Rubber O-rings Research Articles

Abstract P449: A Murine Model of Mid-Thoracic Aortic Coarctation

Vascular pressure can directly affect cardiovascular structure and function. Understanding the mechanisms, however, is complicated because conditions or interventions that chronically raise blood pressure (e.g. excess angiotensin II) can also have direct effects on the vasculature that occur independent of changes in blood pressure. One approach to mitigating this problem is to obstruct flow in a vascular segment sufficiently to reduce blood pressure in the segment downstream of the obstruction, while pressure upstream either stays the same or increases. As a result, all factors other than pressure are expected to be the same in upstream and downstream vascular segments. We have found evidence that differences in intravascular pressure can also affect closely adjacent tissues, specifically perivascular adipose tissue (PVAT). To test this idea in vivo , we developed a method to produce chronic, partial occlusion (or coarctation) of the mid-thoracic aorta in mice. This exposes upstream aortic PVAT depots to significantly higher aortic pressure than downstream aortic PVAT depots. The key to the method is producing a stable occlusion with a diameter small enough to produce a pressure gradient but not so small that the downstream flow is inadequate to support tissue oxygenation. To this end, a thoracotomy was performed to expose the thoracic aorta in adult mice anesthetized with isoflurane and artificially ventilated. A coarctation of the mid-thoracic aorta was produced by tying a ligature around the aorta and a blunted needle on the aorta, then removing the needle. In other mice, a silicone rubber or nitrile O-ring of varying dimensions was placed around the aorta. Mice were allowed to recover for varying periods of time (weeks), then the degree of coarctation was evaluated using both imaging methods (ultrasound) and direct measurement of the pressure gradient (catheters placed in a carotid and a femoral artery) under isoflurane anesthesia. In a group of 9 male mice with coarctation and 4 male mice with sham coarctation, we found an average mean arterial pressure gradient of 11.7 ± 5.0 mmHg (mean ± SEM) in coarct mice and 1.6 ± 2.0 mmHg in sham mice. Systolic pressure gradients averaged 14.0 ± 5.9 mmHg in coarct mice and 1.0 ± 3.2 mmHg in sham mice. These results suggest it is possible to produce a stable pressure gradient across the thoracic aorta of mice as a tool to explore the impact of arterial pressure on vascular and PVAT structure and function.

An Experiment on the Dwell Time Effect of Rubber Seal O-Rings: Friction Force in Intermittent Reciprocating Motion

The adhesive force between two contact surfaces often leads to an increase in the friction force of the rubber seal O-ring after a certain dwell time, forming dwell time effects and affecting the reliability of sealing. The dwell time effect may result in substantial instability with respect to the frictional behavior of rubber O-rings, which needs to be carefully taken into account in the design of rubber seals. Therefore, in this paper, the dwell time effect of the friction force was studied experimentally for intermittent reciprocating rubber seal O-rings coupled with stainless steel 316L and a sealing air medium. The friction force of three kinds of rubber materials, including fluorine rubber (FPM), silicone rubber (SI), and nitrile rubber (NBR), was measured under different dwell times, compression ratios, and seal pressure. The results showed that there was a rolling frictional force, and the second peak value of the frictional force caused by the O-ring’s rolling under shear action and after the maximum static frictional force was observed at the starting stage of reciprocating motion. For FPM O-rings, the rolling friction force was much greater than the maximum static frictional force at about four times the value of the compression ratio at 9% and seal pressure at 0; moreover, the force was much greater at greater compression ratios. The dwell time effect was significant in the friction forces of rubber O-rings. The friction force increases with an increase in dwell time. The increase in maximum static friction force exceeded 50% after 5 dwell days. The increase in seal pressure led to the disappearance of the rolling friction feature and the rapid increase in friction during the starting stage. Under gas seal pressure conditions, the dwell time effect still led to a significant increase in friction force. The obtained results might provide guidance for the material selection of sealing designs.

Experimental study on stress relaxation of rubber O-ring for mechanical seal

The stress relaxation process and its variation law under multiple stresses have an important impact on the performance of rubber O-rings. An O-ring experimental device was developed, the end contact forces of the O-ring under the conditions of the single and multiple stresses were tested, and the contact force retention rate was calculated based on the test results. The change processes and laws of the end face contact force and the retention rate were obtained by the analyses of the experimental data under the different impact factors. The experimental results indicated that the compression ratio of the O-ring can increase the end contact force, but the greater compression ratio results in greater attenuation of contact force and longer attenuation time. The medium temperature hurts the contact force retention rate, and the medium pressure is conducive to stabilizing the contact force retention rate.

Calculation and experimental studies for the spent nuclear fuel shipping cask sealing assembly

One of the safety requirements regarding the shipping cask for spent nuclear fuel is that its leak-tightness should be maintained by preserving the cask body structural integrity and the sealing system tightness under normal and accident transportation conditions. The cask under design has a cylindrical process penetration (port) in its bottomб which is sealed using a plug with a radial seal composed of two rubber O-rings. The cask sealing assembly design was justified by the ANSYS LS-DYNA code calculation results. In particular, the strains of the cask components were calculated when dropped from a height of 1 m with the sealing assembly hitting a vertical bar. The cask was concluded to be leak-tight or leaky based on the strain nature and amount. To verify the adequacy of the results, computer-aided and realistic simulations were undertaken with a 1/2.5 scale mockup cask dropped on a bar from a height of 1 m. The computational and experimental results show a good agreement in terms of the impact response accelerations (overloads) for the mockup cask and bar collision and in terms of the plastic strains for the key components of the mockup bottom port sealing assembly. This proves the adequacy of the numerical cask model that has been developed and the efficiency of the LS-DYNA simulations. The inner rubber O ring compression is reduced by the plastic strains in the cask’s bottom port area, leading to a loose inner radial seal, as shown by the calculations. But the outer seal remains leak-tight, ensuring so the mockup cask tightness. The physical test results have also confirmed that the mockup cask remains leak-tight.

Tailoring the Curing Kinetics of NBR-Based Rubber Compounds for Additive Manufacturing of Rod Seals

The additive manufacturing (AM) of elastomeric parts based on high-viscosity reinforced rubbers has increasingly become a topic of scientific research in recent years. In addition to the viscosity, which is several decades higher during processing than the viscosities of thermoplastics, the flowability of the compound after the printing process and the necessary chemical crosslinking of the printed component play a decisive role in producing an elastic, high-quality, and geometrically stable part. After the first technological achievements using the so-called additive manufacturing of elastomers (AME) process, the knowledge gained has to be transferred first to concrete industrial parts. Therefore, in this study, the cure kinetics of a conventional rubber compound are tailored to match the specific requirements for scorch safety in the additive manufacturing of an industrial 2-component rod seal based on an acrylonitrile butadiene rubber O-ring in combination with a thermoplastic polyurethane as the base body. Experimental tests on a test rig for rod seals demonstrate the functionality of this additively manufactured 2-component rod seal.

Research on Aging State Detection Method of Rubber O-ring Sealing Structure

The rubber seal structure is used extensively in mechanical devices, long-term use may bring major safety hazards and economic losses. In order to ensure the healthy operation of machinery and equipment, it is necessary to test the aging condition of the rubber sealing structure nondestructive online. In order to address the problem of unsteady vibration signals, a complex nonstationary signal is degraded into the sum of multiple product functions by means of global local mean decomposition, and then the energy features in these PF components are extracted, and the first three components with the largest energy eigenvalues are selected to form a sensitive feature vector set. Overall, the results of the search data show that the proposed method can efficiently extract energy features from a large set of original features, and the first three largest energy features can be selected to form a sensitive feature set, which can provide effective data information for the detection of the aging state of Rubber O-ring Sealing Structure (ROSS) in the next step.

The performance of double-layer rubber sealing ring under the action of low temperature environment

Aiming at the sealing failure of a water quality monitoring system in a low-temperature environment, a double rubber O-ring sealing structure was designed, and its sealing performance at low temperatures was studied. Finite element software ANSYS constructed the sealing structure, and the change of sealing performance of rubber O-ring in the process of standard temperature installation and low temperature was studied by a two-dimensional axisymmetric model. The results show that the equivalent strain and stress of the sealing structure show an increasing trend during the installation process. With the effect of the medium pressure, the maximum contact stress of the rubber seal ring increases from 2.6285 MPa at 20 ℃ to 2.6657 MPa at 0 ℃. The contact width decreases gradually with the decrease in temperature. With the initial compression rate increase, the maximum contact stress increases significantly. The simulation results show that the double-layer rubber O-ring structure still has good sealing performance at low temperatures.

A performance degradation model of nitrile butadiene rubber (NBR) O-rings for hydrogen permeation effects under high-pressure.

The integration of molecular chain changes on a microscopic scale to achieve macroscopic performance is crucial in degradation processes concerning O-ring seals. Nonetheless, a comprehensive and compelling mathematical model that can describe molecular chains' material properties and macroscopic material properties simultaneously for O-rings under high-pressure conditions is yet to be established. In this paper, we propose a degradation model based on viscoelasticity and molecular chain statistics for hydrogen permeation. The proposed model aims to establish the relationship between the material molecular chains and macroscopic material properties, with a primary focus on accurately recognizing the performance degradation process of rubber sealing rings. We verify the model's reliability through uniaxial tensile strength experiments and high-pressure hydrogen immersion experiments, respectively. Predictions of the model exhibit favorable conformity with the experimental data concerning the above phenomena. Furthermore, we derive the number of molecular chains and maximum strain of the degradation process. Based on the similarity of the degradation process's descent, it is plausible to speculate that NBR properties' degradation can be characterized by the average number of molecular chains.

SINGLE IMPLANT-RETAINED MANDIBULAR OVERDENTURE: A CASE REPORT

Edentulism is a public health problem, impacting the quality of life of many people worldwide. Factors related to the mandibular ridge minimal support may hinder the common use of complete dentures. The use of overdentures supported by a minimum of one implant can be considered as reliable approach in this situation. Aim: To present a case report of a single implant-supported overdenture in the mandibular symphysis fot public health policies. Case report: A 65-year-old edentulous patient complaining of discomfort in a mandibular denture was referred to the Universidade Federal Fluminense. On clinical examination, residual mandibular ridge resorption and soft tissue trauma were observed, which was in line with the reported discomfort. A mandibular overdenture retained by a single implant in the symphysis region was planned. A hex-type 4.0 mm in diameter and 11.0 mm in length implant was placed and a new set of complete dentures were made till the date of complete osseointegration. After four months, a second surgery exposed the implant platform to fit a ball attachment with a 32 N.cm torque. The denture was relieved on its tissue surface for the placement of a metal attachment matrix with a rubber O-ring inside, using a fast-curing resin, and the patient was locked into maximum intercuspidation during the acrylic polymerization process. Excessive resin was removed and the region was polished for daily use after the process. The patient reported an improvement in chewing condition and restorative esthetics. Conclusions: A minimum requirements protocol has achieved relevant results and may be feasible in public health policies. Maintenance visits are recommended to maintain retention quality and to decrease the risk of failures.

A critical examination of the shelf life of nitrile rubber O-Rings used in aerospace sealing applications

The shelf life of MS29513-016 nitrile O-Rings was determined by accelerated heat aging from 40 to 85 °C for varying aging times up to 50 weeks. The microhardness, tensile strength and 50% tensile stress all rise as a function of aging time while the elongation at break decreases. The crosslink density by solvent swell followed the development or loss of network chains during the aging process. In this case, the net increase in crosslink density showed a good correlation with the hardness, tensile strength and tensile stress results. Property loss is attributed to the labile nature of the sulfur cure system, the high double bound content of the nitrile rubber and the high level of ester plasticizer in the compound. Activation energies were lower than expected due to the sealed plastic packaging which impeded oxygen migration. Nevertheless, results clearly show that the O-Rings are out-of-specification beyond 7 years of shelf life due to the loss of elasticity (elongation at break < 200%). The nominal 15 year shelf life for nitrile rubber used in aerospace sealing applications according to SAE AS5316 needs to be reconsidered in light of the results.

Air, Helium and Water Leakage in Rubber O-ring Seals with Application to Syringes

We study the leakage of fluids (liquids or gases) in syringes with glass barrel, steel plunger and rubber O-ring stopper. The leakrate depends on the interfacial surface roughness and on the viscoelastic properties of the rubber. Random surface roughness is produced by sandblasting the rubber O-rings. We present a very simple theory for gas flow which takes into account both the diffusive and ballistic flow. The theory shows that the interfacial fluid flow (leakage) channels are so narrow that the gas flow is mainly ballistic (the so called Knudsen limit). We compare the leakrate obtained using air and helium. For barrels filled with water we observe no leakage even if leakage occurs for gases. We interpret this as resulting from capillary (Laplace pressure or surface energy) effects.

Fluid Leakage in Static Rubber Seals

Interfacial surface roughness can result in fluid leakage of seals, and in the design of seals it is standard to give an upper limit for the surface root-mean-square (rms) roughness amplitude h_text{rms}. However, h_text{rms} is determined mainly by the long-wavelength roughness, which is (nearly) irrelevant for the sealing. I discuss the parameters which determine the leakage of seals, and present results for static rubber seals with circular cross-section (like rubber O-rings). I also study the influence of the fluid pressure on the interfacial surface separation and the leakrate.Graphical

Research on Key Factors of Sealing Performance of Combined Sealing Ring

In this study, the mechanical properties of a combined seal ring under different loads were numerically calculated using ANSYS. The effect of the working pressure and pre-compression ratio of a rubber O-ring on the contact stress of the combined seal ring was studied. The influence of the wear ring’s chamfer, thickness, and width on the contact stress and contact force of the combined seal ring was analyzed. Studies have shown that it is particularly important to select a compression ratio that is suitable for the working conditions. Under the same conditions of working pressure and compression ratio, upon increasing the wear ring chamfer, the contact pressure is decreased due to the decreasing contact bandwidth between the wear ring and the cylinder wall. This has little effect on the contact stress of the combined seal ring as well as the contact force, while the width of the wear ring is proportional to the latter.

Identification of swelling/shrinking coefficients under CO2 on an FKM O-ring – Comparison with HNBR and influence of reinforcements on the matrices

A better understanding of elastomers’ behavior during Rapid Gas Decompression (RGD) requires advanced knowledge of what is happening during gas sorption and desorption. This will offer to improve numerical simulation phenomena to consider a real environmental use of an O-ring, as for thermal applications. A previous experimental study developed testing protocols to investigate the performance of elastomeric O-rings. The non-contact measurement technique has been validated to identify the swelling and shrinking coefficients during sorption and desorption of carbon dioxide (CO2) from a Hydrogenated Nitrile Butadiene Rubber (HNBR) O-ring. The present work describes the effect of CO2 pressures on Fluorocarbon rubber (FKM) seals behavior coupled with temperature. To evaluate the effect of reinforcing the HNBR and FKM matrices with nanofillers, experimental tests were carried out and compared with those of the two elastomers without fillers. The four materials’ CO2 sorption and desorption coefficients are identified, and their swelling upon decompression is measured. It appears that HNBR is the best candidate under the applied service conditions. On the other hand, the nanofillers introduced in the elastomers may cause some early damages under RGD conditions.

An ultrasonic method for measurement of oil films in reciprocating rubber O-ring seals

In this study, ultrasound has been developed and applied for a rubber O-ring subjected to reciprocating sliding. Under varying reciprocating speeds (2–8 Hz) and normal loads (10–20 N), ultrasonic reflection from the sealing contact was measured for analyzing the oil film formation. Central film thickness measurements were found to be in the range of 1.8–7 µm, which were comparable to the modelling results. In addition, the oil film along the reciprocating path was measured using an array of ultrasound sensors; this mapped the oil film formation covering the length of the reciprocating stroke. The findings have concluded that the ultrasound technique is an effective approach in detecting the oil film formation and contact size for the sealing contact.

A Low-Voltage Dielectrophoretic System Using Thread Based Electrodes for Cell Viability Assessment

We present a disposable low-voltage thread-based electrode system that can differentiate live and dead Saccharomyces cerevisiae cells via field-induced assembly. Our system consists of a silver nanoparticle based conductive thread electrodes embedded in a rubber o-ring. The three-dimensional conductive thread with high aspect ratios were found to facilitate high electric field regions at low voltages. Rapid assembly of biological cells into highly ordered pearl chains was observed at voltages as low as 4V.Thread based devices create DEP forces that are larger by two orders of magnitude for the same applied voltage when compared to most microfluidic e-DEP designs in literature, which rely on planar electrodes to produce the DEP forces. Numerical simulations of electric field intensity in the device using a representative thread geometry also confirmed our experimental findings. The dead cells probed at a voltage of 4V @2.5 MHz was found to aggregate in low electric field regions. The percentage of live and dead cells are estimated using an image recognition algorithm that analyze cells that are viable in a given sample within 60 seconds. The area occupied by the dead-cell aggregate is a direct indicator of cell viability.We are currently exploring the possibilities of three-dimensional assembly of microparticles for point-of-care applications. Figure 1

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.

Dynamic Behavior Analysis of the Winding Rotor with Structural Coupling and Time-Frequency Varying Parameters: Simulation and Measurement

To satisfy the requirements of high speed, large capacity and constant winding, a textile winding rotor needs to work in a wide rotation speed range and frequently pass through critical speed points. Thus, the winding rotor adopts the flexible long shaft coupling structure and flexible support with rubber O-rings. This kind of rotor has a multi-coupling structure and frequency-dependent parameters characteristics, especially representative and universal in the dynamic analysis method of the high-speed rotor. In this paper, an approach was proposed to investigate the dynamic behavior of the winding rotor considering the flexible coupling and frequency-dependent supporting parameters. Firstly, a dynamic model of the winding rotor was established by using a Timoshenko beam element. Its dynamic behaviors were simulated by considering the time-varying rotation speed and the frequency-dependent parameters of flexible support. Secondly, a non-contact measuring device was developed for measuring the vibration displacement of the winding rotor in three different speed-up times. Finally, based on simulation and measurement data, how flexible support parameters and the speed-up time affect the winding rotor passing through the critical speed point of the rotor smoothly is revealed. The methods and findings reported here can be used for theoretical and experimental vibration analysis of other types of high-speed flexible rotors.

Ageing Model of Rubber O-Rings Used in Gas-Insulated Substation Equipment

Ageing Model of Rubber O-Rings Used in Gas-Insulated Substation Equipment

Corrosion damage behaviors of rubber O-rings under simulated acid fracturing conditions

Abstract To explore the damage behavior of O-ring in acid environment, a high-temperature and high-pressure (HTHP) autoclave was used to simulate the service environment of O-ring, and then 168h corrosion test of hydrogenated nitrile butadiene rubber (HNBR) and fluororubber (FM) O-rings were carried out. The corrosion damage behaviors of two kinds of rubber O-rings in the acidizing fluid were studied through determining their tensile strength, elongation at break, hardness, permanent compressive deformation, tensile fracture morphology and sealing property. The results showed that the cross-sectional area and the compression permanent deformation increased, the tensile strength and hardness decreased when the HNBR and FM O-rings under the free state were subjected to acid corrosion. The elongation at break of HNBR decreased, and that of FM rubber increased greatly. Similar with free state, the HNBR and FM O-rings under sealed state also presented the same variation trend. The decrease in the reliability of the O-rings under the sealed state was less significant than that in the free state. In the test, tensile fractures were mostly brittle fractures, HNBR and FM O-rings had obvious corrosion damages such as deformation and swelling. The results could provide a technical basis for the selection of sealing materials, tool optimization design, and construction work in oil and gas fields.