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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(jīng)過聚合反應(yīng)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(wěn)定劑、潤滑劑、填充劑等組合而成的一種產(chǎn)品。

除了用添加劑之外，還采用了與其它樹脂進(jìn)行共混改性的相關(guān)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(jìn)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(jìn)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(jī)大概1-1.5小時。

回收料最多可以用20%與新料進(jìn)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(dǎo)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(jīng)過多次再加工處理。回收料每多回收一次質(zhì)量會出現(xiàn)逐漸下降的狀況。

2、注塑機(jī)選用

UPVC因為熔體粘度較較大、所以分解較為容易，分解產(chǎn)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(tǒng)。

華美達(dá)在產(chǎn)品覆蓋的每一種鎖模力型號，都有專門的UPVC塑化注射系統(tǒng)，并配合UPVC管件產(chǎn)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(zhì)量的產(chǎn)品。

3、模具及澆口設(shè)計

模具溫度可以設(shè)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(nèi)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(yīng)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(jìn)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(xiàn)壓縮或減壓的情況，應(yīng)保持流道順滑流暢。

模具應(yīng)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(jīng)鍍鉻處理，形成保護(hù)作用。

生產(chǎn)完后，應(yīng)用溫和的堿液小心將模面清洗干凈后再噴上油質(zhì)噴霧或硅質(zhì)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(zhǔn)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(zhì)，利用UPVC生產(chǎn)極度光滑的厚壁制品時，應(yīng)采用多級注塑模具填充速度。

6、螺桿轉(zhuǎn)速

應(yīng)該進(jìn)一步配合模塑周期而確定螺桿轉(zhuǎn)速。螺桿面速度不要超過0.15-0.2m/s

7、背壓

背壓可以達(dá)到150bar，當(dāng)然數(shù)據(jù)是越低越好，常見的數(shù)值是5bar。

8、滯留時間

在200℃的溫度之下，機(jī)筒滯留時間大多不能超過5分鐘。當(dāng)溫度是210℃，機(jī)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