Stable grinding to 10‑50 μm feed size is critical pre‑condition before spheroidization / shaping. For natural flake graphite, this step liberates gangue impurities bonded to flake edges; for calcined coke (artificial graphite precursor), it breaks large angular particles and prepares proper particle‑size distribution for follow‑up rounding. Over‑fine particles (<10 μm) generate excessive ultrafine dust in spheroidization; particles larger than 50 μm cannot obtain good sphericity and reduce equipment service life. Closed‑loop impact grinding system equipped with dynamic air classifier is the mainstream industrial solution.
Overall Process Flow
Natural flake graphite
Flotation concentrate → initial sieving (−100 mesh, 150 μm) → drying → closed‑loop impact grinding with air classification → product D50 controlled 10‑50 μm → magnetic separation → feed to spheroidization host.
Artificial graphite (calcined coke)
Calcined coke lump → pre‑crushing to ≤5 mm → drying → closed‑loop impact grinding + dynamic classification → output 10‑50 μm powder → pre‑screening → magnetic separation → pitch mixing & spheroidization.
Important note: 10‑50 μm is the feed particle‑size window entering spheroidization unit, not final finished anode particle size.
Step‑by‑step grinding operation & key parameters
1. Feed preparation before grinding
- Natural flake graphite:
Initial sieve: −100 mesh (150 μm), remove large gangue and interlocked composite particles. Moisture ≤0.5 %. Feed D50:70‑110 μm. - Calcined coke for artificial graphite:
Pre‑crushed to ≤5 mm. Moisture ≤0.5 %. Remove tramp metal via pre‑magnetic‑separation to protect grinding rotor.
All material contact surfaces of grinding system adopt ceramic / polyurethane non‑metallic lining, avoid iron secondary contamination.
2. Closed‑loop impact grinding (core unit for 10‑50 μm output)
Impact grinding relies on high‑speed rotor impact, particle‑to‑particle collision and shear force to break raw material. The integrated dynamic air classifier continuously separates powder by particle size:
- Particles meeting 10‑50 μm range are discharged as spheroidization feed.
- Oversized particles (>50 μm) circulate back into grinding chamber for re‑grinding.
- Ultrafine fraction (<10 μm) is discharged as tailings via dust‑collector, prevent accumulation inside loop.
Adjustable key process parameters
- Rotor speed:
- Natural flake graphite: 2400‑4000 rpm. Higher speed produces finer powder; lower speed outputs coarser fraction.
- Calcined coke: 2800‑4200 rpm. Coke has higher hardness, needs relatively higher rotor speed.
- Dynamic classifier wheel speed: 1200‑2600 rpm
Classifier wheel speed is primary control for upper cutoff D97 ≤50 μm. Increase wheel speed → cut finer; reduce wheel speed → allow coarser particles pass. - System air volume: Match classifier speed. Too low air volume causes material accumulation; excessive air volume brings too many <10 μm ultrafine particles.
- Feeding rate: Stabilize constant feeding. Fluctuating feed rate will drift PSD outside 10‑50 μm target window.
Target particle‑size specification for spheroidization feed
| Index | Target Value |
|---|---|
| D50 | 18‑35 μm (most common production window) |
| D10 | ≥10 μm |
| D97 | ≤50 μm |
| Moisture | ≤0.5 % |
| Magnetic foreign substance | ppm‑level after magnetic separation |
For different anode design:
Fine‑grade spheroidization feed: D50 10‑20 μm; conventional grade: D50 20‑35 μm; coarse grade: D50 35‑50 μm. Adjust classifier wheel speed and rotor speed accordingly.
3. Post‑grinding treatment before spheroidization
- High‑intensity magnetic separation: Remove ferromagnetic wear debris generated in grinding process.
- Optional safety screening: 325‑mesh sieve to remove rare oversize grit.
- Silo buffer: Stabilize particle‑size consistency before feeding into spheroidization host. Do not feed material with wide PSD directly into spheroidization, which causes inconsistent sphericity and low yield.
Common production problems & troubleshooting
| Problem | Root Cause | Countermeasure |
|---|---|---|
| Too many particles＞50 μm in output | Classifier wheel speed too low; feeding overload; rotor wear | Raise classifier wheel speed; reduce feed rate; inspect rotor condition |
| Large amount of powder＜10 μm, high BET | Rotor speed too high; excessive air volume | Lower grinding rotor speed; tune down system air flow; increase ultrafine tailing discharge |
| Particle‑size drift batch‑to‑batch | Unstable feeding; raw feed size fluctuation | Install constant‑rate feeding device; stabilize incoming raw‑material particle‑size |
| Magnetic impurity rising | Steel lining wear inside grinding chamber | Replace with ceramic/polyurethane non‑metallic lining; regular magnetic separation |
| Material agglomeration during grinding | Feed moisture＞0.5 % | Improve upstream drying procedure, strictly control moisture ≤0.5 % |
Critical practical notes
- Do not pursue one‑pass grinding to reach 10‑50 μm. Closed‑loop circulation grinding is required. Single‑pass grinding creates wide particle‑size distribution.
- The 10‑50 μm is pre‑spheroidization feed size. After multi‑pass spheroidization, particle size will be further reduced to final anode D50 15‑18 μm.
- For natural flake graphite: Do not over‑grind below 10 μm, excess fine flakes greatly reduce spheroidization yield and raise BET value.
- For hard calcined coke: Avoid feeding particles larger than 5 mm into grinder; oversized feed accelerates rotor abrasion and introduces metal impurities.
