(1)

P: Poor flow of the molten material leads to the formation of concentric flow marks resembling growth rings on the surface of injection-molded parts, centered around the gate. When low-temperature, high-viscosity molten material with poor flow performance is injected into the cavity in a semi-cured, fluctuating state through the injection port and runner, the material flows along the cavity surface and is continuously pressed by the subsequently injected material, causing backflow and stagnation. This results in the concentric flow marks centered around the gate on the surface of the injection-molded part.

S: To address the causes of this defect, the following measures can be taken: increase the temperature of the mold and nozzle, enhance the injection speed and filling speed, increase the injection pressure and holding pressure, and extend the holding time. Additionally, heating elements can be installed at the gate to raise the localized temperature in that area. It may also be beneficial to appropriately enlarge the cross-sectional area of the gate and runner.

It is preferable to use a circular cross-section for the gate and runner, as this shape achieves the best mold filling. However, if the gate is set in a weak area of the injection-molded part, a square cross-section should be used. Additionally, larger cold wells should be placed at the bottom of the injection port and at the end of the runner. The temperature of the material significantly affects the flow performance of the molten material, so particular attention should be paid to the size of the cold wells, which must be positioned at the end of the flow direction of the molten material along the injection port.

If the primary cause of concentric flow marks resembling growth rings is poor resin performance, a lower-viscosity resin can be selected, provided the conditions permit.

(2)

P: Poor flow of the molten material in the runner causes spiral flow marks on the surface of the injection-molded part. When the molten material flows from a narrow cross-section of the runner into a larger cross-section of the cavity, or if the mold runner is narrow and has poor surface finish, turbulence can easily occur, leading to spiral flow marks on the surface of the molded part.

S: To address this, the injection speed can be appropriately reduced, or a speed control with slow-fast-slow stages can be implemented. The gate of the mold should be placed in thick-walled areas, or directly on the side of the wall, and the gate should preferably be pin-point, fan-shaped, or diaphragm-style. Additionally, the cross-sections of the runner and gate can be enlarged to reduce the flow resistance of the molten material.

Moreover, the flow rate of the cooling water inside the mold should be controlled to maintain a higher mold temperature. Increasing the temperature of the barrel and nozzle within the operational temperature range can also improve the flow properties of the molten material.


(3)

P: Volatile gases cause cloud-like flow marks on the surface of the injection-molded part. When using ABS or other copolymer resin materials, if the processing temperature is too high, volatile gases produced by the resin and lubricants can cause cloud-like flow marks on the surface of the molded part.

S: In this case, the mold and barrel temperature should be appropriately reduced, mold ventilation conditions should be improved, material temperature and filling speed should be lowered, and the gate cross-section can be enlarged. Additionally, consider changing the type of lubricant or reducing its quantity.