Tricot Warp Knitting Machine

Overview

A tricot warp knitting machine makes fabric from a sheet of many parallel yarns called the warp, rather than from one yarn fed across the width as a weft knitter does. Every needle has its own yarn or small group of yarns, and a course of loops is formed across the entire width in a single stroke of the needle bar. Because all needles work at once and the needle stroke is short, tricot machines run extremely fast, commonly two to three thousand courses a minute, and they turn out wide rolls of dimensionally stable fabric used for lingerie, swimwear, sportswear linings, automotive trim and technical textiles.

The machine pulls yarn from a Warp Let-off, forms loops on a Needle Bar with the help of a Guide Bar and a Sinker Bar, sets the pattern with a Shogging Drive drive, runs everything in time from a Main Drive, and draws the cloth off with a Fabric Takedown under Control Electronics.

Warp supply and let-off

The warp comes from several large Warp Beam units, each wound with thousands of parallel ends. Feeding all those ends at even tension is critical because tension sets loop length and fabric uniformity. Each beam has a Let-off Servo that unwinds it at exactly the rate the knitting consumes yarn, closing the loop against a Tension Sensor. A Tension Bar over which the sheet passes smooths out the surges that come as the needle bar accelerates and stops. Different guide bars often draw from different beams, which lets the machine combine a tight ground yarn with a longer-lapping pattern yarn.

The needle bar

The full-width Needle Bar carries one Compound Needle per wale, mounted in groups on cast Needle Block units bolted along the bar. The compound needle is what makes tricot speed possible. Instead of a pivoting latch, it has a fixed hook and a separate Closing Wire that slides up to close the hook. The two parts move on slightly different strokes, so the needle does not have to rise far to clear and close, and a short stroke means high cycle rates with low vibration. The bar rides on a Bar Carrier rocker driven by Drive Eccentric cams on the main shaft, so every needle rises, takes yarn and knocks over in perfect unison.

Guide bars and lapping

The Guide Bar assemblies are what give warp knitting its pattern. Each bar carries a full row of Guide Needle eyelets, one per warp end, held in Guide Block groups. Each course the bars swing through the needle line on the Swing Shaft so the guides wrap their yarn around the needle hooks. Between swings, each bar shifts sideways by a chosen number of needle pitches. That sideways shift is the lap, and the sequence of laps over successive courses defines the fabric: a simple closed lap gives plain tricot, while combining the laps of two or three bars gives locknit, sharkskin, raised and mesh structures. A tricot machine typically runs two to four guide bars.

Sinkers and knock-over

The Sinker Bar carries a row of Sinker elements that sit between the needles. They hold the fabric down while the needles rise so old loops do not lift with them, and they help knock the new loop over the closed hook. A Sinker Cam times the sinker advance and retreat against the needle and guide motion, all referenced to the same main shaft.

Pattern, drive and takedown

The Shogging Drive drive sets the lap of each bar. On electronic machines a Shog Servo moves each bar through a Ball Screw on a Linear Guide Rail, reading the lap sequence from a stored Pattern Reference, which lets a pattern change happen without new pattern chains. The Main Drive uses a Main Motor turning a Main Shaft through a Gearbox Housing and Helical Gear Pair sets so the needle, guide and sinker bars all keep fixed timing. The finished cloth is pulled off by the Takedown Roller and wound onto a Batching Roll by the Takedown Servo, whose draw rate sets stitch length. The Control Electronics ties it together through an Microcontroller, Servo Drive amplifiers, a Power Supply and the Operator Panel panel.

Fabrics, variants and use

Tricot fabric is run-resistant, smooth and stable, which is why it lines jackets and bags, backs laminates and forms the face of warp-knit sportswear and lingerie. The number of guide bars sets how rich the structure can be: two bars make economical liner cloth, while three and four bar machines make patterned and brushed fabrics. The close cousin of the tricot machine is the raschel machine, which uses latch needles and more guide bars for lace and open nets; the tricot machine trades that openwork range for speed and a closed, smooth ground. Working widths run from about 130 to 260 inches, so a single machine can feed a large finishing line with wide rolls at high output.