The main reasons for Cracking

Cracking in injection molding, including surface filamentous cracks, micro-cracks, whitening, cracking due to sticking molds, and trauma crises caused by sticking in the runner, can be classified into demolding cracking and application cracking based on the time of occurrence. The main reasons for these issues are as follows:

Processing Factors:

Processing Pressure: Excessive pressure, high speed, excessive filling, long injection and holding times can lead to excessive internal stress and cracking.

Adjusting Mold Opening: Adjusting the speed and pressure of mold opening to prevent rapid stretching of components and demolding cracks.

Optimizing Mold Temperature: Increasing mold temperature appropriately for easy demolding and reducing material temperature to prevent decomposition.

Preventing Weakness: Preventing cracking due to welding marks, plastic degradation, and decreased mechanical strength.

Proper Mold Release Agent: Using mold release agents appropriately and regularly removing substances adhering to the mold surface.

Residual Stress: Eliminating residual stress by immediately performing annealing heat treatment after molding to reduce crack formation.

Mold Factors:

Balanced Ejection: Ensuring sufficient ejection rods, cross-sectional areas, adequate demolding angles, and smooth mold cavity surfaces to prevent cracking due to residual stress concentration from external forces.

Component Structure: Avoiding overly thin structures, using rounded transitions instead of sharp angles, and minimizing stress concentration points.

Limited Metal Inserts: Minimizing the use of metal inserts to prevent increased internal stress from differential shrinkage.

Venting for Deep Parts: Incorporating adequate venting for deep parts to prevent vacuum formation.

Optimal Runner Design: Ensuring sufficiently large main runners for easy demolding before solidification.

Preventing Adhesion: Ensuring proper alignment of the runner sleeve and nozzle to prevent component sticking to the fixed mold due to cold hard material drag.

Material Considerations:

Recycled Material Content: Excessive recycled content leading to low component strength.

Moisture Control: High humidity causing chemical reactions between plastics and water vapor, reducing strength and causing ejection cracking.

Material Suitability: Materials unsuitable for processing environments or of poor quality, contaminated materials can lead to cracking.

Machine Factors:

Proper Plasticizing Capacity: Ensuring the appropriate plasticizing capacity of the injection molding machine to avoid incomplete mixing and brittleness or degradation issues.

By addressing these factors, you can significantly reduce the occurrence of cracking in injection molding processes.