帶手柄水杯注塑模具設(shè)計
帶手柄水杯注塑模具設(shè)計,手柄,水杯,注塑,模具設(shè)計
第一篇譯文（中文）
2.3注射模
2.3.1注射模塑
注塑主要用于熱塑性制件的生產(chǎn)，它也是最古老的塑料成型方式之一。目前，注塑占所有塑料樹脂消費的30%。典型的注塑產(chǎn)品主要有杯子器具、容器、機架、工具手柄、旋鈕（球形捏手）、電器和通訊部件（如電話接收器），玩具和鉛管制造裝置。
聚合物熔體因其較高的分子質(zhì)量而具有很高的粘性；它們不能像金屬一樣在重力流的作用下直接被倒入模具中，而是需要在高壓的作用下強行注入模具中。因此當(dāng)一個金屬鑄件的機械性能主要由模壁熱傳遞的速率決定，這決定了最終鑄件的晶粒度和纖維取向，也決定了注塑時熔體注入時的高壓產(chǎn)生強大的剪切力是物料中分子取向的主要決定力量。由此所知，成品的機械性能主要受注射條件和在模具中的冷卻條件影響。
注塑已經(jīng)被應(yīng)用于熱塑性塑料和熱固性塑料、泡沫部分，而且也已經(jīng)被改良用于生產(chǎn)反應(yīng)注塑過程，在此過程中，一個熱固樹脂系統(tǒng)的兩個組成部分在模具中同時被注射填充，然后迅速聚合。然而大多數(shù)注塑被用熱塑性塑料上，接下來的討論就集中在這樣的模具上。
典型的注塑周期或流程包括五個階段（見圖2-1）：
（1）注射或模具填充；
（2）填充或壓緊；
（3）定型；
（4）冷卻；
（5）零件頂出。
圖2-1 注塑流程
塑料芯塊（或粉末）被裝入進料斗，穿過一條在注射料筒中通過旋轉(zhuǎn)螺桿的作用下塑料芯塊（或粉末）被向前推進的通道。螺桿的旋轉(zhuǎn)迫使這些芯塊在高壓下對抗使它們受熱融化的料筒加熱壁。加熱溫度在265至500華氏度之間。隨著壓力增強，旋轉(zhuǎn)螺桿被推向后壓直到積累了足夠的塑料能夠發(fā)射。注射活塞迫使熔融塑料從料筒，通過噴嘴、澆口和流道系統(tǒng)，最后進入模具型腔。在注塑過程中，模具型腔被完全充滿。當(dāng)塑料接觸冰冷的模具表面，便迅速固化形成表層。由于型芯還處于熔融狀態(tài)，塑料流經(jīng)型芯來完成模具的填充。典型地，在注塑過程中模具型腔被填充至95%~98%。
然后模具成型過程將進行至壓緊階段。當(dāng)模具型腔充滿的時候，熔融的塑料便開始冷卻。由于塑料冷卻過程中會收縮，這增加了收縮痕、氣空、尺寸不穩(wěn)定性等瑕疵。為了彌補收縮，額外的塑料就要被壓入型腔。型腔一旦被填充，作用于使物料熔化的壓力就會阻止模具型腔中的熔融塑料由模具型腔澆口處回流。壓力一直作用到模具型腔澆口固化。這個過程可以分為兩步（壓緊和定型），或者一步完成（定型或者第二階段）。在壓緊過程中，熔化物通過補償收縮的保壓壓力來進入型腔。固化成型過程中，壓力僅僅是為了阻止聚合物熔化物逆流。
固化成型階段完成之后，冷卻階段便開始了。在這個階段中，部件在模具中停留某一規(guī)定時間。冷卻階段的時間長短主要取決于材料特性和部件的厚度。典型地，部件的溫度必須冷卻到物料的噴出溫度以下。
冷卻部件時，機器將熔化物塑煉以供下一個周期使用。高聚物受剪切作用和電熱絲的能量情況影響。一旦噴射成功，塑煉過程便停止了。這是在冷卻階段結(jié)束之前瞬間發(fā)生的。然后模具打開，部件便生產(chǎn)出來了。
2.3.2注塑模具
注塑模具與它們的生產(chǎn)出來的產(chǎn)品一樣，在設(shè)計、精密度和尺寸方面各不相同。熱塑性模具的功能主要是把可塑性聚合物制成人們想要的形狀，然后再將模制部件冷卻。
模具主要由兩個部件組成：（1）型腔和型芯，（2）固定型腔和型芯的底座。模制品的尺寸和重量限制了模具型腔的數(shù)量，同時也決定了所需設(shè)備的能力。從模具成型過程考慮，模具設(shè)計時要能安全合模、注射、脫模的作用力。此外，澆口和流道的設(shè)計必須允許有效的流動以及模具型腔均勻填充。
圖2-2舉例說明了典型注射模具中的部件。模具主要由兩部分組成：固定部分（型腔固定板），熔化的聚合物被注入的旁邊；在注塑設(shè)備結(jié)尾或排出旁邊的瓣合（中心板）部分。模具這兩部分之間的分隔線叫做分型線。注射材料通過一條叫做澆口的中心進料通道被轉(zhuǎn)運。澆口位于澆口軸套的上面，它逐漸縮?。ㄥF形）是為了促進模具打開時澆注材料的釋放。在多型腔模具中，主流道將高分子聚合熔化物提供到流道系統(tǒng)中，流道系統(tǒng)通過澆口流入每個模具型腔。
中心板支撐主型芯。主型芯的用途是確立部件的內(nèi)部結(jié)構(gòu)。中心板有一個支持或支撐板。支撐板反過來被背對注塑模頂桿空間的U型結(jié)構(gòu)的柱子支撐，注塑模頂桿空間由背面的壓板和墊塊組成。被固定在中心板上的U型結(jié)構(gòu)，為也被叫做脫模行程的頂出行程提供了空間。在固化的過程中，部件從主型芯周圍收縮以至于當(dāng)模具打開的時候，部件和澆口隨著瓣合機構(gòu)一起被帶出來。接著，中央的起模桿被激活，引起脫模板向前移動以至于頂桿能夠推動部件離開型芯。帶有冷卻通道的上下模被提供，冷卻通道通過冷卻水循環(huán)流通來吸收熱塑性高分子聚合熔融物傳遞給模具的熱量。模具型腔也包含好的通風(fēng)口（對于5毫米而言，通風(fēng)口應(yīng)該為0.02到0.08毫米）來確保填充過程中沒有空氣滯留在模具型腔內(nèi)。
1-頂桿 2-頂出板 3-導(dǎo)套 4-導(dǎo)柱 5-下頂針板 6-脫件銷 7-復(fù)位桿 8-限位桿
9-導(dǎo)柱 10-導(dǎo)柱 11-型腔板 12-澆口套 13-塑料工件 14-型芯
現(xiàn)在使用的有六種基本注射模具類型。它們是：（1）雙板模；（2）三板模；（3）熱流道模具；（4）絕熱保溫流道模具；（5）溫流道模具；和（6）重疊壓塑模具。圖2-3和圖2-4闡明了這六種基本注射模具類型。
1.雙板模
一個雙板模具由每塊都帶有型腔和型芯的兩塊平板組成。平板被固定在壓板上。瓣合機構(gòu)包含工件自動拆卸機構(gòu)和流道系統(tǒng)。所有注射模具的基本設(shè)計都有這個思想。雙板模具是用來制作要求大型澆口制品的最合理的工具。
2. 三板模
這種類型的模具由三塊板組成：（1）固定板或壓板被連接到固定壓盤上，通常包含主流道和分流道；（2）當(dāng)模具打開的時候，包含分流道和澆口中間板或型腔固定板是被允許浮動的；（3）活動板或陽模板包含模制件和用來除去模制件的頂出裝置。當(dāng)按壓進行打開的時候，中間板和活動板一起移動，因此釋放了主流道和分流道系統(tǒng)和清除了澆口處模制品的贅物。當(dāng)模具打開的時候，這種設(shè)計類型的模具使分離流道系統(tǒng)和模制件變成了可能。這種模具設(shè)計讓點澆口澆注系統(tǒng)能夠運用。
3. 熱流道模具
在這個注射模具的流程中，分流道要保持熱的，目的是使熔融的塑料一直處于流動的狀態(tài)。實際上，這是一個“無流道”模具流程，有時候它也被叫做無流道模具。在無流道模具中，分流道被包含在自己的板中。熱流道模具除了模塑周期中模具的分流道部分不被打開這點外，其他地方與三板注射模具相似。加熱流道板與剩下的冷卻部分的模具是絕緣的。分流道中除了熱加板，模具中剩余部分是一個標(biāo)準(zhǔn)的兩板模具。
無流道模具相比傳統(tǒng)的澆口流道模具有幾個優(yōu)點。無流道模具沒有模具副產(chǎn)品（澆口，分流道，主流道）被處理或者再利用，也沒有澆口與制件的分離。周期僅僅要求制件被冷卻和從模具中脫離。在這個系統(tǒng)中，從注射料筒到模具型腔，溫度能夠達(dá)到統(tǒng)一。
4. 絕熱保溫流道模具
絕熱流道模具是熱流道模具的一種演變。在這種類型的模具中，分流道材料的外表面充當(dāng)了絕緣體來讓熔融材料通過。在隔熱的模具中，通過保留自己的溫度使模具中的物料一直是熔化的。有時候，一個分料梭和熱探測器被加入模具中來增加柔韌性。這種類型的模具對于多孔中心澆口的制件來說是理想的。
5. 溫流道模具
它是熱流道模具的一種演變。在這種模具中，流道而不是流道板被加熱。這是通過電子芯片嵌入探測器實現(xiàn)的。
6. 重疊壓塑模具
重疊壓塑注射模具顧名思義。一個多重兩板模具其中的一塊板被放在另一塊板的上面。這種結(jié)構(gòu)也可以用在三板模具和熱流道模具上。兩板重疊結(jié)構(gòu)使單一的擠壓輸出量加倍，與一個型腔數(shù)量相同的兩板模具相比，還減少了一半的合模壓力。這種方式也被叫做“雙層模塑”。
2.3.3壓膜機
1. 傳統(tǒng)的注塑機
在這個流程中，塑料顆?；蚍勰┍坏谷胍粋€機器料斗中，然后被送入加熱料筒室。一個活塞壓縮物料，迫使物料漸進地通過加熱料筒中物料被分料梭慢慢散開的加熱區(qū)域。分料梭被安裝在料筒的中心，目的是加速塑料體中心的加熱。分料梭也有可能被加熱，以便塑料能夠內(nèi)外一起被加熱。
物料從加熱料斗流經(jīng)噴嘴進入模具。噴嘴是料斗和模具之間的密封裝置它被用來阻止因為剩余壓力而引起的物料泄露。模具在注塑機的末端被夾具夾緊閉合。對于聚苯乙烯而言，機器末端兩三噸的壓力通常用在之間和流道系統(tǒng)中每個小的投影面積上。傳統(tǒng)的活塞式機器是唯一能生產(chǎn)斑點部分的類型的機器。另一種類型的注塑機將塑料材料充分地混合，以至于僅有一種顏色被生產(chǎn)出來。
2. 柱塞式預(yù)塑機
這種機器使用了分料梭活塞加熱器來預(yù)塑塑料顆粒。塑料顆粒變成熔化狀態(tài)之后，液態(tài)的塑料被倒入一個蓄料室，直到塑料準(zhǔn)備好被壓入模具。這種類型的機器比傳統(tǒng)的機器生產(chǎn)零件的速度更快，因為在制件冷卻的時間中，模具腔被填滿進行噴射。由于注射活塞在流動的物料中工作，因此在壓縮顆粒的時候沒有壓力損失。這種現(xiàn)象能夠應(yīng)用在帶有更多投影面積的大型制件上。柱塞式預(yù)塑機的其他特點與傳統(tǒng)的單一活塞式注塑機是一樣的。圖2-5舉例說明了柱塞式預(yù)塑機。
3. 螺桿式預(yù)塑機
在這種注塑機中，用擠壓機來塑化塑料物料。旋轉(zhuǎn)的螺桿使塑料芯塊向前，提供給擠壓機料筒的加熱內(nèi)壁。熔融的，塑化的物料從擠壓機移動到一個蓄料室，然后通過注射活塞移動到模具中。螺桿的應(yīng)用有以下優(yōu)勢：（1）便于物料更好的混合及塑料溶化后的剪切作用；（2）流動物料硬度的范圍更廣及熱敏材料可以流動；（3）能在更短的時間內(nèi)進行色澤改變；（4）模具制件中的應(yīng)力更小
4. 往復(fù)式螺桿注塑機
這種類型的注塑機使用了一個水平的擠壓機來代替加熱室。螺桿的旋轉(zhuǎn)使塑料物料向前移動通過擠壓機料筒。隨著物料流經(jīng)帶螺桿的加熱料筒，物料從顆粒狀態(tài)變?yōu)樗芰先廴跔顟B(tài)。螺桿往復(fù)的過程中，傳遞給模制物料的熱量是由螺桿和擠壓機的料筒壁之間的摩擦和傳導(dǎo)引起的。當(dāng)物料向前移動的時候，螺桿返回到在擠壓機料筒前方?jīng)Q定物料容量的行程開關(guān)處。
在這個時候，與典型擠壓機類似的擠壓過程結(jié)束了。當(dāng)物料注射到模具中，螺桿向前移動來轉(zhuǎn)移料筒中的物料。在這個注塑機中，螺桿既充當(dāng)活塞，又充當(dāng)螺桿。模具中的澆口截面凍結(jié)阻止回流之后，螺桿開始旋轉(zhuǎn)并且向后移動，進行下一個周期。圖2-5展示了往復(fù)式螺桿注塑機。
這種形式的注塑有幾個優(yōu)點。它更有效地塑化熱敏感材料，由于螺桿的混合作用更快地混合色澤。給材料加熱的文都能夠更低，并且整個周期時間可以更短。
第一篇英文原文
2.3 Injection Molds
2.3.1 Injection Molding
Injection molding is principally used for the production of thermoplastic parts, and it is also one of the oldest. Currently injection-molding accounts for 30% of all plastics resin consumption. Typical injection-molded products are cups, containers, housings, tool handles, knobs, electrical and communication components (such as telephone receivers), toys, and plumbing fittings.
Polymer melts have very high viscosities due to their high molecular weights; they cannot be poured directly into a mold under gravity flow as metals can, but must be forced into the mold under high pressure. Therefore while the mechanical properties of a metal casting are predominantly determined by the rate of heat transfer from the mold walls, which determines the grain size and grain orientation in the final casting, in injection molding the high pressure during the injection of the melt produces shear forces that are the primary cause of the final molecular orientation in the material. The mechanical properties of the finished product are therefore affected by both the injection conditions and the cooling conditions within the mold.
Injection molding has been applied to thermoplastics and thermosets, foamed parts, and has been modified to yield the reaction injection molding (RIM) process, in which the two components of a thermosetting resin system are simultaneously injected and polymerize rapidly within the mold. Most injection molding is however performed on thermoplastics, and the discussion that follows concentrates on such moldings.
A typical injection molding cycle or sequence consists of five phases (see Fig. 2-1):
(1) Injection or mold filling;
(2) Packing or compression;
(3) Holding;
(4) Cooling;
(5) Part ejection.
Fig. 2-1 Injection molding process
Plastic pellets (or powder) are loaded into the feed hopper and through an opening in the injection cylinder where they are carried forward by the rotating screw. The rotation of the screw forces the pellets under high pressure against the heated walls of the cylinder causing them to melt. Heating temperatures range from 265 to 500 °F. As the pressure builds up, the rotating screw is forced backward until enough plastic has accumulated to make the shot. The injection ram (or screw) forces molten plastic from the barrel, through the nozzle, sprue and runner system, and finally into the mold cavities. During injection, the mold cavity is filled volumetrically. When the plastic contacts the cold mold surfaces, it solidifies (freezes) rapidly to produce the skin layer. Since the core remains in the molten state, plastic flows through the core to complete mold filling. Typically, the cavity is filled to 95%~98% during injection.
Then the molding process is switched over to the packing phase. Even as the cavity is filled, the molten plastic begins to cool. Since the cooling plastic contracts or shrinks, it gives rise to defects such as sink marks, voids, and dimensional instabilities. To compensate for shrinkage, addition plastic is forced into the cavity. Once the cavity is packed, pressure applied to the melt prevents molten plastic inside the cavity from back flowing out through the gate. The pressure must be applied until the gate solidifies. The process can be divided into two steps (packing and holding) or may be encompassed in one step (holding or second stage). During packing, melt forced into the cavity by the packing pressure compensates for shrinkage. With holding, the pressure merely prevents back flow of the polymer melt.
After the holding stage is completed, the cooling phase starts. During cooling, the part is held in the mold for specified period. The duration of the cooling phase depends primarily on the material properties and the part thickness. Typically, the part temperature must cool below the material’s ejection temperature.
While cooling the part, the machine plasticates melt for the next cycle. The polymer is subjected to shearing action as well as the condition of the energy from the heater bands. Once the shot is made, plastication ceases. This should occur immediately before the end of the cooling phase. Then the mold opens and the part is ejected.
2.3.2 Injection Molds
Molds for injection molding are as varied in design, degree of complexity, and size as are the parts produced from them. The functions of a mold for thermoplastics are basically to impart the desired shape to the plasticized polymer and then to cool the molded part.
A mold is made up of two sets of components: (1) the cavities and cores, and (2) the base in which the cavities and cores are mounted. The size and weight of the molded parts limit the number of cavities in the mold and also determine the equipment capacity required. From consideration of the molding process, a mold has to be designed to safely absorb the forces of clamping, injection, and ejection. Also, the design of the gates and runners must allow for efficient flow and uniform filling of the mold cavities.
Fig.2-2 illustrates the parts in a typical injection mold. The mold basically consists of two parts: a stationary half (cavity plate), on the side where molten polymer is injected, and a moving half (core plate) on the closing or ejector side of the injection molding equipment. The separating line between the two mold halves is called the parting line. The injected material is transferred through a central feed channel, called the sprue. The sprue is located on the sprue bushing and is tapered to facilitate release of the sprue material from the mold during mold opening. In multicavity molds, the sprue feeds the polymer melt to a runner system, which leads into each mold cavity through a gate.
The core plate holds the main core. The purpose of the main core is to establish the inside configuration of the part. The core plate has a backup or support plate. The support plate in turn is supported by pillars against the U-shaped structure known as the ejector housing, which consists of the rear clamping plate and spacer blocks. This U-shaped structure, which is bolted to the core plate, provides the space for the ejection stroke also known as the stripper stroke. During solidification the part shrinks around the main core so that when the mold opens, part and sprue are carried along with the moving mold half. Subsequently, the central ejector is activated, causing the ejector plates to move forward so that the ejector pins can push the part off the core. Both mold halves are provided with cooling channels through which cooled water is circulated to absorb the heat delivered to the mold by the hot thermoplastic polymer melt. The mold cavities also incorporate fine vents (0.02 to 0.08 mm by 5 mm) to ensure that no air is trapped during filling.
Fig. 2-2 Injection mold
1-ejector pin 2-ejector plate 3-guide bush 4-guide pillar 5-ejector base plate
6-sprue puller pin 7-push-back pin 8-limit pin 9-guide pillar 10-guide pillar 11-cavity plate
12-sprue bushing 13-plastic workpiece 14-core
There are six basic types of injection molds in use today. They are: (1) two-plate mold; (2) three-plate mold, (3) hot-runner mold; (4) insulated hot-runner mold; (5) hot-manifold mold; and (6) stacked mold. Fig. 2-3 and Fig. 2-4 illustrate these six basic types of injection molds.
Fig. 2-3 This illustrates three of the six basic types of injection molding dies
(1) Two-plate injection mold (2) Three-plate injection mold (3) Hot-runner mold See Fig. 2-4 for the other three types.
Fig. 2-4 This illustrates three of the six basic types of injection molding dies
(1) Insulated runner injection mold (2) Hot manifold injection mold (3) Stacked injection mold See Fig. 2-3 for the other three types.
1. Two-Plate Mold
A two-plate mold consists of two plates with the cavity and cores mounted in either plate. The plates are fastened to the press platens. The moving half of the mold usually contains the ejector mechanism and the runner system. All basic designs for injection molds have this design concept. A two-plate mold is the most logical type of tool to use for parts that require large gates.
2. Three-Plate Mold
This type of mold is made up of three plates: (1) the stationary or runner plate is attached to the stationary platen, and usually contains the sprue and half of the runner; (2) the middle plate or cavity plate, which contains half of the runner and gate, is allowed to float when the mold is open; and (3) the movable plate or force plate contains the molded part and the ejector system for the removal of the molded part. When the press starts to open, the middle plate and the movable plate move together, thus releasing the sprue and runner system and degating the molded part. This type of mold design makes it possible to segregate the runner system and the part when the mold opens. The die design makes it possible to use center-pin-point gating.
3. Hot-Runner Mold
In this process of injection molding, the runners are kept hot in order to keep the molten plastic in a fluid state at all times. In effect this is a ‘runnerless’ molding process and is sometimes called the same. In runnerless molds, the runner is contained in a plate of its own. Hot runner molds are similar to three-plate injection molds, except that the runner section of the mold is not opened during the molding cycle. The heated runner plate is insulated from the rest of the cooled mold. Other than the heated plate for the runner, the remainder of the mold is a standard two-plate die.
Runnerless molding has several advantages over conventional sprue runner-type molding. There are no molded side products (gates, runners, or sprues) to be disposed of or reused, and there is no separating of the gate from the part. The cycle time is only as long as is required for the molded part to be cooled and ejected from the mold. In this system, a uniform melt temperature can be attained from the injection cylinder to the mold cavities.
4. Insulated Hot-Runner Mold
This is a variation of the hot-runner mold. In this type of molding, the outer surface of the material in the runner acts like an insulator for the melten material to pass through. In the insulated mold, the molding material remains molten by retaining its own heat. Sometimes a torpedo and a hot probe are added for more flexibility. This type of mold is ideal for multicavity center-gated parts.
5. Hot-Manifold
This is a variation of the hot-runner mold. In the hot-manifold die, the runner and not the runner plate is heated. This is done by using an electric-cartridge-insert probe.
6. Stacked Mold
The stacked injection mold is just what the name implies. A multiple two-plate mold is placed one on top of the other. This construction can also be used with three-plate molds and hot-runner molds. A stacked two-mold construction doubles the output from a single press and reduces the clamping pressure required to one half, as compared to a mold of the same number of cavities in a two-plate mold. This method is sometimes called “two-level molding”.
2.3.3 Mold Machine
1. Conventional Injection-Molding Machine
In this process, the plastic granules or pellets are poured into a machine hopper and fed into the chamber of the heating cylinder. A plunger then compresses the material, forcing it through progressively hotter zones of the heating cylinder, where it is spread thin by a torpedo. The torpedo is installed in the center of the cylinder in order to accelerate the heating of the center of the plastic mass. The torpedo may also be heated so that the plastic is heated from the inside as well as from the outside.
The material flows from the heating cylinder through a nozzle into the mold. The nozzle is the seal between the cylinder and the mold; it is used to prevent leaking of material caused by the pressure used. The mold is held shut by the clamp end of the machine. For polystyrene, two to three tons of pressure on the clamp end of the machine is generally used for each inch of projected area of the part and runner system. The conventional plunger machine is the only type of machine that can produce a mottle-colored part. The other types of injection machines mix the plastic material so thoroughly that only one color will be produced.
2. Piston-Type Preplastifying Machine
This machine employs a torpedo ram heater to preplastify the plastic granules. After the melt stage, the fluid plastic is pushed into a holding chamber until it is ready to be forced into the die. This type of machine produces pieces faster than a conventional machine, because the molding chamber is filled to shot capacity during the cooling time of the part. Due to the fact that the injection plunger is acting on fluid material, no pressure loss is encountered in compacting the granules. This allows for larger parts with more projected area. The remaining features of a piston-type preplastifying machine are identical to the conventional single-plunger injection machine. Fig. 2-5 illustrates a piston or plunger preplastifying injection molding machine.
Fig. 2-5 The four basic types of injection molding equipment
3. Screw-Type Preplastifying Machine
In this injection-molding machine, an extruder is used to plasticize the plastic material. The turning screw feeds the pellets forward to the heated interior surface of the extruder barrel. The molten, plasticized material moves from the extruder into a holding chamber, and from there is forced into the die by the injection plunger. The use of a screw gives the following advantages: (1) better mixing and shear action of the plastic melt; (2) a broader range of stiffer flow and heatsensitive materials can be run; (3) color changes can be handled in a shorter time, and (4) fewer stresses are obtained in the molded part.
4. Reciprocating-Screw Injection Machine
This type of injection molding machine employs a horizontal extruder in place of the heating chamber. The plastic material is moved forward through the extruder barrel by the rotation of a screw. As the material progresses through the heated barrel with the screw, it is changing from the granular condition to the plastic molten state. In the reciprocating screw, the heat delivered to the molding compound is caused by both friction and conduction between the screw and the walls of the barrel of the extruder. As the material moves forward, the screw backs up to a limit switch that determines the volume of material in the front of the extruder barrel. It is at this point that the re- semblance to a typical extruder ends. On the injection of the material into the die, the screw moves forward to displace the material in the barrel. In this machine, the screw performs as a ram as well as a screw. After the gate sections in the mold have frozen to prevent backflow, the screw begins to rotate and moves backward for the next cycle. Fig.2-5 shows a reciprocating-screw injection machine.
There are several advantages to this method of injection molding. It more efficiently plasticizes the heat-sensitive materials and blends colors more rapidly, due to the mixing action of the screw. The material heat is usually lower and the overall cycle time is shorter.
第二篇譯文
環(huán)保意識的設(shè)計和制造
ECD＆M研究的問題包括：產(chǎn)品與過程集成與材料選擇系統(tǒng)的設(shè)計，評估消費者的需求和產(chǎn)品使用的集成模型的發(fā)展，
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