Is it necessary to run a used injection molding machine without load?

Author:J           Date:2025-10-10

The primary purpose of no-load operation is to conduct a comprehensive inspection of the core systems of a used injection molding machine, eliminating interference from variables such as the plastic and mold. This can reveal potential problems that might not be detected during a static inspection.

1. "Auscultation" of the hydraulic system:

Detecting abnormal noise: After starting the main oil pump motor, listen carefully. A steady roar is normal. However, any piercing "squeaking" (possibly from pump cavitation, wear, or air intake), periodic "knocking" sounds (possibly from bearing or coupling damage), or irregular "banging" sounds all point to serious hydraulic problems. These noises can be masked or misinterpreted under load, but are most clearly heard when no load is applied.

Detecting internal leaks: Run the machine through actions such as mold opening and closing, ejection, and injection platform movement, holding it at the end of stroke for a period of time. Observe the pressure gauge. If pressure is difficult to maintain or continuously drops, this indicates a leak within the cylinder seal or control valve, which can lead to increased energy consumption, slow operation, and instability.

2. "Physical Inspection" of the Mechanical Structure:

Check for Smooth Movement: Observe whether the mold opening and closing, and the ejector's advance and retraction, are smooth and stable, and whether there is any sticking, jittering, or crawling. Any irregularities may indicate wear or insufficient lubrication of the hinge (crank arm), tie rods, or guide rails.

Verify the Safety System: A no-load state is the best time to test the safety door, mechanical bumper, limit switch, and hydraulic safety valve. Repeatedly open and close the safety door to confirm that the machine can only close the mold when it is fully closed. This is the first line of defense for operator safety and must not be omitted.

3. "Checkout" of the Control and Electrical Systems:

Test All Functions: Operate each button and switch on the control panel in turn to verify that the corresponding functions (such as core pulling, thread twisting, and platform advance and retraction) are executed accurately and quickly. This verifies that the PLC outputs, relays, and solenoid valves are functioning properly.

Evaluate System Response: Note the response time from when you press a button until the machine initiates the action. Unusual delays may indicate poor electrical connections or controller processing speed issues.

Practical steps for performing no-load operation:

Ensure safety: Clear the work area and ensure no one is within the machine's range of motion.

Preliminary inspection: Before applying power, manually turn the oil pump coupling several times to ensure it is not stuck.

Jog test: During initial startup, jog the oil pump motor and immediately observe the motor for correct rotation and any abnormalities.

System warm-up: Start the oil pump, but do not turn on the heater. Allow the hydraulic system to run without load for 10-15 minutes to circulate the hydraulic oil and warm it to approximately 40-50°C. Viscous cold oil can mask some problems, and testing after warm-up better reflects actual operating conditions.

Comprehensive test: Test all movements and safety devices in sequence, observing and noting any abnormalities throughout the process.

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