The Difference Between Flat Yarn and Round Yarn Dryer Fabric

When selecting the dryer fabric, many people typically focus on parameters such as price, durability, dimensions, and air permeability, yet often overlook another equally important design factor: the yarn profile.

Currently, the monofilaments used for the dryer fabric on paper machines primarily feature either flat or round yarn structures.

This distinction goes beyond mere appearance, cause the filament shape significantly influences performance in areas such as sheet support, air permeability, and resistance to contamination.

If you are uncertain about which type to choose, this article will help you select the right dryer fabric for your specific paper machine and paper grade.

Advantages of Flat Yarn and Round Yarn Dryer Fabric

Due to differences in filament material, flat-monofilament and round-monofilament dryer fabric exhibit distinct characteristics regarding sheet support, drying performance, and resistance to contamination.

However, it is important to note that filament morphology is merely one factor in dryer fabric design. The fabric structure, weaving method, material quality, and heat-setting process employed all influence the fabric’s final performance. 

Therefore, the selection of a dryer fabric should be based on a comprehensive assessment.

Sheet Support

Flat yarn dryer fabrics are woven from polyester monofilaments with a flat cross-section. Compared to round yarn fabrics, they feature a flatter surface that offers a larger contact area with the paper sheet, thereby providing more uniform and continuous support. 

This enables the fabric to effectively minimize marking on the paper surface and reduce localized sheet deformation.

Round yarn dryer fabrics are woven from round yarns. This results in a softer, more flexible fabric structure, though the contact surface with the paper sheet is consequently less smooth than that of flat yarn fabrics.

Paper Sheet Drying

Differences in airflow are a significant factor contributing to the differing sheet drying capabilities of these two types of dryer fabrics.

Round yarn dryer fabrics feature a smaller cross-sectional area and a higher open area ratio. All of these factors cause this fabric to offer low air resistance and excellent air permeability, resulting in high evaporation capacity.

In contrast, flat yarn dryer fabrics offer increased filament coverage, resulting in slightly lower air permeability. However, they facilitate more uniform air distribution, providing a more stable drying environment for the paper sheet.

High air permeability does not necessarily equate to high drying efficiency. In fact, during actual production, if the permeability of the dryer fabric is mismatched with the paper grade, machine speed, or steam load. It can lead to uneven cross-machine moisture distribution or issues such as localized over-drying or under-drying, thereby adversely affecting paper production.

Therefore, when selecting a dryer fabric, you should make an appropriate choice by comprehensively considering its air permeability in relation to the specific operating conditions, including the type of paper being produced and the paper machine speed.

Fouling Resistance

During paper machine operation, stickies, resins, fillers, and fines easily adhere to the dryer fabric. 

Over time, this affects the fabric air permeability and drying efficiency.

For flat yarn dryer fabrics, the smoother surface prevents contaminants from easily penetrating the fabric structure. Furthermore, adhesive substances adhering to the surface are generally easier to wash away using high-pressure spray systems.

Consequently, these fabrics tend to maintain a cleaner condition, particularly in applications involving recycled waste pulp or operating environments with high levels of sticky contaminants.

The warp and weft of round yarn dryer fabric consist of round filaments, creating deep grooves that allow contaminants to easily penetrate the fabric structure, making them difficult to wash out. 

The long-term accumulation of these contaminants reduces air permeability and can even lead to paper defects, necessitating more frequent cleaning.

Wear Resistance

Due to the larger contact area between the flat yarn dryer fabric and the paper sheet, local contact pressure is reduced. So the flat filament fabric effectively prevents localized wear and maintains good dimensional stability.

But this does not mean that all flat yarn dryer fabrics have a longer service life than those made of round monofilaments.

In fact, the service life of a dryer fabric depends more on factors such as the quality of the polyester monofilament, weaving quality, the heat-setting process, and routine cleaning and maintenance.

Applicable Scenarios of These Two Dryer Fabrics

Flat Yarn Dryer Fabric

The flat yarn dryer fabric offers a superior overall performance. It is widely suitable for applications requiring high paper surface quality, resistance to adhesive buildup, or high contamination resistance, such as the initial dryer sections of paper machines, high-speed paper machines, high-quality paper production lines, and machines processing poor-quality pulp.

Round Yarn Dryer Fabric

The round yarn dryer fabric is mostly suitable for low-speed paper machines, or for the production of ordinary cultural paper and packaging paper, where the requirements for paper surface quality are not high, but the softness of the dry wire is required, or for the production of paper with high air permeability requirements.