Q: How to solve the deformation of injection PP makeup box?
① The methyl arrangement in isotactic polypropylene is the same as that of its molecular chain, which is a very typical long-chain polymer. End-group and chain-folding have little effect on its crystallinity, resulting in highly regular molecular chain, high crystallinity and large shrinkage , About 1.6% to 2.0%, resulting in post-shrinkage caused by pp in the shrinkage of pits, deformation is difficult to solve.
② Cosmetic box structure of the mold usually there will be a very large turning angle, resulting in pp melt turbulence, coupled with the mold of the ramp, the irrational distribution of water channels, resulting in its molded products throughout the molecular orientation is inconsistent, stress concentration , Resulting in deformation.
③ Cosmetic box design usually consider the concealment of its intersection, the use of pouring system, cooling system, the ejection system is very complicated, resulting in instability resulting product deformation.
The solution is as follows:
① Process
Overall, it is to reduce the shrinkage after molding
(1) The material forming temperature needs to be within the specified melting range of the material, and the temperature should be kept as low as possible without affecting the filling stage
(2) under the pressure forming window, you need to ensure sufficient ability to make up, but the packing pressure after the packing stage as low as possible to avoid stress concentration
(3) cooling stage is the most critical, the use of material properties to accept the low mold temperature in the molding process, the need to avoid overheating within the mold and uneven cooling, mold cooling temperature should not exceed 10%
② QA
(1) First, the polypropylene will still be stress-relieved after it is cooled, possibly causing deformation, so the first sample will have to wait for it to cool down sufficiently
(2) SPC and in process QA is very important, these data need immediate feedback to the technical department. The spc ucl and lcl development need to be based on the actual situation of the product
(3) outgoing QA need to make zero mistakes
③ Process Validation
The process department needs to orthogonally test the deformed product to get enough data for subsequent process optimization and mold change recommendations.