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磁性流体密封技术
作者:上海凯日机电设备制造有限公司
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油封, 骨架油封, 石墨填料环, 汽封, 轴封, ...
磁性流体密封技术是在磁性流体的基础上发展的,当磁性流体注入具有磁场的间隙中时,它可以充满整个间隙,成为一种液体“O型密封圈”。

磁性流体真空进给装置是一种把旋转运动传入真空容器的装置,其基本构成为一个永久磁场,两个磁极,一个磁性转动轴和磁性流体。传动轴是一个多级结构,由磁极和转轴组成。在每级环形间隙中,充满了磁性流体。在理想状态下,所有磁性流体密封在每一级极间与磁极之间,形成一系列的“磁性流体密封圈”。每级“磁性流体密封圈”能随的压差0.15-0.2个大气压,整个区域的随能力为密封圈子总的承压能力,为适应真空环境,磁性流体密封圈标准设计压力大于两个大气压,所以说是绝对安全的。

Magnetic fluid Sealing Technique

Sealing techniques of magnetic fluid take advantage of response of Magnetic fluids. When a Magnetic fluid is placed into a gap between the surfaces of rotating and stationary elements in the presence of magnetic fluid, it assumes the shape of a"Liquid O-ring" to comple电话y fill the gap.

The magnetic fluid vacuum rotary feed through is a device that transmits rotary motion into a vacuum chamber. The basic components are permanent magnet, two pole pieces, a magnetically permeable shaft and Magnetic fluid. The shaft (of pole pieces)

contains a multistage structure, completed bye the pole pieces and the shaft, concentrating magnetic flux in the radial gap under each stage. In the ideal situation, all flux lines are confined under each stage, and none are in interstate region. The magnetic fluid is trapped and held in each-stage, forming a series of " Liquid Oring" with intervening regions that are filled with air. Each stage can typically sustain a pressure differential of 0.15-0.2 atmospheres. All stages act in series to provide a total pressure capability for the seal. For vacuum applications Magnetic fluid seals are normally designed to sustain a pressure differential of greater than two atmospheres, thus allowing a safety margin.

■ 特性

密封圈特性:磁性流体包围整个转轴,成为一隔绝空气,水气,烟雾等元素的密封圈,几乎无泄漏的特性,密封圈的泄漏微弱到已无法测量,甚至使用质谱仪也无法测量(1*10-11Torr/e/sec)

Hermetic sealing: The Magnetic fluid surrounding the shaft provides a hermetic seal against gas, vapor, mist and other contaminants.

长寿命特性:"液体O型密封圈"由一个稳定的磁性流体构成,其装置可长期使用10年无需维修。

Long life: A(Liquid O-ring) seal is formed by using an inert, stable, low vapor pressure Magnetic fluid. Units have been in operation for over ten years with no maintenance.

良好可靠性:密封圈由永磁结构和稳定的磁性流体组成,所以机械磨损仅发生在轴承上。

High Reliability: The seal contains a simple, permanent magnetic structure and a non-wearing Magnetic fluid. The only parts subject to mechanical wear are self-contained ball bearings.

无污染特性:因为密封圈无磨损,没有微粒产生,降低了整个系统的污染,而且低的气压可使密封圈便于维修,其真空度可控制在10-8Torr.

Non-contaminating: Since there is no seal wear, there are no particles produced to degrade the system. In addition, low vapor pressure Magnetic fluid maintains seal integrity even in hard vacuums to better than 10-8Torr.

最佳的力矩传输特性:力矩可100%的输送,保证一个无阻碍的单向运行。

Optimum Torque Transmission: Through-shaft construction permits 100 percent torque transmission and provides in-phase rotation without backlash.

低阻尼和高速旋转能力:磁性流体极低的粘滞阻力和磁性流体进行给装置无需接触密封圈的结构,决定了它的稳定操作和高速转动。

Low Viscous Drag and High-Speed Capability: The low viscous drag of the Magnetic fluid, and non-contacting seal configuration of the Magnetic fluid feed through assure its extremely smooth operation and its high-speed capabilities.

磁性流体密封装置的轴承疲劳寿命按照以下的方法来计算

To determine Ball bearing Rating Fatigue Life of Ferro fluid sealed spindles, please use this table and the basic equation below.

L0:壳体端面到负载的距离
Distance fro housing end to load point

L1:真空侧轴承到壳体端面的距离
Distance from load side ball bearing to housing end

L2:轴承间距
Ball bearing span

Cr:轴承基本额定支负载
Dynamic load rating of ball bearing

L3:长度
Total length of shaft

Fa:压差产生的轴向负载
Axial exerted by atmospheric pressure

Cor:轴承基本额定静负载
Static load rating of ball bearing

Fr:径向负载
Radial load

n:转速
Rotation speed

fw:负载系统
Load factor

P:轴承当量动负载
Equivalent load

Lh:额定寿命
Rating fatigue life

●这些负荷能力特指使用SUJ2材料的轴承,如果使用SUS材料的轴承,则使用参数的80%。

This load capacity is for SUJ2 bearings. If bearing are used. Please apply an 80% darting factor.

例1
Example

型号为SFL020NN,其真空侧转由上的径向负载Fr=50kgf,转速n=200rpm时的额定寿命。

For a vacuum application, to obtain the fatigue life factor, Lh, of Model Number SFL202NN, when it is

used under a radial load Fr=50kgf at the shaft end and the rotation speed is n=200rpm.

由于轴承头部承受有Fr=50kgf,以下方法求出轴承6005上的Fr1,Fr2。

Radial load Fr=50kgf is applied at the shaft end, and the radial load on #6005 ball bearing should be distributed to Fr1 and Fr2. The can be obtained from the equation following:

由上述的负载分配求出额定寿命。(由于真空侧轴承不承受的负载比较高,仅计算真空侧轴承的寿命。此外,本计算由于真空压差产生的轴向负载Fa=3.14kgf很小,所以只计算了长向负载。当轴向负载很大时,必须考虑它的影响。)
From the distributed radial load Fr above, the rated fatigue Life Lh is obtained as follows:
(In this case, the Fr of the load side bearing is greater than at the second bearing. Calculate the Radial load at the load side only. For a vacuum application, the Axial load exerted by the atmospheric pressure difference, Fa=3.14kgf, is small enough to disregard. Therefore, only the Radial load is calculated. If the value of Fa is large, please include it in the calculation.)

注:假设fw=2
fw=2 is assumed.(end)
文章内容仅供参考 (投稿) (5/16/2004)
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