PC / ABS injection defects and solutions
PC / ABS injection defects and solutions
PC / ABS are thermoplastic plastics made of polycarbonate and polyacrylonitrile (ABS) alloy. They combine the excellent characteristics of the two materials, the formability of ABS materials and the mechanical properties, impact strength, temperature resistance, ultraviolet (UV) resistance of PC.
1. Silver wire problem
Poor silver wire is the most common problem of PC / ABS materials. Silver wire, also known as crazing, water spray, material spray, etc., is the phenomenon of silver white filamentous stripes on the surface of products in process along the flow direction, and the interference of gas. The generated gas is mainly divided into three components:
(1) Air: air involved in glue melting and injection stage;
(2) Moisture: moisture contained in the material itself;
(3) Pyrolysis gas: gas produced by high temperature hydrolysis / thermal decomposition.
resolvent:
First, check whether the material is dry enough. After confirming that the material is dry enough, adjust the injection molding process to improve the silver wire defects. At the same time, poor injection silver wire is also related to mold exhaust.
2. Flow mark problem
Flow marks are produced during injection of materials due to poor fluidity of materials. Different from crazing, flow marks are not caused by moisture or material decomposition, and their appearance is also different.
resolvent:
It can be avoided by increasing the material temperature to improve the fluidity. Appropriately improving the mold problem to increase the fluidity of the material in the mold and reduce the injection speed can also be solved.
3. Shrinkage and dent problems
Shrinkage is caused by insufficient filling of materials in the mold cavity.
resolvent:
Properly increase the mold temperature and material temperature to improve the material fluidity, prolong the pressure holding time of injection, increase the injection pressure and increase the injection speed to improve the mold filling. You can also increase the gate size and heat the gate runner to reduce and eliminate the shrinkage of products;
4. Warpage deformation problem
Warping deformation of injection molded parts is caused by unreasonable part design, improper gate position and unreasonable injection molding processing conditions, resulting in internal stress, uneven or excessive shrinkage. If the mold temperature is too high or uneven, it will cause difficulty in demoulding the part mucous membrane or uneven cooling, warping deformation will also occur.
resolvent:
(1) Processing technology: lengthen the injection molding cycle, reduce the injection temperature, properly adjust the injection pressure and injection speed, slow down the ejection speed, increase the ejection area and maintain the balance of ejection force;
(2) Product design: increasing the wall thickness, adding stiffeners and reinforcing at the fillet can reduce warpage and deformation;
5. Speckle problem
It is usually caused by "melt fracture" caused by the expansion of melt into the mold cavity during high-speed injection.
resolvent:
(1) Molding process: increase the material temperature, increase the nozzle temperature and slow down the injection speed to reduce the appearance of speckle;
(2) Mold: improve the mold temperature, add overflow groove, increase the gate size and modify the gate shape.
6. Pitting problem
resolvent:
(1) Poor dispersion, add dispersant or oil, raise the temperature and add back pressure.
(2) Pay attention to whether there are mold problems. Try something else.
(3) Whether the baking temperature and time are sufficient.
(4) Mold temperature adjustment.
7. Dent problem
Dents are caused by improper material temperature and improper product design. When the material temperature is too low, not only shrinkage will occur, but also dents will occur. If the material temperature is too high and the mold temperature is too high, the molten material will shrink too much during cooling, resulting in dents.
resolvent:
Adopt appropriate processing problems to improve injection speed and measures.
8. Product "peeling" problem
The peeling problem of plastic products is closely related to the fluid fracture caused by high shear stress. Under low shear stress or rate, the small disturbance caused by various factors is restrained by the melt; Under high shear stress or velocity, the disturbance in the fluid is difficult to suppress and develops into unstable flow; When a critical shear force is reached, the fluid will rupture.
resolvent:
(1) Materials: PC and ABS are partially compatible, so appropriate compatibilizers must be added in the modification process to improve their compatibility. Of course, we need to take the first step to eliminate the bad peeling caused by the mixture;
(2) Mold: the principle of mold design should follow the direction of minimizing shear. Generally speaking, the products with dense skin texture are more prone to peeling (caused by the friction and shear between the melt in the cavity and the inner wall of the cavity during high-speed filling); At the same time, in the gate design, if the gate size is too small, it will lead to excessive shear when the melt passes through the gate, and then lead to peeling on the product surface;
(3) Injection molding process: the main direction is to avoid excessive shear. When the product is difficult to fill, it can be improved by high-speed and high-pressure. Therefore, in the actual injection molding process, we can also consider increasing the injection temperature / mold temperature and improving the material fluidity to reduce the flow resistance in the actual filling process, so as to avoid excessive shear caused by high-speed and high-pressure.
