Foam control

1. Defoamers are added to the system to control foam mainly through the mechanism of reducing the levels of entrained air in the system.
2. Low defoamer levels result in sheet marking from air bubbles and foaming around the wet end of the machine.
3. Excessive defoamer, however, creates its own stable foam which then has the adverse effect of reducing sizing efficiency, strength levels, and internal bond 4. Excess defoamer can impair Yankee adhesion.
5. Poor control of wet-end chemistry leads to foam problems; especially with neutral or alkaline systems.
6. Minimize the adverse effects of foam by:
(a) reducing air entrainment.
— eliminate free falls.
— reduce agitation.
— maintain pump packing in order.
(b) mechanical correction.
— use deaerators – deculators.
— employ knockdown showers.
(c) use appropriate chemicals.
— defoamers.
7. For recycled fibers, the same materials that foamed in the original making are sometimes present in higher concentrations so foaming problems tend to intensify.