Arburg 340 Alarm: Mold Closing Force Limit… — Causes & Fixes
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-08-15
Arburg Error 340 is triggered when the clamping unit detects a resistance force exceeding the mold protection limit during the low-pressure mold closing phase. This is a critical safety alarm designed to prevent mold crash damage. The Selogica...
Arburg Error 340 is triggered when the clamping unit detects a resistance force exceeding the mold protection limit during the low-pressure mold closing phase. This is a critical safety alarm designed to prevent mold crash damage. The Selogica controller monitors the force on the moving platen during the final stage of mold closing — if the force exceeds the programmed mold protection limit, the closing movement is immediately stopped and the platen reverses direction. The mold protection limit is typically set at 10-30% of the maximum clamping force, depending on the mold weight and complexity.
Alarm Details
| Alarm Code | 340 |
|---|---|
| Brand / Machine | Arburg |
| Severity | Critical (Immediate Stop) |
| Component | Clamping Unit / Mold Protection System |
| Affected Systems | Selogica Controller / Clamp |
Troubleshooting Protocol
The first step is to identify and remove any obstruction between the mold halves. Open the mold safety gate and visually inspect the mold parting line. Look for: stuck parts, displaced ejector pins, loose mold inserts, or foreign objects (sprue remnants, fallen tools, debris). Remove any obstructions manually.
A common cause of mold protection alarms is incomplete ejector plate return. If the ejector plate does not return fully to the home position, the ejector pins protrude beyond the mold face and contact the opposing mold half during closing. Check the ejector return mechanism for damage or binding. Verify the ejector stroke setting.
The mold protection force limit may be set too low for the specific mold. Run 10 cycles with the mold protection force set to maximum (to verify no alarms), then gradually reduce the force in 5% increments until the alarm triggers during normal closing. Set the production value at 150% of this threshold. Record the final setting in the mold setup sheet.
A misaligned mold can cause uneven contact forces during closing, triggering the mold protection alarm. Check the mold mounting alignment with a dial indicator on the platen face. Verify that the mold is centered on the machine platen and that the clamp force is evenly distributed across the four tie-bars.
Common Root Causes
The following root causes are ranked by probability based on field experience with this alarm code:
The operator safety gate limit switches (typically two independent switches wired in series for redundancy) are subject to vibration, mechanical wear, and contamination from mold-release spray and debris. A misaligned limit switch fails to confirm the gate is closed, preventing the clamp from initiating the closing sequence. This is the most common cause of clamp timeout alarms. Check each switch's actuation point and adjust the actuator bracket as needed.
Toggle clamp machines rely on automatic lubrication to grease the toggle pins and bushings. A clogged grease line, empty grease reservoir, or failed lubrication pump starves the toggle pins, causing dramatically increased friction. The clamp motor must then generate significantly higher torque to close the mold, often triggering an overload alarm. On hydraulic toggle machines, the increased friction manifests as slow clamp speed and extended cycle time.
Uneven tie-bar loading occurs when the mold is not centered on the platens, the tie-bar nuts are not evenly tensioned, or the mold height adjustment is not uniform. An overloaded tie-bar puts uneven stress on the clamp mechanism, causing binding during the closing stroke. Check tie-bar strain (stretch) using a tie-bar stress meter or ultrasonic tie-bar monitor. The variation between the four tie-bars should be within 5% of the average.
Hydraulic clamp cylinders use piston seals and rod seals that wear over time, allowing oil to bypass the piston. This reduces the effective clamping force and can cause the clamp to drift open during the injection phase. A leaking clamp cylinder seal is detectable by measuring the clamp close speed — a worn seal reduces close speed at the same hydraulic flow rate. Oil leakage visible at the clamp cylinder rod indicates imminent seal failure.
After a mold change, the mold height adjustment (movable platen position) must be set correctly for the new mold. If the mold height is set too low, the clamp cannot build full tonnage. If set too high, the clamp mechanism binds before reaching full close. Reference the mold's specified shut height and set the mold height adjustment within ±0.5mm. Always perform a slow manual close cycle to verify smooth engagement before switching to automatic mode.
Preventive Maintenance
Follow these preventive maintenance measures to reduce the frequency of this alarm:
- Verify safety gate limit switch function daily at startup. Both independent switches should change state reliably when the gate is opened and closed. Adjust or replace switches that show intermittent actuation — a safety gate failure can cause a clamp crash.
- Check toggle pin lubrication system function weekly. Verify the grease reservoir level and that the automatic lubrication pump cycles correctly. Manually grease toggle pins at each mold change if the automatic system is not reaching all lubrication points.
- Measure tie-bar stretch (strain) annually or after any major clamp repair. The variation between the four tie-bars should be within 5%. Uneven tie-bar loading causes accelerated toggle bushing wear and can lead to tie-bar fracture.
OEM Replacement Parts
| Part Name | OEM Part Number | Est. Price |
|---|---|---|
| Arburg Mold Protection Sensor | AR-340-MPS | $250-500 |
| Arburg Clamp Position Transducer | AR-340-CPT | $400-800 |
| Arburg Clamp Cylinder Seal Kit | AR-340-CSK | $300-600 |
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 Mold Protection Alarm | |
| Netstal Alarm 301 |
Frequently Asked Questions
How does Arburg's mold protection system differ from other brands?
Arburg uses a force-based mold protection system on the Selogica controller — it directly measures the force on the moving platen during closing via a load cell or pressure transducer. This is different from position-based systems (some older machines) that only detect an obstruction by measuring the position deviation. Force-based systems are more sensitive and can detect obstructions earlier in the closing stroke, reducing the risk of mold damage.
Can a hydraulic issue cause Arburg Error 340?
Yes. A sticking hydraulic directional valve in the clamp circuit can cause the mold to close faster than expected, leading to a force spike that triggers the mold protection alarm. This is particularly common after hydraulic oil changes or when the oil is cold (below 30°C). Check the hydraulic oil temperature and the condition of the clamp directional valve.
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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