Elastomeric Seals Research Articles

Minimisation of Friction Resistance of Elastomeric Lip Seals on Rotating Shafts

This article presents the results of a study of oil lip seals with a modified outer lip layer texture. In the first step, the interaction of flat rubber samples with different surface layer textures with the steel surface was recognised. Measurements of the friction coefficient of flat samples with different surface layer textures were carried out. The next step was an experimental study of rotating shaft lip seals in standard and prototype versions. The contact width of the sealing lip before and after durability tests was examined, and the clamping force of the lip on the shaft before and after durability tests was measured. The final step was to create a FEM model of the interaction of the sealing ring lip with the shaft to determine the lip seal pressure and width. These calculations, in cooperation with the previously determined friction coefficient and porosity of the lip seal, allowed the calculation of the friction torque. The solution proposed in this article was intended to be simple and viable for industrial applications. Satisfactory results were achieved with prototype rings in terms of reduced resistance to movement, tightness, and durability.

Investigating the influence of operating variables on sealing performance of a V-ring seal stack in the oil and gas industry for enhanced environmental and operational performance

Static V-ring seals, essential components in oil and gas industry valves, have received limited attention compared to rotary and reciprocating seals in previous research. This study fills this gap by meticulously investigating the performance of these seals under conditions involving minimal or no rotational movement, offering valuable insights into their functional capabilities. The objectives of this experimental study are to develop an experimental setup mirroring industrial conditions to assess the performance of seals used in oil and gas valves. Accordingly, two fluorinated elastomer seals (AFLAS) and three Polytetrafluoroethylene (PTFE) seals were employed together as a single seal stack to understand the leakage behavior as well as the range of safe operating conditions under delayed gas leakage. The operating conditions for the experiments have been adopted to simulate drilling rigs. Hence, temperatures ranging from room temperature to 394.15 K and 477.15 K, diverse pressures from 4.14 MPa to 68.95 MPa, and variable motion speeds (0 RPM, 2 RPM, and 10 RPM) were incorporated in the experiments. The study revealed a positive correlation between leakage rate with both pressure and dynamic motion, reflecting valve opening and closing actions. In contrast, a negative correlation was noted between leakage rate and temperature in both static and dynamic conditions. At 68.95 MPa, the highest observed leak rate was 2.96 × 10−4 mol/s at room temperature, nearly ninety-five times higher than the rate recorded at 4.14 MPa (3.08 × 10−6 mol/s). Also, at an elevated temperature of 477.15 K, the leak rate significantly decreased to 1.08 × 10−5 mol/s, approximately twenty-six times lower than the room temperature rate. Furthermore, the study revealed that the influence of motion on leak rate diminished significantly at high temperatures compared to low temperatures, indicating a complex interplay between motion, temperature, and leakage behavior in the tested seals. Additionally, this investigation encompasses a thorough imaging analysis of the seals, aimed at assessing structural changes and the overall seal condition under varying operational circumstances. This research promises to guide customized sealing material development, enhancing safety and environmental performance in the oil and gas sector, making a valuable contribution to the industry.

Machine Learning Aided Optimization of Non-Metallic Seals in Downhole Tools

Machine learning-based optimization analysis is conducted to improve the performance and reliability of non-metallic seals that undergo dynamic loading. Non-metallic seals, mostly made from elastomeric materials such as rubber, are widely used in the oil and gas industry due to their combination of hyper-elastic behavior and lack of plastic deformation under pressure and temperature cycles. However, these elastomeric materials could soften at elevated temperatures or during cyclic loading which makes them more prone to extrude from the seal region. For simple seals such as O-rings, thermoplastic anti-extrusion backup rings can be used to resist rubber extrusion. For more complex molded or bonded seals subject to cyclic loads and temperature cycles, minimizing the rubber damage and maintaining the seal integrity becomes more challenging as there may be inadequate room for backup rings. Additionally, the rubber may also experience repeated long stroke lengths during service which can cause surface abrasion. Non-metallic seals are extensively used in Sand Control Tools, a class of completion equipment. In the development of these molded and bonded seals, advanced optimization analysis techniques are important to make the seal design sufficiently robust to meet the stringent requirements of industry codes and regulations. Machine learning-based optimization analysis allows for increasing the seal performance and reliability. The Mullins effect is included in the elastomeric material model to capture the material softening effects under cyclic loading. Machine learning-based optimization starts with a feasible design space that is defined based on the controlling design parameters related to the geometry of the seal. Comprehensive Finite Element Analysis is performed on each design sample under the target cyclic load and temperature cycles. The key response parameters of the non-metallic seal are selected as the principal strain and the contact stress in the rubber which together indicate the damage and seal-ability states of the design. A Performance Objective Index is defined as a function of the key response parameters. The FEA results covering the entire design space provide the simulation-driven training data to build the surrogate model using multi-layer neural networks. The optimum design solution is found from the surrogate model which correlates the Performance Objective Index to the design parameters. The results of this study reveal that the performance of the seal is greatly affected by the ratio of the elastomeric seal volume to the gland volume into which the seal is molded. As opposed to the base design, the optimum design shows a solid performance with no signs of extrusion when the principal strain of the rubber is kept below the elongation limit throughout the load cycles, and when sufficient contact stress is developed to maintain the seal.

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.

Oil Leakage Prediction through Cut Part of Double Elastomeric Seal

Oil Leakage Prediction through Cut Part of Double Elastomeric Seal

Theoretical and Experimental Analysis of a Non Contacting Elastohydrodynamic Sealing

This paper presents a novel elastohydrodynamic sealing concept for the contactless sealing of spool valves. The basic goal is that the spool and the sleeve can be manufactured with standard mechanical engineering precision. High initial gaps are compensated for the elastic deformation of an elastomer seal driven by a self-regulating hydrodynamic effect. The final gap reveals a small leakage within the range normal for precisely manufactured spool valves and also features a low friction since a direct, solid contact between the seal and the sleeve is prevented. This sought-after behavior in ideal conditions is compared with imperfect situations by means of a simulation study and experiments. The simulation uses a Finite Element model which takes the seal‘s elastic deformation, the mechanical contact, the sealing gap pressure and the surface roughness into account. A simple prototype of the sealing system was produced to test its functionality in real conditions. Leakages of QLeak <= 18 ml/min @180 bar were recorded. However, an unexpectedly high friction occurred indicating an actual contact between the seal and the sleeve. The component roughness was identified as the cause of this behavior.

Smart Quantum Tunneling Composite Sensors to Monitor FKM and FFKM Seals.

Operators of industrial machinery relentlessly pursue improving safety, increasing productivity, and minimizing unplanned downtime. Elastomer seals are ubiquitous components of this machinery. In general, static seals are designed to be compressed at a fixed level of compression, taking gland geometry, loading condition, temperature range of operation, fluid media exposure, and other factors into account to ensure the safe operation of equipment. Over time, seals experience compression set, chemical-induced swelling, erosion, and other phenomena which can compromise the compressive force generated by the seal and cause leaking. This is particularly important in critical applications, where high pressure, high temperature, and aggressive media are present, and fluorinated elastomers are common materials for seals. Further, changes in operating conditions at manufacturing plants, either intentional or through regular process variation, create unknown operating conditions for seals. This unknown and variable application environment makes seal performance hard to predict. Therefore, machinery utilizing seals is, at best, serviced preventatively at certain intervals, where seals are removed, and the remaining useful life of the seal is unknown. This leads to unnecessary machinery downtime and increases consumable costs for manufacturers. In the worst case, the seal is run to failure, creating machinery and plant safety concerns. Both scenarios are undesirable for manufacturers using industrial machinery. This paper reports on the development of "smart" intrinsic self-sensing seals, which enable performance monitoring of the compression behavior of seals while in use. In addition, this paper examines quantum tunneling elastomeric composites (QTC) to demonstrate a method of component performance monitoring by modifying the underlying elastomeric material itself. This paper studies QTC sensor-based fluorinated (FKM) and per-fluorinated (FFKM) compositions, which are modified to incorporate varying levels of carbon nanostructure (CNS) material. The resulting seal's resistive properties are shown to be a function of the level of compression, the first time this phenomenon has been demonstrated in high-performing FKM and FFKM seal materials.

Experimental researches of elastomeric materials to stabilize the oscillation of power grid structures

This paper proposes a new type of insulator, has both insulating and damping properties to improve the operational reliability of overhead power lines' structures (OHPL). In order to assess an effectiveness of the new insulator's design have made laboratory tests of a insulator model with different types of elastomer seals, differed of the rubber marks and the type of reinforcement. An experiment consist of two stages: at the first stage an object of study has been exposed to cyclical vibration, at the second – the impact of an impulsively load. Results of the research showed, that the most effective are the elastomeric gasket with a minimum rigidity characteristics without reinforcement. Using insulators with such dampers allows to reduce the first maximum impulse to a support by an average of 20% and reduce the frequency and amplitude characteristics of the system. Based on this was developed a new type of elastomer reinforcing with steel sheet elements in the form of a truncated cone.

Elastomeric seal stress analysis using photoelastic experimental hybrid method

Stress freezing is an important and powerful procedure in 3-dimensional experimental stress analysis using photoelasticity. The application of the stress freezing technique to extract stress components from loaded engineering structures has, however, declined over the years even though its principles are well established. This is attributed to huge costs arising from energy consumption during the process. In addition, significant time is needed to generate the desired information from isoclinic and isochromatic fringes. To overcome the limitations of stress freezing in photoelasticity and transform it into an economical device for stress analysis in an engineering environment, a new stress freezing cycle that lasts 5 h is proposed. The proposed technique is used in several applications of elastomeric seals with different cross-sectional profiles to assess their suitability. It was found that reducing the cycle time can lead to huge energy savings without compromising the quality of the fringes. Moreover, the use of isochromatic only to extract stress components leads to a shorter processing time to achieve desirable information since the process of obtaining isoclinic data is involving. In this paper, results of stress analysis from stress-frozen elastomeric seals with various cross-sections using the new stress freezing cycle are presented.

NSTX-U Machine Core Vacuum Seals Upgrade Design

The vacuum in the National Spherical Torus Experiment Upgrade (NSTX-U) is in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.66\,\times \,10 ^{-6}$ </tex-math></inline-formula> Pa ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\,\times \,10 ^{-8}$ </tex-math></inline-formula> torr). To enhance vacuum seals and lower gas permeation in the NSTX-U and therefore ensuring operation safety and quality, the machine core vacuum seal design has been upgraded using double elastomeric seals and pumped interspaces (guard channels). In NSTX-U machine core, there are six major vacuum seals, including upper and lower vacuum vessel main flanges, upper and lower bellows flanges, and two in the ceramic isolation ring assembly that are mounted to the upper vacuum vessel main flange. The elastomeric seals are commercially available and customized fluorocarbon (Viton) O-rings. To ensure appropriate O-ring compression ratios for the vacuum seal, the O-ring grooves are customized with appropriate tolerances considering specific situations for each seal. In this upgrade, the vacuum in each interspace is designed to reach 13.33 Pa (0.1 torr), thus the overall pressure difference crossing each double O-ring seal is expected to be reduced by at least three orders of magnitude, and accordingly the overall rates of leakage and permeation will be lowered by three orders of magnitude. The corresponding pump-down times for each seal, at room temperature, are estimated at about 60 s. In addition, the vacuum pumped interspaces will be able to function as a real-time leak monitor.

Effect of polymer seal’s chemical and mechanical properties on automotive sealed chain’s transmission loss

ABSTRACT An automotive sealed chain consisting of an elastomeric seal between chain plates prevents the entry of external contaminants. But, the presence of a seal induces high transmission loss due to the frictional force. In the present study, a comparative transmission loss test between two ANSI-B29.1 520 series sealed chains of equal geometric dimensions (5/8” pitch) was carried out. The tests revealed a significant difference of 38% in their transmission losses between the chains. To understand these observed differences in the chain performance, the material analysis of the seals (nitrile butadiene rubber) was performed, which showed a significant difference in their composition. The increased seal hardness due to difference in chemical properties resulted in a 21% increase in friction coefficient between the seal and the plates. The seal thickness reduction, the effect of lubricant, and the difference in the frictional forces between chains yielded differences in the transmission losses.

Development and validation of a surface profiling system for end of line monitoring of microstructured elastomer seals based on chromatic confocal microscopy

Chromatic confocal surface profilometry has been a widespread technique in industrial applications for many years. Beside excellent resolution and speed, the contactless measuring capability make it ideal in applications where no physical contact is possible, (e.g. measurement of fluid levels), or where physical contact could damage the part to be inspected (e.g. high precision lenses or coatings). Since these systems rely on the spectral analysis of the reflected light, if the reflectance of the examined specimen is low, the measurement speed and accuracy can substantially degrade. In this paper, we present a high-intensity chromatic confocal surface profiling system based on an infrared superluminescent diode and custom designed optics. Due to its very small etendue, the superluminescent source allows orders of magnitude higher illumination intensity than conventional LED sources. We mounted the designed optics on a 5-axis precision positioning stage, which allows topography measurements along 5° of freedom on complex shaped samples, with a wide focus range (>350 μm) and a high scanning speed (>10 kHz). The paper presents the design procedure and the figures of merit of the device, and measurement results of microstructured elastomer samples are also shown.

Rotary Shaft Seals: Correlation of Wear Formation at the Sealing Edge and Shaft under Various Operating Conditions

Elastomeric rotary shaft seals are a common seal type for various industrial applications. They are comparably cheap and easy to use and offer an overall good performance. But the wear behavior of these sealing systems is not fully understood and not predictable so far. If a lip seal fails, it causes high maintenance costs and environmental damage. In this article, various tribological conditions are considered. For this purpose, the sealing systems are tested with multiple operating conditions relevant to practice. Three test series are conducted with rotary shaft seals BAUM5X7 75FKM585 on plunge ground shafts. The tests are carried out with two different circumferential velocities of the shaft (4.2 and 10 m/s), three different oil sump temperatures (40, 80, and 120 °C), two different lubricant types (FVA 3 and PG 3), and five different test durations (between 100 and 625 h). For a complete acquisition of the system condition, all shaft surfaces are measured in 2D and 3D before and after the test runs and the wear of the sealing edges is evaluated with a recently developed laser line triangulation method on the complete circumference of the sealing rings. Results show large amounts of wear, depending significantly on the operating conditions. A strong correlation of the wear effects in the tribocontact area of the sealing system becomes evident. This article helps to understand and avoid critical operating conditions concerning abrasive wear.

Tribological Properties and Wear Mechanisms of Polyurethane Sealing Material Over a Wide Temperature Range

The service environment has an important influence on the friction and wear properties of elastomeric seals. This study is devoted to investigating the tribological properties of polyurethane against 316L stainless steel under a wide temperature range of –50 °C to +60 °C. The significant characteristics such as coefficient of friction (COF), wear rate, and worn surface morphologies of samples were examined and compared. The results indicated that the different temperatures exhibited significantly diverse tendencies on the evolution characteristics of COF, including the fluctuation and stability. The COF took longer to establish equilibrium at low temperatures, and the A-COF after stability was the lowest at 60 °C. Compared with cold environment, high temperatures (i.e., 60 °C) accelerated the wear of polyurethane. Moreover, polyurethane worn surfaces presented different damage morphologies with changes in temperature. Three different mechanisms of wear, including abrasive wear, fatigue wear, and roll formation, gradually changed with increasing temperature. This study provides insights into the wear mechanism associated with temperature and is useful for designing and selecting proper operating conditions for prolonged applications of the sealing material under extreme circumstances.

The influence of the surface roughness, creep and relaxation on the performance of elastomeric liners for sustainable glass bottle closures

Glass bottles having a metal closure are preferred for oxygen sensitive beverages e.g. beer. Using thinner closure which comprise polyvinyl chloride-free component is more sustainable. However, protecting the sealing performance as a result of metal closure thickness reduction is challenging. Here we show the relation between the leakage in beer bottles and surface roughness of three different thermoplastic elastomer seals. Compression relaxation and creep-recovery behavior of seals have been analyzed by using a dynamic mechanical analyzer. The results showed that metal downsizing was possible with Liner A (low density polyethylene (LDPE)/styrene-ethylene-butylene-styrene) and B (LDPE/ styrene-butadiene-styrene), but not with Liner C (high-density polyethylene/butyl rubber). Optimizing smaller surface topography parameters such as the surface roughness depth Rz, kurtosis Sku, average void volume Vvv, arithmetic mean peak curvature Spc, the density of surface peaks Spd and higher peak material volume Vmp, peak material portion Smr resulted in a better sealing performance. Liner C was found to show an increased leakage risk, since there was a high level of stress relaxation leading to a reduced sealing force. The sealing liner material with low relaxation, low elastic modulus and high creep recovery compliance was found to ensure better sealing when thinner metal closures are used.

Leakage failure of elastomeric seal using gelatine hydrogel

The elastomeric seals have numerous applications in various fields varying from pressure cookers to space shuttles. These critical applications make the failure analysis of elastomeric seals very much crucial. Here, elastic leakage of the seal due to hydraulic pressure is investigated using an experimental study. In the current work, the effect of various parameters on the critical pressure recorded before leakage is studied by conducting experiments on a small transparent setup. Gelatine hydrogel which is transparent and can be easily synthesized is used as a seal material to study the effect of the gelatine concentration and specimen length on the critical pressure. The study indicated the positive effect of gelatine concentration and specimen width on the critical pressure. Relationship of the critical pressure with the gelatine concentration and specimen width follows power law. Power coefficient for the critical pressure and gelatine concentration lies between 1.4 and 1.9. However, for the critical pressure and specimen width the power coefficient lies between 0.93 and 1.51.

Development and evaluation of nitrile rubbers seals for power transformer application

Mineral insulating oil (MIO) and natural ester insulating (NEI) oil are used in power transformers as an insulating fluid, while elastomeric seals are usually composed of nitrile rubber (NBR). The proprieties of these seals can change in contact with insulating oil. Variation in sealant properties is undesirable in power transformers. In this work, the variation of some elastomer properties was evaluated before and after accelerated aging in MIO and NEI. The developed elastomeric compositions showed variation in the stress and strain at break after the aging test. It also appeared that MIO penetrated the samples and that dioctylphthalate (DOP) migrated or was extracted into MIO and NEI. The samples vulcanized with peroxide showed better results than those vulcanized with sulfur.

The sealing mechanism of radial lip seals: A numerical study of the tangential distortion of the sealing edge

The sealing behaviour of elastomeric radial lip seals is essentially affected by the sealing mechanism in the contact area between the sealing edge and the shaft surface. The relative motion between radial lip seal and shaft deforms the sealing edge tangentially in the circumferential direction. This mechanical deformation is considered essential for the sealing mechanism. In this study, a numerical approach is employed to simulate this deformation. A three-dimensional multiscale model serves this purpose. The radial lip seal geometry is described on the macro-scale. On the micro-scale, an artificial rough surface with a stochastic roughness distribution is applied to an ideal sealing edge surface. A new meshing algorithm is used to discretise different sealing edge surfaces and automatically generates structured hexahedral meshes of the sealing edges. Mesh transitions connect the resulting finely meshed sealing edge to the coarsely meshed global macro-scale mesh of the radial lip seal. The paper introduces the modelling method used to simulate the deformation of radial lip seals. Results are presented and discussed with reference to the sealing behaviour. This contributes to a better understanding of the sealing mechanism of radial lip seals. Keywords: radial lip seal, finite element analysis, surface roughness, elastic deformation, elastomers.

Ускоренные ресурсные испытания отечественных опытных образцов эластомерных уплотнений для системы подводной добычи нефти и газа

This work was performed with the aim of confirming the competence of Russian industrial enterprises in the development of subsea production system facilities and applies to elastomeric seals of Christmas tree and tubing hanger, and is intended to confirm the service life of elastomeric seals. The essence of the method is to test the cyclic effect of pressure, temperature and several cycles of axial movement on not aged (new) seals and on aged (at the end of the warranty period of storage and operation) seals.

Characterising the friction coefficient between rubber O-rings and a rigid surface under extreme pressures

Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces.