13 common bad defects of injection molded products
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13 common bad defects of injection molded products
Written By Jasmine HL
1. Dissatisfaction (lack of plastic)
Process issues: the plasticizing temperature is too low, the nozzle temperature is too low, the
injection time is too short, the injection speed is too slow, and the mold temperature is too low;
Mold problems: The runner is too small, the gate is too small, the gate location is not reasonable,
the exhaust is poor, and there is debris in the cavity;
Raw material problems: poor fluidity, mixed with debris.
2. Flash
Process issues: 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, errors in the matching dimensions of the core and cavity,
non-parallel template combinations, and excessive exhaust grooves;
Equipment problems: the template is not parallel and the template is not tightly closed;
Problems with raw materials: Excessive liquidity.
3. Deformation
In terms of 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 the demolding;
In terms of mold: improper gate position, insufficient number of gates, improper ejection
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position, uneven force.
4. Flow marks
In terms of process conditions: the material temperature is too low to completely plasticize, the
injection speed is too low, the injection pressure is too small, the holding pressure is not enough,
the mold temperature is too low, and the injection amount is insufficient;
In terms of mold: the gate is too small, the number of gates is too small, the runner gate is rough,
and the surface finish is poor;
In terms of equipment: the system fails after the temperature control and the oil pump pressure
drops;
In terms of raw materials: too many volatiles, poor fluidity, mixed with miscellaneous materials.
5. Bubble
In terms of process conditions: low injection pressure, insufficient holding pressure, insufficient
holding time, and high material temperature;
In terms of mold: poor venting, unreasonable gate location, too small gate size;
In terms of raw materials: the moisture content is not dried or the drying time is not enough, and
the shrinkage is too large.
6. Shrink
In terms of process conditions: insufficient feeding amount, too short injection time, too short
holding time, too high material temperature, too high mold temperature, and 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: the injection pressure is not enough, and the nozzle is clogged with
foreign objects;
In terms of raw materials: excessive shrinkage.
7. Unstable size
In terms of process conditions: the injection pressure is too low, the barrel temperature is too
high, the holding time varies, and the injection cycle is unstable and the mold temperature is too
high;
In terms of mold: uneven gate size, inaccurate cavity size, loose core, too high mold temperature
or no water channel;
In terms of raw materials: there are changes in grades, uneven particle sizes, and volatile
substances.
8. Difficult demoulding
In terms of process conditions: the injection pressure is too high, the holding time is too long, the
injection volume is too high, and the mold temperature is too high;
Equipment: Insufficient ejection force and insufficient ejection distance;
In terms of mold: no mold release slope, insufficient finish, improper ejection method, improper
cooperation accuracy, poor exhaust, and template deformation.
9. Silver pattern
In terms of process conditions: material temperature is too high, injection speed is too fast, the
injection pressure is too large, uneven plasticization, and too much release agent;
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In terms of mold: the gate is too small, the mold finish is poor, and the exhaust is poor;
In terms of equipment: back pressure is too low, and nozzles have castings;
In terms of raw materials: the moisture content is not dried, and the lubricant is excessive
10. Charred
In terms of 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;
In terms of mold: the gate is too small, the exhaust is poor, the cavity is complicated, and the
cavity finish is poor;
In terms of raw materials: there are impurities in the material, and powder in the granular
material.
11. Discoloration
In terms of process conditions: material temperature is too high, the injection pressure is too
high, the molding cycle is long, mold is not cooled, the nozzle temperature is high;
In terms of mold: the gate is too small;
In terms of equipment: there are obstacles in the barrel or nozzle, and the screw speed is high.
The core is not concentric with the center of the nozzle;
In terms of raw materials: material pollution, colorant decomposition, high volatile content.
12. Weld marks
In terms of process conditions: low injection pressure, short injection time, low material
temperature, too large clamping force, and inappropriate mold release agent;
In terms of mold: the mold temperature is too low, the runner is small, the gate position is
incorrect, and the exhaust is poor;
Equipment: Poor plasticization;
In terms of raw materials: the fluidity is too poor, the lubricant is too much, and the material has
foreign matter.
13. Gloss defect
In terms of process conditions: the material temperature or mold temperature is too low, the
injection pressure is too low, the injection speed is too large or too small, and the cooling time is
too short;
In terms of mold: the mold roughness becomes larger, the gate is too small, the runner is too thin,
and the exhaust is poor;
Equipment: insufficient 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 agents or release agents is excessive or the
quality is not good, and foreign matter is contained.
