The reason why plastic is brittle

A large part of the brittleness of products is caused by internal stress. There are many reasons for brittleness of products, mainly including:
A equipment aspect
(1) There are dead corners or obstacles in the barrel, which is easy to promote the degradation of the molten material.
(2) The plasticization capacity of the machine is too small, and the plasticization of 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 product brittle.
(3) The ejection device is tilted or unbalanced, and the top dry cross-sectional area is small or improperly distributed.
2. Mold aspect
(1) If the gate is too small, consider adjusting the gate size or adding auxiliary gates.
(2) If the diversion channel is too small or improperly configured, it should be arranged as reasonably balanced as possible or the size of the diversion should be increased.
(3) Poor mold structure causes abnormal injection cycle.
3. Process
(1) The temperature of the barrel and nozzle is too low, adjust 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 speed of the screw preplastic, make the material slightly loose, and reduce the degradation of the plastic caused by shear overheating.
(3) The mold temperature is too high and it is difficult to demold; The mold temperature is too low, the plastic cools prematurely, the fusion of the weld seams is poor, and it is easy to crack, especially for high-melting point plastics such as polycarbonate.
(4) The cavity core should have an appropriate demolding slope. When the core is difficult to demold, the cavity temperature should be increased to shorten the cooling time; When the cavity is difficult to get off, reduce the cavity temperature and extend the cooling time.
(5) Try to use metal inserts as little as possible, such as polystyrene such brittle plastic with a large ratio of hot and cold, and can not be added to insert injection molding.
4. Raw materials
(1) When the raw material is mixed with other impurities or doped with inappropriate or excessive solvents or other additives.
(2) Some plastics such as ABS, etc., under the condition of moisture, heating will have a catalytic cracking reaction with water vapor, so that the parts have a large strain.
(3) Too many times of plastic regeneration or too high content of recycled material, or too long heating time in the barrel, will promote the brittle cracking of the parts.
(4) The quality of the plastic itself is not good, such as large molecular weight distribution, and the composition containing uneven structure such as rigid molecular chains is too large; Or contaminated by other plastic doping, bad additives, dust impurity pollution, etc. are also the causes of brittleness.
5. Product design
(1) The product has sharp corners, notches or parts with a large difference in thickness that are prone to stress cracking.
(2) The product design is too thin or too hollowed.