【作者】 毛亚郎；

【导师】 计时鸣； 孙毅；

【作者基本信息】 浙江工业大学 ， 机械电子工程， 2016， 博士

【摘要】 球磨破碎装置作为一种主要破碎装置,广泛地被应用于水泥、陶瓷、玻璃、矿粉、颜料等粉体制备工业中。粉体制备是一个高能耗的产业,球磨破碎过程被认为是粉体加工中最耗能的一环。为提高球磨效率,通常认为介质的冲击能量越大越有利。但这忽视了球磨时非限制料层在介质球间的破碎特征:料层颗粒受介质球冲击时会产生快速滑移,最终只有很小一部分颗粒被夹持并破碎。料层的夹持形态(夹持厚度和范围)限制了冲击破碎的质量,影响了球磨破碎的能耗。由于对非限制料层的夹持形态及其破碎机理的研究相对不足,致使当前对球磨过程的建模只能依赖于球磨试验和经验公式,未将介质直径、颗粒形态和冲击能量等影响球磨破碎的关键参数纳入模型中,难以从机理上改进和优化球磨破碎过程。为揭示球磨破碎机理,围绕球磨料层夹持形态及其破碎质量模型这一核心问题开展了研究。利用料层夹持实验,分析了挤压下介质球径和颗粒粒度对非限制料层厚度的影响,构建了石英砂料层夹持厚度数学模型;利用石英砂的落球实验分析了初始料层厚度、落球冲击能量、落球直径和颗粒粒度对料层破碎质量的影响,构建了落球冲击下非限制料层夹持形态的数学模型;根据料层夹持颗粒完全破碎的所需冲击能量,对低能未完全破碎和高能完全破碎的质量进行了分析,构建了基于料层夹持形态的单次冲击破碎质量模型。根据粉磨总体平衡模型,结合球磨机DEM的介质冲击能量谱,构建了基于料层单次冲击破碎质量的选择函数和破碎函数,建立了揭示料层颗粒破碎机理的球磨过程模型;最后通过实验球磨机进行了不同工况下的粉磨实验和粉磨产品预测,验证了球磨过程模型。论文的主要创新性成果如下:(1)针对非限制料层颗粒受介质球挤压时,大部分颗粒被排挤出破碎区域,真正被夹持和破碎的颗粒少的现象,提出了一种介质球间静态料层夹持厚度的实验检测方法。利用料层颗粒破碎瞬间挤压力的突变特性,通过对压力传感器和位移传感器实时数据的分析,获取了该瞬时料层的夹持厚度,构建了料层夹持厚度数学模型。(2)料层颗粒受冲击破碎的持续时间很短,夹持破碎瞬时的料层厚度和夹持范围的检测非常困难,提出了一种根据料层破碎质量变化趋势确定料层夹持厚度和夹持范围的方法。根据介质球在非高速冲击时非限制料层颗粒滑移破碎现象不明显的特征,发现初始料层厚度对破碎质量影响很小,通过不同料层厚度的落球实验确定了料层夹持厚度为2层颗粒的厚度。通过不同冲击能量、不同落球直径和不同颗粒粒度的落球实验,根据料层夹持形态模型及其破碎质量反求料层的夹持范围,分析影响料层夹持范围的关键因素,构建了非限制料层夹持范围计算模型。(3)根据料层颗粒破碎质量变化趋势在不同冲击能量水平的显著性差异:低能量水平时破碎质量随输入能量的增加而线性增加,高能量水平时破碎质量随输入能量的增加趋缓,发现料层夹持范围内的颗粒总质量(夹持破碎质量)是破碎质量变化趋势改变的转折点。为此提出了基于料层夹持破碎质量划分低能冲击和高能冲击的方法,为构建料层未完全破碎质量模型和完全破碎质量模型提供了理论支持,解决了完全依据冲击能量计算料层破碎质量的弊端。(4)为提高球磨能效,弥补仅从宏观角度研究的不足,结合微观料层夹持破碎模型和宏观介质运动,提出了基于单次料层冲击破碎质量和冲击能量谱构建球磨过程模型的方法。通过构建基于料层夹持形态的单次冲击破碎模型的球磨选择函数和破碎函数,结合离散元的介质冲击能量谱,将影响料层破碎的微观因素(介质球径与颗粒粒度形态特征)纳入到球磨过程模型中。本论文提出了一种基于单次料层冲击质量破碎模型和冲击能量谱构建球磨过程模型的方法,从微观料层夹持破碎角度揭示了球磨机理,为球磨质量预测、球磨参数优化和球磨装置设计提供了理论支撑。更多还原

【Abstract】 The ball milling as one of the main powder processing devices has been widely used in many powder processing industries such as cement,ceramic,glass,mineral powder,painting.The powder processing is the energy intensive industry,and the ball milling is the most energy-consumption equipment in the powder processing.In order to improve the efficiency of ball milling,many researchers think that the more impact energy,the more beneficial for the powder broken.While they give too little care to the broken characteristics of these unconfined particles which stay on the media,as the particles will slip rapidly when be impacted by the media,and only a small part of the particle will been nipped and been broken.However,the nipped configuration of particle beds including the nipped height and range has an important effect on the breakage mass and the energy consumption.But there is shortage for the study of the nipped configuration of particle beds and its breakage mechanism.The modeling the comminution processing in ball milling only depends on trial mill and empirical equations,and the media diameter,particle size and the impact energy have not been considered.It is difficult to improve and optimize the comminution processing in ball mill.In order to analyze comminution mechanism of ball mill,a study on the nipped configulation of particle beds and the model of breakage mass was carried out.The height of the nipped particles is calculated by the compression test of the unconfined particles beds and the mathematical model of the nipped height of quartz particle beds has been built.The influence of the bed height,impact energy,ball diameter and particle size on the nipped height and range of particle beds has been analyzed by the falling ball impact tests,and the mathematical model of the nipped configuration of the unconfined particles bed has been established.The mass of incomplete breakage in low impact energy and complete breakage in high impact energy are analyzed and a single-impact breakage mass model is established based on the nipped particles configuration.The selection function and breakage function for the single-impact breakage mass of the particle beds has been set up according to the population balance model(PBM),combined with the impact energy spectra of the media in ball mill.The comminution process model in ball mill has been built as well.Finally,the grinding experiments have been carried out in the testing ball mill.The outcome predicted by the comminution process model is basically consistent with the experimental result,thus the mass model has been proved correctly.The mainly study innovation results in this article are listed as following:(1)For the phenomenon that most of the particles are pushed out of the nipped area and only a few particles are caught and broken when particles are compressed by media,A method to measure the statically nipped height of particle beds has been presented.According to leap features of the stress force when particles are broken,the distances between media are measured by displacement sensor and the mathematical model of the nipped height of quartz particles has been built.(2)The duration of impact breakage is very short,and the measure of the nipped height and range is difficult.A method to determine the nipped height and range of particle beds has been put forward according to the trend of the particle breakage mass.Few particles in unconfined beds are broken before nipped and the effect of initial height of particle beds is unobvious.It is concluded that the bed height of the nipped particles is the stack height with 2 layers particles by the falling ball impact test.The influence of bed height,impact energy,impact velocity,ball size,and particle size on nipped configuration has been analyzed,and the mathematical model of nipped range has been set up.(3)According to the significant difference of breakage mass of particle beds in different impact energy levels,the breakage mass increases linearly with the input energy in low energy levels but slowly in high energy levels.The mass of nipped particles is the turning point of breakage mass increasement.A method to distinguish the low energy impact and high energy impact has been put forward according to the mass of nipped particles,which provides the theoretical support for the construction of the model of incomplete and complete breakage mass,and makes up for the deficiency in calculating breakage mass based on the impact energy.(4)In order to improve the energy efficiency and make up for the deficiencies of research in macro-view,a method of modeling the comminution process in ball mill based on single-impact breakage mass and impact energy spectra has been proposed,combined with the microscopic model of the nipped particle beds and the macroscopic media movement.The selection function and breakage function of particle breakage are built based on the nipped configuration of particle beds.The microscopic factors such as ball diameter and particle are incorporated into the function.In this paper,a method of modeling the comminution process in ball mil based on single-impact breakage mass and impact energy spectra has been proposed,and the comminution mechanism of the ball mill has been studied,these will provide the theoretical foundation for predicting the comminution outcome,optimizing the parameter and designing the ball-milling devices.更多还原