How to Address Burn Marks in Plastic Product Processing?
Burn marks are a common defect in the injection molding of plastic products, severely impacting their appearance, strength, and functional performance. Here are key solutions to mitigate this issue:
1. Optimize Mold Venting Design
Poor venting is a primary cause of burn marks. Trapped air or volatile gases under high temperature and pressure can lead to scorching. To address this:
Design vent grooves or venting holes at the final filling positions, thin-walled areas, and complex mold structures.
Regularly clean venting channels to prevent blockages and ensure efficient gas escape.
2. Adjust Injection Molding Parameters
Improper parameter settings, such as excessive injection speed, high back pressure, or overheating in the barrel, can cause localized overheating. Solutions include:
Optimize barrel temperature, injection speed, holding pressure, and dwell time based on material properties.
Minimize the residence time of plastic in the barrel to avoid thermal degradation or oxidation.
3. Ensure Material Dryness and Purity
Hygroscopic plastics (e.g., PA, PC, PET) can hydrolyze under high temperatures if moisture is present, generating gases and burn marks. Mitigation steps:
Thoroughly dry raw materials before processing and store them in moisture-controlled environments.
Strictly screen recycled materials or additives to avoid contaminants or decomposed residues.
4. Maintain Equipment Cleanliness
Carbon buildup or residual material in the barrel, screw, or nozzle can decompose and scorch during processing. Best practices:
Clean equipment regularly, especially when switching materials or colors.
Use specialized purging compounds to remove residues from the screw and barrel.
5. Improve Product Design
Complex geometries (e.g., excessive ribs, uneven wall thickness) can obstruct melt flow or prolong localized residence time, leading to burn marks. Design guidelines:
Avoid sharp corners and dead zones.
Optimize runner systems and gate design to ensure smooth and uniform melt flow.
