Netstal Alarm 405: Injection Pressure Limit Exceeded — Troubleshooting Guide
Published: 2026-05-31
Netstal Alarm 405 triggers when the hydraulic injection pressure exceeds the programmed maximum limit during the injection or hold-pressure phase. This is a cycle-interrupt alarm — the machine aborts the current shot to prevent mold damage...
Netstal Alarm 405 triggers when the hydraulic injection pressure exceeds the programmed maximum limit during the injection or hold-pressure phase. This is a cycle-interrupt alarm — the machine aborts the current shot to prevent mold damage (flashing, mold deflection, core pin bending, or even mold-splitting in extreme cases) and potential barrel/screw damage from attempting to inject against a blocked or frozen nozzle.
Root Cause Diagnosis
(1) Cold nozzle or frozen gate: The most common cause. If the nozzle temperature is too low, a frozen skin of polymer blocks flow at the nozzle tip-to-sprue-bushing interface. Check nozzle thermocouple readings vs actual (infrared thermal gun at nozzle tip surface — should be within ±5°C of setpoint), verify nozzle heater band continuity (measure resistance — open circuit = failed heater band), and check that the nozzle is properly seated against the sprue bushing (gap allows polymer to freeze in the annular space). For hot-runner systems, verify each drop and manifold zone is at temperature and the hot-runner controller is not in alarm.
(2) Blocked check ring (non-return valve): If the check ring fails to close, molten polymer is trapped between the screw tip and the nozzle, rapidly cooling and forming a solid plug that requires extreme pressure to dislodge. The telltale sign: the pressure spike occurs in the first 0.1-0.3 seconds of injection, before the mold cavity begins filling. Purge the barrel and inspect the purge 'button' — if it contains unmelted or degraded polymer chunks, the check ring or screw tip requires disassembly and cleaning.
(3) Temperature control failure: A failed heater band in any barrel zone (especially zones close to the nozzle — Z4/Z5/Z6 on a 6-zone barrel) increases local melt viscosity, requiring higher injection pressure to achieve the same flow rate. The machine controller compensates by increasing hydraulic pressure up to the alarm limit. Check all barrel-zone thermocouples and heater bands for open circuits, and verify solid-state relay (SSR) switching for each zone (SSR stuck ON = over-temperature, causing polymer degradation and gas generation; SSR stuck OFF = under-temperature, causing the cold-plug condition). SSR diagnosis: measure control-signal voltage (typically 3-32 VDC from temperature controller to SSR input) and SSR output voltage (should switch from 0 VAC to full line voltage when DC input is present — if output stays at line voltage regardless of input, SSR is shorted/failed ON).
Alarm Details
| Alarm Code | 405 |
|---|---|
| Brand / Machine | Netstal |
| Severity | High (Cycle Interrupt) |
| Component | Hydraulic System / Injection Unit |
| Affected Systems | Injection Pressure Control |
Troubleshooting Protocol
Identify which zone/component triggered the alarm. Record the error code, timestamp, and any measured deviation values shown on the diagnostic screen.
Power down the machine and follow Lock-Out Tag-Out procedures. Visually inspect the affected component for physical damage, loose connections, polymer leakage, or carbonized material.
Using a multimeter, check resistance/continuity on the affected circuit. Verify SSR functionality and fuse integrity. Compare readings to OEM specifications.
Replace the failed component with an OEM-approved part. Do not substitute with generic equivalents unless validated for the specific machine model and operating conditions.
Restart the machine, verify the alarm is cleared, run a test cycle, and document the root cause, repair performed, and parts replaced in the machine maintenance log.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Engel Alarm 510 | |
| Sumitomo Demag Alarm 220 |
Frequently Asked Questions
How do I clear Alarm 405 and safely restart the cycle?
First, DO NOT simply raise the pressure limit to get through the current shot — this risks mold damage (flashing, core pin bending) and does not address the root cause. Steps: (1) Purge the barrel manually (screw recovery + purge) at reduced RPM and backpressure — observe the purge quality (unmelted particles, discoloration, gas bubbles); (2) Verify all barrel zone, nozzle, and hot-runner (if applicable) temperatures are at setpoint with an independent measurement (infrared gun at each zone); (3) Verify nozzle is properly seated and not leaking (polymer leakage at the nozzle/sprue-bushing interface indicates misalignment or worn nozzle tip radius); (4) After confirming heating zones are functional and nozzle is clear, restart with the first shot at 50% of normal injection speed and 75% of normal injection pressure limit — observe the peak injection pressure during cavity filling; (5) If peak pressure is within normal range, restore normal parameters for the second shot. If peak pressure is still high, stop and investigate further — do NOT run production with an unresolved high-pressure condition.
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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