Flexible Seal Research Articles

Structural evaluation of a compact, semi-closed W-shaped divertor system for JT-60U

A compact, semi-closed W-shaped divertor system has been designed, fabricated and installed in the JT-60U to replace the open divertor system. The new system consists of inclined divertors, a dome and baffles. To meet the structural requirements, a segmented structure with an electrically insulated flexible gas seal was applied. Using FEM codes, the system’s structural integrity was confirmed for the plasma disruptions by electromagnetic and structural analyses, which take into account the effect of halo currents. Substantial reduction of induced electromagnetic forces is attained in the divertor system due to the electrical insulation used for the gas seal structure. In addition, because of its segmented structure, the induced electromagnetic forces on each component unit are found to be limited. The maximum stress intensities and their ranges are obtained within allowable values. Thermal stress arising from the temperature difference between the divertor system and the vacuum vessel during the baking operation is also satisfactory. Furthermore, thermal and thermal stress analyses showed that the plasma facing components have sufficient structural integrity.

Lubrication of Flexible Seals with D-Shaped Cross Section for Reciprocating Motion.

In order to understand the dynamic characteristics of flexible seals for reciprocating motion, the relationship between film behavior between sealing surfaces and friction characteristics is investigated based on direct observations using the optical interferometry technique. A nitrile rubber band with a D shaped cross section instead of actual D-rings was pressed against an oscillating glass plate. The effects of the length of stroke and surface defects are also examined. It has been found that even in the mixed-lubrication regime rather thick oil films are formed during the reciprocation. However, when the length of stroke is less than a certain critical value, the film completely collapses even in the hydrodynamic lubrication range and the reciprocating motion is established by the deformation of the rubber specimen. The surface defects such as dents and bumps bring about local fluctuation in film thickness downstream of these defects.

In-the-ear hearing aid with flexible seal

The in-the-ear hearing aid (10) has a collar (30) which can form a seal in the bony part (3) of the ear canal (1), which reduces the occlusion effect. The collar (30) comprises a tubular portion (31) which is engageable against the wall (9) of the ear canal, a fixing portion (32) and a curved sealing portion (33). Owing to the use of this collar (30) it is not necessary to make a mould of the bony part (3) of the ear canal. This collar enables the hearing aid to be constructed in such a manner that it can be inserted so deep into ear canal that it is substantially invisible.

Cobblestone Oscillations of an SES with Flexible Bag Aft Seal

The high-frequency dynamic response of surface effect ships (SES) equipped with a flexible bag aft seal is studied. The results show dominating vertical accelerations in a frequency range important for passenger comfort and crew work ability. The mathematical model for the craft dynamic response accounts for the motions and accelerations in heave and pitch induced by both the unsteady uniform pressure and the spatially varying air cushion pressure. The effect of a flexible bag aft seal and a variable leakage area under the seals is included. The bag dynamic response is treated as linear and quasistatic. It is shown how the flexible bag reduces the spatial pressure resonance frequencies of a 35 m SES. The variable leakage area under the bag is found important for the response of the craft in low sea states.

Brush-on-disc simulation tribotesting of materials for gas turbine-compliant seal components

A brush-on-disc tribometer was used for high-speed, high-temperature sliding experiments on materials simulating conditions in turbine flexible element gas path seals. Of the polymeric, ceramic and metallic material pairs tested only superalloy wires sliding against ceramic surfaces were promising candidates. After extensive running-in, nickel-based wires wore at a rate close to 10 −8 mm 3/N m when sliding under moderate loads at speeds to 100 m/s and temperatures to 500°C against a Cr 3C 2/NiCr coated counterface whose wear was also very low. Thus, useful seal life under engine operating conditions may result, depending upon allowable initial and minimum effective brush-rotor interferences.

Characterizing the Leakage Flow of Braided Fiber Seals

A new kind of high temperature flexible braided fiber seal has been developed for advanced hypersonic engine applications. Leakage flow experimental observations show that both engine pressure and preload pressure influence leakage flow rate. Al though the Reynolds number is relatively small ( Re < 10), the mass flow rate com parison of air versus helium reveals that the leakage flow is not viscous dominant. The Ergun equation describing flow through porous media is applied to the flow analysis. The two constants in the Ergun equation, designated as the viscous flow constant CL and the inertial flow constant CT, are determined experimentally. For the leakage flow test setup and the seal geometry, test data show that the values of CL and CT vary for different seal fiber architectures. The relative magnitude of the non viscous flow effect can be determined using a dimensionless variable ( ReCT/CL). If this variable is much less than 1, the nonviscous flow effect can be neglected. For the seals tested, the ratio of CT/CL is at the range of about 1 to 2 in most cases. Therefore the criterion for the viscous dominant flow is Re < 0.1. Predictions of seal leakage flow using the Ergun equation show good agreement with experimental data of both fluid media, air and helium.

Water-Jet Flagellator and Test Results on Seal Materials for SES, Seal Vibration Test Results of 30 ton Type SES Test Craft

To evaluate vibration fatigue life of SES flexible seal materials, medium size water-jet flagellator which can simulate the actual vibration of SES flexible seals was made and various types of the flexible seal materials were tested. CR or U on double mesh weave nylon, CR on special weave nylon and Thermo Plastic Polyester Elastomer showed good fatigue life among the tested materials.Then, Thermo Plastic Polyester Elastomer was chosen as SES flexible seals, in order to obtain the data of durability of bow seal for 30 ton SES test craft and to study the relationships between flagellation test and bow seal's vibration test, both tests were conducted.As the results of the tests, it was proved that the maximum acceleration of the lowest part of the bow seal went up to 70 g, the mean frequency of the seals was about 60 Hz, and also the effectiveness of the flagellation test as a accelerated fatigue life test of seal materials was made clear.

Basic Study on Mechanism and Control of Seal-Peeling Robot. Analysis of Seal Peeling Task and Design & Control of Robot.

With the rigid requirements of the automation of the handling of flexible limp seal materials in the industry in mind, this paper deals with a mechanism and control method of a seal-peeling robot. In this paper, we consider the method by which a man peels a seal, and based on this analysis, we make and test a seal-peeling robot. First of all, we analyze a man's seal-peeling task and determine how many and what kinds of basic motions are included in it, and also check how they appear while the task is being carried out. Then we construct a mechanism of the robot based on this analysis. Secondly, we propose a control method for it. We next model the mechanism of glue destruction and analyze how we should control the robot peeling the seal effectively. Finally, we produce a robot based on these analyses and test it to show that it works as expected.

Biodegradation of natural rubber vulcanisates

Rubber has been used to form flexible seals between pipe sections in water mains and sewers for over 100 years. During the past 30 years, instances have been found of rings showing deep pitting due to microbiological attack. The need was to devise compositions resistant to attack which were easy to manufacture and complied with standard physical requirements. By careful choice of ingredients, natural rubber vulcanisates can be prepared which have negligible weight losses under accelerated test conditions and should have a long working life. The avoidance of extractable or degradable ingredients with a generous quantity of an insoluble antioxidant and a chlorinated wax are seen to be effective. Chain scission seems to be an essential prerequisite for microbiological degradation. The capture of transition metal oxidation catalysts from the water over a long period may be a factor in the attack mechanism.

Designer bedpans.

A new bedpan for women has been produced and designed, its manufacturers say, 'to overcome the limitations of existing female urinals'. The Lorann Female Bed- pan has an adjustable base to suit different body sizes, and a flexible perineal seal to provide a leak proof contact. Further information' from Medical Resupply UK Ltd, Homewoodgate House, Nov- ington Lane, East Chiltington, Lewes, Sussex, BN7 3AU.

The development of a flexible bushing seal for rotating shafts

Pressures and speeds now specified for rotary shaft sealing duties frequently exceed the capabilities of rotary shaft lip seals, compression packings or even mechanical face seals. Elaborate pressure balancing arrangements, additional lubrication or cooling may be required to establish a viable sealing system which could still be running close to the operational limitations of the chosen seal type. A measure of unreliability is almost inevitable under such conditions. This paper describes a new and radical approach to the sealing of rotary shafts based on a no-contact self-energized flexible throttle which may be used in endless or split form. The elimination of any seal contact pressure whilst achieving leakage rates of acceptably low levels - lower than many conventional packings for example - has a dramatic effect on power consumption and seal environment temperatures. By taking the conventional rigid throttle bush theory and translating the idea into a pressure responsive flexible clearance seal, PV conditions exceeding 1000 bar m/s have been sustained repeatedly with a variety of fluids. No separate energization of the seal other than by system pressure is normally required. The product is already being used or investigated in water turbine, pump, hydraulic motor and marine sterngland duties and has been evaluated theoretically and practically by BHRA at Cranfield and the National Centre of Tribology, Risley.

Study on Flexible Seal Materiats for SES (1 st Report)

A water-jet flagellator, having the maximum jet speed of 100 kt, was made to evaluate vibration fatigue life of materials for the SES flexible seal. With this device, the fatigue life was investigated on ten conventional Fabric Reinforced Rubber materials.This flagellation test worked very well as a ranking method of the candidate materials, and it was revealed that two materials, NBR (PVC) on plain weave nylon and NR/SBR blend on twill nylon, gave good fatigue life among the materials supplied to the test.

Study on Durability Characteristics of SES Bow Flexible Seal

The flexible bow fingers of Surface Effect Ships (SES) and hovercraft wear away as a result of violent vibration called flagellation when the finger tips of the skirt contact with the water surface. Finger wear is one of the important problems for SES and hovercraft. A water-jet flagellator was made which can simulate the conditions of the actual fingers contacting with the water surface in order to study the durability of flexible fingers for SES bow seals. Two kinds of experiments were carried out using actual size fingers of the Mitsui hovercraft MV-PP 5. One was a flagellation test carried out over many hours from which the wear rate of test fingers was estimated. The other was an acceleration measurement test at the vicinity of the finger tips carried out over a few minutes. In these tests some parameters having influence on finger wear were changed, especially the wetted length of fingers and the water-jet velocity. The essential results are as follows.(1) It seems that this water-jet flagellator can simulate the actual finger motion contacting with the water surface because the wear patterns of test fingers resembel those of the actual hovercraft bow fingers.(2) The finger wear rate increases with wetted length, but remains almost constant above a certain wetted length.(3) The finger wear rate increases very rapidly with water-jet velocity.(4) It seems that there is some relationship between wear rates and amplitudes of finger acceleration.

A second stripper for an EN or FN tandem accelerator

A second stripper has frequently been installed, part way down the high-energy acceleration tube, in an MP or other very large tandem to achieve a higher particle energy and charge state [1–3]. In an EN, FN or similar accelerator the space available in the dead section is very small, approximately 4″ in length and little more than the tube diameter transversely. The 4″ length must also accomodate the flexible bellows and vacuum seals that are necessary between the individual acceleration tubes. A stripper housing 22 foils 0.75″ diameter has been built and successfully installed, in this space, on the FN tandem accelerator at Florida State University. This accelerator has always operated with a 0.75″ diameter aperture in this position so no loss of beam transmission occurs.

A method for repeated sampling of cerebrospinal fluid from conscious guinea pigs

A new method is described for obtaining repeated cerebrospinal fluid (CSF) samples from conscious, unrestrained guinea pigs. A simple, disposable cannula is introduced into the cisterna magna by puncturing the atlanto-occipital membrane. The cannula is equipped with a silicone rubber disc which is glued to the membrane, forming a firm but flexible seal. Daily CSF samples of at least 100 μl can be obtained from unrestrained guinea pigs. Chronically cannulated lactating females continued to suckle their litter successfully, and their milk ejection response was not affected by withdrawal of CSF.

TVA cuts deep slot in dam, ends cracking problem : Aleraham, T J; Sloan, R C Civ Engng, NY, V48, N1, Jan 1978, P66–70

In 1972, cracking in the concrete dam at TVA's Fontana project embarked TVA on a four-year program of investigation, analysis and repair. Thermal expansion in the downstream face of the dam caused a longitudinal thrust that cracked the curved blocks near the left abutment. To retard cracking while a permanent solution could be devised, TVA sprayed reservoir water on the dam face to cool the concrete, pressure-grouted the crack and installed post-tensioned cable tendons to keep the crack from opening further. The final solution was to cut a vertical slot 100-ft deep across the dam to interrupt the longitudinal thrust. The slot was cut by drilling overlapping holes into the top and downstream face of the dam. Two flexible rubber seals prevented the water from entering the slot. Frequent monitoring of the dam shows the slot has solved the cracking problem.

High Pressure Optical Cell for the Study of Biochemical Reactions

An inner fused quartz cuvette with flexible inert seal is described which allows the examination of biochemical solutions at high pressures without contact with metal surfaces. The cuvette is used in a commercially available high pressure optical cell without further engineering.

Two modifications of the Kratky small-angle X-ray camera

A Kratky small-angle X-ray camera has been modified in two respects to provide increased sensitivity and performance. (1) Flexible metal bellows seals have been mounted between the collimation system vacuum cover and the specimen chamber and between the specimen chamber and the tank which provides a vacuum path to the detector. The consequent elimination of four Mylar windows in the X-ray path near the sample resulted in a significant reduction in the background scattering. The degree of improvement depends on several variables including the collimation system geometry, X-ray tube power, and the electronic noise of the counting system. (2) A flat piece of hot-pressed pyrolytic graphite has been mounted as a diffracted beam monochromator. Experimental results show the diffracting efficiency of the graphite to be about 25% – a value sufficiently high that for the same total counting time, the detector will record the same net number of X-ray photons as with balanced filters but with much improved statistics.

Cryostat for imposing compressive forces on contacts using an electromagnet

A cryostat is described which incorporates an electromagnet, inside the experimental chamber, for the accurately controlled imposition of small forces (less-than-or-eq, slant 001 N) on contacts. This is superior to externally loaded systems in that the necessity of using a force transmission shaft (together with flexible vacuum seals) has been avoided and the concomitant shaft heat leaks have been eliminated.

Design of One-Piece Jet-Engine Compressor End Seals

Performance of advanced air-breathing propulsion systems can be significantly improved through the utilization of effective sealing devices. One of the areas in which immediate benefits are realizable from improvements in sealing efficiency is the high-pressure compressor end area. This paper describes the design of a face-type flexible seal and a face-type rigid seal for a compressor end seal based upon the cruise conditions expected in one version of the supersonic transport (SST) jet engine. The seals, non-contacting during operation, operate on air films achieved through the employment of hybrid gas-bearing geometries on the seal faces. The design procedure discussed consists primarily of the selection of the most applicable seal-face geometries force and moment balance, determination of seal tracking capability, establishment of leakage characteristics, thermal gradients, and stress and deflection calculations. The design results indicate that satisfactory seal performance can be obtained with either of the two configurations. Leakage reductions of an order of magnitude compared to that encountered with labyrinth seals commonly used in existing jet-engine systems can be achieved.