Arburg Error 302: Injection Pressure Overload — Troubleshooting Guide
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-08-15
Arburg Error 302 is triggered when the injection pressure during the injection phase exceeds the programmed maximum limit. Unlike Error 301 which protects the screw drive motor during plastication, Error 302 protects the hydraulic or electric...
Arburg Error 302 is triggered when the injection pressure during the injection phase exceeds the programmed maximum limit. Unlike Error 301 which protects the screw drive motor during plastication, Error 302 protects the hydraulic or electric injection cylinder during the forward stroke. The Selogica controller monitors the injection pressure transducer in real-time — if the pressure exceeds the programmed limit for more than 100ms, the injection phase is immediately aborted and the screw retracts to a safe position.
Alarm Details
| Alarm Code | 302 |
|---|---|
| Brand / Machine | Arburg |
| Severity | Critical (Machine Stop) |
| Component | Injection Cylinder / Hydraulic System |
| Affected Systems | Selogica Controller / Injection Unit |
Troubleshooting Protocol
Check the Selogica diagnostic screen to determine whether the overpressure occurred during the velocity-controlled fill phase or the holding-pressure phase. If during fill phase, focus on nozzle and gate obstructions. If during holding pressure, focus on process settings and material viscosity.
A blocked nozzle or partially clogged sprue bushing is the most common cause of injection overpressure during fill. Purge the barrel and inspect the nozzle orifice. Remove the nozzle and check for carbonized polymer deposits. Inspect the sprue bushing for damage or contamination.
A significant change in material viscosity (due to a material lot change, moisture content, or regrind percentage) can cause injection pressure to spike. Check the material supplier's datasheet for the viscosity range. Run a spiral flow test to compare with the baseline.
The injection speed profile may be set too high for the material or mold geometry. Review the speed profile in the Selogica controller. Reduce the initial injection speed by 10-20% and observe the pressure response. A gradual fill profile with slower initial speed and faster mid-fill often reduces peak pressure.
Common Root Causes
The following root causes are ranked by probability based on field experience with this alarm code:
Low oil level is the single most common cause of hydraulic pressure alarms. The pump draws air when the oil level drops below the pump intake, causing cavitation, pressure fluctuations, and eventual pump damage. Check the oil level with all cylinders retracted (clamp open, injection unit retracted). Use only the specified ISO grade (typically ISO VG 46 for most injection molding machines). Mixing different viscosity grades creates erratic pressure response.
Hydraulic oil contamination causes proportional valves, servo valves, and pump wear. Particle contamination (ISO 4406 > 20/18/15) causes valve spools to stick, leading to erratic pressure control and nuisance alarms. Water contamination (emulsified oil, milky appearance) reduces lubricity and causes pump cavitation. Take an oil sample for analysis — particle count and water content (Karl Fischer test) confirm contamination levels.
Piston pumps and vane pumps develop internal wear over time, allowing oil to bypass the pumping elements. This reduces flow rate and maximum pressure capacity. Measure the pump's case drain flow — a worn pump has significantly higher case drain flow than the OEM specification. A typical axial piston pump should have case drain flow below 5% of rated flow; above 10% indicates the pump needs replacement or overhaul.
A pressure relief valve stuck partially open bleeds hydraulic pressure back to the tank, preventing the system from reaching the commanded pressure. Listen for continuous flow noise at the tank return line when the pump is running but no axes are moving — this indicates the relief valve is passing oil. The proportional valve's solenoid coil should be tested for resistance (check against OEM specification) and the valve spool should be inspected for contamination.
Hydraulic accumulators (bladder or piston type) maintain system pressure during peak demand and absorb pressure shocks. A ruptured bladder results in zero accumulator function, causing pressure drops during simultaneous axis movements and pressure spikes when valves close. Check the nitrogen pre-charge pressure with a charging kit — the pre-charge should be approximately 60-70% of the maximum system pressure. A flat accumulator (zero pre-charge) indicates a ruptured bladder.
Preventive Maintenance
Follow these preventive maintenance measures to reduce the frequency of this alarm:
- Take hydraulic oil samples for analysis every 500 operating hours. Test for ISO 4406 cleanliness code, water content (Karl Fischer), and viscosity. Change the oil when the particle count exceeds 20/18/15 or water content exceeds 500 ppm.
- Replace hydraulic return-line filters every 500 operating hours (or per OEM schedule). Never exceed the filter's rated pressure drop — a clogged filter bypass valve opens and allows unfiltered oil to circulate, accelerating pump and valve wear.
- Test accumulator nitrogen pre-charge pressure monthly. Log the pre-charge pressure in the machine maintenance record. A gradual pressure loss indicates a leaking valve core; a sudden loss indicates a ruptured bladder requiring immediate replacement.
OEM Replacement Parts
| Part Name | OEM Part Number | Est. Price |
|---|---|---|
| Arburg Injection Pressure Transducer | AR-302-PT | $350-700 |
| Arburg Hydraulic Valve Block Seal Kit | AR-302-HV | $250-500 |
| Arburg Injection Cylinder Piston Seal | AR-302-CS | $180-400 |
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 410 | |
| Netstal Alarm 301 |
Frequently Asked Questions
Can a cold mold cause Arburg Error 302?
Yes. A mold that is too cold causes the polymer melt to cool more rapidly during filling, increasing its viscosity and the pressure required to fill the cavity. This is particularly problematic for thin-wall parts and materials with narrow processing windows. Check the mold temperature controller settings and verify that the mold is at the correct operating temperature before diagnosing other causes. A temperature difference of 10-15°C below the recommended mold temperature can increase injection pressure by 20-30%.
How do I differentiate between a nozzle blockage and a mold filling issue causing Error 302?
The key diagnostic is the screw position at which the overpressure occurs. If the screw position has barely moved (less than 20% of the shot stroke), the blockage is likely at the nozzle or sprue — purge and inspect. If the screw is more than 50% through the stroke, the issue is likely mold filling — check mold venting, gate design, and injection speed profile. A mid-stroke overpressure (20-50%) suggests a partially blocked gate or a flow restriction in the runner system.
Related Diagnostics & Materials
Netstal Alarm 102: Heating Zone Temperature Out of Range...
Netstal Alarm 102 occurs when the actual temperature of a specific heating band in the injection barrel deviates...
Arburg Error 320: Barrel Heating Control Failure -...
Arburg Error 320 is a critical interlock alarm triggered when the Selogica controller detects no current flow to one...
Engel Alarm 405: Screw Recovery Time Exceeded - Diagnostics & Fix
Engel Alarm 405 is generated by the CC300 controller when the screw recovery (plastication) time exceeds the maximum...
Netstal Alarm 301: Mold Protection Force Exceeded -...
Netstal Alarm 301 is one of the most critical safety alarms in injection molding—it triggers when the clamping unit...
Sumitomo Demag Alarm 220: Clamp Force Not Reached -...
Sumitomo Demag Alarm 220 triggers when the NC5 (or NC5 plus) controller detects that the actual clamping force...
KraussMaffei Alarm MC45: Injection Pressure Limit...
KraussMaffei Alarm MC45 is generated by the MC6 controller (KM's latest-generation control platform) when the...
Wittmann Battenfeld Alarm B6: Ejector Position Fault -...
Wittmann Battenfeld Alarm B6 triggers on the Unilog B8 (or B6/B6P) controller when the ejector system fails to reach...
Arburg Error 290: Screw Rotation Speed Deviation -...
Arburg Error 290 is triggered by the Selogica controller when the actual screw rotation speed (measured by the screw...
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