Cleaning media

The chemical principle of “like-dissolves-like” is used in selecting the right medium. Based on the polarity of a substance, the principle states that contamination is best removed by a substance that possesses a similar structure. In a nutshell:

Aqueous cleaners are mostly used for aqueous (polar) contaminants such as cooling and lubricating emulsions, polishing pastes, additives, salts, abrasion and other solids.

Non-polar contaminants, for example machining oils, greases and waxes, are typically cleaned off using solvents that are also non-polar. Particulate contaminants on the parts such as chips lose their adhesion to the surface when the oil is removed and are cleaned off by means of mechanical processes, for example ultrasonic cleaning and injection flooding.

Aqueous cleaners are available as single or multi-component systems in acidic, neutral and alkaline formulations.

They all possess the same structure in principle. The cleaner always consists of a builder and a surfactant mixture that causes the cleaning effect. Additives such as corrosion inhibitors, inhibitors, complexing agents, etc., can be mixed into this formulation, depending on the intended use. Builders and surfactants have complementary effects, which means that their coordinated combination quickly achieves an optimal cleaning result. The surfactant component is used to adapt the cleaning agent for the process technology, so blast, immersion, injection flooding or ultrasonic cleaning.

Acidic and weakly acidic detergent media (pH range 1 to 5) are used among other things for derusting, descaling, removing tarnish, for deoxidising after deburring, as well as for pickling and activating prior to coating. Acidic cleaners can be used on aluminium components to induce targeted material erosion and to brighten brass parts. Acidic media are used additionally to clean plastic parts. The addition of inhibitors prevents the base material from being attacked.

Neutral cleaning media, also known as neutral detergents, (pH range 7 to 10) are available as formulations either with or without salt. They are suitable for the intermediate and final cleaning of steel, cast iron, light alloys and non-ferrous metals. Polar contamination such as emulsions, salts, pigments, polishing and lapping pastes can be removed with neutral cleaners. Non-polar impurities (greases, oils) are predominantly removed by means of the dispersion and emulsification principles. Neutral activators enable the removal of rust from steel parts, for example during cleaning after TEM deburring.

Alkaline cleaning media (pH range 10 to 14) are capable of ridding components of the strongest contaminants such as heavy oils, particulate dirt, lapping and polishing pastes, corrosion products and deburring residues.

The rinsing technology exerts a substantial influence on the result of aqueous cleaning processes. Loosened contamination is removed by rinsing. The process also creates unblemished surfaces.

Applicable criteria for the selection of an aqueous cleaner include the component material, contaminant composition and requirements for component cleanliness, as well as the system, process and treatment technology.

The cleaning process uses up the builder and surfactant components to differing extents. To ensure a consistently good cleaning performance, it is therefore necessary to keep both components stable within the specified concentration range, i.e. to replenish them based on consumption. The best way to achieve this is by using modular cleaning systems, for which there are different methods for the separate analysis of builders and surfactants. A variety of measuring methods are also available to monitor the contamination level in cleaning and rinsing baths.

The most common solvents include non-halogenated hydrocarbons (HCs), modified alcohols and chlorinated hydrocarbons (CHCs).

Non-halogenated hydrocarbons possess very good dissolving capabilities for animal, vegetable and mineral fats and oils as well as high material compatibility. They are mainly used for degreasing metal.

Modified alcohols, also known as polar solvents, have lipophilic (attracted to fat) and hydrophilic (attracted to water) properties to varying degrees. They can therefore be used to clean off non-polar oils and greases as well as – to a certain extent – to remove polar substances such as emulsions. Their high material compatibility means that they can be used to clean parts made of practically all metals.

Chlorinated hydrocarbons, for instance perchloroethylene, possess a good grease-dissolving capacity and enable effective degreasing of metal and rapid drying in components with complex geometries. They are often used if the components for cleaning will introduce critical oils (e.g. chlorinated or with a high sulphur content) into the cleaning medium.