Paper Machine Headbox

Paper Machine headbox is like the heart of the paper machine whose main function is to uniformly distribute the pulp slurry on the wire section of the machine in the machine direction (M.D) and it also matches the flow rate of the pulp slurry with the speed of the wire section, so that profile of the paper is maintained in machine as well as cross direction and the fiber is properly distributed on the wire section.

Functions of the Headbox:       

1. Headbox controls the fiber dispersion, so that the bond of the fiber are disengage from each other and it makes a uniform slurry of pulp.

2. Headbox controls sheet formation by controlling the flow and distribution of paper slurry on wire section which ultimately controls-

    a. Basis weight/GSM

    b. Caliper of the paper

    c. Overall paper qualities.

3. Headbox controls the forming variables like- 

    a. Jet impingment- It is the process in which a jet of fluid (air, water or other) is directed at a surface and whose main purpose is drying, heat transfer, paper formation, strength enhancement.

    b. Jet speed - Jet speed is the speed at which the paper slurry is ejected on the wire section which is crucial parameter of the headbox to control fiber distribution uniformly. 

   

   Types of Headbox's:

  1. Open type headbox

  2. Air cushion type headbox

  3. Hydraulic type headbox

1. Open Type headbox

Open type headbox operates on low speed paper and board machines and it simply spread the paper slurry on the wire section of the paper machine through the slice opening of the lip. It basically work on the potential head or elevation head energy principal where the pulp slurry flow with the head difference.

2. Air Cushion Type Headbox

Air cushion type headbox operates on high and medium speed machines where the pulp slurry is pumped through the tapered manifold from behind of the headbox and its pressure fluctuation is damped through the air pads in the headbox and then the pulp slurry goes to the different zones and distribution through nozzle and actuators via slice or lip opening on the wire part of the former section by matching the velocity of slurry distribution with the wire section.

3. Hydraulic Type Headbox

Hydraulic type headbox specially operates on the high speed paper machines and it does not have air cushion pads but there we use a PD tank which is also known as Pulsation Damping tank with which we damp pressure variations by using special rubber membrane, dampers of teflon and customised air pressure which pushes the dampers down and we get some deflection of rubber throughout the pipe area in recangular shape and it absorbes the pressure variations of pulp slurry and thus we get uniform flow of pulp slurry which then goes to headbox for further operation.