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第一篇譯文中文
2.3注射成型
2.31注射成型
注塑主要用于熱塑性塑料零件的生產(chǎn)，也是最古老的方法之一。目前注塑成型占所有塑料樹(shù)脂消費(fèi)量的30%。典型的注塑產(chǎn)品是杯，容器，工具外殼，手柄，旋鈕，電氣和通信部件（如電話接收器），玩具，和水暖配件。
聚合物熔體由于其分子量高，所以粘度很高；他們不能像金屬一樣在重力流作用下直接倒進(jìn)模具中,但在高壓下，必須強(qiáng)制進(jìn)入模具中。因此,金屬鑄件的力學(xué)性能主要是由模具壁的傳熱率決定的，這決定了在最后的鑄造中晶粒尺寸和晶粒取向, 在注射成型中的熔體注射在高壓力產(chǎn)生的剪切力是最終在材料的分子取向的主要原因。因此，成品的機(jī)械性能受模具內(nèi)注入條件和的冷卻條件兩者的影響。
注塑已應(yīng)用于熱塑性塑料和熱固性材料,泡沫部分,并已修改以產(chǎn)生的反應(yīng)注射成型(RIM)過(guò)程中,熱固性樹(shù)脂系統(tǒng)的兩個(gè)組件同時(shí)注入和快速聚合在模具內(nèi)。然而大多數(shù)注射成型是熱塑性塑料進(jìn)行,后面的討論集中于這樣的造型。
一個(gè)典型的注塑成型周期或序列由五個(gè)階段組成（見(jiàn)圖2-1）：
(1)注射或模具填充;
(2)包裝或壓縮;
(3)保壓;
(4)冷卻;
(5)部分彈射。
圖2 - 1注射成型過(guò)程
塑料芯塊（或粉末）被裝入進(jìn)料斗，穿過(guò)一條在注射料筒中通過(guò)旋轉(zhuǎn)螺桿的作用下塑料芯塊（或粉末）被向前推進(jìn)的通道。螺桿的旋轉(zhuǎn)迫使這些芯塊在高壓下對(duì)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(qiáng)，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(guò)噴嘴、澆口和流道系統(tǒng)，最后進(jìn)入模具型腔。在注塑過(guò)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(lái)完成模具的填充。典型地，在注塑過(guò)程中模具型腔被填充至95%~98%。
然后模具成型過(guò)程將進(jìn)行至壓緊階段。當(dāng)模具型腔充滿的時(shí)候，熔融的塑料便開(kāi)始冷卻。由于塑料冷卻過(guò)程中會(huì)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(bǔ)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(huì)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(gè)過(guò)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(guò)程中，熔化物通過(guò)補(bǔ)償收縮的保壓壓力來(lái)進(jìn)入型腔。固化成型過(guò)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(kāi)始了。在這個(gè)階段中，部件在模具中停留某一規(guī)定時(shí)間。冷卻階段的時(shí)間長(zhǎng)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(shí)，機(jī)器將熔化物塑煉以供下一個(gè)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(guò)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(kāi)，部件便生產(chǎn)出來(lái)了。
2.3.2注塑模具
注塑模具的多種多樣的設(shè)計(jì)、復(fù)雜程度和大小作為它們的生產(chǎn)部分。功能熱塑性塑料模具，基本上是傳授理想的形狀，然后進(jìn)行聚合物注射件的冷卻。
一種模具是由兩組部件組成：（1）型腔和型芯（2）空腔和型芯的安裝。模塑部件的尺寸和重量限制了模腔的數(shù)量并且還決定了所要求的設(shè)備的能力?？紤]成型工藝，模具必須設(shè)計(jì)的安全地吸收由于夾緊。注塑。脫模帶來(lái)的力。同時(shí)，澆口和流道的設(shè)計(jì)必須允許有效流動(dòng)和統(tǒng)一的模具型腔填充。
圖2-2示出了一個(gè)典型的注塑模具。模具主要由兩部分組成：一個(gè)部分精止不動(dòng)的（模腔板），在那邊熔融聚合物被注入，另一部分可以移動(dòng)（型心板）在截止面上或噴射器的注塑設(shè)備上。兩個(gè)半模之間的分離線被稱為分型線。注射的材料是通過(guò)中央進(jìn)料通道，稱為澆口。物料位于錐形流道，便于套管在打開(kāi)的模具中釋放模具材料。在多數(shù)模具、物料聚合物熔體助長(zhǎng)了流道系統(tǒng)，通過(guò)一個(gè)澆口流向每個(gè)模具型腔。
型芯板塊持有的主要核心。主要的目的是要建立的內(nèi)部核心配置的部分。核心板具有備份設(shè)備或支撐板。支持板作為脫模器依次被支持柱支撐壓緊u型結(jié)構(gòu)中，有后面夾持板和間隔板組成。該U形結(jié)構(gòu)，用螺栓栓在核心板上稱為推板沖程，為脫模沖程提供了空間，部分在凝固過(guò)程中收縮的主要型芯以便模具開(kāi)啟時(shí)，部分和澆口隨著移動(dòng)進(jìn)行到模具一半。隨后中央彈射器被激活，導(dǎo)致脫模板向前以至于頂出推出部分型心。兩個(gè)一半的模具都是通過(guò)冷水提供模具冷卻 通道吸收熱塑性聚合物融化傳遞給模具的熱量。模具型腔通常也合并放氣口（0.02-0.08毫米，直徑為5毫米）以確保填充物中沒(méi)有空氣。
如今有六種基本類型在注塑模具使用中.它們是：（1）兩板模具;（2）三板模;（3）熱流道模具;（4）絕緣熱流道模具;（5）熱管模具，以及（6）堆疊模具.圖. 2-3和圖2-4說(shuō)明了這六種基本類型的注塑模具。
圖2 - 2注塑模具
1 - 頂桿2 - 推板3 - 導(dǎo)套4 - 導(dǎo)柱5 - 頂桿底板6- 鉤料桿銷 7- 推回針8- 針限制9- 導(dǎo)柱10- 導(dǎo)柱11- 腔板 12 - 澆口套13- 塑料工件14- 型芯
1.兩板模
一種雙板模具由兩個(gè)板與腔和型芯安裝在任一模版上.板被固定到壓板上。移動(dòng)一半的模具通常含有推出結(jié)構(gòu)和澆道系統(tǒng)。所有注塑模具的基本設(shè)計(jì)有這樣的設(shè)計(jì)理念。兩板模具是最合乎邏輯的類型對(duì)于一些需要使用那些需要很大澆口零件的工具來(lái)說(shuō)。
2.三板模具
這種類型的模具是由三塊板組成：（1）固定或流道板是連接到靜止的滾筒，通常包含澆道和半流道，（2）中間板或模腔板，包含一半道和澆口，允許在開(kāi)模時(shí)浮動(dòng)，（3）移動(dòng)板或受力板塑造和推出系統(tǒng)部分切除塑造的部分。當(dāng)通道開(kāi)始打開(kāi)，中間板和可動(dòng)板一起移動(dòng)，從而釋放澆道和流道系統(tǒng)和去澆口的成型部件。這種類型的模具的設(shè)計(jì)能夠分隔流道系統(tǒng)和部件當(dāng)模具打開(kāi)時(shí)。這種模具的設(shè)計(jì)可以使用點(diǎn)澆口澆注系統(tǒng)。
3.熱流道模具
在注射成型的過(guò)程中，流道保持熱量以保證熔融塑料是流體狀態(tài)，在任何時(shí)候。實(shí)際上這是一個(gè)'無(wú)澆道'成型工藝而且有時(shí)被稱為是相同的。在無(wú)流道模具中，流道包含在一個(gè)獨(dú)立的板上。熱流道模具類似三板注塑模具，除了模具流道的部分在成型周期打不開(kāi)。加熱流道板與其余的冷模隔熱。除了加熱板是為了流道設(shè)計(jì)，模具剩余部分是一個(gè)標(biāo)準(zhǔn)兩板模。
無(wú)流道成型較傳統(tǒng)澆道式成型有很多優(yōu)點(diǎn)。沒(méi)有成型的副產(chǎn)物（澆口，流道，或主流道）被處理掉或循環(huán)再使用，沒(méi)有從主流到分離。周期時(shí)間是成型部分被冷卻，從模具中頂出。在這個(gè)系統(tǒng)中，一個(gè)均勻的熔體溫度可以從注射模具型腔的汽缸達(dá)到的。
4.絕緣熱流道模具
這是一個(gè)變化的保溫模具。在這種類型的模具中，流道的外表面材料是絕緣體的優(yōu)質(zhì)材料。在絕熱模具中，成型材料鑄造成型仍然通過(guò)保持熱量。有時(shí)一個(gè)分料梭和熱探測(cè)器需要更多的靈活性。這種類型的模具多腔中心澆口部分是理想的。
5.熱管模具
這是一個(gè)變化的保溫流道模具。在熱管模具中，流道是加熱的而不是流道板。這是通過(guò)使用一個(gè)電子嵌入探針完成的。
6.堆疊模具
堆疊注塑模具，顧名思義就是多個(gè)兩板模具放置一起。這種結(jié)構(gòu)也可以用于三板模具和保溫流道模具。堆疊兩模板的構(gòu)造重點(diǎn)提出一個(gè)單一通道要求比同樣數(shù)量的模具減少一般夾緊壓力。這個(gè)方法有時(shí)候被稱為“二級(jí)成型”。
2.3.3模具機(jī)
1.傳統(tǒng)注塑機(jī)
在這個(gè)過(guò)程中,塑料顆粒或顆粒注入機(jī)料斗并注入加熱缸腔內(nèi)。然后柱塞壓縮材料,迫使它逐步通過(guò)加熱缸的溫度區(qū)域,在那里它被分料梭分散的很薄。分料梭安裝在缸的中心，目的是為了加快塑料中心的加熱質(zhì)量。分料梭也可從內(nèi)部加熱處理使塑料內(nèi)外都加熱。
材料從加熱缸流動(dòng)通過(guò)一個(gè)管口進(jìn)入模具。這個(gè)管口是缸和和模具的分割點(diǎn),它是用來(lái)防止產(chǎn)生壓力導(dǎo)致物質(zhì)泄漏。模具是關(guān)閉了有夾鉗一端的機(jī)器。對(duì)于聚苯乙烯,夾鉗上兩到三噸的壓力要用于材料和系統(tǒng)的每一寸空間。傳統(tǒng)的柱塞機(jī)是唯一可以產(chǎn)生雜色部件的注塑機(jī),其他類型的完全將塑料材料融合在一起,只會(huì)產(chǎn)生一種顏色。
2.柱塞式預(yù)塑機(jī)
這臺(tái)機(jī)器使用一個(gè)分料梭加熱器來(lái)預(yù)塑塑料顆粒。融化階段后,液體塑料是被排入一個(gè)存放腔內(nèi)，直到可以進(jìn)入模具。這種類型的機(jī)器生產(chǎn)速度比傳統(tǒng)的機(jī)器快,由于成型室是在冷卻時(shí)不斷釋放能量。由于注射柱塞作用于流體材料,在顆粒壓縮時(shí)沒(méi)有壓力損失。這允許更大的部件有更大的投影面積。它其余的特性與傳統(tǒng)單活塞注射機(jī)相同。圖2 - 5演示了一個(gè)柱塞式預(yù)塑機(jī)。
3.螺桿式預(yù)塑機(jī)
這種注射機(jī)用擠出機(jī)塑化塑料材料。車削螺桿向擠壓機(jī)內(nèi)表面供料。將擠出機(jī)熔融、塑化的材料移動(dòng)到另一個(gè)存放腔,然后從那里被注射柱塞擠入模具。使用螺旋有以下優(yōu)點(diǎn):(1)塑性材料能更好的融合和受力;(2)流動(dòng)材料更硬，熱敏感材料能流動(dòng);(3)顏色變化可以在更短的時(shí)間內(nèi)處理(4)模制品受更小的壓力。
4.往復(fù)式螺桿注塑機(jī)
這種類型的注塑機(jī)在加熱室處采用臥式擠壓機(jī)。塑料材料由于螺桿的旋轉(zhuǎn)被推進(jìn)擠壓機(jī)管道。隨著材料通過(guò)加熱筒與螺桿時(shí),它正在從顆粒變成塑料熔融狀態(tài)。在往復(fù)式螺桿注塑機(jī)中,熱量傳遞到模塑料的熱量是由螺桿之間的摩擦傳導(dǎo)和擠壓機(jī)管道壁。材料移動(dòng)時(shí),螺桿又回到極限狀態(tài),這種狀態(tài)是決定材料在壓力機(jī)管道前的體積的。這時(shí),與典型壓力機(jī)的相似之處結(jié)束了。在材料注入模具時(shí),螺桿向前移動(dòng)，重新塑造管道中的材料。在這臺(tái)機(jī)器中，螺桿的角色既是一個(gè)柱塞又是一個(gè)螺桿。在模型澆口部分已經(jīng)凝固不能回流時(shí)，螺桿開(kāi)始旋轉(zhuǎn)回程，走下一圈。圖2-5是一個(gè)往復(fù)式螺桿注塑機(jī)。
這種注塑方法有幾個(gè)優(yōu)點(diǎn)。它能使熱敏材料更有效地塑化，使顏色融合更快,材料的溫度通常更低，整個(gè)循環(huán)時(shí)間也更短。
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.
Fig. 2-1 Injection molding process
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.
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.
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.
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.
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 mold.
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.
Fig. 2-5 The four basic types of injection molding equipment
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 there- 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
計(jì)算機(jī)制造
1.1計(jì)算機(jī)輔助生產(chǎn)和控制系統(tǒng)
制造技術(shù)已經(jīng)發(fā)展了很多年了，這些年來(lái)，它經(jīng)歷了很多變化，從簡(jiǎn)單到復(fù)雜。這些變化的動(dòng)力是人們?yōu)榱藵M足自己衣食住行的基本需要。為了滿足這些愿望，方法已經(jīng)發(fā)展成從為了獲取食物而制造簡(jiǎn)單的設(shè)備到今天的先進(jìn)制造系統(tǒng)，它用計(jì)算機(jī)制造這樣的產(chǎn)品：例如電視機(jī)，交通工具等。
計(jì)算機(jī)在制造系統(tǒng)中的作用已經(jīng)越來(lái)越重要，計(jì)算機(jī)的能力之一是接收和處理數(shù)據(jù)，使系統(tǒng)更加多功能。計(jì)算機(jī)制造的使用是新時(shí)代的到來(lái)。計(jì)算機(jī)在生產(chǎn)制造控制進(jìn)程方面的應(yīng)用被稱做計(jì)算機(jī)輔助制造(CAM)。它是被建立在這樣的系統(tǒng)上：數(shù)控(NC)，輔助控制(AO，機(jī)器人學(xué)，自動(dòng)牽引系統(tǒng)(AGVS)，自動(dòng)貯存／恢復(fù)系統(tǒng)(AS/RS)，和柔性制造單元(FMS)．一些新的應(yīng)用進(jìn)行了如下簡(jiǎn)要討論。更詳細(xì)的討論，會(huì)在以后的章節(jié)中提出。
許多有聯(lián)系的制造事件被組合在一起進(jìn)而組成一個(gè)特別的應(yīng)用系統(tǒng)，可以被稱為生產(chǎn)和控制系統(tǒng)( PACS)，生產(chǎn)和控制系統(tǒng)從