How to Choose Vibrating Screen Mesh and Aperture Size
- Vibrating Equipment Ltd
- Jul 27
- 7 min read
Choosing the correct screen opening is essential for achieving consistent particle separation.
An opening that is too large may allow unacceptable material to pass through. An opening that is too small may restrict capacity, increase blinding and remove usable product.
The phrase “mesh size” is commonly used, but it can be misleading. For industrial screening, it is usually better to specify the actual aperture in millimetres or micrometres.
Vibrating Equipment Ltd designs and manufactures custom vibrating screens and sieves for different material volumes, particle sizes and processing duties.
What is the difference between mesh count and aperture size?
Mesh count usually describes the number of openings across a particular linear distance, traditionally one inch.
However, mesh count alone does not define the exact opening.
The available opening depends on both:
The number of openings
The diameter of the wire
A thicker wire leaves a smaller clear opening than a thinner wire at the same mesh count.
For this reason, the required screening medium should preferably be specified using:
Aperture width
Wire diameter
Wire material
Type of weave
ISO 4783 provides guidance for selecting aperture and wire diameter combinations for industrial wire screens.
Specify the required aperture
The aperture is the clear opening through which the material must pass.
Large openings are normally expressed in millimetres. Openings below one millimetre are commonly expressed in micrometres.
ISO 565 provides recognised nominal opening sizes for metal wire cloth and perforated screening media. ISO 3310 Part 1 specifies technical requirements for metal wire cloth test sieves with apertures from 125 millimetres down to 20 micrometres.
Production screens do not always use laboratory test sieve construction, but laboratory sieve analysis is often useful for establishing the material’s particle size distribution.
Define what the screen must achieve
Before choosing an aperture, clearly define the screening objective.
Scalping
Scalping removes a relatively small amount of oversized material from the main product stream.
Examples include removing lumps, packaging fragments or oversized particles before processing.
Fines removal
Fines removal separates dust, crumbs or undersized particles from the main product.
This is common before weighing, packaging, optical sorting or further processing.
Grading
Grading divides material into two or more controlled size fractions.
A multiple deck screen may be required where several product grades are produced.
Safety screening
Safety screening removes unexpected foreign objects or agglomerated material before the product enters sensitive equipment.
Dewatering
A dewatering screen separates liquid from solid material.
Aperture selection must consider drainage, solids retention, screen inclination and the behaviour of the wet product.
Identify which fraction must pass
Confirm whether the valuable product should pass through the screen or remain above it.
This affects the machine layout and how the separation performance is assessed.
For example:
If fines are being removed, the main product may remain above the screen while fines pass through
If oversize contamination is being removed, the acceptable product may pass through while the contamination is retained
If the product is being graded, both fractions may be valuable
Specify the largest acceptable particle in the passing fraction and the smallest acceptable particle in the retained fraction.
Use representative particle size data
A single average particle size is rarely enough.
A representative sieve analysis can show how much material lies close to the intended separation point.
Particles close to the aperture size are more difficult to separate than particles that are clearly larger or smaller.
A material with a high proportion of near size particles may require:
More screen area
Better feed distribution
A thinner material bed
Additional residence time
A different vibration setting
A screen cleaning system
Always use a representative sample from normal production.
Consider particle shape
Screening does not depend only on nominal particle diameter.
Long, flat or irregular particles may pass through an opening when correctly orientated, even if one of their dimensions is larger than the aperture.
Examples include:
Plastic flakes
Wood chips
Metal stampings
Elongated grains
Fibre fragments
Flat pieces of recycled material
Where particle shape varies significantly, physical testing is strongly recommended.
Consider moisture and stickiness
Dry, free flowing materials usually screen more easily than damp or cohesive products.
Moist material can:
Adhere to the wire
Form lumps
Block apertures
Coat the screen surface
Carry fines with the oversize fraction
Reduce effective open area
If moisture varies, the screen should be assessed under the most difficult expected condition.
Wet screening may be appropriate for certain materials, but it changes the complete process and requires suitable water handling, drainage and downstream treatment.
Understand open area
Open area is the proportion of the screen surface available for material to pass through.
For woven wire mesh, open area depends on the aperture and wire diameter.
A thinner wire can provide more open area, but it may have lower strength and wear resistance. A thicker wire may last longer but reduce available screening area.
ISO guidance includes open area as an important consideration when selecting aperture and wire combinations for industrial screening.
The correct balance depends on:
Required capacity
Material impact
Abrasion
Screen tension
Required service life
Acceptable separation efficiency
Choose the appropriate screening medium
Woven wire mesh
Woven wire provides a wide range of fine and medium aperture sizes.
It often offers good open area and is widely used for grading, fines removal and general industrial screening.
The wire diameter and weave should suit the material and expected loading.
Perforated plate
Perforated plate provides a robust screening surface with round, square or shaped openings.
It is often selected for coarser material, high impact duties or applications requiring a rigid surface.
Polyurethane panels
Polyurethane may offer useful wear and noise characteristics in abrasive or wet applications.
Panel design, aperture shape and open area must be considered carefully.
Rubber screening media
Rubber media may reduce impact noise and resist certain abrasive materials.
It is generally used for heavier applications rather than very fine screening.
Wedge wire
Wedge wire can be used where drainage, dewatering or resistance to clogging is important.
The slot width and orientation must suit the product and required separation.
Prevent blinding and pegging
Blinding occurs when fine or sticky material covers the screen openings.
Pegging occurs when particles become trapped inside individual apertures.
Possible solutions include:
Changing the aperture shape
Changing the wire diameter
Adjusting vibration frequency or amplitude
Reducing the feed rate
Improving material distribution
Using ball cleaning decks
Using suitable screen cleaning devices
Drying or conditioning the feed material
Using a different screening medium
Introducing wet screening where appropriate
The cause should be identified before selecting a solution. Increasing vibration without understanding the material may increase wear or damage the product.
Consider screen area and bed depth
A correct aperture will not perform properly if too much material is placed on a small screen.
The feed should be distributed across the available width rather than concentrated in one narrow stream.
An excessive material bed can prevent smaller particles from reaching the screen surface. They may remain trapped above the deck and leave with the oversize material.
Screen area must therefore be selected from:
Required throughput
Bulk density
Particle size distribution
Aperture size
Open area
Moisture
Number of decks
Required separation efficiency
Consider a multiple deck screen
A multiple deck screen can produce several fractions within one machine.
For example:
The upper deck removes large oversize material
The middle deck produces the main product grade
The lower deck removes fines
Each deck must have sufficient area, and the discharge points must be arranged to prevent the separated fractions from mixing again.
A multiple deck machine can save floor space, but it may be more complex to inspect and clean.
Test the material before final selection
A laboratory sieve test is useful for understanding particle size distribution, but production screening introduces additional factors such as feed depth, vibration, material travel and continuous loading.
A representative machine trial can help confirm:
Required aperture
Expected capacity
Separation quality
Product damage
Likelihood of blinding
Suitable screen angle
Suitable vibration settings
Required deck area
Testing is particularly important for damp, irregular, fragile or near size materials.
Common screen selection mistakes
Ordering by mesh number alone
Mesh count without wire diameter does not fully define the opening.
Choosing the aperture from the average particle size
The complete particle size distribution and required product specification must be considered.
Ignoring open area
Two screens with the same nominal aperture may have different capacities because of wire diameter and construction.
Ignoring material shape
Flat or elongated particles can behave differently from spherical particles.
Using laboratory results as a guaranteed production capacity
Laboratory sieving identifies size distribution but does not reproduce every condition of an industrial screen.
Reducing the aperture without increasing screen area
A finer aperture generally places greater demand on the available screening surface.
Information required for a vibrating screen quotation
Provide:
Material description
Particle size distribution
Bulk density
Moisture content
Material temperature
Required throughput
Required separation point
Number of required fractions
Preferred screen medium
Construction material
Wet or dry operation
Available production space
Inlet and outlet positions
Cleaning requirements
Existing problems such as blinding or pegging
A representative material sample
Frequently asked questions
Is mesh count the same as aperture size?
No. Mesh count describes the number of openings across a given distance. The actual aperture also depends on wire diameter.
Should I specify a screen in millimetres or mesh?
Specifying the clear aperture in millimetres or micrometres is normally more precise.
Why does material larger than the aperture sometimes pass through?
Long or flat particles may orientate themselves and pass through. Worn or damaged mesh can also create oversized openings.
Why is my screen producing too much oversize material?
Possible causes include excessive feed depth, insufficient screen area, blocked apertures, poor feed distribution or a large proportion of near size particles.
Can one machine produce several grades?
Yes. A multiple deck screen can separate material into several fractions, provided each deck and discharge point is correctly designed.
Contact Vibrating Equipment Ltd
Vibrating Equipment Ltd manufactures bespoke vibrating screens and sieves for food, recycling, aggregates, chemical, plastics and general industrial applications.
Send your material details, required throughput and target separation size to discuss a suitable system.
Telephone: 0800 001 6520 Email: sales@vibratingequipment.co.uk
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