The brittleness of products is largely caused by internal stress. There are many reasons for brittle products, mainly including:
I Equipment
(1) There are obstacles in the barrel, which is easy to promote the degradation of molten materials.
(2) The plasticizing capacity of the machine is too small, and the plasticizing of the plastic in the barrel is not sufficient; The plasticizing capacity of the machine is too large, the plastic is heated and sheared in the barrel for too long, and the plastic is easy to age, making the products brittle.
(3) The ejection device is inclined or unbalanced, and the sectional area of the ejector rod is small or improperly distributed.
(II) mold
(1) If the gate is too small, consider adjusting the gate size or adding an auxiliary gate.
(2) If the splitter channel is too small or improperly configured, it should be arranged in a balanced and reasonable way or the size of the splitter channel should be increased.
(3) The injection cycle is abnormal due to poor mold structure.
III. Process
(1) The temperature of barrel and nozzle is too low, please raise it. If the material is easy to degrade, the temperature of barrel and nozzle shall be increased.
(2) Reduce the back pressure and rotation speed of screw pre molding, make the material slightly loose, and reduce the degradation of plastic due to shear overheating.
(3) Mold temperature is too high, and demoulding is difficult; The mold temperature is too low, the plastic cools prematurely, the fusion joint is poor, and it is easy to crack, especially for high melting point plastics such as polycarbonate.
(4) The cavity and core shall have proper demoulding slope. When the core is difficult to demould, the cavity temperature should be increased to shorten the cooling time; When the cavity is difficult to detach, it is necessary to reduce the cavity temperature and extend the cooling time.
(5) Try to use less metal inserts. Brittle plastics with large cold and hot specific capacity, such as polystyrene, should not be added to the inserts for injection molding.
IV. Raw materials
(1) When the raw materials are mixed with other impurities or doped with inappropriate or excessive solvents or other additives.
(2) Some plastics, such as ABS, will undergo catalytic cracking reaction with water vapor when heated under damp conditions, resulting in large strain in the parts.
(3) Too many times of plastic regeneration, too high content of recycled materials, or too long heating time in the barrel will promote the brittle fracture of the parts.
(4) The quality of plastics itself is poor, for example, the molecular weight distribution is large, and the proportion of components with uneven structures such as rigid molecular chains is too large; Or by other plastic doping pollution, bad additives pollution, dust and impurities pollution is also the cause of brittle.
V. Product Design
(1) The products have sharp corners, notches or parts with large thickness difference that are prone to stress cracking.
(2) The product design is too thin or too many hollows.
