Analysis on the causes of brittleness of plastic p

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Analysis on the causes of brittle plastic products such as plastic bottles

on the one hand, mold

(1) the gate is too small, so we should consider adjusting the gate size or adding an auxiliary gate

(2) if the shunt channel is too small or improperly configured, try to arrange it in a balanced and reasonable manner or increase the size of the shunt channel

(3) abnormal injection cycle caused by poor mold structure

in terms of equipment

(1) there are dead corners or 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 plasticization of plastic in the machine barrel is insufficient; The return period of the plasticizing capacity of the machine is too long, and the plastic is heated and sheared in the machine barrel for too long. The plastic is easy to age, making the products brittle

(3) the ejector is inclined or unbalanced, and the sectional area of the ejector is small or improperly distributed

three aspects of 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 of parts

(3) too many times of plastic regeneration, too high recycled material content, or too long heating time in the barrel will promote the embrittlement of the workpiece

(4) the plastic itself is of poor quality, which is suitable for foreign investment in the central and western regions, Northeast China and Hainan Province. 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 contaminated by other plastics, bad additives, dust and impurities are also the reasons for embrittlement

four process aspects

it measures the deformation of the sample during the experimental process through the deformation measuring device; (1) The temperature of the barrel and nozzle is too low, turn it up. If the material is easy to degrade, the temperature of the barrel and nozzle should 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 caused by shear overheating

(3) mold temperature is too high, and it is difficult to demould; The mold temperature is too low, the plastic cools too early, 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 should have an appropriate demoulding slope. When the core is difficult to demould, the cavity temperature should be increased and the cooling time should be shortened; When the cavity is difficult to take off, reduce the cavity temperature and extend the cooling time

there is a stopover phenomenon after unloading (5) try to use less metal inserts. Brittle plastics with large cold and heat specific capacity, such as polystyrene, cannot be added to insert injection molding

v. product design

(1) the product has sharp corners, notches or parts with great thickness differences that are prone to stress cracking

(2) the product design is too thin or hollowed out too much

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