Metal electroplating is a technology where the final result very precisely reflects the process. It's impossible to correct it at the final stage or visually mask minor flaws. If the surface was improperly prepared, the bath was unstable, or the electrical parameters were set too aggressively or too conservatively, the coating will reveal this sooner or later. Sometimes this is visible immediately after removing the part from the bath, and sometimes only after several months of operation in real-world conditions. This is why electroplating has long been considered a demanding process, yet one of the most predictable when conducted with care.
In practice, galvanization is rarely limited to protection only. anti-corrosion. It allows you to influence the way the metal surface reacts to moisture, oxygen, friction, electric current or contact with chemicals. Very often, it is the thin layer, a few or a dozen micrometers thick, that determines the durability of the element, and not the base material itself, even if it theoretically has very good strength parameters.
What actually happens in a galvanic bath
The entire process is based on electrochemical phenomena. The element to be coated works as cathode, while the bath contains ions of the coating metal. When a voltage is applied, the ions begin to move in the electric field and reduce on the surface of the part. This step is often perceived as a simple step in metal deposition, but in reality, it is a complex structural process.
First of all, nucleation sites appear on the surface, i.e. points where the formation of crystal structure. Their arrangement depends on both the surface cleanliness and the local electric field distribution. Only later do the crystallites begin to grow and coalesce into a continuous layer. The course of this stage directly impacts the coating's smoothness, adhesion, and durability in long-term use. In practice, this means that two parts processed in the same bath with identical parameters can behave completely differently if even a slight difference in the degree of surface preparation is observed.
Current density as a regulator of coating growth
The way sediment grows is most influenced by current density. Typical ranges are between 0.5 a 10 A/dm², However, it's not the value itself that's crucial, but its relationship to the geometry of the part and the nature of the bath. It's the current density that determines the rate of ion reduction and whether crystallite growth will be orderly or overly aggressive.
At high current density, the deposit grows rapidly, but mainly in places where the current reaches most easily. Edges and corners begin to collect excess metal, and cracks appear in the coating structure. internal stresses. Over time, these can lead to microcracks or reduced corrosion resistance. Conversely, too low a current density causes sludge to grow slowly, becoming porous and less mechanically resistant. In practice, working within a stable, moderate range yields the best results, even if this involves extending the process time.
Current shading and the role of detail geometry
At this stage, the topic naturally arises current shading. Electric current always reaches protruding surfaces more intensely than recesses, holes, or the interior of profiles. This phenomenon results directly from the distribution of the electric field in the bath and accompanies every galvanic process.
In practice, this means that the geometry of the part has a significant impact on the uniformity of the coating. Edges tend to grow thicker, while recesses require a longer process time or a change in the suspension method. Very often, simply adjusting the part's orientation in the bath can achieve a much more uniform coating than changing the bath composition or voltage.
The galvanic bath as a constantly changing system
The uniformity and repeatability of the process are also influenced by the fact that the galvanic bath is not a static system. During operation, the metal ion concentration changes, technological additives are consumed, and pH, conductivity, and temperature fluctuate. Typical operating conditions are within the range 18-35°C, at a pH of approximately 4-5 for acid baths and 12-14 for alkaline baths.
Smoothing and leveling additives influence the growth pattern of zinc crystallites, and thus the appearance and uniformity of the coating. Their consumption is not constant and largely depends on the geometry of the treated components. In practice, this means that even small changes in bath composition can quickly alter the nature of the deposit and the quality of the coating.
Surface preparation – the stage that determines quality
At this point, it all naturally comes down to surface preparation. Plating It quickly reveals errors made at this stage. Residual oil, silicone, scale, or machining residues lead to localized adhesion failures, blisters, or coating discontinuities. Some of these defects are not visible immediately after the process, but become apparent during the initial period of operation.
Therefore, every galvanization process begins with:
- degreasing,
- digestion,
- rinsing,
- activation.
Types of galvanic coatings and their functions
Standard galvanic coating thicknesses are in the range 5-30 µm, which allows for very good dimensional accuracy even in precision components. Depending on the operational requirements, various coating metals are used:
- zinc provides anti-corrosion protection
- nickel increases chemical and mechanical resistance
- copper improves conductivity
- tin protects electrical contacts
- chrome increases abrasion resistance
Metal galvanization in Strumet
At Strumet, metal galvanization is treated as a fully thought-out technological process, not a quick step at the end of production. Before a part enters the bath, we analyze the material, geometry, and the conditions under which it will subsequently operate. We work on lines pendant and drum, which allows us to tailor the technology to both large components and small, precise details. At every stage, we monitor the bath composition, pH, temperature, and current density. These parameters determine the coating's structure and its behavior during use, so the process is stable and repeatable.
