Knitted fabric is soft, elastic and easy to deform. In a knitting dyeing machine, a small excess of tension, repeated over hundreds of circulation cycles, can change the width, length and hand feel of a whole batch. This guide explains why stretching happens, how to control it, and what operators should check every run. It is written for dyehouse managers, process engineers and machine buyers.
Knitted structures are built from interlocking loops. Unlike woven cloth, they have no rigid warp and weft threads to resist pulling. When the machine pulls the rope of fabric harder than it needs to, the loops elongate. At high temperature, close to the glass transition range of polyester or when cotton is wet and swollen, the yarn is even more willing to take a permanent set.
Stretch that is locked in during dyeing usually shows up later as poor dimensional stability: length grows, width shrinks, and the fabric relaxes unevenly in finishing or after the first wash. Dimensional change is normally checked against recognised methods such as ISO 5077 (dimensional change in washing and drying). A batch that passes colour but fails shrinkage is still a rejected batch.
Fabric that is stretched in one zone and slack in another takes up dye and liquor differently. This is one cause of shade variation, barre effects and streaking. Stable running keeps every metre exposed to the same liquor flow, temperature profile and residence time, which is the basic condition for right-first-time dyeing.
Speed is expressed in metres per minute and is normally set so that the fabric completes one cycle within a target time, commonly around one to three minutes depending on rope length. Running faster than the fabric can tolerate raises drag in the pipe and tension at the guide wheel. Lightweight, high-stretch fabrics such as elastane blends and fine-gauge jersey are the most sensitive.
The nozzle turns pump pressure into liquor velocity, and that velocity carries the fabric. If the nozzle is too tight for the fabric weight, or the main pump delivers more flow than the fabric needs, the liquor drags the fabric at the throat. Too little flow causes the opposite problem: fabric stalls, piles up and is then yanked forward. Both create tension spikes.
The guide wheel lifts the fabric out of the barrel and feeds it back to the nozzle. If it turns faster than the fabric, it pulls; if slower, the fabric rubs and can wind around it. Fixed-speed drives cannot follow the changing load during heating, so tension drifts as the batch runs.
Programs copied from woven-fabric recipes are a common mistake. Woven fabric tolerates higher speed and tension; knits do not. Steep heating gradients, hard cooling at the end of the cycle and heavy loads above rated capacity all raise the risk.
Start from the lowest speed that gives good liquor exchange and level dyeing, then raise it only if shade tests demand it. Use a lower speed for heavy loads, elastane blends and during the high-temperature hold. Many dyehouses keep a speed table per fabric family so operators do not guess.
The goal is a fabric rope that is carried, not pulled. Check that load weight matches the rated capacity and that the liquor ratio is enough to float the fabric. Overloading forces fabric to run tight and packed. Loading to about 70–90% of rated capacity is a common way to leave room for movement, but confirm against your machine manual.
Sew the rope carefully so the seam does not create a thick spot at the nozzle. Keep the fabric length per rope balanced, and avoid mixing different weights in one rope. A smooth, unobstructed path from barrel to nozzle to guide wheel means fewer stops and starts.
Ramp pump speed instead of switching it on hard. Use proportional heating and cooling so temperature and viscosity change gradually. Dosing chemicals in stages, ideally with a metering device, also avoids shocks caused by sudden liquor changes.
Quick rule: if you can see the rope tighten when the pump ramps or the temperature changes, the setting is too aggressive. Slow down first, then fine-tune the nozzle and guide wheel.
A high temperature and high pressure liquid flow dyeing machine is designed around one principle: let the liquor move the fabric, so that mechanical parts do as little pulling as possible. Zhejiang Yadong Machinery Co., Ltd builds these machines in Haining, Zhejiang, and the design features below are taken from the manufacturer's own Model SK product page.
In a jet machine the main pump sends liquor through the nozzle at speed, and the fabric is carried by that flow. The manufacturer states that large-flow nozzles improve levelling, and that a high-head, high-quality main pump gives stable, efficient running. Stable pump output means stable driving force, which is the first requirement for low tension.
The dyeing barrel structure matters as much as the nozzle. On the SK model, the fabric enters the main barrel quickly after the tail section, piles up and moves in a gentle wriggling motion. This reduces the creases caused by long compression and supports smooth high-speed running, including with two-strand input. The declared fabric speed range is 150–600 m/min, which gives a wide window to choose a gentle speed for knits.
The Yadong guide wheel automatically adjusts its speed to follow the fabric running speed. This directly addresses the mismatch problem described earlier and lowers the probability of abrasion and winding.
Fewer forced contact points, smoother barrel geometry and proportional control all reduce pulling. Optional systems listed for the SK series include a proportional heating and cooling device, a proportional dosing device, a meter-length measuring device and a pH control system. Each one removes a sudden change from the process.
| Item | SK-1 | SK-2 | SK-4 |
|---|---|---|---|
| Max. temperature | 140 °C | 140 °C | 140 °C |
| Max. pressure | 4 kg/cm² | 4 kg/cm² | 4 kg/cm² |
| Capacity (approx.) | 150–300 kg | 300–600 kg | 600–1200 kg |
| Main pump | 25 HP | 50 HP | 100 HP |
| Fabric speed | 150–600 m/min | ||
The SK page describes suitable fabrics as most woven and warp-knit fabrics and some knitted fabrics, including polyester, T/R, T/C, nylon, rayon, Tencel and filament. For pure weft-knit jersey or elastane-rich knits, compare the Model SP, Model SF and Model HP pages, or send your fabric details through the technical support team. If liquor consumption is also a target, see the ultra-low liquor ratio liquid flow dyeing machine and the company's sustainable approach. Note that at very low liquor ratios fabric floats less, so tension control matters even more.
Confirm the cycle time after loading and again once the batch reaches temperature. A cycle that becomes longer over time can mean overloading, pump wear or a partly blocked filter. A cycle that becomes shorter can mean the fabric is being pulled too hard.
Look at the fabric at the sight glass or when taking samples. Selvedge curling, sharp creases and rope marks are early warnings that the fabric is under uneven tension or is packed too tightly. Adjust speed or liquor level before the crease is set by heat.
Fabric wrapping around the guide wheel or nozzle needs immediate attention. Check guide wheel synchronisation, seam condition and rope twist. Untwist the rope before continuing if needed.
Record actual fabric speed, pump pressure and motor current. A rise in current at constant speed usually means increased load or drag. Compare against the previous good batch.
Do not: raise pump speed to "fix" a slow cycle without first checking load weight, filters and nozzle condition. It often turns a slow-running problem into a stretching problem.
There is no single number. Choose the lowest speed that gives level dyeing and a normal cycle time, then verify with a shrinkage test. Heavier and more elastic fabrics need lower speed.
Sometimes, with adjusted settings and a lighter load. Discuss your fabric with the manufacturer first; the Q&A page is a good starting point.
Need help choosing a knitting dyeing machine? Send us your fabric type, weight and batch size. The Yadong team can recommend a suitable model and setup.
Hotline: 0086-573-87096337
E-mail: gsj@yadong.com.cn
Address: No. 375, Xichuan Road, Haining City, Zhejiang, China
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