Effect of ball milling time on the microstructure and compressive properties of the Fe–Mn–Al porous steel

In the present work,Fe–Mn–Al–C powder mixtures were manufactured by elemental powders with different ball milling time,and the porous high-Mn and high-Al steel was fabricated by powder sintering.The results indicated that the powder size significantly decreased,and the morphology of the Fe powder tended to be increasingly flat as the milling time increased.However,the prolonged milling duration had limited impact on the phase transition of the powder mixture.The main phases of all the samples sintered at 640℃ were α-Fe,α-Mn and Al,and a small amount of Fe2Al5 and Al8Mn5.When the sintering temperature increased to 1200℃,the phase composition was mainly comprised of γ-Fe and α-Fe.The weight loss fraction of the sintered sample decreased with milling time,i.e.,8.3wt% after 20 h milling compared to15.3wt% for 10 h.The Mn depletion region(MDR) for the 10,15,and 20 h milled samples was about 780,600,and 370 μm,respectively.The total porosity of samples sintered at 640℃ decreased from ~46.6vol% for the 10 h milled powder to ~44.2vol% for 20 h milled powder.After sintering at 1200℃,the total porosity of sintered samples prepared by 10 and 20 h milled powder was ~58.3vol% and ~51.3vol%,respectively.The compressive strength and ductility of the 1200℃ sintered porous steel increased as the milling time increased.

Realtime Vision-Based Surface Defect Inspection of Steel Balls

In the proposed system for online inspection of steel balls, a diffuse illumination is developed to enhance defect appearances and produce high quality images. To fully view the entire sphere, a novel unfolding method is put forward based on geometrical analysis, which only requires one-dimensional movement of the balls and a pair of cameras to capture images from different directions. Moreover, a realtime inspection algorithm is customized to improve both accuracy and efficiency. The precision and recall of the sample set were 87.7% and 98%, respectively. The average time cost on image processing and analysis for a steel ball was 47 ms, and the total time cost was less than 200 ms plus the cost of image acquisition and balls' movement. The system can sort 18 000 balls per hour with a spatial resolution higher than 0.01 mm.

WEARING PERFORMANCE OF STEEL BALLS IN WET GRINDING

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Effect of Ball Scribing on Iron Loss of CGO and HGO Electrical Steel

The effect of ball scribing on iron loss of conventional grain-oriented ( CGO) and high-permeability grain-oriented ( HGO) electrical steel was investigated. In this paper,ball scribing was achieved by self- designed ball scribing instrument and a computer-controlled system capable of providing high accuracy and automatic measurements was developed for the magnetisation and measurement at high and low flux densities. The results showed that after ball scribing,iron loss of two types of steel ( C711 and H668 ) apparently decreases ( 5. 5% and 8. 2% respectively after 16mm scribing at 1. 2T) ,and at high and low flux densities, CGO and HGO electrical steel performs differently. Through the formation and development of free magnetic poles and secondary magnetic domains due to compressive stress,primary magnetic domain spacing of grain- oriented electrical steel becomes smaller,which reflects as a reduction of iron loss in the macroscopic magnetic properties. Through iron loss formula derivation,the effect of domain refinement on grain-oriented electrical steel was also interpreted.

Structural optimization for ball valve made of CF8M stainless steel

The mechanical and chemical properties of CF8M were studied through experiments. An application of CF8M in valve body was analyzed by using finite element method(FEM) to evaluate the structural safety. An optimization containing several variables based on the response surface method(RSM) was conducted to find the optimum dimension of the valve. The results show that using this process can save valve mass as well as the computational expense effectively.

Automatic Detection of Steel Ball's Surface Flaws Based on Image Processing

A new method to detect steel ball's surface flaws is presented based on computer techniques of image processing and pattern recognition. The steel ball's surface flaws is the primary factor causing bearing failure. The high efficient and precision detections for the surface flaws of steel ball can be conducted by the presented method, including spot, abrasion, burn, scratch and crack, etc. The design of main components of the detecting system is described in detail including automatic feeding mechanism, automatic spreading mechanism of steel ball's surface, optical system of microscope, image acquisition system, image processing system. The whole automatic system is controlled by an industrial control computer, which can carry out the recognition of flaws of steel ball's surface effectively.

Preparation and Characterization of Stainless Steel/TiC Nanocomposite Particles by Ball-milling Method

A stainless steel/10wt%TiC nanocomposite particles were prepared by high-energy ball-milling method using stainless steel, carbon and titanium as raw materials. The evolution of phase composition, microstructure and specific surface area of the stainless steel/TiC nanocomposite particles with increasing ball-milling time in the range of 0-100 h were investigated by XRD, SEM, TEM and BET techniques. The results showed that the stainless steel/TiC nano-composite particles were fabricated when the ball-milling time was longer than 20 h. However, the nanocomposite particles were soldered and agglomerated again when the ball-milling time was longer than 60 h. The microstructure of the composite particles transformed from lamellar structure to nanostructure during the repeated process of the cold welding and cracking. TEM image reveals clearly that the in-situ TiC nanoparticles with grain size of 3-8 nm are in the interior of the stainless steel/TiC nanocomposite particles obtained by ball-milling 100 h.

EFFECT OF SULFUR ON PROPERTIES OF BALL BEARING STEEL

5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness KICWere studied. It was shown that as the sulfur content increases the sulfur content dissolved in the steelsubstrate remains unchanged. The best contact fatigue property appears at the sulfur content of0.045% （wt.）, and the influence of sulfur content on the fracture toughness of bearing steel is notobvious. Finally, the mechanism of the role of sulfur was investigated.

Effect of Ball Scribing on Power Loss Separation of Fe-3%Si Grain-oriented Silicon Steel

Power loss of Fe-3%Sigrain-oriented silicon steelwas measured after ballscribing with different spacing using a self-designed tool.Three different sections of power loss,including hysteresis loss,abnormalloss,and eddy current loss,were measured and calculated,respectively.The loss variation and ratio were analyzed based on the experimentaldata.At 1.0 T,hysteresis loss of tested steelwith scribing spacing of 8 mm descends by 8.2% compared to samples without scribing,which is similar to the totalloss variation,and abnormalloss descends by 16.8%.At 1.0 T,hysteresis loss ratio of the steelwith scribing spacing of 16 mm ascends from 55.7% to 57.9%,and eddy current loss increases from 17.4% to 24.1%,while abnormalloss descends from 26.9% to 23.7%.The experimentalresults show that the reduction of power loss after scribing is mainly due to decreasing of hysteresis loss and abnormalloss.

Mechanical Property of Low Chromium Semi-Steel Grinding Ball Prepared by Cross Rolling

The preparing method,rolling technology and mechanical properties of low chromium semi-steel grinding ball by cross rolling were studied.The results show that when the low chromium semi-steel bar is forged from55mm to50mm,cross-rolled into grinding ball at 1 000-1 050℃,air cooled and tempered at 550℃for 2h,the best mechanical properties,especially the abrasive resistance under the action of hard abrasive,can be obtained.

Electrochemical corrosion of steel balls in wet grinding

Rest potentials for the steel ball electrode and the pyrite electrode as well as the combination potentials and the galvanic currents developed in the pyrite steel ball couple were measured. The data demonstrate that the galvanic couples are going to form between the pyrite particles and the steel balls when they contact with each other. The initial combination potential and the initial galvanic current of the pyrite ball couple while bubbling with oxygen are greater than those in aeration of air. The combination potential and the galvanic current decrease more quickly with time while bubbling with oxygen than they do in aeration of air. In an experiment of simulating wear differences, a galvanic current, which is smaller than that developed in the pyrite ball couple, exists between two different ball electrodes in wear degree on the surface of them. Under different grinding time conditions, the equivalent corrosion current density calculated from marked ball wear data by applying Faraday’s law correlates well with those estimated from polarization curves of pyrite and ball electrodes, and the former is always greater than the latter.

Low-Energy Multi-Impact Fracture Resistance of Cross Rolled Low Chromium Cast Semi-Steel Containing Rare Earth Grinding Ball

The low-energy multi-impact fracture resistance of the cross rolled low chromium cast semi-steel containing RE grinding balls was studied. Moreover, its damage mode was analyzed by means of metallographic examination, scanning electron microscopic examination and drop ball test. The results show that it can obtain extractive impact fracture resistance after proper heat treatment. More advantages were obtained for the ball worked in the condition of low-imp ductility act. The main reasons are the function of RE and the change in morphology of eutectic carbide network.

联合载荷作用下精密轴系角接触球轴承钢球与保持架动力学行为分析

针对联合载荷作用下精密轴系角接触球轴承钢球与保持架的相互作用行为,基于滚动轴承动力学理论建立了精密轴系动力学分析模型,分析了转速、载荷、轴承结构参数对钢球与保持架动力学行为的影响,并通过保持架转速试验验证了模型的准确性,结果表明:力矩载荷对钢球与保持架动力学行为的影响程度较径向载荷明显;在径向载荷作用下,当转速小于40000 r/min时钢球与保持架的作用力随轴向预紧力增大而增大,当转速大于40000 r/min时钢球与保持架的作用力随轴向预紧力增大先减小后增大;在力矩载荷作用下,钢球与保持架的作用力随着力矩载荷的增大先增大再减小而后急剧增大;增大保持架兜孔间隙与外沟曲率半径系数有利于减小钢球与保持架的作用力。

提高大红山铜矿铜回收率及降低介耗的研究

针对玉溪矿业有限公司大红山铜矿一选厂浮选给矿产品中合格粒级含量过低、过磨粒级含量较高、铜选别回收率较低等问题,在研究选厂给矿性质的基础上,基于球径半理论公式推导了该段磨矿作业中钢球的最佳配比,并将该方案分别在实验室和现场进行验证。对于推导出的一段球磨机初装方案m(Φ70 mm)︰m(Φ50 mm)︰m(Φ40 mm)︰m(Φ30 mm)=15︰25︰35︰25,在实验室试验和工业试验中进行验证,结果表明:该方案能够提高-0.020+0.010 mm可选粒级及-0.074+0.018 mm易选粒级的含量,有效减少了过粉碎现象,降低了介质消耗,提高了铜精矿回收率,实现了降本增效。

球压痕法获取不同变形率下316L不锈钢的力学性能

核电焊接结构由于在加工过程中受到冷作硬化导致局部区域力学性能发生改变且难以准确获取,利用ABAQUS有限元分析软件建立了弹塑性材料下的压痕实验三维模型进行数值模拟,通过识别载荷-深度曲线中的相关参数,结合量纲分析法理论计算316L奥氏体不锈钢材料在不同变形率下的力学性能参量。结果表明,随着变形率的不断增大,材料的塑性降低,硬度增大,且力学性能参数如屈服强度、抗拉强度及硬化指数均相应增大。

风电轴承大尺寸钢球光球加工技术

针对国内现有风电轴承大尺寸钢球光球机加工精度低,加工效率低的问题,对钢球在光球机动、静磨盘沟道内的运动规律、受力特点和磨削机理进行分析,光球时钢球受到的磨削力与动、静磨盘沟道深度比有关,并基于ADAMS仿真得到最佳动、静磨盘沟道深度比为7∶3,去两极和环带、成形、走圆工序最佳动磨盘转速分别为90,120,90 r/min。样机试验结果表明,改进后光球机的光球效率提高了30%,球形误差至少提高了0.2 mm,表面粗糙度Ra值至少减小了0.03 mm。

泥石流排导槽混凝土材料磨蚀特性研究

我国泥石流灾害频发多发,危害十分严重。排导槽在防治泥石流的实践中扮演了至关重要的作用,但也出现了很多冲磨破坏的情况,极大地影响排导槽安全功能及运行寿命。排导槽的冲刷磨蚀问题是泥石流减灾亟需解决的关键技术难题之一。针对排导槽工程中混凝土过流表面的冲磨破坏现象,本文通过向混凝土中复掺不同材料(纳米二氧化硅、微硅粉、聚丙烯纤维和引气剂)和涂抹聚脲保护层两种途径,提高混凝土的抗冲耐磨性能。为此,采取水下钢球法的磨蚀实验方法,研究两种混凝土试件的抗冲磨强度、磨损率、磨损系数和平均磨蚀深度等参数指标,综合比较其抗冲耐磨性能。结果表明,两者都能提高混凝土的抗冲耐磨性,聚脲的抗冲磨强度比复掺材料混凝土提高了约5~18倍,磨损率和磨损系数均降低约78%~98%,平均磨蚀深度减小了一个数量级,并且弹性聚脲抗冲磨性能远大于刚性聚脲。分析其抗冲磨机制,认为复掺材料主要通过增加集料与水泥石的接触面积、改善混凝土内微结构、增强黏结性等来增强抗冲耐磨性能。聚脲材料则依靠自身大量氢键的断裂-新生循环、强活动性链段的松弛型变、以及自由基团氧化反应的胶黏层显著提高耐磨性。因此,建议在泥石流排导槽磨损修复加固措施中,优先考虑涂抹聚脲保护层来延长排导槽的使用寿命。

钢球堵塞引起S30432屏式过热器爆管的失效特征分析

以试运行阶段就发生因钢球堵塞造成过热蠕变爆管的某600MW超超临界锅炉屏式过热器为例,通过宏观检查、尺寸测量、化学成分分析、力学性能分析、金相分析、维氏硬度试验和扫描电镜观察等方法,并与相邻管子进行对比,得出了钢球堵塞引起S30432爆管失效的特征。结果表明:爆口部位的管径、壁厚、蠕变孔洞、蠕变裂纹及老化程度等方面存在明显特征,除爆口部位及弯管部位外的各项试验结果均符合标准对新管的要求,但其材质状态已明显差于相邻管子。

基于直线扫描的引信钢球分层成像检测算法

针对现有的火药引信装配正确性检测方法中存在的无法准确检测遮挡严重的零件的问题,提出了引信中钢球分层成像定位检测算法。将X射线源直线移动扫描待测物体形成多个虚拟的小孔径,结合光学合成孔径原理对所有小孔径进行合成,将合成的虚拟大孔径成像在不同距离深度的平面上,实现对目标的定位和检测。试验结果表明:所提算法能够在火药引信钢球相互重叠的情况下利用深度信息进行分层成像,提供待测物体的深度信息,能够对不同层次的目标进行检测,确定待检测物体的数量,解决了现有的检测方法在检测过程中出现的漏检问题。

AISI-304不锈钢薄壁管滚珠旋压工艺参数的正交优化研究

针对小直径不锈钢薄壁管滚珠旋压参数不当引发的一系列问题,选取φ6 mm×0.5 mm×10 mm的AISI-304不锈钢管为研究对象,建立其有限元模型,运用Abaqus软件对其成形过程进行仿真,分析了不同工艺参数(减薄量、进给比、旋压角)对其等效应力和均匀塑性应变的影响,最后运用正交试验法对工艺参数进行优化。结果表明:优化后的工艺参数组合为:减薄量0.2 mm、进给比0.05 mm/r、旋压角25°。在此工艺参数组合下,AISI-304不锈钢管的等效应力值和均匀塑性应变值达到最优,其值分别为642.22 MPa和0.06。