TL;DR
Plugged die holes stop pellet extrusion and back-pressure the die. Clear the holes immediately with a die punch, and investigate moisture or temperature conditions that caused plugging.
What you might see
- no pellets extruding from affected die holes
- die surface pressure rising
- motor current spiking without proportional throughput
- pellets crumbling at the exit cutter
Likely causes
Conditioner temperature or moisture above maximum for the formula, causing premature gelatinization in the die
Die stored without oil fill, causing the holes to rust and bind
Raw material particle size too coarse for the die hole diameter
Die temperature dropping during a production pause causing material to set in the holes
Required tools
- Die punch tool (sized for die hole diameter)
- Die oil
- IR thermometer for die temperature
- LOTO kit
Safety first
- The pellet die is hot (above 80 deg C) during operation. Allow cool-down before opening the die access door or touching the die.
- Lock out the pellet mill before reaching near the die or roller area.
Procedure
- 1
Stop pellet mill feed and reduce die speed. Observe whether the plugging self-clears over 30 seconds. If not, proceed to manual clearing.
Warning: The pellet mill die and rollers rotate at high speed and the die is hot. Lock out before reaching near the die area. - 2
Lock out the pellet mill and allow the die to cool below 60 deg C before opening the die access door.[1]
- 3
Open the die access door and use a die punch tool to clear plugged holes. Drive the punch through each plugged hole to clear the blockage.
- 4
Inspect the cleared material. Gelatinized, rubbery plugs indicate overconditioned material. Dry, powdery plugs indicate feed was too dry.[1]
- 5
Check the conditioner steam temperature and moisture addition against the recipe. Adjust conditioning temperature and moisture to the specification.
- 6
If the die was stored dry, fill the holes with die oil before the next startup and run a short oil flush before introducing feed.
- 7
After clearing all holes, restart under reduced feed rate and monitor extrusion quality before returning to full production.
Sources
CPM California Pellet Mill CPM 7900 / 7700 Pellet Mill (Feed) general technical documentation, CPM California Pellet Mill
Pellet mill die maintenance and plugging prevention, general feed pelleting practice (general)
More guides for CPM California Pellet Mill CPM 7900 / 7700
How to diagnose main shaft bearing wear on a CPM 7900 Pellet Mill
Main shaft bearing wear causes excessive vibration and can lead to die-to-roller misalignment. Measure vibration and check bearing temperature at each scheduled inspection.
How to assess roller wear on a CPM 7900 Pellet Mill
Worn rollers reduce pelleting efficiency and pellet durability. Measure roller-to-die gap and inspect roller surface. Replace when gap exceeds the maximum or surface is deeply grooved.
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