基于永磁环阵列的磁流体支撑及润滑特性研究

在本文中初步探讨了一种永磁环阵列的磁流体支撑及润滑特性，以期获得一种对固定目标区域精准支撑与润滑的方法，并实现低摩擦. 以3D打印树脂材料为基底，在其表面嵌入正方形点阵排布的永磁环阵列，分别在各磁体表面注入特定体积的磁流体，使其在各永磁环表面形成封闭的液体结构. 采用自行设计的支撑力测试系统及往复式摩擦磨损试验机分别对该液体结构支撑及润滑性能进行测试. 结果表明:在磁场作用下的磁流体，除自身磁化和内聚产生液体支撑力外，被磁流体密封于其液体结构内的气体将进一步提升支撑能力；而对于该磁环阵列结构而言，被吸附于其表面的磁流体支撑能力随着磁铁间距的增加而减小，并逐渐趋于稳定，同时磁极排布方式对支撑力也会有所影响；当磁流体密封结构的支撑能力大于外载荷时，即摩擦对偶完全被磁流体支撑，此时可获得0.005的低摩擦系数. 可见该磁流体液环密封结构所形成的液-气混合支撑力显著高于单一液体支撑，而磁环阵列结构可进一步提升总体支撑能力，当该支撑力高于负载时可避免摩擦副间的直接接触，在静止或低速状态下实现低摩擦. 该研究结果对于解决精密低速滑动机构中常出现的“冷焊”及“爬行”现象具有一定应用价值. 

Magnetic Fluid Support and Lubrication Properties Based on Arrayed Magnets

In this paper, to achieve low friction, the magnetic fluid support and lubrication properties based on arrayed magnets were studied. A 3D printed resin material was used as a substrate, and four permanent magnet rings (N35 NdFeB, Φ5 mm×Φ2 mm×1 mm) with square array were embedded into the substrate’s surface. When magnetic fluid was injected to the surface of each magnet, a closed liquid structure on the magnet surface can be formed. As a plate approaching to the liquid surfaces, the magnetized fluid as well as the gas sealed in the liquid ring can generate the supporting force. More importantly, such kind of support was not dependent upon relative motion or other facilities. In this way, low friction may be expected even at a very low speed. A home-made supporting force testing system was used to measure the bearing capacities of the liquid structures. Meanwhile, a reciprocating friction tester was applied to verify the lubrication performance of such structures. The supporting test result showed that under the magnetic field, magnetic fluid can produce liquid supporting force due to the magnetization. Since each of the magnetic nanoparticle dispersed in the fluid can be regarded as a tiny permanent magnet, the magnetic dipole in the particles would be rotated and turned along the direction of the external magnetic field. Such magnetizing process of the fluid may produce an attractive force in each particle, which expressed itself as a magnetic body force or magnetic pressure in the liquid. This kind of force may play as the liquid bearing capacity when undergoing the extrusion process. In addition, the gas sealed by the magnetic fluid ring also generated gas support. In the pressing course, based on the ideal gas equation, the smaller gas volume was, the higher pressure it behaved. To enhance the bearing capacity, the magnetic arrays on the substrate surface were designed. The experiment result showed that total support force increased a lot compared with single magnet. Further research found that the support capacity of the arrayed surface decreased with the increase of the magnet center distance. When the center distance of the four magnets was small, the total force was higher than that of the four times of the single magnet. As the center distance was large enough, the effect between each magnet can be ignored and the total force equaled the four times of the single magnet. Besides, the direction of the magnetic pole may also affect the total support behavior. The frictional experiment showed that when the total supporting capacity was greater than that of the normal load, the friction pair was completely separated and a low friction coefficient of 0.005 can be achieved. The friction force only came from the shear of the viscous lubricant. As the bearing capacity was lower than the normal load, friction coefficient increased obviously. As can be seen, the liquid/gas mixed support force formed by the magnetic fluid-sealed structure was significantly higher than that of the single liquid support, and the magnet arrayed structure can further enhance the total support force. For precision sliding mechanisms, "cold welding", adhesive wear and "stick-slip" phenomena seriously affect the service life and movement accuracy of the mechanism. Such design would be significant for solving these phenomena.