Solving Streaks in Circular Knits After Circular Knitting Machine Stops

Introduction

Circular knitting machines are a cornerstone of modern textile manufacturing, prized for their ability to produce seamless tubular fabrics efficiently. However, a persistent challenge faced by textile producers is the appearance of streaks—visible lines or indentations in the weft direction—after the machine stops and restarts. These imperfections vary in appearance, ranging from fine, well-defined lines to broader, more diffuse bands, depending on fabric structure, yarn type, and machine conditions.

In dyed fabrics, these streaks often result in uneven coloration, leading to quality control issues. When severe, they can force manufacturers to discard defective sections, increasing material waste and production costs. Given the competitive nature of the textile industry, minimizing these defects is crucial for maintaining product consistency and profitability.

This article provides an in-depth examination of the root causes of streak formation in circular knitting machines and offers detailed, actionable solutions to mitigate the problem.

Understanding Streak Formation: Key Causes

Streaks occur due to tension inconsistencies in the yarn during machine stoppage and restart. Several mechanical and operational factors contribute to this issue:

1. Abrupt Changes in Yarn Tension During Stoppage

When a circular knitting machine stops suddenly, the yarn delivery system does not always decelerate uniformly. This abrupt halt creates a tension imbalance between the yarn fed before and after the stoppage. As a result:

The loop structure changes slightly, leading to a visible demarcation line.

The degree of streak severity depends on the machine’s braking system and deceleration rate.

2. Wear and Tear in Gear and Spindle Mechanisms

The drive gear and main spindle are subject to constant friction and minor oscillations during operation. Over time, this causes:

Gear tooth wear, leading to backlash and inconsistent yarn feed.

Shaft wear, resulting in slight misalignment that alters yarn tension.

Formation of positioning grooves, which disrupt smooth gear movement.

These mechanical degradations contribute to tension variations, manifesting as streaks in the fabric.

3. Slippage in the Yarn Delivery Adjustment System

The yarn delivery mechanism relies on precise friction between:

The adjustment disc (which controls yarn feed rate).

The drive belt (which transmits motion from the motor).

If the belt is worn or insufficiently tensioned, or if the adjustment disc surface is degraded, slippage occurs. This leads to:

Inconsistent yarn feed rates during machine deceleration and acceleration.

Tension spikes that distort loop formation.

4. Degradation of Yarn Carrier Components

The yarn carrier (also called the yarn feeder) must maintain precise yarn positioning. Common issues include:

Worn drive teeth (causing irregular yarn movement).

Clogged or dirty guides (increasing friction).

Loose or stretched drive belts (resulting in inconsistent feed).

Any of these problems can alter yarn delivery per needle cycle, leading to streak formation.

5. Excessive Play in the Needle Bed and Cam System

The needle bed and cams must remain tightly aligned to ensure uniform stitch formation. However, wear over time can cause:

Vertical play in the needle bed, leading to slight misalignment during machine stoppage.

Cam wear, altering the needle movement path.

Loose triangle seat chassis, introducing instability during high-speed operation.

These factors contribute to tension inconsistencies that appear as streaks.

Advanced Solutions to Minimize Streaks

To address these issues, manufacturers must implement both mechanical adjustments and operational best practices. Below are detailed strategies to reduce or eliminate streaks:

1. Optimize Machine Deceleration and Braking

Gradual deceleration: Adjust the machine’s braking system to slow down smoothly rather than stopping abruptly.

Programmable logic controller (PLC) settings: Modern machines allow fine-tuning of deceleration curves to minimize tension spikes.

Soft-start mechanisms: Ensure the machine ramps up speed gently upon restarting.

2. Enhance Yarn Tension Control

Install active tensioners: These devices dynamically adjust yarn tension in real time, compensating for fluctuations.

Increase warp tension slightly: This stabilizes yarn movement during transitions.

Use pre-tensioning guides: These help maintain consistent tension before the yarn enters the knitting zone.

3. Upgrade Wear-Prone Components

Replace steel wire runways with polymer-coated tracks: Reduces friction and wear.

Use hardened steel gears and shafts: Extends component lifespan.

Install high-quality drive belts with anti-slip coatings: Ensures consistent yarn feed.

4. Improve Needle Bed and Cam Stability

Reduce virtual play in the lifting rod: Tighten adjustments to minimize oscillation.

Regularly inspect and replace worn cams: Ensures precise needle movement.

Stabilize the triangle seat chassis: Prevent excessive lifting during high-speed operation.

5. Implement Preventive Maintenance Protocols

Schedule regular lubrication: Reduces friction in moving parts.

Monitor belt tension weekly: Prevents slippage-related issues.

Conduct vibration analysis: Detects early signs of gear or bearing wear.

Conclusion: Achieving Consistent Fabric Quality

Streak formation in circular knitted fabrics is a multifaceted issue, stemming from mechanical wear, tension imbalances, and suboptimal machine settings. By implementing the solutions outlined above—ranging from tension control enhancements to mechanical upgrades—manufacturers can significantly reduce or eliminate these defects.

Investing in high-quality components, adopting advanced tension control systems, and adhering to strict maintenance schedules will yield long-term benefits, including:

Higher fabric consistency (reducing dyeing and cutting defects).

Lower material waste (improving cost efficiency).

Extended machine lifespan (minimizing downtime).

For textile manufacturers seeking to enhance product quality, addressing streak formation should be a priority. By combining technical adjustments with proactive maintenance, they can achieve smoother production runs and superior fabric output.

Would you like further details on specific machine models or tension control technologies? Let us know how we can refine these recommendations for your production setup.