Multiphase Flow and Wear in the Cutting Head of Ultra-high Pressure Abrasive Water Jet

Abrasive water jet cutting technology is widely applied in the materials processing today and attracts great attention from scholars, but many phenomena concerned are not well understood, especially in the internal jet flow of the cutting head at the condition of ultra-high pressure. The multiphase flow in the cutting head is numerically simulated to study the abrasive motion mechanism and wear inside the cutting head at the pressure beyond 300 MPa. Visible predictions of the particles trajectories and wear rate in the cutting head are presented. The influences of the abrasive physical properties, size of the jewel orifice and the operating pressure on the trajectories are discussed. Based on the simulation, a wear experiment is carried out under the corresponding pressures. The simulation and experimental results show that the flow in the mixing chamber is composed of the jet core zone and the disturbance zone, both affect the particles trajectories. The mixing efficiency drops with the increase of the abrasive granularity. The abrasive density determines the response of particles to the effects of different flow zones, the abrasive with medium density gives the best general performance. Increasing the operating pressure or using the jewel with a smaller orifice improves the coherency of p articles trajectories but increases the wear rate of the jewel holder at the same time. Walls of the jewel holder, the entrance of the mixing chamber and the convergence part of the mixing tube are subject to wear out. The computational and experimental results give a qualitative consistency which proves that this numerical method can provide a reliable and visible cognition of the flow characteristics of ultra-high pressure abrasive water jet. The investigation is benefit for improving the machining properties of water jet cutting systems and the optimization design of the cutting head.

Cutting Characteristics of Force Controllable Milling Head

In order to control cutting force and its direction i n milling operation, a new milling head was developed. The head has two milling cutters, which are connected by a pair of gears and rotate in opposite direction respectively. Both up-cut and down-cut can be carried out simultaneously by t hese milling cutters. The each depth of cut, the ratio of up/down cutting depth , by these cutters can be also selected. The cutting force characteristics were experimentally discussed by changing the ratio. The cutting force and its locus can be also changed by the selection of the ratio of up/down cutting depth. For practical usage of the head the analytical prediction method of the cutting forc e characteristics under selected cutting condition was proposed based on the ene rgy approach method proposed, in which both of cutting force characteristics of a single milling cutter and the combined milling cutter under a selected up/dow n cutting depth ratio were analytically estimated based on the two dimensional c utting data. It was experimentally shown that in NC milling machine the cutting force locus was controlled in pre-determined direction under various tool paths .

Large Chip Production Mechanism under the Extreme Load Cutting Conditions

There has existed a great deal of theory researches in term of chip production and chip breaking characteristics under conventional cutting and high speed cutting conditions,however,there isn＇t sufficient research on chip formation mechanism as well as its influence on cutting state regarding large workpieces under extreme load cutting.This paper presents a model of large saw-tooth chip through applying finite element simulation method,which gives a profound analysis about the characteristics of the extreme load cutting as well as morphology and removal of the large chip.In the meantime,a calculation formula that gives a quantitative description of the saw-tooth level regarding the large chip is established on the basis of cutting experiments on high temperature and high strength steel2.25Cr-lMo-0.25V.The cutting experiments are carried out by using the scanning electron microscope and super depth of field electron microscope to measure and calculate the large chip produced under different cutting parameters,which can verify the validity of the established model.The calculating results show that the large saw-toothed chip is produced under the squeezing action between workpiece and cutting tools.In the meanwhile,the chip develops a hardened layer where contacts the cutting tool and the saw-tooth of the chip tend to form in transverse direction.This research creates the theoretical model for large chip and performs the cutting experiments under the extreme load cutting condition,as well as analyzes the production mechanism of the large chip in the macro and micro conditions.Therefore,the proposed research could provide theoretical guidance and technical support in improving productivity and cutting technology research.

Modeling and simulation of crushing process of spiral mining head

According to the characteristics of spiral mining head for deep seabed cobalt-rich crust, the kinematic model, cutting loads model, quantity of cutting picks model of mining head, granularity distribution model and energy consumption model were constructed. Based on these models, computer simulation program of cutting loads was developed with VB software. The mechanical parameters of mining head were obtained in the cutting depth range of 5160 mm. Making use of the simulation results, the effect of cutting depth of spiral mining head on the mining process was studied. The results show that the maximum force of single pick is 4.7051kN, the maximum force and torque of spiral drum of mining head are respectively 34.1668kN and 3.8795kN·m at the cutting depth of 160mm.

Design and test of a multi-edge toothed cutting device for membraneimpurity mixed material

As the existing residual film crushing device in Xinjiang cannot directly crush membrane-impurity mixed material,by analyzing the compressive and cutting force characteristics of residual film material layer and cotton stalk,the cutting conditions of mixed materials were obtained,and the method of cutting was determined.A multi-edge toothed cutters was created,and a cutting device was built.It was preliminarily determined that the number of teeth in the cutters was 8,the clearance between the teeth and between the tooth and fixed blade was 3 mm,the speed of the high-speed cutter was 800 r/min,and the speed difference between the high-and low-speed cutters was-300 r/min.Test results show that the ratio of residual film to total residual film sampling mass was(2.22±0.30)%,(19.19±2.02)%,(58.94±3.19)% and(20.65±2.05)%,respectively,when the maximum outer profile size in the range of[0,20)mm,[20,100)mm,[100,500)mm and[500,~)mm.The mass of cotton stalks with lengths of[0,50)mm,[50,100)mm and[100,~)mm accounted for(32.57±1.5)%,(27.77±1.3)%and(39.66±1.75)%,respectively,and the cutting power consumption was(85.41±15.63)kJ.The test results can provide a basis for the subsequent membrane-impurity mixed material cutting technology,as well as some guidance for the separation of it.

内旋风铣削双头螺杆转子切削力仿真分析

双头螺杆转子在内旋风铣削过程中通常会产生较大的切削力,进而影响工件表面质量。为探究内旋风铣削双头螺杆转子切削力的变化规律,借助有限元分析软件ABAQUS,基于椭圆形转子廓形的形成原理,构建了其三维运动学简化模型,实现了不同偏心距下的仿真分析,并验证了仿真分析的可行性,得到了应力分布云图和X与Y两个方向的切削力曲线。

考虑齿圈柔性的采煤机截割部行星传动动态特性研究

为研究均质煤层及夹矸煤层2种煤体工况下的采煤机截割部行星传动系统响应特点,综合考虑各构件的支撑刚度、轮齿啮合刚度及齿圈柔性等因素,建立了截割部行星传动平移-扭转耦合动力学模型。分别分析了刚性/柔性齿圈行星传动系统在2种煤体工况下的太阳轮与行星轮啮合力波动变化特点、行星架输出转速变化规律以及太阳轮中心浮动轨迹曲线。研究发现柔性齿圈状态下,太阳轮与行星轮啮合力幅值呈长周期波动变化,均质煤层工况下的齿圈柔性改善了两轮的啮合力状态且对行星架输出转速波动具有一定的稳定作用,研究成果可为传动系统的设计提供一定的理论指导作用。

新型悬臂式掘进机横轴截割头的研制

作为煤矿采掘机械中破岩落煤的关键部件,横轴式截割头相比纵轴式截割头在硬岩截割时具有更好的破岩效率和适应性。相比山特维克AHM105横轴截割头结构,通过在联接结构、头体结构、齿座结构、大端结构等方面的创新,采用八方结构联接、前后截割头体结合防剪切销组焊、J形坡口齿座、一体化耐磨头体大端等结构,成功研制了新型悬臂式掘进机横轴截割头,通过井下应用验证了该截割头在截割全岩过程中具有较高的可靠性和稳定性。研究内容为横轴式截割头的研发和创新提供了参考,具有一定的实用和推广价值。

CJ 9.7 tex强捻纱生产实践

为了解决强捻纱断头多、生产效率低等问题,介绍以100%细绒棉为原料生产CJ 9.7 tex强捻纱的原棉指标、纺纱工艺流程,分析细纱工序断头多、钢丝圈飞圈多、开车留头率低,络筒工序红灯率高、切疵多、捻接失败率高、张力断头多等问题的原因及改善措施。指出:优选钢丝圈圈型、优化锭速曲线、降低锭子速度、增加锭脚回丝圈数,能改善强捻纱细纱生活,且飞圈减少、留头率提高;增加络筒找头次数、大吸嘴负压,调整大吸嘴与筒纱的距离、纱头退捻代码、喂入臂代码等,能降低络筒红灯率、捻接失败率,减少张力断头及筒纱垮边。

薄壁水泥土防渗墙挖掘机链锯切割施工技术研究

受工况条件及施工成本等因素限制,在江西某老旧水库除险加固工程中,采用以挖掘机为链锯式切割钻具动力的薄壁水泥土防渗墙施工技术。该技术通过采取自主创新的链锯间距调节器、切割刀头快速更换装置等质量控制措施,有效提高了防渗墙的工程质量和施工效率,降低了施工成本。详细介绍了薄壁水泥土防渗墙的施工工艺、垂直度保障体系、平整度控制、冷缝控制等质量控制措施以及质量检测指标,可为类似工程施工提供参考。

A Design of Forming Hods on Machining Corrected Cycloidal Gears

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高精度无心车床刀盘系统动态特性分析

无心车床是线性棒料表面处理的重要设备,刀盘系统是无心车床的重要部分,可以直接影响加工精度。这里以XF-WXC无心车床刀盘系统为研究对象,对刀盘系统进行模态分析,得到前六阶固有频率和模态振型,再通过设置不同工况转速,分析不同转速对刀盘系统模态频率的影响规律,并基于模态分析结果进行不同工况下的谐响应分析,研究刀盘系统的动态特性。分析结果表明:刀盘系统的刀尖位置为受力变形最大部位;易发生共振的激励频率在278Hz、449Hz和480Hz附近,在共振频率处的最大形变位移为0.036mm;同时利用实际切削实验结果验证仿真分析的可靠性。为无心车床的进一步优化设计提供理论依据。

拔除下颌近中水平完全埋伏阻生牙保留颊侧骨板的效果探讨

目的:探讨微创手术拔除下颌近中水平完全埋伏阻生牙时保留颊侧骨板的效果。方法 :选取近中低位水平埋伏阻生牙86颗,随机分为2组,试验组以球钻开窗,暴露牙冠远中面,保留颊侧骨板,使用仰角手机配合加长车针行多次T形截冠,去除牙冠,微创拔除。对照组采用球钻去除远中及颊侧骨板,暴露远中及颊部牙冠,T形截冠,其余操作均一致。观察2组患者术后肿胀程度、开口受限程度以及疼痛视觉模拟量表(VAS)评分,检测C反应蛋白水平以及抗溶血链球水平;1个月后检查邻近第二磨牙牙周探诊深度(probing depth,PD)、出血指数(bleeding index,BI)及临床附着丧失(clinical attachment loss,CAL)水平。采用SPSS 25.0软件包对数据进行统计学分析。结果:试验组术后肿胀程度显著轻于对照组(P<0.05),开口受限与疼痛程度无显著差异(P>0.05)。试验组C反应蛋白水平显著高于对照组(P<0.05),抗溶血链球菌水平2组之间比较无显著差异(P>0.05)。术后1个月,对照组PD和CAL均显著高于试验组(P<0.05),2组BI比较无显著差异(P>0.05)。结论:保留颊侧骨板微创拔除下颌近中水平完全埋伏阻生牙患者术后反应更轻,创口愈合更好。

采掘装备截割煤层过程中截齿温度场特性研究

采掘装备在截割煤层过程中,不同性状的煤岩体会导致截齿温度发生变化。为了探究截齿温度场的变化特性,分析了截齿截割煤层过程的热源分布情况,利用热源法建立了截割煤层过程中截齿温度场的理论计算模型,并考虑到采掘装备的实际工况条件,推导了喷雾系统对流换热系数的计算过程。以MG2×55/250-BWD型采煤机为研究对象,基于ABAQUS有限元软件建立了截齿旋转截割煤岩模型,研究了不同工况下截齿温度场的分布情况与变化规律;接着,基于Fluent流体仿真软件建立了喷雾冷却模型,获取了不同喷雾压力下截齿的对流换热系数,进而将换热系数带入ABAQUS有限元模型来模拟水喷雾冷却下截齿截割煤岩过程的温度场;最后,搭建了滚筒截割煤岩温度采集实验台,设计了截齿温度采集系统,开展了不同工况下滚筒截割煤岩实验,分析了截齿温度场的变化规律,验证了理论计算与仿真模型的正确性。结果表明,不同工况下截齿的温度场具有不同的分布形态,且最高温度与滚筒转速、牵引速度、煤岩坚固性系数呈正相关性;水喷雾压力与截齿温度呈反比,与常规条件相比水喷雾冷却能使截割温度场温度降低20%以上。研究成果为基于截齿温度场的煤岩性状识别提供新的理论和方法。

基于STFF-ShuffleNet的掘进机截割头故障诊断

目的为了解决掘进机截割头故障振动信号信息量大且难以充分提取和现有的掘进机截割头故障诊断模型参数量多且计算量大,训练需要耗费大量时间,部署和使用对硬件设备的性能要求严苛的问题。方法提出一种小体积和运行速度快的轻量化网络模型时空特征融合(STFF)-ShuffleNet用于掘进机截割头故障诊断研究。ShuffleNet在模型进行时空特征提取时引入深度可分离卷积提高模型的运算效率,再对融合后的时空特征做通道混洗和分组卷积,既解决了通道分组的问题又提高了诊断精度。通过悬臂式掘进机截割头实验台模拟不同故障条件,将采集到的振动信号输入模型中进行测试。结果实验表明,STFF-ShuffleNet模型对掘进机截割头的诊断与其他传统模型相比参数量少,收敛速度快,运行效率更高,更容易满足掘进机截割头故障诊断高实时性要求,准确率达到99.3%。结论STFF-ShuffleNet模型对提高掘进机截割头故障诊断效率和降低硬件要求提供了一种新的解决思路。

双圆弧内齿轮车齿切削仿真及试验研究

针对目前双圆弧内齿轮加工难、精度差、效率低的问题,提出了一种采用车齿工艺加工双圆弧内齿轮的方法。根据车齿加工原理,梳理了刀具与工件的相对位置,建立了双圆弧内齿轮车齿加工数学模型;运用Vericut进行双圆弧齿形的成型仿真,验证了车齿加工内齿轮的可行性与准确性;利用Abaqus对车齿过程中的切削力进行仿真计算,获得了加工参数对切削力的影响规律;使用六轴数控机床完成了双圆弧内齿轮的车齿加工,螺旋线精度检测结果符合设计要求。上述研究结果拓展了双圆弧齿轮的加工工艺,提升了内齿轮加工精度和效率,为后期双圆弧内啮合及行星传动奠定了基础。

钻孔辅助硬岩掘进机的截割头设计

基于EBZ200H型硬岩掘进机,首先探讨了钻孔辅助截割硬岩掘进机截割头的主要设计参数,并对截割头的三维建模过程进行了详细描述。然后针对钻孔辅助截割新型硬岩掘进工艺的特点,对截割头进一步的优化提出了一些改进设想。最后,采用标准截割头和改进后的截割头对35号商砼浇筑的模拟岩壁进行截割对比试验。试验结果表明:改进后的截割头效率约为标准型截割头效率的143%。这为后续全新“钻孔+截割”高效硬岩掘进工艺的完善和改进,提供了重要参考。

矿用硬岩巷道机械化掘进破岩形式研究现状及展望

硬岩巷道快速掘进是实现煤矿智能高效开采的重要环节,悬臂掘进机、TBM和底切割装备都在尝试解决这一难点,掘进技术和装备的发展直接影响采矿的安全生产和经济效益。首先,总结了悬臂掘进机在硬岩截割工况的适用范围和截齿消耗现状,分析截割破岩形式的现场试验,发现在较高的岩石强度条件下,截齿消耗量较正常磨损翻倍,掘进速度与开采速度的不匹配,严重制约了矿井生产。其次,分析了滚刀破岩形式和装备在矿山领域的应用和新产品现状,得出移动式矿用掘进设备采用滚刀挤压破岩,块状渣土少,粉末多,刀盘推力小,导致破岩能力不足。最后,分析了线性底切割破岩技术和非线性底切割技术的原理和装备研发现状。结果表明:随着振荡频率的提高,切削力显著降低,非线性底切割破岩单位体积消耗能量少,优势明显。但在硬岩条件下的掘进效率、设备稳定性等关键问题有待验证,非线性底切割技术有望突破未来矿山硬岩掘进的技术难题。

铣刀多重刀齿分布及其动态切削行为特性

受刀齿误差影响,铣刀沿轴向存在多种刀齿分布,振动作用下具有多重刀齿分布的铣刀,其切削行为呈现多时变特性,导致切削过程中切削层厚度变化和铣削表面形貌分布具有复杂性和不确定性。依据铣刀结构和刀齿误差,获取沿铣刀轴向的多重刀齿分布序列,构建振动作用下多重刀齿分布的瞬时切削层厚度和铣削表面形貌分布解算模型,揭示沿铣刀轴向的单齿、多齿不等齿距和多齿等齿距分布的动态切削行为特征,阐明刀齿误差和铣削振动对铣刀瞬时切削层厚度及铣削表面形貌分布多样性的影响机制,并进行试验验证。结果表明,采用上述模型与方法,可揭示出振动作用下多重刀齿分布铣刀的动态切削行为及铣削表面的形成过程。

PDC磨损齿切削破岩数值模拟研究

现有文献针对切削齿的数值模拟研究较少考虑磨损高度对切削齿温度、切削载荷的影响,然而聚晶金刚石复合片(PDC)切削齿磨损后受力恶化、热磨损加剧会导致其快速失效。为探讨这一问题,基于弹塑性力学和岩石力学,以Drucker-Prager准则为岩石的本构模型建立磨损齿的三维动态旋切仿真模型,运用数值模拟的方法分析在不同磨损高度、切削深度、前倾角的条件下切削齿的受力状态以及温升幅度。结果表明:与未磨损齿相比,磨损齿的切削载荷随磨损高度的增加而变大,且切削齿(直径13.4 mm、总高8 mm)磨损高度为1.5 mm时达到最大;切削齿磨损越严重,吃入到同一深度所需的力越大;前倾角增加,导致切削载荷也会变大。因此磨损齿在切削钻进过程中,磨损高度越高、前倾角越大,切削齿的失效风险越高;随着切削齿磨损高度增加,切削齿温升显著增加,在模拟条件下可提高54%~103%。