FLUID SEALING research at BHRA Fluid Engineering has its roots in the early years following the 1939–45 war. In 1945 the then Ministry of Aircraft Production felt that the…
Abstract
FLUID SEALING research at BHRA Fluid Engineering has its roots in the early years following the 1939–45 war. In 1945 the then Ministry of Aircraft Production felt that the equipment designer needed sound, basic information on the way hydraulic jack seals functioned and the factors affecting their performance. D. F. Denny was therefore seconded to Imperial College, London, to undertaken programme of research on reciprocating oil seals, which resulted in the publication of a 120‐page volume: “The sealing mechanism of flexible packings”, recently reprinted to meet a continuing demand.
Summarizes briefly the dramatic advances made in the reliability of mechanical seals for rotating shafts in the process chemical and petrochemical industries over the last 30…
Abstract
Summarizes briefly the dramatic advances made in the reliability of mechanical seals for rotating shafts in the process chemical and petrochemical industries over the last 30 years. Shows that expected mean time before failure has improved from tens of days to years over that time.
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Gabriel Dämmer, Hartmut Bauer, Rüdiger Neumann and Zoltan Major
This study aims to investigate the suitability of a multi-step prototyping strategy for producing pneumatic rotary vane actuators (RVAs) for the development of lightweight robots…
Abstract
Purpose
This study aims to investigate the suitability of a multi-step prototyping strategy for producing pneumatic rotary vane actuators (RVAs) for the development of lightweight robots and actuation systems.
Design/methodology/approach
RVAs typically have cast aluminum housings and injection-molded seals that consist of hard thermoplastic cores and soft elastomeric overmolds. Using a combination of additive manufacturing (AM), computer numerical control (CNC) machining and elastomer molding, a conventionally manufactured standard RVA was replicated. The standard housing design was modified, and polymeric replicas were obtained by selective laser sintering (SLS) or PolyJet (PJ) printing and subsequent CNC milling. Using laser-sintered molds, actuator seals were replicated by overmolding laser-sintered polyamide cores with silicone (SIL) and polyurethane (PU) elastomers. The replica RVAs were subjected to a series of leakage, friction and durability experiments.
Findings
The AM-based prototyping strategy described is suitable for producing functional and reliable RVAs for research and product development. In a representative durability experiment, the RVAs in this study endured between 40,000 and 1,000,000 load cycles. Frictional torques were around 0.5 Nm, which is 10% of the theoretical torque at 6 bar and comparable to that of the standard RVA. Models and parameters are provided for describing the velocity-dependent frictional torque. Leakage experiments at 10,000 load cycles and 6 bar differential pressure showed that PJ housings exhibit lower leakage values (6.8 L/min) than laser-sintered housings (15.2 L/min), and PU seals exhibit lower values (8.0 l/min) than SIL seals (14.0 L/min). Combining PU seals with PJ housings led to an initial leakage of 0.4 L/min, which increased to only 1.2 L/min after 10,000 load cycles. Overall, the PU material used was more difficult to process but also more abrasion- and tear-resistant than the SIL elastomer.
Research limitations/implications
More work is needed to understand individual cause–effect relationships between specific design features and system behavior.
Originality/value
To date, pneumatic RVAs have been manufactured by large-scale production technologies. The absence of suitable prototyping strategies has limited the available range to fixed sizes and has thus complicated the use of RVAs in research and product development. This paper proves that functional pneumatic RVAs can be produced by using more accessible manufacturing technologies and provides the tools for prototyping of application-specific RVAs.
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Hua-Lin Yang, Xiulong Li, Weiwei Sun, Fang Deng and Jie Du
This paper aims to present the mixed elastohydrodynamic lubrication (EHL) model and obtain the leakage characteristics for the skeleton reciprocating oil seal.
Abstract
Purpose
This paper aims to present the mixed elastohydrodynamic lubrication (EHL) model and obtain the leakage characteristics for the skeleton reciprocating oil seal.
Design/methodology/approach
The model consists of a finite element analysis of the contact pressure, a fluid mechanics analysis of the fluid film, a contact analysis of the asperity contact pressure, a deformation analysis of the seal lip and an iterative numerical simulation process.
Findings
Simulation results show that the leakage is in direct proportion to the seal roughness and speed, and in inverse proportion to the fluid viscosity. Comparisons with the experimental results verify the validity of the mixed EHL model.
Originality/value
This study provides a helpful method to calculate the leakage of the skeleton reciprocating oil seal, which shortens its development cycles.
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Zhen-Tao Li, Yangli Zhou, Xiaoli Yin, Muming Hao, Dechao Meng and Baojie Ren
The purpose of this paper is to investigate the effects of surface topography, including surface roughness, waviness and taper, on the cavitation of liquid film lubricated…
Abstract
Purpose
The purpose of this paper is to investigate the effects of surface topography, including surface roughness, waviness and taper, on the cavitation of liquid film lubricated mechanical seals (LFL-MS).
Design/methodology/approach
A universal governing equation considering cavitation is established, and an equivalent relative density is defined to characterize the cavitation degree. The equation is discretized by the finite volume method and solved by the Gauss–Seidel relaxation scheme.
Findings
Results indicate that both radial length and a circumferential width of the cavitation zone and cavitation degree are affected significantly by the waviness amplitude and taper, but the effect of surface roughness is limited.
Originality/value
Effect mechanism of surface topography on the cavitation of LFL-MS is investigated and cavitation degree is reflected by an equivalent relative density. The results further help to comprehensively explore the cavitation mechanism.
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Liming Teng, Jinbo Jiang, Xudong Peng, Fan Wu and Wenjing Zhao
This study aims to understand how the assembly of rotating ring affects the axial forced vibration of gas face seals.
Abstract
Purpose
This study aims to understand how the assembly of rotating ring affects the axial forced vibration of gas face seals.
Design/methodology/approach
A three-mass kinematic model is established to investigate the axial movement of the rotating ring with bilateral constraints. The separation, collision and frictional sliding of the rotating ring in sleeve are discussed under rotor excitation. The effects of operating parameters and O-ring dynamic characteristics on the separation degree and film thickness disturbance are analyzed. A dimensionless axial characteristic force is defined to determine the critical conditions for the occurrence of separation. Several effective methods to eliminate the separation are proposed based on the adjustment of typical installation parameters.
Findings
Under rotor excitation, there may be two collisions between the rotating ring and the sleeve surfaces in one excitation period. This will cause self-excited vibration of the fluid film, increasing the risk of seal failure. The separation and collision can be prevented by increasing the equilibrium ratio, the installation radius of the O-ring on the outer surface of the rotating ring and the friction in the sleeve.
Originality/value
The results develop the modeling of multibody dynamics of gas face seals, enabling more accurate prediction of vibration characteristics.
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In his introduction to this paper the author likened the function of the tribology centres to that of a two‐way bridge—for the drawing in of information about industry's…
Abstract
In his introduction to this paper the author likened the function of the tribology centres to that of a two‐way bridge—for the drawing in of information about industry's tribological problems and for the outflow of remedial advice and help.
S. Alliney, A. Strozzi and A. Tralli
A finite element model for the elastohydrodynamic lubrication problem is presented. A coupling between the hydrodynamic equation and the foundation compliance equation is…
Abstract
A finite element model for the elastohydrodynamic lubrication problem is presented. A coupling between the hydrodynamic equation and the foundation compliance equation is performed, then the resulting functional problem is given an ‘extended’ variational formulation. Some preliminary numerical results are also presented.
Cavitation damage in the form of spongy, pitted surfaces is widely associated with pump impellers, marine propellers and sliding bearings. It used to be rare as a form of damage…
Abstract
Cavitation damage in the form of spongy, pitted surfaces is widely associated with pump impellers, marine propellers and sliding bearings. It used to be rare as a form of damage on mechanical seals, but the number of cases has been increasing in the last few years. This is due, on the one hand, to conditions of application which are becoming increasingly demanding, and on the other hand to the growing use of ceramic materials. For although the latter make excellent face materials, they are far more sensitive to cavitation erosion than metallic face materials.
A class of exact solutions to the elastohydrodynamic problem to be used as test cases is presented. A numerical solution to the elastohydrodynamic problem according to the…
Abstract
A class of exact solutions to the elastohydrodynamic problem to be used as test cases is presented. A numerical solution to the elastohydrodynamic problem according to the Petrov—Galerkin method is developed. The appearance of spurious numerical undulations in the film profile is examined. A comparison between analytical and numerical results is employed to determine which numerical schemes limit the outcome of numerical oscillations without compromising the solution accuracy.