铝业毕业论文

汽蚀是液力机械中常见的故障之一，由于进口池或管路设计不合理，以及未充分考虑大气压、温度、介质气化压力的变化等常常因为汽蚀而引起泵的过早失效。已经安装服役的泵几乎没有办法完全克服泵本身汽蚀性能差造成的汽蚀破坏（《泵手册》第一分册）。本文将主要介绍减轻在役泵汽蚀破坏的方法，这些方法在实际应用中均取得了明显的效果。一、汽蚀的产生原因汽蚀是由液体汽化引起的，液体分子逸出液体表面，成为气体分子的过程，称为“汽化”。液体的汽化程度与压力的大小、温度高低有关。溶解于液体中的气体，在压力和温度变化时也会释放出来，形成汽穴。当液体内部压力下降，低于液体在该温度下的饱和蒸汽压时，在局部区域形成汽泡或汽穴；而在压力升高的地方汽泡突然被四周的压力压破，液流因惯性以极高的速度向汽泡的中心挤压，对设备造成水力冲击。这种微泡的产生、溃裂以及对过流表面产生物理和化学作用的整个过程称为汽蚀。如果液体中不含任何杂质，即使在压力很低时也不会发生汽蚀。国外的汽蚀研究者通过试验认为，超高纯水的抗拉强度（即产生空穴的极限）远远超过通常的金属材料的抗拉强度。但通常的液体中总是含气体或固体，这些杂质成为汽蚀核子，在一定条件下诱发空穴的发生。含砂水流由于水与砂的比重不同，砂粒运动轨迹与流线脱离，可能会加速汽蚀的发生。笔者在论文“泥浆泵的汽蚀及抗磨抗汽蚀材料”（《润滑与密封》1993）中进行了详细介绍。二、在役泵的汽蚀诊断方法泵的使用者通常无法利用制造厂流量一定时扬程的下降来判定汽蚀是否发生的方法。在役泵是否发生汽蚀，除在汽蚀破坏后观察法外可以采用（1）超声波法；（2）泵体外噪声法；（3）振动法等方法判断。观察法：破坏表面观察法是在事后观察方法，根据破坏的表面形状来进行判断。由于汽蚀、铸造气孔、冲刷磨损、腐蚀等均会造成金属表面形状与理想形状的不同。汽蚀破坏的金属表面通常显现蜂窝状，它是由局部高速水打击金属而使金属表面疲劳破坏，所以蜂窝孔一般是与外部相通的，大多数的坑槽与金属表面垂直。铸造缺陷的疏松往往深藏在金属内部，有时由于水流的冲刷将金属内部的疏松、气孔呈于表面而误认为是汽蚀，但当我们用机械的方法继续去处表面时会发现其内部仍有气孔。冲刷磨损痕迹往往出现与水流方向相同的沟槽，但要注意有时有水流旋涡。噪声法：泵体外噪声法比较简单，可以不与泵体接触。但由于噪声法受周围环境噪声的影响较大，当显示其强度最高时。一般水泵汽蚀已达到非常强烈的阶段，这时人耳已能通过强烈的汽蚀爆裂声判别汽蚀工况。因此，泵体噪声法不太适合现场监测汽蚀的发生。振动法：这种方法是通过加速度计探头测量泵体振动频率的一种方法，方法简单，但灵敏度较低。特别对于大泵，泵体刚度大。对泵内局部汽蚀引起的汽泡溃裂所产生的激振反应迟钝，同时，泵上振源较多。由于汽蚀引起的振动常被掩没在其它振动之中。因此，振动法只适宜作为现场监测汽蚀的辅助手段。超声法：超声波法测量汽蚀方法简单，调试方便，且不受其它环境噪声的干扰，对汽蚀的发生和发展敏感性强。因此，作为泵站现场监视汽蚀是一种比较理想的方法。另外，抚顺石油学院化工机械研究所赵会军介绍了用电测法预测离心泵汽蚀性能(《石油化工高等学校学报》1997)。三、减轻在役泵的汽蚀破坏的方法1、进水池在使用现场，对发生汽蚀（包括其它故障）的泵查看进水池的流动状况是十分必要且又方便易行的。如果池表面能看到强力的旋涡，应该考虑加破涡板。另外，管口与进水池的几何尺寸也应注意。如：管口离池壁的距离是否合适，是否有气泡进入泵吸入管。注意水池水位是必要的，抬高进水池水位可以减轻甚至彻底阻止汽蚀的发生。解台泵站对进水口改造，汽蚀浸蚀减少45%左右。齐鲁石化的刘克旺、孙敬河等人在循环泵进口添设破涡板后泵的汽蚀不再发生且流量从不稳定的8500、8000m3/h分别提高到稳定的9700、8200m3/h。2、进水管路进口管路的设置除应该尽量使管路损失小（如尽量少的弯头和不必要的阀门）外，让进水管不得有高于泵进口的部位以防止管内积气。1995年赤水天然气化肥厂在循环泵进口橡胶膨胀接为1000mm，而管子为800mm。为此增加了放气管，解决了由于其阻造成的压力下降，解决了汽蚀问题。3、调整泵流量新疆电力设计院王卫东建议由于我国采用的原阻力计算公式来源于原苏联，其阻力计算值比实际的大，阻力计算宜采用新公式进行。否则，泵在大流量运行容易发生汽蚀(《西北电力技术》2000)。在水泵设计选型与实际有一定的偏差时，水泵产生汽蚀和经济运行可以通过切削叶轮来加以解决，以期达到消除汽蚀，运行经济的目的，实践证明，这种方法确实行之有效。4、利用引射结构喷射装置在原理上相当于液-液喷射泵。在泵的出口处引出一高压水引到如图所示的高压水室内，高压水通过环形喷嘴进入泵的吸入管内。高压水与吸入管内的水混合、交换能量，混合后的混合水能量相对于原吸入管的水能量增加，从而满足泵进口所必须的汽蚀余量。浙江大学的吴昱等人对此进行了介绍(浙江大学硕士学位论文2003年)，论文中介绍了引射装置的引回流量宜控制在2%-5%之间。张德煌老先生在长沙曾采用过类似方法对100口径的多级泵进行试验，取得了明显效果。其方法是用1/2的管将平衡盘后的水引至泵进口，泵系统的装置汽蚀余量降低了。武汉大学的郭迪龙等人介绍了一种射流－离心泵装置。这种装置相当于射流泵与离心泵串联工作，对大吸程的泵十分有效，但一般不适合于在役泵的改造。5、进口补气补气的方法并不能防止汽蚀空穴的产生，但适当补气会减轻空穴破裂时产生对流道边壁的破坏，补入的气体象一层保护流道边壁的海绵。这种方法在水轮机等中普遍采用，但向泵内补气由于补气量难于掌握使用非常少。武汉水利电力学院孙寿、颜锦文对补气防水泵汽蚀进行了研究并取得了一定效果，但同时指出：补气防治水泵汽蚀，技术性很强，只有补气流量、补气位置和补气方式洽当，才能取得好的效果。否则，会使泵的流量、扬程和效率下降很多，引起不良后果。6、采用抗汽蚀材料不同的材料抗汽蚀能力有十分明显的区别。影响材料抗剥蚀能力的因素很多，通常具有高硬度和高弹性的材料抗剥蚀能力较强。国外推荐低碳铬镍合金钢，如13Cr4N作为在汽蚀状态下工作的水力机械材料，具有较好的抗剥蚀性能。郑州机械研究所陈岩进行了不同材料抗汽蚀性能的比较(《热加工工艺》2000)，结果如下表材料HT200QT400-15QT600-3ZG230-450ZG310-570失重试验时间h15材料ZG40CrZG20SiMnZG1Cr18Ni9TiZG0Cr13Ni4MoZG0Cr13Ni6Mo失重试验时间h1530长沙水泵厂的朱旭仁提供的资料，其材料与汽蚀失重见下表材料HT200QT600-3ZG310-57018-8失重对无法避免汽蚀时采用耐汽蚀材料是有效的。如：凌城泵站对7#和10#机组，叶轮室将原铸钢换为不锈钢，运行几年未发现其实破坏斑痕。武定门站将铸铁改为QT42-10，使用寿命提高2倍以上。解台泵站用铸铁与铜对比,铜叶轮抗汽蚀效果明显。7、叶轮保护层对叶轮涂层的方法比较常用，非金属涂料涂敷采用环氧树脂、尼龙粉、聚胺脂等。在流道表面堆焊合金或喷涂合金的方法在对汽蚀破坏也取得了一定效果，如不锈钢焊条堆焊法、不锈钢板镶焊修补法、合金粉末喷焊。就非金属和合金（包括不锈钢）的几种方法比较。非金属涂层方式经济，但应当对其操作工艺严格控制，以防止涂层脱落的现象。采用合金粉末喷焊效果好但成本高，且有些地方可能无法进行。如：某泵站采用金属合金粉末喷焊处理的叶片，取得了较好的抗汽蚀效果，使用寿命可延长。中国长城铝业公司郝百顺用H-l对泵叶轮进行了耐汽蚀磨损涂层的应用研究。引滦工程大张庄泵站原泵汽蚀严重，采用柔软陶瓷复合材料修复经过4年4000h的输水检查未发现汽蚀破坏。水利部松辽委察尔森水库管理局王明臣介绍了TS216耐磨修补剂在水轮机转轮抗气蚀中的应用效果良好。连云港币自来水公司马援东采用激光熔覆方法对铸铁和铸钢处理后，抗汽蚀性能分别是喷焊工艺处理的和倍。8、修整叶片头部修整叶轮头部对降低叶片进口的水流速度，减小叶轮进口排挤，提高泵的抗汽蚀能力是有效的。实践证明尽管进口叶片减薄，在汽蚀环境中常常叶轮寿命更长。一般修整叶轮头部是叶片头部背面修薄，在靠近叶轮前盖板多修一些。2001年长沙水泵厂对流量5040m3/h，扬程的泵进行修整（同时对喉部修整），经试验发现汽蚀余量下降左右。

这个铝指的是替位原子，就是铝取代锌的位置，AZO中假如形成氧化铝或者铝都会降低AZO的导电性能。可能我表述的不准确，对掺铝氧化锌薄膜来说，透明导电性是研究的主要方向，所以说降低电学性能就是电阻率升高。当掺过量Al原子时，过多Al原子聚集的境界，出现境界、引起晶格畸变、杂质堆积、破坏晶体结构，这些原因都会导致薄膜的电阻率升高。

信息管理与信息系统毕业论文专卖

首先要告诉你的是铝业进出口有限公司营销策略的英文是The marketing strategies of aluminium enterprises in importing and exporting.我帮你找了些资料，希望会对你有帮助;D Aluminium Demand This Year Will Be About Million Tons, A 24 Percent Rise From 2007DUBLIN, Ireland--(BUSINESS WIRE)--Research and Markets ( announced the addition of China Industry Research and Investment Analysis: Aluminium Mining and Dressing Industry to their of the exits for a . recession is... China. In fact, China's continuing demand for metals for its economic growth is buffering the impact of a . recession on mining producers. China's economy expanded last year at its strongest pace in 13 years, marking the fifth consecutive year of double-digit growth. A . recession only has a minimal impact on China's demand for is the third-best performing industrial metal in the price is rising because of a supply shortage. High demand growth for primary alumina in China will be a key support for prices going STUDY: ALUMINUM ENGINE BLOCKS IN BRAZILThe supply is tight and the demand is higher than ever. China is the world's largest aluminum producer but there is a scarcity because of snowstorms in China in 2008. On the demand side, China has become the world's largest aluminum products maker and consumer. Chinese demand this year will be about million tons, a 24 percent rise from 2007. The country will account for 35% of total demand by 2020 from 13% in 2000."China Industry Research and Investment Analysis: Aluminum Mining and Dressing Industry, 2008"", is an invaluable asset for anyone who wants to invest in the aluminum mining and dressing industries, to import into China, to partner with one of the key Chinese corporations, or to compete in the segment. The report provides in-depth analysis and detailed insight into China's aluminum mining and dressing industries, market drivers, basic industry indices, competitive landscape, key enterprises and their strategies, as well as technologies and investment report is divided into 8 parts (a total of 19 chapters):1. Industry overview2. Basic indices3. Economic operation4. Competitive landscape5. Key enterprises6. Business strategy7. Market investment8. TechnologyData source: national statistics, market research and monitoring, industry associations and institutions, import-export statistics, and 2008, China's domestic consumption, investments, and exports are all expected to continue their rapid growth. In addition, China's hosting of the 2008 Olympics will give rise to an Olympic boom that will boost domestic consumption. Get the report and see how China impacts the world!Content Outline:Part 1 Industry Overview1 Definition of the industry and an overview of its development2 Analysis of the industry’s macro environment and impact3 Analysis of the industry’s international market4 Analysis of the industry’s domestic marketPart 2 Basic indices5 Analysis of the industry’s scale and condition: 2004-20076 Analysis of the industry’s asset status: 2004-2007Part 3 Economic operation7 Analysis of the industry’s gross industrial output value: 2004-20078 Analysis of the industry’s sales revenue: 2004-20079 Analysis of the industry’s gross profit: 2004-200710 Analysis of the industry’s import/export sector: 2007Part 4 Competitive landscape11 Analysis of the industry’s competitive landscape12 Comparative analysis of the competitiveness of the industry’s key enterprisesPart 5 Key enterprises13 Comparative analysis of the economic indicators of the industry’s key enterprisesPart 6 Business strategy14 Development bottlenecks and coping strategies of the industry15 Analysis of enterprise development strategies in the industry and recommendationsPart 7 Market investment16 Comparison and analysis of investment activity coefficients and investment returns in the industry17 Analysis of the industry’s investment environment and investment risksPart 8 Technology18 Current situation and trends of the newest technology applications in the industry19 Development trends of and operating capacity forecast for the industry 156EJEP’s seminar advances strategy on Aluminium exports to EUIn its drive to promote Jordan’s exports of Aluminium products, the Euro-Jordanian Action for the Development of Enterprise (EJADA) held a seminar in Amman last month under the auspices of its Euro-Jordanian Export Programme (EJEP). Addressing the seminar, Mr Vogt Otfried (project consultant) presented the export penetration strategy for Aluminium extruders and fabricators into European markets. detailed his findings over the prospects that exist for Jordanian Aluminium extruders and fabricators to export to EU countries, and he summarized his recommendations on how best to prepare a penetration strategy taking into consideration the existing demand and supply factors governing the EU . Otfried summarised the results of the Inward Buying Mission that took place in Jordan during the 3rd week of September 2005 when six European buyers (extruders and fabricators) held one-to-one business meetings with their Jordanian counterparts (SMG members). In the strategy, Mr Otfried recommended that Jordanian companies within this sector should: become sub-suppliers to extruders in the Western European countries; cooperate with EU companies in promising industries other than Construction as the prices in Construction standard profiles in Europe are hardly cost effective. The companies should concentrate on added value manufacturing processes and aim at establishing joint ventures with partners in Central Europe and the Balkan States to enable them to participate in tender bids in Europe. Addressing Jordanian Aluminium fabricators Mr. Otfried suggested that, to penetrate the EU market, several significant changes need to be managed successfully on a short term and to start in the non-EU states through establishing partnerships. He said that the first results from the Inward Buying Mission for the Aluminium fabricators are promising and fabricators should build-upon the business opportunities that were presented to them under this mission. On the other hand, Mr Otfried recommended that Aluminium manufacturers should consolidate through establishing their own sector representative association. Mr Otfried recommended that the association be grouped by product. A sample association structure was presented to the participants during the meeting. “The meeting was quite fruitful, and we hope that regular visits by experts would enhance our production quality and our export potential to enable us to penetrate efficiently into EU markets,” said Mr. Mohammad Marashdeh, general manager of Arab Aluminium Industry Co., extruder. He indicated that the sector needs ample support in the field of investment in training through donor programmes, and he lauded the Royal Scientific Society’s support which has benefited the sector through the bringing in of experts to give advice on Clean Product, and on methods to save energy and reduce water consumption. Marashdeh suggested that outsourcing by EU companies from Jordan would be the most viable option to enhance exports of Aluminium profiles and casts. Mr. Naji Al-Naji, sales manager of Modern Aluminium Industries Co., extruder, hailed the seminar as an eye opener and said, “More visits by experts are needed to upgrade the industry to European standards.” On the fabricators side, Mr. Shadi Izmiqna, projects manager of Al-Faqeer Industrial Co., said the meeting was useful as it pegged our industry’s capabilities against the standards in Europe. “The comparison enables ground for improvement and hence there would be always need for experts’ visits to evaluate the scope of development that we would require to attain European standards…Visits by SMG sector members to EU industries would also give us a hands-on knowledge of procedures implemented there. On his part, Mr. Omar Shegem, managing partner of Petra Aluminium Co. said, “EJEP has implemented its role as an entity geared towards helping Jordan’s Aluminium exports.” However he was critical of the buying mission that visited Jordan. “The Inward Buying Mission included two European companies that were more interested in exporting to Jordan; however one company from one of the Baltic States has shown interest to buy from our company,” Shegem declared.