高分子专外 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聚合物加热到熔

2、融状态,在高压力和冷却到室温(低于Tg或Tm)保持其形状。Shaping involves shear, bulk and elongational deformations of the polymer melt, which have different viscoelastic characteristics塑造包括剪切、批量和聚合物熔体的拉伸变形,不同的粘弹性特征。.From: Principles of Polymer Engineering (McCrum et al. 1995) Extrusion Films and sheets薄膜和薄板 Fibers and filamen

3、ts纤维和细丝 Pipes, tubing and profiles管道油管和概要文件 Wire coating Injection Molding喷射造型法 Thermoforming热压成型 Blow Molding吹塑法 Compression and Transfer Molding压送模塑法Extrusion挤出 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. 制造无尽的等截面的产品切割、锯、切、滚或减少特定长度。 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. -挤出机固体原料转换成均匀的熔体泵,通过以均匀的速度死亡。Following the die, a train of equipme

5、nt ensures the extrudate cools to the right shape with the required molecular orientation. -挤出机固体原料转换成均匀的熔体泵,通过以均匀的速度死亡。Extrusion: Extruder挤压机: Plastication塑化作用 Cold polymer granules fed into a hopper and supplied to the screw by gravity冷聚合物颗粒送入料斗和提供螺丝的重力 Granules advance between the flights of the

6、screw and the hot walls of the barrel颗粒之间的航班提前螺钉和热桶壁 As the polymer advances along the extruder, it becomes liquid随着聚合物的进步在挤出机,它变成液体(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冲模.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. 挤出物的现象:肿胀发生在模具出口。 Explanation: Polymer liquid is

9、stressed as the cross section decreases解释:聚合物液体和截面减少压力 Swelling is due to unrelaxed stresses (rubber elasticity). 肿胀是由于unrelaxed压力(橡胶弹性)。 Swell ratio (DS/DC) depends on residence time in constrained region (die). 膨胀率(DS / DC)取决于停留时间限制地区(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注塑机器是最常见的(热塑性塑料和热固性材料)。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)型坯注塑钢棍。B) Parison is infl

16、ated by air and take the shape of the mold. - b)型坯膨胀的空气和模具的形状。C) The mold opens and the bottle is released. - c)模具打开,瓶子被释放。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部分交联聚合物之间two-halves模具模具上部的降低,聚合物压缩交联反应完成控制、模具和产品发布的开放 Advantages:Flow over shorter distances, thus less frozen-in stresse

18、s流在较短的距离,从而减少frozen-in压力便宜,方便模具设计便宜,方便模具设计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. 测量的部分交联聚合物加热锅,它撞上了一个激烈的模具。Forcing polymer through a gate leads to homogen

19、ization and pressure increase and heating迫使聚合物通过门和加热均匀化和压力将会增加。.Cross-linking is completed and solidified sample released. -交联完成和固化样品释放。Use for the production of precision shapes (electronic industry). 用于生产精密形状(电子行业)。27加工和制备热塑性塑料的加工和制造材料的描述转换从股票形式(酒吧,棒、管、板、小丸等)或多或少带有复杂的产物。聚合物高低有被证明特别适合各种挤出和注塑模具技术。在平

20、价店ticular以下主要加工和制造业务现在使产品和组件制成形状复杂的批量生产规模很大。最重要的加工和制作技术为热塑性塑料利用他们的一般低熔点的温度和shapethe材料从融化。挤出和注塑应用最广泛的是usedprocesses。螺杆挤出机的接受原始材料颗粒形态和热塑性塑料挤出机螺杆穿过蚁穴桶;材料加热接触加热桶和表面机械动作的螺钉,融化。融化是压缩圆锥的螺钉,最终通过死亡来extrud-ed形状形成管,板材,棒材或者也许是挤出更多的compli概要文件上。连续工作的螺杆挤出机和挤压产品是腾飞它就会死。或者削减成一定长度。它是重要的,熔融粘度必须足够高,以防止崩溃或失去控制的双螺杆的变形,当它

21、离开死亡,而且可能有水或空气喷出口快速冷却。高熔体粘度可以通过使用材料的高摩尔质量。冷却的速率可能决定了在挤压的结晶度的程度在水晶保利梅尔,因此影响机械和其他属性。注塑描述过程中聚合物熔体被迫卷入模具,在那里它冷却直到固体。模具然后分割成两半,允许产品剔除;随后的零部件模具夹在一起,再一次,一个进一步的数量的熔岩注入和循环反复。ma-chine结束的注射是最常见的一种阿基米德螺杆(相似,螺杆挤出机),可以产生,每一次循环,一杯熔融聚合物预定大小,然后再将其注入模具通过往复式ram行动。particu-larly注射成型提供了一个有效的方式获取复杂的形状在大型的生产运行。随着大小和/或长宽比注射成型增加它变得更diffi-cult,以确保一致性在聚合物在注射过程中,保持足够clamp-ing力量保持模具期间关闭的灌装。反应注射成型过程已经被用来解决这两个问题,本质上是通过执行大部分的polymerising反应在模具。吹塑代表一个发展的空心挤压在文章fabri