When you commit capital to a PET preform mold, the supplier’s internal quality checks determine whether your production line runs at target cycle times or sits idle for rework. Buyers who rely solely on the supplier’s final “pass/fail” summary often discover dimensional drift, uneven wall thickness, or gate vestige issues only after the mold is bolted into their machine.
A structured PET preform mold quality inspection before shipment gives you the data to accept, conditionally accept, or reject a tool while the supplier still bears the cost of correction. This article maps the checks a procurement team or quality manager should request—and the measurable evidence they should receive.
Why Buyers Need a Pre-Delivery Checklist
Molds for PET bottle production operate under high pressure (typically 8–14 MPa injection pressure) and temperature (280–300 °C melt temperature). Small deviations in core alignment, cooling channel placement, or cavity surface hardness multiply into measurable defects: off-center neck finishes, variable wall thickness, or stress cracks during blowing.
A supplier’s standard QC card may list ” inspected OK” without stating which instruments were used, how many cavities were sampled, or what the tolerance bands were. A buyer-directed PET preform mold quality inspection shifts the burden of proof to documented, repeatable tests.
The checklist below follows the sequence used at HEYAN Mold since 2018: dimensional check first, then material/hardness, surface finish, functional trial, and finally packaging integrity. Each section includes the tool, the acceptance criterion, and the evidence you should request.
1. Dimensional Verification
What to Verify
PET preform molds must hold tight tolerances across multiple cavities over millions of cycles. The critical dimensions include:
| Dimension | Typical Tolerance | Inspection Tool |
|---|---|---|
| Cavity diameter (body) | ±0.01 mm | CMM or bore gauge |
| Core diameter (inner profile) | ±0.01 mm | CMM or air gauge |
| Neck finish pitch diameter | ±0.02 mm | Thread gauge / optical comparator |
| Cavity-to-cavity spacing | ±0.03 mm | CMM across full mold base |
| Overall mold base flatness | ≤0.05 mm | Surface plate + dial indicator |
| Cooling channel alignment | Within 0.5 mm of design | Borescope or flow verification |
Evidence to Request
Ask for a dimensional report that records measurements for every cavity, not just a random sample. The report should include:
- Instrument serial numbers and calibration dates
- Ambient temperature at time of measurement
- Raw measurement data (not just “pass/fail”)
- Date and inspector signature
[Figure: sample dimensional inspection report showing 32-cavity measurement matrix]
If the supplier measures only one cavity per row, ask them to justify the sampling plan. For a 48- or 96-cavity tool, cavity-to-cavity variation in preform weight is often the first signal of dimensional drift, so full-cavity data reduces risk.
2. Hardness and Material Integrity
What to Verify
Core and cavity inserts in PET molds are typically machined from S136 or NAK80 stainless steel, then heat-treated to HRC 48–52. Insufficient hardness leads to galling and dimensional growth; excessive hardness increases cracking risk under thermal cycling.
| Component | Target Hardness | Test Method |
|---|---|---|
| Cavity inserts | HRC 48–52 | Rockwell hardness tester |
| Core inserts | HRC 48–52 | Rockwell hardness tester |
| Slide / lifter components | HRC 45–50 | Rockwell hardness tester |
| Mold base (plate steel) | HRC 28–32 | Brinell or Rockwell B |
Evidence to Request
Request a hardness map: at least three points per insert (gate end, body center, base end). The report should note the heat treatment batch number and the furnace chart.
Also ask for material certificates (mill test reports) matching the steel grade on the purchase order. Mismatched steel grades are a common root cause of premature corrosion in PET molding, where moisture and acetaldehyde byproducts accelerate cavity pitting.
[Figure: hardness test point layout on a 16-cavity core plate]
3. Surface Finish and Polish Inspection
What to Verify
PET preform surface quality directly affects bottle clarity and blow uniformity. The cavity and core surfaces must achieve a mirror polish, typically Ra 0.01–0.02 μm, with no visible tool marks, pitting, or orange peel.
| Surface | Target Roughness | Inspection Method |
|---|---|---|
| Cavity forming surface | Ra ≤ 0.02 μm | Profilometer + visual under 10× magnification |
| Core forming surface | Ra ≤ 0.02 μm | Profilometer + visual under 10× magnification |
| Venting grooves | Clear of burrs | Borescope |
| Gate area | No swirl marks or erosion | Visual at 20× magnification |
Evidence to Request
Ask for surface roughness traces from a profilometer, not just a handwritten Ra value. The trace should show the measurement path length and cutoff wavelength.
For visual defects, request macro photographs of each cavity’s gate zone and body zone. A supplier who balks at photographing 32 cavities likely has not inspected them individually.
4. Mold Trial and Sample Evaluation
What to Verify
The mold trial is the most consequential step in PET preform mold quality inspection. A trial on the supplier’s machine should simulate your production conditions as closely as possible: resin grade, melt temperature, injection speed, hold pressure profile, and cooling time.
| Check | Acceptance Criterion | Measurement Tool |
|---|---|---|
| Preform weight per cavity | ±1.5% of nominal | Precision balance (0.01 g resolution) |
| Wall thickness distribution | Minimum variation across 4 quadrants | Ultrasonic wall thickness gauge |
| Gate quality | No cold slugs, no drooling | Visual inspection + weight check |
| Neck finish integrity | No flash, dimensionally stable | Thread gauge + optical measurement |
| Color and clarity (for virgin PET) | No haze, no streaks | Visual under consistent lighting |
| Cycle time | Within 5% of quoted value | Stopwatch / machine log |
Evidence to Request
Request:
- Trial parameter sheet: actual temperatures, pressures, and cycle settings used
- Sample set: minimum one shot from every cavity, labeled by cavity number
- Weight chart: individual cavity weights plotted on a run chart across at least 5 consecutive shots
- Residual stress check (optional but valuable): polarized light inspection for birefringence patterns, which indicate uneven cooling or excessive injection speed
If the supplier quotes a cycle time of 6 seconds but trials the mold at 9 seconds “to be safe,” ask for a written explanation. The cooling circuit design may be undersized, or the steel selection may not support the claimed throughput.
[Figure: sample weight distribution chart for 48-cavity trial run]
5. Documentation and Packaging Standards
What to Verify
Even a dimensionally perfect mold can arrive damaged if lifting points are improperly marked, cooling fittings are unprotected, or electrical connectors are knocked loose in transit.
| Item | Check |
|---|---|
| Lifting points | Marked with SWL (safe working load) ratings; balanced for overhead crane |
| Cooling fittings | Plugged with threaded caps, not tape; labeled IN / OUT per circuit |
| Electrical connectors | Protected with rigid caps; pinout diagram attached |
| Ejector system | Greased and retracted; no bare steel exposed to moisture during sea freight |
| Spare parts | Gate inserts, O-rings, heater bands packed in separate, labeled box |
| Documentation | 2D assembly drawing, spare parts list, maintenance manual, hardness report, trial report |
Evidence to Request
Request photographs of the packed mold from three angles, plus a close-up of the packing list. If the mold ships by sea in a wooden crate, the crate should be IPPC-treated (ISPM-15 mark) to avoid customs delays.
6. HEYAN Mold Inspection Workflow
At HEYAN Mold, established in 2018, the pre-delivery protocol follows the sequence above. The production team runs dimensional checks on a coordinate measuring machine (CMM), records hardness at three points per insert, and trials every multi-cavity mold on a dedicated injection machine using the customer’s specified PET resin grade when possible.
The engineering team holds 27 patents covering hot-runner balance, cooling circuit layout, and gate design. These designs are validated during the trial phase: if cavity-to-cavity weight variation exceeds 1.5%, the hot-runner manifold is disassembled and rebalanced before shipment.
Production capacity scales from 8 to 96 cavities depending on project requirements. The inspection depth scales with complexity: a 96-cavity tool receives full-cavity CMM data, while an 8-cavity prototype receives proportionate documentation focused on dimensional and trial evidence.
All customers receive:
- Pre-shipment photos of the packed mold
- PDF inspection report with raw data
- Spare parts list with part numbers and material specs
- Video clip of the mold trial (link, not file attachment, to avoid email size limits)
[Figure: sample pre-shipment packing photo showing lifting point labels and cooling fitting protection]
Conclusion: Request the Data Before You Pay the Balance
A mold purchase is not complete when the tool is machined. It is complete when you have evidence that the tool meets the dimensions, hardness, surface finish, and functional standards your production line requires.
Send your supplier this checklist—or your own variant—before the final payment milestone. A supplier with internal discipline will already have most of this data. A supplier without it will either generate it (which costs them time) or reveal gaps you can address before the mold crosses an ocean.
Next steps:
- Download our technical parameter sheet to align your incoming inspection criteria with HEYAN Mold’s standard report format.
- Send your preform drawing or bottle specification for a mold feasibility review and formal quotation.
- Schedule a live video factory inspection to observe the trial phase of your order in real time.
Contact the HEYAN Mold team with your project details and receive a checklist-matched proposal within two business days.
— HEYAN Mold Operations Team
