Analyze the conditions and solutions of paper machine foam

The paper machine will produce foam. When the slurry contains more free air and more surface active substances, it is easy to form stable bubbles, which float on the surface of the slurry to form foam.

In severe cases, the foam overflows, which brings trouble to the operation. The foam floats on the surface of the container, and the stagnation time is long, and the problem of slurry will occur. When the liquid level fluctuates, the floating layer ruptures and becomes a slurry of slurry that flows down, causing holes in the paper, or even sticking and pressing. In less severe cases, foam spots or pinholes can also form when air bubbles are removed by suction at the vacuum box. Therefore, the foam problem often becomes a very head-scratching problem in wet-end operation.

1) Conditions for the generation of paper machine foam

In addition to the problem of air contained in the slurry mentioned above, the severity of the foam problem often depends on the amount of surface-active substances in the slurry.

Many substances in plant fiber raw materials, such as lignin, polysaccharides, resins, a small amount of fat, protein, phenolic substances and pectin, etc., become surface active substances and remain in the pulp after cooking and bleaching. In addition, the rosin size added in the sizing process, including sodium rosin, is also a surface active substance, and the starch and animal glue used for the surface sizing agent will also be returned to the paper machine system with the broke paper. When the content of these substances in the slurry increases, it is easy to generate foam.

There are generally the following reasons:

a) The pulp in the pulping part is not washed cleanly, or the bleached pulp is not washed cleanly, and the residual chlorine is high. At this time, a large amount of surface active substances remain in the pulp, resulting in foaming in the feeding system of the paper machine.

b) The amount of sizing is large, so that the slurry contains more rosin salt, or the pH value of the slurry is high, so that the sizing material is not well precipitated on the fiber, and the rosin acid soap exists in the slurry. , will result in an increase in foam.

2) Solution

Regarding the paper machine foam, degassing can be used to reduce the air in the slurry, thereby reducing the foam; or try to avoid mixing air into the slurry. For the increase of foam caused by the above reasons, it can be solved accordingly, that is, to strengthen the pulp washing in the pulping workshop; to minimize the foaming substances contained in the incoming pulp.