Jetting refers to when the plastic melt, due to being injected at high speed, does not adhere well to the mold walls but instead forms a wavy or linear flow path inside the mold. This phenomenon often leaves visible flow marks on the surface of the molded product, especially near the injection point.
How to Avoid Jetting Situation?
To reduce or avoid jetting, consider the following methods:
Adjust Injection Speed: Reduce the speed of the molten plastic injection, allowing the melt sufficient time to fill the mold evenly.
Optimize Gate Design: Improve the shape and size of the gate to ensure smoother entry of the melt into the mold.
Increase Mold Temperature: Raise the temperature of the mold to improve the flowability of the melt as it enters the mold.
Adjust Melt Temperature: Appropriately increase the melt temperature to improve its fluidity.
As For Brightlx, here is a detailed solution
We use a hot runner or hot sprue together with the gate/pin-point gate/valve gate, which can significantly improve the quality of injection molded parts by reducing defects such as waviness and shrinkage. Here's why these technologies are effective:
Hot Runner System
A hot runner system maintains the molten plastic in a heated state within the runner system (the channels through which the plastic travels to reach the mold cavities). This system eliminates the need to re-melt solidified runners with each cycle, leading to several benefits:
Consistent Temperature Control: The plastic remains at a uniform temperature, reducing the likelihood of premature cooling and solidification that can cause uneven flow and result in waviness on the surface of the part.
Material Efficiency: Since the plastic in the runners remains molten and does not need to be ejected with the part, material wastage is minimized. This also means fewer stress points from potential gate areas, which can lead to defects.
Reduced Cycle Time: The cycle time is generally shorter because the molten plastic does not need to be re-melted, allowing faster production rates.
Valve gates incorporate mechanical valves (typically either pneumatic or hydraulic) that control the flow of plastic into the mold cavity very precisely:
Precision Flow Control: The ability to precisely open and close the gate at the right times allows for better control over the volume and pressure of the plastic entering the mold. This precision helps in filling the mold optimally and uniformly.
Elimination of Overpacking: By precisely controlling when the flow of plastic stops, valve gates help prevent overpacking of the mold, which can lead to shrinkage as the packed material cools and contracts.
Reduced Thermal Stress: The valve gate helps in managing the thermal stresses imparted on the material, ensuring that it flows into the mold cavities at consistent temperatures and pressures, further minimizing the chances of defects like shrinkage and warping.
Combined Benefits
When hot runner systems or hot sprues are used together with valve gates, the advantages complement each other, leading to:
Improved Surface Quality: The constant temperature and flow control lead to parts with smoother surfaces and fewer visual defects like waviness or sink marks.
Decreased Shrinkage and Warping: Uniform temperature maintenance and the ability to control the filling and packing phases accurately reduce the internal stresses that cause shrinkage and warping.
Increased Efficiency and Quality: The combination of these systems enables faster cycles and higher-quality outputs, no need to cut the gate, which are crucial for high-volume, high-precision manufacturing environments.
Thus, employing both a hot runner or hot sprue system and valve gate technology together in the injection molding process provides a highly effective way to enhance part quality, reduce material waste, and improve overall production efficiency.
