Water flow to headbox, excess

1. Consistency of the stock in the headbox is of utmost importance. When water flow is either greater than that which gives the critical velocity in the headbox (avoiding flocculation), or is greater than that which can be drained effectively, then it is excessive.
2. If the slice is not properly adjusted, formation will be impaired because the excess water flow will give too high a head with too fast a jet speed for the wire speed.
3. With a poorly designed distribution system, it is possible to have very heavy channeling in the headbox.
— if the flow is greater than needed, the tendency to channel is accentuated and will give streaks.
— channeling, in certain cases (e.g., cross flow distributor), contributes to skating on the forming fabric.
— channeling is greatly aggravated if the filler level is high in the headbox stock.
4. If there is too much water on the forming fabric for the drainage elements to handle, a rough, wormy, or patchy sheet will result.
5. If the sheet skates on the forming fabric, the basis weight across the machine will vary in an irregular manner that cannot be corrected at the slice.
— excess water will aggravate basis weight variation under such conditions.
6. By skillful use of an on-machine traversing beta gauge, these points can be traced and the best operating conditions found for each grade.