TL;DR
A screw that won't turn on the Roboshot is either frozen material in the barrel or a drive system fault. Never force the screw to turn manually before diagnosing the cause.
What you might see
- screw recovery alarm or timeout on controller
- no screw rotation during plastication phase
- drive motor or hydraulic motor overload alarm
- screw stuck fully forward after injection
Likely causes
Material frozen in the barrel from a cold barrel zone or an extended downtime
Drive motor or hydraulic motor fault preventing rotation
Screw seized due to metal contamination or lack of purge compound
Screw back-pressure set too high preventing metered screw rotation
Required tools
- Milacron Roboshot controller access (alarm codes, zone temperatures)
- Purge compound
- LOTO kit
- Multimeter (for heater band checks if a zone is cold)
- Replacement heater band (if a zone heater failed)
Safety first
- Hot melt can spray violently from the nozzle during purging. Wear face protection and heat-resistant gloves and stand to the side of the barrel, not in front.
- Never reach into the feed throat while the screw is energized or while the machine has power.
- Lock out the main disconnect and release all hydraulic pressure before inspecting the screw or barrel.
Procedure
- 1
Record any alarm codes from the Roboshot controller before clearing them.
- 2
Check all barrel zone temperatures on the controller. Any zone significantly below setpoint indicates a heater failure that may have frozen material in that zone.[1]
- 3
Allow the barrel to soak at setpoint temperature for 15 minutes if any zone was cold before attempting screw rotation.
- 4
Attempt to rotate the screw in manual mode at the lowest back-pressure setting. Do not apply full torque if the screw will not turn.
- 5
If the screw still will not turn, check the drive motor fault status on the controller. A drive motor alarm requires electrical investigation.[1]
- 6
On the hydraulic drive variant, check the hydraulic motor pressure and flow. A failed hydraulic motor shows low flow with normal pressure.
- 7
If the drive is healthy and the barrel is at temperature, suspect screw seizure from metal contamination. Lock out the machine and perform a visual inspection of the feed throat for any metal debris.
- 8
If seizure is confirmed, the barrel must be cooled, disassembled, and the screw cleaned or replaced by a qualified technician. Do not force rotation.
- 9
After resolving the cause, purge the barrel with a commercial purge compound before returning to production material.
Sources
Milacron Roboshot All-Electric Injection Molding Machine Operator Manual, Milacron
Milacron Roboshot Injection Molding Machine Operation and Maintenance Manual, screw and barrel maintenance procedures (general)
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