Air bubbles

1. Ensure you have well washed pulp from pulp mill.
— do not confuse with high chemical usage in stock preparation area.
2. Raise chest levels so agitators do not entrain air.
3. Check for leaking pumps and gland water flow.
— be sure glands are weeping.
4. Check defoamer and increase flow if needed.
— excess defoamer will reduce internal sizing and adversely affect Yankee coatings.
5. Adjust headbox deflector and secondary slice to reduce turbulence.
— use a steam shower over the forming fabric or over the dandy roll.
6. Decrease the headbox consistency if conditions permit.
7. Adjust slice so that there are no side currents and slice discharge is well controlled.
8. Reposition apron relative to the breast roll to minimize stock turbulence.
9. Check wire tension, breast roll shower and forming board position to eliminate stock jumping.
10. If stock is jumping, level dewatering elements, install lower angle foils or increase spacing of foils.
11. Ensure that table roll deflectors are set close to forming fabric and close to following roll.
12. If dandy is throwing water, reduce volume of shower water and adjust shower angle as required.
13. Adjust dandy so that area of contact is uniform across the forming fabric.
14. Check operation of deaerator or vacuum system.
15. Check setting of forming board to ensure adequate room for uniform, minimum breast roll discharge.
16. Air bubbles are formed when air in the stock comes out of solution.
— bubbles may be broken up by air or steam showers, but it is best to completely eliminate air in the stock.
See Air in the system.