Sheet formation or forming is the process by which a suspension of fibres in water is converted to a mat of fibres which then goes on to become a single or multi layered sheet.
The papermaking industry categorises its products in many ways. One such way is by the grammage of the finished sheet. Although most of the papermaking principles are the same for each of these types of product, the ways in which they are manufactured have their own distinct differences.
The invention and development of the continuous paper machine is detailed in the History category of this wiki.
Sheet forming takes place at the wet end of the machine, where a dilute suspension of fibres is poured onto an endless mesh belt through a narrow slot known as the 'slice'.
The ratio of the stock speed to the forming fabric speed is known as the efflux ratio. This along with the angle the stock hits the forming fabric, and the position it hits it, all have a significant effect on sheet formation and first pass retention.
This 'endless belt' was originally made of phosphor bronze and was called the 'the wire'. Today it is usually made of a synthetic polymer material and is now called the 'forming fabric', although many people still use the term wire..
As the fibre travels through the forming section de-watering takes place and the slurry of fibres becomes a mat of fibres. Dewatering is aided by such devices as table rolls, foils, vacu-foils and vacuum boxes, which are underneath the forming fabric. This part of the Fourdrinier, where the dewatering equipment also supports the fabric is known as the forming table or forming section.
Early machines had a flat horizontal wire section and this configuration has become known as the Fourdrinier process. Since that time many other configurations have been developed and are listed below.
Multi-ply machines for making boards may be variations on the Fourdrinier or on the vat former. In each case the set of equipment that generates each ply is known as the 'former'.
The principals of sheet formation are the same, no matter what equipment is used.
We will look at these different types of paper
We will also look at all the different types of equipment on which these different products are made
If you would like a simple explanation showing the difference between a twin wire former and a twin wire Fourdrinier, watch this short video.
Pages in category "Sheet Formation"
This category contains only the following page.