PIM充模过程的边界层效应及机理分析

通过对注射坯进行局部密度测试及采用SEM方法观察注射坯截面上粉末-粘结剂的分布状态,揭示了PIM充模过程的边界层效应.将边界层及两相流理论应用于PIM充模过程的研究,分析表明:普通的边界层效应及粉末、粘结剂粘度和密度的差异带来的偏析现象是产生PIM边界层效应的原因.凡是影响模壁吸引熔体分子及影响熔融注射料粘度的因素均会对PIM的边界层效应产生影响.模拟结果表明:随着注射温度由430K升高到450K,PIM的边界层效应变得明显;而入口的注射料流量由60cm3/s增加到80cm3/s,这种效应反而略有减轻.     

PIM粉末-粘结剂固液两相流的动力学基本方程

假设PIM颗粒－粘结剂两相流动中，粉末颗粒为大小不一的球形，粉末颗粒与气体分子具有类似的物理及动力学特性。利用类似于气体分子动力论的方法来研究PIM两相流动中粉末颗粒相的运动。将PIM注射充模过程中粉末颗粒的运动与气体分子运动进行比较，从Boltzmann方程出发分析了粉末颗粒的物理及动力学参数，建立行数值模拟和分析粉末－粘结剂两相分离现象奠定了理论基础。     

粉末注射成形充模过程中粉体分布的数值模拟

以316L不锈钢为喂料的注射过程为研究对象,使用双流体模型模拟注射过程中坯体内粉末体积分数的分布,得到出现严重两相分离区域的直观三维分布图,并应用工业CT(industrial computed tomography)对模拟结果进行验证。结果表明:该方法可以得到注射成形零件中任意区域粉体的分布;注射试样在浇口的下方区域,以及模壁、顶点区域,易出现较严重的两相分离,导致后续的烧结过程中出现收缩不均匀,是应该重点关注的区域;随注射速率从30 cm3/s提高到90 cm3/s,两相分布合理区域的体积呈先增大后减小的趋势,在70 cm3/s时达到最大;模拟结果中粉末体积分数分布曲线的变化趋势和变化幅度都与CT检测结果相符,实验验证了模拟结果的可靠性。     

粉末注射成形模拟分析的研究现状与发展

粉末注射成形(PIM)是集塑料成形与传统粉末冶金工艺优势而产生的一种新型零部件近净成形技术。叙述了粉末注射成形的优点和有待解决的难题,利用模拟软件可以有效地避免或减少PIM各个阶段的缺陷,重点介绍了国内外在PIM喂料充模模拟技术上已经取得的成果和待解决的问题,依据目前的PIM喂料充模模拟研究现状,对PIM模拟的发展进行了展望,认为以Burracuda软件为基础的粉末颗粒模拟研究将成为PIM喂料充模模拟的主要发展趋势,并为粉末注射成形喂料模拟技术的进一步发展提供参考。     

铁基混合料成分偏析分析方法

在利用粉末冶金工艺制备铁基混合粉末过程中,由于铁基零部件各组分的密度及粒度差异,混合料经常存在偏析现象,这会引起烧结产品尺寸和性能的不稳定,因此对混合料的成分偏析程度进行测试或评定具有实际意义。本文系统总结了铁基混合料成分偏析分析方法,包括耐扬尘性分析法、成分分析法、色泽观察法、烧损测试法;在实际工程中,可以根据实际需求选取上述试验方法。     

降低成本 发展钛粉末注射成形产业

自从10多前年第一个钛粉末注射成形工业产品问世以来,注射成形钛基材料的应用一直在逐年增长,随着技术的进步和粉末成本的降低,其应用增长速度正在加快。(1)钛和粉末注射成形(PIM)先进材料是提高产品应用性能的关键,钛合金是其中最重要的一种。但其应用因成本太高而导致了对低成本工艺的研究,包括粉末冶金和PIM。金属PIM是在塑料注塑成形的基础上发展起来的,是一种有效的低成本生产工艺,适于小型(一般400g以下)而形状复杂零件的生产,基本工艺为粉末与粘结剂混合→注射成形→溶剂脱脂→热脱脂/预烧→烧结。粘结剂除去的方法有热…     

纳米晶W-Ni-Fe粉的流变行为和烧结特性

研究了W-Ni-Fe纳米晶粉在注射成形中喂料的流变行为,纳米晶W-Ni-Fe粉采用机械合金化(MA)的方法制备,并将此粉末与蜡基粘结剂混合以形成一种喂料,讨论了MA球磨时间,纳米晶粉末体积和温度对喂料流变性的影响,随球磨时间增加,喂料的粘度以及粘度对剪切速率的敏感性降低,因此,在较长的球磨时间下,这种粉末喂料的流动性和成形性变好,随粉末体积增加,喂料的粘度遵循公式呈非线性增加,此时n=0.68.MA粉末喂料的粘度随温度和剪切速率的变化较小,所以注射温度和注射速度的变化对这种MIM注射坯的质量影响较小,本文也讨论了采用MA制备的W-Ni-Fe纳米粉末的烧结特性,实验结果表明球磨可以导致在液相烧结温度以下合金达到很高的密度,大的晶格畸变、晶粒细化和超饱和固溶体的形成,强化了烧结工艺。     

粘结剂种类及用量对预混合钢粉粉末性能影响的研究

将钢铁粉末中的合金元素进行粘结处理制备成预合金钢粉末是一种减少粉末在操作过程中扬尘和成分偏析的新技术.研究了不同粘结剂种类和用量对预混合钢粉粉末流动性、松装密度、合金元素粘结率的影响.发现粘结处理大幅改善了预混合钢粉的性能,而不同粘结剂对预混合钢粉性能的影响各不相同.当使用0.1%(质量分数)的粘结剂时预混合粉对C的粘结率达到76%～90%,对Cu的粘结率达到38%～72%;粉末的流动性为21.7～24.6s/50g,且不随放置时间增加而发生明显的改变.粘结剂加入量增加时预混合钢粉中合金元素粘结率和粉末流动性继续提高,粘结剂加入量为0.2%(质量分数)时对C和Cu的最高粘结率分别达到94%和80%,粉末流动性达到约21s/50g,粉末的松装密度可以通过改变石蜡加入量进行调节.     

粉末注射成形钛合金粘结剂体系的研究进展

钛及钛合金具有低比重、高比强度、优异的生物相容性以及良好的耐腐蚀性等特点,在航空航天、生物医疗、化工、船舶、汽车等领域极具应用潜力。钛合金粉末注射成形技术（powder injection molding,PIM）提高了材料的利用率,实现了中小型复杂形状钛产品的大批量、低成本制备,显著地推动了钛及钛合金产品的生产及应用。目前关于粉末注射成形钛合金粘结剂体系的相关文献报道十分有限,新型粉末注射成形钛合金粘结剂体系的开发处于停滞不前的状态。本文分析总结了不同粉末注射成形钛合金粘结剂体系的研究现状,并针对目前存在的问题提出改进措施。     

基于体积平均法的NH4 Cl水溶液凝固行为研究

根据合金凝固理论和体积平均多相模型,对NH4Cl-70%H2O凝固过程进行了数值模拟和实验验证.虽然研究者已研究过NH4Cl-70%H2O凝固过程,但是只针对单个现象进行分析,比如通道偏析的形成、对流形式以及晶粒的形成.在前人研究的基础上,本文首次通过数值模拟和实验对比两种手段相结合的方式全面地研究了氯化铵水溶液凝固整个计算域的全部现象,尤其再现了等轴晶在铸锭中的下落漂移现象以及由此引起的对流,并且更深入地探究了偏析的形成原因.通过计算发现等轴晶从型壁处沉降并逐渐向铸型底部积聚,直到体积分数达到一临界值后,柱状晶停止生长,完成柱状晶向等轴晶转化过程.由于溶质再分配,底部晶粒集中的区域形成了负偏析,在尚未凝固的上部区域形成较大范围的正偏析.通过实验验证发现,等轴晶在铸锭中的下落漂移现象和对流形式的预测值与实验值较为一致,从而全面揭示出凝固过程中固相的移动和对流是产生宏观偏析的关键因素.     

The effect of amount of possession of the trait of hostility on accuracy of perception of hostility in others.

Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of rates of infection of two methods of emergency ventricular drainage

The rates of infection of two methods of external ventricular drainage in use at Atkinson Morley's Hospital--namely, (a) percutaneous drainage with Rickham reservoirs and (b) tunnelled ventriculostomies--were compared in this retrospective review. Percutaneous drainage of CSF with Rickham reservoirs was associated with a 27% rate of infection as identified by positive microbiological cultures; tunnelled ventriculostomy catheters had a 10% infection rate. The difference in the infection rate between the two methods was statistically significant (P < 0.015). Other variables examined, including the age and sex of the patients and the reasons for ventricular drainage, were not associated with an increased rate of infection. Most infections from either method were caused by a coagulase negative staphylococcus. The average duration of ventricular drainage before identification of positive cultures was 5.7 days for Rickham reservoirs and 6.0 days for ventriculostomies.     

浅析《野草》的版画特征

鲁迅先生一生热爱美术作品,对版画中木刻兴趣尤甚.<野草>作为其"写心之作",亦呈现出一些与木刻版画一致的审美特征:一是具有木刻版画的色彩特征,多对比、多冷色,有阴郁的美感;二是具有木刻版画的力度特征,环境描写、人物刻画处处刀锋毕现,遒劲有力,有一种"力之美".     

四辊破碎机车刀架的改造

针对四辊破碎机车刀架车削中存在的几个问题,详细介绍了电动车刀架的结构和工作原理,建立主要设计参数的数学表达式,并进行适当的分析。改造后,这种电动车刀架运行平稳、可靠、方便、省力,取得了预期的效果。     

转炉炉壳热应力分析

根据实际转炉建立实体模型。以有限元为手段,考虑了炉衬和炉壳材料的物性参数随温度变化的特点和炉衬与炉壳之间膨胀间隙,计算了转炉炉壳在温度载荷和炉衬膨胀压力同时作用下的热应力。所得结果可为转炉炉壳设计提供依据。     

Comparison of the results of surgical and conservative treatment of fractures of the diaphysis of the tibia

In this paper is treated the fundamental problematic of the fracture of the diaphysis of the tibia and the therapeutic results after the conservative and operative treatment are confronted. Among 518 patients with 433 open fractures and 35 with closed fractures of the diaphysis of the tibia, successful treatment of more 2/3 was obtained in the period from 1968 to 1972. Following our casuistics and literature, whose results are similar, we find out that the average total treatment of the osteosynthesis of the fracture of the diaphysis was shortened for 2,5 months depending upon the type and the localisation of the fracture. Apolied methods of the operative and conservative and conservative treatment in relation to the velocity of the medical cure as well as to the extreme anatomical-functional results are analised. We noticed that osteosynthesis, made by the intermedullary nail and the extension of the canals or by a small AO table, by the achieved stability makes conditions of immediate motions and an early rehabilitation. Because of that it gives the best functional results.     

Results of treatment of cancer of the cardia

Cancer of the cardia is traditionally discussed with cardiac cancer of the lower portion of the esophagus and upper gastric cancer invading the esophagus, and the specific characteristics of cancer of the cardia have never been clearly defined. We reviewed the outcome of 172 patients with adenocarcinoma of the cardia who had undergone radical surgery between 1949 and 1994 in the Division of Gastrointestinal Surgery of the Cancer Institute Hospital. The centers of the tumors were located within 2 cm above and below the boundary between the esophagus and the stomach, and their longitudinal diameter was less than 8 cm. We divided the patients into an early period (1949-1979; n = 79) and a late period (1980-1994; n = 93), and focused on the historical transition. There were no differences in patient gender or histology between the two periods. However, the late period was associated with fewer cases of esophageal invasion and shorter longitudinal diameter, as the age of the population advanced. The number of advanced cancers such as the localized and infiltrative type had decreased, and early cancer and early clinical stage had become more common, but despite the fact that the number of early cancers had increased, extended dissection, such as thoracic and paraaortic lymph node dissection, was performed more frequently. By clinical stage, the long-term outcome markedly improved in Stage I patient in the late period, and tended to improve in Stage II and III patients. This appears to have been attributable to the prevention of micrometastasis by extended dissection, although the number of early cancers is another major potential cause. There were no differences in the outcome of Stage IV patients between the two periods, and further advances in multimodality therapy must be awaited. The range of resection is basically proximal gastrectomy, and if there are adequate indications, the prognosis is favorable. In view of the status of lymphatic flow and lymph node metastasis, and long-term results, lateroaortic lymph node dissection is important. Since the number of early cancer patients has been increasing, if intraabdominal recurrence is prevented, intrathoracic lymph node dissection will contribute greatly to the outcome of such patients.     

焦炭热性能指标意义浅析

通过对焦炭在高炉内的历程及其变化规律的剖析,阐述焦炭热性能指标的意义,形象地把焦炭在高炉内的损耗分为三部分(M1,M2,M3)。指出M2对焦比及焦炭价格有一定的指导作用。     

参与式农业基地建设行动方案设计

为了编制实用性强的基地建设行动方案,首先,确定参与式发展的主体,搭建一个"决策框架";其次,针对行动目标,提出不同参与主体,如管理者、农民、消费者等团队与个人的目标及行动内容;最后,工作应向重塑伙伴式合作关系,挖掘农民自我发展潜力,完成三大角色的转换,打造农业基地文化等方向推进.