Arburg 301 Alarm: Injection Unit Overload… — Causes & Fixes
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-08-15
Arburg Error 301 is triggered when the Selogica controller detects an overload condition on the injection unit's screw drive motor. This alarm indicates that the torque required to rotate the screw during plastication exceeds the programmed...
Arburg Error 301 is triggered when the Selogica controller detects an overload condition on the injection unit's screw drive motor. This alarm indicates that the torque required to rotate the screw during plastication exceeds the programmed maximum limit. The Selogica Direct controller continuously monitors the screw drive motor current as a proxy for torque — when the current exceeds the threshold for more than 500ms, Error 301 is triggered and the screw rotation is stopped immediately.
Alarm Details
| Alarm Code | 301 |
|---|---|
| Brand / Machine | Arburg |
| Severity | High (Machine Stop) |
| Component | Injection Unit / Screw Drive |
| Affected Systems | Selogica Controller |
Troubleshooting Protocol
Navigate to Selogica Diagnostics > Drives > Screw. Read the motor current at the time of fault. Compare with rated current on the motor nameplate. A reading 20%+ above rated current indicates mechanical overload — check for seized screw, bridged feed throat, or solidified polymer in the barrel.
Switch to manual mode and attempt screw rotation at low RPM (10-20 rpm). Listen for unusual mechanical noise — grinding or scraping indicates screw-to-barrel contact. If the screw does not rotate at all, the drive coupling may be sheared or the motor may be seized.
Use a needle pyrometer to measure actual barrel temperatures at all zones. Compare with thermocouple readings. Cold zones (especially the feed zone) can cause the screw to bind on un-melted polymer pellets. Verify the cooling water temperature in the feed throat zone — excessive cooling can cause the polymer to solidify on the screw.
If the screw rotates freely when the barrel is hot, the issue is likely a mechanical blockage in the check ring or nozzle. Remove the nozzle and check ring assembly. Inspect the check ring for cracks or wear. Check the screw tip for damage.
Common Root Causes
The following root causes are ranked by probability based on field experience with this alarm code:
Servo motor encoders (absolute or incremental) provide position and velocity feedback to the drive amplifier. A loose encoder coupling, contaminated encoder disk, or broken encoder wire causes the drive to lose position feedback, triggering an overload alarm. The drive will typically show a specific encoder fault code (Fanuc: SV0400 series; Siemens: F0780x). Check the encoder cable for flex fatigue damage at the cable carrier entry point.
Ball screws in injection and clamp axes wear over time, especially in all-electric machines where the ball screw carries the full injection force. Worn ball nuts increase friction and create uneven load on the servo motor, causing the drive to draw excessive current. Measure backlash by zeroing the axis position, advancing 1mm manually, then measuring the return-to-zero error. Backlash exceeding 0.1mm indicates ball screw replacement is needed.
Servo motors generate significant heat under continuous high-torque operation. The motor's cooling fan (typically an externally mounted axial fan) can fail due to bearing wear or dust accumulation. Without cooling, the motor's internal temperature rises until the PTC thermistor embedded in the motor windings trips, triggering the overload alarm. Clean the cooling fan grille weekly in dusty environments and check fan rotation monthly.
The servo drive amplifier's IGBT (insulated-gate bipolar transistor) power stage is the most failure-prone component in a servo system. IGBTs fail by short-circuit or open-circuit due to thermal cycling, overvoltage (regenerative braking spikes), or age. A failed IGBT typically produces a drive-specific fault code (e.g., Fanuc SV0300, Yaskawa A.Er). The drive's DC bus voltage should be checked — a shorted IGBT causes the DC bus to collapse.
Servo motor bearings fail due to normal wear, shaft currents (common on VFD-driven motors), or contamination. Failed bearings produce audible noise (grinding, whining) and increase motor vibration, which the drive interprets as torque ripple and compensates by increasing current. Listen for bearing noise with a stethoscope rod at the motor housing. Replace bearings at the first sign of noise to avoid catastrophic failure that can damage the encoder.
Preventive Maintenance
Follow these preventive maintenance measures to reduce the frequency of this alarm:
- Clean servo motor cooling fan grilles weekly in dusty environments. Check fan rotation monthly. A failed cooling fan reduces motor service life by 50% due to overheating of the motor windings and bearing grease degradation.
- Perform motor bearing vibration analysis annually. Use a vibration meter to measure velocity (mm/s RMS) at the motor housing in three axes. An increase of 2× over baseline indicates bearing wear. Schedule bearing replacement at 4× baseline.
- Check ball screw backlash and smoothness of travel every 6 months. Lubricate ball screws with the specified grease (typically lithium-complex EP2) every 500 operating hours. A ball screw with excessive backlash should be replaced before it causes servo motor overload.
OEM Replacement Parts
| Part Name | OEM Part Number | Est. Price |
|---|---|---|
| Arburg Screw Drive Motor | AR-301-SDM | $3,500-6,000 |
| Arburg Screw Drive Coupling | AR-301-SDC | $500-900 |
| Arburg Drive Belt Set | AR-301-DB | $200-400 |
Prices are estimated US market ranges. Contact your OEM distributor for exact pricing. {zone} = zone-specific variant.
Same Alarm on Other Machine Brands
If you operate multiple injection molding machine brands, the same fault may appear under different alarm codes:
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Engel Alarm 420 | |
| Netstal Alarm 401 |
Frequently Asked Questions
What is the difference between Arburg Error 301 and Error 302?
Error 301 indicates an overload on the screw drive motor during plastication (screw rotation). Error 302 indicates an overload on the injection cylinder during the injection phase (screw forward movement). Both are current-monitored overload protections, but they protect different phases of the molding cycle. Error 301 stops screw rotation; Error 302 stops injection forward movement. The troubleshooting approach is different — Error 301 points to plastication issues (temperature, back pressure, material feeding), while Error 302 points to injection issues (nozzle blockage, mold filling obstruction, material viscosity).
Can a worn check ring cause Arburg Error 301?
Indirectly, yes. A worn check ring allows melt to flow backward during injection, which reduces the shot size delivered to the cavity. The controller compensates by increasing the screw recovery time and stroke. If the screw is commanded to travel further back to build the next shot, it may encounter insufficient melt in the barrel, causing the screw drive motor to work harder to compact the softened pellets. This increased torque can trigger Error 301, particularly when processing high-viscosity materials like PC or PEEK.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org