钢轨打磨用复合砂轮磨削温度场的研究

为研究钢轨打磨用钎焊金刚石插片复合砂轮磨削时的温度场，用复合砂轮和树脂锆刚玉砂轮在不同压力下磨削65Mn钢工件，并对比其磨削温度。基于试验数据，用有限元法分析复合砂轮磨削钢轨时的温度场。结果表明:随着磨削压力的增大，砂轮产热增大，但复合砂轮磨削产热相对较小。相对于相同条件下用树脂砂轮打磨时，用复合砂轮打磨钢轨时的磨削表面最高温度降低近10%。      

烧成条件对树脂结合剂金刚石砂轮的影响

本实验研究的是树脂结合剂(热硬性酚醛树脂)金刚石砂轮烧成时升温时间及升温速度与烧成效果的关系,并进行了磨削对比试验,由此求出能获得最佳磨削性能的烧成条件。 材料与方法 1.材料 试验是用七种砂轮对一种硬质合金进行对比磨削试验。砂轮按图1所示的温度——时间关系烧制,然后保温一定时间,此时,温度为168℃。     

精磨玻璃t-BMI金刚石砂轮的研究

提高砂轮寿命和磨削效果是树脂结合剂金刚石砂轮制造研究的关键问题、本课题采用烯丙基、环氧树脂及丁晴橡胶对双马来酰亚胺树脂改性增韧，得到了具有耐热温度较高，韧性良好，成型工艺性能稳定等特点的增韧双马来酰亚胺(t—BMI)热固性树脂；用该结合剂研制出的玻璃磨边机专用t—BMI金刚石精磨砂轮磨削效果好，砂轮使用寿命长，能消除磨削时的玻璃崩边现象，明显提高玻璃的表面质量，可替代直边机或斜边机上的同类进口砂轮。     

陶瓷-金属结合剂CBN结块的研制及其性能研究

目前钢轨打磨使用的主要是树脂砂轮，具有材料去除率低、磨削温度高等问题。因此，利用钎焊超硬磨料技术研制新型陶瓷-金属结合剂CBN磨具，并对比陶瓷-金属CBN结块和树脂锆刚玉结块在相同条件下的磨削性能，如材料去除率、磨屑分布和磨削温度等。试验结果表明:相比于树脂锆刚玉结块，陶瓷-金属结合剂CBN结块的材料去除率可提高124%，磨削温度峰值可降低15～50 ℃。      

静电喷涂涂层砂轮磨削钛合金工件温度研究

针对钛合金材料难磨削加工的特点,设计了一种静电喷涂砂轮涂层系统和实验砂轮,完成了干式磨削钛合金的实验,分析了不同磨削条件对磨削温度的影响规律。研究表明:采用静电喷涂固体润滑剂涂层砂轮磨削加工钛合金,在同样的加工条件下,磨削深度为0.2 mm时,未涂层砂轮磨削温度接近900℃,涂层砂轮磨削温度不超过600℃。固体粉末静电喷涂润滑砂轮涂层可有效降低磨削温度。      

磁控微粉砂轮固化工艺对砂轮磨削性能的影响

目的研究砂轮在固化过程中,固化温度和固化时间对砂轮磨削性能的影响。方法通过测试两种固化工艺制备的砂轮的抗压强度、硬度以及其加工硬质合金YG8的磨削比、表面粗糙度、加工非球面的形状精度随固化温度的变化,来评价固化温度对磁控微粉砂轮磨削性能的影响。结果砂轮的磨削性能与其固化温度、时间有直接关系。磨削比随着固化保温时间的增长呈先增长后下降的趋势。固化温度决定砂轮固化速率和砂轮对过度固化的敏感程度,170℃固化能使砂轮在较短时间达到最佳磨削性能,但是固化时间超过8 h时,其性能会迅速衰减。130℃固化有利于防止砂轮过度固化而造成性能急剧降低。通过对固化工艺的研究,170℃/5 h+130℃/5 h固化工艺下制备的砂轮磨削性能最佳,该砂轮磨削YG8得到最佳的面形精度为365 nm,最佳表面粗糙度为3 nm。结论砂轮在固化过程中,固化温度与固化时间直接影响树脂的固化反应速率与固化程度,通过对固化工艺的实验研究,在本实验条件下得到了最优的固化工艺参数。     

树脂砂轮硬化工艺与酚醛树脂液使用妙招

酚醛树脂作为砂轮的结合剂在硬化过程中对于硬化温度和硬化时间的选择，常存在一些令人头痛的问题，对于此问题，我们提请用户在选择使用树脂液时要特别注意树脂液的粘度、固体含量、游离酚等指标。采用不同质量的树脂液，砂轮的强度将有很大差别。选择质地优良、价格低的结合剂，如2124-1型液体酚醛树脂，在硬化过程中，温度在110—120℃时，其水份的蒸发量会很大，同时会有游离酚、游离醛等有害气体挥发，故在110—120℃完全蒸发和挥发对固结、热固成型很重要，一定要注意在此温度下的保温时间，一般应在4小时左右，使大量水份和游离酚、游离醛等低挥发物质充分排出。     

关于普通砂轮与cBN砂轮加工工件时的温度实验

在许多磨削应用领域,磨削速度取决于温度效应,例如：表面烧伤、残余应力、微裂纹等。热损伤是常见的影响生产力因素之一,由于价格优势,在加工过程中大量使用普通砂轮。与普通砂轮相比,cBN砂轮具有良好的热传导性能,它的磨削速度更快,消除了影响生产力的顾虑。本文研究了使用普通砂轮和cBN砂轮加工型号为52100钢时表面的最高温度。此实验在干磨和湿磨的条件下进行。     

面向绿色制造的快速点磨削磨削液供给参数计算

高速／超高速磨削条件下，砂轮边缘的高速空气带会阻碍磨削液注入磨削区。空气带压力与砂轮速度的平方成正比。快速点磨削是一种新型高速／超高速磨削技术，接触区很小，实际磨削功率低，冷却及散热效果好。在分析了高速／超高速磨削砂轮周围旋转空气带动压力及速度分布特点的基础上，根据热力学原理及快速点磨削特点，分析并建立了磨削液的供给流量和供液速度的理论模型。在此基础上，建立了面向绿色制造的快速点磨削的磨削液喷嘴直径及供液压力的工程计算公式。     

氮化硅陶瓷磨削热特性与表面成形机制

目的探究氮化硅陶瓷磨削热特性与热特性对表面成形的影响。方法首先,通过反求法得出传入工件、磨屑与砂轮的热量分配比公式;其次,使用K型热电偶和测力仪得到磨削参数与磨削区温度和热量分配比的关系;最后,通过对磨削表面形貌和粗糙度的检测寻找出最优磨削质量时的温度范围。结果砂轮线速度由25 m/s增加到50 m/s时,磨削温度由256℃增加到819℃,传入砂轮、工件与磨屑的热量分配比分别由82.4%减小到64.4%、12.1%增加到24.3%、5.5%增加到11.3%。磨削深度由5μm增加至30μm时,磨削温度由289℃增加到869℃,传入砂轮、工件与磨屑的热量分配比分别由76.1%减小到53.9%、17.3%增加到30.3%、6.6%增加到15.8%。工件进给速度由2000 mm/min增加到7000 mm/min时,磨削温度由772℃减小到513℃,传入砂轮、工件与磨屑的热量分配比分别由71.1%增加到78.3%、21.1%减小到11.7%、5.8%增大至10.1%。随着磨削温度由256℃增加到869℃时,表面粗糙度先由0.2708μm减小到0.2472μm,后增加至0.3182μm。采用定速比磨削可使磨削温度降低25～127℃,减少传入工件的热量分配比。结论适当的高温有利于表面塑性变形的形成,表面质量提高,但温度过高时会形成热裂纹,温度在489～662℃之间,表面质量最好。在提高砂轮线速度的同时,可适当增加进给速度,以达到降低磨削温度,减少传入工件热量与增加磨削效率的目的。     

Rheology Feature of Simple Metal Melt

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 k Hz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more {110}116 grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, {110}116 can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of {110}116 grains and therefore enhance the sharpness of Goss texture.     

Laser Cladded TiCN Coatings on the Surface of Titanium

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80?滋m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

Microstructure,Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag(wt%,x=0.2,0.5 and0.8)alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.     

Growth Morphologies of a Binary Alloy with Low Anisotropy in Directional Solidification

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.