What causes the wavy marks on plastic products and how do plastic manufacturers solve this problem?
(1) Defect feature
The main manifestation of the wavy marks on the surface of Plastic Products is: in the plastic manufacturing process, the surface of the plastic part produces a wavy, spiral or cloud-like wave-shaped uneven phenomenon with the gate as the center.
(2) Cause and elimination of defects
The main reason for the flow mark is that the plastic melt flows inappropriately in the mold cavity. The specific analysis is as follows.
1) Injection mold
A. If the cross-sectional area of the gate and runner of the mold produced by the plastic factory is too small, the plastic melt cannot flow smoothly in it, and the flow rate is slow, which is easy to produce wave marks. Therefore, the cross-sectional area of the gate and runner should be appropriately enlarged.
B. If cold material enters the mold cavity, it is easy to produce wave marks. Therefore, a large cold material well should be set at the end of the main runner and branch runner of the mold.
C. If the cooling system design of the mold is not good, it will lead to uneven cooling and the appearance of flow marks. Therefore, attention must be paid to the design of the cooling system.
D. If the position and shape of the gate are set improperly, when the plastic melt flows from the narrow cross section of the runner into the larger cross section of the mold cavity, it is very easy to produce turbulence, resulting in the formation of flow marks. Therefore, the gate should be set in the thick wall area or directly on the side of the wall, and its shape is best used as a handle, fan or membrane type.
2) Injection molding process
A. If the holding time is too short when the injection molding manufacturer custom plastic product, the surface of the plastic part is easy to produce wave marks. Therefore, the holding time can be appropriately extended.
B. If the mold temperature is too low, the flow of plastic melt is slow, and it is easy to produce wave marks. To this end, reduce the amount of cooling water entering, and check whether the mold heating system is working properly.
C. If the injection speed is too fast, the plastic melt flow rate will be too fast, and turbulence will be easily produced in the mold cavity, which will lead to the generation of flow marks. Therefore, the injection speed can be appropriately reduced, or a slow, fast, and slow graded injection can be used.
D. If the injection speed is too slow, the plastic melt in the mold cavity flows slowly, and the melt in the mold cavity is squeezed to form backflow and stagnant flow, which leads to the generation of flow marks. Therefore, the injection speed should be appropriately increased.
3) Raw materials
A. Some plastic raw materials, such as ABS or other copolymer resins, will produce volatile gases when they are plasticized at high temperatures, which will cause the surface of the plastic part to produce a cloud-like flow mark. Therefore, the processing temperature can be appropriately reduced.
B. Some resins, such as PC, PPO, and PSF, have poor fluidity. Some resins of the same brand have different fluidity. Poor fluidity is often the main cause of flow marks. Therefore, resins with good fluidity should be used as raw materials.
C. If the amount of lubricant is too small, the plastic melt flowability is poor, and it is easy to produce wave marks. Therefore, the amount of lubricant added should be appropriately increased.