According to the different media used for cleaning, the cleaning systems are divided into two categories: the cleaning system using liquid media such as water, various aqueous solutions and organic solvents is called wet cleaning system, and the cleaning system using air and other gases as media is called dry cleaning system. Industrial cleaning in the most common, a large number of the use of wet cleaning, that is, the cleaning medium is given priority to with liquid, the following mainly introduces the role of cleaning medium in wet cleaning.

1. The role of cleaning media

The cleaning medium plays an important role in the cleaning process, which is mainly manifested in the following two aspects:

(1) Effect of transmission force

As we all know, soap is a kind of household cleaning material with strong cleaning power. However, if it is directly applied to clothes stained with dirt, its cleaning power cannot be exerted well. Only after the soap is dissolved in water to form an aqueous solution, the soap molecules can be absorbed on the surface of the dirt and penetrate into the inside, and at the same time, the soap molecules can be absorbed on the fibers of the clothes to push out the air in the fine holes between the fibers, so that the fabric and the dirt are wetted and infiltrated by the washing liquid to expand, and the binding force between the clothes and the dirt is weakened, and at the moment, the dirt on the clothes is transferred into the water by mechanical stirring or rubbing, heating and the like. In some physical cleaning processes using mechanical forces, such forces as ice force, mechanical stirring force, and ultrasonic wave cannot be exerted without the transmission of water or a medium such as a solvent.

(2) Disperse and stabilize dirt and prevent re-adsorption

Cleaning medium can disperse and retain the dirt dissociated from the surface of the object to be cleaned in a stable state, so the dirt does not.

It will be adsorbed on the washed surface again, and the dirt can be permanently removed as the medium flows and changes.

The ability of different cleaning media to disperse dirt is different. For example, when an object with oily dirt on its surface soaked in water is cleaned by ultrasonic wave, the oily dirt will be separated from the surface of the object to be cleaned and dispersed into the water, but when the ultrasonic wave stops, the oily dirt will re-attach to the surface of the object to be cleaned. This is because the dispersion stability of water to oily dirt is poor, so pure water is not suitable for cleaning oily dirt. In this case, surfactant aqueous solution and organic solvent with strong dissociating and dispersing effect on oily dirt are used as media, and the washing effect is better.

2. Classification of cleaning power

Cleaning force is the main force to remove pollutants from the surface of the workpiece to be cleaned and disperse them stably in the cleaning medium, thus completing the cleaning process. Cleaning force can be roughly divided into dissolving force, dispersing force, surface activity force, chemical reaction force, adsorption force, physical force, enzyme force, etc. The cleaning force that plays a role in different cleaning processes is also different. Here, only four forces commonly used in wet cleaning are briefly explained.

(1) Solvency dispersion forces

The reason why water and organic solvent can effectively remove dirt is that they have the function of dissolving and dispersing dirt. This force of water and organic solvent is called dissolving force and dispersing force. This is the most common cleaning power. Different solvents have different dissolving and dispersing abilities for different dirt, so it is generally necessary to select solvents for the dirt to be removed in order to achieve better cleaning effect.

(2) Surface activity

The substance that can significantly reduce the surface tension of solution is called surfactant. Surfactant has the ability to adsorb on the surface of the cleaning object and reduce the energy of its surface, so that the dirt can be dissociated and dispersed from the cleaning object surface. This unique force of surfactant is called surface active force. Cleaning with surface active force is characterized by less damage to the object to be cleaned, and generally good removal ability for different types of dirt.

(3) Chemical reaction force

Chemical reagents, such as acid, alkali, oxidant and metal ion chelating agent, can chemically react with dirt to dissociate and disperse the dirt and remove it from the surface of the object to be cleaned. The function of these chemical reagents is called chemical reaction force. It is hoped that the chemical reagent will only react with dirt and not act on the object to be cleaned, but it is impossible to do this completely in practice. Therefore, it is generally required that the influence of selected chemical reagents on the surface of the object to be cleaned should be minimized, and cleaning should be carried out on this premise.

(4) Physical force

The acting force that separates and disperses dirt by physical actions such as hot soaking, steam bath, circulating flow, spray washing and ultrasonic wave is called physical force. In all kinds of cleaning processes, physical force is always necessary. When cleaning by physical force, it is generally necessary to pay attention to the improvement of efficiency and the full utilization of energy.