Removing more noil uses more cotton for each kilogram of combed sliver. The extra cost may be justified by the yarn requirement, but the noil percentage cannot prove that on its own. The removed material must contain the fibres and defects that the process needed to exclude.
The useful question is how well the comber selects material. A good result retains suitable fibres while meeting the yarn's needs for strength, evenness, appearance and processing performance. A higher waste percentage can improve some of those results and leave others unchanged.
This guide explains the cotton-combing cycle, then works through the measures used to judge that choice. All worked figures are invented. They illustrate the method and are not noil targets, machine settings or commercial price forecasts.
Noil is a stream of material, not a quality grade
Combing noil is the material removed during combing. It contains many short fibres, but it need not consist only of short fibres. It can also contain longer fibres, neps and other matter removed from the lap. Its exact contents depend on the feed and the process.
The intended product determines what counts as a useful result. A fine yarn with a strict appearance requirement may justify a different balance from a coarser yarn. The preparation and spinning route also matter. A noil rate that works for one cotton and yarn cannot be assigned to all combed products.
The material delivered as combed sliver is the other half of the decision. Test it alongside the noil. Clean-looking noil does not show that the sliver is suitable, and a low noil weight does not establish that valuable fibre has been saved.
How the combing cycle selects fibres
A cotton comber works on successive fringes of a lap. Several heads usually work together, and their delivered material is combined into sliver. The sequence below explains the main actions. Exact timing and geometry depend on the installed machine.
Hold the lap and comb its leading fringe
The feed roller advances a controlled length of lap. The nipper jaws hold it while the circular comb passes through the projecting fringe. Fibres that remain securely held can pass through this action; material that is not retained can enter the noil stream.
The combing lecture hosted by Zhongyuan University of Technology illustrates the nipper, circular comb, top comb and detaching rollers. Its cycle diagrams show why grip and timing work together. A change in one part affects how the fringe is presented to another.
Join each fringe to the preceding web
After circular combing, the nippers open and move toward the detaching rollers. Those rollers return part of the previous web so that the newly combed fringe can overlap it. They then turn forward to draw the new portion through.
This joining action is called piecing. It converts repeated deliveries into a continuous web. Poor overlap can introduce mass variation even when the average noil rate looks correct.
A Toyota Industries technical disclosure on detaching rollers describes the linked forward and reverse motions. It also explains the top comb's action on the trailing portion during detaching. The disclosure is useful for the mechanism; it is not an operating instruction for another machine.
Control the trailing fibres and clear the comb
The top comb acts as fibres are drawn through it. It helps retain short fibres and unwanted matter for removal by the circular comb in a following cycle. The circular-comb brush clears material from that comb so the action can repeat.
Graf's comb-system guide treats the top comb, circular comb, holders and brushes as a system. Its selection guidance depends on cotton properties, machine type and yarn requirements. A good component cannot compensate for every mismatch elsewhere in that system.
Why one adjustment can change several outcomes
Feed length per cycle, feed timing, detachment distance and top-comb action can all affect the result. They influence which fibres are held, which can reach the detaching rollers and how much material is processed in each cycle.
Forward and backward feeding differ in when the lap advances during the nipper movement. This changes the way fibres are presented for combing and detaching. Do not transfer a setting between these arrangements merely because the displayed noil percentage is the same.
Fibre length is not a rigid sieve opening. A fibre's position, straightness and grip help determine whether it is retained. The process can remove some longer fibres as well as shorter ones. This is why a fixed noil percentage cannot define one exact length cutoff for every lap.
Current machinery offers controls for these linked actions. Rieter's E 90 information describes coordinated movements, a controlled lap drive and quality monitoring. Its published capability concerns that machine. It does not prescribe the most useful extraction for a particular mill order.
When a problem appears, check whether the machine still matches its approved setup. Wear, poor grip, damaged comb elements or a changed lap can alter the result. Make inspections and adjustments through the maker's procedures and qualified personnel. Raising noil to conceal a mechanical fault can add material cost without removing its cause.
Measure noil on the feed basis
For a closed trial with a known feed mass:
Noil percentage = noil mass ÷ comber feed mass × 100
Use a consistent moisture basis and the same trial interval. Net weights exclude containers and packaging. Identify other waste and any change in material held inside the process.
If the only two outputs are sliver and noil, with no stock change or other loss, the equivalent formula is:
Noil percentage = noil ÷ (sliver + noil) × 100
Suppose 1,000 kg of feed becomes 850 kg of sliver and 150 kg of noil. The extraction is 15%. Dividing 150 by 850 gives 17.65%, which expresses noil relative to sliver. It is not the same percentage.
The two-output formula needs its assumptions. It will miss material that leaves through another waste point or remains in the machine at the end. A trial that begins with one stock level and ends with another should account for that change before the result is compared.
Moisture can also change the apparent extraction. A noil sample that dries before weighing may not share the lap's mass basis. Record sampling and weighing conditions. ApparelDiary's moisture regain and receiving-weight guide explains the difference between regain and moisture content used in such corrections.
Keep the measured result distinct from the control-panel setting. A setting describes the intended condition. Collected masses show the result over the stated test. If they disagree, investigate the basis and collection method before changing the machine to make the figures match.
Separate extraction rate from removal efficiency
Consider an idealised fibre-only balance. The feed contains 1,000 kg of dry fibre, with 20% by mass below a chosen short-fibre cutoff. It therefore contains 200 kg of short fibres and 800 kg of longer fibres.
The comber removes 150 kg of noil. In this invented example, 80% of that noil mass is short fibre. Assume no fibre breakage, no other loss and no change in stock. Use the same cutoff and mass-based definitions for all three streams.
Fibre group | Feed | Noil | Retained sliver |
|---|---|---|---|
Short fibres | 200 kg | 120 kg | 80 kg |
Longer fibres | 800 kg | 30 kg | 770 kg |
Total | 1,000 kg | 150 kg | 850 kg |
The noil rate remains 150 ÷ 1,000 × 100 = 15%. Short-fibre removal efficiency is a different calculation:
120 ÷ 200 × 100 = 60% of the incoming short-fibre mass removed
The retained sliver contains 80 ÷ 850 × 100, or 9.41% short fibre by mass. Comparing that concentration with the original 20% gives a decrease of about 52.94%. That is not the 60% removal efficiency, because the mass of the retained stream is smaller than the feed.
Longer-fibre loss is 30 ÷ 800 × 100 = 3.75% of the incoming longer-fibre mass. This measure asks how much of that group left in the noil. It does not imply that every longer fibre would have been suitable for the intended yarn.
Four measures now describe one process: noil percentage, short-fibre removal efficiency, retained short-fibre concentration and longer-fibre loss. Each has a different denominator. Write the denominator beside the result instead of calling all four combing efficiency.
Real samples are less tidy. Fibre damage can shift fibres between length groups, and test methods estimate length distributions from samples. A percentage by number cannot be multiplied by kilograms as if it were a mass fraction. The ideal balance explains the logic; actual process conclusions need compatible measurements and their uncertainty.
Collect samples that can explain a change
Take matched samples of the incoming lap, delivered sliver and noil. Their identities should link to the same cotton and stable running condition. A new lap or a recent setting change may still be moving through the head when an output sample is collected.
Assess the length distribution of the retained fibre and the noil, not just their mean lengths. Two samples can share a mean while having different shares at the short end. Record the cutoff used for short-fibre reporting and whether the result is by number or weight.
Keep nep and trash results separate where the method permits. A lower fibre-nep count does not prove that seed-coat fragments fell by the same amount. Nor does a smooth web prove that all defects have been removed.
Confirm that the instrument and preparation method accept the sample type. Dense noil, mixed waste and clean sliver are not automatically equivalent test materials. If a method requires a particular preparation, apply it consistently and avoid changing the sample by picking out unwanted pieces.
Retain the connection to each combing head when a fault may be local. Combining all noil into one sample can hide a head that loses longer fibres while another removes too little unwanted material. A whole-machine average is useful for material planning; it may be a poor tool for locating a fault.
Check where the waste collection path joins other streams. If one collector receives material from several heads, its sample describes that combined stream. It cannot establish which head produced a particular fibre group. Use the maker's approved collection method for any separate head test. Also allow for material already in the collection path when a trial starts. Labelling the sample with a clock time does not, by itself, prove that all its contents came from the new setting. These details matter most when the apparent change is small.
Compare yarn made at the same count and twist
The purpose of the trial is the yarn, so keep the final product comparable. Use the same intended count, twist, spinning route and later processing conditions. Verify the actual values rather than rely only on machine settings.
A 2022 compact-yarn study by Çelik, Çoban and Sarıoğlu examined noil percentage together with yarn linear density and twist. The responses included strength, elongation, evenness, imperfections and hairiness. Its results did not support treating all quality measures as one response. This reinforces the need to examine each required property within the study's stated conditions.
Breaking force also needs a count basis. A fictional yarn that breaks at 3.6 N carries 360 cN. At 18 tex, its tenacity is 360 ÷ 18 = 20 cN/tex. At 20 tex, the same breaking force gives 18 cN/tex. Comparing force alone would hide the difference in mass per unit length.
ApparelDiary's yarn count conversion guide helps keep those units consistent. Normalising force does not remove every effect of count or structure, so a controlled noil trial should still aim for the same yarn product.
ISO 2062:2009 covers single-end breaking force and elongation of yarn from packages using constant-rate-of-extension testing. ISO currently lists that edition as published, with a revision under development. Choose the applicable method and full test conditions before the trial. The public scope alone is not a complete laboratory procedure.
Include later processing evidence where it matters to the order. A change that helps a laboratory average may add little value if winding and fabric performance were already satisfactory. Equally, a small improvement can matter when it removes a recurring defect in the final fabric. Judge that effect from a linked trial, not from the noil rate alone.
Use quality limits to screen the options
The following invented trial has one yarn count, one twist level and one feed group. Its stated requirements are at least 18 cN/tex tenacity and no more than 150 imperfections per kilometre. These limits are examples only.
For this table, the imperfection total adds thin places at −50%, thick places at +50% and neps at +200%, using one test method. A total made with other thresholds would not be directly comparable.
Noil extraction | Mean tenacity | Imperfections per km | Result against the stated limits |
|---|---|---|---|
12% | 17.4 cN/tex | 180 | Fails both |
15% | 18.2 cN/tex | 140 | Meets both means |
18% | 18.4 cN/tex | 130 | Meets both means |
The 15% option is the lower-extraction candidate that meets these example means. It is not yet a proven production optimum. Its tenacity margin is only 0.2 cN/tex, so variation and measurement uncertainty matter. Test enough independent production to determine whether it can meet the agreed acceptance rule.
The 18% option has more margin and fewer counted imperfections in this fictional set. That may justify its cost if those differences reduce failures or improve a required fabric result. It may add little value if the lower-extraction option already provides reliable performance.
Do not average away a failed property. Stronger yarn does not cancel an unacceptable appearance result unless the product agreement explicitly allows that tradeoff. Record every requirement, including any elongation or hairiness limit omitted from this small example.
Calculate the material cost at equal sliver output
Compare alternatives at a fixed amount of acceptable combed sliver. Suppose the mill needs 1,000 kg. For this cost illustration, sliver and noil are the only outputs, moisture bases match, and later process losses are outside the comparison.
At 15% noil, feed required is 1,000 ÷ 0.85 = 1,176.47 kg. Noil is 176.47 kg. At 18%, feed required is 1,000 ÷ 0.82 = 1,219.51 kg, with 219.51 kg of noil.
The higher-extraction option uses about 43.04 kg more feed and produces the same extra amount of noil. If feed costs 2.70 currency units/kg and noil sells for 1.00, the net extra material cost, using unrounded masses, is:
(1,000 ÷ 0.82 − 1,000 ÷ 0.85) × (2.70 − 1.00) ≈ 73.17 currency units
Suppose it also adds 18 currency units of operating cost for this quantity. The total extra cost is about 91.17, or 0.0912 per kg of sliver. That is the benefit the higher extraction would need to recover elsewhere in this simplified comparison.
Actual noil values may differ between trials. Fibre length, cleanliness, moisture basis and the sale agreement can affect what a buyer will accept. Do not assume the same credit if the removed material has changed. Include the relevant sale terms and handling costs in the mill's own calculation.
A noil sale is not a reason to create more noil. It is a credit against material cost after the yarn requirement has been met. The economic aim is useful accepted output, not the largest volume of a saleable by-product.
Keep extraction and production rate separate
Noil affects sliver output even when the machine processes the same feed per hour. Raising nip rate is not the only way a production figure changes.
For an illustrative machine with eight active heads, assume each head feeds 70 g/m lap at 5 mm per nip and runs at 450 nips/min. Feed rate is:
8 × 70 × (5 ÷ 1,000) × 450 × 60 ÷ 1,000 = 75.6 kg/h
The first division converts millimetres to metres. The second converts grams to kilograms. These are dimensional assumptions for the example, not settings for a named comber.
With 15% noil and no other loss, sliver output while running is 75.6 × 0.85 = 64.26 kg/h. At 18% noil, it becomes 75.6 × 0.82 = 61.992 kg/h. The feed rate has not changed, but the retained output has.
If the 15% case runs for 90% of scheduled time, the average becomes 64.26 × 0.90 = 57.834 kg per scheduled hour. Keep this time allowance separate from the material yield. Applying the noil deduction twice would understate output.
Check the lap mass, feed per nip, number of active heads and time basis behind any quoted rate. A head stopped for a lap issue changes the actual result even if the nominal machine speed remains the same.
Look for differences between heads
An acceptable machine average can conceal an uneven distribution. In a simple example, two heads receive equal feed masses and show 12% and 18% noil. Their combined extraction is 15%, but neither head is working at that rate.
The average says little about whether their slivers have the same length distribution or quality. Check grip, component condition, feed and the approved settings at the individual heads before changing the whole machine.
With unequal feed masses, weight the average by feed. A head using 100 kg at 12% makes 12 kg of noil. A second using 300 kg at 18% makes 54 kg. Combined extraction is 66 ÷ 400 × 100 = 16.5%, rather than the simple average of 15%.
Online monitoring can help locate a change in time. Trützschler's 2024 customer magazine identifies online noil monitoring on its TCO 21XL. Use such information with an understanding of what the system measures. A monitor trend still needs a matched collection or quality check when the cause is unclear.
Do not use one label for different preparation routes
Reducing noil on a fully combed stream and blending carded with combed sliver are different process choices. Equal overall material yield would not make their fibre populations or yarn results identical.
A study of two semi-combed yarn routes compared those approaches. The authors evaluated yarn properties and cost within their particular experiment. The work is useful evidence that the route itself needs testing; its outcome is not a universal guarantee for either method.
If an order allows a different preparation route, make that change explicit in the development trial. Preserve the material identities and verify the required yarn and fabric results. Do not substitute a route merely because a quality label sounds similar.
Make the decision from the complete trial
Before adopting a noil change, the mill should be able to explain the measured extraction, the fibres retained and removed, and the final yarn outcome. It should also know the cost at equal acceptable output and the effect on production time.
Keep the accepted result tied to its cotton group, yarn count, twist, machine configuration and test basis. A new raw material or product may need a new trial. A result that is economical for one order can be a poor choice for another.
The aim is a reliable selection process. Retain fibres that serve the product, remove what prevents the yarn from meeting its requirements, and make the extra cost visible whenever the balance changes.
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