Effect of Running-In (Load and Speed) on Surface Characteristics of Honed Gears

The initial running-in cycles alter the surface integrity characteristics and influence gear performance. This article shows how the surface characteristics of honed spur gears evolved due to the combined effect of running-in load (0.9 or 1.7?GPa) and speed (0.5 or 8.3 m/s) in Forschungsstelle fur Zahnräder und Getriebebau tests. Running-in affected the surface layers to a depth of 5 µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks, and relaxed residual stresses. It also enhanced the amount of phosphorous from extreme pressure (EP) additives at the surface. The surface contact fatigue failure—that is, micropitting—was promoted by running-in speed rather than load.     

A new magnetorheological finishing process for ferromagnetic cylindrical honed surfaces

In today’s industries, the internal surface finishing of cylindrical objects is highly demanded to improve their functional performance in various engineering applications. During the traditional honing operation, the finishing forces produced by abrasives on the workpiece surface are not easily controllable and also produce various surface defects. Therefore, to further improve the surface integrity of the traditionally cylindrical honed surface made of ferromagnetic or non-ferromagnetic materials, a new magnetorheological (MR) finishing process has been used with a controlled magnetic field. The experimentation is performed on the honed surface made of gray cast iron, which is generally used as a cylinder liner. The percentage change in surface roughness values, i.e., Ra, Rq and Rz, reduced by 77.44%, 70.16% and 72.16%, respectively, with better improvement in surface after 90 minutes of finishing. The experimental results demonstrated the effectiveness of present process for improving the functional applications of ferromagnetic cylindrical honed surface after removing the various surface defects such as deeper grooves, honing grooves with shaper edges, torn and folded metals, and cavities or holes. The applications of new MR finishing process can also be useful in the internal finishing of injection barrel of a molding machine, cylindrical molds and dies, hydraulic cylinder, etc.     

如何提高液压缸筒用无缝钢管材料利用率

液压缸筒用高精度无缝钢管只有内径几何尺寸精度达到H9～H10,内表面粗糙度Ra≤0.8μm,才能满足在制作液压缸筒时高精度无缝钢管经过珩磨后内孔尺寸精度达到H7～H8,内表面粗糙度Ra≤0.2μm,否则,需要预留大量的珩磨及车削加工余量。即便如此,高精度无缝钢管的材料利用率依然比较低下,不仅需要对高精度无缝钢管内孔进行1～5mm的珩磨,而且需要对外圆进行0.5～1mm的车加工。改变传统的高精度无缝钢管冷拔生产工艺,在生产液压缸筒用高精度无缝钢管初期,对钢管的内表面进行微量珩磨和外表面抛光,再进行制头、润滑处理、冷拔、矫直、剪切和检验,那么,得到的高精度无缝钢管几何尺寸精度高、内外表面好。这样一来,制作液压缸筒时,可减小内孔珩磨量至0.5～2mm,并且高精度无缝钢管外表面直接作为液压缸筒的外表面使用,有效的提高液压缸筒用高精度无缝钢管的材料利用率、生产效率,尤其是产品质量能够得到进一步提高。