We have defects in the gate area during the process of injection mould. What is the reason for this phenomenon? Is there any good way to solve it?
Causes Of Light Line In Injection Mould
In the point gate design perpendicular to the direction of the part, a radiation system consisting of different color depths and glosses centered on the gate appears on the surface of the part during injection molding, called a ray of light.
There are generally three manifestations, namely dark lines with dark background, dark lines with dark background and dense and white dark lines around the gate.
Such defects mostly occur when injecting polystyrene and modified polystyrene mixtures, and are related to the following factors: the two materials have differences in rheology, colorability, etc., and the flow rates of the stratosphere and turbulent layer of the pouring system.
There are differences in heating conditions; plastics produce burnt wires due to thermal decomposition; gaseous substances interfere with the plastics when entering the mold.
https://www.sciencedirect.com/science/article/abs/pii/S0263436823002123
Injection Mould Light Line Solution
- When using mixed plastics, the plastics must be mixed well and the particle sizes of the plastics must be the same and uniform.
- Plastic and colorant should be mixed evenly. If necessary, appropriate dispersant should be added and mixed mechanically.
- The plasticization must be complete and the plasticizing performance of the machine must be good.
- Reduce the injection pressure and speed, shorten the injection and holding time, increase the mold temperature, increase the nozzle temperature, and reduce the front furnace temperature.
- Prevent the degradation of plastics from causing increased viscosity of molten materials and coked materials: for example, pay attention to whether the screw and barrel are worn and have dead ends, or the heating system is out of control, and improper processing operations may cause plastics to decompose due to long-term heating. This can be achieved by polishing the inner surfaces of the screw and barrel front.
- Improve the gate design, such as enlarging the gate diameter, changing the gate position, changing the gate to a rounded corner transition, trying to locally heat the gate, and adding a cold slug well at the end of the runner.
Causes Of Cold Spots In Injection Mould
Cold spots mainly refer to the foggy or brightcolored spots near the gate of the part or the curved scars starting from the gate that look like earthworms sticking to it.
They are caused by the plastic front entering the cavity or due to excessive pressure holding. It is caused by the cold material that is later squeezed into the mold cavity.
The front material transfers heat due to the cooling effect of the nozzle or runner, and is partially cooled and solidified before entering the mold cavity. When it expands through the narrow gate and is injected into the mold cavity, the melt ruptures, and is then heated by the subsequent heat. The molten material pushes around and becomes a cold material spot.
Solution To Cold Spots In Injection Mould
- The cold material well must be opened. The form, size and position of the gate should also be considered to prevent disparity in the cooling rate of the material.
- The center of the nozzle should be adjusted well, and the matching size of the nozzle and the mold feed should be designed to prevent material leakage or cold material from being brought into the cavity.
- The mold exhaust is good. The interference of gas will cause turbidity patterns on the gate.
- Increase the mold temperature. Slow down the injection speed, increase the injection pressure, reduce the holding pressure and injection time, and reduce the holding pressure.
- Dry the plastic well. Use less lubricant to prevent powder from being contaminated.
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