Seal Extrusion Research Articles

Failure analysis and structural improvement of helicopter landing gear seals based on experiments and three-dimensional numerical simulation

The utilization of O-ring seal structures in landing gears has historically been associated with high rates of failure. Therefore, this study analyzes helicopter landing gear friction failures based on experimental and numerical simulations. The model is designed to replicate the failure phenomena including “seal extrusion”, “seal leakage”, “seal wear”, and “seal distortion”, and to further investigate causes of failure. Corresponding failure criteria are also presented. Addressing the deficiencies inherent in the original O-ring structure, three composite seal structures—namely, the VL seal, double triangle seal, and T-seal—are introduced to enhance the respective seal structure of the buffer pillar. The findings exhibit that, following the transition to the composite seal structure, the strain peaks are optimized. Finally, this paper offers optimal contact pressure ranges for the optimized seals.

Research on the Dynamic Characteristics of Mechanical Seal under Different Extrusion Fault Degrees

In order to explore the dynamic characteristics of the mechanical seal under different fault degrees, this paper selected the upstream pumping mechanical seal as the object of study. The research established the rotating ring-fluid film-stationary ring 3D model, which was built to analyze the fault mechanism. To study extrusion fault mechanism and characteristics, different dynamic parameters were used in the analysis process. Theoretical analysis, numerical simulation, and comparison were conducted to study the relationship between the fault degree and dynamic characteristics. It is the first time to research the dynamic characteristics of mechanical seals in the specific extrusion fault. This paper proved feasibility and effectiveness of the new analysis method. The fluid film thickness and dynamic characteristics could reflect the degree of the extrusion fault. Results show that the fluid film pressure fluctuation tends to be more intensive under the serious extrusion fault condition. The extrusion fault is more likely to occur when the fluid film thickness is too large or too small. Results illustrate the opening force is affected with the fluid film lubrication status and seal extrusion fault degrees. The fluid film stiffness would not always increase with the rotating speed growth. The seal fault would occur with the increasing of rotating speeds, and the leakage growth fluctuations could reflect the fault degree.

Quick Profile Die Balancing of Automotive Rubber Seal Extrusion by CAE Technology

The extrusion process of a type of automotive rubber seal was considered by using Computer Aided Engineering (CAE) technology. Based on the die balancing requirement, CAE technology was utilized to speed up the die development and balancing process. The rubber material was EPDM and unacceptable extrusion deformation was found by using a parallel die. More balancing dies were then designed following the procedures proposed by the die balancing method and the effect of them was evaluated with respect to CAE analytical results. It was found that the addition of an opening section in the die would provide a more uniform velocity distribution at the die exit than the parallel die. The length of opening section was also found to affect the die balancing and so an optimum length of the opening section was determined by CAE analysis. Further optimization of the die was carried out by adjusting the local length of the opening section. Finally, a real die was cut based on the optimization results and used for production. Ideal profile products were obtained and very small and acceptable deviation from the die was observed, which validated the advantage and accuracy of CAE technology combined with die balancing requirement.

Development of a robot control method for curved seal extrusion for high productivity in an advanced Toyota production system

Recent Japanese enterprises have been promoting global production to realize uniform quality worldwide and production at optimal locations for survival amid severe competition. The authors considered the necessity of including the above method in the strategic application of the Toyota production system (TPS), and clarified Advanced TPS as the global production by manufacturing technology. In the future, reformation of the production workshops transformed by robotics and IT will be necessary in order to keep the same quality worldwide and production at optimum locations. Thus manufacturing technology had to be improved for mass production by developing the latest robot control methods. So far, the authors have established a robot control method for global production called RCM-EPC. RCM-EPC contains a three-core robot control method with (i) locus and speed control of the external point (-LSC), (ii) simulation for optimizing the operation position (-SOP) and (iii) constant speed control for robot movement (-CSC). Furthermore robots are applied to several applications in order to improve productivity and achieve a high-quality appearance. In particular, the authors here introduce an up-to-date glass-integrated curved seal extrusion (CSE), which is a new technology for use in manufacturing: the automobile-window mole as an example for Toyota – one of the most advanced automotive manufacturing enterprises in the world. With the demonstration of a 50% reduction in manufacturing costs using Advanced TPS, the authors have achieved high productivity and quality assurance in global production.

Modelling and Optimization of Composite Rectangular Reciprocating Seals

A computational model of rectangular reciprocating seals, previously developed for elastomeric seals, has been extended to cover the mechanics and elastohydrodynamics (EHD) of composite seals comprising two polytetrafluoroethylene (PTFE) and one central elastomeric part, chemically bonded together. The model is demonstrated on a rotary vane actuator application and shown to produce realistic results regarding the contact pressure, film thickness, leakage, hydrodynamic friction force, and seal extrusion. Total computational time is very short, typically up to five hundredths of a second (0.05 s) on a 1.5 GHz personal computer. The main purpose of the model is the analysis and optimisation of said composite seal such that it outperforms the elastomeric seal (of exactly the same dimensions) in terms of leakage, hydro-dynamic friction, and extrusion in a wide range of operating conditions. For this goal, the PTFE-to-seal volume ratio of the composite seal is initially varied between zero and 90 per cent, and the results on leakage, hydrodynamic friction force, average film thickness in the sealing contact, and extrusion length of the composite seal are plotted and compared with those of the elastomeric seal for nominal operating conditions at three temperatures (−54, +22, and +99 °C) and for both flooded and starved lubricating conditions in order to find a first approximant to the optimum PTFE-to-seal volume ratio that gives the composite seal better overall sealing performance. Then, using the selected approximant of the optimum ratio, a parametric study is performed to compute the effects of seal interference (proportional to contact pressure), contact velocity, seal corner radius, and degree of lubricant starvation of the sealing contact on leakage, friction, and seal extrusion at the previously mentioned three temperatures for both flooded and starved contacts, thus establishing the regions of operating conditions and design parameters that benefit one seal or the other. It was found that, overall, the composite seal, despite a small (insignificant) disadvantage on leakage, significantly outperformed the elastomeric seal in terms of hydrodynamic friction and extrusion. Further optimization is possible, depending on performance priorities (for example, if leakage is valued more than friction, or wear more than leakage, etc.).

Transient elastohydrodynamic lubrication of rectangular elastomeric seals for linear hydraulic actuators

A numerical model developed previously by the author to study rectangular rubber seals for reciprocating piston rods in hydraulic actuators is extended to include transient effects, considering the sealed pressure and the stroking velocity of the piston rod as time variables. The model incorporates various improvements regarding the treatment of seal extrusion, non-linear seal elasticity effects, as well as the modelling of back-up rings at the air side of the actuator, all of which have been dealt with individually in previous studies by the author. These new features are combined in the present model for a complete analysis of the leakage and friction performance of the seal-ring system under real transient operating conditions of industrial and aircraft actuators, including thermal effects and rough-contact analysis, and covering the widest applicable range of sealed pressures (over 0.1 MPa) and operating temperatures (− 60 to + 140°C).

Analytical study of the extrusion of rectangular elastomeric seals for linear hydraulic actuators

Rectangular elastomeric seals used on reciprocating piston rods in high-pressure hydraulic actuators often suffer from extrusion damage at the low-pressure side of the actuators. The extrusion takes place at the narrow clearance between the rod and the actuator, where the seal develops a ‘nip’ under conditions of high sealed pressure and/or high friction with the rod, which is amplified in the absence of a back-up ring. This form of strain can lead to permanent damage of the seal and impair the sealing performance of the system. This paper deals with the modelling of this kind of seal extrusion. Algebraic equations were developed to describe the shape and contact pressure of the extruded part of the seal with the rod. A study is presented about the effects of various operating parameters on the extent of seal extrusion in order to minimize the risks of damage. It was found that only the use of a back-up ring can adequately cancel the seal extrusion mechanism.

ＣＳＥモールの開発

ＣＳＥモールの開発

A solution to the problem of end cap seal extrusion

A solution to the problem of end cap seal extrusion

Experimental Study of Pneumatic Seal Extrusion

An experimental study of pneumatic seal extrusion is presented. Direct visual observations are made. An empirical formula for calculating extrusion based on the geometric characteristics of the sealing system is presented.

Seal extrusion: KSIESKI, K.T. Lubrication Engineering, Vol 26, No 6 (Jun 1970) pp 198–205

Hysteretic behavior in the direction of sliding is investigated for kinematically constrained slideways, using a special system produced to study the limits of performance of thin-film polymer on glass bearings. A typical configuration for a superprecision instrument slideway using PTFE pads and a Zerodur counterface is known to exhibit around 200-nm sliding hysteresis. Moreover, this value is strongly dependent on the total load on the bearing system. The pattern of dependence is consistent with an established model of contract under oblique forces, although the materials conditions at the interface are much more complex than those assumed in that model. Full isolation of these properties is not possible with the present experiments, but they indicate that the shear modulus of the interface layer is more than ten times greater than that of bulk polymer.