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Weldable organic coatings
Improved corrosion protection
- The corrosion protection in the body cavities, seams and flanges is improved considerably thereby preserving the vehicle value for a long time. This significantly increases the service life and recycling intervals. This is all the more important when thinner sheet steel is used such as high-strength steel grades.
- Improved corrosion protection on components relevant to safety ensure that the vehicle safety remains constant over the entire vehicle service life.
Reduction of production depth
Most important advantages:
- Reduction of production depth for automotive manufacturers by eliminating cost intensive and environmentally polluting production steps.
- Reduction of electro-deposition painting (EDP) for service and customer parts by use of weldable primers (EDP substitute system).
- Expansion of guarantee against rusting through which starts in body cavities and seams.
Production and technical data
The substrate for organic coatings can be all common steel grades and dimensions of electro-zinc coated and hot-dipped galvanised sheet steel depending on the application.
The metal surface is cleaned, chemically pretreated and coated with the liquid organic lacquer, applied by rolls in one continuous run through the plant. Cross-linking is accomplished in the burning furnace.
Since the coating is applied directly to the plain, galvanised sheet steel, intensive cleaning and pretreatment are possible, which otherwise would require extensive spraying and dipping processes at the automotive manufactures.
Application by a roll system produces an extremely uniform, dense, and pore-free coating with relatively low layer thicknesses and high yield for the coating material. Ecological aspects can better be taken into consideration by having the coating process accomplished by the steel manufacturer, because the coating materials can be applied more efficiently and ecologically.
2 Measurement of layer thickness by x-ray fluorescence analysis
3 Reception test of lacquer viscosity
Weldable thin-film coatings
Weldable primers (EDP substitute systems)
Application and processing properties
Improved corrosion protection in cavities, seams and flanges
protection in the flange
area under extrem conditions
Organically coated sheet steel has a significantly higher corrosion protection in the flange and cavity area thereby providing important protection against rusting through because it prevents the formation of red rust even without secondary protective measures.
Excellent forming behaviour
Due to the improved tribological conditions the coatings provide a significant increase in the working range during deep drawing in comparison to galvanised surfaces. Additionally, the limiting drawing ratio shifts to higher values.
For deep drawing the working range is designated by the range in which a pressed part can be deep-drawn without faults, i. e. wrinkles or fractures. The good sliding properties therefore allow production of difficult deep drawn parts.
Good welding properties
spot welding
During resistance spot welding of the conductive pigment coatings the required minimum spot weld diameter can be achieved with lower welding currents in comparison to galvanised surfaces. Moreover, the welding current range is increased.
Alternative joining processes
Due to the good wetting properties of organic coatings and the favourable surface structure the stability and bonding strength of adhesive connections are improved in comparison to pure zinc surfaces. Mechanical joining processes such as clinching or projection joining are alternative joining methods for realising modern vehicle concepts particulary for mixed material constructions for car bodies using precoated sheet steel.
Studies of mechanically joined, organically coated sheet steel in combination with the use of adhesives have shown that the dynamic component properties can be improved.