第十六讲真空系统的操作与维护

(上接2008年第3期第80页) 3.2 机械泵抽气系统清洁真空的获得 油封机械真空泵(简称机械泵)广泛应用于真空系统中,多数作为前级真空泵.由于科学技术的发展,对清洁真空的要求愈来愈普遍.因此机械泵中的油蒸气返油问题便愈来愈受到重视.我们把机械泵油流向高真空端的现象叫做机械泵的返油.     

涡轮分子泵轴承的油脂润滑

一、引言 近年来,采用涡轮分子泵获得“清洁”超高真空的场合日益增多,因而有关涡轮分子泵“清洁”程度或返油水平的研究和讨论成了重要的论题[1、2、3]。 大多数的测试表明:在操作无误的情况下,涡轮分子泵可将油蒸汽的返流率降低到传统测量方法的可检水平以下。但是,只要分子泵内有油面存在,就构成一种炭氢蒸发源,操作偶有失误,泵油就有可能以气相或表面迁移等方式向泵的进口侧返流污染被抽容器。因此,进一步降低涡轮分子泵运油水平的最好措施;是彻底取消油润滑的轴承,以空气动压轴承或磁悬浮轴承代替。采用这两种支承的分子泵虽已有商品问…     

前级真空泵抽速对涡轮分子泵抽空性能的影响

一、前言 涡轮分子泵是一种能获得清洁超高真空的真空获得设备。它具有在极宽范围内抽速恒定、对被抽气体无选择性、起动快、操作方便等特点,目前已广泛应用于高能物理,表面物理,等离子体技术,各种分析仪器,电真空器件生产和真空技术各领域。 目前所生产的涡轮分子泵,是必需在有前级泵的条件下工作的真空泵。实验表明,由于级泵抽速的不同和前级泵联接管道的差异,对涡轮分子泵的性能测试结果有较大影响。涡轮分子泵的性能测试规程,规定其前级抽速是涡轮分子泵对不同气体名义抽速的 0.02至0.1倍。据此,如测定110升/秒抽速的涡轮分子泵性能时,…     

真空技术及应用系列讲座第十六讲真空系统的操作与维护

(上接2008年第4期第111页) 3.2.2.4 延长前级管路和提高前级压力 延长抽气系统的前级管路可以明显降低油蒸气的返流量,返流量与管路的分子流流导有一定关系.实验表明,适当延长前级真空管路,并且压力上升至10 Pa,油蒸气的返流率可以降低95%.图23给出一只900 L/min的单级机械泵接上不同长度的管路时,其油蒸气返流率随管路长度变化的实验曲线,右边的纵坐标标出空气分子流的流导值.     

《真空物理学和工艺》

《真空物理学和工艺》(Vacuum Ph-ysics and Technology)一书于一九七九年在纽约出版。 这是一本颇有名望的真空专业书籍,由多位作者分章节集体编写。书的内容相当广泛:分子输送、表面物理、全压测量、分压测量、高真空的获得(前级泵、扩散泵、分子泵、喷射泵、水银扩散泵、吸附泵),超高真空的获得(基本原理、收气泵、离子泵、低温泵、涡轮分子泵),金属和玻璃真空系统,材料(金属、玻璃、陶瓷、弹性体、密封体、气体)的真空性能,真空设备的制造,保护装置,高真空系统的设计、操作和维修,可烘烤的超高真空系统和其操作上的特殊要求,检漏技巧(…     

新型分子增压泵的性能测试

本文详细介绍了新型分子增压泵的测试方法,对分子增压泵的极限真空、返油率、抽速及工作频率等性能进行了测试分析.测试结果表明,该泵可以在过渡流段替代罗茨泵来获得清洁真空系统.在兰州重离子加速器TR2终端真空差分系统前两级选用了新型分子增压泵,并根据测试结果确定其工作频率.最后给出了在TR2终端真空差分系统使用分子增压泵后的实验结果,表明该泵能够满足清洁、大流量差分真空系统的使用要求.     

无油排气质谱

一、无油排气系统 从1974年开始,在北京仪器厂的协助下我们组装了一台无油真空系统专用于大功率发射管的排气,(1)该系统以两级吸附泵或带分子筛吸附阱的机械泵为前级,以冷钛泵为主泵、钛升华泵为辅泵。这样的组成方案目前在电真空器件的研制单位、包括使用无油真空技术制作发射管的厂家中是广泛应用的。这类排气台提供无油清洁真空的效果如何?在应用中应注意一些什么问题?这便是本实验所要探讨的。 目前我们使用的无油排气台如图1所示; 它与当初报导的系统(1)相比,几年来作过如下几点改进: l、用活性氧化铝挡油饼(配合机械泵)代替了分子筛挡…     

机械泵的返油(节译)

3.机械泵的返油 (原文第一、二两节从略,以下编号顺序仍按原文──校注) 一个设计良好的扩散泵真空系统,即使在扩散泵进口采用高效液氮冷阱、也仍然会出现某种程度的碳氢化物污染。这种污染的根源一般都归因于扩散泵返油、但是实际上在大多数情况下都可以查到机械泵油的痕迹。 考察旋片泵在从大气压下开始工作直到达到其极限压强时在旋片泵扩散泵间联接管道内气流状态所发生的变化可以看出、在粗抽阶段(压强降至1毫巴以前)管路中高密度气流占绝对优势因而阻止了机械泵油向扩散泵方向的返扩散。可是,随着压强的下降,气流变为过渡态,蒸汽分子…     

轴流分子泵研究(四)──关于单叶轮在过渡流区域内的抽气特性

1.引言 为阐明轴流分子泵的抽气机理,笔者不久前曾对轴流叶轮在分子流区域内的抽气特性进行了研究(1)(2)。 在用油扩散泵作前级泵时,前级真空端的真空度要保持在10～(-4)乇以上,这时构成轴流分子泵的全部叶轮就可以认为形成分子流。但是若只是用油旋转泵作前级泵时,前级真空端的真空度则变为10～(-3)～10～(-2)乇。其结果,据我们推测,在构成轴流分子系的叶轮中靠近出气侧的几个叶轮上,气体分子之间的碰撞次数等于叶板与气体分子之间碰撞次数,即变成所谓的过渡流状态。关于过渡流区域的研究甚少,对它怎样处理目前还没有一个准确的方法。 Scb…     

油蒸汽流泵的抽速表达式

通常将油扩散泵和扩散喷射泵(油增压泵),统称为油蒸汽流泵。其工作原理与涡轮分子泵相似。在涡轮分子泵中。由高速旋转的叶片带走气体分子,以完成抽气过程。而在油蒸汽流泵中,抽气过程是由各级喷嘴吹出的高速蒸汽射流,把被抽气体(空气)分子携带到前级压力端。实践证明,无论是涡轮分子泵、油扩散泵或扩散喷射泵,在其相应压力范围内,都具有平滑的抽速特性曲线。 多年来各国学者已对油蒸汽流泵的抽气过程,进行过深刻的分析和讨论。最近德国学者M.Wutz更从气体动力学的角度来探讨油扩散泵的机理,提出了泵的何氏系数的计算表达式。国内许多专家…     

Weitbereich-Turbomolekularpumpen und Membranvorvakuumpumpen als trockene HV- und UHV-Pumpsysteme

The development of new turbomolecular pumps with increased critical backing pressures up to 30 mbar made it possible to use oilfree diaphragm pumps as backing pumps. The combination of a wide-range turbomolecular pump with a diaphragm pump represents an inexpensive, compact and technical dry vacuum pumping system for high and ultrahigh vacuum applications. The interaction of wide-range turbomolecular pumps with diaphragm pumps is discussed in terms of gas throughput, compression ratio, ultimate pressure and power consumption of the turbomolecular pump and selection criteria for the diaphragm backing pump are shown.     

Wasserstoff in Hochvakuumsystemen mit Turbomolekularpumpen bei verschiedenen Vorpumpen

The combination of diaphragm pumps with wide‐range turbomolecular pumps constitutes a small but powerful oil‐free high vacuum pumping system. Turbomolecular pumps show gas dependent compression ratios, the lowest for hydrogen. Thus, the high vacuum can be governed by the hydrogen partial pressure. In the present investigation the residual gas composition of a turbomolecular pump and different backing pumps shows no improvement if diaphragm pumps with low ultimate pressure are replaced by rotary vane or Roots pumps. In this case the ultimate pressure in the high vacuum chamber is basically determined by the ratio of outgassing to pumping speed and not by the product of compression ratio and backing pressure. However, the hydrogen partial pressure increased if the ultimate pressure of the diaphragm pump was raised. At a backing pressure of 0.5 mbar the high vacuum reached a stable value not improvable by reduction in backing pressure.     

串联分子泵获得10-9 Pa真空的实验研究

介绍了采用两级分子泵串联系统获得10^-9Pa真空度的实验研究。实验证明，通过串联一台分子泵，可以有效地提高系统对氢气的压缩比，显著提高系统的极限压强。     

Improvements in the performance of turbomolecular pumps

A new range of turbomolecular pumps, nEXT, has been developed. This incorporates a new damping mechanism and pumping stage options. A new Siegbahn drag stage in combination with a regenerative mechanism are described in their combination with pure turbomolecular stages. Consequent increased backing pressures, high compression ratios and the facilitation of a boost port being used to create additional pumping capacity in the viscous flow regime will be described.     

Kenngrößen von Turbo‐Molekularpumpen

Graphs of “high‐vacuum pressure as a function of backing pressure” (“p_HV versus p_VV”) and “compression as a function of backing pressure” (“K versus p_VV”) are presented in this article. The performance of any turbomolecular pump can be fully and reliably evaluated with the aid of these graphs. Until now these graphs have only seldom been shown in catalogs. The catalogs generally lack the so‐called “limit lines” (“Q as a function of p_{VV, Kmax}”). For a prescribed gas throughput Q, the limit line indicates what minimum pressure must be generated by the backing pump at the fore‐line port of the turbomolecular pump so that a stable pressure exists at the high‐vacuum side of the turbomolecular pump. Using the gas‐type‐specific limit line and the corresponding, usually well‐documented pumping‐speed curve, one can already describe the functional proficiency and performance of a selected combination of turbomolecular pump plus backing pump in an approximate manner – but not yet completely. In this article we also indicate analytical functions which excellently describe the pressure dependence of the compression and pumping speed.     

Konstruktion und Eigenschaften von turbinenartigen Hochvakuumpumpen

Turbomolecular pumps are essentially axial-flow compressors designed for pumping rarefied gases. Original designers adapted more or less traditional axial-flow compressor stage arrangements using mathematical modeling based on studying molecular trajectories inside alternating rotating and stationary blade rows. Recent designs trends lean toward hybrid stage arrangements, which incorporate turbomolecular and turbodrag stages within the same body and mounted on the same shaft. The new pumps achieve much higher compression ratios (10 to 100 times) permitting higher discharge pressures and allowing the use of oil-free backing pumps. At the present time, there are four types of turbine pumps: multistaged axial-flow turbomolecular pumps, molecular drag pumps (usually of the Holweck type), hybrid pumps with modified downstream stages but the same number of rotors, and compound pumps which combine the axial stages with additional drag pumps in the same body. Turbine-type high-vacuum pumps, unlike vapor-jet pumps and cryopumps, permit relatively simple engineering solutions for increasing their pressure regime to an almost arbitrarily high level, including the possibility of discharging directly to atmosphere. This provides opportunities for further improvements.     

Die Entwicklung der Turbomolekularpumpe innerhalb der letzten drei Jahrzehnte

Development of turbomolecular pumps within the last three decades On the occasion of the 30^th anniversary of the “Vakuum in Forschung und Praxis” in 2018, the author puts the turbomolecular pump at the centre of the historical overview. From the first experiments, which led to the development of this key component of modern vacuum generation in high and ultra-high vacuum technology, to further developments up to the present day, individual technological advances made by Pfeiffer Vacuum – especially those of the last 30 years – are presented and future development trends are shown.     

New Turbomolecular Pump with Central Opening for Free Axial Access. Eine neue Turbomolekularpumpe mit zentraler Öffnung für freien axialen Zugang

Standard turbomolecular pumps show typically one annular active intake area on the high vacuum flange side (single‐flow pumps). The central circular part of the inlet of the compressor turbine is blind for pumping. The new design proposes a central opening of a turbomolecular pump all along the axis. This central bore can be used e.g. for mounting of feed throughs, manipulators, windows or for coupling to further vacuum devices, in particular also for enclosing tube‐like vacuum systems. This design allows a multi‐use of a pumping port at a vacuum vessel without reducing there the pumping speed. Moreover, the new design is ideal for axial or radial differential pumping arrangements as e.g. needed for all gas jet like set‐ups or other pressure reduction stages.     

Performance increase in turbomolecular pumps with curved type blades

Mostly, flat-type blades are used in the turbomolecular pumps in both rotor and stator sections. In this study, performance characteristics of the turbomolecular pumps consist of one rotor or rotor-stator pair with flat-type blades is calculated in different flow regimes. Next, the same calculations are realized for the curved-type blades in dissimilar geometries. Following, these performance characteristics are compared to find out which combination is the most efficient in terms of maximum pumping speed and maximum compression ratio. In case of turbomolecular pump consists of only one rotor, flat blades give the best performance. However in rotor-stator pairs, the performance of the flat-type only blades is surpassed by a combination of rotor with flat-type blades and stator with curved-type blades. Consequently, it is concluded that curved-type blades should also be considered in stator sections in addition to the flat-type blades in order to increase the performance of the multi-stage turbomolecular pumps.     

Überlastgrenzen bei Hochvakuumpumpen

High-vacuum pumps have a limited inlet pressure above which they cannot function. Recognizing and dealing with the approaching overload conditions is an important aspect of vacuum system operation. This paper outlines the basic considerations for selecting the pressure at which the high vacuum pumps are started, emphasizing the importance of mass flow (throughput) limits rather than the pressure as such. Some basic parameters, such as the ratio of pumping speeds of the roughing pump and the high vacuum pump are associated with the choice of the cross-over pressure. Practical engineering recommendations are offered for system design and operation. Adverse system effects (e.g., backstreaming and oil loss) resulting from pump overload are noted for momentum transfer pumps (diffusion pumps and turbomolecular pumps) and capture pumps (sputter-ion pumps and cryogenic pumps). To prevent any adverse effect, normally, the transient pressure rise during switching should not be longer than a few seconds.