How to check the electrical box of a used injection molding machine

Author:J           Date:2025-10-10

Step 1: Power-off Static Inspection (Observe the Cleanliness of the Used Injection Molding Machine)

Appearance and Sealing:

Inspect the electrical box casing for severe rust, deformation, or deteriorated seals. This affects its ability to resist oil, dust, and moisture.

Check the cooling fan or filter for blockage and ensure adequate ventilation.

Internal Cleanliness:

Open the electrical box door and first inspect the overall cleanliness of the interior. Excessive dust, oil, or metal powder is a clear sign of poor maintenance, which can lead to short circuits and poor heat dissipation.

Pay special attention to any signs of rat nests or insect nests, which may have caused fatal damage to the cables.

Component Condition and Age:

Observe the brand and model of key components, such as PLCs (programmable logic controllers), drives, and power modules. Recognizing reputable brands (such as Siemens, Mitsubishi, B&R, and Fanuc) is a guarantee of quality.

Inspect for Burn Marks: Carefully inspect the terminals and surrounding areas of contactors, circuit breakers, and fuse holders for signs of arc burns, blackening, or discoloration.

Capacitor Inspection: Observe the electrolytic capacitors on the motherboard, power supply, and other locations for bulging, leakage, or bulging top covers. These are typical signs of capacitor failure and potential sources of major failure.

Step 2: Power-On Dynamic Inspection (Function and Stability Test)

Only after the static inspection is complete can the power supply be turned on for a power-on test.

Power Supply and Display:

Turn on the main power supply and observe the electrical box for any unusual sparking sounds or smoke.

Check that the control system (touch screen or digital controller) boots up properly and that the screen display is clear, without flickering or defects.

Listen and Smell:

Listen for any unusual buzzing sounds or humming sounds from relays failing to close.

Smell carefully for any odors suggestive of burning plastic or insulation.

Input/Output (I/O) Test:

This is crucial for verifying the proper functioning of all electrical functions.

Input Test: Activate various limit switches, safety door switches, etc. on the operator panel. At the same time, check inside the electrical box to see if the corresponding PLC input indicator lights up. This accurately determines whether the entire circuit from the sensor to the PLC is intact.

Output Test: In manual mode, press each action button one by one (such as mold close, injection table advance, pre-molding, etc.). Observe whether the PLC output indicator lights up, the corresponding relay or output module energizes, and the solenoid valve emits a clear "click" sound. If the indicator lights up but the valve does not operate, the problem may be with the output module, intermediate relay, or valve coil.

Step 3: Professional Inspection (Highly Recommended)

Parameter Backup: If possible, have a technician back up all parameters of the machine's PLC and driver. If lost, restoring these parameters will be extremely difficult and expensive.

Cable Inspection: Spot-check the main power and control cables to see if the insulation is aged or brittle.

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