Paper production process
A step-by-step guide to our paper production procedures:
Recyclable paper is mixed with process water and then stirred in a giant stainless steel vat, called a pulper, to make a fibre suspension. Impurities are removed using a series of screens. Ink can be removed during white recovered fibre production by mixing the pulp stock with soap and blowing air through it to create a foamy ink residue. (The residue is sometimes re-used as a secondary raw material.)
The paper making apparatus is very large. It removes water from a solution comprised of roughly 1% fibre and 99% water.
Only by diluting the stock in this way can it be used to make thin, uniform paper quickly.
At the wet end of the paper machine sits the headbox, which distributes a uniform jet of watery stock to be produced .The suspension of water and fibre emerges from the slice. Optimum settings ensure that the fibres will weave together in a tight mat.
The liquid falls onto the wire or forming fabric. Beneath the wire, foils (short for hydrofoils) remove water and improve fibre uniformity.
The wire passes over suction boxes that vacuum out the water, leaving a soft mat of pulp that forms the paper sheet, or web.
By now the wire has travelled 30-40 meters. In a couple of seconds the water content has dropped to 75-80% and the web has lost its wet sheen.
The next stage of water removal consists of passing the paper web through a series of nip rollers that squeeze the water out of the pulp mat. This pressure also compresses the fibres so they intertwine to form a dense, smooth sheet.
This reduces the water content to around 45 to 55%.
The paper web now web travels through an enclosed space containing numbers of large rotating cylinders. They are warmed up to 130º C using steam heat, often efficiently produced by burning the factory’s waste material. The paper is now 80 to 85% dry.
Wet sizing solution is now applied to the paper in order to add a thin layer of starch to the surface. Starch contributes to stiffness and the bonding of the fibres within the sheet of paper.
After the sizing is applied the paper passes through another set of steam-heated drying cylinders. In all, the paper web may travel 400 meters through the dry end. In the process it will lose roughly 93% of its water.
To give the containerboard a smooth and glossy surface, especially necessary for printing, the paper passes through the calender. This is a set of smooth rollers, which can be hard or soft, that press the paper, embossing a smooth face on the still-rough paper surface.
Real-time quality control
Producing high-quality paper depends on maintaining extremely fine control over countless variables in the manufacturing process. The sheet of paper is now inspected by an automated measuring device that detects imperfections.
After completing its 500-metre journey the containerboard exits from the paper machine and is automatically wound onto a jumbo reel. It weighs 50 tonnes and with a diameter of up to five metres and width up to eleven metres.
On a regular basis, samples of containerboard are taken to an adjacent testing room. Most facilities have computer-controlled machines that automatically test the paper samples.