Important Properties of Forming Fabric in Papermaking

The forming fabric is a crucial component of the paper machine that carries the paper forming, dewatering, and wet paper web transfer. The quality of the paper and the stability of the paper machine operation are all determined by the forming fabric.

Structure of Forming Fabric

Since the transition from copper mesh to polymer materials, the more common types of forming fabric have been divided into several categories:

Single layer and 1.5 layer fabric forming fabric, which is commonly used in regions such as the United States and India, is mostly suitable for low-speed paper machines.

Double layer and 2.5 layer fabric forming fabric are currently widely used in the market.

Triple layer forming fabric (traditional three-layer fabric, SSB, IWB) provides higher fiber support index and achieves finer and smoother paper surface.

Flatness of Forming Fabric Surface

The flatness of the forming fabric surface has an impact on the flatness, two-sided difference, and smoothness of the wet paper web on the opposite side (often exposed on the outside of the paper). Generally speaking, the more fiber support points there are, the smaller the difference in the thickness of the warp and weft yarn of the surface layer, and the more uniform the overall distribution, the better the flatness of the forming fabric surface, and the corresponding smoothness and delicacy of the paper.

Forming Fabric Thickness of Weft and Warp Yarn

At present, the forming fabric used in high-speed paper machines are mostly designed with 2.5 or 3 layers. Therefore, for the fabric surface layer, the smaller the thickness of the warp and weft yarn used, the finer and smoother the paper surface will be. For the bottom weft yarn (the main wear surface), thicker threads are selected to ensure the wear resistance of the forming fabric.

Forming Fabric Air Permeability

The commonly used air permeability is CFM, which represents the total amount of air passing through one square foot per minute at a pressure of 125Pa. The higher the breathability, the better the water filtration performance of the pulp.

Forming Fabric Fiber Support Index

The number of fiber support points refers to the number of warp and weft points that support fibers within a range of one square centimeter on the front of the forming fabric. Generally speaking, the larger the number of fiber support points, the higher the retention rate of fibers and ash in the paper. When the number of fiber support points is low and the net is dehydrated too quickly and the vacuum value is large, it is easy for fibers (long fibers) to be sucked into the forming fabric. When the paper is peeled off from the fabric surface, it is very easy to cause “pulling” on the paper surface. This single fiber that is pulled out can easily cause problems such as surface sticking of the felt, increased paper lint in the dryer, paper lint impurity of the adhesive, and coating streaks in the back section.

Thickness of Forming Fabric

For forming fabric, the water holding space is often not given much attention, and the thickness of the fabric is more important. Due to the increasing speed of paper machines, how to quickly dehydrate them has become very important. We often find that under the same design, when we need to improve the dehydration performance or want a smoother mesh surface while maintaining the same speed, we need to reduce the thickness of the mesh to shorten the dehydration path, which can also better improve the problem of water splashing in the mesh.

Forming Fabric Material

The current forming fabric mainly uses two materials for warp and weft yarn: polyester and nylon. The characteristic of polyester is good shape stability, while the characteristic of nylon is good wear resistance. Therefore, the design of mainstream forming fabric mostly adopts a structure of polyester material+ thick and wear-resistant nylon weft at the bottom, which can balance the stability and wear resistance of the forming fabric. In addition, polyester and nylon are both high molecular weight polymers, and surface graft modification can endow the forming fabric with more characteristics, such as heat resistance, high strength, stability, acid and alkali resistance, low water absorption, etc.