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編號(hào)
無錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
相關(guān)資料
題目： 同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)及擠壓部件設(shè)計(jì)
信機(jī) 系 機(jī)械工程及自動(dòng)化專業(yè)
學(xué) 號(hào)： 0923081
學(xué)生姓名： 陳 玉
指導(dǎo)教師： 戴寧（職稱：副教授 ）
（職稱： ）
2013年5月25日
目 錄
一、畢業(yè)設(shè)計(jì)（論文）開題報(bào)告
二、畢業(yè)設(shè)計(jì)（論文）外文資料翻譯及原文
三、學(xué)生“畢業(yè)論文（論文）計(jì)劃、進(jìn)度、檢查及落實(shí)表”
四、實(shí)習(xí)鑒定表
無錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
開題報(bào)告
題目： 同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)及擠壓部件設(shè)計(jì)
信機(jī) 系 機(jī)械工程及自動(dòng)化 專業(yè)
學(xué) 號(hào)： 0923081
學(xué)生姓名： 陳 玉
指導(dǎo)教師： 戴寧 （職稱：副教授）
（職稱： ）
課題來源
自擬課題
科學(xué)依據(jù)（包括課題的科學(xué)意義；國(guó)內(nèi)外研究概況、水平和發(fā)展趨勢(shì)；應(yīng)用前景等）
（1）課題科學(xué)意義
擠壓加工技術(shù)作為一種經(jīng)濟(jì)實(shí)用的新型加工方法廣泛應(yīng)用于食品生產(chǎn)中，并得到迅速發(fā)展。采用擠壓技術(shù)來加工食品，只要簡(jiǎn)單地更換擠壓模具，便可以很方便地改變產(chǎn)品造型。
擠壓研究?jī)?nèi)容包括原料經(jīng)擠壓后微觀結(jié)構(gòu)及物理化學(xué)性質(zhì)的變化，擠壓性能及原料本身特性對(duì)產(chǎn)品質(zhì)量的影響等，為擠壓技術(shù)在新領(lǐng)域的開發(fā)應(yīng)用奠定了基礎(chǔ)。擠壓機(jī)有多種機(jī)型，本文主要研究螺桿擠壓機(jī)，它主要由一個(gè)機(jī)筒和可在機(jī)筒內(nèi)旋轉(zhuǎn)的螺桿等部件組成。
螺桿擠壓機(jī)按螺桿數(shù)量分為單螺桿擠壓機(jī)和雙螺桿擠壓機(jī)兩大類。單螺桿與雙螺桿擠壓機(jī)的主要差別是其中物料的允許水分范圍以及加工能力的差別應(yīng)是最值得注意的方面。本文主要研究雙螺桿擠壓機(jī)。雙螺桿擠壓機(jī)是多螺桿擠壓機(jī)中的一種，是在單螺桿擠壓機(jī)的基礎(chǔ)上發(fā)展起來的。在雙螺桿擠壓機(jī)的機(jī)筒中，并排安放兩根螺桿，故稱雙螺桿擠壓機(jī)。
雙螺桿擠壓機(jī)按螺桿方向不同，可分為同向旋轉(zhuǎn)和反向旋轉(zhuǎn)兩大類，本文主要研究同向雙螺桿擠壓機(jī)。同向旋轉(zhuǎn)相較反向旋轉(zhuǎn)，其優(yōu)越性是很明顯的，但這并非說同向旋轉(zhuǎn)不存在問題。首先是推送效率問題，反向旋轉(zhuǎn)式螺桿的擠壓建立在類似于齒輪泵的原理上，物料在雙螺桿內(nèi)的流動(dòng)不是由于摩擦牽引作用，而是因?yàn)闄C(jī)械的強(qiáng)制推送，物料能均勻分配給兩螺桿，所以推送效率高。但雙螺桿同向旋轉(zhuǎn)式，按螺桿旋轉(zhuǎn)方向，物料只送往螺桿轉(zhuǎn)向端，物料分布偏向一方，其推送性只及反向旋轉(zhuǎn)的一半左右。
（2）擠壓機(jī)的研究狀況及其發(fā)展前景
與傳統(tǒng)生產(chǎn)工藝相比，擠壓加工極大地改善了谷物食品的加工工藝，縮短了
工藝過程，豐富了谷物食品的花色品種，降低了產(chǎn)品的生產(chǎn)費(fèi)用，減少了占地面積，大大降低了勞動(dòng)強(qiáng)度，同時(shí)也改善了產(chǎn)品的組織狀態(tài)和口感，提高了產(chǎn)品質(zhì)量。
本世紀(jì)30年代末期，首次把擠壓機(jī)應(yīng)用于方便食品谷物的生產(chǎn)中，1936年第一臺(tái)應(yīng)用于谷物加工的單螺桿擠壓蒸煮機(jī)問世，并在行業(yè)中取得成功。40年代末期，隨著擠壓技術(shù)的發(fā)展，擠壓機(jī)的應(yīng)用在食品領(lǐng)域中進(jìn)一步擴(kuò)大，深受歡迎。50年代初，迅速發(fā)展的擠壓蒸煮由于省時(shí)省力，很大程度上取代了當(dāng)時(shí)的餅干焙烤。利用擠壓技術(shù)處理淀粉等，取得了較好的糊化效果。60年代中期，擠壓機(jī)進(jìn)一步發(fā)展完善，到了70年代，許多國(guó)家紛紛展開擠壓機(jī)理的探討，進(jìn)一步研究各種谷物及蛋白類食物在擠壓過程中發(fā)生的一系列變化。目前美國(guó)生產(chǎn)的大型擠壓機(jī)生產(chǎn)能力已達(dá)每小時(shí)幾頓至十幾噸，擠壓產(chǎn)品遍及全國(guó)各地及食品業(yè)和飼料業(yè)，有關(guān)擠壓技術(shù)和設(shè)備的專利已達(dá)百余份。日本長(zhǎng)期以來對(duì)擠壓技術(shù)及理論，尤其是谷物膨化淀粉的性質(zhì)方面做了大量的研究。1979年生產(chǎn)的擠壓食品就有300多種，大規(guī)模地把擠壓技術(shù)應(yīng)用于快餐食品及飼料生產(chǎn)工業(yè)中。西方許多國(guó)家如英國(guó)，法國(guó)，德國(guó)，意大利，瑞士等對(duì)擠壓技術(shù)也做了大量的研究。近年來，國(guó)外擠壓食品已成為一大類方便食品。
量的研究。近年來，國(guó)外擠壓食品已成為一大類方便食品。
隨著人民生活水平的提高和飲食結(jié)構(gòu)的變化，隨著對(duì)擠壓機(jī)理研究的不斷深入和新型擠壓設(shè)備的研制開發(fā)，擠壓食品的品種和產(chǎn)量將會(huì)日益增多，并朝著高效節(jié)能，產(chǎn)品風(fēng)味多樣化和美味化方向發(fā)展。
（3）同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)的研究狀況及發(fā)展前景
雙螺桿擠壓技術(shù)近幾年發(fā)展迅速。研究表明,與單螺桿擠出技術(shù)相比,雙螺桿擠出技術(shù)具有無法比擬的優(yōu)越性能,如物料能充分、徹底混合揉捏,并且在雙螺桿擠出機(jī)運(yùn)轉(zhuǎn)時(shí),由于雙螺桿互相嚙合而具有自行擦凈的功能,避免了單螺桿擠出機(jī)經(jīng)常出現(xiàn)的螺桿堵塞的物料在套筒表面產(chǎn)生結(jié)焦的現(xiàn)象。同時(shí)雙螺桿擠壓機(jī)還具有廣泛的原料適應(yīng)性這一顯著優(yōu)點(diǎn),解決了單螺桿擠壓機(jī)無法處理高水分和高脂肪物料這一瓶頸。雙螺桿擠出機(jī)因其具有突出的高效工作性能,受到了食品行業(yè)的廣泛重視。作者根據(jù)收集的相關(guān)文獻(xiàn),對(duì)雙螺桿擠壓機(jī)在食品工業(yè)中的應(yīng)用、雙螺桿擠壓加工對(duì)食品中營(yíng)養(yǎng)成分的影響、雙螺桿擠壓技術(shù)的發(fā)展前景等進(jìn)行綜合的分析和論述,期望有益于我國(guó)雙螺桿食品擠壓蒸煮的研究與發(fā)展。
食品成分十分復(fù)雜,通常是若干種原料混合在一起加工,進(jìn)入擠出機(jī)的物料更是由多種復(fù)雜多變的生物高分子混合構(gòu)成,而且,食品擠壓過程往往或高或低地伴隨著一定量的水分進(jìn)行,構(gòu)成所謂的低濕擠壓加工和高濕擠壓加工。兩種水分含量不同的擠壓蒸煮加工,對(duì)擠壓系統(tǒng)運(yùn)行的影響也有極大差別,因此雙螺桿擠壓機(jī)在物理模型建立和數(shù)學(xué)模型求證方面存在困難,這也是擠壓技術(shù)面臨的最大問題。這一問題的解決,將會(huì)大大提高雙螺桿擠壓技術(shù)的研究水平。從世界食品發(fā)展潮流看,擠壓食品占有重要地位。由于它能為消費(fèi)者提供色、香、味、營(yíng)養(yǎng)俱全的食品,是其它食品加工手段不可比擬的。發(fā)達(dá)國(guó)家已把蒸煮擠壓食品單列為一大類食品,并在保健食品擠壓技術(shù)、功能性食品擠壓技術(shù)、超臨界流體擠壓技術(shù)、米粉擠壓技術(shù)、點(diǎn)心與早餐等即食谷類食品加工、擠壓太空食品等方面開展了廣泛深入的研究。我國(guó)在這一新興領(lǐng)域也開展了一些研究工作,但尚缺乏深度及廣度。因此從事該領(lǐng)域的研究將大有作為。目前有關(guān)雙螺桿擠壓膨化機(jī)在水產(chǎn)飼料加工中的報(bào)道很多。但對(duì)有關(guān)魚肉雙軸擠出組織化的研究尚缺乏系統(tǒng)性。水產(chǎn)品不但將成為人們攝取動(dòng)物蛋白質(zhì)的主要來源之一,而且也可以緩解人增地減、食品不足、優(yōu)質(zhì)蛋白質(zhì)缺乏的問題。利用雙螺桿擠壓技術(shù)研究開發(fā)低值水產(chǎn)資源,將具有顯著的綜合效益。
擬采取的研究方法、技術(shù)路線、實(shí)驗(yàn)方案及可行性分析
擬研究方法、技術(shù)路線：
根據(jù)課題所確定的擠壓機(jī)種類，用途及生產(chǎn)能力確定和面機(jī)的主要構(gòu)件（例如螺桿，機(jī)筒）機(jī)構(gòu)形式和尺寸參數(shù)，運(yùn)動(dòng)參數(shù)及動(dòng)力參數(shù)（電機(jī)功率）。
根據(jù)擠壓機(jī)主要構(gòu)件的形式，性質(zhì)及運(yùn)動(dòng)參數(shù)，擬定整機(jī)的機(jī)械傳動(dòng)鏈和傳動(dòng)系統(tǒng)圖。計(jì)算并確定各級(jí)傳動(dòng)的傳動(dòng)比，皮帶轉(zhuǎn)動(dòng)，齒輪轉(zhuǎn)動(dòng)等傳動(dòng)構(gòu)件的結(jié)構(gòu)參數(shù)及尺寸，擬定機(jī)器的結(jié)構(gòu)方案圖。
根據(jù)結(jié)構(gòu)方案圖，在正式圖紙上擬定傳動(dòng)構(gòu)件及執(zhí)行構(gòu)件的位置，然后依次進(jìn)行執(zhí)行構(gòu)件及傳動(dòng)系統(tǒng)設(shè)計(jì)機(jī)體，操縱機(jī)構(gòu)設(shè)計(jì)，密封及潤(rùn)滑的結(jié)構(gòu)設(shè)計(jì)。
研究計(jì)劃及預(yù)期成果
研究計(jì)劃：
2012年10月12日-2012年12月31日：按照任務(wù)書要求查閱論文相關(guān)參考資料，完成畢業(yè)設(shè)計(jì)開題報(bào)告書。
2013年1月1日-2013年1月27日：學(xué)習(xí)并翻譯一篇與畢業(yè)設(shè)計(jì)相關(guān)的英文材料。
2013年1月28日-2013年3月3日：畢業(yè)實(shí)習(xí)。
2013年3月4日-2013年3月17日：同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)的主要參數(shù)計(jì)算與確定。
2013年3月18日-2013年4月14日：同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)總體結(jié)構(gòu)設(shè)計(jì)。
2013年4月15日-2013年4月28日：部件圖和零件圖設(shè)計(jì)。
2013年4月29日-2013年5月20日：畢業(yè)論文撰寫和修改工作。
預(yù)期成果：
根據(jù)提供的主要構(gòu)件參數(shù)而計(jì)算出的傳動(dòng)構(gòu)件的參數(shù)，尺寸及機(jī)體等是合理的，可以進(jìn)行正常的生產(chǎn)組裝，最終達(dá)到同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)的工作要求。
特色或創(chuàng)新之處
機(jī)器操作噪音小。故障率低，使用壽命長(zhǎng)。
已具備的條件和尚需解決的問題
1、設(shè)計(jì)方案思路已經(jīng)非常明確，已經(jīng)具備使用CAD制圖的能力和了解同向旋轉(zhuǎn)型雙螺桿擠壓機(jī)原理結(jié)構(gòu)等知識(shí)。
2、使用CAD制圖能力尚需加強(qiáng)，結(jié)構(gòu)設(shè)計(jì)能力尚需加強(qiáng)。
指導(dǎo)教師意見
指導(dǎo)教師簽名：
年 月 日
教研室（學(xué)科組、研究所）意見
教研室主任簽名：
年 月 日
系意見
主管領(lǐng)導(dǎo)簽名：
年 月 日
英文原文
Mixing effects of constituting elements of mixing screws in single andtwin screw extruders
D.J. van Zuilichem, E. Kuiper, W. Stolp, T. Jager
Department of Food Technology and Nutritional Sciences, Wageningen Agricultural Uniíersity, Food and Bioprocess Engineering Group, P.O. Box 8129,
Bomenweg 2, 6700 EV Wageningen, Netherlands
Received 21 April 1998; accepted 29 March 1999
Abstract
In extrusion, mixing of solids and melts has always been problematic, leading to diverse models describing the melting process. It isfound that for foods based on cereals, only a few are valid, due to the simultaneous presence of water and high viscous non-Newtonian material. Mixing trials are summarised for single and twin screw extruders, with particulate solids of different particle sizes like, maizegrits, wheat flour, sucrose crystals and glucose syrup. Special mixing-heads for single screw extruders like, pineapple-heads, and slottedflight sections for counter-rotating twin screw extruders are investigated. The effects of screw geometry on mixing has been measured using co-rotating twin screw extruder modular elements like: single lead elements, mixing paddles and reversed pitch elements in a translucent model extruder by means of a study of flow phenomena and residence time distribution RTD measurements. Mixing effects are reported and their influences on viscous dissipation, residence time, curve spread and stagnancy are explained. 1999 Elsevier Science S.A. All rights reserved.
Keywords: Single screw extruders; Twin screw extruders; Mixing
1. Introduction
Part of the definition of food extrusion cooking is thatthe food material on its way through the open channel of a single screw extruder s.s.e. , is sheared, mixed and com-pressed. In the case of a twin screw extruder t.s.e. With closely intermeshing screws, the food is transported in so-called C-shaped chambers, which are enclosed by the neighbouring intermeshing screw and the barrel wall see Fig. 1 .The food powder is taken up at the feed port in the C-shaped chamber of one screw, is conveyed, internally mixed, forced through the gaps and clearances of this screw or eventually transferred to the neighbouring screw and finally this C-shaped chamber delivers its content at wx the die 13,23 . The differences in the way of operation between s.s.e.’s and t.s.e.’s are obvious and each of them will ask for its own design of modular screw parts that will enhance and improve the mixing effects of the screws wx 14,17 .Mixing operations in cooking extruders can be distin-guished in three different types: the first one is coarse mixing or longitudinalraxial mixing. The second one is dispersive mixing or comminution of the disperse phase.The third one is distributive mixing or radial mixing. The operative mechanism to realise coarse mixing is the rota-tional movement of the screws, causing residence time distribution RTD . In case of plug flow however, there will be no coarse mixing. These different mechanisms are responsible for the mixing effects. For dispersive mixing the function of the comminution is to break agglomerates
of the disperse phase into smaller ones. The operative mechanism is the existence of elongational forces andror shear stresses. Distributive mixing is caused by the action of a screw element, distributing the concentration of the disperse phase over the total volume of the chamber or channel of the extruder cross-section in such a way that the concentration of the disperse phase in each volumetric element equals the averaged concentration. This require- ment is stricter when the elementary volume to be consid-ered is smaller. Although totally different, the three mech-anisms described are not independent of each other. The anisms described are not independent of each other. The three types of mixing should therefore be carefully distinguished. It is possible to design screws with mixing elements on different locations, provoking a certain combination of the three mixing types at a certain axial location.The possibilities of these combinations are strongly dependent of extruder geometry, properties of food materials and properties under extrusion conditions. Although a lot of knowledge is gathered concerning the use of well-known mixing elements from the plasticating industry, incorporation of this knowledge into designs of s.s.e.’s and t.s.e.’s are not always successful for food products and other biopolymers. There are several reasons for this phenomenon. The first disturbing factor when comparing plastic polymers with biopolymers is the difference in feed to the extruder, e.g., the presence of multiple solids, water and eventually vegetable oil in the case of biopolymers.Secondly, biopolymers do not have a well-defined melt-index like many chemical polymers and in general theirviscosity behaviour differs from that of chemical polymers wx 1 . Thirdly, there are a number of degradation reactions of irreversible nature occurring simultaneously when a biopolymer is subjected to a temperature and stress field in an extruder, changing the physical and chemical properties wx drastically from location to location 15 . In this field numerous papers have been published by well-known au-
thors from research institutions like CAFTrRutgers university, IFR Norwich, INRA, CEMEF France. The aim of this article is summarising the possibilities and solutions for mixing problems for single screw and counter-rotating twin screw extruders and giving better insight in the functions of screw elements in co-rotating twin screw extruders.
2. Mixing mechanisms
2.1. Longitudinal or axial mixing
When food particles during their lifetime in an extruder are subjected to axial mixing, this can be seen and measured by a changing RTD. Extremes in this case are plug flow, where all particles have the same residence time, or a wide RTD which is caused by axial mixing. Some particles will stay in the extruder cooker for a process time shorter than the average, whilst others will dwell for much longer than the average when different flow systems are compiled see Fig. 2 . Fig. 3 shows the theoretical RTD for a material with a coefficient ns1 in the power-law equation for the shear dependency of the viscosity in an s.s.e.This figure also shows the RTD data, measured when
processing corn grits in a Battenfeld s.s.e. at two moisture y1 . contents v s0.142, 0.20 kg kg and screw revolu- w y1 wx tions ranging from Ns1.33, 1.66, 2.0 rev s 22 . The RTD data are represented as an ‘cumulative exit age’ or F-function, which shows the fraction F of the inflow,
wx which has left the extruder after t seconds 3,4,16 . The E-function, the derivative of the F-function, shows the so-called ‘exit age’ distribution of food particles, fed into the extruder at an infinite small time and is related to the F-function with: t Ft s Et dt 1 H 0 The average residence time t of the food material in the cooking extruder is calculated with: ts tE t dt .2 H When the F-function in Fig. 3 is observed, it follows that most of the corn grits have an exit age between t and t , 0 whereas t (3r4t . These measurements show that for a 0 single screw extruder there is a strong influence of the moisture content and the number of revolutions of the screw on the shape of the F-function and the breakthrough wx point 3 .The operating principle of twin screw extruders can be described with the existence of two parallel series of Continuously Stirred Tank Reactors CSTR , where each wx C-shaped chamber represents such a CSTR 13 . In Fig. 4,
a schematic is given of this principle and the leakage-gaps and -flows between the chambers and between the series CSTR’s are indicated. The leakage flows through the calendar-, side-, flight- and tetrahedron-gaps Q , Q , Q , csf. Q , res. and forced conveying of the chambers results in a t wx nett positive mass flow from feed port to the die 13,17 .This approach was the basis of a series of publications of the Wageningen research group on the RTD of extrusion wx cooking, which is described below 8–12,24–26,28 . The RTD’s of t.s.e.’s are more asymmetric compared to a
cascade of CSTR’s. The different parallel series of C-shaped chambers in a t.s.e., can be summed up to an RTD model of CSTR’s in series. These CSTR’s travel from feed port to die, during which the chamber volume changes and these chambers loose material in the opposite direction
wx see Fig. 4 . Jager et al. 11 presented a way by which the RTD could be calculated. The average residence time and the curve widths are calculated from the uncorrected E-curve using Todd’s method of recording the passing-by of 16%, 84% and 92% of tracer material. They are corrected with a systematical error as calculated by a Monte Carlo wx procedure 18 . The uncorrected average residence time is calculated using equations for the zero, first and second
. time moment M , M , M of the measured extinction 012. Ct as: M s t iCt dt .3 H i tsM rM 4 10
And M2 1 U N s 5 2 MM yM 02 1 NU gives the number of mixers of a series of CSTR’s. A
higher number of NU stands for a flow that resembles a more plug-flow nature. RTD models can be divided in curve-fit models, which describe the curve shape and in models that describe the axial mixing in the extruder reactor in a predictive andror descriptive way. An example of a descriptive model is the plug-flow model with wx axial dispersion 16 . The axial dispersion is described with a constant effective longitudinal dispersion coefficient IDe 2 y1. wx . m s 21 . The Peclet number Pe , the ratio of the average axial convective transport and the transport by dispersion is equal to: : í L Pes 6 IDe : in which L is the extruder length and í is the average axial velocity. The axial dispersion model and a model of a wx cascade of CSTR’s do give comparable RTD’s 16 . Jager wx wx has shown in 1991 11 and 1992 12 that both models for
extruders can be combined and that Pe and N are related as: Pe2 U N s 7 U yPe 2Pey1q10 It is possible to use this RTD-model for different twin screw extruder designs, to evaluate their working behaviour. This can be realised by introducing a so-called chamber mixing-coefficient, which describes the ratio of mixed and total leakage flows in each CSTR of the model. The value of this coefficient is expected to be dependent on the gap-dimensions between the chambers. Especially narrowly intermeshing counter-rotating t.s.e.’s may have such narrow RTD’s, that they contribute, without mixing elements, very little to axial mixing. The gaps in co-rotat-
ing t.s.e.’s act differently than those in counter-rotating
t.s.e.’s, since they allow considerable larger leakage flows
wx and increased axial mixing 13 . The influence of a certain
constituting element on axial mixing can be measured with
wx the RTD-response 8 .
2.2. Dispersiíe mixing
For successful dispersive mixing a shearrelongational stress field is needed to break particulates and fluids into smaller pieces or to disperse them in the viscous liquid. The stresses are related to velocity gradients, e.g., for shear:tUshg 8 . ˙U y2 . in which t sshear stress N m , hsdynamic viscos- y1 . ity Pa s , gsshear rate s . ˙The separation of particles occurs normally perpendicular to the velocity gradient see Fig. 5 . In the case of solid and liquid particulates, the magnitude of stresses determine the dispersion. Shear stresses are as effective for dispersion as elongational stresses. In the case of slightly elastic liquids, which is the case for many foods, the stresses in an
elongational flow may therefore be much larger than in shear flow. Machine parts in extruders, subjecting the material to elongational flow, like calendar gaps, tetrahedron gaps and internal mixing elements are good dispergators for this reason. The shear rate calculated over the channel depth is usually too low to cause dispersion. A possible solution is to increase the leakage gaps in s.s.e.’s and t.s.e.’s and indeed single screw extruder cookers with fairly deep channels, large flight gaps and high rpm have become popular. For t.s.e.’s the total leakage flow is obviously larger. For counter-rotating cooker-extruders the calendar gap is most suitable for dispersion, whilst in co-rotating t.s.e.’s a comparable dispersion effect only can be realised by installing many kneading discs. It is known that s.s.e.’s and t.s.e.’s of the self-wiping type are only suitable for dispersive mixing actions with special arrangements.U . From t shg Eq. 8 follows that the viscosity ˙should be high to provide attractive shear stresses. This means for food particles, that dispersive mixing should take place early in the melting process, as close as possible to the feed section.Elements that provide the total mass flow to pass through a high shear zone, are called shear elements. For single screw food extruders some designs have become popular, of which must be mentioned the use of shear rings on the screw which is imitated from the so-called ‘blister’design in plasticating extrusion and the shear effect of mixing pins, in, e.g., expander cookers. In twin screw extruder cookers the most remarkable design is the one wx used in APV-Baker t.s.e.’s, an adjustable barrel valve 19 .Here an adjustable valve of which the position can be controlled from the topside of the barrel, is mounted between two blister discs, of which both are providing shear and control the degree of fill at the same time. The behaviour of food material in co-rotating t.s.e.’s, provided wx with such a barrel valve is investigated 26 . Another
design, well-known in counter-rotating t.s.e.’s, is the so-called drossel element, a pressure barrier with relatively short length, made as a two-start short pitch screw ele-wx ment. This design was investigated by Jager et al. 10 for food products in a conical counter-rotating t.s.e.2.3. Distributiíe mixing This mixing effect can be based on particle distribution always unavoidably combined with shear effects at the same time. For distributive mixing the effects of mixing are more or less proportional to the total shear g, written as Weighted Average Total Shear WATS .dí t WATSsgs dt 9 H d x 0y1 . in which dírd xsaverage shear rate s , tstotal resiwx dence time s , gsshear – 3 . For single screw extrusion some distributive mixing element designs have become popular see Fig. 6 , like the pineapple mixing section, the slotted screw flights, the mixing pins in expander designs and the special design of wx static and reciprocating pins of the Buss co-kneader 5 . The cavity transfer mixing section from Fig. 6 has not yet proven its use in food extrusion, due to cleaning problems.However, for twin screw extruders there are design limitations and only the combination of pairs of slotted screw flights, kneading blocks and reversed screw elements are applied. When using these elements, there willbe an intensive exchange of solids and melt between the screws and within the screw channels providing optimalmixing and by means of this a constant product quality will follow.
中文譯文
單螺桿和雙螺桿擠壓機(jī)中混合元件的混合性能
摘要:
在擠壓加工中固體和熔體混合一直存在問題，導(dǎo)致描述熔化過程的模型不同。研究發(fā)現(xiàn)，基于谷物的食物，只有少數(shù)是有效的，由于同時(shí)存在水和高粘性的非牛頓材料?；旌显囼?yàn)總結(jié)了單雙螺桿擠壓機(jī)用于不同粒徑的固體顆粒，比如玉米糝、面粉、蔗糖晶體和葡萄糖漿的固體顆粒時(shí)的效果。研究了特殊單螺桿擠壓機(jī)的混合頭，比如銷釘螺桿以及異向旋轉(zhuǎn)雙螺桿擠壓機(jī)中的溝槽式螺桿段?；旌下輻U的幾何形狀的影響已使用同向旋轉(zhuǎn)雙螺桿擠壓機(jī)模塊化元素來衡量，如：如單頭元件、混合漿板和一個(gè)透明擠出機(jī)模型中的反向傾斜元件（RTD測(cè)量）測(cè)量。報(bào)告顯示混合效果，并解釋他們的粘性耗散，停留時(shí)間，曲線傳播和停滯帶來的影響。
關(guān)鍵詞：?jiǎn)温輻U擠壓機(jī)； 雙螺桿擠壓機(jī)； 混合
1、介紹
食物擠壓成型定義的一部分是食物原材料通過開放渠道的單螺桿擠出機(jī)時(shí)被剪切、混合和壓縮。然后在雙螺桿擠壓機(jī)中下有緊密嚙合的螺桿,食品在所謂的C形室中被傳輸,由相鄰嚙合的螺桿和螺筒密閉。
食品粉末由一根螺桿從材料倉(cāng)內(nèi)獲得,在內(nèi)部對(duì)其進(jìn)行混合并傳輸,用壓力通過縫隙或螺桿的間隙最終轉(zhuǎn)移到鄰近的螺桿,最后這個(gè)C形室輸送其到末端。單螺桿擠壓機(jī)和雙螺桿擠壓機(jī)的運(yùn)作方式區(qū)別很明顯但是都要求自身的模塊化螺桿零件的設(shè)計(jì)可以加強(qiáng)和改善螺桿混合效果。
圖一：C形腔室
食用混合操作擠出機(jī)可以分為三種不同類型:第一個(gè)是粗混合或縱向混合。第二個(gè)是分散的混合或粉碎分散相混合。第三種是分布混合或徑向混合。螺桿實(shí)現(xiàn)了粗糙的運(yùn)行機(jī)制的