振动辅助磁针磁力研磨法对管件焊缝表面氧化皮的去除实验

Removal of Oxide Scale on Weld Surface of Pipe Fittings by Vibration Assisted Magnetic Needle Magnetic Grinding

目的去除焊接管件焊缝处的氧化皮,改善焊缝处的应力状态。方法采用振动辅助磁针磁力研磨法去除导磁材质管件经焊接处理后焊缝表面的氧化皮,利用超景深电子显微镜观察氧化皮的去除情况;利用X射线能谱分析仪对焊缝表面氧化皮的成分进行分析,根据氧化皮及管件材料主要元素的占比情况,分析检测焊缝表面氧化皮是否被完全去除。结果焊缝表面氧化皮经振动辅助磁针磁力研磨后被完全去除。通过对比振动辅助磁针磁力研磨前后的表面形貌发现,表面颜色由黑变光亮,氧化皮得到有效去除。通过EDS成分分析可知,氧化皮的主要成分为C元素,质量分数为88.62%;管切面显示基体的主要成分为Fe元素,质量分数为67.09%。通过振动辅助磁力研磨法去除氧化皮后,管表面的元素组成与研磨前相比C元素降低了85.52%,Fe元素增加了63.06%。表面残余应力由原始的+17.5 MPa变为−186.0 MPa。经研磨后,氧化皮基本被完全去除。结论焊缝表面成分的检测结果证实,从表面形貌分析中得到氧化皮被完全去除的结论是正确的,同时也表明振动辅助磁针磁力研磨对完全去除焊缝表面的氧化皮具有可行性。

Magnetic needle magnetic grinding technology,as a kind of surface finishing technology,has the advantages of good flexibility and adaptability.Besides,it can also conduct finishing process on small parts,complex outer surfaces and inner surfaces of pipes.Due to the existence of defects such as oxide scale at the weld joints,the service performance of the parts is seriously affected.This article uses vibration assisted magnetic needle magnetic grinding technology to grind welded pipe fittings,and explores the effect of removing oxide scale on the weld surface and the improvement of the residual stress state,which provides a new method for weld surface treatment.In order to compare the effects of vibration assisted magnetic needle magnetic grinding and single magnetic needle magnetic grinding on the processing effect,an iron welded pipe with an outer diameter of 35 mm and a wall thickness of 4 mm was selected as the experimental object.It was cut along the axial direction and its original appearance was recorded by a VHX-500 ultra-depth-of-field microscope at the same time.The welded pipe fitting was placed in a magnetic grinding device for testing.The grinding medium were magnetic needles ofϕ0.5 mm×5 mm,the rotation speed of the magnetic pole plate was 480 r/min,the processing time was 40 minutes,and the amplitude in the vibration assisted magnetic grinding test was±3 mm.By comparing the surface morphology of the inner surface of welded pipe fittings with and without vibration assisted grinding,the effect of vibration assisted magnetic needle magnetic grinding on the processing quality and efficiency under the same processing conditions was explored.In order to explore the effect of oxide scale removal at the weld,the cut surface of the welded pipe was polished to expose the matrix,and the inner wall of the welded pipe before and after processing was analyzed by X-ray energy dispersive spectroscopy(EDS).The element composition was compared with that the matrix element composition to verify whether the oxide scale had completely removed.An X-ray diffractometer was used to detect the residual stress before and after grinding at the weld of the pipe fittings,and the influence of the vibration assisted magnetic needle magnetic grinding method on the stress state of the welded pipe fittings was explored.Compared with a single magnetic needle magnetic grinding technology,the vibration assisted magnetic needle magnetic grinding technology can effectively improve the grinding efficiency and obtain a better grinding effect.It can be obtained by splitting the component elements.The main components of the welded pipe fitting are composed of C,Cr,Fe,Mo and Si.The content of Fe is the highest at 67.09%.After processing,the surface elements of the pipe are approximately the same as the matrix elements,and the presence of oxide scale cannot be found on the surface morphology either,indicating that the oxide scale has been completely removed.Through the detection of the surface residual stress,it can be seen that the residual stress at the weld has changed from the original tensile stress of 17.5 MPa to the compressive stress of 186.0 MPa.The vibration assisted magnetic needle magnetic grinding technology can well deal with the surface defects of welded pipe fittings,especially the difficult-to-handle areas on the pipe inner surface.The oxide scale after grinding can be completely removed,and the residual stress state will also change from the original tensile stress to the compressive stress,which can effectively improve the fatigue strength and service life of the weld joints of the welded pipe fittings.