Screen blinding and pegging both reduce effective open area, but they are not the same problem. Blinding covers the screening surface with fine or cohesive material, while pegging occurs when near-size particles lodge inside the apertures.
The visible symptom may be reduced throughput, carryover, poor drainage or frequent cleaning, but the correct response depends on the obstruction mechanism and the operating conditions that created it. This guide explains the common causes and the information that should be reviewed before media or operating changes are proposed.
Blinding and Pegging Are Different Problems
| Condition | What happens | Typical evidence |
|---|---|---|
| Blinding | Fine, moist, sticky, fibrous or cohesive material covers the panel surface and prevents feed from reaching the openings. | A coated or smeared surface, reduced drainage, build-up across multiple apertures and frequent cleaning. |
| Pegging or plugging | Near-size particles become lodged within individual apertures. | Particles visibly trapped in openings, local blockage aligned with aperture shape and repeated lodging after cleaning. |
| Combined condition | Surface build-up and lodged particles occur together. | A coated deck with individual near-size particles retained in the openings beneath or within the build-up. |
The terms are sometimes used loosely in plant discussions, but the distinction matters. A change intended to release a lodged particle may not address cohesive fines covering the surface. Likewise, adding water to a pegging problem may not correct an aperture geometry mismatch.
Why Blinding and Pegging Affect Screening Performance
Both conditions reduce effective open area. When openings are covered or blocked, undersize material has fewer opportunities to pass through the deck. Fines may remain in the oversize stream, recirculating load may increase and the screen may become a process bottleneck.
The consequences depend on the circuit. A trash screen may lose drainage and require repeated cleaning. A sizing screen may carry undersize material forward with the oversize fraction. A crushing circuit may return more material for reprocessing. These effects should be confirmed with site data rather than assumed from the appearance of the panels alone.
Moisture, Clay and Cohesive Fines Can Cause Blinding
Moisture can cause fine particles to adhere to each other and to the screening surface. In a dry-screening duty, damp fines may smear across the deck instead of dispersing and passing through the apertures. Clay-bearing or sticky material can create a continuous layer that covers otherwise suitable openings.
Water is not automatically a problem or a solution. In wet screening, correctly applied water may help material move and keep openings clear. Poor water distribution, excessive water in the wrong location or insufficient drainage can create different build-up conditions. The review should consider how the material behaves with the actual water load and spray arrangement.
Fibrous material can also bridge across openings or collect on the surface. The Bell Creek case shows why the material itself and the drainage requirement must be understood before an aperture arrangement is selected.
Review
- Moisture variation during normal operation
- Clay, fibre or sticky fines in the feed
- Whether build-up smears, cakes or bridges across openings
- Water addition rate and spray distribution
- Drainage direction and standing water
- Changes in behaviour between dry and wet conditions
Near-Size Material Is a Common Cause of Pegging
Pegging risk increases when a large proportion of the feed is close to the aperture dimension. These particles can enter an opening but fail to pass completely, becoming wedged in the aperture. Particle shape and orientation influence whether the material lodges or releases.
A nominal aperture that appears correct for the required cut can still peg if the near-size fraction is high or the geometry does not suit the particle shape. The answer is not automatically a larger opening because a larger aperture may change the product specification or allow oversize material to pass.
A recent particle size distribution is therefore important. It should be considered with photographs of the lodged material, aperture orientation and the required product cut.
Review
- Percentage of feed near the cut size
- Particle shape, including flat or elongated material
- Aperture size, shape and orientation
- Whether lodged particles are consistent in size and shape
- Product specification and acceptable misplaced material
- Changes in crusher settings or upstream feed preparation
Bed Depth and Feed Distribution Influence Build-Up
Excessive bed depth can limit stratification and trap fines above the screening surface. The lower layers remain under pressure while undersize particles struggle to reach available openings. Local overloading can also compact moist or cohesive material against the deck.
Uneven feed distribution creates different conditions across the screen width. One section may carry a deep, overloaded bed and develop blinding or pegging while another section remains underused. This can produce uneven wear and make a deck-wide open-area percentage misleading.
A very shallow or unstable bed can also affect separation. The aim is a balanced material presentation that supports stratification and uses the available deck area consistently.
Review
- Feed presentation across the width of the screen
- Bed depth from feed end to discharge end
- Local lanes of build-up or concentrated impact
- Changes in feed rate during the shift
- Rolling, surging or unstable material movement
- Wear patterns that indicate uneven loading
Screen Motion Affects Particle Release
Screen motion influences stratification, particle presentation and the ability of lodged material to release. If motion is inadequate or inconsistent, material may compact, fines may remain on the surface and near-size particles may not clear the apertures.
A media change should not be used to mask a mechanical or operating problem. Stroke, speed, direction of motion, deck angle and machine condition should be checked against the screen manufacturer’s requirements by appropriately qualified personnel.
Evidence to record
- Whether build-up is uniform or concentrated in specific areas
- Any change in performance after maintenance or operating adjustments
- Screen speed, stroke and motion data where available
- Loose panels, damaged supports or uneven panel seating
- Whether two comparable screens behave differently under similar feed conditions
Aperture Geometry Can Increase or Reduce Pegging Risk
Aperture size is only one part of the opening. Shape, orientation, bridge geometry, relief angle, panel thickness and particle pathway influence how material enters and leaves the aperture. Two openings with the same nominal dimension can behave differently in the same feed.
Square openings are often a starting point where product control is important. Slotted openings can support drainage or directional material behaviour, depending on orientation. Flexible or specialised designs may help release near-size particles in selected duties. None of these options is universally correct.
The screening problem should guide the aperture discussion. Persistent plugging may justify reviewing geometry and flexibility. Slow drainage may require a different orientation or opening style. Off-spec product may indicate that an apparently open design is allowing unsuitable particle orientations to pass.
Media Flexibility Can Influence Material Release
Different media materials and formulations respond differently under vibration and load. A more flexible panel or bridge can create secondary movement that may help release lodged near-size particles or disrupt surface build-up in a suitable application.
More flexibility is not automatically better. The panel must still maintain the required opening, support the material load, resist the wear environment and provide acceptable product control. A formulation selected for release behaviour in one zone may not suit a high-impact or heavily abrasive zone.
The material decision should therefore consider flexibility, aperture design, wear, moisture, impact and deck position together.
Wear Can Change Aperture Behaviour
As media wears, aperture edges can round, bridges and margins can lose support and the opening can deform. These changes may affect particle release, product sizing and the way near-size material lodges in the panel.
A panel should not be assessed only by the amount of material remaining. Inspect whether the aperture still retains its intended geometry, whether panel movement has changed and whether support wear is affecting seating or flexibility.
Review
- Rounded or distorted aperture edges
- Cracked, torn or sagging panels
- Worn bridge and margin areas
- Loose panels or damaged fastenings
- Material packed beneath panels
- Worn stringers, rails or fastening points
- Changes in blinding or pegging through the wear cycle
Distinguish the Symptom Before Selecting a Solution
| Observed condition | Likely mechanism to investigate | Start by reviewing |
|---|---|---|
| Fine material coats the deck surface | Blinding | Moisture, clay, fibre, material adhesion, water distribution, media surface and feed loading. |
| Individual particles are trapped in openings | Pegging or plugging | Near-size fraction, particle shape, aperture geometry, orientation, flexibility and wear. |
| Build-up is concentrated on one side | Uneven feed or local overloading | Feed presentation, bed depth, screen level, sprays and support condition. |
| Standing water accompanies build-up | Restricted drainage | Aperture orientation, water load, blocked openings, panel layout and downstream drainage. |
| Condition worsens as panels wear | Changing aperture or panel behaviour | Edges, bridges, margins, formulation, seating, fastening and replacement timing. |
| Frequent cleaning restores performance briefly | Recurring root cause remains | Material condition, aperture/media match, feed distribution, motion and operating variability. |
The table identifies review areas, not a diagnosis. More than one mechanism may be present.
Corrective Action Should Follow the Root Cause
Confirm the obstruction
Determine whether the condition is surface blinding, aperture pegging or a combination. Record photographs during operation and shutdown where possible.
Review the feed
Check moisture, clay, fibre, particle shape, near-size fraction and any recent upstream changes.
Review operating conditions
Assess feed distribution, bed depth, water application, screen motion and whether the condition changes through the shift.
Review aperture and media
Compare the required cut with aperture geometry, orientation, panel flexibility, formulation and wear condition. Do not increase opening size without considering product control.
Review the complete deck
Identify whether different zones need different priorities and whether supports, fastenings or panel seating contribute to the condition.
Validate the change
Track effective open area, throughput, product sizing, recirculating load, drainage, cleaning frequency and panel wear against the agreed objective.
Published Examples of Blinding and Plugging Solutions
The following results were reported by Polydeck for the named applications. They are not Carmaky project results and are not predictions or guarantees for another screen.
Bell Creek Gold Mine
Polydeck reports that fibrous blasting residue was blinding trash circuit screens. A POLYDEX arrangement using slotted and VR apertures was applied. Reported results included a 32% throughput increase, more than 2.5 times improvement in drain rate and the ability to bypass the secondary trash screen.
Toquepala Mine
Polydeck reports that a media-only retrofit using POLYDEX MAXI on the top deck and RUBBERDEX on the bottom deck reduced plugging from 24% to 6.4% and increased undersize throughput by 3%.
How Polydeck Approaches Blinding and Pegging
Polydeck evaluates blinding and pegging as application problems rather than treating them as reasons to replace one material with another automatically. The review considers feed characteristics, near-size content, moisture, bed depth, feed distribution, vibration, aperture geometry, formulation, flexibility, deck zones and support condition.
Polydeck’s range includes polyurethane, rubber and wire options with different aperture and formulation choices. Carmaky works with clients to organise the application information before discussing a Polydeck media or deck solution.
Blinding and Pegging Review Checklist
- Is the surface covered, are particles lodged in apertures, or are both conditions present?
- What material is creating the build-up or blockage?
- What are the feed size distribution and near-size fraction?
- How do moisture, clay, fibre and water addition change during operation?
- Is feed distributed across the full deck width?
- Where is bed depth excessive or unstable?
- Are screen motion and machine condition within the required operating range?
- What are the aperture size, shape, orientation and current wear condition?
- Does media flexibility suit the duty without compromising product control or strength?
- Are panels, fastenings and supports correctly seated and serviceable?
- What throughput, product, recirculating-load, drainage and cleaning data are available?
This checklist supports an application review and does not replace a site-specific technical assessment.
Related Screen Media Resources
How Open Area Affects Screening Throughput
How blocked or underused openings affect usable screening area and passage opportunities.
Understanding Screen Media Selection
The application information needed before media and aperture options are recommended.
Polyurethane vs Rubber Screen Media
A practical material comparison with application-specific qualifications.
Review a Blinding or Pegging Problem
Share the current panel arrangement, feed information and operating symptoms with Carmaky for an application-specific discussion, or use the Screen Panel Questionnaire to organise the information for review.