Background
An iron ore beneficiation plant in Minas Gerais, Brazil was processing fine iron ore concentrate through dewatering screens before the final filtering and pelletizing stage. The screens classified and dewatered iron ore fines at approximately 0.15mm cut point β a very fine aperture application.
The existing screen media was wedge wire stainless steel panels. In the acidic iron ore process water (pH 4.5β5.5), the stainless steel was corroding despite its grade. Panel life was 6β8 weeks. Additionally, the fine iron ore particles were pegging the wedge wire slots progressively β efficiency dropped measurably within 2β3 weeks of each panel change.
Challenge: Very Fine Aperture in Acidic Slurry
The 0.15mm (150 micron) cut point is at the fine end of PU screen panel capability. Standard PU panels are typically reliable from 0.5mm upward. Fine PU panels (below 0.5mm) require precision molding and specific PU formulation to maintain aperture accuracy at this scale.
The application required: - Aperture: 0.15mm slot - Chemical resistance to acidic iron ore process water (pH 4.5β5.5) - High G-force screen compatibility (the screens ran at 4.5G) - Cold-flex properties not required (Minas Gerais has a mild climate)
Solution
Fine-aperture PU panels specifically formulated for acidic wet fine mineral screening were trialed:
- 75 Shore A hardness (harder than standard 65 Shore A to maintain dimensional stability at 0.15mm aperture)
- Acid-resistant PU compound (polyester-based PU degrades in acid; polyether-based PU was specified for better acid resistance)
- Slot aperture orientation: perpendicular to ore flow direction to maximize open area and minimize blinding
- Panel dimensions: 305Γ305mm bolt-down to suit existing screen frames
Trial Results
One dewatering screen deck was converted to fine PU panels. The adjacent deck retained wedge wire for direct comparison.
Aperture maintenance: - Wedge wire: effective aperture increased from 0.15mm to approximately 0.22mm by week 4 due to corrosion enlarging the gaps - PU panels: aperture remained stable at 0.15mm throughout the 12-week trial (no corrosion)
Panel life: - Wedge wire: 6β8 weeks to replacement - PU panels: at 12-week inspection, approximately 25% wear β projected life 40β48 weeks
Dewatering efficiency: The stable PU aperture maintained consistent product moisture content throughout the trial. The wedge wire screen showed increasing product moisture from week 3 onward as apertures enlarged from corrosion, allowing finer water-bearing particles to pass.
Full Conversion
All dewatering screens were converted to fine PU panels. The benefits compound: consistent product quality (stable moisture content), longer panel life (6β8Γ improvement), and elimination of stainless steel corrosion as a maintenance issue.
The plant's metallurgist noted that the more consistent dewatering improved pelletizing feed quality β reduced moisture variability helped the pelletizing process maintain consistent green pellet strength.
Key Points
Corrosion destroys dimensional accuracy of metal screens. In acidic slurry, stainless steel screens lose their aperture precision through corrosion. PU panels maintain aperture accuracy because they don't corrode.
Polyether PU outperforms polyester PU in acidic environments. This is a compound chemistry detail that matters in acidic mineral processing. Standard PU panels may use polyester-based chemistry that degrades in acid. Specify polyether-based PU for acidic applications.
Fine aperture PU (below 0.5mm) requires specialist sourcing. Not all PU panel manufacturers produce fine apertures reliably. Confirm the manufacturer's track record with the specific aperture you need before committing.
Elephant Rubber supplied the fine-aperture PU dewatering panels for this project.