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plastics in commonly used transparent raw materials features and injection molding process
Date: 2019-11-17 10:00
Views: 2528
Source: Internet
due to plastics tool has weight light, tough property good, molding easy and cost low and other advantages, therefore in 现代业 and day use product in, 越 越 more using/adopting plastics 代替玻璃, especially used for optical device and packaging industrial 方面, development is speed. is due to requirements its transparent property need good, wear resistant parts need high, impact resistant tough parts need good, therefore for plastics formed 份, injection molding 整 process process, equipment and mold and other, requirements 严格, ensure this used for 代替玻璃 plastics （ below/following transparent plastics ）, surface quality good, from to use requirements.
currently market upper generally use transparent plastics has polymethyl methacrylate (PMMA) （即俗称亚 add force or has machine 玻璃（代号pmma）, polycarbonate (PC) （代号pc）, terephthalic acid ethylene glycol 脂（代号pet）, transparent nylon, propylene styrene copolymer （as）, polysulfone (PSU) （代号psf） and other, its in 我们接触 most more is pmma, pc and pet三 types plastics, due to has 限, lower 面就以 this types plastics is 例, transparent plastics features and injection molding process.
transparent plastics property can
transparent plastics 首先必 must has high transparency degree, its need has strong/high degree and wear resistance, can impact resistant, heat resistant parts need good, chemical resistance need excellent, water absorption need small, has this can in use in, can meet/satisfy transparent degree requirements long 久不变, lower 面列出 table/sheet, comparison lower pmma, pc and pet property can.
injection molding process precautions
transparent plastics due to light transmittance need high, for plastics products surface quality requirements 严格, can has 任何斑纹, gas 孔, 泛白, 雾晕, black spots, color, gloss and other defect, in injection molding process for raw materials, equipment, mold, product design, need separation attention/notes. its 次, due to transparent plastics more is melting point high, flow property 差, therefore is ensure product surface quality, need in machine high temperature degree, injection pressure, injection speed degree and other process parameters as fine micro adjustment, make plastics can 充满模, also generate internal stress 而引起 product deformation and cracking.
lower its in raw materials 准备, for equipment and mold requirements, injection molding process and product raw materials 处理几方面, 谈谈应 attention/notes 事项.
raw materials and drying
due to in plastics in has 任何一点杂质, can can effect/influence product transparent degree, therefore in 储存, 运输, add material process in, must attention/notes 密封, ensure raw materials dry 净. especially is raw materials in has water separation, add hot rear 会引起 raw materials 变质, therefore need drying. and, add material must use drying material 斗. also need attention/notes is drying process in, 输入 空 gas most good 应经 滤, remove wet, ensure 不会污染 raw materials.
machine 筒, screw and its parts 清洁
is anti raw materials and in screw and parts 凹陷处存 has material or 杂质, especially heat stabilized property resin in, therefore in use front, machine rear application screw agent dry parts, make its viscous has 杂质, has screw agent 时, can use pe, ps and other resin screw. 当临时停 machine 时, is anti raw materials in high temperature lower time long, understanding drop, will drying machine and machine temperature degree reduce, 如pc, pmma and other machine temperature degree need drop 至160℃ below/following. （ material temperature degree for/regarding pc应 drop 至100℃ below/following ）
mold, product design precautions
is anti 止出现回 flow or cooling 不均造 formed plastics molding defect, generate surface defects and 变质, generally in mold design 时, attention/notes below/following 几点.
a）壁 thick amount uniform 一致, demolding degree need large;
b） 渡部 separation 应逐步圆 slip 渡, anti has 尖角, generate, especially is pc product 一定不 need has 缺口;
c） gate. runner can can wide large, coarse short, according to shrinkage cold process gate 位置, necessary add cold material 井;
d） mold surface light 洁, coarse degree low （ most good low 于0.8）;
e）排 gas 孔. must 足够, and 时排出空 gas and melt in gas 体;
f） remove pet outer, thick need thin, generally small 于lmm.
injection molding process precautions
is decrease/reduce internal stress and surface quality defect, in injection molding process 方面应 attention/notes below/following 几方面 issues.
a）应 selection specialized screw, belt/tape mono temperature 控射咀 injection molding machine ;
b) injection temperature degree in plastics resin separation understanding front lower, use relatively high injection wet degree;
c） injection pressure: generally relatively high, 以克服熔 material viscosity large defect, pressure high generate internal stress formed demolding difficult and deformation;
d） injection speed degree: in meet/satisfy 充模 情况 lower, generally low, most good can using/adopting slow fast slow more grade injection;
e） holding pressure time and molding cycle: in meet/satisfy product 充模, generate 凹陷, bubbles lower; amount short, amount decrease low material in machine 筒停留 time;
f） screw speed and back pressure: in meet/satisfy quality front lower, amount low, anti generate understanding drop can can;
g） mold temperature degree: products cooling good bad, for quality effect/influence large, therefore mold temperature need can control its process, has can can 话, mold temperature high good.
other issues
due to is need anti upper surface quality 恶化, generally injection molding amount less use demolding agent; use use material large 于20％.
for/regarding remove pet outer, products 都应进行 rear 处理, remove internal stress, pmma应 in 70－80t hot ring drying 4 small 时; pc应 in 清洁空 gas, 甘油. liquid 体石腊 and other add hot 110-135℃, time product 而定, most high need 10 more small 时. 而pet必 must di toward tensile 工序, can to good mechanical properties.
transparent plastics injection molding process
remove above issues, transparent plastics has process features, separation lower:
pmma process features
pm－ma viscosity large, flow property 稍差, therefore must high material temperature, high injection pressure injection molding 才行, its in injection temperature degree effect/influence large injection pressure, injection pressure improve/increase, has improvement product shrinkage rate. injection temperature degree scope/range relatively wide, melt temperature degree is 160℃, separation understanding temperature degree 达270℃, therefore material temperature adjustment scope/range wide, process property relatively good. improvement flow property, can from injection temperature degree 手. impact property 差, wear resistance good, easy 划花, easy 脆裂, improve/increase mold temperature, improvement cold process, this defect.
pc process features
pc viscosity large, melt material temperature degree high, flow property 差, therefore must relatively high temperature degree injection molding （270－320t between ）, versus for material temperature adjustment scope/range relatively narrow, process property 不如pmma. injection pressure for flow property effect/influence relatively small, viscosity large, still need relatively large injection pressure, versus is anti internal stress generate, holding pressure time need amount short. shrinkage rate large, dimensions stability, product internal stress large, easy cracking, therefore use improve/increase temperature degree is pressure improvement flow property, and from improve/increase mold temperature degree, improvement mold structure and rear decrease/reduce cracking can can. injection speed degree low 时, gate easy 生波纹 and other defect, 放射咀 temperature degree need mono control, mold temperature degree need high, runner, gate retardant force need small.
pet process features
pet molding temperature degree high, material temperature adjustment scope/range narrow （260-300℃）, 但熔化 rear, flow property good, process property 差, 且往往 in in need add anti plant/unit. machine strong/high degree and property can injection rear high, must through tensile and modified can improvement property can. mold temperature degree control, is anti warpage. deformation important factors, therefore using/adopting hot runner mold. mold temperature degree need high, 否则会引起 surface gloss and demolding difficult.
transparent plastics parts defect and solutions
due to 篇幅关系, this 里 讨论 effect/influence product transparent degree defect. its defect large has below/following 几项:
（一）银纹: due to and cold process in, internal stress toward property effect/influence, direction generate force, make resin flow upper orientation, and non flow orientation generate light rate different 而生闪 light filament 纹, its expand rear, can can make product cracks. remove in injection molding process and mold upper attention/notes outer, most good product as 退火处理, 如pc material can add hot to 160℃ above maintain 3-5 separation 钟, again cooling can.
（二） bubbles: due to resin inner water gas and other gas 体排不出, （ in mold cold process in ） or 因充模不足, cold surface also fast cold 凝而形 formed “ true 空泡”.
（三） surface gloss 差: mold coarse degree large, 另一方面 cold 凝 早, make resin can mold surface 状态, has this make its surface micro small 凹凸不平, make product gloss.
（四）震纹: is from gate is in formed 密集波纹, its causes in melt viscosity large, front material already in type cold 凝, rear material also 冲破此 cold 凝面, make surface 出现震纹.
（五）泛白, 雾晕: main/primary due to in gas in 灰尘落入 raw materials in or raw materials water amount large 而引起.
（六）白烟, black spots: main/primary due to plastics in machine inner, local hot make machine resin generate separation understanding or 变质而形 formed.
its methods table/sheet 4.
