Sometimes, at the start of production, you observe the following phenomenon on the cleaning bath at the beginning of the week: An oil-like, yellowish or brownish layer floats on the surface of the cleaning bath and you wonder what it is. At first, one will suspect oil residues that have separated from the bath, e.g. during a resting phase. But it does not necessarily have to be oil. It can also be components from the cleaning product itself.
It is also possible that surfactants (wetting agent components) have separated from the bath and are now also forming an oil-like layer on the bath surface. But how can you differ between oil and surfactants?
This can be easily checked with the following method. Take some of the oil-like layer and put it into a container with warm water.
Both components are then mixed intensively and the behaviour of the mixture is observed. If a new phase separation occurs quickly, it is very likely to be oil residues. If, however, the oily phase can be worked into the water, it can be assumed that it is surfactants/wetting agents from the cleaning product.
How does an oily layer affect the subsequent process steps?
When corresponding top layers appear, you should quickly look for the causes, because in the case of oil, the goods are first cleaned in the bath, but then “oiled” again when they are lifted out by the oil top layer. The cleaning is therefore redundant. The discharge of the oil with the fabric also contaminates the subsequent process zones. In the case of a top coat of surfactants/wetting agents, the cleaned surface is usually not affected, but the discharged surfactants can lead to foaming problems in the downstream zones. Therefore, a top layer should always be removed from the bath by suitable measures such as overflow, oil separator, etc.
In the case of a covering layer of surfactants, it is often enough to switch on the air injection in the bath or to circulate the bath in some other way in order to work the deposited layer back into the bath.
Why does the covering layer form?
A top layer of oil is created by cleaning larger quantities of heavily oiled material or using demulsifying cleaner systems that cause targeted phase separation.
The top layer of surfactants/wetting agents can be caused by an unsuitable cleaner. Direct heating in the cleaning bath and its usually very hot heating surfaces can cause local overheating of the cleaner in the area of the heating surface. This can then lead to the separation of the surfactants/wetting agents from the rest of the cleaner. As a result, small surfactant droplets rise and form a corresponding covering layer on the surface of the cleaning bath.
This is to be expected in particular if no bath circulation is available that enables a rapid mass transfer at the heating surface. Often it is sufficient to switch on the existing bath circulation/air injection to solve the problem. If necessary, one should also switch to a less temperature-sensitive cleaning product.