薯類去皮機(jī)的結(jié)構(gòu)設(shè)計【輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計】

薯類去皮機(jī)的結(jié)構(gòu)設(shè)計【輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計】,輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計,薯類去皮機(jī)的結(jié)構(gòu)設(shè)計【輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計】,薯類,去皮,結(jié)構(gòu)設(shè)計,輕型,立式 附表三江西農(nóng)業(yè)大學(xué)畢業(yè)論文（設(shè)計）任務(wù)書論文（設(shè)計）課題名稱薯類去皮機(jī)的結(jié)構(gòu)設(shè)計學(xué)生姓名院（系）工學(xué)專業(yè)班級學(xué)生聯(lián)系方式Email 電話指導(dǎo)教師職稱教授學(xué)歷博士畢業(yè)論文（設(shè)計）要求：1、好學(xué)上進(jìn)，能吃苦耐勞，刻苦鉆研，有相應(yīng)專業(yè)知識具備獨立工作能力；2、能敏感及時地查閱到國內(nèi)外與本課題相關(guān)的資料和文件；3、會計算機(jī)繪圖，能通過計算機(jī)繪圖繪制相應(yīng)的零件、部件和組件，繪制出總裝配圖；4、總圖紙量不少于1.5張零號圖；5、工作量要符合我院畢業(yè)設(shè)計的要求；6、根據(jù)畢業(yè)設(shè)計的要求在規(guī)定的時間內(nèi)完成畢業(yè)答辯所需要的全部工作。畢業(yè)論文（設(shè)計）內(nèi)容與技術(shù)參數(shù)：第一階段：現(xiàn)場了解情況；查閱國內(nèi)外有關(guān)資料和文件分析紅薯深加工種類與加工方法，定性找到相關(guān)裝置；第二階段：研究清洗機(jī)機(jī)構(gòu)的原理，給出紅薯清洗機(jī)設(shè)備動力與傳動系統(tǒng)及其零部件的設(shè)計思想；第三階段：給出總體方案，畫出工作草圖，通過計算機(jī)繪圖繪制相應(yīng)的零件和部件，繪制出總裝配圖；第四階段：撰寫出設(shè)計說明書；根據(jù)畢業(yè)設(shè)計的要求在規(guī)定時間內(nèi)完成畢業(yè)答辯所需要的所有工作。畢業(yè)論文（設(shè)計）工作計劃：第一階段：現(xiàn)場了解情況；查閱國內(nèi)外有關(guān)資料和文件分析單元組合式傳動輸送機(jī)方法，定性找到相關(guān)裝置；第二階段：研究單元組合式傳動輸送機(jī)機(jī)構(gòu)的原理，給出單元組合式傳動輸送機(jī)力與傳動系統(tǒng)及其零部件的設(shè)計思想；第三階段：給出總體方案，畫出工作草圖，通過計算機(jī)繪圖繪制相應(yīng)的零件和部件，繪制出總裝配圖；第四階段：撰寫出設(shè)計說明書；根據(jù)畢業(yè)設(shè)計的要求在規(guī)定時間內(nèi)完成畢業(yè)答辯所需要的所有工作。接受任務(wù)日期： 2008 年 12 月 25 日要求完成日期： 2009 年 5月 12 日 學(xué) 生 簽 名： 指導(dǎo)教師簽名： 院長（主任）簽名： 2畢業(yè)論文題目學(xué)校代碼：10410 學(xué) 號：20050426本 科 畢 業(yè) 設(shè) 計題目： 輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計 學(xué) 院： 工 學(xué) 院 姓 名： 金 道 煌 學(xué) 號： 20050426 專 業(yè)： 機(jī)械設(shè)計制造及自動化 年 級： 2005級 指導(dǎo)教師： 張 廬 陵 二OO九年 五 月- 16 -輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計摘 要馬鈴薯為植物的塊莖，形狀為圓形或橢圓形，其結(jié)構(gòu)由表皮層、形成層、外果肉和內(nèi)果肉四部分。馬鈴薯品種可分兩大類，一類是淀粉含量較高的，適宜于作為生產(chǎn)淀粉的原料，另一類是蛋白質(zhì)含量較高，適宜作為蔬果或制成多種食品1。馬鈴薯營養(yǎng)豐富，除直接食用外，還可以加工成食品、全粉、淀粉等經(jīng)濟(jì)價值較高的食品，通過加工可以大幅度提高鮮薯的商品價值2。鑒于馬鈴薯的很多特點，馬鈴薯得到了廣泛的利用。a.馬鈴薯可鮮食，鮮食用馬鈴薯主要用作家庭餐館烹調(diào)，我國主要用來制作菜肴、面點小吃等大眾食品。果外除蒸烤鮮馬鈴薯作主食外，還有咖哩飯、燉薯快以及色拉涼拌菜。馬鈴薯可制成方便食品、快餐食品、休閑食品，如馬鈴薯粉、馬鈴薯全粉、脫水馬鈴薯片（條）、速凍薯條（薯泥）、蒸薯條、罐裝和去皮馬鈴薯、馬鈴薯脆片、馬鈴薯膨化小食品等；b，加工成淀粉及相關(guān)產(chǎn)品：由于馬鈴薯淀粉的優(yōu)良特性，不僅是制作高級方便面、面類最為理想的添加淀粉，而且還是肉制品、魚糜制品等的添加劑或原料。馬鈴薯淀粉也是粉條的優(yōu)質(zhì)原料。出馬鈴薯淀粉外，也可得到相關(guān)產(chǎn)品，包括各種變性淀粉、飴糖、葡萄糖、膳食纖維制品等。C,其他制品：馬鈴薯提取淀粉后的殘渣可制成馬鈴薯發(fā)酵飼料、提取蛋白等5。去皮（peeling）用于多種水果和蔬菜的加工中以除去不需要或不可食的物質(zhì)，并改善成品的外觀。主要的考慮因素包括通過盡可能減少去掉的部分以及可能降低能源、勞力和物質(zhì)成本來降低總成本。這里，介紹摩擦去皮方法：食品被放置在金剛砂滾軸上或內(nèi)壁排列著金剛砂的轉(zhuǎn)筒中，在磨損力的表面除去食品的表皮后又被大量的水沖洗干凈。該方法的優(yōu)點是由于過程是在溫室下進(jìn)行而具有的能源成本低以及資本成本低、無熱損傷，食品外觀良好的優(yōu)點，不規(guī)則食品表面（如馬鈴薯上的“孔眼”）會破壞去皮產(chǎn)品的外觀，需要手工去除3。關(guān)鍵詞：馬鈴薯、去皮清洗、農(nóng)產(chǎn)品、食品機(jī)械 Abstract Potato tuber for plants for circular or elliptic shape, structure, by cuticular layer and layer, the pulp and pulp within four parts. Potato varieties can be divided into two kinds, one kind is starch content high, suitable for the production of raw materials as starch content of protein, another kind is higher, suitable for various fruits or food.Potato nutrition is rich, besides direct edible, but also can be processed into food, powder, starch, etc, the economic value of higher food processing can be greatly improved through the value of fresh chips.In view of many of the characteristics of the potato, potato has been widely used. a. can be fresh potatoes, fresh potatoes used mainly for cooking the family restaurant, China is mainly used to create dishes such as pasta snack food of the public.In addition to fresh fruit outside the potato for food, there are curry rice, stew and potato salad cold fast food. Potatoes can be made from convenience foods, fast foods, snack foods, such as potato flour, potato powder, dehydrated potato chips (article), frozen French fries (potato mud), steamed potato chips, canned and peeled potatoes, potato crisps , extruded snacks such as potato; b, processed into starch and related products: potato starch as a result of the excellent features, not only is the production of high-level instant noodles, flour add the most ideal type of starch, but also meat, surimi products such as additives or raw materials . Potato starch is also of high quality raw materials. The potato starch, but also related products available, including a variety of modified starch, maltose, glucose, dietary fiber products. C, other products: potato residue after starch extraction can be made from potato fermented feed, extract proteinSkin peeling (for) of fruits and vegetables processing to remove need not eat or not, and improve the physical appearance of the product. The main factors including through minimize removed part and may reduce the labor and material costs energy, reduce the total cost. Here introduces friction peel method: food is placed on the walls or emery roller drum lined up in the emery, wear away the food of skin surface by the amount of water after washing clean. The advantage of this method is due process is conducted in greenhouse with low cost and the energy of capital cost is low, no heat, the advantages of good food appearance, irregular food surfaces (such as potato holes) destroys peel product appearance, need manual removal. Key words: Potatoes、Peel cleaning、Agricultural、Food machinery目錄前言- 1 -1.馬鈴薯去皮機(jī)工作原理- 2 -1.1去皮清理的原理- 2 -1.2去皮設(shè)備- 2 -2軸的設(shè)計- 4 -21軸的材料- 4 -22軸的強(qiáng)度計算- 4 -23軸的結(jié)構(gòu)尺寸初步確定- 5 -3.滾動軸承的設(shè)計- 6 -3.1.滾動軸承類型的選擇- 6 -3.2.滾動軸承部件的組合設(shè)計.- 7 -4.電動機(jī)的選擇.- 7 -5.齒輪的結(jié)構(gòu)設(shè)計- 8 -5.1.齒輪材料及熱處理- 9 -5.2.齒輪相關(guān)參數(shù)的初步確定- 9 -5.3.校核齒輪強(qiáng)度- 10 -6.圓筒的結(jié)構(gòu)設(shè)計- 12 -7.軸承座的結(jié)構(gòu)設(shè)計- 12 -8.圓盤的結(jié)構(gòu)設(shè)計- 13 -參 考 文 獻(xiàn)- 15 -致謝- 16 - 前言綜觀食品加工業(yè)對加工技術(shù)的要求，食品加工技術(shù)的發(fā)展趨勢大致如下：第一，提高原料的利用率。由于食品生產(chǎn)企業(yè)利潤較低，提高原料的利用率是企業(yè)降低生產(chǎn)成本的重要途徑。第二，提高工作效率，便于實現(xiàn)大規(guī)模生產(chǎn)。第三，營養(yǎng)性和穩(wěn)定性高，現(xiàn)在人們對食品的要求越來越高，大家都很關(guān)注食品的營養(yǎng)功效4。中國的薯類產(chǎn)量占世界總產(chǎn)量的28%，居世界第一位。近年來薯類的生產(chǎn)和加工發(fā)展十分迅速，尤其是美國、英國、德國和日本等國以發(fā)展優(yōu)質(zhì)專用化的薯類品種，先進(jìn)適用的技術(shù)裝備，高質(zhì)量的加工制品和規(guī)?；a(chǎn)經(jīng)營方式等，推動著當(dāng)今世界薯類加工業(yè)的發(fā)展。中國在薯類的種植和深加工上也加大了開發(fā)力度，形成了產(chǎn)前、產(chǎn)后良性循環(huán)的發(fā)展優(yōu)勢。尤其是加工后的薯類食品更是受到許多消費者的青睞，且在食品工業(yè)中所占的比例也越來越大2。馬鈴薯屬塊莖類作物，馬鈴薯塊莖中富含淀粉、維生素和糖，其塊莖中的主要物質(zhì)如下：（1）淀粉和糖分，馬鈴薯淀粉由直鏈淀粉與支鏈淀粉組成，糖分占馬鈴薯塊莖總質(zhì)量的1.5%左右，主要為葡萄糖、果糖、蔗糖。（2）含氮物，馬鈴薯塊莖中的含氮物包括蛋白質(zhì)和非蛋白質(zhì)兩部分，以蛋白質(zhì)為主，富含球蛋白，這是全價蛋白質(zhì)，幾乎含有所有的必需氨基酸，在營養(yǎng)上具有重要意義。（3）脂肪，在馬鈴薯塊莖中，脂肪含量為0.04%-0.94%。（4）有機(jī)酸 （5）維生素，馬鈴薯中含有多種維生素。（6）酶類，馬鈴薯中含有淀粉酶、蛋白酶、氧化酶等2。馬鈴薯深加工可制成馬鈴薯粉、淀粉以及各種風(fēng)味的休閑食品。馬鈴薯營養(yǎng)豐富，因此，對馬鈴薯進(jìn)行深加工具有重要價值。1.薯類去皮機(jī)工作原理1.1去皮清理的原理1水果及塊根、塊莖類蔬菜的外皮在加工成食品之前，大多需要除去表皮。由于原料的種類不同，皮層與果肉結(jié)合的牢固程度不同，生產(chǎn)的產(chǎn)品不同，對原料的去皮要求也各異，果蔬去皮的基本要求是去皮完全、徹底、原料損耗少。目前，果蔬加工中常用的去皮方法有機(jī)械去皮和化學(xué)去皮。機(jī)械去皮應(yīng)用較廣，既有簡易的手工去皮又有特種去皮機(jī)。按去皮原理不同可分為機(jī)械切削去皮、機(jī)械磨削去皮和機(jī)械摩擦去皮。(1)機(jī)械切削去皮 是采用鋒利的刀片表面皮層。去皮速度較快，但不完全，且果肉損失較多，一般需用手工加以修整，難以實現(xiàn)完全機(jī)械作業(yè)，適用于果大、皮薄、肉質(zhì)較硬的果蔬。目前，蘋果、梨、柿等常使用機(jī)械切削去皮，常用的形式為旋皮機(jī)。旋皮機(jī)是將待去皮的水果插在能旋轉(zhuǎn)的插軸上，靠近水果一側(cè)安裝（或手持）一把刀口彎曲的刀，使刀口貼在果面上。插軸旋轉(zhuǎn)時，刀就從旋轉(zhuǎn)的水果表面將皮車去。旋皮機(jī)插軸的轉(zhuǎn)動有手搖、腳踏和電動幾種動力形式。在旋車去皮之前應(yīng)有選果工序，以保證水果大小基本一致。(2)機(jī)械磨削去皮 是利用覆有磨料的工作面除去表面皮層?？筛咚僮鳂I(yè)，易于實現(xiàn)完全機(jī)械操作，所得碎皮細(xì)小，便于用水或氣流清除，但去皮后表面較粗糙，適用于質(zhì)地堅硬、皮薄、外形整齊的果蔬。胡蘿卜、番茄等塊根類蔬菜原料去皮大多采用機(jī)械磨削去皮機(jī)。(3)機(jī)械摩擦去皮 是利用摩擦因數(shù)大、接觸面積大的工作構(gòu)件而產(chǎn)生的摩擦作用使表皮發(fā)生撕裂破壞而被去除。所得產(chǎn)品表面質(zhì)量好，碎皮尺寸大，去皮死角少，但作用強(qiáng)度差，適用于果大、皮薄、皮下組織松散的果蔬，一般需要首先對果蔬進(jìn)行必要的預(yù)處理來弱化皮下組織。常見到的機(jī)械摩擦去皮機(jī)如采用橡膠板作為工作構(gòu)件的干法去皮機(jī)。(4)化學(xué)去皮 又稱堿液去皮，即將果蔬在一定溫度的堿液中處理適當(dāng)?shù)臅r間，果皮即被腐蝕，取出后，立即用清水沖洗或搓擦，外皮即脫落，并洗去堿液。此法適用于桃、李、杏、梨、蘋果等的去皮及橘瓣脫囊衣。桃、李、蘋果等的果皮由角質(zhì)、半纖維素等組成，果肉由薄壁細(xì)胞組成，果皮與果肉之間為中膠層，富含原果膠及果膠，將果皮與果肉連接。當(dāng)果蔬與堿液接觸時，果皮的角質(zhì)、半纖維素被堿腐蝕而變薄乃至溶解，果膠被堿水溶解而失去膠凝性，果肉薄壁細(xì)胞膜較能抗堿。因此，用堿液處理后的果實，不僅果皮容易去除，而且果肉的損傷較少，可以提高原料的利用率。但是，化學(xué)去皮用水量較大，去皮過程產(chǎn)生的廢水多，尤其是產(chǎn)生大量含有堿液的廢水。1.2去皮設(shè)備10：離心擦皮機(jī),離心擦皮機(jī)是一種小型間歇式去皮機(jī)械。依靠旋轉(zhuǎn)的工作構(gòu)件驅(qū)動原料旋轉(zhuǎn)，使得物料在離心力的作用下，在機(jī)器內(nèi)上下翻滾并與機(jī)器構(gòu)件產(chǎn)生摩擦，從而使物料的皮層被擦離。用擦皮機(jī)去皮對物料的組織有較大的損傷，而且其表面粗糙不光滑，一般不適宜整只果蔬罐頭的生產(chǎn)，只用于加工生產(chǎn)切片或制醬的原料。常用去皮機(jī)處理馬鈴薯、胡蘿卜、番茄等塊根類蔬菜原料1。 圖1-1 去皮機(jī)結(jié)構(gòu)1- 機(jī)座 2-電機(jī)安裝支座 3電動機(jī) 4主動齒輪 5從動齒輪 6軸 7軸承座 8、9、10軸承 11圓盤 12圓筒 13排污口 14卸料口去皮機(jī)（如圖1-1）由工作圓筒12、旋轉(zhuǎn)圓盤11、卸料口14、排污口13及傳動裝置等部分組成。工作圓筒內(nèi)表面是粗糙的，內(nèi)表面焊有直徑10mm的鋼棒，然后植金剛砂；圓盤采用風(fēng)扇葉片式結(jié)構(gòu)設(shè)計，采用金剛砂黏結(jié)表面，具體會在后面零件介紹中講解。圓盤這種結(jié)構(gòu)特點除兼有去皮功能外，主要用來拋起物料，當(dāng)物料從加料口落到旋轉(zhuǎn)圓盤凹凸表面時，因離心力作用被拋至圓筒壁，與筒壁粗糙表面摩擦達(dá)到去皮的目的。去皮工作時，水通過噴嘴送入圓筒內(nèi)部，卸料口的閘門由把手鎖緊，擦下的皮用水從排污口排去，已去皮的物料靠離心力的作用從打開閘門的卸料口自動排去。為了保證正常的工作效果，這種去皮機(jī)在工作時，不僅要求物料能夠完全拋起，在擦皮室內(nèi)呈翻滾狀態(tài)，不斷改變與工作構(gòu)件間的位置關(guān)系和方向關(guān)系，便于各塊物料的不同部位的表面被均勻去皮，并且要保證物料能被拋至筒壁。因此，必須保證足夠高的 圓盤轉(zhuǎn)速，同時擦皮室內(nèi)物料不得填充過多，一般選用物料充滿系數(shù)為0.50.65，依次進(jìn)行生產(chǎn)率的計算。 2軸的設(shè)計一切作回轉(zhuǎn)運動的傳動零件（例如本設(shè)計中的齒輪和圓盤），都必須安裝在軸上才能進(jìn)行運動及動力的傳遞。軸的主要功用是支承回轉(zhuǎn)零件及傳遞運動和動力。軸的設(shè)計包括結(jié)構(gòu)設(shè)計和工作能力計算兩方面的內(nèi)容。軸的結(jié)構(gòu)設(shè)計是根據(jù)軸上零件的安裝、定位以及軸的制造工藝等方面的要求合理地確定軸的結(jié)構(gòu)形式和尺寸。軸的結(jié)構(gòu)設(shè)計不合理，會影響軸的工作能力和軸上零件的工作可靠性，還會增加軸的制造成本和軸上零件裝配的困難度。軸的工作能力計算指的是軸的強(qiáng)度、剛度和振動穩(wěn)定性等方面的計算，多數(shù)情況下，軸的工作能力主要取決于軸的強(qiáng)度。21軸的材料軸的材料主要是碳鋼和合金鋼。由于碳鋼比合金鋼價廉、對應(yīng)力集中的敏感性較低，同時也可以用熱處理或化學(xué)熱處理的辦法提高其耐磨性和抗疲勞強(qiáng)度，故采用碳鋼制造軸尤為廣泛，其中最常見的是45鋼。查機(jī)械設(shè)計表11.1“軸的常用材料及其主要機(jī)械性能”，可選擇軸的材料為45鋼，熱處理方法采用正火。相關(guān)機(jī)械性能如下：毛坯直徑100mm，硬度170217HBS，抗拉強(qiáng)度極限為590M，屈服強(qiáng)度極限為295M，彎曲疲勞極限為255M。22軸的強(qiáng)度計算 進(jìn)行軸的強(qiáng)度校核計算時，應(yīng)根據(jù)軸的具體受載及應(yīng)力情況，采取相應(yīng)的計算方法，并恰當(dāng)?shù)剡x取其許用應(yīng)力。對于僅僅（或主要）承受扭矩的軸（傳動軸），應(yīng)根據(jù)扭轉(zhuǎn)強(qiáng)度條件計算。對只受扭矩或主要承受扭矩的傳動軸，應(yīng)按扭轉(zhuǎn)強(qiáng)度條件計算軸的直徑。若有彎矩作用，可用降低許用應(yīng)力的方法來考慮其影響。扭轉(zhuǎn)強(qiáng)度條件為： （1） 式中 -軸的扭轉(zhuǎn)切應(yīng)力，M； T-軸所受的扭矩，N.mm ； -軸的抗扭截面模量，m；n-軸的轉(zhuǎn)速，r/min ；p-軸所傳遞的功率，kw ；-軸的許用扭轉(zhuǎn)切應(yīng)力，M 。對實心圓軸，=/16/5，以此代入式（1），可得軸的直徑， d=c (mm)(2) c為取決于軸材料的許用扭轉(zhuǎn)切應(yīng)力的系數(shù)，其值可查機(jī)械設(shè)計表11.3“幾種軸的材料的和C值”，可得45鋼的為3040，C值為118107。在這里，取C值為116代入式子（2） 得：d 其中p等于0.50KW，n等于320r/min.所以，d=15.40 mm 考慮到軸上開鍵槽和切制螺紋，為了補(bǔ)償軸的削弱，按上式計算的軸應(yīng)適當(dāng)取大些。取軸的最小直徑為20mm。23軸的結(jié)構(gòu)尺寸初步確定 1車螺紋，與螺釘聯(lián)接，用于防止圓盤在旋轉(zhuǎn)工作時向上軸向移動。2銑鍵槽，與圓盤聯(lián)接。3與封油擋圈聯(lián)結(jié)，擋圈有防水防塵的作用，保護(hù)軸承；同時，擋圈下面壓著唇形密封圈，使?jié)櫥驮趥鲃友b置內(nèi)得到充分利用。4依次安裝深溝球軸承和單向推力球軸承，兩軸承之間裝有隔套，這樣可以保證軸承轉(zhuǎn)動而不至于摩擦力大卡死。5注意其尺寸特點，其直徑比兩端稍小12個毫米，這樣有助于軸承的安裝，同時表面粗糙度要求不高，減少加工量。6安裝深溝球軸承，也得安裝一個唇形密封圈。7聯(lián)接圓螺母，該螺母具有自鎖功能，起到固定上面深溝球軸承的作用。8銑鍵槽，與大齒輪聯(lián)接9車螺紋，與螺釘聯(lián)接，起防止從動齒輪向下移動的 3.滾動軸承的設(shè)計常用的滾動軸承絕大多數(shù)已經(jīng)標(biāo)準(zhǔn)化，并由專業(yè)工廠大量制造及供應(yīng)各種常用規(guī)格的軸承。本節(jié)將根據(jù)具體的工作條件正確選擇軸承的類型和計算所需的尺寸。滾動軸承利用滾動體將軸于外部構(gòu)件分隔開，從而用滾動摩擦代替了滑動摩擦。軸承的內(nèi)、外圈和滾動體，一般是用軸承烙鋼制造的，熱處理后，硬度一般不低于60HRC，這些元件一般都經(jīng)過150攝氏度的回火處理，所以通常當(dāng)軸承的工作溫度不高于120攝氏度時，元件的硬度不會下降10。3.1.滾動軸承類型的選擇 查機(jī)械設(shè)計表8.1“滾動軸承的主要類型、尺寸系列代號及其特征（GB/T272-93），根據(jù)本設(shè)計的結(jié)構(gòu)要求和受力情況分析，選擇一個單向推力軸承和一對深溝球軸承配合使用。（1） 單向推力球軸承.結(jié)構(gòu)簡圖、承受負(fù)荷方向： 特性：推力球軸承的套圈與滾動體多半是可分離的，單向推力球軸承只能承受單向的軸向負(fù)荷，兩個圈的孔不一樣大：內(nèi)孔較小的是緊圈，與軸配合；內(nèi)孔較大的是松圈，與機(jī)座固定在一起。極限轉(zhuǎn)速較低，適用于軸向力大而轉(zhuǎn)速較低的場合。沒有徑向限位能力，不能單獨組成支承，一般要與向心軸承組成組合支承使用。（2） 深溝球軸承.結(jié)構(gòu)簡圖、承受負(fù)荷方向：特性：主要承受徑向負(fù)荷，也可同時承受少量的雙向的軸向負(fù)荷，工作時內(nèi)外圈軸線允許偏斜-。摩擦阻力小，極限轉(zhuǎn)速高，結(jié)構(gòu)簡單，價格便宜，應(yīng)用最廣泛，但軸承沖擊負(fù)荷能力較差。3.2.滾動軸承部件的組合設(shè)計.要想保證軸承順利工作，除了正確選擇軸承類型和尺寸外，還應(yīng)正確設(shè)計軸承裝置。軸承裝置的設(shè)計主要是正確解決軸承的安裝、配合、緊固、調(diào)節(jié)、潤滑、密封等問題10。1-油封擋圈，與工作軸之間采用間隙配合。2深溝球軸承，能承受較大徑向力，只能承受較小的軸向力。3隔套，非標(biāo)準(zhǔn)件，根據(jù)設(shè)計要求選擇材料，確定尺寸。4單向推力球軸承，能承受較大軸向力，沒有徑向限位功能。5唇形密封圈，用于封油。6隔套，同3。7深溝球軸承 此外，軸承組合結(jié)構(gòu)設(shè)計要合理，保證充分的潤滑和可靠的密封，對提高軸承的壽命和保證正常工作是非常重要的。4.電動機(jī)的選擇電動機(jī)選擇要考慮多方面因素，根據(jù)電動機(jī)的功率、轉(zhuǎn)速、結(jié)構(gòu)特點、應(yīng)用場合和安裝方式，查相關(guān)資料選擇合適的電動機(jī)。查閱機(jī)械零件設(shè)計手冊相關(guān)內(nèi)容如下：Y系列（IP44）封閉式籠型三相異步電動機(jī).1） 結(jié)構(gòu)特點：采用封閉自冷式結(jié)構(gòu)，能防止任何方向的濺水對電動機(jī)的影響，一般只有一個軸伸端。2） 性能及特點：電動機(jī)效率高、耗電少、性能好、噪聲低、振動小、體積小。根據(jù)工作軸功率P=550W，轉(zhuǎn)速=320r/min,可選擇型號為Y90S-6型電動機(jī)。型號 額定功率（KW） 轉(zhuǎn)速（r/min） 電流（A） 效率（%） 功率因數(shù) 重量（kg）Y90S-6 0.75 910 2.25 72.5 0.75 23運行可靠，維修方便，絕緣等級為B級。3） 應(yīng)用場合：農(nóng)用機(jī)械、食品機(jī)械、攪拌機(jī)、磨粉機(jī)等。 根據(jù)電動機(jī)的型號，查機(jī)械手冊確定電動機(jī)的安裝方式并確定電動機(jī)的外形尺寸和安裝尺寸，然后合理地把電動機(jī)安裝在機(jī)架上。5.齒輪的結(jié)構(gòu)設(shè)計 齒輪傳動是機(jī)械傳動中最重要、應(yīng)用最廣泛的一種傳動。其優(yōu)點是：傳動效率高、工作可靠、使用壽命長、傳動比準(zhǔn)確、結(jié)構(gòu)緊湊和功率和速度使用范圍廣。齒輪傳動應(yīng)滿足如下的基本要求：1.傳動平穩(wěn)，要求瞬時傳動比不變，盡量減小沖擊、振動和噪聲，保證較高的運動精度。2.承載能力高，要求在尺寸小、重量輕的前提下，齒輪的強(qiáng)度高、耐磨性好，能達(dá)到預(yù)定的工作壽命。在齒輪設(shè)計時，只要齒輪設(shè)計合理，齒輪材料及熱處理選擇合適，制造質(zhì)量高，達(dá)到規(guī)定的制造精度，就能達(dá)到預(yù)定的功能要求。 表5-1 漸開線圓拄齒輪基本齒廓（GB/T1356-2001）7 參考機(jī)械原理第七版相關(guān)資料：標(biāo)準(zhǔn)齒輪是指m、a、均取標(biāo)準(zhǔn)值，具有標(biāo)準(zhǔn)的齒頂高和齒跟高，而且分度圓齒厚等于齒槽寬的齒輪。GB1356-88中規(guī)定分度圓壓力角的標(biāo)準(zhǔn)值為a=和分別稱為齒頂高系數(shù)和頂隙系數(shù)，GB1356-88中規(guī)定其標(biāo)準(zhǔn)值為： =1 =0.255.1.齒輪材料及熱處理由齒輪傳動的失效形式可知，設(shè)計齒輪傳動時，應(yīng)使齒面具有較高的抗磨損、抗點蝕、抗膠合等能力，而齒根要有較高的抗折斷的能力。因此，對齒輪材料性能的基本要求為：齒面應(yīng)有足夠的硬度，而齒芯要有一定的韌性。選擇45鋼，熱處理方式采用表面淬火，HRC（齒面）40-50，齒輪加工精度為9級.5.2.齒輪相關(guān)參數(shù)的初步確定根據(jù)相關(guān)設(shè)計要求和資料可初步確定齒輪的某些參數(shù)，然后對齒輪進(jìn)行齒面接觸疲勞強(qiáng)度計算和齒根彎曲疲勞強(qiáng)度計算，如果強(qiáng)度符合要求，則選用這些參數(shù)；如果強(qiáng)度不符合要求，則需再修改這些參數(shù)。1.參考機(jī)械原理，漸開線標(biāo)準(zhǔn)齒輪不發(fā)生根切是的最小齒數(shù)=，用標(biāo)準(zhǔn)齒條形刀具切制標(biāo)準(zhǔn)齒輪時，因a=及=1，則=17.2. 查機(jī)械零件設(shè)計手冊表15-2“漸開線圓柱齒輪模數(shù)（GB/T1357-1987）”，本設(shè)計可選擇模數(shù)m有：1、1.25、1.5、2、2.5、3.3.根據(jù)主動齒輪轉(zhuǎn)速（即電動機(jī)轉(zhuǎn)軸轉(zhuǎn)速）和從動軸轉(zhuǎn)速（即工作軸轉(zhuǎn)速）可確定傳動比和齒輪齒數(shù)比。=910r/min, =320r/min.在這里，取模數(shù)m=2mm. 主動齒輪齒數(shù)=25，分度圓直徑=m=50mm. 從動齒輪齒數(shù)=68，分度圓直徑=m=136mm. 取齒輪寬度系數(shù)為0.2，則有： 從動齒輪寬度=136*0.2=27.2，取=25mm. 為了防止兩齒輪因裝配后軸向稍有錯位而導(dǎo)致實際嚙合齒寬的減少，常使大齒輪（這里是從動齒輪）寬度=；小齒輪（這里是主動齒輪）寬度=+510mm 所以，主動齒輪寬度=25+5=30mm.5.3.校核齒輪強(qiáng)度齒面接觸疲勞強(qiáng)度，齒根彎曲疲勞強(qiáng)度.下面設(shè)計過程中，所查的圖、表均可以查閱機(jī)械設(shè)計.a.確定許用應(yīng)力 查圖6.14，得=1100 M；查圖6.15，得=300 M， 查表6.5，得=1.1，=1.5，u=/=68/25=2.72 N=60J 式中為齒輪轉(zhuǎn)速.r/min,J為每轉(zhuǎn)一圈時同一齒面的嚙合次數(shù)；為齒輪的工作壽命.h; 所以，=60*910*1*5*12*250=8.19* =/u=8.19*/2.72=3.01* 查圖6.16，得=1，查圖6.17得=1. =1000 M， =300*2*1/1.5=400 M，b.驗算齒面接觸疲勞強(qiáng)度條件. 計算工作轉(zhuǎn)矩： T=9.55*=9.55*=7870.88 Nmm 確定載荷系數(shù)K：由表6.2查得=1.5；由9級齒輪精度，取=1.32；由硬齒面，非對稱布置，取=1.2，=1.1則K=1.5*1.32*1.2*1.2=2.61 查圖6.12，得=2.5；查表6.3，得=188.0，因齒數(shù)較少，取=0.86所以，=2.5*188.0*0.68 =621.85 M齒面接觸疲勞強(qiáng)度滿足要求.c.驗算齒根彎曲疲勞強(qiáng)度條件查表6.4得，=2.62，=1.59，=2.24，=1.75，取=0.82，則：=*2.62*1.59*0.82=82.54 M1000 M，=*/=81.24 M1000 M，兩齒輪的齒根彎曲疲勞強(qiáng)度均滿足要求?？偨Y(jié)：齒輪傳動設(shè)計的主要內(nèi)容包選擇齒輪材料和熱處理、確定精度等級和主要參數(shù)。設(shè)計過程是先由設(shè)計準(zhǔn)則確定強(qiáng)度條件，再由強(qiáng)度條件確定齒輪的大?。ǚ侄葓A直徑或模數(shù)），并可進(jìn)一步計算出多組能滿足強(qiáng)度條件的齒輪主要幾何尺寸。根據(jù)設(shè)計要求，從多組齒輪參數(shù)中選擇較優(yōu)秀的作為最終的齒輪參數(shù)。最后設(shè)計出齒輪的結(jié)構(gòu)，并繪制齒輪的零件工作圖。 每次機(jī)械設(shè)備結(jié)構(gòu)的設(shè)計都是在以前該類設(shè)備結(jié)構(gòu)上的技術(shù)升級，在參考以前同類設(shè)備的結(jié)構(gòu)特點的同時，在某些零件或在某些技術(shù)環(huán)節(jié)上加上自己的創(chuàng)新點，使自己設(shè)計后的產(chǎn)品在同類產(chǎn)品中更具有技術(shù)上、價格上的競爭力。下面將介紹本設(shè)計中，在三個零件上于以往同類機(jī)械設(shè)備的不同處。6.圓筒的結(jié)構(gòu)設(shè)計 圖6-1 圓筒的結(jié)構(gòu)1-不銹鋼棒 2圓筒壁 3與法蘭聯(lián)接部分 4、5圓筒蓋組件圓筒的結(jié)構(gòu)特點主要體現(xiàn)在內(nèi)壁，內(nèi)壁均勻地焊接二十個直徑為10mm的不銹鋼棒，然后在整個圓筒內(nèi)壁植金鋼砂（包括在不銹鋼棒上），這種結(jié)構(gòu)特點更有利于對農(nóng)產(chǎn)品的去皮，特別是對薯類農(nóng)產(chǎn)品。第一，由于不銹鋼棒的存在，物料在圓筒內(nèi)旋轉(zhuǎn)時會不斷的翻滾，這樣，就能對物料各個面進(jìn)行去皮，達(dá)到均勻去皮的效果。第二，對于像薯類這樣的農(nóng)產(chǎn)品，由于有些地方凹凸，在去皮工作時就有死點，往往有些地方?jīng)]有去皮，對于要求高的去皮效果，就要采用手工去皮的方法來處理這些死點，而采用不銹鋼棒焊接內(nèi)壁，當(dāng)薯類農(nóng)產(chǎn)品在翻滾去皮工作時，當(dāng)凹進(jìn)去的地方剛好碰到直徑為10毫米的不銹鋼棒，照樣可以達(dá)到良好的去皮效果。圓筒與清理槽之間采用法蘭聯(lián)接。值得注意的是，圓筒蓋組件和不銹鋼棒都是焊接在圓筒上，而且圓筒壁上要開卸料口。筒蓋組件和不銹鋼棒焊接時，應(yīng)先把它們都擺好在其焊接的位置，同時焊接，這樣做可以使焊接后變形均勻而且變形量小；再者，應(yīng)先焊接好圓筒蓋組件和不銹鋼棒之后，再在筒壁上開卸料口，如果先開卸料口再焊接，會使圓筒變形量增大、變形不均勻和應(yīng)力不均勻，這樣，影響圓筒零件的質(zhì)量。7.軸承座的結(jié)構(gòu)設(shè)計軸承座在設(shè)計中是至關(guān)重要的一部分，它是整個機(jī)械設(shè)備的傳動部分，軸承座結(jié)構(gòu)設(shè)計的合不合理會影響設(shè)備的傳動精度，此設(shè)計中，將整個傳動部分，包括軸承座、軸承、齒輪以及密封圈可組裝在一起，做一個單獨的零件使用，這種設(shè)計可使整個傳動部分更加牢靠地結(jié)合在一起，而且便于拆卸。 圖7-1 軸承座 圖7-2 軸承座總成圖7-1表示了軸承座的尺寸和結(jié)構(gòu)特點，圖7-2表示了軸承座與轉(zhuǎn)動軸、軸承、從動齒輪及密封圈等的裝配和關(guān)系。軸承座總成可以看做一個單獨的零件安裝在清理槽上，這種結(jié)構(gòu)便于安裝、拆卸，而且結(jié)構(gòu)緊湊，在傳動工作時傳動平穩(wěn)、振動小、噪聲小。圖7-2中，9表示潤滑油口。8.圓盤的結(jié)構(gòu)設(shè)計圓盤的結(jié)構(gòu)特點決定圓盤的作用，在設(shè)計中要求圓盤能夠有去皮功能外，還要有拋起物料的作用，當(dāng)物料從加料口進(jìn)入圓盤內(nèi)后，物料首先落到圓盤上，圓盤隨著工作軸轉(zhuǎn)動，物料也在圓盤上旋轉(zhuǎn)翻滾，采用怎樣的圓盤結(jié)構(gòu)才能使物料在圓盤上旋轉(zhuǎn)的同時可以被拋起呢？這里可以模仿風(fēng)扇葉片式結(jié)構(gòu)。 圖8-1 圓盤如上圖所示，圓盤由三部分焊接而成，圓盤上表面都是金鋼砂黏結(jié)表面，有去皮的功能，起拋起物料作用的是上面的凹凸葉片式結(jié)構(gòu)，在旋轉(zhuǎn)工作時，物料順著向上的面拋起。 參 考 文 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2006中文版實用教程M，大連理工大學(xué)出版社，2006.致謝值此論文完成之際，謹(jǐn)向在課題研究和論文撰寫過程中指導(dǎo)和幫助過我的老師和同學(xué)們致以誠摯的謝意。本文是在導(dǎo)師張廬陵老師細(xì)致的指導(dǎo)和嚴(yán)格的要求下完成的。導(dǎo)師以深厚的理論功底和過人的科研智慧為學(xué)生指明了設(shè)計方向，傳授給學(xué)生科學(xué)研究的方法，并且嚴(yán)格細(xì)致地糾正我設(shè)計中的疏漏之處，而他們身先士卒的實干精神和一絲不茍的治學(xué)態(tài)度更是令我由衷的敬佩。在論文寫作期間，無論在文字和內(nèi)容上，導(dǎo)師都給了精心的指導(dǎo)，學(xué)生受益匪淺。在此，學(xué)生向?qū)煴硎局孕牡母兄x并致以最深的謝意。在論文完成過程中，還得到過涂敏、羅星、裴小斐、肖健等同學(xué)的幫助，在此表示衷心的感謝，感謝同學(xué)們在理論知識、設(shè)計材料上給予的方便和建議。最后向關(guān)心和支持我的設(shè)計和論文工作的朋友們表示衷心的感謝。金道煌于江西農(nóng)業(yè)大學(xué) 2009年5月 輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計輕型立式薯類去皮機(jī)結(jié)構(gòu)設(shè)計 設(shè)計者：設(shè)計者：金道煌金道煌 指導(dǎo)老師：指導(dǎo)老師：張廬陵張廬陵 班班 級：級：機(jī)制機(jī)制052052班班 學(xué)學(xué) 號：號：2005042620050426去皮機(jī)的設(shè)計程序去皮機(jī)的設(shè)計程序去皮機(jī)的工作原理去皮機(jī)的工作原理創(chuàng)新設(shè)計點創(chuàng)新設(shè)計點圓筒的機(jī)構(gòu)設(shè)計圓筒的機(jī)構(gòu)設(shè)計圓盤的結(jié)構(gòu)設(shè)計圓盤的結(jié)構(gòu)設(shè)計軸承座的結(jié)構(gòu)設(shè)計軸承座的結(jié)構(gòu)設(shè)計去去皮皮機(jī)機(jī)工工作作原原理理示示意意圖圖1 1底座底座 2 2電機(jī)安裝支座電機(jī)安裝支座 3 3電動機(jī)電動機(jī) 4 4主動齒輪主動齒輪 5 5從動齒輪從動齒輪 6 6軸承座軸承座 7 7清理槽清理槽 8 8、9 9、1010軸承軸承 1111圓盤圓盤 1212 圓筒圓筒 1313排污口排污口 1414卸料口卸料口創(chuàng)新設(shè)計思想創(chuàng)新設(shè)計思想 我設(shè)計的去皮機(jī)對某些關(guān)鍵零件和傳動裝置進(jìn)行了合理地改進(jìn)，例如對圓筒和圓盤的結(jié)構(gòu)改進(jìn)、對傳動裝置的改進(jìn)，大大提高了去皮效果，而且去皮均勻，以往難去皮的凹面也得到了很好的去皮，該設(shè)備具有適用范圍廣，效率高，能耗低，堅固耐用，價格低廉。圓筒的設(shè)計圓筒的設(shè)計相比以前去皮機(jī)結(jié)構(gòu)，該圓筒的特點在于：圓相比以前去皮機(jī)結(jié)構(gòu)，該圓筒的特點在于：圓筒的內(nèi)壁均勻地焊接20根直徑為10mm的不銹鋼棒，而且筒的內(nèi)壁（包括不銹鋼棒）是金鋼砂黏結(jié)表面，這種結(jié)構(gòu)可以提高去皮的工作效率，而且對薯類農(nóng)產(chǎn)品凹表面也能達(dá)到很好的去皮效果，解決了以往還要手工去凹面皮層的問題。圓盤設(shè)計圓盤設(shè)計 在去皮機(jī)中，圓盤是個重要零件，它不僅要具備去功能，而且要求它獨特的結(jié)構(gòu)能夠在旋轉(zhuǎn)工作時將物料拋起，從而使物料與圓筒內(nèi)壁接觸，達(dá)到進(jìn)一不的去皮效果，所以，采用什么樣的圓盤結(jié)構(gòu)能達(dá)到這兩點是圓盤設(shè)計中至關(guān)重要的一點。本設(shè)計，模仿風(fēng)扇葉片式結(jié)構(gòu)，來設(shè)計了一個合理的圓盤。具體結(jié)構(gòu)如下：圓盤結(jié)構(gòu)簡圖圓盤是焊接件，與軸聯(lián)接，上表面是工作面，上表面是金鋼砂黏結(jié)表面，葉片式薄鋼具有去皮的作用外，還能很好地把物料向上拋起。軸承座的結(jié)構(gòu)設(shè)計軸承座的結(jié)構(gòu)設(shè)計 軸承座是安裝軸承、軸、及軸類零件的裝置，往往軸承座是機(jī)械設(shè)備很重要的傳動部分。軸承安裝在軸承座上、軸安裝在軸承上、齒輪安裝在軸承上，這些都要考慮很精確地安裝尺寸，同是還要考慮密封問題、潤滑問題及各類組件使用、安裝問題。對于很重要的傳動部分，要求結(jié)構(gòu)緊湊、傳動平穩(wěn)。本設(shè)計中設(shè)計的軸承座與軸承、軸等零件安裝后可做為一個整體，便于拆卸，而且結(jié)構(gòu)緊湊。具體，如下頁圖。軸承座軸承座總成請各位老師批評指正！請各位老師批評指正！謝謝 謝！謝！A simplified twin screw co-rotating food extruder: design, fabrication and testingS.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 LankaDepartment of Postharvest Technology, School of Agriculture, Food and Environment, SilsoeCollage, Cranfield University, Silsoe, Bedfordshire MK45 4DT,UKReceived 6 July 1998; accepted 10 February 1999AbstractA 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 themachine 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 120C, 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 mixturesNomenclaturea Die diameter (mm)B Channel width (mm)C Screw circumference (mm)d Screw core diameterD Outer diameter of screws (mm)H Flight depth (mm)M Moisture content (% wet basis)n Number of fight turnsN 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.clarkecran-eld.ac.uk0260-8774/99/$ see front matter1999 Elsevier Science Ltd. All rights reserved.PII: S 0 2 6 0 - 8 7 7 4 ( 9 9 ) 0 0 0 4 9 71. IntroductionExtrusion 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-ange 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 powerIn 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 boxIn 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 controlHeating 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 sensorPressure 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 evaluationA 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 ofvariable 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 formatExperiment 1Fixed settings:Speed (N) 125 rev/minDie size (a) 5 mm diameterVariables:Barrel temperature (t) two levels (100C and 120C)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).120CFeed moisture content (M).15%6. Testing and evaluationA 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 ofvariable 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 formatExperiment 1Fixed settings:Speed (N) 125 rev/minDie size (a) 5 mm diameterVariables:Barrel temperature (t) two levels (100C and 120C)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).120CFeed moisture content (M).15%Table 1Results 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 1.38Variables:Die orifice diameter (a) two levels (3, 4 mm)Speed (N) four levels (100, 125, 150, 175 rev/min)4. Results and discussion4.1. Machine performanceGenerally 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 feedingproblems 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 characteristicsIt 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 120barrel 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/minFig. 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 120C, 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 120C.Fig. 8. Pressure and expansion ratio as a function of speed with 3 mm die size, feed moisture 15% and barrel temperature 120C.8. ConclusionsThe 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, temperaturesensor 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 ofmachine 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.ReferencesFrame, 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 extrusionTechnology. 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. 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