Analysis of the causes of silver lines in injection molded products

Silver lines on injection molded products, including surface bubbles and internal pores. The main cause of defects is interference from gases (mainly water vapor, decomposition gas, solvent gas, air). The specific reasons are analyzed as follows:
1. Regarding the machine:
(1) The material barrel and screw are worn or there is a dead angle in the material flow through the rubber head and rubber ring, which decomposes due to long-term heating.
(2) The heating system is out of control, causing excessive temperature and decomposition. Heating elements such as thermocouples and heating coils should be checked for any issues. Improper screw design can cause problems or easily introduce air.
2. In terms of molds:
(1) Poor exhaust.
(2) The frictional resistance of the runner, gate, and cavity in the mold is high, causing local overheating and decomposition.
(3) Uneven distribution of gates and cavities, as well as unreasonable cooling systems, can lead to uneven heating and local overheating or blockage of air channels.
(4) The cooling passage leaks water into the mold cavity.
3. Regarding plastics:
(1) Plastic has high humidity, excessive proportion of recycled materials added, or contains harmful debris (debris is easily decomposed). The plastic should be thoroughly dried and debris should be eliminated.
(2) When absorbing moisture from the atmosphere or from colorants, the colorants should also be dried, and it is best to install a dryer on the machine.
(3) Excessive or uneven mixing of lubricants, stabilizers, etc. added to plastics, or plastics themselves containing volatile solvents. When it is difficult to balance the degree of heating of mixed plastics, decomposition may also occur.
(4) Plastic is contaminated and mixed with other plastics.
4. In terms of processing:
(1) When setting the temperature, pressure, speed, back pressure, or the speed of the glue motor to be too high, causing decomposition, or when the pressure and speed are too low, the injection time, pressure holding is insufficient, or the back pressure is too low, and due to the inability to obtain high pressure and insufficient density, the gas cannot be melted and silver lines appear, appropriate temperature, pressure, speed, and time should be set, and multi-stage injection speeds should be used.
(2) Low back pressure and fast rotation speed easily cause air to enter the material barrel, and as the molten material enters the mold, if the cycle is too long, the molten material will decompose due to prolonged heating inside the material barrel.
(3) Insufficient material quantity, excessive feeding buffer pad, low material temperature or mold temperature all affect the flow and forming pressure of the material, promoting the generation of bubbles.