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Blow Molding molds sit at the intersection of heat, pressure, cooling water, and polymer additives. When a mold is not cleaned and protected correctly, the first symptoms usually show up as cosmetic defects, longer cycle time, unstable wall thickness, and higher scrap. A practical maintenance routine keeps surface finish consistent, protects venting, and preserves dimensional accuracy, which directly supports repeatable bottle quality on PET, PP, and PE programs. BOHANG supplies blow molding equipment and molds as part of an integrated production setup, so the recommendations below are written from a manufacturer’s perspective and match real factory conditions.
Most “mold dirt” is not random. It is a predictable mix of:
Polymer residue from degraded material at hot spots and corners
Additive deposits such as slip agents and antiblocks that migrate and plate out
Oil mist and dust pulled into the mold area by compressed air and plant airflow
Hard-water scale in cooling circuits, which reduces heat transfer and raises cycle time
Corrosion films caused by moisture, fingerprints, and inconsistent storage protection
The key is to clean the right area with the right method. Aggressive cleaning on the wrong surface can damage polish, round edges, or open parting lines.
A short daily routine is more effective than occasional deep cleaning:
Wipe external surfaces after shutdown using lint-free cloths to remove oil film and dust before it bakes on during the next heat-up.
Keep vents open and dry. Vents that are partially blocked can cause haze, burn marks, incomplete forming, and unstable release.
Control compressed air quality. Use filtration and water separation so moisture does not enter the cavity and start corrosion, especially during night shifts.
Inspect parting lines for resin smearing. Early removal prevents burrs and flashing that later require rework.
Protect after cleaning with a light, compatible rust-preventive film on exposed steel surfaces when the mold will sit idle.
Different surfaces demand different tools:
Use non-abrasive cleaning first. A solvent that dissolves resin residue is safer than scraping.
For polished cavities, avoid aggressive pads that can change gloss and create “shadow” marks on bottles.
When buildup is stubborn, heat the mold to a warm, safe handling temperature and reapply cleaner. Warmth improves removal without mechanical force.
Clean vents with dedicated thin tools that match vent geometry. The goal is to clear, not widen.
Pinch-off areas should be kept sharp and uniform. Avoid metal-to-metal scraping that rounds the edge and increases flash risk.
Cooling efficiency has a direct effect on cycle time. Even thin scale layers can reduce heat transfer and create temperature imbalance across cavities. Use a controlled descaling process compatible with your channel material, then flush thoroughly to prevent chemical residue from accelerating corrosion.
| Interval | What To Do | What It Prevents |
|---|---|---|
| Every shift | Visual check of vents, parting line, and release behavior | Haze, burns, sticking, flash |
| Daily | Wipe down, remove oil film, dry cavity area, apply light protection for idle molds | Corrosion, baked-on stains |
| Weekly | Deep clean vents and pinch-off; check for resin smear; verify cooling water flow trend | Scrap spikes, cycle drift |
| Monthly | Cooling circuit flush or descaling based on water hardness; inspect for early rust spots | Longer cycles, uneven cooling |
| Quarterly or per production hours | Dimensional check, alignment check, surface finish evaluation, replace wear components as needed | Long-term drift, leakage, repeated defects |
A stable interval is better than a “when problems happen” approach. Tie the schedule to production hours and the resin family used.
Many molds are damaged outside the press:
Use dedicated lifting points and controlled lifting angles to avoid bending alignment features.
Do not store molds wet. Dry the cavity and cooling interfaces first, then apply protection.
Keep molds covered to prevent dust settling into vents and on polished steel.
Record every maintenance action. A short log makes troubleshooting faster and prevents repeated mistakes.
Haze or dull patches: cavity film, vent restriction, oil mist deposition
Burn marks: blocked vents, trapped air, overheating at local hot spots
Sticking or inconsistent release: residue on cavity, surface wear, incorrect protection oil left on forming surface
Flash at parting line: parting line contamination, pinch-off wear, alignment drift
Cycle time creep: cooling scale, flow restriction, uneven cooling temperature
Maintenance success is not only about chemicals and brushes. It depends on mold design details, vent strategy, cooling layout, and how the machine clamps and aligns the mold. BOHANG provides blow molding machines, line-support automation, and molds in one product ecosystem, which helps keep mold changeover, alignment, and operating parameters consistent across a production line. For projects that require stable repeatability, BOHANG can support mold design, process guidance, and practical maintenance standards matched to your bottle type and material range.
A clean blow molding mold is not just “nice to have”. It is a controllable production variable that protects cycle time, surface finish, and scrap rate. Build a routine that prioritises vents, parting lines, cavity protection, and cooling efficiency, then document results by production hours. Share your bottle drawings, resin type, and target output, and BOHANG can recommend a maintenance and cleaning plan aligned with your mold structure and production goals.
