How to Inspect a Used Injection Molding Machine Before You Buy

A used injection molding machine is not a gamble if you inspect it properly. Almost everything that makes a machine a good or bad buy — worn screw, stretched tie bars, tired hydraulics, a repaint hiding hard years — leaves evidence you can check. Most buyers inspect in the wrong order: paint first, one short run, then the price. This checklist works the other way round: documents, the machine standing still, the machine running, then the paperwork that proves its grade. The same sequence applies in person or remotely, through the photos, videos and documents the seller sends you.

Step 1: Start With the Nameplate and Documents

Before you look at the machine at all, verify what it claims to be.

Read the nameplate. The metal plate fixed to the machine shows the manufacturer, model, year of manufacture, serial number, clamping force (often in kN — divide by 10 for tonnes), shot weight and motor power. Ask for a close-up photo and cross-check it against the listing. A machine sold as “200T, year 2020” should carry a plate that says exactly that — as the plate photo on our PowerJet BJ200-S6 page shows. A missing or ground-off plate is not a small detail: without it, the year and origin are whatever the seller says they are.

Check the documents. Ask what comes with it: operation manual, electrical and hydraulic diagrams, and any service records the previous owner kept. Records are rarely complete on a used machine — but a seller who can show past maintenance is telling you the machine was looked after, and the diagrams will save your technicians real time later. Confirm the serial number matches on the plate, the documents and any invoice. One machine, one identity, everywhere.

Confirm the electrical specification. Most Chinese-market machines are wired 380V/50Hz — check the plate’s voltage and frequency against your factory supply before it ships, not after it lands.

Step 2: Mechanical Inspection — the Machine Standing Still

Work from clamping end to injection end, looking for wear, damage and leaks rather than cleanliness.

Tie bars and platens. Tie bars should be straight — no scoring, pitting or chrome flaking — with nuts fully seated. Platens should be flat and crack-free; check around the tie-bar holes and T-slots, where oversize-mold abuse shows first. Damaged tie bars are expensive and signal a life of overloaded molds.

Clamping unit and ejector. On a toggle machine, check the crosshead, pins and bushings for play and grease. On a direct hydraulic clamp, inspect the cylinder seals for weeping. The clamp should close and lock without shuddering or drifting. Check the ejector plate and pins for bending or uneven wear.

Hydraulics. Inspect the pump and motor area, hoses and every visible fitting. Fresh oil under one fitting is a leak that travels with the machine; a film of old grime is normal. Burnt-smelling, black oil in the tank suggests overheating or neglected changes.

Screw and barrel — the heart of the machine. Standing still, check the outside: heater bands complete, nothing baked onto the barrel covers, hopper and feed throat clean. The real wear signs appear when the machine runs (Step 4): long plasticising time, inconsistent melt, and material drooling from the nozzle when it shouldn’t — symptoms of a worn screw, barrel or non-return valve. A screw and barrel set is one of the few expensive wear items on the machine — its condition must be proven, not assumed.

Step 3: Electrical and Controller Check

Power it on — a machine that cannot be powered for inspection is a project machine, whatever the seller calls it.

Controller. Note the brand and model — it determines spare-part availability and whether your technicians can run the machine. The screen should boot cleanly, show no persistent alarm, and accept parameter changes. Ask for running video, not a switched-on photo.

Safety devices. Test, don’t assume: open the safety gate mid-cycle and the machine must stop; press the emergency stop and motion must cease; test both gate interlocks. Defeated safety switches tell you the machine was run by people who cut corners.

Heating. Every barrel zone should climb to its set temperature and hold it. A zone that never reaches setpoint, or overshoots wildly, means a failed heater band, thermocouple or controller output — individually cheap parts, but a machine that cannot hold melt temperature cannot hold part quality.

Cabinet and motors. In the electrical cabinet, look for burnt smells, scorched terminals and amateur rewiring; listen to the motor and pump under power for bearing whine, knocking or hunting at idle.

Step 4: The Running Test — Dry Cycle and Nozzle Purge

This is the test that matters most — and the one a remote buyer should demand on unedited video, serial plate in frame.

Dry cycle. The machine runs clamp close, clamp open and ejector strokes repeatedly, no mold fitted. Watch and listen: movements should be smooth and repeatable, and leaks invisible standing still show themselves under pressure. Slow or jerky strokes mean wear that must be priced in.

Nozzle purge. With the barrel at temperature, the screw rotates and material is purged through the nozzle. The melt should come out smooth, even and consistent, with steady screw recovery. Ragged, pulsating melt, long recovery or excessive drool means screw, barrel or non-return valve wear.

What this test proves — and what it does not. A dry-cycle and purge test proves the clamp unit, hydraulics, ejector, electrics and basic plasticising all work. It does not prove the machine will make your part to your standard: holding pressure on a real mold, cooling behaviour and cycle time on your product only show in a production trial. That is why MoldMach’s listing standard is labelled exactly as it is — dry cycle & purge tested — production trial before shipment: every listing carries the dry-cycle and purge test, with a full molded trial for featured units and for any buyer after a deposit, always before shipment, so you approve real parts before paying the balance. Ask any seller which test level the price includes, and get the answer in writing.

Step 5: Questions to Ask the Seller

1. Why is the machine being sold, and what was it producing?
2. What was replaced or repaired on this unit? Can I have the itemised list?
3. Any known faults, leaks or alarms?
4. Is the test video of this exact unit, unedited, serial plate visible?
5. Which test level is included in the price — dry cycle and purge, or a production trial too?
6. What grade is this machine, and what documentation backs that grade?
7. What is included: manuals, diagrams, spare parts, tools?

Step 6: Red Flags

• Fresh paint over everything, including the nameplate area — paint is cheap, hiding history is not
• Refusal of a specific photo angle, a plate close-up, or a running video “until you pay”
• Controller replaced with a different brand and no explanation of what else changed
• Leaks explained away with “they all do that”
• The running video shows a different unit from the photos
• No stock number, no serial number, no documents — nothing that ties the paperwork to the iron

Step 7: How Refurbishment Grading Should Be Documented

An inspection is a snapshot; a grade is a claim about work done — and only worth something when documented per machine. A transparent grading system looks like this:

Grade	What it means
A	Fully refurbished: worn parts replaced (itemised list), hydraulics and electrics serviced, safety devices tested, repainted, test-run
B	Checked and serviced: tested under power, faults found are fixed, wear items inspected, sold in honest working condition
C	As-is / project machine: basic power-on check only, priced for buyers who will rebuild it themselves

Demand three things behind the letter: the itemised refurbishment list for this unit, the test evidence (this machine’s dry-cycle and purge video), and the grade stated on the machine’s own page or invoice — not in a chat message. A grade without a list is marketing. All three are published on our refurbishment page and on every listing in our current stock. Companion guides: what grading does to prices, and the full process of buying from China.

Put This Checklist to Work

Browse our current machines — every unit is a real machine with a stated grade and the dry-cycle & purge test standard behind it — and run this checklist against any listing, ours included. For a deeper inspection of a specific machine, message us on WhatsApp at +86 156 0798 6886 or email sales@moldmach.com with the stock number and the checks you want filmed. We reply within 24 hours in English, Vietnamese or Spanish, and ship to Vietnam, Malaysia, Indonesia, the UAE, Mexico and beyond.

Frequently Asked Questions