CN103438221A - Optimization method for improving pressure endurance capability of magnetic fluid sealing device - Google Patents

Abstract

The invention discloses a magnetic fluid sealing device (as shown in a figure 1). Magnetic fluid is injected into a gap of a magnetism-conducting circuit constructed by a high-performance permanent magnet, a pole shoe with good magnetic conductivity and a shaft, and a plurality of fluid O-rings are formed. When the magnetic fluid is subjected to differential pressure effect, the magnetic fluid moves in a non-uniform magnetic field, at this time, the non-uniform magnetic field enables the magnetic fluid to generate magnetic force capable of resisting the differential pressure, so as to further reach a new balance, and the sealing effect is achieved. However, when the sealing gap is larger than 0.5 mm (commonly smaller than 1 mm), nanoscale ferromagnetic solid particles in the magnetic fluid can segregate towards a zone with high magnetic field intensity under the effect of the non-uniform magnetic field, so that the pressure enduring capability of the device is reduced. The invention provides a method. Through adding magnetic solid particles with the grain size of 1 mu. m-10 mu. m to the magnetic fluid, the pressure enduring capability of the device is improved, and the service life of the device is prolonged.

Description

A kind of optimization method that improves the magnetic fluid seal device voltage endurance capability

Technical field

The invention belongs to the mechanical engineering technical field of sealing technology, specifically, the present invention relates to a kind of method that improves the magnetic fluid seal device voltage endurance capability.

Background technique

In magnetic fluid seal device, the seal clearance that the pole shoe of design and axle form usually is between 0.1mm to 0.2mm.Under magnetic fields, magnetic liquid is filled in seal clearance.Now, the ferromagnetic particle of the nanometer scale in magnetic liquid can steady in a long-termly suspend, and is dispersed in uniformly in base load liquid, makes seal arrangement have good voltage endurance capability.But in some special devices, be generally less than 1mm when seal clearance requires to be greater than 0.5mm() time, particle in magnetic liquid is under the effect of non-uniform magnetic-field, can assemble along with the variation of the magnetic field gradient zone high in magnetic intensity produces, be that solid particle quantity in the zone that per unit volume internal magnetic field intensity is high is greater than the solid particle quantity in the zone that magnetic intensity is low, cause magnetic liquid solid particles inside skewness, the whole voltage endurance capability of magnetic liquid descends, thereby affects the service behaviour of seal arrangement.

Summary of the invention

Technical problem to be solved by this invention is, in magnetic fluid seal device, the seal clearance of pole shoe and axle is greater than 0.5mm(and is generally less than 1mm) time, ferromagnetism solid particle segregation under the non-uniform magnetic-field effect of the nanometer scale in magnetic liquid, cause the magnetic retention particle size distribution inhomogeneous, cause the magnetic liquid voltage endurance capability to descend.

The technical solution used in the present invention is:

In preparing the process of magnetic liquid, add the ferromagnetism solid particle between appropriate 1 μ m to 10 μ m in magnetropism liquid, due to the second order law of buoyancy of magnetic liquid, additional magnetic retention particle can long-term stability be suspended in magnetic liquid.The micron-sized solid magnetic uniform particles of stable suspersion is distributed in magnetic liquid, hinder the motion that the nano-solid particle is caused by the non-uniform magnetic-field effect, reduce the segregation of nano-solid particle, effectively improved the distribution of nano magnetic particle in magnetic liquid.Moreover, under magnetic fields, the same meeting of micron-sized ferromagnetic particle is along magnetic line of force direction chaining, and then it is corresponding to the magnetic field generation to drive magnetic liquid integral body, forms the liquid "O"-ring.Therefore, the method can improve the whole voltage endurance capability of magnetic liquid, forms reliable sealing.

Theoretical foundation of the present invention is the second order law of buoyancy.According to the second order law of buoyancy, the magnetic bodies be immersed in magnetic liquid has from suspension characteristic, and the magnetic bodies stable suspersion that magnetic liquid can be much bigger by density ratio self gets up.Magnetic bodies is suspended in magnetic liquid, and the magnetic line of force in the magnetic field himself formed in equilibrium position is symmetrical.When magnetic bodies departs from equilibrium position, it is symmetrical that the distribution of the magnetic line of force will no longer keep, and the magnetic line of force of its moving direction produces compression, thereby cause the density of line of magnetic force in per unit volume to increase, and magnetic intensity H increases.

According to fluid, flow for the Bernoulli equation in permanent situation

$p^{*}+\frac{1}{2}{\mathrm{\ρ}}_f{V}^2+{\mathrm{\ρ}}_f\mathrm{gh}-{\mathrm{\μ}}_0{\∫}_0^H\mathrm{MdH}=C$

Under the minor variations condition, can think that the h of non-equilibrium position and equilibrium position and V are changed to 0.

Have $p_1^{*}-{\mathrm{\μ}}_0{\∫}_0^{H_1}\mathrm{MdH}=p_2^{*}-{\mathrm{\μ}}_0{\∫}_0^{H_2}\mathrm{MdH}$

Boundary conditions provides $p_1^{*}=p_1$ With $p_2^{*}=p_2$ Have

$\mathrm{\Δp}=p_1-p_2={\mathrm{\μ}}_0{\∫}_{H_2}^{H_1}\mathrm{MdH}$

H in formula ₁for the magnetic intensity of non-equilibrium position, H ₂magnetic intensity for equilibrium position.

Hence one can see that, it is larger that magnetic bodies departs from equilibrium position, and the magnetic line of force compression degree of its this side of moving direction is larger, and change of magnetic field strength is larger, it is larger that magnetic liquid produces the magnetic pressure that hinders the magnetic bodies motion, forces magnetic bodies again to be returned to equilibrium position.In like manner, at the opposite side of magnetic bodies motion, because the magnetic line of force sparse same generation that becomes hinders the magnetic pressure of magnetic bodies motion, and along with the degree that departs from equilibrium position increases and increases.

Magnetic is flooded thing and is immersed in magnetic liquid, can think that magnetic floods thing and be subject to the active force of magnetic liquid and non-magnetic object and flood thing to be subject to the active force of magnetic liquid similar.Therefore, with under state of rest, non-magnetic object floods thing and is subject to the magnetic liquid active force and explains that magnetic bodies floods the active force that thing is subject to magnetic liquid:

By boundary conditions, drawn, the surperficial back-pressure that is submerged in the nonmagnetic object of magnetic liquid is p, and magnetic liquid is expressed as the active force that floods object:

in formula, S is the surface area of object

Utilize fluid to flow for the Bernoulli equation in permanent situation

$p^{*}+\frac{1}{2}{\mathrm{\ρ}}_f{V}^2+{\mathrm{\ρ}}_f\mathrm{gh}-{\mathrm{\μ}}_0{\∫}_0^H\mathrm{MdH}=C$

With boundary conditions p=p ^*+ p _n, and definition

Have $p^{*}=C-{\mathrm{\ρ}}_f\mathrm{gh}+{\mathrm{\μ}}_0{\∫}_0^H\mathrm{MdH}$

So have

Use the divergence formula:

? $F=-{\∫}_{V_0}\▿[C-{\mathrm{\ρ}}_f\mathrm{gh}+{\mathrm{\μ}}_0{\∫}_0^H\mathrm{MdH}+\frac{{\mathrm{\μ}}_0}{2}{M}_n^2]{\mathrm{dV}}_0$ V in formula ₀it is the volume that S surrounds

Because C is constant, so

Due to $\▿{\∫}_0^H\mathrm{MdH}=M\▿H$ And $\▿\frac{1}{2}{M}_n^2=M_n{\▿M}_n$

Relation above substitution obtains $F={\∫}_{V_0}({\mathrm{\ρ}}_{f}g\▿h-{\mathrm{\μ}}_{0}M\▿H-{\mathrm{\μ}}_0{M}_n{\▿M}_n){\mathrm{dV}}_0$

If

with

all with volume V ₀irrelevant, and definition mean value

with for

$\stackrel{\‾}{M}=\frac{1}{V_0}{\∫}_{V_0}M{\mathrm{dV}}_0$ With $\stackrel{\‾}{M_n}=\frac{1}{V_0}{\∫}_{V_0}{M}_n{\mathrm{dV}}_0$

The power of the liquid effects that is magnetic on nonmagnetic object:

$F=({\mathrm{\ρ}}_{f}g\▿h-{\mathrm{\μ}}_0\stackrel{\‾}{M}\▿H-{\mathrm{\μ}}_0\stackrel{\‾}{M_n}{\▿M}_n)V_0$

Only consider the power perpendicular to the liquid level direction, it is exactly buoyancy F _zif h is parallel with the z axle, F _zjust become

$F_z=({\mathrm{\ρ}}_{f}g-{\mathrm{\μ}}_0\stackrel{\‾}{M}\frac{\∂H}{\∂z}-{\mathrm{\μ}}_0\stackrel{\‾}{M_n}\frac{{\∂H}_n}{\∂z})V_0$

So, changing the externally-applied magnetic field gradient, the object that always can make density be greater than magnetic liquid flies in magnetic liquid, or the object that makes density be less than magnetic liquid sinks to the magnetic liquid bottom.

The present invention compares had beneficial effect with prior art:

At first analyze the withstand voltage situation of single utmost point tooth both sides (as shown in Figures 2 and 3) on pole shoe:

Suppose: 1. the gravity of magnetic liquid itself and magnetic force are compared and can be ignored;

2. the magnetic line of force can be similar to circular arc and replace, and thinks etc. that magnetic field line and the magnetic line of force coincide;

3. the surface tension of ignoring magnetic liquid.

For the Bernoulli equation, have

$p_1^{*}-{\mathrm{\μ}}_0{\∫}_0^{H_1}\mathrm{MdH}=p_2^{*}-{\mathrm{\μ}}_0{\∫}_0^{H_2}\mathrm{MdH}$

Because supposed to wait magnetic field line and the magnetic line of force to coincide, so the surface, medial and lateral of magnetic liquid is along the magnetic line of force.Again because the magnetization intensity vector M of magnetic liquid is parallel with magnetic intensity vector H, so M is also the magnetic line of force along circular arc.Therefore, at the Normal direction M of the magnetization intensity of magnetic liquid both side surface _ndo not exist.

So boundary conditions provides $p_1^{*}=p_1$ With $p_2^{*}=p_2$

Substitution obtains $\mathrm{\Δp}=p_1-p_2={\mathrm{\μ}}_0{\∫}_{H_2}^{H_1}\mathrm{MdH}$

When the pressure of magnetic liquid both sides equates, Δ p=0, at this moment the magnetic fluid sealing film is in free state.

When a side pressure raises, when the pressure difference of the difference institute balance of the magnetic force of both side surface reaches maximum, i.e. Δ p _max, be called sealability: $\mathrm{\Δp}={\mathrm{\μ}}_0{\∫}_{H_{\min }}^{H_{\max }}\mathrm{MdH}$

If the magnetic intensity of whole seal clearance is all very high, whole magnetic fluid sealing film, under the saturation magnetization state, has:

Δ p=μ ₀m _s(H ₁-H ₂) M in formula _ssaturation magnetization for magnetic liquid

Hence one can see that, and the sealability of magnetic fluid seal device depends on the magnetic field gradient of the seal clearance between pole shoe and axle.

Known by above-mentioned analysis, control the magnetic field gradient of seal clearance well, can guarantee additionally to add the magnetic solid particle stable suspersion of tool between 1 μ m to 10 μ m of magnetic liquid, and improve the uniformity of integrated solid particle size distribution in magnetic liquid by stable suspersion, improve the sealability of magnetic fluid seal device.Minimizing is under large gap condition, and the nano particle in magnetic liquid is due to the caused seal failure of the segregation under the impact of non-uniform magnetic-field.

The accompanying drawing explanation

Fig. 1 sealed structural representation

The distribution situation of magnetic liquid on Fig. 2 pole shoe

The withstand voltage situation of the single utmost point tooth of Fig. 3 both sides

embodiment

In preparing the process of magnetic liquid, add the ferromagnetism solid particle between appropriate 1 μ m to 10 μ m in magnetropism liquid, due to the second order law of buoyancy of magnetic liquid, additional magnetic retention particle can long-term stability be suspended in magnetic liquid.The micron-sized solid particle of stable suspersion be evenly distributed on magnetic liquid in, hinder the motion that the nano-solid particle is caused by the non-uniform magnetic-field effect, reduced the segregation of nano-solid particle, effectively improve the distribution of solid particle in magnetic liquid.Moreover, under magnetic fields, the same meeting of micron-sized ferromagnetic particle is along magnetic line of force direction chaining, and then it is corresponding to the magnetic field generation to drive magnetic liquid integral body, forms the liquid "O"-ring.

Described method is applicable to adopt the magnetic fluid seal device of keryl, machine oil base and the sealing of diester based magnetic liquid.The magnetic-particle adopted is between 1 μ m to 10 μ m, comprise the ferromagnetic particle of ferriferrous oxide particles.

Claims (1)

1. a magnetic liquid rotating sealing device.This device comprises: cover, bearing, rubber seal, permanent magnet, pole shoe, magnetic liquid, screw, adjusting pad, flange plate.Magnetic liquid is injected in the gap of the magnetic conductive loop that pole shoe that high performance permanent magnet, magnetic conduction are good and axle form, can forms several liquid "O"-rings.When the magnetic liquid pressure difference is done the used time, can in non-uniform magnetic-field, move, at this moment inhomogeneous magnetic field will make magnetic liquid create antagonism pressure reduction magnetic force so that reach new balance, so just played the effect sealed.

It is characterized in that:

By adding the micron-sized non magnetic solid particle between 1 μ m to 10 μ m in magnetropism liquid, as wear-resisting, corrosion resistant silica or aluminium oxide ceramics powder, under the prerequisite that does not reduce the integral sealing ability, the sealability Problem of Failure that alleviation causes because of magnetic liquid solid particle segregation, extended the working life of device, and can reduce costs.

Described method is applicable to adopt the magnetic fluid seal device of keryl, machine oil base and the sealing of diester based magnetic liquid.Non-magnetic particle between 1 μ m to the 10 μ m adopted comprises silica, aluminium oxide, aluminium nitride, alpha-silicon nitride powders.

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