Injection Molding
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Black specks and burnt particles problem of injection molded products
Fenómeno del problema
When PVC injection molded pipe fittings are produced using calcium-zinc stabilizers, black specks appear on the surface and inside of the products; the number of black specks increases as production time extends; in severe cases, the product defect rate reaches more than 15%.
Análisis de la causa
The '2079851475616104452 machine screw and barrel have retention zones (dead corners), where the calcium-zinc-unstable PVC melt decomposes and carbonizes under long-term heating; excessive nozzle temperature causes local overheating and degradation of the material; the stabilizer and PVC resin are mixed unevenly; the regrind proportion is too large, and partially degraded material is processed again.
Solución
Clean the screw and barrel to eliminate retention dead corners; reduce the nozzle temperature by 5-15°C and use a short nozzle to reduce residence time; use a high-speed mixer to fully mix at 120°C for 8-10 minutes; control the regrind proportion to no more than 20%; add 0.2-0.3 phr phosphite-type antioxidant to the formulation to capture decomposition free radicals.
Conclusión clave
The core of the '2079851475616104452 black speck problem lies in eliminating retention zones and controlling local overheating; combined with uniform stabilizer dispersion and regrind management, it can be effectively solved.
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