Underbody Coating

UNDERBODY COATING

INTRODUCTION

In case of steel or aluminum, the raw material is composition of different types of ferrous and non-ferrous alloys ,this alloys were chosen depend upon the mechanical property requirement in order to manufacture the required product.

After manufacturing a required product it's very difficult to sustain under many circumstances like moisture, light, water, and also some external collisions to the surface of the body.

Due to chemical composition and nature of raw material tends to corrode easily, therefore results in reduce the life span of the product.

In order to overcome this difficulties, the research and developers came with concept called as UNDERBODY COATING.

WHAT IS UNDERBODY COATING?

It's an extra layer provided to base material with certain thickness in order to avoid rust and corrosion. In other words it's acts as a protective layer against moisture, collision of stones from the tires or bad road condition, and water exposure during rainy season.

Automotive underbody coating process:-

The overall coating process includes 5 steps

1)Pre-treatment:-It is a process removes and cleans excess material from the base part so that enabling surface structure to bond for corrosion protection layer.

2)Electrodepositing:-The electrodepositing process have following steps

i)Phospating:- In the phosphate tank, a zinc phosphate crystal coating is formed as the substrate (building block) for the electro-deposition process of coating. The body is dipped into the tank to ensure that the phosphate coating is formed on the internal surfaces also. Once out of the phosphate dip tank, the body is rinsed by spary and dipping to wash off any extra phosphate that may be on the vehicle body. The body is then sent through an air blow off and accumulator system to dry it. The vehicle body must be completely dry prior to electro-deposition painting to allow the formation of a uniform paint layer.

ii) Electro-deposition stage:-It is the primary anti-corrosive coating is applied using an electro-chemical process similar to electroplating. Essentially, the vehicle bodies are given a strong negative electrical charge and immersed in a dip tank of positively charged paint. Plates placed along the sides and the bottom of the tank charge the paint. These plates connected to the positive side of a large DC power supply. The vehicle body and the carrier cradle are connected to the negative side of the power supply by wipers mounted on the cradle and a bus bar suspended over the electro-deposition tank.

This process is called cathodic electro deposition because the paint is deposited on the negatively charged body called the cathode. Without getting into the chemical particulars, the cathodic method is superior to the anodic method (where the body is positively charged) for several reasons. They are,

1. a) Superior corrosion resistance
   
2. b) Lower film thickness
   
3. c) Lower electric current requirement
   
4. d) Better ability to reach highly recessed areas without overcoming the easily reached areas.
   
   Once out of the electro-deposition dip tank, the vehicle body is rinsed with several sprays of re-circulated, filtered electro-deposition paint. It is also rinsed by fresh and recirculated deionized water. The rinsing removes any gragout (non-film layer paint) still on the body.

iii) Oven:-The oven will complete the electro-deposition paint process by curing. During oven curing, the individual paint molecules become cross-linked with the adjacent paint molecules. The paint becomes chemically intertwined to form a single, uniform surface.

3)Sealing:- The next step in the Paint Shop process is to apply the sealing compound. This provides additional protection against corrosion for selected areas of the vehicle body. The seal deck consists of various robots that are used to apply the sealing compound to the body. Sometimes these robots have a vision system. This system is a series of cameras, which identify particular body areas for sealant application. Following the robotic sealers are the manual stations. Here the workers check the sealants sprayed by robots are ill-equipped to reach.

4) Primer:- The fourth coating step is the application of a primer surface or simply primer. It can be water-borne, solvent-borne or a powder. These primers are used to improve adhesion between the E-coat and topcoat, provide chipping protection, enhance paint appearance and also be environmentally compatible with emission regulations.

5)Top-coat:The final step in the body coating process is to apply the topcoat, which consists of two layers—the basecoat and clear coat. The basecoat contains the primary colouring pigment and the clear coat provides a protective coating against environmental effects, corrosion, and UV light degradation promotes unmatched colour retention and provides a smooth unblemished even finish.

Types of undercoating:-

i)RUBBERIZED UNDERCOATING:-

Rubberized undercoating is easy to apply, and generally offers the best protective coating for your car’s undercarriage. It cushions surfaces against moisture, rust, dings, and dents. Rubberized undercoating is safe to use on quarter panels and wheel wells and dries with a soft rubbery finish.

ii)ASPHALT-BASED UNDERCOATING:-

Asphalt-based undercoating offers a higher level of protection suitable for large trucks, recreational vehicles, and heavy machinery. It’s formulated with some bits of rubberized material to aid in noise reduction. It offers extra protection against chips and moisture but is not paintable and, therefore, only suitable for undercarriages.

iii)POLYURETHANE UNDERCOATING:-

Polyurethane coating is easy to apply and works by sealing up cracks and seams. The compound displaces salt and moisture and protects the unoxidized metal from rust. It’s often sold in canisters that are ready to preload into an application gun. It, however, requires some surface prep work before application, like degreasing, and applying an etching primer to the bare metal.

iv)WAX OR PARAFFIN-BASED UNDERCOATING:-

Wax or paraffin-based undercoating sprays are the cheapest and quickest options available. However, their results don’t last long, and you may have to apply a fresh coat after only a few months. In addition, the wax isn’t very adhesive on a metal surface. Its main advantage is that it seeps quickly into cracks and seams, and offers moderate protective properties against moisture.

Advantages of undercoating:-

1. It provides a layer of protection against corrosion.
2. It will extend the life of your vehicle, hence re-sale value of the car might be high
3. It can be applied to minor damaged areas.
4. It may help to reduce interior noise and also reduce the noise from underneath of an car.
5. Heat insulation for the interiors which is coming from the underneath of the car.
6. Anti chip protection , which protects from collision of stones from the tires, and from bad roads.

Disadvantages :-

1. It won’t do anything about the corrosion which is already present(major damages).,
2. It adds weight to the vehicle, results reduce in fuel economy(Research done that there is a reduction of mileage of 1.6km for every 3 to 4 liters of fuel)

3 . Risk of damage during application, an improper coat to body may cause extra damage to car.

4.Cost will be high for the aged vehicle, from 6th year its starts rusting(the term may be varied depend upon the weather condition of that area).