subject: Forming Fabrics [print this page] Once the stock / pulp enters the headbox on the paper machine it is put onto the wire section of the machine at a consistency of around 1%.The stock needs to be applied evenly across the width of the paper machine wire. The paper machine wire is now transporting the stock and beginning the dewatering process required to form a sheet of paper. In the past the wire of the machine was exactly that, it was made from a non-ferrous wire such as bronze. These days the wire of the paper machine is more commonly made of plastic and is called the forming fabric.
Having synthetic forming fabric has allowed paper machines to operate at much faster speeds.The synthetic components have allowed for the fabrics to be engineered to give a cross directional stability that would not have been possible with the traditional paper machine wire. There are multiple designs of forming fabric dependant on what kind of product or specifications the mill requires. The top of the fabric has to be hard wearing, allow easy drainage but not mark the sheet. The underside of the fabric can be coarser.
The open area has to be as high as possible while still retaining as many fibres, and any fillers, as possible.There are often 2 or 3 layers to a modern forming fabric.The job of the forming fabric is to help dewater the stock while forming a good sheet to go on to the paper machine drying section. The traditional Fourdrinier machine had only one wire. Modern paper machines producing multiple layer products can have two or three wires, or forming fabrics. Although made from plastic / synthetic strands the forming fabrics are still finely woven. Under the forming fabric there are a number of devices to aid the dewatering process, such as suction boxes with HDPE or ceramic tops. These suction boxes are connected to vacuum pumps to help remove excess water.
As the sheet gets dries, it is possible to increase the vaccum on the suction boxes. It is possible on a well set up machine to see a distinct line across the Paper Machine wet end. By the time the sheet gets to the end of the forming fabric enough water must have been removed so that the sheet is strong enough to pass over the dryer sections without breaking. The average lifespan of a paper machine forming fabric would be between 45 and 60 days.
