Firbimatic Spa

Aqueous detergents and solvents: focus on recycling potential, solvent power, viscosity and surface tension

— 01 / 07 / 2022

To determine if aqueous or solvent-based cleaning is better is a constant in the sector of machines for metal parts cleaning .
You should look at the entire cleaning task and consider all factors.

Both methods can provide quality cleaning results but it is important to understand the drawbacks and the advantages.

Comparison of Aqueous vs Solvent Cleaning

For example, aqueous matrix cleaners are able to emulsify and condense contaminants so that they can be rinsed off easily.

Detergents, surfactants, emulsifiers are added in these cases to improve the performance of the cleaning agents; acqueous cleaning works with a combination of detergents, high heat and agitation, also known as ultrasonics.

In all cases, the washing cycle is structured in such a way that after the washing phases there are rinsing “stations” to eliminate dirt residues.

On the other hand, we have solvents that favor the dissolution of oils and fats in the detergent itself.

The metal components are immersed in the solvent (or treated through spray solutions) which is constantly distilled and filtered.

The components are treated and cleaned through the vaporization of the pure solvent in order to reach even the most remote corners; finally, drying takes place under high vacuum.

What are the possibilities of reusing and recycling the washing agent

From this first comparison it is reasonable to think that solvent-based washing systems are preferable to aqueous ones because the chances of recycling are much higher.

The untreated water tanks where the components are immersed must be constantly replaced while the solvent, through an appropriate distillation process, can be reused continuously.

In addition, when the amount of residues and oils is high, the system provides a separate distillation unit: contaminated solvent and clean solvent are located in two separate tanks.

SOLVENT POWER, VISCOSITY and SURFACE TENSION of the solvent-based cleaning agent

The comparison between aqueous detergents and solvent-based detergents introduces the concept of cleaning power of the chosen washing agent.

In a non-aqueous solution this parameter is evaluated through the KB (Kauri – butanol) value between 10 and +1000: the closer you are to the maximum threshold, the more you are confident that you have chosen an agent with a high cleaning power.

However, a high cleaning power could be incompatible with the treated materials because it is too aggressive.

This type of evaluation cannot be done with aqueous matrix cleaners.

Viscosity and surface tension

The evaluation of these parameters is necessary when the metal components treated have a highly complex geometry.

When we talk about surface tension we refer to the force that attracts molecules to the surface of a liquid.

A high surface tension results in a strong tendency of the molecules to concentrate in restricted areas and vice versa.

The solvents have a lower surface tension than that of water, this allows them to penetrate into blind holes and small spaces, removing the deepest dirt even in components with complex geometry.

Viscosity, on the other hand, is a measure of a liquid’s resistance to flow: a low value identifies a liquid capable of flowing easily around surfaces, in and out of confined spaces.

By comparing water and solvent we have:

acqua (25° C) 0.891 mPas
Idrocarburi (25° C) 1. 1 mPas
Alcol Modificato (20°C) 3.2 mPas



There is no washing solution that is universally suitable for all types of industrial metals.

The choice of the washing method is influenced (in addition to the type of metal to be treated) by the level of complexity of the component, residues and contaminations, standards and washing requirements and much more.

It is important that, in addition to achieving the cleaning standards required by the reference sector, the washing system guarantees repeatable and economical results over time.

A washing plant is defined as economical on the basis of:

  1. PURCHASE COSTS: machine price, installation cost, costs for modernization interventions;
  2. MANAGEMENT COSTS: incurred for the purchase of solvents, additives and cleaners, energy costs;
  3. LABOR COSTS: hours of work required to monitor the machine during the cleaning activity.

The sum of these costs (referring to the lot or single piece) provides an estimate of the economic efficiency of the washing system.

Find out more about our solvent washing systems and request a comparison with FIRBIMATIC consultants!

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