The headbox is the heart of the paper machine, what is its task and composition?
Its main tasks:
1. Can effectively disperse fibers.
The high-turbulence headbox can generate high-intensity micro-turbulence, which can effectively disperse fibers, prevent fiber sedimentation and re-flocculation, and effectively improve the strength of paper sheets.
2. Distribute the paper material evenly along the transverse direction of the paper machine (determine the transverse quantitative distribution of the paper web).
3. The spraying is stable, ensuring that the pulp speed is coordinated with the wire speed (determining the longitudinal quantitative distribution of the paper web). Before the paper material is sent to the headbox, it is a suspension composed of solid fibers, fillers, liquid water, glue and a small amount of air. important influence.
4. In the process of conveying the paper material to the headbox, it is required that the section of the upper paper material flow forms a rectangle along the full width of the paper machine, and the speed and motion of each point along the full width and full height of the rectangular cross section The distribution of the paper is uniform, so that the pulp flow on the web can be guaranteed to be stable, without deflection, cross flow and large eddy current, so as to obtain paper with uniform characteristics in all directions.
In the process of pulp flow, it is required that the paper material on the net must be a uniformly dispersed fiber suspension, and the state of the random arrangement of fibers in the pulp flow should be improved as much as possible, so that the fibers of the paper material are as uniform as small snowflakes during dehydration. Deposit on the net without flocculation and make the probability of fibers arranged in all directions as close to equal as possible, so as to ensure the uniformity of paper fiber distribution.
Headboxes can be roughly divided into four types: the first type is called an open type headbox, and the slurry speed on the Internet depends on the height of the slurry level in the box, and the overflow method is often used to adjust and control it; the second type It is an air cushion type headbox, the top of the box is closed, the pulp level in the box is kept constant, and the flow rate of the paper material on the net is controlled by adjusting the pressure of the air cushion above the liquid surface; the third type is called full flow headbox It does not have a large box, and the pressure of the pulp pump is usually used to achieve the pulp speed required for the online; the fourth type is a full-flow air cushion combined headbox, which is an addition to the general full-flow headbox An air cushion box is added on the top, and the air cushion pressure in the air cushion box is used to adjust the speed of the online pulp.
Usually headbox is used in cresent-former tissue paper making machine,fourdrinier culture paper making machine and kraft paper making machine.