Seal Friction Research Articles

Multi-Physical Field, Coupled, Mixed Lubrication Analysis of Hydraulic Reciprocating Vacuum Lip Seal

Engineering practice has demonstrated that seal failure can result in severe leakage and wear, reducing the efficiency of hydraulic systems and even leading to major safety risks. Currently, analyses of the thermal aspect of seal interfaces are relatively limited, with most studies focusing on mechanical analysis. However, in actual applications, temperature has a significant impact on sealing performance. In this paper, nonlinear elastomechanics, viscous fluid mechanics, micro-contact mechanics, micro-deformation theory, and thermodynamics are coupled to establish a mixed lubrication model considering the thermal effect. The reliability of the mixed lubrication model is verified through experiments, and the temperature distribution of the oil film in the sealing area and the temperature distribution of the seal ring are simulated. Finally, the effects of the reciprocating speed, root mean square roughness, fluid medium pressure, and seal pre-compression on seal friction force and leakage are investigated. The results show that the heat generated in the sealing area accumulates at the bottom of the V-ring. Under the same conditions, compared with the instroke, the temperature-rise area of the outstroke is biased to the left and the increase in temperature is greater. In addition, the piston rod speed and the preliminary compression of the seal ring have a greater impact on the overall seal friction force and leakage. Under a lower seal pre-compression, the RMS roughness has a great influence on the leakage and friction in the outstroke, while the impact of the internal stroke is limited.

A pressure-triggered isobaric sequential liquid sampling system for full-ocean-depth: Design and field deployment

Collecting pressure-retaining deep-sea liquid samples is important for the research on in-situ environment and life. A pressure-triggered isobaric sequential liquid sampling system (PTISLSS) was developed for the collection of seawater at target depths. The sampling system comprises six independent seawater collection modules, each containing a titanium sample container and a pre-charged accumulator. A motor-driven sampling mechanism was designed to open and close the fluid channels at depth. Theoretical studies have indicated that the mechanism can generate a contact pressures of up to 160 MPa to ensure the sealing of the samples. The relationship between the pressure of pre-charged gas and the volume of fluid sample has been derived considering the effects of seal friction. The sampling system was built for full-ocean-depth sampling operation and the reliability of the system was tested at a pressure of 120 MPa. The field test was conducted in the West Philippine Basin on a recent scientific research cruise. Pressurized seawater from depths of 2000 to 4500 meters was recovered, and the pressure-retaining rate exceeded 93.5%. The developed sampling system presents satisfactory performance and high operational efficiency, and it will have a wide range of applications in the field of large-scale deep-sea sampling.

The improvement of wear and corrosion resistance of nickel-graphite coating with modified graphite phase size

The corrosion resistance, friction and wear properties of an abradable seal coating are highly dependent on the size and distribution of lubrication phase. In this work, nickel-graphite (Ni-G) coatings were fabricated by a supersonic atmospheric plasma spraying system (SAPS) and a standard atmospheric plasma spraying system (APS), respectively. The effect of size and distribution of graphite phase on the performance of Ni-G coatings was investigated. The results suggested that the SAPS coating had an average single graphite phase area of 35.4 ± 5.1 μm2, which is approximately 35.4 % less than that of the APS coating, while the average graphite phase width and length in SAPS coating decreased by 22.2 % and 16.7 % compared to the APS coating. The fine distributed graphite phase improved the formation of structure with a small cathode and a large anode, which effectively increased the corrosion resistance of SAPS coating. The reciprocating sliding friction facilitated the creation of a uniform and uninterrupted lubricant layer, attributed to the finely dispersed graphite phase of SAPS coating. In comparison to the as-sprayed and subsequent corroded APS coatings, the friction coefficients of the SAPS coating exhibited a reduction of approximately 9.1 % and 13.3 %, respectively. The aforementioned findings showed that the small-sized graphite phase was conductive to the improvement of corrosion resistance, friction and wear properties of Ni-G abradable coatings.

Soft Sensor Technology for the Determination of Mechanical Seal Friction Power Performance

Mechanical seals ensure the internal sealing of centrifugal pumps from the surrounding environment. They are one of the most critical components in a centrifugal pump. For this reason, the condition of mechanical seals should be monitored during operation. Mechanical seal friction power is an important component of mechanical losses in centrifugal pumps and is used as an indicator of wear and therefore seal condition. The soft sensor described in this paper is based on temperature measurements at the seal and can be used for determining the frictional power performance. A major factor in determining frictional power performance is the heat transfer between the mechanical seal and the medium inside the pump. For calculating the heat transfer, the stationary temperature fields in the rings of the mechanical seal are described by transmission efficiencies. The root mean squared error was determined for steady-state operating conditions to assess the quality of the soft sensor calculation. The frictional power performance can be determined by recording the temperature at the mechanical seal mating ring and the medium. The algorithm detects when the steady-state operating conditions change but does not map the dynamic changes between the stationary operating conditions.

Study on the thermal-stress coupling simulation and surface friction of mechanical seal for water pump

In view of the problems that the mechanical seal for the water pump is prone to deformation, friction and wear, and loss of sealing performance in the process of use, taking the temperature change of end surface as the research entry point, the temperature distribution, stress and strain diagram of rotating ring, and stationary ring are obtained by thermal-stress coupling simulation. The temperature change of stationary ring is studied by the experiments, and the friction state of end surface of rotating ring and stationary ring are observed. The results indicate that the test temperature of stationary ring is slightly lower than simulation temperature, which is related to the thermocouple fixed on the side of the stationary ring for temperature measurement. In addition, comparing the micro morphology of end surface of rotating ring before and after the experiment, it is found that there is significant plastic deformation on the inner diameter of rotating ring, which is related to the stress generated by the thermal-mechanical coupling of inner diameter of rotating ring exceeding the material limit, consistent with the simulation results.

Influence of diamond-like carbon coatings and micro-texturing on friction and wear of seal interfaces: Experiment and simulation study

For mechanical seal friction vice in dry friction conditions, due to friction wear serious failure, is the slurry pump and other instruments in the operation of the process of the urgent need to solve the problem. In this paper, in order to optimize and enhance the friction and wear problem of mechanical seal end face of slurry pump. Surface treatment of mechanical sealing rings with diamond-like carbon (DLC) coating and surface microtexturing, and at different rotational speeds and normal forces, the surface hardness, wear coefficient and dry friction coefficient of the sealing rings were analyzed by experimental comparison, and the wear morphology was collected by electron microscopy, having analyzed the results of the sets of, the end face structure of the mechanical seal was optimized. Based on Archard wear model simulation calculations, the seal ring wear depth and wear quality were obtained. The results show: under dry friction conditions, the synergistic effect of the DLC coating and the surface micro-texture (MT), the coefficient of friction is reduced by approx. 68% and the quality and depth of wear is minimized. Excessive speeds and normal forces are more prone to wear behavior caused by abrasive wear. Simulation results of surface treatment groups, DLC / MT group maximum wear depth is the smallest; wear quality test and simulation of the maximum error within 15.7%. The results of the study can provide a basis for a phosphoric acid plant slurry pump mechanical seal design.

Multi-Field Coupling Numerical Analysis and Experimental Validation of Surface-Textured Metal Seals in Roller Cone Bits

Metal seals play a crucial role in ensuring the dependable functioning of the bearing system in roller cone bits. Due to the intricate nature of downhole conditions, the microstructure design of sealing end faces, specifically the surface texture, is rarely used in metal seals. This study focuses on examining the applicability of surface texture technology in metal seals for cone bits to enhance the lubrication characteristics and friction and wear properties of liquid film between end faces. A multi-field coupling model of surface-textured metal seals was established and experimentally verified. The liquid film carrying the capacity and sealing performance of five different shapes of surface-textured end faces (circle, ellipse I (horizontal), ellipse II (vertical), triangle, and chevron) were investigated under varying rotational speeds and environmental pressures. The influences of texture parameters, including depth and area ratio, on the lubrication characteristics and friction reduction effects of surface-textured metal seals were investigated, and the microscopic wear morphology characteristics of the sealing end faces were analyzed. The results show that surface textures can effectively improve the liquid film state and comprehensive performance of metal seals. Specifically, triangle textures significantly enhance the hydrodynamic pressure effect and weaken the abrasive wear and adhesive wear of the end faces. However, when the environmental pressure is p ≥ 30 MPa, the surface textures gradually lose the advantages of dynamic lubrication but can still reduce friction. The proper texture depth and area ratio can achieve zero leakage (obtained theoretically) and minimal friction in metal seals.

Tribological investigation of friction coefficient in pneumatic seals with a special pin-on-disc setup

This article presents an experimental method for measuring friction in seals for pneumatic actuators using a pin-on-disk tribometer in a linear reciprocating sliding motion. A special device was designed to test a segment of seal cut out of a seal ring to replicate the working conditions of the piston seals. Friction tests were carried out with spring-energised seals made of graphite-filled PTFE. The counterpart for the friction test was a portion of an actual cylinder barrel of a pneumatic actuator. The coefficient of friction was measured under different loads to replicate several mounting preloads. Moreover, the experimental results were compared to the friction coefficient measured with a flat pin of the same seal material against a flat counterpart. The comparison between the two test setups allowed the authors to study the effect of the contact geometry and the applied load on the tribological performance of the seal. These preliminary measurements of stiffness and coefficient of friction are the basis for further investigations and measurements of elastic, viscoelastic and friction properties at the lip-barrel contact to develop a wear-damage model of lip seals.

Design, manufacture, and experiments of lightweight CFRP hydraulic cylinder tube without metal liner

AbstractHydraulic cylinders are widely used in aircraft rudder surface control, landing gear retraction, flaps and speed brakes retraction, ground steering driving, and engine thrust reverser control. The huge weight of hydraulic cylinders severely limits the aircraft's potential for increased range, maneuverability, energy efficiency, and carrying capacity. To achieve the maximum weight reduction, the carbon fiber reinforced polymer (CFRP) hydraulic tube without a metal liner is designed in this paper. In response to the lack of a parameter calculation method for CFRP hydraulic tubes, the accurate calculation method is developed through mechanical modeling and analysis of parameter influence law. For the structure design challenges of connection, sealing, and friction of CFRP hydraulic tube without metal liner, we have proposed and verified the wave contour inlaid structure, three leak‐proof solutions of the connection interface, the leak‐proof structure of the wound CFRP body and the seal friction pair. For the difficulties of multi‐material and high‐precision molding, a new process of split manufacturing‐combined molding is developed to achieve high‐precision and low‐cost manufacturing. Finally, the prototype is manufactured and tested by the presented method, and its weight reduction ratio is 56.64% compared with the original metal hydraulic tube. This study has further matured the application of CFRP hydraulic tubes without metal liners and has great lightweight benefits in aircraft.Highlights CFRP hydraulic tube without metal liner is designed to reduce weight. An accurate calculation method of CFRP parameters is developed. Connection structure, leak‐proof structure, and seal friction pair are designed. The high‐precision and low‐cost molding process is innovatively proposed.

Mechanical seal friction condition monitoring based on bispectral characteristics

PurposeThe purpose of this paper is to investigate the monitoring of the friction condition of mechanical seals.Design/methodology/approachAcoustic emission signals from the friction of the seal end face were obtained, and their bispectral characteristics were extracted. The variation of non-Gaussian information with the degree of friction was investigated, and by combining bispectral characteristics with information entropy, a bispectral entropy index was established to represent the friction level of the seal end face.FindingsIn the start-up stage, the characteristic frequency amplitude of the micro-convex body contact is obvious, the friction of the end face is abnormal, the complexity of the system increases in a short time and the bispectral entropy rises continuously in a short time. In the stable operation stage, the characteristic frequency amplitude of the micro-convex body contact varies with the intensity of the seal face friction, the seal face friction is stable and the bispectral entropy fluctuates up and down for a period of time.Originality/valueThe bispectral analysis method is applied to the seal friction monitoring, the seal frequency domain characteristics are extracted, the micro-convex body contact characteristic frequency is defined and the bispectral entropy characteristic index is proposed, which provides a certain theoretical basis for the mechanical seal friction monitoring.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2023-0242/

Evaluation of the operating conditions of the Stirling engine heat exchangers

The development of modern energy is inextricably linked with the further improvement of heat engines, which are still the only primary sources of mechanical energy on an industrial scale. Given the existing environmental problems, Stirling engines can be a good alternative to internal combustion engines and turbines. Of the many problems of creating such a sufficiently powerful and economical engine, it is customary to consider three main ones: 1) efficient transfer of large heat fluxes in the heater, regenerator and refrigerator; 2) creation of reliable and durable seals to hold the working fluid in the cylinder; 3) ensuring minimal friction in bearings and seals. And yet, of the three listed problems, the first should be given more attention, first of all, due to the unique conditions associated with the continuously changing thermo and mechanical loads. The instability of the loads is further complicated by the sharply different heat transfer coefficient on the external and internal heat transfer surfaces. That is, there are factors that contradict the requirements for the size of the heat transfer surface, the friction resistance of the working medium and the dead volume of the engine as a whole. In this regard, it is of interest to search for possible ways to reduce the effect of negative factors of non-stationary heat transfer in the calculation of heat exchangers. The current lack of suitable theoretical methods of calculation forces the use of semi-empirical methods. The aim of the paper is to assess the significance of the unique, characteristic of Stirling engines, the negative phenomenon of the delay in the flow of the working fluid in heat exchangers. For this purpose, a real kinematic diagram of the movement of the engine pistons with a rhombic drive by R. Meyer, created using the design program, is used. The analogue is the 4–235 type real engine of the Philips Company. In the calculations, a step-by-step procedure for calculating the time-varying parameters of the working fluid is used. The need for such a solution is due to the fact that in the rhombic drive of R. Meyer, the pistons movement and the change in the displaced volumes complexly depend on the angle of rotation of the engine shaft. In addition, the exact value of the real change in volume is possible only when the terms of the analytic equation of volume change under consideration are decomposed into a Fourier series.

Enhancing Quality Control of Chip Seal Construction through Machine Learning-Based Analysis of Surface Macrotexture Metrics

Efforts to enhance quality control (QC) practices in chip seal construction have predominantly relied on single surface friction metrics such as mean profile depth (MPD) or friction number. These metrics assess chip seal quality by targeting issues such as aggregate loss or excessive bleeding, which may yield low friction numbers or texture depths. However, aggregate loss, particularly due to snowplow operations, does not always result in slippery conditions and may lead to uneven surfaces. The correlation between higher MPD or friction number and superior chip seal quality is not straightforward. This research introduces an innovative machine learning-based approach to enhance chip seal QC. Using a hybrid DBSCAN-Isolation Forest model, anomaly detection was conducted on a dataset comprising 183,794 20 m MPD measurements from actual chip seal projects across six districts in Indiana. This resulted in typical 20 m segment MPD ranges of [0.9 mm, 1.9 mm], [0.6 mm, 2.1 mm], [0.3 mm, 1.3 mm], [1.0 mm, 1.7 mm], [0.6 mm, 1.9 mm], and [1.0 mm, 2.3 mm] for the respective six districts in Indiana. A two-step QC procedure tailored for chip seal evaluation was proposed. The first step calculated outlier percentages across 1-mile segments, with an established limit of 25% outlier segments per wheel track. The second step assessed unqualified rates across projects, setting a threshold of 50% for unqualified 1-mile wheel track segments. Through validation analysis of four chip seal projects, both field inspection and friction measurements closely aligned with the proposed methodology’s results. The methodology presented establishes a foundational QC standard for chip seal projects, enhancing both acceptance efficiency and safety by using a quantitative method and minimizing the extended presence of practitioners on roadways.

Effect of Slide Diamond Burnishing on the Surface Layer of Valve Stems and the Durability of the Stem-Graphite Seal Friction Pair

This study analysed the condition of the surface layer of valve stems made of 317Ti steel after polishing and burnishing. Surface roughness, microhardness, and residual stress tests were carried out. The tests were carried out to determine the effect of the condition of the surface layer (especially non-standard parameters of surface roughness) of the stems on the durability of valves and to determine the possibility of obtaining a favourable state by means of sliding burnishing. Significant differences were observed in the values of the roughness parameters that determine the tribological properties of the surface, and higher surface microhardness and residual compressive stresses were obtained after burnishing. The durability of the stem-graphite seal in a reciprocating movement was tested, and the failure-free operation time of valves with burnished stems was approximately four times longer, which is the premise for recommending sliding diamond burnishing as a finishing treatment for valve stems.

Research on friction state monitoring method of liquid film seal during start-up based on acoustic emission

This paper proposes a method based on acoustic emission to achieve nondestructive testing of the friction state of a liquid film seal. However, the acoustic emission signal is susceptible to noise, and extracting the feature signal is challenging. To address these issues, we propose a signal processing method based on singular value decomposition and adaptive variational mode decomposition (SVD-AVMD). Additionally, we investigate the acoustic emission mechanism of the liquid film seal using the strength theory of shear strain energy and CEB contact model. We design a liquid film seal friction experiment based on acoustic emission technology to extract the characterization signal of the friction state of the liquid film seal using SVD-AVMD. Finally, we apply a convolutional neural network to identify the friction state of the liquid film seal. The results demonstrate that SVD-AVMD has a significantly better ability to capture the center frequency of each mode component and to recover each mode component compared to simple variational mode decomposition. SVD-AVMD can filter out background noise while retaining the most useful information to the maximum extent possible. Furthermore, the root mean square of the extracted AE signal is consistent with the description of the AE mechanism, achieving the goal of studying and judging the friction state of the liquid film seal end face. Finally, we show that combining the convolutional neural network and acoustic emission time-frequency characteristics can improve the recognition accuracy of the friction state of the liquid film seal.

Performance Analysis of the C/C Composite Cylindrical Reverse Inter-Shaft Gas Film Seal

The reverse inter-shaft gas film seal is a gas path seal used in the intermediate bearing cavity of an aero-engine, which is challenging to implement due to its special installation and usage conditions. This paper proposes a C/C (Carbon/Carbon) composite cylindrical reverse inter-shaft seal structure and carries out a performance simulation analysis based on bidirectional fluid–solid coupling technology. The results show that the cylindrical reverse inter-shaft gas film seal with double-layer C/C composite sealing rings with different material mesoscopic parameters can balance seal leakage and friction power consumption and is beneficial to improving the comprehensive performance of the seal. As the mesoscopic parameters of the inner sealing ring material increase in warp and weft density, the sealing leakage rate decreases, and the gas film force and gas friction power consumption all increase. As the pressure difference increases, the sealing leakage rate and gas film force increase. As the rotation speed of the inner and outer rotors increases, the seal leakage rate increases, and the gas film force decreases. A C/C composite sealing ring cylindrical reverse inter-shaft gas film seal has a lower leakage rate and larger gas film force than a graphite sealing ring cylindrical reverse inter-shaft seal, which confers certain performance advantages. The work in this paper can provide a reference for the design of reverse inter-shaft seals.

Temperature- and Frequency-Dependent Nonlinearities of an Integrated Hydro-Pneumatic Suspension with Mixed Gas-Oil Emulsion Flow

Hydro-pneumatic suspension (HPS) systems are increasingly being implemented in commercial vehicles and various industrial equipment, which is mainly attributed to the integration of adaptable nonlinear pneumatic stiffness and hydraulic damping properties. The integrated HPS design with a shared gas-oil chamber, however, leads to gas-oil emulsion flow within the suspension chambers, which intricately affects the internal and external properties of the HPS, especially under variations in temperature and excitation frequency. This study experimentally and analytically investigated the temperature- and frequency-dependent properties of the hydro-pneumatic suspension with the gas-oil emulsion. Laboratory experiments were performed under three different near-constant temperatures (30, 40, and 50 °C) in the 0.5–8 Hz frequency range. An analytical model of the HPS was formulated considering the effects of temperature on internal fluid properties, gas-oil emulsion flow between the coupled chambers, the dynamic seal friction, and polytropic change in the gas state. The internal parameters, including the gas volume fraction, the discharge coefficient of the emulsion, and the dynamic friction components, as well as the external stiffness and damping characteristics, were determined. The relationships between these properties and the system temperature, velocity, and excitation frequency were further investigated. The simulated responses obtained under different excitations showed reasonably good agreement with the experimental results of the HPS. The results suggested that increased temperature yielded greater equivalent stiffness and comparable damping properties of the system. The gas volume fraction, discharge coefficient, and magnitude of seal friction generally tended to increase with increasing temperature. Increased excitation frequency led to greater hysteresis in hydraulic damping force and seal friction, and reduced seal friction magnitude and Stribeck effect.

Research on Dynamic Seal Friction Torque Compensation for a Low-Slow-Small UAV Tracking System

To ensure reliable and accurate operation in a complex field environment for Low-Slow-Small unmanned aerial vehicle (LSS-UAV) tracking systems, a dynamic seal shafting structure consisting of a labyrinthine structure and a magnetic fluid seal ring is designed to protect important equipment, such as the infrared sensor, visible CCD and the laser rangefinder from erosion and oxidation by the external environment. A friction torque model is established for the system’s dynamic seal structure to ensure tracking accuracy of the system. The simulation results show that the closed-loop speed accuracy of the system is improved by nearly 10 fold after adding friction torque compensation. The actual test results show that including friction torque compensation can effectively reduce the start-up delay and speed fluctuation error, and the speed fluctuation error is reduced by more than 80% compared to that without friction torque compensation. The tracking accuracy of the dynamic LSS-UAV is reduced from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$56.44 \mu $ </tex-math></inline-formula> rad to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14.86 \mu $ </tex-math></inline-formula> rad after adding friction torque compensation, which meets the requirement of smooth and accurate tracking for LSS-UAV tracking systems, and verifies the effectiveness and accuracy of compensation for the dynamic seal friction torque.

Study of wear and friction heat generation models of finger seals based on energy theory of tribology system

Finger seals have a good application prospect in gas and steam turbine for power generation as an advanced contact flexible seal. The wear and friction heat generation properties of the finger seal have significant effects on leakage and life. In this study, a bilateral wear model and friction heat generation model were established to calculate the wear volume and temperature of the finger seal and rotor. In particular, the friction heat generation model considered the effect of wear and deformation (centrifugal and thermal) of both the finger seal and rotor. Both models were expressed as functions of the finger seal configuration, material properties, operating conditions, and several relevant parameters. To determine these parameters, a ball-disk friction and wear experiment and a finger seal wear and friction heat generation experiment were conducted. Both models were validated with experimental data, and both errors were less than 12%.

Experimental research on the friction and leakage of the metal rubber seal for reciprocating motion

Metal seals are widely used to solve the sealing problem in severe conditions. For reciprocating motion sealing problems, a metal rubber seal was proposed by combining the metal rubber (MR) materials with an axial opening C-shape jacket. In this research, to study the reciprocating sealing performance of metal rubber seals, a series of leaking experiments were carried out with a dynamic sealing test system. The friction force of the MR seal was measured under a variety of hydraulic pressure and velocity conditions. The static leakage principle of MR seals for axial sealing was presented based on Persson’s contact mechanics, and a circular gap leakage model was employed to describe the leakage during reciprocating motions. The static and dynamic leakage experiments of metal rubber seals for axial sealing were conducted, and the influence factors of leakage rates were analyzed.

Effect of snake-biomimetic surface texture on finger sealing performance under hydrodynamic lubrication

In recent years, surface textures have been found with extraordinary potential to improve lubrication of friction pairs, reduce viscosity, and improve wear resistance. To study the effects of surface textures in the finger sealing, as inspired by the snakeskin, four texture forms with different layouts are presented in this paper and comprehensive performance analysis is carried out under the condition of hydrodynamic lubrication. First, a numerical model of finger seals with surface textures under hydrodynamic lubrication is proposed based on the Reynolds equation. Then, finger seal performance analysis is carried out considering different texture surfaces in terms of forms, layouts, and geometric parameters. The results show that: (1) When the texture profile is consistent with the direction of rotor motion, it is beneficial to create better hydrodynamic pressure and improve sealing performance; (2) To achieve good friction and wear resistance of a textured finger seal, the texture depth should be as shallow as possible (<25 μm); (3) When the texture depth is equal to the seal clearance, the average dimensionless pressure reaches the greatest with smallest friction coefficient; (4) With the increase of the texture density, the average dimensionless pressure increases rapidly first and then gradually flattens, while the friction coefficient performs oppositely. Given the manufacturing economy, the suitable texture density is around 20% ∼ 40%.