Grinding & Milling Equipment — Technical Specification
1. Process Objective
Reduce dehulled flaxseed kernels (with or without hull fractions) into controlled particle-size flours and meals at a design capacity of 2 MT/hr max (typical: 1.2–1.8 MT/hr depending on target fineness). Four milling paths available: hammer mill (coarse), disc mill (medium), pin mill (fine), cryogenic mill (ultra-fine, reduced oxidation).
2. Equipment Configuration — ASCII Flow Diagram
Dehulled kernels / middlings
|
v
[ Feed hopper with dosing screw ] ← VFD-controlled feed rate
|
+───→ [ Hammer Mill ] 2,800–3,600 rpm Screen 0.8–3.0 mm Coarse meal
|
+───→ [ Disc Mill ] 1,200–1,800 rpm Gap 0.1–2.0 mm Medium flour
|
+───→ [ Pin Mill ] 6,000–12,000 rpm No screen Fine flour
|
+───→ [ Cryogenic Mill ] −150 °C 1.5–2.5 kg N2/kg Ultra-fine, cold
↓ ↓
Liquid N2 ──→ Exhaust vapour
↓
[ Product cyclone + bag filter ]
↓
[ Metal detector ] ← CCP-2
↓
[ Packing / silo ]
3. Equipment Table
| Unit |
Type |
Model (Example) |
Capacity (MT/hr) |
Power (kW) |
Material (food-contact) |
Manufacturer (suggested) |
| Hammer Mill |
Swing-hammer, horizontal shaft, screen basket |
Schutte-Buffalo 15-24 |
1.5–2.0 |
37–45 |
SS304 chamber, AR400 hammers, SS304 screen |
Schutte-Buffalo / Jacobsen |
| Disc Mill |
Single/double rotating disc, adjustable gap |
Bühler MJZS-80 |
1.0–1.8 |
30–37 |
Ni-hard discs, SS304 housing |
Bühler / Perten |
| Pin Mill |
Vertical, two counter-rotating pin discs |
Hosokawa Alpine 160UPZ |
0.5–1.2 |
22–30 |
SS316L disc, WC-Co pins |
Hosokawa Alpine / Kemutec |
| Cryogenic Mill |
Integrated N₂ injection, screw feeder, hammer/impact mill |
Air Products / Praxair Cryo-Grind |
0.3–0.8 |
30 (mill) + 15 (N₂ system) |
SS304, cryo-rated seals, PTFE gaskets |
Air Products / custom |
4. Detailed Technical Parameters — Set Points & Tolerances
4.1 Hammer Mill (2,800–3,600 rpm, 0.8–3.0 mm screen)
| Parameter |
Set Point |
Tolerance |
Notes |
| Rotor speed |
3,200 rpm |
±50 rpm |
VFD-controlled |
| Tip speed (rotor Ø 600 mm) |
100 m/s |
±5 m/s |
Adjustable via VFD |
| Number of hammers |
24 (4 rows × 6) |
— |
Reversible (4 wear faces) |
| Hammer thickness |
6 mm |
±0.5 mm |
AR400 steel |
| Screen aperture |
1.5 mm |
±0.05 mm |
Interchangeable: 0.8 / 1.0 / 1.5 / 2.0 / 3.0 mm |
| Screen open area |
35–45 % |
— |
Staggered hole pattern |
| Hammer-to-screen clearance |
8 mm |
±1 mm |
Critical for grind efficiency |
| Feed rate |
1.5 MT/hr |
±0.2 MT/hr |
For 1.5 mm screen |
| Motor full-load amps |
75 A |
±5 A |
At 380 V, 50 Hz |
| Product temperature rise |
+15 °C max |
— |
Above ambient |
| Target particle size (d50) |
400 µm |
±50 µm |
With 1.5 mm screen |
4.2 Disc Mill (1,200–1,800 rpm)
| Parameter |
Set Point |
Tolerance |
Notes |
| Rotating disc speed |
1,500 rpm |
±30 rpm |
VFD-controlled |
| Stationary / rotating disc diameter |
300 mm |
±0.5 mm |
Ni-hard cast-iron |
| Disc gap (closed) |
0.5 mm |
±0.05 mm |
Adjustable by handwheel |
| Disc gap adjustment range |
0.1–2.0 mm |
±0.05 mm |
Micrometer dial |
| Groove pattern |
Radial, 30° included angle |
— |
Factory set; re-cut at refurb |
| Feed rate |
1.2 MT/hr |
±0.2 MT/hr |
For medium grind |
| Motor power draw (nominal) |
25 kW |
±2 kW |
At 1.5 mm gap |
| Product temperature rise |
+12 °C max |
— |
Above ambient |
| Target particle size (d50) |
200 µm |
±30 µm |
At 0.5 mm gap |
4.3 Pin Mill (6,000–12,000 rpm)
| Parameter |
Set Point |
Tolerance |
Notes |
| Rotor disc speed |
10,000 rpm |
±200 rpm |
Belt-driven + VFD |
| Stator disc speed (counter-rotating) |
8,000 rpm |
±200 rpm |
Belt-driven + VFD |
| Relative tip speed |
200 m/s |
±10 m/s |
Sum of both rotors |
| Number of pins (rotor disc) |
48 |
— |
WC-Co, Ø 8 mm × 40 mm |
| Number of pins (stator disc) |
48 |
— |
WC-Co, Ø 8 mm × 40 mm |
| Pin arrangement |
4 concentric rings (staggered) |
— |
Optimised for flaxseed |
| Feed rate |
0.8 MT/hr |
±0.1 MT/hr |
For fine flour |
| Motor power draw (total) |
25 kW |
±3 kW |
Both motors combined |
| Product temperature rise |
+20 °C max |
— |
Highest heat of all mills |
| Target particle size (d50) |
80 µm |
±15 µm |
For fine bakery flour |
| No-load amps (rotor) |
12 A |
±2 A |
Per motor at 380 V |
4.4 Cryogenic Mill (−150 °C, N₂ 1.5–2.5 kg N₂/kg)
| Parameter |
Set Point |
Tolerance |
Notes |
| Grinding chamber temperature |
−150 °C |
±10 °C |
Pt100 RTD, PID-controlled |
| Liquid nitrogen flow rate |
2.0 kg N₂/kg product |
±0.3 kg/kg |
Self-regulating valve |
| Product feed rate |
0.5 MT/hr |
±0.1 MT/hr |
Max 0.8 MT/hr |
| Product temperature at discharge |
−100 °C |
±10 °C |
Oil oxidation prevention |
| Nitrogen gas exhaust temperature |
+5 °C |
±5 °C |
Heat exchanger exit |
| Oxygen in exhaust gas |
< 1 % vol |
— |
Oxygen sensor interlock |
| Mill rotor speed (hammer type) |
3,000 rpm |
±50 rpm |
VFD |
| Target particle size (d50) |
30 µm |
±5 µm |
Ultra-fine |
| Specific energy |
60 kWh/MT |
±5 kWh/MT |
Mill + N₂ production |
| N₂ usage per batch |
1,000 kg N₂/MT |
±150 kg N₂/MT |
At 0.5 MT/hr |
| Parameter |
Target |
Verification Method |
Frequency |
| Hammer mill — d50 particle size |
400 ± 50 µm (1.5 mm screen) |
Sieve analysis (Ro-Tap, 20 min) |
Every 2 hr & after screen change |
| Disc mill — d50 particle size |
200 ± 30 µm |
Sieve analysis (Ro-Tap, 20 min) |
Every 2 hr & after gap adjustment |
| Pin mill — d50 particle size |
80 ± 15 µm |
Laser diffraction (Malvern Mastersizer) |
Every 4 hr |
| Cryogenic mill — d50 particle size |
30 ± 5 µm |
Laser diffraction |
Every 4 hr & per batch |
| Throughput (hammer mill) |
≥ 1.5 MT/hr |
Belt scale / weigh hopper |
Continuous |
| Throughput (cryogenic) |
≥ 0.5 MT/hr |
Nitrogen flow integrator |
Per batch |
| Product temperature rise |
≤ 20 °C above ambient |
IR thermometer at outlet |
Hourly |
| Metal detector rejection (CCP-2) |
100 % of ferrous ≥ 1.0 mm, SS ≥ 1.5 mm |
Test wands (Fe, SS, Cu) |
Start of every shift |
| Specific energy consumption |
≤ 30 kWh/MT (hammer), ≤ 80 kWh/MT (cryo) |
Energy meter |
Monthly |
| Element |
Specification |
| CCP ID |
CCP-2 |
| Hazard |
Physical — ferrous and non-ferrous metal fragments from mill wear (hammers, pins, discs, screens) |
| Critical Limit |
Ferrous ≥ 1.0 mm: reject. Stainless steel ≥ 1.5 mm: reject. Non-ferrous (Cu, Al) ≥ 1.5 mm: reject. |
| Monitoring Device |
In-line metal detector (e.g., Mettler-Toledo Safeline, Thermo Scientific APEX) with auto-eject |
| Monitoring Frequency |
Continuous production; manual test with test wands every 60 min |
| Monitoring Personnel |
Line operator |
| Corrective Action |
1. Isolate affected product (from last clean test). 2. Reject and quarantine. 3. Investigate source (inspect mill components). 4. Replace worn hammers/pins/screens. 5. Log incident in HACCP record. |
| Verification |
Third-party metal detector calibration every 6 months; daily shift-start test with Fe/SS/non-Fe wands |
| Record Keeping |
CCP-2 log (hourly); auto-ejection event log (digital, 90-day retention) |
Pre-Grinding OPRP — Mill Wear Monitoring
| Equipment |
Hazard Controlled |
Monitoring |
Frequency |
| Hammer mill |
Metal fragments from hammer/screen wear |
Visual inspection of hammers + screen integrity |
Every shift |
| Disc mill |
Metal fragments from disc contact |
Visual inspection of disc grooves & gap |
Every 4 hr |
| Pin mill |
Metal fragments from pin fracture |
Pin count + visual check |
Every 4 hr |
| Cryogenic mill |
Metal fragments + seal failure |
Visual + oxygen sensor |
Every 2 hr |
7. Maintenance Schedule
7.1 Daily (shift-end, ~30 min total)
| Task |
Time (min) |
Performed By |
| Hammer mill — inspect hammers for wear/cracks; rotate/replace as needed |
10 |
Operator |
| Disc mill — check disc gap; inspect for scoring |
5 |
Operator |
| Pin mill — visual pin count (confirm none missing) |
5 |
Operator |
| Cryogenic mill — check N₂ line for frost/leaks; verify door seal integrity |
5 |
Operator |
| Metal detector — run test wand (Fe, SS, Cu); log result |
5 |
Operator |
7.2 Weekly (~3 hr)
| Task |
Time (min) |
Performed By |
| Hammer mill — measure hammer tip wear (dial calliper); replace if < 80 % original width |
30 |
Maintenance tech |
| Hammer mill — rotate hammers to fresh face; replace screen if holes > 110 % of spec |
30 |
Maintenance tech |
| Disc mill — remove discs; measure groove depth; dress if < 1 mm remaining |
30 |
Maintenance tech |
| Pin mill — remove pin disc; check each pin torque (10 N·m); replace any loose pins |
30 |
Maintenance tech |
| Cryogenic mill — check N₂ valve calibration; inspect PTFE seals |
30 |
Maintenance tech |
| All mills — lubricate feed screw bearings & shaft seals (food-grade) |
15 |
Maintenance tech |
| Metal detector — sensitivity check with all three test pieces |
15 |
QC / Tech |
| Cyclone & bag filter — clean; check for wear |
15 |
Operator |
7.3 Monthly (~6 hr)
| Task |
Time (min) |
Performed By |
| Hammer mill — replace all hammers (set of 24); rotate or replace screen basket |
60 |
Maintenance team |
| Disc mill — replace discs (both rotors); replace shaft seals |
60 |
Maintenance team |
| Pin mill — replace all pins on both discs (96 pins total) |
90 |
Maintenance team |
| Cryogenic mill — complete seal replacement (PTFE gaskets, O-rings, shaft seals) |
60 |
Maintenance tech + OEM |
| All mills — motor bearing re-grease; shaft alignment check (laser) |
30 |
Maintenance tech |
| All mills — VFD parameter backup & firmware check |
15 |
Electrical tech |
| Dust collection system — duct inspection; fan bearing replacement (if vibration > 5 mm/s) |
30 |
Maintenance tech |
| Full particle-size analysis QC correlation — compare mill lab sieve vs. reference |
15 |
QC lab |
| Update spare parts inventory & maintenance log |
15 |
Maintenance lead |
7.4 Annual (during shutdown, ~24 hr)
| Task |
Time (min) |
Performed By |
| Hammer mill — complete rotor refurbishment (re-build shaft, bearings, keyways) |
300 |
Maintenance team + OEM |
| Disc mill — complete disc & housing reconditioning; replace all bearings |
240 |
Maintenance team |
| Pin mill — complete rotor & stator disc replacement; rebalance both assemblies |
240 |
Maintenance team + OEM |
| Cryogenic mill — full overhaul: mill section, N₂ injection nozzles, heat exchanger, control valves |
360 |
OEM service engineer |
| All mills — Megger test (all motors > 20 MΩ); motor bearing replacement |
120 |
Electrical tech |
| All mills — structural weld inspection; vibration analysis baseline |
60 |
Maintenance team |
| Metal detector — factory calibration + report (OEM service) |
60 |
OEM service engineer |
| HACCP CCP-2 re-validation — 8-hr challenge test with calibrated test pieces |
240 |
QC + Production |
8. Safety Interlocks & Emergency Stops
| Interlock / E-Stop |
Trigger |
Action |
Location |
| E-Stop (red pushbutton) |
Manual press |
Shuts all mill drives + feed screws + dust collection |
Each mill panel + line ends |
| Mill door interlock |
Access door limit switch |
Stops rotor immediately; brake engages (< 5 s stop) |
Each mill chamber door |
| Overload relay (motor) |
Amperage > 110 % of FLA for 5 s |
Trips motor; stops feed |
Each motor starter |
| Vibration sensor (mill bearing) |
Vibration > 12 mm/s RMS |
Trips mill drive |
Each bearing housing |
| Bearing temperature sensor |
Temp > 85 °C |
Alarms at 75 °C; Trips at 85 °C |
Each bearing housing |
| Feed chute plug detector |
Rotation sensor < 2 rpm |
Stops feed screw; alarms |
Feed hopper screw |
| Cryogenic mill — O₂ sensor |
O₂ > 1.5 % vol in exhaust |
Stops mill; vents N₂; alarms |
Exhaust duct |
| Cryogenic mill — low N₂ pressure |
N₂ pressure < 0.3 MPa |
Stops feed; maintains N₂ purge |
N₂ supply line |
| Cryogenic mill — door seal pressure |
Seal pressure < 0.1 MPa |
Does not start / stops mill |
Chamber door |
| Metal detector reject confirmation |
Reject signal not confirmed in 2 s |
Stops belt / conveyor downstream |
Metal detector exit |
9. Utility Requirements
| Utility |
Specification |
Connection |
Consumption (per line) |
| Electrical power |
380–480 V, 3-phase, 50/60 Hz |
Hardwired to MCC |
55 kW (peak, hammer mill); 80 kW (cryogenic) |
| Compressed air |
0.6–0.8 MPa, oil-free, dry (dew point −20 °C) |
¾″ NPT |
0.8 m³/min (pneumatic gates, metal ejector) |
| Liquid nitrogen (cryogenic mill) |
−196 °C, 99.99 % purity, 0.8 MPa max |
Vacuum-jacketed pipe, DN25 |
1,000 kg/MT product |
| Cooling water (cryogenic heat exchanger) |
10–20 °C, 0.3 MPa, SS304 line |
2″ flange |
30 L/min |
| Dust extraction |
100 m³/min at −3 kPa |
200 mm duct flange |
15 kW fan |
| Plant air ventilation (O₂ monitoring area) |
6 air changes/hr |
— |
5 kW fan |
10. Common Spare Parts List
| Part |
Part Number (Example) |
Qty in Stock |
Lead Time |
Criticality |
| Hammer set — AR400 (24 pcs) |
SB‑HAM‑24‑AR400 |
2 sets |
1 week |
High |
| Screen basket — 1.5 mm (SS304) |
SB‑SCR‑15‑304 |
2 |
2 weeks |
High |
| Screen basket — 3.0 mm (SS304) |
SB‑SCR‑30‑304 |
1 |
2 weeks |
Medium |
| Screen basket — 0.8 mm (SS304) |
SB‑SCR‑08‑304 |
2 |
2 weeks |
High |
| Disc mill disc pair (Ni-hard) |
MJZS‑80‑DISC‑PAIR |
1 |
8 weeks |
High |
| Pin mill rotor pin disc (complete) |
160UPZ‑ROT‑DISC |
1 |
10 weeks |
High |
| Pin mill stator pin disc (complete) |
160UPZ‑STAT‑DISC |
1 |
10 weeks |
High |
| Pin mill pin — WC-Co (single) |
160UPZ‑PIN‑WC |
100 |
1 week |
Medium |
| Cryogenic mill — shaft seal kit |
CG‑SEAL‑KIT |
2 |
4 weeks |
High |
| Cryogenic mill — PTFE door gasket |
CG‑GASK‑DOOR |
4 |
2 weeks |
High |
| Cryogenic mill — N₂ injection nozzle |
CG‑NOZ‑LN2 |
3 |
6 weeks |
Medium |
| Metal detector test wand set (Fe/SS/Cu) |
Safeline‑TEST‑SET |
2 |
1 week |
High |
| Mill motor — bearing set (SKF 6317 / 7317) |
SKF‑6317‑C3 |
4 each |
1 week |
Medium |
| VFD — spare drive (55 kW) |
Siemens G120 / ABB ACS880 |
1 |
4 weeks |
High |
| Food-grade grease — Klüber 4-302 |
— |
5 kg |
2 weeks |
Low |
11. Calibration Requirements
| Instrument / Device |
Range |
Standard |
Tolerance |
Calibration Frequency |
Responsibility |
| Mill tachometer (all mills) |
0–15,000 rpm |
Stroboscope |
±10 rpm |
6 months |
Maintenance |
| Feeler gauge (screen clearance / disc gap) |
0.05–2.00 mm |
Micrometer (NIST-traceable) |
±0.01 mm |
6 months |
QC |
| Sieve shaker (particle size QC) |
38 µm–4.75 mm |
ASTM E11 calibration sieves |
±2 % aperture |
12 months |
QC lab |
| Laser diffraction analyser (cryogenic QC) |
0.01–2,000 µm |
NIST SRM 114P |
±3 % d50 |
12 months |
QC / external lab |
| Cryogenic mill — Pt100 RTD |
−200 to +50 °C |
Ice-point + dry-well calibrator |
±0.5 °C |
6 months |
QC |
| Cryogenic mill — O₂ analyser |
0–25 % vol |
Certified calibration gas (1 % O₂ in N₂) |
±0.1 % |
3 months |
QC / external |
| Cryogenic mill — N₂ flow meter |
0–5 kg/min |
Coriolis master meter |
±0.5 % of reading |
12 months |
Maintenance |
| Metal detector (CCP-2) |
Fe ≥ 1.0 mm, SS ≥ 1.5 mm, Cu ≥ 1.5 mm |
Certified test wands (traceable to NIST) |
100 % detection at critical limit |
Start of each shift (function); 6 months (full cal) |
Operator (daily); OEM (annual) |
| Energy meter (kWh) |
0–100 kW |
Reference power analyser |
±0.5 % |
12 months |
Electrical tech |
| IR thermometer (product temp) |
0–100 °C |
Blackbody calibrator |
±1 °C |
6 months |
QC |
Document version: 1.0 — Author: Process Engineering — Approved: QA Manager