How does a paper machine work?

medium paper machine

Paper making machine is a kind of necessary equipment for every paper making mill. It can be divided into long screen type, round screen type, net type, stacking type and with decorative roller if they are divided according to the structure of the screen. A paper machine can be thought to be a combination of multiple equipments. The components of the machine are divided into two parts: wet section and dry section. The components of wet section include a flow equipment, a screen part and a press part. The components of dry section include a dryer, a calender, and a rewinder.

The raw materials are added, sized, filled and purified to become a pulp having paper making properties, and then the pulp is fed into flow device of the paper machine at a concentration of 0.3%-1.3%. After the distribution and leveling of the pulp by flow distributor and head box, the pulp is uniformly and stably transported to the forming screen surface. The pulp is filtered and dehydrated on the screen to form a continuous wet paper web. The screen is mainly provided with dewatering such as roll, vacuum suction box, and roll. When the wet paper web is dehydrated to a moisture content of about 20%, it can be stripped off from the screen surface and sent to the press section for further dehydration.

The press section is composed of several sets of roll press felts, and the wet paper web is supported by press felts and is mechanically pressed between the press rolls for dewatering. In order to maintain good dewatering performance of the press felt, the upper roll is provided with a felt washing device. After the press section, the dryness of the wet paper web is generally about 40%.

After dehydrated by the press section, wet paper web needs to be further dehydrated by heating and drying, etc. The drying section of the paper machine has a plurality of drying cylinders, which can be heated from the inside by steam, and the dry felt is coated on the drying cylinder to enable the paper web is pressed against the cylinder surface to improve heat transfer efficiency. After thorough drying, a calender of 6-8 rolls is used to improve the overall web surface quality.

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fiber crops, waste paper, or rags. Many kinds of paper are made from wood with nothing else mixed into them. This includes newspapers, magazines and even toilet paper. Pulp is one of the most abundant raw materials.

A pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fibre board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods (kraft and sulfite processes). The finished product may be either bleached or non-bleached, depending on the customer requirements.

A paper machine (or paper-making machine) is an industrial machine which is used in the pulp and paper industry to create paper in large quantities at high speed. Modern paper-making machines are based on the principles of the Fourdrinier Machine, which uses a moving woven mesh to create a continuous paper web by filtering out the fibres held in a paper stock and producing a continuously moving wet mat of fibre. This is dried in the machine to produce a strong paper web.

The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorine, such as chlorine dioxide, oxygen, ozone and hydrogen peroxide.

Chemical pulp is produced by combining wood chips and chemicals in large vessels called digesters. There, heat and chemicals break down lignin, which binds cellulose fibres together, without seriously degrading the cellulose fibres. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. The kraft process is the dominant chemical pulping method, with the sulfite process second. Historically soda pulping was the first successful chemical pulping method.