Fabric Bowing and Skew on Tricot and Raschel: A Diagnostic Guide
Bowing and skew are geometry faults, not surface faults: a course that should run straight across the width instead arcs toward one selvedge, or sits at an angle so the pattern leads on one side and lags on the other. Nearly every article published on the subject was written for woven cloth or for circular knits, which is why the cures they list – temple tension, weft insertion, cylinder rotation direction, yarn twist balance – name parts that a tricot or raschel machine simply does not have.
If you run warp knitting and your roll has bowed, the usual search results will not tell you where to look. This guide separates the advice that does transfer from the advice that does not, and gives a checking order built around the variables a warp-knitted line actually has.
What the inspection table is measuring
The fault is read the same way whatever machine the fabric came from. An inspector traces the real path of a course across the width, then measures how far it departs from the line that should sit perpendicular to the selvedge. Published practice expresses that departure as the offset divided by the fabric width, converted to a percentage, and takes the reading at several places along the roll rather than trusting one spot.
Two consequences are worth holding on to. The measure is proportional to width, so a wide raschel fabric carries a much larger absolute offset than a narrow one at the same percentage – the same reading, a very different look on the cutting table. And none of the standard references name an acceptable limit. Tolerance is a commercial term, not a published constant, which means it has to be written into the order rather than assumed.
Why the standard advice does not transfer
The published cause lists are specific to how each fabric is formed. Read across them and the mismatch is obvious.
| Fabric route | What carries yarn across the width | What the literature blames |
|---|---|---|
| Woven | The weft, inserted pick by pick | Unequal temple force at the two selvedges, roller speeds out of step, poor feed at the stenter, crooked seams at batching |
| Circular knit | A course laid by needles around a rotating cylinder | Twist level and twist balance in the yarn, machine rotation direction, uneven tension in dyeing and finishing |
| Warp knit (tricot, raschel) | Nothing – every end runs lengthwise from a beam and is looped in place | Not covered by the published sources at all |
That last row is the whole problem. A warp-knitted fabric has no picks, no temple, and no rotating cylinder, so a fault list built from those three parts has nothing left to point at. What usually happens next is familiar: the mill blames the dyehouse, the dyehouse blames the mill, and nobody has a checking order to settle it.
One part of the published advice does carry over. The causes attributed to dyeing, drying and heat setting – uneven tension across the width, uneven feed into the stenter, groups of rollers running at slightly different speeds – act on cloth rather than on loom parts, so they apply to a warp-knitted roll exactly as they apply to a woven one. It is the formation-side half of the advice that has to be rebuilt.
A checking order for a tricot or raschel line
The list below is a diagnostic sequence, not a set of measured results. It is ordered so that the cheapest question that can eliminate the largest area comes first.
Check the greige first, off the take-up, before anything wet. This single step splits the problem in half. If the fabric leaves the machine straight and arrives bowed after dyeing or heat setting, no machine setting is the cause and the finishing-side list above is the one to work through. If the bow is already there in greige, finishing is not the place to look.
Then work outward from the beam. Is warp tension even across the full beam width, or is one side running softer than the other? Beam build, flange condition, and the way partial beams are combined all show up as a tension difference that is constant across the width of the fabric – which is exactly the signature of a fault that grows steadily toward one selvedge.
Look at how the fabric is pulled, not only at how it is formed. Take-up and batching apply force across the whole width. A roller out of parallel, a cloth edge tracking off, or a batch building harder on one side will pull geometry into the roll after the loops are already formed.
Then the geometry of bars and bed. Guide bar alignment relative to the needle bed, threading across the width, and elements worn on one side of the machine more than the other all change where loops sit relative to their neighbours. A fault that is worse at one end of the bed, and repeats in the same place roll after roll, points here rather than at the beam.
Finally, read the construction itself as evidence. Light, fine-gauge fabrics expose this family of faults earlier than heavy ones – the published sources make that point for woven goods, and the reason is geometric rather than specific to weaving, so it holds for open warp-knitted structures too. If the same machine produces a visible bow in a light quality and none in a heavy one, that is a sign of an existing small tension difference being revealed, not of a new fault appearing.
If your greige is straight, stop looking at the machine
If the roll measures straight coming off the take-up and only bows after wet processing or heat setting, then the machine settings are not your variable, and the finishing causes in the published literature apply to you directly and without translation. If instead the bow is measurable in greige, the opposite holds: the finishing advice is not applicable, and the checks belong on let-off tension, take-up and batching, and bar-to-bed geometry, in that order.
This guide does not apply to woven fabric, where the temple and the inserted weft are genuine variables, nor to circular knits, where yarn twist balance and machine rotation direction are. If your fabric came off either of those, the widely published cause lists already describe your situation and are worth following as written.
Write the tolerance into the order
Third-party inspection services list bowing and skew among the defects they routinely check for, which means it is a live reject reason at the buyer end rather than a cosmetic argument between technicians. Because no public source names an acceptable figure, an order that says only that no bowing is permitted cannot be argued in either direction.
Four things make it arguable: the measuring method, stated as offset divided by width; how many places along the roll get measured; whether the limit applies to greige or to finished fabric; and the agreed figure itself. A recognised test method for bow and skew exists whose scope covers knitted as well as woven fabrics, and naming it settles the method question – though the document itself sits behind a paywall, so the limit still has to be negotiated and written down rather than inherited from a standard.
Machine-side checks cost a shift of attention; a rejected shipment costs the order. If you are tracing this on a specific configuration, the variables differ between a tricot machine and a raschel machine, particularly in how the take-up and the beam arrangement are laid out. For machine and configuration enquiries, our company site is at grandstarcn.com, and our engineers are glad to look at a described fault pattern with you.
Frequently Asked Questions
Why does my tricot fabric bow when the machine settings have not changed?
Check the greige roll before any wet process. A pattern that only appears after dyeing or heat setting points at tension and feed downstream, not at the knitting line. If the arc is already visible as cloth leaves the take-up, look instead at warp let-off evenness across the beam, batching rollers out of parallel, or worn elements on one side of the bed.
Is bowing a knitting fault or a dyeing fault?
Either, and a single measurement separates them. Take a reading from greige goods straight off the machine. Straight there and distorted later means the wet-processing and heat-setting route introduced it. Distorted already means formation-side variables are involved. Skipping that split is why this argument so often runs for weeks between a mill and its dyehouse.
How much bow is acceptable on warp-knitted fabric?
No published reference sets a figure, so the limit is whatever your contract says. Agree four points in writing: the method, stated as offset divided by fabric width; how many readings are taken along each roll; whether greige or finished goods are judged; and the permitted percentage. Without those, a rejection is difficult to contest either way.
Can bowed fabric be straightened after knitting?
The remedy published for circular knits is to re-run the goods and, where the distortion justifies it, to pass them through dedicated straightening equipment of the weft-straightener type. Those sources address circular goods, so treat the approach as worth trialling on warp-knitted qualities rather than as proven for them, and confirm with a sample before committing a full lot.
Hey, I’m Vincent!
Solving complex challenges with precision and creativity in the warp knitting industry. Passionate about advancing textile engineering and turning innovative ideas into reality. Shaping the future of warp knitting.
