In simple cases, a liquid or flowable substance to be controlled on, a web can be water, e.g. when a web of material, a flat formation, a roller or the like is to be humidified or dehumidified. The liquid can also contain various chemicals, for example dyes, impregnating substances and/or solid substances. It can also be a foam.
It is known to apply substances by means of magnetically pressed rollers It is also known to use rollers pressed by magnetic force, which are either dipped into a liquid or are supplied by a feeding roller. In both cases, on the surface of the application roller a thin film of liquid is created, which is then transferred by the application roller at the contact point. In the wedge formed in front of the contact point an accumulation of liquid can result.
In application roller with a smaller diameter applies less substance and the amount of applied substance increases with the diameter of the roller. A weaker or stronger pressing force applied to the rollers results, for instance, in a textile surface with different depth effects, but the amount of applied substance is basically determined by the diameter of the application roller.
The surface structure of an application roller also influences the amount of applied substance. As a rule, application rollers with structured, rough or engraved surfaces, or with wire wrappings apply more substance than rollers with smooth surfaces. The nature of the substance to be applied, its adhesion to the roller and the absorption capability of the substrate also have influence on this type of amount determination.