Managing Edge Curl in Forming Fabrics

Edge curling in forming fabrics poses a notable challenge for both paper makers and fabric manufacturers, especially for Fourdrinier machines. This issue can disrupt both paper quality and manufacturing efficiency, ultimately affecting profitability. To effectively tackle these challenges, it is crucial to understand the root causes of upward edge curl and identify actionable management strategies.

Strategies for Paper Makers:

Consequences of Upward Edge Curl

Upward edge curl negatively impacts the paper-making process in several ways:

Reduced Deckle/Finished Paper Width

Upward edge curl can lead to a significant reduction in the deckle or finished paper width. When fabric edges curl upward, paper width can shrink by as much as 5-10%. This limitation not only reduces the quantity of paper produced but also affects profitability, as manufacturers may struggle to meet the specifications required by clients or market demands.

Difficulty in Setting Edge Cutter Nozzles

Edge curl complicates the alignment of edge cutter nozzles. If fabric edges are unstable, accurately positioning the nozzles becomes challenging. This misalignment raises the risk of paper breaks during the cutting process, resulting in production delays and increased waste. For example, production downtime can increase by 15%, translating to substantial financial losses.

Uneven Sheet Formation and Lower Paper Quality

Upward edge curl leads to uneven sheet formation, causing variations in thickness and density. Paper makers depend on consistent quality to maintain customer satisfaction and uphold their brand reputation. An estimated 30% of quality complaints arise from issues linked to edge curl, highlighting the need for effective management to ensure product integrity.

Understanding the Causes of Edge Curl

Recognising the root causes of edge curling is vital for effective management. Several key factors contribute to this persistent issue:

Fabric Weave Pattern

Historically, single-layer fabrics were more prone to downward edge curl. However, the introduction of multilayer fabrics—such as 1.5-layer, double-layer, and 2.5-layer—has led to an increase in upward edge curl. The weave pattern differences between layers create tension that contributes to upward curl. For instance, the top layer is crafted for a smooth finish, while the bottom layer aims for durability, resulting in contrasting stresses.

Structural Imbalance

Structural imbalance is another factor exacerbating edge curl. Often, fabric manufacturers utilize larger-diameter weft yarns on the machine side to boost fabric lifespan. Conversely, finer weft yarns are used on the top side for optimal sheet release. This uneven combination results in varied stress distribution, aggravating upward edge curl, especially in multilayer fabrics.

Material Differences

The choice of materials used in fabric construction significantly influences edge curling. Polyamide, for example, is commonly employed on the machine side for durability. However, it absorbs up to ten times more moisture than polyester. This disparity impacts moisture absorption dramatically, especially since the pulp is composed of 99% water. Such differential absorption leads to edge curling, particularly under high moisture conditions.

High Edge Wear

High edge wear contributes to upward curling. This wear typically occurs just inside the fabric edge, often due to variations in roll surfaces or stationary elements like suction boxes that make inconsistent edge contact. In multilayer fabrics, the resulting wear pattern may lead to upward curling, posing challenges for production efficiency.

Effective Strategies for Managing Edge Curl: for Paper Makers

While fabric manufacturers are working diligently to address these issues, paper makers can adopt several actionable strategies to effectively manage edge curling:

1. Optimise machine tension and alignment: Fine-tune tension settings and ensure proper roll alignment to distribute stress evenly and reduce edge strain.

2. Inspect and maintain rolls and stationary elements: Regularly check roll surfaces and stationary components (e.g., suction boxes) for uneven wear or damage at the edges to prevent excessive fabric wear.

3. Enhance cleaning protocols: Use high-pressure micro-travel showers to remove pulp and contaminants that exacerbate edge stress. Consistent cleaning prevents buildup that worsens curl.

4. Monitor fabric condition: Track caliper, edge wear, and curl progression with real-time data to detect issues early and adjust operations accordingly.

Edge curling may stem from manufacturing and operational challenges, but Paper Makers can take control to minimise its impact.

Strategies for Forming Fabric Manufacturers:

How can Forming Fabric Manufacturers reduce edge curling?

 1. Raw material selection: Use high-shrinkage, high-shrink-force weft materials (polyester & polyamide) on the bottom to keep edges flat or slightly upcurled for smooth paper making. Collaborate with suppliers for low-edge-curl materials. Using alternate polyamide weft at top surface also reduces edge curl potential of multilayer forming fabric.

 2. Weaving parameters: Set bottom warp tension nearly double the top warp to balance plain top and twill bottom weaves in SSB fabrics, reducing curl stress.

 3. Heat setting: Apply higher CD tension (lower CD shrinkage) during heat setting to minimise edge curl in multilayer/SSB fabrics.

 4. Finishing: Use edge-forming treatment to keep edges downward. When soaked, edges may rise slightly but won’t disrupt production. Note: Paper Makers may see edge wrinkles during mounting—these resolve under tension. Avoid overdoing edge forming to prevent flappy edges.

 5. Lab testing: Pre-test curl potential post-heat setting to guide raw material choices and edge-forming adjustments.

Let’s design fabrics that power seamless production and top-quality paper!

 Visit www.pmccentre.com for innovative edge curl solutions.