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How to detect and repair hydraulic line leaks in plastic injection molding machine?

2025/09/12 By le zhan

plastic injection molding machine 16-2

Hydraulic line leaks are one of the most common and devastating field failures in plastic injection molding machine. A small leak can quickly escalate into a slippery and dangerous situation. A persistent leak can reduce press performance, contaminate parts, and force the late shift production line to shut down. Leaks typically manifest as visible oil stains, pressure loss, unexpected drops in the oil tank level, intermittent cylinder pressure failures, or water accumulation at the bottom of the machine. However, not all leaks are obvious; many begin as small leaks and gradually worsen over weeks. Leaks are primarily caused by fatigue in the hose assembly, aging O-rings, wear caused by vibration, overpressure events, improper fittings or crimping, and other factors. Therefore, it is important to select the appropriate hoses and fittings based on the system’s operating pressure and implement appropriate safety systems.

Why do hydraulic leaks occur in plastic injection molding machines?

Hydraulic lines in plastic injection molding machines are subject to various stresses that accelerate wear. Examples include vibration from the toggle and ejector pins, pressure spikes during injection, high ambient temperatures in the platen area, and frequent mold changes that require hose movement. Common causes of leaks include:

  1. Hose fatigue and aging. Hoses deteriorate from repeated flexing and heat aging. Rubber and polymer hoses can harden, crack, or internally delaminate, especially near hot platens or exhaust ports.
  2. Improper specifications. Using hoses or fittings that are not rated for the working pressure can lead to premature failure.
  3. Field assembly or poorly crimped ends can cause leaks.
  4. Improper routing and inadequate strain relief. Hoses that rub against sharp edges, pass through moving parts, or are twisted can wear or internally break.
  5. Reused or misthreaded fittings, the use of incorrect sealants, or flange wear on ORFS fittings can all lead to leaks at the fitting.
  6. Component failure. Cracked fittings, corroded manifolds, or damaged cylinders can appear to leak from the hose.
  7. Overpressure events and cavitation. Pressure spikes can stress the hose wall. Cavitation can cause pitting in metal components, leading to leaks.
    By correlating the timing of symptom onset with the failure mode, you can quickly identify the possible cause. For example, leaks that occur only after a long production run can indicate thermal degradation; leaks that occur after a mold change can indicate routing or strain issues.

Utilizing Inspection Technology for Inspection

Early detection of hydraulic line leaks can reduce downtime and prevent safety incidents. Therefore, a layered inspection strategy should be adopted for plastic injection molding machines—starting with low-cost visual inspections and upgrading to diagnostic tools as necessary. Visual inspections can be performed daily or before a shift to check for moisture on hose ends, fluid accumulation around fittings, discoloration on the boots, or streaking on the manifolds. Check the fluid level in the reservoir and note any unexplained drips. Then, wipe the suspected area, run the machine briefly, and check for fresh oil. This “clean start” approach can help find slow leaks. Also, note whether oil drips run along the hose or frame before dripping onto the floor.

Ultrasonic leak detection can also be performed. Micro leaks generate ultrasonic waves when pressurized. Handheld ultrasonic detectors can scan fittings and joints without stopping the machine and can find leaks that are invisible to the naked eye. They are particularly useful in noisy factories. Contamination and oil analysis are also necessary. Metallic wear particles or moisture in the oil can accelerate seal wear. Regular oil analysis and particle counting can help identify systemic issues that increase the risk of leaks.

Utilizing Inspection Technology for Inspection

Emergency Isolation and Safe Temporary Repairs

When a hydraulic leak occurs on a plastic injection molding machine, safety and control measures must be prioritized before attempting repairs. When a leak occurs, you must immediately stop the fluid loss, eliminate the potential hazard, and maintain production integrity before performing repairs. First, lock out and tag out the machine, shut down the machine, and control electrical and hydraulic power according to the LOTO procedure. Tag out and clearly sign the machine. Next, place absorbent pads and a drip pan under the leak, release any residual pressure according to the machine-specific procedure, and observe for 15-30 minutes. Where feasible, isolate the leaking circuit by closing the shutoff valve or switching to a redundant circuit. For hoses leaking at joints, seal the line with a rated blind fitting or temporarily replace it with a certified spare fitting.

For very low-pressure leaks, using a rated emergency clamp or hydraulic hose patch sleeve according to the manufacturer’s instructions can be a short-term mitigation measure. At the same time, the component is removed from the ground for appropriate repair. Then, document the incident, including the plastic injection molding machine ID, location, estimated leak rate, and any temporary measures taken. Notify production planners and the safety team, and schedule an inspection during the next scheduled downtime.

Improve the quality of delivery

Replacing Plastic Injection Molding Machine Hoses, Fittings, and Seals

Repairing a plastic injection molding machine can restore its reliability and safety. The correct approach is to replace the faulty component with the correctly specified part and install it according to validated procedures.

The first decision to make is whether to replace or repair a hydraulic hose. For hydraulic hoses, it is recommended to replace the entire hose assembly, including new fittings and crimped connections, rather than attempting to cut and install the hose in the field. The hose’s inner layer may delaminate, and hidden damage often extends beyond the visible fitting. Fittings with damaged threads or sealing surfaces should be replaced. You should replace damaged seals and O-rings at the connector with materials suitable for the fluid and temperature.

To determine the correct part, match the hose’s working pressure and temperature ratings to the machine’s maximum working pressure and temperature, allowing for an appropriate safety margin. Then, confirm fluid compatibility and use the correct threads. Before assembly, clean all mating surfaces and wipe them with a lint-free cloth. Lubricate the O-rings with a compatible hydraulic fluid. Replace the hose to the appropriate length, avoiding excessive slack but never stretching it. Refill with clean, filtered hydraulic fluid and bleed the air as needed. Repairs performed according to these standards can minimize the likelihood of recurrence.

Implement a preventive and proactive maintenance plan.

For plastic injection molding machines, establish a practical program centered around inspection, replacement, and continuous improvement. Conduct daily visual inspections for leaks and fluid reservoir levels, weekly checks on critical hoses and fittings, and monthly detailed inspections, including thermal scans and ultrasonic inspections. Use a standardized inspection checklist to record hose condition, signs of wear, clamp integrity, and hose labels. For high-load injection molding, inspection frequency should be increased.

Replace hoses within their useful life, not just when a failure occurs. Maintain the recommended replacement interval based on operating hours, cycles, and environmental conditions. At the same time, maintain a stockpile of critical spare hoses, fittings, seals, and a small supply of OEM-certified hoses. Maintenance personnel should also be trained in hydraulic safety, LOTO procedures, proper crimping inspections, and the use of diagnostic tools. After each leak incident, conduct a root cause analysis and implement corrective actions, including procedural and design changes.

Proactive Detection Prevents Downtime

Effective handling of hydraulic line leaks in injection molding machines is both a safety issue and a way to reduce downtime and quality losses. Timely and accurate testing, strict adherence to the emergency procedure of powering off, depressurizing, and sealing, and the use of proper assembly pressure testing procedures can significantly reduce recurring failures and extend equipment life. Proactive leak detection and certified repairs can reduce safety incidents, lower scrap and pollution costs, and prevent downtime.

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