2J550×3000双轴搅拌机设计【说明书+CAD】
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河南理工大学万方科技学院本科毕业设计(论文)中期检查表指导教师: 赵武 职称: 副教授 所在院(系): 机械与动力工程学院 教研室(研究室): 机械制造教研室 题 目0-2J5503000双轴搅拌机学生姓名马磊专业班级07机制2班学号0720150127一、选题质量: 该生此次所选择的题目为双轴搅拌机设计,内容涉及到对搅拌机的总体布置和理论研究,还有一些机械零件和机械结构的设计计算与校核,与专业课程紧密联系,符合专业培养目标,在设计工作中,需要对所学知识综合地加以运用,使之能够熟练应用有关参考资料、计算图表、手册;熟悉有关的国家标准和部颁标准,体现了综合训练的要求。工作量大与生产,经济,社会等的结合紧密,选题质量较高。二、开题报告完成情况:从适合实际工作环境出发,确定了明确的课题设计方向;并对双轴搅拌机在使用中经常出现的问题有一定的研究,且应用在设计计算中;已经开始对课题进行设计计算,并有了突破性的进展,设计过程已经快速地展开,确定了工作的内容和方法;同时,已完成了对相关资料的查阅,对课题有了总体的分析。开题报告顺利完成。三、阶段性成果:总体布置方案和主要结构参数已确定,并完成一些标准件的选型及和大多数零部件的设计计算工作。结构设计和校核工作正在进行中,部分零件图的绘制已经基本完成,英文翻译工作还未完成,已着手开始制作设计说明书的工作。四、存在主要问题:1.因为是通过轴带动叶片进行工作,对安装叶片角度和材料选择不是很确定;2.预加水双轴搅拌机可以使水的雾化和双轴的搅拌,使物料得到充分的浸润,并搅拌成球,能为成球机成球提供有利条件,对改善料球性能,提高料球质量,降低能耗,提高立窑产量具有十分重要的作用。3.局部结构设计思路不清晰;设计内容不够连贯,系统性不强;在整体结构及零部件结构上存在一定问题;在选用零件和确定结构工艺参数时缺少经验和参考;4.对资料搜集方法比较少,获得资料不够充分,得到的资料比较陈旧;五、指导教师对学生在毕业实习中,劳动、学习纪律及毕业设计(论文)进展等方面的评语: 指导教师: (签名) 年 月 日河南理工大学万方科技学院本科毕业(论文)设计开题报告题目名称2J5503000双轴搅拌机设计学生姓名马磊专业班级07机制2班学号0720150127一 选题的目的和意义:双轴搅拌机为螺旋式搅拌机,它的搅拌部件是两根形状对称的同步螺旋转子,两根螺旋轴在旋转时速度同步、方向相反。双轴搅拌机由电机驱动,可用减速机控制转子转动速度,达到最佳的搅拌效果。双轴搅拌机的主要部件包括,机械外壳、两根螺旋转轴、电机驱动装置、联动装置、配管和盖板等,必要时双轴搅拌机还可搭配减速机使用。双轴搅拌机的螺旋轴是最重要的工作部分,两根螺旋轴的旋转方向相反,都具有轴承座、轴承套、轴承盖、叶片和联动装置。包括彼此平行的第一和第二搅拌轴、搅拌叶片和卧式搅拌桶,所述搅拌叶片从第一和第二搅拌轴向四周伸出,并在轴向依次等距排列而在圆周方向依顺时针或逆时针彼此相差一固定角度,使在第一和第二搅拌轴上的搅拌叶片分别形成旋向相反的螺旋状排列;所述第一和第二搅拌轴彼此同步转动并且其叶片交错通过由该第一和第二搅拌轴轴线所确定的平面;在所述搅拌桶一端的顶部设有进料口,而在所述搅拌桶另一端的底部设有出料。采用这种结构,搅拌机的搅拌叶片在搅拌干粉砂浆的同时将干粉砂浆从进料口排向进料口,从而实现生产的连续,有效的提高了生产效率。双轴搅拌机的螺旋轴在运行过程中受到的磨损最为严重,可采用刚玉陶瓷等耐磨材料制造。双轴搅拌机在工作时,物料通过进料口进入筒体,两根螺旋轴在电机驱动下反向现转,物料受旋转作用而随之运动,相互混合完成搅拌。双轴搅拌机的两根螺旋轴之间的区域,旋转方向不同的物料相互挤压作用,能提高混合搅拌效果。双轴搅拌机是混合干燥物料的理想设备,适用于在输送干粉状物料的同时加水搅拌,从而均匀加湿各种干粉物料。一般来说,双轴搅拌机所搅拌的物料含水分不超过20%。双轴搅拌机在火力发电厂、矿山等粉状物料加湿场合较为常见。鉴于双轴搅拌机所具有的标准的机械特性,我选择了这个设计课题。这是我们毕业前的最后一次作业,这让我们对以前学过的相关机械方面的课程进行了一次全面系统复习。这次设计我将独立完成一台双轴搅拌机的完整设计,这对我来说是一个不小的挑战,但也是一次重要的锻炼机会。课题的主要内容是结合生产实际,完成一台生产能力 为Q = 30 t/h的2J5503000双轴搅拌机设计。二 国内外研究现状简述:强制搅拌机强制搅拌机,本实用新型属于灰砂砖生产中的混合料搅拌设备,其主要解决双轴搅拌机加水量不易控制,搅拌力小,使物料易结团结仓的问题,该机包括行星搅拌机构,涡流搅拌机构,搅拌鼓,排料机构,搅拌机架及底架等部分,搅拌鼓的中心位置设置有涡流搅拌机,在涡流搅拌机两侧机架上,对称布置有两行星搅拌机,两行星搅拌机作相对旋转,涡流搅拌机与搅拌鼓呈反向旋转,该机搅拌力大,解决了结团结仓等问题。 一种适用于灰砂砖生产搅拌混合料的强制搅拌机,包括行星搅拌机构,涡流搅拌机构,搅拌鼓,搅拌机架,排料机构及底架等部分组成,其特征在于搅拌鼓位置于底架上的大齿圈的轴承座上,搅拌鼓的中心位置设有涡流搅拌机,在涡流搅拌机两侧机架上,对称布置有两行星搅拌机。 JW350型强制式搅拌机主要技术参数出料容量 350L 进料容量 560L 额定功率 5.5kw 最大粒径 40mm 主轴转速 35转/分 外形尺寸 13001200 混凝土搅拌机混凝土搅拌机,包括通过轴与传动机构连接的动力机构及由传动机构带动的滚筒,在滚筒筒体上装围绕滚筒筒体设置的齿圈,传动轴上设置与齿圈啮合的齿轮。本实用新型结构简单、合理,采用齿轮、齿圈啮合后,可有效克服雨雾天气时,托轮和搅拌机滚筒之间的打滑现象;采用的传动机构又可进一步保证消除托轮和搅拌机滚筒之间的打滑现象。 搅拌机还可衩被分为: 星式搅拌机 防险搅拌机 立式搅拌机 混凝土搅拌机 双轴搅拌机 单轴搅拌机 防滑混凝土搅拌机 JS双卧轴混凝土搅拌机 主要技术参数 出料容量 500L 进料容量 800L 生产能力 2428m3/h 骨料最大粒径 60 搅拌轴转 36转/分 搅拌叶片 27 搅拌电机型号 Y180m4 (B3) 功率 18.5kw 卷扬电机型号 YEZ13254 (B5) 功率 5.5kw 水泵电机型号 50DWB208A 功率 0.75KW 料斗提升速度 18m/分 外形尺寸运输 305023002680 工作 446130505225 整机重量 4100kg 卸料高度 1500mm 立式搅拌机搅拌机包括有电动机、搅拌筒、传动轴、搅拌桨叶,其中在传动轴上还松套有一反向搅拌桨叶,该反向搅拌桨叶的轴套通过链条与位于传动轴一侧的中间轴上端的链轮相连,与链轮同轴的被动齿轮则与固定在传动轴下端的主动齿轮相啮合。本实用新型的两个搅拌桨叶是反向转动的,使得在搅拌过程中,原料能在两个搅拌桨叶之间形成对流,从而彻底解决了传统搅拌机对原料搅而不拌的问题。 新型搅拌机系换代产品,是化工和建材行业搅拌设备无可替代的产物,实现了正确“搅和拌”的问世,从而淘汰其它搅拌设备所以承但的重任。它以其超常规的构思和精锐的技术含量,合理的设计水准,填补了国际空白。其广泛用于油漆、涂料、染料、制革、医药、饮料、粘胶剂、食品、洗涤品、化妆品及各种固态物体等。有取之不尽的财富。对物体分散、乳化、均质、调色等较之传统搅拌机的搅拌效果更加理想、直观、是搅拌行业的一次革命。 双轴搅拌机用于预加水成球工艺流程中,其工作原理是,当定量的生料粉由下料口流入搅拌槽中,经若干个具有一定压力的水雾化洒向生料粉,由定性长度的轴经搅拌叶搅拌匀后形成含一致的球核,并输送到预加水盘式成球机中去。整个搅拌机的搅拌时间分为雾化区,拌匀区,卸料区三个区域。搅拌叶片上焊硬质合金刀头,耐磨性能好,使用寿命长。 主要参数 单位 型号 2J40 2J45 2J50 2J55 2J60 搅拌叶直径 mm 400 450 500 550 600 进出料口中心距 mm 3000-3260 搅拌轴速度 r.p.m 50.4 50.4 48 45 41 生产能力 t/h 11-15 15-20 20-25 25-30 40-50 使用螺旋角 12-21 12-21 12-21 12-21 12-21 配用电机 型号 Y160M-4 Y160L-4 Y180M-4 Y180L-4 Y250M-6 功率 kw 11 15 18.5 22 37 配用减速机 ZQ40-VI-2Z ZQ50-VI-4Z ZQ50-VI-Z ZQ65-VI-4Z ZQ75-VI-2Z 搅拌湿度 % 1.5 1.5 1.5 1.5 1.5 外形尺寸 mm 5614*850*880 4870*900*1130 5683*890*1430 5225*1286*828双轴搅拌机在国内一直被作为一个简单的助力机械装备,双轴搅拌机在技术已经基本成熟,产品应用很普遍,由于它只是生产过程中的辅助设备,产品不需要很高的科技含量就能够满足要求,国内厂家所生产的产品已经能够满足生产中的要求,其中大多数都是机械传动式双轴搅拌机。但由于我国的机械制造水平普遍较低,所生产的产品难以占领国际高端产品市场。在国外,双轴搅拌机研究水平比较高,用两根呈对称状的螺旋轴的同步旋转,双轴搅拌机的外壳多采用优质金属结构,具备良好的密封性,在搅拌机搅拌各种粉状物料时,可避免灰尘外漏和飞扬的问题,在各种场合都已经得到广泛应用。国外一些厂家的生产技术已经比较成熟,例如:德国威克(Wacker)机械公司,美国KNIGHT机械公司,韩国KOREA HOIST机械公司等这些技术先进,性能优良的双轴搅拌机已经走进国内市场。双轴搅拌机的设计制造比较普遍,一般的机械厂都可以生产,我国陕西中隆建材机械公司,上海申银机械有限公司,江苏总能电力设备有限公司,四川射洪通用机械有限公司,巩义市环城机械有限公司,河南荥阳万山矿山机械厂,河南省锐泰机械制造有限公司,郑州天一机械有限公司等三、毕业设计(论文)所采用的研究方法和手段:1工作原理双轴搅拌机由两根搅拌轴,轴上按螺旋推进方向安装搅拌叶及搅拌槽组成的搅拌系统,为使原料达到成型的需要,在搅拌机入料端稍后处的上部,设有加水装置,使得物料形成较大的球状块料旋转时两轴的方向由内向外,将物料搅起,靠搅拌叶旋转时的推力(搅拌叶与搅拌轴轴线夹角为10-20度)形成物料流,螺旋向前推进,最后物料经漏料箱进入承接皮带,进入到下台处理设备中。图2-1 双轴搅拌机结构示意1 轴承座; 2 出料口; 3 搅拌叶; 4 搅拌轴;5 搅拌槽;6 齿轮座;7 联轴器;8 减速器;9 三角带轮;10 驱动电动机2 结构设计特点合格生料粉经稳流计量后进入双轴搅拌机。双轴搅拌机由电机通过三角皮带传动,经ZQ圆柱齿轮减速机、十字滑块联轴器带动主动轴旋转,由配对齿轮带动从动轴转动。主、从动轴上装有可以转动角度的浆叶式搅拌叶,在轴向力和一定圆周力作用下作螺旋状旋转在进料端约1.2米处装有雾化喷嘴,物料被搅拌同时喷雾受湿并向前推进。物料在挤压揉磋等力的作用下形成团粒母核。物料被搅拌叶推动在槽内向前运动至出料口。 从结构上看,双轴搅拌机要较单轴搅拌机复杂,但它磨损小,搅拌质量好,生产率高,双轴搅拌机较之立轴式和单轴式搅拌机,具有明显的优越性。双轴搅拌机优点总结如下:1. 搅拌机外形尺寸小、高度低、布置紧凑,装载运输便利,而且结构合理坚固,工作可靠性好;2. 搅拌机容量大,效率高。与同容量自落式相比,搅拌时间可缩短一半以上,而且物料运动区域位于卸料门上方,卸料时间也比其他机型短,因而生产率高;3. 拌筒直径比同容量立轴式小一半,搅拌轴转速与立轴式基本相同,但叶片线速度要比立轴式小一半,因此叶片和衬板磨损小、使用寿命长,并且物料不易离析;4.物料运动区域相对集中于两轴之间,物料行程短,挤压作用充分,频次高,因而搅拌质量好。2.1外壳的设计形式传统的U型槽底容易出现搅拌死角,从而导致两轴负载过大以致断裂。另外他们将两端墙板焊死在机壳上,这样就使得在轴或叶片受损维修时很不方便,工作量也相当大。将双轴搅拌机槽底做成欧米嘎型(),以防止搅拌死角。两边再焊上钢板制成机槽,槽口两边焊有角钢用以固定机盖,槽机底部焊有支承垫用以支承槽体。机槽两端墙板不是焊死在机壳上,而是通过螺栓与机壳联结,这样做的目的是为了在维修时便于将损坏的轴吊起,省去拆叶片麻烦,检修空间增大,工作量减小,还可缩小两端轴孔直径,便于密封防漏,如图2-2所示。图2-2 搅拌槽壳体2.2 轴与叶片的安装方法的设计以前,大多在整个轴上都安装叶片,生料进口处叶片角度比较大,用以快速输送物料,但是我们发现这样搅拌叶片的磨损较大,靠进料口槽体端密封处漏灰严重,从而齿轮内进灰较多,加快了传动部件的磨损,影响生产效率。因此,针对这些问题对轴的结构进行改造,即在轴的搅拌进口端焊接两螺旋叶片使粉料不断向前输送,减少槽体端部密封处的积料。这样有利于防止打坏叶片、折断轴。在搅拌轴上正确安装带有刀片的叶片,调整好了角度后,再将叶片安装在钻有莫氏锥度孔的轴上,如图2-3所示。叶片在双轴上三个部位的安装角度是各不相同,叶片安装角度一般选用=20度左右,双轴搅拌机叶片角度必须要与粘土可塑性相适应,双轴搅拌机工作分三个阶段:第一阶段是雾化水与原料的混合搅拌阶段;该阶段轴的长度为0.7m 左右(包括螺旋叶片轴段),安装的叶片数是8只,安装角度为25,通过雾化喷水和机械翻动搅拌两个手段以达到液固均化的目的。第二阶段是使含煤生料湿润的阶段,为使其能充分湿润,生料在这一阶段的运行速度应慢一些;该阶段轴的长度为1.5m左右,安装的叶片数是20个,安装角度为15,其主要特征是机械搅拌。第三阶段是形成球核的阶段;该阶段轴的长度为1.0m左右,安装的叶片数是12个,安装角度为20,其中最后4只的安装角度是0,其目的是为了挡料。图2-3 搅拌机工作简图在调整叶片角度的同时,要注意叶片的转速,这两方面也是相互影响的,在确定转速时首先要确定物料在搅拌机内搅拌的时间,而搅拌时间又影响着形成球核的产量,因此搅拌时间、叶片角度、转速、湿润时间等之间要相互配合好,一般出搅拌机的球核直径为1-2mm的占20%-75%较好。其中每个叶片焊牢在叶片杆上,然后按照要求调整角度焊接在方垫片上。经过这样的处理后,叶片在推动物料时就不会出现角度混乱,另外把搅拌轴头的轴肩R适当调大,减小应力,防止应力集中,如图2-4所示。 图2-4 叶片安装图2.3 传动机构的设计传动装置是双轴搅拌机工作过程中的关键。设计的传动路线 为电机皮带ZQ减速机联轴器齿轮传动装置搅拌轴。 将双轴搅拌机传动装置整体放置出料口端,使生料不能进入齿轮和轴承。同时给两传动齿轮制作一个油池,用于齿轮的润滑,能减小磨损,提高使用寿命。常用的减速机有三种型式,圆柱齿轮减速机、行星减速机和摆线针轮减速机。其中采用圆柱齿轮减速机较合适,而采用行星减速机和摆线针轮减速机常会出现因搅拌机主轴起动时扭矩大,传动系统刚度不足,故障多,有漏油问题。相对而言圆柱齿轮减速机传动稳定,噪音小,齿面接触稳定,在润滑保养良好的条件下,运转稳定。2.4 密封装置的设计对密封装置的要求相当高,可采用双道压盖填料密封装置,填料采用橡胶石墨石棉盘根,两边采用压盖压紧,内压盖、外压盖和密封盖固定采用沉头螺栓紧固,见图2-5。图2-5 密封装置1 密封圈;2 压板1;3 密封盖;4 端面板;5 垫板;6 轴套2.5 雾化装置的设计水的雾化的好坏,是预加水成球的关键条件之一。它通过雾化器来实现,雾化器设在搅拌机进料口的一端,其作用是担负着生料和水的第一道均匀混合工序的喷水任务,为下一道机械搅拌工序创造良好的均合基础,达到液固均化的目的。为了保证雾化效果,必须对水压、水质、喷嘴及喷嘴布置有一定的要求:1.结构简单,制造方便,成本低,无特殊工艺装备,维修方便,使用寿命长;2.在低能量条件运行应保证足够的喷水能力,MP型550kg/h,以利用于减少喷嘴组合数量,便于布置;3.水质要干净纯洁,尽量少含泥沙等杂质,以防喷嘴堵塞。水质不好时需在水箱出水口增加过滤网,并定期清洗;4.喷嘴要有适宜的喷射角度,保持适宜的水量和良好的雾化效果,使布水均匀,直接喷向料层,不能喷向机壳再流向物料;喷嘴离料层距离保持300 mm左右,不能过近,否则,不能保证接触料层被水充分雾化。由于喷嘴的布置形式直接影响搅拌效果和球核的质量,因此应注意:1.喷嘴在搅拌机中的布置原则应分布在进料口落料流及落料区,以实现操作点无粉尘污染;2.保证喷嘴至料面的垂直距离S300 mm,目的是使雾滴同生料粉接触,提高生料的湿润渗透性,否则影响成球的均匀性,并增加清理特大球的工作量;3.多嘴组合应用喷嘴能进一步提高液固均化程度,但多嘴数量要适当;4.喷嘴喷射方向及覆盖面必须在生料面区域内,不得喷射在机槽侧壁上,否则将造成机槽侧壁粘料严重,难以清理,并增加搅拌叶片的阻力,从而提高搅拌的功率消耗,同时也会造成局部生料过湿,影响成球质量。综合各方面的条件,选用MP-型离心压力喷嘴式雾化器(见表2-1)比较合理,其主要特点有:加大了喷液能力,提高到了550 kg/h以上,雾化角为90至120,效果好,而且可减少喷嘴数量。MP型喷嘴内衬中心有一冲水孔,出水口有4个月牙形分水刀,心部4个螺旋槽与垂线相交成45至95角;表2-1 MP-型雾化器规格参数流量kg/h雾化角 喷嘴孔径mm雾化压力MPaLmmDmm含水量%所需水量t/h喷嘴数量个5508520.19732M161.512-143.6-4.210-12 四、主要参考文献:1 许林发主编. 建筑材料机械设计(一) .武汉:武汉工业大学出版社, 19902 褚瑞卿主编. 建材通用机械与设备.武汉:武汉理工大学出版社, 19963 朱昆泉,许林发.建材机械工业手册.M.武汉:武汉工业大学出版社,2000.74 胡家秀主编.机械零件设计实用手册.北京:机械工业出版社,1999.105 李益民主编.机械制造工艺设计手册.北京:机械工业出版社,1995.106 甘永立.几何量公差与检测M.上海:上海科学技术出版社,2001.47 钱志锋,刘苏工程图学基础教程M.北京:科学出版社,2001.98 徐灏.机械设计手册M.北京:机械工业出版社,1991.99 赵忠.金属材料与热处理M.北京:机械工业出版社,1991.510 阎瑞敏,常敏.水泥工业自动控制预加水成球技术及装备M.江苏科学技术出版社,1990.1011 黄有丰.预加水成球技术及其应用M.北京:中国建筑工业出版社,1991.912 徐锦康.机械设计M.北京:高等教育出版社,2004.413 王旭,王积森.机械设计课程设计M.北京:机械工业出版社,2003.814 张一公.常用工程材料选用手册M.北京:机械工业出版社,1998.615 盛君豪.减速机使用技术手册M.北京:机械工业出版社,199216 吴瑞琴.滚动轴承产品样本M.北京:机械工业出版社,中国石化出版社,200017 刘伟辉.预加水成球常见问题与对策J. 吉林建材.2003(1),21-23.18 孙素贞.对提高预加水成球设备性能的探讨J.Research & Application of Building Materials.2001(2),22-23.19 朱卫权.双轴搅拌机主轴断裂原因J. 砖瓦1998(3),11.20 谢序文.双轴搅拌机断轴原因分析及处理措施J. Cement.1995(5),10-11.21 余易茗.双轴搅拌机的改造 J.中国建材设备.1995(2),32-33.22 蒙强.4503000m 双轴搅拌机的改造 J.四川水泥.2005(2),30.23 潘村禾.对预加水双轴搅拌机结构改进J.水泥.1997(10),21-22.24 彭其雨.提高立窑预加水成球质量的情况介绍J. 福建建材.2002(4),18-19.25 刘玉金.亦谈双轴搅拌机进料端密封装置的改进J. 水泥.1995(12),23.五、毕业设计(论文)进度安排(按周说明):第57周 毕业实习,收集资料,完成开题报告。第810周 完成实习报告,总体方案设计,初步完成设计计算,外文翻译第1113周 完成总装图和零件图的绘制和设计说明书。第1415周 修改和完善,准备毕业答辩。六、指导教师审批意见(对选题的可行性、研究方法、进度安排作出评价,对是否开题作出决定): 指导教师: (签名)年 月 日 河南理工大学万方科技学院本科毕业论文附录:外文资料与中文翻译外文资料:Comparing mixing performance of uniaxial and biaxial bin blenders Amit Mehrotra and Fernando J. MuzzioDepartment of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ, 08855, United StatesReceived 17 February 2009; revised 30 May 2009; accepted 14 June 2009. Available online 27 June 2009.AbstractThe dynamics involved in powder mixing remains a topic of interest for many researchers; however the theory still remains underdeveloped. Most of the mixers are still designed and scaled up on empirical basis. In many industries, including pharmaceutical, the majority of blending is performed using “tumbling mixers”. Tumbling mixers are hollow containers which are partially loaded with materials and rotated for some number of revolutions. Some common examples include horizontal drum mixers, v- blenders, double cone blenders and bin blenders. In all these mixers while homogenization in the direction of rotation is fast, mediated by a convective mixing process, mixing in the horizontal (axial) direction, driven by a dispersive process, is often much slower. In this paper, we experimentally investigate a new tumbling mixer that rotates with respect to two axes: a horizontal axis (tumbling motion), and a central symmetry axis (spinning motion). A detailed study is conducted on mixing performance of powders and the effect of critical fundamental parameters including blender geometry, speed, fill level, presence of baffles, loading pattern, and axis of rotation. In this work Acetaminophen is used as the active pharmaceutical ingredient and the formulation contains commonly used excipients such as Avicel and Lactose. The mixing efficiency is characterized by extracting samples after pre-determined number of revolutions, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Results show the importance of process variables including the axis of rotation on homogeneity of powder blends.Graphical abstractThe dynamics involved in powder mixing remains a topic of interest for many researchers; however the theory still remains underdeveloped. Most of the mixers are still designed and scaled up on empirical basis. In many industries, including pharmaceutical, the majority of blending is performed using “tumbling mixers”. In all these mixers while homogenization in the direction of rotation is fast, mediated by a convective mixing process, mixing in the horizontal (axial) direction, driven by a dispersive process, is often much slower. In this paper, we experimentally investigate a new tumbling mixer that rotates with respect to two axes: a horizontal axis (tumbling motion), and a central symmetry axis (spinning motion).Keywords:Powder mixing ; Cohesion; Blender ; Mixer; Relative standard deviation; NIR; AcetaminophenArticle Outline1.Introduction2.Materials and methods2.1. Near infrared spectroscopy2.2. Bin blenders used in this study: uni-axial blender (Blender 1), bi-axial blender (Blender 2)2.3. Experimental method3.Results4.ConclusionReferences1. IntroductionParticle blending is a required step in a variety of applications spanning the ceramic, food, glass, metallurgical, polymers, and pharmaceuticals industries. Despite the long history of dry solids mixing (or perhaps because of it), comparatively little is known of the mechanisms involved 1, 2 and 3. A common type of batch industrial mixer is the tumbling blender, where grains flow by a combination of gravity and vessel rotation. Although the tumbling blender is a very common device, mixing and segregation mechanisms in these devices are not fully understood and the design of blending equipment is largely based on empirical methods. Tumblers are the most common batch mixers in industry, and also find use in myriad of application as dryers, kilns, coaters, mills and granulators 4, 5, 6, 7 and 8. While free-flowing materials in rotating drums have been extensively studied 9 and 10, cohesive granular flows in these systems are still not completely understood. Little is known about the effect of fundamental parameters such as blender geometry, speed, fill level, presence of baffles, loading pattern and axis of rotation on mixing performance of cohesive powders or the scaling requirements of the devices. However, conventional tumblers, rotating around a horizontal axis, all share an important characteristic: while homogenization in the direction of rotation is fast, mediated by a convective mixing process, mixing in the horizontal (axial) direction, driven by a dispersive process, is often much slower.In this paper, we experimentally investigate a new tumbling mixer that rotates with respect to two axes: a horizontal axis (tumbling motion), and a central symmetry axis (spinning motion). We examine the effects of fill level, mixing time, loading pattern and axis of rotation on the mixing performance of a free-flowing matrix of Fast Flo lactose and Avicel 102, containing a moderately cohesive API, micronized Acetaminophen. We use extensive sampling to characterize mixing by tracking the evolution of Acetaminophen homogeneity using a Near Infrared spectroscopy detection method. After materials and methods are described in Section 2, results are presented in Section 3, followed by conclusions and recommendations, which are presented in Section 4.2. Materials and methodsThe materials used in the study are listed in Table 1, along with their size and morphology. Acetaminophen is blended with commonly used excipients and is used as a tracer to evaluate the degree of homogeneity achieved as a function of number of revolutions. Acetaminophen is one of the drugs most widely used in mixing studies, and Avicel and Lactose are commonly used pharmaceutical excipients. In the interest of brevity their SEM images are not included in this paper, but can be found in “Handbook of Pharmaceutical excipients”.2.1. Near infrared spectroscopyAcetaminophen homogeneity was quantified using near infrared spectroscopy. A calibration curve was constructed for a powder mixture containing (in average) 35% avicel PH 102, 62% lactose and 3% acetaminophen. Near infrared (NIR) spectroscopy can be a useful tool to characterize acetaminophen. Samples are prepared by keeping the ratio of Avicel to lactose randomized in order to minimize effects of imperfect blending of excipients during the actual experiments on the accuracy of the results. The Rapid Content Analyzer instrument manufactured by FOSS NIR Systems (Silver Spring, MD) and Vision software (version 2.1) is used for the analysis. The samples are prepared by weighing 1 g of mixture into separate optical scintillation vials; (Kimble Glass Inc. Vineland, NJ) using a balance with an accuracy of 0.01 mg. Near-IR spectra are collected by scanning in the range 11162482 nm in the reflectance mode. Partial least square (PLS) regression is used in calibration model development using the second derivative mathematical pretreatment to minimize the particle size effects. As shown in Fig. 1, excellent agreement is achieved between the calibrated and predicted values. Fig. 1.Fig. 1. Near Infrared (NIR) spectroscopy validation curve. The equation used to predict acetaminophen concentration is validated by testing samples with known amounts of acetaminophen concentration. The y axis represents the concentration calculated from the equation and the x axis represents the actual concentration. Thus a perfectly straight line at 45 would represent the best calibration model. Each point on the graph represents a single sample. The concentration of acetaminophen examined here ranges from 0 to 8%.2.2. Bin blenders used in this study: uni-axial blender (Blender 1), bi-axial blender (Blender 2)Due to its widespread use, a cylindrical blender 1 with a capacity of 30 L is chosen as a reference blender in the study. As shown in Fig. 2, this blender has a circular cross section and tapers at the bottom. It can be used with or without baffles, which are mounted on a removable lid. In this study all the experiments are conducted without the use of baffles. Mixing performance in this device is used to provide a base-line for evaluating the mixing performance of a newly developed blender 2 with a capacity of 40 L, which is also cylindrical, in order to determine the effect of dual axis of rotation on mixing performance. The blender shown in Fig. 2(b) has two axis of rotation. The spinning rate of precession relative to the central axis of symmetry is geared to be half of that of the rate of rotation around the horizontal axis. Fig. 2.Fig. 2. Pictorial representation of (a) bin blender 1 and (b) bin blender 2 showing the corresponding axis of rotation.2.3. Experimental methodTwo types of initial powder loading used in the experiments: topbottom loading and sideloading, which are schematically represented in Fig. 3. To avoid agglomeration, the API, acetaminophen, was delumped prior to loading it into the blender by passing it through a 35 mesh screen. In order to characterize mixing performance, a groove sampler was used to extract samples from the blenders at 7.5, 15, 30, 60, 120 revolutions. The thief was carefully inserted in the bin, and a core was extracted at each point of insertion (each “stab”) minimizing perturbation to the powder bed remaining in the blender. Approximately 7 samples are taken from each thief stab, and a total of five stabs are used at each sampling time, as shown in Fig. 4 so a total of 35 samples are taken at each sampling point. Fig. 3.Fig. 3. Schematic of the loading pattern used in the study. In topbottom loading, Avicel is loaded first into the blender followed by Lactose on top of it and finally Acetaminophen is uniformly sieved over. In sideside loading avicel is placed at the bottom and then Acetaminophen is only sieved only in half part of the blender and is sandwiched between lactose and Avicel. Fig. 4.Fig. 4. (a) Thief sampler (b) top view of the sampling position scheme.The experimental plan used in this study is as follows: Fill level: blender 160% Fill level: blender 260%, 70%, 80% Loading pattern: blender 1 sideside loading, topbottom loading Loading pattern: blender 2 sideside loading, topbottom loading Speed: blender 115 rpm, 20 rpm, 25 rpm Speed: blender 2 rotational/spinning:15/7.5 rpm, 20/10 rpm, 30/15 rpm Sampling time: blender 1, blender 27.5, 15, 30, 60, 120 revolutions3. ResultsThe homogeneity index used is the RSD, where C is the concentration of each individual sample, C_ is the average concentration of all samples and n is the total number of samples obtained at a given sampling time.We examine the effect of fill level on mixing performance. Previously there have been studies on the effect of fill level in the Bohle bin blender, Gallay bin blender and V- blender and double cone blender 11, 12 and 13. All the aforementioned blenders have only one axis of rotation, therefore the objective of this study is to examine how dual axis impact mixing performances at high fill levels. To avoid repetition, studies for fill level are not conducted for bin blender 1. Results available from a previous study using MgSt as a tracer showed that mixing in a uni-axial blender slowed down quite dramatically as the fill level exceeded 70%. Moreover, results for acetaminophen can be assumed to be similar to those obtained in previous work by Muzzio et al. 11 and 13, for a single axis rectangular bin blender 11, which have shown that even after few hundred revolutions homogeneity achieved with a 80% fill level is very poor as compared to 60% fill level.To examine the effect of fill level in a dual axis blender, experiments were performed in blender 2 with the top-bottom loading pattern for a rotational speed of 15 rpm and with spinning speed of 7.5 rpm. The fill levels examined are 60%, 70% and 80% respectively and samples are taken after 7.5, 15, 30, 60, 120 revolutions. Typical results are shown in Fig. 5, which shows the RSD vs. number of blender revolutions. As expected for non-agglomerating materials, the curves show a rapidly decaying region. The slope of the curves in this region, in semi-logarithmic coordinates, is used to define the mixing rate. The curves then level off to a plateau that indicates the maximum degree of homogeneity that is achievable in the blender for a give material. Fig. 5.Fig. 5. Mixing curves for different fill levels in blender 2. The RSD of acetaminophen is plotted as a function of number of revolutions. The loading pattern in top-bottom and the blender rotational speed is 15 rpm with spinning speed of 7.5 rpm.Similar to previous studies with other tumbling blenders we observe that blending performance is adversely affected by increasing fill levels. As shown in Fig. 5, the curve for 80% fill performs more poorly than those for 60% and 70% fill; as fill level increases, RSD curves decay more slowly, signifying a slower mixing process. However, the effect is not as pronounced as in other bin blenders and after about only 100 revolutions, the same plateau (the same asymptotic blend homogeneity) is achieved for all three fill levels.Next, the effect of rotational speed is investigated in the blender 1 with one axis of rotation and is compared to the blender 2 with dual rotation axis. Experiments were conducted for both blenders with top-bottom and side-side loading. Experiments were performed at 60% fill level and the rotation speeds considered for blender 1 are 15 rpm, 20 rpm and 25 rpm respectively. As shown in Fig. 6 and Fig. 7, when plotted as a function of blender revolutions, there is not much of an effect of rotation speed on the homogeneity index (RSD) of acetaminophen at 60% fill level. It is observed that mixing performance at 20 rpm and 25 rpm is slightly better than at 15 rpm, however the differences in the performance of the blender under different speeds are probably too small to be significant. RSD curves decay with the same slope, indicating similar mixing rates. In the study reported here, the fill level is only 60%, and all the rotational speeds are enough to achieve homogenization. The aforementioned studies were conducted at 85% fill level. For such a high fill level, at low speeds, a stagnant core is known to occur at the center of many blenders, requiring higher shear stress per unit volume to achieve homogenization. Moreover, the flow properties of MgSt are known to be strongly different than those of most materials, and are known to have a deep impact on the flow properties of the mixture as a whole. Furthermore, MgSt is famously known to be a shear sensitive material. Thus an expectation that lubricated and unlubricated blends would show similar behavior with respect to shear is probably unwarranted. Fig. 6.Fig. 6. Mixing curves for top-bottom loading experiments with 60% fill level. RSD is plotted as a function of number of revolutions. Dotted lines correspond to experiments in the blender 1, while solid lines represent data points from the blender 2. Fig. 7.Fig. 7. curves for sideside loading experiments with 60% fill level. RSD is plotted as a function of number of revolutions. Dotted lines correspond to experiments in the while solid lines represent data points from the 2.Subsequently, experiments were performed using the blender 2 at three rotation speeds: 15 rpm, 20 rpm and 30 rpm, and as explained before, the corresponding spinning speeds were 7.5 rpm, 10 rpm and 15 rpm. Fill level considered for both side-side and top-bottom loading was 60%.Again, it was observed that varying rotation and spinning speeds did not make much difference in mixing rate. As shown in Fig. 6 and Fig. 7, mixing curves for blender 2 vary only slightly with rotation speed. For the top-bottom loading pattern it appears that mixing improves slightly when rotation speed is increased (the plateau is slightly lower for higher rotation speeds, indicating an improvement in the levels of asymptotic homogeneity), but no significant changes with speed are observed in side-side loading pattern.The blending performance of both blenders is compared at different rotation speeds for both side-side and top-bottom loading patterns. To make a fair comparison, the fill level was kept as 60% for both blenders, a condition for which both blenders achieve effective mixing at long enough times. Due to geometric similarity of the two blenders, this comparison help evaluate the effect of spin (rotation with respect to the central symmetry axis) on mixing performance. As shown in Fig. 6, the mixing curves for the blender 2 lie below those for the blender 1 for each rotation rate, indicating faster mixing. Note that the final RSD asymptote reached for both blenders is also different, with the blender 2 showing a lower asymptote (better final mixed state, presumably due to a lesser effect of the slow mixing mode in the horizontal direction) than blender 1.Similar results were obtained for the side-side loading pattern, as displayed in Fig. 7. The RSD curves for the blender 1 for all the three rotation rates lie above the blender 2. It is therefore confirmed that spinning a blender in direction perpendicular to the rotation axis helps in enhancing mixture homogeneity; however, for the materials examined here, the rotation rate does not have much effect on mixing performance. Finally, a comparison is made between the two loading patterns for both blenders. Again, to achieve a fair comparison, all experiments are performed at 15 rpm and 60% fill level. As evident in Fig. 8, in both blenders topbottom loading gives a more rapid decay of the RSD, indicating faster homogenization as compared to sideside loading pattern. However, for both loading modes, blender 2 achieves faster homogenization. Fig. 8.Fig. 8. Comparison between the mixing curves of the blender 2 and the blender 1 for topbottom and sideside loading pattern. Dotted lines correspond to experiments in the blender 1, while solid lines represent data points from the blender 2. Experiments are performed at 15 rpm with 60% fill level.As reported in previous studies, all the RSD curves in this paper exhibit a common trend with respect to time, characterized by an initial period of rapid homogenization due to convective mixing, followed by a period of much slower homogenization typically controlled by dispersion or shear. This trend is shown schematically in Fig. 9. The first regime is a fast exponential decay and the second one is a slow exponential asymptote to a limiting plateau. The first part represents a rapid reduction in heterogeneity driven by the bulk flow (convection); the slope of the RSD curve, in semi-logarithmic coordinates, is the convective mixing rate. The second part is driven by individual particle motion (dispersion) or by the slow erosion of API agglomerates due to shear. Fig. 9.Fig. 9. A typical mixing plot, with RSD plotted against number of revolutions. The two solid lines emphasize on the two distinctive mixing regimes.When only one mixing mechanism is present (a situation that can be achieved by careful control of the initial loading pattern), a simple mass-transfer model, represented in Eq. (1) can be used, as in past studies 14, to capture the evolution of the RSD in powder systems. In this model, an exponential curve decaying towards a plateau is fitted to the mixing curves, where is the standard deviation, the final standard deviation, A is an integration constant, signifies t
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