Comparing Process Workflows: No Substitute for Diverse Options

İzzet Aydın / General Manager - Hillebrand Chemicals Kimyasal Pazarlama Ltd. Şti.

Market Significance

Galvanizing technology is used as corrosion protection in electrical and electronic engineering as well as in numerous commercial applications for functional and decorative purposes. Galvanizing technology prevents annual losses of EUR 150 billion in the field of corrosion and wear. • 1 kg zinc protects 1,000 kg of screws, • 0.1 g gold protects 5,000 electronic connections against corrosion. • A vehicle contains on average 3,000 coated parts and an Airbus contains 2 million coated parts.

Types of corrosion protection

Passive Corrosion Protection

Passive corrosion protection covers all areas relating to complete protection of materials prone to corrosion. Conversion coatings: • Phosphate coatings, • Anodic oxidation layers, • Passivation layer, • Tin layer.

Active Corrosion Protection

• Active cathodic corrosion protection with external electrical connection. • Active cathodic corrosion protection without external electrical connection. The objective here is to protect against rust when the metal comes into contact with water. Here, non-pure metals are sacrificed.

Electroplated zinc

In electrolytically separated zinc coatings, a post-treatment with passivation is standard practice to improve corrosion resistance against salt spray, humid air and climate change testing.

The following color tones are possible

Passivation is available in blue, black, clear and yellow. With additional coating, the coating thickness can be increased to between 0.5 μ and 2.0 μ.

Advantages

Increased corrosion resistance (delay of zinc corrosion and base metal corrosion) provides corrosion protection at unchanged zinc coating thickness and can be further improved with the use of topcoats. Solid lubricant additives help achieve the desired tribological properties. Hot processes (water removal) should achieve strengths from 1,000 MPa onwards after the coating process for hydrogen bake-out.

Layer properties of galvanized coatings:

• Excellent layer thickness distribution with uniform separation in cavities (internal threads and nuts). No material buildup. Strong separation screw friction numbers are not observed due to excessive coatings. No problems as long as bolts are small (<M6 ). • Stressed coatings provide advantages in bending, edge curling and self-loosening fasteners. • Wear resistant, in debris processing, mechanical adjustment, feeding, transportation. • Very good conductivity, advantage in current and heat distribution. • Optical, silver colors and black. • Haptic, metallic feel.

Functional properties of galvanic coatings

• High dimensional accuracy through fine reproducible coatings. • Negligible placement tolerance through metallic hard coating of 300 HV. • Very good calibrability No risk of local over-coating, including small dimensions and internal threads. • Stable high-temperature dissolution torque. • Good adhesive surface for other coating combinations (powder, cathodic protection) and fastener safety paint.

Coating system:

Acidic zinc

The electrolytic acidic zinc method is preferred due to its high electrolytic efficiency and the resulting high separation rate for coating fastening elements in barrel use. The method is particularly suitable for: * Cast iron / frame applications, * Sintered metals, * Hardened steel.

Disadvantages:

Layer distribution – high consumption. Depending on the model - flaking formation.

Alkaline zinc

Cyanide-free, alkaline zinc processes are used in both decorative and functional applications, for example in drum sections and housings.

Advantages:

• Formable surfaces, • High brightness, • Good surface distribution even on difficult-shaped parts, minimal flaking.

Zinc

Corrosion resistance values are described in DIN 50969.

Corrosion values of zinc systems

Table - minimum layer thickness and passivated (clear, iridescent) zinc and zinc alloys with regard to inspection during testing in accordance with DIN EN ISO 9227-NSS.