Understanding and Resolving Weft-Direction Streaks in Circular Knitting Machines After Stoppage

Circular knitting machines are widely used in the textile industry for their efficiency and ability to produce a variety of fabric types. However, one of the persistent issues faced during the production process is the appearance of weft-direction streaks in the fabric following machine stoppage. These streaks, often subtle but sometimes prominent, not only impact the visual uniformity of the fabric but also pose challenges in dyeing and cutting operations. If not effectively managed, such issues can result in substantial material waste and reduced production efficiency.

Circular knitting machines typically produce streaks that appear as fine indentations or lines running in the weft (horizontal) direction of the fabric. These streaks form a boundary that differentiates the fabric knitted before the stoppage from that produced after the machine resumes operation. While in some fabrics this boundary is very distinct, in others it manifests as a broader area with less obvious contrast.

The severity and visibility of the streaks depend on several variables, including:

Fabric type: Different fibers and yarn blends react differently to tension changes.

Machine type and condition: The operational state and wear level of machine components significantly influence streak formation.

Yarn characteristics: Yarn elasticity, thickness, and structure can amplify or mask streaking effects.

Dyeing sensitivity: Some fabrics may show color variation more prominently when streaks are present, especially after the dyeing process.

When these weft-direction streaks are prominent, they disrupt the uniform appearance of the knitted fabric. In dyed fabrics, even minor tension variations during knitting can translate to noticeable color inconsistencies. This issue complicates the cutting and alignment process during garment production, often leading to material rejection or excessive trimming to remove flawed sections—both of which increase manufacturing costs and waste.

Identifying the root causes of streaks is critical for implementing effective solutions. Below are the most common mechanical and operational factors contributing to this problem:

When the machine stops or restarts, abrupt fluctuations in yarn delivery can cause temporary imbalances in yarn tension. This leads to variations in loop size, forming visible streaks in the fabric.

The drive gear and main spindle are essential in maintaining consistent yarn feed. Over time, oscillation during machine operation—particularly during stops—can lead to wear in gear positioning grooves and the spindle shaft. These mechanical changes affect the stability of the yarn tension during stop-and-go cycles.

The yarn delivery system often includes a yarn delivery adjustment disc and a drive belt. If these components are worn or suffer from reduced contact pressure, the friction coefficient changes. This alters the consistency of yarn delivery, especially during stoppage, contributing to streak formation.

Wear or clogging in the teeth of the yarn carrier drive mechanism can result in inconsistent yarn feeding. Additionally, if the drive belt is worn or not properly tensioned, it may slip during machine shutdown or startup, changing the yarn length delivered per stitch and forming streaks.

The yarn delivery system consists of several interconnected drive belts. If any of these belts are loose, damaged, or aged, they can lead to uneven yarn tension when the machine stops or starts again. This transient tension variation directly contributes to visible weft-direction marks in the fabric.

To address the streaking issue, manufacturers and machine operators can adopt a combination of mechanical adjustments, routine maintenance practices, and operational techniques. Below are proven methods to minimize or eliminate streaks caused by machine stoppage:

One effective solution is to increase the deceleration time of the knitting machine before a complete stop. Gradual deceleration reduces gear oscillations and minimizes the sliding effect between the drive belt and the adjustment disc. This helps to maintain stable yarn tension throughout the shutdown process, avoiding sudden changes that would otherwise leave visible marks in the fabric.

Slightly increasing the warp tension before stoppage can help stabilize yarn feed and prevent drastic fluctuations during the stop and restart. Care should be taken to avoid over-tightening, as excessive tension can cause other issues, such as yarn breakage or needle damage.

The triangle seat chassis controls the knitting cam movement. By minimizing its virtual (loose or excessive) position, operators can reduce unnecessary oscillation between the gear and shaft. Likewise, reducing the virtual position between the needle bed and the triangle ensures consistent loop formation, particularly during deceleration and reacceleration phases.

Selecting circular knitting machines equipped with more wear-resistant parts can significantly reduce maintenance frequency and enhance machine stability. For example, machines that avoid using steel wire runways or wave bead mechanisms—which are prone to wear—can provide better consistency in yarn delivery and tension control.

During high-speed knitting, excessive lifting of the triangle seat chassis can cause vertical displacement and instability, especially when the machine stops abruptly. By maintaining the lifting amount within controlled limits, the fabric tension and yarn delivery path remain more stable, reducing the likelihood of streak formation.

In addition to the methods outlined above, factories should implement routine maintenance protocols and operator training programs to ensure long-term control of weft-direction streaks. Some of the best practices include:

Regular inspection of gear and spindle wear: Replace worn parts before they affect performance.

Drive belt tension checks: Ensure all belts in the yarn delivery system are correctly tensioned and replaced as necessary.

Lubrication and cleaning schedules: Clean drive mechanisms and apply appropriate lubricants to reduce friction and prevent clogging.

Operator training: Educate machine operators on the importance of controlled deceleration and proper yarn handling during stops and restarts.

Not all fabrics respond the same way to machine stoppages. Therefore, factories should tailor their streak-prevention strategies based on the specific fabric being produced:

For synthetic fibers like polyester or nylon, which are less forgiving of tension changes, extra care should be taken to ensure smooth yarn delivery and even tension across all feeders.

For cotton or blended fabrics, more tolerance is allowed, but the visual appearance of streaks can still be prominent, especially after dyeing.

For fine-gauge or high-density knits, tighter control of machine components and minimal mechanical play is crucial to maintaining uniform quality.

The formation of weft-direction streaks in circular knitted fabrics after machine stoppage is a common but manageable issue. These streaks are often caused by mechanical wear, uneven yarn delivery, or abrupt tension changes during stop-start cycles. Left unchecked, they can lead to significant color variation in dyed fabrics and cause complications during garment manufacturing.

By identifying the specific root causes—whether gear wear, drive belt slippage, or component misalignment—and implementing targeted solutions such as extended deceleration time, tension adjustments, and the use of wear-resistant parts, manufacturers can greatly reduce the incidence of streaks. Additionally, combining these methods with routine maintenance and operator training ensures consistent fabric quality, minimizes waste, and boosts overall production efficiency.

In an industry where precision, consistency, and quality are paramount, addressing the challenge of weft-direction streaks is essential. Through technological upgrades and attention to operational detail, circular knitting operations can achieve higher yields and deliver superior fabric that meets the increasingly stringent demands of the textile market.