The theoretical foundations of raw-cotton cleaning technology were laid by Burnashev [1] and further developed by Muhsinov [2], who examined feeding and cleaning processes within continuous-flow ginning technology. Subsequent studies concentrated on individual working elements: Ibrogimov [3] and Dzhuraev [4] investigated the design parameters of feeding devices and feed-grid-bar systems, respectively, while Usmanov et al. [5] proposed a combined drying-and-cleaning line for raw cotton.

More recent work has focused on optimizing drum arrangement and working-element geometry. Fayziyev [6] examined stripping peg-spike drums for fine-trash cleaning sections; Khakimov [7] and Bozorov [8] analyzed how the number of installed drums affects both cleaning efficiency and fiber quality; Djurayev et al. [9] evaluated the cleaning performance of currently operating cotton cleaners; and Raxmonov [10] proposed upgraded working elements for fine-trash cleaners.

A separate group of studies addressed the structural and deformation behavior of seed cotton as it passes through cleaning equipment [11]-[15], establishing that the geometric dimensions and bulk density of cotton locks change substantially during processing. Most recently, Parpiyev et al. [16] reported detailed studies of cotton movement, equipment performance, and grid-bar positioning within industrial cleaning lines operating at Uzbek ginneries.

Despite this substantial body of work, none of the cited studies has quantitatively linked the progressive structural transformation of cotton locks to a correspondingly differentiated, stage-wise technological clearance between the working elements and the grid/mesh surfaces. In current practice, this clearance is kept constant—typically Δ = 15 mm—throughout the entire cleaning line, regardless of how the physical dimensions of the cotton locks change from one section to the next.

A structural and technological analysis of the working elements described above highlights two critical issues:

In standard peg-spike cleaners, a mesh surface with 6 × 50 mm openings is positioned at a constant 15 mm clearance beneath the cylinder. Trash particles larger than 6 mm therefore cannot pass through the mesh and remain mixed with the cotton mass; moreover, repeated spike impacts compress the cotton, increasing its bulk density and further embedding fine trash particles within the fiber structure. In saw cleaners, trash separation occurs as cotton locks are dragged along grid bars (20 mm in diameter, with a 40 mm inter-bar gap). The working clearance between the saw-tooth tips and the grid bars is likewise kept constant at 15 mm across all processing stages.

Seed cotton undergoes marked structural changes during processing: as large, dense locks disintegrate into smaller units, their geometric volume decreases substantially. A uniform 15 mm clearance creates a mismatch across the line: in the early stages, oversized locks are subjected to excessive mechanical friction and seed damage, whereas in later stages the now-smaller locks fail to make active contact with the grid bars, sharply reducing cleaning efficiency.

Optimizing seed-cotton cleaning technology requires a dynamic approach, in which the working clearances between the cylinders and the grid surfaces are progressively adjusted to match the changing physical dimensions and density of the cotton locks as they move through the cleaning line.

Research aim: to evaluate the structural transformation of seed cotton during cleaning and to establish rational, differentiated technological clearances across peg-spike and saw-drum sec tions that maximize cleaning efficiency while preserving fiber and seed quality.

To achieve this aim, the following objectives were addressed:

To quantify the structural transformation of seed cotton locks during sequential cleaning using a structural indicator K, while distinguishing it from the mass fraction of single-seed locks; To evaluate the cleaning performance of a standard line (Δ = 15 mm) versus a proposed line redesign incorporating a differentiated clearance schedule (Δ = 18 → 15 → 12 mm); To determine the individual and cumulative cleaning efficiency of peg-spike and saw-drum sections for fine and coarse trash under both configurations.

Novelty: for the first time, a quantitative structural indicator of cotton-lock composition is linked to a stage-wise, differentiated clearance schedule for a combined peg-spike/saw-drum cleaning line, providing a practical route to increasing cleaning efficiency without additional fiber or seed damage.

To quantify changes in the structural composition of seed cotton during processing, the structural indicator K was evaluated using the following relationship:

where M is the total number of individual cotton locks in the tested sample, and N is the total number of seeds in that sample.

To prevent confounding structural loosening with lock dispersion, the structural indicator K was treated as a metric of lock fragmentation, whereas the proportion of single-seed locks (P_single, %) was recorded as an independent dimensional distribution metric based on physical sorting into seed-count categories (1-seed, 2-seed, up to 10-seed locks). Samples weighing 50 g each were extracted before processing and after passing through each cleaner section.

Experimental investigations were conducted on a laboratory test bench at the Tashkent Institute of Textile and Light Industry (Figure 1).

Figure 1.Experimental test bench (schematic configuration with 4 peg-spike drums and 1 saw drum shown).

Variant 1 (Control/standard configuration): represents the conventional industrial setup, consisting of 32 drums in total: 4 peg-spike drum (PD) sections and 4 saw-drum (SD) sections. A constant technological clearance of Δ = 15 mm was maintained between the main working elements and the grid/mesh surfaces across all stages.

Variant 2 (Proposed combined line redesign): featured 24 peg-spike drums (6 sections) and 6 saw drums arranged in an alternating sequence. The operational clearance was differentiated stage-wise: In the initial 4 sections (2 PD + 2 SD), clearance was set to Δ = 18 mm; In the subsequent 2 sections (1 PD + 1 SD), clearance was set to Δ = 15 mm; In the remaining 6 sections, clearance was set to Δ = 12 mm.

Physical Justification of Clearances: The clearance values (18 mm, 15 mm, and 12 mm) were determined directly from the empirical geometric envelope of the cotton locks measured across the stages. Initially, multi-seed locks exhibit mean diameters of 20 mm to 26 mm; setting Δ = 18 mm prevents aggressive mechanical pinching, minimizes seed damage, and permits the release of large coarse debris without crushing. As locks disintegrate into intermediate clusters (15 mm - 18 mm), the clearance is narrowed to Δ = 15 mm. In the final sections, where over 85% of locks disintegrate into single-seed units with diameters of 12 - 14 mm, reducing the gap to Δ = 12 mm ensures active contact between the cotton tufts and the grid bars, eliminating inactive bypass.

Waste fractions separated from each individual section were collected, weighed, and categorized into fine and coarse trash. Individual section cleaning efficiency (ΔC) and cumulative efficiency (Kcum) were calculated relative to both the initial trash content (Ctotal = 12.53%, Cfine = 4.89%, Ccoarse = 7.64%, moisture content W = 8.8%) and the localized, pre-section trash content (C_i):

where C_i is the cotton trash content prior to the cleaning section (%), C_i−1 is the trash content of the cotton after the section, and C_i − C_i−1 = ΔC is the trash separated in that section.

Experimental analysis revealed that as seed cotton moves through sequential cleaning passes, its structural composition changes significantly: the initially large and irregular cotton locks are progressively disintegrated into smaller units under mechanical impact. Table 1 shows the dynamic variation of the structural indicator K and lock distribution across three cotton varieties.

As shown in Table 1, the proportion of single-seed locks reached 75.48%, 74.65%, and 70.93% after cleaning through one set of peg-drum and saw-drum sections, and 87.32%, 96.00%, and 87.54% after processing through two sets of sections, respectively. That is, the cotton locks predominantly transformed into near-spherical shapes with an effective diameter of 14 mm - 16 mm [13]. In subsequent peg drums of a standard line, this transformation causes spike impacts to strike the upper fiber layer rather than lock edges, weakening trash expulsion. In saw drums with excessive clearance, a compact single-seed lock engaged by a saw tooth may pass through without contacting the grid bar, reducing separation efficiency.

Table 1.Variation of seed cotton structural composition during cleaning.

Based on the structural results above, the possibility of enhancing cleaning efficiency was investigated by introducing a variable clearance between the drums (peg and saw) and the grid surfaces, matched to the evolving structural composition of seed cotton, together with a partial replacement of peg-drum sections by saw-drum sections. The experiments were conducted in two variants in the laboratory of the Tashkent Institute of Textile and Light Industry (Figure 1).

Variant 1 consisted of 32 drums, with the clearance between the drums and the grid bar or mesh surface set to Δ = 15 mm across all 4 peg-drum and 4 saw-drum sections. Variant 2 consisted of 24 peg drums (6 sections) and 6 saw drums, with the clearance set to Δ = 18 mm in the initial 4 sections (2 PD + 2 SD), Δ = 15 mm in the subsequent two sections (1 PD + 1 SD), and Δ = 12 mm in the remaining six sections. The waste separated from each cleaning section was weighed individually to calculate the respective cleaning efficiencies; the results are presented in Table 2 and Figure 2.

Table 2.Influence of the clearance between drums and mesh/grid surfaces on trash separation from seed cotton (Ctotal = 12.53%, Cfine = 4.89%, Ccoarse = 7.64%, W = 8.8%).

As presented in Table 2, in Variant 1 the cleaning efficiency for total, fine, and coarse trash was 80.70%, 30.57%, and 50.13%, respectively. In Variant 2, these figures were 95.06%, 35.28%, and 59.78%—higher by 14.36, 4.71, and 9.65 percentage points, respectively.

In the first four cleaning sections (3 PD + 1 SD) of Variant 1, with a constant clearance of Δ = 15 mm, a total of 5.37% of trash was separated (2.29% in the three PD sections and 3.08% in the SD section), comprising 2.43% fine and 2.94% coarse trash. In contrast, in the first four sections of Variant 2 (2 PD + 2 SD), with Δ = 18 mm, a total of 8.06% of trash was separated (1.91% in the two PD sections and 6.15% in the two SD sections), comprising 2.73% fine and 5.27% coarse trash. This confirms that widening the clearance to Δ = 18 mm and replacing a peg drum with a saw drum increases the separation of both fine and coarse trash.

For these initial sections, the cleaning efficiencies for total, fine, and coarse trash were 42.62%, 19.15%, and 23.47% in Variant 1, compared with 64.33%, 22.27%, and 42.06% in Variant 2.

In cleaning sections 5 - 8, the total, fine, and coarse trash separation rates were 3.70%, 0.95%, and 2.75% for Variant 1, and 2.80%, 1.10%, and 1.70% for Variant 2—that is, 0.9 percentage points higher overall in Variant 1. This was primarily attributable to higher trash-separation rates at the 2nd and 3rd saw-drum positions in Variant 1 relative to the corresponding 3rd and 4th saw-drum positions in Variant 2. However, this result alone does not indicate that the saw drums in the 6th and 8th cleaning sections of Variant 1 operate more efficiently than those in Variant 2; this apparent discrepancy is clarified by the individual-section efficiency analysis in Figure 2.

The individual cleaning efficiency of the peg drums and saw drums was determined relative to the fine and coarse trash content of the cotton prior to the corresponding cleaning section, using Equation (2). It should be emphasized that the cleaning efficiencies reported in Table 2 were calculated relative to the initial total trash content of the cotton (K = ΔC/Ccum × 100%), not relative to the local fine/coarse trash content entering each section. Because peg drums separate only fine trash, evaluating their efficiency relative to the initial fine-trash content of the cotton gives a more representative picture. Likewise, determining the true individual efficiency of sequential cleaning sections requires accounting for the reduction in trash content already achieved by the preceding sections; Figure 2 presents

Figure 2.Individual cleaning efficiency of the peg-drum and saw-drum sections for fine and coarse trash, Variant 1 (left) and Variant 2 (right).

the individual efficiencies obtained on this basis.

In Variant 1, when calculated relative to the total initial trash content, the cleaning efficiency for fine trash on the 1st, 2nd, and 3rd peg drums was 7.02%, 5.35%, and 4.71%, respectively (Table 2), whereas the individual cleaning efficiency (relative to local fine-trash content) was 18.0%, 17.46%, and 17.82%, respectively. In the four saw-drum sections, the individual cleaning efficiencies for fine and coarse trash were 9.56% and 37.5%, 8.21% and 36.05%, 6.79% and 33.90%, and 6.11% and 27.46%, respectively.

In Variant 2, the cleaning efficiency on the initial three peg drums, relative to total initial trash content, was 10.61%, 3.99%, and 3.59%, respectively, while the individual cleaning efficiency was 27.2%, 17.48%, and 21.43%, respectively. In the six saw-drum sections, the individual cleaning efficiencies for fine and coarse trash were 19.16% and 49.41%, 11.02% and 37.8%, 20.0% and 48.51%, 8.26% and 44.17%, 16.45% and 43.94%, and 11.54% and 41.67%, respectively (Figure 2). As these results show, the individual cleaning efficiency of the sections in Variant 2 is consistently and substantially higher than in Variant 1.

Although the cleaning efficiency calculated relative to total trash content at the 2nd and 3rd saw drums was nominally higher in Variant 1 than in Variant 2, Figure 2 shows that their individual efficiency for fine and coarse trash was only 8.21% and 36.05% (2nd SD) and 6.79% and 33.90% (3rd SD) in Variant 1, compared with 11.02% and 37.8%, and 20.0% and 48.51% at the corresponding positions in Variant 2—confirming the superior performance of Variant 2 once local trash content is accounted for.

Table 3 presents the individual cleaning efficiency for cleaning sections 5 - 8 of the line, calculated both relative to the total trash content of the cotton and relative to the fine and coarse trash content before and after each section.

It is well established that the cleaning efficiency of a given section depends on the trash content of the cotton entering it and on the number of cleaning sections already traversed: a higher initial trash content, and fewer preceding cleaning passes, both result in a larger proportion of weakly bonded trash and, consequently, higher separation efficiency.

Table 3.Overall and individual cleaning efficiency of cleaning sections 5 - 8.

In sections 5 - 8, the cotton in Variant 1 had passed through one additional peg drum and one fewer saw drum than in Variant 2. Because one fewer saw-drum pass had been applied, the pre-cleaning trash content entering these four sections was higher in Variant 1, which explains the higher efficiency values calculated relative to total trash content for Variant 1 in this range. However, once individual efficiency is considered (Table 3), Variant 2 outperforms Variant 1 at every one of these four sections—by 5.9, 24.25, 2.65, and 11.74 percentage points, respectively.