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PVC塑料注塑成型工藝過程分析
pvc也叫做硬PVC,它主要是氯乙烯單體經過聚合反應之后而做成的一種無定形熱塑性樹脂,在通過添加一定的添加劑,例如穩定劑、潤滑劑、填充劑等組合而成的一種產品。
除了用添加劑之外,還采用了與其它樹脂進行共混改性的相關辦法,使它更加具有明顯的實用價值。這些樹脂有CPVC、PE、abs、EVA、MBS等。
UPVC的熔體粘度較高,流動性較差,即使提高注射壓力以及熔體溫度,流動性的變化也較小大。此外,樹脂的成型溫度與熱分解溫度非常接近,可以進行成型的溫度范圍較窄,它是一種比較難于成型的材料。
1、塑料的處理
處于室溫24小時之后,吸水量如果是少于0.02%的話,就會形成無須烘干的情況。如過必須要進行干燥處理,可以放到60-70℃的熱氣爐3小時,或著80℃的干燥機大概1-1.5小時。
回收料最多可以用20%與新料進行混合,回收料的用量要看制品的最終用途而確定。濫用回收料可能會導致注塑工作失敗,不單是回收了的成分過多,更多的原因是因為物料經過多次再加工處理。回收料每多回收一次質量會出現逐漸下降的狀況。
2、注塑機選用
UPVC因為熔體粘度較較大、所以分解較為容易,分解產物對于鐵有著較大的腐蝕作用,其注塑成型必須要用專用的塑化部件和溫控系統。
華美達在產品覆蓋的每一種鎖模力型號,都有專門的UPVC塑化注射系統,并配合UPVC管件產品抽芯的要求備有專用的安全門裝置。一般情況下只要注射量可以滿足重量要求,選用這一系列UPVC專用注塑裝置可以成型出高質量的產品。
3、模具及澆口設計
模具溫度可以設置為40℃。而且流道整個長度一定要短,直徑則要比較大,用來逐漸減小壓力損失以及保壓能傳遞到模腔。澆口越短越好,模切面一定要圓形,射嘴口的直徑最小是6mm,成圓錐形,內角成5。
主流道的模切面也要圓形,與冷料井組合而成,通過切面半徑連接主流道和澆口,直徑可為7mm。
澆口應用切圓面形的半徑連接塑件,越短越好,模切面要順滑。
冷料井可防止半凝固的物料進入模腔,它的重要性常被忽略。
澆口的位置要正確,使物料在流道上順利流動,不會停留在尖角、碎片和金屬的痕跡里,以免出現壓縮或減壓的情況,應保持流道順滑流暢。
模具應用不銹鋼鑄造,鉻的含量至少13%,最好16%,洛氏硬度至少有55,硬鋼模具可經鍍鉻處理,形成保護作用。
生產完后,應用溫和的堿液小心將模面清洗干凈后再噴上油質噴霧或硅質噴霧。
4、熔膠溫度
可用空射法度量,由185-205℃不等。從射出的物料光滑程度可得知UPVC的準確熔膠溫度。如物料在射出后粗糙不平,就證明物料并非均一(塑化不足),表示所定的溫度太低;如射出后起泡沫并冒出大量煙霧,就表示溫度過高。
5、注射速度
射速要慢,否則過分剪切會使物料降質,利用UPVC生產極度光滑的厚壁制品時,應采用多級注塑模具填充速度。
6、螺桿轉速
應該進一步配合模塑周期而確定螺桿轉速。螺桿面速度不要超過0.15-0.2m/s
7、背壓
背壓可以達到150bar,當然數據是越低越好,常見的數值是5bar。
8、滯留時間
在200℃的溫度之下,機筒滯留時間大多不能超過5分鐘。當溫度是210℃,機筒滯留時間就不可以超過3分鐘。
以上就是UPVC塑料原料的注射成型工藝分析匯總,提醒大家的是在注射速度以及背壓方面需要的別注意。
部分型號部分物性表
EVA (ethylene vinyl acetate copolymer #) /7350M/ Taiwan plastic
Use: foaming
Characteristic notes: characteristics: good chemical resistance, good elasticity, high flexibility.
Important parameters: melt flow rate: 2.5 g/10min density: 0.938 g/cm3, tensile strength: 4 MPa, elongation at break: 78% bending modulus: 14 MPa hardness: 38 VEKA softening point: 60 C, embrittlement temperature: -70 C, filler content: 18%.
Manufacturer: Limited by Share Ltd of Taiwan plastic industry
EVA (ethylene vinyl acetate copolymer #) /1828/ Korea China
Use: wire and cable material
Characteristic notes: good elastic and mechanical properties. Additive: antioxidant
Important parameters: melt flow rate: 4 g/10min density: 0.95 g/cm3, tensile strength: 18 MPa, elongation at break: 800% hardness: 26 VEKA softening point: 44 C embrittlement temperature: -76 C.
Manufacturer: Korea Hwa comprehensive chemical company
EVA (ethylene vinyl acetate copolymer #) /1020 VN 5/ France Total
Use: Film
Characteristic notes: high transparency and good mechanical properties
Important parameters: melt flow rate: 2 g/10min density: 0.94 g/cm3 tensile strength: 28 MPa breaking elongation: 620% VEKA softening point: 64 C
Manufacturer: Total Petrochemical Industries Co
EVA (ethylene vinyl acetate copolymer #) /250/ DuPont dow
Use: hot-melt
Characteristic notes: cold resistance, copolymer, good toughness, good flexibility, elasticity. FDA first level certification in the United States
Important parameters: melt flow rate: 25 g/10min density: 0.921 g/cm3 tensile strength: 11 MPa breaking elongation: 900% hardness: 75 VEKA softening point: 42 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /260/ DuPont dow
Use: hot-melt
Characteristic notes: cold resistance, copolymer, good toughness, good flexibility, elasticity. FDA first level certification in the United States
Important parameters: melt flow rate: 6 g/10min density: 0.955 g/cm3 tensile strength: 24 MPa breaking elongation: 900% hardness: 80 VEKA softening point: 46 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /265/ DuPont dow
Use: other
Characteristic notes: cold resistance, copolymer, good toughness, good flexibility, elasticity. FDA first level certification in the United States
Important parameters: melt flow rate: 3 g/10min density: 0.951 g/cm3 tensile strength: 29 MPa breaking elongation: 900% hardness: 83 VEKA softening point: 49 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /PA-500/ Repsol of Spain
Use: Film
Characteristic notes: easy to process, excellent mechanical and optical properties
Important parameters: melt flow rate: 0.4 g/10min density: 0.924 g/cm3 tensile strength: 21 MPa breaking elongation: 600% VEKA softening point: 90 C
Manufacturer: YPF of Spain
EVA (ethylene vinyl acetate copolymer #) /EB561/ West Lake
Use: other
Feature remark: good sealing, good impact strength, good optics and stability
Important parameters: melt flow rate: 0.55 g/10min density: 0.929 g/cm3 tensile strength: 25 MPa breaking elongation: 550%
Manufacturer: West Lake Chemical Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /FD53/ Italy
Use: Film
Characteristic notes: good sealing performance, high elasticity, toughness and best processing performance
Important parameters: melt flow rate: 0.4 g/10min tensile strength: 30 MPa fracture elongation: 700% hardness: 39 VEKA softening point: 67 C embrittlement temperature: -80 C
Manufacturer: Italy Eni
EVA (ethylene vinyl acetate copolymer #) /G MU76000/ Leander Basil
Use: other
Important parameters: melt flow rate: 32 g/10min density: 0.941 g/cm3, tensile strength: 9.4 MPa, elongation at break: 760% hardness: 30 VEKA softening point: 54 C embrittlement temperature: -76 C.
Manufacturer: Liane Basel Industrial Corporation
EVA (ethylene vinyl acetate copolymer #) /4355/ DuPont dow
Use: other
Characteristic notes: 1 wt% methacrylic acid heat stabilizer: BHT antioxidant high molecular weight, high thermal viscosity system
Important parameters: melt flow rate: 6 g/10min density: 0.952 g/cm3 filler content: 25%
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /BM05-6/ Ishida
Use: other
Characteristic notes: good physical strength, resistance to stress cracking and high crumple
Important parameters: melt flow rate: 0.5 g/10min density: 0.927 g/cm3, tensile strength: 23 MPa, elongation at break: 700% hardness: 47 VEKA softening point: 88 C embrittlement temperature: -70 C.
Manufacturer: Zhao he electrician Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /EM21-1/ Ishida
Use: other
Characteristic notes: kneading, transparency, high surface gloss and high degree of shape
Important parameters: melt flow rate: 12 g/10min density: 0.932 g/cm3, tensile strength: 15 MPa, elongation at break: 750% hardness: 34 VEKA softening point: 64 temperature embrittlement temperature: -70 C, filler content: 15%
Manufacturer: Zhao he electrician Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /FM22-1/ Ishida
Use: other
Characteristic notes: high molding, crumple and high resistance to stress cracking
Important parameters: melt flow rate: 20 g/10min density: 0.938 g/cm3, tensile strength: 15 MPa, elongation at break: 800% hardness: 30 VEKA softening point: 56 temperature embrittlement temperature: -70 C, filler content: 20%
Manufacturer: Zhao he electrician Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /MV1055/ Thailand TPI
Use: other
Characteristic notes: excellent elasticity, medium flow, good low temperature resistance
Important parameters: melt flow rate: 8 g/10min density: 0.953 g/cm3 stretching