At the end of this module, you will be able to:
- Identify safety guidelines related to an air-padded headbox system
- Identify the main functions of a headbox
- Define "total head," "jet to wire," and "rush/drag"
- Identify and describe the main components of an air- padded headbox
- Describe the stock flows inside the headbox
The following key questions are answered in this module:
What are the four basic functions of a headbox?To deliver the stock uniformly onto the forming fabric in the cross-machine direction and the machine direction, create controlled turbulence to reduce fiber flocking and develop uniform fabric distribution, coordinate the speed of the stock jet with the speed of the wire, and to ensure that the flow of stock from the slice opening strikes the wire at the correct angle and location.
What is the purpose of the headbox?The purpose of the headbox is to distribute the stock onto the Fourdrinier wire to form the sheet. There are several components inside an air-padded headbox that are designed to distribute the stock evenly across the machine and generate turbulence to keep the fibers dispersed.
What is the primary function of the flow spreading device?The primary function of the flow spreading device is to evenly distribute the stock across the width of the headbox and the machine. Other flow spreading devices are also in use.
What are rectifier rolls and what do they do?An air-padded headbox contains rotating, perforated rolls, call rectifier rolls. The stock flows through the holes of the rectifier rolls, generating a pressure drop that dampens out large-scale turbulence and evens out the velocity profile across the headbox width.
How is the air pad maintained?The air pad inside the headbox is maintained by a source of pressurized air. The source can be mill compressed air or a dedicated air compressor for the headbox. The pressurized air is piped to the top of the headbox and regulated to maintain the stock level inside the headbox.
Below is a transcript of the video sample provided for this module:
A headbox has four basic functions. One, to deliver the stock uniformly onto the forming fabric, also called the wire, in the cross machine direction and the machine direction. Two, to create controlled turbulence to reduce fiber flocking and develop a uniform fiber distribution across the wire. Flocking is the tendency of fibers to clump together. Three, to coordinate the speed of the stock jet with the speed of the wire. This relationship plays a major roll in sheet formation and fiber angle or orientation. Four, and ensure that the flow of stock from the slice opening strikes the wire at the correct angle and location.
Use the additional resources and links below to learn more about this topic: