Selection and Indicators of Polyester Forming Fabric

In the papermaking industry, polyester forming fabric are used in the forming section of paper machines. Their selection is a crucial technical decision that directly impacts paper formation quality, dewatering efficiency, operational stability, and production costs. Improper selection of forming fabric can lead to frequent paper defects and shortened lifespan.

Requirements for Forming Fabric Selection

Polyester forming fabric require smooth, burr-free wires, a flat surface, consistent tension across the width, and a specific thickness and density to ensure normal paper machine operation, improve paper quality, and reduce the consumption of polyester forming fabric per ton of paper. In production, the selection of mesh is primarily based on the type of paper machine (fourdrinier, cylinder, twin-wire, or gap former), the length of the paper machine’s wire section, the required wire width, the diameter and width of the cylinder mold, the type of dewatering wire (or transfer wire) in gap formers, the type of paper, and the properties of the pulp. This determines the model, length, and width of the forming fabric.

The selection of polyester forming fabric models includes the weaving series, warp and weft wire diameters, warp weaving density, and weft weaving density. The selection of the forming wire model should be based on the characteristics of the paper machine and the requirements of the paper type. At the same time, the properties of the pulp, fillers, sizing agents and other conditions should also be considered to ensure that the polyester forming wire prints lightly, the paper is fine and smooth, the retention rate of fillers, sizing agents and fine fibers is high, the white water concentration is low, the dewatering performance is good, and the dimensions are stable.

Weaving Classification of Polyester Forming Fabric

The selection of the number of heddles in forming fabric is an important indicator, as the number of heddles determines the texture structure of the molding mesh.
Single layer forming fabric use a two-shed weave, possessing good mechanical properties and dimensional stability, and are not easily damaged by external mechanical forces. However, the radius of curvature of the mesh wires is small, resulting in poor surface flatness. Therefore, single-layer forming fabric are generally suitable for the production of cardboard.

4 shed fabrics with a three-over-one weave have a uniform and flat surface. The mesh wire intersections do not form a straight-line pattern, resulting in lighter wire marking, less fiber loss, and strong dewatering capabilities. They can be used to produce various types of paper, such as newsprint and offset printing paper.

7 shed and 8 shed double layer forming fabric have complex weaving structures and excellent overall structure. They possess both a fine and flat surface and good mechanical strength and dimensional stability. They are widely used in the production of various high-grade papers, such as printing paper and tissue paper, on paper machines.

The 16-shed 2.5 layer forming fabric and the 20-shed and 24-shed SSB triple layer forming fabric are currently the most widely used types of fabrics in the paper industry. The SSB triple layer forming fabric adopts a triple layer structure design: the upper layer uses finer diameter warp and weft threads with a plain weave structure to improve the retention of fine fibers and fillers, and improve the uniformity and smoothness of the paper sheet, while also allowing for easy release of the fabric mark. The lower layer uses thicker diameter warp and weft threads to improve the structural stability and service life of the forming fabric.
The middle layer uses paired weft threads to connect the upper and lower layers, preventing them from rubbing and slipping against each other. The three-layer forming fabric increases fiber support, improving retention rate, paper quality, dewatering capacity, and longitudinal and transverse stiffness, while also offering good service life and operational stability, making it widely used in the market.

For curved forming section wire nip wire paper machine, in addition to using centrifugal force and vacuum force for dewatering, the pressure between the two wires is also utilized. Therefore, the tension of the forming fabric is also a factor in controlling dewatering. Generally, the mesh precision of the dewatering wire should be less than or equal to that of the transfer wire. For low-speed paper machines, while ensuring dewatering performance, it is best to choose a forming wire with high precision to ensure a smooth paper surface.

Four Indicators to Consider When Selecting Forming Fabric

Generally, the elongation of polyester forming fabric does not exceed 1.3% at maximum and is generally not less than 0.3% at minimum. This is related to the number of layers, weaving method, and type of mesh used in the forming fabric. When selecting the fabric, four mechanical lengths need to be considered:

• Minimum operating length: refers to the length of the fabric when all tensioning rollers are raised to the zero position, and the entire roller can still function.
• Maximum operating length: the length of the fabric when all tensioning rollers reach their maximum limit.
• Minimum installation length: The perimeter of the forming fabric when the breast rollers are falling and all tension rollers are at zero position, which is the minimum length of the netting that can be fitted onto the mesh frame.
• Minimum unfolded length: the length of the fabric when it is fully unfolded, which is the minimum length allowed when changing the fabric using a lifting sling.

Among these, the minimum installation length, maximum operating length, and minimum operating length are important criteria for selecting the fabric. To correctly select the length of the polyester forming fabric, accurate measurement of the maximum operating length of the wire frame should be performed, and the elongation of the forming fabric should be understood by accurately measuring the new fabric before putting it into use.