Injection Molding Defects And Solutions -- Plastic Brittleness

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Injection Molding Defects and Solutions -- Plastic Brittleness 2025-10-20

Plastic Brittleness:
Due to poor plastic properties, obvious orientation, high internal stress, and poor structural design of the plastic part, the strength decreases, making it prone to cracking (especially along the flow direction of the material).

18.1 Causes	18.2 Solutions
18.1.1 Material degradation, depolymerization, hydrolysis, or poor-quality pigment (e.g. deterioration).	18.2.1 Replace raw material, color masterbatch, or pigment.
18.1.2 Molding temperature too low or too high.	18.2.2 Increase or decrease molding temperature.
18.1.3 Poor weld lines, warpage or deformation.	18.2.3 Raise mold temperature or injection speed; reduce weld lines; decrease injection and holding pressure to lower molecular orientation and internal stress.
18.1.4 Material too moist or high moisture content (e.g. PA6).	18.2.4 Extend drying time.
18.1.5 Excessive use of regrind material or insufficient feeding.	18.2.5 Reduce ratio of regrind material; ensure smooth feeding from hopper; avoid bridging.
18.1.6 Mold temperature too low; poor plasticization.	18.2.6 Raise mold and barrel temperature; reduce screw speed.
18.1.7 Poor part design (insufficient strength, sharp corners, notches).	18.2.7 If possible, modify product design to reduce notches or add radii (R) to sharp corners.
18.1.8 Plastic layer around metal insert too thin, insert not preheated sufficiently, or contaminated.	18.2.8 Modify product or mold design to ensure sufficient encapsulation; clean metal insert thoroughly.
18.1.9 Contaminants or incompatible materials in plastic.	18.2.9 Replace raw material.
18.1.10 Poor plasticization, or pellets too large or uneven.	18.2.10 Lower screw speed, increase back pressure and melt temperature.
18.1.11 Improper mold release agent or dirty mold.	18.2.11 Replace mold release agent and clean mold.
18.1.12 Obvious shrinkage orientation, uneven filler distribution.	18.2.12 Reduce injection speed and screw speed, raise mold temperature, minimize molecular orientation.
18.1.13 Uneven shrinkage, poor cooling, or high residual stress.	18.2.13 Increase mold temperature, reduce injection speed, improve mold cooling system, and reduce stress.
18.1.14 Contact of plastic part with solvent.	18.2.14 Avoid contact with solvents.
18.1.15 Holding pressure too high or holding time too long.	18.2.15 Lower holding pressure and shorten holding time.
18.1.16 Screw speed too fast.	18.2.16 Reduce screw speed.
18.1.17 Injection speed too fast or too slow.	18.2.17 Lower or increase injection speed appropriately.
18.1.18 Improper gate size, position, or design causing high internal stress, strong orientation, or uneven filler distribution.	18.2.18 Modify gate position, reduce injection and screw speed, ensure smoother melt flow and more uniform fiber distribution.
18.1.19 Hot runner temperature too high or thermocouple failure causing material decomposition.	18.2.19 Lower hot runner temperature or replace thermocouple.