Underbody Coating and its Purposes

UNDERBODY COATING AND ITS PURPOSES:

Modern automotive coating methods consist of five main steps. They include the following:

• Pretreatment: removes and cleans excess metal and forms an appropriate surface structure enabling bonding of a corrosion protection layer.
• The next step is electrodeposition (ED) of the anti-corrosion or rust prevention layer.
• A sealer like Poly Vinyl Chloride (PVC) is applied for anti-corrosion, elimination of water leaks, and minimization of chipping and vibrational noise.
• A primer is then applied to promote adhesion between the surface and the basecoat; it also imparts a smoother surface for subsequent layers and has anti-chipping properties.
• Finally, the topcoats that include a basecoat and clearcoat are applied; they provide
  surface properties that are sought after, including color, appearance, gloss, smoothness, and weather resistance.

The areas of an automobile depicted in Figure 1 show where these five steps of coating and other additional coatings are used. As can be realized when examining this figure, a significant number of specific coatings and materials are needed in addition to the above-listed steps to manufacture a salable automobile.

Figure 1: Summary of coating tasks for specific areas of car

What is Underbody Coating?

Underbody coating (UBC) is a thick resilient coating applied to the underbody or chassis of an automobile to protect against impact damage from small stones, which would rapidly chip ordinary paint, allowing rusting to begin.

Figure 2: Underbody Coating

The overlapping, spot welded metal sheets must be sealed in such a way that no humidity can penetrate between the metal sheets and water in the vehicle interior, which may lead to corrosion there.

On the weld seams, high viscous polyvinylchloride (PVC) plastisol material is mostly sprayed as paths with airless application or extruded by flat stream nozzles using robots or manually. It is applied partially two-dimensionally, for instance, in wheel arches, underbody of the car and in the rocker panel area.

Purpose of Underbody Coating:

This treatment is designed to provide long-term protection from rust to the under chassis. It protects the underbody substrates from:

• Environmental conditions
• Impacts
• Dampens sound and vibration
• Insulates against cold and heat
• Protects against Corrosion
• Seals off seams
• Hides welds, repairs & bodywork with spray

Figure 3: Underbody of car, before and after Coating