Used Injection Molding Machine Inspection Checklist
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Buying a used injection molding machine can save 40-60 percent versus new. But a bad purchase leads to downtime and expensive repairs. Here is a practical inspection checklist.
Before visiting the machine, check:
- Available hours and maintenance records
- Number of mold changes (more changes = more wear on tie bars)
- Original manufacturer specifications and manuals available
- Reason for selling (upgrade? shutdown? problem machine?)
On-site mechanical inspection:
Injection unit:
- Check screw and barrel for wear marks. Measure screw outer diameter at feed zone vs metering zone
- Run screw rotation at low speed - listen for unusual noise
- Check barrel heater bands: heat to setpoint and measure actual temp with contact pyrometer
- Inspect nozzle tip and check ring for scoring
Clamping unit:
- Check tie bar parallelism and straightness. Uneven wear indicates alignment issues
- Run through full open/close cycle at low speed - check for smooth movement
- Listen for hydraulic cylinder seal noise (chattering = worn seals)
- Ejector system: cycle fully forward and back
Hydraulic system:
- Check oil temperature: should be below 55 degrees C after warm-up
- Inspect oil for water contamination (milky appearance) or burnt smell
- Leak test: run at full pressure and hold - check for pressure drop over 30 seconds
- Look at all hose condition (dry rot, bulging, cracked fittings)
Electrical:
- Turn controller on and off to check for parameter battery backup failure
- Check all safety gates and limit switch function
- Verify heater thermocouple readings match pyrometer
Test run:
- Run at least 20 cycles with a simple mold
- Check shot weight consistency over 10 consecutive shots
- Record cycle time and compare to spec
- Verify the machine can reach and hold its rated injection pressure
Red flags - walk away if:
- Maintenance records falsified or missing
- Tie bar nut tightening marks show recent major adjustment
- Oil smells burnt (indicates overheated operation)
- Platen surface has been re-machined (possible crash damage)
Where are you looking for used machines? Share your experience below.
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