Troubleshooting Methods for Cooling Water Leakage in Plastic Molds

Cooling water leakage is a common and troublesome problem in injection molds. Leaks cause uneven cooling, mold rust, product shrinkage, poor surface quality, and even electrical hazards or machine damage. Effective troubleshooting follows a logical sequence: from external to internal, from simple to complex, from static inspection to dynamic pressure testing. This article provides a complete, step‑by‑step guide to detect, locate, and resolve cooling water leaks.

1. Preparations and Safety Measures

Before inspection, stop the machine, close the main water valve, release residual pressure, and prevent high‑pressure spray. Prepare basic tools including a pressure gauge, air gun, soapy water, sealing tape, dry cloth, and flashlight. For internal leakage, an air compressor or mold water tester is used for pressure‑hold testing. Always confirm whether the leak is external or internal before disassembly.

2. Check External Leak Points

External leaks are visible and easy to locate. Common areas include water pipe connectors, quick couplings, plugs, O‑rings, flanges, and manifold blocks. Repeated connection and disconnection often wear seals or deform quick couplings. Aging, cracking, or missing O‑rings are major causes. Loose threads or damaged sealing surfaces also lead to dripping or spraying. In most cases, retightening, replacing O‑rings, or changing quick couplings solves the problem immediately.

3. Detect Internal Leakage Using Pressure Testing

Internal leaks are hidden and cannot be seen directly. The most reliable method is air pressure testing. Disconnect all hoses, seal inlet and outlet ports, and apply compressed air at 0.4–0.6 MPa. Hold pressure for 10 to 30 minutes. If pressure drops continuously, internal leakage exists. Apply soapy water to plugs, baffles, insert interfaces, and parting lines. Bubbles reveal the exact leak location. Water pressure testing can also be used, with leakage observed at parting lines, ejector pin holes, or guide pillar areas.

4. Inspect Critical Internal Components

Common internal leak points include pipe plugs, baffles, cooling channels near cavities or cores, cross holes, and insert sealing areas. Insufficient Teflon tape, damaged threads, failed sealant, or deformed baffles cause channel crossover or seepage. Leaks near cavities often result in water marks or rust on molded parts. For leaks at insert joints, check O‑ring grooves, fit clearance, and flatness. Repacking plugs, replacing baffles, or re‑sealing inserts usually resolves these issues.

5. Check for Fatigue Cracks and Wear Damage

Long‑term thermal cycling and mechanical vibration can cause micro‑cracks, especially at stress concentrations such as channel corners, hole edges, and welds. These cracks start as minor seepage and gradually worsen. Older molds also suffer from rust and erosion, which enlarge clearances and damage sealing surfaces. Dye penetrant testing or visual inspection after polishing helps detect tiny cracks. Repairs may include welding, reaming, re‑tapping, or replacing damaged sections.

Standard Troubleshooting Sequence

Visually inspect all external connections and eliminate obvious leaks.

Perform air or water pressure testing to confirm internal leakage.

Apply soapy water to locate exact leak positions.

Disassemble relevant parts and check O‑rings, plugs, baffles, threads, and cracks.

Repair or replace damaged components.

Re‑test pressure to ensure no further leakage before production.

Summary

Cooling water leakage troubleshooting follows the principle of exterior first, interior later; simple first, complex later. Most leaks occur at connectors, plugs, O‑rings, and baffles. Hidden internal leaks require pressure testing and soapy water detection. Regular maintenance, including seal replacement, channel cleaning, and anti‑rust treatment, greatly reduces leakage. Systematic inspection minimizes downtime, prevents mold damage, and ensures stable cooling and consistent product quality.