Seal Contact Research Articles

Brush Seal Performance with Ideal Gas Working Fluid under Static Rotor Condition

The study investigated how variations in pressure ratio affect the leakage flow of a brush seal for both contact and clearance structures, in which the clearance is measured as the distance between the bristles tip and the rotor surface. This investigation utilized the Reynolds-Averaged-Navier–Stokes (RANS) equations alongside a two-dimensional axisymmetric anisotropic porous medium model. To verify the model’s accuracy and dependability, the obtained results were compared with previous numerical results and experimental observations, showing a satisfactory level of agreement. The results indicate that the predominant pressure drop occurs downstream of the bristle pack with the clearance model exhibiting a higher leakage rate compared to the contact model. Leakage increases proportionally with the pressure ratio, while axial velocity gradually rises and radial velocity experiences a significant increase. In conclusion, the leakage in the brush seal contact structure is significantly lower than in the clearance structure, resulting in the best performance.

Analytical method for contact characteristics of rubber shaft seals under dynamic eccentricity considering viscous effect

This study introduces a methodology for analyzing the viscous effect on rubber shaft seals under dynamic eccentricity. It models the radial motion of the shaft seal and quantifies the viscous force arising from the viscous effect. A 3-D FEM with a noncircular shaft is established, equating viscous force to the interference distribution equation. Then, simulated mounting yield contact characteristics. Findings indicate increased interference with the viscous effect and heightened sensitivity of contact characteristics to eccentricity and rotational speed variations. This approach enhances precision in calculating rubber shaft seal contact characteristics under dynamic eccentricity.

Study on the prediction of high-speed rotary lip seal wear in aero-engine based on heat-fluid-solid coupling

PurposeThis paper aims to investigate the effect of frictional heat on the wear of high-speed rotary lip seals in engines.Design/methodology/approachIn this research paper, the authors focus on the high-speed rotating lip seal of aircraft engines. Using the hybrid lubrication theory, a thermal-fluid-solid coupled numerical simulation model is established to investigate the influence of parameters such as contact pressure distribution, temperature rise and leakage rate on the sealing performance under different operating conditions. By incorporating the Rhee wear theory and combining simulation results with experimental data, a method for predicting the wear of the rotating seal lip profile is proposed. Experimental validation is conducted using a high-speed rotating test rig.FindingsThe results indicate that as the speed increases, the rise in frictional heat leads to a decrease in the sealing performance of the lip seal contact region. The experimental results show a similar trend to the numerical simulation results, and considering the effect of frictional heat, the predicted wear of the lip seal profile aligns more closely with the actual wear curve. This highlights the importance of considering the influence of frictional heat in the analysis of rotating seal mechanisms.Originality/valueThis study provides a reference for the prediction of wear profiles of engine high-speed rotary lip seals.

Measurement and prediction of thermal performance of automotive transmission radial lip seals

The paper reports on the use of a developed novel and specific test-rig for the assessment of performance of radial lip seals of automotive transmissions, with particular emphasis on determination of thermal performance. The test-rig can accommodate original components from a donor vehicle, thus accurately represents vehicular conditions. The specific aim is to experimentally determine the effect of shaft surface roughness parameters on the generated contact temperature. Excessive exposure to high temperatures can accelerate degradation and aging of elastomeric seals, resulting in increased wear. Corundum and CBN (Cubic Boron Nitride) ground shafts are used to ascertain the effect of surface roughness parameters in the shaft seal conjunction. An analytical thermal model is also developed in combination with temperature measurements to determine the exact temperature in the lip seal-shaft contact. It is shown that depending on the type of shaft surface grinding process some potential correlation exists between roughness parameters and generated contact temperatures. It is also shown that the contact temperature can be several degrees Celsius higher than those measured in the proximity of the seal contact.

Preliminary Wear Investigations With Pressure Actuated Leaf Seals for Superheated Steam Turbine Application

Abstract Pressure actuated leaf seals (PALS) are a promising technology for the modern load-follow operation of power plants and turbines. Their strength lies in their radial adaptivity, which enables a significantly smaller radial gap height than conventional labyrinth seals. In this paper, which is a continuation of ISUAAAT16-022 from 2022, the operating behavior with compressed air and shaft rotation up to 3000 rpm is investigated, including an analysis of the wear caused by frictional contact between the shaft and the seal leaves. This includes both concentric and eccentric contact behavior. The test seal with a nominal diameter of 300 mm is designed in such a way that it can be used in a similar design in subsequent industry-related superheated steam tests. In addition to the seal performance before, during, and after the wear-in process, the frictional torques, temperatures in the flow and on the shaft-contacting leaves as well as the material removal on leaves and shaft running surface are analyzed. The results show a basically robust operating behavior of the seal with moderate performance deterioration, which can be directly attributed to the increase in the clear gap. However, the shaft wear is higher than for other contact seals, so further investigations are necessary before use in practice is feasible.

Contact Mechanics between Torus and Pit Border for Developing Air-Seeding Seal in Aspirated Bordered Pits

Bordered pits in conifers have been recognized as a significant evolutionary characteristic that served to impede the spread of embolisms between tracheids. Nevertheless, there was a lack of comprehensive understanding regarding the mechanical properties of the torus and the pit border in relation to the formation of contact seals in aspirated pits. A solid mechanics model was developed to study aspirated bordered pits, incorporating the elastic deformation of the torus–margo structure and the contact behavior between the torus and the pit border. Ten pit samples were reconstructed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) pictures in order to develop mechanical models for pits in the stems of Platycladus orientalis. Due to the limited contact area on the torus surface, the contact pressure between the torus and the pit border exceeded the air pressure in aspirated bordered pits. The external force and the duration required to seal pits decreased when the pit diameter increased and the pit depth decreased. The augmentation of the torus and margo mass necessitated a lengthier duration for the closure of cavities. The findings presented in this study offered theoretical support for the capillary-seeding hypothesis. The aspiration in bordered pits mechanically depended on the structural and material characteristics of the torus and margo.

Influence of Top Seal Damage on Contact Seal in Ram Blowout Preventer.

Top seal failure of ram blowout preventer (BOP) is one of the main factors leading to well control risk. The constitutive model and parameters of nitrile butadiene rubber (NBR) were optimized by compression and tensile tests, and the failure analysis model of the contact seal of the ram BOP top seal was built. The nonlinear contact mechanical behavior of the connection part of the BOP top seal was analyzed by the finite element method. Then, the influence of corrosion and wear defects at the top seal position of the 2FZ35-70 BOP under rated working pressure on the contact seal were studied, and the results showed that the overall contact pressure distribution of the top seal corrosion defects was uniform, the local contact pressure of the corrosion pit edge increased, and the top contact pressure decreased. The overall contact pressure of the wear defect of the top seal decreased linearly, the contact pressure at the maximum depth of the wear defect was the smallest, and the contact pressure gradually decreased to both sides. Ultimately, to guarantee the safety and reliability of the ram BOP, it is suggested that the acceptable depths of the seal corrosion pit and the wear at the top of the ram BOP are 4.0 mm and 0.2 mm, respectively, thus the reliability evaluation problem of the quantitative seal of the ram BOP top seal is solved.

An Antioxidant and Intelligent pH-Sensitive Composite Film Based on Gelatin and Persian Gum Using Purple Carrot Extract

The present research is aimed at developing novel intelligent pH-sensitive films based on Persian gum and gelatin using purple carrot extract. To this end, films were developed by mixing polymer solutions containing Persian gum (5%) and gelatin (5%), in equal proportions and partially replacing distilled water of solutions with purple carrot extract at 0, 15, 30, and 45%. Total anthocyanin content, antioxidant activity, color indices, and tensile strength of films were evaluated. Purple carrot extract incorporation in the film caused a slight reduction in the lightness and an increase in the anthocyanin content, DPPH inhibition, yellowness, redness, and tensile strength. The sample containing 45% extract (anthocyanin concentration was 2.39 mg/ml) was selected as the best pH-sensitive film based on mechanical and antioxidant properties and evaluated in terms of moisture content, moisture absorption, pH, heat seal ability, thickness, contact angle, FTIR, X-ray diffraction, and colorimetric tests. The sensitivity of the film to pH changes was assessed in the range of 2-12. The color of the film changed from pink to blue as a function of pH. The results proved that films based on Persian gum, gelatin, and purple carrot extract could be used as novel food grade biomaterials to monitor the freshness/spoilage of food.

Numerical Simulation of Assembly Process and Sealing Reliability of T-Rubber Gasket Pipe Joints

Underground pipelines are vital parts to urban water supply, gas supply, and other lifeline systems, affecting the sustainable development of cities to a great extent. The pipeline joint, which is a weak link, may be seriously damaged during natural disasters such as earthquakes. The failure of pipe joints can cause leakage accidents, resulting in system failure and interruption, and even some secondary disasters. Herein, based on uniaxial and plane tensile test results of a T-rubber gasket material, the assembly process and sealing performance of a T-rubber gasket joint of a ductile iron pipe are numerically simulated using the Ogden third-order strain energy density function to fit the material constant. The simulation accounts for severe nonlinearities, including large deformations, hyperelasticity, and complex contacts. The effects of the assembly friction coefficient, assembly depth, and radial clearance deviation of the socket and spigot on the seal contact pressure are analyzed. The results suggest that the entire history of the deformation and stress variations during assembly can be clearly visualized and accurately calculated. For the different friction coefficients, the assembly depth corresponding to the sliding friction condition of the spigot pipe was 74 mm, while the minimum pushing force required to assemble the T-rubber gasket joint of a DN300 ductile iron pipe was 6.8 kN at the ideal situation with a friction coefficient of 0. The effective contact pressure of the rubber gasket seepage surface under various operating conditions is much higher than the normal pressure of municipal pipelines, thus indicating that the rubber gasket joint exhibits the ideal sealing performance. Furthermore, a certain deviation, which is about 20 mm, is allowed for the assembly depth of the rubber gasket joint such that the axial displacement of the pipe joint can be adapted under an earthquake or ground displacement.

A new design for the RF electron gun of the Iranian Light Source Facility (ILSF)

A new π mode RF electron gun is proposed for the Iranian Light Source Facility. This RF gun will be fabricated using a newly developed method based on clamping the parts together instead of vacuum brazing. In this method, RF contact and vacuum seal are mutually provided by a special copper gasket. The first section of this article describes the new π mode RF gun and its expected performance in detail. The report of our recent R&D tests on the new fabrication method is discussed in the next section. We performed the RF and vacuum measurements on a single-cell structure, and the copper gasket provided suitable RF contact, and a vacuum pressure of 2.5×10−7 mbar was also reached after 1 h of pumping with a turbo-molecular pump without baking. In the last section, we investigated using a high-current and low-emittance DC triode electron gun to be mounted on the RF gun as an alternative cathode assembly. The simulation results of this proposed scheme were compatible with our previous studies. The research and development of the new π mode RF electron gun and the proposed cathode assembly will begin soon.

Methodology for Counter Torque, Power Loss, and Frictional Heat for Brush Seals Under Eccentric Transients

Turbomachinery brush seals are used for achieving close clearance control with the aid of flexible bristles. Frictional forces between bristle tips and rotor surfaces induce counter torque, power loss, and heat generation during turbomachinery transients; all of these determine the overall efficiency, operation life, and stability of turbomachinery application. As a result of manufacturing tolerances, rotor dynamics-induced shaft deflections, and additional gyroscopic loads in aviation engines, eccentric rotor rub occurs toward brush seals in transients, causing partial rotor–seal contact with nonlinear radial interference and uneven tip force distribution. There is an inherent error in the current power loss and frictional heat rate analyses, as well as in counter torque methodologies, since they do not account for the uneven tip force distribution. In this study, a nonlinear radial interference profile of eccentric rotor contact conditions has been derived and its effect on contact angle has been examined with a comparative analysis with concentric rotor expansion. The methodology for counter torque, power loss, and generated frictional heat rate analyses has been detailed, and eccentric condition formulations have been derived with the surface integration of dynamic bristle tip force functions adopted from brush seal dynamic stiffness tests. Analysis of nonlinear interference and uneven contact force profiles has been conducted based on the combined effects of assembly conditions and eccentricity levels. Results obtained using the developed closed-form equations for eccentric rotor contact are compared with concentric rotor expansion and simple eccentric rotor rub analyses, which do not account for uneven tip forces.

Thermal compression and accumulation effect on lubrication regime transition mechanism of water seal

Research on the thermo-elastic water bearings (TWB) performance is mature, and the temperature effect on bearings lubrication regime transition is studied. The (TWB) lubrication model and numerical simulation of bearings forms the standard. However, the thermal compression and accumulation effect (TCAE) on the water temperature increase from the reciprocating frictional force in a enclosed seal system is ignored. This causes the seal lubrication mechanism and effecting on lifespan factors of TCAE has not been clarified. Thus, we propose the seal working at high pressure with a reciprocating speed of 0.1–0.6 m/s and temperature of 5–25 ℃. Taking the fluid-solid-thermal and wear (FSTW) simulation with measurement reveals the TCAE to seal performance. Results indicate that the seal contact regime increases vastly and the film formation dynamic characterize is hampered due to the TCAE even at the low initial temperature of 5 ℃. The improved insight is that the seal lubrication under TCAE transits obviously from the mixed lubrication to wear regime and degenerates to the elastic-hydraulic lubrication with the speed increasing. The seal lubrication transition mechanism and factors of failure with TCAE is discussed. Moreover, this study of TCAE also builds a framework for thermal models such as mechanical seals, lip seals, and others.

Measuring Maritime Paint Thickness under Water Using THz Cross-Correlation Spectroscopy

The shipping industry is a major contributor to global greenhouse gas (GHG) emissions, which is why it is important to optimize every aspect of the efficiency of ocean-going vessels. This includes the antifouling paint that ensures hydrodynamic efficiency. Measuring the thickness of the antifouling on top of all other paint layers using THz cross-correlation spectroscopy (THz-CCS) underwater could enable vessel operators to monitor the state of the paint on ship hulls and plan any vessel’s sailing route and maintenance optimally. However, due to the high absorption of water in the THz domain, measuring through any significant amount of water is impossible, making a water removal method necessary. This study shows how a THz-CCS system can be packaged for underwater measurements using a molded silicone contact seal. In combination with a spectroscopic model for data treatment, the thickness of a single paint layer is retrieved underwater. This paves the way for a more advanced system capable of measuring multilayer maritime paint underwater, which will enable shipping companies to continuously monitor the paint layers’ thickness.

Current Strategies to Control Recurrent and Residual Caries with Resin Composite Restorations: Operator- and Material-Related Factors

This review addresses the rationale of recurrent and/or residual caries associated with resin composite restorations alongside current strategies and evidence-based recommendations to arrest residual caries and restrain recurrent caries. The PubMed and MEDLINE databases were searched for composite-associated recurrent/residual caries focusing on predisposing factors related to materials and operator's skills; patient-related factors were out of scope. Recurrent caries and fractures are the main reasons for the failure of resin composites. Recurrent and residual caries are evaluated differently with no exact distinguishment, especially for wall lesions. Recurrent caries correlates to patient factors, the operator's skills of cavity preparation, and material selection and insertion. Material-related factors are significant. Strong evidence validates the minimally invasive management of deep caries, with concerns regarding residual infected dentin. Promising technologies promote resin composites with antibacterial and remineralizing potentials. Insertion techniques influence adaptation, marginal seal, and proximal contact tightness. A reliable diagnostic method for recurrent or residual caries is urgently required. Ongoing endeavors cannot eliminate recurrent caries or precisely validate residual caries. The operator's responsibility to precisely diagnose original caries and remaining tooth structure, consider oral environmental conditions, accurately prepare cavities, and select and apply restorative materials are integral aspects. Recurrent caries around composites requires a triad of attention where the operator's skills are cornerstones.

Characterization and Tribological Behavior of Electroless-Deposited Ni-P-PTFE Films on NBR Substrates for Dynamic Contact Applications

The use of rubber in dynamic contacts often results in severe degradation and wear of the rubber surface, which is why dynamic rubber seal contacts are usually oil lubricated to ensure their functionality. However, the increasing demand for more convenient and environmentally friendly sealing solutions has prompted the development of dry low-friction rubber coatings. In this work, and for the first time, Ni-P and polytetrafluoroethylene (PTFE) particles were co-deposited by electroless plating on Nitrile Butadiene Rubber (NBR), as a low-cost solution to improve the NBR tribological behavior. A cationic surfactant, cetyltrimethylammonium bromide (CTAB), was added to the plating bath to ensure a homogeneous and efficient incorporation of PTFE into the Ni-P. The optimized PTFE incorporation reached 6.8%, and the composite coating adhesion to NBR was 20% higher than that of nickel-phosphorous (Ni-P) films. The tribological properties of the coatings evaluated by pin-on-disk tests showed a marginal decrease in the coefficient of friction (CoF) (10%, 1 N load), compared to that of Ni-P. However, the tested PTFE-based coatings displayed significantly smoother surfaces with less debris and cracks, clearly demonstrating the benefits of the PTFE in terms of wear resistance for loads up to 5 N.

Influence of surface grooving methods on steady and dynamic performance of spiral groove gas face seals

In this paper, a structural form called double-sided spiral groove gas face seal is considered. Steady-state performances, such as film load-carrying capacity and film stiffness, of gas face seals with single-sided groove on the stator, single-sided groove on the rotor, and double-sided groove are compared. Introducing axial and angular excitations, coupled with gas lubrication, seal rings vibration, contact mechanics, and instantaneous changes in fluid film thickness, the complete dynamic behavior history is obtained. Two dynamic performance indicators, logarithmic decrement and period valley, are defined. The effects of groove depths and equilibrium film thickness on the dynamic performance of gas face seals with three different surface grooving methods are studied. Combined with the transient sealing performance and film dynamic coefficients, the mechanisms of several typical unstable conditions are analyzed. The results show that the double-sided grooving method has both high gas film load-carrying capacity and gas film stiffness when the equilibrium film thickness is relatively large. In addition, double-sided grooving has both advantages of high gas film damping of single-sided grooving on the stator and high gas film stiffness of single-sided grooving on the rotor, which can ensure stable operation under various operation conditions.

On the accuracy of cell-attached current-clamp recordings from cortical neurons.

Cell-attached current-clamp (CA/CC) recordings have been proposed to measure resting membrane potential and synaptic/agonist responses in neurons without disrupting the cell membrane, thus avoiding the intracellular dialysis that occurs in conventional whole-cell recordings (WC). However, the accuracy of CA/CC recordings in neurons has not been directly assessed. Here, we used concomitant CA and WC current clamp recordings from cortical neurons in brain slices. Resting membrane potential values and slow voltage shifts showed variability and were typically attenuated during CA/CC recordings by ~10–20% relative to WC values. Fast signals were slowed down and their amplitude was greatly reduced: synaptic potentials by nearly 2-fold, and action potentials by nearly 10-fold in CA/CC mode compared to WC. The polarity of GABAergic postsynaptic responses in CA/CC mode matched the responses in WC, and depolarising GABAergic potentials were predominantly observed during CA/CC recordings of intact neonatal CA3 hippocampal pyramidal neurons. Similarly, CA/CC recordings reliably detected neuronal depolarization and excitation during network-induced giant depolarizing potentials in the neonatal CA3 hippocampus, and revealed variable changes, from depolarization to hyperpolarization, in CA1 pyramidal cells during sharp wave ripples in the adult hippocampus. Thus, CA/CC recordings are suitable for assessing membrane potential but signal distortion, probably caused by leakage via the seal contact and RC filtering should be considered.

Percolation interpretation of film pressure forming mechanism of mechanical seal and calculation method of film pressure coefficient

The conclusion that the film pressure coefficient is inferred from the existing film pressure coefficient calculation method based on the assumption of microleakage at the sealing interface is about 0.5 seriously affects the accuracy of the mechanical seal contact pressure design. The composition of the fluid film pressure between the contact mechanical sealing interfaces was analyzed from a microscopic point of view, the formation mechanism of the film pressure is explained based on the percolation theory, and the fractal parameter calculation model of equivalent rough contact surface was proposed. The fluid-infiltrated sealing interface area on the inside and outside of the sealing line is discussed and determined, and a calculation method for the film pressure coefficient of the contact mechanical seal based on the percolation theory is established, and its correctness is verified by theoretical analysis and numerical simulation. The research shows that the film pressure coefficient can be determined by the calculation method of the film pressure coefficient established in this paper regardless of whether the sealing interface is leaky or not; the film pressure coefficient is related to the morphology parameters and the porosity of the sealing interface. For the four groups of rotating and stationary rings seal end face groups with different morphology parameters given in the paper, when the porosity is between 0 and 0.312, the film pressure coefficient is between 0 and 0.0547; when the porosity is between 0.312 and 0.593, the film pressure coefficient is between 0.0547 and 0.1791; at the initial porosity, the film pressure coefficient reaches 0.5374. The research results provide a theoretical basis for mechanical seals’ design and engineering application.

Seal contact performance analysis of soft seals on high-pressure hydrogen charge valves

Seal contact performance analysis of soft seals on high-pressure hydrogen charge valves

Rheological Characterization and EHL Simulation of a Grease in a Lubricated Sealing Contact

This contribution provides an insight into the tribological behavior of grease-lubricated contacts in pneumatic spool valves. As the properties of the grease are strongly non-Newtonian, multiple measurements were performed to parameterize two viscosity models, the Herschel-Bulkley and the Palacios-Palacios model. These models are integrated into an EHL simulation of the sealing contact and qualitatively compared for two temperatures. For that system, the total friction force is rather unaffected by the choice of the viscosity model. In addition, qualitatively similar results with about 10 % deviation from the non-Newtonian behavior could be obtained using a Newtonian approximation of the lubricant.