Face Seal Research Articles

Are Diamond Surface Coatings Immune to Dry Running?

It is well understood that mechanical seal performance is dependent upon the tribology of the seal face materials. Published material is available claiming the advantages of Polycrystalline Diamond (PCD) and its suitability for extended running under dry conditions; indeed, one such claim suggests that PCD coated faces are immune to dry running. In order to investigate this claim, the author undertook a series of rigorously controlled tests to evaluate the performance of mechanical seal faces coated with a Polycrystalline Diamond coating (PCD) against others with Diamond - Like Carbon (DLC) coatings. Seal surface topography was accurately measured before and after testing and was used to evaluate the wear behaviour. From the test results obtained it is concluded that neither coatings are suitable for extended dry running use. However, it was evident that seal faces coated with a new form of DLC identified as, Plasma Assisted - Chemical Vapour Deposition (PA-CVD) performed 18 times longer than the PCD coated ones before reaching a predetermined friction induced temperature. Publications can be cited as evidence that PCD coated seal faces are capable of producing very high frictional temperatures that could, in a dry running situation, allow certain liquid fuels such as flashing hydrocarbons to reach their auto-ignition temperatures. In addition, it was revealed that the PCD coated seal units are being sold at a higher cost than the equivalent DLC coated ones by a factor of three.

Time-fractional heat transfer equations in modeling of the non-contacting face seals

The paper presents a mathematical model of a heat transfer process for non-contacting face seals. For a slewing ring (rotor), a time fractional Fourier law obtained from fractional calculus was applied. Heat exchange in the stator was described using Laplace’s equation. Heat flux generated in the medium layer separating the rings is discharged first to a working ring and the to a surrounding medium. Distribution of temperature fields in sealing rings was determined with the use of analytical methods, using integral transformation method. The fractional heat conduction equation (for the rotor) was considered in the light of the case 0<α⩽2 with the special attention paid to α=1 for the classical heat conduction equation.The proposed way of solving is very broad and involves many theoretical and practical problems, which were taken into account and described in the work. Finally, numerical results are presented graphically for various values of both operational and geometric parameters and order of fractional derivative.

Influence analysis of secondary O-ring seals in dynamic behavior of spiral groove gas face seals

The current research on secondary O-ring seals used in mechanical seals has begun to focus on their dynamic properties. However, detailed analysis of the dynamic properties of O-ring seals in spiral groove gas face seals is lacking. In particular a transient study and a difference analysis of steady-state and transient performance are imperative. In this paper, a case study is performed to gauge the effect of secondary O-ring seals on the dynamic behavior (steady-state performance and transient performance) of face seals. A numerical finite element method (FEM) model is developed for the dynamic analysis of spiral groove gas face seals with a flexibly mounted stator in the axial and angular modes. The rotor tilt angle, static stator tilt angle and O-ring damping are selected to investigate the effect of O-ring seals on face seals during stable running operation. The results show that the angular factor can be ignored to save time in the simulation under small damping or undamped conditions. However, large O-ring damping has an enormous effect on the angular phase difference of mated rings, affecting the steady-state performance of face seals and largely increasing the possibility of face contact that reduces the service life of face seals. A pressure drop fluctuation is carried out to analyze the effect of O-ring seals on the transient performance of face seals. The results show that face seals could remain stable without support stiffness and O-ring damping during normal stable operation but may enter a large-leakage state when confronting instantaneous fluctuations. The oscillation-amplitude shortening effect of O-ring damping on the axial mode is much greater than that on the angular modes and O-ring damping prefers to cater for axial motion at the cost of angular motion. This research proposes a detailed dynamic-property study of O-ring seals in spiral groove gas face seals, to assist in the design of face seals.

A Comparative Study on the Performance of Typical Types of Bionic Groove Dry Gas Seal based on Bird Wing

A series of bionic grooves based on bird wing, such as cluster spiral groove, multi-array spiral groove and flow-split spiral groove, are introduced to improve the film stiffness and sealing properties of dry gas seal. A theoretical model solved with Finite Difference Method (FMD) is developed to study the static sealing performance, such as film stiffness and leakage rate of these bionic groove dry gas seals. Then, a performance comparative study between the bionic groove dry gas seals and common spiral groove dry gas seal with different groove geometry parameters such as groove depth ratio, spiral angle and micro groove number under different average linear velocity at seal ring face and seal pressure is carried out. The closing force, film thickness and leakage rate of dry gas seals with bionic grooves and common spiral groove are measured experimentally. Results show that cluster spiral groove and multi-array spiral groove dry gas seals have superiority in the film stiffness and stiffness-leakage ratio compared with common spiral groove under the condition of high-speed and low-pressure, while flow-split spiral groove dry gas seal has no obvious advantages of performance. Film stiffness of cluster spiral groove dry gas seal and stiffness-leakage ratio of multi-array spiral groove dry gas are 20% and 50% larger than that of common spiral groove dry gas seal, respectively, which are verified by the experimental results.

Drawing the Line: Seals, Script, and Regionalism in Protopalatial Crete

A boundary between eastern and central Crete has been proposed for the Protopalatial period on the basis of the distribution of various types of material culture, most notably pottery. The distribution of Protopalatial seal groups, the production of which can be localized to specific regions on the island, is here added to this discussion. Malia and eastern Crete show a preference for prismatic seals with hieroglyphs and pictographic images, whereas central Crete produces mainly seals of other shapes with round seal faces and ornamental motifs. Evidence from seals is discussed in conjunction with evidence for the earliest attestations of script in Crete. From this perspective, a hypothesis is here suggested that, in contrast to what was previously thought, in Middle Minoan I/II Cretan Hieroglyphic was “at home” in Malia and the eastern part of the island, while Linear A was native in southern and possibly north-central Crete. In this context, the Hieroglyphic Deposit of Knossos is seen as intrusive in north-central Crete. This article explains the presence of Hieroglyphic documents at Knossos on the basis of theories that view the Minoan palaces as ritual centers potentially open to corporate groups from various regions on the island.

Active Pipeline's Defective Areas Maintenance Technique by Means of Well-bond Joints

Background. Pipeline strengthening technique by applying well-bond joints filled with molten metal or an alloy has been examined. The main disadvantage of the above mentioned technique is that it is difficult to ensure under-joint area sealing.Objective. To develop the strength increasing technique of the high pressure pipelines parts using the well-bond joints filled with molten metal enabling to achieve high efficiency of medium and small diameters tubes strengthening.Methods. Strength increasing technique of a working pipeline with the help of well-bond joints.Results. Improved active pipeline's defective areas maintenance technique has been offered. We have also offered face seal design that makes it easier to form under-joint layer that has optimal parameters.Conclusions. The offered technique improves the efficiency of strengthening the average and small pipes diameter.

Spiral-grooved gas face seal for steam turbine shroud tip leakage reduction: Performance and feasibility analysis

In order to minimize shroud leakage and its effect on aerodynamic loss of steam turbines, a new shroud seal design by employing spiral-grooved gas face seal theory is presented. To verify the method, a flow numerical simulation was conducted to investigate the effect of the new shroud seal on aerodynamic loss in steam turbine rotor row. The results show, compared with a traditional two-tooth labyrinth seal, the new shroud seal leakage is reduced by 99.3%, and the rotor row efficiency is improved by 1.9%. Furthermore, a feasibility analysis including lift and stiffness of gas film, tracking response of primary ring and deformation of mating ring was presented. The present design is a potential approach to further improve turbine stage performance.

Performance of Facepiece Respirators and Surgical Masks Against Surgical Smoke: Simulated Workplace Protection Factor Study.

Objective:Surgical smoke generated during electrocautery contains toxins which may cause adverse health effects to operating room (OR) personnel. The objective of this study was to investigate the performance of surgical masks (SMs), which are routinely used in ORs, more efficient N95 surgical mask respirator (SMRs) and N100 filtering facepiece respirator (FFRs), against surgical smoke.Methods:Ten subjects were recruited to perform surgical dissections on animal tissue in a simulated OR chamber, using a standard electrocautery device, generating surgical smoke. Six respiratory protective devices (RPDs) were tested: two SMs, two SMRs, and two N100 FFRs [including a newly developed faceseal (FS) prototype]. Fit testing was conducted before the experiment. Each subject was then exposed to the surgical smoke while wearing an RPD under the tests. Concentrations inside (Cin) and outside (Cout) of the RPD were measured by a particle size spectrometer. The simulated workplace protection factor (SWPF) was determined by the ratio of Cout and Cin for each RPD-wearing subject.Results:For the SMs, the geometric means of SWPFtotal (based on the total aerosol concentration) were 1.49 and 1.76, indicating minimal protection. The SWPFtotal values of the SMRs and N100 FFRs were significantly higher than those of the SMs: for the two SMRs, the SWPFtotal were 208 and 263; for the two N100s, the SWPFtotal values were 1,089 and 2,199. No significant difference was observed between either the two SMs or the two SMRs. The SWPFtotal for the novel FS prototype N100 FFR was significantly higher than the conventional N100 FFR. The correlation between SWPFtotal and fit factor (FF) determined for two N95 SMRs was not significant.Conclusions:SMs do not provide measurable protection against surgical smoke. SMRs offer considerably improved protection versus SMs, while the N100 FFRs showed significant improvement over the SMRs. The FS prototype offered a higher level of protection than the standard N100 FFR, due to a tighter seal. While we acknowledge that conventional N100 FFRs (equipped with exhalation valves) are not practical for human OR use, the results obtained with the FS prototype demonstrate the potential of the new FS technology for implementation on various types of respirators.

Temporal changes in filtering-facepiece respirator fit

ABSTRACTA three-year study examined changes in N95 filtering-facepiece respirator (FFR) fit at six-month intervals and the relationship between fit and changes in weight for 229 subjects. During each visit, subjects performed a total of nine fit tests using three samples of the same FFR model. Inward leakage and filter penetration were measured for each donned respirator to determine face seal leakage (FSL). A total of 195 subjects completed the second visit and 134 subjects completed all seven visits. Acceptable fit was defined as 90th percentile FSL ≤ 5% and at least one fit factor ≥ 100. An unacceptable fit was observed for 14, 10, 7, 12, 15, and 16% of subjects on Visits 2–7, respectively. The predicted risk of an unacceptable fit increased with increasing length of time between fit tests, from 10% at Year 1 to 20% at Year 2 and to 25% at Year 3. Twenty-four percent of subjects who lost ≥ 20 lb had an unacceptable fit; these percentages ranged from 7–17% for subjects with lower weight losses or any degree of weight gain. Results support the current OSHA requirement for annual fit testing and suggest that respirator users who lose more than 20 lb should be re-tested for respirator fit.

コイルドウェーブスプリング (CWS) における非線形変形特性の解析

In general, springs are flexible machine elements used for controlled application of force (or torque) or for storing and release of mechanical energy. A coiled wave spring (CWS), also known as a scrowave spring is a compression spring made of coiled wire or thin plate with waves giving a spring effect and offers the unique advantage of space savings when used to replace conventional coil springs. By reducing spring operating height, the coiled wave springs also offers a decreased spring cavity. A production cost savings is realized with a smaller assembly size and less material used in the manufacturing process. CWS makes it possible to accommodate higher thrust load within the limited axial space depending on the size of the wire (or plate), the number of waves, the height of waves, and the number of turns. In recent years, CWS with very high performance are widely applied to “Slip Clutch” and “Multi-Tooth Cutter”, “Retaining Ring”, “Face Seal”, and so on. However, nonlinear characteristics observed in large deformation of CWS has not been made clear yet. The large deformation analysis has been eagerly looking forward to as calculation formula. As it is, there exists no persuasive analysis. In this research, these nonlinear characteristics and spring constant for CWS are analyzed theoretically. A nonlinear large deformation theory is applied and exact analytical solutions are derived in terms of elliptic integrals, and then put into a nondimensional formula to facilitate the common understanding of large deformation phenomenon. Moreover, three concepts for the spring constant are newly proposed. In this study, some experiments were presented and the experimental results were compared with the theoretical formulas. As a results, the relation between the applied axial compression force and the nonlinear deflection obtained from the experiments is in good agreement with the relation predicted by the analytical theory.

Improving the reliability of radial face seals of aircraft engine rotor supports

The article presents an advanced radial face contact seal with increased operational life. High efficiency of the radial mechanical seal is ensured by the joint application of the hydrostatic and hydrodynamic lubrication principles. The hydrodynamic effect is achieved by applying the structure of fine grooves on the rotor hub. The dependence of the flow force value in the slot for a fixed-size gap on the rotor speed is presented. A prototype has been made and tested on a dynamic test bed intended for the realization of operating conditions of support seals making up a part of an aircraft engine. The results of theoretical and experimental studies are presented. Ways of improving the seal reliability due to improving the surface mechanical properties are proposed. A pattern of the development of a functional failure of the seal assembly is presented. The most adverse operating conditions and the main reasons of increased wear of the sealing surfaces are indicated.&nbsp; Methods of achieving high anti-friction characteristics of contact surfaces by applying nanostructured nonporous chrome-diamond coatings are proposed. Issues concerning the creation of advanced coatings with a positive gradient of depth mechanical properties are discussed. Anti-friction, anti-seize silver-diamond coatings and the use of diffusion molecular reinforcement technology are at the basis of the production of advanced coatings. The paper indicates the importance of anti-friction and extreme-pressure additives contained in the oil.

Research of serviceability of pulsed face seals with pumpback structures

The article discusses characteristics of pulsed face seals, analyzes their work process, and investigates the parameters of seal working efficiency. The experience of investigating seals by leading companies and institutions is presented. Experimental studies on the measurement of water leaks and the frictional torque at variouspressure differentials, rotor speed and spring rates have been conducted. Computational research for the case of air used as the seal working fluid has also been carried out. The dependences of the frictional moment on the rotor speed for seals with different mutual arrangement of pumpback structures have been compared on the basis of the experimental data provided by Stuttgart university. The change of pressure in a pumpback structure is analyzed for the following cases: remote structures, coincidence of structures, proximity of structures. A series of tests has been carried out to estimate the reliability of a pulsed seal. The test results are used for the investigation of experimental frictional torque dependences at different rotation speeds, pressure differentials and spring rates. It has been established that the optimum value of the spring rate is a prerequisite for ensuring the required sealing characteristics.

Self-adaptive surface texture design for friction reduction across the lubrication regimes

Surface texturing has been shown to reduce friction and improve durability in mechanical face seals and metal forming operations, and lightly loaded thrust bearings. However, the success has been limited to conformal contacts and low load high speed operating conditions, i.e. hydrodynamic lubrication dominated regime. Both experiments and numerical simulations have shown that textural patterns, under higher loading and/or slower speeds may increase friction and even cause the lubrication film collapse. Specific designs of surface texture pattern, as its shape, depth and density, are required for different lubrication regimes. Our own study has shown (Hsu et al 2014 J. Phys. D: Appl. Phys. 47 335307) that large/shallow dimple reduces friction in hydrodynamic lubrication regime, whereas small/deep dimple shows benefit in mixed/boundary lubrication regimes (if the textural designs can provides hydrodynamic/hydrostatic lift forces to reduce the machine loading). In considering an engine component typically experiences duty cycles that may cross various lubrication regimes, a multiscale surface texture design appears attractive. This type of mixed shape texturing combines textures designed for low load, high speed operating conditions and the textures that are designed for high load, low speed operations. In this paper, two types of multiscale surface texture designs are presented. Ball-on-three-flats (BOTF) wear tester (under high loading conditions) is used to evaluate the performance of these multiscale texture designs along with the baselines of un-textured surfaces under the same surface preparation procedures. Two texture designs with only a single shape dimples are included in the study. Results suggest that multiscale surface texture design not only further reduces friction in comparison to the textures with single shape dimples, but also shows the effectiveness across hydrodynamic regimes to the mixed lubrication regimes.

Thermo-hydrodynamic characteristics of spiral groove gas face seals operating at low pressure

Thermo-hydrodynamic behaviors of spiral groove gas face seals are investigated for the cases of low seal pressure. Pressure and temperature fields of gas film are calculated, and then influence of thermal distortion on seal performance are analyzed. It is found that spiral grooves lead to complex film temperature distributions and rotational speed results in the increase of whole film temperature. But the shear heat and pumping effect of spiral grooves have little influence on film temperature gradient along the leakage direction. The face thermal distortion, forming divergent clearance along the leakage direction, makes the opening force decrease and the leakage increase. A higher seal pressure and clearance will result in a larger thermal distortion. And the rotational speed may enhance the face thermal distortion further in some low pressure cases.

Analysis of a Hydrodynamic Spiral Grooved Upstream Pumping Face Seal Considering Cavitation

A numerical analysis of an oil-lubricated spiral grooved upstream pumping face seal, accounting for the occurrence of cavitation, have been performed in this paper. The “equivalent flow model”, which is a theoretical scheme for taking the JFO boundary condition into hydrodynamic lubrication theory, was applied to the analyses by a finite difference treatment of the Reynolds equation that dealt with the geometry of logarithmic spiral groove. The calculated results were compared respectively based on Reynolds model and JFO model. The load capacity, cavitation ratio, frictional torque and leakage rate were also theoretically calculated. The difference between the theoretical results based on two boundary conditions for cavitation occurrence is considerable. The JFO boundary condition should be used in theoretical studies on sealing characteristics rather than Reynolds equation, especially in the conditions of less groove depth and high rotary speed.

Shaft seal for separation of water and air with low frictional torque

A new type of shaft seal was specifically designed to separate water and air with a low frictional torque. The proposed water-sealing system, which was implemented as a shaft seal, has two hydrated seal lips fabricated from polyvinyl formal. An aqueous solution of polyethylene glycol, which is a non-Newtonian fluid, was injected between the seal lips to support the lubrication and sealing action at the dynamic seal faces. These configurations are based on a biomimetic approach, namely, the mechanism in a natural synovial joint. The water-sealing system exhibited a lower frictional torque than that of oil and mechanical seals, and the friction was not influenced by the applied water pressure. The prevention of water leakage from the water phase to the air phase was also confirmed for water pressure up to 0.8MPa. The proposed water-sealing system may contribute to the improvement of the recovery efficiency of natural energy systems utilizing water flows, tidal currents, and ocean currents, in which the rotating speed of a shaft is low under high water pressure.

A parametric and dynamic analysis of non-contacting gas face seals with modified surfaces

The application of various modifications such as micro-channels, compartments, micro-pores, texturing in mechanical non-contacting seals causes changes of dynamic properties of the medium layer. This paper presents the results of analyses pertaining to the impact of surface topography on the vibrations of cooperating rings. The balance of forces working in a seal affects non-contacting operation, i.e. maintaining the stability of the medium layer separating the rings. The consequences thereof include: controlled leak, small wear of sliding surfaces and prolonged lifespan.The presented model of gas face seals includes the non-linear Reynold׳s equation as well as the equations of dynamics describing the vibrations of the stator which were solved simultaneously with the use of numerical methods. The conducted analyses of the modeled seals and the obtained results may be useful when designing and choosing surface topography to the set operating conditions. It results in longer working time and reliable operation of devices in which those seals were installed.

Direct and inverse heat transfer in non-contacting face seals

The subject of this paper was to develop a mathematical model of a non-contacting face seal describing the phenomenon of the heat transfer in the system: sealing rings – fluid film. The function of non-contacting face seals used in rotor machines is to separate the working agent from the external environment. The nature of operation of non-contacting face seals allows the fluid to leak through the clearance not bigger than a few micrometres. During the operation of the rotor machine between the co-operating rings, an intense conversion of mechanical energy into heat occurs. At first, the heat flux generated in the fluid film is channelled to the sealing rings and then to the surrounding fluid.The solution of the presented model was conducted with the use of analytical methods for the direct and the inverse heat transfer problem. The distribution of the temperature fields in the sealing rings for the direct heat transfer problem was determined with the use of Fourier–Bessel series as the surface function of two variables (r,θ) for the cross-section of a ring. The inverse heat transfer problem was solved with the use of Trefftz functions.The presented computational methods allow a more detailed identification of the phenomenon of the heat transfer in non-contacting face seals and indicate a direction of further research and preparation of new computational methods.

A Mixed Thermoelastohydrodynamic Lubrication Analysis of Mechanical Face Seals by a Multiscale Approach

This article presents an improvement to a previous multiscale approach used to model the mixed lubrication regime in a mechanical face seal. The physical mechanisms considered by the improved model are the surface roughness effects on the fluid film lubrication, the thermal deformations, and the heat transfer in the seal rings due to viscous and dry friction. The developed numerical model determines the pressure distribution by taking into account the effect of cavitation and contact asperity between the surfaces. Heat dissipation, heat transfer, and deformations are computed from the heat dissipated at the seal interface by a finite element technique. The multiscale model significantly reduces computation time while maintaining the accuracy of the results. The results obtained through a parametric study show that there are different operating zones where the lubricating film thickness is controlled by the roughness height or by the thermal effect.

Study of the fluid film vaporization in the interface of a mechanical face seal

This paper presents numerical simulations of the effect of an increase in feeding temperature on a mechanical seal operating with water. A transient numerical model using the homogeneous fluid theory was developed to analyze the vaporization of the fluid film in a mechanical seal interface. Heat transfer in the contiguous solids and faces deformations are considered. After a validation of the model by comparison with experiments, a parametric study is presented. For moderate temperature rise, the vaporization of the fluid in the contact has no significant effect on the seal performance. However, above a temperature threshold, the mechanical seal can exhibit unstable behavior which can be detrimental for its life expectancy.