Sealing mechanism of magnetic fluids

Sealing is one of the most successful apphcatious of magnetic fluids. However, the sealing pressure difference is not satisfactory. This paper theoretically analyzes the mechanism of magnetic fluids sealing. Main factors that have significant effects on the sealing ability include viscous stress on the interracial surface, magnetic surface tension, and the shape of the interracial surface. The sealing pressure with magnetic fluids decreases with increase of rotational speed. Experiments were carried out to study the stability of the interface between magnetic fluids and water. It has been shown that stability of the interface will be damaged by washing of water when the relative flow between water and magnetic fluid becomes turbulent.

Coaxial Twin-shaft Magnetic Fluid Seals Applied in Vacuum Wafer-Handling Robot

Compared with traditional mechanical seals,magnetic fluid seals have unique characters of high airtightness,minimal friction torque requirements,pollution-free and long life-span,widely used in vacuum robots.With the rapid development of Integrate Circuit（IC）,there is a stringent requirement for sealing wafer-handling robots when working in a vacuum environment.The parameters of magnetic fluid seals structure is very important in the vacuum robot design.This paper gives a magnetic fluid seal device for the robot.Firstly,the seal differential pressure formulas of magnetic fluid seal are deduced according to the theory of ferrohydrodynamics,which indicate that the magnetic field gradient in the sealing gap determines the seal capacity of magnetic fluid seal.Secondly,the magnetic analysis model of twin-shaft magnetic fluid seals structure is established.By analyzing the magnetic field distribution of dual magnetic fluid seal,the optimal value ranges of important parameters,including parameters of the permanent magnetic ring,the magnetic pole tooth,the outer shaft,the outer shaft sleeve and the axial relative position of two permanent magnetic rings,which affect the seal differential pressure,are obtained.A wafer-handling robot equipped with coaxial twin-shaft magnetic fluid rotary seals and bellows seal is devised and an optimized twin-shaft magnetic fluid seals experimental platform is built.Test result shows that when the speed of the two rotational shafts ranges from 0-500 r/min,the maximum burst pressure is about 0.24 MPa.Magnetic fluid rotary seals can provide satisfactory performance in the application of wafer-handling robot.The proposed coaxial twin-shaft magnetic fluid rotary seal provides the instruction to design high-speed vacuum robot.

Motion State Analysis and Seal Ability Study on the Magnetic Fluid Seal of Reciprocating Shaft

The authors have studied the motion mechanism of the magnetic fluid in a reciprocating seal gap,on the basis of which the authors obtain an anti pressure formula of the reciprocating shaft magnetic fluid seal from general Navier Stokes equation.In order to verify the correctness of the anti pressure formula,the authors have calculated the magnetic field distribution of seal structure and have gotten the maximum still anti pressure.Finally,the authors have verified the influence of speed and stroke on the seal anti pressure.

Characteristics of a magnetic fluid seal and its motion in an axial variable seal gap

With suitable assumptions a hydrodynamic model for the magnetic fluid motion in an axial variable gap seal was con- structed, and the solution to the equations of the model was deduced. The characteristics of a magnetic fluid seal and its motion, including the speed and pressure distribution, and the seal capacity of a magnetic fluid rotating seal were systematically described. The factors affecting seal capacity and ways to improve seal capacity based on the hydrodynamic model are discussed. The basic condition for dynamic seal availability is presented. The rotating speed and radius of the shafts should be decreased. The work can provide proof of a seal design or suggest ways to improve the seal capacity of magnetic fluid seals.

Numerical Analysis of Magnetic Fluid Sealing Performance

The sealing performance of magnetic fluid is related to the magnetic fluid itself. Many factors can influence the magnetic field and the seal pressure differences of magnetic fluid seals, such as the sealing gap, the shaft eccentricity, the shaft diameter, the volume of the magnetic fluid and the centrifugal force. These factors are analyzed by numerical computation. When the seal material and structure are the same, the seal pressure difference is directly proportional to the magnetic field intensity and the saturation magnetization of the magnetic fluid. The sealing performance of the magnetic fluid will reduce with the increase of the sealing gap and shaft eccentricity. The sealing performance will increase with the volume of the magnetic fluid and decrease with the increase of the shaft diameter taking gravity into account. The increase of the shaft diameter is the same as the reduction of the volume of the magnetic fluid. The magnetic fluid cross-section can change because of the centrifugal force. Some improvements can reducc the influence of the centrifugal force. The centrifugal force can be utilized to improve the sealing performance.

A New Design of Magnetic Fluid Seal for Liquids

Direct contract between the sealed liquid and the magnetic fluid in a dynamic system under magnetic field may lead to an unstable interface, consequently, break down the seal. Aiming at this problem, a new magnetic fluid seal (MFS) was developed. In this new MFS, a soft iron bushing with high permeability was introduced on the shaft and nonferrous shields were installed beside the bushing and the pole pieces. The parameters of the bushing and the shields were optimized in a seal simulation facility The results show that the bushing with a thickness of 7 mm and shields with a width of 8 mm are best for sealing a shaft 20 mm in diameter. The MFS designed based on the optimum parameters shows good performance and long life span for sealing lubricating oil.

Experimental Verification and Research for the Distortion in the Integrated Frequency Responses of the High-Pressure Sealed Cabin and Magnetic Field Sensor

Although magnetotelluric sounding method applied to the land is advanced, there are many difficulties when it is applied to marine environment, one of which is how to lay magnetic field sensors down to the seafloor to complete measurements. To protect the magnetic field sensors from intense erosion and high pressure, suitable high-pressure sealed cabins must be designed to load them. For the consideration of magnetic measurement and marine operation, the sealed pressure cabin should be nonmagnetic and transportable. Among all optional materials, LC4 super.hard aluminum alloy has the highest performance of price/quality ratio to make the sealed pressure cabin. However, it does not mean that the high-pressure sealed cabin made using LC4 will be perfect in performance. In fact, because of its weak magnetism, the pressure cabin made using LC4 has distorting effect on frequency responses of the magnetic field sensors sealed in it. This distorting effect does not affect the use of the magnetic field sensor, but if we want to eliminate its effect, we should study it by experimental measurements. In our experiment tests, frequency sweep magnetic field as excitation signal was used, and then responses of the magnetic field sensor before and after being loaded into the high-pressure sealed cabin were measured. Finally, normalized abnormal curves for the frequency responses were obtained, through which we could show how the high-pressure sealed cabin produces effects on the responses of the magnetic field sensor. Experimental results suggest that the response distortion induced by the sealed pressure cabin appears on mid- and high-frequency areas. Using experimental results as standardization data, the frequency responses collected from seafloor magnetotelluric measurements can be corrected to restore real information about the seafloor field source.

Experimental study on a magnetofluid sealing liquid for propeller shaft

The selecting and preparing method of the basic material of magnetic fluid was introduced. By using a chemical method, the magnetic micropowder Fe 3O 4 was successfully yielded, and an oil-base as a working carrier and dispers ing agent was determined. The preparation process of the magnetic fluid and prescription of the oil-base magnetic fluid were discussed. The simulation experimental rig of magnetic fluid sealing for propeller shaft was designed. The sealing ability experiment was conducted and results were analyzed. The pressure of sealing is up to 2 MPa.

Computer Aided Modeling and Deign of a New Magnetic Sealing Mechanism in Engineering Applications

This article introduces a new type of magnetic sealing mechanism that reduces the lubrication oil pollution and media gaseous leakage in general reciprocating machinery including air compressors and refrigerators. The feasible function and reliable performance of this new sealing mechanism are introduced and analyzed in this paper. The computer aided design, modeling and analysis are being used to study this new sealing mechanism, and the prototype of this sealing mechanism is being tested. The study indicated the proper function of this sealing mechanism. The major advantages of this sealing mechanism include: improved sealing capacity to prevent the gaseous leakage and oil leakage, simple and compact in structure, lower precision requirement on surfaces of reciprocating pistons and shafts in production and manufacturing, and longer services in sealing life span. Also there is almost no frictional loss during the reciprocating motion of piston or shaft.

A New Magnetic Sealless Coupling Axial Flow Blood Pump

For rotating blood pump, the sealing problem is a very important one to solve. In this paper, it was introduced that we designed and made a small axial flow pump, applying the magnetic coupling method. The pump consisted of two pump housings, a brushless DC motor, an impeller with five wanes, a pair of magnetic discs, a spacer, an inlet and an outlet areas , bearings, a support frame, and etc. The pump is made of titanium and is 125 mm length, 147 ml volume, total 380g of weight. Performances of outputting, sealing, heat creating and damage to blood by the pump were investigated in vitro experiment. Results showed for external experiment that: (1)The pressure created by the pump was 90 mmHg, the flow rates were 1.2 L/min, 4 L/min, 5.9 L/min and 7.8 L/min correspondingly to 5000 rpm, 6000 rpm, 7000 rpm and 8000rpm rotation speeds. The hydrodynamic performance of the axial flow blood pump was enough to meet a patient need when the blood pump was used as a left ventricular assistant device. (2)The hemolysis test was studied by the normalized index of hemolysis(NIH). The NIH result of the axial flow pump was 0.08 g/100 L. (3)The outside temperature of the pump didnt change obviously in 120 hours of rotation, and the sealing function was very well.

Research on Parameters Optimization of Rectangular Pole Teeth for Magnetic Fluid Seals

To optimize the magnetic fluid seal design,the single-factor method is usually used to study the e ect of the rectangular pole teeth structure parameters on the sealing capacity of the magnetic fluid seal by current research,and the design formula is obtained.However,the supporting data is too few to make the results universalizable.In this paper,to obtain a wider range of applicable design formulas,a large number of modeling and simulation experiments are conducted using the co-simulation analysis experimental method of MATLAB and COMSOL.The influence of structure parameters of rectangular pole teeth and the coupling e ects of the structure parameters on the sealing capacity of sealing devices has been studied under di erent lengths of pole piece(L_(p))and seal gap(L_(g)).The results explain the influences of tooth height(L_(h)),tooth width(L_(t)),groove width(Ls),and their coupling e ects on the theoretical sealing capacity of magnetic fluid seals,and more widely applicable design formulas for pole teeth structure parameters are given.The design formulas can help to obtain good design parameters directly or reduce the optimization range when the magnetic fluid seals need to be optimized to meet the miniaturization and lightweightrequirements of magnetic fluid sealing devices or improve the sealing capacity under the same seal size.

The Studies of Some Key Technologies in Magnetic Disk Drives

This paper introduces some final results of some key technologies in magnetic disk drives. We dicuss the design and experiment of thin film head, magnetic fluid exclusion seal system, head disk interface and the engineering appilcations of these technologies in magnetic disk drives.

Interpretation method of nuclear magnetic resonance dual-TW logging in oil-wet tight sandstone reservoirs

Fluid typing from nuclear magnetic resonance(NMR)logging in oil-wet tight sandstone reservoirs is proving to be diffi cult;thus,research into the NMR logging response mechanism and analysis methods is critical.The NMR response mechanism and theoretical method were investigated based on the oil-water distribution in the pores under oil-wet conditions.The data processing method is studied based on NMR dual-TW activation principle,and the equations of macroscopic magnetization vector,fl uid volume,and relaxation parameters are derived,which is a nonlinear inversion problem.The simulated annealing algorithm is used,and the fl uid relaxation parameters,oil volume,and water volume of the fl ushing zone are calculated.An ideal reservoir model is set up,and simulation results indicate that the above-mentioned NMR relaxation theory and algorithms are valid.A case study is conducted in Huanjiang Oilfi eld in the Ordos Basin,China.The calculated oil saturation of the fl ushing zone is consistent with the oil saturation calculated using the Archie formula,and the test results indicated that the new method is applicable.Moreover,the fl uid-typing cross-plot combined with oil test data is constructed on the basis of the saturation of the fl ushing zone,improving the accuracy of fl uid identifi cation.

Numerical and experimental study of magnetic fluid seal with large sealing gap and multiple magnetic sources

To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was designed.Magnetic field distributions under the pole pieces of the magnetic fluid seal with single and multiple magnetic sources were simulated by finite element method and its sealing pressure difference could be calculated according to the theoretical formula of the magnetic fluid seal.The effects of sealing gap height and magnetic source amount on the sealing capability were investigated experimentally.The theoretical and experimental results were compared,analyzed and discussed.The results demonstrated that the magnetic fluid seal with multiple magnetic sources was an effective method to improve the sealing capability for the rotary shaft with large gaps.The theoretical results agreed well with the experimental results when the height of the single edge gap was equal to 0.4 mm.However,it was found that when the height of the single edge gap was larger than 0.4 mm,the difference between the theoretical values and experimental values increased with the gap height because part of magnetic source had less or even no effect on magnetic fluid sealing capability.

Magnetic fluid based squeeze film between porous circular disks with sealed boundary

Efforts have been made to study the effect of the magnetic fluid lubricant and the seal-ing of the boundary for the squeeze film between two circular disks when the upper disk having aporous facing with its boundary sealed, approaches the non-porous lower disk normally. The modi-fied Reynolds equations for the fluid region and the governing Laplacian equation for the pressurein porous region are solved with appropriate boundary conditions. Expressions are obtained forpressure, load carrying capacity and the response time. The results are presented graphically. Thecombined effect of the magnetic fluid lubricant and sealing of the boundary increases the load car-rying capacity significantly and hence the performance of the bearing can be enhanced considera-bly by sealing the boundary and taking a magnetic fluid as lubricant.

Effects of medium fluid cavitation on fluctuation characteristics of magnetic fluid seal interface in agricultural centrifugal pump

The fluctuation law of magnetic fluid seal interface of an agricultural centrifugal pump is theoretically unknown;the pressure and velocity fluctuations are crucial factors that cause interface fluctuation.In this study,the pressure and velocity fluctuations of the sealing interface on an agricultural centrifugal pump during cavitation were investigated based on the methods of Ansys CFX numerical calculation and experimental verification.The results demonstrated that at the same flow rate,the pressure fluctuation amplitude of the sealing interface decreased gradually from the shaft surface to the bottom of the polar tooth.At different flow rates,the amplitude of the pressure fluctuation decreased with an increase in the flow rate.The cavitation of the medium aggravated the impact and water hammer of the liquid,leading to the occurrence of the jitter phenomenon in the sealing interface to accelerate the fluctuation frequency of the axial velocity of the sealing liquid,which accelerated the emulsification of the magnetic fluid.This law can provide a reference for the design of magnetic fluid sealing devices for agricultural centrifugal pumps.

Theory analyses and applications of magnetic fluids in sealing

Magnetic fluids are the suspensions composed of magnetic nanoparticles,surfactants,and non-magnetic carrier liquids.Magnetic fluids are widely used in various fields,especially in sealing,because of their excellent features,including rapid magnetic response,flexible flow ability,tunable magneto-viscous effect,and reliable self-repairing capability.Here,we provide an in-depth,comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories:static sealing,rotary sealing,and reciprocating sealing.We summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present,particularly focusing on the recent progress of magnetic fluid seals.Although magnetic fluid sealing technology has been commercialized and industrialized,many difficulties still exist in its applications.At the end of the review,the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.

传统密封与磁流体密封在水轮机主轴上的运用分析

传统密封技术在水轮机主轴上应用广泛,但随着技术的发展和设备性能的提高,传统密封技术的局限性逐渐显现。而磁流体密封技术作为一种新兴的密封技术,具有无接触、无磨损、高密封性能等优点,为水轮机主轴密封技术的发展提供了新的方向。对此,针对传统密封与磁流体密封在水轮机主轴上的运用进行分析,探讨两种技术的优缺点与发展趋势。

高温磁流体动密封结构散热特性分析与优化

针对某型高温磁流体动密封结构在工作时磁流体温度过高的问题,提出了在原有结构上增加冷却水道和隔热气孔的结构优化方案,以降低高温工作环境中的磁流体工作温度,使其工作温度在要求的工作范围内。通过对比该密封装置在结构优化前后两种热源温度下的温度场、压力场和速度场,进而分析该密封结构的散热特性及优化的可行性。分析结果表明,温度和结构的变化对压力场和速度场并无明显影响;增加散热水道和隔热气孔能有效降低整体结构温度。优化后,在热源温度为700℃或500℃时,磁流体域最高温度分别降低了173℃和95℃,均极大地降低了磁流体在工作时的温度。该结构优化方案可将磁流体的温度降低至正常工作范围,提高结构的使用寿命,并为磁流体密封结构的优化提供了一定的参考。

大型土工离心机磁流体密封结构性能研究

大型土工离心机由于主轴轴径大、线速度高,使得现有磁流体密封结构很难满足安装、发热等要求。设计一种新型剖分式磁流体密封装置,利用有限元数值分析方法研究剖分式结构变形、极靴组件结构参数对密封性能的影响及密封装置温度分布,考虑实际加工能力,运用正交试验对结构参数进行优选。结果表明:结构参数对密封性能的影响程度由大到小依次为密封间隙、永磁铁高度、永磁铁宽度、槽宽、齿宽、齿高;优化后密封装置的各结构参数分别为密封间隙0.5 mm、齿宽2 mm、齿高2 mm、槽宽2.8 mm,永磁铁宽度11 mm、永磁铁高度22 mm;优化后的密封压力值为0.97 MPa,高于未优化前的0.54 MPa,同时高于工况要求的0.1 MPa;大轴径磁流体密封在工作时,存在轴套积热问题,需要在轴套部位开设冷却腔。