Changing molds on a blow molding ma chine is routine maintenance that directly affects your production uptime and bottle quality. Whether you run a JNDWATER semi-automatic PET blower or a fully automatic rotary blow molding machine, the mold change procedure follows the same core principles. This guide walks you through the complete process — preparation, removal, installation, testing, and troubleshooting — based on 17+ years of field experience supplying 9,000+ production lines to 125+ countries.
Safety Preparation Before Mold Change
Proper preparation is non-negotiable. Skipping safety steps can cause injury, equipment damage, and costly downtime.
WARNING: Never attempt a mold change while the machine is powered on or the hydraulic system is pressurized. Always follow your facility’s Lockout/Tagout (LOTO) procedure.
Required Tools
| Category | Tools | Purpose |
| Hand Tools | Torque wrench, Allen key set, screwdrivers, brass hammer | Bolt loosening/tightening, adjustments |
| Lifting | Overhead crane, hoist, or mold fixture | Safe mold handling |
| Nettoyage | Solvent, lint-free cloths, compressed air | Cavity and channel cleaning |
| Lubricants | High-temp grease, mold release agent, rust oil | Guide pin lubrication, protection |
| PPE | Heat-resistant gloves, goggles, steel-toed boots | Personal protection |
Machine Shutdown Procedure
- Stop production and allow heater bands to cool below 50°C (122°F).
- Depressurize the hydraulic system and verify the gauge reads zero.
- Lockout/Tagout — disconnect main power and apply your lock.
- Drain cooling water from mold channels before disconnecting lines.
Step 1 — Remove the Old Mold
Start by labeling every connection (cooling lines, air hoses, heater wiring, thermocouples) with colored tape or numbered tags — this prevents confusion during reinstallation. Take a photo before disconnecting.
Loosen Bolts in a Diagonal Pattern
Loosen mounting bolts gradually in a diagonal (star) pattern — never in sequence around the perimeter. This prevents the mold from binding on the guide pins. Loosen each bolt one quarter-turn, working to the opposite bolt next, until all are hand-loose. Store bolts in a labeled container.
PRO TIP: The most common field mistake we see is loosening bolts in a circle. This shifts the mold unevenly and pinches the guide pins. Always work diagonally.
Lift and Store the Old Mold
Blow molds can weigh 50 kg to over 1,000 kg. Never lift manually. Attach lifting eye bolts to designated points, verify the sling angle is under 60° from vertical, and lift 1-2 cm first to check for binding. Tap gently with a brass hammer to break the seal if needed — never a steel hammer. Store the mold on a wooden pallet or rubber mat, never directly on concrete.
Step 2 — Inspect and Prepare the New Mold
Verify the new mold matches your machine before installing. Mismatches damage both mold and machine.
| Check | What to Verify | Risk if Wrong |
| Force de serrage | Mold needs less than machine max | Flash, overload |
| Mold Height | Fits machine daylight range | Won’t mount |
| Mounting Pattern | Bolt holes match platen | Insecure fit |
| Stroke Length | Accommodates mold opening | Demolding failure |
| Cooling Channels | Diameter matches fittings | Poor cooling |
Clean the cavity and cooling channels with solvent and compressed air. Run a fingernail along the parting line — it should feel perfectly flat; any nick causes flash. Apply a thin coat of molybdenum disulfide (MoS2) grease to guide pins and bushings. Avoid over-greasing, which attracts dirt.
Step 3 — Install the New Mold
Align the mold with the guide pins and hand-tighten two diagonal bolts, then insert the rest. This is the most critical step — improper torque causes post-changeover quality issues.
| Pass | Torque Level | Action |
| 1 | 30% of spec | Snug all bolts in crisscross pattern |
| 2 | 70% of spec | Tighten same pattern |
| 3 | 100% of spec | Final torque with click-type wrench |
CAUTION: Always follow your machine’s torque chart. Typical values range from 80 Nm (M12) to 340 Nm (M20). Wrong torque can cause bolt failure during production.
Reconnect lines in reverse order of removal (electrical → air → water), using your labels and photo. Open the water supply and check every fitting for leaks. Remove LOTO devices and restore power.
Step 4 — Test and Calibrate
Run a no-load test cycle first to verify alignment without material. Then produce 5-10 sample bottles at reduced speed and inspect for:
- Flash — excess material at parting line (bolts or pressure issue)
- Uneven wall thickness — stretch ratio or temperature issue
- Warping — cooling or blow timing issue
Adjust blow pressure, temperature, and timing until samples are consistent. Document all parameters in a changeover log to speed up the next change.
Mold Change by Machine Type
JNDWATER offers several blow molding machine types, each with slight mold-change differences:
| Machine | Mold Change Notes |
| Semi-auto PET | Manual mold loading, single or double cavity, 30-60 min. Ideal for 0.5-10L bottles. |
| Fully automatic rotary | Integrated heating oven and servo clamping; mold change via quick-lock platens, 60-120 min. |
| 5-gallon / 4L machines | Larger molds require crane handling; verify the wider daylight opening. |
Quick Mold Change (QMC) Systems
If you change molds more than 2-3 times per week, a Quick Mold Change system pays for itself. Toolless quick-lock mechanisms, self-sealing fluid couplings, and servo adjustments cut changeover from hours to under 30 minutes. For high-mix lines producing multiple bottle sizes, QMC typically recovers dozens of production hours per month, with payback in 6-15 months.
Common Problems After Mold Change
| Problème | Likely Cause | Fix |
| Flash at parting line | Bolts undertorqued; clamp force low | Retorque bolts; raise clamp pressure |
| Uneven wall thickness | Stretch ratio off; preform temp uneven | Adjust preform heating; check stretch rod |
| Difficulty demolding | Insufficient mold cooling; ejector issue | Increase cooling time; verify ejector pins |
| Fuite d’eau | Cooling line not sealed | Retighten fittings; replace O-ring |
Mold Storage and Maintenance
- Stockage : Keep molds in a dry, temperature-controlled area on pallets; never on concrete.
- Rust prevention: Apply rust preventive oil to cavity surfaces between uses.
- Nettoyage: Flush cooling channels monthly to prevent scale buildup.
- Lubrification : Re-grease guide pins every 3 months or 500 cycles.
- Inspection : Check parting line and vents before each reinstallation.
Foire aux questions
How long does it take to change a mold on a blow molding machine?
For a semi-automatic PET blow molding machine, about 30-60 minutes. Fully automatic rotary machines may take 60-120 minutes. A QMC system reduces this to 15-30 minutes.
What tools are needed to change a blow molding machine mold?
Essential tools include a torque wrench, Allen key set, screwdrivers, a brass hammer, a hoist or crane for heavy molds, cleaning cloths, mold release agent, and high-temperature lubricating grease.
Can I change the mold myself or do I need a technician?
Trained operators can perform standard mold changes following the manual. For first-time changes, complex multi-cavity molds, or calibration issues, have a certified technician supervise. JNDWATER provides on-site training and commissioning for its blow molding machines.
How often should blow molding molds be replaced?
With proper maintenance, PET blow molds typically last 3-5 years. Replace when you see persistent flash, uneven wall thickness, or visible cavity wear.
Conclusion
Changing molds on a blow molding machine is a systematic process built on safety, precision, and proper technique. Follow the four-step procedure — preparation, removal, installation, and testing — to minimize downtime and ensure consistent bottle quality from the first cycle.
For more on JNDWATER blow molding machines, our company and certifications, or industry guides, explore our resource library.
Need Help with Your Blow Molding Operation?
JNDWATER’s engineering team has 17+ years of experience helping manufacturers worldwide optimize production. Whether you need a new Machine de moulage par soufflage, mold change training, or a quick mold change solution, we’re here to help.
17+ years of experience in blow molding machine design, manufacturing, and technical service across 125+ countries. Certified in plastics engineering and industrial safety management.
