The headbox is the heart of the paper machine, what is its task and composition?

The headbox is a key part of a modern paper machine. Its function is to ensure that the paper material is evenly and stably connected to the Internet along the full width of the paper machine, and to ensure proper flow and flow rate, so as to form a uniform wet paper sheet on the Internet. creating condition. The structure and properties of the flow stock are decisive for sheet formation and paper quality.

Its main tasks:

① It can effectively disperse fibers.

The high-turbulence headbox can generate high-strength micro-turbulence, which can effectively disperse fibers, prevent fiber precipitation and re-flocculation, and effectively improve the strength of paper sheets. ② Distribute the paper stock evenly in the transverse direction of the paper machine (determines the transverse quantitative distribution of the paper web). ③ Stable shotcrete to ensure that the pulp speed is coordinated with the wire speed (determines 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, rubber and a small amount of air. important influence.

In the process of conveying the paper stock to the headbox, it is required that the cross-section of the paper material flow on the top line forms a rectangle along the full width of the paper machine, and the distribution of the speed and the guessing of each point along the full width and full height of the rectangular cross-section It is uniform, so as to ensure the stability of the pulp flow on the Internet, without turbulence, 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 Internet must be a uniformly dispersed fiber suspension, and the state of non-directional arrangement of fibers in the pulp flow should be improved as much as possible, so that the fibers of the paper material are very uniform like small snowflakes during dehydration. It can be deposited on the wire without flocculation and the probability of arranging the fibers in all directions as close as possible is nearly equal, so as to ensure the uniformity of the distribution of the fiber structure of the paper.

The headbox can be roughly divided into four types: the first type is called an open headbox, and the speed of the pulp on the Internet depends on the height of the pulp level in the box, and is often adjusted and controlled by overflowing methods; the second type is called an open headbox. It is an air-cushion headbox. The top of the box is closed, and the height of the pulp in the box is kept constant. By adjusting the pressure of the air cushion above the liquid surface, the flow rate of the online paper material is controlled; the third type is called full-flow headbox. It does not have a large box, and usually uses the pressure of the flushing pump to achieve the pulp speed required for the Internet; the fourth type is a full-flow air-cushion combined headbox, which is used in a general full-flow headbox. An air-cushion box is added, and the air-cushion pressure in the air-cushion box is used to adjust the pulping speed.

Among these four types of headboxes, the first two are used more in our country, among which the air-cushion headbox is more advanced. The headbox is generally composed of three main parts: distributor, weir pool and weir plate. ① Spreader. The distributor consists of a square cone distribution main pipe and a series of tube bundles on its sides connected to the weir pool. The online paper material is even and consistent.

The weir pool is the main body of the headbox, and its function is to maintain a stable flow rate of the paper material according to the requirements of the speed of the paper machine; Spray onto the wire at a certain flow rate and angle to form a uniform wet sheet. ② Weir pool. The weir pool is the main component of the headbox, and its function is to keep the paper material in the weir pool with a static pressure head adapted to the pulp speed and wire speed of the weir plate according to the running speed of the paper machine, and with the help of the rectifying element (even The role of pulp roller, stepped diffuser, etc.), to generate appropriate turbulence to disperse the flocculation of fibers and stabilize the flow rate of the paper material, ensure the uniform dispersion of the paper material on the Internet and eliminate the speed gradient of the paper material on the Internet.

③ Weir plate. On the Fourdrinier wire paper machine, the paper material is sprayed onto the wire surface of the Fourdrinier wire at a certain speed and angle from the jetting port of the weir plate of the headbox, and the filtering effect is caused by the pressure difference generated by the dewatering element under the Fourdrinier wire. , so that the fibers and additives in the paper material are deposited on the wire surface, and gradually dehydrated to form paper sheets.