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如何制造高光無(wú)痕的注塑件?
高光注塑技術(shù)又稱快速熱循環(huán)注塑技術(shù),使用此技術(shù)可以很好地復(fù)制模具表面的任何形狀,使制品件表面無(wú)熔痕,表面高光達(dá)到鏡面效果;提高塑件強(qiáng)度和表面硬度;使薄壁成型提高注塑流動(dòng)性,提高產(chǎn)品品質(zhì)和強(qiáng)度;使厚壁成型注塑周期可降低60%以上;無(wú)需后續(xù)環(huán)境污染嚴(yán)重噴涂工藝,可減少工藝流程,節(jié)省能源與材料。
這樣可以直接降低塑料制品的成本,也能更好的保護(hù)環(huán)境和操作人員的人身健康。
高光注塑的工藝原理:
在合模前及合模過(guò)程中對(duì)模具進(jìn)行加溫、合模完成后,溫度達(dá)到設(shè)定條件即進(jìn)行注射。注射過(guò)程中模具繼續(xù)維持高溫,這樣可以使膠料注射時(shí)在模具內(nèi)保持很好的流動(dòng)性。注射完成,在保壓冷卻時(shí),則對(duì)模具進(jìn)行降溫處理,又可以大大縮短制品的冷卻時(shí)間,從而提高生產(chǎn)效率。
傳統(tǒng)的做法是采用模溫機(jī)對(duì)模具進(jìn)行加溫,但這種方法的不足之處如下:
1.無(wú)法滿足高光注塑中快速升溫及快速降溫的需要;
2.升溫幅度較小,制品表面的熔接痕只能得到減輕而無(wú)法消除;
3.由于塑料硬度越高,流動(dòng)性越差。因此采用此種工藝制品表面的硬度只能達(dá)到HB級(jí)無(wú)法滿足實(shí)際使用需要;
4.模具升溫時(shí)受熱膨脹,降溫時(shí)又會(huì)收縮,使鎖模力很不穩(wěn)定。容易造成制品打不滿,燒焦,內(nèi)應(yīng)力大等各種缺陷。
而在此工藝基礎(chǔ)上發(fā)展而來(lái)的蒸汽高光注塑技術(shù)則針對(duì)以上缺陷分別做了改進(jìn):
1.此技術(shù)在模具中開(kāi)水管,需要升溫時(shí)通蒸汽,需要降溫時(shí)通冷水,冷卻完畢后,可以用壓縮空氣將殘留水分吹出,以確保能實(shí)現(xiàn)快速升溫、降溫;
2.以最大程度地消除熔接痕夾、水紋、缺膠等各種制品故障;
3.由于升溫幅度較大、以使用H甚至2H硬度級(jí)別的塑料,使制品表面硬度大大提高;
4.由于在模具內(nèi)部開(kāi)設(shè)管道時(shí),只對(duì)模具內(nèi)表面進(jìn)行升溫或降溫,模具的整體膨脹較小,因此減少了由于鎖模力的不穩(wěn)定而帶來(lái)的各種制品缺陷。
要生產(chǎn)出高品質(zhì)的高光制品,需要注塑機(jī)、模具、溫控設(shè)備高光制品專用塑料、以及鍋爐、冷卻裝置等方面相配合:
1.塑機(jī)的配置
①鎖模機(jī)構(gòu)剛性要好;由于整個(gè)生產(chǎn)過(guò)程中要不停地升溫和降溫。因此要求注塑機(jī)的鎖模機(jī)構(gòu)必須剛性、強(qiáng)度要好、以確保鎖模力的準(zhǔn)確與穩(wěn)定。從而保證制品的表面質(zhì)量。
②選用大鎖模的注塑機(jī):使用此工藝時(shí)由于無(wú)法再使用氣體輔助注射,因此生產(chǎn)制品所需要的鎖模力會(huì)比較大。
③根據(jù)情況選用較小的射膠量:如生產(chǎn)平板電視機(jī)、液晶顯示屏外框等產(chǎn)品時(shí),不需要較大射膠量,在選擇注塑機(jī)時(shí)盡量選擇小射膠量的注塑機(jī)。制品實(shí)際重量在注塑機(jī)理論射膠量的30%~80%之間最佳。如機(jī)器射膠量過(guò)大,膠料在料筒內(nèi)停留時(shí)間長(zhǎng)容易分別分解,制品表面會(huì)產(chǎn)生銀絲等缺陷。
④配備專用螺桿生產(chǎn)高光制品所用到的塑料硬度較高,其熔融指數(shù)相對(duì)較低,因此要求螺桿塑化要好。同時(shí)螺桿的剪切又不能太大,否則膠料會(huì)容易分解。
2.模具的配置
①模具內(nèi)表面要求非常高的光潔度,以確保制品的表面質(zhì)量;
②模具內(nèi)部開(kāi)設(shè)管道必須合理,以確保可以快速升溫和降溫;
③模具內(nèi)部的管道應(yīng)該導(dǎo)熱性能良好;
④由于生產(chǎn)過(guò)程中需要不停加溫及降溫,模具選用的鋼材要好;
⑤在使用過(guò)程中要尤其注重模具的保養(yǎng),確保干燥,無(wú)塵。
3.溫控設(shè)備的配置
①溫度控制要非常準(zhǔn)確,這是制品質(zhì)量的重要保證
②溫控設(shè)備的反應(yīng)要非常快以保證較高的生產(chǎn)效率
4.專用塑料
生產(chǎn)表面質(zhì)量較高的產(chǎn)品時(shí),常用的塑料有ABS、PC+ABS或PMMA+ABS。其中,ABS的硬度最低,PMMA+ABS的硬度最高,可達(dá)H、甚至2H。但硬度越高,熔融指數(shù)也相對(duì)越低。流動(dòng)性會(huì)變差,因此可根據(jù)生產(chǎn)需要選取適當(dāng)?shù)乃芰稀?br />
蒸汽無(wú)痕高光注塑技術(shù)大大改善了制品的表面質(zhì)量和表面強(qiáng)度,并可取消后續(xù)的噴涂或噴漆等工藝、既保護(hù)了環(huán)境和操作人員的人身健康,又因減少工藝流程,省去了昂貴的二次加工費(fèi)用,在大幅度降低生產(chǎn)成本的同時(shí),節(jié)省能源與材料。
部分型號(hào)部分物性表
EVA (ethylene vinyl acetate copolymer #) /EF529AA/ West Lake
Use: other
Characteristic note: 18.5%EVA polymer
Important parameters: melt flow rate: 2.5 g/10min density: 0.94 g/cm3 tensile strength: 24 MPa breaking elongation: 800% VEKA softening point: 67 C
Manufacturer: West Lake Chemical Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /EVA 807I/ Fainplast in Italy
Use: other
Characteristic notes: foamed properties can be crosslinked
Important parameters: density: 0.18 g/cm3 molding shrinkage: 2% tensile strength: 3 MPa fracture elongation: 280% hardness: 57
Manufacturer: Italy Fainplast company
EVA (ethylene vinyl acetate copolymer #) /EF563/ West Lake
Use: other
Characteristic notes: good clarity, toughness, 6.5%EVA copolymer
Important parameters: melt flow rate: 1.1 g/10min density: 0.932 g/cm3 tensile strength: 22.7 MPa breaking elongation: 770%
Manufacturer: West Lake Chemical Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /EM518AA/ West Lake
Use: other
Characteristic note: 18.5%EVA polymer
Important parameters: melt flow rate: 2.5 g/10min density: 0.94 g/cm3, tensile strength: 12 MPa, elongation at break: 645% bending modulus: 48 MPa hardness: 32 VEKA softening point: 68 degrees.
Manufacturer: West Lake Chemical Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /EVA 801S/ Fainplast in Italy
Use: other
Characteristic notes: foamed properties can be crosslinked
Important parameters: density: 0.32 g/cm3 molding shrinkage: 1.8% tensile strength: 3.2 MPa fracture elongation: 380% hardness: 62
Manufacturer: Italy Fainplast company
EVA (ethylene vinyl acetate copolymer #) /EF575/ West Lake
Use: other
Feature remark: good clarity and toughness. 7.5%EVA copolymer
Important parameters: melt flow rate: 0.55 g/10min density: 0.929 g/cm3 tensile strength: 24 MPa breaking elongation: 550%
Manufacturer: West Lake Chemical Co., Ltd.
EVA (ethylene vinyl acetate copolymer # viima /0218/ America)
Use: other
Important parameters: melt flow rate: 2 g/10min density: 938 g/cm3 tensile strength: 37 MPa breaking elongation: 700%
Manufacturer: America viima
EVA (ethylene vinyl acetate copolymer # Toyo /535/)
Use: other
Important parameters:
Manufacturer: Dongyang Textile Co., Ltd., Japan
EVA (ethylene vinyl acetate copolymer #) /EVA-1120/ America Bamberg
Use: other
Characteristic notes: composite elastic toughness, flexibility, high environmental stress resistance
Important parameters: melt flow rate: 2 g/10min density: 0.938 g/cm3, tensile strength: 15.2 MPa, elongation at break: 720% bending modulus: 60 MPa VEKA softening point: 62.8 degrees.
Manufacturer: American company Bamberg
EVA (ethylene vinyl acetate copolymer #) /9305/ France akema
Use: other
Important parameters: melt flow rate: 150 g/10min VEKA softening point: 40 C
Manufacturer: Arkema
EVA (ethylene vinyl acetate copolymer #) /EF446/ West Lake
Use: other
Characteristic notes: 6.0%EVA copolymer. High rigidity, good mechanical properties, low temperature embrittlement
Important parameters: melt flow rate: 2 g/10min density: 0.925 g/cm3 tensile strength: 26 MPa breaking elongation: 770%
Manufacturer: West Lake Chemical Co., Ltd.
EVA (ethylene vinyl acetate copolymer #) /3176/ DuPont dow
Use: hot-melt
Important parameters: melt flow rate: 30 g/10min density: 0.94 g/cm3 VEKA softening point: 54 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /9309/ France akema
Use: other
Important parameters: melt flow rate: 40 g/10min hardness: 70 VEKA softening point: 77 C
Manufacturer: Arkema
EVA (ethylene vinyl acetate copolymer #) /9314/ France akema
Use: Film
Important parameters: melt flow rate: 2 g/10min hardness: 55 VEKA softening point: 70 C
Manufacturer: Arkema
EVA (ethylene vinyl acetate copolymer #) /9318/ France akema
Use: Film
Important parameters: melt flow rate: 7 g/10min hardness: 38 VEKA softening point: 60 C
Manufacturer: Arkema
EVA (ethylene vinyl acetate copolymer #) /3861/ DuPont dow
Use: other
Important parameters: melt flow rate: 2 g/10min density: 0.95 g/cm3 VEKA softening point: 56 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer # /28-05/ Hyundai)
Use: other
Important parameters:
Manufacturer: Korea modern petroleum chemical company
EVA (ethylene vinyl acetate copolymer #) /3120/ DuPont dow
Use: hot-melt
Important parameters: melt flow rate: 1.2 g/10min density: 0.93 g/cm3 VEKA softening point: 84 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /3130/ DuPont dow
Use: hot-melt
Important parameters: melt flow rate: 2.5 g/10min density: 0.93 g/cm3 VEKA softening point: 76 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /3165/ DuPont dow
Use: hot-melt
Important parameters: melt flow rate: 0.7 g/10min density: 0.94 g/cm3 VEKA softening point: 69 C
Manufacturer: Dow DuPont Co