Flow marks of injection defects

The causes of flow marks include: lower melt temperature, mold temperature, lower injection speed, injection pressure, or too small runner and gate, and too large flow resistance. According to the observation and analysis using the visual injection molding mold, the flow mark may be generated because the front part of the melt flow is cooled on the wall surface of the cavity, and it continuously rolls over with the melt behind and the cooling effect.

01. Poor melt flow leads to ring-shaped wave flow marks on the surface of the plastic part centered on the gate

When the low-temperature high-viscosity melt with poor flow performance is injected into the cavity in the semi-solidified fluctuating state in the injection port and runner, the melt flows along the surface of the mold cavity and is squeezed by the subsequent melt injected continuously to form reflux and stagnation. In order to produce annual ring-shaped wave flow marks centered on the gate on the surface of the plastic part. According to the cause of this failure, the temperature of the mold and the nozzle can be increased to increase the injection rate and filling speed. Increase injection pressure and holding pressure and increase time. A heater can also be installed at the gate to increase the local temperature at the gate. The cross-sectional area of the gate and runner can also be enlarged appropriately. The gate and runner cross-section is best to use a round, this section can get the best mold filling. However, if a gate is provided in a weak area of the plastic part, a square cross-section should be used.

In addition, a large cold cavity should be set at the bottom of the injection port and the end of the flow channel. The temperature of the material has a greater impact on the flow performance of the melt. The more attention should be paid to the size of the cold cavity, the location of the cold cavity must be set in the melt The end of the material along the direction of the injection port. Sign up for the Zhenye injection molding series of 4 days this month. If the main cause of the annual ring-shaped wave flow mark is the poor resin performance, low-viscosity resin can be selected under conditions that are sufficient.

02. The flow of molten material in the flow channel is not smooth, resulting in spiral wave flow marks on the surface of the plastic part

When the molten material flows into the cavity of a larger cross-section from a narrow cross-section of the runner, or the mold runner is narrow and the finish is poor, the fluid easily forms turbulent flow, resulting in the formation of spiral wave flow marks on the surface of the plastic part. In this regard, the injection speed can be appropriately reduced or the injection speed can be controlled slowly, quickly and slowly. The gate of the mold should be set at the thick wall part or directly at the side of the wall. The gate form is preferably shank, fan or diaphragm. The cross section of the runner and gate can also be enlarged appropriately to reduce the flow resistance of the flow material. In addition, the flow of cooling water in the mold should be controlled to keep the mold at a higher temperature. If the temperature of the barrel and nozzle is properly increased within the process operating temperature range, it will help to improve the flow performance of the melt.

03. Volatile gas causes cloud-like wave marks on the surface of plastic parts

When using ABS or other copolymer resin raw materials, if the processing temperature is high, the volatile gas generated by the resin and lubricant will cause the cloud-like wave mark on the surface of the plastic part. In this regard, the temperature of the mold and the barrel should be appropriately reduced, the exhaust conditions of the mold should be improved, the material temperature and the filling rate should be reduced, the gate cross section should be appropriately expanded, and the type of lubricant should be replaced or the number should be reduced.