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Abstract: it lists  plastic injection molding process of 17 most common plastics include  HDPE, PP, PS, PVC, PA6, PA66, PBT, PET, PC, ABS, SAN, PMMA, POM, CA, PPO, etc. It summarizes key process parameters setting based on experience. These process parameters include temperature setting, pressure setting, stroke setting, etc. It will be very useful and instructive to those plastic process engineers who work on plastics manufacturing. 

Keywords: process parameter, common plastics, plastic injection molding


1.High   density polyethylene (HDPE)
DescriptionProcess Parameter & advice
Temperature of screw barrel

feeding area of barrel 30~50℃ (50℃)

Area 1            160~250℃(200℃)

Area 2            200~300℃ (210℃)

Area 3              220~300℃ (230℃)

Area 4            220~300℃ (240℃)

Area 5            220~300℃ (240℃)

Nozzle            220~300℃ (240℃)

The temperature in the brackets is   recommended as the basic set value, the utilization rate of the stroke is 35%   and 65%, the ratio of the flow length to the wall thickness is 50:1 to 100:1.

Material melt temperature220~280℃
Constant temperature of the barrel220℃
Mould temperature20~60℃
Injection pressureMaterial has good flow performance, and avoid   the high injection pressure, advise to use 80 to 140MPa (800 ~ 1400bar). Some   thin-walled packaging containers except for 180MPa (1800bar)
Holding pressureThe shrinkage is high and need to hold   the product for a long time. The size accuracy is the key factor, holding   pressure is about 30% ~ 60% of the injection pressure.
Back pressure5 ~ 20MPa (50 ~ 200bar), and the place   with too low back pressure is easy to cause the uneven weight and dispersion   of the products.
Injection speedrequires high injection speed for thin-walled   packaging containers, and medium injection speed is often more suitable for   other types of plastic products.
Screw speedhigh screw speed (1.3m/s) is allowed. As   long as the cooling time is finished, the plasticizing process is finished.   The torque requirement of the screw is low.
Metering stroke0.5 ~ 4D (minimum value to maximum), and   the measurement stroke of 4D is very important to provide enough long   standing time for the molten material.
Residual materialfrom 2 to 8mm, depending on the measurement   range and screw diameter
PredryIt is not necessary to predry; if the   storage condition is not good, it can be dried at 80 degrees centigrade at   the temperature of 1H.
Recovery ratecan reach 100% recovery
Shrinkage rate1.2 to 2.5%; it is easy to twist; the   shrinkage degree is high; after 24h, no contraction (after forming   contraction)
Gate systemThe point gate of the gate system; the   heating type heat flow path, the heat insulation type heat flow path, the   inner cast-in-place sleeve; the cross section area is relatively small, it is   sufficient for the thin section products.
Shutdown periodNo other materials are needed for special   cleaning in the machine shutdown period;
Barrel equipmentStandard three stage screw is used. For   the packing container products, the mixing section and the shear section have   special geometric shape (L:D = 25:1), straight through nozzles and check   valves


2. Polypropylene (PP)
DescriptionProcess Parameter & advice
Temperature of screw barrel

feeding area of barrel 30~50℃ (50℃)

Area 1            160~250℃(200℃)

Area 2            200~300℃ (220℃)

Area 3            220~300℃ (240℃)

Area 4            220~300℃ (240℃)

Area 5            220~300℃ (240℃)

Nozzle            220~300℃ (240℃)

The temperature in the brackets is   recommended as the basic set value, the utilization rate of the stroke is 35%   and 65%, the ratio of the flow length to the wall thickness is 50:1 to 100:1.

Material melt temperature220~280℃
Constant temperature of the barrel220℃
Mould temperature20~70℃
Injection pressureMaterial has good flow performance, and   avoid the high injection pressure, advise to use 80 to 140MPa (800 ~   1400bar). Some thin-walled packaging containers except for 180MPa (1800bar)
Holding pressureThe shrinkage is high and need to hold   the product for a long time, around 30% of cycle time. Holding pressure is about 30% ~ 60% of   the injection pressure.
Back pressure5 ~ 20MPa (50 ~ 200bar)
Injection speedrequires high injection speed for   thin-walled packaging containers, and medium injection speed is often more   suitable for other types of plastic products.
Screw speedhigh screw speed (1.3m/s) is allowed. As   long as the cooling time is finished, the plasticizing process is finished.
Metering stroke0.5 ~ 4D (minimum value to maximum), and   the measurement stroke of 4D is very important to provide enough long   standing time for the molten material.
Residual materialfrom 2 to 8mm, depending on the   measurement range and screw diameter
Pre-dryIt is not necessary to pre-dry; if the   storage condition is not good, it can be dried at 80 degrees centigrade at   the temperature of 1H.
Recovery ratecan reach 100% recovery
Shrinkage rate1.2 to 2.5%; it is easy to twist; the   shrinkage degree is high; after 24h, no contraction (after forming contraction)
Gate systemPoint gate or multi point gate; heated   hot runner, heat insulation hot runner, pouring sleeve; location of gate is the   most thick point of the product, otherwise large shrinkage can occur easily.
Shutdown periodNo other materials are needed for special   cleaning in the machine shutdown period; Resistance to temperature rising.
Barrel equipmentStandard three stage screw is used. For   the packing container products, the mixing section and the shear section have   special geometric shape (L:D = 25:1), straight through nozzles and check   valves



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Cathy Jun. 12, 2017

Führung is a young but fast-growing brand of Chinese plastic injection moulding machines. It was created in 2013 in order to develop new series high quality plastic injection machines for high-end customers from European and American.

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