Shaft Seal Research Articles

A design based on centrifugal inertia of rotational oil film for reducing pressure at shaft hole

Shaft seal covers a very wide range of machinery and applications. Lip seals, which are used for sealing shafts against the exit or ingress of liquids, are a type of shaft seal. Reducing the wear of the sealing ring and extending its service life can increase the time interval for machine maintenance and inspection. In this paper, a disk structure for reducing the pressure difference between the inside and outside of the lip seals is proposed. The disk structure forms a layer of rotating oil film on the seal ring, so the oil pressure near the seal ring is less than in a sealing chamber. First, based on the similarity principle and the hypothesis of von Kármán, a theoretical model of the rotating oil film was established, and the dominant influence of inertia of circumferential velocity and viscosity of radial velocity on pressure distribution was expounded. Then, an experimental device that can measure pressure distribution and temperature was constructed, and a pressure distribution measurement experiment was conducted. Based on theoretical models and experiments, it was proved that the rotating disk could generate a pressure drop and the pressure drop was a function of the square of the rotating speed. The influence of temperature and oil film thickness was studied, and it was found that the increase in the temperature and oil film thickness weakened rotational flow inertia and enhanced radial flow viscosity, increasing pressure within the oil film. Additionally, it was observed that the oil in the sealing chamber produced a sunken liquid level due to the stirring of the rotating disk, which would reduce the boundary pressure at the periphery of the oil film and produce a greater pressure drop inside the oil film.

Study of the Influence of Macrogeometry Parameters on the Tightness of Shaft–Seal Joints

The factors influencing the reliability and durability of the joint between a shaft and a rubber reinforced seal are analyzed. It has been established that the theory of tightness of such joints has not yet been developed. The quality of a joint is usually assessed by the amount of leakage. It has been revealed that the amount of leakage depends on the materials from which the shaft and seal are manufactured, the roughness of the shaft surface, the presence of dust in the friction zone, the quality of the sealed liquid, and the operating temperature. In addition, the durability of the work is influenced by macrogeometry parameters like deviation from the perpendicularity of the seal to the shaft, deviation from coaxiality, and radial runout of the shaft. A multifactorial experiment has been carried out, as a result of which an empirical relationship has been established between the radial runout of the shaft, rotational speed, and interference in the joint according to the criterion of the onset of leaks. Analysis of the obtained dependence showed that the radial runout should be compensated by interference in the joint, and with an increase in the rotation speed, the compensation value should be greater due to the fact that the working edge of the seal does not have time to follow the shaft. An empirical relationship between the amount of interference and leakage has been obtained, which indicates that with lower interference, leakage will be greater. The research results can be used at the stage of designing assembly units with seals to reduce the influence of radial runout and deviations from the coaxiality of the shaft relative to the seal.

Multiphase Conjugate Heat Transfer Analyses on the Assembly Situation of Rotary Shaft Seals

Rotary shaft seals prevent the exchange of fluid at shaft passages. Their function and service life depend decisively on the temperature in the contact area between the sealing edge and the shaft. Since the temperature depends on both the generation of frictional heat in the contact area and the heat transfer to the surrounding sealing system, the design of the sealing system is crucial. Within the scope of this work, multiphase conjugate heat-transfer analyses were performed considering different assembly situations. The computed results were presented and contrasted to experimental data. This resulted in a valid model for predicting the temperature in the sealing system, which provided insight into the influence of the sealing surroundings on the contact temperature.

Tribological Behavior Characterization and Fault Detection of Mechanical Seals Based on Face Vibration Acceleration Measurements

A mechanical seal is a common type of rotating shaft seal in rotating machinery and plays a key role in the fluid seal of rotating machinery, such as centrifugal pumps and compressors. Given the performance degradation caused by the wear to the face of the contact mechanical seal during operation and the lack of effective predictive maintenance monitoring methods and evaluation indexes, a method for measuring the acceleration of the mechanical seal face’s vibration was pro-posed. The influence of face performance degradation and rotational speed change on the tribo-logical regime of the mechanical seal was investigated. The proposed fault detection model based on support vector data description (SVDD) was constructed. A mechanical seal face degradation test rig verifies the usability of the proposed method. The results show that in the mixed lubrication (ML) regime, the vibration sensitivity of the face increases with the increase in rotational speed. With the decrease in the face performance, the vibration-sensitive characteristic parameters of the face in-crease and change from the ML regime to the boundary lubrication (BL) regime. The incipient fault detection model can warn about incipient faults of mechanical seals. Here, the axial detection result predicted that maintenance would be required 10.5 months earlier than the actual failure time, and the radial and axial detection results predicted required maintenance 12 months earlier than the actual failure.

Measurement device and automation solution for analysing tribologically damaged radial shaft seals

A new measurement device is introduced for analysing worn radial shaft seals (RSSs). This device enables unified and reproducible analysis and allows an automated nanoindentation for reliably detecting material changes at the seal edge.

The effect of seasonal variation of medium viscosity on centrifugal desanding in shaft seal water system of suction dredger: Numerical simulation and mechanism study

As a lubrication medium, the shaft-seal water often carries substantial sand particles in the cutter suction dredger, causing severe wear and tear of the internal components of the slurry pump. It has been proved that the shaft seal water system could be optimized by introducing a hydro cyclone to prolong the service life of the slurry pump. However, it was found that the seasonal variation of water viscosity would produce an obvious effect on the centrifugal separation of sand particles. Therefore, in this study, the influence of seasonal viscosity change on the flow field characteristics and sand particle separation was systematically studied by computational fluid dynamics (CFD). The simulation results showed that the fluid and pressure field in hydro cyclone has good symmetry under different viscosity. While with the increase of viscosity, the fluid resistance coefficient increases, resulting in a downward trend of turbulent kinetic energy and an upward trend of negative pressure zone, which is not conducive to sand particle separation. Moreover, to verify the consistency between simulation and actual industry, the grade efficiency of sand particles was studied and discussed. The average particle size of sand could be reduced from 37.8 μm to 8.1 μm, and the separation efficiency could reach 90% under better suitable dredging conditions (Salinity: 34%, Temperature: 20 °C). Further, the experimental and industrial results showed that the fish hook effect inevitably existed in practice due to the entrainment of coarse particles. This study would provide theoretical support for the subsequent optimization of the shaft seal water system.

A non-uniform pressure distribution model on the end face in screw expander and shaft seal leakage characteristics{fr}Etude des paramètres de la Structure sur les fuites d'arbres dans un expandeur à vis basé sur un nouveau modèle de distribution de pression non uniforme sur la face d'extrémité

Pressure distribution on the end face of screw expanders is the primary premise for calculating shaft seal leakage and axial force. Different from other types of expanders, pressure distribution on the screw expander end face is not only affected by operating conditions but also closely related to rotor geometric parameters. To illustrate the leakage characteristics of shaft seal in screw expanders, a non-uniform pressure distribution model on the end face was proposed, and a thermodynamic leakage model in the shaft seal was established. Labyrinth seal, the most widely used sealing assembly, was taken as an example to study the effects of shaft seal parameters on leakage. The influence of four main parameters, namely tooth tip clearance, cavity depth, cavity width, and clearance on the rotor end face, on the leakage of the shaft seal was studied. The results show that pressure on the screw expander end face is non-uniformly distributed, and the average pressure is far less than the highest operating pressure. Moreover, the leakage through the shaft seal rises rapidly with the increase of end face clearance and tooth tip clearance, and a 0.1 mm increment of them can lead to increased leakage up to 108.6% and 52.5%, respectively. And the leakage drops with the increment of cavity width. There is an optimal depth-to-width ratio of about 0.13 for minimum leakage. Clearance on the rotor end face has the most significant influence on the leakage of the seal, followed by the tooth tip clearance, cavity width, and cavity depth.

Radial shaft seal with different relative velocities and on a 3D printed counter surface

PurposeThe purpose of this study is asking for a methodologically representable relation between different relative velocity approaches, counter surfaces and the tribological behavior of the radial shaft seal (RSS).Design/methodology/approachThe tribological behavior between the seal and the counterpart is examined experimentally to submit significant measured values. The correlations among seal elements, relative velocity approaches and counter surfaces with more aspects are searched.FindingsA basis for future research regarding optimization options for service life extension of the RSS under different operation environments has been set. New insights for the performance of 3D-printed counter surface are gained as well as the application possibility of that is searched.Originality/valueThe applied measuring procedure in investigation part especially the usage of different approaches in relative velocity approaches is designed with originality. In particularly, the usage of a 3D-printed counter surface comes for the first time in a scientific work.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0325/

A parametric optimization approach for radial shaft seal production processes for rubber waste reduction

While engineered rubber products (ERP) offer excellent mechanical and thermal properties suited for demanding industrial applications, the diversity of materials, equipment and processes involved in their processing poses challenges to their cleaner production. Existing literature canvasses recycling and reusing of products at the end-of-life (EOL) stage of the ERP life cycle to control their environmental impact. This research is focused on modes of reducing waste generated in the ERP production processes to minimize the environmental impact at the production stage of the life cycle. A novel experimental procedure grounded on the Shainin System (SS) principles is developed for parametric optimization in complex batch process settings. Unlike the established design of experiment (DoE) approaches based on statistical models, the proposed experimental procedure is based on sequential observational plans to reduce the search space while identifying the dominant family(ies) of causes (called Red X) of niggling defects. The application of the proposed experimental procedure is illustrated at an auto-ancillary cluster in India for reducing the rejection of radial shaft seals (RSS) due to rubber moulding defects. The case study's findings showed a reduction in the cluster's carbon footprint (i.e. 11,715 kg CO2-eq across the cluster), and overall production cost (saving of USD 1.20 million/annum) due to process improvements in the RSS moulding and assembly process.

Multiscale Structural Mechanics of Rotary Shaft Seals: Numerical Studies and Visual Experiments

Although rotary shaft seals have been used successfully in many industrial applications for decades, their tribological behavior is still not completely understood. In-depth knowledge of the structural mechanics is essential for the design and optimization of such sealing systems. High complexity results from the multiscale interactions in the tribological system rotary shaft seal. Large macroscopic deformations occur due to the hyperelastic material behavior of elastomers coupled with microscopic tangential distortions of the sealing edge surface in the contact area. This paper includes both numerical and experimental studies on the tribological behavior of rotary shaft seals. A multiscale finite element model provides the simulation of the macroscopic deformations and the microscopic displacements. A test rig equipped with a hollow glass shaft enables in situ visual contact analyses, qualitative determinations of pressure distributions and quantitative measurements of elastomer surface distortions. The optical phenomenon of frustrated total internal reflection enables qualitative evaluations of the pressure distribution. Particle image velocimetry (PIV) is employed to quantify the tangential distortions. The test rig enables the measurement of the friction torque with the same configuration. The results of the numerical and experimental investigations for the radial load, friction torque and tangential distortions are compared and discussed. This serves to validate the simulation methods and the correlation of the measured parameters. This finally results in a solid and validated basis for further tribological investigations of rotary shaft seals.

Radial shaft seals: How ageing in oil and hyper-viscoelasticity affect the radial force and the numerically predicted wear

In this paper, a comprehensive finite element model is revised and improved to investigate the role of ageing and viscous effect in the clamping force decrease and the predicted wear. The finite element model considers the effects of actual seal geometry, seal wear, shaft wear, temperature, rubber viscoelasticity and ageing. The comprehensive modelling approach, the application of actual seal geometry determined by newly developed measurement approaches, and temperature- and ageing-dependent hyper-viscoelastic constitutive constants obtained by simultaneous consideration of quasi-static and dynamic test results are the novel characteristics of this study. It was found that the applied ageing has a moderate while the viscous nature of rubber has a significant effect on the clamping force and predicted wear of seals.

Preventing drift of oxygen isotopes of CO2-in-air stored in glass sample flasks: new insights and recommendations

ABSTRACT It is known that the oxygen isotope composition of CO2-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes. A drying method to remove any water sticking to the inner walls by evacuating the flasks for more than 72 h while heating to 60 °C significantly decreases drift of the oxygen isotopes. Moreover, flasks not dried with this method showed higher differences among drift rates of individual flasks. This is explained through the buildup of H2O molecules sticking to the inner walls. Humidity of the air samples in the flasks as well as surface characteristics will lead to differences among flasks. Results also show that permeability of water is higher through Viton O-ring flask seals than through polychlorotrifluoroethylene (PCTFE) shaft seals, and that the stability of flasks sealed with the latter is significantly better over time.

Characterisation of the conveying effect of turned radial shaft seal counter-surfaces using a simplified hydrodynamic simulation model

AbstractA typical sealing system for rotating shafts consists of the radial shaft sealing ring (RSS), the lubricant and the shaft counter-surface (SCS) of the rotating shaft. The properties of the machined surface of the SCS have an impact on the sealing system. The structural pattern of the SCS influences the lubricant flow along the axial direction. In this paper, a simplified micro scale hydrodynamic simulation model is presented in order to study and determine the axial flow of the lubricant induced by the SCS of the sealing system, isolated from the effects induced by the seal, to allow for a rating of the shaft surface. The influence of the seal was neglected to allow for a simplified simulation. Simulated shaft surfaces corresponding to different machining parameters of machined SCS are used as input. These variants of SCS were created using a kinematic model which simulates an ideal surface machining process of the shaft. A micro scale hydrodynamic simulation model is used to investigate the influence of machining parameters on the lubricant flow along the axial direction across the tribo-contact. From this investigation, the connection between parameters applied for machining of the SCS and conveying effects can be estimated. The simulation model is also validated with experimental results of hard turned shafts of different machining parameters. Differences between manufactured real surfaces and kinematically simulated surfaces are the cause of deviations between the results.

Fractional Order Active Disturbance Rejection Control for Canned Motor Conical Active Magnetic Bearing-Supported Pumps

Active magnetic bearings (AMBs) are electromagnetic mechanism systems in which non-contact bearings support a rotating shaft using attractive forces generated by electromagnets through closed-loop control. For complete support of a five degree of freedom (DOF) rotor system, most AMB structures include two radial actuators and one for the axial direction. Conical active magnetic bearings (CAMBs) is one of the development directions of conventional magnetic bearings in which the requirement of the axial bearing can be eliminated. In this paper, we propose a structure with a CAMB integrated into a canned motor pump to eliminate the need for mechanical bearings and shaft seals. However, this system necessitates a more complicated control strategy due to a significant coupling effect between rotor motion and hydrodynamic disturbances. This paper presents a fractional order active disturbance rejection control (FOADRC) including a fractional order extend state observer (FOESO) and a proportional derivative controller (PD) to track and reject lumped disturbances actively. The proposed controller achieves better performance than the integer-type ADRC and traditional PID controller. The control performance of the proposed FOADRC is illustrated in terms of very good disturbance rejection capability that is demonstrated through MATLAB/Simulink simulation results.

Study on the Sealing Performance of O-ring under High-Pressure Environment

The sealing properties of the O-ring of the hydraulic cylinder plunger rod under a high-pressure environment are related to a variety of factors. In this paper, we first establish a simulation model based on an O-ring reciprocating shaft seal under a high pressure-environment through finite element software and study the influence of the compression rate, static pressure, and reciprocating speed of the plunger rod on the sealing performance of O-ring through the simulation model, and then analyze the maximum stress of O-ring during installation, hydrostatic loading and reciprocating motion with the variation of structural parameters. The results indicate that the compression rate of the installation process has a significant effect on the sealing performance of the enhanced O-ring. In the hydrostatic loading process, the equivalent stress of the O-ring is increased with the increase of the compression rate, when the static pressure is low and decreases, and when the static pressure is high, and the equivalent stress shows an increasing trend and the same increase; in the reciprocating motion process, when the static pressure is low, the equivalent stress and contact stress of the O-ring does not change significantly with the compression rate, and when the static pressure is high, there is an obvious phenomenon of abrupt change. The frictional stress of the reciprocating motion is increasing, then decreases, and then increases with the change in static pressure.

Retracted: Friction Performance Analysis of Reactor Coolant Pump Shaft Seal Based on Sensor and Computer Simulation

Retracted: Friction Performance Analysis of Reactor Coolant Pump Shaft Seal Based on Sensor and Computer Simulation

Multi-step prediction of main pump leakage in nuclear power plants with an additive model

With the global demand of clean and low-carbon emission energy sources, safety in the nuclear power industry has gained widespread attention. The accurate and timely long-term fault prognostics of critical equipment in nuclear power plants (NPPs) helps to effectively schedule maintenance, thus reducing operation and maintenance costs while ensuring safety. Unpredictable future load and operations make long-term prediction of time series data in NPPs quite challenging. In this study, we proposed a framework for multi-step prediction based on an empirical mode decomposition (EMD) algorithm, which decomposed complex time series data into several components with simple trends. The useful signal and noise in the components were then divided by a relative ratio method. Candidate prediction models from the model library were trained and tuned on the signal-dominated components. The appropriate model was selected for prediction according to the characteristics of each component signal, and the prediction results were summed and smoothed with an additive model. The proposed method, noted as the denoised EMD method using an additive method (EMD-AM), was applied to the leakage prediction at shaft seals in the reactor coolant pump (RCP) of five different NPPs. Root mean square error (RMSE), mean absolute percentage error (MAPE) and mean absolute scaled error (MASE) were selected to determine the prediction accuracy and uncertainty. Compared with EMD-AM and EMD method using long short-term memory (EMD-LSTM), the experimental results show that the denoised EMD-AM has the overall advantage of simplicity and accuracy.

Multiphase Computational Fluid Dynamics of Rotary Shaft Seals

The primary task of rotary shaft seals is to prevent an unwanted fluid transfer between two areas. In shaft passages of gearboxes, for example, rotary shaft seals avoid the leakage of transmission oil to ambient air. This means the flow in the lubricant film in the sealing gap between the sealing edge and the shaft surface consists of at least two phases. Taking the phenomenon of cavitation into account, the flow consists of three phases. This study aims to provide an in-depth understanding of the multiphase flow in the lubricant film of rotary shaft seals. As experimental studies of the flow processes on a microscale have proven to be quite difficult, a simulation-based approach is applied. Computational fluid dynamics (CFD) serves to compute the transient multiphase flows in the lubricant film in the sealing gap. The computational domain is a three-dimensional microscale model of the lubricant film. The results show the transient hydrodynamic pressure buildup and the dynamic phase interactions during operation. This study provides far-reaching insights into the multiphase flow processes in the lubricant film in the sealing gap and simulation-based evidence of the lubrication and sealing mechanism of rotary shaft seals.

Numerical Prediction of Internal Flows in He/LOx Seals for Liquid Rocket Engine Cryogenic Turbopumps

Cryogenic turbopumps are used in high-performance, lightweight liquid rocket engines for space applications. The development of bearings and shaft seals for cryogenic turbopumps requires detailed characterization of the internal flow, taking into account the effects of boiling and multi-component two-phase flow. Here, a flow network solver was developed to analyse the secondary flow circuit of a cryogenic turbopump where the propellant is mixed with high-temperature helium after bearing cooling. The network solver is based on an extension of a classic 1D homogeneous model, originally developed for a pure substance, to the case of two-phase multi-component flow. The solver is capable of predicting pressures, temperatures, flow rates, and species concentrations in a complex two-phase flow in the presence of non-condensable gases. The unsteady mass, momentum, and energy conservation equations are implemented in conjunction with the thermodynamic equations of state using a general-purpose finite volume formulation, where the pressure drop and the heat transfer are calculated using correlations. The numerical tool was validated by comparing its predictions with experimental data obtained during tests on the secondary circuit of an oxygen turbopump developed at Avio S.p.A. A number of engine operating conditions were considered (inlet helium temperature in the range of 250–280 K, helium/liquid oxygen drain in the range of 165–230 K). The predicted temperature values showed good agreement with the experimental data in most conditions.

Assessment of the Lubricity of Grease‐Sealing Rotary Shaft Seals Based on Grease Properties

AbstractGrease‐lubricated sealing systems have an increased risk of starved lubrication. For this work, the lubricity of 23 greases in a rotary shaft sealing system was evaluated with a new test and evaluation method. The lubricity was then correlated with rheological and other grease properties. These grease properties are either available by the data sheet or can be measured with low effort. The results of the correlation allow a preselection of greases which are expected to lubricate rotary shaft seals well. This can support manufacturers and users in considering the lubrication of the sealing system early in the development process.