Rotary Shaft Seals Research Articles

Friction and wear of PTFE seal materials

AbstractShaft seals made from polytetrafluoroethylene (PTFE) materials, called PTFE lip seals, have been successfully used for decades in the chemical industry. Owing to their chemical and thermal stability, PTFE lip seals are used instead of elastomeric lip seals in many automotive and hydraulic applications. This paper deals with the fundamental tribological properties and effects of filled PTFE materials employed in rotary shaft seals, mainly on the basis of experimental work done in the authors' laboratory. The tribological components of a sealing system and the main influences on the sealing function are briefly surveyed. The test methods and conditions used are also described. The experimental results show that the fillers used in the PTFE compounds, as well as the topography of the shaft, play a crucial role in fluid sealing.

Inter-asperity cavitation and global cavitation in seals:: an average flow analysis

A universal, average Reynolds equation was previously developed to model the combined effects of inter-asperity cavitation and global cavitation in lubricating films between rough surfaces. In this study, the universal, average Reynolds equation is applied to two types of rotating shaft seals: lip seals and mechanical face seals. Inter-asperity cavitation is shown to affect the sealing mechanism of lip seals and to influence the behavior of new, worn, and wavy mechanical face seals.

Design aspects of modern rotary shaft seals

Rotary shaft seals, or alternatively rotary lip seals, made from synthetic elastomers are used in a wide range of applications under very varied conditions. They provide an economical means of sealing against rotating shafts, preventing the system lubricant from leaking out and also external contamination from entering. When designing the seal to run under specified conditions, there are many factors to take into account. In this paper it is not possible to cover all the aspects of seal design nor can a comprehensive catalogue of the options available on the market be given. Instead, the reader is presented with some salient facts and guidelines on current technology and made aware of the functional problems facing the designer.

Theory of lubrication of elastomeric rotary shaft seals

Current knowledge of the principles of rotary lip seal operation is assessed through a review of the experimental foundation and the key theoretical models. Studies of the existence of the lubricating film, the load support mechanism, the sealing mechanism, the thermal effects and the followability are described.

Fluorocarbon launches new PTFE rotary shaft seal range

Fluorocarbon launches new PTFE rotary shaft seal range

Slippery seals combat friction

Stiction is a major cause of lost power and energy in systems with moving parts such as electric motors. In this article Blue Diamond, discusses the benefits of treating O-ring and rotary shaft seals with its SSHT non-stick process, which can dramatically reduce friction losses.

Radical sealing device proves its reliability

‘Radical in design and concept’ was a phrase used to describe James Walker's patented RotaLion when it was launched in 1985. Over ten years later this rotary shaft seal is still considered innovative.

A Teaspoon Pump for Pumping Blood with High Hydraulic Efficiency and Low Hemolysis Potential.

Virtually all blood pumps contain some kind of rubbing, sliding, closely moving machinery surfaces that are exposed to the blood being pumped. These valves, internal bearings, magnetic bearing position sensors, and shaft seals cause most of the problems with blood pumps. The original teaspoon pump design prevented the rubbing, sliding machinery surfaces from contacting the blood. However, the hydraulic efficiency was low because the blood was able to "slip around" the rotating impeller so that the blood itself never rotated fast enough to develop adequate pressure. An improved teaspoon blood pump has been designed and tested and has shown acceptable hydraulic performance and low hemolysis potential. The new pump uses a nonrotating "swinging" hose as the pump impeller. The fluid enters the pump through the center of the swinging hose; therefore, there can be no fluid slip between the revolving blood and the revolving impeller. The new pump uses an impeller that is comparable to a flexible garden hose. If the free end of the hose were swung around in a circle like half of a jump rope, the fluid inside the hose would rotate and develop pressure even though the hose impeller itself did not "rotate"; therefore, no rotating shaft seal or internal bearings are required.

A new concept in rotary shaft seal design

A new concept in rotary shaft seal design

TWO-DIMENSIONAL BINGHAM PLASTIC FLOW IN A CYLINDRICAL PRESSURISED CLUTCH

An examination of the capability of an energised electro-rheological fluid to act as a rotating shaft seal is reported. A two-dimensional laminar flow model based on a Bingham plastic flowing between parallel plate electrodes indicated that leakage would always occur whenever the shaft was in rotation, whatever the magnitude of the pressure gradient along the sealing annulus. This result was confirmed in experiments, the results of which show some discrepancy between theory and experiment in the magnitude of the leakage rate. However this error is accountable and is acceptable in the area of immediate interest-shaft speed of circa 1000/1500 rpm and at maximum yield or electro-stress.

High Technology of Sealing Solved by Ferrofluids

The ferromagnetic rotary shaft seals are for the present the most important industrial applications of magnetic fluid (ferrofluid) technology developed mainly in the last decade.

Analytical Solution of the General Linear Viscoelastic Radial Load Equation for Rotary Shaft Seals

The viscoelastic radial load equation for a cylindrical shell representing the seal was derived from the static solution by the correspondence principle and from first principles. The equation decoupled in space and time by a normal mode analysis was solved both by conventional methods with an impact initial condition and rather more efficiently by the Laplace transform method, for a general linear Maxwell body in plane stress. The solution was in the form of a recurrence relation, allowing representation of material properties by any number of Maxwell elements. When subjected to the standard creep test, step radial load, the seal responded with an impact displacement, followed by transient and finally steady creep. The equation was also solved by the finite element method with the semidiscrete approximation. The solution for stress relaxation and oscillatory strain are given in the Appendix. Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4–7, 1992

Finite Element Solution of the Radial Load Equation for Rotary Shaft Seals

Displacement equations for static conical seal structures were solved by the Ritz-Galerkin finite element method. The constitutive equation was Hooke's law with the plane stress assumption. Finite strains relative to the initial or free configuration were used in conjunction with the strain-dependent modulus of the material. The nonlinearity of the transverse shear stress resultant or radial load thus predicted, was in exact agreement with the experiment almost up to the maximum possible displacement. The mechanism by which the radial load became nonlinear was not simply additive in the geometric and material contributions. Instead, the geometric non-linearity, while having a negligible effect by itself on the radial load, had the property of more than doubling the maximum strain in the structure, therefore amplifying the effect of the strain-dependent modulus on the radial load. Both local and global algorithms for solving nonlinear equations gave the same results, suggesting that the solution found was unique. Experimental radial loads of seal structures with radius-to-thickness ratios between 6 and 42 were favorably predicted by the program. Measured seal thermal expansions were also in very good agreement with program predictions.

Development of Rotary Shaft Seals for Primary Coolant Pumps for Nuclear Reactors

Electricity generated by nuclear power is now common in Japan. The present commercialized status of nuclear power generation technology has been established due to efforts of many engineers and also as a result of information accumulated from other advanced countries. Presently 23 percent of total electricity generated in Japan depends on nuclear power, and in the long run, this proportion is expected to increase further. Although accumulation of various important technological knowledge is required in nuclear power generation, the conversion of heat generated in nuclear reactors into electrical energy by means of a working medium is one of the most essential problems in the relevant technology. This paper deals with rotary shaft seals used in the circulation pump for the primary coolant, as an important functioning component in such a system. Once this sealing system causes trouble such as excessive leakage, it results in quite serious social problems; i.e., not only power failure but also possibly radio...

Rotary shaft seals

This paper reviews the state-of-the-art of rotary shaft seal technology and shows that the apparent simple appearance of shaft seals belies the complex phenomena controlling their performance. Heat transfer, fluid dynamics, mechanical vibration and the chemistry of elastic materials all interact to prevent the leakage of fluid. The components, when correctly chosen, are able to function in a wide range of applications and continuing development keeps them abreast of a mechanical power unit, and is severely criticized if unsatisfactory, the best chance of success and reliability comes from giving it due consideration from the beginning.

Analysis of the static and dynamic behaviour of a magnetic liquid seal

A rotating shaft seal, using ferrofluid between biconical truncated magnetic poles, is analysed both in static and dynamic conditions. After solving Laplace's equation and allowing an approximate expression for the magnetic potential, the magnetic forces acting on the working fluid are obtained. It is thus possible to determine the baric field existing in static conditions and the highest tolerable pressure jump. In the case of dynamic working the flow is schematized by two interior regions, where the azimuthal velocity prevails, and four boundary layers on the walls, where meridional transport of fluid takes place. Assuming laminar motion, by means of a perturbation procedure it is possible to see that in the interior, to a first approximation, two potential vortexes exist, whose circulations, after imposing the rotational equilibrium of the fluid about the symmetry axis, are found to be equal to about one half of the rotating pole peripheral circulation. This allows the determination of the baric field in the rotating fluid and of the friction moment exerted on the shaft.

Ferromagnetic liquids - Their magnetic properties and applications

Ferromagnetic liquids are here defined as colloidal suspensions of single domain particles with diameters between 40-200 A. The magnetic properties are best described as superparamagnetic and the classical theory of Langevin paramagnetism, modified to include a particle size distribution, applies to these systems. Liquids have been prepared with saturation magnetisations between 50 G and 1000 G, their viscosity increasing from approximately 1 cp to 104cp as the magnetisation increases. The colloidal particles have magnetic, hydrodynamic and physical sizes which are different. The mode of magnetisation may, therefore, be complex arising either through physical rotation of the particle (Brownian rotation) or a rotation of the magnetisation within an essentially static particle (Neel rotation). The actual process can have a profound effect on the properties of the ferromagnetic liquids. Ferromagnetic liquids have a viscosity which is anisotropic in a magnetic field and a magnetic birefringence which produces interesting domain observations in polarised white light. The use of ferromagnetic liquids in devices is very closely related to their stability in magnetic field gradients and a criterion in terms of the change in particle concentration in the field gradient ∇/n <1cm-1can be defined. Although stable ferromagnetic liquids are currently used in rotating shaft seals and as damping fluids the use of the unique properties of ferromagnetic liquids in devices has not yet been fully exploited.

Elastohydrodynamic Lubrication of Offset O-Ring Rotary Seal

A fundamental research into the lubrication mechanism and operation of a new type of rotary shaft seal has been conducted. Optical interference technique was successfully used to study the film profiles with optically smooth elastomer seals. Elastohydrodynamic lubrication was found to exist over a wide range of operating conditions. A study of the other performance variables for the Offset-Seal define its useful application range to be between the Packing-Gland and Face-Seal.

Some factors of rotary shaft seal design and effects of lubricants on related elastomers

Some factors of rotary shaft seal design and effects of lubricants on related elastomers

Performance of a Modified Packed-Gland Seal

An experimental investigation of the mechanics of hydrodynamic lubrication and heat generation and dissipation of packed-gland rotary shaft seals was performed on a somewhat novel design. The design differs from conventional stuffing-box seals in that the packing was inverted so that it rotated with the shaft. It was also skewed so as to enhance heat transfer and lubrication. Further, the gland was loaded hydraulically so that the axial pressure applied to the packing was readily controllable. These modifications proved to be successful in that much improved stability of operation was obtained through lowered coefficients of friction (with water as the sealed fluid) and interface temperature which prolonged seal life without serious detriment to leakage. Some rheological data on Teflon-asbestos packing is presented as well as kinetic coefficients of friction. Motion picture frame photographic sequences of the packing interface showing packing deterioration and lubricant film cavitation are included also.