Underbody Coating

UNDERBODY COATING

INTRODUCTION:

Vehicles around the world are driven in different conditions such as sand, mud, snow and road (tar or concrete). The under surface of the vehicle is prone to damage like corrosion, scratches, stone chipping,etc. To prevent these kind of damages "Underbody Coating" has been introduced.

PURPOSE:

Underseal (often called undercoating) is a thick resilient coating applied to the underbody or chassis of an automobile to protect from small stones which would rapidly chip ordinary paint, allowing rust to begin.

UNDERBODY COATING:

Underbody coating uses a selant or chemical which may be applied by the robots or manually so that it reaches every single surface properly. This coating applied after the ED coating is done to the full body of vehicle againg after maximum five to six years to use.

HISTORY:

Typically, phospate conversion coatings were used. Some firms galvanized part or all of their car bodies before the primer coat of paint was applied. If a car is body-on-frame, then the frame (chassis) must also be rust proofed. In traditional automotive manufacturing of the early- and mid-20th century, paint was the final part of the rustproofing barrier between the body shell and the atmosphere, except on the underside. On the underside, an underseal rubberized or PVC-based coating was often sprayed on. These products will be breached eventually and can lead to unseen corrosion that spreads underneath the underseal. Old 1960s and 1970s rubberized underseal can become brittle on older cars and is particularly liable to this.

The first electrodeposition primer was developed in the 1950s, but were found to be impractical for widespread use. Revised cathodic automotive electrocoat primer systems were introduced in the 1970s that markedly reduced the problem of corrosion that had been experienced by a vast number of automobiles in the first seven decades of automobile manufacturing. Termed e-coat, "electrocoat automotive primers are applied by totally submerging the assembled car body in a large tank that contains the waterborne e-coat, and the coating is applied through cathodic electrodeposition. This assures nearly 100% coverage of all metal surfaces by the primer. The coating chemistry is waterborne enamel based on epoxy, an aminoachol adduct, and blocked isocyanate, which all crosslink on baking to form an epoxy-urethane resin system."

E-coat resin technology, combined with the excellent coverage provided by electrodeposition, provides one of the more effective coatings for protecting steel from corrosion. For modern automobile manufacturing after the 1990s, nearly all cars use e-coat technology as base foundation for their corrosion protection coating system.

ED Coating(Electro Deposition Coating):

It is a process which uses electric current to deposit the paint or chemical to deposit on the full body vehicle.

TYPES OF UNDERBODY COATING:

• Rubberized Underbody coating: This coating is very easy to apply and is one of the best protective coats that can be applied to a car. It provides a soft rubbery finish once it dries off.

• Asphalt based Underbody coating: It is used when higher level of protectionis required and is suitable for trucks, recreational vehicals and heavy machinery. Its 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 under carriages.

• Polyurethane Underbody coating: It seals the cracks and seams which is easy to apply. This undercoat prevents the metals from Oxidizing from salts and moisture. This undercoat is sprayed on the undebody usingspray guns.

• Wax or Paraffin based Underbody coating: It is for temporary or short term undercoats are easiest to apply and are the cheapest of all. It provides moderate protection and is not recommended for long term or high protection.

PROCESS/STEPS INVOLVED:

1. FOR NEW CARS -

• Pre-treatment
• Electrodeposition (ED)
• Rust proof materials - PVC/Sealer
• Primer
• Top-coat

Pre-treatment:

The first step in Preparing BIW for subsequent coating is the pre-treatment process. Pre-treatment consists of cleaning the body surface to remove remaining oils from the stamping process and welding residures through three primary liquid dip process of degreasing, conditioning and phosphating. The degreasing solution is composed of alkaline salts and surfactants and include caustic soda, tri-sodium phosphate and sodium carbonate. The surfactants are types of detergants for emulsifying oils and lubricants in BIW.

Electrodeposition (ED):

The metal underbody and frames of automobiles are coated to prevent corrosion, whereas other areas like the roof are not rust-proofed. When not coated to prevent corrosion, the structural metals (or other matrerials) are primed before applying additional coatings. The ED processes are modified as per the BIW material property. This ED coating provides rust and corrosion protection.

Rust proof materials - PVC/Sealer:

The third step is underbody coating and seam sealing using PVC and Urethane. The sealant is applied around and inside the doors, hood, trunk, front dash, exterior and interior of metal joints and outer area of the back wheel well.

Primer:

The fourth 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 top coat, providechipping protection, enhance paint appearance and also be environmentally compatible with emission regulations.

Top-coat:

The final step in the body coating process is to apply the top coat, which consists of two layers- the base coat and clear coat. The base coat 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 unblemish even finish.

2. FOR USED/OLDER CARS-

For used/older cars the underbody coating process is different. Here the rust intially removed by use of certain chemical or scrubbing. Once the rust and dirt are removed the underbody is thoroughly washed and is dried using high pressure blowers to ensure there is no moisture or specs of dirty still remaining on the underbody. Once the underboady is completely dried, the coating is sprayed uniformly. Multiple layers of coating are applied depending on the requirement of customer.

Application of Underbody coating -

Benifits of Underbody Coating:

• Rust Prevention -
  • Ideally any additional underbody coating should be applied when the car is brand new and clean. Car manufacturers use thick paints and sealants for the underbody, but adding an underbody coat especially in coastal cities is useful. Salt water tends to corrode cars really badly.
  • On bad roads, flying stones and pebbles can chip off the original underbody coating and leave the metal exposed. Using an aftermarket underbody coating offer extra protection.
• Sound insulation - The thicker underbody coatings used on cars also act as effective sound dampeners. They can reduce road noise and tyre noise and make the cabin seem quieter – due to the sound absorptive nature of rubberized paints.

• Easy maintenance - A uniform black underbody coating gives a car a clean look. It also makes the car easier to maintain by just hosing the underside down. You can be confident that slush build up won’t lead to rusting easily. Most underbody coats these days come with a five-year warranty, which is the lifetime of such a coating.

Downsides to Underbody Coating:

• High cost - Cost of underbody coating has come down, but is still expensive. This is because underbody coating offered by a car dealer is one way in which they make money off the customer.

• Risk of damage during application - Care must be taken while applying underbody coating. This thick rubberized paint if not applied properly, can get into moving mechanical parts and cause premature failure – such as into the U-joint or CV joints in a cars propeller shaft or drive shafts. They can also hinder smooth movement of suspension components, if applied incorrectly. And there’s also the risk of overspray on to the car’s paint finish on the lower edges of the car.

Conclusion:

Underbody coating for a vehicle is essential but makesure that your dealer is providing trusted coatings and its warranty.