The composition of the wire section of a Fourdrinier paper machine

The composition of the wire section of the Fourdrinier paper machine:

The wire part of the Fourdrinier paper machine is referred to as the Fourdrinier wire or the wire case for short. It is a typical fourdrinier network department. The main component of the net case is an endless fine woven net (metal woven net, generally made of phosphor bronze; or plastic net). The forming wire sleeve runs between two large rolls, with the breast roll near the headbox and the flat roll on the other end. The breast roll is usually used to support the web. In some papermaking systems, the breast roll also functions as a dewatering element or a vacuum former. The folding roller plays the role of supporting the net and removing moisture from the paper. Most of the power for rotating the screen is applied to the flat roller and the screen driving roller (turning roller).

The various elements between the breast roller and the flat roller have the dual functions of supporting the net and dewatering. According to specific needs, a variety of different dehydration devices can be used. The forming on the wire table of the old paper machine is basically composed of a forming plate, a table roll, a dewatering plate, a vacuum suction box and a flat roll. At present, most paper machines use a forming plate immediately after the breast roll, followed by a dewatering plate assembly, and then the net goes through a series of dewatering devices with gradually increasing vacuum levels: from a low vacuum wet suction box to a high vacuum dry Type vacuum box, and finally a high-vacuum roll.

The rewinding roller device brings the net back to the breast roller. The tension roller and guide roller are used to automatically maintain the correct tension and eliminate lateral displacement. A set of spray pipes keeps the net clean and removes dirt deposits.

Low-speed paper machine (such as those below 400m/min) are often equipped with a shaking mechanism to make the net swing laterally to improve the evenness of the paper. These low-speed paper machines are also equipped with rubber edge plates along the edges of the wire to block the slurry during the initial forming stage. Because the paper sheet is formed instantaneously on the high-speed paper machine, it is not necessary to use shaking and edge fixing devices.

Some Fourdrinier wire paper machines are equipped with a facing roller (watermark roller), which is installed above the wire in the vacuum box area and lightly pressed against the paper surface. The facing roller is covered with mesh cloth to compact the paper and improve the evenness of the paper. Some facing rollers have patterns on the mesh surface, which can be transferred to the paper to form watermarks or other specific patterns.

Usually a narrow strip is cut off on both sides of the paper web that then leaves the roll. Due to the low basis weight and unstable formation on both sides of the paper web, the general strength is poor, which may be the cause of the breakage of the paper web during transfer. The trimming is done by a high-pressure water jet called a water needle, which is located just above the net in front of the roll. The cut paper edge is taken away by the screen driving roller (turning roller) and washed into the pit of the vulcanized roller, where it is repulped, and then enters the damaged paper pulp flow system.

The forming process of the paper sheet of the Fourdrinier paper machine:

Pulp with a concentration of about 0.3%-1% is sprayed evenly onto the net from the lip of the headbox at a speed close to the net. As the endless Fourdrinier wire moves forward, the moisture in the pulp is discharged from the mesh by gravity or vacuum suction. As the pulp is dehydrated on the net, the fibers and fillers in the pulp are deposited on the net to form a wet paper sheet. The dewatering capacity of the paper sheet in the wire section accounts for more than 95% of the total dewatering capacity of the entire paper machine, and the dryness of the paper sheet leaving the wire section is 18%-23%; the high-speed paper machine can reach 27%.