Underbody Coating
Under-Body Coating
Under Body coating refers to the coating od panels which cover the exposed underbody parts and surfaces of the car. The entire car frame gets coated before the exterior and interior panels are assembled onto it. The underbody panel gets a thicker coating as it exposed to the road and has to protect underlying surfaces and parts of the car.
Unlike the other parts of the car frame which gets coated once by the OEM, the underbody panel can be coated multiple times at a service centre. Underbody coating is also the most exposed and hence gets worn out from time to time.
The main purpose of coating is to protect the underlying surfaces and parts from debris on the road, subsequent scratches, water splashes, subsequent corrosion and damage from heat.
A good coating is essentially the one which is more aesthetic, environmentally safe, corrosion resistant, water resistant – with higher durability. The relative cost, area covered, and thickness of coating also adds to the quality of the coat.
Although the purpose of coating is the same, previously varnishing, spray painting and powder coating was used as manual techniques. To adapt to mass production and automation requirements and improve quality of the coat, electro-deposition or electrolytic coating process is currently being used in OEMs. Ensuring even coating is a major concern and the new method has proved effective.
Automotive Coating is a complete chemical process – various chemicals are used in each step. As a pre-requisite to the coating process, the surfaces to be coated are first thoroughly cleaned and polished to remove grease and weld debris. Alkaline salts, emulsifiers, lubricants and surfactants are used for cleaning while phosphating is used to condition the surfaces and polish them. This is a crucial step as it ensures even and better coating deposition on the surface [1].
The clean frame is dipped into a solution of resins, binders and paint pigments contained in a electrolytic tank and then electricity is supplied. The electrolytic reaction Coates the surfaces evenly. While the pigments are responsible for colour and gloss, the resins are important for corrosion resistance, durability and scratch resistance. Later the frame is taken out to be heated at 160 degree for 10 minutes to improve adhesion.
As a third and final step, the underbody is specially coated, using PVC for chipping resistance. A primer is applied as first layer to impart toughness and durability, a basecoat is applied for colour and a topcoat is applied to provide scratch resistance and gloss as seen in Figure 1.
Figure 1: Underbody Coating layers[1].
References:
- M, Mahajan & A, Varade & N, Mahajan & V, Patil. (2019). Review on Automotive Body Coating Process. International Journal of Engineering and Management Research. 9. 103-106. 10.31033/ijemr.9.2.11.