃式温深剖面仪(Expendable Bathythermograph,XBT)、温盐深测量仪(Conductivity Temperature Depth,CTD)、全球海洋实时观测网(Array for Real-time Geostrophic Oceanography,Argo)等是目前进行海水温深测量的主要仪器。其中XBT因其现场测量简便、效率高、硬件成本低等特点,正在被大规模使用。本文主要介绍有关海洋温度测量的背景及演化历史,分析对比了国内外相关仪器设备的发展现状,总结了国产化产品还存在的差距和不足,另外对传感器、结构设计、数据通讯传输、数据后处理、可靠性研究等关键技术和研究热点进行了详细介绍,最后对未来无人平台的技术发展路线给出了思路和见解,开展投弃式温深剖面仪的相关技术研究和产品研制对实现国产化有积极的推动意义。

镁合金真空低压消失模铸造新技术

介绍了一种新的铸造技术——真空低压消失模铸造的工作原理。建立了其在充型过程中的物理模型与数学模型,分析了其铸造工艺的特点及影响因素,以及在铸造高精度、复杂镁合金铸件方面的优势。作为压力铸造、低压铸造的补充,真空低压消失模铸造新技术在铸造高质量和高精度的镁合金铸件中具有广泛的应用前景,另外还可用于铸造高精度、复杂的铝合金铸件。展示了用该新技术铸造成形的复杂的电机壳体、排气管等镁合金铸件。

水泥基复合多孔吸声材料的制备方法和性能

以普通硅酸盐水泥、膨胀珍珠岩、陶粒主要原料,加以一定的辅助材料,研制出一种新型水泥基复合多孔吸声材料。该种材料具有吸声性能好、成本低、对环境无污染等优点。试验分析不同骨料、水灰比、骨料颗粒粒径对吸声性能的影响。结果表明,这些因素对其吸声性能影响明显。

面向21世纪的消失模铸造技术

对国内外消失模铸造的现状进行了评估；对其发展前景进行了预测；对我国消失模铸造的进一步发展提出了建议。

聚醚类破乳剂的扩链与支化改性

B61聚醚用己二酸扩链引入羧基官能团,然后用三乙撑四胺、D-山梨醇、D-木糖、季戊四醇等对扩链产物进行支化,合成了若干扩链支化型破乳剂。测定它们的相对分子质量和相关官能团,分析其性能与结构的关系;测定改性产物的界面张力,分析界面张力与破乳性能间的关系。结果表明,B61聚醚经扩链后,对某些原油的破乳能力有所提高,破乳能力与界面张力间有一定的相关性,但无明显的对应关系;扩链破乳剂支化后破乳能力进一步增强,多胺类支化剂优于多元醇支化剂。

气化模-精铸-负压复合铸造工艺研究

主要研究ReplicastCS复合工艺的气化模的成型工艺、制壳工艺、失模工艺及紧实负压工艺 ,采用该工艺可解决用消失模工艺铸造碳钢。

投弃式海流电场剖面仪研制

本文分析了投弃式海流电场剖面仪的发展,简介了海流感生电场的基本原理,提出了投弃式海流电场剖面仪的技术方案.根据投弃式海流电场剖面仪的实际需求,研发了XCP海流电场传感器,并通过XCP探头的自旋转(16r/s),实现了将海流电场信号AM调制并频移至海流电场传感器的超低噪声频段,解决了在高噪声背景下快速测量纳伏级微弱海流电场信号.设计实现了XCP探头前端弱信号处理电路,对海流电场微弱信号进行滤波提取的同时可实现对海流电场同向分量进行硬件电路补偿,在一定程度上克服了XCP探头下沉引起感生电场的强干扰.在XCP探头内部采用SoPC技术实现对海流电场信号、罗盘线圈信号和温度信息的快速测量及其数字化处理,并将数字信息以UART协议及LVDS物理层数传方式发送到XCP浮筒端.开创了长度2km、直径0.1mm漆包线动态数据传输技术,解决了XCP探头和XCP浮筒之间的数字化数据传输问题.根据XCP探头所采集的海流电场信号与罗盘线圈信号的同相分量In、正交分量Qn、基线量Bn数据,研究了XCP探测方法,从而计算出了海流的东向与北向相对速度分量VEr、VNr.采用所研发的XCP,在我国南海海域首次采集到海面至海下千米深度的XCP海流电场信息和海洋温度信息.

近35年苏南典型地区的城镇扩展动态研究——以1966～2001年常熟市为例

利用常熟市不同时期 (1 966、1 984、1 992、1 999、2 0 0 0、2 0 0 1年 )、不同类型卫星遥感影像 (Corona、TM、SPOT、ETM +)进行多波段合成 ,图像增强处理与精校正 ,建立不同影像城镇用地解译标志 ,通过人机交互判读 ,获得不同时期的各乡镇城镇用地矢量图的方法。统计出 35年来常熟市城镇建设用地扩大近 6 .4倍。城镇扩展空间上受到地貌条件和城市经济水平以及政策决策影响 ,城镇多数沿河流或交通线方向扩展 ,各城镇间扩展数量和相对速率有明显差异 ,且存在一定地理分布规律。结合社会经济的统计资料 ,分析发现城镇扩展与不断增加的城镇人口、GDP极显著相关 ,各乡镇单位城镇面积创造的GDP有较大的差异。

企业科研投入与经营绩效的实证研究——信息业与制造业上市公司的比较

以披露研发信息的信息业与制造业上市公司为样本,针对其行业特征以及对科研投入的依赖性进行分析,利用面板数据建立多元线性回归方程模型,考察科研投入与企业绩效的关系。结果表明,企业科研投入与盈利能力之间的关系并不明显,但对企业成长能力有显著的促进作用;高研发密度和高效率的人工费用投入,以促进信息业主营业务收入增长能力和整体盈利能力增长速度的提高,对制造业主营业务收入的增长能力也有显著的贡献。

MIS3晚期典型阶段气候模拟的初步研究

我国大量地质资料反映了全球海洋氧同位素 3阶段 (MIS 3)晚期具有间冰阶海侵、暖湿的气候环境特征。对这一阶段的气候成因论证 ,将为现代温室效应的气候增温提供重要的历史相似型。本文使用含有陆面过程的全球 9层大气环流谱模式 (AGCM +SSiB) ,采用地球轨道参数驱动的太阳辐射、北半球第四纪冰盖和东亚植被预置的下垫面对 35kaB .P .气候进行了敏感性模拟试验。研究结果表明 :(1 )MIS 3晚期中、低纬度大部分大陆全年温度增加 ,欧亚大陆腹地气温增高主要是冬季增温贡献 ,反映太阳辐射变化通过大气环流作用引起的更加显著的气候效应。南北海陆水汽交换的加强首先使低纬度季风区降水收益。 (2 )相当于LGM 50 %规模的第四纪冰盖不仅仅具有高纬度区降温效应 ,还强化了辐射纬向差异造成的南北温差 ,从而增强了水汽从低纬度区向高纬度区输送的能力 ,使青藏高原、南亚和非洲季风区的降水进一步增加。 (3) 35kaB .P .东亚植被对辐射的低纬度区增温具有增强效应 ,而对冰盖高纬度区降温具有减缓效应 ,结果扩大了欧亚内陆的降水增加范围 ,使中国高降水带向北推移。 (4)中国各大区域 35kaB .P .气候类型不尽相同。当中国东部与太平洋在同纬度带的热力差异减小时 ,东西向水汽输送减弱 ,造成东部沿海降水减少 ;但当欧?

镁合金负压消失模铸造充型过程的研究

镁合金负压消失模铸造充型过程的直接观察实验的结果表明 ,不抽真空时 ,金属前沿呈微凸形平缓地向前推进 ;抽真空时 ,因在模样分解产物的排除方向上存在一正的压力梯度 ,金属液优先沿模样壁充填型腔使流动形态呈不规则的凹形形态。提高真空度 ,不规则的流动形态的凹度更大且充型时间明显缩短。浇注方式对流动形态和充型时间的影响不大 ,与顶注和侧注相比 ,底注时充型过程最为平稳 ,且其充型时间最长。根据试验结果 。

消失模铸造充型过程的研究进展及展望

从充型特性以及传热和传质两个方面回顾了消失模铸造充型过程的研究进展。指出了以往研究中的不足和以后的发展方向。