2J550×3000雙軸攪拌機設計【說明書+CAD】,說明書+CAD,2J550×,3000雙軸攪拌機設計【說明書+CAD】,j550,攪拌機,設計,說明書,仿單,cad 河南理工大學萬方科技學院 本科畢業(yè)設計（論文）中期檢查表 指導教師： 趙武 職稱： 副教授 所在院（系）： 機械與動力工程學院 教研室（研究室）： 機械制造教研室 題 目 0-2J550×3000雙軸攪拌機 學生姓名 馬磊 專業(yè)班級 07機制2班 學號 0720150127 一、選題質量： 該生此次所選擇的題目為雙軸攪拌機設計，內容涉及到對攪拌機的總體布置和理論研究，還有一些機械零件和機械結構的設計計算與校核，與專業(yè)課程緊密聯(lián)系，符合專業(yè)培養(yǎng)目標，在設計工作中，需要對所學知識綜合地加以運用，使之能夠熟練應用有關參考資料、計算圖表、手冊；熟悉有關的國家標準和部頒標準，體現(xiàn)了綜合訓練的要求。工作量大與生產，經濟，社會等的結合緊密，選題質量較高。 二、開題報告完成情況： 從適合實際工作環(huán)境出發(fā)，確定了明確的課題設計方向；并對雙軸攪拌機在使用中經常出現(xiàn)的問題有一定的研究，且應用在設計計算中；已經開始對課題進行設計計算，并有了突破性的進展，設計過程已經快速地展開，確定了工作的內容和方法；同時，已完成了對相關資料的查閱，對課題有了總體的分析。開題報告順利完成。 三、階段性成果： 總體布置方案和主要結構參數(shù)已確定，并完成一些標準件的選型及和大多數(shù)零部件的設計計算工作。結構設計和校核工作正在進行中，部分零件圖的繪制已經基本完成，英文翻譯工作還未完成，已著手開始制作設計說明書的工作。 四、存在主要問題： 1.因為是通過軸帶動葉片進行工作，對安裝葉片角度和材料選擇不是很確定； 2.預加水雙軸攪拌機可以使水的霧化和雙軸的攪拌，使物料得到充分的浸潤，并攪拌成球，能為成球機成球提供有利條件，對改善料球性能，提高料球質量，降低能耗，提高立窯產量具有十分重要的作用。 3.局部結構設計思路不清晰；設計內容不夠連貫，系統(tǒng)性不強；在整體結構及零部件結構上存在一定問題；在選用零件和確定結構工藝參數(shù)時缺少經驗和參考； 4.對資料搜集方法比較少，獲得資料不夠充分，得到的資料比較陳舊； 五、指導教師對學生在畢業(yè)實習中，勞動、學習紀律及畢業(yè)設計（論文）進展等方面的評語： 指導教師： （簽名） 年 月 日 河南理工大學萬方科技學院 本科畢業(yè)（論文）設計開題報告 題目名稱 2J550×3000雙軸攪拌機設計 學生姓名 馬磊 專業(yè)班級 07機制2班 學號 0720150127 一 選題的目的和意義： 雙軸攪拌機為螺旋式攪拌機，它的攪拌部件是兩根形狀對稱的同步螺旋轉子，兩根螺旋軸在旋轉時速度同步、方向相反。雙軸攪拌機由電機驅動，可用減速機控制轉子轉動速度，達到最佳的攪拌效果。 雙軸攪拌機的主要部件包括，機械外殼、兩根螺旋轉軸、電機驅動裝置、聯(lián)動裝置、配管和蓋板等，必要時雙軸攪拌機還可搭配減速機使用。 雙軸攪拌機的螺旋軸是最重要的工作部分，兩根螺旋軸的旋轉方向相反，都具有軸承座、軸承套、軸承蓋、葉片和聯(lián)動裝置。包括彼此平行的第一和第二攪拌軸、攪拌葉片和臥式攪拌桶，所述攪拌葉片從第一和第二攪拌軸向四周伸出，并在軸向依次等距排列而在圓周方向依順時針或逆時針彼此相差一固定角度，使在第一和第二攪拌軸上的攪拌葉片分別形成旋向相反的螺旋狀排列；所述第一和第二攪拌軸彼此同步轉動并且其葉片交錯通過由該第一和第二攪拌軸軸線所確定的平面；在所述攪拌桶一端的頂部設有進料口，而在所述攪拌桶另一端的底部設有出料。采用這種結構，攪拌機的攪拌葉片在攪拌干粉砂漿的同時將干粉砂漿從進料口排向進料口，從而實現(xiàn)生產的連續(xù)，有效的提高了生產效率。雙軸攪拌機的螺旋軸在運行過程中受到的磨損最為嚴重，可采用剛玉陶瓷等耐磨材料制造。 雙軸攪拌機在工作時，物料通過進料口進入筒體，兩根螺旋軸在電機驅動下反向現(xiàn)轉，物料受旋轉作用而隨之運動，相互混合完成攪拌。雙軸攪拌機的兩根螺旋軸之間的區(qū)域，旋轉方向不同的物料相互擠壓作用，能提高混合攪拌效果。 雙軸攪拌機是混合干燥物料的理想設備，適用于在輸送干粉狀物料的同時加水攪拌，從而均勻加濕各種干粉物料。一般來說，雙軸攪拌機所攪拌的物料含水分不超過20%。雙軸攪拌機在火力發(fā)電廠、礦山等粉狀物料加濕場合較為常見。 鑒于雙軸攪拌機所具有的標準的機械特性，我選擇了這個設計課題。這是我們畢業(yè)前的最后一次作業(yè)，這讓我們對以前學過的相關機械方面的課程進行了一次全面系統(tǒng)復習。這次設計我將獨立完成一臺雙軸攪拌機的完整設計，這對我來說是一個不小的挑戰(zhàn)，但也是一次重要的鍛煉機會。課題的主要內容是結合生產實際，完成一臺生產能力 為Q = 30 t/h的2J550×3000雙軸攪拌機設計。 二 國內外研究現(xiàn)狀簡述： 強制攪拌機 強制攪拌機，本實用新型屬于灰砂磚生產中的混合料攪拌設備，其主要解決雙軸攪拌機加水量不易控制，攪拌力小，使物料易結團結倉的問題，該機包括行星攪拌機構，渦流攪拌機構，攪拌鼓，排料機構，攪拌機架及底架等部分，攪拌鼓的中心位置設置有渦流攪拌機，在渦流攪拌機兩側機架上，對稱布置有兩行星攪拌機，兩行星攪拌機作相對旋轉，渦流攪拌機與攪拌鼓呈反向旋轉，該機攪拌力大，解決了結團結倉等問題。 一種適用于灰砂磚生產攪拌混合料的強制攪拌機，包括行星攪拌機構，渦流攪拌機構，攪拌鼓，攪拌機架，排料機構及底架等部分組成，其特征在于攪拌鼓位置于底架上的大齒圈的軸承座上，攪拌鼓的中心位置設有渦流攪拌機，在渦流攪拌機兩側機架上，對稱布置有兩行星攪拌機。 JW—350型強制式攪拌機 主要技術參數(shù) 出料容量 350〈L〉 進料容量 560〈L〉 額定功率 5.5kw 最大粒徑 40mm 主軸轉速 35轉/分 外形尺寸 Φ1300×1200 混凝土攪拌機 混凝土攪拌機，包括通過軸與傳動機構連接的動力機構及由傳動機構帶動的滾筒，在滾筒筒體上裝圍繞滾筒筒體設置的齒圈，傳動軸上設置與齒圈嚙合的齒輪。本實用新型結構簡單、合理，采用齒輪、齒圈嚙合后，可有效克服雨霧天氣時，托輪和攪拌機滾筒之間的打滑現(xiàn)象；采用的傳動機構又可進一步保證消除托輪和攪拌機滾筒之間的打滑現(xiàn)象。 攪拌機還可衩被分為： 星式攪拌機 防險攪拌機 立式攪拌機 混凝土攪拌機 雙軸攪拌機 單軸攪拌機 防滑混凝土攪拌機 JS雙臥軸混凝土攪拌機 主要技術參數(shù) 出料容量 500〈L〉 進料容量 800〈L〉 生產能力 24—28m3/h 骨料最大粒徑 60 攪拌軸轉 36轉/分 攪拌葉片 2×7 攪拌電機型號 Y180m—4 （B3） 功率 18.5kw 卷揚電機型號 YEZ1325—4 （B5） 功率 5.5kw 水泵電機型號 50DWB20—8A 功率 0.75KW 料斗提升速度 18m/分 外形尺寸運輸 3050×2300×2680 工作 4461×3050×5225 整機重量 4100kg 卸料高度 1500mm 立式攪拌機 攪拌機包括有電動機、攪拌筒、傳動軸、攪拌槳葉，其中在傳動軸上還松套有一反向攪拌槳葉，該反向攪拌槳葉的軸套通過鏈條與位于傳動軸一側的中間軸上端的鏈輪相連，與鏈輪同軸的被動齒輪則與固定在傳動軸下端的主動齒輪相嚙合。本實用新型的兩個攪拌槳葉是反向轉動的，使得在攪拌過程中，原料能在兩個攪拌槳葉之間形成對流，從而徹底解決了傳統(tǒng)攪拌機對原料攪而不拌的問題。 新型攪拌機系換代產品，是化工和建材行業(yè)攪拌設備無可替代的產物，實現(xiàn)了正確“攪和拌”的問世，從而淘汰其它攪拌設備所以承但的重任。它以其超常規(guī)的構思和精銳的技術含量，合理的設計水準，填補了國際空白。其廣泛用于油漆、涂料、染料、制革、醫(yī)藥、飲料、粘膠劑、食品、洗滌品、化妝品及各種固態(tài)物體等。有取之不盡的財富。對物體分散、乳化、均質、調色等較之傳統(tǒng)攪拌機的攪拌效果更加理想、直觀、是攪拌行業(yè)的一次革命。 雙軸攪拌機用于預加水成球工藝流程中，其工作原理是，當定量的生料粉由下料口流入攪拌槽中，經若干個具有一定壓力的水霧化灑向生料粉，由定性長度的軸經攪拌葉攪拌勻后形成含一致的球核，并輸送到預加水盤式成球機中去。整個攪拌機的攪拌時間分為霧化區(qū)，拌勻區(qū)，卸料區(qū)三個區(qū)域。攪拌葉片上焊硬質合金刀頭，耐磨性能好，使用壽命長。 主要參數(shù) 單位 型號 2J40 2J45 2J50 2J55 2J60 攪拌葉直徑 mm ￠400 ￠450 ￠500 ￠550 ￠600 進出料口中心距 mm 3000-3260 攪拌軸速度 r.p.m 50.4 50.4 48 45 41 生產能力 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° 配用電機 型號 Y160M-4 Y160L-4 Y180M-4 Y180L-4 Y250M-6 功率 kw 11 15 18.5 22 37 配用減速機 ZQ40-VI-2Z ZQ50-VI-4Z ZQ50-VI-Z ZQ65-VI-4Z ZQ75-VI-2Z 攪拌濕度 % 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 雙軸攪拌機在國內一直被作為一個簡單的助力機械裝備，雙軸攪拌機在技術已經基本成熟，產品應用很普遍，由于它只是生產過程中的輔助設備，產品不需要很高的科技含量就能夠滿足要求，國內廠家所生產的產品已經能夠滿足生產中的要求，其中大多數(shù)都是機械傳動式雙軸攪拌機。但由于我國的機械制造水平普遍較低，所生產的產品難以占領國際高端產品市場。 在國外，雙軸攪拌機研究水平比較高，用兩根呈對稱狀的螺旋軸的同步旋轉，雙軸攪拌機的外殼多采用優(yōu)質金屬結構，具備良好的密封性，在攪拌機攪拌各種粉狀物料時，可避免灰塵外漏和飛揚的問題，在各種場合都已經得到廣泛應用。國外一些廠家的生產技術已經比較成熟，例如：德國威克(Wacker)機械公司，美國KNIGHT機械公司，韓國KOREA HOIST機械公司等這些技術先進，性能優(yōu)良的雙軸攪拌機已經走進國內市場。 雙軸攪拌機的設計制造比較普遍，一般的機械廠都可以生產，我國陜西中隆建材機械公司，上海申銀機械有限公司，江蘇總能電力設備有限公司，四川射洪通用機械有限公司，鞏義市環(huán)城機械有限公司，河南滎陽萬山礦山機械廠，河南省銳泰機械制造有限公司，鄭州天一機械有限公司等 三、畢業(yè)設計（論文）所采用的研究方法和手段： 1工作原理 雙軸攪拌機由兩根攪拌軸，軸上按螺旋推進方向安裝攪拌葉及攪拌槽組成的攪拌系統(tǒng)，為使原料達到成型的需要，在攪拌機入料端稍后處的上部，設有加水裝置，使得物料形成較大的球狀塊料旋轉時兩軸的方向由內向外，將物料攪起，靠攪拌葉旋轉時的推力(攪拌葉與攪拌軸軸線夾角為10-20度)形成物料流，螺旋向前推進，最后物料經漏料箱進入承接皮帶，進入到下臺處理設備中。 圖2-1 雙軸攪拌機結構示意 1 軸承座； 2 出料口； 3 攪拌葉； 4 攪拌軸；5 攪拌槽；6 齒輪座； 7 聯(lián)軸器；8 減速器；9 三角帶輪；10 驅動電動機 2 結構設計特點 合格生料粉經穩(wěn)流計量后進入雙軸攪拌機。雙軸攪拌機由電機通過三角皮帶傳動，經ZQ圓柱齒輪減速機、十字滑塊聯(lián)軸器帶動主動軸旋轉，由配對齒輪帶動從動軸轉動。主、從動軸上裝有可以轉動角度的漿葉式攪拌葉，在軸向力和一定圓周力作用下作螺旋狀旋轉在進料端約1.2米處裝有霧化噴嘴，物料被攪拌同時噴霧受濕并向前推進。物料在擠壓揉磋等力的作用下形成團粒母核。物料被攪拌葉推動在槽內向前運動至出料口。 從結構上看，雙軸攪拌機要較單軸攪拌機復雜，但它磨損小，攪拌質量好，生產率高，雙軸攪拌機較之立軸式和單軸式攪拌機，具有明顯的優(yōu)越性。 雙軸攪拌機優(yōu)點總結如下: 1. 攪拌機外形尺寸小、高度低、布置緊湊，裝載運輸便利，而且結構合理堅固，工作可靠性好； 2. 攪拌機容量大，效率高。與同容量自落式相比，攪拌時間可縮短一半以上，而且物料運動區(qū)域位于卸料門上方，卸料時間也比其他機型短，因而生產率高； 3. 拌筒直徑比同容量立軸式小一半，攪拌軸轉速與立軸式基本相同，但葉片線速度要比立軸式小一半，因此葉片和襯板磨損小、使用壽命長，并且物料不易離析； 4.物料運動區(qū)域相對集中于兩軸之間，物料行程短，擠壓作用充分，頻次高，因而攪拌質量好。 2.1外殼的設計形式 傳統(tǒng)的U型槽底容易出現(xiàn)攪拌死角，從而導致兩軸負載過大以致斷裂。另外他們將兩端墻板焊死在機殼上，這樣就使得在軸或葉片受損維修時很不方便，工作量也相當大。 將雙軸攪拌機槽底做成歐米嘎型（ω）,以防止攪拌死角。兩邊再焊上鋼板制成機槽，槽口兩邊焊有角鋼用以固定機蓋，槽機底部焊有支承墊用以支承槽體。機槽兩端墻板不是焊死在機殼上，而是通過螺栓與機殼聯(lián)結，這樣做的目的是為了在維修時便于將損壞的軸吊起，省去拆葉片麻煩，檢修空間增大，工作量減小，還可縮小兩端軸孔直徑，便于密封防漏，如圖2-2所示。 圖2-2 攪拌槽殼體 2.2 軸與葉片的安裝方法的設計 以前，大多在整個軸上都安裝葉片，生料進口處葉片角度比較大，用以快速輸送物料，但是我們發(fā)現(xiàn)這樣攪拌葉片的磨損較大，靠進料口槽體端密封處漏灰嚴重，從而齒輪內進灰較多，加快了傳動部件的磨損，影響生產效率。 因此，針對這些問題對軸的結構進行改造，即在軸的攪拌進口端焊接兩螺旋葉片使粉料不斷向前輸送，減少槽體端部密封處的積料。這樣有利于防止打壞葉片、折斷軸。在攪拌軸上正確安裝帶有刀片的葉片，調整好了角度后，再將葉片安裝在鉆有莫氏錐度孔的軸上，如圖2-3所示。 葉片在雙軸上三個部位的安裝角度是各不相同，葉片安裝角度一般選用α=20度左右，雙軸攪拌機葉片角度必須要與粘土可塑性相適應，雙軸攪拌機工作分三個階段： 第一階段是霧化水與原料的混合攪拌階段；該階段軸的長度為0.7m 左右（包括螺旋葉片軸段），安裝的葉片數(shù)是8只，安裝角度為25°，通過霧化噴水和機械翻動攪拌兩個手段以達到液固均化的目的。 第二階段是使含煤生料濕潤的階段，為使其能充分濕潤，生料在這一階段的運行速度應慢一些；該階段軸的長度為1.5m左右，安裝的葉片數(shù)是20個，安裝角度為15°，其主要特征是機械攪拌。 第三階段是形成球核的階段；該階段軸的長度為1.0m左右，安裝的葉片數(shù)是12個，安裝角度為20°，其中最后4只的安裝角度是0°，其目的是為了擋料。 圖2-3 攪拌機工作簡圖 在調整葉片角度的同時，要注意葉片的轉速，這兩方面也是相互影響的，在確定轉速時首先要確定物料在攪拌機內攪拌的時間，而攪拌時間又影響著形成球核的產量，因此攪拌時間、葉片角度、轉速、濕潤時間等之間要相互配合好，一般出攪拌機的球核直徑為1-2mm的占20%-75%較好。 其中每個葉片焊牢在葉片桿上，然后按照要求調整角度焊接在方墊片上。經過這樣的處理后，葉片在推動物料時就不會出現(xiàn)角度混亂，另外把攪拌軸頭的軸肩R適當調大，減小應力，防止應力集中，如圖2-4所示。 圖2-4 葉片安裝圖 2.3 傳動機構的設計 傳動裝置是雙軸攪拌機工作過程中的關鍵。設計的傳動路線 為電機皮帶ZQ減速機聯(lián)軸器齒輪傳動裝置攪拌軸。 將雙軸攪拌機傳動裝置整體放置出料口端，使生料不能進入齒輪和軸承。同時給兩傳動齒輪制作一個油池，用于齒輪的潤滑，能減小磨損，提高使用壽命。 常用的減速機有三種型式，圓柱齒輪減速機、行星減速機和擺線針輪減速機。其中采用圓柱齒輪減速機較合適，而采用行星減速機和擺線針輪減速機常會出現(xiàn)因攪拌機主軸起動時扭矩大，傳動系統(tǒng)剛度不足，故障多，有漏油問題。相對而言圓柱齒輪減速機傳動穩(wěn)定，噪音小，齒面接觸穩(wěn)定，在潤滑保養(yǎng)良好的條件下，運轉穩(wěn)定。 2.4 密封裝置的設計 對密封裝置的要求相當高，可采用雙道壓蓋填料密封裝置，填料采用橡膠石墨石棉盤根，兩邊采用壓蓋壓緊，內壓蓋、外壓蓋和密封蓋固定采用沉頭螺栓緊固，見圖2-5。 圖2-5 密封裝置 1 密封圈；2 壓板1；3 密封蓋；4 端面板；5 墊板；6 軸套 2.5 霧化裝置的設計 水的霧化的好壞，是預加水成球的關鍵條件之一。它通過霧化器來實現(xiàn)，霧化器設在攪拌機進料口的一端，其作用是擔負著生料和水的第一道均勻混合工序的噴水任務，為下一道機械攪拌工序創(chuàng)造良好的均合基礎，達到液固均化的目的。 為了保證霧化效果，必須對水壓、水質、噴嘴及噴嘴布置有一定的要求： 1.結構簡單，制造方便，成本低，無特殊工藝裝備，維修方便，使用壽命長； 2.在低能量條件運行應保證足夠的噴水能力,MP型>550kg/h,以利用于減少噴嘴組合數(shù)量,便于布置； 3.水質要干凈純潔，盡量少含泥沙等雜質，以防噴嘴堵塞。水質不好時需在水箱出水口增加過濾網，并定期清洗； 4.噴嘴要有適宜的噴射角度，保持適宜的水量和良好的霧化效果，使布水均勻，直接噴向料層，不能噴向機殼再流向物料；噴嘴離料層距離保持300 mm左右，不能過近，否則，不能保證接觸料層被水充分霧化。 由于噴嘴的布置形式直接影響攪拌效果和球核的質量,因此應注意： 1.噴嘴在攪拌機中的布置原則應分布在進料口落料流及落料區(qū)，以實現(xiàn)操作點無粉塵污染； 2.保證噴嘴至料面的垂直距離S≥300 mm，目的是使霧滴同生料粉接觸，提高生料的濕潤滲透性，否則影響成球的均勻性，并增加清理特大球的工作量； 3.多嘴組合應用噴嘴能進一步提高液固均化程度，但多嘴數(shù)量要適當； 4.噴嘴噴射方向及覆蓋面必須在生料面區(qū)域內，不得噴射在機槽側壁上，否則將造成機槽側壁粘料嚴重，難以清理，并增加攪拌葉片的阻力，從而提高攪拌的功率消耗，同時也會造成局部生料過濕，影響成球質量。 綜合各方面的條件，選用MP-Ⅰ型離心壓力噴嘴式霧化器（見表2-1）比較合理，其主要特點有：加大了噴液能力，提高到了550 kg/h以上，霧化角為90°至120°，效果好，而且可減少噴嘴數(shù)量。MP型噴嘴內襯中心有一沖水孔，出水口有4個月牙形分水刀，心部4個螺旋槽與垂線相交成45°至95°角； 表2-1 MP-Ⅰ型霧化器規(guī)格參數(shù) 流量 kg/h 霧化角 噴嘴孔徑mm 霧化壓力MPa L mm D mm 含水量 % 所需水量 t/h 噴嘴數(shù)量 個 550 85° 2 0.197 32 M16×1.5 12-14 3.6-4.2 10-12 四、主要參考文獻： [1] 許林發(fā)主編. 建筑材料機械設計(一) .武漢：武漢工業(yè)大學出版社, 1990 [2] 褚瑞卿主編. 建材通用機械與設備.武漢：武漢理工大學出版社, 1996 [3] 朱昆泉，許林發(fā).建材機械工業(yè)手冊.[M].武漢：武漢工業(yè)大學出版社，2000.7 [4] 胡家秀主編.機械零件設計實用手冊.北京：機械工業(yè)出版社，1999.10 [5] 李益民主編.機械制造工藝設計手冊.北京：機械工業(yè)出版社，1995.10 [6] 甘永立.幾何量公差與檢測[M].上海：上?？茖W技術出版社，2001.4 [7] 錢志鋒，劉蘇工程圖學基礎教程[M].北京：科學出版社，2001.9 [8] 徐灝.機械設計手冊[M].北京：機械工業(yè)出版社，1991.9 [9] 趙忠.金屬材料與熱處理[M].北京：機械工業(yè)出版社，1991.5 [10] 閻瑞敏，常敏.水泥工業(yè)自動控制預加水成球技術及裝備[M].江蘇科學技術出版社，1990.10 [11] 黃有豐.預加水成球技術及其應用[M].北京：中國建筑工業(yè)出版社，1991.9 [12] 徐錦康.機械設計[M].北京：高等教育出版社，2004.4 [13] 王旭，王積森.機械設計課程設計[M].北京：機械工業(yè)出版社，2003.8 [14] 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Abstract The 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 abstract The 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; Acetaminophen Article Outline 1. Introduction 2. Materials and methods 2.1. Near infrared spectroscopy 2.2. Bin blenders used in this study: uni-axial blender (Blender 1), bi-axial blender (Blender 2) 2.3. Experimental method 3. Results 4. Conclusion References 1. Introduction Particle 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 methods The 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 spectroscopy Acetaminophen 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 1116–2482 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 method Two types of initial powder loading used in the experiments: top–bottom loading and side–loading, 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 top–bottom loading, Avicel is loaded first into the blender followed by Lactose on top of it and finally Acetaminophen is uniformly sieved over. In side–side 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 1–60% ? Fill level: blender 2–60%, 70%, 80% ? Loading pattern: blender 1 — side–side loading, top–bottom loading ? Loading pattern: blender 2 — side–side loading, top–bottom loading ? Speed: blender 1–15 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 2–7.5, 15, 30, 60, 120 revolutions 3. Results The 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 side–side 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 top–bottom loading gives a more rapid decay of the RSD, indicating faster homogenization as compared to side–side 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 top–bottom and side–side 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 σ is the standard deviation, σ∞ the final standard deviation, A is an integration constant, λ signifies t