Injection Molding Process Parameters of 17 Most Common Plastics
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) | |
| Description | Process 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 temperature | 220~280℃ |
| Constant temperature of the barrel | 220℃ |
| Mould temperature | 20～60℃ |
| Injection pressure | Material 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 pressure | The 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 pressure | 5 ~ 20MPa (50 ~ 200bar), and the place with too low back pressure is easy to cause the uneven weight and dispersion of the products. |
| Injection speed | requires high injection speed for thin-walled packaging containers, and medium injection speed is often more suitable for other types of plastic products. |
| Screw speed | high 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 stroke | 0.5 ~ 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 material | from 2 to 8mm, depending on the measurement range and screw diameter |
| Predry | It 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 rate | can reach 100% recovery |
| Shrinkage rate | 1.2 to 2.5%; it is easy to twist; the shrinkage degree is high; after 24h, no contraction (after forming contraction) |
| Gate system | The 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 period | No other materials are needed for special cleaning in the machine shutdown period; |
| Barrel equipment | Standard 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) | |
| Description | Process 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 temperature | 220~280℃ |
| Constant temperature of the barrel | 220℃ |
| Mould temperature | 20～70℃ |
| Injection pressure | Material 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 pressure | The 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 pressure | 5 ~ 20MPa (50 ~ 200bar) |
| Injection speed | requires high injection speed for thin-walled packaging containers, and medium injection speed is often more suitable for other types of plastic products. |
| Screw speed | high screw speed (1.3m/s) is allowed. As long as the cooling time is finished, the plasticizing process is finished. |
| Metering stroke | 0.5 ~ 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 material | from 2 to 8mm, depending on the measurement range and screw diameter |
| Pre-dry | It 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 rate | can reach 100% recovery |
| Shrinkage rate | 1.2 to 2.5%; it is easy to twist; the shrinkage degree is high; after 24h, no contraction (after forming contraction) |
| Gate system | Point 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 period | No other materials are needed for special cleaning in the machine shutdown period; Resistance to temperature rising. |
| Barrel equipment | Standard 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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