Rotary Seal Research Articles

Research on Simulation System of Rotor-Dynamics of Ball-Bearing and Turbo-Pump Rotor

In this paper, considering the effect of inertia ball, the static calculation model of angular contact ball bearings is established, the ball and the inner and outer raceway contact series parallel connection stiffness, deduced the formula of stiffness of the bearings, the use of FORTRAN language rotor-dynamics of the bearing calculation program, through the existing literature examples verify the correctness of the program. Combined with the actual turbo-pump rotor system of turbo-pump radial ball bearing radial bearing radial load stiffness is calculated, considering the additional influence of sealing fluid induced stiffness, at variable speed under the condition of calculation of bearing seal rotor system whirling frequency, the results accord with the actual engineering. In this paper, a multi factor simulation system for rotor-dynamics is developed, which provides a reference for design phase analysis of turbo-pump rotor-dynamics.

Rotor Sealings based on a Metal–Rubber Elastic Porous Material for Turbomachinery

The problems of making efficient rotor seals for turbomachinery has been outlined. A design of a seal with a sealing element made of metal-rubber elastic porous material has been proposed. A model of thermal processes in this seal during contact interactions with the rotor has been developed. The need to determine the range of changes in the parameters of the structure of the metal-rubber material, which makes it possible to use it as a sealing element for rotor seals made using existing technologies for structural damping systems, has been revealed. The results of studies of friction processes have been presented and the types of wear of the metal-rubber material in the rotor seal have been determined.

Demagnetization of Nd2Fe14B, Pr2Fe14B, and Sm2Co17 Permanent Magnets in Spallation Irradiation Fields

Prompted by the need for radiation-resistant permanent magnets for insertion devices (IDs) of high-brilliance next-generation synchrotrons such as the National Synchrotron Light Source II, the demagnetization of Nd2Fe14B and Pr2Fe14B was studied after exposure to a mixed irradiating field. Degradation and damage of the permanent magnetic material by components of electromagnetic showers induced in magnets by intense high-energy electron beams will alter the magnetic field structure of the IDs. Plate-like Nd2Fe14B magnets were irradiated to 1.8 Grad dose and were evaluated against Pr2Fe14B magnets irradiated to a lower dose of 20 Mrad. In addition, annular Sm2Co17 and Nd2Fe14B magnets integrated within a ferrofluidic feedthrough (FFFT) rotary seal were also irradiated to dose levels of 2 Grad for Sm2Co17 and 20 Mrad for Nd2Fe14B. Post-irradiation measurements of the magnetic intensity revealed that severe demagnetization exceeding 85% occurs in Nd2Fe14B magnets after only 50 Mrad dose and over 87% for Pr2Fe14B after 10 Mrad dose. The annular-shaped Sm2Co17 magnets of the FFFTs were almost insensitive to irradiation up to a dose of 2 Grad. Annular-shaped Nd2Fe14B magnets also showed resistance to demagnetization, a direct consequence of the annular shape which is characterized by the removal of the stronger demagnetizing field present at the center of a disk-like magnet. The sensitivity of boron-based permanent magnets to neutron energy (thermal versus fast) was also assessed via specifically designed experiments and discussed.

Process Influences on the Materials Interface of an Injection Molded Hard‐Soft‐Component

Combining a soft thermoplastic elastomer with a hard polymeric material by multi‐component injection molding provides a novel and sophisticated alternative for mounting a vulcanized dynamic elastomeric seal part into a rigid housing. Such assembly injection molding is new and challenging, but promises several economic advantages. The main issue within such a development is the assurance of sufficient bond strength between soft and hard component, in order to withstand the service load conditions safely. This paper studies certain process influences on the interface condition between the materials. The strength of the adhesive bond of composite test specimens consisting of a hard outer ring and a soft inner ring with integrated rotary seal lip are evaluated. The injection molded and investigated composite parts consist of glass fiber reinforced polybutylene terephthalate (PBT‐GF30) as hard component and a thermoplastic polyurethane (TPU) as soft component. The required force to reach delamination between hard and soft component is monitored and correlated with the surface structure and properties of differently plasma pre‐treated hard components. Supposed a material combination and the contact temperature are defined the surface conditions of the hard component play the major role with respect to the adhesion bond strength.

A multiscale wear simulation method for rotary lip seal under mixed lubricating conditions

Abstract The macroscale simulation methods are commonly used to study wear of rotary lip seals. These methods oftentimes do not address effects of microscopic interfaces, which, according to experimental studies, are important factors in the wear of rotary lip seal. Hence, a multiscale wear simulation method for rotary lip seal under mixed lubricating conditions is proposed, in which the effects of microscopic aspects of interacting surfaces are taken into account. The simulation results indicate that the wear of rotary lip seal can be reduced by reducing axial asperity density while increasing the circumferential asperity density. The results also indicate that wear of the rotary lip seal is susceptible to axial asperity density when it is within a particular range.

Thermal-Mechanical Coupled FE Analysis for Rotary Shaft Seals

The aim of this paper is to model the steady-state condition of a rotary shaft seal (RSS) system. For this, an iterative thermal-mechanical algorithm was developed based on incremental finite element analyzes. The behavior of the seal’s rubber material was taken into account by a large-strain viscoelastic, so called generalized Maxwell model, based on Dynamic Mechanical Thermal Analyses (DMTA) and tensile measurements. The pre-loaded garter spring was modelled with a bilinear material model and the shaft was assumed to be linear elastic. The density, coefficient of thermal expansion and the thermal conductance of the materials were taken into consideration during simulation. The friction between the rotary shaft seal and the shaft was simplified and modelled as a constant parameter. The iterative algorithm was evaluated at two different times, right after assembly and 1 h after assembly, so that rubber material’s stress relaxation effects are also incorporated. The results show good correlation with the literature data, which state that the permissible temperature for NBR70 (nitrile butadiene rubber) material contacting with ~80 mm shaft diameter, rotating at 2600/min is 100°C. The results show 107°C and 104°C for the two iterations. The effect of friction induced temperature, changes the width of the contact area between the seal and the shaft, and significantly reduces the contact pressure.

Research on Effects of Groove Shape Optimization on Cavitation and Lubricating Characteristics for Microgroove Rotary Seal

ABSTRACTThis article studies the effects of groove shape optimization on cavitation and lubricating characteristics of microgroove rotary seals (MGRS). A lubrication model considering cavitation effects for MGRS is established to obtain the variation in cavitation and lubricating characteristics with operating conditions. Furthermore, an optimization model of groove shape based on the lubrication cavitation model is developed and an optimal groove is obtained by co-designing the parameters of both groove shape structures and molded lines. The effects of optimal grooves and ordinary spiral grooves on cavitation and lubricating characteristics are compared and validation tests are carried out. Theoretical and experimental results indicate that the lubrication cavitation model based on the mass conservation boundary condition for MGRS could accurately predict the cavitation region of ordinary spiral grooves. Optimal grooves improve the pressure distribution of the groove area and restrain the generation of a cavitation region; therefore, the fluid bearing capacity and dynamic stiffness of optimal grooves are much larger than those of ordinary spiral grooves.

Design of a continuous wave mud pulse generator for data transmission by fluid pressure fluctuation

High-speed downhole transmission technology is in high demand for measurement while drilling (MWD) and logging while drilling (LWD) systems which have had major roles in increasing the geo-steering and formation evaluation capacity of reach wells, difficult horizontal wells and branch wells as well as increasing drilling rates. This paper presents the conceptual design and performance of a novel continuous wave mud pulse generator with the goal of transmitting data using hydraulic pressure waves. The generator includes the rotary valve, drive shaft and bearings, rotary and static seals, motor and reducer, resolver, pressure balance structure and lower centralizer; all of these components are mounted within a rotary drill collar. In particular, the rotary valve is the key important part of the continuous wave mud pulse generator. Based on the concept of a sinusoidal signal output, an improved arc-fillet-line triangular valve orifice is designed according to the relationships between the fluid differential pressure of a thin-walled cutting edge and the fluid flow area calculated from the relative rotation angle of the rotor to the stator through the established polar coordinate equations. The highly similar sinusoidal pressure signals can be achieved by optimized valve structures, which were verified by computational fluid dynamics (CFD) simulations, where the valve flow pattern characteristics and the impact law between the gap of the stator/rotor and pressure waveform were also obtained. Moreover, the drive capability response curves of the motor driver unit with and without a load are precisely determined, and current ground hydraulic experiments indicate that the designed continuous wave mud pulse generator performs well as a whole. The generated real pressure waves exhibit clear spectrum structures with a distinctive characteristic signal.

Appropriateness of the Use of End Seals with Crossed Crests for the High Pressure Cylinder

The efficiency of operation of the steam turbines of a high power is defined by the values of steam leakage through the seals, and first of all through the end seals that can occupy more than 30% of the length of high pressure rotor. The seals of a step type used at the present time change their performances if the crests are worn down during the overhaul period and can be restored at mid-life and/ or subjected to capital repairs. Therefore, the search for the rotor seal construction that would allow for an increase in the reliability of turbine operation is rather vital. The purpose of this research was to estimate appropriateness of the replacement of HPC step-type seals by noncontact seals with crossed crests. The method used for the solution of stated problem was the computation investigation of the flow of viscous high temperature steam through the sealing sector with crossed crests at different values of the radial clearance and axial movements. The flow rate comparison data showed that the original step-type seal with the radial clearance of 0.7 mm can be replaced by the noncontact seal with crossed crests with the radial clearance of 0.5 to 0.6 mm at the typical operation to provide a reliable operation. Moreover, steam leakages through the front end seal can be reduced for the offered structure option in comparison with the original option.

Сross-flows of air and stack gases in the gaps of regenerative air heater

The cross- flows of air and emitted gases that occur in the regenerative air heater (RAH) in the case of unsatisfactory adjustment of seals result in a reduction of the efficient operation of the boiler unit. Seal clearances put up the main resistance to the air cross-flows and this allowed us to present the hydraulic circuit of rotor seals for the RAH. To define the cross-flows we assumed that the power unit operates at nominal operating conditions. To define the geometric characteristics of the RAH we calculated the cross area of seal gaps. When the rotor and the regenerative air heater casing are exposed to thermal stresses a nonuniform circumferential change in peripheral and axial clearances will be observed during their cyclic heating and cooling. A method of mass balances was used as the computation model. Appropriate methods were developed to define the above change during the RAH operation and the cross-flows were estimated for the specified value of seal clearances. The experience gained in the RAH operation showed that the air cross –flows may reach ~ 30 % and higher in the case of insufficiently precise regulation. The main values of the cross-flow of air and heating emitted gases are observed in radial seals. Therefore, the attention should be paid to the precise regulation of the seals and the development of the methods used for the control of seal clearances during the hot-state RAH operation.

Advances in high-pressure rotary sealing

Some types of rotating equipment employ a high-pressure lubricant between a pair of polymeric rotary seals. In hydraulic swivels, the lubricant transmits pressure between relatively rotatable components. In other equipment, such as an oilfield rotating control device (RCD), one seal excludes a high-pressure process fluid, whilst another retains the high-pressure lubricant. This article describes advancements in the life and pressure capacity of such seals.

Wear Behavior of Rotary Lip Seal Operating in a Magnetorheological Fluid Under Magnetic Field Conditions

A magnetorheological fluid (MRF) is one of many smart materials that can be changed their rheological properties. The stiffness and damping characteristics of MRF can be changed when a magnetic field is applied. This technology has been successfully employed in various low and high volume applications, such as dampers, clutches, and active bearings, which are already in the market or are approaching production. As a result, the sealing performance of MRF has become increasingly important. In this study, the wear properties of seals with MRFs were evaluated by a rotary-type lip seal wear tester. The test was performed with and without a magnetic field. The leakage time was monitored during the tests in typical engine oil conditions. The results showed that the wear resistance of the seal with MRF was decreased under the magnetic field.

Experimental investigation and application on the cutting performance of cutting head for rock cutting assisted with multi-water jets

In the field of rock breaking, considerable challenges, including high power dissipation, dust, and sharp pick wear, can be solved efficiently by using high-pressure water jet assistance during cutting. Hence, a new high-pressure rotary seal device was designed to stably apply the water jet technology to a roadheader for a rotating speed of 50 r/min and a water pressure of 40 MPa. In addition, three types of cutting heads assisted by the water jet, namely, the center water jet cutting head (CWJCH), the front water jet cutting head (FWJCH), and the rear water jet cutting head (RWJCH) were designed and machined by studying the relative position between the pick and the water jet. Comparative tests of the rock-breaking performance were conducted by varying the water pressure on the three cutting heads and an ordinary cutting head (OCH) at the cutting head test bench. The experimental results show that the CWJCH has the characteristics of minor cutting, advanced resistance, and dust concentration; the FWJCH ranks second in rock-breaking performance. However, in removing dust, the performance of the FWJCH is poorer than the RWJCH. Compared to the OCH, for a water pressure of 40 MPa, the reductions in the cutting resistance, advance resistance, and dust concentration are 40.37, 51.53, and 71.44% for the CWJCH; 30.58, 24.06, and 55.66% for the FWJCH; and 16.56, 34.02, and 70.21% for the RWJCH.

Study of Separation Characteristics of Micro-groove Rotary Seal Considering Different Cavitation Boundary Conditions

Micro-grooves have superior hydrodynamic characteristics; therefore, the operating state of the micro-groove rotary seals (MGRSs) used in wet clutches of vehicles change from mixed lubrication to full-film hydrodynamic lubrication with increased rotating speed. These transition characteristics of the lubrication state of the MGRS are called “separation characteristics.” However, simultaneously the increase in rotating speed also leads to the cavitation effect. In contrast to the convergent wedge-shaped gap, “negative effects” exist in the diverging gap that lead to the reduction in the hydrodynamic pressure on the sealing end face. When the pressure is less than the cavitation pressure, the oil film undergoes cavitation and then ruptures. Thus, a large cavitation region reduces the bearing capacity of the oil film. Cavitation effects significantly influence the separation characteristics of the MGRS. Here we report on a theoretical model that has been developed through coupling asperity contact, fluid lubrication with micro-grooves and axial motion dynamic characteristics of the seal. Separation characteristics of the MGRS under Reynolds and Jakobsson–Floberg–Olsson (JFO) cavitation boundary conditions are systematically investigated in this study. The results show that pressure distribution and fluid bearing force under the Reynolds cavitation boundary condition are larger than those under the JFO condition, while friction torques are almost the same under both conditions. The cavitation region is observed in experiments and found to become larger with increases in speed. The JFO cavitation boundary condition predicts larger separation speed of the MGRS than does the Reynolds cavitation boundary, and the separation speed predicted by the JFO cavitation boundary condition is significantly closer to the experimental result than that predicted by the Reynolds condition. For the best separation characteristics of the MGRS, selected micro-groove parameters are as follows: N g = 35–40, β = 17–23° and h g = 15–25 μm.

Effect of Relative Velocity Between Rough Surfaces: Hydrodynamic Lubrication of Rotary Lip Seal

Since the sixties, most of numerical studies that model the rotary lip seal lubrication have been restricted by assuming that one of the two opposing surfaces is smooth: either the lip or the shaft. This hypothesis, although it is verified only for a shaft roughness ten times smaller than that of the seal, is the best solution to avoid the transient term “∂h/∂t” in the deterministic approach. Thus, the subject of the present study is twofold. The first part validates the current hydrodynamic model with the international literature by assuming the asperities on the lip and shaft as a two-dimensional cosine function. In the second part the Reynolds equation for rough surfaces with relative motion is solved. The numerical results show that the relative motion between rough surfaces impacts significantly the load support and the leakage rate, but affects slightly the friction torque.

Numerical and experimental study on the separation characteristics of microgroove rotary seals

The microgroove rotary seals used in the wet clutches of a vehicle operate in a mixed-lubrication state at low rotational speeds. When the speed increases to a certain value, the full-film hydrodynamic-lubrication state occurs in the sealing end face. The transition characteristics of the microgroove rotary seal in this operating state are called the separation characteristics and the critical speed is called the separation speed. In this paper, the separation characteristics of microgroove rotary seals are studied. First, a theoretical model considering the asperity contacts, the fluid lubrication with microgrooves and the axial motion dynamic characteristics of the seal is established. Then, the variation in the separation characteristics is studied systematically using the microgroove parameters, such as the number Ng of microgrooves, the groove width ratio δθ, the extent δr of the radial seal dam and the spiral angle β. The optimum ranges of the microgroove parameters are determined: Ng = 40–50, δθ = 0.65–0.75 and δr = 0.7–0.8 for radial grooves and Ng = 30–40, δθ = 0.5–0.7, δr = 0.7–0.8 and β = 12–17° for spiral grooves. Finally, the variations in the microgroove parameters of the separation characteristics are verified by several experiments. The experimental results are in good agreement with the simulation results.

Failure Analysis of the Multi-Level Series Rotary Seal Device under High-Pressure Water

High-pressure water jets are used to assist roadheaders in breaking hard rock. The failure life of the high-pressure rotary seal (HPRS) is significant, due to how it affects the safety and efficiency of the roadheader. Here we investigate the mechanical behaviour of the HPRS with a series of experiments. Single-level rotary seal device based studies were conducted to investigate the effect of seal forms, materials, operating pressure and spindle speed on friction torque and leakage. The best seal form from the three kinds of forms was chosen to test the failure life of the multi-level series rotary seal device and the relationships between the operating pressure, spindle speed, temperature, leakage and failure life were analysed. The failure life of rotary seals from Levels 1 to 4 was observed to be 15, 11, 5, and 4 days respectively. The increase in temperature of Levels 1 and 2 was perceived to be slow at the beginning phase of the test, while it rose sharply until the failure occurred, whereas in the case of Levels 3 and 4 it was instantaneous.

Abrasive wear study of an acrylonitrile butadiene rubber (NBR) rotary seal in dry and muddy contact using a micro-abrasion tester

Rotary dynamic seals are widely used in machinery in order to retain fluids and to exclude external contaminants by allowing the free shaft movement. One of the most recurrent failure of seals is caused by abrasive wear under prolonged sliding contact. It is mainly produced either by partial dry running (two-body abrasion) and/or by interacting with abrasive hard fine particles, which are immersed in the fluids generating three-body abrasive wear. This work aims to study both types of abrasion using a micro-scale abrasion tester. For this, small samples were extracted from an Acrylonitrile Butadiene Rubber (NBR) lip of an actual dynamic seal. The testing was conducted in dry contact to generate two-body abrasive wear, as well as in a wet/muddy environment in order to reproduce three-body abrasion. The load was selected in order to approach the actual mean contact pressure of seals against rotary shafts. Hence, a stress relaxation test of the NBR samples was carried out to characterize the viscoelastic behavior. The wear scar morphologies and wear progression were analyzed in detail by optical microscopy, SEM analysis and optical profilometry. Finally, the experimental test was suitable to reproduce two-body and three-body abrasion on the samples since the particular wear patterns on small wear scars were obtained by short experiments.

Design and Performance of a Novel Dynamic Rotary Sealing Device for Roadheader with High-Pressure Water-Jets Assistance

Design and Performance of a Novel Dynamic Rotary Sealing Device for Roadheader with High-Pressure Water-Jets Assistance

Material Research of Rotary Sealing Device for Combined Cutting System

In order to solve the rotary sealing problem of rotary shaft in drum shearer combined cutting system, the material and structure of combined cutting system rotary sealing device needs to be selected and designed. In the paper, the rotary sealing structure of four grades in series was designed first, and then the material of NBR-40 and PTFE 4FT-4 under the separate static and dynamic sealing tests were carried out on the combined tooth-slip-ring sealing test-bed. The tests show that the NBR-40 O-Ring with PTFE 4FT-4 tooth-slip-ring has no low-pressure leakage problem and low leakage in the sealing progress, the sealing effect of which is the best.