An airlaid web can meet its average mass target while one side remains too light. It can also feel thick yet lose strength when wet. These are different problems, so a useful process review must connect fibre delivery, web formation, bonding and the intended end use.
The airlaid nonwoven process uses air to carry fibres onto a collecting surface. This guide focuses on short-fibre webs, including pulp blends used in absorbent products. It follows the material through the line and shows how to check the results. The worked figures are invented teaching examples, not machine settings or product limits.
Understand what the airlaid process actually controls
EDANA's manufacturing overview separates web formation from bonding and later treatment. In short-fibre airlaid forming, air delivers fibres to a forming head and then to a moving belt. The loose web still needs a suitable bonding route before it becomes a useful fabric.
That distinction matters when choosing equipment. A forming system may spread a blend well but cannot, by itself, prove wet strength, low lint or fluid handling. Those outcomes also depend on the materials, bonds and later treatment. Ask which part of the process each supplier's result describes.
Airlaid is also a broad family name. Short-pulp forming and systems for longer textile fibres do not share every operating limit. A fibre length, line speed or weight range from one machine should not become a general rule for the whole field.
In this guide, machine direction means the direction of web travel. Cross direction means across the width. The terms help locate a problem: a narrow weak band running along the roll calls for a different investigation from a brief fault across the entire width.
Follow the fibre from feedstock to wound roll
Start with the raw material specification. Identify the pulp grade, other fibres, binder components and any added powder. Record the moisture basis, lot numbers and storage condition. A delivery that looks unchanged can still alter the balance if its moisture or composition differs.
Pulp sheets need to be separated into fibres before forming. The ANDRITZ airlaid overview describes defibration, forming, drying and fibre recycling as distinct parts of its systems. Its equipment also supports different bonding routes and the addition of suitable powders.
At the forming stage, compare what enters the system with what reaches the web. Feed settings alone do not measure retained material. Collected dust, rejected lumps, recycled fibre and stock remaining inside the line can explain a gap between the two.
The ANDRITZ technical brochure describes a drum system that draws the fibre mixture onto a wire with suction. It also shows how several forming heads can create layers with different functions. This is one documented equipment design, not a description of every airlaid machine.
After forming, the chosen bonding and drying stages must suit the web. Measure the final state at a named point, such as before winding or after a defined conditioning step. Compaction, moisture change and stretching can make results from different points hard to compare.
Record roll identity from the start of the trial. A test result without its time and position cannot reliably locate the material that needs a hold, a repeat check or release.
Define the product before choosing the recipe
An absorbent wipe, a pad core and a filter do not need the same balance of properties. Write the end-use requirements before adjusting the fibre blend. Otherwise, a trial can improve one easy-to-measure result while damaging the function that matters most.
For a wipe, consider wet integrity, surface lint and how it handles its intended liquid. For a layered absorbent structure, distinguish liquid entry, movement through the structure and storage. For a filter, fabric weight alone says little about the required filtration performance.
Create a short specification with three parts. First, state the composition and physical dimensions. Next, list the relevant performance tests and conditions. Finally, define the decision rule, including any separate limits for local results and averages.
Agree what a composition percentage means. A dry-mass percentage differs from a percentage of material delivered to the factory. A binder percentage based on the finished web also differs from binder add-on based on the fibres alone.
Keep liquids and solids in separate columns on the trial sheet. For a liquid binder, record both its delivered mass and its solids fraction. This makes the recipe easier to scale and prevents water from being counted as lasting fibre or binder mass.
Calculate the retained mass needed at line speed
Consider an ideal steady run with a full web width of 2.00 m and a speed of 30 m/min. The target is 90 g/m² on a dry-solids basis. Assume the width and speed refer to the same measurement point, with no change in area between that point and the dry-mass measurement.
Area produced per hour = width × speed × 60.
Area = 2.00 × 30 × 60 = 3,600 m²/h.
Retained dry mass per hour = area × target mass per area ÷ 1,000.
Retained dry mass = 3,600 × 90 ÷ 1,000 = 324 kg/h.
The factor 1,000 converts grams to kilograms. This result is the dry material retained in the full-width web. It is not automatically the total raw feed rate, the saleable output or the wet mass leaving a binder pump.
Suppose the retained dry recipe contains 70% pulp, 15% bonding fibre and 15% latex solids. The components then balance as follows.
Retained dry component | Share of final dry web | Required rate |
|---|---|---|
Pulp | 70% | 226.8 kg/h |
Bonding fibre | 15% | 48.6 kg/h |
Latex solids | 15% | 48.6 kg/h |
Total | 100% | 324.0 kg/h |
The pulp and bonding fibre together contribute 275.4 kg/h, equivalent to 76.5 g/m² at this area rate. The latex adds 13.5 g/m² of dry solids. Their sum gives the target of 90 g/m².
These figures assume full retention and no other solid component. An actual feed plan must account for measured losses, recycle flows and any carrier sheet. Include the carrier once in the mass balance, with a clear statement of whether it is part of the product target.
Keep moisture, binder solids and add-on separate
Suppose the incoming pulp contains 8% water by its delivered mass. Its dry fraction is therefore 0.92. To supply the example's 226.8 kg/h of dry pulp with full retention:
Delivered pulp rate = 226.8 ÷ 0.92 = about 246.52 kg/h.
This is a wet-basis moisture calculation. If a supplier states moisture regain on a dry-fibre basis, that value needs a different conversion. Always identify the denominator before adjusting the feeder.
Now suppose the latex contains 50% solids by mass. With full solids retention, 48.6 kg/h of dry binder requires 48.6 ÷ 0.50 = 97.2 kg/h of liquid latex. The remaining 48.6 kg/h is the non-solid portion of that delivered material. This simple balance does not establish a drying duty or a curing recipe.
The binder is 15% of the final dry web, but its add-on relative to the dry fibres is different:
Binder add-on = 48.6 ÷ 275.4 × 100 = about 17.65%.
Both percentages describe the same example. They differ because one divides by the final web and the other by the fibres before binder addition. A trial report should name that basis beside the value.
If line speed rises to 36 m/min while width and retained mass stay fixed, the area rate becomes 4,320 m²/h. The dry basis weight falls to 324 × 1,000 ÷ 4,320 = 75 g/m². Holding 90 g/m² at the higher speed would require 388.8 kg/h retained dry mass, a 20% increase.
That calculation says nothing about whether the forming, bonding or drying equipment can handle the change. Each part still needs a trial within its approved operating range.
Measure the width profile instead of trusting the mean
Take a separate illustrative sampling exercise. All specimens have equal area and use the same agreed conditioning and test basis. Five positions run from left to right across the web. These five positions explain the calculation; they are not a standard sampling plan.
Position across the web | Profile A, g/m² | Profile B, g/m² |
|---|---|---|
Left | 74 | 88 |
Left centre | 86 | 89 |
Centre | 92 | 90 |
Right centre | 98 | 91 |
Right | 100 | 92 |
Arithmetic mean | 90 | 90 |
Both sets total 450 g/m² across their five readings. Yet profile A ranges from 74 to 100, while profile B ranges from 88 to 92. The identical mean hides a large difference in local mass.
NIST defines the sample coefficient of variation as the sample standard deviation divided by the mean. For these positive mass measurements, express that ratio as a percentage:
CV% = sample standard deviation ÷ mean × 100.
For profile A, subtract 90 from each reading, square the differences and add them. The total is 440. Divide by 5 − 1, then take the square root. The sample standard deviation is about 10.49 g/m², giving a CV of about 11.65%.
For profile B, the sum of squared differences is 10. Its sample standard deviation is about 1.58 g/m², and its CV is about 1.76%. Keep unrounded values during calculation before rounding the final results.
The CV describes these readings. It does not establish a lot acceptance rule or prove stable production. Also retain the positions: a left-to-right rise may suggest a distribution issue that the single CV cannot locate.
Repeat the agreed profile checks over time and across relevant rolls. Distinguish changes across the width from changes along the roll. Pooling both into one number can hide the pattern needed to guide an investigation.
For specimen preparation and basic unit checks, see ApparelDiary's fabric GSM testing guide. Apply a nonwoven method when the product requires it.
Keep layer mass separate from blend composition
A layered web adds another set of denominators. Suppose a development design assigns 20 g/m² to an upper layer, 50 g/m² to a middle layer and 20 g/m² to a lower layer. The total is 90 g/m². These are hypothetical final dry-layer contributions, with no separate carrier outside the stated total.
At the earlier area rate of 3,600 m²/h, the layers require 72, 180 and 72 kg/h of retained dry material. Together they still total 324 kg/h. The middle layer accounts for 50 ÷ 90 × 100, or about 55.56%, of that dry mass.
This layer split does not establish the pulp or binder share within each layer. A complete design needs both the layer allocation and the composition of each layer. Keep those entries in separate parts of the recipe, then check that their totals agree.
Also state where binder is counted. If a later application adds dry solids across the structure, it must appear somewhere in the final layer balance. Do not add it to a layer target that already includes it and then count it again in the total web.
An attractive layer diagram is a design proposal, not proof of fluid performance. Trial the complete structure and examine whether the intended functions survive bonding and converting. Where layers cannot be separated cleanly for measurement, record that limitation instead of presenting a guessed layer mass as a measured result.
Choose bonding for the required performance
The ANDRITZ brochure describes several routes. Latex bonding applies binder and then dries and cures it. Thermal bonding uses suitable fusible components within the blend. Multi-bonding combines routes, while suitable composite structures can use hydroentanglement. Its hydrogen-bonding route uses a combination of pressure, moisture and temperature. Source: airlaid bonding options.
Choose a route through evidence from the intended product. A stronger dry specimen does not settle whether a wet wipe sheds fibres. A soft pad does not settle whether its layers remain intact during converting. Test those outcomes directly under agreed conditions.
Treat a change in binder type as a material change, even when its nominal percentage stays the same. Obtain its technical data and current safety information. Supplier instructions, equipment limits and product requirements should govern the trial, rather than a generic temperature found in an unrelated example.
Record the route and actual conditions with each sample. Without those details, a useful result may be impossible to reproduce or explain when production later changes.
Separate thickness, density and directional strength
Thickness depends on how the web is measured. ISO 9073-2:1995 addresses nonwoven thickness under specified pressure. An unloaded impression of loft should not be compared directly with a compressed test result.
For an illustrative specimen on one consistent test basis, suppose basis weight is 90 g/m² and measured thickness is 1.50 mm. The apparent bulk density is:
Density = 0.090 kg/m² ÷ 0.00150 m = 60 kg/m³.
If the same basis weight is measured at 1.00 mm under another condition, the calculated density becomes 90 kg/m³. That change does not prove that more fibre has entered the specimen. The volume used in the calculation has changed.
Do not turn apparent density into a porosity percentage without the material information and assumptions needed for that calculation. A blend, coating or carrier can make a single solid-density assumption unsuitable.
Random fibre placement also does not guarantee equal finished strength in every direction. Compare machine and cross directions using the same method and specimen basis. If illustrative breaking forces are 36 N and 30 N, their machine-to-cross ratio is 1.20. It is a directional comparison, not a safety factor or an acceptance limit.
Preserve the individual force results with the ratio. Two fabrics can have equal ratios while differing greatly in the force required to break them.
Match each test to a clear question
Use ISO 9073-1:2023 as a reference for nonwoven mass per unit area. For breaking force and elongation, ISO 9073-3:2023 covers the strip method in conditioned or wet states. Its catalogue also identifies a corrected version from 2025. Specify the applicable text and test conditions in the laboratory request.
Absorption needs special care. ISO 9073-6:2025 covers liquid absorbency time, capacity and wicking, but excludes fabrics containing superabsorbent materials. Do not cite it as evidence that such a product passed an applicable absorption method. Select a suitable method for that material and intended use.
Speed of liquid entry and amount retained answer different questions. A product may accept liquid quickly yet fail a later retention requirement. Define the liquid, dose, timing, applied load and other relevant conditions in the chosen test arrangement rather than using the word “absorbent” alone.
For dry lint, ISO 9073-10:2003 provides a relevant nonwoven test scope. Dry lint results should not silently stand in for wet-use shedding. Add the appropriate end-use check when the product will be used wet.
The public catalogue descriptions identify scope; they do not supply every laboratory instruction. Use the full applicable method for a conformity claim, and label developmental checks clearly when they use a different procedure.
Investigate faults with a controlled comparison
When a width profile is uneven, first check the measurement and sample map. Then review the relevant feed distribution, forming condition and collection system with the equipment team. Do not assume that adding total fibre will correct a narrow weak band; it may raise the already heavy areas too.
For visible lumps, retain specimens and inspect the upstream material and opening stage. Check whether the fault follows a raw-material lot or a change in operation. If it occurs at regular intervals, retain the time and spacing rather than describing it only as “occasional.”
When strength changes without a large basis-weight shift, compare blend identity, bonding records and test conditions. A mass result cannot show whether the correct binder reached every location. Keep wet and dry results distinct while reviewing the evidence.
Avoid changing feed, speed, suction and bonding conditions together without a planned experiment. Even if the result improves, the team may not know which change caused it. Start with a reasoned hypothesis and a safe, approved trial, then retain both successful and unsuccessful results.
Review hazards before the work starts. OSHA identifies paper and pulp among materials that can present combustible-dust hazards. The actual material and process require a suitable site assessment. Guarding, isolation, extraction and maintenance controls belong in the approved operating system, not in improvised adjustments during a trial.
For binder changes, ApparelDiary's guide to reading a safety data sheet for chemical trials helps connect supplier information to the planned work.
Turn a good trial into a repeatable product
A trial record should connect the recipe to the physical roll and its test results. Keep the raw-material lots, retained-mass basis, key process records, sampling map and test methods together. Record when the line changed from start-up to the defined trial condition.
Before comparing two settings, define what would count as a useful improvement. It might be a smaller width difference while wet strength stays above an agreed limit. This gives the team a balanced decision instead of a search for whichever number happens to improve.
Keep a baseline sample from the same material lot where practical. Run the planned change, allow the defined transition period and take samples at recorded positions. A return to the baseline can help reveal a time-related shift, although it does not remove every possible source of bias.
Do not treat several pieces cut from one short section as several independent production trials. They describe variation within that section. Evidence across time, raw-material lots and normal operating changes is needed before claiming that a result is repeatable in routine production.
Separate full-width production from accepted product. Edge trim, start-up material and rejected sections affect saleable yield, even when the forming balance is correct. Recycled trim also needs a traceable route so that it is not counted as fresh feed twice.
Release requires more than a pleasing average. Check the agreed local limits, the roll coverage and the end-use requirements. Where evidence is missing, name the open question and retain the relevant material while it is resolved.
For purchasing, ask suppliers for results that match the proposed construction and method. A broad claim about an airlaid product family cannot establish the performance of one recipe. Request the conditions behind a result and confirm what changes would require fresh approval.
Questions that often arise in airlaid projects
Can higher airflow solve poor formation?
Not as a general rule. First identify the equipment, fibre blend and observed fault. Airflow interacts with the forming system, so an unsupported universal setting or formula is not a sound basis for adjustment. Use the maker's limits and a controlled trial.
Does more binder always make a better product?
The answer depends on the required balance of properties. Compare the intended performance, handling and cost with an agreed test plan. A higher strength result alone does not prove that the whole product has improved.
Can one average certify an entire roll?
No single average describes every local position. The sampling plan determines what the evidence can represent. Retain individual readings, their locations and the rule used for release, alongside the reported mean.
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