Headbox Optimization Services: Frequently Asked Questions

Q: Why is ‘forming the sheet’ the most important step in papermaking? A: Stock distribution at the wet end sets the stage for every step that follows, from pressing through drying, coating and calendering. Mechanical issues with the headbox often restrict proper formation and induce uncontrollable profile variations. Q: What is the ‘apron’ and what part does it play in the overall process? A: The headbox frontal area is called the apron (lower lip). The importance of the apron can be seen from the following facts: The apron is normally the reference for wet end setup. Typically, the breast roll is aligned to the apron, and the table is aligned to the breast roll. The apron position has a direct correlation to jet-to-wire/rush-drag. Stock flow across the apron face affects formation/fiber orientation. Q: What are the ways to achieve apron improvement? A: There are two means of apron improvement: Mechanical Stress Thermal Improvement Mechanical Stress uses force (brass plates, clamps and lead mallets) in order to reduce variation "peaks." This method only re-distributes the variation over a wider area, but does not eliminate the problem. It is considered a short-term solution. The proven and best method used by Honeywell is Thermal Improvement, employing a combination of heat and cold water. Thermally improved aprons tend to retain their shape so the degree of variation reduction is significantly higher. Q: How do improved aprons contribute to improved production? A: Properly aligned aprons deliver improved formation and fiber orientation while reducing the bending force required to "block" the lip-to-apron opening. This increases the control range of the lip for enhanced profile variation reduction. Reduced variation, coupled with more uniform drying, could easily deliver production increases in the range of one percent or more.