Formation Mechanism Of Common Defects In Thick-Walled Transparent Plastic Parts And Solutions

Formation mechanism of common defects in thick-walled transparent plastic parts and solutions
1. The formation mechanism and solution of the short shot
Short shot and underfilling are also called short shots and underfilling, which means that during the injection molding process, the mold cavity is not completely filled by the melt, thus
Lead to the phenomenon of partial shortage of injection products [23].
(1) Reasons for the formation of short shots
The main reason for the undershoot is that the resistance of the melt is too large or the temperature drops too fast during the filling process, which causes the melt to lose
Law continues to flow.
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The reason for the injection molding machine: improper selection of injection molding equipment, and the product quality exceeds the maximum injection capacity of the injection molding machine;
If the diameter of the nozzle hole is too small, the cross-sectional area of ​​the flow is small, which is easy to be cooled, causing the melt to block the feed channel or consume the injection pressure.
If the diameter is too large, the flow cross-sectional area will be large, and the pressure per unit area of ​​the plastic entering the mold will be low, resulting in insufficient injection pressure.
The reason for the mold: the mold's gating system is defective, if the feed port is not selected properly, the runner is too narrow, and the number of gates
Insufficient or improper structure, short shot will occur; improper exhaust design in the cavity, residual air cannot be discharged in time during the injection process
In addition to making the filling incomplete; when the product is a mold with multiple cavities, the unbalanced filling will cause short shots.
Material reasons: plastic materials have poor fluidity, the melt is not heated enough or the temperature drops too fast during the flow process.
The influence of the injection molding process: the nozzle temperature is too low, causing the cold material to enter the mold; the melt temperature and the mold temperature are too low,
The injection pressure is too small or the holding pressure is insufficient; the injection speed is too slow, and the low-speed flow of the melt is rapidly cooled and the flow is blocked.
(2) The solution to arrears
Change to an injection molding machine with a plasticization capacity that meets the requirements, increase the injection volume or increase the barrel temperature; appropriately increase the runner and gate
The cross-sectional size of the mold cavity; the flow distance of the melt in the mold cavity is too long or there are thin-walled parts, and the cold material cavity can be set; improve the injection molding machine and
Exhaust system of the mold; adjust the process conditions to increase the mold temperature or melt temperature, increase the injection pressure and injection speed
Degree; when the fluidity of the raw material is too poor, you should switch to a resin with better fluidity