High-performance lift augmentation dynamic seals for turbine bearing compartments

Conventional bearing shaft seal systems used in gas turbine engines are often limited to a sliding velocity of about 100 m/s, differential pressure of 3 bar, gas temperature of 300°C and a seal life less than 8000 h. Advanced engines will require bearing shaft seal systems to operate up to sliding velocity of 200 m/s, differential pressure of 6 bar, gas temperature of 500°C and seal life in excess of 30?000 hours. For seals operating in these advanced conditions, a design with no rubbing contact will be required to achieve long life and reliability. A good validated approach is the use of a gas lift augmentation seal. The design objective for a seal of this type is to have the faces of the seal seek an equilibrium position to avoid any contact. The gap must be small enough to ensure a minimal air leakage, but it must be large enough to limit power dissipation, due to shear in the gas film, and face deformation by shaft displacement, misalignment and vibration. Dynamic seals for a bearing compartment have the following main functions: provide static and dynamic sealing in order to prevent oil leakage from the bearing oil compartment to the air compartment and consequently no oil smell pollution by the use of bleed air; control air leakage to the bearing oil compartment in order to improve performance of the engine and to reduce oil consumption; reduce volume of the oil tank and lubrication system and hence provide weight reduction; to operate in extreme conditions of temperature and with normal and reverse pressure; and reduce the mean time between overhaul (MTBO) and have a very long life. Techspace Aero and Burgmann have carried out design, development and testing of lift augmentation carbon seals and demonstrated that high life and performance levels of these seals are possible in a gas turbine engine environment.     

New radial shaft seal concepts for sealing hydraulic pumps and motors

Dr.-Ing. Eberhard Bock, Freudenberg Dichtungs- und Schwingungstechnik KG, Dipl.-Ing. Rolf Vogt and Dipl.-Ing. (FH) Peter Schreiner, Freudenberg Simmerringe KGThe development of radial shaft seals for hydraulic pumps and motors is challenging. The mechanical and thermal loads exerted on the sealing lip increase dramatically as the pressure rises. As a result, the long operating life generally expected of these seals is often only obtained from leakage-generated lubrication, giving rise to a conflict of interests. This article examines the different pressure radial shaft seals currently available on the market, and describes the development of a seal with a sealing edge profile design that considerably extends its service life. The feature also presents a new seal concept which, in addition to introducing measures that improve lubrication by adding a special structural feature, increases the flexibility of the sealing lip by reducing the contact pressure.     

机械密封端面接触状态的声发射监测研究

有效监测机械密封的端面接触状态有助于对密封失效做出早期预警。针对密封声发射信号难以降噪的问题,提出基于神经网络粒子滤波和最小二乘支持向量机的声发射建模方法。首先通过机械密封的端面膜厚测量,研究声发射能量在密封启动过程中的变化规律;接着利用人工神经网络构建信号的状态空间,再通过粒子滤波算法对状态空间滤波降噪;最后从滤波信号中提取特征,并利用最小二乘支持向量机构建机械密封端面接触状态的检测模型。实验数据证明该方法能有效实现机械密封端面状态的无损检测,具有良好的工业前景。     

Non-contacting seals for critical service process pumps

To improve the quality of life, man has learned to manufacture countless chemicals, pharmaceutical and biotechnological products, petroleum fuels, and numerous metal products. The processing of these products and their by-products has had a major impact on the environment. Tougher air and water quality standards have led to the development of new sealing systems that far exceed performance requirements for emission control. New seal technology has resulted in non-contacting non-leaking seals for conventional pumps handling difficult services. Design and application of this seal technology is presented in this article. Comparison of competing technologies is discussed and life cycle costs are given. Clearly, gas lubricated non-contacting seals for pumps are becoming the choice of sealing technologies for plant operators on difficult services. These systems are proving to be very economical.     

A fracture mechanics based model for the analysis of seal effectiveness

The fluid containment in vessels, pipes, containers, etc. often requires the use of seals in order to assure the absence of leak in the junction zones. Sealing mechanism is typically achieved through the use of elastomeric elements that form contact with the surrounding rigid materials the containers are made of. A proper design and safety evaluation of the containment capacity of seals requires the careful evaluation of the contact pressure distribution between the soft (seal) and hard (vessel) elements. In the present paper such a problem is considered and solved through contact stress and strain evaluation based on fracture mechanics; numerical and experimental analyses on elastomeric elements are considered in order to verify the proposed modeling procedure. It is shown that the desired safety level against leakage can be ensured on the basis of the classical fracture mechanics parameters when the seal crack tip exists, or through contact strain assessment when the stress singularity vanishes. Such results can be useful in the design of seal shapes and for estimating the pressure to be applied to the sealed bodies in order to guarantee no leaks. Finally, some final relevant conclusions on the present study on leak containment are drawn.     

Contact stress analysis on the X‐shape ring

A X‐ring is a loop of elastomer with X‐shaped cross‐section used as a mechanical seal or gasket. Such a X‐ring is designed to be seated in a groove and is compressed during assembly between two or more parts, creating a seal at the interface. The seal is designed to have line contact between the X‐ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the X‐ring shell body. This study aims to detect the contact stress and the deformed shape of a X–shaped ring shell under various compression conditions. For this analysis, four experiments were conducted to obtain material properties of the elastomer. The contact stress analysis is performed by applying material properties that we obtained through experiments. A contact stress analysis is carried out by finite element analysis.     

Designing mechanical seal for stable operation using advanced computer tools

A new generation of computer tools, to simulate and optimise seal behaviour under realistic operating conditions, is accelerating the pace of seal technology for improved performance and reliability. John Crane International has developed a comprehensive analytical tool, which solves for the complete two-dimensional transient heat transfer in equilibrium with interface loads and seal component distortions. It can also be used to design seals to give the most consistent seal behaviour and consequently improved reliability.     

液膜密封振动及冲击动力学特性

液膜密封运行过程因工况瞬时变化、系统振动及润滑不足等因素易引发端面接触冲击,严重影响密封寿命。建立考虑端面接触的液膜密封动力学模型,采用直接数值求解方法对运动方程、质量守恒空化边界雷诺方程、微凸体接触方程在全时间域内耦合求解,研究了液膜空化、轴向扰动及运行工况瞬变对密封稳定性与冲击特性的影响。结果表明:液膜空化有效提高了系统抗干扰能力,膜厚越小,受扰动后震荡频率越大且恢复至稳定状态的时间越长;发生端面冲击时膜厚振动频率显著大于全液膜状态下所受扰动情况。随转速及密封腔压力变化值的不断扩大,接触载荷值及冲击频率均不断增大,冲力响应越显著,在端面接触发生瞬间有明显的速度方向突变。     

Compressor seals for hydrogen recycle service

Hydrogen recycle service has presented a special challenge for centrifugal compressors and particularly the casing seals, mainly because of contamination from process gas. This feature, reproduced with permission from the Turbomachinery Laboratory, reviews a simplified process to identify the sources of contaminants affecting both dry and wet seals. It lists precautions for the application of dry seals in this service, and discusses improvements to materials used for a wet seal design. Finally, it highlights two case histories where retrofits with the improved liquid film seal have significantly reduced sour seal oil leakage rates.     

偏心率和转速对迷宫密封力和动力学参数影响分析研究

通过数值方法和商用CFD(计算流体动力学)软件对密封-转子系统进行建模和求解,研究了5种偏心率和5种转速下的计算机求解时间、流场压力分布、密封力的变化情况,并对泄漏量影响分析和迷宫密封动力学参数影响进行分析研究。研究结果表明:该方法能较好地模拟计算迷宫密封泄漏量和动力学参数,得到腔室压力随着偏心率增大而增大,密封切向力随着偏心率、转速的增大而增大,密封径向力随着偏心率、转速的增大而负向增大;通过密封长度、密封间隙、密封压差对泄漏量影响计算,三者变化率分别为6.62%,65.21%和69.97%,表明密封间隙和压差变化是影响泄漏量变化的重要影响因素;通过密封压差和密封长度对动力学参数影响分析,得出增大密封压差和密封长度不利于系统稳定、增大密封间隙会使得系统趋于稳定。     

The design and selection of materials for a general purpose mechanical seal

The predominant requirements for mechanical seals for use on modern continuous process plants are reliability, safety and ease of fitting & maintenance. Many users do not have specific engineering skills to select specially designed seals for particular applications. Nor do they have the fitting skills on process plants to deal with complex mechanical seals which may have many individual components which require expert fitting on the plant itself. The need was therefore identified for a general purpose mechanical seal which was easy to select for a particular application, and was both safe and reliable in operation. This paper describes the design, testing, development and areas for application of the Flexibox FFET general purpose cartridge seal for standard metric and inch shafts and a wide range of process and industrial machines, handling liquids — as varied as water, oil, chemicals and slurries.     

Salvaging the cost of discarded lip seals

With its new OmniLip-RS, Furon Company calims to have launched the very first rebuildable lip seal. A new concept in sealing, the device is designated to eliminate the higher replacement costs and material waste associated with throw-away metal-cased seals… while bridging the performance gap between elastomer lip seals and more costly mechanical face seals.     

Vakuum‐Lineardurchführungen mit Magnetflüssigkeitsdichtungen

Vacuum linear feedthroughs with magnetic fluid seal A magnetic fluid sealed feedthrough is a device that transmits linear motion into a vacuum chamber with minimal frictional resistances and minimal contamination level.They are widely employed in high and ultra‐high vacuum equipment among others in semiconductor fabrication industry and robotics applications. The operating conditions of magnetic fluid seals during reciprocating motion are so different from those with rotating motion that the use of their conventional structures for reciprocating motion seals yield no good results. Analysis of sealing mechanism of magnetic fluid seal in reciprocating motion shows that the operation of these seals is affected by the carry‐over and the magnetic fluid deformation in the sealing gap, which depends on the velocity of reciprocating motion. The reduction of magnetic fluid quantity in the sealing gap,caused by the reciprocating motion of the shaft is reason of the seal failure. In the paper a short characteristic of magnetic fluid sealing technology , principle of sealing, behaviour of the ferrofluid and seal failure mechanism in the linear motion of the shaft are given. Moreover some new structure designs of vacuum linear feedthroughs with magnetic fluid seals, which have practical application value are presented.     

离心式压缩机密封动态特性分析及稳定性评价

稳定性问题是离心压缩机在向高端化方向发展过程中遇到的主要瓶颈,密封间隙内流体周向流动导致的压力在圆周方向不均匀分布是导致失稳的主要原因。采用数值模拟的方法预测密封的动力特性系数,有助于加强对密封机理的理解,实现密封结构的优化进而提高转子的稳定性和设计的可靠性。本文使用数值模拟的方法,首先基于ANSYS APDL语言,开发了参数化程序来构建迷宫密封、孔式阻尼密封及蜂窝密封的几何模型,采用ANSYS CFX软件,计算并比较三种密封的刚度及阻尼等动力学特性参数,研究结果表明孔式阻尼密封及蜂窝密封相对于迷宫密封可以提供更大的刚度和阻尼、且具有较好的密封特性。在此基础上,以孔式阻尼密封为对象,研究比较了不同孔间距,不同孔径的孔式阻尼密封,找到影响阻尼密封动力学参数的基本规律。最后以一台九级合成气压缩机转子为例,比较不同密封对转子稳定性的影响。CFD计算的结果预测了密封的动力特性以及密封结构参数对转子动力学特性的影响,可以指导密封的设计和压缩机改造,综合考虑性能和制造成本,实现优化设计。     

Investigating the performance of square ring under uniform squeeze rate and internal pressure

Transportation and controlling fluid flow under high pressures in pumps, valves, boilers and heat exchangers is a common exercise in the industries. The main challenge, however that has confronted designers and manufacturers of pumps and valves along with those responsible for the maintenance and upkeep of such types of machinery is managing leakages at the positions where the seals are used. One fundamental feature of seal packing is the ability of the seal to ′flow′ into the groove spaces and effectively block fluid from passing through them. The square ring has shown good ‘flow’ behavior in addition to offering low contact stresses. This research seeks to investigate the performance of the square ring. The Hertz contact theory and photoelastic experimental hybrid method are used in the study of the performance of the square ring under a squeeze rate of 20 % and varying internal pressure. It was observed that while increasing the applied internal pressure, the deformation length and angle increased due to the high stresses produced by the applied pressure. Additionally, was initiated at an internal pressure of 0.98 MPa.     

低熔封接玻璃组成及其发展

综述了低熔封接玻璃的组成特点，给出了大量低熔玻璃组成实例，批出了低熔封接玻璃的封接低温化和无铅化发展方向，磷酸盐玻璃是首选组成之一。新的制备工艺和新的玻璃形成体系将对封接玻璃发展起着十分重要的作用。     

Effects of Liquid Contaminants on Heat Seal Strength of low‐density polyethylene Film

Heat sealing is commonly applied for making form‐fill‐seal packages fabricated from thermoplastic films. One of the challenges frequently faced by the industry is inadvertent contamination of film–film interface by the product during filling, which can compromise package seal strength. In this study, the effects of dwell time (0.5–1.5 s), jaw pressure (28–1860 kPa), jaw configuration (narrow versus wide contact area) and jaw temperature (150°C–180°C) on the interface temperature and seal strength of a linear low‐density polyethylene (LLDPE) film were investigated. Three different film–film interface conditions were studied: (1) no contaminant; (2) with water contaminant; and (3) with vegetable oil contaminant. In the presence of liquid contaminant, jaw pressure played an important role in displacing the liquid from the seal area to form intact seals. Short dwell time (0.3 s) and low jaw temperature (150°C) was not favourable for forming intact seals in both water‐contaminated and vegetable oil‐contaminated films. The optimum jaw temperature and dwell time required to produce intact seals for oil contaminated films was 180°C and 0.3 s, respectively, whereas a combination of 165°C jaw temperature and 1 s dwell time was required to form intact seals for water‐contaminated films. Within the experimental conditions investigated, interface temperatures of 130°C–140°C resulted in the most optimum seal strength for both water‐contaminated and clean film specimens. Above 140°C, a weakening of seal strength was observed, presumably because of the change in melt flow characteristics and possible initiation of thermal degradation of the polymer. Copyright © 2011 John Wiley & Sons, Ltd.     

Feasibility of using a non-destructive ultrasonic technique for detecting defective seals

The feasibility of using a non-destructive ultrasonic technique for detecting defective seals was studied. It was found that ultrasonic velocity could be used to distinguish defective seals (containing wrinkles, voids, minute amounts of carrot, beef pieces, moisture or bentonite as contaminants) from a good seal. Also, there was a systematic correlation between ultrasonic velocity and the levels of contaminant.     

On friction reduction in rubber lip seals for rotating shafts

Rubber lip seals are widely used in the automotive industry, for sealing marine stern tubes, drainage pumps and as the seals built in to roller bearings. All seal users have the same requirements irrespective of usage: tightness and high durability.     

Effects of viscoelastic properties of engine cover sealing system on noise and vibration attenuation

Automobile engine cam cover seals are made of elastomeric materials and used to seal the interfaces between cover and underlying structures. The design of engine cam cover seals has been traditionally focused on the sealability aspects. Recently, there has been additional demand that these seals be designed as vibration isolators to attenuate the radiated noise from the engine. To accomplish this goal, the frequency-dependent viscoelastic properties of the sealing components will have to be considered during the design process. This article examines the frequency-dependent viscoelastic properties of some commonly used elastomeric seals at various mounting configurations. An analytical spatial transmissibility method is used for evaluating the design of elastomeric sealing system for reducing vibration and radiated noise.