ginning & fibre quality series the effect of lint cleaning

Ginning & Fibre Quality Series

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Modern lint cleaning, in most cas-es, refers to the fixed or control-led-batt saw type lint cleaner (see

Figure 1), which was introduced to gin op-erations largely after 1945 and quickly be-came widespread. Its introduction followed the advent of mechanised harvesting, which also increased the amount of trash or plant matter found in cotton harvested compared to hand-harvested cotton.

In these systems ginned lint is formed into a thick batt of around 250 grams per square metre depending on the gin feed, on a slow continually revolving condenser drum. The formed batt is doffed from the condenser drum and fed with minimal draft through two or three close set rollers to a nip point between a fluted feed roller and fixed feed bar or plate (see photo).

Typically, the feed roller or feed plate is resiliently mounted. The batt is then combed from the nip point onto a circular saw with a surface speed in excess of 1500 metres per minute. The draft or combing ratio, such as the ratio of the surface speeds between the final feed roller and the saw, is most usually fixed and set between 24 and 30, although higher and lower values

are known. The fibre transferred onto the saw is cleaned by grid bars, which deflect fibre bundles back into the saw teeth at the same time as expelling heavier discrete trash particles that are subject to greater centrifugal force than the fibre. Most mod-ern lint cleaners use between five and eight grid bars.

Fibre is removed from the saw by a circu-lar brush or doffing cylinder (called a brush) revolving at a fixed ratio of typically 1.35 times the speed of the saw. Lint doffed by

the brush can be subject to further identical lint cleaning passages or can be collected and compressed into a bale.

Short fibre and nepsThe elements of the system described above work well to clean

trashy cotton but they also create higher levels of short fibre con-tent (SFC) and neps, which are small fibre entanglements that have a hard central knot that is detectable. Neps are unsightly and ruin the appearance of raw fibre sold into spinning mills. At the spinning mill, high SFC and nep numbers lead to excessive waste and poorer yarn quality.

Ultimately these properties affect final fabric quality and per-ceptions of a particular cotton growth’s quality. With a move to-wards production of longer, finer cotton, there are questions from the Australian cotton industry about the applicability of the fixed-batt saw lint cleaner and the settings, which govern how the fibre is cleaned.

Over many years, trials involving cotton subject to multiple lint cleaning passages have shown incremental increases in fibre dam-age with increased number of lint cleaner passages. Albeit slowly, the ginning industry has moved towards new lint cleaner designs that nominally reduce fibre damage.

While these advances affect some positive changes to fibre quality, it is still unclear where the greatest proportion of damage to fibre occurs in the lint cleaner. There is agreement that fibre is damaged during the combing of the batt from the feed works onto the fast moving saw, particularly at higher combing ratios.

But there is little information on the relative impact of this transfer point particularly with respect to particular fibre proper-ties and removed from the effects of other ‘cleaning’ points in the system such as the grid bars and the brush. Furthermore there is little information on how these elements, and combing ratios

34 — THE AUSTRALIAN COTTONGROWER AUGUST–SEPTEMBER 2010

The effect of lint cleaning on cotton fibre quality

By Stuart G. Gordon, Kevin M. Bagshaw and Frederick A Horne

Long, fine cotton suffers more damage during lint cleaning than shorter, coarser cottons. Damage can be reduced in lint cleaning, without affecting leaf grade, by combinations of increasing the draft on the batt prior to combing at the feed bar, increasing fibre moisture, reducing

the combing ratio and/or reducing saw speed.

Photo showing the nip point between the fluted feed roller and the feed bar and the position of this point with respect to the saw.

Ginning & Fibre Quality Seriesand saw speeds should be adjusted for particular fibre types. This lack of information confounds improvements by plant breeders, agronomists and growers, who are bringing new varieties with longer, finer fibre to the gin.

CSIRO has recently completed a series of experiments aimed at understanding the particular effects of the working elements and settings of the lint cleaner on fibre quality. The motivation for this work has been the introduction of new CSIRO cotton varieties with longer and finer fibre and an ambitious objective of modify-ing the current fixed-batt saw lint cleaner to reduce its damaging effects on fibre quality.

MAteriAlSThree different types of cotton were selected for these experi-

ments:• A short, coarse cotton (short-coarse);• An Australian base grade (Australian-std.); and,• A long, fine cotton (long-fine).

Table 1 lists the HVI properties – upper half mean length (UHML), micronaire (MIC), tenacity (STR) and uniformity index (UNI), of the cotton used in this study. Table 2 lists selected Ad-vanced Fiber Information System (AFIS) PRO measurements on

AUGUST–SEPTEMBER 2010 THE AUSTRALIAN COTTONGROWER — 35

FiGUre 1: Cross-section of a commercial fixed batt saw lint cleaner

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Ginning & Fibre Quality Seriessamples of the same cotton – upper quartile length (UQL), short fibre content (SFC), neps and trash. The AFIS PRO is an instru-ment that uses an electro-optical sensor to assess the number and size or length of neps, trash and fibre mechanically individualised from a sliver specimen prepared by hand from a given sample.

MetHodA purpose built, laboratory-scale lint cleaner with independent

variable speed drives for the saw and feed rollers was used for the trials. Multiple independent variables (for example, lint cleaner ele-ments, settings and conditions, were examined for their effect on each fibre property, such as the number of neps). Two separate experiments were conducted in this way.

In the first experiment, the effects of the lint cleaner elements (the feed bar, grid bars and brush) on the individual fibre properties of the three cottons were tested. Each type of cotton was tested in replicate through the lint cleaner treatments listed in Table 3. One of the lint cleaner elements (such as the feed), was progressively removed from each treatment in order to determine the residual effect of the remaining elements.

For Experiment 1, fibres samples were processed through the laboratory lint cleaner using a combing ratio of 23 and a saw speed of 870 r/min (a surface speed of 685 m/min), with the brush geared at the same ratio as an industrial cleaner. It is noted that only a light batt density was tested in Experiment 1, for ex-ample a BD1 – see Experiment 2 below.


tABle 4: experiment 2Variable No. of tests Cottons: C1, C2 and C3 3Combing ratio: • CR1 = 23

• CR2 = 50 2

Batt density: • BD1 = 100 g/m2

• BD2 = 250 g/m2 2

Saw speed (surface speed): • SS1 = 500 m/s• SS2 = 865 m/s 2

Moisture content: • MC1 = 4.8% – 25°C & <30% RH

• MC2 = 6.2% 27°C & >70% RH

2

Total no. tests 48

tABle i: HVi fibre properties of test cottonsCotton sample UHML(w)

inchesMIC μg/

inchSTR cN/

texUNI (%)

Short-coarse 1.03 5.2 28.5 80.3Australian-std. 1.13 4.4 33.0 82.2Long-fine 1.23 4.0 34.0 82.0

tABle 2: AFiS Pro fibre properties of test cottonsCotton sample UQL(w)

inchesSFC(w) (%) Neps(n)

count/gTrash(n) count/g

Short-coarse 1.076 12.44 199 47Australian-std. 1.180 10.26 247 64Long-fine 1.231 11.38 424 44

tABle 3: experiment 1Variable No. of testsCottons: C1, C2 and C3 3Treatments:• T1 = Control • T2 = Standard – includes feed bars (FB),

grid bars (GB) & brush (BR)• T3 = No grid bars – but includes FB & BR• T4 = No feed or grid bars – but includes (BR) 4Total no. tests 12

FiGUre 2: the effect of lint cleaner elements on neps for the three cotton types

BR = brush, FB = feed bar and GB = grid bar. Error Y-bars indicate least significant differences of means at the 5% level.

FiGUre 3: the effect of lint cleaner elements on SFC(w) for the three cotton types


FiGUre 4: the effect of lint cleaner elements on trash content for the three cotton types


Ginning & Fibre Quality SeriesIn the second experiment the effects on the three cottons, of

combing ratio, fibre loading (batt density), saw speed and mois-ture content were tested. Combing ratios and saw speeds were changed by adjusting the variable speed drives on the lint cleaner.

Batt densities were adjusted by increasing the weight of fibre sample processed through the laboratory lint cleaner. Batt density and combing ratio are settings that affect the total draft applied to fibre in its passage from the condenser drum through to the feed plate onto the saw. High density batts require an inherently larger combing ratio to be applied to them and vice versa for low density batts.

A hypothesis tested in this study is that a low combing ratio ap-plied to a low density batt results in less fibre damage and cleaner fibre. The proposed hypothesis is that lower inter-fibre friction between fibres in lighter batts gripped at the feed plate and feed bar nip allows fibre to be combed rather than torn and broken from this nip point by the saw.

The benefits of this hypothesis assume that the combed fibre is properly held by the saw teeth. A low combing ratio means more saw teeth are applied per fibre resulting in cleaner, more open fibre. The ease of combing a lighter batt mitigates the action of the increased number of saw teeth acting on fibre as a result of the lower combing.

A small conditioning room was built to house the laboratory lint

AUGUST–SEPTEMBER 2010 THE AUSTRALIAN COTTONGROWER — 37

FiGUre 5: the effect of lint cleaner elements on UQl(w) for the three cotton types

BR = brush, FB = feed bar and GB = grid bar. Error Y-bars indicate least significant differences of means at the 5% level. FiGUre 8: the average effect of lint cleaner

settings on trash for all three cotton types

BD = batt density, Condition = moisture content, CR = combing ratio and SS = saw speed. High = high BD, wet cotton, high CR and high SS; Average = grand average trash count for all cottons and Low = low BD, dry cotton, low CR and low SS. Error Y-bars indicate least significant differences of means at the 5% level.

FiGUre 6: the average effect of lint cleaner settings on neps for all three cotton types

BD = batt density, Condition = moisture content, CR = combing ratio and SS = saw speed. High = high BD, wet cotton, high CR and high SS; Average = grand average nep count for all cottons and Low = low BD, dry cotton, low CR and low SS. Error Y-bars indicate least significant differences of means at the 5% level.

FiGUre 7: the average effect of lint cleaner settings on SFC for all three cotton types

BD = batt density, Condition = moisture content, CR = combing ratio and SS = saw speed. High = high BD, wet cotton, high CR and high SS; Average = grand average SFC for all cottons and Low = low BD, dry cotton, low CR and low SS. Error Y-bars indicate least significant differences of means at the 5% level.

FiGUre 9: the average effect of lint cleaner settings on UQl for all three cotton types

BD = batt density, Condition = moisture content, CR = combing ratio and SS = saw speed. High = high BD, wet cotton, high CR and high SS; Average = grand average UQL for all cottons and Low = low BD, dry cotton, low CR and low SS. Error Y-bars indicate least significant differences of means at the 5% level.

Ginning & Fibre Quality Seriescleaner so that samples could be conditioned for at least 48 hours and tested under the prevailing conditions. Two conditions were sought; dry and wet. Samples subject to dry conditions were kept at less than 30 per cent RH and 25°C, while samples subject to wet conditions were kept at >70 per cent RH and 27°C for the prescribed time. The resulting moisture of cotton samples con-ditioned in the wet and dry conditions was 6.2 per cent and 4.8 per cent respectively. Table 4 lists the number and combination of treatments tested in Experiment 2.

Samples were tested using an AFIS PRO. The fibre properties of most interest in this analysis were the number of neps, short fibre content by weight (SFCw), upper quartile length by weight (UQLw) and trash count by number (Tn).

results: experiment 1Figures 2 through 5 show the effect of the lint cleaner ele-

ments on fibre damage. Across all cotton types, the feed of the lint cleaner created the most damage measured in terms of neps and SFC, although the effects were muted in the shorter, coarser cotton. While nep levels in the short-coarse cotton increased by around 10 per cent after the standard treatment (FB, GB and BR), in the Australian standard and long, fine cottons the increase was in the order of 12 per cent and 20 per cent respectively. The removal of grid bars reduced nep levels in the longer cottons by only four per cent and did not change nep levels in the short-coarse cotton. Across all the cottons, the removal of the FB and GB together removed any significant difference in neps between the control and brush samples.

The FB also has a significant effect on fibre length, although this is dependent on the length of fibre being processed. The length characteristics of the short-coarse did not change signifi-cantly through any treatment, while the long-fine and Australian-standard cottons lost 0.3 and 0.4 mm of their UQL respectively after passage through the standard treatment. The differences for both cottons through the standard treatment were significant at the one per cent level. But the GB and BR did not affect the UQL of either cotton. Increases in SFC were highest in the longer cot-ton samples subject to the standard treatment.

Grid bars on the model system did not improve the cleanliness of the cotton as much as expected. The main cleaning point ap-pears to be at the transfer of the fibre onto the saw, with only a small subsequent contribution from the grid bars. The level of

cleaning did not improve, or improved only marginally, for the Australian standard cotton when grid bars were added. It is inter-esting to note that the brush removed relatively greater amounts of trash from the short-coarse and Australian-standard cottons than the grid bars.

The ability of the fixed batt saw lint cleaner to adequately clean long-fine fibre is questioned. The standard treatment reduced trash counts by only 14 per cent in this cotton compared with 28 per cent and 31 per cent for the short-coarse and Australian-standard cottons respectively.

results: experiment 2Figures 6 through 9 show the effects of lint cleaner settings

on fibre quality. While nearly all treatments had negative impacts on fibre quality, particularly for the long, fine cotton (see Figure 10), batt density consistently had the largest effects (see Figures 6 through 9).

Neps were significantly affected by all treatments – BD, Con-dition, CR and SS. Interestingly, higher batt density resulted in reduced nep counts although higher CR and SS, as expected, resulted in higher nep counts. It was expected that a lower batt density would also have resulted in lower nep content.

One possible reason for this ambiguity to our original hypoth-esis may have been that the lighter batt was not properly trans-ferred into the saw teeth at the feed and was therefore subject to greater action from the grid bars. Fibre equilibrated under wet conditions was better able to resist nep formation.

Fibre length was affected especially by batt density. Both UQL and SFC were adversely affected by high batt density, although this effect was greater in the long, fine cotton. Smaller differences were seen as a result of higher combing ratio and saw speed. Moist cotton resisted breakage better than dry cotton.

Low batt density enabled cotton to be cleaned better by the saw and grid bars. Low trash levels were associated with low batt den-sity and as expected, higher combing ratio and saw speed. Drier cotton had lower trash levels although the level of trash was not significantly different from the moist cotton.

ConClUSionThe results show the greatest damage to fibre occurs at the

point where fibre is transferred or ‘combed’ from the batt held at the nip point between the feed roller and feed bar, onto the saw. The extent of damage at this point is determined by the density of the batt, the moisture of the cotton, the combing ratio, saw speed and importantly the type of cotton.

The results show less damaging effects on fibre quality occur when lower batt density, combing ratio, saw speed, and cotton that is equilibrated to beyond six per cent moisture, are used. This was particularly so when these settings were applied to long, fine cotton. When applied to shorter, coarse cotton the effects were less pronounced.

These results represent a summary of data collected over the past two years from experiments conducted at CSIRO on a pur-pose built experimental lint cleaner. These data support a larger, more ambitious project to modify the controlled-batt saw type lint cleaner.

The authors gratefully acknowledge the financial support of the Australian Cotton Research and Development Corporation (CRDC), the Cotton Catchment Communities CRC and CSIRO in preparing this work. The authors also gratefully acknowledge the input by Dr Robert Long on the analysis of data for this paper.

CSIRO Materials Science and Engineering, PO Box 21, Belmont VIC, 3216, Australia.


FiGUre 10: XY plot showing measurements on all 48 treatments in experiment 2 for the relationship between neps and UQl

Circled points highlight greater change in properties to the long, fine cotton after treatment by higher BD, CR and SS under drier conditions.

ginning & fibre quality series the effect of lint cleaning

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