Performance of the head box
As the junction of "flow" and "forming" in paper machines, the basic task of the head box is to provide good prerequisites for paper sheet forming, that is, to evenly distribute the paper material along the width direction of the paper machine, ensuring uniform pressure distribution, speed distribution, flow distribution, concentration distribution, as well as controllable and uniform fiber orientation; Effectively disperse pulp fibers, prevent fiber agglomeration, and provide and maintain stable sizing head and pulp web ratio according to process requirements.
In the long-term development of pulp and paper technology, although various structural forms of headboxes have emerged, their main functions remain basically unchanged, namely pulp spreading, homogenization, and spraying.
Specifically, the basic functions of the head box are manifested in five aspects:(1) Provide a uniform and stable jet flow to the entire width of the paper machine, avoiding horizontal jet flow, no directional tributaries or longitudinal stripes;
(2) Provide a stable lip plate with geometric dimensions that meet the requirements, unaffected by temperature, pressure, and lip opening degree;
(3) Form a fiber suspension with few flocs and good dispersion;
(4) Provide a control system that can meet the process requirements for the quantitative distribution of banners, drop points, spray angles, and spray speeds;
(5) Provide convenient measures to keep the slurry box clean and easy to operate and maintain.
A good head box must have the following performance:
(1) Capable of producing a quantitative, uniform, and stable paper web without longitudinal streaks on the web;
(2) The lip area of the slurry box should not be affected by pressure, temperature, and lip opening degree to ensure uniform distribution of the horizontal direction;
(3) Avoid the occurrence of slurry hanging or sticking in the slurry box;
(4) Easy to maintain cleanliness inside the box;
(5) The speed ratio of the slurry mesh is controllable.
Therefore, the head box must achieve:
(1) Can evenly distribute the slurry towards the direction of the paper machine;
(2) The sprayed slurry should have a uniform velocity profile, concentration profile, and turbulence profile.
