Electroplating Technology

Prior treatment of substrate layers is essential when using surface coating techniques. Pre-treatment may consist of several steps. The composition of the base material, various contaminants, the type of surface treatment technique to be applied subsequently, and the condition upon delivery—namely the type and density of coatings and foreign layers, as well as problematic areas created during processing—all determine the pre-treatment requirements. Therefore, permanent layers created on the surface of the base material for corrosion and wear protection must be carefully processed both before and frequently after application. Pre-treatment (preparation) involves working on parts to be coated, modified or stripped of coatings through coating and surface treatment techniques, creating defined surface textures and surface morphologies. These processes help establish a defined component surface that is a prerequisite for strong bonding of component surfaces or surface modifications. Using these methods, component surfaces with reproducible characteristics are created to provide a starting point for the desired surface quality. For example, layers that can remain on metal surfaces such as wax or oil films, as well as reaction products such as oxides and sulfides, create a separating layer effect between the metal and coating, affecting or preventing proper adhesion of the coating. Which pre-treatment methods should be selected (see Figure 1) depends on the type of substrate material such as metal, ceramic, glass or fiber, their contamination levels, and surface topography (flatness, waviness, roughness).

Figure 1: Pre-treatment options

Although optimal pre-treatment of products to be processed with surface techniques should be emphasized, methods for evaluating pre-treatment results often allow for only a "good or bad" assessment. Table 2 contains general information concerning determination of cleaning effectiveness. Table 1: Overview of methods for determining cleaning effect with pre-treatment The connection between the desired purity level and the appropriate pre-treatment method is demonstrated in Table 2 through an example of residual surface oiling. Table 2: Purity levels for surface treatment processes and appropriate test methods for typical initial conditions of residual surface oiling at 2500 mg x m-2.

Surface Treatment Methods

To distinguish between pre-treatment methods, the change in surface condition resulting from the previous method is examined. These changes are primarily divided into the following groups:

Cleaning

• Change in surface texture, • Reaction at edge areas. From another perspective, pre-treatment methods are categorized into the following system: • Removing, • Applying, and • Modifying methods. A third approach groups methods according to the following effect principles: • Mechanical methods, • Methods that change shape (rolling, drawing), • Grinding with geometrically defined cutting tools (turning, milling), • Grinding with geometrically undefined cutting tools (sanding, polishing), • Steel method, • Thermal processing removal method (scraping), • Laser removal process, • Plasma method (plasma arc, ion bombardment), • Chemical and electrochemical methods, • Oiling, • Acid cleaning, etching, electrochemical polishing. Figure 2 provides an overview of the most important pre-treatment and post-treatment methods. Figure 2: Effect principles of pre-treatment methods The initial conditions of component surfaces are classified according to the criteria given below: • Surfaces that have not yet been coated, and • Layers consisting of coated surfaces that have undergone pre-processes. More detailed characteristics of coatings specific to types such as rust and mill scale on steel are provided in Table 4. Table 4: Initial condition of uncoated steel surfaces (degree of rusting) ISO 8501-1, 8501-2, or DIN 55928.

1) Mill scale or coatings are considered as adhering to the material if they cannot be lifted with the tip of a knife.

İzzet Aydın General Manager Hillebrand Chemicals Kimyasal Pazarlama Ltd. Şti

References •Galvanotechnik in Frage und Antwort, 6. Auflage. •Galvanische Legierungsabscheidung und Analytik. •Grundbegriffe der Chemie. •Verfahren der Oberflächentechnik.