Interpretation of mill vibration signal via wireless sensing

Tumbling mills emit vibration that can be captured to assess its performance. We interpret the vibration signature of a one meter diameter mill in response to changes in mill speed, rock/particle size, quantity of balls, and slurry viscosity. A ±500 g tri-axial accelerometer with a wireless transmitter located on the surface of the mill shell transmits vibration signal to a receiver connected to a PC. The quality of the vibration signal is preserved due to the use of wireless transfer of data. The filtered vibration signal in the frequency domain is averaged which is then used as a parameter for comparison purpose. This approach to signal analysis is most suitable to compare vibration response of a mill to changes in operating parameters. The mill shell vibration signature turned out to be an excellent indicator to establish the differences in mill performance under wet versus dry grinding conditions, coarse versus fine grinding, changes in mill speed, ball load, etc. The broader implication of the main observations in the context of development of a diagnostic tool to assess the mill performance is highlighted.     

Modeling ball impact on the wet mill liners and its application in predicting mill magnetic liner performance

Numerous studies have been conducted in the past and models have been developed to simulate ball motions in horizontal mills. Equations and computer programs have been published to calculate falling velocity of the grinding media upon impacting the mill shell (liner). However, these equations and programs are only suitable for dry mill applications.To accurately simulate the impact of falling balls on the liners in wet mills, the authors have developed models to determine the ball impact location and velocity as the ball contacts the mill liner. Drag and buoyancy forces are considered when the ball submerges in the pulp inside the mill. Models can be used to enhance mill liner design and optimize the operation of horizontal wet mills such as horizontal ball mills.The models are applied to calculate the falling ball impact on the metal magnetic mill liners. Various scenarios are simulated and results are used to predict the performance of magnetic mill liners in various ball mill applications.     

基于振动信号分析的球磨机工况检测技术的研究与应用

实时有效的检测球磨机的工作状态,使其稳定的运行在最佳工作点附近对于整个选矿流程的稳定和高效具有极其重要的意义。从系统组成、信号分析和实际应用三个方面,对基于振动信号分析的球磨机工况检测技术的研究与应用进行综合介绍。     

Measurement system of the mill charge in grinding ball mill circuits

Investigation of a dry fine grinding circuit has shown significant influence of the mill load (powder filling) on the production capacity. To improve the circuit performance at industrial scale, alternative ways of mill load measurement were investigated. Detection of strain changes in the mill shell during mill rotation, by using a piezoelectric strain transducer, provided very interesting results, allowing evaluation of the weight of the mill charge and control of the powder filling to obtain an optimal level. Power draw has thus been increased by about 5% compared to the old configuration where mill motor power input was used to control the mill charge. By measuring mechanical vibration with the transducer, additional useful information has been obtained about the behavior of the cataracting and cascading balls inside the mill shell. Finally an important factor was simplicity and low investment cost of the total installation, as many fine grinding mills operate in relatively small circuits that do not warrant large investment for alternative measurement methods.     

基于筒壁振动信号的磨机工况监测系统

磨机是磨矿过程的核心设备,提高磨机工况监测水平对磨矿过程的优化控制具有重要意义。本文介绍了一种磨机工况监测系统的硬件装置。该装置可以实现对磨机筒壁振动信号的高速高精度采集,并具有空间定位和无线通讯功能,经实验验证符合生产现场的实际需求且运行稳定可靠。     

Experimental analysis of charge dynamics in tumbling mills by vibration signature technique

Up until now, real time identification of the dynamics of the charge in a tumbling mill has not been accomplished. This paper examines the possibility of correlating the vibration signature of tumbling mills to characterize the motion of the charge and the state of grinding. Vibration signals were picked up using accelerometers mounted directly on the mill shaft of a 90-cm diameter mill. The time domain signals were transformed to frequency domain by using fast Fourier transform (FFT). The Fourier spectra in the frequency domain were methodically interpreted and correlated to establish the prevailing mode of the charge motion under any operating condition. The grinding behavior under dry as well as wet grinding conditions were analyzed by following the variations in the vibration signature as a function of speed of the mill, volumetric filling, powder loading, and time of grinding.Experimental results clearly show that the dominant peak in the FFT spectra is quite sensitive to the variations in any mill operating parameter. This feature has been employed to detect undesirable operating conditions such as surging, mill over-load, etc. Finally, it is demonstrated that by proper interpretation of the vibration signature of the mill, it is possible to predict the charge dynamics and establish the state of grinding.     

球磨机的动态建模研究

磨矿分级流程模拟仿真系统可实现各种操作条件下的产品粒度在线检测,为操作参数优化提供指导,而球磨机是磨矿分级回路的重要设备单元,因此球磨机的数学模型是该流程仿真系统的基础。借助磨矿动力学与物料平衡有关理论,分析现场实际运行参数与磨机功耗的关系,通过引入选择函数建立球磨机的动态数学模型,基于灰盒神经网络理论建立了磨机功耗预测模型,并利用Matlab的Simulink组件建立了仿真模型,对所建模型进行仿真分析。模型的效验与扰动试验验证了所建模型的有效性与合理性。     

基于矩阵PBM的煤粉超细粉碎过程研究

建立基于研磨过程机理的煤粉超细研磨动力学模型可以预测超细磨出料的粒度分布和指导优化磨机的研磨效率,降低研磨能耗,对制备低灰分的超净煤具有非常重要的作用。通过田口(Taguchi)正交实验设计,使用实验室1. 5 L立式搅拌磨机考察了不同煤的物性参数、磨介尺寸和煤粉比处理量对于超细研磨的影响,将基于研磨过程特征的动力学模型——矩阵粒群平衡模型(Matrix Population Balance Model,M-PBM)用于煤粉的搅拌磨机超细研磨出料的粒度预测,并结合Rosin-Rammler粒度分布模型,精确地预测出料产品在任意筛下累积含量对应的颗粒粒度。通过极差分析,探讨了煤的灰分、磨介尺寸和煤粉比处理量对于超细研磨能耗和比通量的影响大小,基于对煤粉超细研磨过程中煤-灰解离过程的分析并结合Tomoyoshi的比表面积能耗公式,探讨了煤的灰分与能耗的关系,并进一步建立了煤的灰分、磨介尺寸和煤粉比处理量与磨机研磨比通量和能耗的关系式,研究发现搅拌球磨机湿法超细研磨的粒度变化规律符合一阶线性动力学假设,在定搅拌转轴转速和所考查的研磨粒度变化范围内,煤的灰分对搅拌磨机的比通量和能耗的影响是最大的,建立的研磨能耗和比通量关系式表明在10μm(p50)以下的超细粉磨粒度范围内,煤的研磨能耗随着灰分的提高、磨介尺寸的减小(磨介尺寸在0. 3～1. 8 mm)和比处理量的增大而减小,而比通量随着灰分的提高、磨介尺寸的减小和比处理量的增大而增大。     

Control of the mill charge behavior in dry tumbling mills

Powder filling of a dry mill has a large influence on grinding capacity and wear rate of grinding media and liners. In particular low powder filling levels can cause extensive wear rates. This paper discusses the influence of some operating parameters of the mill circuit on powder filling, when airflow through the mill is applied. An method of warning against low powder filling levels inside the mill is shown, a piezoelectric strain transducer installed on the mill shell accomplishing this task.     

基于Lacey指数的球磨机介质分层行为研究

为弄清球磨机各运行参数对其内部介质分层行为的影响程度,本文针对球磨机运行时内部磨矿介质的轴向分层行为进行了研究。借助离散元工具及Lacey混合指数相关理论,进行了正交仿真实验,对介质填充率、筒体转速率、提升条数量和提升条迎球较面角度四个参数对介质分层的影响进行了研究,得出结论：对球磨机内介质分层行为影响最大的因素是球磨机筒体内提升条数量,球磨机转速率和介质填充率次之,影响最小的因素是提升条冲击面角度。当筒体转速率为67 RPM、提升条数量为0个、提升条角度为55°时,筒体内的介质颗粒的混合效果最差,颗粒分层行为最明显。     

球磨机在煤样制备中的应用

介绍了球磨机在煤样制备中的工作特性,阐明球磨机的设计、建模及工作原理,验证了球罐转速控制和钢球介质装入量对研磨效果的影响,并提出球磨机在煤样制备中的应用技巧。     

鞍千预选精矿陶瓷球搅拌磨再选试验研究

鞍千选矿厂现有流程磨矿产品存在粗细分布不均匀、再磨效率低、能耗高、磨矿效果差等问题,影响后续分选过程,导致精矿指标差。针对以上问题,为改善预选精矿磨矿效果,提升最终精矿指标,有必要采用更适于细磨的立式搅拌磨机,对搅拌磨机各项参数进行系统的研究。本文在鞍千预选精矿工艺矿物学分析的基础上,进行了搅拌磨磨矿—弱磁分选工艺流程试验。试验结果表明：预选精矿TFe品位为39.62%,主要以磁铁矿形式存在,粗细粒级分布不均。通过对陶瓷球搅拌磨工艺参数的优化试验研究,确定了搅拌磨最佳工艺参数：介质充填率为100%,搅拌器转速1000 r/min,料球比0.7,介质尺寸6 mm,磨矿浓度50%,磨矿时间2.80 min,磨矿产品经过一段弱磁选,可以获得品位67.01%,回收率89.93%的精矿指标。该工艺流程简单,指标良好,可为选矿厂工艺流程改造提供参考。     

振动磨矿机试验测试及应用

介绍了振动磨矿机和球磨机在研磨效率、能量消耗、介质磨损方面相比较的试验测试结果，并评述了振动磨矿机的特点及其应用范围。     

基于ADAMS的章动球磨机的运动仿真分析

介绍了利用章动原理设计的一种新型球磨机。将建立的章动球磨机SolidWorks三维模型导入机械动力学仿真分析软件ADAMS中,对影响章动球磨机性能的关键参数进行了仿真分析。结果表明在最优参数下,可以得到磨粉介质的最佳运动状态,为章动球磨机的性能改进提供了理论依据。     

The effect of ball size on breakage rate parameter in a pilot scale ball mill

The objective of this study is to investigate the effect of ball size on grinding kinetics in a pilot scale ball mill. Six different ball media gradings were tested. Comparative tests were conducted in batch ball mill having 1.2 m diameter and 0.6 m length at constant operating condition of mill such as media mass, mill speed and input specific energy. Feed samples were ground batchwise and representative sample was taken from inside the mill for each determined grinding period. Grinding process in ball mill was modeled and the specific rate of breakage was calculated for the each test. The results indicated that the relationship between different breakage rate and particle size has a maximum for each ball size distribution. Consequently, a new equation to correlate maximum ball size and particle size at maximum breakage occurs is proposed.     

Optimisation of the secondary ball mill using an on-line ball and pulp load sensor – The Sensomag

The ball load and pulp load have a significant influence on the ball mill product size and production capacity. To improve the circuit performance at industrial scale these variables must be tweaked to levels where the plant can get grind and capacity benefits. In most grinding circuits the influence of these variables are not quantified because it is difficult to obtain precise measurements of the pulp load for an industrial scale mill and the conventional method of obtaining ball load measurements that involves crash stops is not attractive. A comprehensive investigation was performed on an industrial scale mill to quantify the effects of both ball and pulp load. A wide range of ball and pulp loads were tested and the findings are reported in this paper. The Sensomag, a sensor developed by Magotteaux, was used to obtain ball and pulp load measurements during the experimental work.     

塔磨机技术综述

塔磨机是一种新型湿式细磨和超细磨设备,该设备在选矿厂碎磨车间和烟气脱硫石灰石浆液制备等领域逐渐得以应用.本文主要介绍了国内外塔磨机的发展状况、粉磨机理、主要结构及各部件之间的装配关系,以及塔磨机常用的工艺位置、给料和排料颗粒粒度和工艺流程.     

Closed circuit ball mill – Basics revisited

Since the early days, there has been a general consensus within the industry and amongst grinding professionals that classification efficiency and circulating load both have a major effect on the efficiency of closed circuit ball mills. However, the effect of each is difficult to quantify in practice as these two parameters are usually interrelated. Based on experience acquired over the years and the investigative work conducted by F.C. Bond, it was established that the optimum circulating load for a closed ball mill – cyclone circuit is around 250%. This value is used as guideline for the design of new circuits as well as to assess the performance of existing circuits.The role of classification in milling appears to have been neglected in the current efforts to reduce the energy consumption of grinding. Two past approaches, experimental and modelling, for quantifying the effects of classification efficiency and circulating load on the capacity of closed ball mill circuits, are revisited and discussed in this paper. Application to the optimisation of existing circuits and design of new circuits is also discussed, with special attention to the development of more energy efficient circuits.     

Experimental investigation of load behaviour of an industrial scale tumbling mill using noise and vibration signature techniques

Mill load (i.e. the load level of coal powder), which is critical in improving the production capacity and energy efficiency of pulverizing system in thermal power plant, has not been effectively monitored and controlled industrially. This paper investigates the load behaviour in an industrial scale tumbling mill under practical working conditions. A microphone and an accelerometer were installed to pick up mill noise and inlet trunnion vibration signals, respectively. By analyzing the sensitivity distributions of mill noise energy and mill vibration energy, characteristic power spectra (CPS) of mill noise and mill vibration were obtained. The CPS energy, centroid frequency and frequency domain variance of the mill noise and mill vibration were then investigated and compared under various working conditions.Experimental results show that the CPS energy of both mill noise and mill vibration can accurately represent the mill load. Moreover, the centroid frequency and frequency domain variance of mill noise can also be used to determine mill load. By combining these characteristics of mill noise and mill vibration, an improved estimation of mill load can be achieved.     

Investigation on measuring the fill level of an industrial ball mill based on the vibration characteristics of the mill shell

A novel characteristic variable of fill level has been proposed, in order to reduce the influence of various factors on measuring the fill level and improve the measurement accuracy of the fill level. A relationship was developed between the fill level and the angular position of the maximum vibration point on the mill shell through theoretical calculation and on-site experiments. This relationship was studied theoretically with two assumptions. The vibration signals were then collected by an accelerometer mounted directly on the mill shell, and analyzed on the time domain to obtain the maximum vibration point on the mill shell, in order to study the correlation between the fill level and this angular position.Both the results of theoretical calculations and experiments show that the position of the maximum vibration point on the mill shell moves to a lower angular position as the fill level increases. Comparison of the traditional and the new characteristic variable of the fill level reveals that the characteristic variable proposed in this paper is more superior and stable. It shows potential for measuring the fill level more accurately.