Critical rule: control particle temperature, not only hot‑air inlet temperature. Free surface moisture evaporates near 100 °C; crystal‑water starts slow surface dehydroxylation above 160‑180 °C, ruining LOI, flame‑retardant and electrical performance. Cable‑grade ATH target LOI ≥34‑35 %.
Recommended particle temperature (real powder temperature)
- Optimal working window: 100‑120 °C (best for cable‑grade / flame‑retardant ATH)
- Upper safe limit: ≤140 °C (short‑term peak; avoid sustained residence above 140 °C)
- Risk zone: >160 °C → partial crystal‑water loss, LOI drop, even with no visible color change.
For ultrafine / sub‑micron ATH (from wet bead mill): prefer 90‑110 °C, to minimize hard irreversible agglomerates.
Parameter reference for different dryer types
1. Tray / vacuum dryer (filter cake, lab‑pilot)
- Vacuum drying: 90‑110 °C, moderate vacuum.
- Remove free moisture, keep crystal‑water intact; low agglomeration for sub‑micron batches.
2. Flash dryer (typical upstream of dry grinding line, filter‑cake ATH)
- Outlet material temperature: 100‑120 °C.
- Inlet hot‑air can be higher, but short residence time; monitor powder outlet temperature, not inlet air.
- Final residual free‑moisture target ≤0.3 % for feeding into ACM / ring‑roller mill.
3. Spray dryer (for wet‑bead‑milled sub‑micron ATH slurry)
Evaporative cooling keeps particle much cooler than inlet air.
- Inlet air: 160‑190 °C
- Outlet air temperature: 95‑110 °C (main control set‑point)
- Never allow outlet air >120 °C for cable‑grade ATH. Higher outlet creates hard agglomerates and risk of local dehydroxylation.
Common industrial mistakes
- Only watch hot‑air inlet temperature, ignore actual particle/outlet‑air temperature. High inlet air is acceptable only with very short residence time and strong evaporative cooling.
- Material dead‑zones inside dryer: ATH stays long‑time at elevated temperature → local over‑decomposition, even if average sensor reading looks good.
- Pushing temperature higher to speed‑up drying; faster drying creates harder agglomerates for ultrafine grades.
Practical quality‑check indicators
Even temperature sensors look normal, verify:
- LOI of final powder: LOI drop signals hidden thermal decomposition.
- Powder oil‑absorption: sharp rise indicates heavy agglomeration from too‑aggressive drying.
Quick summary table
| ATH Product Grade | Target Particle Temperature | Max allowable particle temperature | Notes |
|---|---|---|---|
| Cable‑grade flame‑retardant ATH | 100‑120 °C | 140 °C | Preserve LOI ≥34‑35 % |
| Ultrafine / sub‑micron ATH (wet‑process) | 90‑110 °C | 120 °C | Minimize hard agglomerates |
| General‑grade filler ATH | 100‑130 °C | 140 °C | Not for high‑performance cable |
Core takeaway: Set your control target on powder/outlet‑air temperature, not heater‑inlet setpoint. Residence time is equally important as temperature.
