What Is Screen Blinding?
Screen blinding occurs when apertures in the screen panel become blocked by particles that are too large to pass through but lodge in the opening rather than being rejected over the screen surface. Once an aperture is blocked, that area of screen becomes inactive, reducing effective screening area and cutting screening efficiency dramatically.
Blinding is the most common problem with vibrating screens in mineral processing and is the primary reason screen efficiency drops below design. A screen that is 30% blinded will have its effective capacity reduced by approximately 30%.
Type 1: Near-Size Particle Blinding
Particles with dimensions very close to (but slightly larger than) the aperture size are the most likely to wedge and blind. They enter the aperture partway and become mechanically locked. This is called near-size or pegging blinding.
π‘ The Near-Size Rule
Particles between 0.75Γ and 1.25Γ the aperture size are "near-size" and are responsible for most blinding. On a 10mm aperture screen, particles from 7.5mm to 12.5mm are the problem particles. If your feed contains a high proportion of particles in this range, blinding will be severe regardless of screen type.
Type 2: Wet/Sticky Material Blinding
Wet, clay-bearing or naturally adhesive materials (certain iron ores, bauxite, laterite) form a paste that fills apertures from the top surface, gradually filling all openings until the panel is completely blocked. This type of blinding often occurs overnight when the screen is stopped β?the material settles into apertures and dries/sets.
Prevention: Use anti-blinding panel designs (see below). Install spray bars to keep feed material wet and fluid. Ensure screen is restarted and run for 5 minutes before stopping again.
Type 3: Inadequate Vibration Amplitude
The vibrating motion of the screen serves two purposes: conveying material over the surface and clearing particles from apertures. If vibration amplitude is too low β?due to bearing wear, unbalanced exciters, or incorrect counterweight setting β?particles are not ejected from apertures and blinding accumulates rapidly.
Prevention: Verify screen amplitude at four corners with a vibration meter. Design amplitude for mineral ore screens is typically 6β?0mm peak-to-peak. If below 4mm, investigate and restore exciter performance.
Anti-Blinding PU Screen Panel Designs
| Design | How It Works | Best For |
|---|---|---|
| Standard slot aperture | Elongated opening sheds particles better than round | General mineral screening |
| Crowned (domed) surface | Raised centre deflects near-size particles to edge | Near-size blinding problems |
| Dimpled / pyramid surface | Surface texture prevents flat particles from lying flat over apertures | Flat, platy particles |
| Flip-flow panels | Panel flexes with each vibration cycle, physically ejecting lodged particles | Wet, sticky, fine materials |
| Modular wedge-wire/PU hybrid | Self-cleaning wire sections with PU support | Dewatering of fine coal/mineral |
Aperture Size Selection to Minimise Blinding
Selecting the correct aperture size can significantly reduce blinding tendency:
- For a cut size of 10mm: use 10mm round aperture (maximum near-size blinding) OR use 12mm slot aperture (reduced blinding, slight efficiency loss)
- Slot apertures blind less than round apertures for the same cut size
- Square apertures have intermediate blinding tendency
- Open area should be maximised β?higher open area means more apertures, so even if some blind, total throughput is maintained
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