The causes and solutions for
PP injection molding failure are as follows:
I. Note
Fault analysis and troubleshooting:
(1) The process conditions of transparent PP plastic are not properly controlled. Should be adjusted appropriately.
(2) The injection capacity of the injection molding machine is less than the weight of the plastic part. Should be replaced with a larger size injection molding machine.
(3) The flow path and gate cross section are too small. Should be appropriately increased.
(4) The flow distance of the melt in the cavity is too long or has a thin wall portion. A cold pocket should be provided.
(5) The mold is poorly exhausted, and the residual air in the cavity causes the underfill. The exhaust system of the mold should be improved.
(6) The flow properties of the raw materials are too poor. Resin with better flow properties should be used.
(7) If the temperature of the barrel is too low, the injection pressure is insufficient or the injection time of the feed is too short, which may cause a low injection. The amount of control over the process parameters should be increased accordingly.
Second, flashing flash
Fault analysis and troubleshooting:
(1) Insufficient clamping force. It should be replaced with a larger size injection molding machine.
(2) The pin hole or guide pin of the mold is seriously worn. Machining methods should be used for repair.
(3) There are foreign matter impurities on the mold clamping surface. It should be cleared.
(4) The molding temperature or injection pressure is too high. Should be appropriately reduced.
Third, the surface stomata
Fault analysis and troubleshooting:
(1) When the mold flow path of the thick-walled plastic part and the gate size are small, surface pores are easily generated. The runner and gate dimensions should be properly scaled.
(2) The plastic part wall is too thick. The wall thickness should be minimized during design.
(3) If the molding temperature is too high or the injection pressure is too low, it will cause pores on the surface of the plastic part. The molding temperature should be appropriately lowered to increase the injection pressure.
Fourth, flow marks
Fault analysis and troubleshooting:
(1) The melt and mold temperature are too low. High cylinder and mold temperatures should be appropriate.
(2) The injection speed is too slow. The injection speed should be properly accelerated.
(3) The nozzle aperture is too small. Replace the nozzle with a larger aperture.
(4) There is no cold hole in the mold. A cold material hole should be added.
Five, silver wire
Fault analysis and troubleshooting:
(1) The moisture and volatile content of the molding material are too high. The raw materials should be pre-dried.
(2) The mold is poorly exhausted. The vent hole should be increased to improve the exhaust performance of the mold.
(3) The nozzle is in poor contact with the mold. The position and geometry of both should be adjusted.
(4) When the silver wire is always present in a certain part, the surface of the corresponding cavity should be inspected for surface scratches. If there is a phenomenon of surface damage, machining should be used to remove the surface surface of the cavity.
(5) Silver streaks are produced when different types of resins are mixed. Mixing of dissimilar resins should be prevented.
Six, weld line
Fault analysis and troubleshooting:
(1) The melt and mold temperature are too low. The barrel and mold temperature should be increased.
(2) The gate position setting is unreasonable. The gate position should be changed.
(3) The volatile content of the raw material is too high or the mold is poorly exhausted. The volatile materials in the raw materials should be removed and the exhaust system of the mold should be improved.
(4) The injection speed is too slow. Should be accelerated as appropriate.
(5) There is no cold hole in the mold. A cold material hole should be added.
(6) There are foreign matter impurities on the surface of the cavity. It should be cleaned.
(7) The design of the gating system is unreasonable. The filling performance of the gating system should be improved so that the melt flows smoothly in the cavity.
Seven, black bars and charred
Fault analysis and troubleshooting:
(1) The specifications of the injection molding machine are too large. Should be replaced with a smaller size injection molding machine.
(2) The flowability of the resin is poor. An appropriate amount of external lubricant should be used.
(3) The injection pressure is too high. Should be appropriately reduced.
(4) The mold is poorly vented. The mold exhaust system should be improved, the vent hole should be increased or the mosaic structure should be used, and the mold clamping force should be appropriately reduced.
(5) The setting of the gate position is unreasonable. The gate position should be changed to allow the melt in the cavity to flow evenly.
Eight, bubbles
Fault analysis and troubleshooting:
(1) The size of the gate and runner is too small. Should be appropriately increased.
(2) The injection pressure is too low. Should be properly improved.
(3) The moisture content in the raw material is too high. The raw materials should be pre-dried.
(4) The wall thickness of the plastic part changes too much. The shape and structure of the plastic parts should be reasonably designed to avoid sudden changes in wall thickness.
Nine, cracking and whitening
Fault analysis and troubleshooting:
(1) The melt and mold temperature are too low. The barrel and mold temperature should be increased.
(2) The structural design of the casting system of the mold is unreasonable. The mold runner and gate structure should be improved so that the melt does not generate turbulence during filling.
(3) The cooling time is too short. The cooling time should be extended as appropriate.
(4) The design of the demolding ejection device is unreasonable. It is best to use a pneumatic stripping device.
(5) The injection speed and pressure are too high. Should be appropriately reduced.
Ten, bending deformation
Fault analysis and troubleshooting:
(1) The mold temperature is too high or insufficiently cooled. The mold temperature should be appropriately lowered or the cooling time should be extended. For the elongated plastic parts, the method of fixing the tire after fixing can be adopted.
(2) Uneven cooling. The cooling system of the mold should be improved to ensure that the plastic parts are cooled evenly.
(3) The selection of gates is unreasonable. A reasonable gate form should be chosen for the specific situation. In general, multi-point gates can be used.
(4) The mold is eccentric. It should be checked and corrected.
XI, poor mold release
Fault analysis and troubleshooting:
(1) The injection speed and pressure are too high. Should be appropriately reduced.
(2) The surface finish of the mold cavity is too poor. The surface finish should be improved by grinding and plating.
(3) Improper control of mold temperature and cooling conditions. When the plastic part is stuck at the core, the mold temperature should be increased and the cooling time should be shortened; if the plastic part is stuck at the surface of the cavity, the mold temperature should be lowered and the cooling time should be extended.
(4) The ejection area of the demolding mechanism is too small. The ejector area should be increased.
Twelve, shrinkage deformation
Fault analysis and troubleshooting:
(1) Insufficient pressure. The injection time of the feed should be extended appropriately.
(2) Insufficient injection pressure. Should be properly improved.
(3) The mold temperature is too high. Should be appropriately reduced.
(4) The gate cross-sectional area is too small. Should be appropriately increased.
(5) The processing temperature is too low. The barrel temperature should be increased appropriately.
Thirteen, vacuum holes
Fault analysis and troubleshooting:
(1) Insufficient pressure. The injection time of the feed should be extended appropriately.
(2) The mold temperature is too low and the barrel temperature is too high. The mold temperature should be properly increased to reduce the barrel temperature.
(3) Insufficient injection pressure. Should be properly improved.
(4) The flow properties of the raw materials are too good. Resin with a lower melt index should be used.
