The principle and solution of foam formation

Foam is a common phenomenon. Generally speaking, pure liquids will not produce foam. Due to the uniformity of the liquid surface and interior, it is impossible to form an elastic film. Bubbles produced in pure liquids will burst immediately when they come into contact with each other or escape from the liquid. The interfacial tension between air and liquid is too high, resulting in the bubbles being unable to exist stably.

However, when an insoluble gas enters a liquid with low surface tension under the action of external forces, it will be isolated by the liquid to form stable bubbles. Surfactants are often the main cause of foam. This is because the surfactant molecules have the characteristics of hydrophilic and hydrophobic end groups, which can form a surfactant layer around the bubbles, in which the hydrophobic end faces the bubbles and the hydrophilic end faces the water, thereby reducing the interfacial tension between the bubbles and the liquid and stabilizing the existence of the bubbles. When the bubbles rise to the surface of the liquid, because there are also surfactant molecules between the air and liquid interfaces, a stable double layer including the surfactant layer on the bubbles and the liquid surfactant is formed. These stable double layers are composed of a surfactant monolayer on the air-liquid interface and a surfactant monolayer on the liquid-air interface, respectively.

According to the foam formation mechanism, the bubble monomers form a tight spherical ring. According to the water permeation process of the drainage effect between the bubbles, the water between the bubble interfaces will be displaced and concentrated in the gaps between the bubbles. Due to this drainage effect, the narrow spacing between the bubbles promotes the formation of octahedral foam bodies, which are called foam aggregates composed of tight hexagonal foams.

Various types of surfactants are added to metalworking fluids, such as emulsified cutting fluids, semi-synthetic cutting fluids, rolling fluids, industrial cleaning agents, etc., which can cause a lot of foam, and have become a headache for many manufacturers. It not only affects the production schedule, but also affects the product quality. It may cause uneven hot and cold processing, resulting in inaccurate processing precision. Excessive foam can prevent the processing fluid from entering the processing area. Some foams even have a corrosive effect, causing damage to the workpiece and even production equipment and parts.

There are two main ways to solve the foam problem. One is to add defoaming agents, which have a fast defoaming speed, but they are consumables and require repeated purchases and manual supervision. The other is to use mechanical defoaming equipment, which operates physically and mechanically, continuously and uninterruptedly, and does not require manual supervision, but the initial investment is large. In addition, metalworking fluid manufacturers can also use low-foaming surfactants as raw materials for product development to solve the foam problem at the source.