SJ90單螺桿擠出機結(jié)構(gòu)設(shè)計,SJ90單螺桿擠出機結(jié)構(gòu)設(shè)計,sj90,螺桿,擠出機,結(jié)構(gòu)設(shè)計 附錄1 英文翻譯 A DESIGN ABOUT MAIN MACHINE OF THE EXTRUDER Both the elastic melt(Fig.1)and the hydrodynamic melt extruders(Fig.2)involve shearing the material between two rotating disks to change it from a solid To a semi-liquid melt(external heat is initially required to begin the operation but once started，the conversion of mechanical input into heat keeps the material fluid). In both devices，the material is fed to the periphery area between the rotating disks and then flows to the disks enter. Both the elastic melt and the hydrodynamic extruders depend on entirely different phenomena to move the material through the extruder. In the case of the elastic melt extruder，the movement of material is dependent on the theological properties of the melt To function in an elastic melt extruder, the melt must be a viscoelastic (i.e., somewhat rubbery or capable of exhibiting a significant amount of elastic behavior at the Shear rates existing in the machine)．It is this elastic property that produces the internal pressure which moves the melt through the device． In contrast, a purely viscous liquid can be extruded from the hydrodynamic extruder since the driving force is derived from the geometry of the rotors between which the material is being sheared．Briefly，the driving pressure is created by internal pressure differentials created when the melt is forced to now into a smaller cross-section. In the reciprocating ram type of extruder (Fig.3),a special valving system is provided so that the pulsating flow from two alternately operative pistons can be combined into a single smooth How stream，which effectively provides a continuous output，By using ，two alternating cylinders，each may be reloaded with material while the other is extruding, thus eliminating the batch characteristics of the conventional ram extruder．The purpose of this arrangement was to develop an arrangement was to develop an efficient extruder which would not degrade shear-sensitive thermoplastic materials. 0f the three named，the elastic melt extruder has thus far received the most attention. Some of the major problems originally involved，such as rather low out-put, high thrust bearing loads，and difficulty in feeding the material to the shear area, appear to have been solved to a large extent. The first commercial unit to be offered is shown in Fig.4 .There is current interest in the possibility of using the elastic melt extruder as a plasticizing device and even as a film or profile extrusion production unit. Such extruders are also being evaluated for plastication operations in blow molding and injection molding. Extruder design Component parts common to all standard single screw extruders are shown in Fig．5．Basically，the extruder consists of a steel cylinder in which a solid or cored shaft, running the entire length of the cylinder is rotated. This rotating shaft has a continuous helical channel cut into it, which constitutes the extruder screw. The length of the helical channel usually extends the entire length of the screw from the feed throat of the extruder barrel to the forward end of the screw. The helical ridge of metal left when machining the screw channel in the metal blank is called the screw flight .The distance between flights，or lead，is usually equal to the outer diameter of the screw. This is done primarily for ease of machining．Normally the screw flight diameter is the same as the inner diameter of the cylinder minus a carefully specified clearance provided to allow for rotation． The extruder cylinder or barrel is lined with a hard alloy，usually integrally cast XalloyTM，and may be provided with both heating and cooling systems. The thermocouples of the temperature control，system are placed in wells' at equal intervals along the barrel. Four to six control zones are normally used for longer barrel extruders with length-to-diameter ratios(L／D) in the range of 20：1 to 28：1． Power for rotating the screw is supplied by a variable speed motor drive through a gear reduction unit，a coupling，and the thrust bearing assembly of the extruder．The thrust bearing assembly must be ruggedly designed to take the very high backward loadings on the screw developed by pressures generated at the for Ward end of the screw. After the granules have passed through the extruder barrel have been fully plasticized, the melt is forced through a breaker plate which may also be used to support a screen pack, the functions of both being 1) to insure that contaminants are not passed on to the die and 2) to create a back pressure to help stabilize flow of material through the extruder. A streamlined valve is mulch more useful in controlling melt pressure and has replaced the screen pack for this purpose in recent extruders. After the melt passes through the plate and screen pack or valve. It flow through an adapter which channels the flow to the die． Extruder size The size of a single screw extruder is specified by the inside diameter of the barrel. Commonly available standard size are 1.5，2, 2.5，3.25，3.5，4.5，6,and 8 in with sizes above8 in available on special order. Average output capacities which may be developed with different sizes of plasticizing extruders are correlated with screw size in Fig6.which is presented only as a rough guide; actual output rates depend heavily on the material being run as well as on the equipment; that is，drive HP，screw design, etc． Barrels The American extruder industry has generally standardized on barrels which have centrifugally cast-in，special alloy liners for pressures up to 10.000 psi .For pressures greater than that, a steel tube with a cast-in liner is shrink fitted into a larger outer barrel. Bimetallic liners are designed to be corrosion-and Wear resistant. Various thicknesses of lining material are available. European manufacturers have resorted to nitride barrels with less wear resistance，though some bimetallic cylinders are now manufactured there under licensing agreements. Barrel supports should be oriented to allow attachment of substantially heavy dies without barrel deflection．They should also provide a rigid connection between the frame and the transmission, and should be designed to assure barrel freedom for longitudinal expansion and contraction；such sliding contacts should be designed to minimize heat losses to the support8 proper. The machine with the least number of components requiring careful alignment in relation to the base is the one which will naturally be less likely to require field alignment either at time of installation or when work has to be done on the barrel。 The L/D ratio of an extruder is an important characteristic of the barrel design，since it determines the relative amount of inner barrel surface available for shear of mixing and heat transfer. The ratio is defined as the length of the barrel from the rear of the feed hopper to the breaker plate，divided by the nominal inside diameter of the barrel. Although extruders are available in a wide range of L／D ratios from 16：1 to 30：1，most common ratios are 20：1 and 24：1. Machines with standard ratios as high as 30:1 are also being currently produced. Present trends indicate future predominance of 24：1 and 28：1 L/D extruders. Vented barrels should have an L／D ratio of at least 24：1 to accommodate the two stage screw used in this process. Vented machines may be valved internally or externally to control the flow rate of the polymer from the metering to the vent zone．Nonvalved systems also work satisfactorily. Three different types of vented single screw extruders are shown in Fig.7. Barrel heating-cooling: The most poplar method Of heating the extruder barrel in the past has been with external electrical resistance heater in the form of bands or straps which are simply wrapped around the outer diameter of the steel barrel in multiple units and fastened in place．Several heaters are usually wired together to act as one unit or zone .Bank type are available in different widths, sizes, and wattages. Sufficient heating capacities should be supplied so the extruder is capable of processing the various types of resin．A watt density Of 25 to 45 watts／in is usually sufficient. A current trend in electrical resistance heating of extruder barrels is towards so-called “cast-in-aluminum heaters.'’ This type consists of a form-fitting series of cast aluminum blocks between which the barrel is sandwiched and in Which are embedded electrical resistance heating elements，The use of the aluminum block heaters is said to provide more even heat distribution along the heating zone since the excellent thermal conductivity of the aluminum minimizes localized overheating which might occur at heater element locations. Also, cooling fins can be incorporated to aid in air-cooling the barrel. Another commercially available type of extruder uses induction heating to heat the steel barrel. Induction heating provides high watt densities for fast, efficient use of electrical heating． Cooling of the extrusion cylinder may be provided to carry away excess heat and to permit rapid changes in operating temperature which might be demanded when changing running conditions or controlling the temperature to a constant value．Excess heat arises from the mechanical work which is done on the material by the screw. As a matter of fact，this is the chief source of heat input to the material. The external heating system is used mainly to start up the extruder and t supply heat to maintain a constant temperature. Cooling of the extrusion cylinder may be provided to carry away excess heat and to permit rapid changes in operating temperature which might be demanded when changing running conditions or controlling the temperature to a constant value．Excess heat arises from the mechanical work which is done on the material by the screw. As a matter of fact，this is the chief source of heat input to the material. The external heating system is used mainly to start up the extruder and t supply heat to maintain a constant temperature. Cooling systems in popular use employ water cooling coils forced air circulation around the outside of the barrel and jacketed barrels in which a refluxing liquid is used to carry away the heat to an external cooling coil or combinations of these methods． The most popular cooling system is a series of air blowers corresponding to the heating zones. These simply direct a blast of ambient temperature air onto the barrel itself or onto fins on the barrel or cast heaters. Although this is less efficient than water cooling，it has the advantages of avoiding thermal shock and of providing the gentle cooling desired for this operation. In one type of jacketed barrel cooling system，a special liquid with appropriate boiling point and vapor pressure occupies a portion of the volume in the sealed jacket the balance of the volume of the jacket being filled with the liquid's vapor，the two phases being in equilibrium. When cooling is desired，cool air is blown onto a finned condenser connected to the sealed jacket. The vapor in the jacket condenses and the liquid starts to boil by heat absorbed from the cylinders．If the temperature drops too rapidly，boiling (and hence cooling) also ceases，there by providing an element of self—regulation. Screws Of the many extruder screw designs in common use today，the most widely used is shown in Fig．8, top．In this constant pitch, gradual transition metering screw，channel depth is greatest in the feed section and is constant until it smoothly decreases through the transition section to the constant depth of the metering section at the forward end Of the screw．Four other screw designs are shown in the lower part of Fig．8. The screw design is considered optimum when the granules entering the screw in the feed section are fully plasticized into a homogeneous melt prior to the entry of the mass into the metering section. The melt is pumped through this latter section to the die at a uniform rate. In the feed section，the screw channel is designed to have a conveying capacity in excess of that of the transition and metering sections. This is done to avoid starving the forward sections． Studies of the feeding of solid granule through extruder screws have resulted in the following conclusions： 1) the maximum granule conveying rate will be achieved when the friction between the inner Wall Of the barrel and the granules is at a maximum and the friction between the granules and the screw is at a minimum，and，2) the optimum helix range of the screw depends on the friction between the plastic and the screw and barrel．in most cases this angle is in the neighborhood of 15 to 20 degrees． The materials of construction for feed screws vary，but in most cases a 4140 alloy steel is used．With few exceptions, all modern screws are hollow bored for liquid Cooling and heating. Since there is appreciable wear between the snug fitting screw and the barrel and since some plastics compound are highly abrasive, care must be taken in the selection of fight hardening methods．Flame hardening of the fight is adequate for most extrusion processes but specific applications where wear is a problem may require coating with Stellte#6 Chrome-plating the screw is a standard procedure. Chromed screws are more corrosion resistant and it is usually easier to remove plastic material from them and to clean them. 英文翻譯 塑料擠出機設(shè)計 圖1中的彈性熔體擠出機和圖2的彈性流體擠出機，都涉及到了使物料由固態(tài)變?yōu)榘胍簯B(tài)，在兩個轉(zhuǎn)盤間發(fā)生剪切物料的問題。在這兩種裝置中，物料被喂送到兩個轉(zhuǎn)盤之間的圓柱空間，而后流到盤子的中央。 彈性熔體擠出機和彈性流體擠出機均取決于物料通過擠出機的不同 狀態(tài)，而物料的運動又取決與熔體的特性。若使出用彈性熔體擠出機，熔 體必需是粘彈性體。正是這種彈性的存在才會產(chǎn)生—種驅(qū)使熔體通過的內(nèi) 壓。 相比之下，一種純粘性流體能夠從彈性流體動力機出機中擠出，因為那種擠壓力來自于旋翼的幾何外形，在這些旋翼中，物料受剪切，簡而言之，那些產(chǎn)生于當熔體通過一個很小的截面時內(nèi)壓不均。 在連續(xù)柱塞擠出機中，如圖3，由于提供一種調(diào)系統(tǒng)工程，故來自于交替的工作柱塞的交替液流匯和成一股光滑的流柱，從而保證了擠出的連續(xù)性，通過使用兩個交替運行的預(yù)料筒，當一個柱塞被擠壓時，另外一個就 被堵住，這樣，彌補了傳統(tǒng)的柱塞式的不足。這種裝備將會使高效擠出機 有更大的發(fā)展，并且它不會削弱對熱塑性物料的剪切作用。 以上三種被命名的機器，彈性熔體擠出機引起了最大的關(guān)注，最初遇 到的一些問題諸如，輸入低、止推軸承承載高，喂送物料至剪切區(qū)難等。 從某種程度上說，這些問題逐漸得解決。第一臺被接受的經(jīng)濟模型如圖4 所示，它曾引起人們的注意，有可能把彈性熔體機當作一種擠塑機，甚至 是擠出生產(chǎn)線。這樣的擠出機在吹風定型，注入模具時也被認為是進行擠 塑操作。 擠塑機的設(shè)計 對于所有標準化的單螺桿擠出機而言，它的組成部分如圖5所示，基本上它是由一個鋼制機筒組成，在筒內(nèi)固體或者在筒的整個長度上都能運轉(zhuǎn)的中心軸旋轉(zhuǎn)著，這根回轉(zhuǎn)軸上且有連續(xù)的旋轉(zhuǎn)槽，這樣就形成了擠出機的螺桿。 螺旋槽的長度延伸到螺桿上從擠出機的加料口到螺桿前端的整個長度。 當加工螺桿上的槽時，螺旋狀的凸起被稱為螺棱，兩個螺棱之間的距離或?qū)С掏ǔ５扔诼輻U的外徑，這樣做的目的主要是考慮到加工容易，通常螺桿的外徑等于機筒的內(nèi)徑減去一個精心策劃的間隙，這個間隙能滿足螺桿的旋轉(zhuǎn) 擠出機的機筒或襯套都鑄成合金，并且它們都具有加熱和冷卻系統(tǒng)，溫度控制系統(tǒng)的熱電偶沿著機筒等間距的布置正在其上的凹窩內(nèi)，對于長徑比在20：1至28：1范圍內(nèi)且機筒較長的擠出機而言，通常采用四至六個控制區(qū)段。 同轉(zhuǎn)螺桿的動力是一個變速電機通過擠出機的齒輪減速器、聯(lián)軸器、止推軸承來提供的所設(shè)計的止推軸承必需能夠承擔起作用在螺桿后面的較高的載荷，這種載荷是由螺桿前端外的壓力而產(chǎn)生。 當顆粒經(jīng)過擠出機筒并近一步塑化后，熔體通過一個能支撐過濾網(wǎng)的分流板被擠壓，它的作用在于：（1）確保內(nèi)容物不直接流向口模；（2）產(chǎn)生一種被壓以穩(wěn)定通過擠出機的物料流。在新的擠出機中，在控制熔體壓力和取代分流板過濾網(wǎng)或者是調(diào)節(jié)閥后它將流近口模，在其上面有通向開口的通道。 擠出機尺寸 單螺桿擠出機的尺寸受筒內(nèi)徑的限制，通常，許多的標準尺寸系列為：1.5、2、2.5、3.25、3.5、4.5、6、8英寸，如尺寸大于8英寸，將按特例考慮。 如圖6所示，隨著塑料擠出機尺寸變化的平均輸出功率與螺桿尺寸息息相關(guān)，這為我們設(shè)計提供了方向。實際的輸出值除于設(shè)備有關(guān)外，很大程度上取決與運動物料，也就是說，驅(qū)動機器、螺桿設(shè)計都很重要。 機筒 美式擠出機工業(yè)已經(jīng)將擠出筒標準化，為壓力達到目的10000帕，機內(nèi)鑄以特殊合金套。為了達到更高的壓力，具有合金套的鋼管壓縮裝配到一個更大的機筒內(nèi)。設(shè)計的可更換的襯套有很好的耐磨性和抗磨性，度層材料的厚度允許有變化。 盡管一些可變化筒目前在特殊條件下能制造出來，歐洲的制造商仍把注意力投向抗磨性差的氮化機筒。機筒的支架應(yīng)確認可使用很重的口模帶有附件，這是在機筒無偏斜的條件下來看的。在支架與傳動系統(tǒng)之間還應(yīng)提供一種剛性接觸，已確保機筒在長度方向上有膨脹和收縮的余地?；瑒舆B接設(shè)計應(yīng)使支架上的組成的機不需要器人熱量損失最小。這樣的機器是由經(jīng)過細心排成直線的幾個為數(shù)不過的構(gòu)件組成的一種機器。實際上，無論機筒是在工作還是不在工作的時候，它都不需要排成直線的空間。 一個擠出機的長徑比是機筒設(shè)計的一個重要的參數(shù)，因為它決定了機筒內(nèi)表面的剪切、混合和熱傳遞的能力，它的值定義為在機筒上從前面的加料口到分流板之間的長度除以機筒的內(nèi)徑。 擠出機有一個從表面上看16：1到30：1較寬的范圍，但最普通的長徑比是20：1和24：1。象長徑比高達30：1的標準長徑比的機器即將產(chǎn)生出來，目前的趨勢表明長徑比為24：1和28：1的擠出機會成為將來的主流。 為了適應(yīng)生產(chǎn)過程中的二階螺桿，排氣式機筒的長徑比至少為24：1，為了控制從計量段到排氣段聚合物的流率，排氣式擠出機應(yīng)有內(nèi)外調(diào)節(jié)系統(tǒng)。無排氣系統(tǒng)也可達到到正常的效果。圖7所示為三種不同的排氣式單螺桿擠出機。 機筒的加熱和冷卻：在過去擠出機機筒最普遍的加工方法是使用圈狀或帶狀的電阻加熱器，它們纏繞在機筒的外徑上并緊固在其上。許多加熱器通常捆在一起作為一個整體或單元，提狀類型的加熱器可以有不同的寬度、尺寸以及瓦特。這樣的擠出機應(yīng)供應(yīng)給充足的熱能量，以加工不同類型的樹脂，每分鐘有24至25瓦特的瓦特密度通常是充足的。 目前的趨勢是機筒上的加熱器將面臨所謂的鑄鋁加熱器的挑戰(zhàn)。這種加熱器主要是由一系列的鑄鋁組成，在這些鑄鋁塊中插入機筒并在其中嵌入了電阻加熱元件，沿著加熱段，鑄鋁加熱器可以使熱量分布均勻。由于鋁的良好的傳導性，它可以使發(fā)生在加熱器元件處的局部過熱傾向減少為最小，同時，冷卻元件也可能與元件放在一起從而達到空冷機筒的目的。 另外一種較經(jīng)濟的擠出機采用電感應(yīng)加熱器來加熱，機筒電感應(yīng)加熱可以供給高的瓦特密度以實現(xiàn)高效的電感應(yīng)加熱。 擠出機的冷卻系統(tǒng)應(yīng)該能散發(fā)多余的熱量，并且允許在工作溫度下較快的變化，當改變運行狀態(tài)或?qū)囟瓤刂圃谝粋€常值時，哪個工作溫度上許可的。多余的熱量產(chǎn)生于螺桿作用在物料上的機械加工中，實際上這是熱量產(chǎn)生的主要來源。外部的加熱系統(tǒng)主要用來起動擠出機以及供給熱量以維持一個常溫。常用的冷卻系統(tǒng)是采用水管冷卻和水套冷卻，水管冷卻使機筒外側(cè)的空氣與之對流；對水套冷卻而言，回流的液體就可以將熱量帶到外面，冷卻水管中或者類似于這些方法的物體中。 最受歡迎的冷卻系統(tǒng)是由對著加熱段的鼓風機，這些鼓風機可以把周圍的一股股熱空氣吹向機筒或者機筒的散熱片上或者鑄鋁加熱器。盡管風冷不如水冷效果好，但它具有避免冷擊和冷卻柔和的優(yōu)勢。 在有襯套的機筒的冷卻系統(tǒng)中，有適當?shù)姆悬c和氣壓的一種特殊氣體占據(jù)了密封的一部分容積，充滿那種液體蒸汽的襯套有兩個平衡段。當需要空冷時，冷空氣就吹向一個與密封套相聯(lián)的葉片冷凝器，這時襯套中的蒸汽就被冷卻，而當它吸收了來自機筒的熱量后就會沸騰，如果溫度下降的太快，沸騰就會停止，所以應(yīng)供給一個自動調(diào)節(jié)元件。 螺桿 在今天的日常使用中，在眾多的擠出機螺桿設(shè)計中，使用最廣泛的螺桿如圖8所示，對這種等距漸變的計量螺桿而言，在加料段的槽深最大并且是個常值；而在熔融段槽深自然的減小，而在均化段槽深又保持不變。在圖8的下面，給出了四種不同的螺桿設(shè)計方案。 當進入螺桿加料段的顆粒在進入均化段之前被塑化成一種均勻的熔體時，螺桿的設(shè)計要合理化，后來熔體以恒定的速率被推向與口模相連的計量段。 從擠出機螺桿的固體顆粒喂進的研究可以得到如下的結(jié)論：（1）當機筒內(nèi)壁與顆粒之間的摩擦達到最大，而顆粒與螺桿之間的摩擦處于最小值時，將會得到最大的固體傳送率，（2）螺桿上合理的螺桿角取決于塑料與螺桿和機筒之間的摩擦，在大多數(shù)情況下，螺旋角的取值在15至20度之間。 對喂進作用的螺桿而言，它的制造材料有多種，但大多數(shù)采用一種4140的合金。除了少數(shù)的例子外，所有的現(xiàn)代螺桿都被鉆成空的，用于液體的冷卻和加熱。由于在布置恰當?shù)穆輻U與機筒之間存在著磨損，而且一些聚合物有很高的腐蝕性，因此對螺棱淬火方法的選擇要倍加小心。對大多數(shù)擠出機而言，螺棱的淬火足以達到要求，但是磨損是一個主要的問題，因此要求螺棱的表面要鍍Stellite#6. 烙化螺桿是一個標準化的過程。經(jīng)烙化的螺桿有很強的抗腐蝕性，通常它可以輕而易舉地將塑化物質(zhì)從它上面移開，并且可以清潔自身。