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如何制造高光無痕的注塑件?
高光注塑技術又稱快速熱循環注塑技術,使用此技術可以很好地復制模具表面的任何形狀,使制品件表面無熔痕,表面高光達到鏡面效果;提高塑件強度和表面硬度;使薄壁成型提高注塑流動性,提高產品品質和強度;使厚壁成型注塑周期可降低60%以上;無需后續環境污染嚴重噴涂工藝,可減少工藝流程,節省能源與材料。
這樣可以直接降低塑料制品的成本,也能更好的保護環境和操作人員的人身健康。
高光注塑的工藝原理:
在合模前及合模過程中對模具進行加溫、合模完成后,溫度達到設定條件即進行注射。注射過程中模具繼續維持高溫,這樣可以使膠料注射時在模具內保持很好的流動性。注射完成,在保壓冷卻時,則對模具進行降溫處理,又可以大大縮短制品的冷卻時間,從而提高生產效率。
傳統的做法是采用模溫機對模具進行加溫,但這種方法的不足之處如下:
1.無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法消除;
3.由于塑料硬度越高,流動性越差。因此采用此種工藝制品表面的硬度只能達到HB級無法滿足實際使用需要;
4.模具升溫時受熱膨脹,降溫時又會收縮,使鎖模力很不穩定。容易造成制品打不滿,燒焦,內應力大等各種缺陷。
而在此工藝基礎上發展而來的蒸汽高光注塑技術則針對以上缺陷分別做了改進:
1.此技術在模具中開水管,需要升溫時通蒸汽,需要降溫時通冷水,冷卻完畢后,可以用壓縮空氣將殘留水分吹出,以確保能實現快速升溫、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硬度級別的塑料,使制品表面硬度大大提高;
4.由于在模具內部開設管道時,只對模具內表面進行升溫或降溫,模具的整體膨脹較小,因此減少了由于鎖模力的不穩定而帶來的各種制品缺陷。
要生產出高品質的高光制品,需要注塑機、模具、溫控設備高光制品專用塑料、以及鍋爐、冷卻裝置等方面相配合:
1.塑機的配置
①鎖模機構剛性要好;由于整個生產過程中要不停地升溫和降溫。因此要求注塑機的鎖模機構必須剛性、強度要好、以確保鎖模力的準確與穩定。從而保證制品的表面質量。
②選用大鎖模的注塑機:使用此工藝時由于無法再使用氣體輔助注射,因此生產制品所需要的鎖模力會比較大。
③根據情況選用較小的射膠量:如生產平板電視機、液晶顯示屏外框等產品時,不需要較大射膠量,在選擇注塑機時盡量選擇小射膠量的注塑機。制品實際重量在注塑機理論射膠量的30%~80%之間最佳。如機器射膠量過大,膠料在料筒內停留時間長容易分別分解,制品表面會產生銀絲等缺陷。
④配備專用螺桿生產高光制品所用到的塑料硬度較高,其熔融指數相對較低,因此要求螺桿塑化要好。同時螺桿的剪切又不能太大,否則膠料會容易分解。
2.模具的配置
①模具內表面要求非常高的光潔度,以確保制品的表面質量;
②模具內部開設管道必須合理,以確保可以快速升溫和降溫;
③模具內部的管道應該導熱性能良好;
④由于生產過程中需要不停加溫及降溫,模具選用的鋼材要好;
⑤在使用過程中要尤其注重模具的保養,確保干燥,無塵。
3.溫控設備的配置
①溫度控制要非常準確,這是制品質量的重要保證
②溫控設備的反應要非常快以保證較高的生產效率
4.專用塑料
生產表面質量較高的產品時,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H、甚至2H。但硬度越高,熔融指數也相對越低。流動性會變差,因此可根據生產需要選取適當的塑料。
蒸汽無痕高光注塑技術大大改善了制品的表面質量和表面強度,并可取消后續的噴涂或噴漆等工藝、既保護了環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用,在大幅度降低生產成本的同時,節省能源與材料。
部分型號部分物性表
EVA (ethylene vinyl acetate copolymer /1045/ Nuoxuemu chemical #)
Use: Film
Feature remark: VAC content 2%
Important parameters: melt flow rate: 0.5 g/10min
Manufacturer: Nuoxuemu chemical company
EVA (ethylene vinyl acetate copolymer /3507/ Nuoxuemu chemical #)
Use: Film
Feature remark: VAC content 5%
Important parameters: melt flow rate: 0.3 g/10min
Manufacturer: Nuoxuemu chemical company
EVA (ethylene vinyl acetate copolymer #) /3124/ DuPont dow
Use: hot-melt
Characteristic notes: line speed and film thickness
Important parameters: melt flow rate: 7 g/10min density: 0.93 g/cm3 VEKA softening point: 77 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /1061/ America Serra nice
Use: Film
Important parameters: melt flow rate: 0.3 g/10min density: 0.924 g/cm3 tensile strength: 19 MPa breaking elongation: 560% VEKA softening point: 92 C
Manufacturer: Celanese Co of the United States
EVA (ethylene vinyl acetate copolymer #) /1070/ America Serra nice
Use: other
Important parameters: melt flow rate: 2.8 g/10min density: 0.931 g/cm3, tensile strength: 14 MPa, elongation at break: 690% VEKA softening point: 81 C embrittlement temperature: -85 C.
Manufacturer: Celanese Co of the United States
EVA (ethylene vinyl acetate copolymer #) /1241/ America Serra nice
Use: other
Important parameters: melt flow rate: 10 g/10min density: 0.932 g/cm3, tensile strength: 13 MPa, elongation at break: 710% hardness: 40 VEKA softening point: 72 C embrittlement temperature: -76 C.
Manufacturer: Celanese Co of the United States
EVA (ethylene vinyl acetate copolymer #) /1645/ America Serra nice
Use: other
Important parameters: melt flow rate: 28 g/10min density: 0.936 g/cm3 tensile strength: 11 MPa breaking elongation: 700% hardness: 35 VEKA softening point: 61 C
Manufacturer: Celanese Co of the United States
EVA (ethylene vinyl acetate copolymer #) /2850A/ America Serra nice
Use: other
Important parameters: density: 0.941 g/cm3 tensile strength: 2 MPa fracture elongation: 350% flexural modulus: 11 MPa hardness: 12
Manufacturer: Celanese Co of the United States
EVA (ethylene vinyl acetate copolymer #) /FL 01418/ Mobil Exxon
Use: other
Important parameters: hardness: 87 VEKA softening point: 52 C
Manufacturer: Exxon Mobil Corp
EVA (ethylene vinyl acetate copolymer #) /VH620S/ Japan Sea
Use: other
Important parameters:
Manufacturer: Japan Offshore Oil Resources Development Co., Ltd.
EVA (ethylene vinyl acetate copolymer # atofina) /20-20/
Use: other
Important parameters: melt flow rate: 20 g/10min density: 0.94 g/cm3, tensile strength: 12.5 MPa, elongation at break: 650% hardness: 84 VEKA softening point: 49 C filling content: 20%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /28-420/
Use: other
Important parameters: melt flow rate: 420 g/10min density: 0.95 g/cm3, tensile strength: 2.5 MPa, elongation at break: 850% hardness: 62 VEKA softening point: 40 C filling content: 28%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /28-800/
Use: other
Important parameters: melt flow rate: 800 g/10min density: 0.95 g/cm3, tensile strength: 1.5 MPa, elongation at break: 300% hardness: 57 VEKA softening point: 40 C filling content: 28%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /33-25/
Use: other
Important parameters: melt flow rate: 25.5 g/10min density: 0.96 g/cm3, tensile strength: 12 MPa, elongation at break: 900% hardness: 66 VEKA softening point: 40 C filling content: 33%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /33-45/
Use: other
Important parameters: melt flow rate: 43 g/10min density: 0.96 g/cm3, tensile strength: 10.5 MPa, elongation at break: 900% hardness: 64 VEKA softening point: 40 C filling content: 33%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /33-400/
Use: other
Important parameters: melt flow rate: 400 g/10min density: 0.96 g/cm3, tensile strength: 2.5 MPa, elongation at break: 900% hardness: 45 VEKA softening point: 40 C filling content: 33%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /40-55/
Use: other
Important parameters: melt flow rate: 55 g/10min density: 0.96 g/cm3, tensile strength: 5 MPa, elongation at break: 1000% hardness: 46 VEKA softening point: 40 C filling content: 39.5%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /28-05/
Use: other
Important parameters: melt flow rate: 6.5 g/10min density: 0.95 g/cm3, tensile strength: 33 MPa, elongation at break: 850% hardness: 82 VEKA softening point: 43 C filling content: 28%
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /28-150/
Use: hot-melt
Important parameters: melt flow rate: 155 g/10min density: 0.95 g/cm3, tensile strength: 6 MPa, elongation at break: 850% hardness: 70 VEKA softening point: -40 C filling content: 27.5%.
Manufacturer: France atofina company
EVA (ethylene vinyl acetate copolymer # atofina) /28-25/
Use: other
Important parameters: melt flow rate: 25.5 g/10min density: 0.95 g/cm3, tensile strength: 13 MPa, elongation at break: 850% hardness: 76 VEKA softening point: 41 C filling content: 28%
Manufacturer: France atofina company