Selection of Forming Fabric Under Different Production Conditions

Paper Machine Forming Fabric

As a critical consumable fabric responsible for dewatering and transport within a paper machine, the judicious selection of polyester forming fabric is paramount to both the quality of the finished paper product and the stable operation of the machine. Selection criteria mandate that the fabric strands be smooth and free of burrs, the surface be flat, and the tension across the fabric width be uniform. Furthermore, the density and thickness of the forming fabric must be strictly controlled to ensure the paper machine’s normal production, thereby enhancing paper sheet quality and reducing the consumption of forming fabric per ton of paper produced.

In papermaking, the selection of polyester forming fabric is mainly based on the type of paper machine, machine speed, paper type and paper weight.

Parameters to Consider When Selecting Forming Fabric

The specifications of a forming fabric encompass its weave series, the diameters of its warp and weft threads, and the density of the warp and weft threads within the woven structure. The selection of its model needs to be based on the characteristics of the paper machine and the requirements of the paper type. Furthermore, consideration must be given to the properties of the pulp, as well as the fillers and sizing agents utilized. It is necessary to ensure that the forming fabric printing is light, the paper surface is delicate 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 dimensional stability is strong.

Selection of the Mesh Count for Forming Fabric

The mesh count is a key characteristic of forming fabric; it determines the fabric’s textural structure.

Single Layer Forming Fabric

The two-shed weaving method of single layer forming fabric has good mechanical properties and dimensional stability, making the mesh less susceptible to external mechanical damage. However, the curvature radius of the wire is small and the surface flatness is poor, so single layer forming fabric is generally used for the production of paperboard. In contrast, the “three-up, one-down” weave pattern employed in four-shed fabrics creates a forming surface that is uniform and exceptionally smooth; furthermore, the wire crossover points do not form linear patterns. This design results in minimal wire marking on the finished paper, reduced loss of fine fibers, and superior dewatering performance, thereby enabling the production of a wide variety of paper grades, including newsprint and offset printing paper.

Double Layer Forming Fabric

Double layer forming fabric consists of 7 or 8 shed, with complex weaving techniques and a good structure. It has both a fine, even, and flat wire surface and good mechanical strength and stability, making it widely applicable to the production of high-grade printing paper and thin paper.

2.5 Layer and Triple Layer Forming Fabric

The 16-shed 2.5 layer forming fabric and the 20-shed and 24-shed triple layer forming fabric is currently the most widely used fabric types on the market. The SSB triple layer forming fabric features a three-tier structural design—comprising upper, middle, and lower layers. The upper layer utilizes finer-diameter warp and weft threads arranged in a plain weave pattern, thereby enhancing the structural stability and service life of the fabric. The middle layer employs paired weft threads to tightly integrate the upper and lower layers into a cohesive unit, effectively preventing any relative friction or slippage between them. The structure of the triple layer fabric increases fiber support and improves retention rates. It is widely adopted in the market due to its superior advantages, including high paper quality, strong dewatering performance, high longitudinal and cross-directional stiffness, excellent operational stability, and extended service life.

Factors Influencing Dewatering in Forming Fabric

In twin-wire paper machine featuring a curved forming zone, dewatering is achieved not only through the utilization of centrifugal and vacuum forces but also through the pressure generated between the two wire fabrics; consequently, the tension of the forming fabric serves as a key factor in controlling the dewatering process. Generally, the warp density of the dewatering fabric is equal to or lower than that of the transfer fabric; this configuration ensures that the paper sheet is fully formed and results in a smooth, fine surface finish. Furthermore, for high-speed paper machines, it is advisable to select polyester forming fabrics with a relatively lower warp density—provided that the surface quality of the paper sheet is maintained—whereas for low-speed paper machines, the preference should be for fabrics with a higher warp density—provided that dewatering efficiency is ensured—in order to guarantee the flatness of the paper sheet’s surface.

Typically, the elongation rate of a forming fabric does not exceed 1.3% at its maximum, nor fall below 0.3% at its minimum. This elongation rate is primarily determined by the fabric’s layer count, weaving method, material molecular weight, and the specific model selected. Therefore, when determining the length of a forming fabric, it is generally necessary to specify four key mechanical lengths: the minimum operating length, maximum operating length, minimum installation length, and minimum unfolded length.