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附錄1
成型機及其工藝的調(diào)節(jié)
成型機剪切性能高低由擠出機的螺桿結(jié)構(gòu)所決定。但擠出質(zhì)量優(yōu)劣與擠出效率高低，還在于擠出工藝與擠出機剪切性能相適應。否則低剪切擠出機采用過高擠出速度擠出，難以生產(chǎn)擠出高質(zhì)量型材制品，高剪切擠出機在過低擠出速度下運行，難以有效發(fā)揮擠出效率。不同剪切性能擠出機都有一定的工藝控制范圍，是有限度的。業(yè)內(nèi)倡導的擠出工藝路線為“馬鞍型”即加熱區(qū)設定溫度要高一些，恒溫區(qū)設定溫度要低一些，保溫區(qū)設定溫度要高一些。但不同剪切性能擠出機在不同擠出速度下運行，“馬鞍型”的“鞍”與“座”高低是完全不同的。
在木塑復合型材擠出時，要最大限度發(fā)揮不同剪切性能擠出機的擠出效率，建立螺桿加熱區(qū)供料段、壓縮段與恒溫區(qū)熔融段、計量段所需熱量與所供熱量的平衡是關鍵所在。依據(jù)擠出機剪切性能特點，不同剪切性能擠出機，擠出不同規(guī)格塑料異型材，應分別采取不同的擠出工藝，以適應制品質(zhì)量性能的需求。木塑復合型材擠出，物料由玻璃態(tài)轉(zhuǎn)化為熔融態(tài)共計有兩種熱源，一種是由電加熱器提供的外加熱，一種是由螺桿在旋轉(zhuǎn)過程中對物料壓延、摩擦、剪切產(chǎn)生的熱量。在開機生產(chǎn)時，物料的熔融主要以外加熱為主，在正常生產(chǎn)階段，物料的熔融主要以螺桿對物料壓延、摩擦、剪切產(chǎn)生的內(nèi)熱為主。具有關資料表明：在型材擠出中，內(nèi)熱所占擠出機所供熱量的比例，大致在65％以上。外加熱溫度控制系統(tǒng)主要是通過電器儀表元件實施溫度設定與顯示。當顯示溫度超過設定溫度指標參數(shù)時，加熱圈即刻斷電，停止加溫，并由螺桿油冷裝置與螺筒風冷裝置進行強制冷卻；當顯示溫度達不到設定溫度指標參數(shù)時，加熱圈就一直不間斷工作。由于內(nèi)熱主要受擠出機螺桿特性、加料與擠出速度的制約，不受外加熱溫度控制系統(tǒng)的影響。當?shù)图羟袛D出機擠出速度過高時，即使供料段與壓縮段外加熱圈工作頻率提高，間歇時間很短，其顯示溫度亦可能達不到設定溫度；即使熔融段與計量段外加熱停止工作并啟動螺桿與螺筒冷卻裝置運行，顯示溫度仍可能遠遠高于設定溫度。同時由于反映顯示溫度的測溫點熱電偶安裝在擠出機螺筒壁上，與螺筒內(nèi)物料有一定距離，儀表顯示溫度與物料實際溫度在不同工況下則有一定梯度，存在不同對應關系。一般情況下加料段與壓縮段物料即存在外加熱，又存在剪切熱，為雙向加熱，顯示溫度基本等同于物料溫度；熔融段與計量段物料顯示溫度未達到設定溫度時，亦為雙向加熱。當顯示溫度超越設定溫度時，熱量開始由內(nèi)向外傳遞，可稱之為逆向傳熱，顯示溫度低于物料溫度。由此可知低剪切擠出機擠出速度較高時，螺桿熔融段、計量段物料實際溫度不僅高于設定溫度，也高于顯示溫度。因此當顯示溫度在設定溫度區(qū)域運行時，設定溫度參數(shù)基本等同于物料溫度，是物料塑化熔融的控
制目標與依據(jù)。當顯示溫度偏離設定溫度區(qū)域運行時，顯示溫度可假定為物料溫度，即取代設定溫度成為物料塑化熔融的控制目標與依據(jù)。設定溫度只是增加或減少外供熱的調(diào)控手段。對于低剪切擠出機，由于給料段、壓縮段壓縮比較小，所提供的內(nèi)熱遠遠滿足不了玻璃態(tài)物料塑化要求，故給料段、壓縮段溫度設定應高一些，因配方不同，大致在190~200℃左右，盡管在提高擠出速度情況下，顯示溫度依然偏低，但提高設定溫度的目的，是為了供料段、壓縮段電加熱圈，一直不間斷工作，只要顯示溫度在180~185區(qū)間，物料緊包裹于螺桿，處于微熔狀態(tài)，不出現(xiàn)排氣孔冒料現(xiàn)象，可視為正常；熔融段、計量段設定溫度應低一些，因配方不同，大致在165~175℃左右，盡管在提高擠出速度情況下，顯示溫度依然偏高，但降低設定溫度的目的，是為了熔融段、計量段電加熱圈適時停止加熱，并啟動螺桿油冷與螺筒風冷對物料進行冷卻，只要顯示溫度在180~185℃區(qū)間，擠出型坯截面未出現(xiàn)氣孔、麻點等癥狀，可視為擠出速度正常。反之即使給料段、壓縮段溫度設定的再高，加熱圈不間斷工作，排氣孔物料疏松，呈豆腐渣狀，未包裹住螺桿，從螺筒排氣孔出現(xiàn)冒料現(xiàn)象；熔融段、計量段設定溫度再低，電加熱圈已停止工作，螺桿油冷與螺筒風冷一直對物料進行冷卻，擠出型坯已出現(xiàn)氣孔、麻點等癥狀，可視為擠出速度已到極限，應及時降低擠出速度或加料與擠出速度。
排氣孔冒料是低剪切擠出機塑化不良的表征。但并非排氣孔冒料都是低剪切擠出機所造成的。導致排氣孔冒料主要有以下原因：①加料速度過快，所增加的剪切熱不足于平衡所增加的給料量需要的熱量，導致的塑料塑化不良；②擠出速度過快，所增加的剪切熱不足于平衡物料在給料段與壓縮段停留時間減少而損失的熱量，導致的塑料塑化不良；③配方采用CPE抗沖改性劑時，加工助劑添加量偏少，物料摩擦性能差，到排氣孔時塑化不良；④配方中潤滑劑過量，物料在擠出機內(nèi)移動擠出速度過快，到排氣孔時塑化不良；⑤擠出機螺桿與螺筒軸向間隙過大，漏流嚴重或螺桿給料段、壓縮段溫度過高，導致物料“過塑化”，已轉(zhuǎn)化為體的物料經(jīng)歷了壓縮段第一次壓力高峰后，到排氣孔時應力釋放，體積膨脹，粘附在螺棱端面，隨螺桿轉(zhuǎn)動被排氣段螺筒刮落在排氣孔管壁上，積累到一定程度從排氣孔溢出。前兩種排氣孔冒料均和擠出機剪切性能差有關，第三種與第四種排氣孔冒料主要與配方有關，第五種排氣孔冒料主要與擠出機磨損及剪切性能高有關。在判斷排氣孔冒料原因時，應綜合考慮，不可盲目而定。如屬于試驗配方發(fā)生的排氣孔冒料應調(diào)整配方；如屬于擠出機磨損，應調(diào)整擠出機螺桿與螺筒間隙；如發(fā)現(xiàn)物料在排氣孔“過塑化”應調(diào)整加料擠出速度比；前三種排氣孔冒一般表現(xiàn)為扭距升高，后兩種排氣孔冒一般表現(xiàn)為扭矩降低。
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附錄2
Shear properties in the molding machine height determined by the extruder screw structure. But extrusion quality fit and unfit quality and extrusion efficiency high and low, but also in the extrusion process with the shear properties in the extruder. Otherwise low shear extrusion machine adopts the high speed extrusion, it is difficult to produce extrusion profiles products with high quality, high shear extrusion machine running under low speed, difficult to play extrusion efficiency effectively. Different shear performance extruder has certain scope of process control, there is a limit. Industry advocacy of extrusion process route is "saddle type" means heating area set temperature, lower temperature zone set temperature, heat preservation zone set temperature. But different shear extrusion machine performance under different extrusion speed run, "saddle type" of "saddle" and "bridge" is completely different.
When wood plastic composite profiles extrusion, to play a maximum efficiency of different shear performance of the extruder extrusion, establish screw heating zone feeding section, compression and constant temperature zone melting section, the metering section of calories and heating load balance is the key. Extruder based on shear properties, shear properties in the different extrusion machine, extrusion plastic different profile with different specs, should respectively take different extrusion process, in order to meet the needs of the product quality performance. Wood plastic composite profiles extrusion, the glassy state material into molten total there are two kinds of heat source, one kind is provided by the electric heater heating, one kind is by screw for material in the process of rotary rolling, the heat generated by the friction, shear. During post production, material outside heating's molten core, in normal production, the molten material mainly by the screw on the rolling material, friction, shear internal heat. With relevant data show that in profile extrusion, the internal heat of extruder by heating load, the proportion of roughly the above 65%. Outside the heating temperature control system mainly through electrical instrumentation components implement temperature setting and display. When temperature more than set temperature parameters, heating coil power immediately, stop the heating, and the screw barrel screw oil cooling device with air cooling device for cooling; When the temperature of the display is short of set temperature parameters, heating coil has been uninterrupted work. Due to internal heat mainly by extruder screw characteristics, feeding and extrusion speed, not affected by heating temperature control system. When low shear extruder extrusion speed is too high, even if the feeding section and compression section of outer heating coil working frequency increases, intermittent time is short, its temperature also may not reach setting temperature; Even if fused segment and outside heating metering section to stop working and start the screw and screw cylinder cooling device operation, display temperature could still far higher than the set temperature. And due to reflect the temperature of the temperature measuring point thermocouple installed on the extruder screw are compared.in addition, a certain distance with screw tubes inside material, instrument show the actual temperature and material temperature under different conditions has a certain gradient, there are different corresponding relations. Usually charging and compression section material is heated, again there is a shear heat, heating for two-way, according to basic equivalent material temperature; Fused segment and the metering section material according to the temperature did not reach the set temperature, also for two-way heating. When the temperature beyond set temperature, heat started by passing outside introversion, could be called reverse heat transfer, temperature is lower than the temperature of the material. Thus the low shear extruder extrusion at high speeds, screw the molten material actual temperature, measuring paragraphs not only higher than the set temperature, also higher than that of temperature. So when the temperature in the operation of the region set temperature, set temperature parameters of the basic equivalent to the material temperature, is the material plasticizing melting control goal and the basis. When run display area of temperature deviates from the set temperature, temperature can be assumed to material temperature, namely the replaced set temperature as plasticizing molten material control goal and the basis. Outside the set temperature is increasing or decreasing heating control. For low shear extrusion machine, due to compression, compression paragraphs are small, provided by the internal heat is far cannot satisfy the glassy state material plasticizing requirements, therefore, feeding temperature setting, compressed paragraphs should be higher, because of the different formula, roughly around 190 ~ 200 ℃, although in improving extrusion speed case, show the temperature is still low, but to increase the temperature of the set purpose, in order to feed, compressed paragraphs electric heating circle, has been non-stop work, as long as the temperature within the range of 180 ~ 185, tightly wrapped in screw, material in micro molten state, not a vent to risk phenomenon, can be regarded as normal. Melting, metering section set temperature should be lower, because of the different formula, roughly around 165 ~ 175 ℃, although in improving extrusion speed case, show the temperature still on the high side, but reduce the purpose of the set temperature, to melt, metering section electric heating circle timely stop heating, and start the screw oil cooling and screw cylinder air-cooled cooling, the supplies as long as the temperature within the range of 180 ~ 185 ℃, extrusion parison section did not appear the symptom such as porosity, pitting, can be regarded as normal extrusion speed. And even feeding high temperature setting, compressed paragraphs, heating coil non-stop work, vent loose materials, and shows shape of bean curd, wrapped in not screw, screw tubes from vent appear to take material phenomenon; Molten set temperature, measuring paragraphs again low, electric heating circle has stopped work, screw oil cooling and screw cylinder air-cooled cooling, have been carried out on the material extrusion parison has symptoms such as porosity, pitting, can be regarded as extrusion speed has been to the limit, should be timely to reduce speed or charging and extrusion speed.
Vent risk is low shear extrusion machine characterization of plasticizing adverse. But not vent take material are caused by the low shear extrusion machine. Lead to vent at material basically has the following reasons: 1) feeding too fast, the increase of shear heat enough to balance the increased quantificationally need quantity of heat, caused by the plastic plasticizing bad; (2) the speed too fast, the increase of shear heat enough to balance the material stay in feeding period and compression time reduced and the heat loss, caused by the plastic plasticizing bad; (3) formula using CPE impact modifier, processing AIDS add quantity is less, the material friction performance is poor, to vent plasticizing bad; (4) the formula of lubricant, excessive material in the extruder mobile speed too fast, to vent plasticizing bad; (5) with screw extruder screw barrel axial clearance is too large, serious leakage flow or screw feeding period, compression temperature is too high, lead to material "plasticizer", has been transformed into body material after compression section of the first peak pressure, stress release to vent, volume expansion, adhesion in screw arris end face, with the screw rotation was exhaust section of screw barrel scraping on the vent pipe wall, accumulated to a certain extent from the vent overflow. First two vent take material are associated and shear properties of extruder, the third and fourth vent risk is mainly related to formula, 5 kinds of vents to risk is mainly related to the extrusion machine wear and high shear performance. In judging vent take material reason, should be comprehensive consideration, not blindly. If belong to the experimental formula of vent take material should be adjusted formula; If belong to extrusion machine wear and should be adjusted with screw extruder screw barrel clearance; As found material in the vent "plasticizing" should adjust the feeding speed ratio; The first three vent risk generally characterized by higher torque, the latter two vent take general performance for lower torque.