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What are the common defects in injection molding products?

Sep 11-2020     Views: 513


The followings are some of the common defects of injection molded products  and the reasons for the defects.


1. Dissatisfaction (lack of glue)

  • Process problems: plasticizing temperature is too low, the nozzle temperature is too low, the injection time is too short, the injection speed is too slow, the mold temperature is too low;

  • Mold problems: the runner is too small, the gate is too small, the gate position is unreasonable, the exhaust is poor, and there is debris in the cavity;

  • Raw material problems: poor fluidity, mixed with debris


2. Flash

  • Process problems: too high plasticizing temperature, too long injection time, too much feed, too high injection pressure, too high mold temperature, and debris between the templates;

  • Mold problems: mold deformation, core and cavity matching size error, template combination is not parallel, the exhaust groove is too deep;

  • Equipment problem: the template is not parallel, and the template is not tightly closed;

  • Raw material problem: excessive liquidity.


3. Deformation

  • Process conditions: the material temperature is too high, the mold temperature is too high, the holding time is too short, and the cooling time is too short to force demoulding;


  • In terms of mold: improper gate position, insufficient gate quantity, improper ejection position causes uneven force.


4. Flow marks

  • Process conditions: material temperature is too low and not fully plasticized, injection speed is too low, the injection pressure is too small, holding pressure is not enough, mold temperature is too low, and injection volume is insufficient;

  • Mold aspect: the gate is too small, gate quantity is too few, runner gate is rough, surface finish is poor;

  • In terms of equipment: after temperature control, the system fails and the oil pump pressure drops;

  • In terms of raw materials: too much volatile matter, poor fluidity, mixed with miscellaneous materials.


5. Bubbles

  • Process conditions: low injection pressure, insufficient holding pressure, insufficient holding time, and high material temperature;

  • Mold aspect: poor exhaust, unreasonable gate location, gate size is too small;

  • In terms of raw materials: the moisture content is not dried or the drying time is not enough, and the shrinkage rate is too large.


6. Shrinkage

  • Process conditions: insufficient feeding amount, too short injection time, too short holding time, too high material temperature, too high mold temperature, too short cooling time;

  • In terms of mold: the runner is too small, the gate is too small, and the exhaust is poor;

  • In terms of equipment: insufficient injection pressure and foreign matter in the nozzle;

  • In terms of raw materials: the shrinkage rate is too large.


7. Unstable size

  • Process conditions: injection pressure is too low, the barrel temperature is too high, pressure holding time changes, the injection cycle is unstable, mold temperature is too high;

  • Mold aspect: uneven gate size, inaccurate cavity size, loose core, too high mold temperature or no water channel;

  • In terms of raw materials Variations in grades, uneven particle sizes, and volatile substances.


8. Difficult to demold

  • Process conditions: injection pressure is too high, the pressure holding time is too long, the injection volume is too much, mold temperature is too high;

  • Equipment: insufficient ejection force, insufficient ejection;

  • In terms of mold: no demolding slope, insufficient finish, improper ejection method, improper matching accuracy, poor exhaust, and template deformation.


9. Silver pattern

  • Process conditions: too high material temperature, too fast injection speed, too much injection pressure, uneven plasticization, too much release agent;

  • Mold aspect: the gate is too small, mold finish is poor, poor exhaust;

  • Equipment aspect: back pressure is too low, the nozzle has cast material;

  • In terms of raw materials: moisture content is not dried, excessive lubricant


10. Burnt

  • Process conditions: the material temperature is too high, the injection pressure is too high, the speed is too fast, the downtime is too long, and the release agent is not clean;

  • Mold aspect: the gate is too small, poor exhaust, complex cavity, poor cavity finish;

  • In terms of raw materials: there are sundries in the material, and powder in the pellets.

  • In terms of surface finishing solutions


11. Discoloration

  • Process conditions: the material temperature is too high, the injection pressure is too large, the molding cycle is long, the mold is not cooled, and the nozzle temperature is high;

  • Mold aspect: the gate is too small;

  • Equipment: there are obstacles in the barrel or nozzle, and the screw speed is high. The core is not concentric with the nozzle center;

  • In terms of raw materials: material pollution, colorant decomposition, high volatile content.


12. Weld line

  • Process conditions: low injection pressure, short injection time, low material temperature, too much clamping force, inappropriate release agent;

  • In terms of mold: mold temperature is too low, the runner is small, gate position is wrong, poor exhaust;

  • Equipment: poor plasticization;


In terms of raw materials: poor fluidity, too much lubricant, and foreign matter in the material.


13. Gloss defect

  • Process conditions: material temperature or mold temperature is too low, the injection pressure is too low, injection speed is too high or too small, and cooling time is too short;

  • Mold aspect: mold roughness becomes larger, the gate is too small, the runner is too thin, and exhaust is poor;

  • Equipment: insufficient material supply;

  • In terms of raw materials: the raw materials are not dried or contain volatile substances, the raw materials are easily degraded, the amount of auxiliary or release agent is too large or the quality is not good, and they contain foreign matter.


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