Scope: 200L tight-head drums, chemical drums and other large hollow containers. For buyers inspecting goods and for production technicians tuning machines. In this article, 3-layer sandwich means a 3-extruder recycled-core structure (virgin inner/outer layers, recycled core); 2-layer means virgin-inside/recycled-outside or recycled-inside/virgin-outside.
Uneven wall thickness, flash, and warping usually come down to four causes: parison and mold, process parameters, material, or machine condition. Work in this order — measure wall thickness first, check clamping second, suspect material last — and you will waste the least time.
1. Measure top, middle, and bottom along the drum, at the parting line and away from it, to locate the thin spots first.
2. Check the parison wall-thickness control settings: thicken where it is thin, thin where it is thick, changing one point at a time.
3. Check mold zone temperatures: a zone far off the others points to a blocked cooling line or a heater fault.
4. Check plasticizing: unmelted particles or melt temperature swings point to screw speed and heater bands.
5. Check the blow-up ratio: if corners and bottom stay thin, the mold and parison sizes may not match — do not just add thickness everywhere.
6. Multi-layer machines need one extra check: core distribution for a 3-layer sandwich, inner/outer ratio for a 2-layer drum, then adjust each extruder's output ratio.
1. Stop and clean the parting line: remove residue and burrs, close the mold again, and see if the flash is gone.
2. Check clamping force settings and the clamping unit: add force if it is short; worn mechanisms with large play need repair.
3. Check parting-line wear: a mold worn into grooves is fixed by mold repair, not by parameter tuning.
4. Lower blow pressure: use only enough pressure, stepping down until flash disappears while the drum stays fully formed.
5. Check parison size and shot size: an oversized parison or excess material gets reduced first.
6. Check venting: clean blocked vent slots.
1. Check wall thickness first: warping is often the result of uneven walls, so even out thickness (Section 1) before anything else.
2. Extend cooling time: demold only when fully cooled and see if warping eases.
3. Check mold cooling circuits: balance flow and temperature across zones.
4. Check material: if the recycled ratio or batch just changed, fix the material first before judging anything else.
5. Check blow-up ratio and demolding temperature: dial back overstretching or demolding while too hot.
1. Measure wall thickness first: data before guesswork.
2. Check mold and clamping next: parting line, clamping force, and cooling circuits are hardware problems that parameters cannot cover.
3. Tune process parameters after that: pressure, temperature, cooling time — one variable at a time.
4. Suspect material last: batch or recycled-ratio changes affect both shrinkage and plasticizing.
5. Hardware problems go to the machine supplier: molds worn beyond tolerance, clamping-unit precision loss, or a faulty wall-thickness control system are fixed faster by repair than by tuning.
*Source: Shandong Tongjia Intelligent Equipment Co., Ltd., October 2026.*
