What are Forming Wires / Fabrics?
Forming fabrics (wires) are continuous synthetic mesh belts installed in the wire section of a paper or board machine.
Belt receive pulp slurry (≈99% water + fibers) from Head Box, water drain through the mesh belt by gravity and vacuum, and form the wet paper/board web. Their performance directly affects quality, drainage, runnability, sheet formation, and machine uptime.
Key Role:
a) Support pulp as it exits headbox.
b) Enable rapid water removal by gravity and vacuum.
c) Provide uniform fiber distribution → better paper/board strength and surface.
d) In a multi-wire board machine, multiple forming fabrics operate simultaneously or in staged formers to handle heavier board grades and higher production speeds.
Importance & Benefits
Sheet Quality: Correct weave gives uniform fiber distribution and reduced machine direction/ cross direction variation.
Dewatering Efficiency: Proper drainage improves production speed and lowers energy cost in pressing/drying. Durability & Life: Good fabrics resist abrasion, hydrolysis, and breakage — lowering downtime.
Runnability: Stable machine operation without breaks and increases productivity.
Specifications
Forming fabric specs vary by machine speed, stock type, and paper/board grade. Here are typical parameters:
1. Material
Polyester (PET): Most common due to high dimensional stability, strength, low stretch.
Polyamide (PA): Sometimes used for enhanced abrasion resistance (but absorbs moisture more).
2. Layers / Construction
Single Layer: Simple, less costly, suitable for low-to-medium speeds. Double Layer: Better stability and wear resistance. 2.5 Layer: Extra fine top for good fiber support + wear resistance.
Triple Layer / SSB (Sheet Support Binding): Best formation, high speed, improved retention & low wire marking — suited for heavy packaging board machines
3. Performance Parameters
Mesh/Weave: Determines drainage and fiber support.
Fibre Support Index (FSI): Higher = better sheet support.
Drainage Index (DI): Higher = more efficient water removal.
Tensile Strength: Depends on machine speed and l Dimensional Stability & Low Elongation: For consistent runnability.
How to Select Forming Wire (Fabric)?
Forming wire selection must balance formation, drainage, strength, and life. There is no “one-type-fits-all” wire.
A. Key Inputs You Must Define First
Before finalizing a fabric, always freeze these:
1.Machine related
Machine speed (m/min)
Former type (Fourdrinier / DuoFormer / Multi-wire gap former)
Vacuum capacity & dewatering elements
Wire tension limits
2.Stock related
Fiber type (Virgin / Recycled / Mixed)
Fines & ash %
Retention aid program
Layer consistency at head box
3.Product related: 1. GSM range. 2. Surface quality requirement. 3. Strength vs bulk priority
B. Core Selection Parameters
1. Fabric Layer Construction
| Fabric Type | When to Use | |
| Single layer | Low speed, coarse furnish, bottom layers | |
| Double layer | Moderate speed, better wear resistance | |
| 2.5 layer | Board machines – balance of drainage + formation | |
| Triple layer / SSB | High speed, top layer, printing surface | |
Rule: Higher layer count → better sheet support, less wire marking, higher cost.
2. Fiber Support Index (FSI)
High FSI = better fine fiber retention & smoother sheet
Needed for top layers and coated boards
Less critical for back or filler layers
3. Drainage Index (DI)
High DI = faster water removal
Needed for recycled fiber & high ash furnishes
Too high DI → formation issues
4️. Wire Marking Sensitivity
Printing or coated boards → fine surface weave
Kraft / liner → marking less critical
5️. Wear & Lifetime
Abrasive furnish → thicker wear side yarn
High vacuum → stronger base fabric
Forming Wires for Different Layers in Multi-Wire Board Machine
In a multi-layer board machine, each layer has a different job, so wire design must be different.
1. Top Layer (Surface / Printing Layer)
Function: 1. Visual appearance. 2, Printability. 3. Coating hold-out
Fabric Requirement
| Parameter | Preferred |
| Fabric type | 2.5 layer / Triple layer (SSB) |
| Fiber support | Very high |
| Drainage | Moderate (controlled) |
| Wire marking | Minimum |
| Yarn diameter | Fine on sheet side |
Reason
Prevents fiber penetration
Gives smooth surface
Improves coating uniformity
Single layer fabrics on top layer to be avoided (leads to roughness & wire marking)
2. Middle Layer (Bulk / Strength Layer)
Function: 1. Thickness (caliper). 2. Internal bonding. 3. Cost control
Fabric Requirement
| Parameter | Preferred |
| Fabric type | Double layer / 2.5 layer |
| Fiber support | Medium |
| Drainage | High |
| Wire marking | Not critical |
Reason
Faster drainage allows higher machine speed
Coarser structure improves bulk
3. Back Layer (Bottom / Reverse Side)
Function: 1. Support. 2. Stiffness. 3. Often hidden side
Fabric Requirement
| Parameter | Preferred |
| Fabric type | Single layer / Double layer |
| Fiber support | Low–Medium |
| Drainage | Very high |
| Wear resistance | Very high |
Reason:
Heavy recycled fiber needs fast drainage
Wear is maximum on bottom wires
Cost-effective solution
Common Selection Mistakes:
Same wire specification used for all layers
High drainage wire on top layer → poor formation
Over-fine fabric on recycled back layer → blinding
Ignoring vacuum capacity while selecting fabric
Simple Thumb Rules for forming wire selection:
Top layer = formation first, drainage second
Middle layer = balance of drainage & bulk
Back layer = drainage & wear life first
Higher ash/fines → higher FSI needed
Higher speed → higher layer construction required
When to Change Forming Wire Design
Change fabric if you see:
Persistent wire marking
Poor formation despite chemistry
Frequent wire cleaning issues
High vacuum load but slow drainage
Sheet crushing or delamination
Forming Fabric (Wire) Manufacturer and Supplier
Indian Supplier: 1. Wire and Fabriks, 2. Shalimar wires, 3. Voith
International Supplier: 1. Heimbach, 2. Astenjohnson, 3. Albany.
Conclusion
successful forming wire selection depends on understanding machine capability, furnish characteristics, and end-product requirements together. Applying clear thumb rules—formation first on top layer, balanced design in middle layer and back layer for drainage & durability