電動絞肉機的設(shè)計,電動絞肉機的設(shè)計,電動,絞肉機,設(shè)計 江西農(nóng)業(yè)大學(xué)畢業(yè)設(shè)計(論文)任務(wù)書 設(shè)計（論文） 課題名稱 電動絞肉機的設(shè)計與研究 學(xué)生姓名 李帝 院（系） 工學(xué)院 專 業(yè) 機械設(shè)計制造及其自動化 指導(dǎo)教師 肖懷國 職 稱 副教授 學(xué) 歷 畢業(yè)設(shè)計（論文）要求： 1. 要求在完成論文期間，積極主動，查閱大量文獻，獨立創(chuàng)新； 2. 按時完成畢業(yè)設(shè)計內(nèi)容，方案切實可行； 3. 獨立繪制裝配圖和零件圖； 4. 圖紙量不少于1.5張A0； 5. 獨立完成畢業(yè)設(shè)計說明書，格式正確，要求字數(shù)不少于5000字； 6. 完成電子文檔，并打印裝訂成冊。 畢業(yè)設(shè)計（論文）內(nèi)容與技術(shù)參數(shù)： 1. 熟悉電動絞肉機的整個設(shè)計過程 2. 電動絞肉機可實現(xiàn)對不同肉種的加工. 畢業(yè)設(shè)計（論文）工作計劃： 1. 了解本機工作原理，明白設(shè)計意義； 2. 查閱資料并畫出機械機構(gòu)草圖； 3. 通過計算確定零件尺寸，并掌握零件主要參數(shù)及材料熱處理方式； 4. 寫設(shè)計說明書； 5. 根據(jù)設(shè)計說明書的計算尺寸，畫出各零件圖； 6. 畫出機械總裝配圖。 接受任務(wù)日期 2012 年 2 月 7 日 要求完成日期 2012 年 5 月 5 日 學(xué) 生 簽 名 李帝 2012年 5 月 1日 指導(dǎo)教師簽名 年 月 日 院長（主任）簽名 年 月 日 編 號 20080970 江西農(nóng)業(yè)大學(xué) 工學(xué)院 畢業(yè)設(shè)計材料 題 目 電動絞肉機設(shè)計 專 業(yè) 機械設(shè)計制造及其自動化 學(xué)生姓名 李帝 材 料 目 錄 序號 附 件 名 稱 數(shù)量 備注 1 畢業(yè)設(shè)計論文 1 2 零件圖 15 3 總裝圖 1 4 設(shè)計任務(wù)書 1 二〇一二年 五月 電動絞肉機的設(shè)計 目錄 摘要 .I Abstract .II 1緒 論 .1 1結(jié) 構(gòu) 及 工 作 原 理 .2 1.1絞肉機的結(jié)構(gòu) .2 1.2絞肉機的工作原理 .2 3絞龍的設(shè)計 .3 3.1絞龍的設(shè)計 .3 3.1.1絞龍的材料 .4 3.1.2絞龍直徑 .4 3.1.3絞龍的轉(zhuǎn)速 .4 3.2絞筒的設(shè)計 .4 4 傳動系統(tǒng)的設(shè)計 .4 4.1電機的選擇 .5 4.2 帶輪的設(shè)計 .5 4.3齒輪傳動的設(shè)計計算 .8 4.4齒輪軸的設(shè)計與校核 .11 4.4.1各軸的轉(zhuǎn)速計算 .12 4.4.2各軸輸入功率計算 .12 4.4.3各軸輸入扭矩計算 .12 4.4.4 按彎扭合成強度校核軸徑 .12 5絞 刀 設(shè) 計 .13 5.1絞刀的設(shè)計 .13 5.1.1刀刃的起訖位置 .14 5.1.2刀刃的前角 .14 5.1.3刀刃的后角 .14 5.1.4刀刃的刃傾角 .15 5.1.5刀片的結(jié)構(gòu) .15 6生產(chǎn)能力分析 .16 6.1絞刀的切割能力 .16 6.2 絞肉機的生產(chǎn)能力G .16 6.3功率消耗N .16 7絞肉機的使用與日常維護簡介 .16 8設(shè)計小結(jié) .18 參考文獻 .19 I 摘要 絞肉機是肉類加工企業(yè)在生產(chǎn)過程中將原料肉按不同工藝要求加工規(guī)格不 等的顆粒狀肉餡,廣泛適用于各種香腸、火腿腸、午餐肉、丸子、咸味香精、寵 物食品和其他肉制品等行業(yè)。本文論述了絞肉機的結(jié)構(gòu)、工作原理、主要技術(shù) 參數(shù)、傳動系統(tǒng)、典型零件的結(jié)構(gòu)設(shè)計及生產(chǎn)能力分析。希望對本次設(shè)計的探 索和研究能設(shè)計出實用經(jīng)濟的家用絞肉機，更好的方便人民的生活食品工業(yè)的 現(xiàn)代化水平，在很大程度上依賴于食品機械的發(fā)展及其現(xiàn)代化水，離開現(xiàn)代儀 器和設(shè)備，現(xiàn)代食品工業(yè)就無從談起。 食品工業(yè)的發(fā)展是設(shè)備和工藝共同發(fā)展的結(jié)果，應(yīng)使設(shè)備和工藝達到最佳 配合，以設(shè)備革新和創(chuàng)新促進工藝的改進和發(fā)展，以工藝的發(fā)展進一部促進設(shè) 備的發(fā)展和完善。兩者互相促進、互相完善，是使整個食品工業(yè)向現(xiàn)代化邁進 的必要條件。 關(guān)鍵詞：絞肉機；擠肉樣板；絞刀；絞龍；螺旋供料器；齒輪強度 II Abstract Is meat processing enterprise in stage production of raw meat will according to different process request processing specifications vary granular meat, widely used in all kinds of sausage, ham bowel, lunch meat ball, salty, essence, pet food and other meat products, etc.Many practical machines in our life are from mechanical design, this paper elaborates on the meat choppers structure,operating principlemain ,technical parameter, transmission system andstructural design and production capacity analysis of typical parts are mannyintroduced.It is hoped that a practical and economical household meat chopper could be designed according to the authors exploration, which would be convenient for the life of people. instruments and equipment the modern food industry cannot survive. The food industry is the development of the equipment and the result of the development of common technology should make the equipment and technology reach the best with equipment and innovation to promote the innovation process improvement and development, in order to promote the development of the technology into a equipment of development and perfection. Both promote each other, mutual perfect, is to make the whole food industry on the necessary conditions to modernization. Key words: meat chopper;crowded meat model;reamer;stranding cage;screw feeder;gear strength 1 1緒 論 絞 肉 機 是 肉 類 加 工 企 業(yè) 在 生 產(chǎn) 過 程 中 ， 將 原 料 肉 按 不 同 工 藝 要 求 加 工 規(guī) 格 不 等 的 顆 粒 狀 肉 餡 ， 以 便 于 同 其 它 輔 料 充 分 混 合 來 滿 足 不 同 產(chǎn) 品 的 需 求 絞 肉 機 為 系 列 產(chǎn) 品 ； 工 作 時 利 用 轉(zhuǎn) 動 的 切 刀 刃 和 孔 板 上 孔 眼 刃 形 成 的 剪 切 作 用 將 原 料 肉 切 碎 ， 并 在 螺 桿 擠 壓 力 的 作 用 下 ， 將 原 料 不 斷 排 出 機 外 。 可 根 據(jù) 物 料 性 質(zhì) 和 加 工 要 求 的 不 同 ， 配 置 相 應(yīng) 的 刀 具 和 孔 板 ， 即 可 加 工 出 不 同 尺 寸 的 顆 粒 ， 以 滿 足 下 道 工 序 的 工 藝 要 求 。 隨著國民經(jīng)濟的發(fā)展和人民生活水平的 提高，人民對食品工業(yè)提出了更高的要求?，F(xiàn)代食品已朝著營養(yǎng)、綠色、方便 、功能食品的方向發(fā)展，且功能食品將成為新世紀的主流食品。食品工業(yè)也成 為國民經(jīng)濟的支柱產(chǎn)業(yè)，作為裝備食品工業(yè)的食品機械工業(yè)發(fā)展尤為迅猛。 在肉類加工的過程中，切碎、斬拌攪拌工序的機械化程度最高，其中絞肉 機、斬拌機、攪拌機是最基本的加工主械.幾乎所有的肉類加工廠都具備這3種 設(shè)備。國內(nèi)一些大型肉類加工廠先后從西德、丹麥、瑞士、日本等引進了先進 的加工設(shè)備，但其價格十分昂貴。目前中、小型肉類加工企業(yè)所使用的大部分 設(shè)備為我國自行設(shè)計制造的產(chǎn)絞肉機是為中、小型肉類加二企業(yè)所設(shè)計的較為 理想的、絞制各種肉餡的機械，比如生產(chǎn)午餐肉罐頭和制造魚醬、魚圓之類的 產(chǎn)品，它將肉可進行粗、中、細絞以滿足不同加工工藝的要求，該機亦可作為 其他原料的擠壓設(shè)備。 絞 肉 機 零 部 件 主 要 采 用 優(yōu) 質(zhì) （ 鑄 鐵 件 ） 或 不 銹 鋼 制 造 ， 對 加 工 物 料 無 污 染 ， 符 合 食 品 衛(wèi) 生 標 準 。 刀 具 經(jīng) 特 殊 熱 處 理 ， 耐 磨 性 能 優(yōu) 越 ， 使 用 壽 命 長 。 該 機 操 作 簡 單 、 拆 卸 組 裝 方 便 調(diào) 節(jié) 或 更 換 。 2 1結(jié) 構(gòu) 及 工 作 原 理 1.1絞肉機的結(jié)構(gòu)（下圖） 絞肉機主要由動力機構(gòu)以及傳送機構(gòu)和切割機構(gòu)組成，其中動力機構(gòu)主要 為電動機，皮帶輪，減速器。被切割物料的傳送機構(gòu)主要是進肉斗，絞筒，絞 龍。而切割機構(gòu)主要為絞刀，擠肉樣板，以及旋蓋。 1.2絞肉機的工作原理 工作時，先開機后放料，由于物料本身的重力和螺旋供料器的旋轉(zhuǎn)，把物 連續(xù)地送往絞刀口進行切碎。因為螺旋供料器的螺距后面應(yīng)比前面小，但螺旋 軸的直徑后面比前面大，這樣對物料產(chǎn)生了一定的擠壓力，這個力迫使已切碎 的肉從格板上的孔眼中排出。 用于午餐肉罐頭生產(chǎn)時，肥肉需要粗絞而瘦肉需要細絞，以調(diào)換格板的方 式來達到粗絞與細絞之需。格板有幾種不同規(guī)格的孔眼，通常粗絞用之直徑為8 10毫米、細絞用直徑35毫米的孔眼。粗絞與細絞的格板，其厚度都為101 2毫米普通鋼板。由于粗絞孔徑較大，排料較易，故螺旋供料器的轉(zhuǎn)速可比細絞 時快些，但最大不超過400轉(zhuǎn)/分。一般在200400 轉(zhuǎn)/ 分。因為格板上的孔眼總 3 面積一定，即排料量一定，當供料螺旋轉(zhuǎn)速太快時，使物料在切刀附近堵塞， 造成負荷突然增加，對電動機有不良的影響。 絞刀刃口是順著切刀轉(zhuǎn)學(xué)安裝的。絞刀用工具鋼制造，刀口要求鋒利，使 用一個時期后，刀口變鈍，此時應(yīng)調(diào)換新刀片或重新修磨，否則將影響切割效 率，甚至使有些無聊不是切碎后排出，而是由擠壓、磨碎后成漿狀排出，直接 影響成品質(zhì)量，據(jù)有些廠的研究，午餐肉罐頭脂肪嚴重析出的質(zhì)量事故，往往 與此原因有關(guān)。 裝配或調(diào)換絞刀后，一定要把緊固螺母旋緊，才能保證格板不動，否則因 格板移動和絞刀轉(zhuǎn)動之間產(chǎn)生相對運動，也會引起對物料磨漿的作用。絞刀必 須與格板緊密貼和，不然會影響切割效率。 螺旋供料器在機壁里旋轉(zhuǎn)，要防止螺旋外表與機壁相碰，若稍相碰，馬上 損壞機器。但它們的間隙又不能過大，過大會影響送料效率和擠壓力，甚至使 物料從間隙處倒流，因此這部分零部件的加工和安裝的要求較高。 絞肉機的生產(chǎn)能力不能由螺旋供料器決定，而由切刀的切割能力來決定。 因為切割后物料必須從孔眼中排出，螺旋供料器才能繼續(xù)送料，否則，送料再 多也不行，相反會產(chǎn)生物料堵塞現(xiàn)象。 3絞龍的設(shè)計 3.1絞龍的設(shè)計 絞龍又名螺旋供料器其作用是向前輸送物料，并在前端對肉塊進行擠壓。 如圖31所示，設(shè)計上采用一根變螺距、變根徑的螺旋，即螺距后大前小，根 徑后小前大，這樣使其絞龍與絞龍之間的容積逐漸減小實現(xiàn)了對物料的擠壓作 用。絞龍的前軸分為兩個部分的連接，分別是與軸承配合的圓形軸和與絞刀連 接的方形軸，后軸與凸緣聯(lián)軸器連接傳遞動力以實現(xiàn)對被絞物料的輸送與擠壓 的雙重作用。 4 3.1.1絞龍的材料 絞龍為鑄件所以其材料可選灰色鑄鐵可選為HT150。 3.1.2絞龍直徑 5.2CGKD G生產(chǎn)能力 K物料綜合特性系數(shù) -物料得填充系數(shù) 物料的堆積密度 C與螺旋供料器傾角有關(guān)的系數(shù) 3.1.3絞龍的轉(zhuǎn)速 由于絞龍只有一種工作轉(zhuǎn)速，則從電機至絞龍的運動路線為定比傳動，其 總的傳動比可利用帶傳動、齒輪傳動等構(gòu)機逐級減速后得到。絞籠的轉(zhuǎn)速不易 太高，因為輸送能力并不是隨轉(zhuǎn)速增加而增加。當速度達到一定值以后，效率 反而下降，且速度過高，物料磨擦生熱，出口處的壓力升高，易引起物料變性 ，影響絞肉質(zhì)量，因此絞籠的轉(zhuǎn)速一般在200一400r/min比較適宜。經(jīng)查食品加 工過技術(shù)裝備綜合考慮本機選用326r/min。 3.2絞筒的設(shè)計 由于肉在絞筒內(nèi)受到攪動，且受擠壓力的反作用力作用，物料具有向后倒流的 趨勢，因此在絞籠的內(nèi)壁上設(shè)計了8個止推槽.沿圓周均勻分布，絞筒內(nèi)壁與絞 籠之間的間隙要適當，一般為2- 3mm。間隙太大會使物料倒流;間隙太小絞籠與絞筒內(nèi)壁易碰撞。 絞筒的材料可選用鑄鐵，選HT150 4 傳動系統(tǒng)的設(shè)計 由于絞龍只有一種工作轉(zhuǎn)速，所以無需變速裝置，然而考慮到絞龍的轉(zhuǎn)速 5 與被加工肉的加工質(zhì)量，本設(shè)計選擇兩級傳動，第一級由電動機輸出的帶輪傳 動，并實現(xiàn)一次減速，第二級傳動為齒輪傳動，因為對生產(chǎn)衛(wèi)生要求較嚴格， 故齒輪需要采用閉式傳動型，所以采用一級減速箱的傳動，則從電機至絞龍的 運動路線為定比傳動，其總的傳動路線為：電動機高速軸小皮帶輪 大皮帶輪 齒輪軸大齒輪絞龍。 4.1電機的選擇 由上面的介紹可知，整個傳動路線是電動機輸出然后經(jīng)過帶輪與齒輪的兩級減 速傳遞到絞龍與絞刀的， N= 4(KW)WG G絞肉機的生產(chǎn)能力，1000kg/h W切割1kg物料耗用能量，其值與孔眼直徑有關(guān)，d小則w大，當d 3mm， 取w0.0030kw.h/kg。 傳動效率，取0.75 所以根據(jù)N4kw，查機械設(shè)計課程設(shè)計表2- 239，選擇Y系列的三相鼠籠電動機其同步轉(zhuǎn)速n1500r/min，滿載時為1440r/m in，型號為Y112M- 4。多以整個傳動系統(tǒng)的傳動比為 4.41 ，取為4.4，所以依據(jù)前面的 總 =1440326 傳動設(shè)計，初定傳動比分配為 =4.4= x 其中 為皮帶輪的傳動比，先設(shè)為1.總 12 1 76， 為減速箱的減速比，初定為2.5。,2 4.2 帶輪的設(shè)計 選用普通V帶傳動，動力機位Y系列三相異步電動機，功率P=4kw，轉(zhuǎn)速n= 1440，計算步驟參照機械設(shè)計帶輪設(shè)計步驟。 計算項目 計算內(nèi)容 計算結(jié)果 定V帶型號和帶輪直徑 工作情況系數(shù) 由表 =1.2 計算功率 = P=1.24 =4.8kw 選帶型號 查機械簡明設(shè)計手冊 A型 小帶輪直徑 由機械設(shè)計表 取 =100mm1 6 大帶輪直徑 =ix =176mm 2 1 查機械設(shè)計簡明手冊選 =180mm（為滑動率，取=1%）2 計算項目 計算內(nèi)容 計算結(jié)果 計算帶長 求 = = =140 1+22 100+1802 求 = = =40 2-12 1801002 初取中心距 a=2X( )280mm1+2 帶長 L= +2a+ = 199+2500+ L=886mm 2 1092500 基準長度 由機械設(shè)計圖 11.4 基準長度 選用 900 求中心距和包角 中心距 a= + -4 14（ -） 2-82 = + 900- 1404 14 （ 900- 140） 2-8402 =287mm 小輪包角 = - 601180 2-1 = - 60 180 180100577.28 =163.271 120 求帶根數(shù) 7 帶速 v= = D1n1601000 90960601000 v=7.54 傳動比 i= = i=1.76 1 2 1440818.18 帶根數(shù) 查機械設(shè)計表11.7、11.8，,11.10 =1.32kw；0 =0.95； =0.87； =0.15kw；0 計算項目 計算內(nèi)容 計算結(jié)果 Z= （ 0+0） = 4.8（ 1.32+0.15） 0.950.87 =3.96 取z=4根 求軸上載荷 張緊力 500 （ ）+q0= 2.5 2 500 （ ）+0.10 4.87.544 2.50.950.95 7.542 =135.4N 0 （由機械設(shè)計表 11.4 q=0.10 ） 軸上載荷 =2z 0sin12 =24135.4 =1071.3N sin163.22 8 帶輪結(jié)構(gòu)設(shè)計 由于帶速v 30 ，帶輪用 HT200制造。小帶輪采用整體式結(jié)構(gòu)，大帶輪采用腹 板式結(jié)構(gòu)，見下圖。 綜上整理帶傳動參數(shù)如表： 小帶輪直 徑 1 大帶輪直徑2 傳動比 i 帶基準長度 根數(shù)Z 中心距a 100mm 180mm 1.76 900mm 4 287mm 4.3齒輪傳動的設(shè)計計算 查機械設(shè)計簡明手冊，選擇兩齒輪的材料均為40 ,并經(jīng)調(diào)質(zhì)及表面淬火， 齒面硬度為45- 50HRC。閉式傳動的齒輪，主要失效形式是彎曲疲勞折斷和磨粒磨損，磨損尚無 完善的計算方法，故只進行彎曲疲勞強度計算。 校核步驟按機械設(shè)計齒根彎曲疲勞強度計算： 先初定兩齒輪間的中心距： ， 根據(jù) 321)(HaamuKTAC 式中：配對材料修正系數(shù)Cm1 螺旋角系數(shù)Aa476 載荷系數(shù)K1.6 9 小齒輪額定轉(zhuǎn)矩 )(7.46819541 MNnPT 齒寬系數(shù) 0.4（查簡明機械設(shè)計手冊表 10-3）a 由前面初定，再查簡明機械設(shè)計手冊表10-2（GB1357-87）齒數(shù)比u=i=2.5 許用接觸應(yīng)力 則PaH10829.0.lim a80mm（查機械設(shè)計表12.4）,.6185.24076)15.2(47632a 計算項目 計算內(nèi)容 計算結(jié)果 1.初步計算 轉(zhuǎn)矩 由前表查得 =46.7N.M1 1 齒寬系數(shù) 由表12.13，取 =1.0 =1.0 彎曲疲勞極限 由圖 12.23 =500Mpa 1 =350Mpa2 初步計算的許用 彎曲應(yīng)力 0.7 1 1 =0.7 500 =350Mpa1 0.72 2 =0.7350 =245Mpa2 值 由表，取 =1.45 =1.45 初取齒輪齒數(shù) 取小齒輪齒數(shù) =30 =30 1 1 2=75 齒形系數(shù) 由圖機械設(shè)計圖12.21 =2.6 1FY =2.2 2 應(yīng)力修正系數(shù) 由 機械設(shè)計 圖 12.22 10 6.1SaY ， 7.2 初步計算的齒輪模數(shù)m m 3 121 =1.41 查機械設(shè)計表12.3取 m=1.5 初步齒寬b b= 40mm 1取 32mm2取 計算項目 計算內(nèi)容 計算結(jié)果 2.校核計算 圓周速度v v= = =1.95m/s 1160100045.7818.18601000 v=1.08 精度等級 由表 選9級等級 齒數(shù)z和模數(shù)m 由前計算，m=1.5； =30， =i =75 =301 2 1 1 =752 使用系數(shù) 查表 =1 動載系數(shù) 查表 =1.2 重合度 = 1.883.2（ 11+12） cos =1.88-3.2 （ ）=1.9 =1.9 130+175 重合度系數(shù) =0.25+ =0.25+ =0.77 0.75 0.751.72 齒間載荷分配系數(shù) 由表， = = 載荷系數(shù)K 110.69 K= =1.251.11.41.25 K=2.4 11 彎曲最小安全系數(shù) 由表 12.14 =1.2 應(yīng)力循環(huán)次數(shù) =60 =601274.3 11 14400 =2.41 108 =60 =60168.5722 14400 =0.61 108 彎曲壽命系數(shù) 由機械設(shè)計圖 12.24 =0.92 1 =0.982 尺寸系數(shù) 由機械設(shè)計圖 12.25 =1.0 許用彎曲應(yīng)力 = = 1 11 5000.9211.25 （式12.19） =368Mpa 1 = = 2 22 3500.9811.25 =274.4Mpa2 驗算 =1 21 111 = 2.631.580.69 22.412968075753 =94.8Mpa1 1 =2 12222 12 =94.8 2.181.812.631.58 88.3Mpa2= 2 綜上可知本齒輪設(shè)計符合要求。 4.4齒輪軸的設(shè)計與校核 齒輪軸的結(jié)構(gòu)如下： 4.4.1各軸的轉(zhuǎn)速計算 =1440高 = =齒 14401.76818.18 = =327.27低 818.182.5 4.4.2各軸輸入功率計算 = =4 高速 軸 1 = 0.960.97=3.7248kw齒輪軸 高速 軸 = 0.90.97=3.25kw低速 軸 齒輪軸 4.4.3各軸輸入扭矩計算 =9550 =955041440Nm=26.5 Nm高 高 高 =9550 =95503.7248818.18 Nm=43.8 Nm齒 齒 齒 =9550 =95503.25327.27 Nm=94.9 Nm低 低 低 4.4.4 按彎扭合成強度校核軸徑 （1）畫出齒輪軸的的受力圖（如下） （2）作出水平內(nèi)的彎矩圖（如下） 13 支點反力為 = = =2069/2=1030,齒輪左側(cè)軸承截面彎矩為： 支 1支 2 22 1 =1030X =6077Nmm，齒輪右側(cè)軸承處截面彎矩 =1030X29Nmm 2 2 （3）作出垂直面內(nèi)彎矩圖（如下） 以相同的方法求出支點反力 =-73.56 =837.5N1 ,1 故 = X =-4345Nmm，同理 =49410Nmm11 2 2 (4) 合成彎矩為 M= 2+2 （5）對齒輪截面經(jīng)行安全校核 ，當量彎矩M= =181510Nmm,齒輪截面 = =181500/ =19.9M 2右 +()2 0.14533 pa,許用彎曲應(yīng)力=60Mpa,故危險截面滿足，設(shè)計的齒輪軸有足夠的 強度。 5絞 刀 設(shè) 計 絞刀的作用是切割物料。它的內(nèi)孔為方形，安裝在絞籠前端的方軸上隨其 14 一起旋轉(zhuǎn)，刀刃的安裝方向應(yīng)與絞籠旋向相同。絞刀的規(guī)格有2刃、4刃、8刃 。 絞刀用ZG65 Mn材料制造，淬火硬度為HRC55 - 60，刃口要鋒利，與樣板配合平面應(yīng)平整、光滑。 5.1絞刀的設(shè)計 絞刀的幾何參數(shù)對所絞出肉的顆粒度以及產(chǎn)品質(zhì)量有著很大的影響，現(xiàn)對 十字刀片的各主要幾何參數(shù)進行設(shè)計。 十字刀片其每一刃部的絞肉(指切割肉的)線速度 分部其刃部任一點位置上只有法向速度 。 v 再從任一葉刀片的橫截面上來看，其刃部后角 較大，而前角 及刃傾角 都為零。 因此，該刀片的幾何參數(shù)(角度)不盡合理。故再將以一葉刀片的與網(wǎng)眼扳 相接觸的一條刀刃為對象，分析刀片上各參數(shù)的作用及其影響，設(shè)計各參數(shù)。 5.1.1刀刃的起訖位置 絞肉時，絞肉機的十字刀片作旋轉(zhuǎn)運動。從式I可以看出，在轉(zhuǎn)速一定的 條件下，刀刃離旋轉(zhuǎn)中心點越遠，則絞肉(指切割肉的)線速度越快。并且在螺 桿進科速度也一定的條件下，假定絞肉時刀片所消耗的功全部轉(zhuǎn)化為熱能，則 任一與網(wǎng)眼板相接觸的刀刃，在單位時間內(nèi)產(chǎn)生的熱量為： VFQ 式中：Q單位時間內(nèi)任一與網(wǎng)眼板相接觸的刀刃切割肉所產(chǎn)生的熱量（Js） F鉸肉時任一與網(wǎng)眼板相接觸的刀刃上的切割力（N） 任一刀刃切割肉的線速度（ms） 所以，絞肉(切割肉)的線速度越快，則所產(chǎn)生的熱量也越大，因此絞肉的 線速度不能很高。 根據(jù)經(jīng)驗，我們知道一般絞肉時刀刃切割肉的錢速度處在30一90mmin之間最 為理想，因此由這些數(shù)據(jù)可估算出刀刃的起訖位置，即刃的起點半徑 和終點 半徑R。 5.1.2刀刃的前角 在刀片旋轉(zhuǎn)速度以及螺桿進料速度都一定的情況下，前角大，切割肉所需 的力和切割肉所產(chǎn)生的熱都小；反之，則大。但前角很大時，則因刀具散熱體 積小而使切割肉時所產(chǎn)生的溫度不能很快冷卻。因此，在一定的條件下，前角 有一合理的數(shù)值范圍： 15 一般?。?(肉質(zhì)軟取大值，反之取小值)4025 5.1.3刀刃的后角 刀刃后角的目的：一是減小后刀面與網(wǎng)眼板(包括三眼板)表面的摩擦；二 是在前角不變的情況下，增大后角能使刀刃鋒利。 刀片磨損后將使刀刃變鈍，使肉在絞肉(切割)過程中變形能增加，同時由 于磨損后刀片的后角基本為零，加大了刀片與網(wǎng)眼扳的摩擦，兩者都使絞肉過 程中產(chǎn)生的熱量增多。 另外，在同樣的磨鈍標準V B下，后角大的刀片由新用到鈍所磨去的金屬體積較大。這說明增大后角可提高 刀片的耐用度，但同時也帶來的問題是刀片的N B磨損值大(反映在刀體材料的磨損過大這一方面)，并且刀刃極度也有所削弱， 故后角也有一合理的數(shù)值范圍： 一般?。?(肉質(zhì)軟取大值反之取小值)53 5.1.4刀刃的刃傾角 從分析由前刀面和后刀面所形成的刀刃來得知刀傾角 對刀片性能的影響 情況。 在任一葉刀片的法剖面內(nèi)，當把刀刃放大看時，可以把刀刃看成是一段半 徑為 的圓弧，由于刀刃有刃傾角 ，故在線速度方向剖面內(nèi)的刀刃將變成橢r 圓弧(斜剖刀刃圓柱所得) 橢圓的長半徑處的曲率半徑，即為刀刃實際純圓半徑 。 er0 其關(guān)系為： cos0ner 由此可見，增大刀傾角 的絕對值，可減小刀刃的實際鈍圓半徑 ，這就er0 說明增大刃傾角就可使刀刃變得較為鋒利。 一旦刀刃的起訖半徑r及R確定后，其最大初始刃傾角 就可確定了max0 r/acsinmx0 初始刃傾角按下式計算： )/(20 bRractg 式中：r刀刃起始點半徑(mm)； R刀刃終止點半徑(mm)； b葉刀片外端寬度（mm）; 初始刃傾角；0 16 5.1.5刀片的結(jié)構(gòu) 根據(jù)以上對絞刀各個幾何參數(shù)的分析，具體結(jié)構(gòu)可參照零件圖，此絞刀的 特點：后角取4 ，刀片的壽命較長；前角取30 ，以減小絞肉所需的力及功增 加刃傾角，以提高刀刃的鋒利度；采用全圓弧形的前刀面結(jié)構(gòu)，以改善刀刃的 強度；采用可換式刀片結(jié)構(gòu)，以節(jié)約刀體材料并可選用不同幾何參數(shù)刀片。 6生產(chǎn)能力分析 6.1絞刀的切割能力 根據(jù)需要被絞的肉質(zhì)不同可以選用不同類型的絞刀，一般來說絞刀的刃越多其 切割效率越好，但磨損強度也隨之提升。絞刀的切割能力與多因素有關(guān)。 6.2 絞肉機的生產(chǎn)能力G 生產(chǎn)能力G（kg/h）： AF1 式中： 被切割1kg物料的面積，其值與孔眼直徑有關(guān)（ ）；1 hcm/2 A絞刀切割能力利用系數(shù)，一般為0.70.75； 6.3功率消耗N 功率消耗N可用下式計算： (kw)WG 式中：W切割1kg物料耗用能量，其值與孔眼有關(guān)（kw h/kg）； 傳動效率； 由生產(chǎn)能力計算可知，在N、D一定的條件下，絞刀的刃數(shù)越多，生產(chǎn)能力 越大。但是不同刃數(shù)的絞刀應(yīng)與不同孔徑的擠肉樣板相匹配，才能得到較為合 理的生產(chǎn)量和功率消耗。 7絞肉機的使用與日常維護簡介 每 次 使 用 絞 肉 機 前 ， 得 簡 單 沖 洗 一 下 。 一 般 而 言 ， 絞 肉 機 在 上 次 用 完 后 都 是 及 時 清 洗 過 的 ， 使 用 前 的 清 洗 ， 主 要 是 沖 掉 機 器 內(nèi) 外 的 浮 塵 等 。 另 一 個 17 好 處 是 ， 使 用 前 的 沖 洗 會 使 絞 肉 比 較 變 得 輕 松 流 暢 ， 也 會 使 工 作 結(jié) 束 后 的 清 洗 變 得 比 較 省 事 。 絞 肉 機 正 常 使 用 的 情 況 下 一 年 內(nèi) 不 需 重 新 加 油 ； 絞 肉 機 潤 滑 油 品 類 為 黃 油 ； 加 油 孔 位 置 ： 機 身 頂 部 兩 個 螺 栓 孔 后 部 （ 背 向 絞 肉 部 件 的 方 向 ） 的 一 個 螺 栓 孔 可 方 便 加 油 （ 一 定 要 加 注 黃 油 ， 不 能 加 液 體 機 油 ） 。 絞 肉 機 機 箱 部 分 正 常 情 況 下 不 需 做 維 護 保 養(yǎng) ， 主 要 是 防 水 和 保 護 好 電 源 線 、 避 免 電 源 線 破 損 及 做 好 清 潔 等 。 絞 肉 部 件 的 日 常 維 護 ： 每 次 使 用 完 畢 后 ， 需 將 絞 肉 三 通 、 螺 桿 、 刀 片 孔 板 等 拆 卸 下 來 ， 清 除 殘 留 物 后 再 按 原 次 序 裝 回 。 這 樣 做 的 目 的 一 方 面 保 證 機 器 及 加 工 食 物 的 衛(wèi) 生 ， 另 一 方 面 可 保 證 絞 肉 部 件 拆 裝 靈 活 ， 方 便 檢 修 和 更 換 ， 刀 片 和 孔 板 是 易 損 件 ， 使 用 一 段 時 間 后 可 能 需 要 更 換 。 18 8設(shè)計小結(jié) 在大四即將畢業(yè)之前，通過這幾十天的學(xué)習，我覺得自己的專業(yè)知識和獨 立思考問題的能力有了很大的提高，對我走向社會從事專業(yè)工作有著深遠的影 響?，F(xiàn)在談?wù)剬Ρ敬萎厴I(yè)設(shè)計的認識和體會。 首先，經(jīng)過這么多天的繁瑣的機械設(shè)計，我懂得了堅持的重要性，因為我 們的動手能力相對比較薄弱，平時這方面的訓(xùn)練量又少，多以剛開始做起來特 備不順手，感覺很浮躁，但最終我還是堅持下來了，并懂得了堅持的可貴之處 。這次設(shè)計中我做了許多重復(fù)性的工作，耽誤了很多的時間，但是這些重復(fù)性 的工作卻增強了我的實踐能力和動手能力，積累了設(shè)計經(jīng)驗。同時也得到一條 經(jīng)驗，搞設(shè)計不能只在腦子里想它的結(jié)構(gòu)，必須動手，即使你想的很完美，但 是到實際的設(shè)計過程時，會遇到許多意不到的問題。 其次，我學(xué)會了查閱資料和獨立思考。當開始拿到畢業(yè)設(shè)計題目時，心里 真的是一點頭緒也沒有，根本不知道從那里下手。在肖老師的細心指導(dǎo)下，我 開始查閱相關(guān)書籍，借鑒他人的經(jīng)驗，結(jié)合自己的構(gòu)想，再利用自己所學(xué)過的 專業(yè)知識技能。設(shè)計師一個嚴謹?shù)倪^程，他們的邏輯性非常的強，不能有半點 的馬虎與大意。 最后真誠的感謝肖懷國老師的諄諄教導(dǎo)，還有各位同學(xué)不厭其煩的幫助，因為 有你們的幫助，我才能夠完成這次繁雜的設(shè)計。再次誠摯的向你們說聲謝謝！ 19 參考文獻 【1】 邱宣懷、郭可謙、吳宗澤等.機械設(shè)計第4版.北京：高等教育出版社 ，2010. 【2】 中國機械工程學(xué)會中國機械設(shè)計大典，江西科學(xué)技術(shù)出版社 【3】 唐金松主編簡明機械設(shè)計手冊，上?？萍技夹g(shù)出版社 【4】 劉鴻文.材料力學(xué).4版.北京：高等教育出版社.2010. 【5】 .何銘新、錢可強.機械制圖.5版.北京：高等教育出版社.2008. 【6】 陳于萍，周兆元主編互換性與測量技術(shù)基礎(chǔ)第二版 機械工業(yè)出版社 【7】 張裕中主編食品加工技術(shù)裝備M第一版北京：中國輕工業(yè)出版社 【8】 蔣曉、沈培玉、苗青.AutoCAD2008中文版機械設(shè)計標準實例教程.北京： 清華大學(xué)出版社.2008. 【9】 鄭文緯、吳克堅.機械原理.7版.北京：高等教育出版社.2010. A simplified twin screw co-rotating food extruder: design, fabrication and testing S.A.M.A.N.S. Senanayake a, B. Clarke b,* Division of Agricultural and Plantation Engineering, The Open University of Sri Lanka, Nawala, Nugegoda, Sri Lanka Department of Postharvest Technology, School of Agriculture, Food and Environment, Silsoe Collage, Cranfield University, Silsoe, Bedfordshire MK45 4DT,UK Received 6 July 1998; accepted 10 February 1999 Abstract A simplified co-rotating twin screw food extruder was designed, fabricated and tested in England, followed by extensive testing in Sri Lanka. It was built as a model to meet the specific product and financial constraints of less developed countries and was expected to be used in those countries to widen the production capabilities of extruded foods. The machine had an estimated delivery of 10 kg/h and was made mainly with mild steel. Two types of screw were made, one with a constant pitch of 14 mm and the other with varying pitch in segments of 14, 12 and 10 mm. The machine was powered by a 2.2 kW electric motor with electronic speed control .The machine also had electrical heating with a temperature controller and a pressure sensing device. The cost of fabrication of the machine was estimated at ￡2000 with most of the parts built in a fairly simple workshop. A mixture of rice and dried banana was successfully extruded as a potential snack food and on the basis of maximum expansion the best results was obtained from a barrel temperature of 120°C, screw speed 125 rpm, feed moisture 15% and with a die orifice size of 3 mm. When the alternative compress ion screw was tested very similar results were achieved with no significant improvement in product expansion. ? 1999 Elsevier Science Ltd. All rights reserved. Keywords: Twin screw extruder; Design; Low cost; Snack food; Continuous cooker; Local construction; Cereal mixtures Nomenclature a Die diameter (mm) B Channel width (mm) C Screw circumference (mm) d Screw core diameter D Outer diameter of screws (mm) H Flight depth (mm) M Moisture content (% wet basis) n Number of fight turns N Speed angular (rev/min) p Pitch (mm) Q Delivery rate (mm3/min) S Total helical length of screws (mm) t Temperature (℃) T Residence time (min) a Overlap angle of screw fights (degrees) d Calender gap (mm) e Side clearance (mm) q Product density (g/mm3 ) / Helix angle (degrees) * Corresponding author. Fax: +01525-863277; e-mail: b.clarke@cran- ?eld.ac.uk 0260-8774/99/$ ± see front matter?1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 9 9 ) 0 0 0 4 9 – 7 1. Introduction Extrusion cooking is finding ever increasing applications in the food process industry. Apart from providing a means of manufacturing new products, it has successfully revolution is many conventional manufacturing processes (Harlow, 1985, Frame, 1994). Today, extruders come in a wide variety of sizes, shapes and method of operation. There are three types of food extruder found in industry: hydraulic ram, roller and screw type extruders (Frame, 1994). The screw extruders are very different to the other two having special features such as continuous processing and mixing ability. Single and twin screw types are both widely used in the food process industry. Unfortunately, most of the food extruders available in the market are either so costly that less developed countries cannot afford to buy them except by some form of assistance or outside investment or else are not appropriate for the wide variety of materials that need to be processed. As a result the growth of extrusion technology of food into these countries has been hindered despite its many advantages. Fig. 2. Plan drawing of the twin screw extruder with drive system. 1-V belt pulley, 2-gear box, 3-food seal, 4-ˉange clamp bolt, 5-die plate, 6-die, 7-two segments of the extruder chamber, 8-extruder screw. were made so that they could be externally screwed to the die plate.2.5. Drive system The machine was driven by an electric motor of 2.2kW using a twin belt drive between the motor and a gearbox shown in Fig. 2. The speed reduction in the box was2.08 while an electronic speed controller was used to control the speed continuously over the range required. Fig. 3. Front portion of barrel showing provision for heaters, temperature and pressure sensors. 1-slots for heaters, 2-end flanges, 3-side flanges to barrel, 4-hole for pressure sensor, 5-twin holes to form the barrel. 2. Motor power In twin screw extruders the motor power is utilized mainly to compress and shear the food dough that squeezes through various gaps in the intermeshing screws and the gap between the screws and the barrel. When dealing with a wide range of foods under different process conditions the shear resistance can vary widely because of changes in the rheological behaviour which would prevent accurate estimate of the motor power. Owing to the unknown character therefore of the novel materials a motor power was selected based on that used for similar materials in similar sized extruders with a safety margin and from exploratory trials in the Brabender extruder. Rossen and Miller (1973) give a range of specific energy consumption figures for different extruders which ranged from 0.02 to 0.10 kWh/kg. At 10kg/h throughput this gave a maximum power requirement of 1 kW while the Brabender trials tended to indicatea power requirement of about half of this value. The 2.2 kW, 3 phase AC motor used was amply capable of supplying this power plus all other drive friction losses. 3. Gear box In the co-rotating extruder the two screw shafts are driven at the same speed in the same direction. The main problem is that they are very close together. The gearbox was designed to drive two pinions, coupled to the shafts by shear pins, by using a gear wheel of more than double the width of the pinions. In this way the two pinions could ?t side by side driven simultaneously and maximise their diameter space as shown in Fig. 2. Lubricated phosphor bronze thrust bearings were used to resist the axial load generated by the material along the shaft. 2.6. Heating and temperature control Heating of the barrel to give necessary thermal input for cooking the food was done by two sets of cartridge heaters having capacities of 800 and 1200 W. The heaters were positioned in the grooves made on the top and bottom of the barrel towards the die end as shown in Fig. 3. A single temperature controller was set up together with a thermocouple to sense the temperature inside the barrel very close to die plate. Owing to the shortness of the barrel only one thermocouple was considered necessary. In an early design heaters were also used near to the feed hopper but were not used as they tended to cause premature gelatinization of the starch and blockage of the feed. 4. Pressure sensor Pressure measurements are not so important in the commercial production processes as it cannot be directly controlled to monitor the product characteristics. Neither was such a device needed as a safety measure as this was covered by an overload cut out on the electrical supply. However, in experimental work the measurement of pressure is useful to ascertain the relationship between the pressure and the other controllable parameters such as die size, temperature, moisture content and speed. In this study, a device was built using strain gauges mounted on a small cantilever beam in order to measure the pressure inside the extruder barrel (Fig. 4). A four arm strain gauge bridge was fixed at the point of maximum bending moment. The pressure was tapped from a small hole made in the die end of the barrel in which a plunger, sealed by an O-ring, actuated the cantilever beam to transmit the pressure force. The strain in the beam was detected as a voltage difference. This feature could have been used as an automatic safety cut-out but reliance was placed instead on belt slip in the initial drive stage and the motor itself had an overheating cut-out. Fig. 4. Position of pressure and temperature sensors on the extruder barrel. 1-location of strain gauges on the pressure sensor, 2-cantilever support to plunger, 3-temperature sensor. 5. Testing and evaluation A range of rice and banana mixtures were selected as being both novel yet having high potential as processed foods in Sri Lanka. These materials are cheap and common crops in most developing countries and represent an opportunity to produce an attractive, nutritious and tasty snack food. This would provide labour, utilisation of excess perishable fruits in season and a means of storing them for at least one year in appropriate packages. The main product qualities were assessed as part of the same programme and shown to be satisfactory by Gamlath (1995). The rice was prepared in the form of grits (<800 lm) and the banana was dried and milled to a similar sized powder which was mixed and flood fed from the feed hopper. Extrusion trials were carried out as given below. Sixteen combinations of variable levels were studied in two sets of experiments. In both sets the throughput was measured when the flow became stable. Initial trials indicated no significant difference in performance due to the variable pitch screws as a means of compressing the feed so all subsequent trials and the results quoted in this paper are for the fixed pitch screws. The extrudate diameter was measured using a vernier calliper immediately after extrusion and before any further drying took place which could cause some further reduction in ratio but not to affect the general result. All tests were replicated three times making 48 individual trials carried out in a fully randomised format Experiment 1 Fixed settings: Speed (N) 125 rev/min Die size (a) 5 mm diameter Variables: Barrel temperature (t) two levels (100°C and 120°C) Feed moisture content (M) four levels (15%, 20%, 25%, 30%) Experiment 2. This experiment was carried out using fixed settings of barrel temperature and the feed moisture determined in experiment 1 on the basis that maximum product expansion represented the best quality. Fixed settings: Barrel temperature (t).120°C Feed moisture content (M).15% 6. Testing and evaluation A range of rice and banana mixtures were selected as being both novel yet having high potential as processed foods in Sri Lanka. These materials are cheap and common crops in most developing countries and represent an opportunity to produce an attractive, nutritious and tasty snack food. This would provide labour, utilisation of excess perishable fruits in season and a means of storing them for at least one year in appropriate packages. The main product qualities were assessed as part of the same programme and shown to be satisfactory by Gamlath (1995). The rice was prepared in the form of grits (<800 lm) and the banana was dried and milled to a similar sized powder which was mixed and flood fed from the feed hopper. Extrusion trials were carried out as given below. Sixteen combinations of variable levels were studied in two sets of experiments. In both sets the throughput was measured when the flow became stable. Initial trials indicated no significant difference in performance due to the variable pitch screws as a means of compressing the feed so all subsequent trials and the results quoted in this paper are for the fixed pitch screws. The extrudate diameter was measured using a vernier calliper immediately after extrusion and before any further drying took place which could cause some further reduction in ratio but not to affect the general result. All tests were replicated three times making 48 individual trials carried out in a fully randomised format Experiment 1 Fixed settings: Speed (N) 125 rev/min Die size (a) 5 mm diameter Variables: Barrel temperature (t) two levels (100°C and 120°C) Feed moisture content (M) four levels (15%, 20%, 25%, 30%) Experiment 2. This experiment was carried out using fixed settings of barrel temperature and the feed moisture determined in experiment 1 on the basis that maximum product expansion represented the best quality. Fixed settings: Barrel temperature (t).120°C Feed moisture content (M).15% Table 1 Results of Experiment 1 (Die orifice diameter=5 mm, screw speed=125 rpm) Temperature (°C) Feed moisture (%) Throughput (g/s) Expansion ratio Pressure (MN/m2) 100 15 3.76 1.01 2.97 100 20 2.56 1.00 2.38 100 25 2.04 1.00 1.83 100 30 1.25 1.00 1.38 120 15 2.16 1.06 2.91 120 20 2.00 1.05 2.07 120 25 1.18 1.01 1.59 120 30 1.02 1.00 1.38 Variables: Die orifice diameter (a) two levels (3, 4 mm) Speed (N) four levels (100, 125, 150, 175 rev/min) 4. Results and discussion 4.1. Machine performance Generally the extruder performed very satisfactorily.The extrudates produced by the machine were fairly well expanded. During extrusion operations it did not become necessary to dismantle the barrel lengthways by splitting into two halves as it never seized up. In order to clean the screw and barrel the latter barrel was very easily pulled o. from the screws within a few minutes after extrusion. This was in part due to a shorter than usual barrel length. This suggests that the horizontal splitting of the barrel was not essential which would make the machining process of the barrel far easier. No serious difficulties were encountered as far as the operation of the machine is concerned, except initial feeding problems due to a temperature rise close to the feed hopper. This happened because some heaters were installed a little too close to the feed point so these were later removed and the difficulties were overcome as mentioned earlier. Many extruders have cooling facilities in this region but these were not found to be necessary. Those heaters further from the feed point and close to the die end proved to be sufficient to gelatinize the rice grits. The extrudate was observed to change from a powder at feed to a continuous, expanded extrudate at exit although quantitative assessments of the degree of gelatinization were not carried out. 7. Extruder settings and product characteristics It can be seen from Table 1 and Fig. 5 that the throughput dropped with each increase of feed moisture content at both the barrel temperatures used. When the feed moisture was increased from 15% to 30%, the throughput was reduced by 66.8% and 52.7% at 100℃ and 120℃barrel temperatures, respectively. This effect was probably caused by an increase in backflow allowed by the reduced viscosity which the increase in moisture produced. Another important observation made was the variation of product expansion with the pressure and feed moisture content. The expansion was found to be highest at the lowest moisture content with associated highest pressures (Fig. 6) and a steady reduction in both expansion ratio and pressure as moisture content increased. The product was well gelatinised but with low expansion ratio. The second series was designed to test a wider range of parameters and if possible increase the expansion ratio which was thought to depend on the die diameter. The results of Experiments 2 are tabulated in Table 2 below. Fig. 5. Throughput as a function of feed moisture content with die diameter 5 mm and screw speed 125 rev/min. Fig. 6. Pressure and expansion ratio as a function of feed moisture content at feed moisture 15%, die diameter 5 mm and screw speed 125 rev/min Fig. 7 and Table 2 show that the throughput increased with the speed due to increased rate of material conveyance. The pressure changes with screw speed was not found to be significant. The product expansion, however, showed a downward trend with the increase of speed as evident from Fig. 8. This reduction can be attributed to the reduction of pressure and lower degree of gelatinization due to reduced residence time. At settings of 125 rpm, feed moisture 15%, temperatures 120°C, die size 3 or 4 mm diameter a very acceptable product was achieved. The overall performance of the machine was found to be quite satisfactory in achieving all the parameter settings and measurements required. Each trial only lasted a few minutes in running time which was mainly spent in reaching equilibrium conditions indicated by the temperature reading but after 48 trials no significant wear was observed even though the prototype was in mild steel. Cleaning and maintenance was quick and simple and in the event of a complete seizure of the screws the barrel could be split on this machine. The gearbox was of a bolted construction to permit modifications but future designs should be welded together. The 2.2 kW motor was found to be amply capable and most of the time it only consumed about 0.5kW. No mechanical breakdowns were experienced. The prospects for use of this design in developing countries seem to be good from these experiments. Scale up to a higher capacity would bring some difficulties as discussed by Levine (1989); Singh, Smith and Frame (1998) and Yacu (1992) and although these issues were not addressed they are not considered to be insurmountable. Fig. 7. Throughput as a function of speed with feed moisture 15% and barrel temperature 120°C. Fig. 8. Pressure and expansion ratio as a function of speed with 3 mm die size, feed moisture 15% and barrel temperature 120°C. 8. Conclusions The following conclusions were made from this study. · Simplified extruders for specialised applications can successfully be made and operated in less developed countries to process local food materials. · All components can be made in an unsophisticated workshop except gears, seals, motor, temperature sensor and heaters. · Simple machining processes such as drilling and boring can be used to produce twin holed barrels to accommodate the intermeshing screws. Horizontal splitting of the barrel is not essential in this type of machine so that fabrication of the barrel for these machines can be simple enough for developing country manufacture. · A simple construction of gear box, using straight spur gears driven by a single large gear wheel is quite adequate to run the twin screws in the same direction. · An attractive and acceptable snack food was produced from the prototype machine from mixture of cereals and fruits. References Frame, N. D. (1994). The technology of extrusion cooking. Blackie Academic and Professional, London. Gamlath, G. G. S. G. (1995). Nutritional, Physico-chemical and sensory evaluation of extruded cereals with perishables. Ph.D. thesis, Cranfield University, Bedford, England. Harlow, N. (1985). Revolutionising a cereal need. Food Processing, pp. 29-30. Harper, J. M., & Jansen, G. R. (1985). Production of nutritious precooked foods in developing countries by low cost extrusion Technology. Food Review International, 1, 27± 97. Harper, J. M. (1979). Food extrusion: critical reviews in food science and nutrition. Florida: CRC press. Harper, J. M. (1992). A comparative analysis of single and twin screw extruders. In J. L. Kokini, C.-T. Ho & M. V. Karwe, Food extrusion science and technology. New York: Marcel Dekker. Hauck, B. W. (1985). Comparison of single and twin screw extruders- 2. Food Trade Review (Suppl. 5-9). Hauck, B. W., & Ben Gera (1987). Single and twin screw extruders. Milling, pp. 18±20. Jansen, G. R., & Harper, J. M. (1980). Applications of Low cost ex