TL;DR
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.
What you might see
- elevated vibration at the pellet mill housing
- bearing temperature above 80 deg C
- audible grinding or rumbling at the main shaft
- die-to-roller gap difficult to maintain consistently
Likely causes
Bearing lubrication interval missed or incorrect grease grade used
Bearing contamination from fine feed particles entering through the shaft seal
Excessive die-roller compaction force over-loading the bearing beyond its design capacity
Bearing age beyond rated service life
Required tools
- Vibration meter
- IR thermometer
- Grease gun with correct grease grade
- LOTO kit
- Replacement bearings (matched to shaft nameplate)
Safety first
- Lock out before any main shaft or bearing cover removal.
- Feed dust in and around the pellet mill is a fire hazard. No open flame or spark-generating tools near the mill.
Procedure
- 1
Measure vibration velocity at the main shaft bearing housing on the drive-end and non-drive-end with a vibration meter.[1]
- 2
Measure bearing housing temperature with an IR thermometer. Record both readings for trending.
- 3
Check the main shaft bearing lubrication. Add grease per the lubrication schedule. Do not over-grease, which raises bearing temperature.
Warning: Re-greasing a running pellet mill main shaft requires working near the rotating shaft end. Use a grease gun extension to maintain clear distance from the rotating parts. - 4
Inspect the shaft seal condition. A failed seal allows fine feed material into the bearing housing, rapidly increasing wear.[1]
- 5
If vibration is above 0.4 in/s or temperature above 80 deg C, reduce production rate and plan bearing replacement at the earliest outage opportunity.
- 6
At the next outage, remove the main shaft and inspect bearing rolling elements and races for pitting, flaking, or contamination.
- 7
Replace both drive-end and non-drive-end bearings together to restore uniform shaft support.
Sources
CPM California Pellet Mill CPM 7900 / 7700 Pellet Mill (Feed) general technical documentation, CPM California Pellet Mill
Pellet mill main shaft bearing maintenance and vibration monitoring, general feed pelleting practice (general)
More guides for CPM California Pellet Mill CPM 7900 / 7700
How to clear die hole plugging on a CPM 7900 Pellet Mill
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.
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.
Stop fixing the same fault twice.
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