Research on product size and grinding dynamics of vibration mills

In order to improve vibration mills grinding effect and increase productive efficiency, prime factors of vibration mills were gained much attention. The purpose of this study is to reveal product size distribution and grinding dynamics of vibration mills by orthogonal experi-ments. The metallurgical refractory materials were used as research object. In order to explore the relationships between grinding effect and primary factors, lots of milling experiments were carried out. Based on the results, the conclusions can be summarized： as time runs, the size distri-bution shows exponential trend, and range becomes more and more narrow. Also the quantitative analysis result between grinding effect and primary factors was obtained by non-linear regres-sion： high frequency, high amplitude and low fill ratio can increase grinding speed.

Experimental Study of Machinability in Millgrinding of SiCp/Al Composites

An attempt was made to investigate the machinability of Si Cp/Al composites based on the experimental study using mill-grinding processing method. The experiments were carried out on a high-speed CNC machining center using integrated abrasive cutting tool. The effects of combined machining parameters, e g, cutting speed（vs）, feed rate（vf）, and depth of cut（ap）, with the same change of material removal rate（MRR） on the mill-grinding force and surface roughness（Ra） were investigated. The formation mechanism of typical machined surface defects was analyzed by SEM. The experimental results reveal that with the same change of material removal rate, lower mill-grinding force values can be gained by increasing depth of cut and feed rate simultaneously at higher cutting speed. With the same change of MRR value, lower surface roughness values can be gained by increasing the feed rate at higher cutting speed, rather than just increasing the depth of cut, or increasing the feed rate and depth of cut simultaneously. The machined surface of Si Cp/Al composites reveals typical defects which can influence surface integrity.

Optimization of Preventive Grinding of Backup Roll against Contact Fatigue Cracking

In order to optimize the current grinding procedure of the backup roll of 2050 continuously variable crown (CVC) mills, the behavior of rolling contact fatigue (RCF) cracking was investigated. Two RCF short cracks, including vertical short crack and ratcheting short crack initiated from ratcheting, were observed. The behavior of both RCF cracks was analyzed in detail. Then a modified grinding procedure was proposed according to the behavior of RCF cracks and the preventive grinding strategy.

WEARING PERFORMANCE OF STEEL BALLS IN WET GRINDING

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Electrochemical performances of hydrogen storage alloys treated using a new milling technique

A new self-made additive of amidocyanogen-acetic salt was used in wet ball-grind technique （WBGT） for preparing hydrogen storage alloys, and the effect on the electrochemical performance of the alloy electrode was investigated in detail. It was found that the prepared electrode had perfect electrochemical performances, such as rapid activation, high capability, high-rate discharge （HRD） ability, and good stability. The first discharge capacitance at 0.2 C （throughout this study, n C rate means that the rated capacity of a hydrogen storage alloy （full capacity） is charged or discharged completely in 1/n h） reached 278 mAh·g^-1 and the discharge capacitance reached the maximum of 322 mAh·g^-1 only after two charge-discharge cycles. For the dry method, wet method, and WBGT, the high rate discharge （HRD） values （C5 c/C0.2c ratio） were approximately 0.59, 0.76, and 0.83, respectively. The stable discharge capacity at 3 C increased from 275 mAh·g^-1 （dry method）to 295 mAh·g^-1 （WBGT）.

THE SELF-GRINDING MECHANISM AND AFFECTING FACTORS OF BULK MATERIAL IN FLUID MOTION

The fluidity and classification of bulk material (loose body) were introduced, the self-grinding mechanism and the affecting factors of bulk materials in various forms of phase, state and motion were investigated. A rotational-flow-state centrifugal autogenous grinder was developed on the basis of applying self-grinding mechanism of bulk material,the result tested by the autogenous grinder was compared with that tested by 4R Raymond mills, and fine particles with extremely high specific area were obtained. The feasibility of the developed new-type autogenous grinder in the view of fluid motion of bulk material was proved.

Morphology Study of Particle Breakage Mechanisms in a Horizontal Stirred Mill: Automated and Manual Point Counting Approaches

High-speed stirred mills are utilized to grind particles below 10mm. Grinding sulphide minerals to as low as 10mm achieve adequate mineral liberation for successful downstream mineral processing operations, such as flotation and leaching. Particle breakage mechanism such as fracture or abrasion, determines the morphological surface features of the product particles. It is anticipated that particles, which break along grain boundaries (intergranular) produce rough surfaces, whereas particles that break across the grain boundaries (transgranular) possess smoother surfaces. In this study, particles are ground in a stirred mill and their morphological features were analyzed using automated and manual detection methods. Literature and conventional belief are that high-speed stirred mills break particles by attrition. This paper showed that fracture is also an important breakage mechanism along with attrition. Breakage mechanism is a factor of input stress intensity, in the form of the mill agitator speed, and type of mineral. It is observed that at higher agitator speed galena fractures along the grain boundaries, whereas quartz, abrade across the grain boundaries.

Evaluating the Effects of Crystallinity on Drug Release Behaviour in Itraconazole- or Miconazole-Loaded PLGA Microparticles Prepared Using a Co-Grinding Method

This study aimed to prepare and characterize itraconazole (ITCZ)- or miconazole (MCZ)-loaded poly (lactide-co-glycolide) (PLGA) microparticles (MP) using a co-grinding method with ball milling, which is a solvent-free and convenient procedure. PLGA MP was prepared by grinding for 60 min, and the fixed theoretical drug loading was set at 9.1% and 16.7% for both drugs. The obtained loading efficiency for both drugs was estimated to be approximately 100%. The average diameters of the drug-loaded PLGA MP were approximately 20 - 35 μm. Powder X-ray diffraction (PXRD) or differential scanning calorimetry (DSC) confirmed amorphization of ITCZ and MCZ in ITCZ- or MCZ-loaded PLGA MP in all formulations. The drug release percentage from 9.1%-loaded ITCZ-PLGA7505 MP at 24 h was almost 50%, which was higher than that of ITCZ powder. The drug release percentage from MCZ-loaded PLGA7505 MP at 4 h was over 80%, which was higher than that of MCZ powder. This enhancement of release rate is caused by the amorphization of ITCZ or MCZ in the PLGA matrix. MCZ-loaded PLGA7510 MP showed a sustained release profile up to 24 h, suggesting that MCZ exists in an amorphous form in the PLGA matrix;however, the release rate declined owing to the large molecular weight of PLGA. Therefore, the release enhancement of antifungal drugs loaded on PLGA MP could be achieved by their amorphization using a co-grinding method with ball milling.

Influences of milling and grinding on machined surface roughness and fatigue behavior of GH4169 superalloy workpieces

Surface topography of superalloy GH4169 workpieces machined by milling and grinding is different significantly. Meanwhile, surface roughness, as one of the main indicators of machined surface integrity, has a great influence on the fatigue behavior of workpieces. Based on analyzing the formation mechanism and characteristics of surface roughness utilizing different machining processes and parameters, the machined surface roughness curve can be decoupled into two parts utilizing frequency spectrum analysis, which are kinematic surface roughness curve and stochastic surface roughness curve. The kinematic surface roughness curve is influenced by machining process,parameters, geometry of the cutting tool or wheel, the maximum height of which is expressed as Rz＇.By subtracting the kinematic part from the measurement curve, the stochastic surface roughness curve and its maximum height Rz＂ can be obtained, which is influenced by the defects of cutting tool edge or abrasive grains, built-up edges（BUE）, cracks, high frequency vibration and so on. On the other hand, the results of decoupling analysis of surface roughness curves indicate that Raand Rz values of milling GH4169 are 2–5 times and 1–3 times as high as those of grinding, while Rz＂ value of milling is 13.85%–37.7% as high as that of grinding. According to the results of fatigue life tests of specimens machined by milling and grinding, it can be concluded that fatigue behavior of GH4169 decreases with the increase of Rz＂monotonically, even utilizing different machining processes.

Fiber-reinforced composites in milling and grinding:machining bottlenecks and advanced strategies

Fiber-reinforced composites have become the preferred material in the fields of aviation and aerospace because of their high-strength performance in unit weight.The composite components are manufactured by near netshape and only require finishing operations to achieve final dimensional and assembly tolerances.Milling and grinding arise as the preferred choices because of their precision processing.Nevertheless,given their laminated,anisotropic,and heterogeneous nature,these materials are considered difficult-to-machine.As undesirable results and challenging breakthroughs,the surface damage and integrity of these materials is a research hotspot with important engineering significance.This review summarizes an up-to-date progress of the damage formation mechanisms and suppression strategies in milling and grinding for the fiber-reinforced composites reported in the literature.First,the formation mechanisms of milling damage,including delamination,burr,and tear,are analyzed.Second,the grinding mechanisms,covering material removal mechanism,thermal mechanical behavior,surface integrity,and damage,are discussed.Third,suppression strategies are reviewed systematically from the aspects of advanced cutting tools and technologies,including ultrasonic vibration-assisted machining,cryogenic cooling,minimum quantity lubrication(MQL),and tool optimization design.Ultrasonic vibration shows the greatest advantage of restraining machining force,which can be reduced by approximately 60%compared with conventional machining.Cryogenic cooling is the most effective method to reduce temperature with a maximum reduction of approximately 60%.MQL shows its advantages in terms of reducing friction coefficient,force,temperature,and tool wear.Finally,research gaps and future exploration directions are prospected,giving researchers opportunity to deepen specific aspects and explore new area for achieving high precision surface machining of fiber-reinforced composites.

Compound machining of silicon carbide ceramics by high speed end electrical discharge milling and mechanical grinding

A compound process that integrates end electrical discharge (ED) milling and mechanical grinding to machine silicon carbide (SiC) ceramics is developed in this paper. The process employs a turntable with several uniformly-distributed cylindrical copper electrodes and abrasive sticks as the tool, and uses a water-based emulsion as the machining fluid. End electrical discharge milling and mechanical grinding happen alternately and are mutually beneficial, so the process is able to effectively machine a large surface area on SiC ceramic with a good surface quality. The machining principle and characteristics of the technique are introduced. The effects of polarity, pulse duration, pulse interval, open-circuit voltage, discharge current, diamond grit size, emulsion concentration, emulsion flux, milling depth and tool stick number on performance parameters such as the material removal rate, tool wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface under different machining conditions is examined with a scanning electron microscope and an energy dispersive spectrometer. The SiC ceramic was mainly removed by end ED milling during the initial rough machining mode, whereas it is mainly removed by mechanical grinding during the later finer machining mode; moreover, the tool material can transfer to the workpiece surface during the compound process.

选矿粗磨工艺中TZJK-350耐磨渣浆泵过流件开发与应用

本文针对钼选矿厂一段磨矿粗磨工艺中TZJK-350金属渣浆泵过流件磨损快的问题,研究了耐磨耐腐蚀陶瓷材料特性、制作工艺和工程适应性等,通过工业试验将TZJK-350金属泵替换为陶瓷泵,大幅提升了粗磨工艺中渣浆泵的使用寿命和可靠性。应用实践表明,陶瓷泵使用寿命是金属泵的4倍,降低了检修维护成本,稳定了生产工艺,该设备具有非常高的推广应用价值。

锯片铣刀V形微刃磨削修整及微沟槽铣削试验研究

针对尺度较大的微沟槽阵列结构加工成本高、效率低的问题,提出数控对磨修整的方法,在三轴加工中心上利用金刚石油石将锯片铣刀刃口区域修整出V形微刃,并使用修整后的锯片铣刀对铝合金材料进行角度120°、深度160μm的微沟槽阵列铣削试验。试验结果表明:修整后的锯片铣刀V形微刃两侧刃口规则整齐,锯片铣刀铣削后的微沟槽角度误差平均值为1.2°,沟槽深度误差为1.5μm,说明对锯片铣刀修整后进行V形微沟槽铣削的加工方法可行。

南芬选矿厂北山矿石选矿工艺试验

为配合南芬铁矿绿色矿山选矿提效及高效利用北山原矿石,在工艺矿物学研究的基础上,对北山矿石进行了选矿工艺流程试验。试验结果表明:采用辊磨前干抛—高压辊磨—辊磨产品湿式抛尾—阶段磨矿—弱磁选工艺,干抛和湿抛可提前抛除合计产率23.26%的尾矿,大幅降低了后续入磨矿量,提升了入磨矿样铁品位,最终获得的铁精矿产率为30.77%,TFe和mFe含量分别为68.17%和60.22%,TFe和mFe回收率分别为66.63%和98.16%。

半自磨机磨球充填率预测研究

为了在磨矿实际生产中实时掌握半自磨机内磨球的充填率,以磨球磨损动力学理论为基础,推导出了磨矿生产条件下磨球在半自磨机内磨球充填率的计算公式,并给出了磨球速率指数的测定方法。利用该公式,按照磨球的耐磨性、半自磨机的有效容积、日补加钢球的数量及其直径、排矿格子板格子孔尺寸可以对磨球的充填率进行计算。将该公式运用于磨矿生产,很好地预测了半自磨机内钢球的充填率,这对于半自磨机磨矿生产中确定补加钢球数量以及评价钢球耐磨性具有重要的指导意义。

高压辊磨机碎磨新工艺国内外研究及应用现状

高压辊磨机作为国内外选矿领域“多碎少磨”设备和选择性粉碎设备应用的主流,在选矿行业中的应用较为成熟,由于其具备单次处理矿石量大、粉碎效率高、且其粉碎产品粒度细的优点,因此被金属与非金属行业所广泛应用。对高压辊磨机的工作原理及粉碎过程进行了简要介绍,结合实际案例对高压辊磨机三种破碎工艺在矿山中的应用及优缺点进行了分析;对高压辊磨机在选矿行业的典型应用进行了介绍;对高压辊磨机新工艺在国内外的应用进行了重点阐述并就新工艺在选矿行业中的应用进行了展望,高压辊磨机联合搅拌磨/塔磨机工艺、高压辊磨机联合风力分级机工艺、两段高压辊磨机串联工艺、两高压辊磨并联工艺以及高压辊接双层振动筛节能降耗优势明显,有望为物料高效粉碎提供新的方案。

基于标准砂轮的立铣刀精确螺旋槽磨削位姿算法研究

为了提高整体式立铣刀螺旋槽结构参数的磨削精度,通过完善螺旋槽轮廓成形计算方法,提出了一种基于标准砂轮的立铣刀精确螺旋槽磨削位姿算法。对螺旋槽磨削过程的砂轮和运动关系进行参数化建模;根据砂轮的运动轨迹计算出砂轮做空间螺旋运动形成的包络面,并由空间包络原理接触条件计算砂轮磨削形成的螺旋槽轮廓方程;根据螺旋槽的前角、芯厚、槽宽参数的几何定义,建立各参数关于砂轮位姿的函数关系;将砂轮位姿求解问题转换成数学优化问题,采用智能算法进行快速求解。通过仿真试验对算法的求解精度和适应性进行了分析,验证了算法的有效性。

高压辊磨对超微细粒嵌布磁铁矿破碎和预选的影响

针对某超微细粒嵌布贫磁铁矿开发难度大、原矿入磨品位偏低、磨矿能源消耗高的问题,本文进行高压辊磨—预选工艺试验,通过对比两种破碎产品的粒度特征、相对可磨度、Bond球磨功指数、预选指标,并结合破碎产品的表面形貌和内部微裂纹,研究高压辊磨所产生的微裂纹对于磨矿和分选的影响。结果表明:相对于常规破碎,辊压产品中<0.074 mm粒级质量分数增加了14.69个百分点,>2 mm的粗粒级质量分数降低了8.59个百分点;在160 kA/m预选磁场强度下,辊压产品的铁品位为31.96%,提高了1.46个百分点;磁性铁的回收率高达99.45%,提高了1.17个百分点,抛尾率提高了5.03个百分点。相对可磨度试验结果表明,当磨矿细度达到<0.03 mm粒级质量分数为85%时,辊压产品的耗时相对于常规破碎缩短了42.13%。辊压产品的Bond球磨功指数(目标粒度<0.15 mm)降低了27.90%。偏光显微镜和SEM扫描电镜结果表明,辊压产品结构疏松多孔、微裂纹发育充分,能产生大量的晶界裂纹,解离更充分。

基于接触区域自适应调整的圆弧头立铣刀后刀面磨削轨迹精确计算方法

为保证圆弧头立铣刀后刀面的加工精度,提出一种基于接触区域自适应调整的圆弧头立铣刀后刀面磨削轨迹精确计算方法。通过圆弧头立铣刀结构特征分解构建了后刀面的数学模型;通过计算砂轮和后刀面之间的磨削接触区域,自适应修正砂轮姿态,避免磨削干涉,实现了后刀面几何参数控制的准确性和一致性,并保证了曲面的光滑连接。最后,在VC++平台算法模块开发的基础上,通过加工仿真和磨削试验验证了该算法的有效性。