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:
<ul>
<li>Available hours and maintenance records</li>
<li>Number of mold changes (more changes = more wear on tie bars)</li>
<li>Original manufacturer specifications and manuals available</li>
<li>Reason for selling (upgrade? shutdown? problem machine?)</li>
</ul>

On-site mechanical inspection:

Injection unit:
<ul>
<li>Check screw and barrel for wear marks. Measure screw outer diameter at feed zone vs metering zone</li>
<li>Run screw rotation at low speed - listen for unusual noise</li>
<li>Check barrel heater bands: heat to setpoint and measure actual temp with contact pyrometer</li>
<li>Inspect nozzle tip and check ring for scoring</li>
</ul>

Clamping unit:
<ul>
<li>Check tie bar parallelism and straightness. Uneven wear indicates alignment issues</li>
<li>Run through full open/close cycle at low speed - check for smooth movement</li>
<li>Listen for hydraulic cylinder seal noise (chattering = worn seals)</li>
<li>Ejector system: cycle fully forward and back</li>
</ul>

Hydraulic system:
<ul>
<li>Check oil temperature: should be below 55 degrees C after warm-up</li>
<li>Inspect oil for water contamination (milky appearance) or burnt smell</li>
<li>Leak test: run at full pressure and hold - check for pressure drop over 30 seconds</li>
<li>Look at all hose condition (dry rot, bulging, cracked fittings)</li>
</ul>

Electrical:
<ul>
<li>Turn controller on and off to check for parameter battery backup failure</li>
<li>Check all safety gates and limit switch function</li>
<li>Verify heater thermocouple readings match pyrometer</li>
</ul>

Test run:
<ul>
<li>Run at least 20 cycles with a simple mold</li>
<li>Check shot weight consistency over 10 consecutive shots</li>
<li>Record cycle time and compare to spec</li>
<li>Verify the machine can reach and hold its rated injection pressure</li>
</ul>

Red flags - walk away if:
<ul>
<li>Maintenance records falsified or missing</li>
<li>Tie bar nut tightening marks show recent major adjustment</li>
<li>Oil smells burnt (indicates overheated operation)</li>
<li>Platen surface has been re-machined (possible crash damage)</li>
</ul>

Where are you looking for used machines? Share your experience below.

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