Burn marks on plastic products during injection molding are primarily caused by defects related to residual gas in the mold cavity. So, how can we improve this situation?
Switch to Materials with Good Thermal Stability
Using materials with excellent thermal stability can effectively resist molecular chain breakage at high temperatures, thereby reducing burn marks caused by material thermal decomposition.
Opt for Materials with Good Lubricity
Employing plastics with high lubricity can lower the flow resistance of the melt in the mold, reducing localized overheating due to friction and subsequently avoiding the formation of burn marks.
Avoid Using Recycled Materials
Given that recycled materials may contain more impurities and damaged molecular chains, they are more prone to producing burn marks during reprocessing. Therefore, whenever possible, recycled materials should be avoided in injection molding production.
Ensure Precise Temperature Control of the Injection Molding Machine
Maintaining precise temperature control of the injection molding machine is crucial. By accurately controlling the temperatures of the barrel and mold, plastic burnout due to excessive heat can be avoided, while ensuring uniform flow of the melt.
Regularly Clean the Outer Side of the Nozzle
Deposits and residues on the outer side of the nozzle can obstruct the normal flow of plastic, increasing the risk of burn marks. Therefore, the nozzle should be cleaned regularly to keep it clean and unobstructed.
Reduce Residence Time in the Barrel
Prolonged residence time of plastic in the barrel of the injection molding machine can lead to thermal decomposition and burnout. By optimizing the production process and reducing the residence time of the plastic in the barrel, the incidence of burn marks can be effectively reduced.
Use an Injection Molding Machine with an Appropriate Capacity
Using a smaller capacity injection molding machine that matches the product specifications can reduce the number of cycles and residence time of the plastic in the barrel, thereby lowering the likelihood of burn marks.
Optimize the Gate Design
The gate is a crucial channel for plastic to enter the mold. By shortening the gate length and ensuring a reasonable gate design, the flow resistance of the plastic in the gate area can be reduced, avoiding the formation of black streaks. These streaks are typically caused by the decomposition of plastic materials or additives, as well as material retention due to damage on the surface of the barrel screw.
