Inspection Checklist for Buying Used Plastic Injection Molding Machinery (My Practical Guide)

Before You Even Visit: My “Pre-Inspection” Questions

I like to start with a quick interrogation—friendly, of course. It saves time and filters out machines that are more “museum exhibit” than “production asset”.

• Why is the machine being sold? Capacity change, plant closure, upgrade… or chronic issues?
• What was it molding? Filled materials (glass fiber), abrasive additives, flame retardants—these accelerate wear.
• Operating hours and cycles? Ask for counter screenshots or service logs to confirm.
• Maintenance history? Oil changes, filter schedule, pump service, screw/barrel replacement, tie-bar checks.
• Any major repairs? Servo drives, pumps, hydraulics, clamping unit, control boards.
• What’s included? Manuals, schematics, safety documentation, spare parts, robot interface, conveyors, thermolators?
• Can it be tested under power? If the answer is “no”, I treat the price as “unknown condition”.

On-Site Inspection Checklist: What I Always Review

1) General Condition & First Impressions (Yes, They Matter)

I begin with a slow walk-around. Not because I enjoy suspense, but because bad maintenance leaves clues everywhere.

• Cleanliness: Excess oil, dust layers, burnt residue—often signals neglect.
• Corrosion: Rust on tie bars, platen surfaces, connectors, cabinet hinges.
• Improvised fixes: Cable ties as “engineering”, taped sensors, bypassed interlocks.
• Noise and smell (when running): whining pumps, burning odor, overheating cabinets.

Wear signal: If the machine looks like it has survived a war zone, it probably has—and you may inherit the battlefield.

2) Injection Unit: Screw, Barrel, Non-Return Valve (The Money Zone)

In injection molding, the screw and barrel are like the engine and gearbox. If they’re worn, your process stability evaporates.

• Screw condition: Ask if it’s original. Check for wear, pitting, and history of abrasive materials.
• Barrel wear: Look for inconsistent melt, unstable cushion, increased recovery time.
• Non-return valve (check ring): Worn check rings cause poor repeatability, drifting shot weight.
• Nozzle and seat: Inspect for leakage, damage, or “creative” sealing solutions.
• Injection carriage guides: Excess play, rough movement, unusual marks.

Wear signals I watch for: fluctuating injection pressure, inconsistent part weights, long plastification times, and unexplained scrap rates in the machine’s past life.

3) Clamping Unit: Tie Bars, Platens, Toggle/Hydraulic Clamp

The clamp is where mechanical wear hides in plain sight. A machine can “close” and still be out of spec.

• Tie bar condition: Check for scoring, rust, uneven lubrication patterns.
• Platen flatness and damage: Dents, cracks, or deformation can cause mold alignment issues.
• Toggle mechanism: Look for play, unusual noise, worn pins and bushings.
• Clamping force consistency: Ask for clamping force verification records if available.
• Mold height adjustment: Smooth operation? Any binding or unusual backlash?

Wear signal: uneven mold parting line, flash on one side, or repeated mold damage can point to alignment issues.

4) Hydraulic System: Pumps, Valves, Oil, Filters (The Leak Detective Phase)

Hydraulics are often the difference between “ready to run” and “ready to drain your budget”. I inspect like a detective.

• Hydraulic oil condition: Check color and smell. Dark, burnt oil suggests overheating or long intervals.
• Filters: Ask when last changed. Check indicators if installed.
• Pumps: Listen for cavitation (a harsh, gravelly sound) and monitor temperature rise.
• Valves and manifolds: Look for sweating, dampness, and residue around fittings.
• Hoses and seals: Cracking, stiffness, bulging—especially near hot zones.

Wear signals: slow response, pressure instability, overheating oil, recurring alarms, and “mysterious puddles” under the base.

5) Electrical Cabinet & Control System: The Brain Test

A used machine can be mechanically solid but electronically “temperamental”. Controls matter because downtime doesn’t care about your schedule.

• Control interface: Test keys, touchscreen responsiveness, parameter access.
• Alarm history: Ask to view alarm logs. Repeated servo, temperature, or pressure alarms are red flags.
• Fans and cooling: Dirty filters and failed fans lead to overheating and random faults.
• Wiring quality: Look for messy retrofits, burnt terminals, and non-original connectors.
• Backups: Confirm availability of parameters, software versions, and configuration backups.

If you’re looking at DEMAG Second Hand machines, the good news is that DEMAG is widely used and supported—still, I always verify the control generation, spare parts availability, and service documentation.

6) Heaters, Thermocouples, and Temperature Stability

Temperature control is one of those “small” things that becomes a big thing when you’re chasing cycle time and consistency.

• Heater bands: Check for hot spots, uneven heating, and signs of frequent replacements.
• Thermocouples: Inspect mounting and cable integrity; loose probes cause unstable readings.
• Barrel insulation: Missing or damaged insulation can mean higher energy use and unstable melt.

Wear signal: temperature overshoot, slow heating, or zones that constantly alarm during warm-up.

7) Pneumatics, Water Lines, and Auxiliary Connections

Even if your core machine is perfect, a cracked water manifold or unreliable air prep unit can ruin your day.

• Air leaks: Listen for hissing, inspect FRL (filter-regulator-lubricator) unit condition.
• Water circuits: Look for corrosion, scale buildup, and leaking quick couplings.
• Robot/EUROMAP interfaces: Verify connectors and I/O readiness if automation is planned.

8) Safety: Doors, Interlocks, Emergency Stops, Guarding

Safety is not optional—and it’s not “nice to have”. I check it early, because if safety is compromised, everything else is a negotiation.

• Guarding: Doors, light curtains (if present), fixed guards all intact.
• Interlocks: Test that the machine behaves correctly when doors open.
• E-stops: Check function and reset behavior.
• CE compliance and labeling: Look for plates, warnings, and documentation consistency.

Wear signal: bypassed switches or “temporary” solutions that have clearly become permanent.

9) Documentation & Traceability (The Hidden Superpower)

I love good documentation because it accelerates commissioning and maintenance. Missing manuals mean slower ramp-up and more risk.

• User manuals and maintenance guides
• Electrical and hydraulic schematics
• Spare parts lists
• Service reports and inspection protocols
• Machine identification: serial numbers match documentation

My Quick “Test Run” Checklist (If the Machine Can Be Powered On)

• Warm-up: stable heating without repeated alarms.
• Dry cycle: clamp open/close, ejector, core pulls (if present), injection carriage movement.
• Pressure stability: no strange spikes, no hunting behavior.
• Repeatability: consistent cycle behavior across multiple runs.
• Leak check: inspect again after running—leaks love to appear when oil is hot.

Key Questions I Ask the Supplier (So I Don’t Buy Surprises)

• What is the machine’s real condition? “As-is” or inspected/refurbished? What exactly was done?
• Is there a warranty? Even a limited one signals confidence.
• Can you provide a detailed inspection report? Measurements, tolerances, replaced parts.
• Can I see it under power and, ideally, molding? A dry cycle is good; molding is better.
• What’s the delivery scope? Loading, packaging, export docs, commissioning options.
• What support is available after delivery? Remote help, on-site service, spare parts sourcing.

Typical Red Flags I Don’t Ignore

• Seller avoids test runs or cannot answer basic maintenance questions.
• Frequent oil leaks, patched hoses, or “temporary” sealants everywhere.
• Unstable injection or plastification behavior with no clear explanation.
• Repeated alarms in history logs (especially servo/drive or temperature control).
• Missing documentation, missing CE elements, or unclear ownership history.

When I’m evaluating DEMAG Second Hand injection molding machines, I’m especially attentive to control versions, serviceability, and whether the machine has been professionally checked before it leaves the warehouse.

Why Professional Inspection & Refurbishment Pays Off (My Favorite “Boring” Advantage)

Here’s the funny part: the most “exciting” machines to buy are often the worst ones—because mystery always sounds like a bargain… until you’re stuck waiting for parts, chasing leaks, or explaining downtime to your team.

A professional review and pre-delivery refurbishment drastically reduces risk. It helps you:

• Start production faster with fewer commissioning surprises.
• Reduce unplanned downtime by catching wear before it becomes failure.
• Stabilize process quality through verified tolerances and repeatability.
• Protect your investment with documented condition and service actions.

At UDO KRICHBAUM TRANSITUS, we focus on used and refurbished industrial machinery for plastics processing, and we know what production environments demand: reliability, transparency, and realistic delivery promises. If you’re considering a DEMAG Second Hand machine (or any used injection molding equipment), I recommend choosing a supplier that can show you what has been checked, what has been replaced, and what condition the key components are in—before the machine arrives at your plant.