The headbox is a key component of a modern paper machine and the key hub connecting the two parts "conveying" and "forming". It is also one of the fastest-growing components of modern paper machines, especially new and modern high-speed paper machines, with a speed of several kilometers per minute and a width of more than ten meters. On this high-speed wide paper machine, it only takes a fraction of a second to tens of seconds from the headbox to eject the pulp to the setting.
In such a short period of time, the wire section alone is difficult or even impossible to produce sheets with a consistent basis weight and good uniformity. It must be ensured that the paper stock coming out of the headbox along the full width of the paper machine is stable and uniform to ensure that the fibers are fully dispersed. Provides and maintains a stable proportional relationship between shot speed and wire speed.
The traditional open headbox is far from being able to meet the production requirements of new paper machines. Although the overall structure of the headbox has not changed much over the past few decades, the unit is more finely tuned. A more uniform and stable pulp flow can be formed over the entire width of the paper, with little interference from transverse and longitudinal speeds.
Some of the key improvements in modern headboxes are: First, the installation of a pulse attenuator in front of or inside the headbox; and second, the installation of a conical header inside the headbox to generate uniform pressure and flow in the transverse direction of the web , which controls the overall adjustment of the layout according to lateral positioning and moisture distribution, thereby improving the quality of various papers.
The header box and the sandwich former are the representatives of the paper industry level in the past two or three decades. This headbox provides decoupled control of the fiber distribution and transverse basis weight fluctuations of the sheet. In the past, this was achieved by controlling the pressure on the netting pulp and adjusting the shape of the weir, which would change the flow pattern of the pulp, destroy the non-directional distribution of fibers, and affect the quality of the paper.
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