(1) Poor melt flow results in annual ring-shaped wave flow marks on the surface of the plastic part centered on the gate.
when the low-temperature and high-viscosity melt with poor flow properties is injected into the cavity in a semi-solidified and fluctuating state in the injection port and runner, the melt flows along the surface of the mold cavity and is squeezed by the continuously injected subsequent melt to form backflow and stagnation. , So as to produce annual ring-shaped wave flow marks centered on the gate on the surface of the plastic part.
In view of the cause of this failure, the temperature of the mold and the nozzle can be increased, and the injection rate and mold filling speed can be increased. Increase injection pressure and holding pressure and increase time. A heater can also be installed at the gate to increase the local temperature of the gate. The cross-sectional area of the gate and runner can also be appropriately enlarged. The cross-section of the gate and runner is best to be round, which can obtain the best mold filling. However, if the gate is set in the weak area of the machining uhmw plastict, a square section should be used. In addition, larger cold slug holes should be set at the bottom of the injection port and the end of the runners. The material temperature has a greater influence on the flow performance of the melt. The more attention should be paid to the size of the cold slug hole, the position of the cold slug hole must be set in the melt. The end of the material along the flow direction of the injection port.
If the main cause of annual ring-shaped wave flow marks is poor resin performance, a low-viscosity resin can be used when conditions permit.
(2) The poor flow of the melt in the flow channel leads to spiral wave flow marks on the surface of the plastic machining. When the melt flows from the narrow section of the flow channel into the cavity of the larger section or the mold flow channel is narrow and the finish is poor, the flow material is easy to form turbulence, 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 in stages by slow, fast, and slow. The gate of the mold should be set in the thick wall part or directly on the wall side. The gate type is best to adopt the handle, fan or diaphragm type. It is also possible to appropriately expand the runner and gate section 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 appropriately increased within the operating temperature range of the process, it is beneficial to improve the flow properties of the melt.
(3) Volatile gas causes cloud-like wave flow 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 cloud-like wave flow marks on the surface of the cnc machining services. In this regard, the temperature of the mold and 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 section should be appropriately expanded, and the lubricant should be replaced or reduced in quantity.