cBN-Ti-B-Al-SiC系在高温高压下的烧结

文章通过采用细cBN颗粒,以Ti-B-Al-SiC系粘接剂在高温高压下烧结PcBN复合片,通过扫描电子显微镜、XRD以及微观显微硬度分析,并与cBN-TiN-Al系烧结的PcBN复合片相对比。分析发现：Ti-B-Al-SiC系粘接剂合成的PcBN复合片cBN-cBN键合多,显微硬度高于用TiN-Al系粘接剂合成的PcBN复合片,而且通过XRD分析发现产生了新相：TiN、TiB2、AlB2、BCo、Ti5Si3,并且没有发现原材料SiC的存在,这可能是由于在高温高压下SiC被分解。采用细cBN颗粒,以Ti-B-Al-SiC系粘接剂合成的PcBN复合片显微硬度高,但相对比较脆,主要是由于生成过多高硬度的TiB2,同时添加单质硼能够与Ti和Al反应,抑制了cBN的分解。     

树脂铅芯烧结理论的探索

粘土型0.5mm细铅芯,是由石墨和粘土经混合、辊压、挤出、烘干、烧结成型,我们称之为粘土型细铅芯.它的烧结与粘土混合物性质有关,在焙烧到足够高的温度时,粘土的气孔率随温度升高而逐渐降低,铅芯结构趋愈致密,达到烧结温度时.铅芯挠曲强度达到最高值,因此,可以沿用传统的(?)2mm粗芯制造方法去生产粘土型细铅芯,工艺简单.但铅芯挠曲强度却不高.要使细铅芯挠曲强度达到2000g/mm~2以上,就必须研究不加粘土的0.5mm树脂石墨型细铅芯(简称树脂铅芯),79年到86年,铅笔行业随着0.5mm活动铅笔的开发,树脂铅芯同样面临着一个开发、研究、直到生产的创业过程.树脂铅芯在我国的开发,一定程度上比0.5mm活动铅笔的开发更艰难些.随着大连、哈尔滨铅笔厂引进日本生产技术后,上海也参照大连PVC树脂的生产方法投入了生产.但是引进日本的生产方法,包括哈尔滨的Pi-lot的烧结技术都是采用开放式电阻炉.只能间隙地生产,这就使0.5mm树脂细铅芯的烧结工艺停滞在目前状态.尽管引进的配方、工艺、设备有它的独特性,但是只要烧结的方法都符合树脂铅芯的烧结理论,烧结0.5mm树脂细铅芯的方法就有多种途径.因此.深入研究树脂铅芯烧结理论对探索树脂铅芯的生产和提高树脂细芯的质量十分重要,本文就此和从事树     

关于多晶复合材料的讨论

简述了超硬材料中复合材料烧结体的概念,对PCD、PDC、cBN和PcBN中的一些常识性问题进行了讨论。     

SLS内置热源与烧结件间距对烧结件的密度影响

选择性激光烧结件的烧结密度除了会受成型机参数影响外,在加工时也会受相邻烧结件的影响.为了研究相邻烧结件之间的相互影响关系,提出了内置热源的概念.通过在选择性激光烧结过程中加入内置热源,研究水平方向和垂直方向内置热源与烧结件之间不同间距对烧结件密度的影响.结果显示,当设定烧结功率为30 W的内置热源与设定烧结功率为15 W的烧结件之间的间距在1～8 mm时,对烧结件的密度有较大影响,且其对烧结件密度的影响随着内置热源与烧结件间距的增大而减小,当间距大于8 mm时,其影响可以忽略不计.     

一种印刷电子连续干燥烧结试验装置的设计

为降低印刷电子产品干燥烧结加工的生产成本,采用卷对卷印刷技术是必然选择。目前,在实验室有关干燥烧结研究中,干燥烧结的对象还处于静止不动的状态,为了研究在卷对卷印刷时,干燥烧结对象处于运动状态下连续干燥烧结工艺的相关问题,设计了一种用于印刷电子干燥烧结的试验装置。该试验装置由步进电机驱动,PLC控制,外部循环导热油进行温度控制,加热辊加热干燥烧结对象。组装测试结果表明,试验装置加热辊表面温度均匀,对干燥烧结的均匀性影响小;该装置既可以模拟卷对卷连续运动状态,又能适应实验室制备的样品长度较短的情况,节省实验费用。     

针织加热织物的设计及其电热性能测试

为开发发热稳定且均匀的电热织物,对织物所用镀银纱线的最大负载电流和电阻稳定性进行了测试。通过改变镀银纱线和涤纶纱线横列的排列方式织造了5种不同的加热织物,测试了织物通电过程中的电阻稳定性、升温特性以及表面温度均匀性。结果显示:镀银纱线(10 cm)的最大负载电流为0.213 A,所能承受的最高温度为110℃;加热织物通电后温度升高并达到稳定状态,当镀银纱线和涤纶纱线横列排列方式为3∶2时织物达到的平衡温度最高,而电阻变化相对较大;通过分析5种织物的红外温度图像可知,当镀银纱线和涤纶纱线横列排列方式为1∶2时,其表面温度分布均匀性最好。     

纳米金刚石-立方相氮化硅烧结体的高温高压制备与表征

采用直接相变的方法制备出了纳米金刚石-立方相氮化硅的烧结体。将石墨与六方相氮化硅的混合粉末经氮气保护球磨26小时后,在约18 GPa、2000℃的压力/温度条件下进行烧结。对烧结产物的X射线衍射分析和扫描电镜分析表明,烧结体中的石墨和六方相氮化硅全部转变成纳米金刚石和纳米立方相氮化硅。烧结体的硬度测试结果显示其平均维氏硬度约为39 GPa。     

纳米B6O—B4C超硬复合材料的高温高压烧结与表征

B6O是近几年来在国际上引起广泛关注的一种新型超硬材料。它具有低密度、高导热性、耐磨性、高硬度和较好的化学稳定性。在高温高压（3～5GPa,1500～1900K）下通过“一步法”合成了高性能纳米结构B6O超硬复合材料,并分析了合成压力、合成温度、初始材料等条件,对合成样品的物理化学性能、微观结构、相组成的影响。合成样品中B6O微粒在几十到几百纳米之间,属纳米级别。试验在较低的压力下（～3GPa）合成烧结良好的圆柱形样品,用维氏硬度计测量其硬度在32GPa,跟立方氮化硼复合片（PcBN）硬度相当,并且具有较好的断裂韧性。最初的切削实验表明以烧结良好的B6O复合材料制成的工具样品可以高速、干式切削各种陶瓷、金属材料。     

基于SQUID的复合材料承载电气特性

描述了三维编织复合材料的电阻测试基本方法,针对材料的特性,采用SQUID技术研究三维编织复合材料的电磁参数测试方法,分析了不同载荷下材料的电阻、电磁变化规律。试验结果表明：三维编织复合材料的电气特性受制造参数和承载方式的影响,三维编织复合材料越厚,电阻值越小;表面编织角越小,电阻越小;纤维含量越高,电阻越小。承载状态下电阻在拉伸较小时呈现出线性增加,当拉伸超过6%时,电阻的增加呈现非线性增加,三点弯曲对电阻有着较大影响,加载时要比卸载时电阻、电磁量变化大。     

B_6O超硬复合材料的高压烧结

在高温高压（3～5GPa,1500～1900K）下通过＂一步法＂合成了纳米结构B6O超硬复合材料,对合成样品的物理化学性能、微观结构、相组成进行检测。复合材料平均硬度在32GPa,跟立方氮化硼复合片（PcBN）硬度相当。文章对复合材料内部残余应力及断裂韧性进行了分析。对抛光的样品进行了X射线衍射和扫描电镜、透射电镜分析。结果表明在此条件下合成的样品具有较好的烧结特性。     

双锥面熔体微分静电纺中电场分布的有限元分析

为获得最佳的熔体微分静电纺丝结构参数,采用有限元分析软件ANSYS对多层锥面无针熔体微分静电纺丝中的电场分布进行模拟,分析了双锥面特征设计参数对纺丝尖端场强的影响,分别讨论了内圈直径和内圈伸出距离对内外圈纺丝尖端及纺丝路径场强分布的影响。ANSYS数值模拟结果表明:增加锥面层数会减弱最外圈纺丝尖端的电场强度;对于双锥面熔体纺丝装置,内锥面直径大小对纺丝尖端场强分布的影响不明显;当内锥面伸出距离增大时,内外圈纺丝尖端场强的差值先减小再增大;当内锥面直径为26 mm,内圈伸出距离为6 mm时,内外圈纺丝尖端电场强度分布最相似,能够保证内外锥面制备的纤维射流间距相同,实验结果和模拟结果一致。     

预应力钢绞线车间工艺设计

预应力钢绞线生产应用现状:市场用量以年均20%以上的速度增长,拥有进口预应力钢绞线生产设备的企业约30家,国产设备的企业50多家,一些钢铁企业开始尝试建设预应力钢绞线车间。从线材表面预处理、拉丝、绞线及稳定化处理等方面阐述预应力钢绞线车间工艺设计,以1×7和1×19结构钢绞线为例,介绍生产设备和工艺参数。生产1×19结构钢绞线拉丝机进线最大直径16.0mm,最大速度15m/s,出线抗拉强度2100MPa,卷筒直径1200mm,盘卷质量4t;中频回火炉感应加热功率800kW;张力轮直径2500mm,最大张力490kN;双收/放线机收线轮外径2900mm,内径1200mm,张力3920N,生产线最大速度135m/min。对车间的平面布置和环保提出要求。     

Milk fouling at direct ohmic heating

Direct ohmic heating (Joule’s heating) is a technology to warm up the food using an electric energy where electric current is passed through a material which gets heated by virtue of its electrical resistance. Advantages over conventional indirect heating methods are speed and uniformity of heating. On the other side, the direct ohmic heating of liquid foods has some problems, for example corrosion and deposits creation on electrodes (fouling). The present research on fouling concentrates upon the effects of material and surface properties of electrodes, and upon the effect of power frequency. This work evaluates influence of material (stainless steel, TiN and graphite electrodes), flow rate, electric current density (at constant frequency 50 Hz) and temperature (in a limited temperature range 65–75 °C), upon the fouling of skimmed milk. Results prove that the stainless steel electrodes are the worst while the graphite electrodes, where no fouling was observed, are the best, thus confirming the significant role of corrosion and electrochemical phenomena. The paper analyzes also another phenomenon typical for direct ohmic heating and it is an inner overheating of the formed fouling layer, representing a risk of overburning. Theoretical results show that the most intensive overheating occurs at relatively very thin deposit layers, depending upon the specific electrical conductivity of deposits.     

国内外常用陶瓷cBN磨料的性能对比（上）

文章根据cBN磨料在陶瓷砂轮中的作用,凭借单颗粒抗压强度仪、扫描电镜、差热分析仪等先进精密仪器对国内外有代表性的8种磨料进行了常温性能、微观形貌、高温性能和耐腐蚀性能分析。实验表明,国产部分单晶cBN磨料的常温和高温性能已达到相当高的水平,甚至超过了国外产品的性能;同时,由于cBN磨料高温性能的提高,在陶瓷cBN砂轮制作过程中可以适当提高烧成温度以增加砂轮贴块的强度。     

弱磁场对胰蛋白酶活性和构象的影响

本文采用100 mT磁场处理胰蛋白酶2 h,并利用红外光谱、圆二色谱等研究了磁场处理前后胰蛋白酶活性及结构的变化,采用抑菌圈法测定了胰蛋白酶水解梅鱼蛋白所得酶解液的抑菌活性变化。结果表明,经100 mT磁场处理2 h后单位浓度酶解液的抑菌圈直径得到提高,其中大肠杆菌(Escherichia coli)抑菌圈直径由(4.71±0.22) mm提高至(8.54±0.23) mm,酶活相较于未处理组高52.5 U/min;弱磁场处理后,胰蛋白酶氨基酸总量下降,必需氨基酸占比上升;红外光谱峰整体蓝移,α-螺旋和β-折叠含量增加。     

国内外常用陶瓷砂轮的cBN磨料的性能对比（下）

文章根据cBN磨料在陶瓷砂轮中的作用,凭借单颗粒抗压强度仪、扫描电镜、差热分析仪等先进精密仪器对国内外有代表性的8种磨料进行了常温性能、微观形貌、高温性能和耐腐蚀性能分析。实验表明,国产部分单晶cBN磨料的常温和高温性能已达到相当高的水平,甚至超过了国外产品的性能;同时,由于cBN磨料高温性能的提高,在陶瓷cBN砂轮制作过程中可以适当提高烧成温度以增加砂轮贴块的强度。     

Needleless electrospinning: influences of fibre generator geometry

The fibre generator shape and dimension are key factors affecting the needleless electrospinning process and fibre fineness. In this work, cylinder with rounded rim, disc and ball were used as spinnerets to electrospin polyvinyl alcohol and polyacrylonitrile solutions. A finite element method was used to analyse how the spinneret geometry affected the electric field generated during electrospinning and the associated changes in fibre diameter and productivity. For cylinder spinnerets, increasing the rim radius reduced the discrepancy of electric field intensity between the cylinder end and middle area, which affected the fibre productivity. The electrospinning failed to operate when the rim radius was over 20?mm. With decreasing cylinder diameter, the electric field intensity in the middle area increased, improving the fibre productivity. Thinner disc spinnerets increased the electric field intensity, resulting in finer nanofibres and higher productivities. Ball spinnerets produced evenly distributed electric field, but failed to electrospin fibres when the diameters were below 60?mm. It has been found that strong and narrowly distributed electric field in the fibre-generating area can significantly facilitate the mass production of quality nanofibres.     

Effect of dimensions on the hating times and wieght losses of cylindrical beef joints

The heating time and weight loss of cylindrical joints of lean beef in twenty-five length/diameter combinations (five lengths from 28 to 160 mm and five diameters from 14 to 80 mm) were measured when heating the meat to a minimum internal temperature of 74°C in a natural convection oven at 175°C.
Cooking weight loss was not affected by joint diameter but decreased very slightly with length. Heating time to 74C increased with joint length and asymptotically approached the heating time for an infinitely long cylinder. The variation of heating time with joint diameter and length was predicted using a mathematical model.
Comparison of the results with other published work showed that weight loss from the lean component of joints is not affected by fat cover.     

Ohmic heating behaviour and electrical conductivity of two-phase food systems

Ohmic heating behaviour and electrical conductivity (EC) of two-phase food systems were studied. Food systems were comprised of a liquid phase using 4% w/w starch solution with 0.5% w/w salt, and a solid phase containing carrot puree and cubes of different sizes (6 and 13 mm) in different concentrations (30 and 50% w/w). A set of experiments was carried out for a wide range of particle concentrations from 0 to 60% w/w. With respect to the particle location, experiments were conducted using 30% w/w cubes (6 mm) placed in parallel, in series and in well-mixed conditions with the liquid phase. Ohmic heating was applied to the food systems using a static cell (20-mm-long Teflon cylinder with 35 mm diameter and 25 mm wall thickness) at a constant voltage gradient of 12.5 V/cm. Electrical conductivity values were calculated as a function of particle size, concentration, location and temperature. It was observed that the heating time increased along with particle size and concentration. Overall values of EC ranged from 0.2 to 1.8 S/m, increasing with the process temperature as it ranged from 20–80 °C, and decreasing as particle size or concentration increased. With respect to the particle location within the ohmic cell, the thermal behaviour was different when the two phases were in parallel, in series or in mixed condition. However, there was no significant difference between overall values of EC when liquid and solid phases were separated as compared with the mixed condition.     

连续型热处理炉的改进设计

为解决传统热处理炉维修周期长、生产环境差、功率消耗大等问题,对其进行改进:(1)参数设计及优化。给出热处理炉总功率、加热时间和炉长的计算方法,改进后的热处理炉加热温度为950℃,Dv值为40 mm·m/min,可处理1.0~2.5 mm钢丝10根。(2)热处理炉改为分体式结构,上下同时采用电加热,结合处采用快卸式压紧螺栓压紧。保温和耐火材料采用晶体纤维加热模块、纤维板和纤维保温毯等,破损的保温材料可回收使用。(3)电气部分采用智能型温控仪加可控硅控制。以国内某公司为例,热处理炉改进后使用半年,钢丝产量比炉体改造前高出5%,消耗电量降低2.5%,综合统计增加经济效益约15.2万元。