PREPARATION OF METALS
As for the preparation of metals and therefore to obtain a perfect finished object it is not enough to deposit with the best electrolytic solutions, it is also necessary to prepare the piece in the most suitable way. There is a first mechanical phase and a second chemical phase.
As for the mechanical phase, there are equipment such as vibrators, tumblers, turbo, and brighteners that refine the piece making the surface homogeneous, free of porosity and inclusions. This phase can however generate oxides on the surface or involves the use of pastes, soaps or products that “dirty” the object that will then be removed with the second chemical phase.
DIRT
During the machining cycle, as we have seen, it is very frequent that the parts are contaminated by external products. To this must be added also the working times, the stopping times between the various phases and the environmental conditions. These are the main causes that modify the state of the surfaces of the materials, influencing the following galvanic processes.
From a chemical point of view, soils can be divided into three macro-categories:
- Organic: may be petroleum-derived or synthetic products. Soaps, waxes and fatty oils fall into this category.
- Inorganic: are oxides, such as welding residues or products derived from heating.
- Mixed: for example hardening operations or dirty glove prints.
The operation of removing dirt is an action that requires specific steps.
1. WASHING
Degreaser washing is the process that aims to remove foreign materials from the metal, which derive from previous treatments, and prepare it for future steps. The effect will depend both on the way the piece has been washed and on the solutions used.
These detergents are mainly composed of two elements: surfactants and adjuvant salts.
Surfactants are used to facilitate the process of emulsification of dirt, making it chemically removable from the surface of a piece, and to change the wettability during washing.
The adjuvant salts help or complete the cleansing action.
2. DEGREASING AND DEGREASING PROCESSES
It consists in eliminating the layer that may have remained on the piece even after a first chemical washing or that has been formed in later stages.
It can be by simple immersion or electrolytic.
IMMERSION:
As in washing, specific products are used whose action can be assisted by:
- Air insufflation
- Ultrasound
- Shaking of pieces
ELECTROLYTE:
This is done by passing current through the solution where the part to be cleaned serves as one of the two electrodes (it can be cathode or anode depending on the type of solution studied). In this case, in addition to the cleaning of the liquid, there is also an electrochemical reaction with hydrolysisin which water is then divided into hydrogen and oxygen.
The electrolytic process is able to clean thanks to:
– deterrence of dissolved solution products,
– reduction of oxides due to the formation of hydrogen during hydrolysis
– the oxidative power of organic compounds by the oxygen released by water during hydrolysis
– the same gas formation that facilitates the movement of the solution by mixing the solution by regenerating the liquid in contact with the metal
TYPES OF DEGREASING AGENTS
Alkaline degreasers: composed of a combination of alkaline salts with surfactants, with a wide spectrum of action and more delicate for surfaces.
Acid and neutral degreasers: composed of acid or neutral salts and surfactants. Generally more expensive and therefore less used.
3. NEUTRALISATION
To neutralize the alkaline components and to dissolve the residual oxides coming from the previous degreasing, the pieces are subjected to a slight acid treatment which also acts as a re-activation of the piece making it suitable and receptive for the following steps.
ECOLOGICAL PROBLEMS
Surfactants are often dangerous to the environment because they alter life cycles. Here are some of the substances that should not be present in surfactants:
- Complexing
- Fluoride
- Silicate
- Phosphate
- Chromed
This text contains a brief description of the preparation of metals that EUROTecniche has drawn up thanks to the know-how acquired in more than twenty years of experience and thanks to the in-depth study of our laboratory technicians.
If you have any questions, please write to cs@eurotecniche.com or info@eurotecniche.com. Thank you for your attention!