Cooling circuits are hidden inside the mold, but they strongly influence cycle time, warpage and dimensional stability. A mold can look clean and still contain blocked, leaking or cross-connected water lines.
TL;DR
Test every circuit separately for both pressure and flow. Pressure confirms containment; flow reveals restriction. Record the inlet, outlet, pressure, hold time, flow and discharge condition for each circuit.
Five cooling-system red flags
- A circuit cannot pass water or compressed test medium.
- Pressure falls with no visible external leakage.
- Water crosses into another circuit or the mold cavity.
- Discharge contains heavy rust or scale after flushing.
- Seller cannot identify circuit routing or inlet/outlet pairs.
Why pressure testing is not enough
A partially blocked channel may hold pressure while providing poor heat removal. A complete inspection combines:
- visual inspection;
- pressure holding;
- flow measurement;
- comparison between circuits;
- leakage and cross-connection checks.
Preparation
- Identify and label all ports.
- Remove incompatible fittings or damaged hoses.
- Confirm a safe test pressure for the mold and components.
- Protect electrical and hot-runner systems from water.
- Use clean test equipment and controlled drainage.
Do not apply arbitrary high pressure to an unknown mold.
Pressure test procedure
Connect one circuit at a time. Fill and vent trapped air where appropriate. Raise pressure to the agreed test level, isolate the circuit and record pressure over a defined hold time. Inspect plugs, fittings, parting surfaces and cavity areas for leakage.
Flow test procedure
Supply controlled water and measure outlet flow. Compare parallel circuits under the same pressure. A large difference indicates restriction, incorrect routing or internal damage. Record temperature if a more detailed thermal assessment is required.
Signs of internal problems
- delayed or weak outlet flow;
- rusty or contaminated discharge;
- pressure loss without external leakage;
- water appearing at another port;
- evidence of previous plugging or drilled repair;
- local corrosion near fittings.
Cleaning and repair
Possible actions include flushing, controlled descaling, ultrasonic or specialist cleaning, replacing fittings, removing damaged plugs or drilling and rebuilding channels. Cleaning chemicals must be compatible with mold steel, seals and hot-runner components.
If a channel cannot be restored, the mold maker must evaluate alternative cooling. Added hoses or external bubblers are not automatically equivalent to the original design.
Acceptance record
| Circuit | Inlet/Outlet | Test pressure | Hold time | Flow | Result/Action |
|---|---|---|---|---|---|
| C1 | |||||
| C2 |
Add photographs of the gauge, connections and discharged water. Link the report to the mold number.
FAQ
Can compressed air replace a water test?
Air can help locate leaks, but it does not prove water flow or cooling performance. Use procedures appropriate to the mold and site safety rules.
Is rusty water an automatic rejection?
Not always. It is a warning that the circuit needs cleaning and further inspection. Persistent restriction or internal leakage is more serious.
Should the mold be trialed after cleaning?
Yes. Cooling changes can affect cycle time and product dimensions.
Request a cooling-circuit inspection
Provide the mold layout, circuit labels and any previous test information. Require circuit-by-circuit pressure and flow results before final acceptance.
Send the product, mold and machine information.
Share the part drawing or sample, material, target output, available mold details and injection-machine specifications. We will identify the checks needed before purchase, modification or trial.