鲍杰开题报告 - 副本.doc

毕业设计（论文）材料之二（2）本科毕业设计(论文)开题报告题目： 轴颈50泵用机械密封设计 The Design of Mechanical Seals for Pumps with 50mm Diameter of Axle课 题 类 型： 设计 实验研究 论文 学 生 姓 名： 学 号： 专 业 班 级： 学 院： 指 导 教 师： 开 题 时 间： 3月10日 1、 毕业设计（论文）内容及研究意义、研究现状和发展趋势一）、课题研究的意义 要想研究机械密封就应该先看看机械密封于填料密封的区别优点：密封可靠在长周期的运行中，密封状态很稳定，泄漏量很小，按粗略统计，其泄漏量一般仅为软填料密封的1/100；使用寿命长在油、水类介质中一般可达12年或更长时间，在化工介质中通常也能达半年以上；摩擦功率消耗小机械密封的摩擦功率仅为软填料密封的10%50%；轴或轴套基本上不受摩损；维修周期长端面磨损后可自动补偿，一般情况下，毋需经常性的维修；抗振性好 对旋转轴的振动、偏摆以及轴对密封腔的偏斜不敏感；适用范围广机械密封能用于低温、高温、真空、高压、不同转速，以及各种腐蚀性介质和含磨粒介质等的密封。对现今许多工厂的“零泄漏”需要，盘根无法达到此要求；根本适应范围广，随意性更大，但对于在工厂，经常更换或维护将对工厂造成很大损失。缺点：结构较复杂，对制造加工要求高；安装与更换比较麻烦，并要求工人有一定的安装技术水平；发生偶然性事故时，处理较困难；一次性投资高。 虽然其在造价上高于填料密封但是在化工工业中即使是一点点的泄露都可能会造成很大的危害，故而在化工行业中对机械密封的使用越来越多特别是在化工泵中。一般而言，机械密封结构主要有以下6种：一是单端面、双端面及多端面密封；二是内装式和外装式密封；三是平衡型和非平衡型密封；四是单大弹簧与多小弹簧密封；五是静止式和旋转式密封；六是内流型和外流型密封。各种同结构形式的机械密封适应于不同的场合。例如，作为某型尿素泵而言，其机械密封是内装单端面大弹簧平衡型。这种机械密封的结构比较简单，易于生产制造，便于安装，它适用的场合主要有：一是腐蚀性介质；二是勃度较大的介质；三是含有颗粒的介质。此种密封技术在化工厂中得到了广泛, 它的使用情况是：一般适用于压力比较低的情况或介质危险等级较低的情况。在进行冲洗液选择时，应该根据实际需要确定，一般可以选用自冲洗的冲洗液和外部冲洗的冲洗液。对于高参数的机械密封体来说，它非常适用于压力等级高、转速快、温度高的运行环境。例如某厂使用的某高速离心泵，就有非常大的出口压力和极快的转速。在这样极为苛刻的条件下, 机械密封被设计成内流型、静止式、单端面和多弹簧型。一是在这种设计中，在静环的一侧放置弹簧，可以避免受到离心力的影响,因此非常符合高速运转的需要。二是采用内流型的设计，当介质发生泄漏时，其泄露方向刚好与离心力的方向相反, 也非常适用于高压力的环境。三是该泵机机械密封分为两级, 其中二级机械密封是将两列相同机械密封进行串联的方式,密封压力被平均分配到两列机械密封上。由于采取的这些措施得法, 因此，确保了该型泵的机械密封的平稳运行。随着社会的发展，密封技术也得到了迅速的发展, 机械密封得到了更加广泛的应用，其应用的实效性越来越佳，尤其是一些新型密封技术的诞生，给机械密封带来了极大的发展空间。如控制平衡比技术、弹性伸缩的波纹管密封技术等。当生产的介质是剧毒性、易燃易爆性时，必须严格控制介质的泄漏量。以某化工厂的氨泵为例, 该泵采用的是两级机封串联的方式, 其一级结构是波纹管密封式, 是不锈钢焊接式弹性体结构, 动环是端面镶嵌石墨，其二级是B W气体机封, 该气体机封采用的技术是密封面改形。将深槽刻在动环的密封面上，其平面的外缘则是16个锥形体。它的工作原理就是：利用热变形产生的波浪面来形成锥形块的轴承, 其更多流体则能够到达锥形块的前缘。因为出口的区域相对要小，从后缘可离开的流体比较少, 于是，在静止面与旋转面之间就形成了流体压力。这种流体可以有效地使两者分开，从而达到了密封之目的。在动环（静环）与同外部轴承进行连接的地方具有很深的环形槽, 可以使轴承和密封部位得到有效的隔离，从而不会因受到因温度变化而带来的影响。随着机械密封技术的不断提高，它在化工机泵方面备受青睐，应用的方面日益广泛。特别是一些新技术、新工艺和新材料的引进，它的结构形式日趋多样化、材料日益多元化，质量要求越来越高，因此，我们应该不断探究机械密封技术，提高其在化工机泵方面的应用水平，以便更好地为社会发展服务。二）、本课题的发展现状与前景1、研究现状 我国炼化企业最早是在20世纪60年代初开始在离心泵上用机械密封，至今有40多年的历史。到20世纪90年代，密封技术以接近世界先进水平，在高温、低温、高压、悬浮颗粒的介质的密封方面做了一些工作。但是技术发展水平不平衡，各地机械密封制造和维修水平存在一定差距。随着新技术不断的涌现，机械密封的技术水平也不断提高，目前机械密封得到了广泛的应用，已成为压缩机、离心泵的主要密封方式。就机械密封的通用性而言，他以大量取代填料密封之类的老式密封技术，并显示出巨大的优越性。通常，机械密封的性能难以预测，使用寿命远低于滚动轴承的寿命，这就意味着需要停车更换机械密封，浪费了大量的人力、物力。并要支付巨额的维修费用，并发生爆炸、着火、人身伤害事故等。2、发展趋势1）、发展方向 (1)接触式密封减少泄漏、减小磨损、提高可靠性和工作稳定性、延长使用寿命。 (2)非接触式密封减少泄漏、提高流体膜刚度和工作稳定性、延长使用寿命。2）、发展趋势 随着科技进步和工业的发展，高参数机械密封实用化的要求越来越高。具体可用下图来表示机械密封技术的发展趋势。周速V(mS_)机械密封技术的发展趋势 3）、发展特点 (1)技术不断创新新技术、新概念、新产品、新材料、新工艺和新标准不断涌现；高参数(如高压、高速、高温、大直径)、高性能(如干运转、零泄漏、无油润滑、浆液)和高水平(如高痧v值、大型剖分式、监控)的密封产品大量研制；失效机理(如疱疤、热裂、空化一汽蚀、橡胶密封圈泡胀和老化)、失效分析(如可靠性和概率)和失效监控(如流体膜、摩擦状态和相态)的研究和应用。 (2)使用范围不断扩大机械密封不仅机泵阀采用，而且工艺设备(如反应釜、转盘塔、搅拌机、离心机等)都采用。 (3)发展要求重视密封系统过去只重视单独密封件，现在已经发展到重视整个密封系统，而且已制订了新的密封系统标准(API一 682“离心泵与转子泵的轴封系统”标准)。 (4)注意安全和环境保护过去只注意眼睛可视的“泄漏”，不注意眼睛看不见的易挥发物的“逸出”；现在发展到要求控制易挥发物的逸出量，也就是说从要求“零泄漏”到要求“零逸出”。美国摩擦学家和润滑工程师学会(简称STlE摩润学会)已制订了SP30等易挥发物逸出量控制规定的指南。 (5)要求不断提高在石油化工方面，为了延长工艺装置的检修周期和装置的操作周期，要求机械密封的工作寿命由1年延长到2 年，国外由2年延长到3年(API682中作了明确规定)。 (6)研制产品要求实用化不仅要求研制出新产品，更重要的是使所研制产品得到实际应用。二、毕业设计（论文）工作计划时间任务第一周阅读相关资料并完成开题第二周第二周:外出实地观察学习第三周根据使用要求确定最高工作压力 工作温度与速度以及耐腐蚀 耐颗粒防止断面液膜汽化 防止微量介值泄露污染环境等技术第五、六周按技术条件确定补偿环的形式和结构，设计和选用非补偿环和其辅助密封圈的结构第七、八周按技术条件确定补偿环组件的结构和型式和结构，设计补偿环 辅助密封圈 弹性元件 机构件等，极可能采用标准构建并画出设计图纸第九、十周进行机械密封主要参数密封端面机械变形计算，在相同厚度的最大和最小轴之间，以及不同的最大轴径之间比较，然后修真设计，得出尺寸系列.第十一十四周标准化和工艺审核检查图纸 修改图纸 画装备图第十五、十六周拟定毕业论文初稿第十七周修改完善论文完成答辩三、主要参考文献 1赵林源.机械密封实用方法与技巧M.北京：石油工业出版社 ，20092英J.D.萨默-史密斯实用机械密封M.北京：机械工业出版社，19933程德才.机械密封设计制造与使用M.北京：机械工业出版社，1993 4魏孔瑜.泵用机械密封初始倾斜对性能的影响分析J.甘肃科技,第28 卷第4 期2012 年2 月5王宇.泵用机械密封的失效因素分析J.炼油与化工,2011年第3期6张巍.高温油泵机械密封冷却系统改进J.设备管理与维修2012 57李勇.关于化工机泵机械密封的应用的探讨J.中国石油和化工标准与质量，2010年第3期8伍秋明.水泵机械密封的渗漏原因与解决措施J.施工技术，2012年7月9赵俊.耐磨蚀和耐腐蚀泵用新型机械密封开发应用J.水泵技术，2011第6期 10M. Vila a, J.M.Ultra-high performance of DLC-coated SI3N4 rings for mechanical seals J .Science Direct,2008四、附录A:外文文献及翻译Ultra-high Performance of DLC-coated Si3N4 Rings for Mechanical SealsAbstract Silicon nitride (Si3N4)-based ceramics are useful materials for tribological purposes due to their superior mechanical properties. One of their applications is as mechanical face seals. However, Si3N4 rings failed as self-mated systems, leading to fluid leakage and catastrophic failure under high-sealing loads. In order to improve the tribological behaviour and to provide efficient full-sealing conditions, the coating of the Si3N4 surfaces with a solid lubricating diamond-like carbon (DLC) film is here proposed. Plasma-enhanced chemical vapour deposition (PECVD) DLC coatings with approx. thickness of 1.5 m were deposited on Si3N4 rings by conventional RF glow discharge taking only pure methane or a95:5 methane/silane mixture, under an applied self-bias voltage of 800V. After 419 h of continuous work (4300 km), the self-mated pure DLCring-on-ring tribosystem proved its outstanding performance in sealing of 2 bar of internal pressure of water, at 4ms1, in the range 0.481 kN of applied normal load, without any signs of surface damage and a super low-friction coefficient value less than 0.001. The Si-DLC coatings have a slightly worse performance, with a running-in period and a steady-state friction coefficient of about 0.02. 2008 Elsevier B.V. All rights reserved.Keywords: DLC; Silicon nitride; Seals; Sliding wear1、Introduction Mechanical seals, formed by uncompressible static and dynamic matted rings, are extensively used to prevent liquid or gas leakage in moving machine elements. Important applications involve water or aqueous solutions circulation, like in refrigeration systems and pumps for specific purposes. These require alternative materials to metallic ones, namely advanced ceramics, in order to overcome rust or prevent chemical attack from acid or basic media. As examples, ceramic seals are nowadays used in hot chemical water-based extreme environments like in automobile water pumps 1 and in chemical pumps 2. Moreover, ceramics, being harder, are an adequate option for the seal designer in applications where the specific sealing loads are high or when the operating fluid contains abrasive particles. As it has been previously studied 3, silicon nitride (Si3N4) ceramics are good candidates for mechanical seals, not onlydue to their superior corrosion resistance but also due to theirlow density, high hardness and relatively high-fracture toughnessfor a ceramic material. The tribological performance ofmechanical seals including Si3N4 ringswas evaluated in a rotarytribometer simulating sealing operating conditions. The hybrid mechanical seal system involving a Si3N410 wt.% SiC composite against cemented carbide (WCCo) proved to be adequate for sealing of aqueous solutions, presenting outstanding values of the Si3N4 wear coefficient (K= 2.9109 mm3 N1 m1) and friction coefficient (f = 0.02) 3. However, WCCo is a very heavy material, which is a disadvantage whenever large dimensions are required, due to power consumption, and dynamic loading associated to centre-of-mass eccentricities, causing adverse vibrations in the rotating system. An obvious solution could be the Si3N4 self-mated pair, but in this situation the ceramic showed a poor tribological response (K=7108 mm3 N1 m1) and friction coefficient (f = 0.12), with fluid leakage 4. Therefore, there is a need to improve the Si3N4 tribological performance, which can be attained by coating it with a wear resistant low-friction coefficient material, like diamond-like carbon (DLC). DLC coatings possess a unique combination of tribological characteristics, being suitable for demanding applications like mechanical seals. These solid lubricant hard films have already demonstrated their paramount tribological behaviour, as extremely well documented in a very recent reviewfrom Erdemir and Donnet 5.DLCis a combination of sp2- and sp3-hybridized carbon atoms and may contain some hydrogen (between 1 and50 at.%), whose proportion affects both the structure and the properties. DLC coatings present extremely low-wear rates, in the order of 109 mm3 N1 m1, due to the combination of their relatively high hardness (20 GPa) and low-friction coefficient against a large variety of antagonist materials 2. In operating conditions, a very thin fluid film (0.258m) must lubricate the sealing faces in order to guarantee a correctfunctioning 6. However, solidsolid contact occurs during starting and stopping or if occasional overloading occurs during working. The role of DLC may assume a crucial importance in these dry running periods, when a lack of lubricant occurs, which may result in degradation of the ceramic surface. Diamondlike carbon-coated mechanical seals are mentioned as potential DLC applications in a fewworks 1,2,5,711 and, among these,DLC-coated ceramics are referred, like SiC 2,10 and Al2O3 1. However, to our knowledge, there are no works reporting results obtained in a tribological test configuration that simulates the real functioning of mechanical seals. This study discusses the tribological behaviour of different combinations of pure DLC and DLC-Si-coated Si3N4 materialsin a ring-on-ring test configuration. Plasma-enhanced chemical vapour deposition (PECVD) by conventional RF glowdischargewas used to deposit the DLC and DLC-Si films, respectivelytaking only pure methane or gaseous mixtures of methane and silane.2、Experimental The ceramic rings were processed from powder mixtures of 89.3 wt% Si3N4 (HC Stark M11), 3.7 wt.% Al2O3 (Alcoa 116SG) and 7.0 wt.%Y2O3 (HC StarkCfine). These were mixed for 4 h in 2-propanol media using an alumina jar and alumina balls. Then, after pre-conformation to ring shape at lowpressure, the samples were isostatically pressed at 200MPa, followed by full densification (99% of the theoretical density) by pressurelesssintering at 1750 C for 2 h in nitrogen atmosphere. Finally, the Si3N4 rings were ground until final dimensions of 43.7mm (external diameter), 32.2mm (internal diameter) and 7.0mm(thickness). The working surfaces were diamond polished until a final surface roughness of Ra = 0.020.04m. The silicon nitride rings were coated by PECVD provided with a 13.56MHz RF power supply. DLC and silicon-doped DLC films were produced starting a glow discharge from different gaseous mixtures. In the case of the DLC films, from pure methane, resulting in a hydrogenated amorphous carbon (a-C:H) film, and in the case of DLC-Si (a-C:H-Si), from a mixture of methane and silane (CH4:SiH4 volume ratio equal to 95:5). Before deposition, the Si3N4 surfaces were primary cleaned in deionised boiling water and isopropanol, followed by Argon sputtering during 15 min at a bias of 800V. After cleaning, a 200 A a-Si:H film was deposited at 500V from a silane atmosphere to act as an adhesion improving layer. TheDLCand DLC-Si films were grown at800Vbias voltage varying the depo on time to have similar thickness (1.5m), due to different deposition rates. The pressure was kept constant at 1.5102 torr for all the processes. Studies on films structure and composition as a function of applied bias and silane content have been published elsewhere 12. It has been reported that forfilms grown under the present conditions,hardness values arein the 2025 GPa range and the internal stress is compressive with values of approximately 11.5 GPa 13. Raman studies evidenced the increasing sp2 character for films grown at high bonds content, improving the mechanical properties. On theother hand, the sp3 character of the films increases with the silane concentration, when comparing pure DLC and DLC-Si films, also contributing to an improvement of the mechanical performance. Tribological tests were performed in a ring-on-ring planar contact configuration tribometer (TE92-Plint and Partners) that simulates the mechanical sealing process, with a stationary ring fixed to the stator (bottom) part and the dynamic one (upper) at the rotor, operating as described elsewhere 3. The tests were performed at room temperature with a constant water internal pressure of 2 bar. Rotational speeds of 1000 and 2000 rpm, corresponding, respectively, to 2.1 and 4.1ms1 of linear speed, were employed. The load was gradually increased from 0 kN to near1 kN in order to achieve the two critical operating conditions: (i) full sealing, at the minimal effective pressure between the matted faces; (ii) surface inoperability, at the maximum capability of the opposite faces to resist seizure. The tribometer is equipped with a microprocessor that controls the rotational speed, the applied load, the breakdown, starting up and the duration of each step of constant load and sliding speed. For all tests, the friction coefficient was evaluated using a bending-type load cell for friction force acquisition and a load cell for normal force measurement 3. Average friction coefficient values for both DLC and DLCSi self-mated systems were estimated in steady-state full-sealingcondition. This condition was repeated during several steps of 28.8 km each, reaching a total sliding distance between 144 and 259 km. The worn surfaces of the rings were characterized by scanning electron microscopy with chemical analysis (SEM/EDS).3、Results3.1. Self-mated tests of DLC-coated Si3N4 surfaces In the case of the pure DLC-coated rings tested in self-mated configuration, the experiments were carried out during 419 h giving a total sliding distance of 4300 km, involving several running steps under distinct loads, firstly at 1000 rpm and then at 2000 rpm The test started without detectable running in, and the resultant friction values were very low, below the resolution of the equipment in terms of friction coefficient (0.001). Full sealing was attained under an external applied load starting at 0.48 kN, independently of rotational speeds 1000 and 2000 rpm. At the minimal load sealing condition, multiple steps, during 20 h, were performed to validate this regime and to confirm.Fig. 1. SEM micrographs of the surface morphology of the DLC-coated Si3N4 rings: (a) stationary ring; (b) dynamic ring, showing distinct features on the surface (I, preserved regions; II, abrasive marks; III, delaminations). A high magnification is included as an inset The reported outstanding behaviour. After, the applied load was progressively increased to 0.99 kN, the maximum value allowed by the apparatus. The product of the effective pressure at the ring contact by the linear speed (PV) varied in the range (PV)min = 0.95MPams1 to (PV)max = 5.38MPams1, the minimum value corresponding to the onset of sealing and the maximum related to a suitable lifetime. The contact surface morphology of the DLC-coated Si3N4 stationary ring can be seen in Fig. 1(a), without any signs of damage. Fig. 1(b) is a low magnification that illustrates the working surface of a ring width segment of the opposite dynamic face, showing preserved coated regions (I), some abrasive marksalong the sliding direction (II), and regions where film delaminationoccurred (III). This last feature is magnified in the inset of Fig. 1(b), where grooves from the grinding procedure of the subjacent Si3N4 substrate are exposed. The system ran without water leakage and no measurable friction, despite film spalling in dispersed regions at the centre of the ring surface, along the rotation direction.3.2. Self-mated tests of DLC-Si-coated Si3N4 surfaces These tests were performed during 85 h, corresponding to a total sliding distance of 940 km. Complete sealing was achieved for the same load as in the previous tribopair, 0.48 kN, and, again, the applied load was increased to the maximum, 0.99 kN, keeping the sealing performance. The tribological response was thus very similar to the previous pair, for both the angular speeds of 1000 and 2000 rpm. However, a difference occurred on the friction force that took a value measurable by the tangentialload cell, giving a steady-state friction coefficient in the order of0.02. The limit PV values were (PV)min = 0.97MPams1 and the (PV)max = 5.68MPams1, very close to the previous ones, with small differences only related with variations on the rings dimensions. The instantaneous friction coefficient behaviour of the different stages of a test is shown in Fig. 2. In this graph, some initial runs (IIII), until 100 km of accumulated sliding distance, are illustrated together with intermediate (IV) and final runs (V and VI). The first set of runs correspond to the running-in period, where the friction coefficient presents the highest values (0.10), too high for mechanical seals regarding industrialapplications requirements. These runs are representative of the behaviour of several steps at this initial condition. The intermediate run (0.04) denotes a transition of the friction coefficient to the lower values characteristic of the steady-state regime (0.020.004). The morphology of the DLC-Si-coated Si3N4 surfaces after testing was similar for both mating rings. In Fig. 3 it can be seen that the worn surface denote a few signs of abrasion along the sliding direction (Fig. 3(a). The high magnification in Fig. 3(b) evidences discrete marks of film detachments, probably originated during the running-in stageFig. 2. Friction coefficient evolution at different stages of the DLC-Si-coatedtribosystem: IIII, initial runs; IV, intermediate step; V and VI, final runs.Fig. 3. Morphology (SEM views) of the DLC-Si-coated Si3N4 surfaces after testing: (a) general view from a low magnification; (b) high magnification evidencingdiscrete film detachment marks.4、Discussion The result