What are the causes of plastic products bending, and how do plastic manufacturers solve it?

(1) Defect characteristics
The main manifestation of plastic product bending is that the Plastic Product produces rotation or twisting phenomenon during plastic manufacturing, and the flat area has undulating straight edges facing inward or outward bending or twisting.
(2) Causes of defect generation and elimination methods
The main reason for bending is that the high molecular bond undergoes internal displacement under the action of stress, and the existence of internal stress during demolding often causes different degrees of deformation according to different plastic part shapes. Crystalline resins, such as PE, POM, PP, PA, etc., are more likely to cause bending than non-crystalline resins, such as PS, ABS, PC, PMMA, etc. The specific analysis is as follows.

1) Injection mold
A. The cooling system of the mold produced by the injection molding manufacturer is unreasonable, the plastic part is not cooled evenly and not sufficiently, and it is very easy to cause bending. If the temperature of the core is higher than that of the mold wall, the plastic part will bend in the direction of the core after demolding. In the design, the overall consideration of the mold should be made, and the temperature of the mold should be as balanced as possible, and the temperature difference should not be too large.
B. If the mold cavity and core are not cooled separately, it is difficult to control the temperature difference. Generally, the temperature difference between the inlet and outlet of the cooling water should not be too large, especially for multi-cavity molds. The temperature difference should be controlled at 2-3 degrees Celsius.
C. For ring-shaped plastic parts, if side gates or needle gates are used, the molten flow is uneven, which is easy to cause bending. For this reason, disk gates or spoke gates should be used first.
D. If the plastic melt directly impacts the core when entering the mold cavity, it will cause the two sides of the core to be unevenly stressed and bent. For this reason, it should be avoided that the melt directly impacts the core.
E. For rectangular flat plastic parts with a large area, if a straight gate and a point gate on the same straight line are used, it is easy to cause bending deformation. For this reason, a film gate or a multi-point side gate should be used as much as possible.
F. For round plate-shaped plastic parts, side gates should be used as little as possible, but multi-point straight gates or direct center gates should be used.
G. For shell-shaped plastic parts, if side gates are used, bending deformation is likely to occur. For this reason, a straight gate should be used.
H. If the demolding angle of the mold is not enough, it will take a lot of force to push out the plastic part. This force will cause the internal stress to be too large and uneven, resulting in bending. For this reason, there should be a suitable demolding angle.
I. If the ejector area is too small or the ejectors are not evenly distributed, the plastic part will be unevenly stressed, causing bending. For this reason, the plastic part should be evenly stressed and the stress should be balanced.
J. If the mold's ejector or insert is improperly set, the plastic part will be unevenly stressed during demolding, which will also cause bending. For this reason, the ejector or insert should be re-examined.
K. If the ejector cannot output force at the same time during demolding, the plastic part will not be evenly stressed, and bending will occur. For this reason, it is necessary to carefully check whether the position of the ejector is correct.
L. If the mold strength is not enough, it will deform during molding, causing the plastic part to produce additional stress and deformation, which will cause the plastic part to bend. For this reason, the mold rigidity should be strengthened or the injection pressure should be reduced.

2) Injection molding process
A. If the injection pressure is too high during the plastic molding process of the plastic manufacturer, the molecular orientation along the direction of the plastic melt flow and the molecular orientation perpendicular to the flow direction are significantly different. This difference makes the internal stress of the plastic part uneven, and bending occurs. For this reason, the injection pressure should be appropriately reduced.
B. If the temperature of the plastic melt is too high, the temperature at the time of molding and solidification is high, and the plastic part will have a large amount of internal stress in the rapid cooling process, which will cause bending. For this reason, the temperature of the plastic melt can be appropriately reduced.
C. If the plastic melt flows slowly in the mold cavity, the temperature of the melt is high during the flow process, and the internal stress of the plastic part is also high, so it is easy to bend. For this reason