Cluster article
Flour Mill Commissioning: The 30 Days That Decide the Next Ten Years
A structured commissioning sequence for a new flour mill — mechanical completion, dry running, load testing, performance acceptance and the documentation that protects the buyer.
Key takeaways
- Most mills never run at design capacity because commissioning was treated as a handover ceremony rather than a test.
- Insist on a 72-hour continuous performance test at rated capacity before final payment — it is the only number that matters.
- Commissioning failures are 70% installation errors, not equipment defects. The checklist catches them while the installer is still on site.
Why commissioning matters more than purchase price
Two identical plants can end up with 5% different lifetime output depending on how they were commissioned. The difference is not in the machines — it is in whether anyone checked that each machine was doing its job before the installer left site.
The window is short. Once the installation crew demobilises, every defect becomes the buyer’s problem, negotiated at long distance, at the buyer’s cost.
The sequence
Commissioning runs in six phases. Each has an exit criterion. Do not proceed to the next phase until the current one passes.
| Phase | Activity | Exit criterion |
|---|---|---|
| 1 | Mechanical completion inspection | Every item installed per drawing |
| 2 | Electrical and instrumentation checkout | Every motor turns the right way |
| 3 | Dry running (no load) | 4 hours continuous, no faults |
| 4 | Load testing (progressive) | Each section at 100% individually |
| 5 | Integrated run | Full flow sheet at rated capacity |
| 6 | Performance acceptance test | 72 hours at specification |
Phase 1: Mechanical completion
This is a physical inspection, not a paperwork exercise. Walk every floor, every spouting run, every machine.
| Check | Failure found in practice |
|---|---|
| Machines level and grouted | Vibration, premature bearing failure |
| Bolts torqued to specification | Loosening under vibration |
| Spouting slopes adequate | Material accumulation, blockage |
| Spouting joints sealed | Dust emission |
| Flexible connections installed and grounded | Static, dust, vibration transmission |
| Roll gaps set per flow sheet | Wrong extraction from day one |
| Sifter hangers free, not binding | Screen tearing |
| Conveyor belts tracked | Edge damage, spillage |
| Guards fitted | Safety, and insurance |
| Access platforms and ladders | Maintenance impossible without them |
| Drainage and floor falls | Water pooling |
| Explosion vents unobstructed | Statutory, and life safety |
The spouting slope rule
Flour and semolina need 45–50° slope; wheat and bran 40–45°. Anything shallower accumulates material, which sours, blocks and eventually stops the line.
Check every spouting run with an inclinometer. It is a 30-minute job that prevents months of blockages.
Phase 2: Electrical and instrumentation
| Check | Standard |
|---|---|
| Motor rotation direction | Every motor, individually, uncoupled |
| Motor insulation resistance | Above 1 MΩ per kV |
| Overload settings | Matched to nameplate FLA |
| Interlock logic | Tested by deliberate fault injection |
| Emergency stops | Every one, physically tested |
| Level sensors | Filled and emptied, reading verified |
| Temperature sensors | Ice point and hot water check |
| Weighing systems | Static weights across full range |
| Variable speed drives | Full range, no resonance |
| Earthing and bonding | Continuity under 1 Ω everywhere |
| Panel labelling | Matches drawing, matches reality |
Rotation direction is the check that gets skipped and costs the most. A screw conveyor run backwards for ten minutes jams solid and can bend the shaft.
Phase 3: Dry running
Run the entire plant empty for four hours.
| What to observe | Acceptable | Investigate |
|---|---|---|
| Bearing temperatures | Under 60 °C stable | Rising through the run |
| Vibration | Smooth, no resonance | Any beat or surge |
| Noise | Under 85 dB(A) at 1 m | Whine, rattle, scrape |
| Power draw | 8–15% of rated | Above 20% |
| Interlock response | Immediate trip | Any delay |
| Belt tracking | Centred | Any drift |
| Airflow | All aspiration drawing | Any dead section |
Dry running finds alignment, balance and electrical errors. It cannot find process errors — those need load.
Phase 4: Progressive load testing
Do not start the whole plant at full capacity. Load it section by section, from the back.
| Step | Load | Duration | Check |
|---|---|---|---|
| 1 | Cleaning line only, 50% | 2 h | Separation efficiency, dust |
| 2 | Cleaning line, 100% | 4 h | Capacity, impurity removal |
| 3 | Dampening and tempering | 8 h | Moisture accuracy ±0.3% |
| 4 | First break only | 2 h | Roll gap, power, stock appearance |
| 5 | Breaks 1–4 | 4 h | Stock balance across breaks |
| 6 | Full reduction | 4 h | Sifter loading, tailings |
| 7 | Full flow sheet, 70% | 8 h | Integrated stability |
| 8 | Full flow sheet, 100% | 24 h | Rated capacity |
At each step, record: throughput, power, temperatures, product appearance. Compare against the flow sheet design values.
The stock balance check
At each break, weigh or estimate the stock and compare to the flow sheet. If break 2 is receiving 20% more than design, either break 1 gap is too open or the sifter is passing too much — and every downstream passage will be overloaded.
Stock balance is the number that determines whether the flow sheet works. It is almost never checked during commissioning, and it is the reason so many mills never reach design extraction.
Phase 5: Integrated run
Full flow sheet, all sections, at rated capacity, for 24 hours.
Measure continuously:
| Parameter | Target |
|---|---|
| Wheat input | Rated capacity |
| Flour output | Rated × extraction |
| Extraction rate | Per contract |
| Flour ash | Per contract |
| Flour moisture | Per contract |
| Specific power | Per contract kWh/t |
| Bran output and purity | Per design |
| Dust emission | No visible emission |
| Bearing temperatures | Stable |
| Interlocks | No spurious trips |
If any parameter is outside specification, fix it now. Later is more expensive and less likely.
Phase 6: Performance acceptance test
This is the contractual gate. 72 hours continuous at rated capacity.
| Test item | Method | Acceptance |
|---|---|---|
| Capacity | Weighed wheat in, timed | 100% of contract |
| Extraction | Flour weight ÷ wheat weight | Contract value ±1 point |
| Flour ash | Laboratory, per shift | Contract maximum |
| Flour moisture | Laboratory, per shift | Contract ±0.3% |
| Specific power | Metered kWh ÷ tonnes | Contract maximum |
| Flour granulation | Sieve analysis | Per specification |
| Continuous operation | No unplanned stop | Zero stops over 72 h |
Protect yourself in the contract
| Clause | Purpose |
|---|---|
| Performance test defined before signing | Removes ambiguity later |
| Final 10–20% payment on passing | Creates the incentive |
| Retest at supplier’s cost if failed | Prevents argument |
| Wheat specification defined | You cannot test extraction on undefined wheat |
| Measurement method specified | Weighbridge vs belt scale matters |
| Acceptance tolerances stated numerically | “Good extraction” means nothing |
The single most valuable sentence in a flour mill contract is: “Final payment is conditional on a 72-hour continuous performance test at rated capacity meeting the specifications in Annex A.”
Stabilisation: the 4–8 weeks nobody budgets for
A plant that passes its acceptance test is not yet a plant that runs well. Stabilisation is the period during which:
- Operators learn the flow sheet’s behaviour
- Roll gaps are tuned to the actual wheat, not the design wheat
- Sifter screen sizes are adjusted
- Purifier settings are found
- Maintenance routines become habits
- The first set of wear items is replaced
Expect extraction to be 1–3 points below the acceptance figure for the first month, then recover. Budget for it, and do not conclude the plant is defective.
Documentation to demand at handover
| Document | Why |
|---|---|
| As-built drawings | The plant you have, not the one designed |
| Electrical schematics and PLC code | Maintenance cannot work without it |
| PLC backup on removable media | A crashed PLC without backup stops the plant for days |
| Commissioning records | Baseline for all future comparison |
| Lubrication schedule | Per point, with grease type |
| Spare parts list with supplier contacts | Procurement starts here |
| Operating manual in the local language | Not optional |
| Training records with attendee names | Proves who was trained |
| Warranty terms with dates | Start date is often disputed |
| Test certificates for pressure vessels | Statutory |
The PLC backup deserves special mention. A mill with no PLC backup that loses its controller waits 2–6 weeks for a replacement and a program. That single file is worth more than most of the paperwork in the handover folder.