How to Prevent the Flow Mark for the Injection Molded Part?
The reasons for the flow mark and the measures are as follows:
(1) Ring-shaped flow marks occur on the surface of the plastic part due to poor melt flow, which centers on the pouring gate. When the low-temperature and high-viscosity melt with poor flow properties is injected into the cavity in a semi-solidified wave state in the injection port and runner, the melt flows along the surface of the mold cavity and is extruded by the continuously injected subsequent melt to form reflux and stagnation, so an annual ring-shaped flow mark centered on the pouring gate is generated 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 filling speed can be increased. Increase injection pressure, pressure maintaining and time. A heater can also be set at the pouring gate to increase the partial temperature of the pouring gate. The pouring gate and cross-sectional area of the runner can also be appropriately enlarged. A round shape is the best option for the pouring gate and cross-section of the runner. This kind of cross-section can obtain the best filling. However, if pouring gates are placed in weak areas of plastic parts, square cross-sections should be used. In addition, a large cold slug well should be set at the bottom of the injection port and the end of the runner, and the material temperature has a great influence on the flow performance of the melt. More attention should be paid to the size of the cold slug well. The position of the cold slug well must be set at the end along the flow direction of the injection port. If the main reason for the generation of annual ring-shaped flow marks is the poor performance of the resin, a low-viscosity resin can be selected if conditions permit.
(2) The poor flow of the melt in the flow channel leads to a spiral flow mark on the surface of the plastic part. When the molten material flows from a narrow cross-section of the runner into a cavity with a larger cross-section or a narrow mold runner with poor finish, the melted material is likely to form a turbulent flow, resulting in the formation of helical 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 to be slow, fast and slow. The pouring gate of the mold should be set at the thick-walled part or directly on the side of the wall. You'd better adopt fan type or diaphragm type of pouring gates. The cross section of the runner and pouring gate can also be appropriately enlarged to reduce the flow resistance of the melted material. In addition, the flow of cooling water in the mold should be controlled to make the mold have a high 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 melted material.
(3) The volatile gas causes cloud-like flow marks on the surface of the plastic part. ABS or other copolymer resin raw materials are used; if the processing temperature is high, the volatile gas generated by the resin and lubricant will cause cloud-like flow marks on the surface of the plastic part. In this regard, the temperature of the mold and barrel should be appropriately reduced. The discharge conditions of the mold should be improved; the material temperature and filling rate should be reduced, and the cross section of the pouring gate should be appropriately expanded. The variety or quantity of lubricant should be replaced or reduced.
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