Processing Machinery
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Instability during the replacement transition with organotin stabilizers
Fenómeno do problema
During the switch from organotin stabilizers to calcium-zinc stabilizers on a PVC pipe production line, an unstable condition appeared in consecutive batches, sometimes normal and sometimes discolored, with the product yellowness fluctuation range reaching ±6 units.
Análise das causas
Cross-contamination exists between organotin stabilizers and calcium-zinc stabilizers inside the equipment; the chemical incompatibility of the two stabilizers causes abnormal local reactions; residual organotin in the screw and barrel undergoes displacement reactions with calcium-zinc components to generate unstable intermediates; the difference in lubrication formulations of the two stabilization systems causes unstable plasticization state switching; incomplete barrel cleaning with residue exceeding 2% produces interference.
Solução
Use a dedicated purging compound (PVC + large amount of CaCO₃ + stearic acid) to thoroughly clean the screw and barrel; it is recommended to clean 3-5 times; when changing formulations, carry out transition batch production, first producing products with a 50% new-old mixed formulation; after cleaning, test the purging compound color and confirm no discoloration before formally switching; use a lubrication formulation compatible with the calcium-zinc system to avoid sudden lubrication changes.
Conclusão principal
Stabilizer system switching requires strict execution of cleaning procedures and transition batch management; the lubrication difference between new and old systems is an overlooked cause of switching instability.
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