Inspection
Used injection molding machine inspection checklist
Six systems, thirty checks. Written to be worked through on a video call, in the order a machine actually reveals its condition. Print it, or keep it open while the camera is running.
How to run the inspection
Ask for the machine to be warm and under power before the call starts — hydraulic oil at temperature behaves differently from cold oil, and a machine that has been running for half an hour shows leaks that a cold one hides. Allow 45 minutes. Ask for measurements rather than adjectives: “the clearance is 0.35 mm” is a fact, “the screw is in good condition” is an opinion.
Record the call. You will want to compare machines afterwards, and a recording is also the reference point if the machine that arrives is not the machine you saw.
1. Appearance and structure
- Frame free of impact damage, cracks or weld repair — a repaired frame changes the geometry of everything mounted on it.
- Tie-bars bright and even, with no deep scoring, corrosion pitting or chrome flaking.
- Guide rails and slide surfaces polished but not stepped; a visible step means the moving platen has been running on a worn track.
- Safety gates present, moving freely, with their interlocks fitted and functioning — missing guards are both a cost and a sign of how the machine was run.
- No pooled oil under the machine, and no fresh degreaser smell where a leak has just been cleaned up.
2. Clamping unit
- Ask for platen parallelism to be measured with a dial gauge and the number reported. Out-of-parallel platens damage moulds, and the fault is invisible on video without a gauge.
- Toggle links moving smoothly and quietly, with no knocking at the end of stroke and no visible play in the pins and bushes.
- Mould-height adjustment running through its full travel under power.
- Ejector reaching position and returning crisply, with the ejector plate square.
- Clamp force building and holding — ask to see the pressure reading stable during clamp-up.
3. Injection unit: screw and barrel
This is the most expensive wear pair on the machine and the one most often described rather than measured.
- Screw pulled or inspected through the feed opening: flight crests should be square, not rounded, and free of pitting or corrosion.
- Measured screw-to-barrel clearance. Beyond roughly 0.8–1% of screw diameter, the pair needs replacing. Insist on the number.
- Non-return valve (check ring) condition — a worn ring shows up as inconsistent shot weight before it shows up visually.
- Nozzle tip and heater bands intact; all bands heating, none bypassed.
- Barrel heating zones reaching and holding setpoint, with the deviations visible on the controller.
- Shot-weight consistency. Ask for several consecutive shots to be weighed. A drift beyond about ±0.5% means wear is already affecting production.
A worn screw and barrel is not a deal-breaker — it is a price negotiation. Replacement is a known cost and can be quoted before you commit. What matters is knowing before you pay, not after.
4. Hydraulics
- Oil level correct and oil clear — dark, cloudy or milky oil means neglect or water ingress.
- No weeping at cylinder rods, valve blocks, manifolds or hose fittings. Look at the fittings, not the paint.
- Hoses without cracking, chafing or bulging near the crimps; check the date codes on the crimps if they are legible.
- Oil temperature settling around 40–55 °C after half an hour of running. Consistently hotter means the cooler, the pump or the relief settings need attention.
- Pump noise steady, without cavitation whine on demand changes.
- Filter housings present and the last change date known.
5. Electrical, drive and controls
- Cabinet opened on camera: factory wiring, ferrules in place, no improvised splices, no heat discolouration around contactors.
- Date codes on contactors and relays — these are the hardest thing on the machine to fake and the best cross-check on the claimed year.
- Alarm history on the controller, not just the current screen. A recurring alarm is a recurring fault.
- Servo drive starting, stopping and changing speed without squeal, judder or overshoot.
- All axes moving under manual control; limit switches and proximity sensors responding.
- Screen readable and touch or keypad responsive across the whole surface; note the controller model and check parts are still obtainable.
- Emergency stops tested, on every station fitted.
6. Test run, and the paperwork
- Several complete dry cycles: mould close, injection, hold, plasticise, cooling, mould open, ejection.
- Cycle time repeatable across consecutive shots — variation is a symptom, not a setting.
- A mould mounted and sampled if at all possible. Nothing else tells you as much in as little time.
- Hour meter photographed, and treated as one data point rather than as fact.
- Maintenance records requested. Be wary of a machine that keeps having the same component replaced.
- Machine plate photographed: model, serial number, year, and the machine’s own voltage and frequency.
- Full accessories list agreed in writing — screw type, nozzle, hopper, dryer, robot interface, manuals, tools.
Write down what could not be tested. Any machine has something — a function that needs a mould, a mode nobody could demonstrate. It belongs in the condition report. A report with no exceptions in it has not been written honestly.
Turning the checklist into a decision
| What you found | What it usually means for the deal |
|---|---|
| Everything clean, measurements given, alarms empty | Proceed. Price is the only remaining discussion |
| Wear on screw and barrel, measured and disclosed | Proceed with the replacement quoted and written into the contract |
| Minor leaks, tired hoses, dirty oil | Refurbishment item. Cheap now, expensive after shipping |
| Platen parallelism not measured and not offered | Do not proceed until it is measured |
| Alarm history full of the same fault | Ask what was done about it. If the answer is vague, walk |
| Seller unwilling to run it under power | Walk |
Keep reading
Related guides
Run this list on one of our machines
Book a video inspection and we will work down these thirty checks on camera, in this order, and give you the measurements.