Addressing Arc-shaped Fabric in Circular Knitting Machines: Causes, Impact, and Solutions

Arc-shaped fabric is a common issue encountered in circular knitting processes. This type of fabric, where one side is tight while the other is loose, disrupts the smooth winding of fabric rolls, causing several challenges in subsequent processes such as cutting, coating, and printing. The fabric takes on a distinctive fan-shaped or arc-shaped appearance when unwound and laid flat, as the side with looser yarns forms the outer arc, while the side with tighter yarns forms the inner arc. This phenomenon significantly impacts the quality and efficiency of textile production, making it essential for manufacturers to understand the underlying causes and implement effective solutions.

Arc-shaped fabric is visually distinctive. When the fabric roll is unwound and laid flat, it reveals a relaxed, fan-shaped arc. This characteristic occurs due to the uneven tension applied during the knitting process. The fabric’s misalignment disrupts the ideal winding pattern on the circular knitting machine, causing it to shift to one side. As the fabric roll continues to unwind, the deviation increases, making it more difficult to wind large rolls efficiently.

The consequences of arc-shaped fabric extend beyond simple misalignment. It introduces significant complications in the subsequent stages of production, particularly in cutting, coating, and printing. The misalignment hampers the ability to correct fabric deviations, leading to imperfections in the finished product. In addition, the varying tension across the fabric causes inconsistent quality in downstream processes, affecting the overall output.

Understanding the root causes of arc-shaped fabric is crucial for resolving the issue. Two primary factors contribute to this problem: insufficient tension from the expansion rods and misalignment or inclination of the upper traction rollers.

One of the primary causes of arc-shaped fabric is insufficient tension in two of the four expansion rods on the circular knitting machine. In the knitting process, four rods are typically used to expand the fabric tube evenly. However, when two of these rods fail to provide adequate tension, it results in an imbalance.

Explanation of the Issue:

In the knitting machine, rods 1 and 2 are intended to apply tension against the inner surface of the fabric tube, while rods 3 and 4 do not exert enough pressure on the opposite side. As the fabric passes through the upper traction roller, friction resistance on the tighter side (rods 1 and 2) causes the knitted fabric to elongate. The flat yarns, which are elastic, stretch under tension and return to their original length when the force is removed.

On the side with rods 3 and 4, the lower friction resistance results in less elongation and a looser edge. This difference in tension across the fabric tube leads to the formation of a fabric arc, as the side with tighter yarns contracts more, while the looser side remains relaxed, creating a visible imbalance.

Another common cause of arc-shaped fabric is misalignment or improper inclination of the two upper traction rollers, particularly in machines with clamp-type rollers.

Explanation of the Issue:

When the two upper traction rollers are misaligned, one roller may not exert even pressure across the fabric. This can be due to several factors, such as uneven coating on the rollers, foreign objects obstructing the roller, or an issue with one end wrapping flat yarns thicker than the other. These issues create a gap on one side of the fabric, leading to uneven elevation during the knitting process.

The side with the gap receives less tension, causing the fabric to slip and elevate more slowly than the side with the proper alignment. This disparity in elevation speeds results in one edge becoming tighter, while the other becomes looser. As the fabric is wound onto the roll, the side with the tight edge pulls the fabric towards it, creating the characteristic arc-shaped appearance.

By identifying the causes of arc-shaped fabric, manufacturers can take proactive steps to eliminate or mitigate the problem. The following solutions can help restore the balance in fabric tension and ensure a smoother, more efficient knitting process.

To address the issue of insufficient tension from the expansion rods, it is crucial to ensure that all four rods are evenly distributed and maintain consistent tension throughout the fabric tube.

Solution Steps:

Inspect the positioning of the rods to ensure that they are evenly spaced and adhere firmly to the inner surface of the fabric tube.

Ensure that the rods maintain uniform friction resistance around the circumference of the tube, preventing one side from becoming tighter than the other.

Regularly monitor the rods for wear and tear, as any deterioration could lead to uneven tension and exacerbate the issue of arc-shaped fabric.

Misalignment of the upper traction rollers is another critical factor contributing to arc-shaped fabric. Proper alignment and maintenance of the rollers are essential for achieving even tension across the fabric.

Solution Steps:

Perform regular inspections of the upper traction rollers to check for any signs of misalignment, wear, or debris accumulation.

Adjust the rollers to ensure they are perfectly aligned and exert even pressure on both sides of the fabric tube.

Clean the rollers thoroughly before applying new coatings to prevent residue buildup that could affect the fabric tension.

If necessary, replace the rollers or components that are showing signs of damage to ensure smooth and consistent operation.

Arc-shaped fabric is a significant issue in circular knitting machines, but with careful attention to the causes and implementation of the right solutions, manufacturers can minimize its impact on production. By ensuring uniform tension across the expansion rods and maintaining proper alignment of the upper traction rollers, the occurrence of arc-shaped fabric can be significantly reduced. These measures will not only improve the quality of the fabric but also streamline downstream processes such as cutting, coating, and printing. By addressing these key factors, manufacturers can achieve higher-quality end products and enhance overall production efficiency.