TL;DR
Axial clicking or rumbling from the gearbox area indicates thrust bearing wear from high back pressure or lubrication starvation. Check gearbox oil level and back pressure setting before scheduling a bearing replacement.
What you might see
- axial clicking or rumbling noise from the gearbox end
- gearbox oil temperature elevated
- screw pushback increasing at constant process conditions
- gearbox vibration increasing over time
Likely causes
Thrust bearing wear from sustained high melt back pressure loading
Gearbox oil level low or oil degraded past its service interval
Melt back pressure set too high creating excessive axial thrust on the screw
Thrust bearing contamination from gearbox oil degradation products
Required tools
- Gearbox oil per nameplate specification
- Oil sample vial (for analysis)
- IR thermometer for gearbox temperature
- LOTO kit
Safety first
- Lock out the extruder drive before opening the gearbox for oil inspection.
- The extruder gearbox and barrel retain heat for extended periods after shutdown. Allow cooling before touching.
Procedure
- 1
Monitor the melt back pressure readout. If back pressure is set higher than 500 psi for general purpose work, consider reducing it.[1]
- 2
Lock out the extruder drive and check the gearbox oil level via the sight glass or dipstick. Top up with the oil grade specified on the gearbox nameplate.[1]
- 3
Inspect the gearbox oil sight glass for discoloration or metal particle contamination. Dark oil or visible metal particles indicate imminent bearing failure.
- 4
Take an oil sample and send it for spectrometric analysis if an oil analysis program is in place.
- 5
If the noise is intermittent and the oil is clean, plan a bearing inspection at the next screw pull.
- 6
If the noise is continuous or the oil shows metal contamination, stop production and schedule an urgent gearbox inspection.
- 7
During the next screw pull, inspect the thrust bearing assembly for pitting, spalling, or cage damage.
Sources
Davis-Standard Davis-Standard MEDD / Super Blue Single / Twin-Screw Extruder general technical documentation, Davis-Standard
Davis-Standard extruder gearbox and drive maintenance documentation (general)
More guides for Davis-Standard Davis-Standard MEDD / Super Blue
How to correct melt temperature deviation on a Davis-Standard MEDD / Super Blue extruder
Melt temperature above setpoint is usually excessive shear from screw speed or a barrel zone that has drifted. Melt temperature below setpoint usually means a barrel heater or thermocouple failure.
How to diagnose surging output on a Davis-Standard MEDD / Super Blue extruder
Extruder surge is typically caused by inconsistent feed from the hopper, worn screw, or incorrect screw temperature profile. Verify feed zone temperature and throat cooling before adjusting screw speed.
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