材料干燥
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作者:profed5ca94
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发布时间: 2021-02-01
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1544 次浏览
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不同组分的共聚物极性有别，对干燥条件的选择也各有差异，采用不同的干燥方法能达到不同的效果，各种工程塑料干燥方法与效果见附表：
2.3干燥方法与效果
不同组分的共聚物极性有别，对干燥条件的选择也各有差异，采用不同的干燥方法能达到不同的效果，各种工程塑料干燥方法与效果见附表：
2.3.1材料干燥
干燥是所有工程塑料加工的前期准备工作。原料中含有水分时经加热慢慢气化，与熔融的物料产生水解反应。如聚酰胺吸水后在酸或碱的催化作用下，将引起酰胺键的水解，其结果导致物理力学性能下降；聚酯材料中的端羧基遇水后断裂降解，粘度下降；聚碳酸酯材料的氢键水解后使分子量降低。不同高分子材料中的水分子及低分子物质升温融解后形成游离体，放出甲酸、酯类、丙酮、甲醛、乙醛、一氧化碳、二氧化碳等气体，表观现象是塑料开始变色，强度急剧下降。只有在充分干燥彻底的原料加工才能体现塑料原有的综合性能。
干燥条件取决于生产单位的现有能力，推荐采用真空负压干燥，真空度96Kpa、干燥效果好、速度快、干燥均匀；在条件不具备的情况下，采用常压热风干燥，干燥效果较好。
材料干燥程度的好坏可根据射出的料条观察，注射喷咀对空缓慢注射，材料干燥程度的好时所射出的料条应光滑细腻、光洁无泡，透明的物料还应晶莹透明，象柔软的面条一样。在有水分存在的情况下，上述现象遭到破坏，水分轻微时，料中夹有少量气泡，水分多时射出的料条有气体破裂的响声，且料条发泡严重。检查方法，用两块玻璃，中间夹一粒检测的粒料，然后放到该材料所能承受最高温度的加热板上，在玻璃片上平稳加压，将熔粒压，观察料中有无气泡，若无气泡则为合格，可供成型加工使用，否则还需继续进行干燥处理。干燥好的物料避免再次受潮，特别是极性塑料，如PA干燥好的物料在常温常压下最长放置时间不得超过1小时，梅雨天气不得超过半小时。PC、PBT等材料干燥好后在常湿常温下最长放置时间不得超过15分钟。避免再次受潮，以卧式烘厢中取出在料斗中应继续保持加热。料斗式干燥机在停机中途也不得停止加热。
2.3 The effect of drying methods and
Copolymer of different polarities are different components, the choice of the drying conditions vary, different drying methods used to achieve different effects, all kinds of engineering plastics drying method and effect of the Annex:
2.3.1 Material Drying
Dry processing of all preparatory work for engineering plastics. Raw material when heated slowly with water gasification, produce materials with melting hydrolysis. Such as polyamide, after absorbing a catalyst in the acid or alkali, will lead to amide bond hydrolysis, which resulted in decreased physical and mechanical properties; polyester material with water after the rupture of end carboxyl degradation, viscosity decreases; polycarbonate material The hydrogen bond hydrolysis to reduce molecular weight. Different polymer materials and low molecular weight substances in the water molecules to form a loose body heat to melt, emit formic acid, esters, acetone, formaldehyde, acetaldehyde, carbon monoxide, carbon dioxide and other gases, and the apparent phenomenon is the beginning of plastic color, intensity dropped drastically. Only full and thorough drying of plastic raw material in order to realize the comprehensive performance of the original.
Drying conditions depend on units of existing capacity, recommended vacuum drying, vacuum 96Kpa, drying effect is good, fast, dry and uniform; in the conditions are not favorable circumstances, the use of atmospheric air drying, drying is better .
The quality of dried material ejected material can be observed, the slow injection of air injection nozzle, a good material dried material ejected when the article should be smooth and delicate, smooth bubble-free, transparent materials should also be crystal clear, as soft, like noodles. There is water in the presence of these phenomena have been destroyed, water slightly, the compound there are the little bubbles of water for a long time expected to be a gas injection of crashing, and the foam material be serious. Inspection method, two glass, sandwiching a test of the pellet, and then put the material can withstand the highest temperature of heating plate, steady pressure on the glass will melt granulations, with or without bubbles observed compound if there is no bubble was qualified and used for molding, or need to be dried. Good material to prevent drying wet again, especially polar plastic materials as well PA drying up in place under normal temperature and pressure not to exceed 1 hour, rainy weather may not exceed half an hour. PC, PBT and other materials, good drying room temperature and humidity after the longest storage time should not exceed 15 minutes. Avoid re-wet, to remove the horizontal drying chamber should be maintained in the hopper in the heat. Hopper dryer shall not stop half-way stop heating.
