High-orientation PET POY with a linear density between 83 dtex and 330 dtex is converted into water jet warp beams on integrated draw-sizing lines whose front end consists of a swivel-frame creel, multi-roller tension stand, a heated draw zone, a size box, drying cylinders or hot air chambers, and a direct beaming head. Feedstock acceptance requires measurement of elongation at break, tenacity, and filament count according to ASTM D2256-15 and ISO 2060:1995; incoming elongation below 95% or above 140% creates draw ratio redistribution problems across the warp sheet because molecular orientation in the as-spun POY is no longer uniform. Orientation is assessed by birefringence, typically 0.05–0.09 for high-orientation POY measured at 23°C under a polarizing microscope, while package density is held between 0.92 g/cm³ and 1.02 g/cm³ to limit package-to-package tension spikes. The draw-sizing operation itself is governed by the interaction of three independently controlled parameters: draw ratio, first godet temperature, and final set temperature. A draw ratio of 1.60–1.70 is common for standard high-orientation POY, while a first godet temperature of 80–90°C and a final set temperature of 130–150°C are required to convert the partially oriented structure into a low-shrinkage, high-tenacity warp yarn. Any deviation greater than ±2°C in the first godet zone can shift residual elongation by more than 4%, and this shift is directly visible on the water jet loom as periodic warp breaks at the selvedge. Size add-on is maintained between 3% and 6% by dry fiber mass for polyester filament warps, with the lower boundary established by water jet stripping resistance and the upper boundary set by size shedding in heald frames.

Why Does Draw Ratio Distribution Across the Warp Sheet Determine Loom Start-Up Failure Rates?

The draw ratio applied to high-orientation POY is not a single machine setting; it is a distribution that emerges from the interaction of creel tension, godet speed differential, yarn finish uniformity, and the thermal profile across the draw zone. When a draw-sizing line processes 800–1,200 ends simultaneously, a draw ratio difference of 0.05 between the centre and selvedge ends can reduce the tenacity of the selvedge yarns by 0.8–1.2 cN/dtex and raise their elongation at break by 15–25%. This occurs because the edge ends lose more heat to the ambient air during passage over heated godets, and because the sheet width at the draw point is frequently 1,600–2,200 mm while the godet surface temperature uniformity is seldom better than ±1.5°C. The drawn yarn should exhibit a final elongation between 20% and 28%, measured at 500 mm gauge length and 300 mm/min extension rate per ISO 2062:2022, with less than 2.5% coefficient of variation across the beam. In production practice, a beam with elevated elongation variability often passes tensile testing because the average value remains within specification, but loom start-up failure rates increase because water jet insertion imposes a high strain rate on individual ends. The water jet pressure of 1.8–3.5 MPa creates a shock load that is not reproduced by quasi-static tensile testing; therefore, a minimum final tenacity of 3.6–4.4 cN/dtex is not sufficient if the draw ratio distribution is broader than ±0.03. Yarn tension measurements before the first draw godet should be held at 0.10–0.18 cN/dtex for filament counts above 36, and at 0.15–0.25 cN/dtex for filament counts between 24 and 36. Tension sensors mounted on the creel post detect packages with damaged transfer tails or collapsed tube cores that produce intermittent tension drops below 0.05 cN/dtex, which are responsible for under-drawn sections that later appear as thick-thin defects in the weft-wise direction of the woven fabric.

Within the creel zone, tension control is complicated by the fact that POY package density changes progressively from the outer radius to the tube core, and this density shift changes the yarn-to-yarn friction coefficient at the ceramic guide surfaces. The problem is most severe in high-humidity production halls where the equilibrium moisture regain of PET POY remains below 0.4%, but the surface condensation on package wrappers can raise yarn-to-guide friction enough to increase unwinding tension by 0.05–0.12 cN/dtex. A draw-sizing machine equipped with closed-loop tension control at each spindle position, typically using piezoelectric sensors with a response time below 20 ms, reduces the end break rate by a factor of 3–5 compared with open-loop magnetic hysteresis tensioners. The draw point itself is stabilized by a pair of low-draw rollers located before the first hot godet; the speed differential between these rollers and the first hot godet is maintained at 1.5–2.5% to prevent filament slack from entering the drawing zone. A slack filament under the second hot godet will not experience the intended draw ratio and will instead undergo local cold drawing in the size box, which produces a brittle yarn segment with elongation below 10% and a characteristic break in the reed at the water jet loom. Production-scale records from draw-sizing lines running 167 dtex/48 f POY at 600 m/min show that a single slack end per beam is sufficient to reduce loom efficiency by 2–4% during the first 1,000 m of weaving, even if the end does not break during beaming.

When Acrylic Ester Size Dispersions Replace Fully Hydrolysed PVA in Water Jet Warp Preparation

Water jet weaving imposes a fundamentally different size performance requirement than rapier or projectile weaving because the size film must resist instantaneous water impact and subsequent wet abrasion while still being removable in conventional desizing. Acrylic ester size dispersions are frequently selected over fully hydrolysed PVA for fine polyester warp yarns because they form films with high elongation at break, typically 150–300% measured on cast films according to ASTM D882-12, and because their adhesion to PET surfaces remains acceptable after exposure to water at 20–40°C. The size solids concentration in the box is maintained at 6–8% for 83 dtex/36 f, 8–10% for 167 dtex/48 f, and 10–12% for 330 dtex/96 f; the target add-on is then set by squeeze roller pressure and size box viscosity, which is normally 15–25 mPa·s at 50°C measured with a Brookfield viscometer at 30 rpm. A size add-on above 7% on fine denier yarns causes measurable size shedding in the heald frames, increases the frequency of nozzle clogging, and can generate sizing deposits on the reed that alter warp spacing by up to 0.5 mm across a 1,900 mm weaving width. Conversely, a size add-on below 3% on 330 dtex/96 f warp yarns results in filament separation at the point of water jet impact, and the separated filaments then wrap around the weft guide or create hairy warp sheet defects. The selection of a particular acrylic ester dispersion is further constrained by its film-forming temperature, which should be at least 15°C below the minimum size box operating temperature to avoid coagulation on the applicator roll. Coagulation is a known failure mode on draw-sizing lines where the size box is shut down for more than 45 min without circulation, because the dispersion film dries on the roll surface and is subsequently re-wetted, producing gel particles that deposit on the warp ends. Published data for this specific configuration is limited in peer-reviewed literature; however, supplier technical bulletins consistently recommend continuous circulation at 15–20 L/min and a size box temperature of 45–60°C for acrylic ester dispersions used on water jet polyester warps.

The choice between acrylic ester size and PVA is dictated by downstream desizing economics and by the loom’s water treatment system. Fully hydrolysed PVA produces a stiffer warp sheet and can withstand higher water jet pressures, but it requires desizing temperatures above 80°C and extended washing stages that are not always compatible with continuous open-width processing. Acrylic ester sizes, by contrast, can be removed in a 60–70°C alkaline detergent bath, and they do not form insoluble calcium or magnesium soaps in hard water, provided the dispersions are formulated with hard-water-tolerant surfactants. The tensile properties of the sized yarn are evaluated after conditioning at 20±2°C and 65±2% RH for 24 h per ISO 139:2005, and the size add-on is determined by Soxhlet extraction in boiling methanol for 2 h with the mass difference expressed as a percentage of dry unsized yarn mass. A well-optimized acrylic ester formula for water jet beams yields a sized yarn elongation loss of no more than 5% relative to the unsized drawn yarn, because the size film contributes tensile strength but does not significantly restrict filament extension. The largest process conflict in this zone is the requirement to maintain a high squeeze roller pressure for uniform add-on while avoiding over-compression of the warp sheet, which can embrittle the size film at the yarn-to-metal contact points and reduce film toughness by 10–20% when measured by a mandrel bend test.

Immediately after the size box, the wet warp sheet enters a drying section where the removal of water must be rapid enough to prevent size migration but gentle enough to avoid thermal relaxation of the freshly drawn PET structure. Cylinder drying temperatures are typically staged from 120°C in the first bank to 145°C in the final bank, with a residence time of 8–15 s depending on the number of drying cylinders and the machine speed. The residual moisture at the beaming head is maintained below 0.8% by dry mass using an online moisture meter, because residual moisture above 1.2% softens the size film and promotes blocking between adjacent yarn layers on the beam. Blocking is a failure mode in which adjacent ends adhere to one another under winding tension, and when the beam is subsequently mounted on the water jet loom, the let-off motion separates the blocked yarns by rupturing the size film rather than by clean layer separation. This rupture creates local filaments with no size protection, and the first water jet insertion strips those filaments from the warp end. Over-drying above 160°C is equally problematic because it increases the crystallinity of the drawn PET to a point where the elongation at break drops below 15% and the tenacity may fall by 0.3–0.6 cN/dtex as a result of thermal degradation at the size-fiber interface. The drying section should therefore be operated under a slight negative pressure of 20–50 Pa to remove water vapor continuously, and the air renewal rate should be sufficient to keep the dew point inside the enclosure below 30°C. Draw-sizing lines without active humidity control often show a morning-to-afternoon drift in residual moisture of 0.4–0.8% as the production hall accumulates water vapor, and this drift is visible in the beam hardness profile and in the incidence of blocked ends at the loom.

Beam Hardness, Winding Tension, and Selvage Density Under Direct Beaming

The direct beaming head on a draw-sizing line must produce a beam with uniform surface hardness, because water jet looms use a positively driven let-off system that translates beam diameter changes into precise warp tension control. A beam hardness of 70–85 Shore A measured with a 1 kg load per DIN 53505 is typical for polyester water jet warp beams, with the lower limit applying to fine denier warps and the upper limit applying to heavy denier warps. If the hardness varies by more than ±5 Shore A from the core to the outer layer, the let-off motion will generate tension fluctuations of 0.05–0.15 cN/dtex that are sufficient to break selvedge ends during water jet insertion. Selvage density is controlled by the traverse pitch of the beaming head and by the edge build-up program, which should apply a flatter traverse at the beam edges to avoid hard shoulders. A hard shoulder of ±0.5 mm radial height can concentrate warp tension at the selvedge and increase the end break rate by 40–60% during the first 500 m of weaving. Winding tension at the beaming head is normally set to 0.15–0.30 cN/dtex, with the higher value used for yarns that will be woven on high-speed water jet looms above 1,000 rpm. The winding tension must be ramped down as the beam diameter grows, because a constant torque winding program produces a progressively softer outer layer and a harder core, and this hardness gradient causes the warp sheet to become progressively more elastic as the beam unwinds. Modern draw-sizing lines use a closed-loop winding tension profile with a taper of 10–20% from the empty beam diameter to the full beam diameter, and the residual warp density is then checked by measuring beam circumference and surface indentation with a durometer.

On the water jet loom, the warp beam is subjected to cyclic water impact, heald abrasion, and reed friction at frequencies that can exceed 20 Hz. The sized warp must retain filament cohesion under these conditions for at least 1,000–5,000 m of uninterrupted weaving before a maintenance stop, depending on the yarn linear density and the number of harnesses. Size formulations that perform well under quasi-static abrasion tests may still fail on the water jet loom because the water jet creates a localized pressure spike that penetrates the size film and forces water into the inter-filament spaces. A practical acceptance test for water jet warp beams is to examine the warp sheet after 250 loom cycles using a photographic defect detection system that is sensitive to hairiness and filament separation of 0.5 mm or greater. If the number of hairy or separated ends exceeds 2 per 1,000 ends, the beam is rejected or the loom speed is reduced by 10–20%. The operational boundary for acrylic ester-sized polyester warps is reached when the water jet pressure exceeds 3.5 MPa and the size add-on is below 3%, because the combination of high water impact energy and low film mass removes size from the yarn surface at a rate that cannot be compensated by increased size box concentration. In such cases, the warp is unsuitable for high-pressure water jet weaving, and a switch to a stiffer PVA-containing size or a higher add-on condition is required. The conversion of high-orientation POY into water jet warp beams is therefore not a single-step drawing operation but an integrated process in which draw ratio uniformity, size film toughness, drying history, and beam hardness must be controlled simultaneously within the limits described above.