高分子專外 Lecture25

1、Processing of Polymers Increasing use of polymers Light, tough, corrosion resistant and cheap Price: Raw material + Processing Processing of “Solid” Polymers:Polymer heated to the melt state, shaped under high pressure and cooled down to room temperature (below Tg or Tm) to preserve its shape聚合物加熱到熔

2、融狀態(tài),在高壓力和冷卻到室溫(低于Tg或Tm)保持其形狀。Shaping involves shear, bulk and elongational deformations of the polymer melt, which have different viscoelastic characteristics塑造包括剪切、批量和聚合物熔體的拉伸變形,不同的粘彈性特征。.From: Principles of Polymer Engineering (McCrum et al. 1995) Extrusion Films and sheets薄膜和薄板 Fibers and filamen

3、ts纖維和細(xì)絲 Pipes, tubing and profiles管道油管和概要文件 Wire coating Injection Molding噴射造型法 Thermoforming熱壓成型 Blow Molding吹塑法 Compression and Transfer Molding壓送模塑法Extrusion擠出 Most common polymer processing (60% of world production).Manufactures an endless product of constant cross-section that is cut, sawed, ch

4、opped, rolled or reduced to specific length. 制造無盡的等截面的產(chǎn)品切割、鋸、切、滾或減少特定長(zhǎng)度。 Two-part process including “plastication” and “shaping”Extruder converts a solid feedstock into a homogeneous melt and pumps it through a die at a uniform rate. -擠出機(jī)固體原料轉(zhuǎn)換成均勻的熔體泵,通過以均勻的速度死亡。Following the die, a train of equipme

5、nt ensures the extrudate cools to the right shape with the required molecular orientation. -擠出機(jī)固體原料轉(zhuǎn)換成均勻的熔體泵,通過以均勻的速度死亡。Extrusion: Extruder擠壓機(jī): Plastication塑化作用 Cold polymer granules fed into a hopper and supplied to the screw by gravity冷聚合物顆粒送入料斗和提供螺絲的重力 Granules advance between the flights of the

6、screw and the hot walls of the barrel顆粒之間的航班提前螺釘和熱桶壁 As the polymer advances along the extruder, it becomes liquid隨著聚合物的進(jìn)步在擠出機(jī),它變成液體(by melting or by passing through the glass transition玻璃化)The polymer becomes pressurized at it moves along the extruder, so it can easily exit the extruder through a d

7、ie沖模.Extrusion:A.) Conventional; B.) For “fragile” polymers; C.) PVC-type; D.) Nylon-typeScrew Parameters:1) Zones (number, lengths, types)2) Helix angle (f)3) Flight width (W)4) Channel depth (H)5) Screw Length to Diameter ratioExtrusion: Shaping: Die shape dictates the nature of thepolymer product

8、. Circular die: Melt spinning of fibers Slit die: Sheet casting Annular die: Film blowing Pipes (f 12 mm) and tubing (f 12 mm) Wire coating The Die-swell Issue: A polymer extrusion problem Phenomenon: Swelling of the extrudate occurs at the die exit. 擠出物的現(xiàn)象:腫脹發(fā)生在模具出口。 Explanation: Polymer liquid is

9、stressed as the cross section decreases解釋:聚合物液體和截面減少壓力 Swelling is due to unrelaxed stresses (rubber elasticity). 腫脹是由于unrelaxed壓力(橡膠彈性)。 Swell ratio (DS/DC) depends on residence time in constrained region (die). 膨脹率(DS / DC)取決于停留時(shí)間限制地區(qū)(死)。 Parameters which affect the swell ratio: LC, g, MW, TDB DC

10、DS Film Blowing Pipes and TubingExtrusion: Wire CoatingExtrusion: Die-swell IssueSolution : 1) Keep die swelling phenomenon. Why?2) Design die profile to account for die swelling.2) Use pull rolls to draw down extrudate.Injection Molding: Injection + MoldingReciprocating-screw injection molding mach

11、ines are the most common (thermoplastics and thermosets). Reciprocating-screw注塑機(jī)器是最常見的(熱塑性塑料和熱固性材料)。Do we need to apply pressure during molding ? Why ? Injection + Multiple MoldingsCycle time: several seconds to several minutes.Gate Designs: Cause work to be done to make the liquid flow through a sm

12、all constriction, so T increases (h decreases). Important for homogenization Important for control of orientation Important for control of surfaces Pressure, Temperature and Velocity Controls:Thermoforming Application for large formings, thin wall packaging, short-run orprototype products. Much lowe

13、r initial investment than injection molding.With matched molds Pressure-bubble vacuum-snapback techniqueBlow MoldingBlow molding is widely used for producing hollow containers in vast numbers and cheaply. Three major variants: Extrusion-blow molding Injection-blow molding Stretch-blow molding Common

14、 features Formation of a precursor (hollow tube called a parison). One end of parison is closed, so it can be inflated in the heated, softened state. Inflation continues until parison touches the walls of the cooled mold. Mold is opened and bottle released.Extrusion-BlowMolding Four-step ProcessA)Ex

15、trusion of parison in open moldB)Mold closes and parison is inflatedC) D)When parison reaches the walls of the mold, it is cooledThe mold is open and the bottle releasedInjection-Blow Molding Three-steps at three stationsA) Parison is injection molded on to a steel rod. - a)型坯注塑鋼棍。B) Parison is infl

16、ated by air and take the shape of the mold. - b)型坯膨脹的空氣和模具的形狀。C) The mold opens and the bottle is released. - c)模具打開,瓶子被釋放。Compression and Transfer Molding Compression Molding Historically, the first technique for mass production Used currently only for cross-linked polymersPartially cross-linked po

17、lymer between two-halves of mold Upper part of mold is lowered and polymer is compressed Cross-linking reaction is completed under controlled P&T Mold is open and product released部分交聯(lián)聚合物之間two-halves模具模具上部的降低,聚合物壓縮交聯(lián)反應(yīng)完成控制、模具和產(chǎn)品發(fā)布的開放 Advantages:Flow over shorter distances, thus less frozen-in stresse

18、s流在較短的距離,從而減少frozen-in壓力便宜,方便模具設(shè)計(jì)便宜,方便模具設(shè)計(jì)Cheaper and easier mold designCheaper mold maintenance Transfer MoldingMeasured charge of partially cross-linked polymer is heated in a pot, from which it is rammed into a heated mold. 測(cè)量的部分交聯(lián)聚合物加熱鍋,它撞上了一個(gè)激烈的模具。Forcing polymer through a gate leads to homogen

19、ization and pressure increase and heating迫使聚合物通過門和加熱均勻化和壓力將會(huì)增加。.Cross-linking is completed and solidified sample released. -交聯(lián)完成和固化樣品釋放。Use for the production of precision shapes (electronic industry). 用于生產(chǎn)精密形狀(電子行業(yè))。27加工和制備熱塑性塑料的加工和制造材料的描述轉(zhuǎn)換從股票形式(酒吧,棒、管、板、小丸等)或多或少帶有復(fù)雜的產(chǎn)物。聚合物高低有被證明特別適合各種擠出和注塑模具技術(shù)。在平

20、價(jià)店ticular以下主要加工和制造業(yè)務(wù)現(xiàn)在使產(chǎn)品和組件制成形狀復(fù)雜的批量生產(chǎn)規(guī)模很大。最重要的加工和制作技術(shù)為熱塑性塑料利用他們的一般低熔點(diǎn)的溫度和shapethe材料從融化。擠出和注塑應(yīng)用最廣泛的是usedprocesses。螺桿擠出機(jī)的接受原始材料顆粒形態(tài)和熱塑性塑料擠出機(jī)螺桿穿過蟻穴桶;材料加熱接觸加熱桶和表面機(jī)械動(dòng)作的螺釘,融化。融化是壓縮圓錐的螺釘,最終通過死亡來extrud-ed形狀形成管,板材,棒材或者也許是擠出更多的compli概要文件上。連續(xù)工作的螺桿擠出機(jī)和擠壓產(chǎn)品是騰飛它就會(huì)死?；蛘呦鳒p成一定長(zhǎng)度。它是重要的,熔融粘度必須足夠高,以防止崩潰或失去控制的雙螺桿的變形,當(dāng)它

21、離開死亡,而且可能有水或空氣噴出口快速冷卻。高熔體粘度可以通過使用材料的高摩爾質(zhì)量。冷卻的速率可能決定了在擠壓的結(jié)晶度的程度在水晶保利梅爾,因此影響機(jī)械和其他屬性。注塑描述過程中聚合物熔體被迫卷入模具,在那里它冷卻直到固體。模具然后分割成兩半,允許產(chǎn)品剔除;隨后的零部件模具夾在一起,再一次,一個(gè)進(jìn)一步的數(shù)量的熔巖注入和循環(huán)反復(fù)。ma-chine結(jié)束的注射是最常見的一種阿基米德螺桿(相似,螺桿擠出機(jī)),可以產(chǎn)生,每一次循環(huán),一杯熔融聚合物預(yù)定大小,然后再將其注入模具通過往復(fù)式ram行動(dòng)。particu-larly注射成型提供了一個(gè)有效的方式獲取復(fù)雜的形狀在大型的生產(chǎn)運(yùn)行。隨著大小和/或長(zhǎng)寬比注射成型增加它變得更diffi-cult,以確保一致性在聚合物在注射過程中,保持足夠clamp-ing力量保持模具期間關(guān)閉的灌裝。反應(yīng)注射成型過程已經(jīng)被用來解決這兩個(gè)問題,本質(zhì)上是通過執(zhí)行大部分的polymerising反應(yīng)在模具。吹塑代表一個(gè)發(fā)展的空心擠壓在文章fabri